JP5787347B2 - Immobilized photocatalyst for water splitting and method for producing hydrogen and / or oxygen - Google Patents

Description

  The present invention is a water splitting photocatalyst-immobilized product provided with a photocatalyst layer containing a predetermined visible light responsive photo-semiconductor and a hydrophilic inorganic material, and hydrogen and / or oxygen using the water-splitting photocatalyst immobilized product. It relates to a manufacturing method.

  Practical use of high-performance light energy conversion systems that use renewable energy such as solar energy has been in progress in recent years from the perspective of suppressing 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, etc.). Since most of the energy of sunlight is in the visible light region, in order to efficiently perform water splitting with sunlight, it is preferable that most of the energy can use light in the visible light region. The original photocatalyst was only usable in the ultraviolet region (380 nm or less) in the wavelength region where only about 4% of sunlight is contained, but since 2000, light in the visible region is used. Photocatalysts that can completely decompose water and are stable in water have been proposed. Furthermore, a technique for improving conversion efficiency by supporting a cocatalyst on a photocatalyst has been proposed.

For example, GaN carrying _Rh 2-X _Cr X _{O 3} as a co-catalyst: ZnO is the quantum yield of the water decomposition reaction in the vicinity of 400nm is about 5%, as a photocatalyst for hydrogen production using sunlight It is attracting attention (Non-Patent Documents 2, 3, etc.).

  Here, in a water splitting experiment using a photocatalyst on a laboratory scale, a dispersion containing photocatalyst particles is stirred and reacted in a reactor irradiated with light. It is known that when the water splitting reaction is performed without stirring, the reaction efficiency decreases (Non-patent Document 4). Normally, light is irradiated from the upper surface, so in a system that is sufficiently suspended by stirring, the photocatalyst near the water surface absorbs light and decomposes water, so that the generated hydrogen and oxygen are in the gas phase. If the photocatalyst sinks in water, it is likely to be released, but the distance to the water surface becomes longer, and the generated hydrogen and oxygen cannot be diffused from the catalyst surface into the gas phase, and return to water by a reverse reaction. It is thought to be the cause. Further, when the photocatalyst has low wettability, the product gas is easily adsorbed as bubbles on the surface of the photocatalyst, which also inhibits the diffusion of the product gas into the gas phase and causes a reverse reaction.

However, when producing hydrogen as a chemical raw material or energy source using a photocatalyst, for example, assuming that the solar conversion efficiency (η) of the photocatalyst is 10%, Even near the equator where the amount of solar radiation is large, a photocatalyst and reactor area of 25 km ² or more are required. It is not practical to perform the stirring operation in such a large-scale reactor from the viewpoint of the apparatus and the hydrogen production cost.

In addition, since it is difficult to keep the photocatalyst uniformly in the reactor as a powder, it is preferable to fix the photocatalyst in a plate or sheet in advance. Furthermore, even when it is assumed that the photocatalyst replacement / recovery operation is performed, or from the viewpoint of manufacturing efficiency, it is preferable to fix the photocatalyst in advance because the operation is simple. For example, Patent Document 1 proposes a technique in which a photocatalyst carrying iridium oxide as a co-catalyst on titanium oxide is fixed onto a substrate using SiO ₂ as a binder.

  However, as a result of investigations by the present inventors, it has been found that when the photocatalyst is immobilized and water decomposition is carried out, the decomposition efficiency may be significantly reduced. Patent Document 1 also shows that when a photocatalyst and a binder are mixed and used, the oxygen generation rate is reduced as compared to the case where no binder is used (FIG. 3, Patent A and Sample A of Patent Document 1). Comparison with C).

  Therefore, in order to carry out water splitting with a photocatalyst industrially and on a large scale, there is a demand for an immobilization technique that can sufficiently exhibit the photowater splitting performance of the photocatalyst without stirring the photocatalyst. It was.

JP 2001-219073 A

Chem. Soc. Rev., 2009, 38, p.253-278 Nature 2006, 440 (7082), p.295 Chem. Mater. 2010, 22 (3), p.612-623 Latest Trends in Water-Splitting Photocatalytic Technology CM Publishing 2003, p. 61-68

  The present invention provides a photocatalyst-immobilized product that can be used easily and efficiently without reducing the photocatalytic performance of the photocatalyst, and a method for producing hydrogen and / or oxygen using the photocatalyst-immobilized product. The task is to do.

  As a result of intensive investigations by the present inventors, a visible light responsive photocatalyst carrying a cocatalyst and hydrophilic inorganic material particles are applied on a substrate so as to be mixed, and fixed as a photocatalyst layer on the substrate. The inventors have found that a photocatalyst-immobilized product having good photohydrolysis performance can be obtained, and have completed the present invention.

  When the hydrophilic inorganic material particles are not present, the photocatalyst layer is formed by visible light responsive photocatalyst particles having low hydrophilicity, so that water hardly enters between the photocatalyst particles. As a result, only the photocatalyst near the uppermost surface of the photocatalyst layer can be used for the photohydrolysis reaction. However, the coexistence of hydrophilic inorganic material particles makes it easy for water to enter the photocatalyst layer, and can cause a photowater decomposition reaction not only near the top surface of the photocatalyst layer but also inside the photocatalyst layer. Also, the product surface is less likely to adhere to the photocatalyst layer due to the hydrophilic surface, and the diffusion of the product gas into the gas phase is promoted, so the reaction efficiency per unit area and unit photocatalyst amount has been improved. Is done.

