WO2011000886A1 - Photocatalyseurs améliorés et leur utilisation pour la photocatalyse - Google Patents

Photocatalyseurs améliorés et leur utilisation pour la photocatalyse Download PDF

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WO2011000886A1
WO2011000886A1 PCT/EP2010/059313 EP2010059313W WO2011000886A1 WO 2011000886 A1 WO2011000886 A1 WO 2011000886A1 EP 2010059313 W EP2010059313 W EP 2010059313W WO 2011000886 A1 WO2011000886 A1 WO 2011000886A1
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photocatalyst
layer
substrate
present
potential
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PCT/EP2010/059313
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German (de)
English (en)
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Alexandra Seeber
Götz-Peter SCHINDLER
Florina Corina Patcas
Günter Heinz Bruno KREISEL
Susan Schaefer
Sarah Anna Saborowski
Doreen Keil
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Basf Se
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/39—Photocatalytic properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
    • B01J21/063—Titanium; Oxides or hydroxides thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
    • B01J21/066—Zirconium or hafnium; Oxides or hydroxides thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B01J23/44—Palladium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/31—Density
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/33—Electric or magnetic properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/06—Washing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
    • B01J37/348—Electrochemical processes, e.g. electrochemical deposition or anodisation

Definitions

  • the present invention relates to a photocatalyst comprising at least one substrate and a layer of at least one photocatalytically active semiconductor oxide having a layer thickness of at least 0.1 mg / cm 2 , wherein the ribbon potential is 0.01 V to 1, 0 V is changed over a corresponding photocatalyst with a layer thickness of less than 0.1 mg / cm 2 , a method for adjusting the ribbon potential of a photocatalyst at least comprising a substrate and a layer of photoactive substance, characterized in that the photocatalyst layer has a thickness of 0.1 mg / cm 2 to 200 mg / cm 2 , and the use of this photocatalyst in 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 method for the preparation of nanocrystalline metal oxide and mixed metal oxide layers on barrier layer-forming metals, wherein the coating by anodization with spark discharge in an electrolyte, which at least one or more complexing agents, preferably chelating agents, one or more metal alkoxides and at least one alcohol, preferably secondary or tertiary alcohols.
  • an electrolyte which at least one or more complexing agents, preferably chelating agents, one or more metal alkoxides and at least one alcohol, preferably secondary or tertiary alcohols.
  • 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, can be selected individually or in their combination.
  • the properties of the photocatalytically active layers obtained can additionally be influenced by adding further components, such as iron or ruthenium ions, electrically neutral micro- or nanoparticles, etc., to the electrolyte of the anodization to insert these into the photocatalytically active layer. It is not disclosed in this document that the flat band potential of photocatalysts can be selectively changed via the layer thickness.
  • DE 10 2005 043 865 A1 relates to a further development of the method according to the already cited DE 198 41 650 A1.
  • the electrolyte in which the anodization of the substrate is carried out is, for example, gadolinium (III) acetylacetonate hydrate and / or cerium (III) acetylacetonate hydrate a concentration of less than 0.01 mol / l and optionally further components 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.
  • 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 an aqueous solution in which precious metals are preferably 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 elemental 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.
  • an excitation wavelength of less than 400 nm is specified, wherein the addition of doping elements, in particular transition metal elements, contributes to increasing the absorption in the visible range, and thus also the activity of the catalyst.
  • doping elements in particular transition metal elements
  • photocatalysts known from the prior art have activities when used in photocatalyzed reactions, for example in the production of hydrogen from water or alcohols, which are still to be improved. Furthermore, there is a need for photocatalysts that are not limited to the reduction of protons to molecular hydrogen, but are also suitable for other chemical reactions.
  • the photocatalyst according to the invention at least comprising a substrate and a layer of at least one photocatalytically active semiconductor oxide having a layer thickness of at least 0.1 mg / cm 2 , wherein the ribbon potential by 0.01 V to 1, 0 V compared to a corresponding photocatalyst with a layer thickness less than 0.1 mg / cm 2 , changed.
