Substrate comprising a photocatalytic tio2 layer

p0001The invention relates to substrates with a photocatalytic, TiO₂ Containing layer exhibiting improved photocatalytic activity, and a process for their preparation.

p0002The photocatalytic properties of TiO₂Articles have long been known and intensively investigated in the literature. The photocatalytic effect is due to a semiconducting property of the TiO₂, A hole-electron pair being formed by a light quantum which has a relatively long recombination time. By diffusion of holes and electrons to the surface, processes are initiated which develop directly or indirectly over water with subsequent formation of hydrogen peroxide, a strongly oxidative effect. The oxidation potential of more than 3 eV is so high that practically all organic substances which are in contact with such TiO.sub.2₂Particles are oxidized. This process, however, only takes place when a significant amount of UV light is contained in the irradiated light. Since the proportion of the UV light in the visible light is relatively small, the photocatalytic effect is limited by the incident light quanta. By the recombination of the electrons with the holes, the efficiency is further reduced.

p0003Furthermore, it has been found that it is difficult to oxidize by a photocatalytic layer which is applied thereon, and thus the damage to the substrate or the layer, on substrates or surface layers which are self-oxidizable, such as, for example, substrates or layers of organic polymers to prevent. Even with substrates or surface layers made of glass, a direct application of the photocatalytic layer has the disadvantage that sodium ions present in the glass can diffuse into the photocatalytic layer, as a result of which the glass is damaged and / or the photocatalytic process is disturbed.

p0004The object of the present invention was therefore to achieve increased photocatalytic activity and / or to provide protection for substrates or surface layers which are sensitive to the photocatalytic layer.

p0005According to one embodiment of the present invention, a method for producing a substrate with a photocatalytic layer comprising photocatalytically active TiO.sub.2₂ And a matrix material, the TiO₂ Is contained in a concentration gradient enriched in the surface of the photocatalytic layer, comprising the steps of:<ol><li>A) preparing a mixture comprising at least one hydrolyzable titanium compound, an organic solvent and water in a substoichiometric amount, based on the hydrolyzable groups of the titanium compound,</li><li>B) treating the resulting mixture at a temperature of at least 60 ° C to form a dispersion or precipitation of doped TiO₂Particles,</li><li>C) optionally removing the solvent to form a powder of TiO₂And, if appropriate, solvent exchange by the addition of a different solvent,</li><li>D) mixing the obtained TiO₂Particles with a surface modifier to provide surface modification of the TiO₂Particles,</li><li>E) adding an inorganic or organically modified inorganic matrix-forming material,</li><li>F) applying the dispersion to the substrate,</li><li>G) curing the applied dispersion to form a photocatalytic layer and</li><li>H) photocatalytic decomposition of at least the organic groups of the surface-modified TiO 2 enriched on the surface of the photocatalytic layer₂Particles.</li></ol>

p0006In preferred embodiments, the process for the preparation of the TiO.sub.2₂Particles or, for the production of the substrate with photocatalytic layer, additionally at least one dopant is added in step a), and / or hydrothermal treatment or heating under reflux occurs in step b).

p0007The substrate to be provided with the photocatalytic layer may be of any suitable material for this purpose. Examples of suitable materials are metals or metal alloys, glass, ceramics, including oxide ceramics, glass ceramics or plastics. It is also possible, of course, to use substrates which have a surface layer of the abovementioned materials. The surface layer may, for example, be a metallization, an enamelling, a glass or ceramic layer or a lacquering.

p0008Examples of metals or metal alloys are steel, including stainless steel, chromium, copper, titanium, tin, zinc, brass and aluminum. Examples of glass are soda lime glass, borosilicate glass, lead crystal and silica glass. It may be, for example, flat glass, hollow glass such as container glass, or laboratory glass. The ceramic is, for example, a ceramic based on the oxides SiO₂, Al₂O₃, ZrO₂ Or MgO or the corresponding mixed oxides. Examples of the plastic which can be present as a film, as well as the metal, are polyethylene, eg HDPE or LDPE, polypropylene, polyisobutylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl butyral, polytetrafluoroethylene, polychlorotrifluoroethylene, polyacrylates, polymethacrylates such as polymethylmethacrylate, polyamide, polyethylene terephthalate , Polycarbonate, regenerated cellulose, cellulose nitrate, cellulose acetate, cellulose triacetate (TAC), cellulose acetate butyrate, or rubber hydrochloride. A painted surface can be formed from usual basecoats or varnishes.

p0009To produce a photocatalytic layer on the substrate, according to the first embodiment according to the invention, a TiO.sub.2 layer is produced in accordance with the sol-gel process described later₂Particles. The TiO₂Particles can also precipitate to form a precipitate. A powder is obtained by removing the solvent.

p0010According to the methods of the first embodiment according to the invention, a mixture comprising at least one hydrolyzable titanium compound, an organic solvent and water in a substoichiometric amount, based on the hydrolyzable groups of the titanium compound, is first prepared in step a), the mixture also comprising at least one metal compound as Dopant.

p0011The hydrolyzable titanium compound is, in particular, a compound of the formula TiX₄, Where the hydrolyzable groups X, which are different from one another or preferably identical, are, for example, hydrogen, halogen (F, Cl, Br or I, in particular Cl and Br), alkoxy_1-6Alkoxy, especially C_1-4Alkoxy, eg methoxy, ethoxy, n-propoxy, i-propoxy, butoxy, i-butoxy, sec-butoxy and t-butoxy), aryloxy (preferably C_6-10Aryloxy, for example

p0012Phenoxy), acyloxy (preferably C_1-6Acyloxy, such as acetoxy or propionyloxy), or alkylcarbonyl (preferably C,_2-7Alkylcarbonyl, such as, for example, acetyl). An example of a halide is TiCl₄. Preferred hydrolyzable radicals X are alkoxy groups, in particular C._1-4Alkoxy. Concrete and preferably used titanates are Ti (OCH₃) "₄, Ti (OC₂H₅) "₄ And Ti (n- or i-OC₃H₇) "₄.

p0013The mixture also contains water in a sub-stoichiometric amount relative to the hydrolyzable groups of the titanium compound, ie less than one mole of water is present per mole of hydrolyzable groups in the titanium compound. In other words, less than 4 moles of water are added to a hydrolyzable titanium compound having 4 hydrolyzable groups, based on 1 mole of titanium compound. Preferably, not more than 0.7 mol, more preferably not more than 0.6 mol, and more preferably not more than 0.5 mol or 0.4 mol, and not less than 0.35 mol, more preferably not less than 0.30 mol Water, based on 1 mole of hydrolyzable groups in the titanium compound.

p0014In the preferred embodiments for producing doped particles, any suitable metal compound, for example an oxide, a salt or a complex compound, for example halides, nitrates, sulfates, carboxylates (eg acetates) or acetylacetonates, can be used as the metal compound for the doping. The compound should be suitably soluble in the solvent used for the mixture. Suitable metal is any metal, in particular a metal selected from the 5th to 14th group of the periodic table of the elements and the lanthanides and actinides. The groups are listed here according to the new IUPAC system, as reproduced in Römpp Chemie Lexikon, 9th Edition. The metal may be present in the compound in any suitable oxidation precursor.

p0015According to the new IUPAC system, groups 1, 2 and 13 to 18 correspond to the 8 main groups (IA to VIIIA according to CAS), groups 3 to 7 correspond to the side groups 3 to 7 (IIIB to VIIB according to CAS), groups 8 to 10 of the Subgroup 8 (VIII to CAS) and groups 11 and 12 to subgroups 1 and 2 (CU and Zn group, IB and IIB according to CAS).

