WO2011000857A1

WO2011000857A1 - CO-CATALYST IN TiO2 FILMS

Info

Publication number: WO2011000857A1
Application number: PCT/EP2010/059256
Authority: WO
Inventors: Alexandra Seeber; Götz-Peter SCHINDLER; Florina Corina Patcas; Günter Heinz Bruno KREISEL; Susan Schaefer; Sarah Anna Saborowski; Doreen Keil
Original assignee: Basf Se
Priority date: 2009-07-01
Filing date: 2010-06-30
Publication date: 2011-01-06

Abstract

The invention relates to a photocatalyst which contains at least one metal selected from groups 3 to 12 of the periodic system of elements (according to IUPAC), lanthanoids, actinoids and mixtures thereof, the flatband voltage of the photocatalyst being increased by at least 0.05 eV compared to the photocatalyst without said at least one metal. The invention also relates to a method for increasing the flatband voltage of a photocatalyst, said photocatalyst being loaded with at least one metal selected from groups 3 to 12 of the periodic system of elements (according to IUPAC), lanthanoids, actinoids and mixtures thereof, to the use of at least one metal selected from groups 3 to 12 of the periodic system of elements (according to IUPAC), lanthanoids, actinoids and mixtures thereof for increasing the flatband voltage of a photocatalyst, and to the use of the photocatalyst according to the invention in chemical reactions.

Description

Co-catalysts in TiC> ₂ films The present invention relates to a photocatalyst comprising at least one metal selected from groups 3 to 12 of the Periodic Table of the Elements (according to IUPAC), lanthanides, actinides and mixtures thereof, wherein the ribbon potential of the photocatalyst to at least 0.05 eV compared to the photocatalyst without this at least one metal is increased, a method for increasing the flat-band potential of a photocatalyst, wherein the photocatalyst with at least one metal selected from groups 3 to 12 of the Periodic Table of the Elements (according to IUPAC), Lanthanides, actinides and mixtures thereof, the use of at least one metal selected from Groups 3 to 12 of the Periodic Table of the Elements (according to IUPAC), lanthanides, actinides and mixtures thereof to increase the ribbon potential of a photocatalyst, and the use of the photocatalyst according to the invention i n chemical reactions.

Photocatalysts comprising at least one photocatalytically active material and processes for their preparation are already known from the prior art.

DE 198 41 650 A1 discloses a process for the preparation of nanocrystalline metal oxide and mixed metal oxide layers on barrier layer-forming metals, in which the coating by anodization with spark discharge in an electrolyte, which at least one or more complexing agents, preferably chelating preferably with functional group N-CH ₂ -COOH, one or more metal alkoxides and at least one alcohol, preferably secondary or tertiary alcohols. According to DE 198 41 650 A1, by a suitable choice of the concentration ranges of the electrolytic bath components, as well as by the adjustable parameters of the anodization process, predetermined layer properties, in particular with regard to adhesive strength, semiconductor effect, surface condition, photo and electrochromism, as well as with regard to catalytic activity, individually or in their combination. This document further discloses that the properties of the photocatalytically active layers obtained can additionally be influenced by adding further components, such as iron or ruthenium ions, electrically neutral microparticles or nanoparticles, etc., to the electrolyte of the anodization in order to obtain them to insert the photocatalytically active layer.

