WO2007026387A2

WO2007026387A2 - Photocatalytic filters that are coated with titanium dioxide suspensions and other substances and methods for obtaining such filters

Info

Publication number: WO2007026387A2
Application number: PCT/IT2006/000633
Authority: WO
Inventors: Luigino Gravelli
Original assignee: NM TECH LTD. - Nanomaterials and Microdevices Technology
Priority date: 2005-09-01
Filing date: 2006-08-31
Publication date: 2007-03-08
Also published as: WO2007026387A3; ITIS20050002A1

Abstract

The invention relates to filters of various nature for use in air-conditioning and purification systems, particularly filters treated with photocatalytic materials and nanomaterials allowing decontamination from bacterial and viral species, also in the absence of light radiation. Particularly, the invention relates to photocatalytic filters (2) comprising, on the surface of said filters (2), one or more surface layers of compounds having photocatalytic activity comprising photocatalytic titanium dioxide.

Description

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"Photocatalytic filters covered with titanium dioxide suspensions and other compounds and methods for obtaining said filters" DESCRIPTION The invention relates to filters of various nature for use in air conditioning and purification systems, particularly filters treated with photocatalytic materials and nanomaterials allowing decontamination from bacterial and viral species also in the absence of light radiation.

In household, industrial, hospital environments, offices, shops or generally in both public and private rooms, air purification means are used, which are differently configured in order to meet particular requirements.

In addition, the air in these environments requires to be often purified and/or filtered, e.g. in order to abate the smoke that is particularly present in public rooms, or the particulate generated for example from industrial processing, or odours produced in a kitchen, or air pollutants, such as NOx, SOx, CO, organic vapours, C₆H₆, etc., in order to make the stay in these environments more pleasant and salubrious .

In addition, in public environments, and mainly in hospitals, viruses or bacteria found in the air require to be eliminated in order to maintain good hygienic conditions, possibly substantially sterile conditions.

In some industrial fields, the treatment of fumes of particular noxious and/or polluting chemicals being released through the chimneys provides using huge amounts of coal, which has to be periodically replaced, which results in high management costs .

In the car industry, current systems for purifying the air in a vehicle passenger compartment provide using low/medium efficacy filters made of paper, or (also expanded) polymer fiber, which may be impregnated with activated carbons in order to eliminate particulate and fine dust. These filters, which are usually classified according to the EN 779 and EN 1822 standards, do not perform antibacterial functions and do not remove urban pollutants .

In the rail, sea and air public transport, the air requires to be recycled and filtered in order to provide the comfort and health of passengers. In the household field, in kitchen hoods, filters of various types and materials are used to abate the odours generated from food. Said filters have very short saturation times as compared with those described in the invention, as well as very high pressure losses. Furthermore, after a few days of use, these filters are loaded with bacteria. In the household field, again, in the refrigerators, filters should be desirably used, which are capable of abating the odours, such as to preserve the food and abate the bacteria deriving from the decomposition of food.

The above-discussed functions are provided by the known purification means, such as fans, air purifiers, air-treatment stations, air conditioners, kitchen hoods, ventilation or conditioning systems in cars, motor vehicles, lorries, buses, airplanes, trains, ships, fume exhaustion and/or evacuation chimneys, or any other system using said means, which use filters that not only do not eliminate bacteria, but rather allow the same to proliferate, and eliminate urban pollutants such as NOx, SOx, CO, C₆H₆, CO₂, O₃, etc. only by adsorption (active carbons) and in a temporary manner. In addition, they do not eliminate odours and allow mould proliferation.

An object of the invention is to provide improved air-purification filters, which - together with the systems listed below - allow for the actual elimination or reduction of pollutants, bacteria, viruses, or odours found in the air. A non-exhaustive list of systems to which the present invention can be applied comprises: ventilation, purification, conditioning systems, air- treatment stations, air outlets and/or exhaustion and/or inlet channels, kitchen hoods, refrigerators, ventilation or conditioning systems in cars, motor vehicles, lorries, buses, trains, ships, airplanes, fume exhaustion and/or evacuation chimneys, household appliances using an air stream to be moved, conveyed, heated, cooled, ventilated, such as vacuum cleaners, electric brooms, hair driers, computers, etc..

Another object of the invention is to provide improved air purification filters, which - together with the above-listed systems - eliminate urban pollutants such as NOx, SOx, CO, C₆H₆, CO₂, O₃, etc., by turning the compounds into safe substances .

Another object is to provide improved air- purification filters, which - together with the above- listed systems - avoid the proliferation of microorganisms and allow eliminating bacteria and viruses found in the environments in which they are provided.

Another object is providing improved air- purification filters, which - together with the above- listed systems - allow avoiding unpleasant odours to develop in the environments in which they are installed, and/or allow the same to be abated.

Still another object is to provide improved air- purification filters, which - together with the above- listed systems - have photocatalytic and/or anti-mould features .

Another object is to provide improved air- purification filters, which - together with the above- listed systems - have durable self-cleaning features as relates to organic compound.

Another object is providing improved air- purification filters which - together with the above- listed systems - can be cleaned using water alone, without detergents, are long-lasting, can be easily adapted to any system and with a validated functional efficiency.

Another object is to provide improved air- purification filters which - together with the above- listed systems - particularly kitchen hoods or refrigerators are capable of, at the same time, eliminating the odours and abating the bacterial load, as well as preserving food and extending the storage time thereof in the refrigerators.

In the light of the above-discussed objects, the present invention relates to providing photocatalytic air-purification filters 2 having titanium dioxide of Anatase, Rutile or Brookite types as the active element, which may be in association with silver and/or copper or derivatives thereof. Titanium dioxide is a semiconductor material with a crystalline structure, having a valence band that is separated from a conduction band by a determined energy gap. As most materials, when titanium dioxide is hit by an electromagnetic radiation, it absorbs energy from the radiation. When the absorbed energy is greater than the energy gap between the valence band and the conduction band, an electron is promoted from the valence band to the conduction band, thereby an excess electron charge

(e-) is created in the conduction band and an electron hole (h+) is created in the valence band. In the solid state at room temperature, titanium dioxide is in a crystalline form as Anatase, Rutile or Brookite. From the photocatalytic point of view, Anatase is the most active crystalline form and has 3.2 eV energy gap between the valence band and the conduction band. As a result, when this material is irradiated with photons having more than 3.2 eV energy, i.e. an electromagnetic radiation having less than 390 run wavelength, an electron is promoted from the valence band to the conduction band. Particularly, this occurs when titanium dioxide is hit by Ultra Violet (UV) radiation, such as emitted from a ultraviolet lamp, or solar radiation. The electron holes can oxidize most organic contaminants. These electron holes may, for example, react with a water molecule (H₂O) thereby generating a hydroxyl radical (*0H) that is highly reactive. The excess electrons have very high reducing power and can react with the oxygen molecule to form the superoxide anion (O₂*-) • The reaction of water molecule oxidation is shown in the scheme (I) and the reaction of oxygen reduction is shown in the scheme (II) : TiO₂ (h+) + H₂O -> TiO₂ + *0H + H+; TiO₂ (e-) + O₂ -> Ti02 + O₂*- The hydroxyl radical (*0H) is particularly active both for the oxidation of organic and inorganic substances, such as those found in the air, and for the inactivation of micro-organisms that, for example, can be noxious to crops and human beings. Particularly, the organic compounds are oxidized to carbon dioxide and water (H₂O) , the nitrogen compounds are oxidized to nitrate ions (NO₃-) , the sulphur compounds to sulphate ions (SO₄ ^2") . Titanium dioxide also performs, after irradiation with light of a suitable wavelength, a very effective anti-microbial, antibacterial, and anti-mould action. Titanium dioxide is further capable of decomposing many gases or noxious substances, such as thiols or mercaptans, formaldehyde, having an unpleasant odour. The decomposition of these gases or substances eliminates the bad odours associated therewith. In a first aspect of the invention, said photocatalytic filters 2 are made by means of ceramic filters, preferably dichroite, which are made up as follows :

Dichroite ceramic filters having a squared or other reticular shape, having chemical composition

(Fe_xMg)₂Al₄Si₅O₁₈^nH₂O with 90% minimum contents, besides

Mullite Al₆Si₂Oi₃, Aluminium Oxide Al₂O₃, Spinel MgAl₂O₄, as the remaining 10% material having a porosity ranging between 32% and 36%, and 3 ± l,5μm pore diameter, that can be usable up to 1,380⁰C, having 16CSI, 25CSI, 50CSI, 64CSI₁ lOOCSI, 200CSI, 300CSI, 400CSI, 600CSI cells per square inch, with 0.3 mm to 3.000 mm depth, or mixed.

