DE102015107986A1 - photocatalyst - Google Patents

Abstract

The present invention relates to a photocatalyst comprising a pyrochlore or perovskite material. The photocatalyst can be used for water splitting, cleaning and / or disinfection.

Description

The present invention relates to photocatalysts and systems containing such catalysts, such as. As photovoltaic systems and in particular those systems in which water is photocatalytically cleaved. These are z. B. from the DE 103 32 570 A1 Titan dioxide-based systems known. Alternative uses or systems are disinfection or cleaning systems

However, there is a constant need for alternative materials and systems employing these materials, e.g. B. for the photocatalytic water splitting, disinfection and / or cleaning. This object is solved by claim 1 of the present invention.

Accordingly, a photocatalyst absorbing in the wavelength range of ≥ 300 and ≦ 650, comprising a pyrochlore material and / or a perovskite (Schichtperowskit / Doppelperowskit) material of the following structure: A ₂ LnMO ₆ with A selected from the group contains Ca, Sr, Ba or mixtures thereof, Ln selected from the group containing In, Y, La, rare earths or mixtures thereof and M = Nb and / or Ta.

The term "in the wavelength range of ≥ 300 nm and ≤ 650 nm absorbing" means and / or includes in particular that the photocatalyst is catalytically active in this wavelength range, d. H. that it is possible to generate catalytic activity by irradiation with light of at least one wavelength in the specified range. The term "absorbing in the wavelength range of ≥ 300 nm and ≦ 650 nm" does not and / or does not mean that the photocatalyst catalytically over this entire wavelength range is active.

The photocatalyst preferably consists predominantly of a pyrochlore material and / or perovskite material (layer perovskite / double perovskite material) of the stated structure. In this context, the term "predominantly" includes and / or means in particular a proportion in% by weight of ≥ 80%, preferably ≥ 90%, more preferably ≥ 95% and most preferably ≥ 99%.

• – Die beanspruchten Materialien zeichnen sich durch eine hohe thermische und photochemische Belastbarkeit aus und sind zudem langzeitstabil in Kontakt mit Wasser
• – Die beanspruchten Materialien kristallisieren kubisch, also optisch isotrop, und können somit relativ leicht zu transparenten bzw. zumindest transluzenten Keramiken verarbeitet werden.
• – Die beanspruchten Materialien weisen geringe thermische Ausdehnungskoeffizienten auf, so dass eine hohe thermische Wechselbeständigkeit gegeben ist.
• – Die beanspruchten Materialien weisen eine Bandlücke auf, die darauf abgestimmt ist, dass Strahlung mit einer Energie geringer als 2.0–4.0 eV transmittiert wird und Strahlung mit einer Energie größer als 2.0–4.0 eV absorbiert und zur Photokatalyse verwendet wird.
• – Die beanspruchten Materialien können auf mindestens zwei verschiedenen Kationenpositionen n- oder p-dotiert werden, wobei insbesondere die Schichtperowskite(Doppelperowskite) drei unterschiedliche kristallographische Kationenlagen aufweisen, so dass hier eine besonders große Vielzahl an Dotierungsmöglichkeiten besteht.

Surprisingly, it has been found that such materials are able to be photocatalytically active and z. B. to split water, or to be used in disinfecting or cleaning system. In addition, in most embodiments and specific embodiments, the photocatalyst of the present invention provides one or more of the following advantages:

• - The claimed materials are characterized by a high thermal and photochemical resilience and are also long-term stable in contact with water
• - The claimed materials crystallize cubic, so optically isotropic, and thus can relatively easily be processed into transparent or at least translucent ceramics.
• - The claimed materials have low thermal expansion coefficients, so that a high thermal cycling is given.
• The claimed materials have a bandgap that is tuned to transmit radiation having an energy lower than 2.0-4.0 eV and absorbs radiation with an energy greater than 2.0-4.0 eV and used for photocatalysis.
• The claimed materials can be n-doped or p-doped on at least two different cation positions, with the layer perovskites (double perovskites) in particular having three different crystallographic cation layers, so that a particularly large number of doping possibilities exists here.

For the purposes of the present invention, the term "water splitting" is understood in particular to mean that the water reacts to form hydrogen and oxygen or oxygen-containing compounds.

