WO2010126686A2 - Carbon nanotube filters - Google Patents

Carbon nanotube filters Download PDF

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Publication number
WO2010126686A2
WO2010126686A2 PCT/US2010/030203 US2010030203W WO2010126686A2 WO 2010126686 A2 WO2010126686 A2 WO 2010126686A2 US 2010030203 W US2010030203 W US 2010030203W WO 2010126686 A2 WO2010126686 A2 WO 2010126686A2
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carbon nanotubes
filter
certain embodiments
mwnt
single wall
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PCT/US2010/030203
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French (fr)
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WO2010126686A3 (en
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Anna Stirgwolt Brady-Estevez
Menachem Elimelech
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Yale University
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Publication of WO2010126686A3 publication Critical patent/WO2010126686A3/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/021—Carbon
    • B01D71/0212—Carbon nanotubes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material
    • B01D39/20—Other self-supporting filtering material ; Other filtering material of inorganic material, e.g. asbestos paper, metallic filtering material of non-woven wires
    • B01D39/2055—Carbonaceous material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0039—Inorganic membrane manufacture
    • B01D67/0046—Inorganic membrane manufacture by slurry techniques, e.g. die or slip-casting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0039—Inorganic membrane manufacture
    • B01D67/0072—Inorganic membrane manufacture by deposition from the gaseous phase, e.g. sputtering, CVD, PVD
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0039—Inorganic membrane manufacture
    • B01D67/0076—Pretreatment of inorganic membrane material prior to membrane formation, e.g. coating of metal powder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/12—Composite membranes; Ultra-thin membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/021—Carbon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/26—Electrical properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/48—Antimicrobial properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01L—CHEMICAL OR PHYSICAL LABORATORY APPARATUS FOR GENERAL USE
    • B01L3/00—Containers or dishes for laboratory use, e.g. laboratory glassware; Droppers
    • B01L3/50—Containers for the purpose of retaining a material to be analysed, e.g. test tubes
    • B01L3/502—Containers for the purpose of retaining a material to be analysed, e.g. test tubes with fluid transport, e.g. in multi-compartment structures
    • B01L3/5025—Containers for the purpose of retaining a material to be analysed, e.g. test tubes with fluid transport, e.g. in multi-compartment structures for parallel transport of multiple samples
    • B01L3/50255—Multi-well filtration
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/28—Treatment of water, waste water, or sewage by sorption
    • C02F1/283—Treatment of water, waste water, or sewage by sorption using coal, charred products, or inorganic mixtures containing them
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2305/00—Use of specific compounds during water treatment
    • C02F2305/08—Nanoparticles or nanotubes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W10/00—Technologies for wastewater treatment
    • Y02W10/30—Wastewater or sewage treatment systems using renewable energies
    • Y02W10/37—Wastewater or sewage treatment systems using renewable energies using solar energy

Definitions

  • Carbon nanotubes have tubular structures formed by graphene sheets rolled into seamless cylinders with diameters of, for example, about 0.6 namometers to a few tens of nanometers, and lengths that can reach micrometers.
  • a nanotube with only one wall is referred to a single wall carbon nanotube ("SWNT"), while a nanotube with multiple concentric walls is referred to as a multiwall carbon nanotube (“MWNT”).
  • SWNT single wall carbon nanotube
  • MWNT multiwall carbon nanotube
  • Carbon nanotubes (CNTs) have exceptional properties of strength, high surface area, thermal stability, optical activity, thermal and electrical conductivity, and ease of functionalization that tailor them to specific applications [Yu, M.F., et al. Science, 2000. 287(5453): p.
  • CNTs have been assessed or employed for use in environmentally relevant areas as diverse as water treatment, adsorption, environmental sensing, remediation, energy technologies (solar cells, fuel cells, hydrogen storage), and green and high-strength building materials
  • energy technologies solar cells, fuel cells, hydrogen storage
  • green and high-strength building materials [Mauter, M.S. and M. Elimelech Environmental Science & Technology, 2008. 42(16): p. 5843-5859; Savage, N. and M. Diallo Journal of Nanoparticle Research, 2005. 7: p. 331-342; Theron, J., J.A. Walker, and T.E. Cloete Critical Reviews in Microbiology, 2008. 34(1): p. 43-69; Peng, X., Z. Luan et al. Materials Letters, 2005.
  • carbon nanotubes In the field of water treatment, carbon nanotubes generate interest for their advantages of high surface area, relatively small pore size, and cytotoxicity to various pathogens.
  • Several researchers have looked to carbon nanotubes as a scaffold for nanoparticles, such as amorphous aluminum for adsorption of fluoride and nano-scale ceria for removal of arsenate and chromium from water [Peng, X., Z. Luan, and e. al. Materials Letters, 2005. 59: p. 399-403; Di, Z., et al., Chemosphere, 2006. 62(5): p. 861-865; and Li, Y., et al. Chemical Physical Letters, 2001. 350(5-6): p. 412-416].
  • SWNT single-walled carbon nanotube
  • Recent work on nano structured material comprising carbon nanotubes is disclosed in US Patent Nos. 7.211,320 and 7,419,601 (Seldon Technologies), both of which are hereby incorporated by reference in their entirety.
  • Membranes comprising carbon nanotubes useful for filtration by size exclusion are disclosed in US Patent Application Nos. 2009/0321355 and 2010/0025330 (Nanoasis Technologies), both of which are hereby incorporated by reference in their entirety.
  • Nanoporous membranes comprising carbon nanotubes embedded in a matrix are disclosed in US Patent Application No. 2008/0223795 (Lawrence Livermore National Security), which is incorporated by reference in its entirety.
  • SUMMARY One aspect of the invention relates to a filter comprising multiwall carbon nanotubes dispersed on a substrate.
  • the filter further comprises a layer of single-wall carbon nanotubes dispersed on top of the multiwall carbon nanotubes.
  • the multiwall and single-wall carbon nanotubes are present in the filter in an amount sufficient to reduce the concentration of the constituents in fluid that come into contact with the material.
  • Also provided is a method of reducing the amount of constituents in a fluid comprising contacting the fluid with the filter as described herein for a time sufficient to separate, remove, immobilize, modify or destroy at least one constituent from the fluid.
  • the method may be used to remove constituents from water or the air.
  • the filter can be part of an article, such as a water- purification system.
  • Figure 1 depicts FE-SEM images of aerial and cross-section views of carbon nanotube filters.
  • Top row aerial view of MWNT-SWNT filter at 25,00OX magnification (left image), cross-section view of MWNT-SWNT filter at 4,00OX magnification (right image).
  • Middle row aerial view of MWNT filter at 25,00OX magnification (left image), cross-section view of MWNT filter at 4,00OX magnification (right image).
  • Bottom Row Aerial view of SWNT filter at 25,00OX magnification (left image), cross-section view of SWNT filter at 4,00OX magnification (right image).
  • Figure 2 depicts graphically the extent of viral removal by a SWNT-MWNT hybrid filter.
  • the total CNT loading was 0.32 mg/cm 2 , composed of a layer of 0.27 mg/cm 2 of MWNTs covered by a layer of 0.05 mg/cm 2 of SWNTs.
  • Solution chemistry was 10 mM
  • Figure 3 depicts a bar graph summarizing the fluorescence-based toxicity assays of Gram positive and Gram negative bacteria exposed to MWNT or SWNT-MWNT filters over time. Cell suspensions were passed through the filters and incubated in 10 mM NaCl at 37 0 C for the length of time indicated. Error bars indicate one standard deviation.
  • Figure 4 depicts a bar graph summarizing the extent of inactivation of microorganisms in river water and secondary wastewater effluent samples upon exposure to the MWNT and SWNT-MWNT filters. Each sample (100 mL) was filtered through the MWNT or SWNT-MWNT filters and incubated for 1 hr in 0.9% NaCl solution at 37 0 C. Error bars indicate one standard deviation.
  • Figure 5 tabulates selected properties of carbon nanotubes, viruses and bacteria used in the Exemplification provided herein, drawn from the following prior studies: a) Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2008. 42(19): p. 7528-7534; b) Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2009. 43(7): p. 2648-2653; c) Hu, J.Y., et al, Water Science and Technology, 2003. 47(12): p. 163-168; d) Vinuela, E., LD. Algranati, and S. Ochoa, European Journal of Biochemistry, 1967.
  • Figure 6 depicts field-emission SEM images of CNT filters: (a) MWNT Filter under 5000X magnification, (b) SWNT Filter under 5000X magnification, (c) MWNT Filter under 10,000X magnification, (d) SWNT filter under 10,000X magnification, (e) MWNT filter under 100,000X magnification, and (f) SWNT filter under 100,000X magnification.
  • Figure 7 depicts a bar graph comparing viral removal by SWNT and MWNT filters.
  • Filters had 0.32 mg/cm 2 CNT loading and all tests were run at 10 mM total ionic strength: 10 mM NaCl, 1 mM MgCl 2 + 7 mM NaCl, and 1 mM CaCl 2 + 7 mM NaCl.
  • Solution pH for all experiments was maintained at 5.5.
  • MS2 viral concentrations were spiked into the inlet sample and a peristaltic pump maintained 160 Lm -2 Ii '1 flux through the filter. At least two measurements were carried out at each dilution and a minimum of two separate filters were tested for each experimental condition. Error bars indicate one standard deviation.
  • FIG. 8 tabulates results of experiments relating to viral removal on MWNT filter, viral and MWNT electrophoretic mobilities, and MS2 hydrodynamic radii.
  • MWNT filter CNT loading was 0.32 mg/cm 2 , and flux was maintained at 160 Lm -2 Ii "1 . All solution chemistries were at pH 5.5 unless otherwise noted, a) SWNT Filter log viral removal measurements were obtained by the filtration procedure, followed by the PFU quantification method, b) Electrophoretic (EPM) mobility measurements of MWNT reported are the average of at least three experimental runs at each solution condition, c) EPM measurements were taken of the MS2 viral particles, at a concentration of 1011 viral particles per mL.
  • EPM Electrophoretic
  • FIG. 9a depicts a graph showing MS2 viral removal by the MWNT filter as a function of flux. MWNT loading on the filter was 0.32 mg/cm 2 . Experiments were performed with a background solution of 10 mM NaCl, and a pH of 5.5. At least two measurements were made at each dilution and at least two separate filters were tested for each experimental condition.
  • Figure 9b depicts a graph showing the linear correlation between the log viral removal and approach velocity, v m . Error bars indicate one standard deviation.
  • Figure 10 depicts a graph showing the extent of MS2 viral removal by the MWNT filter as a function of ionic strength.
  • the MWNT loading on the filter was 0.32 mg/cm 2 .
  • Solution pH for all experiments was maintained at 5.5.
  • MS2 viral concentrations were spiked into the inlet sample, and a peristaltic pump maintained 160 Lm -2 Ii '1 flux through the filter. At least two measurements were carried out at each dilution, and a minimum of two separate filters were tested for each experimental condition. Error bars indicate one standard deviation.
  • Figure 11 depicts a bar graph showing the impact of the presence of various additives (e.g., organic matter) on the extent of viral removal by the MWNT filter at pH 5.5.
  • additives e.g., organic matter
  • MWNT filter CNT loading was 0.32 mg/cm 2 .
  • MS2 viral concentrations were spiked into the inlet sample, and a peristaltic pump maintained 160 Lm -2 Ii '1 flux through the filter. At least two measurements were made at each dilution and at least two separate filters were tested for each experimental condition. Error bars indicate one standard deviation.
  • SWNT single-walled carbon nanotube
  • multiwall carbon nanotubes either alone or in combination with SWNTs, can be used to attain higher viral removal at lower pressures, while also achieving new options for cost and resource efficiency, production, and scale-up.
  • filters comprising multiwall carbon nanotubes
  • MWNTs The MWNT filters described herein provided substantial improvements in surface coverage and viral removal in comparison with earlier SWNT filters tested, while also enabling a lower cost of production which is typical of MWNTs.
  • this highly scalable MWNT-filter technology may be used for viral removal at gravity- driven pressures, it poses new cost-effective options for point-of-use treatment. It is disclosed herein that the actual viral adsorption attained by MWNT filtration depends on several factors, such as the speed of filtration, permeability, filter depth, solution chemistry and pH. It is further disclosed that increasing ionic strength and decreasing pH have been found to increase MS2 viral removal from a solution for MWNT filters.
  • Another aspect of the invention relates to hybrid filters comprising both single wall carbon nanotubes (SWNTs) and multiwall carbon nanotubes (MWNTs).
  • SWNTs single wall carbon nanotubes
  • MWNTs multiwall carbon nanotubes
  • MWNTs were selected to comprise the majority of the depth of the filter matrix due to MWNT matrices' enhanced adsorption of viruses, low cost, and reasonably high permeability.
  • a thin upper layer of SWNTs was then deposited onto the MWNT matrix to take advantage of the beneficial antimicrobial properties of SWNTs, and help inhibit biofilm formation.
  • the nanotube matrix i.e., the MWNTs and SWNTs taken together
  • was supported by a microporous membrane e.g., a highly porous material with micrometer pore size.
  • the bilayer (i.e., hybrid) filter shows significantly higher viral removal than both the SWNT and MWNT filters previously developed, attaining well over 6 log MS2 viral removal at 10 mM NaCl and pH 5.5.
  • the extent of viral removal will vary with the viral contaminated sample and its solution chemistry, the results described herein demonstrate effective removal of several bacteriophages with markedly different properties. Further, the observed enhancement of viral adsorption was at the expense of only a modest reduction of the filter permeability, which remained highly porous and operational in the microfiltration pressure range.
  • the top layer of SWNTs incorporated into the dual filter enabled high levels of inactivation of bacteria.
  • the bacterial inactivation was higher for the SWNT-MWNT filter than the filter composed of MWNTs alone.
  • the strategy for enhancing the filter's cytotoxicity was validated by the confirmed ability of the SWNT-coating to inactivate more effectively across monocultured Gram positive and Gram negative bacteria, along with environmentally present microbes in wastewater and river water alike. These antimicrobial properties are useful for their role in inhibition of bio film growth, which can reduce filter permeability and, thereby, increase energy and cleaning or filter regeneration needed for operation.
  • Another advantage of using only a thin layer of SWNT is that it mediates the inherent toxicity of SWNTs.
  • the design of a SWNT-MWNT filter may consists of a thin coating of SWNTs (about 0.05 mg/cm 2 ) over a base matrix composed of MWNTs (about 0.27 mg/cm 2 ), for a total carbon nanotube (CNT) loading of about 0.32 mg/cm 2 .
  • SWNT carbon nanotube
  • an element means one element or more than one element.
  • a reference to "A and/or B", when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.
  • At least one of A and B can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.
  • the order of the steps or acts of the method is not necessarily limited to the order in which the steps
  • carbon nanotube(s) refer to a nanoscale tubular structure(s) composed of six-member rings of carbon whose bonding patterns create a hexagonal lattice which closes upon itself to form the walls of the cylindrical structure.
  • filter shall mean a material that performs fluid filtration.
  • fluid is intended to encompass liquids or gases.
  • biological sample refers to any sample from a biological source.
  • body fluid means any fluid that can be isolated from the body of an individual.
  • body fluid may include blood, plasma, serum, bile, saliva, urine, tears, perspiration, and the like.
  • chemical or biological interaction or reaction is understood to mean an interaction with the constituent through either chemical or biological processes that renders the constituent incapable of causing harm. Examples of this are reduction, oxidation, chemical denaturing, physical damage to microorganisms, bio-molecules, ingestion, and encasement.
  • Natural organic matter or “NOM” shall mean organic matter often found in potable or non-potable water, a portion of which reduces or inhibits the streaming, or zeta, potential of a filter medium.
  • NOM are polyanionic acids such as, but not limited to, humic acid and fulvic acid.
  • Nanotubes are cylindrical tubular structures that are well known in the art and commercially available. Nanotubes of a variety of materials have been studied, notably carbon nanotubes, boron nanotubes, and nanotubes of boron nitride. Carbon nanotubes have been extensively studied, and their features and methods of fabrication are illustrative of nanotubes in general.
  • Carbon nanotubes are polymers of pure carbon, and exist as both single-wall and multi-wall structures. Examples of publications describing carbon nanotubes and their methods of fabrication are Dresselhaus, M. S., et al., Science of Fullerenes and Carbon Nanotubes, Academic Press, San Diego (1996), Ajayan, P. M., et al., "Nanometre-Size
  • a single-wall carbon nanotube is a single graphene sheet rolled into a seamless cylinder with either open or closed ends. When closed, the ends are capped either by half fullerenes or by more complex structures such as pentagonal lattices.
  • the average diameter of a single -wall carbon nanotube typically ranges of 0.6 nm to 100 nm, and in many cases 1.5 nm to 10 nm.
  • the aspect ratio typically ranges from about 25 to about 1,000,000, and most often from about 100 to about 1,000.
  • a nanotube of 1 nm diameter may thus have a length of from about 100 nm to about 10,000 nm or more.
  • nanotubes can be about 10 nm, such as, for example, when they have been broken down by sonication or other processes.
  • Nanotubes frequently exist as "ropes," which are bundles of 3 to 500 single-wall nanotubes held together along their lengths by van der Waals forces. Individual nanotubes often branch off from a rope to join nanotubes of other ropes.
  • Multi-walled carbon nanotubes are two or more concentric cylinders of graphene sheets of successively larger diameter, forming a layered composite tube bonded together by van der Waals forces, with a distance of approximately 0.34 nm between layers.
  • Carbon nanotubes can be prepared by arc discharge between carbon electrodes in an inert gas atmosphere. This process results in a mixture of single-wall and multi-wall nanotubes, although the formation of single-wall nanotubes can be favored by the use of transition metal catalysts such as iron or cobalt.
  • Single-wall nanotubes can also be prepared by laser ablation, as disclosed by Thess, A., et al., "Crystalline Ropes of Metallic Carbon Nanotubes," Science 273 (1996): 483-487, and by Witanachi, S., et al., "Role of Temporal Delay in Dual-Laser Ablated Plumes," J. Vac. Sci. Technol. A 3 (1995): 1171-1174.
  • a further method of producing single-wall nanotubes is the high-pressure carbon monoxide conversion ("HiPCO") process disclosed by Nikolaev, P., et al., "Gas-phase catalytic growth of single -walled carbon nanotubes from carbon monoxide," Chem. Phys. Lett. 313, 91-97 (1999), and by Bronikowski, M. J., et al., "Gas-phase production of carbon single- walled nanotubes from carbon monoxide via the HiP co process: A parametric study," J. Vac. Sci. Technol. 19, 1800-1805 (2001).
  • HiPCO high-pressure carbon monoxide conversion
  • Certain procedures for the synthesis of nanotubes produce nanotubes with open ends, while others produce closed-end nanotubes. If the nanotubes are synthesized in closed-end form, the closed ends can be opened by a variety of methods known in the art. An example of a nanotube synthesis procedure that produces open-ended nanotubes is described by Hua, D. H. (International (PCT) Patent Application Publication No. WO 2008/048227 A2, which is hereby incorporated by reference in its entirety). Closed ends can be opened by mechanical means such as cutting, or by chemical, or thermal means. An example of a cutting method is milling.
  • Chemical means include the use of carbon nanotube degrading agents, an example of which is a mixture of a nitric acid and sulfuric acid in aqueous solution at concentrations of up to 70% and 96%, respectively.
  • Another chemical means is reactive ion etching.
  • Thermal means include exposure to elevated temperature in an oxidizing atmosphere. The oxidizing atmosphere can be achieved by an oxygen concentration ranging from 20% to 100% by volume, and the temperature can range from 200 to 450° C.
  • the lengths of carbon nanotubes can vary widely.
  • the lengths are expressed herein as average lengths, using numerical or arithmetic averages.
  • the average length is from about 100 nm to about 10,000 nm, from about 100 nm to about 1,000 nm, from about 1,000 nm to about 2,000 nm, from about 2,000 nm to about 3,000 nm, from about 3,000 nm to about 4,000 nm, from about 4,000 nm to about 5,000 nm, from about 5,000 nm to about 6,000 nm, from about 6,000 nm to about 7,000 nm, from about 7,000 nm to about 8,000 nm, from about 8,000 nm to about 9,000 nm, from about 9,000 nm to about 10,000 nm, from about 100 nm to about 5,000 nm, and from about 5,000 nm to about 10,000 nm.
  • the outer and inner diameters of the nanotubes can likewise vary.
  • the outer diameters can range from about 0.6 nm to about 200 nm, while narrower ranges are often preferred for particular applications.
  • the inner diameters can likewise range from about 0.4 nm to about 200 nm, although the optimal diameters for particular applications may be within narrower ranges.
  • the inner diameter may range about 0.4 nm to about 5 nm, or about 0.4 nm to about 1.2 nm.
  • the inner diameter may range from about 1 nm to about 10 nm.
  • the inner diameter may range from about 5 nm to about 200 nm.
  • the carbon nanotubes have outer diameters ranging from about 0.4 nm to 200 nm. In certain embodiments, the carbon nanotubes have inner diameters ranging from about 0.4 nm to about 200 nm. In certain embodiments, nanotube densities range from about 1 x 10 6 cm “2 to about 1 x 10 13 cm “2 .
  • Carbon nanotubes can have a variety of morphologies.
  • carbon nanotubes may have a morphology chosen from horns, spirals, multi-stranded helicies, springs, dendrites, trees, spider nanotube structures, nanotube Y-junctions, and bamboo morphology.
  • Some of the above described shapes are more particularly defined in M. S. Dresselhaus, G. Dresselhaus, and P. Avouris, eds. Carbon Nanotubes: Synthesis, Structure, Properties, and Applications, Topics in Applied Physics. 80. 2000, Springer- Verlag; and "A Chemical Route to Carbon Nanoscrolls," Lisa M. Viculis, Julia J. Mack, and Richard B. Kaner; Science, 28 Feb. 2003; 299, both of which are herein incorporated by reference.
  • the carbon nanotubes may also undergo chemical and/or physical treatments to alter their chemical and/or physical behavior. In certain embodiments, these treatments are done to enable the resulting article to exhibit an improved purification performance.
  • the carbon nanotubes may be chemically or physically treated to achieve at least one of the following effects: remove constituents, add defects, or attach functional groups to defect sites and/or nanotube surface.
  • chemical or physical treatment means treating with an acid, solvent or an oxidizer for a time sufficient to remove unwanted constituents, such as amorphous carbon, oxides or trace amounts of by- products resulting from the carbon nanotube fabrication process.
  • An example of the second type of chemical treatment is to expose the carbon nanotubes to an oxidizer for a time sufficient to create density defects on the surface of the carbon nanotube.
  • the carbon nanotubes comprise atoms, ions, molecules or clusters attached thereto or located therein in an amount effective to assist in the removal and/or modification of constituents from a fluid.
  • the carbon nanotubes described herein may also be treated to alter their properties, as well as the constituents that may be removed from and/or modified within the fluid.
  • the carbon nanotubes are chemically treated with an oxidizer, chosen from but not limited to a gas containing oxygen, nitric acid, sulfuric acid, hydrogen peroxide, potassium permanganate, and combinations thereof.
  • Nanotubes which have been treated with an oxidizer can provide unique properties, either in terms of fluid flow, dispersion of nanotubes in the deposition fluid, or from a functionalization perspective (e.g., having the ability to be particularly functionalized).
  • “functionalized” refers to a carbon nanotube having an atom or group of atoms attached to the surface. Functionalization is generally performed by modifying the surface of carbon nanotubes using chemical techniques, including wet chemistry or vapor, gas or plasma chemistry, and microwave assisted chemical techniques, and utilizing surface chemistry to bond materials to the surface of the carbon nanotubes. Functionalization can occur before and/or after the carbon nanotubes are assembled into a filter. In certain embodiments, these methods are used to "activate" the carbon nanotube, which is defined as breaking at least one C-C or C-heteroatom bond, thereby providing a surface for attaching a molecule or cluster thereto.
  • Functionalized carbon nanotubes comprise chemical groups, such as carboxyl groups, attached to the surface, such as the outer sidewalls, of the carbon nanotube. Further, the nanotube functionalization can occur through a multi-step procedure where functional groups are sequentially added to the nanotube to arrive at a specific, desired functionalized nanotube.
  • a functionalized carbon nanotube is one that comprises inorganic and/or organic compounds attached to the surface of the carbon nanotubes.
  • the organic compounds may comprise linear or branched, saturated or unsaturated groups.
  • Non-limiting examples of such organic compounds include at least one chemical group chosen from: carboxyl, amine, polyamide, polyamphiphiles, diazonium salts, pyrenyl, silane and combination thereof.
  • Non- limiting examples of the inorganic compounds include at least one fluorine compound of boron, titanium, niobium, tungsten, and combination thereof.
  • the inorganic compounds as well as the organic compounds may comprise a halogen atom or halogenated compound.
  • functionalized carbon nanotubes comprise any one or any combination of the above-described inorganic and organic groups. These groups are generally located on the ends of the carbon nanotubes and are optionally polymerized.
  • the functionalized carbon nanotubes may have a non-uniform composition and/or density of functional groups, including the type or species of functional groups across the surface of the carbon nanotubes.
  • the functionalized carbon nanotubes may comprise a substantially uniform gradient of functional groups across the surface of the carbon nanotubes. For example, there may exist, either down the length of one nanotube or within a collection of nanotubes, many different functional group types (i.e., hydroxyl, carboxyl, amide, amine, poly-amine and/or other chemical functional groups) and/or functionalization densities.
  • One process for preparing functionalized carbon nanotubes generally comprises contacting carbon nanotubes with acids, chosen from but not limited to nitric, sulfuric, hydrochloric, and/or hydrofluoric acid or combination thereof, as well as other oxidizers, chosen from but not limited to potassium permanganate, hydrogen peroxide, sodium perchlorate and ozone (see, for example, Cho, H-H. et al. Langmuir 2010, 26(2), 967-981)
  • the acids can be used individually to wash the carbon nanotubes, or be used in various combinations.
  • the carbon nanotubes are first washed in nitric acid and then washed in hydrofluoric acid.
  • the carbon nanotubes are washed in sulfuric acid after being washed in nitric acid.
  • the acid wash is performed to remove any contaminants, such as amorphous carbon, or catalyst particles and their supports which may interfere with the surface chemistry of the nanotube, and producing functional groups (such as hydroxyls and carboxyls, for example) attached to the defect locations on the surface of the carbon nanotubes.
  • This functionalization also provides hydrophilicity to the carbon nanotubes, which is thought to improve the filtration performance of the resulting article.
  • the carbon nanotubes are then subjected to a final distilled water rinse, and suspension in an appropriate dispersant, such as distilled water, or an alcohol, such as ethanol or isopropanol.
  • sonication, stirring and heating is employed throughout this functionalization process to maintain adequate dispersion of the nanotubes while cleaning.
  • the process of making a filter as described herein comprises functionalizing, also known as decorating, the carbon nanotubes with metal nanoparticles.
  • carbon nanotubes which have been already functionalized with hydroxyls and/or carboxyls can be used to bind to the metal nanoparticles.
  • the metal nanoparticles are selected from the group consisting of ferric oxide, aluminum oxide and cerium oxide, and can be used for the adsorption of inorganic contaminants such as metals and arsenic.
  • the metal nanoparticles are selected from the group consisting of silver, zinc oxide, and gold, and can be used to impart or increase antimicrobial activity.
  • a filter described herein includes a porous substrate on which carbon nanotubes are deposited.
  • the porous substrate establishes the lateral dimensions and shape of the filters as they are being formed and provides the finished membranes with structural stability.
  • the porous support substrate may be in any form suitable for the shape of the resulting filter, such as a block, tube (or cylinder), sheet or roll, and may comprise a material chosen from ceramic, carbon, metal, metal alloys, or plastic or combinations thereof.
  • the substrate comprises a woven or non-woven fibrous material.
  • the substrate comprises a polymer.
  • the polymeric material of the substrate comprises single or multi-component polymers, nylon, polyurethane, acrylic, methacrylic, polycarbonate, epoxy, silicone rubbers, natural rubbers, synthetic rubbers, vulcanized rubbers, polystyrene, polyethylene terephthalate, polybutylene terephthalate, Nomex (poly-paraphylene terephtalamide), Kevlar poly (p-phenylene terephtalamide), PEEK (polyester ester ketene), Mylar (polyethylene terephthalate), viton (viton fluoroelastomer), polyetrafluoroethylene, polyetrafluoroethylene), halogenated polymers, such as polyvinylchloride (PVC), polyester (polyethylene terepthalate), polypropylene, and polychloropre
  • the substrate itself can serve a filtering function by size exclusion, its filtering characteristics if any will be substantially more coarse, due to its microporous nature, than those of the nanotubes in the filter.
  • the porosity of the support can vary widely. In certain embodiments, it will be convenient to use a support with a molecular weight cutoff (MWCO) of from about 1 kDa to about 10 MDa, or from about 5 kDa to about 300 kDa.
  • MWCO molecular weight cutoff
  • the porous substrate can have pores ranging in average diameter from about 1 micron to 100 microns, about 1 micron to about 75 microns, about 1 micron to about 50 microns, about 1 micron to about 25 microns, about 1 micron to about 10 microns. In certain embodiments, the pores have an average diameter of about 5 microns. In certain embodiments, the pores may be in the nanometer range, such as between about 3 nm to about 200 nm. The dimensions of the porous substrate will generally be selected to meet the needs of the particular application.
  • the substrates are capable of withstanding pressure differentials of from about 1 atmosphere to about 85 atmospheres without rupturing.
  • the filter is in the form of a flat disk.
  • disks of a relatively small size are often the most appropriate, and a diameter range for these applications is from about 10 mm to about 100 mm.
  • Diameters ranging from 13 mm to 47 mm, specifically disks of 13 mm, 25 mm, and 47 mm, may also be used.
  • the disk thickness may range from about 0.15 mm to about 0.25 mm.
  • discs of diameters larger that about 100 nm may be used, such as, for example, discs between about 100 mm and about 1000 mm.
  • the thickness of the discs can also vary and in some embodiments, for example, the thickness is between about 0.25 mm and about 10 mm.
