EP1848533A1

EP1848533A1 - Amorphous-state composite structures for photocatalysis

Info

Publication number: EP1848533A1
Application number: EP05825610A
Authority: EP
Inventors: Alexey A. Evstratov; Cristian V. Chis
Original assignee: Association pour la Recherche et le Developpement des Methodes et Processus Industriels
Current assignee: Association pour la Recherche et le Developpement des Methodes et Processus Industriels
Priority date: 2004-12-17
Filing date: 2005-12-16
Publication date: 2007-10-31
Also published as: BRPI0515791A; FR2879479A1; JP2008523979A; KR20070101276A; WO2006064168A1; US7820589B2; NO20073516L; US20080085230A1; CN101102846A; FR2879479B1; CA2591030A1

Abstract

The invention concerns photocatalysis. The invention concerns a composite system comprising a photocatalytic component (10) in amorphous state and an active support (12) designed to neutralize the free current carriers of a first type, positive electrons or holes, so as to protect current carriers of the second type against recombination.

Description

AMORPHOUS COMPOSITE STRUCTURES FOR PHOTOCATALYSIS

The present invention relates to a new type of photocatalyst - composite structures in amorphous state - whose operation is based on the phenomenon of forced separation of free charge carriers (electrons, holes) preventing their immediate recombination.

Existing principles and techniques

The photocatalytic effect is based on the phenomenon of the excitation of a semiconductor by light radiation (UV or Visible). The photon excitation leads to the creation of "electron - positive hole" pairs resulting from the passage of electrons from the valence band of the semiconductor to its conduction band. Thanks to the existence of forbidden zones acting as energetic barriers against the recombination of free charge carriers, the latter reach the surface of the solid body, attack the adsorption complexes and thus promote their transformation into final products.

Currently, only semiconductors (crystalline solids) in the form of micro- and nanoparticles are considered promising photocatalysts. Their crystallinities guarantee, on the one hand, an effective separation of charge carriers (e ^~ , h ⁺ ) and avoid their immediate recombination. On the other hand, the sizes of these crystalline particles are dimensioned, preferably in tens or hundreds of nanometers, in order to ensure for a large part of the free carriers accessibility to the contact surfaces. These dimensions are compatible with the distances traveled by charge carriers in a crystalline body during their average lifetimes, as mentioned in reference [1] of the bibliography. In the following, the figures in brackets correspond to bibliographic references at the end of this description.

Figure 1 shows 3 main types of active materials recognized to exhibit significant photocatalytic capabilities. These materials include photocatalytic components generally in the crystalline state.

The most widespread industrial photocatalyst is the product marketed by Degussa - Deutsche Gesellschaft, Germany (trade name: Degussa P25, crystalline titanium dioxide product containing ~ 80% of the anatase phase and ~ 20% of the rutile phase) [2].

Currently, crystalline nanoparticles of titanium dioxide are produced, in most cases, by techniques based on the application of plasma or Sol-gel method. Plasma techniques [cf. 3, for example] use titanium precursors, organic or inorganic, in the gaseous state which ionize at elevated temperatures. In the presence of oxygen, the Ti ⁴⁺ _gas ions transform into TiC> 2 titanium oxide agglomerated into nanoparticles. The Sol-gel method is based on the hydrolysis of metal alkoxide soils whose final products are metal oxides. The nanoparticles of TiC> 2 can be elaborated, respectively, by the hydrolysis of titanium alkoxides under the controlled conditions [4]. More sophisticated methods, such as Layer-by-Layer Self-Assembly (LBL-SA) [5] or Ultrasonic Spray Pyrolysis (USP) [6], are also applied on a laboratory scale for the production of nanoscale crystals. . The techniques described in [5,6] also make it possible to obtain crystalline particles optimized in size (10 -100 nm in diameter). These dimensions are considered the most appropriate for the photocatalytic application.

