Substrate with photocatalytic coating

Description of the invention

The invention relates to a substrate having, on at least part of at least one of its surfaces, a coating having photocatalytic properties.

More specifically, its subject is coatings containing semiconductor substances based on metal oxides, especially titanium oxide, which, under the influence of radiation of appropriate wavelengths, initiate radical reactions causing the oxidation of organic substances.

Thus, the coatings impart new properties to the substrates they coat, especially anti-fouling, fungicidal and bactericidal properties, which may possibly be combined with hydrophilic, anti-cloudiness, optical properties etc.

A wide variety of substrates can be used, particularly those used in the automotive or construction field, such as glazed and curtain walls, cladding, roofing or floor coverings, such as tiles, slates, bars, roof tiles, and more generally any building material. These materials are selected from the group consisting of glass, metal, glass-ceramic, ceramics, cement, brick, wood, stone or recycled materials from natural materials, plastics or fibrous materials such as mineral wool, especially for filtration processes etc.

They can also be classified as transparent materials, used in particular for glazing, such as glass, or flexible or rigid plastic substrates, such as substrates made of polyester or an acrylate such as poly (methyl methacrylate) (PMMA). The substrates can also be classified in the category of non-porous or weakly porous materials (glass) or in the category of (relatively) porous materials such as tiles and ceramics.

Substrates can be distinguished as "made of a single substance, such as glass substrates, or substrates containing superimposed materials or layers thereof, such as screening walls made of coatings, such as a plaster screen.

International patent applications No. WO 97/10186 and WO 97/10185 disclose coatings containing TiO2 crystallized from anatase having photocatalytic properties, these coatings were obtained by thermal decomposition of the corresponding organometallic precursors and / or from "pre-crystallized TiO2 particles enclosed in a mineral or organic binder. .

International Patent Application No. WO 99/44954 discloses an improvement to these types of coatings involving the use of pre-crystallized TiO2 particles encapsulated in a binder that also contains partially crystallized TiO2: thus the binder contributes to the photocatalytic effect of the particles and an improvement in the coating performance in terms of photocatalytic properties is achieved. and durability.

European patents EP-1036826 and EP-1081108 disclose coatings using TiO2 particles in a binder containing zirconium oxide.

Thus, improved known photocatalytic coatings are used on the substrate according to the invention, particularly in terms of the level of photocatalytic parameters, the stability of these parameters over time and / or the mechanical / chemical stability.

The present invention relates to a substrate having, on at least part of at least one of its surfaces, a coating having photocatalytic properties, comprising photocatalytic titanium oxide, in particular crystallized in the form of anatase, in an essentially mineral binder, characterized in that the binder comprises at least one semiconductive oxide. metal selected from the group consisting of Sb2O3 and / or Sb2O5, F: ZrO2, F: Sb2O3, F: ZnO.

Preferably, the substrate comprises photocatalytic titanium oxide, at least a portion of which is incorporated into the coating in the form of pre-formed particles, especially of nanometric dimensions.

Preferably, the substrate comprises photocatalytic titanium oxide, at least a portion of which is formed during the formation of the coating, in particular by thermal decomposition of the precursors.

Preferably, the substrate comprises one or at least one of the semiconductor metal oxides in the binder having an electrical resistance lower than or equal to 10.⁸ ohm-cm.

Preferably, the substrate comprises one or at least one of the binder's semiconductor metal oxides which acts as a catalyst for the reduction of oxygen.

Preferably, the substrate comprises one or at least one of the semiconductor metal oxides of a binder that is doped, especially with a metal or a halogen atom.

Preferably, the substrate comprises one or at least one of the binder's semiconductor metal oxides:

Having the lowest energy level of its conductivity band that is less than or equal to the lowest energy level of the photocatalytic titanium oxide conductivity band;

is close to the most probable electron energy level of an oxygen atom in the redox pair O2 / H2O2 and / or O2 / H2O.

Preferably, the substrate comprises a binder also containing an electrical insulator compound, especially a silicon derivative such as silicon oxide, silicon oxynitride, silicon oxycarbide or silicon nitride.

Preferably, the substrate comprises semiconducting metal oxide or metal oxides in the binder in an amount of at least 25% by weight, more preferably at least 50% and up to 100% by weight.

Preferably, the substrate comprises photocatalytic titanium oxide in a weight ratio to the binder

RTiO2 / binder ranging from 10/90 to 60/40, especially from 10/90 to 50/50.