  • the present invention relates to a photocatalyst comprising at least one substrate and a layer of at least one photocatalytically active semiconductor oxide having a layer thickness of at least 0.1 mg / cm 2 , preferably 0.1 mg / cm 2 to 200 mg / cm 2 , more preferably 0.5 to 100 mg / cm 2 , most preferably 1, 0 mg / cm 2 to 50 mg / cm 2 , wherein the ribbon potential by 0.01 V to 1, 0 V, preferably 0.1 V to 0.7 V compared to a corresponding photocatalyst with a layer thickness of less than 0.1 mg / cm 2 , preferably less than 0.1 mg / mm 2 or greater than 200 mg / mm 2 , more preferably less than 0.5 mg / cm 2 or greater than 100 mg / cm 2 , most preferably less than 1, 0 mg / cm 2 or greater than 50 mg / cm 2 , is changed.
  • the at least one photoactive semiconductor oxide is titanium dioxide and the ribbon potential is at least 0.01 V to 1.0 V, preferably 0.1 V to 0.7 V, compared to the flat band potential of the corresponding photocatalyst with a layer thickness outside the range of at least 0.1 mg / cm 2 , preferably 0.1 mg / cm 2 to 200 mg / cm 2 , more preferably from 0.5 mg / cm 2 to 100 mg / cm 2 , more preferably 1, 0 mg / cm 2 to 50 mg / cm 2 , changed.
  • an energy band of a photocatalyst is understood to mean an energy range in which there are many energetically dense quantum-physically possible states.
  • the so-called conduction band is the lowest unoccupied or partially occupied band
  • the so-called valence band is the highest fully occupied band.
  • the so-called band gap Between these energy bands lies a so-called forbidden area, the so-called band gap.
  • the flat-band potential corresponds to a good approximation of an n-type semiconductor lower edge of the conduction band. This definition is also used in the present patent.
  • 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, 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 optionally metallic or metal oxide charges are generally already known from the prior art.
  • the flat band potential can not be varied by varying the layer thickness, so that they can be used for the reduction of water or alcohols to hydrogen or the reduction of CO or CO 2 to hydrocarbons.
  • the conduction band of the photocatalyst used must be above the energy necessary for the reduction of 2 H + to H 2 , e.g. Above -0.35 V at a pH of 6.
  • the valence band must be below the energy level of the oxidation of 2 H 2 O to O 2 , ie below 1.23 V.
  • the photocatalysts known from the prior art can not catalyze photochemical reactions which require a higher energy than the energy defined by the band gap between conduction band and valence band.
  • the ribbon potential can be selectively changed, can be catalyzed by this catalyst and chemical reactions that require an increased activation energy. This is not possible by the photocatalysts known from the prior art.
  • the photocatalyst according to the invention is present on a substrate.
  • the substrate is selected from the group consisting of metals, semiconductors, glass substrates, ceramic substrates, cellulosic 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.
  • the substrate of the photocatalyst according to the invention is a sheet-shaped metal, for example a metal sheet or a metal mesh.
  • the substrate can have all possible shapes and surface textures.
  • the substrates can according to the invention plan, curved, for example, convex or concave, be formed symmetrically or asymmetrically.
  • the surface of the substrate used may 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 at least titanium dioxide as the photoactive substance.
  • the present titanium dioxide may be present in the anatase or rutile modification or else in the amorphous state or in a mixture thereof.
  • the photoactive substance in particular titanium dioxide, is present on the substrate as a layer.
  • the thickness of this layer is critical to the catalytic activity of the photocatalyst of the invention and is at least 0.1 mg / cm 2 , preferably 0.1 mg / cm 2 to 200 mg / cm 2 , more preferably from 0.5 mg / cm 2 to 100 mg / cm 2 , most preferably 1, 0 mg / cm 2 to 50 mg / cm 2 .
  • the layer present on the substrate generally has a BET specific surface area of 10 to 200 m 2 / g, preferably 20 to 100 m 2 / g, particularly preferably 30 to 80 m 2 / g.
  • BET Brunauer-Emmett-Teller
  • the average pore size of the present titanium dioxide is generally from 0.1 to 20 nm, preferably from 1 to 15 nm, particularly preferably from 2.0 to 10 nm.