However, products from the [3-6] methods still represent "prefabricated" materials which then require solid attachment to support walls to be applied as photocatalytic unit elements. The only mechanism for attaching an existing crystalline particle ("prefabricated") to an external support is its physical adhesion. Physical adhesion, on the other hand, does not lead to the creation of composites with sufficient stabilities. Mechanically very fragile, these systems degrade quickly during use. In order to avoid these difficulties related to manipulations with prefabricated crystalline nanoparticles, it is reasonable to consider replacing them with composite products whose active phase can be chemically grafted in situ on a support. The current scientific literature presents a certain number of sophisticated and costly techniques for the elaboration of composite products with photocatalytic properties (examples: Arc Ion Plating (AIP) [7], Dip-coating [8], Photo-Inducted Sol-gel [ 9], Plasma Associated Metallo-Organic CVD [10,11], Sputtering [12,13], Photo-assisted pulsed laser deposition [14], etc.).

Currently, these methods do not exceed the laboratory scale. On the other hand, their applications make it possible to develop composite structures containing crystalline nanoparticles of TiC> 2 grafted onto different porous supports (SiCk, γ-Al ₂ C> ₃ , activated carbon, etc.). In general, these products exhibit a photocatalytic activity comparable to that of Degussa P25.

The techniques [7-12, 14] and other modern techniques are called for the elaboration of composite photocatalysts whose active phases are presented by crystalline nanostructures. In cases where the active components initially form as disordered structures, they undergo complementary treatments, such as irradiation or calcination, in order to be transformed into a crystalline state, as described in [11].

With the exception of a few rare references (eg [13, 15, 16]), non-crystalline materials are not considered photocatalytic products because of their disordered structures favoring immediate recombination of the charge carriers. Indeed, the absence in the disordered structures of internal energy barriers (forbidden zones) playing against the immediate recombination of the charge carriers is considered as a fatal obstacle preventing amorphous products from competing with the crystalline products. The invention

The invention relates to a composition and a principle of operation of a composite photocatalyst whose active phase consists of nano- and micrometric spherical aggregates of amorphous titanium dioxide, chemically bonded to the surface of a medium exhibiting strong acid or Lewis base properties and thus playing for the active phase the role of a source of an external electric field effecting the forced separation of the free charge carriers by the neutralization (trapping) charges of a first type (negative or positive) in favor of another.

More specifically, the invention results from the assumption that it is possible to operate the amorphous structures as heterogeneous photocatalysts by separating the charge carriers by an external force. The role of this External force can be played by the force of interaction between opposite electrical charges. For example, carriers of the first type, negative or positive, can be selectively neutralized in situ by a carrier exhibiting the particular electrical properties - acceptor properties or those of donor. In this favorable situation, carriers of the second type are protected against immediate recombination.

Thus, the invention relates to amorphous composite structures whose operation is based on the phenomenon of forced separation of free charge carriers (electrons, holes) preventing their immediate recombination.

Accepting supports whose Lewis acidities are important, such as silica, alumina, aluminum phosphate, or zirconium oxide alone or in combination, are used as electron traps, while metal supports exhibiting Strong Lewis base properties are used as hole traps.

Thus, the invention generally relates to a composite system comprising a photocatalytic component in an amorphous state and an active support intended to neutralize the positive charge carriers of a first type, electrons or "holes" positive, in order to protect the charge carriers of the second type against recombination. In one embodiment, the active support is an acceptor support with high Lewis acidity.

Alternatively, the active support is a donor support. According to one embodiment, the photocatalytic element (active component) consists of nano and disordered micro-particles (amorphous) of titanium dioxide chemically bonded to the support in order to ensure efficient transfer of carriers to neutralize towards the mass of the acceptor support or giver.

The invention thus relates, in one embodiment, to the use of titanium dioxide as an active component of photocatalytic systems. It substitutes the structures crystalline polymers currently used in practice, by composite products consisting of amorphous TiO2 nanoaggregates chemically fixed on the surfaces of solid supports having significant electron accepting or donating capacities (acceptor / donor supports).