DE 10 2005 043 865 A1 relates to a further development of the method according to the already cited DE 198 41 650 A1. In order to further increase the photocatalytic activity of the layers obtained, according to DE 10 2005 043 865 A1, the electrolyte in which the anodization of the substrate is carried out, for example gadolinium (III) acetylacetonate hydrate and / or cerium (III) acetylacetonate hydrate in a concentration of less than 0.01 mol / l and optionally further components are added. DE 10 2005 050 075 A1 discloses a method for depositing metals, preferably noble metals, on adherent metal oxide and mixed metal oxide layers. For this purpose, a corresponding substrate is first provided with a metal oxide or a mixed metal oxide layer. The metal cations present in this oxide layer are then reduced in value by an electrochemical treatment, for example titanium ^{4+ is} reduced to titanium ³⁺ . The substrate thus treated, which has an oxide layer in which metal cations are present in reduced form, is subsequently treated with a preferably aqueous solution in which preferably noble metals are present in oxidized form. Due to the reduction potentials of the noble metal cations or of the metal cations present in the oxide layer, deposition of the metals from the aqueous solution on the oxide layer takes place in elementary form, while simultaneously reducing the reduced metal cations present in the oxide layer to their original oxidized form, ie titanium ³⁺ to titanium ⁴⁺ . The amount of elemental metal present on or within the oxide layer after performing this process can be adjusted by the extent to which the metal cations that are reduced in the oxide layer by the electrochemical treatment at the beginning of the process.

M. Ashokkumar et al., Int. J. Hydrogen Energy, Vol. 6, pages 427-438, 1998 disclose semiconducting particulate systems for the photocatalytic production of hydrogen. Accordingly, catalysts suitable for the reduction of water to hydrogen should have a conduction band which is above the hydrogen reduction level and have a valence band which is below the water oxidation level. Furthermore, this document discloses that a number of factors contribute to the catalytic activity of these catalysts, for example surface and / or production method, for example by thermal or photochemical coating. For photocatalysts based on TiO ₂ , an excitation wavelength of less than 400 nm is specified, wherein the addition of doping elements, in particular transition metal elements, contributes to the absorption in the visible range, and thus also the activity of the catalyst in this region of the light , is increased. The fact that the position of the ribbon potential of the photocatalyst can be influenced by metal loading with special metals is not disclosed in the abovementioned document.

The photocatalysts known from the prior art have activities when used in photocatalyzed reactions, for example in the production of water. Hydrogen from water and / or alcohols, which are still to be improved. There is also a need for photocatalysts that are useful not only for the reduction of protons to molecular hydrogen but also for other chemical reactions.

These objects are achieved by the photocatalyst according to the invention containing at least one metal selected from groups 3 to 12 of the Periodic Table of the Elements (according to IUPAC), lanthanides, actinides and mixtures thereof, wherein the ribbon potential of the photocatalyst at least 0.05 eV compared to the photocatalyst without this at least one metal is increased, solved.

The objects are further achieved by a method for increasing the ribbon potential of a photocatalyst, wherein the photocatalyst is loaded with at least one metal selected from Groups 3 to 12 of the Periodic Table of the Elements (according to IUPAC), lanthanides, actinides and mixtures thereof the use of at least one metal selected from groups 3 to 12 of the Periodic Table of the Elements (according to IUPAC), lanthanides, actinides and mixtures thereof for increasing the ribbon potential of a photocatalyst, and by the use of the photocatalyst according to the invention in chemical reactions.

The process according to the invention relates to a photocatalyst comprising at least one metal selected from groups 3 to 12 of the Periodic Table of the Elements (according to IUPAC), lanthanides, actinides and mixtures thereof, wherein the ribbon potential of the photocatalyst is at least 0.05 eV compared to the photocatalyst without this at least one metal is increased. The metal loading of the photocatalyst of the present invention causes the ribbon potential of the photocatalyst to be increased by at least 0.05 eV from the flat-band potential of the corresponding photocatalyst without metal loading.

