Method for producing junction photocatalyst, and junction photocatalyst

Abstract

To provide: a method for producing a junction photocatalyst that has higher catalytic activity than conventional junction photocatalysts; and a contact type photocatalyst.SOLUTION: The present invention provides a method for producing a junction photocatalyst that has a solid mediator between a hydrogen generation photocatalyst and an oxygen generation photocatalyst, the method comprising the step 1 described below. Step 1: A step in which a solid mediator is joined onto an oxygen generation photocatalyst by at least one method that is selected from the group consisting of a photoelectrodeposition method, an impregnation deposition method and a precipitation method, the methods using an organic carboxylic acid compound and the solid mediator or a precursor thereof.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a bonded photocatalyst having a solid mediator between a hydrogen-generating photocatalyst and an oxygen-generating photocatalyst, a bonded photocatalyst, an oxygen-generating photocatalyst bonded with the solid mediator, a method for producing an oxygen-generating photocatalyst bonded with the solid mediator, a photocatalyst composite, use of the bonded photocatalyst, and a method for producing hydrogen. [Background technology]

[0002] In recent years, technology for producing hydrogen and oxygen by splitting water using a photocatalyst and sunlight has been attracting attention. When splitting water using a photocatalyst, it is preferable to use a photocatalyst that catalyzes both the water reduction reaction (proton reduction reaction) and the water oxidation reaction. However, the types of such photocatalysts are limited, and their water splitting activity tends to be low.

[0003] Therefore, methods are being investigated for efficiently splitting water by using a photocatalyst that catalyzes the reduction reaction of water (hydrogen-generating photocatalyst) in combination with a photocatalyst that catalyzes the oxidation reaction of water (oxygen-generating photocatalyst).

[0004] For example, a system that uses a hydrogen-generating photocatalyst and an oxygen-generating photocatalyst to decompose water and generate both hydrogen and oxygen under irradiation with visible light is called the Z scheme. The Z scheme uses a photocatalyst that combines, for example, an oxygen-generating photocatalyst that decomposes water under visible light to generate oxygen, a hydrogen-generating photocatalyst that decomposes water under visible light to generate hydrogen, and a redox mediator. The Z scheme using this photocatalyst enables complete water decomposition (hydrogen:oxygen = 2:1 (stoichiometric ratio)) by repeating a cycle in which electrons generated by the oxygen-generating photocatalyst that do not contribute to water reduction reduce the redox mediator, and the reduced redox mediator is oxidized by holes generated by the hydrogen-generating photocatalyst that do not contribute to water oxidation and returns to the original redox mediator.

[0005] However, in order for the Z scheme using the hydrogen generating photocatalyst and the oxygen generating photocatalyst to function catalytically, a redox mediator (e.g., Fe 3+ / Fe 2+ or I - / IO3 - ) is required, and there is also the problem that the electron transfer efficiency of the redox mediator is low, resulting in low water splitting activity. In addition, it is necessary to select a photocatalyst appropriate for the redox potential of the redox mediator, which narrows the options for photocatalysts.

[0006] On the other hand, as an example of a junction-type photocatalyst that does not use an oxidation-reduction mediator, Patent Document 1 proposes a photocatalyst layer that includes first photocatalyst particles that are responsive to visible light for generating hydrogen, second photocatalyst particles that are responsive to visible light for generating oxygen, and conductive particles that are disposed between the first and second photocatalyst particles and are capable of storing electrons and holes, and have a Fermi level that is more negative than the electronic energy level at the top of the valence band of the first photocatalyst particles and more positive than the electronic energy level at the bottom of the conduction band of the second photocatalyst particles, and the conductive particles are arranged so as to be connected to the first and second photocatalyst particles.

[0007] Furthermore, Non-Patent Document 1 proposes a Z-scheme photocatalyst with a hierarchical structure consisting of ZnRh2O4 / Au / BiVO4. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-124394 [Non-patent literature]

[0009] [Non-Patent Document 1] Toshihiro Takashima et al., J. Mater. Chem. A, 2019, 7, 10372-10378 Summary of the Invention [Problem to be solved by the invention]

[0010] Junction-type photocatalysts, in which a hydrogen-generating photocatalyst and an oxygen-generating photocatalyst are joined via a metal or metal oxide, have a very simple structure and exhibit high catalytic activity in the decomposition reactions of water and other substances under visible light irradiation. However, there is a demand for further enhancement of this catalytic activity.

[0011] The present invention has been made in view of the above circumstances, and provides a junction-type photocatalyst that has higher catalytic activity than conventional junction-type photocatalysts. [Means for solving the problem]

[0012] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by the following method for producing a junction-type photocatalyst and the junction-type photocatalyst.