In a second aspect of the invention, said photocatalytic filters 2 are made by means of polymer fiber filters, preferably expanded polyester synthetic fiber impregnated with activated carbons, and consisting of: a filter with material thickness ranging from about 0.2 mm to about 1.000 mm, entirely consisting of (also expanded) polyester synthetic fiber impregnated with activated carbon, mass per unit area ranging from about 10 g/m² to about 900 g/m², flow rate of the filtering material ranging from about 0.05 m/s to about 2.0 m/s, made of polymer fiber. The filter has a nominal flow discharge of about 0.100 m³/s to about 900 m³/s and a pressure loss at 100% nominal flow discharge of about 1

Pa to about 250 Pa, for those classified Gl to G4 in the

EN 779 standard, corresponding to EUl a EU4 in the

Eurovent standard, and with a pressure loss at 100% nominal flow discharge of about 1 Pa to about 450 Pa, for those classified P5 to F9 in the EN 779 standard, corresponding to EU5 a EU9 in the Eurovent standard, having minimum absorption efficacy of about 75% benzene

(C₆H₆) on 160000 μg/Nmc concentration to about 97% maximum on 150 μg/Nmc concentration. Alternatively, said filters are made by means of other polymer fiber, of the polyester, heat-set polyester, (also expanded) polyurethane, cloth-like, also rotary and/or cup-like and/or paper-like, preferably also impregnated with activated carbons, or entirely impregnated with activated carbon, or mixed or filled with zeolite in pellets or other forms .

In a third aspect of the invention, said photocatalytic filters 2 are made by means of high efficiency and ultra high efficiency glass fiber HEPA and ULPA absolute filters, respectively, which are HEPA- classified HlO a H14 according to EN 1822 standard, corresponding to EUlO to EU14 in the Eurovent standard, and classified as ULPA U15 to U17 according to EN 1822 standard, corresponding to EU15 to EU17 in the Eurovent standard, which - both HEPAs and ULPAs, can have the filter media made of glass microfiber paper, either mini-pleated or deep-pleated, also with corrugated aluminium separators, with efficiency particle efficiency ranging from 1.0 μm to 0.01 μm, or mixed.

In a fourth aspect of the invention, said photocatalytic filters 2 are made by means of plastic filters, also made of polypropylene (PP) , modified polyphenyl oxide (PPO) , polycarbonate (PC) or polystyrene (PS) , or sintered expanded polystyrene (EPS) consisting of a closed-cell, low-weight, rigid expanded material, or mixed. The EPS generally has a specific mass ranging between 10 and 40 kg/me and thus on average consists of 98% volume air and only 2% pure hydrocarbon as the structural material.

In a fifth aspect of the invention, said photocatalytic filters 2 are used on metal supports made of metal material, also aluminium (both meshed and sheet) , (also stainless) steel (both meshed and sheet) , or mixed.

According to the invention, said photocatalytic filters 2 are coated with photocatalytic solutions capable of achieving the objects described above, and can thus be applied to air moving systems for generating a mechanical circulation of air V in said purification means, and for use in purifying the air of a confined, or indoor, household, industrial, hospital environment, offices, shops, public and private rooms in general, or the interior of a car, lorry, bus, train, ship, airplane, or chimneys' fumes, or electrical appliances in which said purification means are provided. This allows making purification systems which provide treating the air in this environment by causing and accelerating the reactions of decomposition and oxidation of substances, particularly, organic polluting substances found in the atmosphere, such as NO, NO₂, SO₂, CO, C₆H₆, etc., either gaseous and/or particulate, which are completely oxidized to form mainly carbon dioxide (CO₂) and water (H₂O) and nitric acid (HNO₃) that is adsorbed by the surface and turned into safe salts. The bacterial load found in said air coming in contact, either directly or indirectly, with the treated filter surface, are also deactivated, because the photocatalytic filters will destroy the bacteria membranes even before they nest on the filters' surface. Similarly, the odours found in the atmosphere surrounding these purification means are eliminated, and no surface moulds are created.

In the first version, plastic filters, metal filters, ceramic filters, polymer fiber filters, paper filters, HEPA filters, and ULPA filters, and sub-groups are provided, which are arranged to filter the air of said environments by means of treatments (coating or covering) with solutions of photocatalytic titanium dioxide energizable by a light source (also UVA) .

In another version, said purification means comprise further light sources to emit a radiation in the 280 to 450 nm ultraviolet A (UVA) wavelength range. This allows the photocatalytic features of said filters to be enhanced.

In a further version, plastic filters, metal filters, ceramic filters, polymer fiber filters, paper filters, HEPA filters, and ULPA filters, and sub-groups are provided, which are arranged in order to filter the air of said environments by means of treatments (coating or covering) with solutions of light-photocatalytic titanium dioxide and other active substances, which operate without using any light source.

It would be appreciated from what has been stated above that one of the novel aspects of the invention is that said photocatalytic filters can operate with or without lighting, ranging between the visible spectrum and the invisible spectrum of light radiation.

In a version, said photocatalytic filters 2 comprise a first titanium dioxide layer, preferably in the form of Anatase and/or modified peroxytitanic acid. Preferably, said photocatalytic filters 2 are coated with further titanium dioxide layers or other compounds, as will be detailed below. In a preferred version, as stated above, said photocatalytic filters 2 comprise, in addition to said first photocatalytic titanium dioxide layer, one or more further photocatalytic titanium dioxide layers, preferably in the form of Rutile, which are interposed between the filter surface and said first layer of photocatalytic titanium dioxide.

In another version, said photocatalytic filters 2 further comprise one or more photocatalytic layers of titanium dioxide in the form of peroxytitanic acid or other compounds with a strong adhesion power, and not oxidisable, which are interposed between the filter surface and said first layer of photocatalytic titanium dioxide .

In another version, said photocatalytic filters 2 further comprise titanium dioxide in the form of Brookite or other compounds with a strong adhesion power and non oxidisable, and/or surfactant stabilizers.

In a particularly preferred embodiment, said photocatalytic filters 2 further comprise silver (Ag) and/or a derivative thereof, preferably a salt such as silver acetate (CH₃COOAg) .

In another preferred embodiment , said photocatalytic filters 2 further comprise copper (Cu) and/or a derivative thereof, preferably cupric oxide (CuO) or a copper (II) salt, such as CuSO₄.

It has been seen that silver or derivatives thereof and/or copper or a copper (II) salt being present on the inventive filters is capable of providing said filters with surprising antibacterial and antiviral properties, in the absence of light radiation, as will be detailed below in the present description.

In a further embodiment of the invention, said photocatalytic filters 2 further comprise at least one component selected from sodium hydroxide (NaOH) , lithium oxide (Li₂O) , heptahydrate sodium sulphite

(Na₂S₂O₃-VH₂O), pentahydrate sodium thiosulphate

(Na₂SO₃ ^• 5H₂O) and/or silica (SiO₂).

According to the embodiments provided above, the photocatalytic filters 2 can be protected from any chemical attack, the isolating features of the photocatalytic filters can be increased, and the titanium dioxide adhesion to the filters can be promoted.

A further object of the present invention is the industrial manufacture of said photocatalytic filters 2, using products that are already known and sold on the market, as well as methods for obtaining these products. In the manufacture of the photocatalytic material, titanium dioxide is used in a colloidal (also amorphous) solution, that may contain silver and/or copper or derivatives thereof as defined above, either powdered or in microspheres, either in laminar or any other form, such as a solution in suitable solvents . These components can be used either individually or aggregated to silica, colloidal silica or other suitable materials for gripping. By "titanium dioxide" is meant an aqueous colloidal solution, also in the amorphous state, containing Anatase and/or solution of modified peroxytitanic acid and/or Rutile and/or Brookite. The compositions listed below can be used either individually or in association with each other. On several substrates, when of an organic nature, the use of a silica-based or peroxytitanic acid-based primer is recommended. To prepare the photocatalytic filters 2 according to the invention, the compositions used will generally have a titanium titer (provided in the form of 100% Anatase , or 70-90% Anatase or Anatase peroxide and the remainder being Rutile or peroxytitanic acid or Brookite) ranging between 0.001 and 15% by weight. The Ag derivative, when provided, will generally have a concentration ranging between 0.001 and 1.0% by- weight. Preferably, the silver derivative will be CH₃COOAg. The copper derivative (II) , when provided, will generally have a concentration ranging between 0.001 and 0.5% by weight, preferably 0.005 and 0.1% by weight.

The surfactant will generally range between 0.001 and 5% by weight. SiO₂, when provided, will be preferably in colloidal form and will range between 0.001 and 10% by weight .

Sodium hydroxide, when provided, will preferably range between 0.001 and 1% by weight. Li₂θ, when provided, will preferably range between 0.001 and 2.0% by weight.

Na₂SO₃-TH₂O, when provided, will preferably range between 0.001 and 2% by weight, while Na₂S₂O₃-SH₂O, when provided, will generally range between 0.001 and 2% by weight .