In a preferred embodiment of the photocatalyst according to the invention, the flat band potential is increased by at least 0.1 eV, compared to the flat band potential of the corresponding photocatalyst without metal loading. In general, an energy band of a photocatalyst is understood to mean an energy range in which there are many energetically dense quantum-physically possible states. In absolute zero, the so-called conduction band is the lowest unoccupied or partially occupied band, and the valence band is the highest fully occupied band. Between these energy bands lies a so-called forbidden area, the so-called band gap. Under the Ribbon potential is the potential at which there is no excess charge and as a result the bands are not bent. For an n-type semiconductor, the Fermi level (level at which the probability of electron residence = Vi) is just below the conduction band. It can be assumed approximately with an n-type semiconductor that the flat-band potential corresponds to the lower edge of the conduction band. Methods for determining the flat band potential are, for example, the capacitance measurement, in particular the evaluation of the Mott-Schottky plot, or the suspension method which was first published in 1983 by Bard et al. M- D. Ward, JR White, AJ Bard; Journal of American Chemical Society 105 (1983) 27-31 and later published in 1994 by Roy et al., AM Roy, GC De, N. Sasmal, SS Bhattacharyy; International Journal of Hydrogen Energy 20 (1994) 627-630, in which the photovoltage is determined as a function of the pH value with the aid of an electron acceptor. Photocatalysts which contain titanium dioxide and at least one metal as metal loading are generally already known from the prior art. The metal loadings reduce the electron-hole pair recombination and thus improve the activity of the catalysts. Furube et al., A. Furube, T. Asahi, H. Masuhara, H. Yasmitha, M. Anpo Chemical Physics Letters 336 (2001) 424-430 indicate that metals with a higher work function than those of the semiconductor (the Fermi level of these metals is lower than that of the semiconductor) a Schottky barrier is formed, which suppresses the electron-hole pair recombination. A depletion zone occurs in the semiconductor and the energy bands are bent to lower energies. At the metal-semiconductor boundary layer, a so-called Schottky barrier is formed, which is highest with Pt as the loading metal. In these prior art catalysts, however, the ribbon potential is not increased by the metal loading.

The reduction of water catalyzed by a semiconductor takes place only when the conduction band of the semiconductor already without metal loading is above the potential necessary for the reduction of 2 H ⁺ to H ₂ , ie at pH = 7 above -0.41 V. The valence band must below the energy level of the oxidation of 2 H ₂ O to O ₂ , ie below 1, 23 V. However, the photocatalysts known from the prior art can not catalyze photochemical reactions which require a higher energy than the reduction of protons to hydrogen, since the energy defined by the band gap between the conduction and valence bands is insufficient. Since in the photocatalyst according to the invention, the flat band potential is increased and the band gap between see line and valence band remains constant at the same time, which diffuse Reflection can be found, thus the valence band is shifted. Therefore, the catalysts according to the invention can also catalyze chemical reactions which require increased energy. This is not possible by the photocatalysts known from the prior art.

In a preferred embodiment, the photocatalyst according to the invention is present on a substrate.

In general, all substrates are suitable for the photocatalyst according to the invention, which with at least one photocatalytically active metal oxide, d. H. a photocatalyst, can be coated. In a preferred embodiment of the photocatalyst according to the invention, the substrate is selected from the group consisting of metals, semiconductors, glass substrates, ceramic substrates, Cellulosefa- fibers and plastic substrates, preferably electrically conductive plastic substrates, and mixtures or alloys thereof. The substrate is particularly preferably a metal selected from the group consisting of titanium, aluminum, zirconium, tantalum, further barrier layer-forming materials and mixtures or alloys thereof.

In a particularly preferred embodiment, the substrate of the photocatalyst according to the invention is a sheet-shaped metal, for example a metal sheet or a metal mesh. According to the invention, the substrate can have all possible shapes and surface textures. According to the invention, the substrates can be planar, curved, for example convex or concave, symmetrical or asymmetrical in shape. The surface of the substrate used can be smooth and / or porous.

The present invention preferably present substrate may have all known to the expert dimensions that are sufficiently current-conducting. With regard to the width, thickness and length of the present invention substrates, there are no general restrictions, for example, rectangular or square shaped substrates with edge lengths of 0.5 to 100 mm, in particular 5 to 50 mm used. Very particular preference is given to using rectangular metal substrates with the dimensions 5 to 10 mm × 60 to 100 mm. The photocatalyst according to the invention preferably contains titanium dioxide as the photoactive substance. In a particularly preferred embodiment, the photocatalyst according to the invention is titanium dioxide. The present titanium dioxide may be in the anatase or rutile modification or a mixture thereof, or may be partially in the amorphous state. The photocatalyst according to the invention is preferably present on the substrate as a layer. The thickness of this layer is generally not limited. For example, the layer of titanium dioxide has a layer thickness of 1 to 200 μm, preferably 5 to 150 μm, particularly preferably 10 to 80 μm. Methods for determining the layer thickness are known to the person skilled in the art, for example according to the eddy current method (DIN EN ISO 2360, DIN 50984) with the layer thickness measuring device Surfix® (from Phynix).