[0013] That is, the present invention relates to the following 1. to 7. 1. A method for producing a bonded photocatalyst having a solid mediator between a hydrogen generating photocatalyst and an oxygen generating photocatalyst, comprising: A method for producing a junction-type photocatalyst, comprising the following step 1: Step 1: A step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation using an organic carboxylic acid compound and a solid mediator or a precursor thereof. 2. A junction-type photocatalyst having a solid mediator between a hydrogen generating photocatalyst and an oxygen generating photocatalyst, A bonded photocatalyst, wherein the coverage of the solid mediator with respect to the electron collection surface area of ​​the oxygen generating photocatalyst is 40% or more. 3. A method for producing an oxygen-generating photocatalyst with a solid mediator attached thereto, comprising the steps of: A method for producing an oxygen generating photocatalyst having a solid mediator bonded thereto, comprising the step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation, using an organic carboxylic acid compound and a solid mediator or a precursor thereof. 4. An oxygen-generating photocatalyst to which a solid mediator is bonded, An oxygen generating photocatalyst to which a solid mediator is bonded, wherein the coverage of the solid mediator with respect to the electron collecting surface area of ​​the oxygen generating photocatalyst is 40% or more. 5. A photocatalytic composite having the above-mentioned bonded photocatalyst on a substrate. 6. Use of the above-mentioned conjugated photocatalyst as a photocatalyst for water splitting or organic matter decomposition. 7. A method for producing hydrogen, comprising irradiating the junction-type photocatalyst or the photocatalyst composite with light in the presence of water or alcohol. [Effects of the Invention]

[0014] The junction-type photocatalyst of the present invention has improved catalytic activity by increasing the coverage of the solid mediator relative to the electron-collecting surface area of ​​the oxygen-generating photocatalyst, and can decompose water into oxygen and hydrogen with high water-splitting reaction efficiency. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an SEM image of Au-BiVO4 in Example 1. [Figure 2] 1 is an SEM image of the junction-type photocatalyst of Example 1. [Figure 3] 1 shows the volume particle size distribution of the bonded photocatalyst (bonded particles) and the like in Example 1. [Figure 4] 1 shows the volume particle size distribution of a mixed sample of Ru-supported SrTiO3 and Au-BiVO4 in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below.

[0017] <Joined photocatalyst> The junction-type photocatalyst of the present invention has a solid mediator between the hydrogen generating photocatalyst and the oxygen generating photocatalyst. The coverage of the solid mediator with respect to the electron collection surface area of ​​the oxygen generating photocatalyst of the junction-type photocatalyst of the present invention is 40% or more from the viewpoint of enhancing catalytic activity.

[0018] In detail, the oxygen generating photocatalyst is directly or indirectly bonded to a part of the solid mediator, the hydrogen generating photocatalyst is directly or indirectly bonded to another part of the solid mediator, and the hydrogen generating photocatalyst and the oxygen generating photocatalyst are bonded at least via the solid mediator. Furthermore, it is preferable that the solid mediator and the hydrogen generating photocatalyst are bonded via an ionic polymer, and it is also preferable that the solid mediator has an ionic group, and that the solid mediator and the hydrogen generating photocatalyst are bonded via an ionic polymer having a charge opposite to that of the ionic group possessed by the solid mediator (preferably an ionic group introduced into the solid mediator). In one embodiment of the bonded photocatalyst of the present invention, the solid mediator has an ionic group, the hydrogen generating photocatalyst has the ionic polymer having an opposite charge to that of the ionic group, and the solid mediator and the hydrogen generating photocatalyst are bonded together by an ionic bond between the ionic group and the ionic polymer. Furthermore, one embodiment of the bonded photocatalyst of the present invention is one in which the solid mediator has an ionic group, the hydrogen generating photocatalyst has an ionic polymer A and, via the ionic polymer A, an ionic polymer B having a charge opposite to that of the ionic group, and the solid mediator and the hydrogen generating photocatalyst are bonded together by an ionic bond between the ionic group and the ionic polymer B. Furthermore, one embodiment of the bonded photocatalyst of the present invention is one in which the solid mediator has an ionic group and, via the ionic group, an ionic polymer B having a charge opposite to that of the ionic group, and the hydrogen generating photocatalyst has an ionic polymer A, and the solid mediator and the hydrogen generating photocatalyst are bonded together by an ionic bond between the ionic polymer B possessed by the solid mediator and the ionic polymer A possessed by the hydrogen generating photocatalyst. When the ionic group of the solid mediator is an anionic group, the ionic polymer A is an anionic polymer and the ionic polymer B is a cationic polymer; when the ionic group of the solid mediator is a cationic group, the ionic polymer A is a cationic polymer and the ionic polymer B is an anionic polymer.

[0019] In the present invention, "bonding" means a state in which the oxygen generating photocatalyst and the hydrogen generating photocatalyst are integrated to such an extent that they do not separate when a photocatalytic reaction is carried out. Furthermore, in the present invention, "electron collecting surface" means an exposed crystal surface in the various structures of the oxygen generating photocatalyst where excited electrons are most likely to collect.