The term "hydrogen" in the meaning of the present invention is intended to explicitly not only mean elementary hydrogen (although this is a preferred embodiment of the invention), but is defined for the purposes of this invention as any chemical compound in which hydrogen in a lower oxidation state (0 or -I) is present as in water (+ I), d. H. Hydrides and / or corresponding metal complexes or metal hydrides should also be understood as hydrogen in the sense of this compound, even if the common usage in the field of chemistry is different.

Preferably, the resulting hydrogen, depending on the application also be implemented directly, z. In hydrogenation reactions or to form metal hydrides; This therefore represents a preferred embodiment of the invention.

It should be noted at this point that by means of the photocatalyst and oxygen or corresponding oxygen compounds are formed in which oxygen is present in a different oxidation state than in water (-II). Of course, this oxygen or the resulting compounds can also be used, if this appears advantageous. It should be noted that often the catalyst-mediated reaction of water is the hydroxy radicals (OH ·), which either too Dimer hydrogen peroxide or react with other reactants (eg, suitable metal ions) to oxygen.

The term "disinfection" or "disinfection" in the sense of the present invention is understood in particular to mean that the germ count is reduced. Microorganisms are understood in particular to be microorganisms (prokaryotes, bacteria, fungal spores, protozoa, (retro) viruses, biofilms, etc.).

The term "purification" in the sense of the present invention is understood in particular to mean that the concentration of undesired organic compounds is reduced. Organic compounds are in this sense in particular pharmaceuticals or their metabolically generated degradation products, herbicides, insecticides, organic dyes, organic solvents, organic precipitants or flocculants, X-ray contrast agents or organic perfumes. By "pyrochlore material" is meant in particular that the material Material of structure A ₂ B ₂ O _x with x ≥ 6 and x ≤ 7 which crystallizes in the pyrochlore crystal structure (Fd-3m).

A is preferably selected from the group consisting of rare earth metals, bismuth, lanthanum, yttrium or mixtures thereof.

B is preferably selected from the group consisting of transition metals, indium, germanium, tin or mixtures thereof, wherein the transition metal is in particular selected from the group consisting of titanium, zirconium, hafnium, niobium or mixtures thereof.

Most preferably, the photocatalyst comprises a material of the following structure: (La _1-abc Ln _a Y _b Bi _c ) ₂ (Ti _1-wxyz Nb _w Zr _x Hf _y Sn _z ) ₂ O ₇ where Ln is a rare earth metal or mixtures of rare earth metals,
a, b, c, w, x, y, z are each independently ≥ 0 and ≤ 1 with a + b + c ≥ 0 and ≤ 1 and w + x + y + z ≥ 0 and ≤ 1.

Preferably, Ln is selected from Ce, Nd, Dy, Tb, Pr, Sm or mixtures thereof.

Particularly preferred pyrochlore materials are selected from the group comprising:
La ₂ Ti ₂ O ₇ , Nd ₂ Zr ₂ O ₇ , Nd ₂ (InNb) ₂ O ₇ , Dy ₂ Zr ₂ O ₇ , Tb ₂ Ti ₂ O ₇ , La ₂ Zr ₂ O ₇ , Sm ₂ Zr ₂ O ₇ , (La, Sm) ₂ Zr ₂ O ₇ , Bi ₂ Ti ₂ O ₇ , Y ₂ Ti ₂ O ₇ , Ce ₂ Ti ₂ O ₇ , Ce ₂ Zr ₂ O ₇ , Bi ₂ Zr ₂ O ₇ , Nd ₂ Ti ₂ O ₇ , Tb ₂ Zr ₂ O ₇ , Pr ₂ Ti ₂ O ₇ , Pr ₂ Zr ₂ O ₇ or mixtures of these substances.

Particularly preferred perovskite materials (layer perovskite / double perovskite materials) are selected from the group comprising (Ba _1-abc Sr _a Ca _b Mg _c ) ₂ (In _1-xy Y _x Ln _y ) (Nb _1-z Ta _z ) O ₆ where Ln is a rare earth metal or mixtures of rare earth metals,
a, b, c, x, y, z are each independently ≥ 0 and ≤ 1 with a + b + c ≥ 0 and ≤ 1 and x + y ≥ 0 and ≤ 1 and z ≥ 0 and ≤ 1.

According to a preferred embodiment, the photocatalyst is partially or predominantly present as a ceramic.