The layer present on the substrate generally has a BET specific surface area of from 10 to 200 m ² / g, preferably from 20 to 100 m ² / g, particularly preferably from 30 to 80 m ² / g. Methods for determining the specific layer thickness are known to the person skilled in the art, for example according to Brunauer-Emmett-Teller (BET) from the N ₂ adsorption isotherm (DIN 66131). The average pore size of the present photocatalyst, in particular titanium dioxide, is generally 0.1 to 20 nm, preferably 1 to 15 nm, more preferably 2.5 to 10 nm. Methods for determining the pore size are known to the person skilled in the art, for example the BJH method , The photocatalyst according to the invention contains at least one metal as metal loading selected from groups 3 to 12 of the Periodic Table of the Elements (according to IUPAC), lanthanides, actinides and mixtures thereof, preferably from the group consisting of V, Zr, Ce, Zn, Au, Ag, Cu, Pd, Pt, Ru, Rh, La and mixtures thereof, most preferably Pd, Cu or Pt or mixtures thereof.

The at least one metal present on the photocatalyst according to the invention may be in elemental form or as a compound, preferably as an oxide. The preferred present palladium or platinum is preferably present in elemental form. The copper present in a further preferred embodiment is preferably in oxidic form (Cu ₂ O or CuO).

The at least one metal is present on the photocatalyst according to the invention in an amount which is sufficient to increase the ribbon potential of the photocatalyst according to the invention by at least 0.05 eV. Preferably, the at least one metal in an amount of 0.001 to 5 wt .-%, more preferably 0.01 to 3 wt%, most preferably 0.1 to 1, 5 wt .-%, each based on the total Photocatalyst, before.

In principle, the photocatalyst according to the invention can be prepared by methods known to those skilled in the art. In a particularly preferred embodiment, the photocatalyst according to the invention is prepared by the following process, comprising at least the steps (A) and (B):

(A) electrochemically treating the at least one substrate in an electrolyte containing at least one precursor compound of the photocatalyst to obtain a photocatalyst-coated substrate; and (B) treating the photocatalyst-coated substrate in another electrolyte containing at least one precursor compound of the at least one metal; to obtain the photocatalyst of the present invention.

The individual steps of the method according to the invention are described in detail below:

Step (A):

Step (A) of the method of the invention comprises electrochemically treating the at least one substrate in an electrolyte containing at least one precursor compound of the photocatalyst to obtain a photocatalyst-coated substrate.

In principle, step (A) of the process according to the invention is carried out in accordance with the process described in DE 198 41 650 A1. The disclosure of DE 198 41 650 A1 is therefore fully part of this invention.

In a preferred embodiment, the electrochemical treatment in step (A) is anodization, more preferably an anodization with spark discharge. For this purpose, at least one substrate is generally introduced into a corresponding electrolyte and subjected to an electrochemical treatment.

The electrolyte used in step (A) generally contains the components necessary to form a layer of photocatalyst. In a preferred embodiment, an aqueous electrolyte is used in step (A) of the process according to the invention, i. H. the solvent used is water.