Preferably, the substrate comprises titanium oxide present in the coating in an amount of from 5 to 100 µg / cm²especially from 10 to 50 µg / cm².

Preferably, the substrate has a coating, the photocatalytic activity of which is at least 2 nm / h / µg / cm²) especially at least 5 or 10 or 20 nm / h / µg / cm²), relative to the total amount of titanium oxide in the coating.

Preferably, the substrate comprises at least one thin layer having an optical function, a thermal function, acting as a barrier to the migration of diffusible substances from the substrate, which is deposited between the substrate and the coating having photocatalytic properties.

Preferably, the substrate is an architectural material, especially glazed, roofing, cladding, material for a floor covering or soffit or a material installed in vehicles, especially glazed, for a car, train, plane or ship, or a material intended for home electrical appliances, especially for the walls of a stove. or glazed walls of a refrigerator / freezer.

Preferably, the substrate is based on a transparent material such as glass or polymer, or ceramic, or based on tile or brick, or based on wood, metal, cement, stone or plaster, or based on fibrous materials such as glass wool insulator or glass yarn reinforcement system.

The substrate according to the invention has at least in part at least one of its surfaces a photocatalytic coating containing photocatalytic titanium oxide (preferably exclusively or predominantly in the form of anatase), which is essentially a mineral binder containing at least one semiconductive metal oxide.

Preferably, a semiconductor oxide is selected which, when exposed to solar radiation, has substantially no photocatalytic activity (or in this case, whose photocatalytic activity is significantly lower than that of TiO2) and exhibits a significant electronic conductivity. Preferably, its resistivity is selected below or equal to 10⁸ ohm-cm, especially less than or equal to 10⁷ or 10⁶ ohm-cm. You can even choose a material with a much lower resistivity, e.g. below 10 ohm-cm. (When expanding, such resistivity may have the binder in its entirety if it contains several semiconductor oxides and possibly other non-conductive compounds).

In fact, as explained in detail below, in this case, semiconductor oxides having some level of electronic conductivity make it possible to obtain a photocatalytic TiO2-containing binder exhibiting enhanced photocatalysis efficiency compared to an electrically insulating binder, e.g., SiO2-based binder. Surprisingly, it has been found that the use of such a "conductive binder makes it possible to increase the photocatalytic properties of the coating as a whole, as well as to increase the durability of its parameters.

This is the difference from International Patent Application No. WO 99/44954. For the production of a coating with increased photocatalytic properties, a binder is used, which is partially crystallized and itself has photocatalytic properties. A significant enhancement of the photocatalytic activity of the lower activity crystallized TiO2 particles is also achieved from the binder. First of all, the electronic conductivity properties of the binder are used, which, moreover, can be completely amorphous, regardless of the photocatalytic activity as such.

It has surprisingly been found that there is a correlation or synergism between the photocatalytic substance and the substance with which it is closely related, namely a binder.

According to the invention, at least some (especially all or most) of the photocatalytic titanium oxide is incorporated into the coating in the form of pre-formed particles. Preferably,

Particles with nanometric dimensions are used. These particles are generally in the form of crystal grain agglomerates, agglomerates with an average size of 5 to 80 nm (e.g. 30 to 60 nm) and crystalline grains having an average size of between 5 and 20 nm (especially 5 to 10 nm). They are generally in the form of a liquid phase dispersion, particularly as a colloidal suspension in an aqueous medium or as a dispersion in one or more organic solvents. These average dimensions correspond to diameters assuming an approximation of their shapes to spheres (even if this is not a necessary condition, it is possible that the particles are lenticular or rod-shaped). As a first approximation, it can be assumed that the presence of the same agglomerates was found in the final coating showing only slight structural or dimensional modifications. In fact, it is observed that when the coating process involves heat treatment, it is generally accompanied by a significant increase in the crystal grain size, e.g. of the order of 1.5 to 2.5, as explained in detail in the above-mentioned International Patent Application No. WO 99/44954.

At least a portion of the photocatalytic titanium oxide is formed during the formation of the coating, particularly by thermal decomposition of the organometallic compound or metal halide type precursors or metal salts. As explained in the above-mentioned International Patent Application No. WO 97/10186, the sol-gel deposition techniques (detailed below) of the sol-gel type or ad hoc precursor pyrolysis allow the in situ formation of photocatalytic "TiO2 particles (either directly from heat deposition or by crystallization). by post-deposition heat treatment). In this case, there are also domains of crystalline TiO2 (in anatase form) distributed inside the binder which may resemble the previously formed particles described in the first embodiment, it is understood that there may also be amorphous TiO2 domains.