p0016Examples of suitable metals for the metal compound are W, Mo, Cr, Zn, Cu, Ag, Au, Sn, In, Fe, Co, Ni, Mn, Ru, V, Nb, Ir, Rh, Os, Pd and Pt. Metal compounds of W (VI), Mo (VI), Cr (III), Zn (II), Cu (II), Au (III), Sn (IV), In (III), Fe (III), Co (II) ), V (V) and Pt (IV) are preferably used. Very good results are obtained in particular with W (VI), Mo (VI), Zn (II), Cu (II), Sn (IV), In (III) and Fe (III). Concrete examples of preferred metal compounds are WO₃, MoO₃, FeCl₃, Silver acetate, zinc chloride, copper (II) chloride, indium (III) oxide and tin (IV) acetate.

p0017The quantity ratio between the metal compound and the titanium compound also depends on the metal used and its oxidation stage. In general, use is made of, for example, such proportions that a molar ratio of metal of the metal compound to titanium of the titanium compound (Me / Ti) is from 0.0005: 1 to 0.2: 1, preferably from 0.001: 1 to 0.1: 1 and more preferably 0.005: 1 to 0.1: 1.

p0018Instead of the metal doping, doping with semimetal or non-metal elements can also be carried out, for example with carbon, nitrogen, phosphorus, sulfur, boron, arsenic, antimony, selenium, tellurium, chlorine, bromine and / or iodine. For this purpose, either the elements as such or suitable element compounds are used as dopants.

p0019The doped TiO₂Particles are characterized in particular by the fact that, with a suitable choice of the doping element and of the process control, they also exhibit photocatalytic activity even in the case of excitation with visible light of a wavelength> 380 nm ("visible light" or "daylight photocatalysts").

p0020The solvent used is an organic solvent in which the hydrolyzable titanium compound is preferably soluble. The solvent is also preferably miscible with water. Examples of suitable organic solvents are, inter alia, alcohols, ketones, ethers, amides and mixtures thereof. Alcohols are preferably used, preferably lower aliphatic alcohols (C.₁-C₆Alcohols), such as ethanol, 1-propanol, isopropanol, sec-butanol, tert-butanol, isobutyl alcohol, n-butanol and the pentanol isomers, in particular 1-pentanol, 1-propanol and 1-pentanol being particularly preferred Are preferred.

p0021The mixture preferably contains a catalyst for hydrolysis and condensation under sol-gel conditions, in particular an acidic condensation catalyst, for example hydrochloric acid, phosphoric acid or formic acid.

p0022The resulting mixture is then heated at a temperature of at least 60 ° C to form a dispersion or a precipitate of doped or undoped TiO₂Particles. This heat treatment is preferably hydrothermal or by heating under reflux. Advantageously, a relatively high dilution is used in the heat treatment, in particular when heated under reflux.

p0023The heat treatment is preferably carried out over a period of from 0.5 to 30 h, preferably from 4 to 24 h, the duration being dependent on the temperature and the pressure applied. For example, anatase is obtained by hydrothermal treatment at 200 ° C. and autogenous pressure after a reaction time of 1 h in nanoparticulate form in a yield of about 35% of theory.

p0024Refluxing is usually carried out over a period of at least 3 h. The solvents used are preferably alcohols having at least 4, preferably at least 5, carbon atoms, for example n-pentanol, hexanol, heptanol or octanol. However, it is also possible to use other polar solvents, for example thiols, such as n-butyl, amyl, hexyl or heptyl mercaptan.

p0025A hydrothermal treatment is generally understood to mean a heat treatment of an aqueous solution or suspension under superatmospheric pressure, for example at a temperature above the boiling point of the solvent and a pressure above 1 bar. In the present invention, heat treatment in a predominantly organic solvent which contains only a little water at all is also referred to as a hydrothermal treatment under overpressure.

p0026In the hydrothermal treatment, the mixture is heat-treated in a closed container or closed autoclave. The treatment is preferably carried out at a temperature in the range from 75 ° C. to 300 ° C., preferably above 200 ° C., more preferably from 225 ° to 275 ° C., for example about 250 ° C. By heating, in particular by the boiling point of the solvent, a pressure (autogenous pressure) is built up in the closed vessel or autoclave. The pressure obtained can, for example, be above 1 bar, in particular 50 to 500 bar or more, preferably 100 to 300 bar, for example 200 bar. As a rule, the hydrothermal treatment is carried out for at least 0.5 h and preferably up to 7 or 8 h.

p0027The heat treatment according to step b) is carried out until the desired doped or undoped TiO₂Particles are formed. The dispersion or the precipitate can be used directly or after solvent exchange for the coating of the substrate. To TiO₂Particles in powder form, the solvent is removed.

p0028The resulting doped or undoped TiO₂Particles of the dispersion, the precipitate or the powder are predominantly crystalline in the anatase form. Preferably, the crystalline portion of the obtained doped TiO₂Particles more than 90%, preferably more than 95% and in particular more than 97%, ie the amorphous fraction is in particular below 3%, eg 2%. The average particle size (X-ray-determined volume average) is preferably not more than 20 nm, more preferably not more than 10 nm. In a particularly preferred embodiment, particles with an average particle size of about 2 to 10 nm are obtained. The TiO 2 prepared according to the invention₂Particles are distinguished from known TiO 2₂Materials in that they are dispersible agglomerate-free. When doping the TiO₂A particularly homogeneous distribution of the doping metals is obtained.

p0029The resulting dispersion can be used as such to coat the substrate. Expediently, a solvent exchange takes place beforehand. It is preferred that the particles are separated from the solvent from the dispersion obtained in step b). All methods known to a person skilled in the art can be used for this purpose. Centrifugation is particularly suitable. The separated TiO₂Particles are then dried (eg at 40 ° C. and 10 mbar). In this form, the particles can also be stored well.

p0030For application to the substrate, the TiO₂Particles are again dispersed in a solvent. The solvents or water listed above are suitable for this purpose, for example. Preference is given to using a water / alcohol mixture and more preferably water alone as solvent.

p0031In a preferred embodiment, an inorganic or organically modified inorganic matrix-forming material is added to the dispersion obtained according to step b) or c). These may be, in particular, inorganic sols or organically modified inorganic hybrid materials or nanocomposites. Examples of this are organically modified oxides, hydrolysates and (poly) condensates of at least one glass or ceramic-forming element M, in particular an element M from the groups 3 to 5 and / or 12 to 15 of the periodic table of the elements, preferably Si, Al , B, Ge, Pb, Sn, Ti, Zr, V and Zn, especially those of Si and Al, most preferably Si, or mixtures thereof. It is also possible to add elements of groups 1 and 2 of the Periodic Table (eg Na, K, Ca and Mg) and groups 5 to 10 of the Periodic Table (eg Mn, Cr, Fe and Ni) or lanthanides in the oxide, hydrolyzate or (poly) condensate. A preferred organically modified inorganic hybrid material is polyorganosiloxanes. Hydrolysates of glass- or ceramic-forming elements, in particular silicon, are particularly preferred for this purpose.

p0032The inorganic or organic-modified inorganic matrix-forming material is preferably added in such an amount that the molar ratio of titanium of the titanium compound to glass- or ceramic-forming element M is 100: 0.01 to 0.01: 100, preferably 300: 1 to 1: 300. Very good results are obtained with a molar ratio Ti / M of about 10: 3 to 1:30. By this addition, an improvement in adhesion is achieved. If an organic-modified inorganic matrix-forming material is used, all or only a part of the glass-ceramic-forming elements M present may have one or more organic groups as non-hydrolysable groups.