  • the composite membrane can also be prepared in the form of rectangular sheets having widths ranging from 1 inch (2.5 cm) to 40 inches (102 cm). Widths of 9.75 inches (24.8 cm), 10 inches (25.4 cm), 20 inches (51 cm), and 40 inches (102 cm) may be used. The lengths of the sheets may range from about four inches (ten cm) to about 400 feet (122 m). For a sheet of these lateral dimensions, the sheet thickness may range from about 0.1 nm to about 1 mm.
  • the thickness of the support is of less importance than the thickness of the nanotubes, since the support need only be thick enough to provide structural support for the nanotubes.
  • One aspect of the invention relates to a filter comprising a layer of multiwall carbon nanotubes dispersed on a porous substrate; wherein the porous substrate is permeable to the flow of a fluid.
  • Another aspect of the invention relates to a filter consisting essentially of a layer of multiwall carbon nanotubes dispersed on a porous substrate; wherein the porous substrate is permeable to the flow of a fluid.
  • Another aspect of the invention relates to a filter consisting of a layer of multiwall carbon nanotubes dispersed on a porous substrate; wherein the porous substrate is permeable to the flow of a fluid.
  • the present invention relates to any one of the aforementioned filters, wherein said porous substrate comprises single or multi-component polymers, nylon, polyurethane, acrylic, methacrylic, polycarbonate, epoxy, silicone rubbers, polystyrene, polyethylene terephthalate, polybutylene terephthalate, poly-paraphylene terephtalamide, poly-(p-phenylene terephtalamide), polyester ester ketone, viton fluoroelastomer, poly-tetrafluoroethylene, polyvinylchloride, polyester, polypropylene, polychloroprene, acetates, and combinations thereof.
  • the present invention relates to any one of the aforementioned filters, wherein the porous substrate is poly-tetrafluoroethylene.
  • the present invention relates to any one of the aforementioned filters, wherein porous substrate comprises a plurality of pores which have diameters between about 0.1 ⁇ m and about 20 ⁇ m, about about 0.1 ⁇ m and about 1 ⁇ m, or about 1 ⁇ m to about 10 ⁇ m, or about 10 ⁇ m to about 20 ⁇ m. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein porous substrate comprises a plurality of pores which have diameters of about 0.1 ⁇ m, about 1 ⁇ m, about 5 ⁇ m, about 10 ⁇ m, about 15 ⁇ m, or about 20 ⁇ m.
  • the present invention relates to any one of the aforementioned filters, wherein the porous substrate has a thickness which is between about 1 nm and about 500 nm. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the porous substrate has a thickness which is between about 50 nm and about 300 nm.
  • the present invention relates to any one of the aforementioned filters, wherein the average length of the multiwall carbon nanotubes is between about 50 nm and about 5000 nm, about 50 nm and about 4000 nm, about 50 nm and about 3000 nm, about 50 nm and about 2000 nm, about 50 nm and about 1000 nm, about 100 nm and about 2000 nm, or about 100 nm and about 1000 nm.
  • the present invention relates to any one of the aforementioned filters, wherein the average inner diameter of the multiwall carbon nanotubes is between about 0.4 nm and about 0.5 nm, or about 0.4 nm and about 1.2 nm.
  • the present invention relates to any one of the aforementioned filters, wherein the average outer diameter of the multiwall carbon nanotubes is between about 1.0 nm and about 2.0 nm, or about 1.2 nm and about 1.6 nm.
  • the present invention relates to any one of the aforementioned filters, wherein a majority of the multiwall carbon nanotubes have pores with diameters between about 0.1 nm to about 200 nm, about 0.1 nm to about 100 nm, about 1 nm to about 100 nm, about 1 nm to about 50 nm, about 1 nm to about 25 nm, or about 1 nm to about 10 nm.
  • the present invention relates to any one of the aforementioned filters, wherein a majority of the multiwall carbon nanotubes have pores with diameters of about 0.1 nm, about 1 nm, about 10 nm, about 20 nm, about 30 nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm or about 100 nm.
  • the present invention relates to any one of the aforementioned filters, wherein the layer of multiwall carbon nanotubes has a substantially planar surface.
  • the present invention relates to any one of the aforementioned filters, wherein the thickness of the layer of multiwall carbon nanotubes is between about 0.1 ⁇ m and about 500 ⁇ m, or about 1 ⁇ m and about 10 ⁇ m.
  • the present invention relates to any one of the aforementioned filters, wherein the loading of multiwall carbon nanotubes is between about 0.01 mg/cm 2 and about 100 mg/cm 2 , about 0.01 mg/cm 2 and about 50 mg/cm 2 , about 0.01 mg/cm 2 and about 10 mg/cm 2 , or about 0.01 mg/cm 2 and about 1 mg/cm 2 . In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the loading of multiwall carbon nanotubes is between about 0.10 mg/cm 2 and about 1 mg/cm 2 .
  • the present invention relates to any one of the aforementioned filters, wherein the loading of multiwall carbon nanotubes is between about 0.20 mg/cm 2 and about 0.80 mg/cm 2 . In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the loading of multiwall carbon nanotubes is about 0.27 mg/cm 2 , about 0.50 mg/cm 2 , about 0.75 mg/cm 2 or about 1 mg/cm 2 . In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein a majority of the multiwall carbon nanotubes are open at both ends.
  • the present invention relates to any one of the aforementioned filters, wherein a majority of the multiwall carbon nanotubes are closed at one end. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein at least one functional group is attached to the surface of a majority of the multiwall carbon nanotubes. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an organic functional group, an inorganic functional group, or combinations thereof.
  • the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an organic functional group which comprises linear or branched, saturated or unsaturated groups. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an organic functional group; and the at least one organic functional group comprises at least one chemical group chosen from carboxyls, amines, polyamides, polyamphiphiles, diazonium salts, pyrenyls, silanes, and combinations thereof.
  • the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an inorganic functional group; and the at least one inorganic functional group comprises at least one fluorine compound of boron, titanium, niobium, tungsten, and combination thereof.
  • the present invention relates to any one of the aforementioned filters, wherein said at least one functional group comprises a halogen atom or halogenated moiety.
  • the present invention relates to any one of the aforementioned filters, wherein said multiwall carbon nanotubes comprise a substantially uniform gradient of functional groups across the surface of said carbon nanotubes and/or across at least one dimension of said filter.
  • the present invention relates to any one of the aforementioned filters, wherein a majority of said multiwall carbon nanotubes have a morphology chosen from nanohorns, cylindrical, nanospirals, dendrites, trees, spider nanotube structures, nanotube Y-junctions, and bamboo morphology.
  • the present invention relates to any one of the aforementioned filters, further comprising a layer of single wall carbon nanotubes disposed over the layer of multiwall carbon nanotubes or disposed between the layer of multiwall carbon nanotubes and the porous substrate.
  • the present invention relates to any one of the aforementioned filters, further consisting essentially of a layer of single wall carbon nanotubes disposed over the layer of multiwall carbon nanotubes or disposed between the layer of multiwall carbon nanotubes and the porous substrate. In certain embodiments, the present invention relates to any one of the aforementioned filters, further consisting of a layer of single wall carbon nanotubes disposed over the layer of
  • the present invention relates to any one of the aforementioned filters, wherein the average length of the single wall carbon nanotubes is between about 50 nm and about 5000 nm, about 50 nm and about 4000 nm, about 50 nm and about 3000 nm, about 50 nm and about 2000 nm, about 50 nm and about 1000 nm, about 100 nm and about 2000 nm, or about 100 nm and about 1000 nm.
  • the present invention relates to any one of the aforementioned filters, wherein the average inner diameter of the single wall carbon nanotubes is between about 0.4 nm and about 0.5 nm, or about 0.4 nm and about 1.2 nm.
  • the present invention relates to any one of the aforementioned filters, wherein the average outer diameter of the single wall carbon nanotubes is between about 1.0 nm and about 2.0 nm, or about 1.2 nm and about 1.6 nm.
  • the present invention relates to any one of the aforementioned filters, wherein a majority of the single wall carbon nanotubes have pores with diameters between about 0.1 nm to about 200 nm, about 0.1 nm to about 100 nm, about 1 nm to about 100 nm, about 1 nm to about 50 nm, about 1 nm to about 25 nm, or about 1 nm to about 10 nm.
  • the present invention relates to any one of the aforementioned filters, wherein a majority of the single wall carbon nanotubes have pores with diameters of about 0.1 nm, about 1 nm, about 10 nm, about 20 nm, about 30 nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm or about 100 nm.
  • the present invention relates to any one of the aforementioned filters, wherein the layer of single wall carbon nanotubes has a substantially planar surface.
  • the present invention relates to any one of the aforementioned filters, wherein the thickness of the layer of single wall carbon nanotubes is between about 0.1 ⁇ m and about 500 ⁇ m, or about 1 ⁇ m and about 10 ⁇ m.
  • the present invention relates to any one of the aforementioned filters, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm 2 and about 100 mg/cm 2 , about 0.01 mg/cm 2 and about 50 mg/cm 2 , about 0.01 mg/cm 2 and about 10 mg/cm 2 , or about 0.01 mg/cm 2 and about 1 mg/cm 2 . In certain embodiments, the present invention relates to any one of the aforementioned filters,
  • the loading of single wall carbon nanotubes is between about 0.01 mg/cm 2 and about 0.40 mg/cm 2 .
  • the present invention relates to any one of the aforementioned filters, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm 2 and about 0.30 mg/cm 2 .
  • the present invention relates to any one of the aforementioned filters, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm 2 and about 0.20 mg/cm 2 .
  • the present invention relates to any one of the aforementioned filters, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm 2 and about 0.10 mg/cm 2 . In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the loading of single wall carbon nanotubes is about 0.05 mg/cm 2 , about 0.1 mg/cm 2 , about 0.15 mg/cm 2 or about 0.2 mg/cm 2 .
  • the present invention relates to any one of the aforementioned filters, wherein a majority of the single wall carbon nanotubes are open at both ends. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein a majority of the single wall carbon nanotubes are close at one end.
  • the present invention relates to any one of the aforementioned filters, wherein at least one functional group is attached to the surface of a majority of the single wall carbon nanotubes. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an organic functional group, an inorganic functional group, or combinations thereof.
  • the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an organic functional group which comprises linear or branched, saturated or unsaturated groups. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an organic functional group; and the at least one organic functional group comprises at least one chemical group chosen from carboxyls, amines, polyamides, polyamphiphiles, diazonium salts, pyrenyls, silanes, and combinations thereof.
  • the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an inorganic functional group; and the at least one inorganic functional group comprises at least one fluorine compound of boron, titanium, niobium, tungsten, and combination thereof. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein said at least one functional group comprises a halogen atom or halogenated moiety.
  • the present invention relates to any one of the aforementioned filters, wherein said single wall carbon nanotubes comprise a substantially uniform gradient of functional groups across the surface of said carbon nanotubes and/or across at least one dimension of said filter.
  • the present invention relates to any one of the aforementioned filters, wherein a majority of said single wall carbon nanotubes have a morphology chosen from nanohorns, cylindrical, nanospirals, dendrites, trees, spider nanotube structures, nanotube Y-junctions, and bamboo morphology.
  • the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 99: 1. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 95:5. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 90:10.
  • the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 85:15. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 80:20. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 75:25.
  • the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 70:30. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 65:35. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 60:40.
  • the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 55:45. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 50:50. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 45:55.
  • the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 40:60. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 35:65. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 30:70.
  • the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 25:75. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 20:80. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 15:85.
  • the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 10:90. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 5:95. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 1 :99.
  • the present invention relates to any of the aforementioned filters, wherein a second layer of multiwalled carbon nanotubes are disposed over the layer of single wall carbon nanotubes (wherein the second layer of multiwall nanotubes can be the same or different than the first layer of multiwalled nanotubes).
  • the present invention relates to any of the aforementioned filters, wherein a second layer of single walled carbon nanotubes is disposed over the second layer of multiwalled carbon nanotubes (wherein the second layer of single wall carbon nanotubes can be the same or different that the first layer of single walled carbon nanotubes).
  • a second layer of single walled carbon nanotubes is disposed over the second layer of multiwalled carbon nanotubes (wherein the second layer of single wall carbon nanotubes can be the same or different that the first layer of single walled carbon nanotubes).
  • the present invention relates to any one of the aforementioned filters, wherein the fluid comprises at least one liquid or gas. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid comprises water. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid is selected from the group consisting of water, wastewater, river water, rain water, well water, petroleum, petroleum byproducts, biological fluids, foodstuffs, animal by-products, fruit juice, natural syrups, natural and synthetic oils used in the cooking or food industry, olive oil, peanut oil, flower oils, and vegetable oils, milk, blood, alcoholic beverages, beer, wine, liquors, medicines, aviation fuels, automotive fuels, marine fuels, locomotive fuels, rocket fuels, industrial and machine oils and lubricants, heating oils and gases, fluids derived from animals, fluids derived from humans, fluids derived from plants, and growing broths used in the processing of a biotechnology or pharmaceutical product.
  • the present invention relates to any one of the aforementioned filters, wherein the fluid has a pH of between about 1 and about 7. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid has a pH of between about 7 and about 14. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid has a pH of between about 3 and about 9. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid has a pH of about 3. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid has a pH of about 5.5. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid has a pH of about 9.
  • the present invention relates to any one of the aforementioned filters, wherein the multiwall carbon nanotubes are present in said filter in an amount sufficient to reduce the concentration of constituents in the fluid that comes into contact with said filter.
  • the present invention relates to any one of the aforementioned filters, wherein the multiwall carbon nanotubes and single wall carbon nanotubes are present in said filter in an amount sufficient to reduce the concentration of constituents in the fluid that comes into contact with said filter.
  • the present invention relates to any one of the aforementioned filters, wherein the fluid comprises one or more constituents selected from the group consisting of salts, metals, nanoparticles, microparticles, organic constituents, pathogens, microbiological organisms, DNA, RNA, natural organic molecules, molds, fungi, natural toxins, synthetic toxins, chemical warfare agents, biological warfare agents, endotoxins, proteins, and enzymes.
  • the fluid comprises one or more constituents selected from the group consisting of salts, metals, nanoparticles, microparticles, organic constituents, pathogens, microbiological organisms, DNA, RNA, natural organic molecules, molds, fungi, natural toxins, synthetic toxins, chemical warfare agents, biological warfare agents, endotoxins, proteins, and enzymes.
  • the present invention relates to any one of the aforementioned filters, wherein the fluid comprises one or more constituents selected from the group consisting of viruses or bacteria. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the filter provides a water permeability of at least 0.01 cc/s- cm 2 -atm. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the filter provides a water permeability of between about 0.01 cc/s-cm 2 -atm and about 100 cc/s-cm 2 -atm.
  • the present invention relates to any one of the aforementioned filters, wherein the filter provides an air permeability of at least 0.01 cc/s-cm 2 -atm. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the filter provides an air permeability of between about 0.01 cc/s-cm 2 -atm and about 100 cc/s-cm 2 -atm.
  • the present invention relates to any one of the aforementioned filters, wherein the porous substrate has been removed (i.e. leaving only one or more layers of carbon nanotubes).
  • the present invention relates to any one of the aforementioned filters, further comprising non-carbon containing nanotubes (such as, for example, tungsten disulfide nanotubes, boron nitride nanotubes, silicon nanotubes, titanium dioxide nanotubes, molybdenum dioxide nanotubes, copper nanotubes (CuNT) or bismuth nanotubes (BiNT).
  • non-carbon containing nanotubes such as, for example, tungsten disulfide nanotubes, boron nitride nanotubes, silicon nanotubes, titanium dioxide nanotubes, molybdenum dioxide nanotubes, copper nanotubes (CuNT) or bismuth nanotubes (BiNT).
  • the non-carbon containing nanotubes are incorporated into one or more of the carbon nanotube layers (i.e. into the MWNT layer(s) and/or SWNT layer(s)).
  • the non-carbon nanotubes are in their own layers.
  • a filter in a deposition process, can be made by vacuum deposition of carbon nanotube dispersions on at least one substrate. Ultrasonication may be used to aid in dispersing and/or deagglomerating carbon nanotubes during deposition.
  • the deposition method comprises placing carbon nanotubes in a suitable organic solvent or liquid and ultrasonicating to disperse the carbon nanotubes during deposition.
  • the organic solvent is a polar organic solvent.
  • a "polar solvent” means a solvent which has a dielectric constant ( ⁇ ) of 2.9 or greater.
  • the polar organic solvent is selected from the group consisting of DMF, THF, ethylene glycol dimethyl ether (DME), DMSO, acetone, acetonitrile, methanol, ethanol, isopropanol, n-propanol, t-butanol or 2- methoxyethyl ether.
  • other solutions, even water can be used to suspend the nanotubes.
  • proper functionalizations could allow one to suspend the CNTs in a variety of solvents.
  • the solution can be placed in a vacuum filtration device equipped with ultrasonication to further ensure that the carbon nanotubes are deagglomerated.
  • the steps of vacuum filtration and ultrasonication are separate.
  • the porous substrate used to trap the carbon nanotubes can also be removed by dissolving in acid or base, or oxidized to leave a freestanding carbon nanotube membrane.
  • the vacuum filtration process may be modified by using electromagnetic fields to align the nanostructures during deposition.
  • the nanostructures are placed in a suitable solvent (organic solvent or liquid), ultrasonicated to disperse them in the solvent, which is then placed in a vacuum filtration apparatus equipped with an ultrasonic probe to keep them from becoming agglomerated during deposition.
  • a suitable solvent organic solvent or liquid
  • an electromagnetic field is applied to align the nanostructures during their deposition. This electromagnetic field can also be arbitrarily modulated in three space adjusted and to result in a woven or partially woven-partially nonwoven structure.
  • the vacuum filtration process may be modified to allow for the creation of multiple layers of carbon nanotubes.
  • a method allows the fabrication of hybrid MWNT-SWNT filters, wherein a base of MWNT are deposited on a porous substrate and a layer of SWNT are deposited on top of the MWNT.
  • a filter may be made by an organic solvent evaporation process, wherein carbon nanotubes are bonded together with an adhesive.
  • adhesives are chemical adhesives, such as glue, metallic adhesives, such as gold, and ceramic adhesives, such as alumina.
  • carbon nanotubes can be mixed with a solvent, such as xylene.
  • this dispersion is next be placed in an ultrasonic bath to de-agglomerate the carbon nanotubes.
  • the resulting dispersion is next poured onto fiber paper to allow the organic solvent to evaporate, optionally with the addition of moderate heating.
  • the carbon nanotubes deposit on the fiber paper.
  • other polymeric materials may be added to the organic solvent to enhance the resulting structure's mechanical stability; the concentration of this adhesive material can be, for example at 0.001-10% of the weight of the solvent used.
  • a filter may be made with metallic oxide nano wires.
  • metal meshes are heated to a temperature ranging from 230-1000 0 C in an oxidative environment to create metallic oxide nano wires on the metal wires of the metal mesh.
  • the metal meshes may comprise a metal chosen from, for example, copper, aluminum, and silicon.
  • the metallic oxide nano wires can be in a size ranging from 1-100 nanometers in diameter, such as 1-50 nanometers in diameter, including 10-30 nanometers in diameter.
  • the surface of the mesh is abraded to provide surface texture to accept and hold the nanotube aliquot deposition to create better substrate attachment.
  • a filter made according to this process is then coated with carbon nanotubes.
  • solutions of well-dispersed single or multi-walled carbon nanotubes are passed through the mesh where they adhere to the metallic oxide surface.
  • This resulting material may or may not be treated thermally, mechanically (e.g., such as by hydraulic pressure), chemically, or through rapid laser heating to enhance structural integrity. It also may or may not be coated with metal, ceramic, plastic, or polymers to enhance its structural activity.
  • the resulting mesh may also be subjected to this nanotube solution treatment a number of times until the proper design criteria are reached. Further modification to the carbon nanotubes and/or support of this membrane can be made to functionalize the materials so that they chemically react with biological molecules to destroy, modify, remove, or separate them.
  • metal meshes such as copper meshes are placed in a chemical vapor deposition chamber in an oxidative environment.
  • the reaction zone is heated to a temperature ranging from 230-1000 0 C to cause creation of metallic oxide nano wires while the chamber is in an atmosphere for a period ranging from, for example, 30 minutes to 2 hours.
  • a dispersion of carbon nanotubes in liquid can then passed through the formed structure.
  • the entire structure can be thermally annealed in vacuum at, for example, about 1000 0 C to strengthen the overall structure.
  • the carbon nanotubes can be treated in a solution of nitric and sulfuric acids to create carboxyl functional groups on the carbon nanotubes.
  • a filter may be made by an air laid manufacturing process.
  • carbon nanotubes can be dispersed evenly, whether in a gas or a liquid solution.
  • a quantity of carbon nanotubes is released as a fan to stir the gas to cause dispersion of the carbon nanotubes in the chamber.
  • This gas may also be mechanically modulated at frequencies sufficient to cause dispersion.
  • the carbon nanotubes are being added to the chamber they are charged to a voltage sufficient to overcome the attractive Van der Waals forces, by passing the nanotubes through a high surface area electrode. This will prohibit agglomeration.
  • the nanotube impregnated gas is now ready for gas phase deposition.
  • the nanostructured material can now be exposed to ionizing radiation to cause the structure to fuse together and/or to coat surface via chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition PECVD, or physical vapor deposition (PVD) processing techniques, or by chemical fusing techniques.
  • CVD chemical vapor deposition
  • PECVD plasma enhanced chemical vapor deposition
  • PVD physical vapor deposition
  • the surface can then be removed and exposed to a sputtering process sufficient to cover the nanostructures and cause them to lock together.
  • the resulting membrane can then be removed from the surface by reversing the charge of the surface causing the membrane to fall away.
  • a filter may be made by a nanostructure polymerization process.
  • a nanomaterial membrane is produced by linking carbon nanotubes to one another through polymer bonding.
  • An envisioned process of this method involves first ultrasonicating a quantity of carbon nanotubes in an acid solution. When using carbon nanotubes, the acid will act to cut the lengths of the nanotubes, to expose their ends, and allow carboxyl ions (COOH) to graft thereto. The resultant carboxyl functionalized product is then treated with concentrated acid to create carboxyl groups (COOH) which are more reactive for cross-linking reactions, such as condensation. This COOH functionalized nanostructure is then reacted at the carboxyl groups to cross-link two nanostructures together. The mixture is then allowed to react until an entire cross-linked network is formed into a carbon nanotube-containing filter.
  • One aspect of the invention relates to a method of reducing the amount of constituents in a fluid, the method comprising contacting the fluid with a filter for a time sufficient to separate, remove, immobilize, modify or destroy at least a portion of one constituent from the fluid; wherein the filter comprises a layer of multiwall carbon nanotubes dispersed on a porous substrate; and the porous substrate is permeable to the flow of the fluid.
  • the present invention relates to any one of the aforementioned methods, wherein said porous substrate comprises single or multi- component polymers, nylon, polyurethane, acrylic, methacrylic, polycarbonate, epoxy, silicone rubbers, polystyrene, polyethylene terephthalate, polybutylene terephthalate, poly- paraphylene terephtalamide, poly-(p-phenylene terephtalamide), polyester ester ketone, viton fluoroelastomer, poly-tetrafluoroethylene, polyvinylchloride,
  • the present invention relates to any one of the aforementioned methods, wherein porous substrate comprises a plurality of pores which have diameters between about 0.1 ⁇ m and about 20 ⁇ m, about about 0.1 ⁇ m and about 1
  • the present invention relates to any one of the aforementioned methods, wherein porous substrate comprises a plurality of pores which have diameters of about 0.1 ⁇ m, about 1 ⁇ m, about 5 ⁇ m, about 10 ⁇ m, about 15 ⁇ m, or about 20 ⁇ m. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the porous substrate has a thickness which is between about 1 nm and about 500 nm.
  • the present invention relates to any one of the aforementioned methods, wherein the porous substrate has a thickness which is between about 50 nm and about 300 nm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the average length of the multiwall carbon nanotubes is between about 50 nm and about 5000 nm, about 50 nm and about 4000 nm, about 50 nm and about 3000 nm, about 50 nm and about 2000 nm, about 50 nm and about 1000 nm, about 100 nm and about 2000 nm, or about 100 nm and about 1000 nm.
  • the present invention relates to any one of the aforementioned methods, wherein the average inner diameter of the multiwall carbon nanotubes is between about 0.4 nm and about 0.5 nm, or about 0.4 nm and about 1.2 nm.
  • the present invention relates to any one of the aforementioned methods, wherein the average outer diameter of the multiwall carbon nanotubes is between about 1.0 nm and about 2.0 nm, or about 1.2 nm and about 1.6 nm.
  • the present invention relates to any one of the aforementioned methods, wherein a majority of the multiwall carbon nanotubes have pores with diameters between about 0.1 nm to about 200 nm, about 0.1 nm to about 100 nm, about 1 nm to about 100 nm, about 1 nm to about 50 nm, about 1 nm to about 25 nm, or about 1 nm to about 10 nm.
  • the present invention relates to any one of the aforementioned methods, wherein a majority of the multiwall carbon nanotubes have pores with diameters of about 0.1 nm, about 1 nm, about 10 nm, about 20 nm, about 30 nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm or about 100 nm.
  • the present invention relates to any one of the aforementioned methods, wherein the layer of multiwall carbon nanotubes has a substantially planar surface.
  • the present invention relates to any one of the aforementioned methods, wherein the thickness of the layer of multiwall carbon nanotubes is between about 0.1 ⁇ m and about 500 ⁇ m, or about 1 ⁇ m and about 10 ⁇ m.
  • the present invention relates to any one of the aforementioned methods, wherein the loading of multiwall carbon nanotubes is between about 0.01 mg/cm 2 and about 100 mg/cm 2 , about 0.01 mg/cm 2 and about 50 mg/cm 2 , about 0.01 mg/cm 2 and about 10 mg/cm 2 , or about 0.01 mg/cm 2 and about 1 mg/cm 2 . In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the loading of multiwall carbon nanotubes is between about 0.10 mg/cm 2 and about 1 mg/cm 2 .
  • the present invention relates to any one of the aforementioned methods, wherein the loading of multiwall carbon nanotubes is between about 0.20 mg/cm 2 and about 0.80 mg/cm 2 . In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the loading of multiwall carbon nanotubes is about 0.27 mg/cm 2 , about 0.50 mg/cm 2 , about 0.75 mg/cm 2 or about 1 mg/cm 2 . In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein a majority of the multiwall carbon nanotubes are open at both ends. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein a majority of the multiwall carbon nanotubes are closed at one end.
  • the present invention relates to any one of the aforementioned methods, wherein at least one functional group is attached to the surface of a majority of the multiwall carbon nanotubes. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an organic functional group, an inorganic functional group, or combinations thereof. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an organic functional group which comprises linear or branched, saturated or unsaturated groups.
  • the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an organic functional group; and the at least one organic functional group comprises at least one chemical group chosen from carboxyls, amines, polyamides, polyamphiphiles, diazonium salts, pyrenyls, silanes, and combinations thereof.
  • the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an inorganic functional group; and the at least one inorganic functional group comprises at least one fluorine compound of boron, titanium, niobium, tungsten, and combination thereof.
  • the present invention relates to any one of the aforementioned methods, wherein said at least one functional group comprises a halogen atom or halogenated moiety.
  • the present invention relates to any one of the aforementioned methods, wherein said multiwall carbon nanotubes comprise a substantially uniform gradient of functional groups across the surface of said carbon nanotubes and/or across at least one dimension of said filter. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein a majority of said multiwall carbon nanotubes have a morphology chosen from nanohorns, cylindrical, nanospirals, dendrites, trees, spider nanotube structures, nanotube Y-junctions, and bamboo morphology.
  • the present invention relates to any one of the aforementioned methods, further comprising a layer of single wall carbon nanotubes disposed over the layer of multiwall carbon nanotubes or disposed between the layer of multiwall carbon nanotubes and the porous substrate. In certain embodiments, the present invention relates to any one of the aforementioned methods, further consisting essentially of a layer of single wall carbon nanotubes disposed over the layer of multiwall carbon nanotubes or disposed between the layer of multiwall carbon nanotubes and the porous substrate.
  • the present invention relates to any one of the aforementioned methods, further consisting of a layer of single wall carbon nanotubes disposed over the layer of multiwall carbon nanotubes or disposed between the layer of multiwall carbon nanotubes and the porous substrate.
  • the present invention relates to any one of the aforementioned methods, wherein the average length of the single wall carbon nanotubes is between about 50 nm and about 5000 nm, about 50 nm and about 4000 nm, about 50 nm and about 3000 nm, about 50 nm and about 2000 nm, about 50 nm and about 1000 nm, about 100 nm and about 2000 nm, or about 100 nm and about 1000 nm.
  • the present invention relates to any one of the aforementioned methods, wherein the average inner diameter of the single wall carbon nanotubes is between about 0.4 nm and about 0.5 nm, or about 0.4 nm and about 1.2 nm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the average outer diameter of the single wall carbon nanotubes is between about 1.0 nm and about 2.0 nm, or about 1.2 nm and about 1.6 nm.
  • the present invention relates to any one of the aforementioned methods, wherein a majority of the single wall carbon nanotubes have pores with diameters between about 0.1 nm to about 200 nm, about 0.1 nm to about 100 nm, about 1 nm to about 100 nm, about 1 nm to about 50 nm, about 1 nm to about 25 nm, or about 1 nm to about 10 nm.
  • the present invention relates to any one of the aforementioned methods, wherein a majority of the single wall carbon nanotubes have pores with diameters of about 0.1 nm, about 1 nm, about 10 nm, about 20 nm, about 30 nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm or about 100 nm.
  • the present invention relates to any one of the aforementioned methods, wherein the layer of single wall carbon nanotubes has a substantially planar surface. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the thickness of the layer of single wall carbon nanotubes is between about 0.1 ⁇ m and about 500 ⁇ m, or about 1 ⁇ m and about 10 ⁇ m.