That is, the gist of the present invention resides in the following (1) to ( 6 ).
(1) A photocatalyst immobilization product for water splitting having a photocatalyst layer on a base material, wherein the photocatalyst layer contains one or more atoms selected from the group consisting of Ga, Zn, Ti, La, Ta and Ba At least one hydrophilic inorganic material selected from the group consisting of a visible light responsive optical semiconductor that is an oxide or an oxynitride, a promoter supported on the visible light responsive optical semiconductor, silica, alumina, and titanium oxide preparative only containing photocatalyst layer has a visible-light-responsive semiconductor cocatalyst is supported, hydrophilic inorganic material and is mixed with features to water splitting photocatalytic immobilizates by comprising.
(2) The visible light responsive optical semiconductor and the hydrophilic inorganic material are in the form of particles, and the particle diameter of the hydrophilic inorganic material is smaller than the particle diameter of the visible light responsive optical semiconductor carrying the promoter, (1) The photocatalyst fixed product for water splitting according to (1).
( 3 ) The photocatalyst for water splitting according to (1) or (2) , wherein the visible light responsive optical semiconductor is at least one selected from the group consisting of GaN: ZnO, LaTiO ₂ N, and BaTaO ₂ N: Mg. Immobilized material.
( 4 ) The promoter is at least one selected from the group consisting of Pt, Pt—Ru, Ru—Ir, Rh—Cr composite oxide, Ru oxide, Ir oxide, Co oxide, and Mn oxide. The photocatalyst fixed material for water splitting according to any one of (1) to (3) .
( 5 ) The photocatalyst immobilized product for water splitting according to any one of (1) to ( 4 ), wherein the hydrophilic inorganic material is silica.
( 6 ) The photocatalyst immobilized product for water splitting according to any one of (1) to ( 5 ) is disposed in water, and water is decomposed by irradiating the photocatalyst immobilized product with light. Hydrogen and / or oxygen Production method.

In the present application, “X: M” means an optical semiconductor X doped with M or dissolved. For example, “GaN: ZnO” is a solid solution of ZnO in GaN, which is an optical semiconductor, and “BaTaO ₂ N: Mg” is a BaTaO ₂ N, which is an optical semiconductor, doped with Mg. It is.

In the present application, “X: M1 / M2” means that the optical semiconductor X is co-doped with M1 and M2. For example, TiO ₂ : Ni / Ta is obtained by co-doping Ni and Ta into TiO _{2 that} is an optical semiconductor.

In the present application, “M1-M2” means that the metal M1 fine particles and the metal M2 fine particles are adjacent to each other and have an intermetallic interaction with each other. For example, Ru—Ir / BaTaO ₂ N: Mg is a BaTaO ₂ N photocatalyst doped with Mg that supports two kinds of metals, Ru and Ir 2, as co-catalysts.

  In the present invention, by allowing a hydrophilic inorganic material to coexist with a visible light responsive photocatalyst in the photocatalyst layer, water can be infiltrated not only into the vicinity of the surface of the photocatalyst layer but also into the interior during the water splitting reaction. As a result, it becomes difficult for the produced gas to adhere to the photocatalyst layer due to the hydrophilic surface, and as a result, diffusion of the produced gas into the gas phase is promoted. Further, stirring in the reactor is unnecessary, and the water splitting reaction can be performed easily. That is, according to the present invention, the photocatalyst-immobilized product for water splitting that can be used simply and efficiently without reducing the photocatalytic performance of the photocatalyst, and hydrogen and / or Alternatively, a method for producing oxygen can be provided.

It is a figure which shows roughly the photocatalyst fixed material of this invention which concerns on one Embodiment. It is a figure for demonstrating the structure of a photocatalyst. It is a figure which shows roughly the evaluation apparatus of the photocatalyst fixed material used in the Example.

1. The photocatalyst immobilized product for water splitting according to the present invention is a photocatalyst immobilized product having a photocatalyst layer on a substrate, and the photocatalyst layer is made of Ga, Zn, Ti, La, Ta, and Ba. A visible light responsive optical semiconductor that is a nitride or oxynitride containing one or more atoms selected from the group, a promoter supported on the visible light responsive optical semiconductor, silica, alumina, and titanium oxide It is characterized by containing at least one hydrophilic inorganic material selected from the group.

  In FIG. 1, the photocatalyst fixed material 100 for water splitting of this invention which concerns on one Embodiment is shown roughly. As shown in FIG. 1, the photocatalyst immobilization product 100 is provided with a photocatalyst layer 10 in which a photocatalyst 1 and a hydrophilic inorganic material 2 are mixed on the surface of a substrate 20. Here, for example, as shown in FIG. 2, the photocatalyst 1 is formed by supporting promoters 1b and 1b on a visible light responsive optical semiconductor 1a. Hereinafter, each component requirement will be described.

1.1. Photocatalyst layer 10
The photocatalyst layer 10 includes (1) a visible light responsive optical semiconductor 1a, (2) a promoter 1b supported on the visible light responsive optical semiconductor 1a, and (3) a hydrophilic inorganic material 2. The visible light responsive optical semiconductor 1a carrying the promoter 1b functions as the photocatalyst 1.