Sodium sulfate, when provided, will preferably range between 0.001 and 2% by weight.

According to a particularly preferred embodiment, the products used are sold and/or manufactured under the name of Titanium from Jokero Invention s.r.l. Via Formichelli 2 - 86170 Isernia (IS) Italy, which are based on titanium dioxide at different concentrations and listed below:

- Titanium R with TiO₂ titer of 0.35%w to 9.70%w (100% peroxytitanic acid) and H₂O as the remainder, particularly of 0.85%w titer;

- Titanium K with TiO₂ titer of 0.35%w to 9.90%w (100% modified Anatase peroxide solution) and H₂O as the remainder, particularly of 0.85%w titer;

- Titanium KR with TiO2 titer of 0.85%w to 2.20%w

(70% modified Anatase peroxide solution + 30% peroxytitanic acid) and H₂O as the remainder, particularly of 0.85%w titer; - Titanium KR-VB with TiO₂ titer of 0.85%w to 2.20%w (70% modified Anatase peroxide solution + 30% peroxytitanic acid) + 0.1%w to 0.009%w silver acetate and H₂O as the remainder, particularly with 0.85%w titer; - Titanium β with TiO₂ titer of 0.5%w to 9.5%w (100% Degusta P25 - consisting of 80% Anatase and 20% Rutile) and H₂O as the remainder, particularly with 3.0%w titer;

- Titanium Ψ with 0.01%w to 9.5%w titer of TiO2 (100% Brookite) + [Ci₄H₂₂O(C₂H₄O)_n] surfactant from about 5.0%w to about 0.001%w also with Silver acetate from about 0.1%w to about 0.009%w, H₂O as the remainder, particularly with 0.5%w titer; - Titanium Ω as such (Anatase TiO₂ 1,49% - colloidal silica SiO₂ 0,91% - sodium hydroxide NaOH 0.05% - lithium oxide Li₂O 0,13% - sodium sulphite Na₂SO₃ -7H₂O 0.015% - sodium thiosulphate Na₂S₂O₃ -5H₂O 0.03% Silver acetate 0.005% - H₂O 97.37%) Titanium ATLS-IG as such (Anatase TiO₂ 1.06%±0.05% colloidal silica SiO₂ 1.93%±0.08% - sodium hydroxide NaOH 0.05% - lithium oxide Li₂O 0.22%±0.02% - sodium sulphite Na₂SO₃ -7H₂O 0.17%±0,01% - sodium thiosulphate Na₂S₂O₃ -5H₂O 0.42%±0,02% - Silver acetate 0.037%±0.003% - sodium sulfate 0.27%±0,002% - H₂O 95.84%). Using these compounds, either individually or in association with each other, photocatalytic filters 2 are obtained that have a high power of eliminating bacteria and viruses and/or a high power of eliminating NOXs. Brief description of the drawings

The invention will be better understood and carried out with reference to the annexed drawings, which illustrate several exemplary and non-limiting embodiments thereof, in which: Fig. 1 is a schematic side view of an embodiment of an apparatus for treating photocatalytic filters;

Fig. 2 is a front view of delivery means of the apparatus from Fig. 1;

Fig. 3 is a front view of heating means of the apparatus from Fig. 1;

Fig. 4 is a further front view of the delivery means of the apparatus from Fig. l which shows means for supplying a photocatalytic solution to the delivery means; Fig. 5 is a front view of a further version of the delivery means of the apparatus from Fig. 1;

Fig. 6 is a schematic view of another embodiment of an apparatus for treating photocatalytic filters;

Fig. 7 shows an image of a control plate in the absence of UVA radiation;

Fig . 8 shows an image of a control plate in the presence of UVA radiation;

Fig. 9 shows an image of a plate treated in accordance with the invention, in the presence of UVA radiation;

Fig. 10 shows the image of a plate treated in accordance with a different embodiment of the invention, in the presence of UVA radiation;

Fig. 11 shows the image of a plate treated in accordance with the invention, in the absence of UVA radiation;

Fig. 12 is an exploded view of an experimental filtering device according to the invention;

Fig. 13 shows a functional block diagram of the device from Fig . 12 ;

Fig. 14, 15 and 16 show the %removed pollutant vs t diagrams for the removal of nitrogen oxides using the photocatalytic filters according to the invention;

Fig. 17 shows the ln(NO_t/N0₀) vs t diagram for the removal of nitrogen oxides using the photocatalytic filters according to the invention.

As stated above, a particular object of the present invention is thus providing air filters that are capable of removing or substantially abating the bacterial load found in the treated air. These antibacterial features are given by silver or derivatives thereof and/or copper or a copper (II) salt being provided on the filters. The antibacterial activity is also performed in the absence of UV radiation or other light source. In order to estimate the antibacterial activity performed by the inventive filters, procedures have been developed which allow evaluating the growth of Escherichia CoIi in the presence/absence of light in thermostatic chambers, with temperature control in different ranges, optimum for growing specific strains. The experiments, both in the presence and in the absence of UVA radiation, have been carried out as follows:

- Under stirring conditions of the suspensions containing Escherichia CoIi and Titanium Dioxide- based products diluted at 10% and 20% in a nutrient medium;

Under stirring conditions of Escherichia CoIi suspensions in contact with the different products deposited on Petri dish bottoms;

- Under stirring conditions of Escherichia CoIi suspensions in contact with the different products deposited on Petri dish bottoms;

- Under conditions of total absence of light under conditions of stirring suspensions containing

Escherichia CoIi and using 10% and 20% diluted titanium dioxide in nutrient medium.

In this series of experiments, the capacity of different products to inhibit the growth of Escherichia CoIi has been investigated. The microorganisms have been seeded in 6-8 mL culture broth contained in a vial and placed at 37°C for 6-8 hours under stirring. At the end, the solution appeared visibly cloudy due to the presence of a great amount of bacteria. Then, a constant aliquot of bacteria has been seeded in the glass dishes. The bacteria have been seeded: in control dishes, containing only the culture medium; in dishes in which the titanium dioxide and silver- based product is provided.

The activity of the various products has been assessed by use in the liquid form and in the solid form. In the first case, the plates have been prepared by diluting various aliquots of the products to be analyzed in the nutrient medium, thereby various final concentrations have been obtained.

In the second case, amounts of 1 mL of the various products have been homogeneously distributed on the bottom of the Petri dishes and caused to dry at a temperature of 60⁰C. The culture media (8mL final volume) have been added to the plates containing the various titanium dioxide films.

After the plates have been seeded, they have been placed in a thermostatic chamber at 37°C for 14 hours and irradiated in the various stirring, or stationary, conditions with UVA light sources, filtered from the infrared component with water filters to avoid local over-heating.

The experiments in the dark have been carried out in a thermostatic chamber by holding the samples in the dark for 14 hours .

After 14 hours, constant aliquots have been taken from each plate, suitably diluted and then seeded in an agar medium, in order to calculate the number of alive bacteria therein. The seeded plates have been placed in a thermostatic chamber at 37°C for 24 hours. Thereafter, the colonies have been counted.

Results: 100% elimination of the bacteria, both in the presence of UVA radiation and in the absence of light sources.

The control plates developed in the absence of titanium dioxide containing colonies of Escherichia CoIi in agar are represented in Fig . 7 with bacterial growth in the absence of UVA and in Fig. 8 with bacterial growth in the presence of UVA.

In Fig. 9 there is illustrated the plate coated with suspended 10% diluted titanium dioxide after contact with Escherichia CoIi, and in Fig. 10 there is illustrated the plate coated with titanium dioxide that has been deposited as a film after contact with Escherichia CoIi. In Fig. 11, there is illustrated the plate coated with suspended 10% diluted titanium dioxide after contact with Escherichia CoIi provided by holding the plates in the dark under stationary conditions . Results: 100% elimination of bacterial culture both under UVA radiation conditions, and without irradiation in the dark.

In a different experimentation, the effect has been investigated of the inventive filters on the removal of bacterial loads and other microorganisms found in neighbouring environments. In these environments, also due to the use of conditioning and ventilation systems, mites, moulds (e.g. Aspergillus, Penicillium, Cladosporium) , dusts, as well as pathogenic germs such as Legionella pneumophila responsible for severe respiratory infections that can develop into often fatal pneumonia can be present . It has been seen that, for example, after the air-conditioning systems have been reactivated, which had been stopped for a certain period of time, the concentration of fungal spores in the outlet air can be as much as 78% higher than the inlet air.

The microbial contamination of the air enclosed in a building can be also supported by ubiquitous microorganisms, associated with droplets, or corpuscles. These are Gram-negative bacteria belonging to the Pseudomonas, Klebsiella kind or also Gram-positive germs such as Staphylococcus aureus, which are involved in pathologies of the respiratory system. As relates to the mycotic presence in the air, the risks related to the inhalation of fungal spores result to be often associated with allergic disorders (asthmatic symptoms, allergic alveolitis, rhinoconjunctivitis) , but they are capable of causing even aspecific inflammatory states, asthma and secondary pneumonia.