p0033The inorganic or organically modified inorganic matrix-forming materials can be prepared by known methods, for example by flame pyrolysis, plasma processes, gas phase condensation processes, colloid techniques, precipitation methods, sol-gel processes, controlled nucleation and growth processes, MOCVD methods and (micro) If solvent-free particles are obtained from the process, these are suitably dispersed in a solvent.

p0034The inorganic sols and in particular the organo-modified hybrid materials are preferably obtained by the sol-gel process. In the sol-gel process, which can also be used for the separate preparation of the particles, hydrolyzable compounds are usually hydrolyzed with water, if appropriate under acidic or basic catalysis, and at least partly condensed. The hydrolysis and / or condensation reactions lead to the formation of compounds or condensates with hydroxy, oxo groups and / or oxo bridges, which serve as precursors. Stoichiometric amounts of water but also smaller or larger amounts can be used. The sol formed can be determined by suitable parameters, eg degree of condensation, solvent or pH, To the desired viscosity for the coating composition. Further details of the sol-gel process are, for example, in<nplcit id="ncit0001" npl-type="b"><text>CJ Brinker, GW Scherer: "Sol-Gel Science", Academic Press, Boston, San Diego, New York, Sydney (1990)</text></nplcit>).

p0035According to the preferred sol-gel process, the oxides, hydrolysates or (poly) condensates are obtained by hydrolysis and / or condensation from hydrolyzable compounds of the abovementioned glass- or ceramic-forming elements which, if necessary, are not produced for the production of the organically modified inorganic hybrid material Hydrolyzable organic substituents.

p0036Inorganic sols are prepared by the sol-gel process, in particular from hydrolysable compounds of the general formulas MX_N Wherein X is as defined in formula (I) below, where two groups X may be replaced by an oxo group, and n is the valency of the element and is usually 3 or 4. Preference is given to hydrolysable Si compounds, in particular of the formula (I) below.

p0037Examples of employable hydrolyzable compounds of elements M other than Si are Al (OCH₃) "₃, Al (OC₂H₅) "₃, Al (OnC₃H₇) "₃, Al (OiC₃H₇) "₃, Al (OnC₄H₉) "₃, Al (O-sec₄H₉) "₃, AlCl₃, AlCl (OH)₂, Al (OC₂H₄OC₄H₉) "₃, TiCl₄, Ti (OC₂H₅) "₄, Ti (OnC₃H₇) "₄, Ti (OiC₃H₇) "₄, Ti (OC₄H₉) "₄, Ti (2-ethylhexoxy)₄, ZrCl₄, Zr (OC₂H₅) "₄, Zr (OnC₃H₇) "₄, Zr (OiC₃H₇) "₄, Zr (OC₄H₉) "₄, ZrOCl₂, Zr (2-ethylhexoxy)₄, And Zr compounds which have complexing radicals, such as, for example, β-diketone and (meth) acrylic radicals, sodium methoxide, potassium acetate, boric acid, BCl₃, B (OCH₃) "₃, B (OC₂H₅) "₃, SnCl₄, Sn (OCH₃) "₄, Sn (OC₂H₅) "₄, VOCl₃ And VO (OCH₃) "₃.

p0038The following statements on the preferred silicon also apply analogously to the other elements M. Particular preference is given to the sol or the organically modified inorganic hybrid material obtained from one or more hydrolyzable and condensable silanes, whereupon at least one silane has a non-hydrolysable organic radical. Particular preference is given to using one or more silanes having the following general formulas (I) and / or (II):         SiX₄     (I) Wherein the radicals X are identical or different and are hydrolyzable groups or hydroxyl groups,         R_ASiX_(4-a)     (II) Wherein R is the same or different and is a non-hydrolyzable radical which optionally has a functional group, X is as defined above and a is 1, 2 or 3, preferably 1 or 2.

p0039In the above formulas, the hydrolyzable groups X are, for example, hydrogen or halogen (F, Cl, Br or I), alkoxy (preferably C,_1-6Alkoxy such as methoxy, ethoxy, n-propoxy, i-propoxy and butoxy), aryloxy (preferably C,_6-10Aryloxy, such as phenoxy), acyloxy (preferably C_1-6Acyloxy, such as, for example, acetoxy or propionyloxy), alkylcarbonyl (preferably C 1 -C 6)_2-7Such as, for example, acetyl), amino, monoalkylamino or dialkylamino having preferably 1 to 12, in particular 1 to 6, carbon atoms in the alkyl group (s).

p0040The non-hydrolyzable radical R is, for example, alkyl (preferably C 1 -C 6)_1-6Such as methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl and t-butyl, pentyl, hexyl or cyclohexyl), alkenyl (preferably C,_2-6Alkenyl, such as vinyl, 1-propenyl, 2-propenyl and butenyl), alkynyl (preferably C_2-6-alkynyl, such as, for example, acetylenyl and propargyl) and aryl (preferably C 1 -C 6)_6-10Aryl, such as, for example, phenyl and naphthyl).

p0041The radicals R and X mentioned may have, as functional groups, one or more conventional substituents, for example halogen, ether, phosphoric acid, sulfonic acid, cyano, amide, mercapto, thioether or alkoxy groups.

p0042The radical R can contain a functional group via which crosslinking is possible. Concrete examples of the functional groups of the radical R are epoxy, hydroxy, amino, monoalkylamino, dialkylamino, carboxy, allyl, vinyl, acryloxy, methacryloyl, methacryloxy, cyano, and aldehyde And alkylcarbonyl groups. These groups are preferably bonded to the silicon atom via alkylene, alkenylene or arylene bridging groups, which can be interrupted by oxygen or sulfur atoms or -NH groups. The abovementioned bridge groups are derived, for example, from the abovementioned alkyl, alkenyl or aryl radicals. The bridge groups of the radicals R preferably contain 1 to 18, in particular 1 to 8, carbon atoms.

p0043Particularly preferred hydrolyzable silanes of the general formula (I) are tetraalkoxysilanes, such as tetramethoxysilane and, in particular, tetraethoxysilane (TEOS). Anorganic sols obtained by acid catalysis, eg TEOS hydrolysates, are particularly preferred. Particularly preferred organosilanes of the general formula (II) are methyltriethoxysilane (MTEOS) and MTEOS hydrolysates, epoxysilanes such as 3-glycidyloxypropyltrimethoxysilane (GPTS), methacryloxypropyltrimethoxysilane and acryloxypropyltrimethoxysilane, where GPTS hydrolysates can advantageously be used.

p0044If an organic-modified inorganic hybrid material is prepared, only silanes of the formula (II) or a mixture of silanes of the formulas (I) and (II) can be used. In the case of the inorganic sols based on silicon, exclusively silanes of the formula (I) are used, where, if appropriate, hydrolyzable compounds of the above formula MX_N Can be added.

p0045If the inorganic sol consists of discrete oxide particles dispersed in the solvent, they can improve the hardness of the layer. These particles are, in particular, nanoscale inorganic particles. The particle size (x-ray-determined volume average) is, for example, in the range 200 200 nm, in particular 100 100 nm, preferably 50 50 nm, eg 1 nm to 20 nm.