(1) Visible light responsive optical semiconductor 1a
The visible light responsive optical semiconductor 1a used in the present invention refers to an optical semiconductor that has the ability to absorb wavelengths in the visible light region and decompose surrounding water. Specifically, a visible light response that absorbs light of 380 nm to 1000 nm, preferably 420 nm to 800 nm, and whose upper end of the valence band is lower than the redox potential of O ₂ / H ₂ O in an acidic solution. Type optical semiconductor, or visible light responsive type light that absorbs light of 400 nm to 1000 nm, preferably 420 nm to 800 nm, and whose lower end of the conductor is higher than the redox potential of H ⁺ / H ₂ in an acidic solution A semiconductor is preferred.

  Examples of the visible light responsive optical semiconductor 1a include nitrides, oxynitrides, composite oxides, and the like.

For example, a nitride or oxynitride containing one or more atoms selected from the group consisting of Ga, Zn, Ti, La, Ta, and Ba can be used as the visible light responsive optical semiconductor 1a in the present invention. . Specifically, 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), TiN _{x Oxynitrides} such as O _y F _z and nitrides such as Ta ₃ N ₅ and GaN: Mg are included, but are not limited to the materials exemplified here. In particular, GaN: ZnO, LaTiO ₂ N, TaON, Ta ₃ N ₅ or BaTaO ₂ N is preferable from the viewpoint of further improving optical water resolution. These optical semiconductors may be a mixture of two or more.

Alternatively, Bi ₂ WO ₆ , BiYWO ₆ , In ₂ O ₃ (ZnO) ₃ , InTaO ₄ , InTaO ₄ : Ni, TiO ₂ : Ni, TiO ₂ : Ru, TiO ₂ Rh, TiO ₂ : Ni / Ta, 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 _{i 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 including oxides, 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), La, and In A compound (Chemistry Letters, 2007, 36, 854-855) can also be used as the visible light responsive optical semiconductor 1a in the present invention.

The visible light responsive optical semiconductor 1a as described above may carry a sensitizer. Examples of the sensitizer include [Ru (bpy) 3] ²⁺ , erythrosine, zinc porphyrin, coumarin, and derivatives of these compounds, CdS, and the like.

It is also possible to use a p-n junction formed by adsorbing a p-type or n-type optical semiconductor on the surface of the visible light responsive optical semiconductor 1a as described above. Examples of p-type or n-type optical semiconductors include 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 Inorganic semiconductors such as Si, SiC, Ge, ZnS, and Fe ₂ O ₃ and organic semiconductors such as fullerene derivatives, porphyrin derivatives, phthalocyanine derivatives, and polythiophene derivatives.

  As shown in FIGS. 1 and 2, the visible light responsive optical semiconductor 1a is preferably in the form of particles. The particle diameter of the primary particles is not particularly limited as long as the visible light responsive optical semiconductor 1a has a size that can function properly in the photocatalyst layer 10. For example, visible light-responsive optical semiconductor particles having a lower limit of the particle diameter of preferably 0.001 μm or more, more preferably 0.005 μm or more, and an upper limit of preferably 500 μm or less, more preferably 200 μm or less can be used. In the present application, the “particle diameter” means a constant tangential diameter (Ferret diameter), and can be measured by a known means such as XRD, TEM, or SEM method.

(2) Cocatalyst 1b
In the present invention, the visible light responsive optical semiconductor 1a carries the promoter 1b. The cocatalyst 1b used in the present invention plays a role of promoting hydrogen generation and / or oxygen generation.

  The promoter 1b is not particularly limited as long as it is supported on the visible light responsive optical semiconductor 1a and plays a role of promoting hydrogen generation and / or oxygen generation. It is preferable to use a metal of Group -14, an intermetallic compound of the metal, a solid solution, a eutectic, or a mixed particle of the metal (hereinafter referred to as “multi-metal particles”). Alternatively, any of these oxides, composite oxides, oxynitrides, sulfides, oxysulfides, or a mixture thereof is preferably used. Here, the “intermetallic compound” is a compound formed from two or more kinds of metal elements and has a crystal structure and an atomic bonding mode different from those of the original metal. “Multi-element metal particles” refers to ultrafine particles composed of two or more metal elements highly dispersed on a photocatalyst and having a metal-to-metal interaction upon catalytic action. “These oxides, composite oxides, oxynitrides, sulfides, oxysulfides” are oxides, composite oxides, acids of Group 2-14 metals, intermetallic compounds or alloys of the metals. Nitride, sulfide, oxysulfide. “A mixture thereof” refers to a mixture of any two or more of the compounds exemplified above.

As the promoter for the oxidation reaction, Mg, Ti, Mn, Fe, Co, Ni, Cu, Ga, Ru, Rh, Pd, Ag, Cd, In, Ce, Ta, W, Ir, Pt or Pb are preferable. Metal, intermetallic compound of the metal, solid solution, eutectic, or multicomponent metal particles of the metal, oxide or composite oxide of the metal, and more preferably Mn, Co, Ni, Ru, Rh, Ir Metal, Ru—Ir, Pt—Ru multi-metal particles, oxides or composite oxides thereof, and more preferably Ir, Ru—Ir, MnO, 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 co-catalyst for the reduction reaction, preferably, Pt, Pd, Rh, Ru, Ni, Au, Fe, Ru—Ir, NiO, RuO ₂ , IrO ₂ , Rh ₂ O ₃ , and Cr—Rh composite oxide , Core-shell type Rh / Cr ₂ O ₃ , Pt / Cr ₂ O _{3 and the} like.