The photocatalytic activity of amorphous TiO2 is due to the artificial separation of the charge carriers (e-, h +) in the external electric field provided by the acceptor / donor support. This forced separation preserves the charge carriers against immediate recombination and allows the carriers of a selected type to keep the states free during their movements to the active surfaces. The carriers of second type are neutralized in situ by the action of the support.

For the purposes of the invention, an example is described which concerns the preparation of composite products of the type "amorphous Nano-aggregates of TiC> ₂ - oxide support with pronounced acceptor capacities".

Amorphous oxide surfaces have several functional groups. Under ambient conditions and up to 250-300 ⁰ C they are enriched in Broensted active sites (acids and alkalis). This active population makes it possible to graft chemically on the oxide surfaces modifiers of different types.

The development of TiC> ₂ composite structures, crystalline and amorphous, on inorganic supports can be carried out by most of the methods mentioned above. From a technological point of view, these composites can be developed in particular by Sol-Gel, Sputtering, CVD Plasma Assistance, ML-ALE-CVD which stands for Molecular Layering or, in the alternative terminology, Atomic Layer Epitaxy [17, 18]. The latter, thanks to its relative simplicity, seems to be better adapted for the development of the proposed products, especially of the "nano-, amorphous microaggregates of TiO2 - Acceptor Support" type, both in laboratory conditions and in industrial conditions. According to the ML-ALE-CVD method, a solid support whose surface is previously functionalized in order to be enriched in Brôensted active sites, is treated in situ with a volatile inorganic precursor (for example, an oxy-halogenated or halogenated product). Me _L θMHal _N , Me _L Hal _N ) or organometallic (for example, an alkoxide - MeL-ORw), then hydrolysis, is transformed into composite material "nanoscale aggregates of oxide support" (reactions (1) and (2) , example with the halogen precursor):

Meiflalw + _x (H - 0) - Support → _w -χHal-Mei, -Oχ - Support + X H-HaI f (1)

_w -xHal-Me _L -0χ - Support + (NX) H ₂ 0 _goes scared → NX (H - 0) -Me _L -0 _x - Support + (NX) H-HaI f (2)

A series of composite products of the type "amorphous TiO ₂ - acceptor support" can be developed using the ML-ALE-CVD method with specific operating parameters. The protection of free charges against in situ recombination by their forced separation can also be carried out by the donor active supports, the role of which consists in enriching the photocatalytic aggregates with electrons. In this case, the high acid Lewis oxide supports (electron acceptors) can be replaced by porous supports containing aggregates of elemental metals dispersed on their surfaces. These donor supports provide complementary electrons to the photocatalytic components thus immobilizing the positive charges (electronic holes). The development of "amorphous nano-microaggregate TiO2-donor support" composite products can be carried out by one of the techniques designed for the creation of oxide deposits on metal surfaces, for example the Sol-Gel technique. FIG. 2 shows a system according to the invention which comprises an active component in the amorphous state, and a Lewis acid acceptor support 12 or a donor support. In the case of an acceptor support the electrons e ^" 14 go towards the support 12. In the case of a donor support the electrons of this support go (arrows in broken lines) to the holes h ⁺ 16 of the component 10.

Detailed example of achievement

The composite products according to the invention contain amorphous nanoscale aggregates of TiC> 2 grafted on silica (SiC> 2) and activated alumina (γ-Al ₂ C> ₃ ) supports, as well as on complex supports (SiO). ₂ * Fe ³⁺ , SiO ₂ * Cr ₂ O ₇ ^2- , SiO ₂ * CrO ₄ ^{2 "} , Y-Al ₂ O ₃ * Fe ³⁺ , γ-Al ₂ O ₃ * Cr ₂ O ₇ ^2" , γ -Al ₂ O ₃ * CrO ₄ ^{2 "} ) The additions of Fe ³⁺ or Cr ⁶⁺ in pure supports have been chosen to better demonstrate the mechanism of operation of the composites" nano-, TiO2 amorphous microaggregates - Support acceptor However, these additions are not essential for the improvement of the photocatalytic properties of the composite products according to the invention.The selected oxides - SiO ₂ , γ-Al ₂ O ₃ - as active supports are strong Lewis acids ( electron acceptors) They are able to immobilize the negative charges (electrons) [19, 20] by leaving "free" the positive charges (electronic holes) in the st surface structures excited by light radiation. Electronic holes are considered as very powerful oxidants favoring the effective degradation of pre-adsorbed products on the surface [21].