  • Methods for determining the pore size are known to the person skilled in the art, for example those developed by Barrett, Joyner and Halenda BJH method.
  • the photocatalyst according to the invention comprises at least one metallic or metal oxide charge selected from the group consisting of Pt, Pd, Cu, Au, Ag, Zr, Ni, W, La, their oxides and mixtures thereof.
  • the optionally present on the photocatalyst according to the invention at least one metallic or metal oxide loading may be present in elemental form or as a compound, preferably as an oxide.
  • the palladium used as a loading is preferably present in elemental form.
  • the copper present as metal loading in a further preferred embodiment is preferably present as copper (I) oxide Cu 2 O.
  • the at least one metallic or metal oxide charge is generally present in a customary amount on the photocatalyst according to the invention.
  • the at least one metallic or metal oxide charge is preferably present in an amount of 0.001 to 5% by weight, particularly preferably 0.01 to 1% by weight, very particularly preferably 0.05 to 0.5% by weight, each based on the total photocatalyst, before.
  • the photocatalyst according to the invention can be prepared by methods known to those skilled in the art, it being important to ensure that the photoactive titanium dioxide is applied with the appropriate layer thickness. Suitable processes for the preparation of the photocatalyst according to the invention are, for example, wet-chemical, electrochemical or photochemical processes and combinations thereof.
  • the photocatalyst according to the invention is prepared by the following process, comprising at least step (A) and optional step (B):
  • Step (A) of the process according to the invention comprises the electrochemical treatment of the at least one substrate in an electrolyte containing at least one precursor compound of titanium dioxide, in order to obtain at least one photocatalytic to obtain a table-active metal oxide coated substrate, wherein the layer thickness is at least 0.1 mg / cm 2 , preferably 0.1 mg / cm 2 to 200 mg / cm 2 , particularly preferably from 0.5 mg / cm 2 to 100 mg / cm 2 , most preferably 1, 0 mg / cm 2 to 50 mg / cm 2 .
  • step (A) of this method is carried out according to the method described in DE 198 41 650 A1.
  • the disclosure of DE 198 41 650 A1 is therefore fully part of this invention.
  • the electrochemical treatment in step (A) is anodization, more preferably an anodization with spark discharge.
  • 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 titanium dioxide.
  • an aqueous electrolyte is used in step (A) of the process according to the invention, i. H. the solvent used is water.
  • 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.
  • 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 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.
  • 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.
  • At least one titanium alkoxide is used, for example tetraethyl orthotitanate, tetraisopropyl orthotitanate, tetrabutyl orthotitanate or mixtures thereof.
  • the at least one precursor compound of titanium dioxide is generally present in a concentration which allows advantageously carrying out 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.
  • 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.
  • 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.
  • solvents 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 under spark discharge is the
  • step (A) of the process 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 15 to 50 V / s, particularly preferably 25 to 40 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 depends on the substrate size and is for example 10 to 500 s, preferably 50 to 200 s, particularly preferably 75 to 150 s.
  • the current intensity I is generally from 0.5 to 100 A, preferably from 1 to 50 A, in particular from 2 to 25 A.
  • the substrate is degreased prior to step (A).
  • the substrate can be treated with an aqueous solution containing at least one surface-active substance, if appropriate 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 of step (A).
  • a titanium dioxide with a layer thickness of at least 0.1 mg / cm 2 preferably 0.1 mg / cm 2 to 200 mg / cm 2 , more preferably from 0.5 mg / cm 2 to 100 mg / cm 2 , most preferably 1, 0 mg / cm 2 to 50 mg / cm 2 coated substrate, ie, the photocatalyst according to the invention.
  • step (B) This can optionally be treated according to the invention in step (B) if the photocatalyst according to the invention is additionally intended to contain at least one metallic or metal oxide charge.
  • the substrate prefferably be rinsed off after step (A) with a suitable solvent, preferably water.
  • a suitable solvent preferably water.
  • 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. Therefore, the present invention also relates to a method wherein the coated substrate obtained after step (A) is thermally treated.