In the present invention, the cocatalyst 1b is more preferably Pt, Pt—Ru, Ru—Ir, Rh—Cr composite oxide, Ru oxide (RuO ₂ ), Ir oxide (IrO ₂ ), Co oxide (CoO , Co ₃ O ₄ ), Mn oxide (MnO, Mn ₂ O ₃ , Mn ₃ O ₄ ), one or more selected from the group consisting of MnO, Mn ₂ O ₃ and Mn ₃ O ₄ are used. Among these, at least one selected from the group consisting of Rh—Cr composite oxide, Ru oxide, Ir oxide, Co oxide, and Mn oxide is particularly preferable.

  Examples of a method for supporting the cocatalyst 1b on the visible light responsive optical semiconductor 1a include an impregnation support and a photo-deposition method. When two or more kinds of cocatalysts are supported, in the impregnation support, in addition to co-impregnation in which the precursors of the respective cocatalysts are impregnated simultaneously, they are supported by sequential impregnation as required. With the impregnation method, the adsorption site cannot be controlled, and one co-catalyst coats the other co-catalyst or the co-catalysts come into contact with each other and become recombination centers, resulting in no effect. If one of them is expected, one promoter is supported by the adsorption method as usual, and the other promoter (preferably a reduction reaction promoter) is supported by the photodeposition method. Here, the photo-deposition method (also called photo-deposition method) is a method in which photo-semiconductor particles 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. Say. The particle diameter of the promoter particles or the precursor of the promoter particles 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.

  When the cocatalyst 1b is a nanoparticle, for example, a colloid method using PVA (polyvinyl alcohol) or PVP (polyvinylpyrrolidone) 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.

  If the amount of the cocatalyst 1b 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 will decline. From such a viewpoint, the loading amount of the promoter 1b on the visible light responsive optical semiconductor 1a is preferably 0.01% by mass or more and 20% by mass based on the visible light responsive optical semiconductor 1a (100% by mass). Hereinafter, it is more preferably 0.01% by mass to 15% by mass, and particularly preferably 0.01% by mass to 10% by mass.

(3) Hydrophilic inorganic material 2
The hydrophilic inorganic material 2 contained in the photocatalyst layer 10 does not absorb visible light and is selected from inorganic compounds having high hydrophilicity. Specifically, Al ₂ O ₃ , Bi ₂ O ₃ , BeO, CeO ₂ , Ga ₂ O ₃ , GeO, GeO ₂ , La ₂ O ₃ , MgO, Nb ₂ O ₃ , Sb ₂ O ₃ , Sb ₂ O ₅ , metal oxides such as Sc ₂ O ₃ , SiO ₂ , Sm ₂ O ₃ , SnO ₂ , TiO ₂ , ZnO, ZrO ₂ , Y ₂ O ₃ , WO ₃ ; SiO ₂ —Al ₂ O ₃ , ZrO ₂ — Complex oxides such as Al ₂ O ₃ ; zeolites; heteropoly acids; etc. can be used. Among these, it is preferable to use Al ₂ O ₃ , TiO ₂ , and SiO ₂ which are general-purpose materials and are inexpensive. SiO ₂ is particularly preferable. In the case of using the SiO _2, it is preferable to use an amorphous SiO _2. By using amorphous SiO ₂ , the photowater decomposition reaction in the photocatalyst layer 10 becomes more efficient.

  As the hydrophilic inorganic material 2, commercially available materials can be used. The oxide or composite oxide used as the hydrophilic inorganic material 2 is an oxide obtained by hydrolysis and condensation on the surface of the photocatalyst 1 using a metal alkoxide (for example, tetraethyl silicate, tetra n-butyl titanate, etc.) as a raw material. Or a metal alkoxide-metal oxide mixture that has been partially solated by hydrolysis and condensation in advance, and is converted into an oxide on the surface of the photocatalyst 1 by contacting it with the photocatalyst Can also be used. At this time, an organic group such as an alkoxy group may be formed on the surface of the hydrophilic inorganic material 2, but the presence or absence thereof is not particularly limited. In any case, organic groups such as alkoxy groups are calcined from the viewpoint of maintaining the hydrophilicity of the photocatalyst surface, and from the viewpoint of avoiding degradation of purity by mixing organic group decomposition products into the product gas in the water decomposition reaction. It is preferable to remove by treatment or the like.

  As shown in FIGS. 1 and 2, the hydrophilic inorganic material 2 is preferably in the form of particles. The specific particle diameter is not particularly limited as long as water can appropriately enter the photocatalyst layer 10 and the photocatalyst 1 can function properly in the photocatalyst layer 10. In particular, the particle diameter is preferably smaller than that of the photocatalyst 1. For example, hydrophilic inorganic material particles having a particle diameter lower limit of preferably 1 nm or more, more preferably 10 nm or more, and an upper limit of 200 μm or less, more preferably 100 μm or less can be used.

  If the amount of the hydrophilic inorganic material 2 in the photocatalyst layer 10 is too large, light absorption by the hydrophilic inorganic material 2 will inhibit the light absorption of the photocatalyst 1 to reduce the reaction efficiency, or the photocatalyst that can be applied per unit area There is a risk that the amount of the amount will decrease. On the other hand, if the amount of the hydrophilic inorganic material 2 is too small, sufficient water supply promotion effect and product gas diffusion promotion effect cannot be obtained. Therefore, the amount of the hydrophilic inorganic material 2 contained in the photocatalyst layer 10 is preferably 1% or more and 300% or less, more preferably 10% or more and 200% or less, and still more preferably 10% or more and 100 based on the weight of the photocatalyst 1. % Or less.