Throughout the testing, a filtering unit has been used, which consisted of a mechanical pre-filter and of a combination of a HEPA filter activated with a titanium dioxide and silver salt solution, according to the invention, capable of holding all the submicroscopic particles and an activated carbon filter for retaining unpleasant odours. The absorption capacity of the filtering unit was 5 mq, the suction rate was 395 mc/hr.

In order to ensure suitable air suction and release, the equipment has been placed at 10 cm minimum distance from any wall, and the upper part has been cleared of any obstruction.

The effectiveness assessment study has been carried out according to the following steps: a) quality/quantity evaluation of the aerodispersed microbial flora with specific research of the following parameters :

- total mesophilic load;

- Gram-negative germs; - Escherichia coli; - Pseudomonas spp . ;

- Staphylococcus spp.. b) quantity evaluation of microorganisms identifiable as microfungi ; c) quality evaluation of microorganisms belonging to the Legionella spp. species.

24 samplings of indoor air have been carried out from three types of neighbouring environments with different intended uses (administrative, sanitary) placed in a public hospital, and particularly:

- Office;

- DH oncology room;

- oto-rhino-laryngology clinic operating room. Each environment fell within the square meter area restrictions as indicated in the functional specifications of the equipment used (max 110 sqm) .

To the purpose of a more accurate microbial characterization, the study has been carried out, in each environment, according to the following sampling times:

- TO: beginning of the work activity (purification system off) ;

- Tl: 3 hours after the air purification system had been turned on; - T2 : 6 hours after the air purification system had been turned on;

- T3 : 9 hours after the air purification system had been turned on.

Sampling mode; The bioaerosol samplings have been carried out with the aid of an impaction air sampler > (Surface Air Sampler SUPER 100 - PBI International) mounting ⁿrodac contact" plates containing agarized culture media specific for each analytic determination included in the experimental protocol.

The equipment has been placed away from possible entry/exit ways, windows and any outlet of conditioned air provided in the rooms and placed at about 1.5 m from the ground. The sampled volume of air has been of 1000 L per each determined parameter. ANALYSIS METHODS

The analytic protocols that have been adopted for determining the above-mentioned microbial parameters are reported herein below. Total aerobic mesophilic load

Culture medium: Plate Count Agar Standard (CM463B - Oxoid) distributed in rodac contact plates (diameter: 6 cm) .

Incubation mode: 32⁰C for 24 hours. Colony counting: at the end of the incubation time, counting all the colonies grown on the agarized medium surface .

Expression of the results: the total number of aerobic mesophilic germs found in the volume of sampled air is expressed as CFU (Colony forming units) /me and calculated by applying the following formula: C = A x 1000/V

Where: C = number CFU/mc; A = number of colonies grown on the agar surface; V = volume of sucked air. Gram-negative germs

Culture medium: MacConkey agar n. 3 (CM 115B - Oxoid) distributed in rodac contact plates (diameter: 6 cm) .

Incubation mode: 32°C for 24-48 hours. Colony identification: first the morphological dye criteria (Gram stain) have been used, then in the presence of Gram-negative bacilli, the colonies have been isolated on nutritive agar to then identify the latter by means of Api 20E miniaturized system (Biomerieux) .

Expression of the results: the number of Gram- negative germs found in the volume of sampled air is expressed as CFU (Colony forming units) /me and calculated by applying the following formula: C = A x 1000/V Where: C = number CFU/me; A = number of colonies identified as Gram-negative germs; V = volume of sucked air.

Escherichia coli; Culture medium: MacConkey agar n. 3 (CM 115B - Oxoid) distributed in rodac contact plates (diameter: 6 cm) .

Incubation mode: 32⁰C for 18-24 hours.

Colony identification: all the colonies developed on the agarized surface in red-violed colour have been considered as possible Escherichia Coli . These colonies have been subjected to the indole test. The presence of colonies capable of degrading the tryptophan aminoacid with indole formation after 18-24 hours at an incubation temperature of 44⁰C confirms that they belong to the species in question.

Indole test : a vial containing 5 ml Trypton water (CMO87B - Oxoid) has been inoculated with the suspected colony and incubated at 44°C for 18-24 hours. At the end of the incubation time, 0,2 ml of Kovacs reagent has been added under stirring. The reagent has been left to react 10 minutes. The formation of a dark-red ring on the Trypton water surface is a positive indole test result . Expression of the results: the number of germs belonging to the species of Escherichia coli found in the volume of sampled air is expressed as CFU (Colony forming units) /me and calculated by applying the following formula: C = Ax 1000/V

Where: C = number CFU/mc; A = number of colonies belonging to the Escherichia coli species; V <= volume of sucked air.

Pseudomonas spp Culture medium: Pseudomonas Agar Base (CM 559B - Oxoid) added with CFC supplement (SRl03 - Oxoid) distributed in rodac contact plates (diameter: 6 cm) . Incubation mode: 32°C for 24-48 hours. Colony identification: all the colonies developed on the surface of the agarized medium have been considered as possible bacteria belonging to the Pseudomonas spp. species. The colonies showing a blue- green or brown pigmentation or a fluorescence could be considered as possible Pseudomonas aeruginosa. All the colonies have been isolated on nutritive agar, and then investigated for more accurate identification by means of Api 20NE miniaturized system (Biomerieux) .

Expression of the results: the number of germs belonging to the species of Pseudomonas spp. found in the volume of sampled air is expressed as CFU (Colony forming units) /me and calculated by applying the following formula: C = A x 1000/V

Where: C = number CFU/mc; A = number of germs belonging to the Pseudomonas spp. species; V = volume of sucked air.

Staphylococcus spp.

Culture medium: Baird-Parker Agar Base (CM 275B - Oxoid) added with Egg Yolk Tellurite Emulsion (SR054C - Oxoid) distributed in rodac contact plates (diameter: 6 cm) .

Incubation mode: 32⁰C for 24-48 hours.

Colony identification: all the colonies developed in black colour (reduction of tellurite to tellurium metal) on the surface of the agarized medium have been identified as possible bacteria belonging to the

Staphylococcus spp. species. Particularly, the black colonies with 1-3 mm diameter surrounded by a clear rim due to proteolytic activity could be considered as belonging to the Staphylococcus aureus species in all probability. In any case, all black colonies have been isolated on nutritive agar, and then investigated for more accurate identification by means of Api STAPH miniaturized system (Biomerieux) . Expression of the results: the number of germs belonging to the species of Staphylococcus spp. found in the volume of sampled air has been expressed as CFU (Colony forming units) /me and calculated by applying the following formula: C = Ax 1000/V

Where : C = number CFU/mc; A = number of germs belonging to the Staphylococcus spp. species; V = volume of sucked air.

Microfungi Culture medium: Sabouraud Dextrose Agar (CM 041B - Oxoid) distributed in rodac contact plates (diameter: 6 cm) .

Incubation mode: 22⁰C for 3-5 days.

Colony counting: all colonies have been counted, which can be identified as microfungi grown on the agarized medium surface.

Expression of the results: the number of colonies that could be identified as microfungi found in the volume of sampled air has been expressed as TFU (Thallus forming units) /me and calculated by applying the following formula:

C = A x 1000/V

Where: C = number TFU/mc; A = number of colonies identified as microfungi; V = volume of sucked air. Legionella spp. Culture medium: Legionella CYE Agar Base (CM 655B - Oxoid) added with LegionellaBCYE supplement (SRIlOA - Oxoid) distributed in rodac contact plates (diameter: 6 cm) . Incubation mode: 37°C in humid atmosphere enriched with 5% CO₂ for 7-10 days.

Colony identification: The colonies growing on BCYE

+ supplement could be considered as possible Legionella if they had the morphological characteristics thereof (white, shiny, circular colonies) , to be confirmed by means of biochemical and serological testing.

Expression of the results: qualitative assessment. The presence of even one individual colony belonging to the Legionella spp. species. It has been expressed as presence/me in the volume of sampled air.

RESULTS

The results of the experiments are shown in Table I.

From these data, a considerable abatement of the total microbial load can be observed, which is apparent after 9 hours operation of the air purifier.

The inventive filters result to be particularly effective against the aerodispersed microfungal load.

As regards the "total mesophilic load" (TML) , and "staphylococcus" , a similar trend is observed for the "DH oncology room" and "operating room" environments, with a gradual reduction in the bacterial concentration. The "office" environment exhibits a different reality, where the irregular movements of people has led to an 5 initial abatement of the values of 62.2% for TML and 90.5% for staphylococcus, but after 6 hours operation (these data are not shown in the table) it is as low as 48.9% and 41.6%, respectively, and then, after 9 hours, it increases to a total abatement value of 80% (TML) and 1085.7% (staphylococcus), respectively. Table I

Staphylococ 90.48 85.71 42.86 95.24 25.00 100

CUS

Pseudomonas 100 100 33 .34 100 .00 0 .0 100 spp.

