JP5765678B2 - Photocatalyst for photowater splitting reaction and method for producing photocatalyst for photowater splitting reaction - Google Patents

Description

  The present invention relates to a photocatalyst for photowater splitting reaction and a method for producing a photocatalyst for photowater splitting reaction, and in particular, has a cocatalyst for oxidation reaction and reduction reaction, and uses the light in the visible light region for water splitting reaction. It is related with the photocatalyst which performs.

  In recent years, the practical application of high-performance light energy conversion systems that use renewable energy such as solar energy has been aimed at controlling global warming and moving away from the depletion of fossil resources. Its importance is increasing rapidly. Above all, the technology that decomposes water using solar energy to produce hydrogen is indispensable not only in the current petroleum refining, ammonia and methanol raw material supply technology, but also in the future hydrogen energy society based on fuel cells. Technology.

The water splitting reaction using a photocatalyst has been extensively studied since the 1970s (Non-patent Document 1). Among these photocatalysts, for example, ZrO ₂ alone has sufficient activity, but in many cases, the cocatalyst plays a big role. In various photocatalysts, it is known that when a noble metal such as Pt, RuO ₂ , NiO or the like is supported on a photocatalyst as a co-catalyst for hydrogen generation (reduction reaction), the reaction rate is remarkably improved (non-patent) Reference 1).

The decomposition reaction of water in the acidic aqueous solution on the photocatalyst particles is estimated as follows. That is,
H ₂ O + 2h ⁺ → 1 / 2O ₂ + 2H ⁺ (1)
2H ⁺ + 2e ⁻ → H ₂ (2)
The effect of the cocatalyst is to promote the reaction by reducing the activation energy of these reactions. However, the promoter is H ₂ + 1 / 2O ₂ → H ₂ O (3)
It is not preferable to catalyze the combustion reaction represented by the formula, since this is the reverse reaction of the water splitting reaction. Accordingly, the promoter used is one that catalyzes (1) and (2) but not (3).

Examples of the bearing of the two types of cocatalyst Pt and RuO ₂ in TiO ₂ hydrogen production rate is improved was reported in 1981, for each reduction reaction is described as functioning as a promoter for oxidation reactions However (Non-Patent Document 2), there has been no example of success in this additional test. At present, stable photocatalysts capable of completely decomposing water such as TiO ₂ generally have a large band gap, and the energy level at the top of the valence band is sufficiently higher than the redox potential of O ₂ / H ₂ O. Since it is at a low level, it is considered that a promoter for oxygen generation (for oxidation reaction) is not necessarily effective (Non-patent Documents 3 and 4), and a promoter for hydrogen generation (for reduction reaction) is used. There has been active research.

Since most of the energy of sunlight is in the visible light region, it is preferable that the photocatalyst can utilize light in the visible light region in order to efficiently perform water splitting with sunlight. Since 2000, a photocatalyst that can completely decompose water without using a sacrificial reagent with light energy in the visible light region and is stable in water has been announced (Non-Patent Document 4). . It has been reported that these photocatalysts are also effective when noble metals such as Pt, RuO ₂ , and NiO are used as hydrogen generation promoters (Non-patent Documents 1 and 5).

As for the visible light responsive photocatalyst capable of realizing the complete decomposition reaction of water in one step, GaN: ZnO (Non-patent Document 6) carrying Rh _2-x Cr _x O ₃ has been used as a co-catalyst for the reduction reaction so far. Are known. This has attracted attention as a photocatalyst for hydrogen production using sunlight, because the quantum yield of water splitting reaction around 400 nm is about 5%. However, in order to use these industrially, further improvement in performance has been desired.

On the other hand, in these visible light responsive photocatalysts, it is known that promoters for oxidation reactions such as IrO ₂ and RuO ₂ promote the reaction (Non-patent Documents 7 and 8). However, these are all systems containing Ag ⁺ ions as a sacrificial reagent, or systems containing mediators such as IO ₃ ⁻ / I ⁻ or Fe ³⁺ / Fe ²⁺ , which are oxidation promoters in the complete decomposition reaction of water in one step. The effect has not been demonstrated.

  That is, no photocatalyst has yet been produced, and no production method has been found for a photocatalyst carrying a cocatalyst for both a reduction reaction and an oxidation reaction to exert their respective effects.

Chem.Soc.Rev., 2009,38,253-278 J. Am. Chem. Soc., 1981, 103, 4685-4690. J. Photochem. Photobio. A: Chem 108, (1997) 1-35 Journal of the Chemical Society of Japan 1984, (2), 258-263. J. Phys. Chem. C, 2007, 111, 7851-7861. Chem. Mater. 2010, 22, 612-623. J. Phys. Chem. A 2002, 106, 6750-6753. Chem. Mater. 2008, 20, 1299-1307.

  Therefore, the present invention is a catalyst for photo-water splitting reaction, which has both an oxidation catalyst and a co-catalyst for reduction reaction on the optical semiconductor, and dramatically increases the photo-water splitting reaction rate under light irradiation. It is an object to provide an efficient and industrially advantageous photocatalyst for water splitting reaction, and a method for producing the same.

The present inventors diligently studied to solve the above problems, and have found the following matters.
(1) The photo semiconductor particles are synthesized, and a co-catalyst for oxidation reaction and a co-catalyst for reduction reaction are supported on the particles. FIG. 1 is a conceptual diagram thereof. These cocatalysts are selected so as to catalyze the reduction or oxidation reaction of water but do not catalyze the reaction of generating water from hydrogen and oxygen, which are the final products of water splitting.

  (2) As methods for effectively supporting the respective cocatalysts, there are two types of methods: a photoadsorption support method (also referred to as a photoreduction deposition support method) and an adsorption support method. Adsorption methods such as impregnation are generally used as methods for supporting the cocatalyst. However, if each of the two types of cocatalyst is supported by the adsorption method, the adsorption site cannot be controlled. There is a problem that the catalyst is coated or the cocatalysts come into contact with each other to become a recombination center, resulting in no effect. On the other hand, if one promoter is supported by the adsorption method as usual and the other promoter (preferably the reduction reaction promoter) is supported by the photo-deposition method, at least the latter is at the reduction site of the photocatalyst. Since this is selectively supported (known document J. Phys. Chem. C 2007, 111, 7554-7560), the above problem is reduced. Here, the photo-deposition method (also referred to as the photo-deposition method) is a method in which a metal salt is reduced by light and supported on the surface of the optical semiconductor particles.