  The thickness of the photocatalyst layer 10 is 0.1 μm or more and 1000 μm or less, preferably 1 μm or more and 100 μm or less. When the photocatalyst layer 10 is too thick, the mechanical strength of the photocatalyst layer 10 is lowered or easily peeled off, and at the same time, it is difficult for light to reach the photocatalyst 1 below the layer, and the utilization efficiency of the photocatalyst 1 is lowered. On the other hand, if it is too thin, the amount of the photocatalyst 1 per unit area is too small and the reaction efficiency is lowered.

  Further, the photocatalyst layer 10 is at least 0.25 nm or more, preferably 1 nm in order to ensure mechanical strength that is not easily broken during use, access to water molecules, and a release path of hydrogen gas and oxygen gas as products. It is important that the porous body has a pore diameter of 5000 nm or less.

1.2. Base material 20
The base material 20 is not limited as long as it is a material that is stable in acidic, neutral, and basic water and is not oxidized by the photocatalyst 1. Specifically, ceramic, metal, methacrylic resin with an anti-oxidation coating, acrylic resin, urethane resin, polyester resin, organic base materials such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, and natural base materials such as wood are used. be able to. In particular, the adhesive force between the photocatalyst layer 10 and the base material 20 can be improved by using a base material that can form polycondensation or hydrogen bonds with the hydrophilic inorganic material. Examples of such a substrate include alkoxysilane (silylating agent), a siloxane compound having a hydrolyzing group, a silane coupling agent, and a silicone resin. There is no limitation in particular about the shape of the base material 20, For example, the base material etc. which have an unevenness | corrugation on the surface other than the flat base material 20 as shown in FIG. 1 may be sufficient. The thickness of the substrate 20 is not particularly limited, and can be appropriately selected according to the equipment scale.

  The photocatalyst immobilization product 100 according to the present invention has the above-described configuration. In the photocatalyst immobilization product 100, by allowing the hydrophilic inorganic material 2 to coexist with the visible light responsive photocatalyst 1 in the photocatalyst layer 10, water is not only supplied to the vicinity of the surface of the photocatalyst layer 10 but also to the inside during the water splitting reaction. In addition to being able to enter, the hydrophilic surface makes it difficult for the product gas to adhere to the photocatalyst layer, and as a result, diffusion of the product gas into the gas phase is promoted. Further, stirring in the reactor is unnecessary, and the water splitting reaction can be performed easily. That is, the photocatalyst immobilization product 100 can be said to be a photocatalyst immobilization product that can be used simply and efficiently without reducing the photocatalytic performance of the photocatalyst 1.

  In addition, in the said description, although the photocatalyst layer 10 explained in full detail the form by which the particulate photocatalyst 1 and the particulate hydrophilic inorganic material 2 were mixed, this invention is not limited to the said form. For example, a form in which a hydrophilic inorganic material is supported or partially coated on a part of the surface of the photocatalyst may be used. Further, the shapes of the photocatalyst and the hydrophilic inorganic material are not limited to particles. However, from the viewpoint of obtaining a photocatalyst immobilized product having a high photocatalytic activity more easily, it is preferable to form a photocatalyst layer in which a particulate photocatalyst and a particulate hydrophilic inorganic material are mixed.

2. Method for Producing Photocatalyst Immobilized Product The photocatalyst immobilized product according to the present invention can be obtained, for example, by mixing the above-described photocatalyst and a hydrophilic inorganic material in a solvent, and applying and drying the substrate. When mixing, the photocatalyst and the hydrophilic inorganic material that are mixed in advance may be dispersed in a solvent, or the photocatalyst and the hydrophilic inorganic material may be added and mixed in the solvent.

  Examples of the solvent used when mixing the photocatalyst and the hydrophilic inorganic material include water, alcohols such as methanol and ethanol, ketones such as acetone, benzene, toluene, xylene, and the like. From the viewpoint of efficient dispersion, it is particularly preferable to use water. For example, the photocatalyst and the hydrophilic inorganic material can be more uniformly dispersed in the solvent by ultrasonic treatment.

  When a solvent in which a photocatalyst and a hydrophilic inorganic material are dispersed is applied to a substrate, a widely used technique may be used. For example, there are a spray method, a dip method, a squeegee method, a doctor blade method, a spin coating method, a screen coating method, a roll coating method and the like.

  Here, in order to improve the applicability of the photocatalyst and the hydrophilic inorganic material, a layer containing the hydrophilic inorganic material may be formed on the substrate in advance, and a solvent containing the photocatalyst and the hydrophilic inorganic material may be applied thereon. it can.

  What is necessary is just to heat to the temperature which the solvent volatilizes as drying conditions after application | coating. Thereby, a photocatalyst layer can be appropriately formed on a substrate. For example, the photocatalyst layer can be formed on the substrate by heat drying at about 40 ° C. to 200 ° C.

3. Method for Producing Hydrogen and / or Oxygen The photocatalyst immobilization product according to the present invention generates hydrogen and / or oxygen by irradiating light from a certain light source and causing a photohydrolysis reaction according to the following reaction formula (1). Can be manufactured.
H ₂ O → H ₂ + 1 / 2O ₂ (1)

  The conditions for the photohydrolysis reaction can be appropriately selected depending on the photocatalyst used, and are not particularly limited.