For the purposes of the present invention, the term "ceramic" in the sense of the present invention means and / or comprises in particular a compact crystalline or polycrystalline material with a controlled amount of pores or without pores.

The term "polycrystalline material" in the sense of the present invention means and / or comprises in particular a material having a volume density of greater than 90 percent of the main component, consisting of more than 80 percent of individual crystal domains, each crystal domain having a diameter of ≥ 0.1 to ≤ 100 μm, preferably ≥ 1 to ≤ 25 μm, and most preferably ≥ 2.5 to ≤ 10 μm, and has a different crystallographic orientation. The individual crystal domains can be connected or diluted with one another via amorphous or vitreous material or via additional crystalline phases.

According to a preferred embodiment of the present invention, the crystalline material has a density of ≥ 90% to ≤ 100% of the theoretical density. This has proven advantageous for many applications of the present invention.

According to a preferred embodiment, the photocatalyst is arranged in layers. This allows a simple and compact design of the system according to the invention.

The present invention also relates to a photocatalyst system containing a photocatalyst of the invention.

According to a preferred embodiment, the photocatalytic system comprises a photovoltaic system. This means in particular that the photocatalyst is at least partially used for water splitting.

According to a preferred embodiment, the photocatalytic system comprises a disinfection system. This means, in particular, that the photocatalyst at least partially reduces the germ number.

According to a preferred embodiment, the photocatalytic system comprises a purification system. This means, in particular, that the photocatalyst at least partially reduces the concentration of undesired organic compounds.

According to a preferred embodiment, the photocatalytic system comprises at least one photocatalyst according to the present invention, which is arranged in layers with a water layer assigned to the photocatalyst. This allows a simple and compact design of the system according to the invention, especially in photovoltaic applications or disinfections of aqueous solutions or water.

According to a preferred embodiment of the present invention, the photocatalytic system according to the invention comprises a p- and / or n-doped photocatalyst. In the event that only one doped material (either p- or n-doped) is present, it is preferred that then another corresponding is present complementary n- or p-doped material.

This embodiment has the advantage that, with a suitable embodiment, the catalyzed reactions, such as the reduction of water and the oxidation of water (in the case of a photocatalytic system) can be spatially separated.

The doping takes place in the case of the pyrochlore materials preferably so that when n-doping [IV] ions, z. Zr ⁴⁺ , Ge ⁴⁺ , or Sn ^{4+ are} replaced by [V] ions such as V ⁵⁺ , Nb ⁵⁺ , or Ta ⁵⁺ . For p-type doping, preference is given to [IV] ions, eg. As Zr ⁴⁺ , Ge ⁴⁺ , or Sn ⁴⁺ replaced by [III] ions such as Cr ³⁺ , Mo ³⁺ , W ³⁺

In the case of the layer perovskite materials, the doping preferably takes place in such a way that with n-doping [V] -ions, eg. For example, Nb ⁵⁺ or Ta ^{5+ are} replaced by [VI] ions such as Mo ⁶⁺ or W ⁶⁺ and / or [III] ions, e.g. For example, Y ³⁺ , In ³⁺ or Ln ^{3+ may be} replaced by [IV] ions such as Ge ⁴⁺ , Zr ⁴⁺ or Hf ⁴⁺ . For p-type doping, [V] -ions, e.g. For example, Nb ⁵⁺ or Ta ^{5+ may be} replaced by [VI] ions such as Ge ⁴⁺ , Zr ⁴⁺ or Hf ⁴⁺ , and / or [III] ions, e.g. For example, Y ³⁺ , In ³⁺ or Ln ^{3+ may be} replaced by [II] ions such as Zn ²⁺ , Mn ²⁺ , or Mg ²⁺ .

Irrespective of the material class, the degree of doping is preferably ≥ 0.01 to ≦ 10% (mol / mol), preferably ≥ 0.1 to ≦ 1% (mol / mol).

According to a preferred embodiment, the photocatalytic system according to the invention comprises a first photocatalyst layer which is n-doped and a second photocatalyst layer which is p-doped (one or both of which comprise or predominantly consist of a photocatalyst according to the invention).

According to a preferred embodiment, the photocatalytic system according to the invention additionally comprises a non-doped photocatalytic layer, which is arranged between the two doped layers, but may optionally be separated therefrom by further intermediate layers.