In order to test the photocatalytic activity of the prepared samples, two reactions of the total oxidation of volatile organic compounds were chosen: photocatalytic incineration of trichloroethane vapor (C ₂ H ₃ Cl ₃ ) and that of toluene vapor (C ₇ H _8):

C ₂ H ₃ Cl ₃ + 2O ₂ 2CO ₂ + 3HCl (3) C ₇ H ₈ + 90? 7CO ₂ + 4H ₂ O (4)

One of the products of the total oxidation of trichloroethane is hydrochloric acid, HCl (reaction (3)). Its high solubility in water (700 HCl volumes per 1 volume of water under standard conditions) makes it possible to monitor the photocatalytic performance of C ₂ H ₃ Cl ₂ trichloroethane by measuring the pH evolution in a downstream stirred vessel. of the test installation. The second technique used to monitor the photocatalytic performance of C ₂ H ₃ CIs and C ₇ H ₈ was the chromatrographic technique (Hewlett-Packard 5890 series II chromatograph with an HP 5972 detector (FID)).

Photocatalytic tests were performed using a laboratory installation. The operating parameters are shown in Table 1. All the composite samples tested contained on their surfaces between 6 and 7% by weight of TiO ₂ in the amorphous state (product No. 3-5 and 7-9 in Table 2 below). or crystalline product N ⁰ 2 in Table 2).

Table 1: Operating conditions

By comparing the photocatalytic samples on the pure supports of silicas and activated alumina, a significant activity for the former and a fairly low activity for the latter (Table 2, samples 3 and 7).

This difference in photocatalytic activity can be explained by features of the dynamic systems "TiO ₂ -SiO ₂ " and "TiO ₂ -γAl ₂ O ₃ ". In fact, the silica capacities as acceptor carriers far exceed that of aluminas, thanks to the presence on the silica surfaces of very powerful Lewis acid sites [19].

The activities of the Degussa P25 samples, both pure and on an acceptor support, remain superior to those of the composite "amorphous TiO2 - pure alumina" (samples 1, 2 and 7 in Table 2), whereas the "amorphous TiO2" composite pure silica "(sample 3) greatly exceeds Degussa P25 products.

Table 2. Photocatalytic activity of the products in the reaction of the total oxidation of trichloroethane C ₂ H ₃ Cl ₃

In an attempt to improve the photocatalytic performance of the composite products, a series of samples on oxide supports doped with electron traps (compounds based on transition metals) was developed. This approach was aimed at creating accepting media at high capacities. As doping compounds, the iron oxides (Fe ₂ θ ₃ ) whose active sites are presented by the Fe ²⁺ and Fe ³⁺ cations are used. Anionic complexes of chromium

(chromates and dichromates - CrC> ₄ ^{2 ~} , Cr ₂ O ₇ ^2- ) were also applied.

The development of the doped supports was carried out by impregnating the initial supports (SiO ₂ , γ-Al ₂ θ ₃ ) in metal salt solutions, followed by their conditioning and heat treatment (conditioning - 24 h, ambient temperature; - 8 h, temperature 110 ⁰ C, calcination - 4 h, temperature 550 ⁰ C).