[0020] The hydrogen generating photocatalyst is not particularly limited, and examples thereof include metal oxides such as TiO2, SrTiO3, La2Ti2O7, SnNb2O6, and compounds thereof doped with one or more metals such as Cr, Sb, Ta, Ir, and La; metal oxynitrides or metal nitrides such as LaTiO2N, BaTaO2N, BaNbO2N, TaON, Ta3N5, and Ge3N4; CuGaS2, CuInS2, Cu(Ga Examples of suitable catalysts include metal sulfides, metal selenides, or metal sulfoselenides such as Cu(Ga,In)S2, CuGaSe2, CuInSe2, Cu(Ga,In)Se2, CuZnSnS4 (CZTS), and CuZnSn(S,Se)4; and metal oxysulfides or metal oxyselenides such as LaTiCuS5O7, LaTiAgS5O7, LaTiCuSe5O7, and LaTiAgSe5O7. These may be used alone or in combination of two or more. Among these, from the viewpoint of enhancing catalytic activity, preferably one or more metal oxides are used, more preferably one or more transition metal oxides are used, even more preferably one or more oxides of elements belonging to Group 4 of the periodic table are used, and even more preferably SrTiO3 is used.

[0021] The oxygen-generating photocatalyst is not particularly limited, and examples thereof include metal oxides such as BiVO, TiO, WO, SrTiO, AgPO, SnNbO, BiWO, FeTiO, FeO, BiMoO, and compounds thereof doped with one or more metals such as Cr, Ni, Sb, Nb, Th, Mo, and W; metal nitrides such as TaN and GeN; and metal oxynitrides such as LaTiON, BaTaON, BaNbON, and TaON. These may be used alone or in combination. Among these, from the viewpoint of enhancing catalytic activity, preferably one or more metal oxides are selected, more preferably one or more transition metal oxides, even more preferably one or more oxides of one or more elements selected from groups 4 and 5 of the periodic table, and even more preferably BiVO.

[0022] The hydrogen generating photocatalyst and the oxygen generating photocatalyst preferably have a co-catalyst on the surface, which promotes the reduction and oxidation reactions of water and the like, thereby improving the efficiency of generating hydrogen and oxygen.

[0023] Examples of co-catalysts for the hydrogen generating photocatalyst include transition metals such as Pt, Pd, Ru, Ni, Au, Fe, Ir, and Rh; metal oxides such as NiO, RuO2, IrO2, and Rh2O3; metal sulfides such as NiS and MoS2; and Cr-Rh composite oxides. These may be used alone or in combination of two or more. Among these, from the viewpoint of hydrogen generation efficiency, preferably one or more selected from transition metals, more preferably one or more selected from metals belonging to Group 10 of the periodic table, and even more preferably Ru.

[0024] Examples of co-catalysts for the oxygen-generating photocatalyst include transition metals such as Mn, Fe, Co, Ir, Ru, Rh, Ni, Sb, Nb, Th, and Cr; oxides and hydroxides of these transition metals; and the like. These may be used alone or in combination of two or more. Among these, from the viewpoint of oxygen generation efficiency, one or more selected from oxides of transition metals are preferred.

[0025] Examples of methods for supporting the co-catalyst on the surface of the hydrogen generating photocatalyst or the oxygen generating photocatalyst include photoelectrodeposition, impregnation, adsorption, precipitation, hydrogen reduction, and electroless plating.

[0026] The impregnation method and the adsorption method involve dispersing the photocatalyst in a solution containing a co-catalyst precursor, and adsorbing the co-catalyst precursor onto the surface of the photocatalyst. Examples of the co-catalyst precursor include chlorides, nitrates, and amine salts of the transition metals.

[0027] It is preferable to reduce the co-catalyst precursor after supporting it on the surface of the photocatalyst. By reducing the co-catalyst precursor to a metallic state, activity increases. Examples of methods for reducing the co-catalyst precursor include photoreduction and chemical reduction.

[0028] The photoreduction method is a method in which a cocatalyst precursor adsorbed on a photocatalyst is reduced by excited electrons generated within the photocatalyst upon irradiation of the photocatalyst with ultraviolet light or visible light. The chemical reduction method is a method in which a cocatalyst precursor is reduced in a hydrogen gas stream at about 400°C or less, preferably 300°C or less. The cocatalyst supported on the surface of the photocatalyst is in particulate form, and the amount of the cocatalyst supported can be adjusted as appropriate.

[0029] The solid mediator is a material that can store excited electrons generated by the oxygen generating photocatalyst that do not contribute to the reduction of water, etc., and positive holes generated by the hydrogen generating photocatalyst that do not contribute to the oxidation of water, etc., and can cause a charge recombination reaction between the excited electrons and the positive holes.

[0030] Examples of the solid mediator include transition metals such as gold, silver, copper, nickel, titanium, manganese, rhodium, palladium, ruthenium, and iridium; transition metal compounds such as oxides, nitrides, and carbides of these transition metals; and doped metal oxides such as tin-doped indium oxide (ITO), metal (B, Al, Ga)-doped zinc oxide, fluorine-doped tin oxide, and antimony-doped tin oxide. These may be used alone or in combination. Among these, from the viewpoint of enhancing catalytic activity, preferably, one or more transition metals or compounds thereof are selected, more preferably, one or more transition metals or compounds thereof containing elements belonging to Group 11 of the periodic table, even more preferably, one or more gold or silver, and even more preferably, those containing gold.