  (3) If the amount of the cocatalyst is too small, there is no effect. If the amount is too large, the cocatalyst itself absorbs and scatters light, thereby preventing the photocatalyst from absorbing light or acting as a recombination center. It is known that the activity decreases. The optimum range of the amount of the cocatalyst for the reduction reaction is described in the literature (Chem. Mater. 2001, 13, 1194-1199, J. Phys. Chem. B 2005, 109, 21915-21921, J. Phys. Chem. B 2006, 110, 13753-13758, Journal of Catalysis 243 (2006) 303-308), it is already known that the content is 0.1 to 4% by mass based on the optical semiconductor particles. Accordingly, the amount of the promoter supported is preferably 0.01% by mass or more and 1% by mass or less, more preferably 0. 0% by mass based on the optical semiconductor particles (100% by mass). 01 mass% or more and 0.5 mass% or less, More preferably, it is 0.01 mass% or more and 0.1 mass% or less, The metal loading of a reduction reaction promoter is preferably 0.01 mass% or more and 20 mass% or less. Preferably, it is 0.01 mass% or more and 15 mass% or less, More preferably, it is 0.01 mass% or more and 10 mass% or less.

  Based on the above considerations, the present inventors have completed the following invention. In order to facilitate understanding of the present invention, reference numerals in the accompanying drawings are added in parentheses, but the present invention is not limited to the illustrated embodiment.

The first aspect of the present invention includes an optical semiconductor (10), an oxidation reaction promoter (20), and a reduction reaction promoter (30). The optical semiconductor (10) includes an oxidation reaction promoter (20) and a reduction reaction promoter ( 30) is a photocatalyst for photo-water splitting reaction, wherein the optical semiconductor (10) utilizes light of 420 nm or more , and an oxidation reaction promoter (20) and a reduction reaction promoter (30). two or more cocatalysts are those is carried, and reduction promoter (30) all SANYO supported in a reduced state to an optical semiconductor (10), and the light water decomposition reaction photocatalyst as There is a light water decomposition reaction photocatalytic, characterized in der Rukoto which produce hydrogen and oxygen by decomposing water (100).

In the first invention, the optical semiconductor (10) absorbs light of 400 nm to 1000 nm (preferably 420 nm to 800 nm), and the upper end of its valence band is O ₂ / OH ⁻ (in a basic solution) or O ₂ / H ₂ O (neutral, in acidic solution) lower than the redox potential and the lower end of the conductor is H ₂ O / H ₂ (neutral, in basic solution) or H ⁺ / H ₂ (acidic solution) It is preferable that the photo-semiconductor particles have a higher oxidation-reduction potential in the middle), and the photo-semiconductor particles may be a mixture of two or more.

  In the first aspect of the present invention, the amount of the metal supported by the oxidation reaction promoter (20) is preferably 0.01% by mass or more and 1% by mass or less based on 100% by mass of the optical semiconductor (10). The amount of the metal supported on the catalyst (30) is preferably 0.01% by mass or more and 20% by mass or less, based on 100% by mass of the optical semiconductor (10).

  In the first aspect of the present invention, the oxidation reaction promoter (20) is a group 2-14 metal, an intermetallic compound of the metal, an alloy, or an oxide, composite oxide, nitride, or oxynitride thereof. , Sulfide, oxysulfide, or a mixture thereof. Here, the “intermetallic compound” is a compound formed from two or more kinds of metal elements, and the atomic ratio of the components constituting the intermetallic compound is not necessarily a stoichiometric ratio, but has a wide composition range. Say. “These oxides, composite oxides, nitrides, oxynitrides, sulfides, oxysulfides” are the metals of Group 2-14, intermetallic compounds of these metals, or oxides, composites of alloys Oxides, nitrides, oxynitrides, sulfides, oxysulfides. “A mixture thereof” refers to a mixture of any two or more of the compounds exemplified above. The “oxide” and “composite oxide” include those in which a part of the metal is partially oxidized. “Nitride” and “sulfide” include those in which a part of the metal is partially nitrided or sulfided, and “oxynitride” and “oxysulfide” are partially nitrided oxides. And those that are partially sulfided, nitrides or sulfides that are partially oxidized.

  In the first invention, the reduction reaction promoter (30) is a group 3-13 metal, an intermetallic compound of the metal, an alloy, or an oxide, composite oxide, oxynitride, or sulfide thereof. , Oxysulfides, carbides, nitrides, or mixtures thereof. Here, the “intermetallic compound” is the same as described above, and “these oxides, composite oxides, oxynitrides, sulfides, oxysulfides, carbides, nitrides” are group 3 to group 13 It refers to a metal, an intermetallic compound of the metal, an oxide of an alloy, a composite oxide, an oxynitride, a sulfide, an oxysulfide, a carbide, or a nitride. “A mixture thereof” refers to a mixture of any two or more of the compounds exemplified above. In addition, “oxide” and “composite oxide” include those in which a part of the metal is partially oxidized, and “oxynitride” also includes partially nitrided oxide. “Nitride” and “sulfide” include those in which a part of the metal is partially nitrided or sulfided, and “oxynitride” and “oxysulfide” are partially nitrided oxides. And those that are partially sulfided, nitrides or sulfides that are partially oxidized.

In the first aspect of the present invention, the optical semiconductor (10) includes GaN: ZnO, ZnGeN ₂ : ZnO, LaTiO ₂ N, CaNbO ₂ N, TaON, Ta ₃ N ₅ , Sm ₂ Ti ₂ O ₅ S ₂ , and La _x In. _2-x Ti ₂ O ₅ S ₂ , or KTaO ₃ , SrTiO ₃ or TiO ₂ doped or co-doped with Cr, Ta, Ni, Sb or Rh is preferred. “KTaO ₃ , SrTiO _3, or TiO ₂ doped or co-doped with Cr, Ta, Ni, Sb, or Rh” is “KTaO ₃ : M”, “SrTiO ₃ : M”, “TiO ₂ : M”. In this case, M represents Cr, Ta, Ni, Sb or Rh, indicating that these metals are doped. In the case of co-doping, M is expressed as “M1 / M2”, which indicates that M1 and M2 are co-doped, and M1 and M2 represent the same metal as M described above. .

The second aspect of the present invention is a method for producing a photocatalyst (100) for water-splitting reaction in which an oxidation reaction promoter (20) and a reduction reaction promoter (30) are supported on an optical semiconductor (10),
The photocatalyst (100) for photohydrolysis reaction uses light of 420 nm or more,
The first step (S2) of forming the photocatalyst intermediate by supporting the oxidation reaction cocatalyst (20) on the photo semiconductor (10) by the adsorption carrying method, and the reduction reaction cocatalyst (30) by the photoadsorption carrying method. It is a manufacturing method of the photocatalyst for photo-water-splitting reaction including the 2nd process (S3) made to carry | support to a photocatalyst intermediate body.