  • the optional step (B) of the process comprises the photochemical treatment of the titania-coated substrate in a further electrolyte containing at least one precursor compound of the at least one metal or metal oxide to obtain the photocatalyst additionally containing at least one metallic or metal oxide loading ,
  • the further electrolyte according to step (B) of the process contains all the components which are necessary to apply at least one metal or a metal oxide to the photocatalyst according to the invention in step (B) of the process.
  • Suitable metals or metal oxides are mentioned above.
  • Suitable precursors for this loading are generally all compounds which can be converted to the corresponding metal or metal oxide loadings under the conditions present in step (B) of the process.
  • suitable precursor compounds for the at least one charge include salts and / or complex compounds of the abovementioned metals or metal oxides, preferably used as metal or metal oxide charge.
  • particularly suitable salts are salts of organic mono- or dicarboxylic acids, in particular formates, acetates, propionates and oxalates or mixtures thereof.
  • halides for example fluorides, chlorides, bromides, nitrates and sulfates or mixtures thereof.
  • Particularly preferred precursors for the at least one metal or metal oxide in step (B) are acetates or halides, especially chlorides.
  • Very particularly preferred precursor compounds for the at least one metal or metal oxide loading are selected from the group consisting of Cu (OOCCH 3) 2, K 2 PdCl 4, HAuCl 4, K 2 PtCl 4, IrCl 3, and mixtures thereof.
  • This at least one precursor compound is generally present in the electrolyte according to step (B) of the process in a concentration of 0.1 to 20 mmol / L, preferably 0.5 to 1.5 mmol / L.
  • an aqueous electrolyte is preferably used, ie the solvent used for the electrolyte according to step (B) is water.
  • the electrolyte according to step (B) optionally contains further additives known to the person skilled in the art.
  • the precursor compounds present in the electrolyte according to step (B) are stabilized by addition of an acid, for example HNO 3 , for example in a concentration of 0.1 to 10% by volume.
  • the photochemical treatment according to step (B) of the process is preferably carried out by irradiation with light, in particular UV light.
  • UV light is understood as meaning high-energy electromagnetic radiation, in particular light having a wavelength of 200 to 400 nm.
  • the UV light preferably used in step (B) is produced by corresponding UV lamps, for example Xe (Hg) arc lamps, black light lamps, diode arrays 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 50 mW / cm 2 , preferably 0.5 to 30 mW / cm 2 , particularly preferably 2 to 15 mW / cm 2 .
  • Step (B) of the process is carried out, for example, by contacting the photocatalyst coated with titanium dioxide obtained from step (A) in a corresponding reactor with the electrolyte according to step (B).
  • any reactor known to the person skilled in the art can be used as the reactor, for example a cuvette.
  • a reactor is used which is permeable to the wavelength range of the light used.
  • the at least one UV light source is then placed at a suitable distance from the cuvette to irradiate the substrate in the electrolyte according to step (B) with UV light.
  • the irradiation is carried out for a time sufficient to apply a sufficient amount of charge to the catalyst surface, for example 1 to 200 minutes, preferably 1 to 30 minutes, most preferably 3 to 10 minutes.
  • the present invention further relates to a method for adjusting the ribbon potential of a photocatalyst comprising at least a substrate and a layer of photoactive substance, wherein the layer of photoactive substance has a thickness of at least 0.1 mg / cm, preferably 0.1 mg / cm 2 to 200 mg / cm 2 , more preferably 0.5 mg / cm 2 to 100 mg / cm 2 , most preferably 1, 0 mg / cm 2 to 50 mg / cm 2 .
  • the flat band potential is varied by 0.01 V to 1.0 V.
  • modified means that the flat band potential of the photocatalyst preferably is at least 0.01 V to 1.0 V, particularly preferably 0.1 to 0.7 V, in each case opposite a photocatalyst with a layer of photoactive substance, in particular titanium dioxide, with a strength outside the range of at least 0.1 mg / cm 2 , preferably outside the range of 0, 1 mg / cm 2 to 200 mg / cm 2 , more preferably outside the range of 0.5 mg / cm 2 to 100 mg / cm 2 , most preferably outside the range of 1, 0 mg / cm 2 to 50 mg / cm 2 , is changed.
  • the method according to the invention for adjusting the ribbon potential of a photocatalyst comprises at least the abovementioned step (A). Therefore, what has been said regarding the production process of the photocatalyst.