p0046According to the invention, for example, inorganic sols of SiO₂, ZrO₂, GeO₂, CeO₂, ZnO, Ta₂O₅, SnO₂ And Al₂O₃ (In all modifications, especially as boehmite AlO (OH)), preferably brine of SiO₂, Al₂O₃, ZrO₂, GeO₂ And mixtures thereof are used as nanoscale particles. Some of these sols are also commercially available, for example, silica sols such as the Levasile^® Of Bayer AG.

p0047An inorganic or organically modified inorganic matrix-forming material can also be a combination of such nanoscale particles with inorganic sols present as hydrolysates or (poly) condensates or organic-modified hybrid materials, which is referred to herein as nanocomposites.

p0048Optionally, organic monomers, oligomers or polymers of all kinds may also be present as organic matrix-forming materials which serve as flexibilizers, which may be conventional organic binders. These can be used to improve the coating ability. As a rule, they are photocatalytically degraded after completion of the layer. The oligomers and polymers may have functional groups via which crosslinking is possible. This possibility of crosslinking is also possible in the case of the above-described organically modified inorganic matrix-forming materials. Mixtures of inorganic, organically modified inorganic and / or organic matrix-forming materials are also possible.

p0049Examples of organic matrix-forming materials which can be used are polymers and / or oligomers which have polar groups, such as hydroxyl, primary, secondary or tertiary amino, carboxyl or carboxylate groups. Typical examples are polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, polyvinylpyridine, polyallylamine, polyacrylic acid, polyvinyl acetate, polymethylmethacrylic acid, starch, gum arabic, other polymeric alcohols such as polyethylene-polyvinyl alcohol copolymers, polyethylene glycol, polypropylene glycol and poly (4- vinylphenol) and monomers derived therefrom Or oligomers. As polyvinyl alcohol, for example, the commercially available Mowiol® 18-88 from Hoechst can be used.

p0050The degree of dilution of the dispersion to be applied according to step d) depends, inter alia, on the desired layer thickness. In general, the dispersion has a solids content of less than 50% by weight, in particular less than 20% by weight and preferably less than 10% by weight, for example 2.5% by weight.

p0051The usual procedures are used for the application, eg dipping, rolling, doctoring, flooding, drawing, spraying, spinning or spreading. The dispersion applied is, if desired, dried and heat-treated, for example for curing or compaction. The heat treatment used for this depends, of course, on the substrate. In the case of plastic substrates or plastic surfaces which as a rule have a barrier layer (see below), very high temperatures can not be used, of course. For example, polycarbonate (PC) substrates are heat-treated at about 130 ° C. for 1 h. In general, the heat treatment is carried out, for example, at a temperature of 100 to 200 ° C. and, if no plastic is present, up to 500 ° C. or more. The heat treatment is carried out, for example, for 15 minutes to 2 hours. Layer thicknesses of 50 nm to 30 μm are generally obtained,

p0052The inorganic sol or the organic-modified inorganic hybrid material serve not only as a matrix-forming material for the photocatalytic layer, but also for improved layer adhesion. TiO₂ Can be present in the layer as a matrix-forming constituent and / or as particles.

p0053The photocatalytic layer is activated, if desired and preferably by irradiation with visible and / or UV light, for example with a mercury high-pressure lamp of 700 W for 1 to 5 min or a xenon lamp of 750 W for 1 to 10 min. Mercury high-pressure lamps have a relatively high proportion of UV light, while the spectrum of xenon lamps corresponds to the sunlight. Preference is given to irradiating with UV light or a high proportion of UV light. Exceptionally active photocatalytic layers are obtained, whereby the efficiency can be increased by up to 10 times compared with the prior art.

p0054As already mentioned above, in the case of substrates which consist of a sensitive material or have a surface layer (for example a coating or an enamel) from such a sensitive material, an immediate application is not possible or is only possible with difficulty. A barrier layer can be arranged between the substrate (optionally with surface coating) and the photocatalytic layer. For this purpose, an inorganic layer of an inorganic matrix-forming material can be used, for which the above-described inorganic sols can be used.

p0055Furthermore, according to the invention, it has been found that it is possible to obtain a photocatalytic layer with a "built-in" barrier layer by a concentration gradient of TiO 2₂ In the photocatalytic layer. This barrier layer can be used advantageously not only for the photocatalytic layers produced according to the invention, but also for the customary photocatalytic layers.

p0056Accordingly, according to the embodiment of the invention, a substrate is provided with a photocatalytic layer comprising photocatalytically active TiO 2₂ And a matrix material, the TiO₂ Is contained in such a concentration gradient that the concentration of TiO₂ Is enriched on the surface of the photocatalytic layer, preferably between the photocatalytically active TiO 2₂ And the substrate is formed with a purely inorganic barrier layer.

p0057These photocatalytic layers with such a concentration gradient of TiO₂In that the concentration of TiO₂ Is greatest at the surface of the photocatalytic layer, can be prepared in particular by a method in which surface-modified TiO.sub.2 is used₂Particles in a matrix-forming material of themselves form a concentration gradient.

p0058The customary TiO 2 known in the art can be used₂Particles for surface modification, which are, for example, commercially available. TiO₂Particles are available, for example, as P25 (d50 = 30-40 nm) from Degussa.

p0059In a second embodiment of the invention, doped or undoped TiO 2₂Particles are used. The doping can be carried out by the methods known in the art, whereby the metallic or non-metallic dopants known in the art can be used, for example the metals and nonmetals mentioned above for the first embodiment according to the invention. Surprisingly, the doping results in an activity increase and often a photocatalytic activity in the visible light region ("visible photocatalysts").

p0060Preference is given to TiO obtained by the sol-gel process₂Particles. The abovementioned hydrolyzable titanium compounds can be used for this purpose. In a preferred embodiment, particles which have been produced according to steps a) and b) are used, with doped or non-doped TiO 2₂Particles can be used.

p0061Of the TiO₂Particles, a dispersion is usually prepared in a solvent. Toluene is suitable for this purpose, for example. It can also contain a slurry of TiO₂Particles in a solvent or a powder of TiO₂Particles without solvent. For this purpose, a surface modifier is added which has at least one hydrophobic or hydrophilic group, with hydrophobic groups being preferred.

p0062Suitable surface modifiers are (preferably low molecular weight or oligomeric, but optionally also polymeric) compounds which on the one hand have one or more groups which react on the surface of the TiO 2₂(Such as, for example, OH groups), or at least have a hydrophobic or hydrophilic group.

p0063Surface modification of the TiO₂For example, by mixing the particles with suitable compounds described below, if appropriate in a solvent and in the presence of a catalyst. Frequently, stirring of surface modifiers with the particles at room temperature is sufficient for a certain period of time, for example over 1 to 3 h. Advantageously, treatment in the ultrasonic bath also often has an effect.

p0064The surface modifiers can be, for example, both covalent (including coordinative in the form of complexes) and ionic (salt-like) bonds to the surface of the TiO₂While dipole-dipole interactions, hydrogen bond bonds, and van der Waals interactions are among the pure interactions. Preference is given to the formation of covalent bonds.

p0065According to the invention it is also preferred that the surface modifiers have a relatively low molecular weight. For example, the molecular weight can be less than 1500, in particular below 1000 and preferably below 700. This, of course, does not exclude a significantly higher molecular weight of the compounds (eg up to 2,000 and more).

p0066As surface modifiers having groups corresponding to the surface groups of the TiO₂For example, hydrolyzable silanes, carboxylic acids, carboxylic acid halides, carboxylic acid esters, carboxylic acid anhydrides, oximes, β-dicarbonyl compounds such as β-diketones, alcohols, polyethers and functionalized polyethers (eg trioxadecanoic acid), amines, alkyl halides and their derivatives.