These two solutions are alternatives or can be combined.

To illustrate the effect of the "conductive binder (this term hereinafter refers to the presence of one or more semiconductor metal oxides in the binder), it is possible to increase its electronic conductivity by doping the binder's semiconductor oxide or oxides with a metal or halogen. This doping, especially with halogen, can be carried out using a deposition technique employing the thermal decomposition of halogenated precursors (which are also precursors of one of the coating oxides or which are a precursor whose sole purpose is to introduce a halogen atom), this technique mentioned above. In order to facilitate the introduction of halogen into the coating, especially starting from metal halide-type precursors, it is possible to heat treat the coating, during or after deposition, in an atmosphere containing a stoichiometric amount of oxygen.

In fact, the term "doping is to be interpreted broadly in the sense that the dopant is introduced into the coating without having to be localized in the binder or on one of the compounds contained in the binder.

The applicants have investigated the reason why with the same amount of photocatalytic TiO2 increased photocatalytic properties were obtained in the case of a conductive binder. Actually, under the influence of appropriate radiation, in the ultraviolet range, electron-hole pairs are formed in the particles of photocatalytic TiO2: holes initiate radical reactions that cause the oxidation of organic substances, electrons act by causing electrochemical reduction. The presence of the conductive binder allows two phenomena to take place:

> on the one hand, it is possible to obtain in photocatalytic TiO₂ photoelectrons that allow electrochemical reduction to take place, mainly oxygen reduction. There is therefore an interaction between the photocatalytic particles and the binder, the photocatalytic particles are the site of the photohole-induced oxidation reaction, while the binder is the site of the photoelectron-induced reduction reaction that is transferred to it. Thus, the redox cycle involving the phenomenon of photocatalysis is optimized, allowing the electrons to operate efficiently;

> on the other hand, such "electron removal is disadvantageous to the spontaneous recombination of the electron-hole pairs produced by the particles, which in this case again makes the particles more efficient."

Two situations may arise, but they are not limiting.

In the first situation, one or at least one of the semiconductor metal oxides of a binder has the lowest energy level of its conductivity band, which level is:

O - lower than or equal to the lowest energy level of the photocatalytic titanium oxide conductivity band;

PL 206 113 B1

Θ - close to the energy level of the electron (the most probable level) of oxygen, E⁰o x, in the redox pair O2 / H2O2 or O2 / H2O.

© - the relative position of the conductivity bands of the binder and the photocatalytic oxide is important: although it is necessary for the conductive adhesive to have a level of electronic conductivity sufficient to transfer the electrons to the surface of the adhesive, it is also necessary that the conductivity band of the adhesive be similar, preferably lower in energy terms, than the photocatalytic TiO2 band so that the electrons can move from one substance to another, © - due to the energy level of E.⁰ox redox par O₂/ H₂ABOUT₂ or o₂/ H₂If it is similar to the conductive band of the binder, two reactions are preferred - reduction (on the binder) and oxidation (on the TiO2) - and the electrons will be able to participate in the desired electrochemical reduction.

A number of oxides meet these two conditions, © and ®.

These are especially titanium oxide TiO2, tin oxide SnO2, antimony oxide (especially Sb2O3 and / or Sb2O5), zinc oxide ZnO, tungsten oxide WO3, cobalt oxide Co3O4, nickel NiO and mixed oxide of cobalt and nickel NiCo2O4. Each of these oxides may also be doped (such as Al: ZnO, Sb: SnO2, F: SnO2, F: ZrO2, F: Sb2O3, and F: ZnO). They can also be mixed oxides containing manganese (manganite family) and mixed oxides containing cobalt (cobaltine families).

It turns out that the Co, Ni or Mn containing oxides mentioned above have an additional advantage: they are compounds which catalyze the oxygen reduction reaction. The above-mentioned redox reaction is again favorable. There are published in the literature studies of the catalytic properties of Ni and Co mixed oxides, especially the publication "Surface properties of Ni and Co mixed oxides: a study by X ray, XPS, BET and PZC, by LA De Faria, JF Koenig, P. Chartier and S . Trasatti (Electrochemica Acta 44 (1998), 1481-1489). Sol-gel methods for obtaining Ni and / or Co oxides are described in the following publications: by F. Svegl et al. in Electrochemica Acta 45 (2000), 4359-4371 by G. Spinolo et al. in Journal of Electroanalytical Chemistry 423 (1997), 49-57, and by JG Kim et al. in Applied Surface Science 165 (2000), 70-84.