  • the photocatalyst according to the invention is suitable to catalyze chemical reactions.
  • Examples of corresponding reactions are, for example, the reduction of protons to molecular hydrogen in aqueous and / or alcoholic solutions, as well as the reduction of CO, CO 2 or organic substances.
  • the present invention also relates to the use of the photocatalyst according to the invention in chemical reactions, preferably in the reduction of protons to molecular hydrogen in aqueous and / or alcoholic solutions, and the reduction of CO, CO 2 or organic substances.
  • Example 1 Preparation of photocatalyst preparing the photocatalyst according to the ® process SOLECTRO
  • Tetraethylorthotitanate 0.05 For the determination of the flat band potential via capacitance measurements with subsequent evaluation according to Mott-Schottky, titanium sheet in the dimensions 3 cm x 1 cm is used as the substrate. Of the total area 1 cm x 1 cm coated with TiO 2 , the remaining area is protected during the coating process with tape. SOLECTRO ® separation takes place under the parameters given in Table 2. Table 2: Coating parameters
  • Tasting Tn is vt O "S
  • the layer thickness is controlled over the time of the coating process. For the lowest layer thickness used, the time is 20 s for the highest 800 s, the exact values are given in Table 3 below.
  • one side of the titanium substrate in the dimensions is 0.8 cm x 4 cm with SOLECTRO ® TiO2 coated. The other side is protected with tape during the deposition process.
  • the control of the layer thickness also takes place over time. Titanium dioxide loading is calculated from the mass difference between coated and uncoated substrate for each sample.
  • Example 2 Position of the energy bands, influence of the layer thickness of the titanium dioxide
  • a titanium sheet is coated with titanium dioxide in various layer thicknesses. There is no additional load applied.
  • corresponding photocatalysts are used in the reduction of protons to hydrogen under irradiation with UV light.
  • capacitance measurements are evaluated using the Mott-Schottky equation. For these measurements, the metal-fixed catalyst layer (1 cm ⁇ 1 cm TiO 2 layer on 3 cm ⁇ 1 cm titanium substrate) is operated as a working electrode. Further components of the experimental setup are a Pt counterelectrode and an Ag / AgCl reference electrode (3M KCl).
  • the measurements can be converted directly into the Mott-Schottky plots using the software FRA (Frequency Response Analysis) Version 2.1.
  • FRA Frequency Response Analysis
  • V 0 the intersection of the linear region with the x-axis.
  • the flat band potential is calculated according to the following equation.
  • the diffuse reflection spectrum of the sample is recorded using a photometer sphere. This makes it possible to determine the proportion of light that is almost completely absorbed by the sample. You get the so-called cut-off wavelength by laying a straight line through the slope and calculating its intersection with the baseline.
  • the energy of the bandgap is calculated according to the following equation.
  • the upper edge of the valence band results from the difference in the flat band potential and the bandgap energy.
  • Table 4 shows the values determined as a function of the layer thickness.
  • photocatalytic activity of the photocatalyst is determined after one hour and is in H 2 .mu.mol / (h g ⁇ A i) indicated.
  • the catalyst used is a titanium sheet coated with titanium dioxide in various layer thicknesses, the titanium dioxide containing 0.13% by weight of Pd in elemental form as metal loading.
  • the photocatalyst is placed in a quartz glass reactor (volume 10 ml) containing a 1: 1 v / v mixture of methanol and water (3.5 ml).
  • this arrangement is irradiated with UV light with an intensity in the UV-A range of 6 mW / cm 2 (LED array, maximum intensity at 365 nm).
  • UV light with an intensity in the UV-A range of 6 mW / cm 2 (LED array, maximum intensity at 365 nm).
  • 250 ⁇ L samples are taken from the gas space of the reactor and analyzed by gas chromatography.
  • the photocatalytic activity is given in ⁇ mol H 2 per time and mass of catalyst ([ ⁇ mol / (h g ⁇ A i)]).
  • Table 5 shows the photocatalytic activities as a function of the layer thickness.
  • the layer thickness of the TiO 2 in mg / cm 2 is indicated on the x-axis of the diagram.