[0031] The electron collection surface of the oxygen-generating photocatalyst depends on the material composition and crystalline system. For example, a method for identifying the electron collection surface involves contacting semiconductor crystal particles, which are the material for the oxygen-generating photocatalyst, with a precursor solution of a metal such as Pt, Au, or Ag, and then supporting the metal particles deposited by photoprecipitation, followed by confirming the crystal plane on which the metal particles are deposited using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The crystal plane on which the metal particles are deposited can be identified by, for example, determining the crystal plane spacing associated with the lattice fringes observed by TEM.

[0032] The electron collection surface of the oxygen generating photocatalyst is, for example, the {010} or {040} surface for BiVO4 (monoclinic scheelite crystal), the {110} surface for TiO2 (rutile crystal), the {101} surface for TiO2 (anatase crystal), the {002} surface for WO3 (monoclinic crystal), the {110} surface for SrTiO3 (perovskite crystal), or the {110} surface for Ag3PO4 (cubic crystal).

[0033] In the bonded photocatalyst, it is preferable that the hydrogen generating photocatalyst is selectively bonded to the solid mediator.

[0034] <Method of manufacturing bonded photocatalyst> The manufacturing method of the present invention is a method for manufacturing a bonded photocatalyst having a solid mediator between the hydrogen generating photocatalyst and the oxygen generating photocatalyst, the method comprising bonding a solid mediator to the surface of an oxygen generating photocatalyst, and then bonding a hydrogen generating photocatalyst to the surface of the solid mediator, The method for producing a junction-type photocatalyst includes the following step 1: Step 1: A step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation using an organic carboxylic acid compound and a solid mediator or a precursor thereof. Specifically, the following production methods (I) and (II) which further include steps 2, 3, and 4 or steps 2', 3', and 4' are preferred.

[0035] That is, a preferred example of the method for producing a junction-type photocatalyst of the present invention is (I) a method for producing a junction-type photocatalyst including the following steps 1 to 4. However, the order of steps 2 and 3 is not critical. Step 3 may be performed after step 2, or step 2 may be performed after step 3, or they may be performed simultaneously. Step 1: A step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation using an organic carboxylic acid compound and a solid mediator or a precursor thereof. Step 2: A step of introducing an ionic group into the solid mediator to obtain an oxygen-generating photocatalyst to which the solid mediator having the ionic group is bonded. Step 3: introducing an ionic polymer having an opposite charge to the charge of the ionic group into the hydrogen generating photocatalyst. Step 4: Mixing the oxygen generating photocatalyst obtained in step 2 to which the solid mediator having an ionic group has been bonded with the hydrogen generating photocatalyst obtained in step 3 to which the ionic polymer has been introduced.

[0036] Furthermore, a preferred example of the method for producing a junction-type photocatalyst of the present invention is (II) a method for producing a junction-type photocatalyst including the following steps 1, 2', 3', and 4'. However, the order of steps 2' and 3' is not critical. Step 3' may be performed after step 2', or step 2' may be performed after step 3', or they may be performed simultaneously. Step 1: A step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation using an organic carboxylic acid compound and a solid mediator or a precursor thereof. Step 2': A step of introducing an ionic group into the solid mediator, and then reacting the ionic group with an ionic polymer having an opposite charge to that of the ionic group, to obtain an oxygen-generating photocatalyst bonded to the solid mediator having the ionic polymer. Step 3': introducing an ionic polymer having an opposite charge to the charge of the ionic polymer into the hydrogen generating photocatalyst. Step 4': A step of mixing the oxygen generating photocatalyst obtained in step 2' to which the solid mediator having the ionic polymer has been bonded, with the hydrogen generating photocatalyst obtained in step 3' to which the ionic polymer has been introduced.

[0037] Step 1: A step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation using an organic carboxylic acid compound and a solid mediator or a precursor thereof.

[0038] Step 1 is a step for producing an oxygen-generating photocatalyst to which a solid mediator is bonded. In step 1, the method for bonding (supporting) the solid mediator on the surface of the oxygen generating photocatalyst is not particularly limited, but it is preferable to use at least one method selected from the group consisting of photoelectrodeposition, impregnation support, and precipitation.

[0039] The photoelectrodeposition method is a method in which a dispersion containing a photocatalyst, a metal salt (a precursor of a solid mediator), and an organic carboxylic acid compound is irradiated with light to reduce the metal salt and deposit and bond (support) metal particles or metal compound particles (a solid mediator) on the surface of the photocatalyst. Examples of the precursor of the solid mediator include ionic salts of mediators such as silver nitrate and gold halide (tetrachloroauric acid).

[0040] The impregnation method involves mixing a photocatalyst with a solution or dispersion in which a metal salt (a precursor of the solid mediator) and an organic carboxylic acid compound are dissolved or dispersed, and then removing the solvent by solid-liquid separation such as filtration, decantation, or centrifugation, or by heating or evaporating the solvent under reduced pressure to support the metal salt on the surface of the photocatalyst.The metal salt is then calcined or reduced to bond (support) metal particles or metal compound particles (solid mediator) to the surface of the photocatalyst.

[0041] The precipitation method is a method in which metal particles or metal compound particles (solid mediator) obtained by reducing a metal salt (precursor of a solid mediator) in a solution containing an organic carboxylic acid compound are mixed with a photocatalyst to bond (support) the metal particles or metal compound particles (solid mediator) to the surface of the photocatalyst.