Thus, a preferred method is to ensure that "the conductive binder is not only electronically conductive, but is also a catalyst for oxygen reduction (at least due to one of the semiconductor oxides it contains, if several of them).

A preferred one or at least one of the semiconductor metal oxides of the binder has:

O - the lowest energy level of the conduction band, which is higher than the level of photocatalytic titanium oxide;

© - electronic states in band gaps, especially those related to structural defects and / or additional bonds. These are in particular Al2O3 alumina and ZrO2 zirconium oxide (these oxides can optionally be doped). Despite the unfavorable position of their conduction bands, this type of oxide has been found to be advantageous in that it has intermediate energy states within their band gaps, which allows them to receive electrons (and approximate E levels).⁰ox O2 / H2O2 or O2 / H2O pairs).

The binder may further include at least one electrical insulator compound, particularly a silicon derivative such as silicon oxide, silicon oxynitride, silicon oxynitride or silicon nitride.

The term "insulator" refers to substances which in particular have a resistivity above 10¹⁰ ohmtm, especially above 10¹² ohm ^ cm.

The great advantage is that the amount of photocatalytic TiO2 in the coating can be varied over a very wide range: even a relatively low content makes it possible to obtain satisfactory photocatalytic properties in any case, thanks to the conductive binder. Particularly in an embodiment where preformed photocatalytic TiO2 particles are used, this can be a great advantage as the high proportion of preformed particles in the coating generally reduces its durability and / or its adhesion to the substrate on which it is deposited. the shell. Thus, a better performance / durability compromise is achieved.

Thus, the weight ratio RTiO2 / photocatalytic titanium oxide binder to the binder can be selected in the range between 10/90 and 60/40, especially 10/90 and 50/50 or 20/80 and 40/60.

With regard to the binder formulation, the binder preferably has a semiconductive metal oxide (s) content of at least 25 wt%, particularly at least 50 and up to 100 wt%. As mentioned above, it may be advantageous to add a non-conductive substance such as SiO2, especially in terms of optical performance: thus the presence of SiO2 may reduce

To sew the overall refractive index of the coating, thereby making it possible, if necessary, to reduce light reflection.

Preferably, the amount of titanium oxide present in the coating is from 5 to 100 µg / cm², especially from 10 to 50 or from 15 to 35 µg / cm². In this case, all the titanium oxide includes both photocatalytic crystallized TiO2 and photocatalytic amorphous TiO2, if this form is present in the binder.

Preferred embodiments of the invention employ coatings in which the binder consists of zirconium oxide or titanium oxide, optionally combined with silicon oxide.

Preferred coatings show, in particular, the photocatalytic activity of the coating, based on the total amount of titanium oxide, of at least 2 nm / h / ^ g / cm.²), especially at least 5, 10 or 20 nm / h / µg / cm²). The fact that this activity is related to the total amount of TiO₂ results from a better estimate of the effect of the binder on its parameters as shown in the examples below.

Preferred coatings, especially when coating glass or transparent substrates to obtain glazing, have interference thicknesses (at least 1 nm, generally from 10 to 300 nm).

In one embodiment of the invention, the coatings are bonded to at least one other layer with interference thicknesses. It can be a layer with thermal properties (low emissivity), having optical properties (to reduce the level of light reflection or to modify the color by an interference effect) or acting as a barrier to the migration of particles diffusing from the substrate: the layer is thus introduced between the substrate and the coating. This is especially useful when the substrate is made of glass to prevent diffusion of alkali metals. The lower barrier layer can be constructed of a silicon derivative such as silicon oxide, silicon oxycarbide, silicon oxynitride or silicon nitride, or based on an optionally doped metal oxide (F: SnO2, Sb: SiO2 etc.). Thus, the coating may be the top layer of e.g. a low emissivity heat reflecting multi-layer system.

The uses for the coated substrates of the invention are mentioned above. It can be virtually any architectural material, especially glazed, roofing or cladding material, floor covering or soffit material. They can also be materials used in vehicles (cars, trains, airplanes, ships), especially glazed, or materials intended for home electrical appliances (stove walls, glazed refrigerator / freezer walls, etc.).

The substrates that can be used are therefore very diverse: transparent materials such as glass or polymer, ceramics, glass-ceramics, wood, metallized cement, stone, external plasters, materials obtained from recycled natural materials, etc.

It is also possible to deposit coatings on mineral wool type fibrous materials for thermal and / or acoustic insulation or any other reinforcing yarn, e.g. for use in the field of filtration.