Microfungi 52.27 95.45 67 .86 100 .00 0 .0 100

Legionella - - - - - spp.

In yet another experimentation, the power of removing Nitrogen oxide (Nox) from the air stream has been assessed.

5 The measurements of the initial nitrogen oxides, of the order of about 0.6 ppm, and at different radiation times have been carried out according to an analytic method based on the chemiluminescence using the following equipment: Nitrogen Oxides Analyzer, Model

108440, Monitor Labs. The device examined as shown in Fig. 12 for the components, and in the functional chart in Fig. 13, consists of two or more Honeycomb K filters, which allow an air stream V to pass therethrough with 3- 6 Pa pressure loss. Said filters K, previously coated

15 with titanium dioxide solution, are activated by a light source L, such as UVA PL-S 9W/10/2P lamp, with light spectrum ranging between 340nm and 420nm. A motor M sucks the air by forcing the latter to pass through said photocatalytic filters with 180 m³/h nominal flow discharge. The motor M has the function of recycling the air R within a reaction chamber B, which is indicated below as the Smog Chamber (Fig. 13 B) . Said device represented in Fig. 12 for the components and in Fig. 13 in the diagram, has support walls D for enclosing said device, and has been placed within the Smog Chamber B, and tested in UVA radiation conditions (lamp L) . The experimental apparatus in Fig. 13 consists of the following components and comprises an inlet E for supplying an air/NOx mixture to the apparatus, a blending chamber A having 25 L volume, a reaction chamber B (Smog Chamber) , consisting of a Lexan parallelepiped of 157 L volume in which the device indicated in Fig. 12 is provided, an analyzer C for measuring the concentration of the nitrogen oxides (NO and NO₂) in the mixture and a recirculation pump P. A main line 1 connects the blending chamber A to the reaction chamber B and the latter with the recirculation pump P. On the main line 1, upstream and downstream of the reaction chamber B, valves J are provided which allow drawing air from the main line 1 to be conveyed to the analyzer C through respective ducts 2 and 3, such as to be able to measure the concentration of nitrogen oxides both before and after the treatment of the air in the reaction chamber B. Finally, a further duct 4 connects the recirculation pump P to the blending chamber A. The main line 1, ducts 2 and 3 and further duct 4 are made of a material that does not alter the concentration of nitrogen oxides, particularly polytetrafluoroethylene. To measure the NOx abatement value, the concentration of nitrogen oxides is monitored in the NOx / air mixture as a function of time, under conditions of the mixture being recycled through the reaction chamber B containing the sample and with the device indicated in Fig. 12 being turned on. The measurement of the initial NOx concentration and the measurement of the NOx in different irradiation times have been carried out by following an analytic methodology based on chemiluminescence, as illustrated in the UNI 10878 standard. After air has been introduced in the inlet E, it reaches the blending chamber A and flows along the main line 1. An initial sampling of air through the duct 2 allows detecting an initial concentration of NOx, which results to be in the order of 0.6 parts per million (PPM). Then, the air flows again along the main line 1 and passes through the reaction chamber B at 5 ± 10% 1/min. flow rate. At preset time intervals, an air stream is taken from the duct 3 in Fig. 13. The filters K indicated in Fig. 12 are lightened with the UVA lamp (L) , the temperature is kept at about 27 ⁰C ± 2 ⁰C. The lightened surface of the examined sample is 225 cm² x 1 filter. The results of the photocatalytic action of the filters K in abating the nitrogen oxides are reported in Fig. 14, 15, and 16, which illustrate the removal of nitrogen oxides in the presence of light. The removal of the nitrogen oxides

(NOx) in the presence of light occurs in a very short time. Three tests on NO and three tests on NO₂ have been carried out to better understand the validity of the testing.

Results : The results under light conditions indicate an overall considerable efficacy of said apparatus (Fig. 12) in removing nitrogen oxides: 100% NO removed in the first 6 minutes 65% NO₂ removed in the first 15 minutes 87% NO₂ removed in the first 10 minutes It should be noted that, without being bound to any particular theory, one of the possible mechanisms of conversion of nitrogen oxide to nitrate ion, provides reacting the latter with the superoxide ion (O₂*^") produced from the oxygen reduction by electrons promoted to the conduction band of the titanium dioxide, according to the following reaction schemes: O₂ + e^{" 1}^ O₂*^" NO + O₂*^{" ■}* NO₃ ^"

In this hypothesis, the NO decay kinetics may have a pseudo-first order behaviour, according to which: In [NO] _t/ [NO] o = k t where [NO] _t represents the concentration of NO at time t, [NO]₀ is the initial concentration of the nitrogen oxide and k the pseudo-first order constant, incorporating the concentration of the superoxide ions (O₂*^") . This hypothesis seems to be consistent with the linearity that is generally observed when In [NO] _t/ [NO] _o is plotted as a function of time. The diagrams are reported in Fig. 17 with the pseudo-first order constants and the life times ( ) that are estimated from the converse of these constants, which represent the time required to decrease the NO concentration to 1/e (e = base of natural logarithms = 2.718) of its initial value .

By observing these times, it appears that, by suitably dimensioning the purification systems, the NO decontamination from ambient air may be carried out in times in the order of a few minutes, regardless of the value of the initial concentration of nitrogen oxide.

In addition to the objects achieved by the photocatalytic filters of the invention as outlined herein, it has been surprisingly found that said photocatalytic filters 2 are also provided with an unexpected antiviral activity.

If compared to the antibacterial activity discussed above, the mechanism in this case is more complicated because the viruses are obligate parasites, which are capable of growing and replicating only within cells . The viruses, in fact, do not possess enzymes capable of producing energy, they have no ribosomes for protein synthesis, and in addition they must use the cell's enzymes to perform vital processes .

It has been observed that the photocatalytic filters 2 according to the invention are capable of carrying out a very high antiviral activity also at very low concentrations. This antiviral activity, as well as the antibacterial one, is conferred to the inventive filters by the provision of silver or a derivative thereof and/or copper or a copper (II) salt and is also performed in the absence of a light source. To check this activity, variable amounts of viral suspension in a Dulbecco's modified medium (D-MEM) with 1% fetal bovine serum (FBS) have been prepared. Different viral concentrations have been used (viral titer) equal to IxIO⁶ and IxIO⁸ units capable of forming cytolysis plaques (Pfu, Plaque Forming Units) . Variable amounts of photocatalytic products (ATLS-OlG having the following composition: TiO₂ 1.49%, SiO₂ 0.91%, NaOH 0.05%, Li₂O 0.13%, Na₂SO₃.7H₂O 0.015%, Na₂S₂O₃.5H₂O 0.03%, CH₃CCOAg 0.005%, H₂O 97.37%) have been added to the various samples. The control was untreated viral solutions . After 5 hours incubation at room temperature, all samples have been diluted to known volumes to titrate the virus . The viral titer of the controls and samples treated with the photocatalytic product has been determined by the following procedure.

Determining a viral titer means calculating the number of infectious virions found in 1 mL solution. One of the method used consists in determining the number of cytolysis plaques produced by a sufficiently diluted viral suspension contacted with a cell monolayer. In this series of experiments, African monkey kidney (Vero) cells have been used. The cells grow at 37⁰C, in the presence of 5% CO₂ in D-MEM, added with 10% FBS, 1% L-glutamine and 1% penicillin- streptomycin. The titration has been carried out in 12- well plates. When the cultures were subconfluent, the viral stock has been diluted to known concentrations in a medium containing 2% FBS. For each dilution, 2 wells in the plate have been infected. After 2 hour- incubation at 37°C, the inoculum has been drawn and the infection has been stopped by adding medium containing, in addition to 1% FBS, 2% human γ-globulin, that have the function of preventing the formation of secondary plaques . The infected cultures have been incubated at 37°C for 2 days and controlled until the lysis plaques were visible. At this time, the cells have been fixed and colored in crystal violet. The plaques found in the wells have been counted at the optical microscope, and the viral titer expressed in Pfu/mL has been obtained by multiplying the number of plaques by the dilution factor.

Results

Different amounts of the ATLS-OlG product, corresponding to 5, 10, 15, 25 and 50 μl have been contacted with Vero cells suspended in 5 mL 10% FBS D-

MEM medium. The addition of this product has been carried out in various times: i) upon re-suspending the cells after trypsinization; ii) on the day after the re-suspension of the cells.