In a preferred embodiment, the, preferably aqueous, electrolyte according to step (A) contains one or more of the following components selected from the group consisting of complexing agents, alcohols and mixtures thereof. Preferred complexing agents are N-chelating agents having at least one -NR'-CH ₂ -COOH radical with R '= H, alkyl or aryl, for example selected from the group consisting of ethylenediaminetetraacetate-di-sodium salt (EDTA-Na ₂ ), nitrilotriacetate tri Sodium salt (NTA-Na _ß ) and mixtures thereof. In the electrolyte used in step (A) of the process according to the invention, at least one complexing agent is present, for example, in a concentration of 0.01 to 5 mol / l, preferably 0.05 to 2 mol / l, particularly preferably 0.075 to 0.125 mol / l , The preferably aqueous electrolyte used in step (A) of the process according to the invention preferably contains at least one alcohol, for example in a concentration of 0.01 to 5 mol / l, preferably 0.02 to 2 mol / l, particularly preferably 0.55 to 0.75 mol / l, before. The electrolyte used in step (A) of the process according to the invention preferably contains at least one alcohol, preferably secondary or tertiary alcohols, for example isopropanol, or mixtures thereof, for example in a concentration of 0.01 to 5 mol / l, preferably 0.02 to 2 mol / l, more preferably 0.55 to 0.75 mol / l, before.

As a precursor compound for the photocatalyst, in particular titanium dioxide, in the electrolyte in step (A) of the process according to the invention preferably at least one metal alkoxide, in particular at least one titanium alkoxide is used, for example tetraethylortho complexes, in particular tetraethyl orthotitanate. or mixtures thereof.

The at least one precursor compound of the photocatalyst is generally present in a concentration which permits advantageous performance of step (A), preferably in a concentration of 0.01 to 5 mol / l, preferably 0.02 to 1 mol / l, for example 0.04 to 0.1 mol / l.

Furthermore, the electrolyte according to step (A) may contain further additives known to the person skilled in the art, for example buffer substances, preferably salts selected from the group consisting of ammonium hydroxide, ammonium acetate and mixtures thereof. These are added, for example, in order to keep the pH of the electrolyte in a corresponding range during the process. The optionally present pH buffer substances are present in the amounts in which they give the corresponding desired pH, preferably these compounds are present in concentrations of 0.001 to 0.1 mol / l, more preferably 0.005 to 0.008 mol / l. In a further preferred embodiment, in addition to water, other solvents may also be present in the electrolyte, for example ketones, such as acetone. These additional solvents are preferably present in an amount of from 0.01 to 2 mol / l, preferably from 0.2 to 0.8 mol / l, more preferably from 0.3 to 0.7 mol / l.

The electrochemical treatment by anodization with spark discharge is known in the art in principle. The following are the preferred process parameters of step (A) of the process according to the invention.

In step (A) of the method according to the invention, the duty cycle (tstrom / tstroms) vt is generally 0.1 to 1.0, preferably 0.3 to 0.7. The frequency f is generally 1.0 to 2.0 kHz, preferably 1.2 to 1.8 kHz. The voltage feed dU / dt in step (A) of the process according to the invention is generally 10 to 100 V / s, preferably 10 to 50 V / s, particularly preferably 10 to 30 V / s. Step (A) is generally carried out at a voltage of 10 to 500 V, preferably 100 to 450 V, more preferably 150 to 400 V. The coating time in step (A) of the process according to the invention depends on the substrate size and is for example 10 to 500 s, preferably 50 to 200 s, particularly preferably 75 to 150 s. In step (A) of the process according to the invention, the current intensity I is generally 0.5 to 100 A, preferably 1 to 50 A, particularly preferably 2 to 25 A.

The amount of photocatalyst deposited in step (A) of the process according to the invention depends on the production parameters set and is, for example, 1 to 50 mg / cm ² . The layer of, for example, titanium dioxide produced in step (A) generally has the properties described above. Further details can be found in DE 198 41 650 A1.

In a preferred embodiment of the method according to the invention, the substrate is degreased before step (A). Processes for this purpose are known to the person skilled in the art, for example the substrate can be treated with an aqueous solution comprising at least one surface-active substance, optionally with simultaneous heating and / or action of ultrasound. After treating with such an aqueous solution, the degreased substrate may be rinsed with a suitable solvent, preferably water, prior to the electrochemical treatment step (A).