Since the coatings used on the substrates according to the invention are also hydrophilic, it is also possible to use, depending on the application, their anti-fouling and / or bactericidal / fungicidal and / or anti-haze properties as required.

It is possible to use a technique involving the thermal decomposition of at least one organometallic precursor or metal halide or metal salt precursor to prepare the coated substrates described above. After the actual deposition phase, a post-deposition heat treatment may or may not be carried out, for example from 30 minutes to several hours at 350-550 ° C (sol-gel cold deposition or pyrolysis type hot deposition).

In another embodiment, it is possible to use a vacuum deposition technique, especially sputtering, preferably magnetic field assisted sputtering. This can be reactive sputtering (using a specially prepared metal / metals or alloys, deposition in the presence of at least oxidizing substances) or non-reactive sputtering (using a target ceramic with the appropriate composition).

The invention is described in more detail below by way of non-limiting examples and drawings:

- In Figs. 1 to 3: details of the likely mechanisms are shown, including the conductive binder at the photocatalytic activity level of the coating;

- In Fig. 4: a graph is provided which shows the photocatalytic activity of the coatings.

Fig. 1 illustrates the first embodiment described above, namely the case where the conductive binder comprises a semiconductor oxide whose lowest conductivity band level is below the photocatalytic TiO2 value. The x-axis represents the increasing energy level of the electron (in eV), the continuous line C1 corresponds to the lowest level of the photocatalytic conductivity band TiO2, and the dotted line C2 corresponds to the value e.g. SnO2, Sb2O3 or ZnO (binder), while the C3 line corresponds to the lowest energy level of the valence band

Of photocatalytic TiO2. The x-axis is the boundary between the shell thickness (left) and its outer surface (right). The horizontal C4 line represents the Fermi level.

Electrons, marked symbolically e^-, they will therefore, thanks to photo-excitation, move from the TiO2 conductivity band to, for example, the one with the lower SnO2 energy. In addition, the electrons tend to reach the surface of the shell.

Fig. 3 shows, along the ordinate, the energy (in eV, at pH = 7) of the lower conductivity band of the various oxides and oxygen levels E⁰ox in O2 / H2O2 and O2 / H2O pairs (E⁰x denotes the most probable level, in the center of the Gaussian distribution, having a width close to 0.8 eV). It can be concluded that, for example, SnO2, which is between the two levels of O2 / H2O2 and / or O2 / H2O pairs, is in a position suitable for electrochemical reduction of oxygen to H2O2 or H2O using electrons that have been released from photocatalytic particles. TiO2, Sb2O3, ZnO and NiO oxides are also suitable; WO3 and Co3O4 are slightly below, but still may be suitable as they differ by less than 0.5 eV, particularly less than 0.4 eV, from the redox potentials of the O2 / H2O vapor, and Co3O4 is a known oxide that catalyzes the reduction of oxygen.

Another solution is illustrated in Fig. 2: in this case, in the same convention as in Fig. 1, the conductivity bands of the conductive binder, e.g. made of ZrO2 or Al2O3, are above the photocatalytic level of TiO2. Their positions in Fig. 3 appear theoretically unfavorable. In fact, these two oxides also allow the formation of electrons from the photocatalytic substance, since they have intermediate energy states in the gaps in their bands (shown symbolically in Fig. 2 through the hatched area along the x axis).

Examples 1 to 5

These five examples relate to a 3 mm clear silica-soda-lime glass substrate coated with a first SiOC coating deposited in a known manner by CVD (chemical vapor deposition) followed by a photocatalytic coating consisting of a SiO2 + TiO2 mixed binder containing preformed TiO2 particles.

The deposition was carried out by the sol-gel method, by the dip-coating method as described in the aforementioned International Patent Application No. WO 99/44954, using a solution O containing binder precursors and also using:

as a solvent: ethanol and ethylene glycol in mass proportions 75/25 as a stabilizer: acetyl acetonate as a TiO precursor₂: Titanium tetrabutoxide (TBT) as SiO precursor₂: tetraethyl orthosilicate (TEOS) and the following dispersion ©:

liquid phase, ethylene glycol, containing crystallized photocatalytic particles, with the following properties:

> specific outer surface of particles:

> particle size:

> crystal grain size of which they are made of> 350 m²/ g = 40 nm particles:

> crystalline phase:

nm over 80% anatase

Then, the solution O and the dispersion © were combined in ad hoc concentrations / proportions so as to obtain a coating with the desired contents of TiO2 and SiO2 and nanoparticles in the binder.