The data presented in Table 2 demonstrate a significant improvement in the photocatalytic activity of samples [γAl ₂ O ₃ - Fe ³⁺ ] * TiO ₂ and [YAl ₂ O ₃ - Cr ⁶⁺ ] * TiO ₂ (samples 8 9) relative to the sample YAl ₂ O ₃ * TiO ₂ (sample 7). This phenomenon can be explained by the presence on the surfaces of the doped aluminas (γAl ₂ O ₃ * Me _x Oy) of the acceptor sites stronger than the initial sites (Al ³⁺ ) [20]. Compared to pure aluminas, these complex supports must therefore be considered as the most effective accepting agents for forced separation of electric charges.

On the contrary, the electron acceptability capacities for the [SiO ₂ - Fe ³⁺ ] and [SiO ₂ - Cr ⁶⁺ ] supports were assumed to be lower compared with those of pure silica: the photocatalytic activities of the samples 4 and 5 remain less important than the activity of Sample 3 (Table 2). This circumstance is probably due to an exceptional power of Si ⁴⁺ sites as Lewis acids [19]. It should be noted that the influences of the original supports (SiC> ₂ and γ-Al ₂ C> ₃ ) on the efficiency of the separation of charges decrease rapidly during their enrichment in doping compounds. For example, the samples 5 and 9 (Table 2) exhibit the same photocatalytic activities, although the sample 5 is prepared on an SiO ₂ support and the sample 9 on a support of γ-Al ₂ C> ₃ .

The best results are obtained using the pure silica acceptor support (sample 3 in Table 2). This fact demonstrates that it is not necessary to provide acceptor additions (electron traps) in the composite products of the type "nano-, amorphous microaggregates of TiO2 - acceptor support" whose supports consist of silicas. FIG. 3 represents the temporal evolution of the toluene concentration downstream of the photocatalytic unit. Curves 22-24 with unfilled triangles, squares and lozenges respectively correspond to curves of Degussa P25 without illumination, composite "Silice - TiO2" without illumination and composite "Alumina - TiO2" without illumination. While curves 25-27 with triangles, squares and filled diamonds correspond respectively to the curves of Degussa P25 with lighting, the composite "Silice - TiO2" with lighting and the composite "Alumina - TiO2" with lighting.

Table 3 below represents the photocatalytic activity of the products in the reaction of the total oxidation of toluene C ₇ H ₈ :

The behavior of the samples with respect to the photocatalytic treatment of the toluene vapor-laden air shown in Table 3 and Figure 3 can be discussed in terms of the adsorption capacity of the porous composites and in terms of electronic properties. active media.

The best photocatalytic capacities are always manifested by the "nano-, TiO2 amorphous silica-acceptor-based microaggregates" composites based on silica (sample 1 in table 3 and curve represented by solid squares in FIG. 3). On the contrary, the cardboard-based composite sample (N ⁰ 4 in Table 3) has no activity because its support does not have the electron accepting ability and therefore can not activate amorphous TiO2 aggregates located on its surface.

In the case of toluene C ₇ H ₈ whose adsorption properties on solid surfaces are much greater compared to those of trichloroethane C ₂ H ₃ Cl ₃ , the sample based on activated alumina having the specific surface area of the The range of 260-270 m ² / g has a higher photocatalytic activity than that of Degussa P25 which has a specific surface area of less than 50 m ² / g.

In the case of toluene and in the case of trichloroethane, the photocatalytic activities are therefore reversed (see Tables 2 and 3). This phenomenon can be explained by the fact that porous supports with high adsorption capacities, such as silicas and activated aluminas, can contribute to the photocatalytic performance of the pre-adsorbed products by transforming, with a high speed, their complexes. adsorption into final products. This assumption is verified by the comparative analyzes of the test results presented in the columns "Adsorption capacity without illumination" and "Photocatalytic activity" of Table 3, as well as by comparison of the curves of the curves obtained with and without illumination of the figure. 3. Moreover, FIG. 4 shows curves representing the crystallinity state of samples by the XRD (X-Ray Diffraction) technique. These curves were obtained during analyzes conducted by Mr. Pierre Gaudon of the Ecole des Mines d'Ales.