  The light source used for the photohydrolysis reaction is not particularly limited, but artificial light sources such as xenon lamps, mercury lamps, metal halide lamps, LED lamps and solar simulators can be used in addition to sunlight. By using these light sources and irradiating light to the photocatalyst layer of the photocatalyst immobilized material disposed in water, a water splitting reaction is caused.

  The irradiation method of the light source is not particularly limited, and in addition to the form in which the photocatalyst layer is directly irradiated, irradiation may be performed using a reflecting mirror, or may be condensed and irradiated using a lens or the like.

  The reaction pressure of the photohydrolysis reaction is not particularly limited, and can usually be carried out in the range of reduced pressure (0.5 kPa) to normal pressure. The reaction temperature is not particularly limited, and the reaction can be performed usually in the range of 0 ° C to 100 ° C, preferably 50 ° C to 80 ° C. The liquid property of the water to be used is not particularly limited, and a range of pH 2 to 13 is preferable, and a range of pH 4.5 to 7.0 is more preferable.

  When the photocatalyst immobilized product is installed in the vicinity of the water surface, that is, when only a small amount of water is present on the photocatalyst layer of the photocatalyst immobilized product, the water in the vicinity of the photocatalyst layer becomes hot due to light irradiation, which may cause a problem. On the other hand, when the photocatalyst immobilization product is installed in a deep part in water, there is a possibility that light does not reach sufficiently, and a reverse reaction may occur before the generated gas reaches the water surface. From such a viewpoint, the photocatalyst immobilized product is preferably installed at a position that is 50 μm or more and 1 m or less from the water surface.

  Hereinafter, the photocatalyst immobilized product according to the present invention will be described in more detail with reference to Examples and Comparative Examples.

<Preparation of photocatalyst>
(Preparation of GaN: ZnO)
The preparation was performed according to the method described in J. Phys. Chem. B 2006, 110, 13753-13758. That is, 1.08 g of Ga ₂ O ₃ (manufactured by Koyo Chemical Co., Ltd.) and 0.94 g of ZnO (manufactured by Kanto Chemical Co., Ltd.) were mixed, and nitriding was performed at 850 ° C. for 15 hours under an ammonia stream (250 mL / min). Processed. When confirmed by XRD and EDX, formation of GaN: ZnO was confirmed.

_{(Rh x Cr 2-x O} 3 / GaN: Preparation of ZnO)
The preparation was performed according to the method described in J. Phys. Chem. B 2006, 110, 13753-13758. That is, ₃ mL of the above GaN: ZnO (0.3 g to 0.4 g) containing Na ₃ RhCl ₆ · 12H ₂ O (manufactured by Mitsuwa Chemical Co., Ltd.) (1.5% by mass of Cr with respect to GaN: ZnO). It was suspended in ˜4 mL aqueous solution, and the solvent was evaporated to dryness while stirring with a glass rod in an evaporating dish on a water bath. Then, in air, calcined at 350 ° C., the _Rh x _{Cr 2-x O 3} as a co-catalyst supported GaN: to obtain a ZnO.

(Preparation of LaTiO ₂ N)
La _{(NO 3)} (manufactured by Kanto Chemical Co., _{Inc.) 3 · 6H 2 O, Ti} (O-iPr) ( manufactured by Kanto Chemical Co., Inc.) _4, citric acid (manufactured by Wako Pure Chemical Industries, Ltd.), ethylene glycol (manufactured by Kanto Chemical Co., Inc.) In methanol, the mixture was mixed at a molar ratio of 1: 1: 10: 30 and polymerized at 373K. Further, after heat treatment at 623K and carbonization, firing in air at 923K was performed to obtain a composite oxide precursor of La and Ti. This precursor was heated to 1123 K at 1 K / min under a NH ₃ gas stream of 100 mL / min, then held at that temperature for 15 hours, and then cooled to room temperature to synthesize LaTiO ₂ N. When confirmed by XRD and EDX, formation of LaTiO ₂ N was confirmed.

(Preparation of Pt—CoO _x / LaTiO ₂ N)
₃ containing the above LaTiO ₂ N (0.3-0.4 g) containing Co (NO ₃ ) ₂ .6H ₂ O (manufactured by Wako Pure Chemical Industries, Ltd.) (0.5 mass% Co with respect to LaTiO ₂ N) It was suspended in -4 mL aqueous solution, and the solvent was evaporated and dried while stirring with a glass rod in a water bath in an evaporating dish. Thereafter, it was fired at 200 ° C. in air. The resulting further _{Pt (NH} 3) (manufactured by ALDRICH Co.) 4 _Cl 2 · _H 2 O The sample was suspended in 3-4mL an aqueous solution containing (3.0 wt% Pt relative LaTiO ₂ N), evaporating dish The solvent was evaporated to dryness while stirring with a glass rod on a water bath. Thereafter, hydrogen reduction was performed at 300 ° C. in a hydrogen stream. As a result, LaTiO ₂ N carrying Pt—CoO _x as a promoter was obtained. CoO _x means a mixture of CoO, Co ₂ O ₃ , and Co ₃ O ₄ .