[0042] The photoelectrodeposition method is preferred from the viewpoint of increasing the coverage of the solid mediator on the electron-collecting surface of the oxygen-generating photocatalyst to 40% or more. The photoelectrodeposition method is a method in which a dispersion containing an oxygen-generating photocatalyst, an organic carboxylic acid compound, and a solid mediator or a precursor thereof is irradiated with light to bond (support) the solid mediator onto the oxygen-generating photocatalyst. At this time, it is thought that the light irradiation generates electrons and holes in the photocatalyst, and the electrons cause the reduction and precipitation of the solid mediator, while the holes cause the oxidation of water, etc. The solvent used in the dispersion is preferably water, but a lower alcohol such as methanol, ethanol, or 2-propanol can also be used as an auxiliary (sacrificial reagent) to promote the consumption of holes.

[0043] The organic carboxylic acid compound is presumed to contribute to the reduction of the metal salt (precursor of the solid mediator) and also acts as an auxiliary agent for bonding (supporting) the solid mediator on the oxygen-generating photocatalyst. Furthermore, the use of the organic carboxylic acid compound improves the coverage of the solid mediator on the electron-collecting surface of the oxygen-generating photocatalyst. For example, in the case of BiVO4 (monoclinic scheelite crystal), the selectivity for the {010} plane, which is the electron-collecting surface, is improved. This allows the solid mediator to be densely bonded to the oxygen-generating photocatalyst, thereby improving catalytic activity.

[0044] From the viewpoint of densely bonding the solid mediator onto the oxygen-generating photocatalyst, the organic carboxylic acid compound preferably includes at least one selected from the group consisting of ether carboxylates, fatty acids, hydroxymonocarboxylic acids, and polycarboxylic acids, more preferably includes ether carboxylates, and specific examples thereof include the following organic carboxylic acid compounds 1) to 4).

[0045] 1) Ether carboxylate Examples of the ether carboxylate include those represented by the following general formula (1). R 1 -O-(EO) n -CH2COOH (1) In the general formula (1), R 1 is preferably a linear or branched alkyl or alkenyl group having 4 to 22 carbon atoms, more preferably a linear or branched alkyl or alkenyl group having 8 to 18 carbon atoms, and even more preferably a linear or branched alkyl group having 8 to 18 carbon atoms (alkyl ether carboxylate), from the viewpoints of water solubility and auxiliary function. The average number of moles n of EO (ethyleneoxy group) added is preferably 1 to 25, more preferably 2 to 12, and even more preferably 3 to 8, from the viewpoints of water solubility and auxiliary function.

[0046] The ether carboxylates include, for example, polyoxyethylene (4.5) lauryl ether acetic acid, and may be potassium salts, sodium salts, or ammonium salts thereof.

[0047] 2) Fatty acids Preferred examples of the fatty acids include those represented by the following general formula (2). R 2 -COOH (2) In the general formula (2), R 2From the viewpoints of water solubility and auxiliary function, is preferably a linear or branched alkyl or alkenyl group having 4 to 22 carbon atoms, more preferably a linear or branched alkyl or alkenyl group having 8 to 22 carbon atoms, and even more preferably a linear or branched alkyl or alkenyl group having 12 to 18 carbon atoms.

[0048] The fatty acid may be, for example, oleic acid, and may be a potassium salt, a sodium salt, or an ammonium salt thereof.

[0049] 3) Hydroxymonocarboxylic acids The hydroxymonocarboxylic acid preferably has a hydrocarbon group having from 2 to 12 carbon atoms, more preferably from 3 to 8 carbon atoms, from the viewpoint of water solubility and auxiliary function.

[0050] Examples of the hydroxymonocarboxylic acid include glycolic acid, lactic acid, glyceric acid, gluconic acid, and pantothenic acid.

[0051] 4) Polycarboxylic acids The polycarboxylic acid preferably has a hydrocarbon group having 2 to 12 carbon atoms, more preferably 3 to 8 carbon atoms, from the viewpoint of water solubility and auxiliary function.

[0052] The polycarboxylic acid is preferably a dicarboxylic acid, such as malic acid, tartaric acid, oxalic acid, malonic acid, maleic acid, succinic acid, or glutaric acid, and an example of a tricarboxylic acid is citric acid.

[0053] The organic carboxylic acid compounds 1) to 4) above may be used alone or in combination of two or more.

[0054] In step 1, in a dispersion liquid containing a photocatalyst, a metal salt (a precursor of a solid mediator), and an organic carboxylic acid compound, the organic carboxylic acid compound is preferably contained (mixed) in an amount of 100 parts by mass or more, more preferably 500 parts by mass or more, and even more preferably 1,000 parts by mass or more, relative to 100 parts by mass of the solid mediator or its precursor (metal salt), from the viewpoint of increasing the coverage of the solid mediator on the oxygen-generating photocatalyst and improving catalytic activity. Also, from the same viewpoint, the amount is preferably 100,000 parts by mass or less, more preferably 50,000 parts by mass or less, even more preferably 20,000 parts by mass or less, preferably 100 parts by mass or more and 100,000 parts by mass or less, more preferably 500 parts by mass or more and 50,000 parts by mass or less, and even more preferably 1,000 parts by mass or more and 20,000 parts by mass or less.