The photocatalytic activity of the coating was measured using palmitic acid as follows: a palmitic acid layer was deposited by spraying a solution in chloroform onto the test sheet. The deposited amount was then determined by weight. The sheets were then exposed to UV radiation (approximately 30 W / m²) and haze caused by the presence of palmitic acid was measured over time. This value was used to determine the rate of palmitic acid decay, expressed in nm / h. This rate can also be related to the total amount of TiO2 (in µg / cm²) present on the tested glazed material (representative of the thickness of the layer), and therefore expressed in (nm / h) / ^ g / cm²).

All the coatings of the five examples contained 50% by weight of the preformed TiO2 nanoparticles and 50% by weight of the binder between SiO2 and TiO2. The coatings were annealed after deposition at a temperature of about 500 ° C.

In Table 1 below, the following data is given for each of the examples (In Example 1, the binder contained 100% SiO2 and was therefore a comparative example):

TiO content₂ versus SiO₂ in the binder, in mole%: "% TiO₂ in a binder;

> the level of photocatalytic activity of the coatings "PA, according to the described plus test, expressed in nm / h / ^ g / cm²), in relation to the total amount of TiO₂ in the shell.

Table 1

<td>Example</td><td>% TiO₂ in a binder</td><td>PA</td>

<td>1 (comparative)</td><td>0 (100% SiO₂)</td><td> 1,1</td>

<td> 2</td><td> 14</td><td> 1,5</td>

<td> 3</td><td> 25</td><td> 2,2</td>

<td> 4</td><td> 50</td><td> 6,8</td>

<td> 5</td><td> 75</td><td> 7,8</td>

Example 6

This example relates to coatings deposited on the same substrate by a technique called "dip coating," containing 50% by weight of preformed TiO2 nanoparticles (those used in the previous examples) and 50% of a 100% zirconium oxide binder.

The method was as follows: zirconium isopropoxide was added to isopropanol. Thereto was added acetylacetone and the solution was diluted with ethanol. This solution was then mixed with a dispersion of nanoparticles in a colloidal suspension in water acidified with nitric acid. After deposition, the coating was annealed at a temperature of about 500 ° C and the photocatalytic activity PA of the coating thus obtained was, determined by the method according to the previous examples, 2.5 nm / h / µg / cm.²).

Examples 7 and 8

These examples are for coatings containing (by weight) only 10% of preformed nanoparticles.

Example 7 is a comparative example, the binder contained 100% SiO2, the deposition was done by dip coating.

Example 8 is the use of an antimony doped 100% SnO2 binder.

In the case of Example 7, a colloidal suspension of TiO2 nanoparticles according to Example 6 and a TEOS-based solution were used.

In the case of example 8, the method of operation was as follows: tin chloride (SnCl2) was dissolved in dimethylformamide. Then, the antimony chloride was dissolved in dimethylformamide and the latter solution was added to the former. Subsequently, the colloidal suspension of TiO2 nanoparticles was added as before and its concentration was adjusted. The coating was deposited by dip coating. Then it was annealed at a temperature of about 500 ° C.

In the case of example 7, the measured photocatalytic activity of PA was

0.1 nm / h / µg / cm²).

In the case of example 8, the measured PA photocatalytic activity was nm / h / µg / cm²).

From these series according to Examples 1 to 8, it can be seen that with the same amount of TiO2, the binder has a direct effect on the photocatalytic activity of the coating, while itself is not (or is slightly) photocatalytic.

This is particularly striking in the case of Example 8, in which the binder contains very few photocatalytic TiO2 nanoparticles.

Thus, the importance of the properties of the semiconductor and electronic binder conductivity was proved.

As a reminder, the following are the electrical resistances of conductive oxides that can be used, compared to the values ​​for glass and SiO2:

<td>Al: ZnO</td><td>₁₀^-3</td>

<td>Sat: SnO2</td><td>₁₀^-2</td>

<td>SnO2</td><td> 5</td>

<td>ZrO2</td><td>₁₀⁷</td>

<td>TiO2</td><td>₁₀⁵</td>

<td>Glass</td><td>₁₀¹²</td>

<td>SiO₂</td><td>₁₀¹⁷</td>

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Then, three runs of Examples A, B, C were made using TiO2 + SiO2 mixed binder and TiO2 nanoparticles in a manner similar to the series of Examples 1 to 5 (same deposition method, same precursors).