  By supporting the latter co-catalyst by the photo-deposition support method, the latter co-catalyst is selectively supported on the reduction site of the optical semiconductor (10). For this reason, two types of co-catalysts, preferably Since the latter adsorption site can be controlled, it is possible to suppress problems such as one of the promoters covering the other promoter and the mutual promoters coming into contact with each other to become recombination centers, resulting in no effect. A photocatalyst (100) for photowater splitting reaction having performance can be produced.

  The photocatalyst (100) for the water-splitting reaction of the present invention is formed by supporting both an oxidation reaction promoter (20) and a reduction reaction promoter (30) on a predetermined optical semiconductor (10). The water splitting reaction can be performed with high activity using the light in the region.

It is a conceptual diagram of the catalyst design of the photocatalyst for photo-water decomposition reaction of this invention. 3 is an explanatory diagram showing an energy structure of the optical semiconductor 10. FIG. It is a flowchart which shows the manufacturing method of the photocatalyst 100 for water-splitting reaction of this invention. (A) And (b) is a schematic diagram of the water splitting activity evaluation apparatus by a photocatalyst. It is a gas generation amount time change by optical water splitting in Example 1, Comparative Example 1 and Comparative Example 2. It is a figure which shows the influence with respect to photocatalytic activity of the amount of promoter support in Example 1. FIG. It is a gas generation amount time change by optical water splitting in Example 2 and Comparative Example 3. It is a figure which shows the influence with respect to photocatalytic activity of the amount of promoter support in Example 2. FIG. It is a gas generation amount time change by the photo-water decomposition in the comparative example 4 and the comparative example 5. FIG.

<Photocatalyst for water splitting>
FIG. 1 is a conceptual diagram showing the catalyst design of the photocatalyst 100 for photo-water splitting reaction of the present invention. The photocatalyst 100 for water-splitting reaction of the present invention includes a photo semiconductor 10, an oxidation reaction co-catalyst 20 and a reduction reaction co-catalyst 30, and the photo semiconductor 10 carries the oxidation reaction co-catalyst 20 and the reduction reaction co-catalyst 30. . In FIG. 1, “CB” indicates a conduction band (conduction band), and “V.B.” indicates a Valence band (valence band). When the optical semiconductor 10 is irradiated with light (hν) having energy greater than the band gap, electrons in the valence band are excited to the conduction band. The excited electrons (e ⁻ ) reduce hydrogen ions to generate hydrogen. The reduction reaction promoter 30 assists the reduction reaction at this time. The holes (h ⁺ ) formed in the valence band oxidize water and generate oxygen. The oxidation reaction promoter 20 assists the oxidation reaction at this time.

(Optical semiconductor 10)
FIG. 2 shows the energy structure of the optical semiconductor 10. As a photocatalyst which comprises the optical semiconductor 10, what kind of compound may be sufficient if the following conditions are satisfy | filled. (1) The potential of electrons (e ⁻ ) generated by light irradiation is more negative than the potential (H ⁺ / H ₂ ) capable of reducing hydrogen ions or water molecules to hydrogen molecules, and holes generated by light irradiation. The potential of (h ⁺ ) is more positive than the potential (O ₂ / H ₂ O) that can oxidize water or hydroxide ions to oxygen molecules. (2) The optical semiconductor 10 is stable even if it is irradiated with light in an aqueous solution and the water splitting reaction proceeds.

As the optical semiconductor 10, a visible light responsive optical semiconductor can be used. Specifically, Bi ₂ WO ₆ , BiYWO ₆ , In ₂ O ₃ (ZnO) ₃ , InTaO ₄ , InTaO ₄ : Ni (“ “Optical semiconductor: M” indicates that the optical semiconductor is doped with M. The same applies hereinafter.), TiO ₂ : Ni, TiO ₂ : Ru, TiO ₂ Rh, TiO ₂ : Ni / Ta (“optical semiconductor: “M1 / M2” indicates that the optical semiconductor is co-doped with M1 and M2. The same applies hereinafter.), TiO ₂ : Ni / Nb, TiO ₂ : Cr / Sb, TiO ₂ : Ni / Sb, TiO _{2 : Sb / Cu, TiO 2:} Rh / Sb, TiO 2: Rh / Ta, TiO 2: Rh / Nb, SrTiO 3: Ni / Ta, SrTiO 3: Ni / Nb, SrTiO 3: Cr, SrTiO 3: Cr / Sb, SrTiO ₃ : Cr / Ta, SrTiO ₃ : Cr / Nb, SrTiO ₃ : Cr / W, SrTiO ₃ : Mn, SrTiO ₃ : Ru, SrTiO ₃ : Rh, SrTiO ₃ : Rh / Sb, SrTiO ₃ : Ir, CaTiO ₃ : Rh, La ₂ Ti ₂ O ₇ : Cr, La ₂ Ti ₂ O ₇ : Cr / Sb, La ₂ Ti ₂ O ₇ : Fe, PbMoO ₄ : Cr, RbPb ₂ Nb ₃ O ₁₀ , HPb _{2 Nb 3 O 10, PbBi 2 Nb} 2 O 9, BiVO 4, BiCu 2 VO 6, BiSn 2 VO 6, SnNb 2 O 6, AgNbO 3, AgVO 3, AgLi 1/3 Ti 2/3 O 2, AgLi 1 / ₃ Sn _2/3 O _2, oxides such _{as, LaTiO 2 N, Ca 0.25 La} 0.75 TiO 2.25 N 0 _{75, TaON, CaNbO 2 N,} CaTaO 2 N, SrTaO 2 N, BaTaO 2 N, LaTaO 2 N, Y 2 Ta 2 O 5 N 2, (Ga 1-x Zn x) (N 1-x O x), (Zn _{1 + x} Ge) (N ₂ O _x ) (x represents a numerical value of 0-1), oxynitrides such as TiN _x O _y F _z , nitrides such as Ta ₃ N ₅ , GaN: Mg, Oxysulfide compounds including sulfides such as CdS, selenides such as CdSe, Ln ₂ Ti ₂ S ₂ O ₅ (Ln: Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er) and La, In ( Chemistry Letters, 2007, 36, 854-855), but is not limited to the materials exemplified herein.