p0067The concept of hydrophilicity / hydrophobicity is well known to the expert as the basic concept of chemistry. Hydrophobic substances or groups emit water while hydrophilic substances or groups attract water. The hydrophilic character can be formed, for example, by hydroxy, oxy, carboxylate, sulfate, sulfonate functions or polyether chains in the substance. Suitable hydrophobic groups are, for example, long-chain aliphatic hydrocarbon groups, for example having 3 to 30 or more carbon atoms, in particular alkyl groups, aromatic groups, or groups which have at least one fluorine atom, preferably being hydrocarbon groups, especially alkyl radicals, having 3 to 20 or more Carbon atoms and 1 to 30 fluorine atoms.

p0068The surface modifiers used are preferably hydrolyzable silanes having at least one non-hydrolyzable hydrophobic or hydrophilic group, those with a hydrophobic group being particularly preferred. These are particularly preferably hydrolyzable silanes which have at least one non-hydrolysable group which contains at least one fluorine atom (fluorosilanes) or a long-chain aliphatic hydrocarbon group, for example having 3 to 30 carbon atoms, preferably an alkyl group or an aromatic group.

p0069The surface modifiers with hydrophobic groups which can be used in addition to the hydrolyzable silanes can, for example, have the formula R 1 -Y, where Y is -COOH, -OH, -COZ, -Z (where Z is a halide such as F, Cl, Br or I) (O) O (O) CB (wherein B is an arbitrary radical of a carboxylic acid or R °, or a functional group of the other compounds described above (optionally comprising another group such as B), and R ° is a long chain aliphatic hydrocarbon group, An alkyl group, for example having 3 to 30 carbon atoms, or an aromatic group, such as, if appropriate, substituted phenyl or naphthyl, or a hydrocarbon group, preferably an alkyl group, having at least one fluorine atom, for example, the remainder of the carboxylic acid and / Remain the hydrophobic group.

p0070The preferred hydrolyzable silanes having a long-chain aliphatic hydrocarbon group as a hydrophobic group have, in particular, the formula (II) (R_ASiX_(4-a)) In which a and X are as defined above, where a is preferably 1 and R is a long-chain aliphatic hydrocarbon group, for example having 3 to 30 carbon atoms. The long-chain aliphatic hydrocarbon group is preferably an alkyl group. If desired, it is also possible to use silanes of the formula (II) in which R is an optionally substituted aromatic group.

p0071According to the invention, particular preference is given to using hydrolysable silane compounds having at least one non-hydrolyzable radical as a hydrophobic group which have the general formula         Rf (R)_BSiX_(3-b)     (III) In which X and R are as defined in formula (I) or (II), respectively, Rf is a non-hydrolyzable group having 1 to 30 fluorine atoms attached to carbon atoms, which is preferably substituted by at least two atoms, preferably an ethylene, propylene, -, ethyleneoxy or propyleneoxy group, are separated from Si, and b is 0, 1 or 2, preferably 0 or 1. R is, in particular, a radical without a functional group, preferably an alkyl group, in particular C._1-4Such as methyl or ethyl. Preferably, the groups Rf 3 to 25 and especially 3 to 21 contain fluorine atoms attached to aliphatic (including cycloaliphatic) carbon atoms. Rf is preferably a fluorinated alkyl group having 3 to 20 carbon atoms, which is optionally interrupted by one or more oxygen atoms.

p0072Examples of Rf are CF₃CH₂CH₂, C₂F₅CH₂CH₂, NC₆F₁₃CH₂CH₂, IC₃F₇OCH₂CH₂CH₂, NC_8thF₁₇CH₂CH₂ And nC₁₀F₂₁-CH₂CH₂.

p0073Fluorine atoms, which are optionally bound to aromatic carbon atoms (eg C₆F₄), will not be considered. The fluorine-containing group Rf can also be a chelating ligand. It is also possible for one or more fluorine atoms to be located on a carbon atom from which a double or triple bond originates. Examples of fluorosilanes which can be used are CF₃CH₂CH₂SiCl₂(CH₃), CF₃CH₂CH₂SiCl (CH₃) "₂, CF₃CH₂CH₂Themselves₃) (OCH₃) "₂, C₂F₅-CH₂CH₂-SiZ₃, NC₆F₁₃-CH₂CH₂SiZ₃, NC_8thF₁₇-CH₂CH₂-SiZ₃, NC₁₀F₂₁-CH₂CH₂-SiZ₃ With (Z = OCH₃, OC₂H₅ Or Cl); IC₃F₇O-CH₂CH₂CH₂-SiCl₂(CH₃), NC₆F₁₃-CH₂CH₂-Si (OCH₂CH₃) "₂, NC₆F₁₃-CH₂CH₂-SiCl₂(CH₃) And nC₆F₁₃-CH₂CH₂-SiCl (CH₃) "₂. Preference is given to 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl) triethoxysilane (FTS).

p0074Examples of hydrolyzable silanes with long-chain aliphatic hydrocarbon group are hexadecyltrimethoxysilane (HDTMS), dodecyltriethoxysilane and propyltrimethoxysilane. Further examples of surface modifiers with hydrophobic groups are heptadecafluomonanoic acid, stearic acid, heptafluorobutyric acid chloride, hexanoic acid chloride, hexanoic acid methyl ester, perfluoroheptanoic acid methyl ester, perfluorooctanoic anhydride, hexanoic anhydride, 2-heptanone oxime, 1,1,1-trifluoro-5,5-dimethylhexane-2,4- Oxime, 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione, 1H, 1H-pentadecafluorooctanol, octanol, hexyl chloride and nonafluorobutyl chloride.

p0075Suitable surface modifiers with hydrophilic groups include unsaturated carboxylic acids, β-carbonylcarboxylic acids, polymerizable double bonds, ethylenically unsaturated alcohols and amines, amino acids, epoxides and diepoxides, in addition to the above-mentioned compound classes.

p0076Specific examples of organic compounds for surface modification with hydrophilic groups are diepoxides such as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, bis (3,4-epoxycyclohexyl) adipate, cyclohexanedimethanol diglycidyl ether, neopentylglycoldiglycidyl ether, 1,6-hexanediol diglycidyl ether, propyleneglycol diglycidyl ether, Bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, unsaturated carboxylic acids such as acrylic acid and methacrylic acid, and β-diketones such as acetylacetonate.

p0077Further particularly preferred compounds for surface modification with hydrophilic groups are hydrolyzable silanes with at least (and preferably) a non-hydrolyzable radical having a hydroxyl, carboxylate or epoxy or glycidyloxy group, which are, in particular, silanes of the formula (II). Examples are glycidyloxyalkyltrialkoxysilanes, for example 3-glycidyloxypropyltrimethoxysilane and 3-glycidyloxypropyltriethoxysilane.

p0078Further examples of surface modifiers are diphosphates, polyphosphates, polyvinyl alcohol, polyvinylpyrrolidone and methylvinylether-maleic anhydride copolymers.

p0079In the surface modification, 1 g TiO.sub.2 is used₂For example 10 ml of solvent. The resultant dispersion with the surface modifier is simply stirred, for example, 2 h, whereby the surface modification of the particles is achieved. The ratio of TiO₂ To added surface modifier, based on mol, preferably from 1: 0.005 to 1: 0.1 and in particular from 1: 0.01 to 1: 0.02, this being in particular for the surface modifier having at least one fluorine atom.