  • E FB is given in volts versus NHE
  • the amount of H 2 is given in ⁇ mol / (g * h).

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Abstract

L'invention concerne un photocatalyseur comprenant au moins un substrat et une couche composée d'au moins un oxyde semiconducteur à activité catalytique d'une épaisseur d'au moins 0,1 mg/cm2, le potentiel de bandes plates étant modifié d'une valeur de 0,01 V à 1,0 V par rapport à un photocatalyseur correspondant présentant une épaisseur de couche inférieure à 0,1 mg/cm2. L'invention concerne également un procédé de réglage du potentiel de bandes plates d'un photocatalyseur comprenant au moins un substrat et une couche de substance photoactive, caractérisé en ce que la couche de photocatalyseur présente une épaisseur de 0,1 mg/cm2 à 200 mg/cm2, ainsi que l'utilisation de ce photocatalyseur dans des réactions chimiques
PCT/EP2010/059313 2009-07-01 2010-06-30 Photocatalyseurs améliorés et leur utilisation pour la photocatalyse WO2011000886A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5616532A (en) * 1990-12-14 1997-04-01 E. Heller & Company Photocatalyst-binder compositions
DE19841650A1 (de) * 1998-09-11 2000-03-16 Univ Schiller Jena Verfahren zur Darstellung von nanokristallinen oder naokristallinhaltigen Metalloxid- und Metallmischoxidschichten auf sperrschichtbildenden Metallen
US6326079B1 (en) * 1995-09-15 2001-12-04 Saint-Gobain Glass France Substrate with a photocatalytic coating
DE102007026866A1 (de) * 2007-06-11 2008-12-24 Gesellschaft zur Förderung von Medizin-, Bio- und Umwelttechnologien e.V. Photokatalytisch aktive Schicht sowie Zusammensetzung und Verfahren zu ihrer Herstellung
DE102007046775A1 (de) * 2007-09-27 2009-04-02 Friedrich-Schiller-Universität Jena Verfahren zur Generierung von nanokristallinen oder nanokristallinhaltigen Metalloxid- und Metallmischoxidschichten auf sperrschichtbildenden Metallen

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5616532A (en) * 1990-12-14 1997-04-01 E. Heller & Company Photocatalyst-binder compositions
US6326079B1 (en) * 1995-09-15 2001-12-04 Saint-Gobain Glass France Substrate with a photocatalytic coating
DE19841650A1 (de) * 1998-09-11 2000-03-16 Univ Schiller Jena Verfahren zur Darstellung von nanokristallinen oder naokristallinhaltigen Metalloxid- und Metallmischoxidschichten auf sperrschichtbildenden Metallen
DE102007026866A1 (de) * 2007-06-11 2008-12-24 Gesellschaft zur Förderung von Medizin-, Bio- und Umwelttechnologien e.V. Photokatalytisch aktive Schicht sowie Zusammensetzung und Verfahren zu ihrer Herstellung
DE102007046775A1 (de) * 2007-09-27 2009-04-02 Friedrich-Schiller-Universität Jena Verfahren zur Generierung von nanokristallinen oder nanokristallinhaltigen Metalloxid- und Metallmischoxidschichten auf sperrschichtbildenden Metallen

Non-Patent Citations (3)

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Title
BERANEK ET AL: "Surface-modified anodic TiO2 films for visible light photocurrent response", ELECTROCHEMISTRY COMMUNICATION, ELSEVIER, AMSTERDAM, NL LNKD- DOI:10.1016/J.ELECOM.2006.11.011, vol. 9, no. 4, 1 April 2007 (2007-04-01), pages 761 - 766, XP022015829, ISSN: 1388-2481 *
KAR A ET AL: "Improved photocatalytic degradation of textile dye using titanium dioxide nanotubes formed over titanium wires", ENVIRONMENTAL SCIENCE AND TECHNOLOGY 20090501 AMERICAN CHEMICAL SOCIETY USA,, vol. 43, no. 9, 1 May 2009 (2009-05-01), pages 3260 - 3265, XP002601178 *
M. ASHOKKUMAR ET AL., INT. J. HYDROGEN ENERGY, vol. 23, no. 6, 1998, pages 427 - 438

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