  • the present invention relates to any one of the aforementioned methods, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm 2 and about 100 mg/cm 2 , about 0.01 mg/cm 2 and about 50 mg/cm 2 , about 0.01 mg/cm 2 and about 10 mg/cm 2 or about 0.01 mg/cm 2 and about 1 mg/cm 2 . In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm 2 and about 0.40 mg/cm 2 .
  • the present invention relates to any one of the aforementioned methods, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm 2 and about 0.30 mg/cm 2 . In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm 2 and about 0.20 mg/cm 2 . In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm 2 and about 0.10 mg/cm 2 .
  • the present invention relates to any one of the aforementioned methods, wherein the loading of single wall carbon nanotubes is about 0.05 mg/cm 2 , about 0.1 mg/cm 2 , about 0.15 mg/cm 2 or about 0.2 mg/cm 2 . In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein a majority of the single wall carbon nanotubes are open at both ends. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein a majority of the single wall carbon nanotubes are close at one end.
  • the present invention relates to any one of the aforementioned methods, wherein at least one functional group is attached to the surface of a majority of the single wall carbon nanotubes. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an organic functional group, an inorganic functional group, or combinations thereof.
  • the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an organic functional group which comprises linear or branched, saturated or unsaturated groups. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an organic functional group; and the at least one organic functional group comprises at least one chemical group chosen from carboxyls, amines, polyamides, polyamphiphiles, diazonium salts, pyrenyls, silanes, and combinations thereof.
  • the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an inorganic functional group; and the at least one inorganic functional group comprises at least one fluorine compound of boron, titanium, niobium, tungsten, and combination thereof.
  • the present invention relates to any one of the aforementioned methods, wherein said at least one functional group comprises a halogen atom or halogenated moiety.
  • the present invention relates to any one of the aforementioned methods, wherein said single wall carbon nanotubes comprise a substantially uniform gradient of functional groups across the surface of said carbon nanotubes and/or across at least one dimension of said filter.
  • the present invention relates to any one of the aforementioned methods, wherein a majority of said single wall carbon nanotubes have a morphology chosen from nanohorns, cylindrical, nanospirals, dendrites, trees, spider nanotube structures, nanotube Y-junctions, and bamboo morphology.
  • the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 99: 1. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 95:5. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 90:10.
  • the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 85:15. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 80:20. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 75:25.
  • the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 70:30. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 65:35. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 60:40.
  • the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 55:45. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 50:50. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 45:55.
  • the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 40:60. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 35:65. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 30:70.
  • the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 25:75. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 20:80. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 15:85.
  • the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 10:90. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 5:95. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 1 :99.
  • the present invention relates to any of the aforementioned filters, wherein a second layer of multiwalled carbon nanotubes are disposed over the layer of single wall carbon nanotubes. In certain embodiments, the present invention relates to any of the aforementioned filters, wherein a second layer of single walled carbon nanotubes is disposed over the second layer of multiwalled carbon nanotubes.
  • the present invention relates to any one of the aforementioned method, wherein the filter does not comprise a porous substrate (i.e. a filter which comprise only one or more layers of carbon nanotubes).
  • the present invention relates to any one of the aforementioned methods, wherein the filters further comprise non-carbon containing nanotubes (such as, for example, tungsten disulfide nanotubes, boron nitride nanotubes, silicon nanotubes, titanium dioxide nanotubes, molybdenum dioxide nanotubes, copper nanotubes (CuNT) or bismuth nanotubes (BiNT).
  • the non-carbon containing nanotubes are incorporated into one or more of the carbon nanotube layers (i.e. into the MWNT layer(s) and/or SWNT layer(s)).
  • the non-carbon nanotubes are in their own layers.
  • the present invention relates to any one of the aforementioned methods, wherein the fluid comprises at least one liquid or gas. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid comprises water. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid is selected from the group consisting of water, wastewater, river water, rain water, well water, petroleum, petroleum byproducts, biological fluids, foodstuffs, animal by-products, fruit juice, natural syrups, natural and synthetic oils used in the cooking or food industry, olive oil, peanut oil, flower oils, and vegetable oils, milk, blood, alcoholic beverages, beer, wine, liquors, medicines, aviation fuels, automotive fuels, marine fuels, locomotive fuels, rocket fuels, industrial and machine oils and lubricants, heating oils and gases, fluids derived from animals, fluids derived from humans, fluids derived from plants, and growing broths used in the processing of a biotechnology or pharmaceutical product.
  • the present invention relates to any one of the aforementioned methods, wherein the fluid has a pH of between about 1 and about 7. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid has a pH of between about 7 and about 14. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid has a pH of between about 3 and about 9. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid has a pH of about 3. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid has a pH of about 5.5.
  • the present invention relates to any one of the aforementioned methods, wherein the fluid has a pH of about 9. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the multiwall carbon nanotubes are present in said filter in an amount sufficient to reduce the concentration of constituents in the fluid that comes into contact with said filter. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the multiwall carbon nanotubes and single wall carbon nanotubes are present in said filter in an amount sufficient to reduce the concentration of constituents in the fluid that comes into contact with said filter.
  • the present invention relates to any one of the aforementioned methods, wherein the fluid comprises one or more constituents selected from the group consisting of salts, metals, nanoparticles, microparticles, organic constituents, pathogens, microbiological organisms, DNA, RNA, natural organic molecules, molds, fungi, natural toxins, synthetic toxins, chemical warfare agents, biological warfare agents, endotoxins, proteins, and enzymes.
  • the fluid comprises one or more constituents selected from the group consisting of salts, metals, nanoparticles, microparticles, organic constituents, pathogens, microbiological organisms, DNA, RNA, natural organic molecules, molds, fungi, natural toxins, synthetic toxins, chemical warfare agents, biological warfare agents, endotoxins, proteins, and enzymes.
  • the present invention relates to any one of the aforementioned methods, wherein the fluid comprises one or more constituents selected from the group consisting of viruses or bacteria.
  • the present invention relates to any one of the aforementioned methods, wherein the filter provides a water permeability of at least 0.01 cc/s-cm 2 -atm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the filter provides a water permeability of between about 0.01 cc/s-cm 2 -atm and about 100 cc/s-cm 2 -atm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the filter provides an air permeability of at least 0.01 cc/s-cm 2 -atm.
  • the present invention relates to any one of the aforementioned methods, wherein the filter provides an air permeability of between about 0.01 cc/s-cm 2 -atm and about 100 cc/s-cm 2 -atm
  • the present invention relates to any one of the aforementioned methods, wherein at least a portion of said constituent is separated, removed, immobilized, modified or destroyed by using at least one of mechanisms selected from the group consisting of particle size exclusion, absorption, adsorption, and chemical or biological interaction or reaction.
  • Non- limiting examples of liquids that may be cleaned using the filters described herein include water, foodstuffs, biological fluids, petroleum and its byproducts, non- petroleum fuels, medicines, organic and inorganic solvents, and the liquid forms of hydrogen, oxygen, nitrogen and carbon dioxide, as may be used for rocket propellants or in industrial applications.
  • one aspect of the invention relates to method of purifying water by contacting contaminated water with a filter as described herein.
  • the present invention relates to any one of the aforementioned methods, wherein the constituents are removed from the fluid to a level of at least 1 log (90%), 2 logs (99%), 3 logs (99.9%), at least 4 logs (99.99%), at least 5 logs (99.999%), at least 6 logs (99.9999%), or at least 7 logs (99.99999%).
  • Non- limiting examples of foodstuffs that can be treated with the filters described herein comprise animal by-products (such as eggs and milk), fruit juice, alcoholic and nonalcoholic beverages, natural and synthetic syrups, and natural and synthetic oils used in the cooking or food industry [such as olive oil, peanut oil, flower oils (sunflower, safflower), vegetable oil, or oils derived from animal sources (i.e., butter, lard)], or any combination thereof.
  • animal by-products such as eggs and milk
  • fruit juice such as eggs and milk
  • alcoholic and nonalcoholic beverages such as olive oil, peanut oil, flower oils (sunflower, safflower), vegetable oil, or oils derived from animal sources (i.e., butter, lard)
  • natural and synthetic oils used in the cooking or food industry such as olive oil, peanut oil, flower oils (sunflower, safflower), vegetable oil, or oils derived from animal sources (i.e., butter, lard)
  • sulfites are often added to wine to prevent dis
  • Biological fluids that may be decontaminated with the filters described herein could be generally derived from an animal, human, plant, or comprise a culture/growth broth used in the processing of a biotechnology or pharmaceutical product.
  • the biological fluids which may be cleaned comprise blood (or blood components), serums, and milk.
  • Biological reagents used in pharmaceutical products are often quite labile and difficult to sterilize by conventional techniques. Removal of small microorganisms (such as Mycoplasma and viruses) cannot be accomplished by conventional filtration.
  • the filters described herein may be used for viral removal.
  • the filters described herein may be used to enable removal of constituents that are created during drug fabrication.
  • the filters described herein can be used for the sterilization of petroleum products.
  • a significant contamination problem is the latent growth of bacteria in petroleum or its derivatives during storage, which has been a problem particularly with aviation fuel. The presence of such bacteria can severely foul and eventually ruin the fuel. Accordingly, a major area of concern in the area of liquid purification is the cleaning bacteria from natural and/or synthetic petroleum products. Natural and/or synthetic petroleum and its byproducts include aviation, automotive, marine, locomotive, and rocket fuels, industrial and machine oils and lubricants, and heating oils and gases.
  • another aspect of the present invention includes a method of cleaning the air to remove any of the previously listed constituents.
  • gases that may be cleaned using the filters described herein include one or more gases chosen from the air or exhausts from vehicles, smoke stacks, chimneys, or cigarettes.
  • the filter When used to clean air, the filter may take a flat form to provide a greater surface area for air flow. Such flat shapes provide the additional benefit of being able to be easily cut into appropriate shapes for various filter designs, such as those used in gas masks, as well as HVAC systems.
  • gases that may be treated according to the present disclosure, such as scrubbed to clean the gas or remove them from exhaust, include argon, acetylene, nitrogen, nitrous oxide, helium, hydrogen, oxygen, ammonia, carbon monoxide, carbon dioxide, propane, butane, natural gas, ethylene, chlorine, or mixtures of any of the foregoing, such as air, nitrogen oxide, and gases used in diving applications, such as Helium/Oxygen mixtures.
  • constituents in one fluid application may actually be a desired product in another.
  • the constituent may contain precious metals or a beneficial pharmaceutical product. Therefore, in one embodiment, it may be beneficial to separate, retain and collect the constituents rather than just removing and destroying them.
  • the ability to "catch and release" desired constituents, enabling the isolation of useful constituents or certain reaction byproducts, may be accomplished by tuning the zeta potential and/or utilizing nano-electronic control of the carbon nanotubes in the filters described herein.
  • Non- limiting examples of constituents that can be removed from fluid using the disclosed filters include, but are not limited to, the following biological agents: pathogenic microorganism, such as viruses (e.g., smallpox and hepatitis), bacteria (e.g., anthrax, typhus, cholera), oocysts, spores (both natural and weaponized), molds, fungi, coliforms, intestinal parasites, biological molecules (e.g., DNA, RNA), and other pathogens, such as prions and nanobacteria.
  • pathogenic microorganism such as viruses (e.g., smallpox and hepatitis), bacteria (e.g., anthrax, typhus, cholera), oocysts, spores (both natural and weaponized), molds, fungi, coliforms, intestinal parasites, biological molecules (e.g., DNA, RNA), and other pathogens, such as prions and nanobacteri
  • prions are defined as small infectious, proteinaceous particles which resist inactivation by procedures that modify nucleic acids and most other proteins. Both humans and animals are susceptible to prion diseases, such as Bovine Spongiform
  • BSE Encephalopathy
  • CJD Creutzfeld- Jacob Disease
  • nanobacteria are nanoscale bacteria, some of which have recently been postulated to cause biomineralization in both humans and animals. It has further been postulated that nanobacteria may play a role in the formation of kidney stones, some forms of heart disease and Alzheimer's Disease. Further, nanobacteria are also suspected of causing unwanted biomineralization and/or chemical reactions in some industrial processes.
  • constituents that can be removed from fluid using the disclosed filters include, but are not limited to noxious, hazardous or carcinogenic chemicals comprised of natural and synthetic organic molecules (such as toxins, endotoxins, proteins, enzymes, pesticides, and herbicides), inorganic constituents (such as heavy metals, fertilizers, inorganic poisons) and ions (such as salt in seawater or charged airborne particles), as well as nanoscale and micron scale particles in general.
  • noxious, hazardous or carcinogenic chemicals comprised of natural and synthetic organic molecules (such as toxins, endotoxins, proteins, enzymes, pesticides, and herbicides), inorganic constituents (such as heavy metals, fertilizers, inorganic poisons) and ions (such as salt in seawater or charged airborne particles), as well as nanoscale and micron scale particles in general.
  • the cleaned fluid specifically clean water
  • the chemical compounds that may be removed from fluid using the article described herein are removal target atoms or molecules that include at least one atom or ion chosen from the following elements: antimony, arsenic, aluminum, selenium, hydrogen, lithium, boron, carbon, oxygen, calcium, magnesium, sulfur, chlorine, niobium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, bromine, strontium, zirconium, yttrium, molybdenum, rhodium, palladium, iodine, silver, cadmium, indium, cesium, tin, barium, lanthanum, tantalum, beryllium, copper,
  • filters described herein include, for example, home (e.g., domestic water and air filtration), recreational (environmental filtration), industrial (e.g., solvent reclamation, reactant purification), governmental (e.g., the Immune Building Project, military uses, waste remediation), and medical (e.g., operating rooms, clean air and face masks) locations.
  • home e.g., domestic water and air filtration
  • recreational environmental filtration
  • industrial e.g., solvent reclamation, reactant purification
  • governmental e.g., the Immune Building Project, military uses, waste remediation
  • medical e.g., operating rooms, clean air and face masks
  • SWNT Filter Preparation Commercially available single-walled carbon nanotubes (SWNTs) with a purity of greater than 95% (w/w) SWNTs were purchased from Stanford Materials (SWNT-90, lot #082106). Based on the manufacturer's data, the as- received SWNTs had lengths of 10 to 20 ⁇ m, an average outer diameter of 1.2 nm, and a specific surface area of 407 m 2 g "1 .
  • Stable suspensions of SWNTs in de -ionized water were prepared for electrophoretic mobility (EPM) measurements (ZetaPALS, Brookhaven Instruments Corp., Holtsville, NY).
  • EPM electrophoretic mobility
  • Probe sonication of SWNTs in deionized water (DI) was performed six times to obtain an adequately stable SWNT suspension.
  • DI deionized water
  • the Sonicator 450 probe (Misonix, Farmingdale, NY) was set at a power output of 4OW for 30 minutes for each sonication, and the mixture was allowed to cool for 30 minutes between sonication rounds. This stable SWNT solution provided the concentrated stock, which was adjusted to different solution conditions for EPM measurements.
  • SWNT EPM measurements Concentrated pre-filtered solutions, acids, or bases were added as necessary to obtain desired solution chemistries for SWNT EPM measurements at each of the conditions tested. Three experimental runs were performed at minimum for each EPM data point.
  • the as-received SWNTs were suspended at a concentration of 0.5 mg SWNT per mL of dimethylsulfoxide (DMSO).
  • DMSO dimethylsulfoxide
  • This SWNT suspension was then probe-sonicated for 15 minutes on the Sonifier 450 probe sonicator (Branson model 102) at a power output of 5OW.
  • the sonicated suspension was allowed to cool, and then vacuum-deposited varying volumes onto a 5 ⁇ m pore size Omnipore PTFE (Millipore, USA) membrane to attain the desired loading of SWNT.
  • Rinses of 50 mL of ethanol followed by 50 mL of deionized water removed residual DMSO from the SWNT filter.
  • MWNT Filter Preparation Multiwall carbon nanotubes (MWNTs) were purchased, as prepared, from NanoTechLabs Inc. (Yadkinville, NC). The MWNTs used have previously been analyzed by TEM, SEM, EDX, and TGA [Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2008. 42(19): p. 7528-7534]. These MWNTs were deposited on a 5- ⁇ m-pore size PTFE membrane (Millipore, USA), by a sonication and filtration procedure similar to the preparation of the S WNT -hybrid filter [Brady-Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481-484].
  • the MWNTs were suspended at a concentration of 0.5 mg/mL in dimethyl sulfoxide (DMSO). The suspension was then probe sonicated for 15 minutes at a power output of 5OW on the Sonifier 450 probe sonicator (Branson model 102), and subsequently allowed to cool. All MWNT suspensions were used within a few hours of preparation to avoid variation in MWNT aggregation, which could alter filter performance. Deposition of 6 mL of the MWNTs from solution was achieved by vacuum filtration through the PTFE membrane to attain a loading of 0.32 mg/cm 2 on the base filter. Ethanol followed by deionized (DI) water were then filtered through the SWNT filters to remove residual DMSO.
  • DI deionized
  • SWNT-MWNT Filter Preparation The lower layer of the SWNT-MWNT filter was composed of commercially available multiwall carbon nanotubes (MWNT) purchased from NanoTechLabs Inc. (Yadkinville, NC). These MWNTs were used in prior work and had been previously analyzed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive x-ray (EDX), and thermogravimetric analysis (TGA), as summarized in Figure 5 [Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2008. 42(19): p. 7528-7534]. Additionally, the electrophoretic mobilities (EPMs) of these MWNTs over varying solution conditions have been measured.
  • EPMs electrophoretic mobilities
  • MWNTs were deposited on the 5- ⁇ m pore size PTFE membrane (Millipore, USA) by a sonication and filtration procedure similar to the preparation of the SWNT-hybrid filter [Brady-Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481-484]. Specifically, MWNTs were added at a concentration of 0.5 mg/mL to dimethyl sulfoxide (DMSO). The suspension was then sonicated for 15 minutes at a power output of 5OW with the Sonifier 450 probe sonicator (Branson model 102) to separate aggregates of the MWNTs and achieve a more uniform dispersion.
  • DMSO dimethyl sulfoxide
  • MWNT suspensions were allowed time to cool, but were used within a few hours of preparation to avoid variation in MWNT aggregation, which could alter filter performance. Bath sonication of the MWNT suspension was also performed for 10 seconds immediately prior to filter deposition to disrupt any aggregates. Deposition of 5 mL (83% of the loading of the previous MWNT filter) of the MWNTs from solution was achieved by vacuum filtration through the PTFE membrane to attain a loading of 0.27 mg/cm 2 MWNTs on the base filter.
  • SWNT-MWNT filter The thin upper coating of the SWNT-MWNT filter was composed of commercially available single-walled carbon nanotubes (SWNTs) with a purity of greater than 95% (w/w) SWNTs (Stanford Materials, SWNT-90, lot #082106).
  • SWNTs single-walled carbon nanotubes
  • SWNTs were suspended in a solution.
  • the dilution of 0.1 mg/mL SWNT in DMSO was selected to provide adequate settling time to ensure full coverage of the SWNT coating layer over the entire MWNT matrix surface.
  • the SWNT suspension was sonicated for 15 minutes with the Sonifier 450 probe sonicator (Branson model 102) at a power output of 5OW.
  • the sonicated suspension was allowed to cool, then re-sonicated in a bath sonicator for 10 seconds immediately prior to the coating procedure, which consisted of vacuum deposition of 5 mL of the 0.1 mg/mL SWNTs onto the MWNT layer that overlaid the 5- ⁇ m pore size PTFE (Omnipore filters, Millipore, USA) membrane. After the SWNT layer of the nanotubes was laid, the dual filter was rinsed with 50 mL of ethanol followed by 50 mL of deionized water to remove residual DMSO.
  • Example 2 ⁇ Filter Characterization of Morphology and Permeability A) MWNT Filter Characterization.
  • the permeability of the MWNT filters was calculated by measuring the transmembrane pressure drops over a range of permeate water fluxes.
  • the filtration system for these experiments consisted of a 47 mm plastic holder (Whatman, USA) for supporting the membranes and a pressurized tank system as described previously [Brady-Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481- 484; Kang, S., et al. Journal of Membrane Science, 2007. 296(1-2): p. 42-50].
  • the surface morphology of the MWNT filter was studied under various magnifications using field emission scanning electron microscopy (FESEM) (Hitachi S-4500, Hitachi, USA).
  • MWNTs were suspended in deionized (DI) water and then six repetitions were performed of sonication for 30 minutes, followed by cooling, and separation of supernatant from the MWNT aggregates. The resulting supernatant, a solution of stable MWNTs in DI water, was then used as the MWNT stock for performing the electrophoretic mobility (EPM) measurements. Concentrated pre-filtered salt solutions, acids, or bases were added as necessary to obtain the desired MWNT suspension immediately prior to EPM measurement (ZetaPals, Brookhaven Instruments Corp., Holtsville, NY).
  • SWNT-MWNT Filter Characterization The permeability of the prepared SWNT-MWNT filters was evaluated by measuring a range of permeate water fluxes and transmembrane pressure drops.
  • the filtration system was composed of a 47-mm plastic holder (Whatman, USA) for membrane support and a pressurized tank system as described previously [Brady-Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481- 484; and Kang, S., et al, Journal of Membrane Science, 2007. 296(1-2): p. 42-50].
  • MS2 viruses were purchased, along with their bacterial host Escherichia coli 15597, from the American Tissue Culture Collection (ATCC).
  • ATCC American Tissue Culture Collection
  • the MS2 bacteriophage commonly used as a conservative viral tracer in aquatic environments [Penrod, S.L., T.M. Olson, and S. B. Grant Langmuir, 1996. 12(23): p. 5576-5587; Redman, J.A., et al., Environmental Science & Technology, 1997. 31(12): p. 3378-3383; and Schijven, J.F., S.M. Hassanizadeh, and R. de Bruin Journal of Constituent Hydrology, 2002.
  • p. 259-279 was selected as a model virus for its ease of quantification and non-infectivity toward humans.
  • the electrophoretic mobility of MS2 in solutions containing varied salt and organic matter concentrations was obtained using a ZS90 Zetasizer instrument (Malvern, UK).
  • the electrolyte solutions were filtered through a 0.22- ⁇ m-pore size cellulose acetate filter.
  • MS2 Size Measurements The sizing experiments of MS2 were performed using a multi-angle light scattering unit (ALV-5000, Langen, Germany). The details of the instrument are described elsewhere [Chen, K.L. and M. Elimelech Langmuir, 2006. 22: p. 10994-11001].
  • the MS2 viral samples were placed in new glass vials (Supelco, Bellefonte, PA) that were previously soaked in a cleaning solution (Extran MA 01, Merck KGaA, Darmstadt, Germany) overnight, thoroughly rinsed in deionized water, and oven dried under dust-free conditions [Saleh, N. B., L. D. Pfefferle, and M. Elimelech Environmental Science & Technology, 2008. 42: p.
  • the MS2 samples used in the sizing experiments were diluted by a factor of 1000 from the original stock. Electrolyte solutions, pH adjusting reagents, and/or SR-NOM were added at least 15 minutes prior to the start of the sizing experiments.
  • the dynamic light scattering measurements were conducted by positioning the detector at 90° with the incident laser beam and the auto-correlation function having been allowed to accumulate for over 15 s [Saleh, N. B., L.D. Pfefferle, and M. Elimelech Environmental Science & Technology, 2008. 42: p. 7963-7969]. The measurements were performed for a time period ranging from 10-20 min to obtain a statistically significant average of the hydrodynamic radius of the MS2 samples for each condition. The average hydrodynamic radius was obtained from the average of the raw data collected in at least two sizing experiments for each condition.
  • SR-NOM Suwannee River natural organic matter
  • the SR-NOM mixtures were refrigerated in the dark until use, and all containers or vials containing SR-NOM mixtures were continuously shielded from light during experiments. All experimental solutions were adjusted to pH 5.5 using NaOH and HCl as necessary, with the exception of the specific tests for viral filtration with varying pH. These solutions were adjusted to pH 5.5, pH 3, or pH 9, as indicated. The various solutions were made up using sodium chloride, magnesium chloride, calcium chloride, sodium bicarbonate, disodium phosphate, SR-NOM (International Humic Substances Society, St. Paul, MN), and sodium alginate (Sigma- Aldrich, St. Louis, MO).
  • Example 2 Viral Preparation for Experiments with SWNT-MWNT Filters. Viral removal on the SWNT-MWNT filters of Example 1 was shown for several types of viruses which were prepared as follows. Three model bacteriophages — MS2, PRD-I and T4 — were purchased from the American Tissue Culture Collection (ATCC), along with their host bacteria, E. coli 15597, E. coli 13706, and E. coli 11303, respectively. MS2 and PRD- 1 viral stocks were suspended at various dilutions in DI water and refrigerated at 4 0 C until experiments were performed. A more highly concentrated stock of T4 was attained by injecting the virus into a suspension of E.
  • ATCC American Tissue Culture Collection
  • Viral filtration on the filters of Example 1 was performed in the same manner as previously described [Brady-Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481-484]. Briefly, viruses were suspended in 10 mL of the background solution to be tested and filtered through the SWNT-MWNT layers and supporting 5- ⁇ m pore PTFE membrane (Millipore, USA) at a constant permeation flux using a peristaltic pump. The filter was preconditioned by flow of the 10 mM NaCl background solution at pH 5.5 (without virus) through the filter. Viral seed stock was then spiked into the 10 mM NaCl solution and pumped through the system.
  • Escherichia coli Kl 2 and Staphylococcus epidermis were selected to model Gram negative and Gram positive bacteria, respectively.
  • the bacterial cultures had each been previously grown (separately) from a single colony of their plated culture.
  • a sterile wire transfer loop inoculated bacteria from discrete homogeneous colonies into individual tubes of LB. These LB tubes were then incubated overnight to the stationary growth phase (37 0 C). 25% (v/v) glycerol was then added to the bacterial suspension to allow freezing of the bacterial culture and storage at -80 0 C.
  • Wastewater effluent and river water samples were modeled by wastewater effluent and river water samples. Wastewater was obtained from a local wastewater treatment plant (Wallingford, CT). The secondary wastewater effluent (a rotating biological contactor) was collected prior to the disinfection stage at the treatment plant. Wastewater effluent was divided into two samples in the lab: (i) as-collected wastewater effluent that contained pathogens and (ii) wastewater effluent that had been filtered through a 0.45- ⁇ m membrane for removal of suspended matter. The original wastewater effluent was then diluted five-fold using filtered wastewater effluent to avoid clogging of the CNT hybrid filter and to allow better imaging of individual microorganisms.
  • the wastewater had a measured pH of 6.9, and an ionic conductivity of 279 ⁇ S (conductivity meter model 32, YSI, USA).
  • Total organic carbon (TOC) and dissolved organic carbon (DOC) TOC analyzer, TOC-V CSH , Shimadzu, USA) were measured as 25.56 mg/L and 16.86 mg/L, respectively, while UV absorption at UV 254 nm (1 cm cell) gave a reading of 0.09 (UV/Vis spectrophotometer model 8453, HP, USA).
  • Bacterial inactivation rates on the filters of Example 1 were measured by a standard fluorescent assay, which confirmed the membrane integrity of the cells.
  • Bacterial suspensions were filtered through the SWNT-MWNT or MWNT filters. The filters were then incubated in the dark for the indicated times in saline solution (154 mM, or 10 mM NaCl) at 37 0 C. After incubation, cells were shielded from light and stained with propidium iodide (PI, 50 ⁇ M) for 15 min, and then counter- stained with SYTO®-9 for 5 min. The cells on the filter were imaged using an epifluorescence microscope (Olympus).
  • Electrophoretic mobility (EPM) measurements which are proportional to zeta potential, gave indication of the relative surface charges of the MWNTs over the range of experimental conditions tested.
  • the MWNT EPM became less negative with increasing ionic strength from -0.82 ⁇ 0.24 x 10 "8 m 2 V “1 s "1 at 1 mM NaCl to -0.50 ⁇ 0.20 x 10 "8 m 2 V “ 1 s "1 at 100 mM NaCl.
  • Compression of the diffuse double layer and reduction of Stern potential of the MWNTs caused lower magnitude EPM values at the higher ionic strengths [Williams, R.A., et al., Particle Deposition and Aggregation: Measurement, Modeling and Simulation. 1995, Woburn, MAboutterworth-Heinemann].
  • Strongly basic and acidic solutions also caused divergence from the -0.59 ⁇ 0.24 x
  • MWNTs are intended to be unfunctionalized, during sonication, defects are formed that can enable partial functionalization [Ye, Y., et al. Applied Physics Letters, 1999. 74(16): p. 2307-2309; and Zhang, J., et al. Journal of Physical Chemistry, 2003. 107(16): p. 3712-3718].
  • SR-NOM played a role in enhancing the negative EPM on the MWNT to -1.03 ⁇ 0.39 x 10 ⁇ 8 m 2 v Vand -1.01 ⁇ 0.41 x 10 ⁇ 8 m 2 V “1 s "1 for the cases of 1 mg/L SR-NOM and 5 mg/L SR-NOM addition to 10 rnM NaCl, respectively.
  • the SR-NOM which contains both hydrophobic and hydrophilic groups as well as metals, is capable of contributing to the negative charge of the MWNT surface.
  • MS2 isoelectric point and electrophoretic mobility for various solution chemistries and pH have previously been reported [Penrod, S.L., T.M. Olson, and S.B. Grant Langmuir, 1996. 12(23): p.
  • MS2 aggregates were larger at 100 mM NaCl, with a radius of 82.38 ⁇ 2.77 nm, than under the 1 mM NaCl conditions, with a radius of 78.22 ⁇ 1.98 nm.
  • Addition of divalent salts at the same equivalent ionic strength had varying impacts on viral surface charge.
  • the pH of the solution also had significant effect on the electrophoretic mobility of the viral capsids, through protonation and deprotonation of amino acid functional groups on the viral surface.
  • the isoelectric point (IEP) of MS2 was previously measured as between pH 3.5-3.9. Below this pH, MS2 is positively charged, while above this pH, the exterior of the viral capsid is negatively charged.