(Preparation of BaTaO ₂ N: Mg)
BaCO ₃ (manufactured by Kanto Chemical Co., Inc.), (manufactured by High Purity Chemical _{Co.) Ta 2 O 5, Mg (} NO 3) 2 · 6H 2 O ( manufactured by Kanto Chemical Co., Inc.) a molar ratio of 100: 46.25: 7.5 with The mixture was mixed and fired at 923 K in air to obtain a composite oxide precursor of Ba, Ta, and Mg. This precursor was heated to 1173 K at 1 K / min under an NH ₃ stream of 200 mL / min, then held at that temperature for 20 hours, and then cooled to room temperature to synthesize BaTaO ₂ N: Mg. It was confirmed by XRD and EDX, BaTaO ₂ N: Mg generation of has been confirmed.

(Preparation of Ru-Ir / BaTaO ₂ N: Mg)
The above BaTaO ₂ N: Mg (0.3-0.4 g) contains RuCl ₃ .nH ₂ O (manufactured by Kanto Chemical Co.) (BaTaO ₂ N: 1.0 mass% Ru with respect to Mg) 3- It suspended in 4 mL aqueous solution, and the solvent was evaporated and dried in the evaporating dish on the water bath with stirring with a glass rod. The obtained sample was subjected to hydrogen reduction at 300 ° C. under a hydrogen stream, and then 3-4 mL aqueous solution containing Na ₂ IrCl ₆ (manufactured by Kanto Chemical Co., Inc.) (BaTaO ₂ N: 0.3% by mass of Ir with respect to Mg). The solvent was evaporated to dryness while stirring with a glass rod in an evaporating dish on a water bath. The obtained sample was further hydrogen reduced at 300 ° C. under a hydrogen stream. As a result, BaTaO ₂ N: Mg on which Ru—Ir was supported as a promoter was obtained.

<Preparation of immobilized photocatalyst>
Example 1
20 mg of RhxCr _{2 -X} O ₃ / GaN: ZnO prepared as described above as a photocatalyst and 20 mg of silicon dioxide (manufactured by Wako Pure Chemical Industries, 70 nm) as a hydrophilic inorganic material are suspended in 200 μL of distilled water, Sufficiently dispersed by sonication for 3-5 minutes. This dispersion was dropped onto a sandblasted Pyrex glass (50 mm square) heated to 60 to 80 ° C. on a hot plate with a pipette, spread with a glass rod and dried to prepare a photocatalyst immobilized product.

(Example 2)
A photocatalyst immobilized product was prepared in the same manner as in Example 1, except that 20 mg of amorphous silica (manufactured by Kanto Chemical Co., Inc.) was used as the hydrophilic inorganic material.

(Example 3)
_{RhxCr 2-X} O 3 / GaN of 20mg, prepared as described above as a photocatalyst: suspended and ZnO, and tetraethoxysilane 20mg (TEOS) (ALDRICH Co.) in distilled water 200 [mu] L, of 3-5 minutes The photocatalyst was sufficiently dispersed by ultrasonic treatment, and at the same time, TEOS was hydrolyzed and converted to SiO ₂ on the photocatalyst surface. This dispersion was dropped onto a sandblasted Pyrex glass (50 mm square) heated to 60 to 80 ° C. on a hot plate with a pipette, spread with a glass rod and dried to prepare a photocatalyst immobilized product.

Example 4
A photocatalyst immobilized product was prepared in the same manner as in Example 1 except that 20 mg of LaTiO ₂ N prepared as described above was used as the photocatalyst.

(Example 5)
A photocatalyst immobilization product was prepared in the same manner as in Example 1 except that 20 mg of BaTaO ₂ N: Mg prepared as described above was used as the photocatalyst.

(Comparative Example 1)
Without the use of hydrophilic inorganic _{materials, Rh x Cr 2-X O} 3 / GaN: except that the ZnO suspension was applied on Pyrex glass were prepared photocatalyst immobilizate in the same manner as in Example 1.

(Comparative Example 2)
A photocatalyst immobilization product was prepared in the same manner as in Example 4 except that the LaTiO ₂ N suspension was applied onto Pyrex glass without using a hydrophilic inorganic material.

(Comparative Example 3)
A photocatalyst immobilization product was prepared in the same manner as in Example 5 except that a BaTaO ₂ N: Mg suspension was applied on Pyrex glass without using a hydrophilic inorganic material.

<Conditions for photohydrolysis reaction>
The prepared photocatalyst immobilization product was used to evaluate the photohydrolysis reaction performance. The photo-water splitting reaction was evaluated by a closed reactor equipped with a vacuum exhaust pump, a circulation pump, a cell containing a photocatalyst immobilized product, a gas sampling valve, and a gas chromatograph analyzer (GC) as shown in FIG. . A 300 W xenon lamp (λ> 300 nm) was used as the light source, a water filter was provided between the lamp and the cell to avoid temperature rise, and the cell was cooled from the outside with cooling water. In the evaluation, the inside of the reactor was deaerated several times in advance and it was confirmed that no air remained. The degree of vacuum was about 4 × 10 ⁴ Pa. Thereafter, light irradiation was started, and the amount of gas produced was measured. The analysis conditions were a column (molecular sieve 5A), carrier gas (argon), and temperature (50 to 70 ° C.).

  In addition, about the photocatalyst fixed material concerning Examples 1-3 and the comparative example 1, it put into the cell with 100 mL pure water (pH = 7), and irradiated the light, and measured the production amount of hydrogen gas and oxygen gas.