[0055] In step 1, the solid mediator or its precursor (metal salt) is preferably contained (mixed) in the dispersion liquid in an amount of preferably 0.1 part by mass or more, more preferably 1 part by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the oxygen-generating photocatalyst, from the viewpoint of increasing the coverage of the solid mediator on the oxygen-generating photocatalyst and improving catalytic activity, and from the same viewpoint, it is preferably 1000 parts by mass or less, more preferably 500 parts by mass or less, and even more preferably 100 parts by mass or less, and is preferably 0.1 part by mass or more and 1000 parts by mass or less, more preferably 1 part by mass or more and 500 parts by mass or less, and even more preferably 5 parts by mass or more and 100 parts by mass or less.

[0056] The light to be irradiated may be either sunlight or artificial light (such as a fluorescent lamp, UV lamp, LED, mercury lamp, xenon lamp, metal halide lamp, sodium lamp, or halogen lamp). The wavelength of the light is preferably 180 to 1000 nm, more preferably 300 to 800 nm, from the viewpoint of increasing the coverage of the solid mediator on the oxygen generating photocatalyst.

[0057] The intensity of the irradiation light is preferably 1 mW / cm from the viewpoint of increasing the coverage of the solid mediator on the electron collection surface of the oxygen generating photocatalyst. 2More preferably, 2 mW / cm 2 More preferably, 5 mW / cm 2 From the same viewpoint, it is preferable that the 2 Less than 100mW / cm 2 or less, more preferably 50 mW / cm 2 The following is the result.

[0058] Step 2: This is a step of introducing an ionic group into the solid mediator (hereinafter referred to as "Mode 1") to obtain an oxygen generating photocatalyst to which the solid mediator having the ionic group is bonded.

[0059] To introduce an ionic group into the solid mediator, a compound containing an ionic group and a group having affinity for the solid mediator may be used. Specifically, when the solid mediator contains gold (atom), silver, or platinum, from the viewpoint of affinity with the metal, a thiol compound having an ionic group or a selenium compound having an ionic group is preferred, and a thiol compound having an ionic group is more preferred.

[0060] The thiol compound having an ionic group has at least one ionic group (ionic substituent), and among the ionic groups, examples of anionic groups include a sulfonic acid group, a phosphonic acid group, a phosphate group, and a carboxy group, and examples of cationic groups include an ammonium group. Among these, from the viewpoint of enhancing catalytic activity, thiol compounds having an ammonium group or a carboxy group are preferred. From the same viewpoint, the ionic group is more preferably an anionic group, and even more preferably a carboxylate anion (carboxy group).

[0061] The thiol compound having an ionic group preferably has an alkylene group having one or more carbon atoms, more preferably two or more carbon atoms, from the viewpoint of enhancing catalytic activity; and from the same viewpoint, preferably has an alkylene group having 18 or less carbon atoms, more preferably 14 or less carbon atoms, and even more preferably 8 or less carbon atoms.

[0062] From the viewpoint of enhancing catalytic activity, the thiol compound having an ionic group preferably has two or less thiol groups, and more preferably has one thiol group.

[0063] When the thiol compound having an ionic group has an acidic group, it may be an acid, a salt, or a mixture thereof.

[0064] As the thiol compound having an ionic group, for example, thiomalic acid, 3-mercaptopropionic acid, thioglycolic acid, (11-mercaptoundecyl)trimethylammonium, etc. are preferably used.

[0065] In step 2, the thiol compound having an ionic group is preferably contained (mixed) in an amount of 0.1 parts by mass or more, more preferably 1 part by mass or more, relative to 100 parts by mass of the oxygen generating photocatalyst bonded (supported) with the solid mediator, from the viewpoint of enhancing catalytic activity, and from the same viewpoint, is preferably contained in an amount of 100 parts by mass or less, more preferably 50 parts by mass or less, and is preferably reacted in an amount of 0.1 parts by mass or more and 100 parts by mass or less, more preferably 1 part by mass or more and 50 parts by mass or less.

[0066] Step 2': This is a step of introducing an ionic group into the solid mediator ("Mode 1"), and then reacting the ionic group with an ionic polymer having an opposite charge to that of the ionic group (hereinafter referred to as "Mode 2") to obtain an oxygen-generating photocatalyst bonded to a solid mediator having the ionic polymer.

[0067] As in the above-mentioned embodiment 1, an ionic group is introduced into the solid mediator, and then the ionic group is reacted (ionic bonded) with an ionic polymer having an opposite charge to that of the ionic group ("embodiment 2"), thereby obtaining an oxygen-generating photocatalyst bonded to a solid mediator into which an ionic group resulting from the ionic polymer has been introduced.