  • NOM and alginate were chosen to model organic matter in natural and engineered aquatic environments due to the prevalence of humic-like substances and acidic polysaccharides in surface waters and wastewater effluent [Barker, D.J. and D. C. Stuckey, Water Research, 1999. 33(14): p. 3063-3082; Barker, D.J., et al. Journal of Environmental Engineering- Asce, 2000. 126(3): p. 239-249; and Manka, J., et al. Environmental Science &
  • alginate may also compete with viruses for binding sites on the MWNT filter [Watson, J.T. and W.A. Drewry, Adsorption off2 bacteriophage by activated carbon and ion exchange. 1971, Water Resources Research Center, University of Tennessee: Knoxville, Tennessee].
  • the filtration was slightly better in the case of 1 mg/L alginate added to 1 mM CaCl 2 + 7 niM NaCl, although only 1.32 ⁇ 0.55 log viral removal was attained. This increase in removal may be due to calcium's ability to form strong bridging and gelation between MS2 and MWNT through binding of the calcium ions to the carboxylic groups of the alginate molecules as described in the Grant's egg box model.
  • MS2 has neutral charge at its isoelectric point at 3.9 and therefore, the surface becomes increasingly positive as pH becomes lower than 3.9 and increasingly negatively charged as pH increases above 3.9. While the exact source of charge on carbon nanotubes is relatively not well understood, CNTs have consistently shown to be negatively charged in aquatic solutions [Sano, M. and S. Shinkai Langmuir, 2001 : p. 7172-7173; and Jiang, L. Q., L. Gao, and J. Sun, Journal of Colloid and Interface Science, 2003. 260: p. 89-94].
  • the MWNT filter experimental data follows trends obtained on the SWNT -hybrid filter, the log MS2 viral removal at each pH is far better than at each condition on the SWNT filter.
  • the log removal of MS2 on the MWNT filter at pH 9 is 4 ⁇ 0.79, while, at the same pH, the SWNT filter attains only 1.04 ⁇ 0.68 log removal.
  • the permeability of the SWNT-MWNT filter indicated a highly porous matrix that operated in the microf ⁇ ltration range of pressures.
  • the SWNT-MWNT filter demonstrated a permeability of 9,361 ⁇ 550 Lm 2 h "1 bar "1 .
  • This value was comparable to the permeabilities of the MWNT and SWNT filters, namely 11,900 ⁇ 435 Lrn Vbar "1 and 13,800 ⁇ 320 Lrn Vbar "1 [Brady-Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481-484], respectively.
  • the one major difference related to the permeability of the SWNT-MWNT filter is that during the preparation of the SWNT-MWNT filter, in addition to the probe sonication of the nanotube suspensions, the mixture was also bath sonicated immediately prior to filter deposition. This likely contributed towards more evenly dispersed nanotubes, causing reduction of preferential flow paths in the filter, and thereby reducing permeability slightly.
  • the SWNT-MWNT filter's ability to remove additional model viruses was tested, as described below.
  • the MS2, PRDl, and T4 viruses are highly varied; with different structures, ribonucleic acids, diameters, and isoelectric points ( Figure 5). These viruses were chosen not to systematically determine how their individual characteristics may govern viral removal, but rather to demonstrate that the filter is effective in removal of a wide range of viruses.
  • the base solution chemistry selected for all viral removal experiments was 10 mM NaCl at pH 5.5 to allow comparison with studies on the MWNT and SWNT filters (not shown). Removal of MS2 virus was first examined to allow comparison of the SWNT-
  • SWNT-MWNT filter would more closely approximate the performance of the MWNT filter since the filter was made up of 83% MWNT and only 17% SWNT. However, it was not anticipated that the dual SWNT-MWNT filter would perform better than the 100% MWNT filter, since the SWNT filter had much lower viral removal. While not intending to be bound by any one theory, it is likely that this improvement is due to the procedural modification made to follow probe sonication with bath sonication immediately prior to nanotube deposition. This method, which was only used in obtaining the SWNT-MWNT data, enabled the matrix to have more uniform surface coverage and higher contact opportunities for adsorption than filters that were prepared from more highly aggregated stocks.
  • Gram negative bacteria is an art recognized term for bacteria characterized by the presence of a double membrane surrounding each bacterial cell.
  • Gram-negative bacteria include Acinetobacter calcoaceticus, Actinobacillus actinomycetemcomitans, Aeromonas hydrophila, Alcaligenes xylosoxidans, Bacteroides, Bacteroides fragilis, Bartonella bacilliformis, Bordetella spp., Borrelia burgdorferi, Branhamella catarrhalis, Brucella spp., Campylobacter spp., Chalmydia pneumoniae, Chlamydia psittaci, Chlamydia trachomatis, Chromobacterium violaceum, Citrobacter spp., Eikenella corrodens, Enterobacter aerogenes, Escherichia coli, Flavobacterium meningosepticum, Fusobacterium spp., Haemophilus influenzae, Haemophilus spp., Helicobacter pylori, Klebsiella spp.,
  • E. coli a rod-shaped Gram negative bacteria, was selected for the inactivation experiments on the carbon nanotube filters. Previous studies had shown higher E. coli inactivation on SWNTs than MWNTs [Kang, S., et al, Langmuir, 2008. 24(13): p. 6409- 6413]. It addition, it had also been shown that the SWNT filter had relatively high inactivation of E. coli, even after only 15 minutes exposure to the nanotubes [Brady- Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481-484]. The SWNT- MWNT filter essentially utilized a topmost layer of nanotubes that were equivalent to those used for the SWNT filter.
  • E. coli demonstrated greater resilience to exposure to the MWNT filter.
  • the 30-minute exposure time led to inactivation of only 58.5 ⁇ 8.5% of this Gram negative bacteria.
  • This value while far lower than that shown for SWNT-MWNT filter exposure, was still significantly higher than inactivation demonstrated in previous direct contact studies between E. coli and MWNTs [Kang, S., et al., Langmuir, 2008. 24(13): p. 6409-6413; and Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2008. 42(19): p. 7528-7534].
  • Gram positive bacteria is an art recognized term for bacteria characterized by having as part of their cell wall structure peptidoglycan as well as polysaccharides and/or teichoic acids and are characterized by their blue-violet color reaction in the Gram-staining procedure.
  • Gram-positive bacteria include: Actinomyces spp., Bacillus anthracis, Bifidobacterium spp., Clostridium botulinum, Clostridium perfringens, Clostridium spp., Clostridium tetani, Cory neb acterium diphtheriae, Corynebacterium jeikeium, Enterococcus faecalis, Enterococcus faecium, Erysipelothrix rhusiopathiae, Eubacterium spp., Gardnerella vaginalis, Gemella morbillorum, Leuconostoc spp., Mycobacterium abcessus, Mycobacterium avium complex, Mycobacterium chelonae, Mycobacterium fortuitum, Mycobacterium haemophilium, Mycobacterium kansasii, Mycobacterium leprae, Mycobacterium marinum, Mycobacterium
  • Staphylococcus epidermis a spherical cocci, was selected to model Gram positive bacteria in the inactivation tests.
  • S. epidermis was demonstrated to have significantly lower inactivation rates than the Gram negative E. coli.
  • the inactivation of the Gram positive bacteria was much higher on the SWNT-MWNT filter (53.1 ⁇ 3.6% at 30 minutes), the rates for S. epidermis were still much lower than those for the Gram negative E.
  • SWNTs [Kang, S., et al, Langmuir, 2007. 23(17): p. 8670-867].
  • Prior staining assays had shown time dependence for inactivation of the Gram positive Bacillus subtiis [Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2009. 43(7): p. 2648-2653].

Abstract

Filters comprising a layer of multiwall carbon nanotubes dispersed on a porous substrate, with or without a layer of single wall carbon nanotubes dispersed on top of the layer of multiwall carbon nanotubes, have been fabricated and shown to be useful for removing constituents from fluids.

Description

Carbon Nanotube Filters
RELATED APPLICATION
This application claims the benefit of priority to United States Provisional Patent Application serial number 61/167,318, filed April 7, 2009; the contents of which are hereby incorporated by reference.
GOVERNMENT SUPPORT
This invention was made with support under National Science Foundation Grant No. BES-0646247. The government has certain rights in the invention. BACKGROUND
Carbon nanotubes (CNTs) have tubular structures formed by graphene sheets rolled into seamless cylinders with diameters of, for example, about 0.6 namometers to a few tens of nanometers, and lengths that can reach micrometers. A nanotube with only one wall is referred to a single wall carbon nanotube ("SWNT"), while a nanotube with multiple concentric walls is referred to as a multiwall carbon nanotube ("MWNT"). Carbon nanotubes (CNTs) have exceptional properties of strength, high surface area, thermal stability, optical activity, thermal and electrical conductivity, and ease of functionalization that tailor them to specific applications [Yu, M.F., et al. Science, 2000. 287(5453): p. 637- 640; Peigney, A., et al. Carbon, 2001. 39(4): p. 507-514; Kim, Y.A., et al. Chemical Physics Letters, 2004. 398(1-3): p. 87-92; Avouris, P. MRS Bulletin, 2004. 29(6): p. 403- 410; Biercuk, M.J., et al. Applied Physics Letters, 2002. 80(15): p. 2767-2769; Berber, S., Y.K. Kwon, and D. Tomanek Physical Review Letters, 2000. 84(20): p. 4613-4616; Ebbesen, T.W., et al. Nature, 1996. 382(6586); Baughman, R.H., A.A. Zakhidov, and W.A. de Heer Science, 2002. 297(5582): p. 787-792; and Ajayan, P. and O. Zhou Carbon Nanotubes, 2001. 80: p. 391-425].
Owing to these characteristics, CNTs have been assessed or employed for use in environmentally relevant areas as diverse as water treatment, adsorption, environmental sensing, remediation, energy technologies (solar cells, fuel cells, hydrogen storage), and green and high-strength building materials [Mauter, M.S. and M. Elimelech Environmental Science & Technology, 2008. 42(16): p. 5843-5859; Savage, N. and M. Diallo Journal of Nanoparticle Research, 2005. 7: p. 331-342; Theron, J., J.A. Walker, and T.E. Cloete Critical Reviews in Microbiology, 2008. 34(1): p. 43-69; Peng, X., Z. Luan et al. Materials Letters, 2005. 59: p. 399-403; Di, Z., et al., Chemosphere, 2006. 62(5): p. 861-865; Li, Y., et al. Chemical Physical Letters, 2001. 350(5-6): p. 412-416; Sinha, N., J.Z. Ma, and J.T.W. Yeow Journal ofNanoscience and Nanotechnology, 2006. 6(3): p. 573-590; Wang, J. Electroanalysis, 2005. 17(1): p. 7-14 ; Wang, X.K., et al. Environmental Science & Technology, 2005. 39(8): p. 2856-2860; Cai, Y.Q., et al. Journal of Chromatography A, 2005. 1081(2): p. 245-247; Wang, CC, et al. Progress in Polymer Science, 2004. 29(11): p. 1079-1141; Kamat, P.V., J. Phys. Chem. C 2007, 111 (7), p. 2834-2860; Girishkumar, G., K. Vinodgopal, and P. Kamat Journal of Physical Chemistry B. 108(52): p. 19960-19966; Liu, Z.L., et al. Langmuir, 2002. 18(10): p. 4054-4060; Liu, C, et al. Science, 1999. 286(5442): p. 1127; Lee, S.M., et al. Synthetic Materials, 2000. 113(3): p. 209-216; Zandonella, C Nature, 2001. 410(6830): p. 734-735; Li, G.Y., P.M. Wang, and X. Zhao, Cement and Concrete Composites, 2007. 29(5): p. 377-382; Schadler, L. S., S. C Giannaris, and P.M. Ajayan Applied Physics Letters, 1998. 73(26): p. 3842-3844; and Banerjee, S., T. Hemraj-Benny, and S. S. Wong. Advanced Materials, 2005. 17(1): p. 17-29]. Their use in environmental applications, however, is still nascent, with few applications proposed or investigated.
In the field of water treatment, carbon nanotubes generate interest for their advantages of high surface area, relatively small pore size, and cytotoxicity to various pathogens. Several researchers have looked to carbon nanotubes as a scaffold for nanoparticles, such as amorphous aluminum for adsorption of fluoride and nano-scale ceria for removal of arsenate and chromium from water [Peng, X., Z. Luan, and e. al. Materials Letters, 2005. 59: p. 399-403; Di, Z., et al., Chemosphere, 2006. 62(5): p. 861-865; and Li, Y., et al. Chemical Physical Letters, 2001. 350(5-6): p. 412-416]. Other studies explored the use of CNTs for adsorption of low molecular weight organic constituents [Lu, CS., YX. Chung, and K.F. Chang Water Research, 2005. 39(6): p. 1183-1189] and toxins [Yan, H., et al. Chemosphere, 2006. 62(1): p. 142-148] from water. Although reasonable constituent adsorption has been demonstrated in some of these studies, the high levels of these constituents in some waters would necessitate large quantities of CNTs for adequate constituent removal.
A limited number of studies have explored the use of CNTs for filtration and separation applications. Srivastava et al. [Srivastava, A., et al. Nature Materials, 2004. 3(9): p. 610-614] have constructed a cylindrical membrane filter comprised of radially aligned multiwall carbon nanotubes (MWNTs) forming a CNT layer several hundreds of micrometers thick. It was shown that the MWNT filter was effective in removing
- ? - hydrocarbons from petroleum wastes as well as bacteria and viruses. Wang et al. [Wang, X.F., et al. Environmental Science & Technology, 2005. 39(19): p. 7684-7691] have developed a composite polymeric ultrafiltration membrane, with oxidized MWNTs incorporated in the top layer. The composite ultrafiltration membrane was shown to have high retention of oil/water emulsions. Lastly, it has been demonstrated that micro fabricated membranes comprised of small-diameter aligned MWNTs can produce high water flux, and selective separation of low molecular weight solutes [Hinds, B.J., et al. Science, 2004. 303(5654): p. 62-65; and Holt, J.K., et al. Science, 2006. 312(5776): p. 1034-1037]. However, the primary separation mechanism of the MWNT filters in the studies discussed above is based on size exclusion or sieving. Such filters often require high pressure for operation and are prone to pore plugging and performance deterioration upon filtration of environmental samples.
A highly permeable single-walled carbon nanotube (SWNT) filter and its use for the effective removal of bacterial and viral pathogens from water at low pressures has also been described [Brady-Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481-484]. The filter described therein utilizes several key properties of SWNTs: their small diameter and high surface area, their tendency to aggregate and form highly porous structures, and their antibacterial properties. In addition, the removal and inactivation of microbes has been demonstrated with SWNT filters; and numerous studies have addressed the cytotoxicity of a range of carbon based nanomaterials [Kang, S., et al., Langmuir, 2008. 24(13): p. 6409- 6413; Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2008. 42(19): p. 7528-7534; Kang, S., et al., Langmuir, 2007. 23(17): p. 8670-8673; Jia, G., et al., Environmental Science & Technology, 2005. 39(5): p. 1378-1383; Zhu, Y., et al., Nanotechnology, 2006. 17(18): p. 4668-4674; Magrez, A., et al., Nano Letters, 2006. 6(6): p. 1121-1125; and Pulskamp, K., S. Diabete, and H.F. Rrug, Toxicology Letters, 2007.
168(1): p. 58-74]. Further, cell membrane lysis has also been imaged for the case of E. coli on the SWNT filter and MWNTs [Brady-Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481-484; Kang, S., et al., Langmuir, 2008. 24(13): p. 6409-6413; and Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2008. 42(19): p. 7528-7534]. In fact, studies have shown that SWNTs are more effective than MWNTs in cell inactivation [Kang, S., et al., Langmuir, 2008. 24(13): p. 6409-6413; and Jia, G., et al., Environmental Science & Technology, 2005. 39(5): p. 1378-1383]. Although cell inactivation is not yet fully understood, several mechanisms have been proposed, including physical membrane damage [Kang, S., et al, Langmuir, 2007. 23(17): p. 8670-8673], physical piercing [Narayan, R.J., CJ. Barry, and R.L. Brigmon, Materials Science and Engineering B, 2005. 123(2): p. 123-129], metal catalyst toxicity [Pulskamp, K., S. Diabete, and H.F. Krug, Toxicology Letters, 2007. 168(1): p. 58-74], disruption of metabolic pathways [NeI, A.N., et al., Science, 2006. 311(5761): p. 622 - 627], oxidative stress [Pulskamp, K., S. Diabete, and H.F. Krug, Toxicology Letters, 2007. 168(1): p. 58- 74; NeI, A.N., et al., Science, 2006. 311(5761): p. 622 - 627; Manna, S.K., et al., Nano Letters, 2005. 5(9): p. 1676-1684; and Shvedova, A., et al., Journal of Toxicology and Environmental Health, Part A, 2003. 66(20): p. 1909-1926], and reactive oxygen species generation [Pulskamp, K., S. Diabete, and H.F. Krug, Toxicology Letters, 2007. 168(1): p. 58-74]. Recent DNA microarray work has shown up-regulation of genes that support theories of inactivation caused by cell membrane damage and oxidative stress [Kang, S., et al., Langmuir, 2008. 24(13): p. 6409-6413]. Low concentrations of iron metal catalysts were recently shown to have negligible effect on cytotoxicity [Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2008. 42(19): p. 7528-7534]. Other important factors, such as surface area and surface chemistry of nanotubes, were shown to influence inactivation of human fibroblasts [Tian, F.R., et al., Toxicology in Vitro, 2006. 20(7): p. 1202-1212].
In addition, the addition of CNTs to membranes has been shown effective in enhancing the Young's modulus and thermal stability of poly(vinyl) alcohol (PVA) composite membranes used in separation processes [Peng, F., C. Hu, and Z. Jiang Journal of Membrane Science, 2007. 297(1-2): p. 236-242]. In another study, incorporating MWNTs in PVA nanocomposite layer was shown to be effective in increasing membrane flux [Wang, X., et al. Environmental Science & Technology, 2005. 39(19): p. 7684-769]. Additionally, the fast flow of water through the interior of CNTs has contributed to a growing interest in aligned membranes for water treatment [Hinds, B.J., N. Chopra, and e. al., Science, 2004. 303: p. 62-65; and Holt, J., et al. Science, 2006. 312(5776): p. 1034- 1037], and even desalination applications.
Recent work on nano structured material comprising carbon nanotubes is disclosed in US Patent Nos. 7.211,320 and 7,419,601 (Seldon Technologies), both of which are hereby incorporated by reference in their entirety. Membranes comprising carbon nanotubes useful for filtration by size exclusion are disclosed in US Patent Application Nos. 2009/0321355 and 2010/0025330 (Nanoasis Technologies), both of which are hereby incorporated by reference in their entirety. Nanoporous membranes comprising carbon nanotubes embedded in a matrix are disclosed in US Patent Application No. 2008/0223795 (Lawrence Livermore National Security), which is incorporated by reference in its entirety.
SUMMARY One aspect of the invention relates to a filter comprising multiwall carbon nanotubes dispersed on a substrate. In certain embodiments, the filter further comprises a layer of single-wall carbon nanotubes dispersed on top of the multiwall carbon nanotubes. In certain embodiments, the multiwall and single-wall carbon nanotubes are present in the filter in an amount sufficient to reduce the concentration of the constituents in fluid that come into contact with the material.
Also provided is a method of reducing the amount of constituents in a fluid, the method comprising contacting the fluid with the filter as described herein for a time sufficient to separate, remove, immobilize, modify or destroy at least one constituent from the fluid. In certain embodiments, the method may be used to remove constituents from water or the air. In certain embodiments, the filter can be part of an article, such as a water- purification system.
Additional aspects, embodiments, and advantages of the invention are discussed below in detail. However, it is to be understood that both the foregoing description and the following description are exemplary only. BRIEF DESCRIPTION OF THE FIGURES
Figure 1 depicts FE-SEM images of aerial and cross-section views of carbon nanotube filters. Top row: aerial view of MWNT-SWNT filter at 25,00OX magnification (left image), cross-section view of MWNT-SWNT filter at 4,00OX magnification (right image). Middle row: aerial view of MWNT filter at 25,00OX magnification (left image), cross-section view of MWNT filter at 4,00OX magnification (right image). Bottom Row: Aerial view of SWNT filter at 25,00OX magnification (left image), cross-section view of SWNT filter at 4,00OX magnification (right image).
Figure 2 depicts graphically the extent of viral removal by a SWNT-MWNT hybrid filter. The total CNT loading was 0.32 mg/cm2, composed of a layer of 0.27 mg/cm2 of MWNTs covered by a layer of 0.05 mg/cm2 of SWNTs. Solution chemistry was 10 mM
NaCl and a pH of 5.5 was maintained for all experiments. Viral concentrations were spiked into the inlet sample and a peristaltic pump maintained 160 Lm-2Ii'1 or 260 Lm-2Ii'1 flux through the filter as indicated. At least two measurements were carried out at each dilution and a minimum of two separate filters were tested for each experimental condition. Error bars indicate one standard deviation.
Figure 3 depicts a bar graph summarizing the fluorescence-based toxicity assays of Gram positive and Gram negative bacteria exposed to MWNT or SWNT-MWNT filters over time. Cell suspensions were passed through the filters and incubated in 10 mM NaCl at 37 0C for the length of time indicated. Error bars indicate one standard deviation.
Figure 4 depicts a bar graph summarizing the extent of inactivation of microorganisms in river water and secondary wastewater effluent samples upon exposure to the MWNT and SWNT-MWNT filters. Each sample (100 mL) was filtered through the MWNT or SWNT-MWNT filters and incubated for 1 hr in 0.9% NaCl solution at 37 0C. Error bars indicate one standard deviation.
Figure 5 tabulates selected properties of carbon nanotubes, viruses and bacteria used in the Exemplification provided herein, drawn from the following prior studies: a) Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2008. 42(19): p. 7528-7534; b) Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2009. 43(7): p. 2648-2653; c) Hu, J.Y., et al, Water Science and Technology, 2003. 47(12): p. 163-168; d) Vinuela, E., LD. Algranati, and S. Ochoa, European Journal of Biochemistry, 1967. 1(1): p. 3-11; e) Overby, L.R., et al., Journal of Bacteriology, 1966. 91(1): p. 442-448; f) Golmohammadi, R., et al., Journal of Molecular Biology, 1993. 234(3): p. 620-639; g) Pieper, A.P., et al., Environmental Science &
Technology, 1997. 31(4): p. 1163-1170; h) Olsen, R.H., J.-S. Siak, and R.H. Gray, Journal of Virology, 1974. 14(3): p. 689-69; i) Harvey, R.W. and J.N. Ryan, Ferns Microbiology Ecology, 2004. 49(1): p. 3-16; j) Dowd, S. E., et al., Applied Environmental Microbiology, 1998. 64(2): p. 405-410; k) Leiman, P.G., et al., Cell, 2004. 118(4): p. 419-429; 1) Fokine, A., et al., PNAS, 2004. 101(16): p. 6003-6008; m) Gerba, C.P., Advances in Applied
Microbiology, 1984. 30: p. 133-168; and n) Trueba, F.J. and CL. Woldringh, Journal of Bacteriology, 1980. 142(3): p. 869-878.
Figure 6 depicts field-emission SEM images of CNT filters: (a) MWNT Filter under 5000X magnification, (b) SWNT Filter under 5000X magnification, (c) MWNT Filter under 10,000X magnification, (d) SWNT filter under 10,000X magnification, (e) MWNT filter under 100,000X magnification, and (f) SWNT filter under 100,000X magnification.
Figure 7 depicts a bar graph comparing viral removal by SWNT and MWNT filters. Filters had 0.32 mg/cm2 CNT loading and all tests were run at 10 mM total ionic strength: 10 mM NaCl, 1 mM MgCl2 + 7 mM NaCl, and 1 mM CaCl2 + 7 mM NaCl. Solution pH for all experiments was maintained at 5.5. MS2 viral concentrations were spiked into the inlet sample and a peristaltic pump maintained 160 Lm-2Ii'1 flux through the filter. At least two measurements were carried out at each dilution and a minimum of two separate filters were tested for each experimental condition. Error bars indicate one standard deviation.
Figure 8 tabulates results of experiments relating to viral removal on MWNT filter, viral and MWNT electrophoretic mobilities, and MS2 hydrodynamic radii. MWNT filter CNT loading was 0.32 mg/cm2, and flux was maintained at 160 Lm-2Ii"1. All solution chemistries were at pH 5.5 unless otherwise noted, a) SWNT Filter log viral removal measurements were obtained by the filtration procedure, followed by the PFU quantification method, b) Electrophoretic (EPM) mobility measurements of MWNT reported are the average of at least three experimental runs at each solution condition, c) EPM measurements were taken of the MS2 viral particles, at a concentration of 1011 viral particles per mL. Each value reported represents the mean EPM, standard deviation and N= number of samples analyzed, d) Each reported value for hydrodynamic radius represents the average of two replicate runs of DLS. e) In some experiments all viruses were removed from the initial concentration and, therefore, at full removal no standard deviation was obtained. Figure 9a depicts a graph showing MS2 viral removal by the MWNT filter as a function of flux. MWNT loading on the filter was 0.32 mg/cm2. Experiments were performed with a background solution of 10 mM NaCl, and a pH of 5.5. At least two measurements were made at each dilution and at least two separate filters were tested for each experimental condition. Figure 9b depicts a graph showing the linear correlation between the log viral removal and approach velocity, v m . Error bars indicate one standard deviation.
Figure 10 depicts a graph showing the extent of MS2 viral removal by the MWNT filter as a function of ionic strength. The MWNT loading on the filter was 0.32 mg/cm2. Solution pH for all experiments was maintained at 5.5. MS2 viral concentrations were spiked into the inlet sample, and a peristaltic pump maintained 160 Lm-2Ii'1 flux through the filter. At least two measurements were carried out at each dilution, and a minimum of two separate filters were tested for each experimental condition. Error bars indicate one standard deviation. Figure 11 depicts a bar graph showing the impact of the presence of various additives (e.g., organic matter) on the extent of viral removal by the MWNT filter at pH 5.5. MWNT filter CNT loading was 0.32 mg/cm2. MS2 viral concentrations were spiked into the inlet sample, and a peristaltic pump maintained 160 Lm-2Ii'1 flux through the filter. At least two measurements were made at each dilution and at least two separate filters were tested for each experimental condition. Error bars indicate one standard deviation.
DETAILED DESCRIPTION
Effective viral and bacterial pathogen removal with a depth filter comprising a porous single-walled carbon nanotube (SWNT) matrix layer of less than ten micrometer thickness has recently been demonstrated [Brady-Estevez, A.S., S. Kang, and M.
Elimelech, Small, 2008. 4(4): p. 481-484]. However, as disclosed herein, multiwall carbon nanotubes (MWNTs), either alone or in combination with SWNTs, can be used to attain higher viral removal at lower pressures, while also achieving new options for cost and resource efficiency, production, and scale-up. One aspect of the invention relates to filters comprising multiwall carbon nanotubes
(MWNTs). The MWNT filters described herein provided substantial improvements in surface coverage and viral removal in comparison with earlier SWNT filters tested, while also enabling a lower cost of production which is typical of MWNTs. In addition, because this highly scalable MWNT-filter technology may be used for viral removal at gravity- driven pressures, it poses new cost-effective options for point-of-use treatment. It is disclosed herein that the actual viral adsorption attained by MWNT filtration depends on several factors, such as the speed of filtration, permeability, filter depth, solution chemistry and pH. It is further disclosed that increasing ionic strength and decreasing pH have been found to increase MS2 viral removal from a solution for MWNT filters. In addition, the addition of divalent salts had varying effects, with CaCl2 increasing MS2 adsorption and MgCl2 decreasing the viral removal. Further, it was found that low levels of organic matter did not impact viral filtration by MWNT filters, but that higher concentrations of SR-NOM and addition of alginate resulted in significant reduction in viral removal.
Since the solution chemistries and pH are highly variable across environmental samples, it is important to assess if a filter technology is adequate for viral removal under specific operating parameters. Pretreatments for pH adjustments and removal of organic matter can help improve MWNT filter performance under more challenging operating conditions. An inverse correlation between filtration speed and viral removal was also confirmed, illustrating that lower approach velocities would be capable of higher filtration performance. The overall excellent performance of the MWNT filter for viral removal across a wide range of environmentally relevant conditions suggests that the MWNT filters may be used for treatment of virally contaminated waters. Another aspect of the invention relates to hybrid filters comprising both single wall carbon nanotubes (SWNTs) and multiwall carbon nanotubes (MWNTs). An understanding of the advantages and limitations of SWNTs and MWNTs filters in terms of cost, permeability, viral removal, and microbial removal and inactivation informed the design of the hybrid filters disclosed herein. One purpose of designing the hybrid filters was to leverage the best strengths that each type of nanotube has to offer. In certain embodiments, MWNTs were selected to comprise the majority of the depth of the filter matrix due to MWNT matrices' enhanced adsorption of viruses, low cost, and reasonably high permeability. In such embodiments, a thin upper layer of SWNTs was then deposited onto the MWNT matrix to take advantage of the beneficial antimicrobial properties of SWNTs, and help inhibit biofilm formation. In certain embodiments, the nanotube matrix (i.e., the MWNTs and SWNTs taken together) was supported by a microporous membrane (e.g., a highly porous material with micrometer pore size).
Development of bilayer SWNT-MWNT filters lays the framework for new possibilities in water filtration. In certain embodiments, the bilayer (i.e., hybrid) filter shows significantly higher viral removal than both the SWNT and MWNT filters previously developed, attaining well over 6 log MS2 viral removal at 10 mM NaCl and pH 5.5. Although the extent of viral removal will vary with the viral contaminated sample and its solution chemistry, the results described herein demonstrate effective removal of several bacteriophages with markedly different properties. Further, the observed enhancement of viral adsorption was at the expense of only a modest reduction of the filter permeability, which remained highly porous and operational in the microfiltration pressure range.