This figure 4 shows that the composite structures according to the invention are amorphous. Indeed, curves 30 and 31 of the products according to the invention based on alumina and silica have crystallinity status values much lower than those of Degussa P25 represented by 29.

FIG. 5 shows surface structure images of supports and composite products according to the invention. These images were obtained using a SEM (Microscope

Scanning Electronics) by Paul Jouffrey of the Ecole des Mines de Saint-Etienne.

More precisely, FIG. 5a shows a surface of a support 32 made of alumina. And Figure 5b shows 33-35 aggregates of TiO2 on support 32 alumina.

Moreover, FIG. 5c shows a surface of a support 36 made of silica. And Figure 5d shows aggregates 37-39 of TiO2 on the silica support 36.

These aggregates are spherical and have a mean diameter of between 500 and 2000 nm.

Advantages of new active products (photocatalytic activity, manufacturing process, application):

The photocatalytic activity of the amorphous "TiC> ₂ - Porous acceptor (donor) support" composites greatly exceeds that of Degussa P25 (commercial photocatalyst, see Table 2, samples 1 and 2). Compared with prefabricated crystalline structures, the "amorphous Nano-microaggregates of TiC> ₂ - porous support" composites are also technologically advantageous (ease of manufacture as ready-to-use active element and reliable fixation). on the surfaces of the supports). Their possible application can therefore be very favorable for the elaboration of photocatalytic elements (reactor sections, active panels, etc.) under industrial conditions. Note that amorphous photocatalytic composites "TiC> ₂ - donor support" can be difficult to achieve in the case where the supports exist in the form of machined parts (tubes, plates, panels, etc.). This disadvantage is caused by the non-porous nature of the metals. Variants and Extensions of the Invention

A search was carried out to show the sterilizing capabilities of the composite products according to the invention.

Figures 6 also shows an experimental device for testing sterilization capabilities. The genetically modified Escherichia coli bacterium (source - INRA, France) was chosen as the test bacterial species.

In a first step shown in FIG. 6a, samples of photocatalytic composites 43 and unmodified supports 44 are impregnated with a bacterial mist 45 for 3 minutes.

This fog 45 is obtained from dry air 47 and a bacterial solution 46 positioned at one end 48.1 of a tube 48. This dry air 47 blown at the end 48.1 passes through the solution 46 so as to form the fog bacterial 45. The fog 45 then flows in the tube 48 and impregnates the samples 43 and 44 which are at an end 48.2 of the tube 48 opposite to 48.1.

In a second step shown in FIG. 6b, a sample of photocatalytic composites 43.1 is exposed to UV-A irradiation (wavelength of 365 nm) under a UV lamp 49. And a sample 43.1 of composite according to the invention is exposed to sunlight.Also, an unmodified support 44.1 is exposed to sunlight. All these exhibitions last 20 minutes. In a third step represented in FIG. 6c, the samples 43.1, 43.2 and 44.1 or their surface were transferred into two Petri dishes 50 containing a nutritive gel 51. These boxes are kept in the dark for 20 hours at 35 ^° C. to promote the development of bacterial colonies. Part 52 of each box 50 has no sample and serves as a reference for the experiment.

Figure 7 shows the development of bacterial colonies in Petri dishes, after storage, for the various samples mentioned above. These tests were carried out in cooperation with Christine Blachère-Lopez, from the Ecole des Mines d'Alès.

In areas 4 and 12 containing only nutrient gel and serving as a reference area, no bacterial colony has developed.

In sectors 1 and 9 of the plates containing samples 44.1 of pure silica (unmodified support) exposed to sunlight, respectively 21 and 6 bacterial colonies referenced 53 developed in 20 hours of incubation. In sectors 3 and 11 containing samples

43.2 of composite according to the invention exposed to sunlight, only a colony of bacteria 53 has developed.