p0080A solvent exchange is then preferably effected with a different organic solvent, such as methyl ethyl ketone, acetone, chloroform or petroleum ether.

p0081Subsequently, an inorganic or organically modified matrix-forming material is added. For this purpose, for example, an inorganic sol or an organic-modified inorganic hybrid material can be added, as explained above for the first embodiment of the invention. The above-mentioned nanoscale particles can also be present.

p0082The surface modifier serves to produce the concentration gradient in the matrix of the matrix-forming material. In the case of a hydrophilic matrix, surface modifiers with a hydrophobic group are used, and in the case of a hydrophobic matrix, surface modifiers with a hydrophilic group are used. This results in a potential difference which results in demixing, so that the surface-modified TiO 2₂Particles are enriched on the surface. Since the matrix-forming materials and the solvent that is used are generally hydrophilic, it is preferably surface-modified with hydrophobic groups.

p0083The applied dispersion is applied to the substrate and the heat treatment is carried out in the usual manner, for example as described above. By the hydrophobic character of the hydrophobic groups on the surface of the TiO₂Particles results in a demixing in the dispersion thus obtained, the surface-modified TiO 2₂Particles after application to the substrate on the surface of the photocatalytic layer. During the hardening of the applied layer, a concentration gradient of the surface-modified TiO 2 is thus obtained₂Particles are formed in the other inorganic or organically modified matrix-forming material or in the matrix formed therefrom. In the lower region of the layer is predominantly the inorganic or organically modified inorganic matrix-forming material or the matrix formed therefrom.

p0084Upon exposure, the photocatalytic activity of the layer at least destroys the hydrophobic organic groups, which is evident in a considerable reduction in the contact angle after irradiation. Due to the concentration gradient, the matrix consisting of the inorganic or organically modified matrix-forming materials used, which essentially contains no TiO 2, is predominantly located at the boundary surface to the substrate₂ . If organically modified inorganic matrix-forming material has been used, the area in the photocatalytic layer in which TiO.sub.2₂Enriched regions and essentially TiO₂Free regions, the photocatalytic oxidation of the organic constituents explained above in the "isolated" barrier layer takes place, so that an inorganic barrier layer also forms there. Thus, according to the invention, a "built-in" barrier layer is formed from inorganic material, which can protect the underlying substrate.

p0085Again, in principle all of the abovementioned substrates can be used. With particular advantage, the photocatalytic layer with a built-in barrier layer is applied to a substrate made of glass or plastic or a surface layer of the substrate made of this material.

p0086It has further been found that a particular hybrid layer of an organically modified inorganic material provides an excellent barrier layer. This barrier layer can be used advantageously not only for the photocatalytic layers produced according to the invention, but also for the customary photocatalytic layers.

p0087According to a second embodiment of the present invention, therefore, a substrate is provided with a photocatalytic TiO.sub.2₂ Containing layer, which is characterized in that a hybrid layer of an organically modified inorganic material is provided between the substrate and the photocatalytic layer. During the first activation by exposure, a gradient in the carbon content is formed on the surface of the barrier layer due to the oxidation of the organic constituents. The gradient material thus obtained has a photocatalytically active TiO 2 on the surface₂ Containing inorganic layer, followed by an inorganic barrier layer which merges with the inorganic-organic hybrid material with increasing layer depth. By diffusing the TiO₂Particles into the surface of the barrier layer during layer formation also forms a gradient in the TiO 2₂Concentration.

p0088This barrier layer offers on the one hand the advantage that a secure protection of sensitive materials is ensured in front of the photocatalytic layer, on the other hand the barrier layer can be applied in a simple manner nashermically and can be applied without cracking in the desired layer thickness. A certain degree of flexibility in the coating is achieved by the organic constituents, surprisingly, despite the organic constituents used, a reliable barrier effect is achieved.

p0089In principle, all substrates mentioned above can be used as the substrate. With particular advantage, the barrier layer is applied to a substrate made of glass or plastic or a surface layer of the substrate made of this material.

p0090The barrier layer is a hybrid layer of an organically modified inorganic material whose organic constituents are at least at the interface to the photocatalytic TiO 2₂Layer have been photocatalytically decomposed to form a purely inorganic protective layer.

p0091To prepare this hybrid layer, the above-described organic-modified inorganic hybrid material is used as a coating composition. All the explanations given above for this material apply, unless otherwise stated, but the hybrid material is not added to the TiO 2₂Containing dispersion but is applied as such to the substrate.

p0092It is preferable to use such an organic-modified inorganic hybrid material in which not more than 10 mol%, preferably not more than 5 mol%, and more preferably not more than 3 mol%, and preferably at least 0.1 mol%, more preferably at least 10 mol% 0.5 mol% and in particular at least 1 mol%, for example 0.1 to 10 mol%, preferably 1 to 3 mol%, of the glass- or ceramic-forming elements M contained have one or more organic groups. Ie, preferably not more than 10 mol% and more preferably not more than 3 mol%; For example, from 0.1 to 10 mol%, preferably from 1 to 3 mol%, of the glass- or ceramic-forming elements M contained have one or more organic groups. Preferably, at least one part or all organic groups have a functional group, via which crosslinking is possible. The hybrid material is preferably prepared by the sol-gel method. Suitable solvents are the abovementioned. Particular preference is given to a hydrolyzate or condensate of silanes of the formula (I) and of the formula (II). If desired, at least some of the silanes of the formula (I) can be replaced by other hydrolysable compounds of a glass- or ceramic-forming element M.

p0093For the production of the hybrid material, a stoichiometric amount of water is preferably added to the hydrolyzable compounds. The resulting coating composition is used, for example, as an 1 to 70% by weight sol / gel (based on the solids content) in an alcohol. A particularly preferred combination of hydrolyzable compounds is TEOS or MTEOS and GPTS.

p0094The organic-modified inorganic hybrid material may preferably comprise the above-mentioned nanoscale particles to form a nanocomposite. Organic polymers are preferably not added to the organic-modified inorganic hybrid material, ie, the coating composition is preferably free of organic polymers.

p0095The hybrid material is applied in a conventional manner, for example by the methods described above. The applied layer is optionally dried and cured, whereby the curing can be effected by heat or irradiation. If desired, the heat treatment can be carried out together with the photocatalytic layer. With regard to the temperature and the duration, the conditions mentioned above for the photocatalytic layer apply. The layer thickness obtained is, for example, 50 nm to 1 μm, preferably 100 nm to 1 μm, for example 100 to 700 nm.

p0096A TiO is applied to the hybrid layer₂Containing composition, the surface-modified TiO₂Particles. Surface-modified TiO₂Particles as described above for the first embodiment of the invention. Surface modifiers having hydrophobic or hydrophilic groups can be used.

p0097In general, photocatalytically active TiO 2₂Particles are dispersed in a matrix, the TiO₂ Can also be part of the matrix. The layer can also be made of TiO₂ consist. The matrix may generally be formed from inorganic or from organic-modified inorganic matrix materials. Accordingly, the composition may also contain inorganic or organic-modified inorganic matrix-forming materials as discussed above. The above-mentioned nanoscale particles can also be present. The composition can however also only TiO₂Particles, so that a photocatalytic layer is composed only of TiO.sub.2₂ Is formed.