As discussed in more detail below, the top layer of SWNTs incorporated into the dual filter enabled high levels of inactivation of bacteria. In fact, throughout the experiments the bacterial inactivation was higher for the SWNT-MWNT filter than the filter composed of MWNTs alone. The strategy for enhancing the filter's cytotoxicity was validated by the confirmed ability of the SWNT-coating to inactivate more effectively across monocultured Gram positive and Gram negative bacteria, along with environmentally present microbes in wastewater and river water alike. These antimicrobial properties are useful for their role in inhibition of bio film growth, which can reduce filter permeability and, thereby, increase energy and cleaning or filter regeneration needed for operation. Another advantage of using only a thin layer of SWNT is that it mediates the inherent toxicity of SWNTs. In certain embodiments, the design of a SWNT-MWNT filter may consists of a thin coating of SWNTs (about 0.05 mg/cm2) over a base matrix composed of MWNTs (about 0.27 mg/cm2), for a total carbon nanotube (CNT) loading of about 0.32 mg/cm2. Such material was designed to attain properties of both MWNT filters and SWNT filters, because 87% (by weight) of the matrix was made from MWNTs, while the top coating (13% of matrix) was comprised of SWNTs. Definitions
All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. For purposes of this invention, the chemical elements are identified in accordance with the Periodic Table of the Elements, CAS version, Handbook of Chemistry and Physics, 67th Ed., 1986-87, inside cover.
The articles "a" and "an" are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.
The phrase "and/or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with "and/or" should be construed in the same fashion, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to "A and/or B", when used in conjunction with open-ended language such as "comprising" can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.
As used herein in the specification and in the claims, "or" should be understood to have the same meaning as "and/or" as defined above. For example, when separating items in a list, "or" or "and/or" shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as "only one of or "exactly one of," or, when used in the claims, "consisting of," will refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or" as used herein shall only be interpreted as indicating exclusive alternatives (i.e., "one or the other but not both") when preceded by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of." "Consisting essentially of," when used in the claims, shall have its ordinary meaning as used in the field of patent law. As used herein in the specification and in the claims, the phrase "at least one," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a non- limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and/or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc. It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.
In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," "composed of," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of and "consisting essentially of shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.
As used herein, "carbon nanotube(s)" refer to a nanoscale tubular structure(s) composed of six-member rings of carbon whose bonding patterns create a hexagonal lattice which closes upon itself to form the walls of the cylindrical structure.
As used herein, "filter" shall mean a material that performs fluid filtration.
As used herein, "fluid" is intended to encompass liquids or gases.
As used herein, "biological sample" refers to any sample from a biological source. As used herein, "body fluid" means any fluid that can be isolated from the body of an individual. For example, "body fluid" may include blood, plasma, serum, bile, saliva, urine, tears, perspiration, and the like.
As used herein "chemical or biological interaction or reaction" is understood to mean an interaction with the constituent through either chemical or biological processes that renders the constituent incapable of causing harm. Examples of this are reduction, oxidation, chemical denaturing, physical damage to microorganisms, bio-molecules, ingestion, and encasement.
As used herein, "natural organic matter" or "NOM" shall mean organic matter often found in potable or non-potable water, a portion of which reduces or inhibits the streaming, or zeta, potential of a filter medium. Exemplary of NOM are polyanionic acids such as, but not limited to, humic acid and fulvic acid. Carbon Nanotubes
Nanotubes are cylindrical tubular structures that are well known in the art and commercially available. Nanotubes of a variety of materials have been studied, notably carbon nanotubes, boron nanotubes, and nanotubes of boron nitride. Carbon nanotubes have been extensively studied, and their features and methods of fabrication are illustrative of nanotubes in general.
Carbon nanotubes are polymers of pure carbon, and exist as both single-wall and multi-wall structures. Examples of publications describing carbon nanotubes and their methods of fabrication are Dresselhaus, M. S., et al., Science of Fullerenes and Carbon Nanotubes, Academic Press, San Diego (1996), Ajayan, P. M., et al., "Nanometre-Size
Tubes of Carbon," Rep. Prog. Phys. 60 (1997): 1025-1062, and Peigney, A., et al., "Carbon nanotubes in novel ceramic matrix nanocomposites," Ceram. Inter. 26 (2000) 677-683. A single-wall carbon nanotube is a single graphene sheet rolled into a seamless cylinder with either open or closed ends. When closed, the ends are capped either by half fullerenes or by more complex structures such as pentagonal lattices. The average diameter of a single -wall carbon nanotube typically ranges of 0.6 nm to 100 nm, and in many cases 1.5 nm to 10 nm. The aspect ratio, i.e., length to diameter, typically ranges from about 25 to about 1,000,000, and most often from about 100 to about 1,000. A nanotube of 1 nm diameter may thus have a length of from about 100 nm to about 10,000 nm or more. In some instances nanotubes can be about 10 nm, such as, for example, when they have been broken down by sonication or other processes. Nanotubes frequently exist as "ropes," which are bundles of 3 to 500 single-wall nanotubes held together along their lengths by van der Waals forces. Individual nanotubes often branch off from a rope to join nanotubes of other ropes. Multi-walled carbon nanotubes are two or more concentric cylinders of graphene sheets of successively larger diameter, forming a layered composite tube bonded together by van der Waals forces, with a distance of approximately 0.34 nm between layers.
Carbon nanotubes can be prepared by arc discharge between carbon electrodes in an inert gas atmosphere. This process results in a mixture of single-wall and multi-wall nanotubes, although the formation of single-wall nanotubes can be favored by the use of transition metal catalysts such as iron or cobalt. Single-wall nanotubes can also be prepared by laser ablation, as disclosed by Thess, A., et al., "Crystalline Ropes of Metallic Carbon Nanotubes," Science 273 (1996): 483-487, and by Witanachi, S., et al., "Role of Temporal Delay in Dual-Laser Ablated Plumes," J. Vac. Sci. Technol. A 3 (1995): 1171-1174. A further method of producing single-wall nanotubes is the high-pressure carbon monoxide conversion ("HiPCO") process disclosed by Nikolaev, P., et al., "Gas-phase catalytic growth of single -walled carbon nanotubes from carbon monoxide," Chem. Phys. Lett. 313, 91-97 (1999), and by Bronikowski, M. J., et al., "Gas-phase production of carbon single- walled nanotubes from carbon monoxide via the HiP co process: A parametric study," J. Vac. Sci. Technol. 19, 1800-1805 (2001).
Certain procedures for the synthesis of nanotubes produce nanotubes with open ends, while others produce closed-end nanotubes. If the nanotubes are synthesized in closed-end form, the closed ends can be opened by a variety of methods known in the art. An example of a nanotube synthesis procedure that produces open-ended nanotubes is described by Hua, D. H. (International (PCT) Patent Application Publication No. WO 2008/048227 A2, which is hereby incorporated by reference in its entirety). Closed ends can be opened by mechanical means such as cutting, or by chemical, or thermal means. An example of a cutting method is milling. Chemical means include the use of carbon nanotube degrading agents, an example of which is a mixture of a nitric acid and sulfuric acid in aqueous solution at concentrations of up to 70% and 96%, respectively. Another chemical means is reactive ion etching. Thermal means include exposure to elevated temperature in an oxidizing atmosphere. The oxidizing atmosphere can be achieved by an oxygen concentration ranging from 20% to 100% by volume, and the temperature can range from 200 to 450° C.
The lengths of carbon nanotubes can vary widely. The lengths are expressed herein as average lengths, using numerical or arithmetic averages. In certain embodiments, the average length is from about 100 nm to about 10,000 nm, from about 100 nm to about 1,000 nm, from about 1,000 nm to about 2,000 nm, from about 2,000 nm to about 3,000 nm, from about 3,000 nm to about 4,000 nm, from about 4,000 nm to about 5,000 nm, from about 5,000 nm to about 6,000 nm, from about 6,000 nm to about 7,000 nm, from about 7,000 nm to about 8,000 nm, from about 8,000 nm to about 9,000 nm, from about 9,000 nm to about 10,000 nm, from about 100 nm to about 5,000 nm, and from about 5,000 nm to about 10,000 nm. The outer and inner diameters of the nanotubes can likewise vary. In certain embodiments, the outer diameters can range from about 0.6 nm to about 200 nm, while narrower ranges are often preferred for particular applications. In certain embodiments, the inner diameters can likewise range from about 0.4 nm to about 200 nm, although the optimal diameters for particular applications may be within narrower ranges. For some water desalination applications, in certain embodiments the inner diameter may range about 0.4 nm to about 5 nm, or about 0.4 nm to about 1.2 nm. For some nanofϊltration membranes, in certain embodiments the inner diameter may range from about 1 nm to about 10 nm. For some ultrafiltration membranes, in certain embodiments the inner diameter may range from about 5 nm to about 200 nm.
Examples of nanotube densities and diameters for various applications are as follows. In certain embodiments, the carbon nanotubes have outer diameters ranging from about 0.4 nm to 200 nm. In certain embodiments, the carbon nanotubes have inner diameters ranging from about 0.4 nm to about 200 nm. In certain embodiments, nanotube densities range from about 1 x 106 cm"2 to about 1 x 1013 cm"2.
Carbon nanotubes can have a variety of morphologies. For example, carbon nanotubes may have a morphology chosen from horns, spirals, multi-stranded helicies, springs, dendrites, trees, spider nanotube structures, nanotube Y-junctions, and bamboo morphology. Some of the above described shapes are more particularly defined in M. S. Dresselhaus, G. Dresselhaus, and P. Avouris, eds. Carbon Nanotubes: Synthesis, Structure, Properties, and Applications, Topics in Applied Physics. 80. 2000, Springer- Verlag; and "A Chemical Route to Carbon Nanoscrolls," Lisa M. Viculis, Julia J. Mack, and Richard B. Kaner; Science, 28 Feb. 2003; 299, both of which are herein incorporated by reference.
In the present disclosure, the carbon nanotubes may also undergo chemical and/or physical treatments to alter their chemical and/or physical behavior. In certain embodiments, these treatments are done to enable the resulting article to exhibit an improved purification performance. In one embodiment, the carbon nanotubes may be chemically or physically treated to achieve at least one of the following effects: remove constituents, add defects, or attach functional groups to defect sites and/or nanotube surface. Herein, "chemical or physical treatment" means treating with an acid, solvent or an oxidizer for a time sufficient to remove unwanted constituents, such as amorphous carbon, oxides or trace amounts of by- products resulting from the carbon nanotube fabrication process.
An example of the second type of chemical treatment is to expose the carbon nanotubes to an oxidizer for a time sufficient to create density defects on the surface of the carbon nanotube.
An example of the third type of the chemical treatment to impart specific functional groups that have a desired zeta potential (as defined in Johnson, P. R., Fundamentals of
Fluid Filtration, 2nd Edition, 1998, Tall Oaks Publishing Inc., which is incorporated herein by reference). This will act to tune the zeta potential or the isoelectric point (pH where the zeta potential is zero) of the carbon nanotubes sufficiently to remove a specific set of desired constituent from a particular fluid. In another embodiment, the carbon nanotubes comprise atoms, ions, molecules or clusters attached thereto or located therein in an amount effective to assist in the removal and/or modification of constituents from a fluid.
The carbon nanotubes described herein may also be treated to alter their properties, as well as the constituents that may be removed from and/or modified within the fluid. For example, in one embodiment, the carbon nanotubes are chemically treated with an oxidizer, chosen from but not limited to a gas containing oxygen, nitric acid, sulfuric acid, hydrogen peroxide, potassium permanganate, and combinations thereof. Nanotubes which have been treated with an oxidizer can provide unique properties, either in terms of fluid flow, dispersion of nanotubes in the deposition fluid, or from a functionalization perspective (e.g., having the ability to be particularly functionalized).
As used herein, "functionalized" (or any version thereof) refers to a carbon nanotube having an atom or group of atoms attached to the surface. Functionalization is generally performed by modifying the surface of carbon nanotubes using chemical techniques, including wet chemistry or vapor, gas or plasma chemistry, and microwave assisted chemical techniques, and utilizing surface chemistry to bond materials to the surface of the carbon nanotubes. Functionalization can occur before and/or after the carbon nanotubes are assembled into a filter. In certain embodiments, these methods are used to "activate" the carbon nanotube, which is defined as breaking at least one C-C or C-heteroatom bond, thereby providing a surface for attaching a molecule or cluster thereto. Functionalized carbon nanotubes comprise chemical groups, such as carboxyl groups, attached to the surface, such as the outer sidewalls, of the carbon nanotube. Further, the nanotube functionalization can occur through a multi-step procedure where functional groups are sequentially added to the nanotube to arrive at a specific, desired functionalized nanotube.
In certain embodiments, a functionalized carbon nanotube is one that comprises inorganic and/or organic compounds attached to the surface of the carbon nanotubes.
The organic compounds may comprise linear or branched, saturated or unsaturated groups. Non-limiting examples of such organic compounds include at least one chemical group chosen from: carboxyl, amine, polyamide, polyamphiphiles, diazonium salts, pyrenyl, silane and combination thereof.
Non- limiting examples of the inorganic compounds include at least one fluorine compound of boron, titanium, niobium, tungsten, and combination thereof. The inorganic compounds as well as the organic compounds may comprise a halogen atom or halogenated compound.
In an aspect of the invention, functionalized carbon nanotubes comprise any one or any combination of the above-described inorganic and organic groups. These groups are generally located on the ends of the carbon nanotubes and are optionally polymerized.
The functionalized carbon nanotubes may have a non-uniform composition and/or density of functional groups, including the type or species of functional groups across the surface of the carbon nanotubes. Similarly, the functionalized carbon nanotubes may comprise a substantially uniform gradient of functional groups across the surface of the carbon nanotubes. For example, there may exist, either down the length of one nanotube or within a collection of nanotubes, many different functional group types (i.e., hydroxyl, carboxyl, amide, amine, poly-amine and/or other chemical functional groups) and/or functionalization densities.
One process for preparing functionalized carbon nanotubes generally comprises contacting carbon nanotubes with acids, chosen from but not limited to nitric, sulfuric, hydrochloric, and/or hydrofluoric acid or combination thereof, as well as other oxidizers, chosen from but not limited to potassium permanganate, hydrogen peroxide, sodium perchlorate and ozone (see, for example, Cho, H-H. et al. Langmuir 2010, 26(2), 967-981) In certain embodiments, the acids can be used individually to wash the carbon nanotubes, or be used in various combinations. For example, in one embodiment, the carbon nanotubes are first washed in nitric acid and then washed in hydrofluoric acid. In another embodiment, the carbon nanotubes are washed in sulfuric acid after being washed in nitric acid.
In certain embodiments, the acid wash is performed to remove any contaminants, such as amorphous carbon, or catalyst particles and their supports which may interfere with the surface chemistry of the nanotube, and producing functional groups (such as hydroxyls and carboxyls, for example) attached to the defect locations on the surface of the carbon nanotubes. This functionalization also provides hydrophilicity to the carbon nanotubes, which is thought to improve the filtration performance of the resulting article. In certain embodiments, the carbon nanotubes are then subjected to a final distilled water rinse, and suspension in an appropriate dispersant, such as distilled water, or an alcohol, such as ethanol or isopropanol. In certain embodiments, sonication, stirring and heating is employed throughout this functionalization process to maintain adequate dispersion of the nanotubes while cleaning.
In certain embodiments, the process of making a filter as described herein comprises functionalizing, also known as decorating, the carbon nanotubes with metal nanoparticles. In certain embodiments, carbon nanotubes which have been already functionalized with hydroxyls and/or carboxyls can be used to bind to the metal nanoparticles. In certain embodiments, the metal nanoparticles are selected from the group consisting of ferric oxide, aluminum oxide and cerium oxide, and can be used for the adsorption of inorganic contaminants such as metals and arsenic. In certain embodiments, the metal nanoparticles are selected from the group consisting of silver, zinc oxide, and gold, and can be used to impart or increase antimicrobial activity. In certain embodiments, the metal nanoparticles are selected from the group consisting of titaniuim oxide and zinc oxide, and can be used to impart or increase photocatalytic activity. In cerain embodiments, the metal nanoparticles are selected from the group consisting of nickel, platinum and semiconductive materials, and can be used to impart or increase catalytic activity. Porous Substrates In certain embodiments, a filter described herein includes a porous substrate on which carbon nanotubes are deposited. The porous substrate establishes the lateral dimensions and shape of the filters as they are being formed and provides the finished membranes with structural stability. The porous support substrate may be in any form suitable for the shape of the resulting filter, such as a block, tube (or cylinder), sheet or roll, and may comprise a material chosen from ceramic, carbon, metal, metal alloys, or plastic or combinations thereof.
In certain embodiments, the substrate comprises a woven or non-woven fibrous material. In certain embodiments, the substrate comprises a polymer. In certain embodiments, the polymeric material of the substrate comprises single or multi-component polymers, nylon, polyurethane, acrylic, methacrylic, polycarbonate, epoxy, silicone rubbers, natural rubbers, synthetic rubbers, vulcanized rubbers, polystyrene, polyethylene terephthalate, polybutylene terephthalate, Nomex (poly-paraphylene terephtalamide), Kevlar poly (p-phenylene terephtalamide), PEEK (polyester ester ketene), Mylar (polyethylene terephthalate), viton (viton fluoroelastomer), polyetrafluoroethylene, polyetrafluoroethylene), halogenated polymers, such as polyvinylchloride (PVC), polyester (polyethylene terepthalate), polypropylene, and polychloroprene.
While the substrate itself can serve a filtering function by size exclusion, its filtering characteristics if any will be substantially more coarse, due to its microporous nature, than those of the nanotubes in the filter. Within this limitation, the porosity of the support can vary widely. In certain embodiments, it will be convenient to use a support with a molecular weight cutoff (MWCO) of from about 1 kDa to about 10 MDa, or from about 5 kDa to about 300 kDa. In terms of pore size, in certain embodiments the porous substrate can have pores ranging in average diameter from about 1 micron to 100 microns, about 1 micron to about 75 microns, about 1 micron to about 50 microns, about 1 micron to about 25 microns, about 1 micron to about 10 microns. In certain embodiments, the pores have an average diameter of about 5 microns. In certain embodiments, the pores may be in the nanometer range, such as between about 3 nm to about 200 nm. The dimensions of the porous substrate will generally be selected to meet the needs of the particular application. These needs include the lateral area through which fluids will pass when the filter is used in purification, filtration, or other treatment of the fluids, as well as the pressure differential that will be imposed across the combined support and membrane during use. In certain embodiments, the substrates are capable of withstanding pressure differentials of from about 1 atmosphere to about 85 atmospheres without rupturing.
In certain applications, the filter is in the form of a flat disk. For some applications, disks of a relatively small size are often the most appropriate, and a diameter range for these applications is from about 10 mm to about 100 mm. Diameters ranging from 13 mm to 47 mm, specifically disks of 13 mm, 25 mm, and 47 mm, may also be used. For disks of diameters between 10 mm and 100 mm, the disk thickness may range from about 0.15 mm to about 0.25 mm. In certain embodiments, discs of diameters larger that about 100 nm may be used, such as, for example, discs between about 100 mm and about 1000 mm. Likewise, the thickness of the discs can also vary and in some embodiments, for example, the thickness is between about 0.25 mm and about 10 mm.
In certain embodiments, the composite membrane can also be prepared in the form of rectangular sheets having widths ranging from 1 inch (2.5 cm) to 40 inches (102 cm). Widths of 9.75 inches (24.8 cm), 10 inches (25.4 cm), 20 inches (51 cm), and 40 inches (102 cm) may be used. The lengths of the sheets may range from about four inches (ten cm) to about 400 feet (122 m). For a sheet of these lateral dimensions, the sheet thickness may range from about 0.1 nm to about 1 mm.
In general, the thickness of the support is of less importance than the thickness of the nanotubes, since the support need only be thick enough to provide structural support for the nanotubes. Selected Filters
One aspect of the invention relates to a filter comprising a layer of multiwall carbon nanotubes dispersed on a porous substrate; wherein the porous substrate is permeable to the flow of a fluid. Another aspect of the invention relates to a filter consisting essentially of a layer of multiwall carbon nanotubes dispersed on a porous substrate; wherein the porous substrate is permeable to the flow of a fluid. Another aspect of the invention relates to a filter consisting of a layer of multiwall carbon nanotubes dispersed on a porous substrate; wherein the porous substrate is permeable to the flow of a fluid.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein said porous substrate comprises single or multi-component polymers, nylon, polyurethane, acrylic, methacrylic, polycarbonate, epoxy, silicone rubbers, polystyrene, polyethylene terephthalate, polybutylene terephthalate, poly-paraphylene terephtalamide, poly-(p-phenylene terephtalamide), polyester ester ketone, viton fluoroelastomer, poly-tetrafluoroethylene, polyvinylchloride, polyester, polypropylene, polychloroprene, acetates, and combinations thereof. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the porous substrate is poly-tetrafluoroethylene.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein porous substrate comprises a plurality of pores which have diameters between about 0.1 μm and about 20 μm, about about 0.1 μm and about 1 μm, or about 1 μm to about 10 μm, or about 10 μm to about 20 μm. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein porous substrate comprises a plurality of pores which have diameters of about 0.1 μm, about 1 μm, about 5 μm, about 10 μm, about 15 μm, or about 20 μm.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the porous substrate has a thickness which is between about 1 nm and about 500 nm. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the porous substrate has a thickness which is between about 50 nm and about 300 nm.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the average length of the multiwall carbon nanotubes is between about 50 nm and about 5000 nm, about 50 nm and about 4000 nm, about 50 nm and about 3000 nm, about 50 nm and about 2000 nm, about 50 nm and about 1000 nm, about 100 nm and about 2000 nm, or about 100 nm and about 1000 nm.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the average inner diameter of the multiwall carbon nanotubes is between about 0.4 nm and about 0.5 nm, or about 0.4 nm and about 1.2 nm.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the average outer diameter of the multiwall carbon nanotubes is between about 1.0 nm and about 2.0 nm, or about 1.2 nm and about 1.6 nm.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein a majority of the multiwall carbon nanotubes have pores with diameters between about 0.1 nm to about 200 nm, about 0.1 nm to about 100 nm, about 1 nm to about 100 nm, about 1 nm to about 50 nm, about 1 nm to about 25 nm, or about 1 nm to about 10 nm. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein a majority of the multiwall carbon nanotubes have pores with diameters of about 0.1 nm, about 1 nm, about 10 nm, about 20 nm, about 30 nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm or about 100 nm.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the layer of multiwall carbon nanotubes has a substantially planar surface.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the thickness of the layer of multiwall carbon nanotubes is between about 0.1 μm and about 500 μm, or about 1 μm and about 10 μm.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the loading of multiwall carbon nanotubes is between about 0.01 mg/cm2 and about 100 mg/cm2, about 0.01 mg/cm2 and about 50 mg/cm2, about 0.01 mg/cm2 and about 10 mg/cm2, or about 0.01 mg/cm2 and about 1 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the loading of multiwall carbon nanotubes is between about 0.10 mg/cm2 and about 1 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the loading of multiwall carbon nanotubes is between about 0.20 mg/cm2 and about 0.80 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the loading of multiwall carbon nanotubes is about 0.27 mg/cm2, about 0.50 mg/cm2, about 0.75 mg/cm2 or about 1 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein a majority of the multiwall carbon nanotubes are open at both ends. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein a majority of the multiwall carbon nanotubes are closed at one end. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein at least one functional group is attached to the surface of a majority of the multiwall carbon nanotubes. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an organic functional group, an inorganic functional group, or combinations thereof.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an organic functional group which comprises linear or branched, saturated or unsaturated groups. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an organic functional group; and the at least one organic functional group comprises at least one chemical group chosen from carboxyls, amines, polyamides, polyamphiphiles, diazonium salts, pyrenyls, silanes, and combinations thereof. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an inorganic functional group; and the at least one inorganic functional group comprises at least one fluorine compound of boron, titanium, niobium, tungsten, and combination thereof.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein said at least one functional group comprises a halogen atom or halogenated moiety.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein said multiwall carbon nanotubes comprise a substantially uniform gradient of functional groups across the surface of said carbon nanotubes and/or across at least one dimension of said filter.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein a majority of said multiwall carbon nanotubes have a morphology chosen from nanohorns, cylindrical, nanospirals, dendrites, trees, spider nanotube structures, nanotube Y-junctions, and bamboo morphology. In certain embodiments, the present invention relates to any one of the aforementioned filters, further comprising a layer of single wall carbon nanotubes disposed over the layer of multiwall carbon nanotubes or disposed between the layer of multiwall carbon nanotubes and the porous substrate. In certain embodiments, the present invention relates to any one of the aforementioned filters, further consisting essentially of a layer of single wall carbon nanotubes disposed over the layer of multiwall carbon nanotubes or disposed between the layer of multiwall carbon nanotubes and the porous substrate. In certain embodiments, the present invention relates to any one of the aforementioned filters, further consisting of a layer of single wall carbon nanotubes disposed over the layer of
- ?? - multiwall carbon nanotubes or disposed between the layer of multiwall carbon nanotubes and the porous substrate.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the average length of the single wall carbon nanotubes is between about 50 nm and about 5000 nm, about 50 nm and about 4000 nm, about 50 nm and about 3000 nm, about 50 nm and about 2000 nm, about 50 nm and about 1000 nm, about 100 nm and about 2000 nm, or about 100 nm and about 1000 nm.In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the average inner diameter of the single wall carbon nanotubes is between about 0.4 nm and about 0.5 nm, or about 0.4 nm and about 1.2 nm.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the average outer diameter of the single wall carbon nanotubes is between about 1.0 nm and about 2.0 nm, or about 1.2 nm and about 1.6 nm.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein a majority of the single wall carbon nanotubes have pores with diameters between about 0.1 nm to about 200 nm, about 0.1 nm to about 100 nm, about 1 nm to about 100 nm, about 1 nm to about 50 nm, about 1 nm to about 25 nm, or about 1 nm to about 10 nm. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein a majority of the single wall carbon nanotubes have pores with diameters of about 0.1 nm, about 1 nm, about 10 nm, about 20 nm, about 30 nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm or about 100 nm.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the layer of single wall carbon nanotubes has a substantially planar surface.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the thickness of the layer of single wall carbon nanotubes is between about 0.1 μm and about 500 μm, or about 1 μm and about 10 μm.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm2 and about 100 mg/cm2, about 0.01 mg/cm2 and about 50 mg/cm2, about 0.01 mg/cm2 and about 10 mg/cm2, or about 0.01 mg/cm2 and about 1 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned filters,
- 0λ - wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm2 and about 0.40 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm2 and about 0.30 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm2 and about 0.20 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm2 and about 0.10 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the loading of single wall carbon nanotubes is about 0.05 mg/cm2, about 0.1 mg/cm2, about 0.15 mg/cm2 or about 0.2 mg/cm2.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein a majority of the single wall carbon nanotubes are open at both ends. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein a majority of the single wall carbon nanotubes are close at one end.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein at least one functional group is attached to the surface of a majority of the single wall carbon nanotubes. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an organic functional group, an inorganic functional group, or combinations thereof.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an organic functional group which comprises linear or branched, saturated or unsaturated groups. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an organic functional group; and the at least one organic functional group comprises at least one chemical group chosen from carboxyls, amines, polyamides, polyamphiphiles, diazonium salts, pyrenyls, silanes, and combinations thereof. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the at least one functional group is an inorganic functional group; and the at least one inorganic functional group comprises at least one fluorine compound of boron, titanium, niobium, tungsten, and combination thereof. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein said at least one functional group comprises a halogen atom or halogenated moiety.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein said single wall carbon nanotubes comprise a substantially uniform gradient of functional groups across the surface of said carbon nanotubes and/or across at least one dimension of said filter.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein a majority of said single wall carbon nanotubes have a morphology chosen from nanohorns, cylindrical, nanospirals, dendrites, trees, spider nanotube structures, nanotube Y-junctions, and bamboo morphology.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 99: 1. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 95:5. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 90:10. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 85:15. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 80:20. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 75:25. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 70:30. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 65:35. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 60:40. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 55:45. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 50:50. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 45:55. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 40:60. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 35:65. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 30:70. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 25:75. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 20:80. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 15:85. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 10:90. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 5:95. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 1 :99.
While some of the embodiments described herein have two layers, a layer of single wall carbon nanotubes disposed over a layer of multiwalled carbon nanonotubes or disposed between the layer of multiwall carbon nanotubes and the porous substrate, other embodiments that have additional layers of alternating multiwalled carbon nanotubes and single wall carbon nanotubes. For example, in certain embodiments, the present invention relates to any of the aforementioned filters, wherein a second layer of multiwalled carbon nanotubes are disposed over the layer of single wall carbon nanotubes (wherein the second layer of multiwall nanotubes can be the same or different than the first layer of multiwalled nanotubes). Further, in certain embodiments, the present invention relates to any of the aforementioned filters, wherein a second layer of single walled carbon nanotubes is disposed over the second layer of multiwalled carbon nanotubes (wherein the second layer of single wall carbon nanotubes can be the same or different that the first layer of single walled carbon nanotubes). One of skill in the art will appreciate that multi-layer structures can be made by the addition of additional layers.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid comprises at least one liquid or gas. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid comprises water. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid is selected from the group consisting of water, wastewater, river water, rain water, well water, petroleum, petroleum byproducts, biological fluids, foodstuffs, animal by-products, fruit juice, natural syrups, natural and synthetic oils used in the cooking or food industry, olive oil, peanut oil, flower oils, and vegetable oils, milk, blood, alcoholic beverages, beer, wine, liquors, medicines, aviation fuels, automotive fuels, marine fuels, locomotive fuels, rocket fuels, industrial and machine oils and lubricants, heating oils and gases, fluids derived from animals, fluids derived from humans, fluids derived from plants, and growing broths used in the processing of a biotechnology or pharmaceutical product.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid has a pH of between about 1 and about 7. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid has a pH of between about 7 and about 14. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid has a pH of between about 3 and about 9. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid has a pH of about 3. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid has a pH of about 5.5. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid has a pH of about 9.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the multiwall carbon nanotubes are present in said filter in an amount sufficient to reduce the concentration of constituents in the fluid that comes into contact with said filter.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the multiwall carbon nanotubes and single wall carbon nanotubes are present in said filter in an amount sufficient to reduce the concentration of constituents in the fluid that comes into contact with said filter.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid comprises one or more constituents selected from the group consisting of salts, metals, nanoparticles, microparticles, organic constituents, pathogens, microbiological organisms, DNA, RNA, natural organic molecules, molds, fungi, natural toxins, synthetic toxins, chemical warfare agents, biological warfare agents, endotoxins, proteins, and enzymes.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the fluid comprises one or more constituents selected from the group consisting of viruses or bacteria. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the filter provides a water permeability of at least 0.01 cc/s- cm2-atm. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the filter provides a water permeability of between about 0.01 cc/s-cm2-atm and about 100 cc/s-cm2-atm. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the filter provides an air permeability of at least 0.01 cc/s-cm2-atm. In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the filter provides an air permeability of between about 0.01 cc/s-cm2-atm and about 100 cc/s-cm2-atm.