Further, as the optical semiconductor 10 in the present invention, in addition to the visible light responsive optical semiconductor, an ultraviolet light responsive optical semiconductor carrying a sensitizer can also be used. Specific examples of the ultraviolet light-responsive optical semiconductor include TiO ₂ , CaTiO ₃ , SrTiO ₃ , Sr ₃ Ti ₂ O ₇ , Sr ₄ Ti ₃ O ₇ , K ₂ La ₂ Ti ₃ O ₁₀ , and Rb ₂ La. ₂ Ti ₃ O ₁₀ , Cs ₂ La ₂ Ti ₃ O ₁₀ , CsLaTi ₂ NbO ₁₀ , La ₂ TiO ₅ , La ₂ Ti ₃ O ₉ , La ₂ Ti ₂ O ₇ , La ₂ Ti ₂ O ₇ : Ba, KaLaZr _{0 .3} Ti _0.7 O ₄ , La ₄ CaTi ₅ O ₇ , KTiNbO ₅ , Na ₂ Ti ₆ O ₁₃ , BaTi ₄ O ₉ , Gd ₂ Ti ₂ O ₇ , Y ₂ Ti ₂ O ₇ , (Na ₂ Ti ₃ O ₇ , K ₂ Ti ₂ O ₅ , K ₂ Ti ₄ O ₉ , Cs ₂ Ti ₂ O ₅ , H ⁺ -Cs ₂ Ti ₂ O ₅ (H ⁺ -Cs is ion-exchanged when Cs is H ⁺ The same applies hereinafter), Cs ₂ Ti ₅ O ₁₁ , Cs ₂ Ti ₆ O ₁₃ , H ⁺ -CsTiNbO ₅ , H ⁺ -CsTi ₂ NbO ₇ , SiO ₂ -pillared K ₂ Ti ₄ O ₉ , SiO _2- pillared K ₂ Ti _2.7 Mn _0.3 O ₇ (J. Mol. Catal. A: Chem. 2000, 155, 131)) (titanium oxide); ZrO ₂ , Na ₂ W ₄ O ₁₃ ;

K ₄ Nb ₆ O ₁₇ , Rb ₄ Nb ₆ O ₁₇ , Ca ₂ Nb ₂ O ₇ , Sr ₂ Nb ₂ O ₇ , Ba ₅ Nb ₄ O ₁₅ , NaCa ₂ Nb ₃ O ₁₀ , ZnNb ₂ O ₆ , Cs ₂ Nb ₄ O ₁₁ , La ₃ NbO ₇ (H ⁺ -KLaNb ₂ O ₇ , H ⁺ -RbLaNb ₂ O ₇ , H ⁺ -CsLaNb ₂ O ₇ , H ⁺ -KCa ₂ Nb ₃ O ₁₀ , SiO ₂ -pillared KCa ₂ Nb ₃ O ₁₀ (Chem. Mater. 1996, 8, 2534.), H ⁺ -RbCa ₂ Nb ₃ O ₁₀ , H ⁺ -CsCa ₂ Nb ₃ O ₁₀ , H ⁺ -KSr ₂ Nb ₃ O ₁₀ , H ⁺ -KCA ₂ NaNb ₄ O ₁₃ ) (above, Nb oxide);

Ta ₂ O ₅ , K ₂ PrTa ₅ O ₁₅ , K ₃ Ta ₃ Si ₂ O ₁₃ , K ₃ Ta ₃ B ₂ O ₁₂ , LiTaO ₃ , NaTaO ₃ , KTaO ₃ , AgTaO ₃ , KTaO ₃ : Zr, NaTaO ₃ : La, NaTaO ₃ : Sr, Na ₂ Ta ₂ O ₆ , K ₂ Ta ₂ O ₆ (pyrochlore), K ₂ Ta ₂ O ₆ (pyrochlore), CaTa ₂ O ₆ , SrTa ₂ O ₆ , BaTa ₂ O ₆ , NiTa ₂ O ₆ , Rb ₄ Ta ₆ O ₁₇ , H ₂ La _2/3 Ta ₂ O ₇ , K ₂ Sr _1.5 Ta ₃ O ₁₀ , LiCa ₂ Ta ₃ O ₁₀ , KBa ₂ Ta ₃ O ₁₀ , Sr ₅ Ta _{4 O 15, Ba 5 Ta 4} O 15, H 1.8 Sr 0.81 Bi 0.19 Ta 2 O 7, Mg-Ta oxide _{Chem.Mater.2004 16, 4304-4310), LaTaO 4} , La 3 TaO 7 ( or, tantalum oxide);

_{PbWO 4, RbWNbO 6, RbWTaO 6} , CeO 2: Sr, BaCeO 3, (Bi 2 W 2 O 9, Bi 2 Mo 2 O 9, BaBi 4 Ti 4 O 15, Bi 3 TiNbO 9, PbMoO 4, (NaBi) _0.5 MoO ₄ , (AgBi) _0.5 MoO ₄ , (NaBi) WO ₄ , (AgBi) _0.5 WO ₄ , Ga _1.14 In _0.86 O ₃ , Ti _1.5 Zr _1.5 ( _{PO 4) 4), NaInO 2} , CaIn 2 O 4, SrIn 2 O 4, LaInO 3, YxIn 2 -xO 3, NaSbO 3, CaSb 2 O 6, Ca 2 Sb 2 O 7, Sr 2 Sb 2 O 7, Sr ₂ SnO ₄ , ZnGa ₂ O ₄ , Zn ₂ GeO ₄ , LiInGeO ₄ , Ga ₂ O ₃ , Ga ₂ O ₃ : Zn, and the like. Examples of the sensitizer include [Ru (bpy) ₃ ] ²⁺ , erythrosine, zinc porphyrin, CdS and the like.

Moreover, as the optical semiconductor 10, the visible light response type optical semiconductor can be used in which a p-type or n-type optical semiconductor is adsorbed on the surface and a pn junction is formed. The optical semiconductor _{used, CuO, Cu 2 O, CuI} , Cu (InGa) S 2, Cu (InGa) Se 2, CuGaS 2, CuGaSSe, CuGaSe 2, CdS, CdTe, CdZnTe, CdSe, Cu 2 ZnSnS 4, CuGa ₅ S ₈ , CuInS ₂ , Cu (InAl) Se ₂ , CuIn ₅ S ₈ , CuAlO ₂ , CuGaO ₂ , SrCu ₂ O ₂ , GaP, GaAs, GaAsP, GaN, InP, InAs, GaInAsP, GaSb, Si, SiC, Inorganic semiconductors such as Ge, ZnS, and Fe ₂ O ₃ and organic semiconductors such as fullerene derivatives, porphyrin derivatives, phthalocyanine derivatives, and polythiophene derivatives can be used, but the materials are not limited to those exemplified here. Absent.