In both cases, the cytotoxic effects have been observed to increase as the added photocatalytic product increased. The presence of 10 μl product induces cytotoxicity that is exhibited by a suffering aspect of the cells, which is enhanced at 15 V and 25 V, where a considerable amount has been clearly observed of dead cells suspended in the medium. The 5 μl dose, on the other hand, has not produced appreciable cytotoxic effects: the cells have survived and have proved to grow almost normally, with a slight suffering, when compared with the control samples.

The virucidal activity of the photocatalytic product has been then measured in two different experiments.

In the first experiment, 1 μl ATLS-OlG has been contacted with HSV-I having IxIO⁶ Pfu viral titer. The incubation has been carried out in 1 ml 1% FBS D-MEM medium. After 5 hour incubation, the virus has been diluted to 1x10³ and IxIO² Pfu concentrations and infection of subconfluent cultures. The cells infected with the virus pre-treated with the photocatalytic product exhibited a lower number of lysis plaques as compared with the control at both virus dilutions (90% plaque inhibition with HSV-I IxIO³ Pfu and 100% plaque inhibition with HSV-I IxIO² Pfu) .

The titer of HSV-I virus has been then traced back both in the controls and treated cells, which was calculated based on what had been obtained with IxIO³ Pfu virus dilution, by multiplying the mean of the cytσlysis plaques both of controls and treated cells by the dilution factor (10³) . In the treated cells, there is more than one order of magnitude reduction in the viral titer as compared with the non-pretreated controls (1.5xlO⁵ Pfu in the controls vs 1.4X10⁴ in the treated cells) .

In the second experiment, the virus, having IxIO⁸ Pfu viral titer, has been incubated with different amounts of ATLS-OlG (1, 2.5 and 5 μL, respectively) . After 5 hour-incubation, the virus has been diluted at 1x10², 1x10³, 1x10⁴ and 1x10⁵ Pfu, and it has been titrated according to the above-described method. Increasing amounts of photocatalytic product have produced a progressive increase in the inhibition of the formation of cytolysis plaques, as shown in Table I.

Table I

As shown by the data reported in the table, the reduction of the HSV-I viral titer is particularly relevant in those samples that have been treated with 5 μL/mL photocatalytic product . In substance, the treatment with 5 μL ATLS-OlG produces an almost total mortality of the viral particles, by inactivating 47 million viruses out of 50 millions found in the control.

In conclusion, the photocatalytic product exhibits an antiviral activity also under extreme dilution conditions.

Accordingly, it should be understood that the photocatalytic filters 2 according to the invention are capable of carrying out a substantial antiviral activity on the air of the treated environment, where the viruses are normally found in amounts as much as 1000 times lower than those found in the experimental conditions as discussed above.

Accordingly, a particular object of the present invention is a method for eliminating or reducing the bacterial, microfungal or viral load in an environment, said method comprising the stage of causing the air from said environment to pass through photocatalytic filters comprising, on the surface of said filters, one or more surface layers of compounds having a photocatalytic activity comprising photocatalytic titanium dioxide, silver or a derivative thereof and/or copper or a copper (II) salt.

Preparation of the photocatalytic filters The titanium dioxide-based colloidal suspensions used are suitable to be distributed in the form of a film on the surfaces of said filters. The titanium- dioxide colloidal suspension described below is suitable to be distributed by means of spray techniques, or by means of techniques providing said filters to be immersed in a bath, the so-called dip-coating method. Said procedure can be also carried out without using any industrial method.

With reference to the Fig. 1 to 5, an embodiment is shown of an apparatus 1 for treating photocatalytic filters 2, which are fed on a conveyor belt 3 moved between a pair of moving rollers 4 that rotate in the direction of rotation indicated by the rotation arrow F2 in Fig. 1, which carries the photocatalytic filters 2, in the direction indicated by the arrow F, to the several regions of the apparatus 1 in which said photocatalytic filters 2 will be subjected to the action of the several treating means 5 being provided in the apparatus 1. The treating means 5 of the apparatus 1 comprise a plurality of delivery means 8 that are arranged to deliver a solution of photocatalytic material to said photocatalytic filters 2 and a plurality of heating means 9 that are positioned along the conveyor belt 3 in an alternating manner relative to the delivery means 8 and arranged to release a stream of heating fluid, preferably hot air, to heat the solution of photocatalytic material provided on said photocatalytic filters 2 and facilitate the evaporation of the same. The plurality of the delivery means 8 comprises, in the embodiment as shown in Fig. 1, first delivery means 10, second delivery means 11, third delivery means 12 and fourth delivery means 13, all of which having the same shape and of which different details are shown in Fig. 1 and 2 for clarity purposes, and isolated from the external environment from an insulation chamber 18 at the top of which there is provided a chimney 19 for controlled release of any vapour that may be generated while the solution is being delivered. The first delivery means 10, and similarly the second, third, and fourth delivery means 11, 12, 13 may comprise, as shown in Fig. 2 and 4, a plurality of delivery elements, 10', 10'' and, 12', 12'', respectively, which are arranged in the direction of the width L' ' of apparatus 1, i.e. in the crosswise direction relative to the feeding direction F, such as to ensure that all the surface of said photocatalytic filters 2 is suitably reached by the photocatalytic solution, and sufficiently covered by the latter in order to ensure the effectiveness thereof. Each of the delivery means 10, 11, 12, 13 of the plurality of delivery means 8 can further comprise, in the version in Fig. 5, which will be better detailed below, an individual delivery element 10' ' ' movable along the width L'', i.e. in the crosswise direction relative to the feeding direction F to deliver the photocatalytic solution on the whole surface of said photocatalytic filters 2. Each delivery element of the plurality of delivery means 8 is provided with a delivery nozzle 30 having a diameter D that can be adjusted according to the distance H of the nozzle 30 of said photocatalytic filters 2, the extension and composition characteristics of said photocatalytic filters 2, the diameter D being variable between about 0.2 and about 1.5 mm. At each of the delivery means 10, 11, 12, 13 of the plurality of delivery means 8, feeding means 20 for the photocatalytic solution are provided, which comprise reservoirs 20' in which the several components of the photocatalytic solution that must be sprayed on said photocatalytic filters 2 are built-up and are communicated with the delivery means 10, 11, 12, 13, by means of respective valves 21 that are shaped for suitably dosing the amount of each component of the photocatalytic solution to be supplied to each of the delivery means 10, 11, 12, 13, in order to obtain a solution of the composition at the desired concentrations. The delivery means 10, 11, 12, 13 are fixed to a bar 22 that can slide on a pair of support rods 23 fixed to a base portion 24 of apparatus 1 and that can be locked at a desired height along said rods 23 by means of locking elements 25, such as to change the delivery height H of the delivery means 10, 11, 12, 13 to adjust it according to the size and characteristics of the photocatalytic filters 2 to be treated. In addition, the position of the delivery elements 10', 10'' of each of the delivery means 10, 11, 12, 13 on the bar 22 can be set and suitably changed, in order to adjust the same according to the characteristics of said photocatalytic filters 2 to be treated, and particularly in order to ensure that the latter are homogeneously coated with the photocatalytic solution. At each of the delivery means 10, 11, 12, 13 control elements 26 are further provided to control the position of the delivery elements 10' , 10' , and the presence and characteristics of the jet delivered thereby. Particularly, the control elements 26 comprise optical sensors 27 being provided with first optical sensors 28, preferably placed on the bar 22 adjacent to each delivery element 10', 10' ', and arranged to detect the range of the jet of sterilizing solution being delivered by each delivery element 10', 10'', and then obtaining the extension of the surface of said photocatalytic filters 2 which is reached by the solution, and second optical sensors 29 being preferably placed on the rods 23, which are movable along the latter and arranged to check the actual delivery of the jet of photocatalytic solution by each of the delivery elements 10', 10''. The number of the optical sensors provided per each of the delivery means 10, 11, 12, 13, can be selected based on the characteristics and size of said photocatalytic filters and/or characteristics of the layer of photocatalytic material which one desires to provide, and/or based on the number of delivery elements 10', 10'', 12', 12'' that are actually provided. Any excess photocatalytic solution, which is delivered externally of the surface occupied by said photocatalytic filters 2 on the conveyor belt 3, and/or which drips from said photocatalytic filters 2, as shown in Fig. 1, is collected on a conveying surface 3' of the conveyor belt 3 and, as this is suitably drilled, is collected on a collection tank 31 provided below the conveyor belt 3. The collection tank 31 can be provided with a recycle system for the collected photocatalytic solution, which provides to draw the built-up solution 32 from the collection tank 31 and supply the same back to the delivery means 8 of the apparatus 1. The plurality of the heating means 9 comprise, in the embodiment shown in Fig. 1, first heating means 14, second heating means 15, third heating means 16, fourth heating means 17, that may have either the same or a different shape relative to each other; particularly, fan means such as shown in Fig. 1, or heat-exchanging means or heating ovens can be used as the heating means 9. The first heating means 14, and similarly the second, third, and fourth heating means 15, 16, 17 can comprise, as shown in Fig. 1, a plurality of heating elements 14' 14" and, 15', 15", 16', 16", and 17', 17", respectively, which are arranged in the direction of the width L" of the apparatus 1, i.e. in the crosswise direction relative to the feeding direction F and/or in the feeding direction F, such as to ensure that the whole surface of said photocatalytic filters 2 is suitably reached by the stream of heating fluid and that all the excess solution found on said photocatalytic filters 2 evaporates between two subsequent delivery steps. The heating means 14, 15, 16, 17 are connected to a further bar 35 that can slide on a further pair of support rods 36 fixed to the base portion 24 of the apparatus 1 and that can be locked at a desired height of said rods 36 by means of further locking elements 37, such as to change the height Hl of the heating means 14, 15, 16, 17 relative to the surface of said photocatalytic filters 2 to be treated, in order to adapt it to the size and characteristics of the photocatalytic filters 2 to be treated. The further bar 35 supporting the heating means 14, 15, 16, 17 can be fastened, by means of a bar 35', provided with locking elements 37' , to the supporting rods 23 of the delivery means 10, 11, 12, 13. At each one of the heating means 14, 15, 16, 17, there are provided further control elements 33 to control the position of the heating elements 14', 14" and 15', 15", 16', 16", and 17', 17' ' and the presence and range of the fluid stream delivered thereby, and thus the extension of the surface of said photocatalytic filters 2 that is effectively reached by said stream. Particularly, the further control elements 33 comprise further optical sensors 34, preferably positioned on the bar 35, which are adjacent to each heating element 14 ',14", 15', 15", 16', 16", and 17', 17" to detect the range of the heating fluid stream as well as further optical sensors, not shown, which are preferably placed on the rods 36 and movable along the latter and arranged to check the actual delivery of the heating fluid by each of the heating elements 14', 14", 15', 15'', 16', 16'', 17', 17" In addition, directing means for the stream can be provided at each of the heating means 14, 15, 16, 17 to guide and concentrate the heating fluid to the surface of said photocatalytic filters, in order to increase the effectiveness of the heating means 14, 15, 16, 17. The heating means 9 can further comprise, in a version not shown, an individual delivery element movable in the direction L' ' crosswise relative to the feeding direction F to deliver the photocatalytic solution on the whole surface of said photocatalytic filters 2. With reference to Fig. 5, an alternative embodiment is shown of the delivery means 10, 11, 12, 13, in which there is provided an individual delivery element 10" ' for each of the delivery means 10, 11, 12, 13, being provided with a body 38 that is slidingly fixed to the bar 22 from which an appendix 39 branches off, which is anchored to a further conveyor belt 40 that is movable between further moving rollers 40' and driven by an electric motor 41, in both ways of the direction indicated by the shifting arrow Fl. Position sensors 42 are further placed on the bar 22 and arranged to define the beginning/end of run of the delivery element 10'''; the position of the position sensors 42 and, thus, the position of beginning/end of run of the delivery element 10''', can be suitably selected and changed based on the size of the photocatalytic filters 2 to be treated. Also in this embodiment, the control elements 26 of the delivery element 10' ' Operation are provided, which comprise first optical sensors 28, which may be either incorporated or connected to the position sensors 42, connected to the bar 22 and arranged to establish the presence of the delivery jet, and second optical elements 29 which are fixed to the rods 23 and arranged to calculate the range of the delivery jet. Upon operation, said photocatalytic filters 2 are manually or mechanically rested on the conveyor belt 3; at the inlet of apparatus 1, said photocatalytic filters 2, which are made of plastic, ceramic, metallic material, during transportation, are rested on the feeding surface 3' of the conveyor belt 3 which faces the treating means 5. The conveyor belt 3 sequentially carries said photocatalytic filters 2 first to a first spraying region in which there are provided the first delivery means 10 that provide delivering the selected solution of photocatalytic material, subsequently to a first heating region in which the first heating means 14 provide to heat the solution being on the surface of said photocatalytic filters 2 to cause the evaporation of the excess solvent or water. This sequence of operations can be repeated for a desired number of times, depending on the size and characteristics of said photocatalytic filters 2. Thereafter, they are carried, again, by the conveyor belt 3, in a further heating region 45, in which further heating means 46, such as an oven 47, provide to further heat said photocatalytic filters that are already provided with the layer of photocatalytic material, in order to consolidate the structure thereof and enhance the adhesion of the photocatalytic material to the surface of said photocatalytic filters 2. In a version not shown, it may be provided applying on said photocatalytic filters 2 the photocatalytic layer and a further intermediate layer to be interposed between said photocatalytic filters 2 and the photocatalytic layer, having the function of protecting the material of said photocatalytic filters 2 from any chemical attack and promoting the adhesion of the layer of photocatalytic material to the latter. This intermediate layer being provided by spraying a primer on said photocatalytic filters, by means of suitable delivery means, such as a solution based on titanium dioxide in the form of Rutile, or silica, or colloidal silica, and drying this primer with relative heating means to facilitate the evaporation of the excess solvent . These operations are prior to the application of the layer of photocatalytic 5 solution, therefore the means arranged for applying the primer and drying the same are provided upstream of the delivery means 8 and heating means 9. With reference to Fig. 6, an alternative embodiment is shown of an apparatus 100 for the treatment of said photocatalytic