In certain embodiments, the present invention relates to any one of the aforementioned filters, wherein the porous substrate has been removed (i.e. leaving only one or more layers of carbon nanotubes).
In certain embodiments, the present invention relates to any one of the aforementioned filters, further comprising non-carbon containing nanotubes (such as, for example, tungsten disulfide nanotubes, boron nitride nanotubes, silicon nanotubes, titanium dioxide nanotubes, molybdenum dioxide nanotubes, copper nanotubes (CuNT) or bismuth nanotubes (BiNT). In certain embodiments, the non-carbon containing nanotubes are incorporated into one or more of the carbon nanotube layers (i.e. into the MWNT layer(s) and/or SWNT layer(s)). In certain embodiments, the non-carbon nanotubes are in their own layers. Selected Filter Fabrication Methods
A variety of processes can be used to fabricate the filters described herein. For example, in a deposition process, a filter can be made by vacuum deposition of carbon nanotube dispersions on at least one substrate. Ultrasonication may be used to aid in dispersing and/or deagglomerating carbon nanotubes during deposition.
For example, in certain embodiments the deposition method comprises placing carbon nanotubes in a suitable organic solvent or liquid and ultrasonicating to disperse the carbon nanotubes during deposition. In certain embodiments the organic solvent is a polar organic solvent. As used herein, a "polar solvent" means a solvent which has a dielectric constant (ε) of 2.9 or greater. In certain embodiments, the polar organic solvent is selected from the group consisting of DMF, THF, ethylene glycol dimethyl ether (DME), DMSO, acetone, acetonitrile, methanol, ethanol, isopropanol, n-propanol, t-butanol or 2- methoxyethyl ether. In certain embodiments, other solutions, even water, can be used to suspend the nanotubes. In addition, proper functionalizations could allow one to suspend the CNTs in a variety of solvents.
In certain embodiments, the solution can be placed in a vacuum filtration device equipped with ultrasonication to further ensure that the carbon nanotubes are deagglomerated. In other embodiments, the steps of vacuum filtration and ultrasonication are separate. In certain embodiments, the porous substrate used to trap the carbon nanotubes can also be removed by dissolving in acid or base, or oxidized to leave a freestanding carbon nanotube membrane.
In certain embodiments, the vacuum filtration process may be modified by using electromagnetic fields to align the nanostructures during deposition. As in the previously described process, the nanostructures are placed in a suitable solvent (organic solvent or liquid), ultrasonicated to disperse them in the solvent, which is then placed in a vacuum filtration apparatus equipped with an ultrasonic probe to keep them from becoming agglomerated during deposition. Unlike the previously described process, when the mixture is vacuum deposited on to a porous substrate, such as one having a pore size up to the centimeter size, an electromagnetic field is applied to align the nanostructures during their deposition. This electromagnetic field can also be arbitrarily modulated in three space adjusted and to result in a woven or partially woven-partially nonwoven structure. The vacuum filtration process may be modified to allow for the creation of multiple layers of carbon nanotubes. For example, such a method allows the fabrication of hybrid MWNT-SWNT filters, wherein a base of MWNT are deposited on a porous substrate and a layer of SWNT are deposited on top of the MWNT.
In another aspect of the present disclosure, a filter may be made by an organic solvent evaporation process, wherein carbon nanotubes are bonded together with an adhesive. Examples of adhesives are chemical adhesives, such as glue, metallic adhesives, such as gold, and ceramic adhesives, such as alumina. According to this process, carbon nanotubes can be mixed with a solvent, such as xylene. In certain embodiments, this dispersion is next be placed in an ultrasonic bath to de-agglomerate the carbon nanotubes. The resulting dispersion is next poured onto fiber paper to allow the organic solvent to evaporate, optionally with the addition of moderate heating. Upon evaporation, the carbon nanotubes deposit on the fiber paper. Additionally, other polymeric materials may be added to the organic solvent to enhance the resulting structure's mechanical stability; the concentration of this adhesive material can be, for example at 0.001-10% of the weight of the solvent used.
In another aspect of the present disclosure, a filter may be made with metallic oxide nano wires. In this type of process, metal meshes are heated to a temperature ranging from 230-1000 0C in an oxidative environment to create metallic oxide nano wires on the metal wires of the metal mesh. The metal meshes may comprise a metal chosen from, for example, copper, aluminum, and silicon. In certain embodiments, the metallic oxide nano wires can be in a size ranging from 1-100 nanometers in diameter, such as 1-50 nanometers in diameter, including 10-30 nanometers in diameter. Advantageously, the surface of the mesh is abraded to provide surface texture to accept and hold the nanotube aliquot deposition to create better substrate attachment. A filter made according to this process is then coated with carbon nanotubes. In the coatings of carbon nanotubes, solutions of well-dispersed single or multi-walled carbon nanotubes are passed through the mesh where they adhere to the metallic oxide surface. This resulting material may or may not be treated thermally, mechanically (e.g., such as by hydraulic pressure), chemically, or through rapid laser heating to enhance structural integrity. It also may or may not be coated with metal, ceramic, plastic, or polymers to enhance its structural activity. The resulting mesh may also be subjected to this nanotube solution treatment a number of times until the proper design criteria are reached. Further modification to the carbon nanotubes and/or support of this membrane can be made to functionalize the materials so that they chemically react with biological molecules to destroy, modify, remove, or separate them.
For example, metal meshes, such as copper meshes are placed in a chemical vapor deposition chamber in an oxidative environment. The reaction zone is heated to a temperature ranging from 230-1000 0C to cause creation of metallic oxide nano wires while the chamber is in an atmosphere for a period ranging from, for example, 30 minutes to 2 hours. A dispersion of carbon nanotubes in liquid can then passed through the formed structure. After this treatment, the entire structure can be thermally annealed in vacuum at, for example, about 1000 0C to strengthen the overall structure. In certain embodiments, the carbon nanotubes can be treated in a solution of nitric and sulfuric acids to create carboxyl functional groups on the carbon nanotubes.
In another aspect of the present disclosure, a filter may be made by an air laid manufacturing process. In this process, carbon nanotubes can be dispersed evenly, whether in a gas or a liquid solution. In a confined chamber, for example, a quantity of carbon nanotubes is released as a fan to stir the gas to cause dispersion of the carbon nanotubes in the chamber. This gas may also be mechanically modulated at frequencies sufficient to cause dispersion. As the carbon nanotubes are being added to the chamber they are charged to a voltage sufficient to overcome the attractive Van der Waals forces, by passing the nanotubes through a high surface area electrode. This will prohibit agglomeration. The nanotube impregnated gas is now ready for gas phase deposition. By applying a pressure different passing the gas though a grounded mesh electrode. The nanotubes will stick to this grounded mesh electrode. At this point the carbon nanotube nanostructured material is in its most fragile state. The nanostructured material can now be exposed to ionizing radiation to cause the structure to fuse together and/or to coat surface via chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition PECVD, or physical vapor deposition (PVD) processing techniques, or by chemical fusing techniques. The surface can then be removed and exposed to a sputtering process sufficient to cover the nanostructures and cause them to lock together. The resulting membrane can then be removed from the surface by reversing the charge of the surface causing the membrane to fall away.
In another aspect of the present disclosure, a filter may be made by a nanostructure polymerization process. In the polymerization process, a nanomaterial membrane is produced by linking carbon nanotubes to one another through polymer bonding. An envisioned process of this method involves first ultrasonicating a quantity of carbon nanotubes in an acid solution. When using carbon nanotubes, the acid will act to cut the lengths of the nanotubes, to expose their ends, and allow carboxyl ions (COOH) to graft thereto. The resultant carboxyl functionalized product is then treated with concentrated acid to create carboxyl groups (COOH) which are more reactive for cross-linking reactions, such as condensation. This COOH functionalized nanostructure is then reacted at the carboxyl groups to cross-link two nanostructures together. The mixture is then allowed to react until an entire cross-linked network is formed into a carbon nanotube-containing filter.
Other processes, such as, for example, spinning/weaving, self-alignment and magnetic alignment may also be used. Selected Methods of Use
One aspect of the invention relates to a method of reducing the amount of constituents in a fluid, the method comprising contacting the fluid with a filter for a time sufficient to separate, remove, immobilize, modify or destroy at least a portion of one constituent from the fluid; wherein the filter comprises a layer of multiwall carbon nanotubes dispersed on a porous substrate; and the porous substrate is permeable to the flow of the fluid.In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein said porous substrate comprises single or multi- component polymers, nylon, polyurethane, acrylic, methacrylic, polycarbonate, epoxy, silicone rubbers, polystyrene, polyethylene terephthalate, polybutylene terephthalate, poly- paraphylene terephtalamide, poly-(p-phenylene terephtalamide), polyester ester ketone, viton fluoroelastomer, poly-tetrafluoroethylene, polyvinylchloride, polyester, polypropylene, polychloroprene, acetates, and combinations thereof. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the porous substrate is poly-tetrafluoroethylene.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein porous substrate comprises a plurality of pores which have diameters between about 0.1 μm and about 20 μm, about about 0.1 μm and about 1
- Υ). - μm, or about 1 μm to about 10 μm, or about 10 μm to about 20 μm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein porous substrate comprises a plurality of pores which have diameters of about 0.1 μm, about 1 μm, about 5 μm, about 10 μm, about 15 μm, or about 20 μm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the porous substrate has a thickness which is between about 1 nm and about 500 nm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the porous substrate has a thickness which is between about 50 nm and about 300 nm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the average length of the multiwall carbon nanotubes is between about 50 nm and about 5000 nm, about 50 nm and about 4000 nm, about 50 nm and about 3000 nm, about 50 nm and about 2000 nm, about 50 nm and about 1000 nm, about 100 nm and about 2000 nm, or about 100 nm and about 1000 nm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the average inner diameter of the multiwall carbon nanotubes is between about 0.4 nm and about 0.5 nm, or about 0.4 nm and about 1.2 nm.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the average outer diameter of the multiwall carbon nanotubes is between about 1.0 nm and about 2.0 nm, or about 1.2 nm and about 1.6 nm.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein a majority of the multiwall carbon nanotubes have pores with diameters between about 0.1 nm to about 200 nm, about 0.1 nm to about 100 nm, about 1 nm to about 100 nm, about 1 nm to about 50 nm, about 1 nm to about 25 nm, or about 1 nm to about 10 nm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein a majority of the multiwall carbon nanotubes have pores with diameters of about 0.1 nm, about 1 nm, about 10 nm, about 20 nm, about 30 nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm or about 100 nm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the layer of multiwall carbon nanotubes has a substantially planar surface.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the thickness of the layer of multiwall carbon nanotubes is between about 0.1 μm and about 500 μm, or about 1 μm and about 10 μm.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the loading of multiwall carbon nanotubes is between about 0.01 mg/cm2 and about 100 mg/cm2, about 0.01 mg/cm2 and about 50 mg/cm2, about 0.01 mg/cm2 and about 10 mg/cm2, or about 0.01 mg/cm2 and about 1 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the loading of multiwall carbon nanotubes is between about 0.10 mg/cm2 and about 1 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the loading of multiwall carbon nanotubes is between about 0.20 mg/cm2 and about 0.80 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the loading of multiwall carbon nanotubes is about 0.27 mg/cm2, about 0.50 mg/cm2, about 0.75 mg/cm2 or about 1 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein a majority of the multiwall carbon nanotubes are open at both ends. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein a majority of the multiwall carbon nanotubes are closed at one end.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein at least one functional group is attached to the surface of a majority of the multiwall carbon nanotubes. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an organic functional group, an inorganic functional group, or combinations thereof. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an organic functional group which comprises linear or branched, saturated or unsaturated groups. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an organic functional group; and the at least one organic functional group comprises at least one chemical group chosen from carboxyls, amines, polyamides, polyamphiphiles, diazonium salts, pyrenyls, silanes, and combinations thereof.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an inorganic functional group; and the at least one inorganic functional group comprises at least one fluorine compound of boron, titanium, niobium, tungsten, and combination thereof.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein said at least one functional group comprises a halogen atom or halogenated moiety.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein said multiwall carbon nanotubes comprise a substantially uniform gradient of functional groups across the surface of said carbon nanotubes and/or across at least one dimension of said filter. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein a majority of said multiwall carbon nanotubes have a morphology chosen from nanohorns, cylindrical, nanospirals, dendrites, trees, spider nanotube structures, nanotube Y-junctions, and bamboo morphology.
In certain embodiments, the present invention relates to any one of the aforementioned methods, further comprising a layer of single wall carbon nanotubes disposed over the layer of multiwall carbon nanotubes or disposed between the layer of multiwall carbon nanotubes and the porous substrate. In certain embodiments, the present invention relates to any one of the aforementioned methods, further consisting essentially of a layer of single wall carbon nanotubes disposed over the layer of multiwall carbon nanotubes or disposed between the layer of multiwall carbon nanotubes and the porous substrate. In certain embodiments, the present invention relates to any one of the aforementioned methods, further consisting of a layer of single wall carbon nanotubes disposed over the layer of multiwall carbon nanotubes or disposed between the layer of multiwall carbon nanotubes and the porous substrate. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the average length of the single wall carbon nanotubes is between about 50 nm and about 5000 nm, about 50 nm and about 4000 nm, about 50 nm and about 3000 nm, about 50 nm and about 2000 nm, about 50 nm and about 1000 nm, about 100 nm and about 2000 nm, or about 100 nm and about 1000 nm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the average inner diameter of the single wall carbon nanotubes is between about 0.4 nm and about 0.5 nm, or about 0.4 nm and about 1.2 nm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the average outer diameter of the single wall carbon nanotubes is between about 1.0 nm and about 2.0 nm, or about 1.2 nm and about 1.6 nm.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein a majority of the single wall carbon nanotubes have pores with diameters between about 0.1 nm to about 200 nm, about 0.1 nm to about 100 nm, about 1 nm to about 100 nm, about 1 nm to about 50 nm, about 1 nm to about 25 nm, or about 1 nm to about 10 nm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein a majority of the single wall carbon nanotubes have pores with diameters of about 0.1 nm, about 1 nm, about 10 nm, about 20 nm, about 30 nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 90 nm or about 100 nm.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the layer of single wall carbon nanotubes has a substantially planar surface. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the thickness of the layer of single wall carbon nanotubes is between about 0.1 μm and about 500 μm, or about 1 μm and about 10 μm.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm2 and about 100 mg/cm2, about 0.01 mg/cm2 and about 50 mg/cm2, about 0.01 mg/cm2 and about 10 mg/cm2 or about 0.01 mg/cm2 and about 1 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm2 and about 0.40 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm2 and about 0.30 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm2 and about 0.20 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm2 and about 0.10 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the loading of single wall carbon nanotubes is about 0.05 mg/cm2, about 0.1 mg/cm2, about 0.15 mg/cm2 or about 0.2 mg/cm2. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein a majority of the single wall carbon nanotubes are open at both ends. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein a majority of the single wall carbon nanotubes are close at one end.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein at least one functional group is attached to the surface of a majority of the single wall carbon nanotubes. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an organic functional group, an inorganic functional group, or combinations thereof.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an organic functional group which comprises linear or branched, saturated or unsaturated groups. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an organic functional group; and the at least one organic functional group comprises at least one chemical group chosen from carboxyls, amines, polyamides, polyamphiphiles, diazonium salts, pyrenyls, silanes, and combinations thereof. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the at least one functional group is an inorganic functional group; and the at least one inorganic functional group comprises at least one fluorine compound of boron, titanium, niobium, tungsten, and combination thereof.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein said at least one functional group comprises a halogen atom or halogenated moiety.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein said single wall carbon nanotubes comprise a substantially uniform gradient of functional groups across the surface of said carbon nanotubes and/or across at least one dimension of said filter.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein a majority of said single wall carbon nanotubes have a morphology chosen from nanohorns, cylindrical, nanospirals, dendrites, trees, spider nanotube structures, nanotube Y-junctions, and bamboo morphology.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 99: 1. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 95:5. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 90:10. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 85:15. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 80:20. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 75:25. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 70:30. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 65:35. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 60:40. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 55:45. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 50:50. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 45:55. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 40:60. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 35:65. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 30:70. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 25:75. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 20:80. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 15:85. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 10:90. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 5:95. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 1 :99.
In certain embodiments, the present invention relates to any of the aforementioned filters, wherein a second layer of multiwalled carbon nanotubes are disposed over the layer of single wall carbon nanotubes. In certain embodiments, the present invention relates to any of the aforementioned filters, wherein a second layer of single walled carbon nanotubes is disposed over the second layer of multiwalled carbon nanotubes.
In certain embodiments, the present invention relates to any one of the aforementioned method, wherein the filter does not comprise a porous substrate (i.e. a filter which comprise only one or more layers of carbon nanotubes).
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the filters further comprise non-carbon containing nanotubes (such as, for example, tungsten disulfide nanotubes, boron nitride nanotubes, silicon nanotubes, titanium dioxide nanotubes, molybdenum dioxide nanotubes, copper nanotubes (CuNT) or bismuth nanotubes (BiNT). In certain embodiments, the non-carbon containing nanotubes are incorporated into one or more of the carbon nanotube layers (i.e. into the MWNT layer(s) and/or SWNT layer(s)). In certain embodiments, the non-carbon nanotubes are in their own layers.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid comprises at least one liquid or gas. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid comprises water. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid is selected from the group consisting of water, wastewater, river water, rain water, well water, petroleum, petroleum byproducts, biological fluids, foodstuffs, animal by-products, fruit juice, natural syrups, natural and synthetic oils used in the cooking or food industry, olive oil, peanut oil, flower oils, and vegetable oils, milk, blood, alcoholic beverages, beer, wine, liquors, medicines, aviation fuels, automotive fuels, marine fuels, locomotive fuels, rocket fuels, industrial and machine oils and lubricants, heating oils and gases, fluids derived from animals, fluids derived from humans, fluids derived from plants, and growing broths used in the processing of a biotechnology or pharmaceutical product.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid has a pH of between about 1 and about 7. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid has a pH of between about 7 and about 14. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid has a pH of between about 3 and about 9. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid has a pH of about 3. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid has a pH of about 5.5. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid has a pH of about 9. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the multiwall carbon nanotubes are present in said filter in an amount sufficient to reduce the concentration of constituents in the fluid that comes into contact with said filter. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the multiwall carbon nanotubes and single wall carbon nanotubes are present in said filter in an amount sufficient to reduce the concentration of constituents in the fluid that comes into contact with said filter. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid comprises one or more constituents selected from the group consisting of salts, metals, nanoparticles, microparticles, organic constituents, pathogens, microbiological organisms, DNA, RNA, natural organic molecules, molds, fungi, natural toxins, synthetic toxins, chemical warfare agents, biological warfare agents, endotoxins, proteins, and enzymes.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the fluid comprises one or more constituents selected from the group consisting of viruses or bacteria.
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the filter provides a water permeability of at least 0.01 cc/s-cm2-atm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the filter provides a water permeability of between about 0.01 cc/s-cm2-atm and about 100 cc/s-cm2-atm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the filter provides an air permeability of at least 0.01 cc/s-cm2-atm. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the filter provides an air permeability of between about 0.01 cc/s-cm2-atm and about 100 cc/s-cm2-atm
In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein at least a portion of said constituent is separated, removed, immobilized, modified or destroyed by using at least one of mechanisms selected from the group consisting of particle size exclusion, absorption, adsorption, and chemical or biological interaction or reaction.
Non- limiting examples of liquids that may be cleaned using the filters described herein include water, foodstuffs, biological fluids, petroleum and its byproducts, non- petroleum fuels, medicines, organic and inorganic solvents, and the liquid forms of hydrogen, oxygen, nitrogen and carbon dioxide, as may be used for rocket propellants or in industrial applications. For example, one aspect of the invention relates to method of purifying water by contacting contaminated water with a filter as described herein. In certain embodiments, the present invention relates to any one of the aforementioned methods, wherein the constituents are removed from the fluid to a level of at least 1 log (90%), 2 logs (99%), 3 logs (99.9%), at least 4 logs (99.99%), at least 5 logs (99.999%), at least 6 logs (99.9999%), or at least 7 logs (99.99999%). Non- limiting examples of foodstuffs that can be treated with the filters described herein comprise animal by-products (such as eggs and milk), fruit juice, alcoholic and nonalcoholic beverages, natural and synthetic syrups, and natural and synthetic oils used in the cooking or food industry [such as olive oil, peanut oil, flower oils (sunflower, safflower), vegetable oil, or oils derived from animal sources (i.e., butter, lard)], or any combination thereof. As one example, sulfites are often added to wine to prevent discoloration and aid in preservation. However, sulfites raise health concerns and should be avoided. One aspect of the present invention could include the targeted removal of sulfites upon dispensing, benefiting the wine industry from the purification process described herein. Biological fluids that may be decontaminated with the filters described herein could be generally derived from an animal, human, plant, or comprise a culture/growth broth used in the processing of a biotechnology or pharmaceutical product. In one embodiment, the biological fluids which may be cleaned comprise blood (or blood components), serums, and milk. Biological reagents used in pharmaceutical products are often quite labile and difficult to sterilize by conventional techniques. Removal of small microorganisms (such as Mycoplasma and viruses) cannot be accomplished by conventional filtration. In certain embodiments, the filters described herein may be used for viral removal. In certain embodiments, the filters described herein may be used to enable removal of constituents that are created during drug fabrication. In another embodiment, the filters described herein can be used for the sterilization of petroleum products. A significant contamination problem is the latent growth of bacteria in petroleum or its derivatives during storage, which has been a problem particularly with aviation fuel. The presence of such bacteria can severely foul and eventually ruin the fuel. Accordingly, a major area of concern in the area of liquid purification is the cleaning bacteria from natural and/or synthetic petroleum products. Natural and/or synthetic petroleum and its byproducts include aviation, automotive, marine, locomotive, and rocket fuels, industrial and machine oils and lubricants, and heating oils and gases.
As many of the foregoing constituents may be dispersed in air, there is a need for an article for cleaning gases. Accordingly, another aspect of the present invention includes a method of cleaning the air to remove any of the previously listed constituents. Non-limiting examples of gases that may be cleaned using the filters described herein include one or more gases chosen from the air or exhausts from vehicles, smoke stacks, chimneys, or cigarettes. When used to clean air, the filter may take a flat form to provide a greater surface area for air flow. Such flat shapes provide the additional benefit of being able to be easily cut into appropriate shapes for various filter designs, such as those used in gas masks, as well as HVAC systems. The following gases that may be treated according to the present disclosure, such as scrubbed to clean the gas or remove them from exhaust, include argon, acetylene, nitrogen, nitrous oxide, helium, hydrogen, oxygen, ammonia, carbon monoxide, carbon dioxide, propane, butane, natural gas, ethylene, chlorine, or mixtures of any of the foregoing, such as air, nitrogen oxide, and gases used in diving applications, such as Helium/Oxygen mixtures.
Further, it should be noted that what might be identified as a constituent in one fluid application may actually be a desired product in another. For example, the constituent may contain precious metals or a beneficial pharmaceutical product. Therefore, in one embodiment, it may be beneficial to separate, retain and collect the constituents rather than just removing and destroying them. The ability to "catch and release" desired constituents, enabling the isolation of useful constituents or certain reaction byproducts, may be accomplished by tuning the zeta potential and/or utilizing nano-electronic control of the carbon nanotubes in the filters described herein.
Non- limiting examples of constituents that can be removed from fluid using the disclosed filters include, but are not limited to, the following biological agents: pathogenic microorganism, such as viruses (e.g., smallpox and hepatitis), bacteria (e.g., anthrax, typhus, cholera), oocysts, spores (both natural and weaponized), molds, fungi, coliforms, intestinal parasites, biological molecules (e.g., DNA, RNA), and other pathogens, such as prions and nanobacteria.
As used herein, "prions" are defined as small infectious, proteinaceous particles which resist inactivation by procedures that modify nucleic acids and most other proteins. Both humans and animals are susceptible to prion diseases, such as Bovine Spongiform
Encephalopathy (BSE or Mad Cow disease) in cows, or Creutzfeld- Jacob Disease (CJD) in humans.
As used herein, "nanobacteria" are nanoscale bacteria, some of which have recently been postulated to cause biomineralization in both humans and animals. It has further been postulated that nanobacteria may play a role in the formation of kidney stones, some forms of heart disease and Alzheimer's Disease. Further, nanobacteria are also suspected of causing unwanted biomineralization and/or chemical reactions in some industrial processes. Other non-limiting examples of constituents that can be removed from fluid using the disclosed filters include, but are not limited to noxious, hazardous or carcinogenic chemicals comprised of natural and synthetic organic molecules (such as toxins, endotoxins, proteins, enzymes, pesticides, and herbicides), inorganic constituents (such as heavy metals, fertilizers, inorganic poisons) and ions (such as salt in seawater or charged airborne particles), as well as nanoscale and micron scale particles in general.
Applications of the cleaned fluid, specifically clean water, include potable water, irrigation, medical and industrial. For example, as a source of de-ionized water for industrial processes including, but not limited to, semiconductor manufacturing, metal plating, and general chemical industry and laboratory uses. More specifically, the chemical compounds that may be removed from fluid using the article described herein are removal target atoms or molecules that include at least one atom or ion chosen from the following elements: antimony, arsenic, aluminum, selenium, hydrogen, lithium, boron, carbon, oxygen, calcium, magnesium, sulfur, chlorine, niobium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, bromine, strontium, zirconium, yttrium, molybdenum, rhodium, palladium, iodine, silver, cadmium, indium, cesium, tin, barium, lanthanum, tantalum, beryllium, copper, fluoride, mercury, tungsten, iridium, hafnium, rhenium, osmium, platinum, gold, mercury, thallium, lead, bismuth, polonium, radon, radium, thorium, uranium, plutonium, radon and combinations thereof. Applications for the filters described herein include, for example, home (e.g., domestic water and air filtration), recreational (environmental filtration), industrial (e.g., solvent reclamation, reactant purification), governmental (e.g., the Immune Building Project, military uses, waste remediation), and medical (e.g., operating rooms, clean air and face masks) locations. EXEMPLIFICATION
The invention now being generally described, it will be more readily understood by reference to the following, which is included merely for purposes of illustration of certain aspects and embodiments of the present invention, and is not intended to limit the invention.
Example 1 ~ Filter Preparation
The experimental results described herein were obtained with filters prepared as outlined below. A) SWNT Filter Preparation. Commercially available single-walled carbon nanotubes (SWNTs) with a purity of greater than 95% (w/w) SWNTs were purchased from Stanford Materials (SWNT-90, lot #082106). Based on the manufacturer's data, the as- received SWNTs had lengths of 10 to 20 μm, an average outer diameter of 1.2 nm, and a specific surface area of 407 m2 g"1. Raman spectra, performed at 532 nm, indicated that the SWNTs were highly ordered (G/D band ratio of 31), unfunctionalized, and had an average outer diameter of 1.2 to 1.6 nm. Thermogravimetric analysis gave 6% (w/w) metals for the SWNT samples.
Stable suspensions of SWNTs in de -ionized water were prepared for electrophoretic mobility (EPM) measurements (ZetaPALS, Brookhaven Instruments Corp., Holtsville, NY). Probe sonication of SWNTs in deionized water (DI), followed by separation of the supernatant from large SWNT aggregates, was performed six times to obtain an adequately stable SWNT suspension. The Sonicator 450 probe (Misonix, Farmingdale, NY) was set at a power output of 4OW for 30 minutes for each sonication, and the mixture was allowed to cool for 30 minutes between sonication rounds. This stable SWNT solution provided the concentrated stock, which was adjusted to different solution conditions for EPM measurements. Concentrated pre-filtered solutions, acids, or bases were added as necessary to obtain desired solution chemistries for SWNT EPM measurements at each of the conditions tested. Three experimental runs were performed at minimum for each EPM data point. The as-received SWNTs were suspended at a concentration of 0.5 mg SWNT per mL of dimethylsulfoxide (DMSO). This SWNT suspension was then probe-sonicated for 15 minutes on the Sonifier 450 probe sonicator (Branson model 102) at a power output of 5OW. The sonicated suspension was allowed to cool, and then vacuum-deposited varying volumes onto a 5 μm pore size Omnipore PTFE (Millipore, USA) membrane to attain the desired loading of SWNT. Rinses of 50 mL of ethanol followed by 50 mL of deionized water removed residual DMSO from the SWNT filter.
B) MWNT Filter Preparation. Multiwall carbon nanotubes (MWNTs) were purchased, as prepared, from NanoTechLabs Inc. (Yadkinville, NC). The MWNTs used have previously been analyzed by TEM, SEM, EDX, and TGA [Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2008. 42(19): p. 7528-7534]. These MWNTs were deposited on a 5-μm-pore size PTFE membrane (Millipore, USA), by a sonication and filtration procedure similar to the preparation of the S WNT -hybrid filter [Brady-Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481-484].