In sectors 2 and 10 containing the composite samples 43.1 according to the invention exposed to UV-A irradiation, no bacterial colony has developed.

In other words, 27 colonies (21 + 6) developed on the surfaces of the non-sterilizing samples 44.1 against a single one on the surfaces of samples 43.1 and 43.2 of the product according to the invention. These data show that the amorphous composite structures TiC> 2 according to the invention show a significant capacity for sterilization both under artificial irradiation (UV "black light", λ = 365 nm) that under sunlight.

These active products can therefore be designed for the photocatalytic abatement of volatile organic compounds of a very wide range, provided that their initial concentrations do not exceed certain limits (for example, for the gaseous phase - 3-r5 ppm, this case corresponds to the conditioning of gas in confined spaces). But these products can also be designed as active products for collective and individual protection against biological contamination.

Another field of application for amorphous composite photocatalysts according to the invention may be the treatment of liquid effluents. Preliminary research was conducted to demonstrate the application of the proposed products for the photocatalytic purification of water contaminated with organic compounds in solution.

Thus, FIG. 8 shows graphical representations of a photocatalytic degradation of acetone and ethanol in a liquid phase using active composites based on amorphous TiO 2 under sunlight.

A curve 55 with triangles represents the degradation yield of acetone, while a curve 56 with squares represents the degradation yield of ethanol.

To obtain these curves 55 and 56, two liquid samples of 25 mL by volume containing 25 mg / L of acetone and ethanol in water were brought into contact with two composite samples S-1T-070504 (sample N ⁰ 3 in Table 2) with masses of 1.1g. Two identical liquid samples were contacted with two samples of 1.1 g of pure silica. Four petri dishes were used as containers. The mixtures were exposed to sunlight under static conditions for 2 days.

The losses of acetone and ethanol during their photocatalytic degradation, taking into account the losses due to evaporation, were checked by the chromatographic method. The degradation yields of the organic products in solution were calculated as the differences between their concentrations remaining in the containers containing the pure silica (C _S i02) and their concentrations in the containers with the photocatalytic composites (C _P h _O to) _ι by compared to the values of

• CsiO2

The first samples were taken in a dark room, before direct exposure of the samples to the sun. Thus the points at 100hOO and HhOO of the first day of the test have a negligible yield.

Then, the containers covered by glass plates were taken out of the dark room on a sunny terrace. On the yield curves 55 and 56, two peaks 57 and 58 correspond to the maximum sunshine time (14h-16h). In two days of testing, the acetone and ethanol solutions in the containers containing the photocatalytic samples were completely degraded.

The variants and extensions of the invention can therefore be envisaged, at least in the field of water treatment, in particular for its purification and sterilization; as well as in the field of collective and individual protection against biological contamination with for example the realization of air conditioning devices in hospitals, the production of clothes and self-sterilizing tools ...

These photocatalytic materials according to the invention can be used on various supports (porous ceramic, glass, cardboard, textile, etc.). BIBLIOGRAPHY

[1] John Wiley & Sons, (1997), Heterogeneous Photocatalysis, Hardcover; [2] www.degussa.com;

[3] I. Nakamura, N. Negishi, S. Kutsuna, T. Ihara, S.

Sugihara, K. Takeuchi, (2000), Role of oxygen vacancy in the plasma-treated TiC ₂ photocatalyst with visible light activity for NO removal, Journal of Molecular Catalysis A: Chemical, 161, 205-212;

[4] Robert D., A. Piscopo, Heintz O., Weber JV, (1999), Photocatalytic detoxification with TiC ₂ supported on glass-fiber by using artificial and natural light, Catalysis Today, 54, 291-296; [5] Tae-Hyun Kim, Sohn BH, (2002), Photocatalytic Thin Films Containing TiC> ₂ Nanoparticles by the layer-by-layer self-assembly method, Applied Surface Science, 201, 109-114;