As the optical semiconductor 10, the visible light responsive optical semiconductor can directly use visible light, and is preferable in terms of manufacturing advantages. Among them, GaN: ZnO, ZnGeN ₂ : ZnO, LaTiO ₂ N, _{CaNbO 2 N, TaON, Ta 3} N 5, Sm 2 Ti 2 O 5 S 2, La x in 2-x Ti 2 O 5 S 2, or doped or co-doped with Cr, Ta, Ni, Sb or Rh KTaO ₃ , SrTiO ₃ or TiO ₂ is preferred.

Furthermore, as the optical semiconductor 10, among others, LaTiO ₂ N, CaNbO ₂ N, Ga _1-x Zn _x N _1-x O _x (x represents a numerical value of 0 to ₁ ), Sm ₂ Ti ₂ S _2. Use of O ₅ is preferable from the viewpoint of high photocatalytic activity, abundance on the ground, and low cost.

  The optical semiconductor 10 is preferably a particle, and the particle size of the primary particle is not particularly limited, but is usually 0.001 μm or more, preferably 0.005 μm or more, and usually 500 μm or less, Preferably it is 10 micrometers or less. The particle diameter of the optical semiconductor 10 can be appropriately measured by a known means such as XRD, TEM, or SEM method.

(Oxidation reaction promoter 20 and reduction reaction promoter 30)
The optical semiconductor 10 supports both the oxidation reaction promoter 20 (oxygen generation side) and the reduction reaction promoter 30 (hydrogen generation side). As the oxidation reaction promoter 20, a metal of Group 2-14, an intermetallic compound of the metal, an alloy, or an oxide, composite oxide, nitride, oxynitride, sulfide, oxysulfide, Alternatively, it is preferable to use any of these mixtures. Here, the “intermetallic compound” is a compound formed from two or more kinds of metal elements, and the atomic ratio of the components constituting the intermetallic compound is not necessarily a stoichiometric ratio, but has a wide composition range. Say. “These oxides, composite oxides, nitrides, oxynitrides, sulfides, oxysulfides” are the metals of Group 2-14, intermetallic compounds of these metals, or oxides, composites of alloys Oxides, nitrides, oxynitrides, sulfides, oxysulfides. “A mixture thereof” refers to a mixture of any two or more of the compounds exemplified above.

The oxidation reaction promoter 20 in the present invention is preferably Mg, Ti, Mn, Fe, Co, Ni, Cu, Ga, Ru, Rh, Pd, Ag, Cd, In, Ce, Ta, W, Ir, Pt or Pb metal, oxide or composite oxide thereof, more preferably metal of Mn, Co, Ni, Ru, Rh, Ir, oxide or composite oxide thereof, and further preferably _{Ir, MnO,} a _{MnO 2, Mn 2 O 3,} Mn 3 O 4, CoO, Co 3 O 4, NiCo 2 O 4, RuO 2, Rh 2 O 3, IrO 2.

  As the reduction reaction co-catalyst 30 in the present invention, a Group 3-13 metal, an intermetallic compound of the metal, an alloy, or an oxide, composite oxide, oxynitride, sulfide, oxysulfide thereof, It is preferable to use any one of carbide, nitride, or a mixture thereof. Here, the “intermetallic compound” is the same as described above, and “these oxides, composite oxides, oxynitrides, sulfides, oxysulfides, carbides, nitrides” are group 3 to group 13 It refers to a metal, an intermetallic compound of the metal, an oxide of an alloy, a composite oxide, an oxynitride, a sulfide, an oxysulfide, a carbide, or a nitride. “A mixture thereof” refers to a mixture of any two or more of the compounds exemplified above.

The reducing reaction assistant catalyst 30, preferably, Pt, Pd, Rh, Ru , Ni, Au, Fe, NiO, RuO 2, IrO 2, Rh 2 O 3, and, Cr-Rh complex oxide, core-shell Rh / Cr ₂ O ₃ , Pt / Cr ₂ O _{3 and the} like.

As the amount of the above-mentioned promoter, the amount of the metal supported by the oxidation reaction promoter 20 is not particularly limited, but is usually 0.01% by mass or more and 1% by mass or less based on the optical semiconductor 10 (100% by mass). The upper limit is preferably 0.5% by mass or less, and more preferably the upper limit is 0.1% by mass or less. The amount of metal supported on the reduction reaction promoter 30 is not particularly limited, but is usually 0.01% by mass or more and 20% by mass or less, preferably 15% by mass or less, based on the optical semiconductor 10 (100% by mass). More preferably, the upper limit is 10% by mass or less.
As used herein, “metal loading” refers to the amount occupied by the metal element in the supported promoter.

<Method for producing photocatalyst for photo-water splitting reaction>
Next, the manufacturing method of the photocatalyst 100 for water splitting of this invention is demonstrated. In addition, the manufacturing method shown below is one Embodiment for the method for manufacturing the photocatalyst of this invention to the last, Comprising: It is not the meaning which excludes another method.

  As shown in the flowchart in FIG. 3, the method for producing a photocatalyst 100 for water-splitting reaction according to the present invention includes the step of preparing the optical semiconductor 10 (S 1), A first step (S2) in which any one of the catalysts 30 is supported by an adsorption supporting method to form a photocatalyst intermediate, and a cocatalyst that is not supported in the first step is subjected to a photocatalytic intermediate by a photoadsorption supporting method. A second step (S3) to be carried on the substrate.

  As a specific form of step S1, there is a method of preparing an optical semiconductor 10 that absorbs visible light and exhibits optical semiconductor characteristics. For example, as a method of preparing GaN: ZnO, J. Am. Chem. Soc. 2005 , 127, 8286.

The specific form of process S2 and process S3 is demonstrated.
Here, the photodeposition support method refers to a method in which a photo semiconductor particle and a metal salt coexist, the metal salt is reduced by light irradiation, and supported on the photo semiconductor particle as a metal or a metal compound.
First, the promoter nanoparticle or the precursor of the promoter particle of either the oxidation reaction promoter 20 or the reduction reaction promoter 30 is dispersed in a solvent such as THF or ethanol. The prepared optical semiconductor 10 is suspended in this dispersion. This suspension is stirred for 1 to 12 hours to adsorb the promoter nanoparticle or the precursor of the promoter particle to the surface of the optical semiconductor. Sonication may be performed during suspension. Thereby, adsorption | suction to the surface of the optical semiconductor of the promoter nanoparticle or the precursor of a promoter particle can be promoted. The particle diameter of the promoter nanoparticle or the precursor of the promoter particle is not particularly limited, but is usually 1 nm or more, preferably 2 nm or more, usually 100 nm or less, preferably 50 nm or less.