Table 2 below lists, for each example in each run (percentages are by weight):

&gt;% TiO nanoparticles₂ &gt;% TiO₂ in the binder&gt;% SiO₂ in a binder

The value of the photocatalytic activity of the coating in total PA ', expressed in nm / h, the value of the photocatalytic activity of the coating in relation to the total amount of TiO₂ in the coating, PA, is expressed in nm / h / (Lig / cm'j, and the amount of Q TiO₂ (contained in nanoparticles and binder) in the coating is expressed in gg / cm².

Table 2

<td>% TiO2 nanoparticles</td><td>% TiO2 in the binder</td><td>% SiO2 in the binder</td><td>PA 'nm-h^-1</td><td>Q = amount of TiO2 (nanoparticles + binder) / mg-cm²</td><td>PA nm-h^-1-mg^-1-cm²</td>

<td></td><td></td><td></td><td></td><td></td><td></td>

<td>A series</td><td></td><td></td><td></td><td></td><td></td>

<td> 0</td><td> 100</td><td> 0</td><td> 18</td><td> 22,3</td><td> 0,81</td>

<td> 20</td><td> 100</td><td> 0</td><td> 128</td><td> 23,7</td><td> 5,40</td>

<td> 35</td><td> 100</td><td> 0</td><td> 159</td><td> 22,9</td><td> 6,94</td>

<td> 50</td><td> 100</td><td> 0</td><td> 231</td><td> 24,8</td><td> 9,30</td>

<td> 65</td><td> 100</td><td> 0</td><td> 210</td><td> 24,1</td><td> 8,71</td>

<td> 80</td><td> 100</td><td> 0</td><td> 167</td><td> 18,5</td><td> 9,03</td>

<td> 100</td><td> 100</td><td> 0</td><td> 222</td><td> 22,7</td><td> 9,78</td>

<td></td><td></td><td></td><td></td><td></td><td></td>

<td>Series B</td><td></td><td></td><td></td><td></td><td></td>

<td> 0</td><td> 14</td><td> 86</td><td> 0</td><td> 1</td><td> 0</td>

<td> 10</td><td> 14</td><td> 86</td><td> 0</td><td> 8,3</td><td> 0</td>

<td> 25</td><td> 14</td><td> 86</td><td> 0</td><td> 17,6</td><td> 0</td>

<td> 50</td><td> 14</td><td> 86</td><td> 58</td><td> 32,7</td><td> 1,77</td>

<td> 75</td><td> 14</td><td> 86</td><td> 233</td><td> 42,1</td><td> 5,53</td>

<td> 90</td><td> 14</td><td> 86</td><td> 535</td><td> 49,7</td><td> 10,77</td>

<td></td><td></td><td></td><td></td><td></td><td></td>

<td>C series</td><td></td><td></td><td></td><td></td><td></td>

<td> 50</td><td> 14</td><td> 86</td><td> 15</td><td> 9,7</td><td> 1,55</td>

<td> 50</td><td> 25</td><td> 75</td><td> 25</td><td> 11,3</td><td> 2,21</td>

<td> 50</td><td> 50</td><td> 50</td><td> 88</td><td> 12,9</td><td> 6,82</td>

<td> 50</td><td> 75</td><td> 25</td><td> 137</td><td> 17,5</td><td> 7,83</td>

Fig. 4 shows the photocatalytic activity of these coatings in the form of a graph: the x-axis is the weight percentage of nanoparticles in the coating and the y-axis is the PA value: it is clearly seen that the more TiO2 is present in the binder, the greater the photocatalytic activity (series C ). The comparison of the B series with the C series clearly shows that the amount of electronically conductive substance in the binder has a significant impact on the level of photocatalytic activity of the coating, as does the amount of TiO2 nanoparticles.

Examples according to the D series

A final series of examples is where the photocatalytic TiO2 was produced in situ by the thermal decomposition of at least partially ad hoc crystallized precursors (which may require post-deposition annealing operations).

PL 206 113 B1

Various types of binder, in addition to TiO2, were used in these examples. TiO2 from thermal decomposition of the precursors was partially crystallized in the anatase (photocatalytic) form and partially in the amorphous form. The coatings were deposited by liquid pyrolysis on a glass substrate, already used in the previous examples.

The following Table 3 lists, by each example of these series:

&gt; type of binder (formula Sb₂ABOUT_x means it is either Sb₂ABOUT₃ or Sb₂ABOUT₅, the stoichiometric oxygen content was not measured);

&gt; amount of TiO₂ in coatings (measured by X-ray fluorescence: expressed in μg / cm²: Q_TiO2;

&gt; PA value, as defined above, in nm / h / ^ g / cm²); and&gt; the total amount of substance in the coating, also expressed in μg / cm² : Q_T.ot.