For the photocatalyst immobilized products according to Examples 4 and 5 and Comparative Examples 2 and 3, the generation of hydrogen gas and the generation of oxygen gas were evaluated separately. That is, the photocatalyst immobilization product was put into a cell together with 100 mL (pH = 7) of an aqueous solution containing 10 vol% of a sacrificial reagent, and irradiated with light to measure the amount of hydrogen gas produced. On the other hand, the photocatalyst immobilized product was put into a cell together with 100 mL (pH = 7) of a 0.01 M AgNO ₃ aqueous solution as a sacrificial reagent, and irradiated with light, and the amount of oxygen gas produced was measured.

<Evaluation results>
Tables 1 and 2 below show the results of comparing the water splitting reaction activities of the photocatalyst immobilized products.

  As is clear from Table 1, the photocatalyst-immobilized product according to Examples 1 to 3 containing the hydrophilic inorganic material in the photocatalyst layer is more water than the photocatalyst-immobilized product according to Comparative Example 1 that does not contain the hydrophilic inorganic material. The initial hydrogen production rate by decomposition is 3.4 to 4.6 times higher, and the oxygen production rate is 5.8 to 7.3 times higher. It is clear that the addition of a hydrophilic inorganic material improves the photocatalytic activity. In the absence of a hydrophilic inorganic material, it is difficult for water to enter between the photocatalyst particles having low hydrophilicity. As a result, only the photocatalyst near the uppermost surface of the photocatalyst layer can be used for the photohydrolysis reaction. By allowing the inorganic material to coexist, water can be easily supplied into the photocatalyst layer, and not only the upper side of the layer but also the internal photocatalyst can be used in the water splitting reaction. As a result of difficulty in adhering to the layer, it is considered that diffusion of the product gas into the gas phase is promoted, and the reaction efficiency per unit area and unit photocatalyst amount is improved. In particular, Example 2 using amorphous silica as the hydrophilic inorganic material had the highest photocatalytic activity.

Further, as is clear from Table 2, even in a system using methanol as a sacrificial reagent, the photocatalyst immobilized product according to Examples 4 and 5 containing a hydrophilic inorganic material is a comparative example 2 that does not contain a hydrophilic inorganic material. As compared with the photocatalyst immobilized product according to No. 3, the initial hydrogen production rate is twice as high, and it is clear that the addition of a hydrophilic inorganic material improves the photocatalytic activity. In addition, even in a system using AgNO ₃ as a sacrificial reagent, the photocatalyst immobilized product according to Examples 4 and 5 containing a hydrophilic inorganic material is different from the photocatalyst immobilized product according to Comparative Examples 2 and 3 that does not contain a hydrophilic inorganic material. In comparison, the initial oxygen production rate is 1.05 to 5.7 times higher, and it is clear that the addition of a hydrophilic inorganic material improves the photocatalytic activity. These are also considered to have improved reaction efficiency per unit area and unit photocatalyst amount for the same reason as in Examples 1 to 3 above.

  Although the present invention has been described with reference to the most practical and preferred embodiments at the present time, the present invention is not limited to the embodiments disclosed herein. In addition, it can be changed as appropriate without departing from the scope or spirit of the invention that can be read from the claims and the entire specification, and the water-catalyzed photocatalyst immobilization product with such a change, and the method for producing hydrogen and / or oxygen are also included. Moreover, it should be understood as being included in the technical scope of the present invention.

  The photocatalyst immobilization product for water splitting according to the present invention can be particularly suitably used when a photowater splitting reaction is carried out on a large scale using a photocatalyst, and a low-cost hydrogen / oxygen production technique can be provided.

DESCRIPTION OF SYMBOLS 1 Photocatalyst 1a Visible light response type optical semiconductor 1b Cocatalyst 2 Hydrophilic inorganic material 10 Photocatalyst layer 20 Base material 100 Photocatalyst fixed substance for water splitting

Claims (6)

A photocatalyst immobilized product for water splitting having a photocatalyst layer on a substrate,
The photocatalytic layer is
A visible light responsive optical semiconductor that is a nitride or oxynitride containing one or more atoms selected from the group consisting of Ga, Zn, Ti, La, Ta, and Ba;
A promoter supported on the visible light responsive optical semiconductor;
At least one hydrophilic inorganic material selected from the group consisting of silica, alumina, and titanium oxide;
Only including,
The photocatalyst layer is a photocatalyst immobilized product for water splitting, wherein the visible light responsive optical semiconductor carrying the promoter is mixed with the hydrophilic inorganic material . The visible light responsive optical semiconductor and the hydrophilic inorganic material are in the form of particles, and the particle diameter of the hydrophilic inorganic material is smaller than the particle diameter of the visible light responsive optical semiconductor carrying the promoter. The fixed photocatalyst for water photolysis according to claim 1. The photocatalyst immobilization product for water splitting according to claim 1 or 2 , wherein the visible light responsive optical semiconductor is at least one selected from the group consisting of GaN: ZnO, LaTiO ₂ N, and BaTaO ₂ N: Mg. The co-catalyst is at least one selected from the group consisting of Pt, Pt—Ru, Ru—Ir, Rh—Cr composite oxide, Ru oxide, Ir oxide, Co oxide, and Mn oxide. Item 4. The photocatalyst immobilized product for water splitting according to any one of Items 1 to 3 . The photocatalyst immobilization product for water splitting according to any one of claims 1 to 4 , wherein the hydrophilic inorganic material is silica. A method for producing hydrogen and / or oxygen, wherein the photocatalyst immobilized product for water splitting according to any one of claims 1 to 5 is disposed in water and water is decomposed by irradiating the photocatalyst immobilized product with light.

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