p0098It has been found that the layer made of the hybrid material is converted into a purely inorganic system by photocatalytic oxidation of the organic portion, at least at the interface to the photocatalytic layer. The photocatalytically active layer is photocatalytically oxidized by the organic components of the underlying hybrid layer. This process is often limited to a few nanometers of the top layer of this layer, since the diffusion of holes and electrons is very short. By the conversion of the uppermost layer of the hybrid layer to an inorganic layer, the destruction process is stopped and an effective barrier layer is obtained, Which prevents diffusion of sodium ions from glass substrates into the photocatalytic layer and protects sensitive plastic substrates against damage by the photocatalytic layer. In addition, the organic groups of the surface-modified TiO₂ Photocatalyst.

p0099In all the described three embodiments, a further increase in the photocatalytic effect can be achieved if an electrically conductive support is used under the photocatalytic layer and / or special electrically conductive particles are added to the photocatalytic layer.

p0100The doped metal oxides used as electrically conductive particles can be, for example, doped tin oxide, such as ITO (indium tin oxide), ATO (antimony doped tin oxide) and FTO (fluorine doped tin oxide), and / or aluminum doped zinc oxide. An electrically conductive polymer such as BAYTRON can also be used by Bayer AG. Suitable semiconductors are, for example, doped germanium or silicon. The electrically conductive particles can, for example, be added as a powder or in the form of a dispersion in a solvent to the dispersion for the photocatalytic layer.

p0101Transparent conductive particles are preferably used. As a result, high light absorption, as is caused, for example, by conductive metal particles, is avoided and more effective photocatalytic layers are obtained.

p0102Alternatively or at the same time, an electrically conductive underlayer can also be provided as a layer under the photocatalytically active layer. The electrically conductive support may be a metal, a semiconductor, an electrically conductive polymer or a doped metal oxide. Examples of the doped metal oxide, the semiconductor or the electrically conductive polymer are the same as mentioned above as examples of the electrically conductive particles. Examples of the metal, which may also be a metal alloy, are steel, including stainless steel, chromium, copper, titanium, tin, zinc, brass and aluminum.

p0103The substrate may be present as a layer on the substrate or the substrate itself. For the application of an electrically conductive layer as a support on a substrate, the methods familiar to a person skilled in the art can be used, for example nasememic processes, deposition processes (sputtering) or metallization. In general, thin layers are sufficient.

p0104In all the embodiments described, the substrates can be fired with the photocatalytic layers in order to arrive at purely inorganic layers. Moreover, particles with a larger diameter, for example in the μm range, can also be incorporated in all layers.

p0105The substrates according to the invention with the photocatalytic layers can, for example, be used as self-cleaning surfaces (optionally supported by irradiation with light) or for air purification.

p0106The layers are also suitable as anti-fogging layers, for example on glass, mirrors, cladding or partitions. Furthermore, magnetic, for example superparamagnetic, particles can be coated.

p0107A particular field of application is the sterilization or protection of all types of instruments, in particular medical, including veterinary and dental appliances and sanitary equipment, against contamination, eg by infectious substances such as prions (eg for BSE control). Important fields of application are food technology and dairy farming.

Examples

p0108The following abbreviations are used:<dl id="dl0001" compact="compact"><dt>TEOS:</dt><dd>Tetraethoxysilane</dd><dt>FTS:</dt><dd>(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl) triethoxysilane</dd><dt>GPTS:</dt><dd>(3-glycidyloxypropyl) trimethoxysilane</dd><dt>HDTMS:</dt><dd>Hexadecyltrimethoxysilane</dd></dl>

example 1

Hydrothermal production of TiO

<u>2</u>

(Anatase)

p01099.6 g (0.034 mol) of titanium isopropoxide (Ti (O.^IPr)₄) Are added to 14.5 g of n-propanol and 0.67 g (0.0068 mol) of 37% HCl are added after stirring at room temperature for 5 min. After 20 minutes, 0.712 g (0.063 mol) of water are added with intensive stirring.

p0110The mixture is then diluted with 41.9 g of n-propanol, followed by treating at 250 ° C. under a pressure of 200 bar for 7 h. The resulting anatase is centrifuged off and dried at 50 ° C. and 10 mbar.

Example 2

Hydrothermal preparation of doped TiO

<u>2</u>

(Anatase, dopant Sn (CH

<u>3</u>

CO

<u>2</u>

) "

<u>4</u>

) "

p01119.6 g (0.034 mol) of titanium isopropoxide (Ti (O.^IPr)₄) Are added to 14.5 g of n-propanol and 0.67 g (0.0068 mol) of 37% HCl are added after stirring at room temperature for 5 min. After 20 minutes, 0.712 g (0.063 mol) of water are added with intensive stirring.

p0112The mixture is then diluted with 41.9 g of n-propanol, and the mixture is treated with 0.635 g (0.0018 mol) of Sn (CH₃CO₂) "₄ And treated at 250 ° C. and 200 bar pressure for 7 hours. The resulting anatase is centrifuged off and dried at 50 ° C. and 10 mbar.

Example 3

Hydrothermal preparation of doped TiO

<u>2</u>

(Anatase, dopant WO

<u>3</u>

) "

p01139.6 g (0.034 mol) of titanium isopropoxide (Ti (O.^IPr)₄) Are added to 14.5 g of n-propanol and 0.67 g (0.0068 mol) of 37% HCl are added after 5 minutes of stirring at room temperature. After 20 minutes, 0.712 g (0.063 mol) of water are added with intensive stirring.

p0114The mixture is then diluted with 41.9 g of n-propanol, whereupon the mixture is mixed with 0.039 g (0.00017 mol) of WO₃ And treated at 250 ° C. and 200 bar pressure for 7 hours. The resulting anatase is centrifuged off and dried at 50 ° C. and 10 mbar.

Example 4

Surface modification of TiO

<u>2</u>

(Anatase) powder with FTS

p0115Of the TiO produced according to Examples 1 to 3₂1.0 g each are stirred with 8.67 g of toluene and then admixed with 0.077 g of FTS. After stirring for 2 hours, the toluene is separated off in a rotary evaporator.

<u>Example 5</u>

Surface modification of TiO

<u>2</u>

(Anatase) powder with HDTMS

p0116Of the TiO produced according to Examples 1 to 3₂1.0 g each are stirred with 8.67 g of toluene and 0.312 g of HDTMS are then added. After stirring for 2 hours, the toluene is separated off in a rotary evaporator.

Example 6

Preparation of a photocatalytic layer with undoped TiO 2

<u>2</u>

p0117To prepare a GPTS hydrolyzate, 5.4 g (0.3 mol) of water are added to 23.6 g (0.1 mol) of GPTS. The mixture is then stirred overnight at room temperature.

p01180.05 g of the FTS-modified undoped TiO 2 prepared according to Example 4₂Powders are dispersed in 1.56 g of MEK (methyl ethyl ketone) and 0.44 g of formamide are then added. The resulting dispersion is mixed with stirring with 4.14 g of the GPTS hydrolyzate prepared.

p0119The resulting coating composition is applied to polycarbonate plates (PC plates) of 10 cm × 10 cm by means of a spincoater at 1000 rpm. The plates are then cured at 128 ° C. for 1 h. The layer thicknesses are from 2 to 3 μm. The contact angle of the resulting layers against water is 101 °.

p0120The coated PC plates are irradiated with a xenon lamp (750 W) for 4 min. After irradiation, the contact angle of the PC plates against water was only 10 °.

p0121To determine the photocatalytic activity of the obtained PC plates, the change in the light absorption at 553 nm over time is determined by a Rhodamine B solution. For this purpose, 20 ml of an aqueous Rhodamine B solution (concentration 6 ppm) are brought into contact with the PC plate, which is irradiated with a xenon lamp (750 W). The absorption of the rhodamine B solution at 553 nm is measured at intervals to monitor the degradation of rhodamine B. After about an hour the whole Rhodamin B is broken down.