10 filters 2, in which similar parts of the apparatus in Fig. 1 are designated with the same numerals, and that differ from the version in Fig. 1 mainly because the layer of photocatalytic material is provided on said photocatalytic filters 2 by dipping the same in a tank

1550 containing a determined amount of photocatalytic material solution. The apparatus comprises a conveyor belt 3, which is moved between a plurality of moving rollers 4' that are arranged relative to each other such as to hold the conveyor belt 3 tensioned and to cause

20 said photocatalytic filters 2 move along a tortuous path through the treating means 5 provided in the apparatus 100. The moving rollers 4' are provided with cleaning means, such as comprising scrapers 61 being arranged to scrape an outer surface 63 of the moving rollers 4', in

25 order, to eliminate any particles, such as grit of ceramic or plastic material, which has detached from said photocatalytic filters, that may spoil the surface 63 of the moving rollers 4 and the conveyor belt and worsen the transportation of said photocatalytic filters 52. The ceramic material grit scraped by the scrapers 61 is collected in suitable containers 62 provided in the vicinity of the scrapers 61. The treating means comprise pre-heating means 48 that can be shaped like a preheating oven 49, such as shown in Fig. 6, or like heat- 0 exchangers, or like fans that pre-heat said photocatalytic filters 2 to prepare the latter to the application of the photocatalytic material solution in the tank 50 where said photocatalytic filters are dipped to receive the photocatalytic solution. The tank 50 is 5 filled with the solution of photocatalytic material to the level designated with Z and is supplied by means of suitable delivery valves 21 from the build-up tanks 20' for the components of this solution, said valves 21 being shaped such as to hold the level Z and the 0 concentration of the photocatalytic solution constant within the tank 50. At the tank 50, there is provided a dip roll 51 that is shaped such as to deflect the path of said photocatalytic filters 2 to dip them into the photocatalytic material solution. A perforated belt 57 5 is provided within the tank, which is driven by a respective electric drive motor 58, the perforated belt filtering the photocatalytic solution, and holds any material that detaches from said photocatalytic filters while they are dipped, and which falls to the bottom of the tank 50. The photocatalytic filter 2 dipped within the selected titanium dioxide solution, previously heated by the device 49, absorbs the required amounts of photocatalytic solution, in a time ranging from 2 seconds to 10 minutes, to be then carried by the perforated belt 57 in the direction indicated by the evacuation arrow F3 to the drying step 7, while the particles of material having a lower size than that of the holes of the perforated belt 57 will fall and be collected at the bottom of the tank 50. The tank 50 is further provided with a circulation system for the solution, comprising a pump 53 that draws the solution from the bottom of the tank 50 and the pump by admitting it in the vicinity of the free surface of the tank 50, and a first filtering system 55 positioned upstream of the suction section of the pump 53 and a second filtering system 56 positioned downstream of the delivery section of the pump 53, which are arranged to filter the solution and eliminate any foreign bodies, and the particles of ceramic or plastic or metallic material that have detached from said photocatalytic filters 2 when they were dipped in the tank 50. The tank 50 is further provided with an inspection door 54 for routine and/or extraordinary cleaning and maintenance operations on the tank 50. Subsequently, said photocatalytic filters 2, provided with the layer of photocatalytic solution, are carried to heating means 59 to cause the evaporation of the excess photocatalytic solution, and to further heating means 60 to complete said operation and increase the adhesion of the layer of photocatalytic material to said photocatalytic filters 2 and the cementing of this layer. As may be seen in this version, the application of the photocatalytic solution on said photocatalytic filters is carried out by means of immersion, in one individual operation. Also in this case, on said photocatalytic filters 2 a primer layer can be applied, in order to promote the adhesion of the layer of photocatalytic material to said photocatalytic filters and protect said photocatalytic filters from damage, these operations being provided upstream of those described above. It should be noted that in both versions of an apparatus for treating the photocatalytic filters 2, whenever the application of a primer layer is provided, the operation of heating the primer layer to evaporate the excess solvent therefrom can be the preheating operation of said photocatalytic filters 2 prior to the first application of the photocatalytic solution in Fig. 1, or the application of the photocatalytic solution by immersion, Fig. 6. The layer of photocatalytic material is provided with one or more titanium dioxide-based liquid solutions, which may contain the components described above, such as Ag and/or Cu or derivatives thereof (particularly, oxides or salts) .