  The suspension is filtered or the solvent is dried up and then calcined in air at 50 to 500 ° C. for 0.5 to 12 hours. In order to support the other promoter on the photocatalyst intermediate prepared in this way, a solution in which the precursor of the promoter to be subsequently supported is dissolved (the solvent is the same as in Step S1 above). Can be used.) The photocatalytic intermediate is suspended. This suspension is irradiated with light in the visible light region (λ ≧ 420 nm) at room temperature in the absence of air and oxygen for several hours, and a metal or a metal oxide serving as a cocatalyst is supported on the electrodeposition. This photodeposition procedure is repeated depending on the type of promoter supported. The firing temperature and the time required for the photo-deposition vary depending on the type of the optical semiconductor 10 and the cocatalysts (precursors) 20 and 30 used.

  The co-catalyst nanoparticles can be obtained, for example, by a colloid method using PVA (polyvinyl alcohol) or PVP (polyvinyl pyrrolidone) as a protecting group (Polymer J. 1999, 31, 1127-1132., Angew. Chem., Int. Ed. 2007, 46, 5397-5401).

  Examples of the precursor of the promoter particles include hydroxides, chlorides, nitrates, carbonates, acetates, oxalates and phosphates of various promoter metals, various alcoholates, phenolates, carboxylates, acetylacetonates, Thiolate, thiocarboxylate complex, ammine complex, various amine complexes, various substituted pyridines, imidazole, bipyridine, terpyridine, phenanthroline, porphyrin complex, various nitrile complexes, etc. can be used, but are limited to the materials exemplified here Is not to be done.

  In the production method of the present invention described above, it is preferable that the oxidation reaction promoter 20 is supported in the first step (S2), and the reduction reaction promoter 30 is supported in the subsequent second step (S3). In the first step (S2), after carrying the cocatalyst, a calcination treatment is performed. In the first step (S2), if the reduction reaction cocatalyst 30 is carried first and the calcination treatment is performed, the activity of the reduction reaction cocatalyst 30 is increased. Therefore, the above order is preferable.

(Measurement conditions of particle size)
In the following examples, the particle diameter of the optical semiconductor was measured with a scanning electron microscope (hereinafter referred to as SEM).
Measuring device: Hitachi, Ltd .: S-4700

The particle diameter of the promoter was measured with a transmission electron microscope (hereinafter referred to as TEM).
Measuring device: JEM-1011 manufactured by JEOL
Acceleration voltage: 100 kV

(Example 1, Comparative Examples 1 and 2)
<Preparation of GaN: ZnO (ZnO / GaN≈0.13 (molar ratio))>
1.08 g of Ga ₂ O ₃ and 0.94 g of ZnO were mixed, and nitriding was performed at 825 ° C. for 13 hours under an ammonia stream (250 mL · min ⁻¹ ). The formation of the photocatalyst was confirmed by XRD (X-ray diffusion) and EDX (energy dispersive X-ray). The band gap energy of the prepared photocatalyst GaN: ZnO was 2.68 eV by measuring the diffuse reflection spectrum.
The particle diameter of the optical semiconductor particles GaN: ZnO by SEM observation was 100 to 500 nm.

<Preparation of MnO nanoparticles>
Under a nitrogen atmosphere, dissolve MnCl ₂ .4H ₂ O (40 mmol) and sodium oleate (80 mmol) in a mixed solvent of ethanol (30 mL), distilled water (40 mL), and hexane (70 mL), and heat at 70 ° C. overnight. did. After separating the organic phase with a separatory funnel and distilling off the solvent, the produced manganese-oleic acid complex (0.4 mmol) was heated in 1-octadecane (10 mL) in the following procedure. . The mixture was heated at 120 ° C. under reduced pressure for 1 hour, and then the temperature was raised to 300 ° C. at 10 ° C. · min ⁻¹ . The mixture was stirred at 300 ° C. with a magnetic stirrer for 30 minutes and then cooled to room temperature. The product was washed with ethyl acetate and then dispersed in THF to obtain MnO nanoparticles. As a result of observation by TEM, the average diameter of the MnO nanoparticles was 9.2 ± 0.4 nm.

<Preparation of Mn ₃ O ₄ / GaN: ZnO>
The prepared GaN: ZnO was suspended in THF in which MnO nanoparticles (0.01 to 0.5 mass% Mn with respect to GaN: ZnO) were dispersed. After sonication, THF (5 mL) containing 16-hydroxyhexadecanoic acid (20 μmol) was added to the suspension and stirred for 3 hours. By this treatment, all MnO nanoparticles were adsorbed on the GaN: ZnO surface. GaN: ZnO adsorbed with MnO was heated from room temperature to 400 ° C. at a rate of 5 K · min ⁻¹ in air and calcined for a total of 3 hours. After firing, MnO changed to Mn ₃ O ₄ , but no significant change in particle size was observed. It has been confirmed by UV-VIS spectrum that the entire amount of MnO nanoparticles is adsorbed, and the amount of metal supported on GaN: ZnO by Mn is 0.01 to 0.5% by mass, similar to the charged amount.

<Preparation of Rh / Cr ₂ O ₃ (core / shell) / GaN: ZnO / Mn ₃ O ₄ >
Mn ₃ O ₄ / GaN: ZnO (0.13 g) is suspended in an aqueous solution of Na ₃ RhCl ₆ (1% by mass Rh with respect to GaN: ZnO), and air is not present using the apparatus shown in FIG. Under visible light (λ> 420 nm) was irradiated for 4 hours to photoreduct Rh (III) to metal Rh. After precipitation of Rh, the obtained sample was suspended in an aqueous K ₂ CrO ₄ solution (0.8 mM, 1.5 mass% Cr with respect to GaN: ZnO), and again irradiated with visible light (λ> 420 nm) for 4 hours. K ₂ CrO ₄ was reduced to Cr ₂ O ₃ . For the light irradiation, a 300 W xenon lamp equipped with a cutoff filter was used. Cooling water was used during light irradiation to keep the solution temperature at room temperature. The product was washed thoroughly with distilled water and dried at 70 ° C. overnight. The metal loading of Rh on GaN: ZnO is 0.75% by mass, and the metal loading of Cr on GaN: ZnO is 0.31% by mass.