In all these examples, the ratio of TiO2 (which is either crystallized or amorphous) to the other components of the coating (binder) is 90 mole% TiO2 to 10 mole% Si or other metal depending on the examples.

Table 3

<td>Examples</td><td>QTiO2</td><td>Qtot</td><td>binder</td><td>PA</td>

<td>D-10</td><td> 15,4</td><td> 15,4</td><td>TiO2</td><td> 19,4</td>

<td>D-11</td><td> 12,1</td><td> 14,6</td><td>SnO₂</td><td> 11,5</td>

<td>D-12</td><td> 12,4</td><td> 15,0</td><td>F: SnO2</td><td> 12,5</td>

<td>D-13</td><td> 11,1</td><td> 12,7</td><td>Al2O3</td><td> 4,8</td>

<td>D-14</td><td> 11,8</td><td> 13,5</td><td>F: Al2O3</td><td> 4,7</td>

<td>D-15</td><td> 15,8</td><td> 18,5</td><td>ZrO2</td><td> 17,8</td>

<td>D-16</td><td> 16,0</td><td> 18,7</td><td>F: ZrO2</td><td> 20,0</td>

<td>D-17</td><td> 19,5</td><td> 25,0</td><td>^Sat2^ABOUTx</td><td> 3,0</td>

<td>D-18</td><td> 17,0</td><td> 21,8</td><td>F: Sb2Ox</td><td> 1,5</td>

<td>D-19</td><td> 19,6</td><td> 21,8</td><td>ZnO</td><td> 1,8</td>

<td>D-20</td><td> 20,3</td><td> 22,6</td><td>F: ZnO</td><td> 2,2</td>

The precursors in each of these examples were of the organometallic compound, halide or metal salt type known in the literature. In the case of Example D-10 completely containing TiO2, the same precursor as in Examples 1 to 5 was used.

Table 4 below summarizes, for these examples, the light transmission values ​​TL measured with the illumination D65 of coated glass and the light reflection values ​​RL (same illumination). The diffusion values ​​of Td, also in%, and the delta Td values, which correspond to the change in the diffusion values ​​of the coatings after subjecting them to the following mechanical abrasion test are also given: the coating is subjected to a dry rub test consisting of a back and forth motion combined with a specific rotation of the filled cylinder. The cylinder fill was 390 g / cm²the movement speed was 50 strokes per minute and the specific rotation speed was 6 revolutions per minute. The Td value was measured after 500 cycles.

Table 4

<td>Examples</td><td>Tl</td><td>Rl</td><td>Td</td><td>delta Td</td>

<td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td>

<td>D-10</td><td> 83,3</td><td> 16,2</td><td> 0,5</td><td> 0,6</td>

<td>D-11</td><td> 86,7</td><td> 13,1</td><td> 0,2</td><td> 0,9</td>

<td>D-12</td><td> 86,3</td><td> 13,4</td><td> 0,3</td><td> 0,5</td>

<td>D-13</td><td> 87,3</td><td> 12,5</td><td> 0,2</td><td> 3,5</td>

PL 206 113 B1 cont. table 4

<td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td>

<td>D-14</td><td> 86,3</td><td> 13,5</td><td> 0,2</td><td> 2,6</td>

<td>D-15</td><td> 81,2</td><td> 18,5</td><td> 0,3</td><td> 1,2</td>

<td>D-16</td><td> 80,9</td><td> 18,8</td><td> 0,3</td><td> 0,6</td>

<td>D-17</td><td> 81,9</td><td> 17,6</td><td> 0,5</td><td> 0,3</td>

<td>D-18</td><td> 83,2</td><td> 15,1</td><td> 1,7</td><td> 1,2</td>

<td>D-19</td><td> 81,9</td><td> 17,4</td><td> 0,7</td><td> 0,4</td>

<td>D-20</td><td> 81,3</td><td> 18,3</td><td> 0,4</td><td> 1,3</td>

These results confirm the previous ones, namely, "conductive binders make it possible to significantly improve the parameters of photocatalytic coatings, as well as obtain abrasion-resistant coatings of good optical quality.

All these results show that it is possible to select the best conductive binders which allow the removal of light electrons from the crystalline photocatalytic domains / particles and allow favorable redox reactions to take place in the coating.