According to a preferred embodiment, the photocatalyst system according to the invention additionally comprises a blocking layer which is electron-conducting, but hole-blocking. This is preferably arranged on the side of the n-doped photocatalyst layer facing away from the water layer.

This hole-blocking blocking layer comprises or consists predominantly of a transparent to translucent material, preferably of the photocatalytic material which is n-doped.

According to a preferred embodiment, the photocatalyst system according to the invention additionally comprises a blocking layer which is hole-conducting but electron-blocking. This is preferably arranged on the side facing away from the water layer of the p-doped photocatalyst layer.

This electron-blocking blocking layer comprises or consists predominantly of a transparent to translucent material, preferably of the photocatalytic material which is p-doped.

Preferably, the photocatalytic system according to the invention further comprises two water layers, which are each assigned to one of the two doped layers.

This allows a simple and compact design of the system according to the invention. Depending on the configuration or specific application, appropriate charge and / or pH compensation must be ensured.

According to a preferred embodiment of the invention, the photocatalyst, preferably the n-doped photocatalyst or in the presence of a plurality of photocatalyst layers, a photocatalyst layer - again preferably this layer is n-doped - additionally provided with a suitable second material, in particular a second material, in which the reaction of the water to hydrogen takes place. This is particularly preferred the group of platinum metals and their alloys, particularly preferably platinum, palladium, iridium, rhenium, ruthenium, rhodium and mixtures and / or alloys of these materials.

The mentioned second material can, as mentioned, for. As platinum or another precious metal. This is preferably on the surface of the pyrochlore material z. B. applied as a partially covering the surface layer or in the form of dots or in the form of a grid.

It is preferred that the dots have an average maximum thickness of ≥ 10 and ≦ 500 nm, preferably ≥ 100 and ≦ 400 nm.

In the case that the second material is applied in the form of a grid, the aspect ratio is preferably ≥ 1:10 to ≦ 1: 1000.

The area ratio of the photocatalyst or the respective photocatalyst layer covered by the second material is preferably ≥ 5% and ≦ 20%, preferably ≥ 10 and ≦ 15%. In this way it is ensured that both redox reactions (once to the hydrogen, once to the oxygen or oxygen-containing compounds) can take place in an optimal manner.

The present invention furthermore relates to the use of a photocatalyst according to the invention for catalytic water splitting, for disinfection and / or for purification, wherein all variations and design possibilities described above and in succession come into question and may be preferred embodiments and embodiments.

The above-mentioned and the claimed components to be used according to the invention described in the exemplary embodiments are not subject to special conditions of size, shape, material selection and technical design, so that the selection criteria known in the field of application can be used without restriction.

Further details, features and advantages of the subject matter of the invention will become apparent from the subclaims and from the following description of the drawings and examples, which are to be understood purely illustrative.

In the figures show

1 a very schematic fragmentary cross-sectional view through a system according to an embodiment of the invention, as well as

2 a very schematic fragmentary cross-sectional view through a system according to a second embodiment of the invention, as well

3 a very schematic cross-sectional view through a system according to a third embodiment of the invention

1 shows very schematic partial cross-sectional view through a photovoltaic system 1 according to an embodiment of the invention. According to 1 The system includes a photocatalyst 20 in the form of a layered ceramic, optionally with platinum dots o. Ä. (Not shown in the figure) is provided.

In the path of the incoming light (in 1 from above) is behind a transparent cover layer 10 (which may simply be made of glass, for example) has a water layer 30 which is associated with the photocatalyst. Behind it is a reflector 40 arranged.

When light hits the system, UV and / or blue light from the photocatalyst becomes 20 absorbs water from the water layer 30 split. The resulting hydrogen is virtually insoluble in water and thus can easily be tapped. The resulting oxygen dissolves only barely in water and can thus be easily removed.

2 shows an alternative system in which the hydrogen and oxygen production are separated. In this system, the photocatalyst comprises 20 two layers 21 . 22 , where one n- and the other is p-doped. Of course, these may optionally be provided with platinum dots or the like (not shown in the figure). At least one of these layers, preferably both, comprise a photocatalyst according to the invention.

The system now includes two layers of water 31 . 32 the one through the top layer 10 and the first photocatalyst 21 is limited, the second through the second photocatalyst 22 and the reflector 40 ,

When light hits the system, hydrogen is generated in one layer of water and either oxygen or, depending on the application, another oxygen-containing compound, such as hydrogen peroxide, in the other.