After step (A) of the process according to the invention, a substrate coated with photocatalyst, in particular titanium dioxide, is obtained. This can be used according to the invention directly in step (B). It is also possible according to the invention that the substrate after step (A) with a suitable solvent, preferably water, rinsed off. Furthermore, it is possible and preferable to treat the coated substrate obtained after step (A) thermally, for example at a temperature of 100 to 600 ^° C., preferably 200 to 500 ^° C., more preferably 300 to 450 ^° C. The thermal treatment of the coated substrate is generally carried out for a sufficiently long time, for example 0.1 to 5 hours, preferably 0.5 to 3 hours. The thermal treatment can be carried out at constant or increasing temperature. An increasing temperature is realized according to the invention, for example, with a heating rate of 15 to 30 ° C / min.

Step (B):

Step (B) of the process comprises treating the photocatalyst-coated substrate in another electrolyte containing at least one precursor compound of the at least one metal to obtain the photocatalyst of the present invention.

In general, according to step (B) of the process, the further electrolyte contains all components which are necessary in order to apply the at least one metal as metal loading in accordance with step (B) of the process according to the invention to the photocatalyst-coated substrate.

Suitable metals are mentioned above. Suitable precursor compounds for these metals are generally all compounds which can be converted into the corresponding metals under the conditions present in step (B) of the process according to the invention. Examples of suitable precursor compounds for the at least one metal are salts and / or complex compounds of the abovementioned preferred metals. Examples of particularly suitable salts are salts of organic mono- or dicarboxylic acids, in particular alcoholates, formates, acetates, propionates and oxalates or mixtures thereof. Also suitable are halides, for example fluorides, chlorides, bromides, nitrates and sulfates or mixtures thereof. Particular preference is given to using as the precursor compounds for the at least one metal in step (B) acetates or halides, especially chlorides. This at least one precursor compound is generally present in the electrolyte according to step (B) of the process according to the invention in a concentration of 0.1 to 20 mmol / L, preferably 0.5 to 1 mmol / L.

In step (B), an aqueous electrolyte is preferably used, ie the solvent used for the electrolyte according to step (B) is water. In addition to the at least one precursor compound of the at least one metal are in the electrolyte in accordance with step (B), if appropriate, further additives known to the person skilled in the art. For example, the precursor compounds present in the electrolyte according to step (B) are optionally stabilized by addition of an acid, for example HNO ₃ , for example in a concentration of 0.1 to 10% by volume.

The treatment according to step (B) of the process according to the invention can be carried out by all methods known to the person skilled in the art. In a preferred embodiment, the treatment in step (B), d. H. the metal loading, by photochemical deposition of the at least one metal on the photocatalyst, in particular by irradiation with light (photochemical treatment).

In the context of the present invention, light is understood as meaning high-energy electromagnetic radiation, in particular light in a wavelength range either between 200 and 400 nm ("UV light") or between 400 and 700 nm ("visible light"). According to the invention, the light preferably used in step (B) is produced by corresponding daylight or UV lamps, for example Xe (Hg) arc lamp, diode arrays, tube lamps and combinations thereof. It is also possible according to the invention to use other high-energy electromagnetic radiation which, in addition to the preferred wavelengths, also has other wavelengths. The light intensity, in particular of the UV radiation, in step (B) is generally 0.1 to 30 mW / cm ² , preferably 0.5 to 10 mW / cm ² , particularly preferably 2 to 5 mW / cm ² .

Step (B) of the process according to the invention is carried out, for example, by bringing the substrate obtained from step (A), which is coated with photocatalyst, into contact in a corresponding reactor with the electrolyte according to step (B). According to the invention, any reactor known to the person skilled in the art can be used as the reactor, for example a cuvette. In particular, a reactor is used which is permeable to the wavelength range of the light used.

The at least one light source is then placed at a suitable distance from the cuvette to irradiate the substrate in the electrolyte according to step (B) with light. The irradiation is carried out for a time sufficient to apply a sufficient amount of metal to the substrate, for example 1 to 200 minutes, preferably 1 to 30 minutes, most preferably 3 to 10 minutes.