Example 7

Preparation of a photocatalytic layer with Sn-doped TiO

<u>2</u>

p01220.05 g of the HDTMS-modified Sn-doped TiO produced according to Example 5₂Powders are dispersed in 1.56 g of petroleum ether and 0.44 g of formamide are then added. The resulting dispersion is mixed with 4.14 g of the GPTS hydrolyzate prepared as in Example 6.

p0123The resulting coating composition is applied to polycarbonate plates (PC plates) of 10 cm × 10 cm by means of a spincoater at 1000 rpm. The plates are then cured at 128 ° C. for 1 h. The layer thicknesses are from 2 to 3 μm. The contact angle of the resulting layers against water is 92 °.

p0124The coated PC plates are irradiated with a xenon lamp (750 W) for 4 min. After irradiation, the contact angle of the PC plates against water was less than 10 °.

p0125The photocatalytic activity of the obtained PC plates is determined by a rhodamine B solution by the same experimental setup as in Example 6 by determining the light absorption at 553 nm. The entire Rhodamine B is degraded after about 35 min.

Example 8

Preparation of photocatalytic layers with TEOS hydrolyzate

p0126To prepare a TEOS hydrolyzate, 12.36 g (0.0594 mol) of TEOS in 15.96 g of ethanol are treated with 9.06 g of water. 0.2 g of concentrated (37%) HCl is then added with stirring. After stirring for 1 h, 0.28 g of GPTS are added and the mixture is stirred at room temperature overnight. A TEOS hydrolyzate containing 2 mol% of GPTS is obtained.

p0127Of the FTS-modified TiO 2 prepared in Example 4₂(Undoped, doped with Sn and doped with W), a 2.5% by weight solution in methyl ethyl ketone is prepared, and 0.2 g of the TEOS hydrolyzate produced, which contains 2 mol% of GPTS (molar ratio Ti: Si = 10: 5).

p0128The resulting coating composition is applied to polycarbonate plates (PC plates) of 10 cm × 10 cm by means of a spin coating device. The plates are then cured at 128 ° C. for 1 h.

Example 9

Determination of the photocatalytic activity of layers with doped TiO

<u>2</u>

p0129To determine the photocatalytic activity, layers are coated with doped TiO 2₂ Investigated. For this purpose, Sn-doped TiO₂(Sn (IV)), W-doped TiO₂(W (VI)), Fe-doped TiO₂(Fe (III)) and In-doped TiO₂(In (III)) in different ratios of Ti to doping metal.

p0130The Sn- and W-doped TiO₂Powders are prepared according to Examples 2 and 3 with Sn (CH₃CO₂) "₄ and where₃ , The amounts of inputs being varied according to the desired ratio Ti to doping agent (0.5 to 10 mol% dopant). In a similar manner, doped TiO 2₂Powder with FeCl₃ and in₂O₃ manufactured. For comparative purposes, unmodified anatase is also prepared under the same conditions.

p0131Of the doped TiOO produced₂A 2.5% by weight solution is prepared in methyl ethyl ketone and mixed with 0.2 g of TEOS hydrolyzate prepared as in Example 8, which contains 2 mol% of GPTS.

p0132The resulting coating composition is applied to polycarbonate plates (PC plates) by means of a spin coating apparatus. The plates are cured at 128 ° C. for 1 h.

p0133The photocatalytic activity is repeated with a Rhodamine B solution (6 ppm in H₂O). The coated plates are in each case contacted with 20 ml of the Rhodamine B solution and then irradiated with UV light for 10 min. The absorption of the Rhodamine B solution is then measured at 553 nm. For comparison, measurements on rhodamine B are also carried out in the same manner without contact with photocatalytic layers and in contact with undoped anatase. The results are shown in the table below. From this it is evident that the doping can be achieved in part by much more rapid degradation rates.<tables id="tabl0001" num="0001"><table frame="all"><title>Table: Absorption at 553 nm after 10 min UV irradiation</title><tgroup cols="5"><colspec colnum="1" colname="col1" colwidth="26mm" /><colspec colnum="2" colname="col2" colwidth="18mm" /><colspec colnum="3" colname="col3" colwidth="18mm" /><colspec colnum="4" colname="col4" colwidth="18mm" /><colspec colnum="5" colname="col5" colwidth="18mm" /><thead><row><entry align="center" valign="top" /><entry namest="col2" nameend="col5" align="center" valign="top">Dopants</entry></row><row><entry align="center" valign="top">Amount (mole%)</entry><entry align="center" valign="top">Fe (III)</entry><entry align="center" valign="top">W (VI)</entry><entry align="center" valign="top">Sn (IV)</entry><entry align="center" valign="top">In (III)</entry></row></thead><tbody><row><entry align="center">As shown in Fig.</entry><entry align="center">1.46</entry><entry align="center">1.42</entry><entry align="center">1.08</entry><entry align="center">1.07</entry></row><row><entry align="center">0 **</entry><entry align="center">0.24</entry><entry align="center">0.31</entry><entry align="center">0.125</entry><entry align="center">0.12</entry></row><row><entry align="center">0.5</entry><entry align="center">0.31</entry><entry align="center">0.04</entry><entry align="center">0.065</entry><entry align="center">0.009</entry></row><row><entry align="center">1.0</entry><entry align="center">0.46</entry><entry align="center">0.03</entry><entry align="center">0.103</entry><entry align="center">-0.043</entry></row><row><entry align="center">5</entry><entry align="center">0.27</entry><entry align="center">0.284</entry><entry align="center">-0.06</entry><entry align="center">0.023</entry></row><row><entry align="center">10</entry><entry align="center">0.084</entry><entry align="center">0.20</entry><entry align="center">-0.08</entry><entry align="center">0.084</entry></row></tbody></tgroup><tgroup cols="5" rowsep="0"><colspec colnum="1" colname="col1" colwidth="26mm" /><colspec colnum="2" colname="col2" colwidth="18mm" /><colspec colnum="3" colname="col3" colwidth="18mm" /><colspec colnum="4" colname="col4" colwidth="18mm" /><colspec colnum="5" colname="col5" colwidth="18mm" /><tbody><row><entry namest="col1" nameend="col5" align="justify">* Measurement without photocatalytic layer ** undoped anatase</entry></row></tbody></tgroup></table></tables>

Example 10

TiO

<u>2</u>

(Anatase) production under reflux

p0134To 29.02 g of 1-pentanol, 19.2 g (0.068 mol) of titanium isopropoxide (Ti (O.^IPr)₄), And after 5 min. Stirring at room temperature with 1.33 g (0.0136 mol) of 37% HCl. After 20 min, 1.42 g (0.079 mol) of water are added rapidly with intensive stirring and stirring is continued for 20 min at room temperature. The mixture is then refluxed at 132 ° C. for 16 h. The resulting anatase is centrifuged off and dried at 50 ° C. and 10 mbar.

Surface modification of reflux TiO

<u>2</u>

(Anatase) powder with TODS

p0135Of the TiO obtained above₂1 g is stirred with 4 g of water and 0.2 g of TODS (trioxadecanoic acid) is then added. After 10 min. Ultrasonic treatment, a transparent solution is obtained.

Dispersing of reflux TiO

<u>2</u>

(Anatase) powder with toluene

p0136Of the TiO obtained above₂1 gram each is stirred with 1.5 g of toluene. After 1 min. Ultrasonic treatment, a transparent solution is obtained.