Specifically, the MWNTs were suspended at a concentration of 0.5 mg/mL in dimethyl sulfoxide (DMSO). The suspension was then probe sonicated for 15 minutes at a power output of 5OW on the Sonifier 450 probe sonicator (Branson model 102), and subsequently allowed to cool. All MWNT suspensions were used within a few hours of preparation to avoid variation in MWNT aggregation, which could alter filter performance. Deposition of 6 mL of the MWNTs from solution was achieved by vacuum filtration through the PTFE membrane to attain a loading of 0.32 mg/cm2 on the base filter. Ethanol followed by deionized (DI) water were then filtered through the SWNT filters to remove residual DMSO. C) SWNT-MWNT Filter Preparation. The lower layer of the SWNT-MWNT filter was composed of commercially available multiwall carbon nanotubes (MWNT) purchased from NanoTechLabs Inc. (Yadkinville, NC). These MWNTs were used in prior work and had been previously analyzed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive x-ray (EDX), and thermogravimetric analysis (TGA), as summarized in Figure 5 [Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2008. 42(19): p. 7528-7534]. Additionally, the electrophoretic mobilities (EPMs) of these MWNTs over varying solution conditions have been measured. MWNTs were deposited on the 5-μm pore size PTFE membrane (Millipore, USA) by a sonication and filtration procedure similar to the preparation of the SWNT-hybrid filter [Brady-Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481-484]. Specifically, MWNTs were added at a concentration of 0.5 mg/mL to dimethyl sulfoxide (DMSO). The suspension was then sonicated for 15 minutes at a power output of 5OW with the Sonifier 450 probe sonicator (Branson model 102) to separate aggregates of the MWNTs and achieve a more uniform dispersion. All MWNT suspensions were allowed time to cool, but were used within a few hours of preparation to avoid variation in MWNT aggregation, which could alter filter performance. Bath sonication of the MWNT suspension was also performed for 10 seconds immediately prior to filter deposition to disrupt any aggregates. Deposition of 5 mL (83% of the loading of the previous MWNT filter) of the MWNTs from solution was achieved by vacuum filtration through the PTFE membrane to attain a loading of 0.27 mg/cm2 MWNTs on the base filter.
The thin upper coating of the SWNT-MWNT filter was composed of commercially available single-walled carbon nanotubes (SWNTs) with a purity of greater than 95% (w/w) SWNTs (Stanford Materials, SWNT-90, lot #082106). The manufacturer reported as- received SWNTs had lengths of 10 to 20 μm, an average outer diameter of 1.2 nm, and a specific surface area of 407 m2 g"1. Raman spectra, performed at 532 nm, indicated that the SWNTs were highly ordered (G/D band ratio of 31), unfunctionalized, and had an outer diameter range of 1.2 to 1.6 nm; and thermogravimetric analysis yielded 6% (w/w) metal (oxides) for the SWNT samples [Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2009. 43(7): p. 2648-2653]. EPM measurements were previously performed for the SWNTs over a range of solution chemistries.
The as-received SWNTs were suspended in a solution. The dilution of 0.1 mg/mL SWNT in DMSO was selected to provide adequate settling time to ensure full coverage of the SWNT coating layer over the entire MWNT matrix surface. The SWNT suspension was sonicated for 15 minutes with the Sonifier 450 probe sonicator (Branson model 102) at a power output of 5OW. The sonicated suspension was allowed to cool, then re-sonicated in a bath sonicator for 10 seconds immediately prior to the coating procedure, which consisted of vacuum deposition of 5 mL of the 0.1 mg/mL SWNTs onto the MWNT layer that overlaid the 5-μm pore size PTFE (Omnipore filters, Millipore, USA) membrane. After the SWNT layer of the nanotubes was laid, the dual filter was rinsed with 50 mL of ethanol followed by 50 mL of deionized water to remove residual DMSO. Example 2 ~ Filter Characterization of Morphology and Permeability A) MWNT Filter Characterization. The permeability of the MWNT filters was calculated by measuring the transmembrane pressure drops over a range of permeate water fluxes. The filtration system for these experiments consisted of a 47 mm plastic holder (Whatman, USA) for supporting the membranes and a pressurized tank system as described previously [Brady-Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481- 484; Kang, S., et al. Journal of Membrane Science, 2007. 296(1-2): p. 42-50]. The surface morphology of the MWNT filter was studied under various magnifications using field emission scanning electron microscopy (FESEM) (Hitachi S-4500, Hitachi, USA). MWNTs were suspended in deionized (DI) water and then six repetitions were performed of sonication for 30 minutes, followed by cooling, and separation of supernatant from the MWNT aggregates. The resulting supernatant, a solution of stable MWNTs in DI water, was then used as the MWNT stock for performing the electrophoretic mobility (EPM) measurements. Concentrated pre-filtered salt solutions, acids, or bases were added as necessary to obtain the desired MWNT suspension immediately prior to EPM measurement (ZetaPals, Brookhaven Instruments Corp., Holtsville, NY).
B) SWNT-MWNT Filter Characterization. The permeability of the prepared SWNT-MWNT filters was evaluated by measuring a range of permeate water fluxes and transmembrane pressure drops. The filtration system was composed of a 47-mm plastic holder (Whatman, USA) for membrane support and a pressurized tank system as described previously [Brady-Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481- 484; and Kang, S., et al, Journal of Membrane Science, 2007. 296(1-2): p. 42-50]. The surface morphology and cross-sectional views of the SWNT-MWNT filter were studied under various magnifications using field emission scanning electron microscopy (FE-SEM) (Hitachi S-4500, Hitachi, USA). Additional FE-SEM images of MWNT and SWNT filters were also taken to visually compare with the dual layer filter. Example 3 ~ Viral Preparation
A) Viral Preparation for Experiments with MWNT Filters. MS2 viruses were purchased, along with their bacterial host Escherichia coli 15597, from the American Tissue Culture Collection (ATCC). The MS2 bacteriophage, commonly used as a conservative viral tracer in aquatic environments [Penrod, S.L., T.M. Olson, and S. B. Grant Langmuir, 1996. 12(23): p. 5576-5587; Redman, J.A., et al., Environmental Science & Technology, 1997. 31(12): p. 3378-3383; and Schijven, J.F., S.M. Hassanizadeh, and R. de Bruin Journal of Constituent Hydrology, 2002. 57(3-4): p. 259-279 was selected as a model virus for its ease of quantification and non-infectivity toward humans. The electrophoretic mobility of MS2 in solutions containing varied salt and organic matter concentrations was obtained using a ZS90 Zetasizer instrument (Malvern, UK). The electrolyte solutions were filtered through a 0.22-μm-pore size cellulose acetate filter. A stock of purified MS2 at a concentration of 1014 PFU/mL, prepared as described previously [Yuan, B. L., M. Pham, and T. H. Nguyen Environmental Science & Technology, 2008. 42(20): p. 7628-7633], was diluted in electrolyte solutions to a final concentration of 5xlO13 PFU/mL for all measurements. This concentration of MS2 was predetermined to ensure detection by the Zetasizer. A minimum of three measurements were conducted to determine the EPM for each electrolyte solution. Clear disposable zeta cells (DTS 1060C, Malvern) were used for all measurements. For electrolyte solutions with pH values lower or higher than 5.5, pH was adjusted by adding high grade hydrochloric acid (HCl) and sodium hydroxide (NaOH).
MS2 Size Measurements. The sizing experiments of MS2 were performed using a multi-angle light scattering unit (ALV-5000, Langen, Germany). The details of the instrument are described elsewhere [Chen, K.L. and M. Elimelech Langmuir, 2006. 22: p. 10994-11001]. The MS2 viral samples were placed in new glass vials (Supelco, Bellefonte, PA) that were previously soaked in a cleaning solution (Extran MA 01, Merck KGaA, Darmstadt, Germany) overnight, thoroughly rinsed in deionized water, and oven dried under dust-free conditions [Saleh, N. B., L. D. Pfefferle, and M. Elimelech Environmental Science & Technology, 2008. 42: p. 7963-7969]. The MS2 samples used in the sizing experiments were diluted by a factor of 1000 from the original stock. Electrolyte solutions, pH adjusting reagents, and/or SR-NOM were added at least 15 minutes prior to the start of the sizing experiments. The dynamic light scattering measurements were conducted by positioning the detector at 90° with the incident laser beam and the auto-correlation function having been allowed to accumulate for over 15 s [Saleh, N. B., L.D. Pfefferle, and M. Elimelech Environmental Science & Technology, 2008. 42: p. 7963-7969]. The measurements were performed for a time period ranging from 10-20 min to obtain a statistically significant average of the hydrodynamic radius of the MS2 samples for each condition. The average hydrodynamic radius was obtained from the average of the raw data collected in at least two sizing experiments for each condition.
Solution Preparations. Stock solutions were made in 750 mL of DI water at 1OX to IOOX higher concentrations than those desired for experimental conditions. Dilutions were then made to ensure precise preparation of the concentrations needed. All solutions were then autoclaved before use, except for the cases testing Suwannee River natural organic matter (SR-NOM), which followed a separate procedure. For SR-NOM samples the seed stock was prepared by suspending SR-NOM powder (International Humic Substances Society, St. Paul, MN) into a volume of DI, and stirring it overnight for complete dissolution in a beaker protected from light by aluminum foil. The next day, vacuum filtration on a 0.45-μm filter (Corning Incorporated, Corning, NY) separated large aggregates from the SR-NOM. Quantification of total organic carbon (TOC) of the filtered sample was then performed on a TOC analyzer (TOC-VCSH, Shimadzu, USA). DI water and salts for the experimental conditions were then pre-autoclaved for the SR-NOM samples, and allowed to cool before addition of the needed amount of SR-NOM. This procedure provided sterility of the background solution while avoiding degradation of the SR-NOM at high temperatures and pressures. The SR-NOM mixtures were refrigerated in the dark until use, and all containers or vials containing SR-NOM mixtures were continuously shielded from light during experiments. All experimental solutions were adjusted to pH 5.5 using NaOH and HCl as necessary, with the exception of the specific tests for viral filtration with varying pH. These solutions were adjusted to pH 5.5, pH 3, or pH 9, as indicated. The various solutions were made up using sodium chloride, magnesium chloride, calcium chloride, sodium bicarbonate, disodium phosphate, SR-NOM (International Humic Substances Society, St. Paul, MN), and sodium alginate (Sigma- Aldrich, St. Louis, MO).
B) Viral Preparation for Experiments with SWNT-MWNT Filters. Viral removal on the SWNT-MWNT filters of Example 1 was shown for several types of viruses which were prepared as follows. Three model bacteriophages — MS2, PRD-I and T4 — were purchased from the American Tissue Culture Collection (ATCC), along with their host bacteria, E. coli 15597, E. coli 13706, and E. coli 11303, respectively. MS2 and PRD- 1 viral stocks were suspended at various dilutions in DI water and refrigerated at 4 0C until experiments were performed. A more highly concentrated stock of T4 was attained by injecting the virus into a suspension of E. coli 11303 host bacterium (suspended in tryptic soy broth) and allowing the phage to infect the bacteria overnight at 37 0C for viral replication. The lysed bacterial cells were then centrifuged to separate out the T4 viral supernatant, which was then filtered through a 0.22-μm pore size membrane to remove remaining cell debris. All of the viral stocks were diluted in 10 mM NaCl at pH 5.5 immediately prior to the filtration experiments. Example 4 ~ Viral Filtration
Viral filtration on the filters of Example 1 was performed in the same manner as previously described [Brady-Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481-484]. Briefly, viruses were suspended in 10 mL of the background solution to be tested and filtered through the SWNT-MWNT layers and supporting 5-μm pore PTFE membrane (Millipore, USA) at a constant permeation flux using a peristaltic pump. The filter was preconditioned by flow of the 10 mM NaCl background solution at pH 5.5 (without virus) through the filter. Viral seed stock was then spiked into the 10 mM NaCl solution and pumped through the system. All experiments were performed at a water flux or filter approach velocity of 160 Lm 2Ii"1 or 260 Lm 2Ii"1 as indicated. Filter permeate samples were collected in an autoclaved glass tube, and the viral concentration was determined by the plaque forming unit (PFU) method [Telliard, W. A., Method 1601: Male- specific (FR) and Somatic Coliphage in Water by Two-step Enrichment Procedure. 2001, United States Environmental Protection Agency]. For PFU measurement, E. coli (ATCC 15597, 13706, and 11303 for MS2, PRDl and T4 bacteriophage, respectively), was used as the viral host bacterium and mixed with the various dilution tubes of the filter permeate with molten soft agar (0.7% TSA). The mixture was then poured onto pre-solidified tryptic soy agar (TSA) plates that, after overnight incubation, would yield plaque forming units of 20-200 PFU/plate to quantify virus presence. All experiments were, at a minimum, duplicated at each dilution, and performed on two or more filters at each condition. Room temperature (23 0C) was maintained throughout the viral filtration experiments. Example 5 ~ Bacterial Preparation
Escherichia coli Kl 2 and Staphylococcus epidermis were selected to model Gram negative and Gram positive bacteria, respectively. The bacterial cultures had each been previously grown (separately) from a single colony of their plated culture. A sterile wire transfer loop inoculated bacteria from discrete homogeneous colonies into individual tubes of LB. These LB tubes were then incubated overnight to the stationary growth phase (37 0C). 25% (v/v) glycerol was then added to the bacterial suspension to allow freezing of the bacterial culture and storage at -80 0C. These frozen stocks were later used to seed LB for overnight incubation (37 0C) to the stationary phase, followed by 50-fold dilution into LB to allow growth over approximately 3.5 hours incubation to the log growth phase. At this exponential growth phase, the E. coli and S. epidermis were diluted to concentrations of 4 x 104 cells/mL into 50 mL of 0.9% (154 mM) or 10 mM NaCl, in preparation for bacterial inactivation experiments.
Example 6 ~ Wastewater and River Water Samples
Microorganisms naturally present in the environment were modeled by wastewater effluent and river water samples. Wastewater was obtained from a local wastewater treatment plant (Wallingford, CT). The secondary wastewater effluent (a rotating biological contactor) was collected prior to the disinfection stage at the treatment plant. Wastewater effluent was divided into two samples in the lab: (i) as-collected wastewater effluent that contained pathogens and (ii) wastewater effluent that had been filtered through a 0.45-μm membrane for removal of suspended matter. The original wastewater effluent was then diluted five-fold using filtered wastewater effluent to avoid clogging of the CNT hybrid filter and to allow better imaging of individual microorganisms.
The wastewater had a measured pH of 6.9, and an ionic conductivity of 279 μS (conductivity meter model 32, YSI, USA). Total organic carbon (TOC) and dissolved organic carbon (DOC) (TOC analyzer, TOC-VCSH, Shimadzu, USA) were measured as 25.56 mg/L and 16.86 mg/L, respectively, while UV absorption at UV 254 nm (1 cm cell) gave a reading of 0.09 (UV/Vis spectrophotometer model 8453, HP, USA).
River water samples were also obtained from the Mill River. The river water samples were immediately transported back to the lab within 15 minutes of collection and maintained at room temperature (23 0C). The river water had a measured pH of 7.5 and an ionic conductivity of 147 μS. TOC and DOC levels of 15.41 mg/L and 10.39 mg/L, respectively, were measured, along with a UV absorption of 0.14 at 254 nm. It was possible to compare the amount of humic-like substances in the environmental samples by normalizing the UV reading at 254 nm by the DOC to obtain the specific UV absorbance (SUVA). The SUVA was 2.5 times higher for the river water than the wastewater, indicating higher concentrations of humic-like substances in the river sample. Example 7 ~ Bacterial Inactivation Assays
Bacterial inactivation rates on the filters of Example 1 were measured by a standard fluorescent assay, which confirmed the membrane integrity of the cells. Bacterial suspensions were filtered through the SWNT-MWNT or MWNT filters. The filters were then incubated in the dark for the indicated times in saline solution (154 mM, or 10 mM NaCl) at 37 0C. After incubation, cells were shielded from light and stained with propidium iodide (PI, 50 μM) for 15 min, and then counter- stained with SYTO®-9 for 5 min. The cells on the filter were imaged using an epifluorescence microscope (Olympus). For each filter 10 representative images were taken, and percentage inactivation was determined by direct counting of Pi-stained inactivated cells divided by the total number of cells that were stained by either PI or SYTO®-9. More details on this technique have been previously reported [Brady-Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481-484; and Kang, S., et al, Langmuir, 2007. 23(17): p. 8670-8673]. Example 8 ~ MWNT Filter Characteristics
Because MWNTs aggregate less in dimethylsulfoxide suspension than SWNTs, it was hypothesized that deposition of the less aggregated MWNTs onto a filter, could yield a more permeable matrix with increased contact opportunities for viral removal, while allowing use of the less expensive MWNTs.
Electrophoretic mobility (EPM) measurements, which are proportional to zeta potential, gave indication of the relative surface charges of the MWNTs over the range of experimental conditions tested. The MWNT EPM became less negative with increasing ionic strength from -0.82 ± 0.24 x 10"8 m2 V"1 s"1 at 1 mM NaCl to -0.50 ± 0.20 x 10"8 m2 V" 1 s"1 at 100 mM NaCl. Compression of the diffuse double layer and reduction of Stern potential of the MWNTs caused lower magnitude EPM values at the higher ionic strengths [Williams, R.A., et al., Particle Deposition and Aggregation: Measurement, Modeling and Simulation. 1995, Woburn, MAboutterworth-Heinemann]. Strongly basic and acidic solutions also caused divergence from the -0.59 ± 0.24 x
10~8m2 V"1 s"1 EPM of the MWNT suspended in 10 mM NaCl at pH 5.5. The most basic condition tested at pH 9 demonstrated a highly negative MWNT EPM of -1.03 ± 0.31 x 10~8 m2 V"1 s"1. In contrast, the acidic pH 3 solution gave 0.11 ± 0.44 x 10"8 m2 V"1 s"1 EPM. This positive electrophoretic mobility measurement was unanticipated since the MWNT nanotubes had not undergone functionalization, and unfunctionalized MWNTs are slightly negatively charged in aquatic systems [Sano, M. and S. Shinkai Langmuir, 2001 : p. 7172- 7173; and Jiang, L. Q., L. Gao, and J. Sun Journal of Colloid and Interface Science, 2003. 260: p. 89-94]. The almost neutral measured value was well within a standard deviation of zero, and may actually reflect a negative charge. Variations in MWNT EPM across electrolyte pH have been shown previously [Saleh, N. B., L. D. Pfefferle, and M. Elimelech Environmental Science & Technology, 2008. 42: p. 7963-7969], and it was proposed that the changes in EPM were due to dissociation of carboxyl functional groups on the MWNT. Although the MWNTs are intended to be unfunctionalized, during sonication, defects are formed that can enable partial functionalization [Ye, Y., et al. Applied Physics Letters, 1999. 74(16): p. 2307-2309; and Zhang, J., et al. Journal of Physical Chemistry, 2003. 107(16): p. 3712-3718].
The addition of calcium and magnesium divalent cations caused similar changes in reducing the -0.82 ± 0.24 x 10"8 m2 V"1 s"1 EPM of the MWNTs in 10 mM NaCl. The 1 mM CaCl2 + 7 mM NaCl solution gave an EPM of -0.45 ± 0.18 x 10"8m2 V"1 s"1, while addition of 1 mM MgCl2 + 7 mM NaCl gave a statistically similar value of -0.44 ± 0.22 x 10"8 m2 V"1 s"1. These reductions in EPM negativity can be attributed to adsorption and charge neutralization by the divalent cations.
SR-NOM played a role in enhancing the negative EPM on the MWNT to -1.03 ± 0.39 x 10~8m2 v Vand -1.01 ± 0.41 x 10~8 m2 V"1 s"1 for the cases of 1 mg/L SR-NOM and 5 mg/L SR-NOM addition to 10 rnM NaCl, respectively. The SR-NOM, which contains both hydrophobic and hydrophilic groups as well as metals, is capable of contributing to the negative charge of the MWNT surface. In contrast, the addition of 1 mg/L alginate to 10 mM NaCl has negligible effect on the MWNT EPM, giving a value of -0.87 ± 0.25 x 10"8 m2 V"1 s"1, which is similar to the -0.82 ± 0.24 x 10"8m2 V"1 s"1 EPM value for 10 mM NaCl without organic matter. Addition of CaCl2 with alginate, however, had a light neutralizing effect, which brought MWNT EPM to -0.63 ± 0.24 x 10"8 m2 V"1 s"1 .
The 1 mM bicarbonate + 9 mM NaCl at pH 5.5 solution exhibited almost neutral MWNT EPM at -0.17 ± 0.28 x 10"8 m2 V"1 s"1. This might be due to the fact that significant amounts of HCl were added to the solution to adjust the pH to 5.5. It is possible that without pH adjustment, a much more basic bicarbonate solution would have contributed to a more negative EPM.
Addition of 1 μM phosphate to 10 mM NaCl had the effect of reducing the negative EPM of the MWNT to -0.58 ± 0.29 x 10"8m2 V"1 s"1 from the -0.82 ± 0.24 x 10"8 m2 V"1 s"1 for 10 mM NaCl alone. These values are, however, within one standard deviation.
As shown in the FESEM images (Figure 6), there were major differences in the morphology of MWNT and SWNT hybrid filters. Commercially available MWNTs and SWNTs were selected for their low cost and availability in large quantities for scale-up production purposes. The SEM images of the SWNT layer showed higher heterogeneity of deposition, with variability in effective pore size, non-uniform coverage, and debris from amorphous carbon that was present in the as-purchased SWNT source. The MWNT layer, in contrast, appeared as a much more unifor/mLy distributed matrix, with the majority of channels free for high permeability, along with more reliable coverage that lacks apparent paths of preferential flow through the filter. Permeability experiments demonstrated that even with this more consistent filter coverage, the MWNT -hybrid filter maintained high flux at low pressures, achieving an average permeability of 11,900 ± 435 Lm^h^bar"1 over the flux range of 565-1638 Lm V1.
The anticipated improvements to viral removal for the more homogeneous MWNT coverage were demonstrated using PFU quantification for the viral removal experiments performed. The MWNT filters with equivalent mass loading as that of the SWNT filters showed significantly higher viral removal, often attaining between 1.5 and 3 log higher viral removal than the SWNT filter. For the 10 mM NaCl case, the MWNT filter achieved 5.38 ± 0.80 log viral removal in comparison with the 3.83 ± 0.41 log viral removal obtained by the SWNT filter. Some enhancements of MWNT viral removal are indicated in Figure 7, which shows how both filters performed at conditions of 10 mM ionic strength in solutions of monovalent and divalent salts. Example 9 ~ Viral Properties
Characterization of the MS2 viral particles was necessary to better understand the mechanisms of viral adsorption to the MWNT filter. Several in-depth studies provide insight to properties of MS2 and its exterior viral capsid [Golmohammadi, R., et al. Journal of Molecular Biology, 1993. 234(3): p. 620-639; and Valegard, K., et al. Nature, 1990. 345(6270): p. 36-41. The MS2 isoelectric point and electrophoretic mobility for various solution chemistries and pH have previously been reported [Penrod, S.L., T.M. Olson, and S.B. Grant Langmuir, 1996. 12(23): p. 5576-5587; Redman, J.A., et al. Environmental Science & Technology, 1997. 31(12): p. 3378-3383; and Yuan, B.L., M. Pham, and T.H. Nguyen Environmental Science & Technology, 2008. 42(20): p. 7628-7633]. The electrokinetic properties and surface charge of MS2 can change significantly with only slight modifications to solution chemistry, affecting both viral aggregation and deposition. Figure 8 presents the MS2 virus EPM and hydrodynamic radius values, along with other parameters to be discussed later.
The electrophoretic mobility, an indicator of surface charge proportional to zeta potential, generally followed trends expected for charged colloidal systems in aquatic solutions. At pH 5.5, the lowest ionic strength of 1 mM NaCl showed the most negative EPM of -1.68 ± 0.14 x 10~8m2 V"1 s"1, which attained a less negative value of -1.00 ± 0.20 x 10"8 m2 V"1 s"1 for the highest ionic strength of 100 mM NaCl tested. As ionic strength increases, enhanced charge screening is possible due to compression of the electric double layer (EDL) around the particle, thereby facilitating higher aggregation or adsorption of virus particles. The DLS measurements confirmed that reduction of the magnitude of EPM of MS2 particles in solution facilitated more aggregation between the like-charged MS2 viruses. Accordingly, MS2 aggregates were larger at 100 mM NaCl, with a radius of 82.38 ± 2.77 nm, than under the 1 mM NaCl conditions, with a radius of 78.22 ± 1.98 nm. Addition of divalent salts at the same equivalent ionic strength had varying impacts on viral surface charge. Calcium effectively reduced the EPM from -1.54 ± 0.08 x 10"8m2 V"1 s"1 for NaCl alone, to -1.06 ± 0.14 x 10~8m2 V"1 s"1 due to specific interactions of calcium with the MS2 capsid surface. In contrast, magnesium salts were shown to lack specific interactions with MS2, thereby increasing the negativity of the EPM to -1.71 ± 0.07 x 10"8 m2 V"1 s"1. Divalent salt addition caused an increase in viral aggregate size for both conditions, however, with a 145.74 ± 4.42 nm radius and a 239.81 ± 8.27 nm radius for the cases of MgCl2 and CaCl2, respectively. The pH of the solution also had significant effect on the electrophoretic mobility of the viral capsids, through protonation and deprotonation of amino acid functional groups on the viral surface. The isoelectric point (IEP) of MS2 was previously measured as between pH 3.5-3.9. Below this pH, MS2 is positively charged, while above this pH, the exterior of the viral capsid is negatively charged. Below the IEP, for 10 mM NaCl at a pH of 3, we recorded a positive EPM of +0.18 ± 0.07 x 10~8m2 V"1 s"1, while the EPM was negative at pH 5.5, and highly negative at -1.93 ± 0.31 x 10~8m2 V"1 s"1 for the most basic condition tested of pH 9. The DLS revealed significantly larger viral aggregates (95.45 ± 3.49) at pH 3 (due to lower magnitude of EPM) than at the higher pH conditions tested (77.79 ± 2.39 at pH 9) Addition of SR-NOM to a background solution of 10 mM NaCl had the effect of neutralizing viral EPM relative to the case of NaCl alone. This effect is concentration dependent with 5 mg/L SR-NOM providing better charge screening than 1 mg/L SRNOM, with EPM measurements of -1.24 ± 0.22 x 10~8m2 V"1 s"1 and -1.43 ± 0.18 xlθ~8 m2 V"1 s"1, respectively. The natural organic matter also contributed to comparable levels of enhanced viral aggregation with hydrodynamic radii of 210.66 ± 6.64 nm and 205.10 ± 6.81 for the addition of 1 mg/L and 5 mg/L of SR-NOM, respectively.
Alginate addition to 10 mM NaCl at 1 mg/L concentration had a similar effect on viral EPM (-1.64 ± 0.07 x 10"8m2 V"1 s"1) as the 10 mM NaCl background solution (-1.54 ± 0.08 x 10"8m2 V"1 s"1). In contrast, when alginate was added to the 1 mM CaCl2 + 7 mM NaCl solution, the EPM was substantially neutralized to -1.06 ± 0.01 x 10"8 m2 V"1 s"1, likely due to specific interactions between calcium and the viral capsid. Cationic bridging of the calcium in the presence of alginate contributed to more aggregation than with monovalent salt alone (133.97 ± 4.35 nm vs. 78.31 ± 2.07 nm), yet far less than in the case of calcium chloride addition in the absence of alginate (239.81 ± 8.27 nm). Neither the addition of 1 μM phosphate or 1 mM bicarbonate solutions (adjusted to pH 5.5) showed any statistical difference in EPM from that of the 10 mM NaCl solution. It is possible that EPM would have significantly changed if the concentrations of phosphate were higher, or the bicarbonate solution was left at its basic unadjusted pH. DLS measurements at these conditions also remained consistent with values obtained for 10 mM
NaCl.
Example 10 - Viral Removal with MWNT Filters
Viral Removal Increases with Decreasing Fluid Approach Velocity. The filter approach velocity plays an important role in determining filter performance. Past studies demonstrated that viral adsorption is inversely proportional to fluid velocity [Funderburg, S.W., et al. Water Research, 1981. 15(6): p. 703-711; Wang, D.S., CP. Gerba, and J.C. Lance Applied and Environmental Microbiology, 1981. 42(1): p. 83-88; and Lance, J.C, CP. Gerba, and D.S. Wang Journal of Environmental Quality, 1982. 11(3): p. 347-351. Colloid filtration theory predicts that log viral removal, log(CCo), is proportional to v~2/3, where CICo is the residual viral concentration at the filter outlet and v is the approach velocity. In our filtration experiments, the highest MS2 viral log removal by the filter was 7.21 ± 0.87 at 60 Lm-2Ii'1 water flux, corresponding to an approach velocity of 0.0016 cm/s (the lowest velocity tested). The log removal declined to 5.38 ± 0.80 at 160 Lm-2Ii'1 water flux (0.0044 cm/s), while filtration at a 0.0072 cm/s approach velocity (260 Lm 2Ii 1 flux) attained 3.68 ± 0.20 log removal. As Figure 9 illustrates, the experimental MS2 viral removal attained by the MWNT-hybrid filter shows the expected dependence on approach velocity.