<Preparation of Rh / Cr ₂ O ₃ / GaN: ZnO>
In the method described in the preparation of Rh / Cr ₂ O ₃ / GaN: ZnO / Mn ₃ O ₄ , GaN: ZnO (0.13 g) was used instead of Mn ₃ O ₄ / GaN: ZnO (0.13 g) as a raw material. Rh / Cr ₂ O ₃ / GaN: ZnO was prepared in the same manner except that was used. The metal loading of Rh on GaN: ZnO is 0.75% by mass, and the metal loading of Cr on GaN: ZnO is 0.31% by mass.

<Light water splitting reaction>
As the light irradiation device, the device shown in FIG. 4A was used (equipped with a 300 W xenon lamp (λ> 420 nm) and a cutoff filter). The photocatalyst 0.1 g prepared above and 100 mL pure water were degassed several times in a reaction vessel connected to a closed circulation system, and it was confirmed that no air remained. Thereafter, light irradiation was started, and the amount of gas produced was measured. Gas chromatography was used for quantification of the product gas.

“Mn ₃ O ₄ / GaN: ZnO” (Comparative Example 1), “Rh / Cr ₂ O ₃ / GaN: ZnO” (Comparative Example 2), and “Rh / Cr ₂ O ₃ / GaN: FIG. 5 shows the result of comparison of the photohydrolysis activity of “ZnO / Mn ₃ O ₄ ” (Example 1).
As shown in FIG. 5, “Mn ₃ O ₄ / GaN: ZnO” (Comparative Example 1) carrying only Mn ₃ O ₄ as an oxidation reaction co-catalyst did not show water splitting activity. On the other hand, both promoters were supported as compared with “Rh / Cr ₂ O ₃ / GaN: ZnO” (Comparative Example 2) supporting only the reduction reaction promoter Rh / Cr ₂ O ₃ (core-shell). “Rh / Cr ₂ O ₃ / GaN: ZnO / Mn ₃ O ₄ ” (Example 1) (Mn supported amount of the catalyst described in the data of FIG. 5 is 0.05 mass%) is higher water. The decomposition activity was shown, and the activity was about 1.8 times that of the conventional catalyst “Rh / Cr ₂ O ₃ / GaN: ZnO” (Comparative Example 2). This demonstrates the effectiveness of loading both promoters for redox on the photocatalyst.

FIG. 6 shows the results of examining the influence of the amount of Mn supported in the water splitting reaction when “Rh / Cr ₂ O ₃ / GaN: ZnO / Mn ₃ O ₄ ” is used (FIG. 4 (a ), Catalyst: 0.1 g, pure water 100 mL, 300 W xenon lamp and cutoff filter). As shown in FIG. 6, it was found that the supported amount of Mn was 0.05% by mass and the highest water splitting activity was obtained, and the optimum supported amount was 0.01 to 0.1% by mass. The reference for the amount of Mn supported (mass%) shown in FIG. 6 is an optical semiconductor, that is, “GaN: ZnO”.

(Example 2, Comparative Example 3)
<Preparation of Ru nanoparticles>
Ru nanoparticles were prepared according to known literature (Polymer J. 1999, 31, 1127-1132.). 2.0 mmol of PVP K-300 (poly (N-vinyl-2-pyrrolidone), mw = 40,000) and 0.05 mmol of RuCl ₃ 3H ₂ O were mixed with ethanol-water (ethanol: water = 1: 1 v / Dissolved in v) to 50 mL. The mixture was heated to reflux at 95-100 ° C. for 2 hours.

<Preparation of RuO ₂ / GaN: ZnO>
In the same manner as described in the preparation of Mn ₃ O ₄ / GaN: ZnO, except that Ru nanoparticles were used as raw materials and the firing time was set to 2 hours in total, “RuO ₂ / GaN: ZnO "was prepared. The amount of metal supported on GaN: ZnO in Ru was 0.01 to 0.1% by mass.

<Preparation of Rh / Cr ₂ O ₃ (core / shell) / GaN: ZnO / RuO ₂ >
Wherein: the _{"Rh / Cr 2 O 3 / GaN} ZnO / Mn 3 O 4 " procedure described in the preparation of, _RuO 2 / GaN raw material: other using ZnO in the same manner, "Rh / _Cr 2 _{O 3} (Core / shell) / GaN: ZnO / RuO ₂ ”was prepared. The amount of metal supported on GaN: ZnO in Rh was 0.75% by mass, and the amount of metal supported on GaN: ZnO in Cr was 0.31% by mass.

Optical water of “Rh / Cr ₂ O ₃ / GaN: ZnO” (Comparative Example 3) and “Rh / Cr ₂ O ₃ / GaN: ZnO / RuO ₂ ” (Example 2) prepared as described above. The degradation reaction activity was evaluated by the apparatus shown in FIG. 4B, and the comparison results are shown in FIG. 7 (catalyst: 0.15 g, pure water 400 mL, 450 W high-pressure mercury lamp (λ> 400 nm) and NaNO ₂ solution filter ). Note that the amount of Ru supported on the “Rh / Cr ₂ O ₃ / GaN: ZnO / RuO ₂ ” catalyst described in the data of FIG. 7 is 0.03% by mass.

Similar to the case of Example 1, compared with “Rh / Cr ₂ O ₃ / GaN: ZnO” (Comparative Example 3) supporting only the reduction reaction promoter Rh / Cr ₂ O ₃ (core-shell). “Rh / Cr ₂ O ₃ / GaN: ZnO / RuO ₂ ” (Example 2) carrying both cocatalysts showed higher water splitting activity, the activity of which is a conventional catalyst “Rh / Cr ₂ It was about 1.5 times that of “O ₃ / GaN: ZnO” (Comparative Example 3).

FIG. 8 shows the results of examining the effect of the amount of Ru supported in the water splitting reaction when “Rh / Cr ₂ O ₃ / GaN: ZnO / RuO ₂ ” is used. As shown in FIG. 8, it was found that the Ru loading amount showed the highest water splitting activity at 0.03% by mass, and the optimum loading amount was 0.01 to 0.05% by mass (FIG. 4B). Apparatus use, catalyst: 0.15 g, pure water 400 mL, 450 W high pressure mercury lamp (λ> 400 nm) and NaNO ₂ solution filter). In addition, the reference | standard of Ru load (mass%) shown in FIG. 8 is an optical semiconductor, ie, "GaN: ZnO."