Claims

1. Photocatalytic filters (2) comprising, on the surface of said filters (2) , one or more surface layers of compounds having photocatalytic activity comprising photocatalytic titanium dioxide.

2. The photocatalytic filters (2) according to claim 1, wherein said filters (2) are made of plastic, metallic, ceramic, polymer fiber, paper material, HEPA filters and ULPA filters. 3. The photocatalytic filters (2) according to claim 1 or 2, wherein said photocatalytic titanium dioxide is in the form of Anatase, Rutile or Brookite, either alone or mixed.

4. The photocatalytic filters (2) according to any claim 1 to 3, comprising, in said one or more surface layers, modified Anatase peroxide, peroxytitanic acid or mixtures thereof.

5. The photocatalytic filters (2) according to any claim 1 to 4, comprising, in said one or more surface layers, silver and/or a derivative thereof, and/or copper or a copper (II) derivative.

6. The photocatalytic filters (2) according to claim 5, wherein said silver and/or derivative thereof is silver acetate. 7. The photocatalytic filters (2) according to claim 5, wherein said copper and/or copper (II) derivative is CuO.

8. The photocatalytic filters (2) according to any claim 1 to 7, comprising in said one or more surface layers, one or more components selected between sodium hydroxide (NaOH) , lithium oxide (Li₂O) , heptahydrate sodium sulfite (Na₂S₂O₃ ^• 7H₂O) , pentahydrate sodium thiosulfate (Na₂SO₃-SH₂O) and/or silica (SiO₂).

9. The photocatalytic filters (2) according to any claim 1 to 8, which can be obtained by coating the filters with one or more photocatalytic layers from a composition of photocatalytic-active compounds, comprising amorphous or powdered titanium dioxide in colloidal solution that may contain silver and/or copper and/or derivatives thereof, preferably powdered, in microspheres, in laminar shape or from a solution in suitable solvents, either separately or aggregated to silica, colloidal silica or materials suitable for gripping. 10. The photocatalytic filters (2) according to claim 9, wherein said composition is an aqueous composition and comprises an aqueous colloidal solution, optionally in the amorphous state containing Anatase and/or modified peroxytitanic acid solution and/or Rutile and/or Brookite.

11. The photocatalytic filters (2) according to claim 9 or 10, wherein said composition has a titanium titer, provided in the form of 100% Anatase , or 70-90% Anatase or Anatase peroxide and the remainder being

5 Rutile or peroxytitanic acid or Brookite, ranging between 0.005 and 15% by weight.

12. The photocatalytic filters (2) according to any claim 9 to 11, wherein said composition comprises a derivative of Ag in a concentration ranging between

100.001 and 1.0% by weight, preferably said silver derivative being silver acetate in amounts ranging between 0.005 and 0.1% by weight.

13. The photocatalytic filters (2) according to any claim 9 to 12, wherein said composition comprises a

15 copper (II) derivative in a concentration ranging between 0.001 and 0.5% by weight, preferably between 0.005 and 0.1% by weight.

14. The photocatalytic filters (2) according to any claim 9 to 13, wherein said composition comprises a

20 surfactant in a concentration ranging between 0.001 and 5% by weight.

15. The photocatalytic filters (2) according to any claim 9 to 14, wherein said composition comprises SiO₂, preferably in the colloidal form, in a

25 concentration ranging between 0.001 and 10% by weight.

16. The photocatalytic filters (2) according to any claim 9 to 15, wherein said composition comprises sodium hydroxide in a concentration ranging between 0.001 and 1% by weight. 17. The photocatalytic filters (2) according to any claim 9 to 16, wherein said composition comprises Li₂O in a concentration ranging between 0.001 and 2.0% by weight .

18. The photocatalytic filters (2) according to any claim 9 to 17, wherein said composition comprises

Na₂SO₃.7H₂O in a concentration ranging between 0.001 and 2% by weight and/or Na₂S₂O₃.5H₂O in a concentration ranging between 0.001 and 2% by weight and/or sodium sulfate in a concentration ranging between 0.001 and 2% by weight .

19. A method for preparing the photocatalytic filters (2) according to any claim 1 to 18, wherein said filters (2) are coated with said one or more surface layers having photocatalytic activity comprising photocatalytic titanium dioxide using a composition of compounds having photocatalytic activity such as defined in any claim 9 to 18, by means of spraying techniques, or by means of techniques providing dipping said filters in a bath, the so-called dip-coating method. 20. The method according to claim 19, wherein a film of 0.02 μm to 3.0 μm of said compounds having photocatalytic activity is formed on said photocatalytic filters (2) .

21. The method according to claim 19 or 20, wherein said photocatalytic filters (2) are thermally treated, after they have been coated with said one or more surface layers of compounds having photocatalytic activity, at a temperature of about 80⁰C to about 1200⁰C. 22. The method according to any claim 19 to 21, wherein said composition comprises 0,85%w TiO2 having 6.0 to 7.0 pH and having mean particle size ranging between about 10 run + 30%.

23. The method according to any claim 19 to 21, wherein said composition comprises 0.85%w TiO2 having

7.0 to 8.5 pH and having an average particle size ranging between about 10 nm + 30%.

24. The method according to any claim 19 to 21, wherein said composition comprises titanium dioxide in a colloidal suspension consisting of 80% Anatase and 20% Rutile, in amounts of 3,0%w TiO2 having 5.0 to 7.0 pH and having mean particle size ranging between about 4 nm and about 30 nm.

25. The method according to any claim 19 to 21, wherein said composition comprises titanium dioxide in a colloidal suspension, which consists of Brookite and surfactant from about 0.001%w to about 5.0%w with silver acetate from about 0.009%w to about 1.0 %w, having 0.5%w TiO2 with 5.0 to 7.0 pH and having mean particle size 5 ranging between about 4 run to about 30 nm.

26. The method according to any claim 19 to 21, wherein said composition comprises titanium dioxide in the form of Anatase in colloidal suspension 1,49% by- weight, colloidal silica 0.91% by weight, sodium

10 hydroxide 0.05% by weight, lithium oxide 0.13% by weight, Na₂SO₃ • 7H₂O 0.015% by weight, Na₂S₂O₃-SH₂O 0.03% by weight, silver acetate 0.005% by weight, H₂O 97.37% by weight, said composition having 6.0 to 7.0 pH and mean particle size ranging between about 7 nm and about

15 15 nm.

27. The method according to any claim 19 to 26, wherein said composition contains distilled water.

28. The method according to any claim 19 to 27, wherein said titanium dioxide is obtained from TiCl₄.

20 29. A method for reducing or abating polluting substances, unpleasant odours, bacteria and/or viruses from air to be treated, which provides conveying a stream of said air to be treated through one or more photocatalytic filters (2) such as defined in any claim

25 1 to 18.

30. The method according to claim 29, wherein said polluting substances are nitrogen oxides .

31. The method according to claim 29 or 30 for avoiding the proliferation of moulds on said filters (2) .

32. The method according to claim 29, for eliminating or reducing the bacterial, microfungal or viral load in an environment, said method comprising the stage of causing the air from said environment to pass through photocatalytic filters comprising, on the surface of said filters, one or more surface layers of compounds having photocatalytic activity comprising photocatalytic titanium dioxide, silver or a derivative thereof and/or copper or a copper (II) salt. 33. The method according to any claim 29 to 32, which further provides irradiating said filters (2) with 280 to 450 nm UVA radiation.

34. The use of the photocatalytic filters (2) according to any claim 1 to 18, in ventilation, purification, conditioning systems, air treatment stations, outlets of exhaustion and/or intake and retake and/or inlet of air, delivery and/or exhaustion and/or inlet of air ducts, kitchen hoods, refrigerators, ventilation and/or conditioning systems in cars, motor vehicles, lorries, buses, trains, ships, airplanes, fume exhaustion and evacuation chimneys, household appliances such as vacuum cleaners, electric brooms, hair driers, computers, and/or other systems using an air stream for moving, conveying, heating, cooling, venting.