In step (B), the at least one metal is deposited on the layer of photocatalyst present on the at least one substrate. Furthermore, the present invention also relates to a method for increasing the ribbon potential of a photocatalyst, wherein the photocatalyst with at least one metal selected from groups 3 to 12 of the Periodic Table of the Elements (according to IUPAC), lanthanides, actinides and mixtures thereof, preferably from the group consisting of V, Zr, Ce, Zn, Au, Ag, Cu, Pd, Pt, Ru, Rh, La and mixtures thereof, most preferably Pd, Cu or Pt or mixtures thereof, is loaded.

In a preferred embodiment, the metal loading takes place by photochemical deposition of the at least one metal on titanium dioxide.

In a further preferred embodiment of the method according to the invention, the flat band potential is increased by at least 0.05 eV, more preferably at least 0.1 eV, relative to the photocatalyst without metal loading.

In a particularly preferred embodiment, the method according to the invention for increasing the ribbon potential of a photocatalyst comprises at least the abovementioned steps (A) and (B). Therefore, what has been said about the production method of the photocatalyst of the present invention applies.

The present invention also relates to the use of at least one metal selected from groups 3 to 12 of the Periodic Table of the Elements (according to IUPAC), lanthanides, actinides and mixtures thereof, preferably from the group consisting of V, Zr, Ce, Zn, Au, Ag , Cu, Pd, Pt, Ru, Rh, La and mixtures thereof, very particularly preferably Pd, Cu or Pt or mixtures thereof for increasing the ribbon potential of a photocatalyst, in particular titanium dioxide. Details and preferred embodiments are already mentioned in the inventive method and apply accordingly for this use. Due to the increased ribbon potential, the photocatalyst according to the invention is suitable for catalyzing chemical reactions. Examples of corresponding reactions are, for example, the reduction of protons to molecular hydrogen in aqueous and / or alcoholic solutions, the reduction of CO or CO ₂ in hydrocarbon compounds such as methanol, formaldehyde or formic acid or the reduction of organic compounds such as methylene blue.

Therefore, the present invention also relates to the use of a photocatalyst according to the invention in chemical reactions, preferably in the reduction of protons to molecular hydrogen in aqueous and / or alcoholic solutions Reduction of CO or CO ₂ in hydrocarbon compounds such as methanol, formaldehyde or formic acid and the reduction of organic compounds such as methylene blue. The present invention will be further illustrated by the following examples. Examples

Example 1: Preparation of the photocatalyst

1 cm x 1 cm TiC> ₂ layers are produced on 3 cm x 1 cm titanium substrates. The electrochemical coating takes place in the aqueous electrolyte mentioned in Table 1 with the coating parameters listed in Table 2: TABLE I Composition of the electrolyte

Table 2: Coating parameters

After coating, the sample for 1 hour at 400 ⁰ C is annealed. The quantities of titanium dioxide are 2-3 mg per sample.

Example 2: Application of the Metals as Metal Loading by Photo Deposition Photo-deposition is a method to deposit metals on the Tiθ ₂ surface. As a result of the irradiation of light energy greater than the bandgap energy of the semiconductor, an electron-hole pair is produced on the semiconductor. The generated electron is used in photo- deposition to reduce metal cations from a precursor solution on the titanium dioxide surface.

The photocatalyst-coated substrates prepared in Example 1 are introduced together with 4 ml of a solution of the corresponding precursor compound into a glass cuvette (Hellma GmbH & Co. KG, layer thickness 13 mm, volume 1 ml). In this reaction vessel is advantageous that the light strikes a flat surface. The cuvette is made of glass B270 Superwite, whose transmission according to the manufacturer is more than 80% at wavelengths between 360 nm and 2500 nm. The light source is a 300 W Xe (Hg) lamp (company L. OT Oriel). The light intensity is set to 2.3 mW / cm ² over the distance to the lamp. After 10 minutes of irradiation, the layer is rinsed with distilled water.