[6] V. Jokanovi, AM Spasi, D. Uskokovi, (2004), Designing of nanostructured hollow TiC> ₂ spheres obtained by ultrasonic spray pyrolysis, Journal of Colloid and Interface Science, 278, 342-352;

[7] T. Matsumea, T. Hanabusab, Y. Ikeuchi, (2002), The structure of TiN films deposited by arc plating, Vacuum, 66, 435-439; [8] Ying Ma, Jian-bin Qiu, Ya-year Cao, Zi-shen Guan,

Jian-nian Yao, (2001) Photocatalytic activity of TiC> ₂ fungi grown on different substrates, Chemosphere, 44, 1087-1092;

[9] N. Kaliwoh, J.-Y.Zhang, I.W. Boyd, (2002), Surfaces Coating technologies, 125, 424; [10] Lecheng L., Hiu Ping Chu, Xijun Hu, Yue Po-Lock,

(1999), Preparation of heterogeneous photocatalyst (TiC ₂ / Alumina) by metallo-organic chemical vapor deposition, Ind. Eng. Res., 38, 3381-3385; [11] M. Karches, M. Morstein, PR Von Rohr et al., (2002), Plasma-CVD Coated Glass Beds as Photocatalyst for Water Decontamination, Catalysis Today, 72, 267-279;

[12] M. D. Stamate, (2000), Dielectric properties of TiO2 thin films deposited by DC magnetron sputtering system, Thin Solid Films, 372, 246-249;

[13] E. Ogino, K. Mori, Y. Kijima et al., (2001), Multilayer Structure and Process for Producing the Same, EP-1068899; [14] J.Y. Zhang, I.W. Boyd, (2002), Structural and electrical properties of tantalum oxide films by photo-assisted pulsed laser deposition, Applied Surface Science, 80, 40-44;

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[17] AA Malygin, MO Bashkin, AB Emelyanov et al., (1993), 5 ^th European Congress on Surface Application and Interface Analysis (Catania - Sicily, Italy), 313;

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[19] H. Noller, JM Parera, (1981), Active sites in catalysis. An approach based on coordination chemistry, J. Res. Inst.Catal. Hokkaido Univ., 29, N ⁰ 2, 95-112;

[20] A. Evstratov, (2001), Economic Incineration of Volatile Organic Compounds (VOCs) Using Oxide Catalysts with Optimized Surface Properties, Recent Progress in Process Engineering, 15, 309-317; [21] K. Rajeshwar, (1996), Photochemical Strategies for Abating Environmental Pollution, Chemistry and Industry, 454-458;

Claims

15441 EN

21 CLAIMS

1 - Composite product comprising a photocatalytic component in an amorphous state fixed on a support, characterized in that this support is an active support intended to protect against rapid recombination of free charge carriers, electrons and positive holes, occurring in the photocatalytic component during from his bright excitement.

2 - Product according to claim 1, characterized in that the photocatalytic component is titanium dioxide.

3 - Product according to one of claims 1 to 2, characterized in that the photocatalytic component takes the form of nano- or microaggregates.

4 - Product according to claim 1, characterized in that the active support operates as a source of an external electric field for the forced separation of free charge carriers and the immobilization of a first type of carriers, electrons or positive holes, favoring each other.

5 - Product according to claim 1, characterized in that the active support operating by virtue of its own electronic capabilities consisting of donor or acceptor capabilities, with or without additions of complementary components, is substituted by its operation to the role of the prohibited area observable in crystalline photocatalytic structures.

6 - Product according to claim 1, characterized in that the active phase of the support comprises acceptor compounds with strong Lewis acidity, such as silica, activated alumina, aluminum phosphate, zirconium oxide , alone or in compositions.

7 - Product according to claim 1, characterized in that the active phase of the support consists of donor compounds, such as metals.

8 - Use of the product according to one of claims 1 to 5 for purification and conditioning contaminated gases or liquids and / or for the sterilization of such contaminated gases or liquids.