[0068] Examples of methods for introducing an ionic group into the solid mediator and then reacting (ionically bonding) an ionic polymer having an opposite charge to that of the ionic group include (i) a method in which an oxygen-generating photocatalyst having a solid mediator bonded (supported) thereto is mixed and reacted with a thiol compound having an anionic group to introduce an anionic group into the solid mediator, and then a polymer having a cationic group having an opposite charge to that of the anionic group (hereinafter simply referred to as a "cationic polymer") is mixed and reacted (ionically bonded) thereto. Another method is (ii) a method in which an oxygen-generating photocatalyst bonded (supported) to a solid mediator is reacted with a thiol compound having a cationic group to introduce a cationic group into the solid mediator, and then a polymer having an anionic group having an opposite charge to the cationic group (hereinafter simply referred to as an "anionic polymer") is mixed and reacted (ionic bonded) with the solid mediator. By these methods, the solid mediator has an ionic group and an ionic polymer, and the ionic group is ionically bonded to the ionic polymer.

[0069] The ionic polymer refers to a cationic polymer or an anionic polymer, and as will be described later, the terms ionic polymer A and ionic polymer B are used for convenience to distinguish the ionicity of the ionic polymers. That is, when ionic polymer A is a cationic polymer, it means that ionic polymer B is an anionic polymer, and when ionic polymer A is an anionic polymer, it means that ionic polymer B is a cationic polymer.

[0070] From the viewpoint of enhancing catalytic activity, examples of the cationic polymer include polymers having quaternary ammonium groups. Specifically, preferred are polymers having quaternary ammonium groups. More preferred are at least one selected from the group consisting of cationized polysaccharides, diallyl quaternary ammonium salt polymers or copolymers thereof, (meth)acryloyloxyethyl quaternary ammonium salt polymers or copolymers thereof, (meth)acrylamidopropyl quaternary ammonium salt polymers or copolymers thereof, and dimethylamine epichlorohydrin polymers. Still more preferred are at least one selected from the group consisting of (a) cationized cellulose, (b) cationized guar gum, (c) diallyl quaternary ammonium salt polymers and diallyl quaternary ammonium salt / acrylamide copolymers, (d) (meth)acryloyloxyethyl quaternary ammonium salt polymers and (meth)acryloyloxyethyl quaternary ammonium salt / acrylamide copolymers, and (e) dimethylamine epichlorohydrin polymers. Of these, (c) is particularly preferred. Quaternary ammonium groups also include protonated tertiary amines.

[0071] (a) Cationic cellulose: The degree of cationic substitution of the cationized cellulose is 0.01 to 1, i.e., the average value per anhydroglucose unit is preferably 0.01 to 1, more preferably 0.02 to 0.5, from the viewpoint of enhancing catalytic activity. The weight-average molecular weight of the cationized cellulose is preferably about 100,000 to 8,000,000, from the viewpoint of enhancing catalytic activity. Examples of commercially available products of (a) include those under the trade names "Poise C-80H" (manufactured by Kao Corporation) and "Polymer JR-400" (manufactured by Dow Chemical Company).

[0072] (b) Cationic guar gum: From the viewpoint of enhancing catalytic activity, the degree of cationic substitution of the cationized guar gum is preferably 0.01 to 1, and more preferably 0.02 to 0.5 cationic groups are introduced into the sugar units. Examples of commercially available products of (b) include the product name "Jaguar C-13C" sold by Rhodia Inc. under the trade name "Jaguar."

[0073] (c) Diallyl quaternary ammonium salt polymer, and diallyl quaternary ammonium salt / acrylamide copolymer: The weight-average molecular weight of the diallyl quaternary ammonium salt polymer is preferably about 30,000 to 1,000,000 from the viewpoint of enhancing catalytic activity, and the weight-average molecular weight of the diallyl quaternary ammonium salt / acrylamide copolymer is preferably about 30,000 to 2,000,000, more preferably about 1,000,000 to 2,000,000, from the viewpoint of enhancing catalytic activity. Examples of commercially available products of (c) include those sold by Noveon under the trade name "Marquardt" under the trade name "Marquardt 100 (weight average molecular weight: 150,000)" and "Marquardt 550 (weight average molecular weight: 1.6 million)."

[0074] (d) (meth)acryloyloxyethyl quaternary ammonium salt polymer, and (meth)acryloyloxyethyl quaternary ammonium salt / acrylamide copolymer: The weight average molecular weight of the methacryloyloxyethyl quaternary ammonium salt / acrylamide copolymer is preferably about 100,000 to 10,000,000, more preferably about 2,000,000 to 6,000,000, from the viewpoint of enhancing catalytic activity.

[0075] (e) Dimethylamine epichlorohydrin polymer (poly-2-hydroxypropyldimethylammonium chloride): The weight average molecular weight of the dimethylamine epichlorohydrin polymer is preferably about 1,000 to 100,000, more preferably about 3,000 to 10,000, from the viewpoint of enhancing catalytic activity. Examples of commercially available products of (e) include those sold by Yokkaichi Synthetic Co., Ltd. under the trade name "Catiomaster" and the trade name "Catiomaster PD-7 (weight average molecular weight: 5,000)".

[0076] The anionic polymer is preferably a polymer having a sulfate group, a sulfonic acid group, a phosphonic acid group, a phosphoric acid group, or a carboxy group, and among these, from the viewpoint of enhancing catalytic activity, a polymer having a sulfonic acid group (sulfonic acid-based polymer) or a polymer having a carboxy group (carboxylic acid-based polymer) is preferred.