3 shows an alternative embodiment to the system 2 , This is with 2 identical, unless otherwise stated in 3 shown.

According to this embodiment, the photocatalyst comprises three layers, namely first a p-doped layer 21 , an undoped intermediate layer 23 and an n-doped layer 22 , This is additionally with platinum dots 50 provided that accelerate the reaction to hydrogen again.

According to another preferred embodiment (not shown in the figures), between the layers (e.g. 21 and 23 in 3 respectively. 22 and 23 in 3 ) still blocking layers as described above.

Experiments have also shown that the photocatalysts described above under UV or blue light irradiation are capable of producing hydrogen. For this purpose, the photocatalyst is coated as a powder after contacting via platinum dots with water, optionally with the addition of sacrificial reagents and irradiated. The photocatalytic activity can be detected by a rain gas evolution.

The individual combinations of the components and the features of the already mentioned embodiments are exemplary; the exchange and substitution of these teachings with other teachings contained in this document with the references cited are also expressly contemplated. Those skilled in the art will recognize that variations, modifications and other implementations described herein may also occur without departing from the spirit and scope of the invention.

Accordingly, the above description is illustrative and not restrictive. The word "comprising" used in the claims does not exclude other ingredients or steps. The indefinite article "a" does not exclude the meaning of a plural. The mere fact that certain measures are recited in mutually different claims does not make it clear that a combination of these measures can not be used to the advantage. The scope of the invention is defined in the following claims and the associated equivalents.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10332570 A1 [0001]

Claims (10)

In the wavelength range of ≥ 300 and ≤ 650 absorbing photocatalyst comprising a pyrochlore material and / or a perovskite material of the following structure: A ₂ LnMO ₆ with A selected from the group containing Ca, Sr, Ba or mixtures thereof, Ln selected from Group containing In, Y, La, rare earths or mixtures thereof and M = Nb and / or Ta. A photocatalyst according to claim 1, wherein the photocatalyst consists predominantly of the pyrochlore and / or perovskite material A photocatalyst according to claim 1 or 2, wherein the pyrochlore material comprises a material of structure A ₂ B ₂ O _x where x ≥ 6 and x ≤ 7, which crystallizes in the pyrochlore crystal structure (Fd-3m), wherein A is selected from the group containing rare earth metals, bismuth, lanthanum, yttrium or mixtures thereof. B is selected from the group containing transition metals, indium, germanium, tin, or mixtures thereof A photocatalyst according to any one of claims 1 to 3, wherein the pyrochlore material comprises a material of the structure (La _1-abc Ln _a Y _b Bi _c ) ₂ (Ti _1-wxyz Nb _w Zr _x Hf _y Sn _z ) ₂ O ₇ where Ln is a rare earth metal or mixtures of rare earth metals, a, b, c, w, x, y, z are each independently ≥ 0 and ≤ 1 with a + b + c ≥ 0 and ≤ 1 and w + x + y + z ≥ 0 and ≤ 1. A photocatalyst according to any one of claims 1 to 4, wherein the perovskite material comprises a material of the structure (Ba _1-abc Sr _a Ca _b Mg _c ) ₂ (In _1-xy Y _x Ln _y ) (Nb _1-z Ta _z ) O ₆ where Ln is a rare earth metal or mixtures of rare earth metals, a, b, c, x, y, z are each independently ≥ 0 and ≤ 1 are with a + b + c ≥ 0 and ≤ 1 and x + y ≥ 0 and ≤ 1 and z ≥ 0 and ≤ 1 A photocatalyst according to any one of claims 1 to 5, wherein the photocatalyst is a ceramic. Photocatalyst system comprising a photocatalyst according to one of claims 1 to 6 The photocatalytic system of claim 7, wherein the system comprises a first photocatalyst layer which is n-doped and a second photocatalyst layer which is p-doped, either or both of which comprises or predominantly comprises a photocatalyst according to any one of claims 1 to 6 , Photocatalyst system according to claim 7 or 8, wherein the photovoltaic system further comprises two layers of water, each associated with one of the two photocatalyst layers Use of a photocatalyst according to any one of claims 1 to 6 for photocatalytic water splitting, cleaning and / or disinfection.

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