Example 2.1

The precursor compound used is a 0.6 mM K ₂ PdCl ₄ solution with concentrated HNO ₃ for stabilization.

Example 2.2

As a precursor compound, a 0.6 mM K ₂ PtCl ₄ solution is used.

Example 2.3

The precursor solution used is a 0.6 mM HAuCl ₄ solution. Example 2.4

As a precursor compound, a 0.6 mM Cu (OOCCH ₃ ) ₂ solution is used.

Example 3 Determination of the Mott-Schottky Flatband Potential

When determining the Mott-Schottky flat-band potential, capacitance measurements are evaluated using the Mott-Schottky equation. For these measurements, the materials of Examples 1 and 2.1 to 2.4 are operated as a working electrode. Further components of the experimental set-up are a Pt counterelectrode and an Ag / AgCl reference electrode (3M KCl). The electrolyte is 40 mL of 1 M KCl Solution used in a 100 ml beaker. The electrodes are immersed in the electrolyte. The working electrode is immersed only with the TiO ₂ -coated third.

For the determination of the Mott-Schottky flat-band potential, the capacitance is determined by means of electrochemical impedance spectroscopy at an electrochemical level with PGSTAT20 (potentiostat / galvanostat) from Autolab® (eco chemie). The measurements can be converted directly into the Mott-Schottky plots using the software FRA (Frequency Response Analysis) Version 2.1.

FIG. 1 shows Mott-Schottky plots of the photocatalysts according to the invention according to Examples 2.1 to 2.4 and titanium dioxide without further metal according to Example 1. The measurement takes place at a frequency of 1000 Hz at a pH of 5.8. The layer thickness is 2.5 mg / cm ² TiO ₂ .

The flat-band potential can be calculated from V0 obtained by extrapolating the linear region from the abscissa section of the x-axis according to the following formula (I).

F - F - -

(I)

For the various catalysts, the flat band potentials listed in Table 3 are determined.

Table 3: According to Mott-Schottky flat band potentials EFb for TiO ₂ - photocatalyst without metal loading according to Example 1 and for photocatalysts according to the invention according to Examples 2.1 to 2.4.

Claims

claims

Photocatalyst comprising at least one metal selected from groups 3 to 12 of the Periodic Table of the Elements (according to IUPAC), lanthanides, Actinoids and mixtures thereof, characterized in that the ribbon potential of the photocatalyst to at least 0.05 eV compared to the photocatalyst without this at least one metal is increased.

2. Photocatalyst according to claim 1, characterized in that the photocatalyst is present on a substrate.

3. Photocatalyst according to claim 1 or 2, characterized in that the at least one metal is selected from the group consisting of V, Zr, Ce, Zn, Au, Ag, Cu, Pd, Pt, Ru, Rh, La and mixtures thereof ,

4. A photocatalyst according to any one of claims 1 to 3, characterized in that the at least one metal in an amount of 0.001 to 5 wt .-%, based on the total photocatalyst, is present.

5. A method for increasing the ribbon potential of a photocatalyst, characterized in that the photocatalyst is loaded with at least one metal selected from groups 3 to 12 of the Periodic Table of the Elements (according to IUPAC), lanthanides, actinides and mixtures thereof.

6. The method according to claim 5, characterized in that the metal loading takes place by photochemical deposition of the at least one metal on the photocatalyst.

7. The method according to claim 5 or 6, characterized in that the ribbon potential by at least 0.05 eV compared to the photocatalyst without

Metal loading is increased.

8. Use of at least one metal selected from groups 3 to 12 of the Periodic Table of the Elements (according to IUPAC), lanthanides, actinides and mixtures thereof for increasing the ribbon potential of a photocatalyst.

9. Use according to claim 8, characterized in that the at least one metal is selected from the group consisting of V, Zr, Ce, Zn, Au, Ag, Cu, Pd, Pt, Ru, Rh, La and mixtures thereof.

10. Use of a photocatalyst according to any one of claims 1 to 4 in chemical reactions.