(Comparative Examples 4 and 5)
_{<Rh x Cr 2-x O} 3 / GaN with both adsorption carrier: Preparation of ZnO / _Mn 3 _{O 4>}
The preparation was carried out according to known literature (J. Phys. Chem. B 2006, 110, 13753-13758). The _Mn 3 _O 4 _{/GaN:ZnO(0.3g~0.4g)} the _{Na 3 RhCl 6 · 2H 2 O} (GaN: 1.0 % by weight relative to _{ZnO Rh), Cr (NO)} 3 · 9H 2 It was suspended in a 3 mL to 4 mL aqueous solution containing O (1.5 mass% Cr with respect to GaN: ZnO), and the solvent was evaporated and dried while stirring with a glass rod in an evaporating dish on a water bath. Thereafter, it was fired at 400 ° C. in air.

_{<Rh x Cr 2-x O} 3 / GaN: Preparation of ZnO>
Wherein _{Rh x Cr 2-x O 3} / GaN: In the procedure described in the preparation of ZnO / _Mn 3 _{O 4,} as a raw _{material, Mn 3 O 4 / GaN:} GaN instead of ZnO: other using ZnO is similarly Te, _{"Rh x Cr 2-x O 3} / GaN: ZnO " was prepared.

Were prepared as described above, _{"Rh x Cr 2-x O 3} / GaN: ZnO " (Comparative Example 4), and _{"Rh x Cr 2-x O 3} / GaN: ZnO / Mn 3 O 4 " ( FIG. 9 shows the result of comparison of the photowater decomposition reaction activity of Comparative Example 5) with the apparatus shown in FIG. 4A (catalyst: 0.1 g, pure water 100 mL, 300 W xenon lamp (λ> 420 nm)).

As shown in FIG. 9, carrying only reduction cocatalyst _{"Rh x Cr 2-x O 3} / GaN: ZnO " (Comparative Example 4) and, an adsorption method both the co-catalyst for the oxidation and reduction reactions The photohydrolysis activity of “Rh _x Cr _{2 -x} O ₃ / GaN: ZnO / Mn ₃ O ₄ ” (Comparative Example 5) supported by (3) was hardly changed. This is because Cr ₂ O ₃ that was selectively deposited on the Rh metal in the photo-deposition support method was also deposited on Mn ₃ O ₄ that is the cocatalyst on the oxidation reaction side in the adsorption support. It is presumed to inhibit the promoter function of ₃ O ₄ . From this, it is clear that it is important to support at least one of the two co-catalysts by photoelectron deposition.

  While the present invention has been described in connection with embodiments that are presently the most practical and preferred, the present invention is not limited to the embodiments disclosed herein. Rather, it can be changed as appropriate without departing from the spirit or concept of the invention that can be read from the claims and the entire specification, and the photocatalyst for photowater splitting and the method for producing the photocatalyst for photowater splitting accompanying such changes are also included. It should be understood as being included within the scope of the present invention.

  The present invention provides a new possibility for a photocatalyst design and production method for performing a water splitting reaction using visible light. Moreover, the system which advances water decomposition more efficiently than before can be constructed | assembled using the photocatalyst of this invention. According to the present invention, a hydrogen production technique by effective water splitting using a photocatalyst can be provided.

100 Photocatalyst for water splitting reaction 10 Optical semiconductor 20 Oxidation reaction promoter 30 Reduction reaction promoter

Claims (8)

A photocatalyst for photo-water splitting reaction comprising a photo semiconductor, an oxidation reaction co-catalyst and a reduction reaction co-catalyst, wherein the photo-semiconductor carries the oxidation reaction co-catalyst and the reduction reaction co-catalyst,
Said optical semiconductor utilizes more light _{420nm, GaN: ZnO, ZnGeN 2} : ZnO, is either _{LaTiO 2 N, CaNbO 2 N,} TaON, and _Ta 3 _{N 5,}
Two or more kinds of promoters are supported as the oxidation reaction promoter and the reduction reaction promoter.
The reduction reaction cocatalyst and the oxidation reaction cocatalyst catalyze the reduction and oxidation reaction of water, respectively, but do not catalyze the reaction of generating water from hydrogen and oxygen, which are the final products of water splitting. ,
The reduction reaction co-catalyst is supported on the optical semiconductor in a reduced state, and the photocatalyst for photo-water splitting reaction decomposes water to generate hydrogen and oxygen. Photocatalyst for photo-water splitting reaction. The amount of the metal supported by the oxidation reaction promoter is 0.01% by mass or more and 1% by mass or less based on 100% by mass of the optical semiconductor, and the amount of the metal supported by the reduction reaction promoter is 100% by mass of the optical semiconductor. The photocatalyst for photo-water splitting reaction according to claim 1, wherein the content is 0.01% by mass or more and 20% by mass or less. The oxidation reaction cocatalyst, Mn, Co, Ni, Ru, and Rh or Ir, oxide or composite oxide, or the light water decomposition reaction photocatalyst according to claim 1 or 2 a mixture thereof. The reduction reaction _{cocatalyst, NiO, RuO 2, Rh 2} O 3, Cr-Rh complex oxide, core-shell _{Rh / Cr 2 O 3, Pt} / Cr 2 O 3, or a mixture thereof, according to claim The photocatalyst for photo-water splitting reaction according to any one of 1 to 3 . The photocatalyst for photo-water splitting reaction according to any one of claims 1 to 4 , wherein the reduction reaction co-catalyst is supported by a photodeposition support method. The particle size of the primary particles of the photocatalyst, and wherein the at 500μm or less than 0.001 [mu] m, according to claim 1-5 light water decomposition reaction photocatalyst according to any one of. The reduction reaction cocatalyst, after adsorbing carrying the oxidation reaction cocatalyst to said optical semiconductor, and characterized in that supported on the reduction site of said optical semiconductor, in any one of claims 1 to 6 The photocatalyst for photo-water decomposition reaction as described. A method for producing a photocatalyst for a photohydrolysis reaction in which an oxidation reaction promoter and a reduction reaction promoter are supported on an optical semiconductor,
The light water decomposition reaction photocatalyst utilize more light _{420nm, GaN: ZnO, ZnGeN 2} : ZnO, is either _{LaTiO 2 N, CaNbO 2 N,} TaON, and _Ta 3 _{N 5,}
The reduction reaction cocatalyst and the oxidation reaction cocatalyst catalyze the reduction and oxidation reaction of water, respectively, but do not catalyze the reaction of generating water from hydrogen and oxygen, which are the final products of water splitting. ,
A first step of supporting the oxidation reaction cocatalyst on the photo semiconductor by an adsorption supporting method to form a photocatalyst intermediate; and a second step of supporting the reduction reaction cocatalyst on the photocatalytic intermediate by a photoadsorption supporting method. A process for producing a photocatalyst for photo-water splitting reaction.

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