Effect of Ionic Strength on MWNT-Hybrid Filter Viral Removal. The ionic strength of the solution contributed to the extent of MS2 viral removal on the MWNT filter. Figure 8 shows that viral removal improved with increasing ionic strength of NaCl, from 5.06 ± 1.43 log removal at 1 mM NaCl to better than 6.56 log removal (full removal obtained for 75% of the tests) at 100 mM NaCl. This dependence of viral adsorption on ionic strength is consistent with previous results obtained for MS2 removal on the SWNT-hybrid filter. This increased viral removal is due to enhanced charge screening and electric double layer
(EDL) compression at higher ionic strengths; causing reduction in repulsive forces between the MS2 and MWNT as shown by the EPM measurements. Increased adsorption of viruses at high ionic strengths has previously been demonstrated in numerous studies [Penrod, S.L., T.M. Olson, and S.B. Grant Langmuir, 1996. 12(23): p. 5576-5587; Lipson, S.M. and G. Stotzky, Applied and Environmental Microbiology, 1983. 46(3): p. 673-682; Grant,
S.B., et al. Water Resources Research, 1993. 29(7): p. 2067-2085; and Redman, J.A., et al. Water Research, 1999. 33(1): p. 43-52]. A visual representation of the effect of ionic strength on efficacy of filtration is shown in Figure 10. Calcium Ions Enhance Viral Removal, but Not Magnesium Ions. The effect of divalent salts upon MS2 viral removal by the filter was first demonstrated by addition of CaCl2. With the ionic strength held constant at 10 mM, a comparison was made between the 10 mM NaCl and the 1 mM CaCl2 + 7 mM NaCl solutions. The addition of CaCl2 increased viral removal by the MWNT filter from 5.38 ± 0.80 log in the absence of the divalent calcium salt to 6.05 ± 0.16 log when 1 mM of CaCl2 was present, as recorded in Figure 8. Divalent cations have previously been shown to increase viral adsorption under many circumstances [Lipson, S. M. and G. Stotzky, Applied and Environmental Microbiology, 1983. 46(3): p. 673-682; Sobsey, M.D., R.M. Hall, and R.L. Hazard, Comparitive reductions of hepatitus-A virus, enteroviruses and coliphage MS2 in miniature soil columns. 1994: p. 203-209; and Moore, R.S., et al. Applied and Environmental Microbiology, 1982. 44(4): p. 852-859]. As shown by the EPM measurements, calcium heightens charge neutralization and likely also allows for cationic bridging between the viral particles and the surface of the MWNT filter to enhance viral adsorption. The addition OfMgCl2 divalent salts had the opposite effect of CaCl2; contributing to greater viral passage though the filter. Addition of 1 mM MgCl2 + 7 mM NaCl reduced viral removal to 3.22 ± 0.29 log, from the 5.38 ± 0.80 log viral removal obtained on the 10 mM NaCl solution. As the EPM data previously illustrated, electrostatic interactions between the MS2 and MWNT become more repulsive with addition of magnesium chloride. The reduction in adsorption could potentially also be due to repulsive hydration [Israelachvili, J.N. and G.E. Adams Journal of the Chemical Society- Faraday Transactions 1, 1978. 74: p. 975; Israelachvili, J.N. and P.M. McGuiggan, Science, 1988. 241(4867): p. 795-800] or steric forces [Penrod, S.L., T.M. Olson, and S.B. Grant Langmuir, 1996. 12(23): p. 5576-5587] between viral particles and the MWNT filter. Natural Organic Matter and Alginate Macromolecules Alter Viral Removal. SR-
NOM and alginate were chosen to model organic matter in natural and engineered aquatic environments due to the prevalence of humic-like substances and acidic polysaccharides in surface waters and wastewater effluent [Barker, D.J. and D. C. Stuckey, Water Research, 1999. 33(14): p. 3063-3082; Barker, D.J., et al. Journal of Environmental Engineering- Asce, 2000. 126(3): p. 239-249; and Manka, J., et al. Environmental Science &
Technology, 1974. 8(12): p. 1017-1020]. The results, as shown in Figure 11, demonstrate that viral filtration remains high at the lower SR-NOM concentrations. The viral removal at 1 mg/L SR-NOM was 5.32 ± 1.32 log, showing negligible deviation from the 5.38 ± 0.80 log removal obtained for 10 rnM NaCl solution in the absence of organic matter. Further increases in natural organic matter, however, negatively impacted filter performance. Only 1.07 ± 0.78 log viral removal was obtained when the SR-NOM concentration reached 5 mg/L. Although addition of organic matter can enhance hydrophobic binding of viruses to inorganic surfaces, it likely reduces hydrophobic binding sites in the case of adsorption to carbon nanotubes through competition for binding sites [Bales, R.C., et al.. Water Resources Research, 1993. 29(4): p. 957-963; Schijven, J.F. and S.M. Hassanizadeh, Critical Reviews in Environmental Science and Technology, 2000. 30(1): p. 49-127; and Watson, J.T. and W.A. Drewry, Adsorption off2 bacteriophage by activated carbon and ion exchange. 1971, Water Resources Research Center, University of Tennessee:
Knoxville, Tennessee]. Another possible explanation for the observed reduction in virus adsorption at high SR-NOM concentration is the presence of repulsive steric interactions due to adsorbed NOM molecules. Studies have previously shown that addition of organic matter has caused enhanced viral detachment and transport through sands and soil columns. A mechanism commonly proposed for reduced adsorption is the increase in the negativity of charge of both the particle and the surface with coating of organic matter, which thereby leads to increased electrostatic repulsion. It is important to note this was not observed in the experiments described herein since addition of SRNOM led to more neutral EPM measurements. Alginate solutions had an even more pronounced effect on MWNT -hybrid filter viral removal, in the case of both monovalent and divalent salt solutions. Extreme reduction of viral removal to only 0.17 ± 0.19 log removal was shown in the case of 1 mg/L alginate added to 10 mM NaCl background solution (see Figure 10). At the experimental pH of 5.5, the carboxylic acid groups of alginate are almost fully deprotonated causing more negative surface charge as confirmed by EPM in comparison with NaCl alone, increasing electrostatic repulsion between alginate molecules and alginate coated particles and surfaces [Lee, S. and M. Elimelech, Environmental Science & Technology, 2006. 40(3): p. 980-987]. The stark reduction in MWNT filter performance might, therefore, be partially due to stabilization of the MS2 particles from adsorbing onto an alginate coated filter. Similarly to the case of SR-NOM, alginate may also compete with viruses for binding sites on the MWNT filter [Watson, J.T. and W.A. Drewry, Adsorption off2 bacteriophage by activated carbon and ion exchange. 1971, Water Resources Research Center, University of Tennessee: Knoxville, Tennessee]. The filtration was slightly better in the case of 1 mg/L alginate added to 1 mM CaCl2 + 7 niM NaCl, although only 1.32 ± 0.55 log viral removal was attained. This increase in removal may be due to calcium's ability to form strong bridging and gelation between MS2 and MWNT through binding of the calcium ions to the carboxylic groups of the alginate molecules as described in the Grant's egg box model. The strength of this calcium bridging with alginate has been shown to increase the stability of bio floes, and might facilitate some minimal attachment of alginate-stabilized MS2 virus to the alginate-coated MWNT. Removal is so low, however, in comparison with the 10 mM NaCl case that calcium bridging is not dominant, and steric interactions likely limit viral adsorption to the filter. The comparison with the SR-NOM solutions is shown in Figure 10. Viral Removal is Sensitive to Solution pH. It was found that viral removal changes significantly over varying pH conditions, as the charges of viral particles and the MWNTs change and electrostatic interactions become more attractive or repulsive. MS2 has neutral charge at its isoelectric point at 3.9 and therefore, the surface becomes increasingly positive as pH becomes lower than 3.9 and increasingly negatively charged as pH increases above 3.9. While the exact source of charge on carbon nanotubes is relatively not well understood, CNTs have consistently shown to be negatively charged in aquatic solutions [Sano, M. and S. Shinkai Langmuir, 2001 : p. 7172-7173; and Jiang, L. Q., L. Gao, and J. Sun, Journal of Colloid and Interface Science, 2003. 260: p. 89-94]. The highest viral removal of MS2 on the MWNT filter occurs at low pH, where the MWNT filter is neutral or slightly negative and the MS2 is slightly positive through protonation of amino acid groups on the capsid, enabling attractive electrostatic interactions. This observation is illustrated by experiments at pH 3, which attain better than 8.13 log viral removal. Viral adsorption to the filter then decreases to 5.38 ± 0.80 log removal as MS2 becomes increasingly negative at pH 5.5, and decreases further to 4.00 ± 0.79 log removal at pH 9. These findings are consistent with DLVO theory, and studies that have shown decreased viral adsorption to negatively charged surfaces at higher pH. Furthermore, although the MWNT filter experimental data follows trends obtained on the SWNT -hybrid filter, the log MS2 viral removal at each pH is far better than at each condition on the SWNT filter. For instance, the log removal of MS2 on the MWNT filter at pH 9 is 4 ± 0.79, while, at the same pH, the SWNT filter attains only 1.04 ± 0.68 log removal.
Influence of Bicarbonate and Phosphate Anions. For viral filtration experiments, 1 mM bicarbonate was added to 9 mM NaCl background solution chemistry. Sufficient volumes of HCl were added to adjust the solution pH to 5.5. The viral removal obtained of 5.37 ± 0.47 log was statistically equivalent to that of 10 niM NaCl alone at 5.38 ± 0.80 log. It is important to note that substantial addition of HCl was needed to reduce the pH to 5.5, and addition of the bicarbonate alone would have yielded a far more basic solution that might have given different MS2 surface charge and viral adsorption due to deprotonation of functional groups on the capsid. Additional experiments comparing bicarbonate with NaCl at unadjusted pH would be needed to draw further conclusions on more comprehensive effects of bicarbonate on SWNT-filter viral removal.
Low levels of phosphate are common in river waters. The average concentration in streams is 0.7 μM [Morel, F. M. M. and J.G. Hering, Principles and Applications of Aquatic Chemistry. 1993, New York, NY: John Wiley & Sons], and therefore, a representative
1 μM phosphate was added to 10 mM NaCl at pH 5.5 in order to model an environmentally relevant condition. There was no statistically significant change to MS2 viral removal from the background solution of NaCl alone, although a slightly higher 5.78 ± 0.03 log value was recorded. The similarity in viral removal between the solutions in both the presence and absence of phosphate may be attributed to the very low concentrations of phosphate added. Example 11 - SWNT-MWNT Filter Characteristics
The permeability of the SWNT-MWNT filter indicated a highly porous matrix that operated in the microfϊltration range of pressures. When tested in a manner similar to the other filters, the SWNT-MWNT filter demonstrated a permeability of 9,361 ± 550 Lm2h"1bar"1. This value was comparable to the permeabilities of the MWNT and SWNT filters, namely 11,900 ± 435 Lrn Vbar"1 and 13,800 ± 320 Lrn Vbar"1 [Brady-Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481-484], respectively. The one major difference related to the permeability of the SWNT-MWNT filter is that during the preparation of the SWNT-MWNT filter, in addition to the probe sonication of the nanotube suspensions, the mixture was also bath sonicated immediately prior to filter deposition. This likely contributed towards more evenly dispersed nanotubes, causing reduction of preferential flow paths in the filter, and thereby reducing permeability slightly.
It was expected that the SWNT coating laid on the MWNT matrix would give the surface of the SWNT-MWNT filter a morphology roughly equivalent to that of the SWNT filter. FE-SEM was performed to provide images of the morphology of all three filter types and allow for comparison (Figure 1). As expected, the surface of the SWNT-MWNT filter appeared similar to that of the SWNT filter. Both filters showed increased bundling of the SWNTs in comparison with the MWNTs on the MWNT filter. This bundling, which causes tighter blocking on some areas of the filter, may also allow flow through gaps between bundles. In contrast, the MWNT filter images show much more consistent coverage of the nanotube matrix. Significant amounts of amorphous carbon were also imaged in the SWNT and SWNT-MWNT filters, due to impurities in the SWNT sample used.
Example 12 ~ Viral Removal with SWNT-MWNT Filters
The SWNT-MWNT filter's ability to remove additional model viruses was tested, as described below. The MS2, PRDl, and T4 viruses are highly varied; with different structures, ribonucleic acids, diameters, and isoelectric points (Figure 5). These viruses were chosen not to systematically determine how their individual characteristics may govern viral removal, but rather to demonstrate that the filter is effective in removal of a wide range of viruses. The base solution chemistry selected for all viral removal experiments was 10 mM NaCl at pH 5.5 to allow comparison with studies on the MWNT and SWNT filters (not shown). Removal of MS2 virus was first examined to allow comparison of the SWNT-
MWNT filter with our SWNT and MWNT filters (Figure 2). The viral removal obtained was 4.05 ± 0.004 at the 260 Lm V1 flux. This value is slightly better than the 3.68 ± 0.2 log MS2 removal obtained on the MWNT filter at this approach velocity. Since this is a rather high flux, additional experiments were also performed at 160 Lm-2Ii"1, which gave complete removal (over 6.9 log, from the initial starting concentration of 7.4 x 106 viral particles per mL). SWNT filter performance had been less effective in MS2 removal at this flux, attaining only 3.83 ± 0.41 log removal, while even the MWNT filter had obtained 5.38 ± 0.80 log removal.
It was expected that the SWNT-MWNT filter would more closely approximate the performance of the MWNT filter since the filter was made up of 83% MWNT and only 17% SWNT. However, it was not anticipated that the dual SWNT-MWNT filter would perform better than the 100% MWNT filter, since the SWNT filter had much lower viral removal. While not intending to be bound by any one theory, it is likely that this improvement is due to the procedural modification made to follow probe sonication with bath sonication immediately prior to nanotube deposition. This method, which was only used in obtaining the SWNT-MWNT data, enabled the matrix to have more uniform surface coverage and higher contact opportunities for adsorption than filters that were prepared from more highly aggregated stocks. Additional experiments were made to provide an initial proof-of-concept that the SWNT-MWNT filter retains various viruses. The filter attained 5.39 ± 0.76 log and complete viral removal of PRDl (from an initial concentration of 1.9 x 106 viral particles/mL) at the flux rates of 260 Lm-2Ii'1 and 160 Lm-2Ii"1, respectively. The T4 virus was also effectively removed, attaining complete viral removal at 160 Lm-2Ii'1 (from 2.6 x 104 viral particles/mL), and 3.84 ± 0.82 log viral removal at the higher flux of 260 Lm 2Ii 1.
It is acknowledged that different viruses will have varying levels of adsorption to CNT-hybrid filters over the wide range of conditions present in the environment. Many environmentally relevant pathogens are not easily culturable or quantifiable, therefore, in these studies bacteriophages were selected as model viruses. This data to provides the proof-of-concept that while adsorption will differ among viruses, the SWNT-MWNT filter is effective for removal of a wide range of viral pathogens. Example 13 ~ Inactivation of Gram Negative Bacteria
The term "Gram negative bacteria" is an art recognized term for bacteria characterized by the presence of a double membrane surrounding each bacterial cell.
Representative Gram-negative bacteria include Acinetobacter calcoaceticus, Actinobacillus actinomycetemcomitans, Aeromonas hydrophila, Alcaligenes xylosoxidans, Bacteroides, Bacteroides fragilis, Bartonella bacilliformis, Bordetella spp., Borrelia burgdorferi, Branhamella catarrhalis, Brucella spp., Campylobacter spp., Chalmydia pneumoniae, Chlamydia psittaci, Chlamydia trachomatis, Chromobacterium violaceum, Citrobacter spp., Eikenella corrodens, Enterobacter aerogenes, Escherichia coli, Flavobacterium meningosepticum, Fusobacterium spp., Haemophilus influenzae, Haemophilus spp., Helicobacter pylori, Klebsiella spp., Legionella spp., Leptospira spp., Moraxella catarrhalis, Morganella morganii, Mycoplasma pneumoniae, Neisseria gonorrhoeae, Neisseria meningitidis, Pasteurella multocida, Plesiomonas shigelloides, Prevotella spp., Proteus spp., Providencia rettgeri, Pseudomonas aeruginosa, Pseudomonas spp., Rickettsia prowazekii, Rickettsia rickettsii, Rochalimaea spp., Salmonella spp., Salmonella typhi, Serratia marcescens, Shigella spp., Treponema carateum, Treponema pallidum, Treponema pallidum endemicum, Treponema pertenue, Veillonella spp., Vibrio cholerae, Vibrio vulnificus, Yersinia enterocolitica, Yersinia pestis.
E. coli, a rod-shaped Gram negative bacteria, was selected for the inactivation experiments on the carbon nanotube filters. Previous studies had shown higher E. coli inactivation on SWNTs than MWNTs [Kang, S., et al, Langmuir, 2008. 24(13): p. 6409- 6413]. It addition, it had also been shown that the SWNT filter had relatively high inactivation of E. coli, even after only 15 minutes exposure to the nanotubes [Brady- Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481-484]. The SWNT- MWNT filter essentially utilized a topmost layer of nanotubes that were equivalent to those used for the SWNT filter. There were only minor differences in SWNT deposition techniques for these two filters involving the initial concentrations of nanotubes in suspension and their sonication procedures, as described above. The elevated inactivation of 91.4 ± 3.0% of the E. coli exposed to the SWNT-MWNT filter was comparable to the slightly lower cytotoxicity levels for shorter exposure times on the SWNT filter [Brady- Estevez, A.S., S. Kang, and M. Elimelech, Small, 2008. 4(4): p. 481-48].
As shown in Figure 3, E. coli demonstrated greater resilience to exposure to the MWNT filter. The 30-minute exposure time led to inactivation of only 58.5 ± 8.5% of this Gram negative bacteria. This value, while far lower than that shown for SWNT-MWNT filter exposure, was still significantly higher than inactivation demonstrated in previous direct contact studies between E. coli and MWNTs [Kang, S., et al., Langmuir, 2008. 24(13): p. 6409-6413; and Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2008. 42(19): p. 7528-7534]. It is possible that the lower levels of salt in the current experiments in comparison to prior studies (10 mM NaCl for the monocultured experiments vs. 154 mM NaCl) contributed to elevated stress for the bacterial cells. Differences in nanotube aggregation states between studies might also play a factor, as it has been suggested that increased dispersivity of the nanotubes can allow for greater cytotoxicity through enhanced contact with cells [Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2008. 42(19): p. 7528-7534]. Example 14 ~ Inactivation of Gram Positive Bacteria The term "Gram positive bacteria' is an art recognized term for bacteria characterized by having as part of their cell wall structure peptidoglycan as well as polysaccharides and/or teichoic acids and are characterized by their blue-violet color reaction in the Gram-staining procedure. Representative Gram-positive bacteria include: Actinomyces spp., Bacillus anthracis, Bifidobacterium spp., Clostridium botulinum, Clostridium perfringens, Clostridium spp., Clostridium tetani, Cory neb acterium diphtheriae, Corynebacterium jeikeium, Enterococcus faecalis, Enterococcus faecium, Erysipelothrix rhusiopathiae, Eubacterium spp., Gardnerella vaginalis, Gemella morbillorum, Leuconostoc spp., Mycobacterium abcessus, Mycobacterium avium complex, Mycobacterium chelonae, Mycobacterium fortuitum, Mycobacterium haemophilium, Mycobacterium kansasii, Mycobacterium leprae, Mycobacterium marinum, Mycobacterium scrofulaceum, Mycobacterium smegmatis, Mycobacterium terrae, Mycobacterium tuberculosis, Mycobacterium ulcer ans, Nocardia spp., Peptococcus niger, Peptostreptococcus spp., Proprionibacterium spp., Staphylococcus aureus, Staphylococcus auricularis, Staphylococcus capitis, Staphylococcus cohnii, Staphylococcus epidermidis, Staphylococcus haemolyticus, Staphylococcus hominis, Staphylococcus lugdanensis, Staphylococcus saccharolyticus, Staphylococcus saprophyticus, Staphylococcus schleiferi, Staphylococcus similans, Staphylococcus warneri, Staphylococcus xylosus, Streptococcus agalactiae (group B streptococcus), Streptococcus anginosus, Streptococcus bovis, Streptococcus canis, Streptococcus equi, Streptococcus milleri, Streptococcus mitior, Streptococcus mutans, Streptococcus pneumoniae, Streptococcus pyogenes (group A streptococcus), Streptococcus salivarius, Streptococcus sanguis.
Staphylococcus epidermis, a spherical cocci, was selected to model Gram positive bacteria in the inactivation tests. S. epidermis was demonstrated to have significantly lower inactivation rates than the Gram negative E. coli. For the 10 mM NaCl solution at pH 5.5, S. epidermis was 34.5 ± 3.4% inactivated on the MWNT filter, in comparison with the higher rates of 58.5 ± 8.5% for E. coli inactivation after 30 minutes of exposure (Figure 3). Although the inactivation of the Gram positive bacteria was much higher on the SWNT-MWNT filter (53.1 ± 3.6% at 30 minutes), the rates for S. epidermis were still much lower than those for the Gram negative E. coli (91.4 ± 3.0%) for the same exposure time. These results for the SWNT-MWNT filter followed similar trends of previously demonstrated enhanced cytotoxicity towards E. coli in comparison with S. epidermis on SWNT samples [Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2009. 43(7): p. 2648-2653].
While the mechanism of nanotube cytotoxicity towards bacteria is not well understood, it has been hypothesized that direct contact with the carbon nanotubes is necessary to attain inactivation [Kang, S., et al, Langmuir, 2007. 23(17): p. 8670-867]. If direct contact with the bacterial surface does govern inactivation, then differences in cytotoxicity may be partially attributed to surface characteristics of the bacteria. S. epidermis, like other Gram positive bacteria, has a thick peptidoglycan layer in its cell wall [Vollmer, W., D. Blanot, and M.A. de Pedro, FEMS Microbiology Review, 2008. 32(2): p. 146-167]. This thick exterior may play a role in helping maintain cell structure under the stresses of exposure to carbon nanotubes.
Example 15 ~ Effect of Exposure Time on Bacterial Inactivation
The inactivation of bacteria increased significantly on the MWNT filter over longer time periods. The staining assay indicated that S. epidermis cytotoxicity was enhanced to 48.1 ± 3.7% after 2 hours, in comparison with 34.5 ± 3.4% at 30 minutes. E. coli showed heightened inactivation of 68.2 ± 4.0% after 2 hrs. This was a substantial increase compared with the 58.5 ± 8.5% inactivation at 30 minutes exposure to the MWNT surface. The level of microbial inactivation also increased on the SWNT-MWNT filter over time. This was consistent with previous testing by Kang et al.that showed E. coli inactivation increased with time at 30 min, 60 min, and 90 min intervals of exposure to
SWNTs [Kang, S., et al, Langmuir, 2007. 23(17): p. 8670-867]. The greatest change from the 30-min inactivation level at the 2 hour interval on the SWNT-MWNT filter was that of S. epidermis. The staining assay demonstrated 61.1 ± 3.3% cytotoxicity at 2 hours, in comparison with the 53.1 ± 3.6% after 30 minutes exposure to the filter surface. Prior staining assays had shown time dependence for inactivation of the Gram positive Bacillus subtiis [Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2009. 43(7): p. 2648-2653].
The inactivation of E. coli on the SWNT-MWNT filter was affected by time to a lesser degree. After 30 minutes exposure to the filter surface, 91.4 ± 3.0% inactivation was already obtained. The E. coli cytotoxicity came even closer to full inactivation with a staining measurement of 93.8 ± 1.9% inactivation after 2 hours. Although this suggests a slight improvement, the values at each exposure time were within one standard deviation of each other. Example 16 — Inactivation of Microbes Naturally Present in River Water and Wastewater Samples
In addition to presenting the inactivation of specific bacteria, the effects of MWNT and SWNT-MWNT filter exposure on microbes naturally present in the environment was also quantified. The river water samples demonstrated less significant differences in cytotoxicity levels between the two filters than those found for the monoculture bacteria. The river water inactivation was 56.8 ± 3.4% for the MWNT filter, while 59.11 ± 2.96% was attained on the SWNT-MWNT filter at the 1-hour exposure time. It has been hypothesized that it is the direct contact between cells and SWNTs that causes cell inactivation [Kang, S., et al., Langmuir, 2007. 23(17): p. 8670-867]. It is possible that the high levels of natural organic matter (15.41 mg/L TOC) in the river water modified the surfaces of the SWNT-MWNT and MWNT filters, thereby reducing the difference between the two filter surfaces for contact with the microbes.
In contrast, the difference in cytotoxicity towards microbes present in the wastewater effluent was much more pronounced between the filters. The MWNT filter only attained 59.11 ± 3.0%, inactivation, while the SWNT-MWNT filter achieved 71.49 ± 3.6%. This may also be attributable to differences in the bacterial populations between the river water and wastewater effluent.
It is important to note that the trend differed for which water sample attained higher inactivation on the distinct filters. The MWNT filter had better inactivation under the solution conditions present in the river water in comparison with wastewater. In contrast, the SWNT-MWNT filter showed higher inactivation under the wastewater conditions than those in the river water sample. Prior work had instead shown river water, with more humic-like substances, to have higher inactivation on both SWNT and MWNT than wastewater [Kang, S., M.S. Mauter, and M. Elimelech, Environmental Science & Technology, 2009. 43(7): p. 2648-2653].
INCORPORATION BY REFERENCE
The contents of the articles, patents, and patent applications, and all other documents and electronically available information mentioned or cited herein, are hereby incorporated by reference in their entirety to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference. Applicants reserve the right to physically incorporate into this application any and all materials and information from any such articles, patents, patent applications, or other physical and electronic documents. EQUIVALENTS
The invention has been described broadly and generically herein. Those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present invention. Further, each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the invention. This includes the generic description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

Claims

We claim:
1. A filter, comprising a layer of multiwall carbon nanotubes dispersed on a porous substrate; wherein the porous substrate is permeable to the flow of a fluid.
2. The filter of claim 1, wherein said porous substrate comprises single or multi- component polymers, nylon, polyurethane, acrylic, methacrylic, polycarbonate, epoxy, silicone rubbers, polystyrene, polyethylene terephthalate, polybutylene terephthalate, poly-paraphylene terephtalamide, poly-(p-phenylene terephtalamide), polyester ester ketone, viton fluoroelastomer, poly-tetrafluoroethylene, polyvinylchloride, polyester, polypropylene, polychloroprene, acetates, and combinations thereof.
3. The filter of claim 1, wherein the porous substrate is poly-tetrafluoroethylene.
4. The filter of any one of claims 1-3, wherein the average length of the multiwall carbon nanotubes is between about 50 nm and about 5000 nm.
5. The filter of any one of claims 1-4, wherein the average inner diameter of the multiwall carbon nanotubes is between about 0.4 nm and about 0.5 nm.
6. The filter of any one of claims 1-5, wherein the average outer diameter of the multiwall carbon nanotubes is between about 1.0 nm and about 2.0 nm.
7. The filter of any one of claims 1-6, wherein a majority of the multiwall carbon nanotubes have pores with diameters between about 0.1 nm and about 200 nm.
8. The filter of any one of claims 1-6, wherein the majority of the multiwall carbon nanotubes have pores with diameters between about 1 nm and about 100 nm.
9. The filter of any one of claims 1-8, wherein the thickness of the layer of multiwall carbon nanotubes is between about 0.1 μm and about 500 μm.
10. The filter of any one of claims 1-9, wherein the layer of multiwall carbon nanotubes has a substantially planar surface.
11. The filter of any one of claims 1-10, wherein the loading of multiwall carbon nanotubes is between about 0.01 mg/cm2 and about 0.50 mg/cm2.
12. The filter of any one of claims 1-10, wherein the loading of multiwall carbon nanotubes is between about 0.2 mg/cm2 and 1 mg/cm2.
13. The filter of any one of claims 1-12, wherein at least one functional group is attached to the surface of a majority of the multiwall carbon nanotubes.
14. The filter of any one of claims 1-13, wherein a majority of said multiwall carbon nanotubes have a morphology chosen from nanohorns, cylindrical, nanospirals, dendrites, trees, spider nanotube structures, nanotube Y-junctions, and bamboo morphology.
15. The filter of any one of claims 1-14, further comprising a layer of single wall carbon nanotubes disposed over the layer of multiwall carbon nanotubes or disposed between the layer of multiwall carbon nanotubes and the porous substrate.
16. The filter of claim 15, wherein the average length of the single wall carbon nanotubes is between about 50 nm and about 5000 nm.
17. The filter of claim 15 or 16, wherein the average inner diameter of the single wall carbon nanotubes is between about 0.4 nm and about 0.5 nm.
18. The filter of any one of claims 15-17, wherein the average outer diameter of the single wall carbon nanotubes is between about 1.0 nm and about 2.0 nm.
19. The filter of any one of claims 15-18, wherein a majority of the single wall carbon nanotubes have pores with diameters between about 0.1 nm and about 200 nm.
20. The filter of any one of claims 1-6, wherein the majority of the single wall carbon nanotubes have pores with diameters between about 1 nm and about 100 nm.
21. The filter of any one of claims 15-20, wherein the thickness of the layer of single wall carbon nanotubes is between about 0.1 μm and about 500 μm.
22. The filter of any one of claims 15-21, wherein the layer of single wall carbon nanotubes has a substantially planar surface.
23. The filter of any one of claims 15-22, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm2 and about 0.50 mg/cm2.
24. The filter of any one of claims 15-22, wherein the loading of single wall carbon nanotubes is between about 0.01 mg/cm2 and 0.2 mg/cm2.
25. The filter of any one of claims 15-24, wherein at least one functional group is attached to the surface of a majority of the single wall carbon nanotubes.
26. The filter of any one of claims 15-25, wherein a majority of said single wall carbon nanotubes have a morphology chosen from nanohorns, cylindrical, nanospirals, dendrites, trees, spider nanotube structures, nanotube Y-junctions, and bamboo morphology.
27. The filter of any one of claims 15-26, wherein the ratio of the mass of the multiwall carbon nanotubes to the mass of the single wall carbon nanotubes is about 80:20.
28. The filter of any one of claims 1-27, wherein the fluid comprises water.
29. The filter of claim 28, wherein the filter provides a water permeability of at least 0.01 cc/s-cm2-atm.
30. A method of reducing the amount of constituents in a fluid, the method comprising contacting the fluid with a filter for a time sufficient to separate, remove, immobilize, modify or destroy at least a portion of one constituent from the fluid; wherein the filter is a filter of any one of claims 1-29.
31. The method of claim 30, wherein the at least one constituent from the fluid is selected from the group consisting of salts, metals, nanoparticles, microparticles, organic constituents, pathogens, microbiological organisms, DNA, RNA, natural organic molecules, molds, fungi, natural toxins, synthetic toxins, chemical warfare agents, biological warfare agents, endotoxins, proteins, and enzymes.
32. The method of claim 30 or 31 , wherein the at least one constituent is removed from the fluid to a level of at least 1 log (90%).
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