[0077] The polymer having a sulfonic acid group is preferably poly(sodium styrene sulfonate).

[0078] The carboxylic acid polymer is preferably a carboxylic acid polymer having a constituent unit derived from an anionic group-containing monomer selected from acrylates, methacrylates, and maleates. The carboxylic acid polymer is preferably a polymer composed of the anionic group-containing monomer, but may also be a copolymer of the anionic group-containing monomer and a monomer other than the anionic group-containing monomer.

[0079] Examples of monomers other than the anionic group-containing monomer include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate and ethyl (meth)acrylate, N-substituted (meth)acrylamides such as N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, isopropyl (meth)acrylamide, and tert-butyl (meth)acrylamide, vinyl ethers such as methyl vinyl ether and butyl vinyl ether, and olefinic hydrocarbons such as styrene, ethylene, propylene, and isobutylene. These may be used alone or in combination of two or more. Among these, (meth)acrylic acid alkyl esters such as methyl (meth)acrylate and ethyl (meth)acrylate are preferred. In this specification, "(meth)acrylic" means "acrylic or methacrylic".

[0080] From the viewpoint of enhancing catalytic activity, the weight-average molecular weight (Mw) of the carboxylic acid polymer is preferably 1,000 or more, more preferably 5,000 or more, and even more preferably 10,000 or more. From the same viewpoint, it is preferably 500,000 or less, more preferably 100,000 or less, even more preferably 50,000 or less, and still more preferably 35,000 or less. From the viewpoint of enhancing catalytic activity, the weight average molecular weight (Mw) of the polymer having sulfonic acid groups is preferably 10,000 or more, more preferably 50,000 or more, and even more preferably 100,000 or more. From the same viewpoint, it is preferably 5,000,000 or less, more preferably 2,000,000 or less, even more preferably 1,000,000 or less, and still more preferably 600,000 or less.

[0081] In this specification, the weight average molecular weight (Mw) of the cationic polymer and the anionic polymer is a value determined by gel permeation chromatography (GPC) using polystyrene as a standard substance.

[0082] In step 2', the ionic polymer is preferably contained (mixed) in an amount of 5 parts by mass or more, more preferably 10 parts by mass or more, relative to 100 parts by mass of the oxygen-generating photocatalyst to which the solid mediator having the ionic group introduced therein is bonded (supported), from the viewpoint of enhancing photocatalytic activity; and from the same viewpoint, the amount is preferably 500 parts by mass or less, more preferably 100 parts by mass or less.

[0083] Step 3: A step of introducing an ionic polymer having an opposite charge to the charge of the ionic group into the hydrogen generating photocatalyst.

[0084] Step 3': A step of introducing an ionic polymer having an opposite charge to the charge of the ionic polymer into the hydrogen generating photocatalyst.

[0085] The step 3 is a step of introducing, into the hydrogen generating photocatalyst, an ionic polymer having a charge opposite to that of the ionic group possessed by the solid mediator in the step 2. For example, when the ionic group possessed by the solid mediator in step 2 is an anionic group, an ionic polymer having an opposite charge may be introduced by mixing and dispersing the hydrogen generating photocatalyst with a polymer having a cationic group, or the hydrogen generating photocatalyst may be mixed and dispersed with a polymer having an anionic group, and then further mixed and dispersed with a polymer having a cationic group to introduce an ionic polymer having an opposite charge. That is, it is a bonded photocatalyst having a solid mediator between a hydrogen generating photocatalyst and an oxygen generating photocatalyst, wherein the solid mediator has an ionic group, the hydrogen generating photocatalyst has an ionic polymer B having an opposite charge to the charge of the ionic group via an ionic polymer A, and the solid mediator and the hydrogen generating photocatalyst are bonded by an ionic bond between the ionic group and the ionic polymer B. This means that the ionic polymer contained in the hydrogen generating photocatalyst is ionic polymer A, and via ionic polymer A, it has ionic polymer B, which has an opposite charge to the charge of the ionic group, and the solid mediator and the hydrogen generating photocatalyst are bonded together by the ionic bond between the ionic group and ionic polymer B. When the ionic group is an anionic group, the ionic polymer A is an anionic polymer and the ionic polymer B is a cationic polymer. When the ionic group is a cationic group, the ionic polymer A is a cationic polymer and the ionic polymer B is an anionic polymer.

[0086] In addition, the step 3' is a step of mixing and dispersing the hydrogen generating photocatalyst together with an ionic polymer having an opposite charge to the ionic group of the solid mediator in the step 2', thereby introducing the ionic polymer having an opposite charge to the charge of the ionic group into the hydrogen generating photocatalyst. For example, if the ionic group possessed by the solid mediator in step 2' is an anionic group, the solid mediator can be made to have a cationic polymer by further mixing and dispersing it with a polymer having a cationic group, and an ionic polymer having an opposite charge can be introduced by mixing and dispersing the hydrogen generating photocatalyst with a polymer having an anionic group, or the hydrogen generating photocatalyst can be mixed and dispersed with a polymer having a cationic group, and then further mixed and dispersed with a polymer having an anionic group to introduce an ionic polymer having an opposite charge. That is, it is a bonded photocatalyst having a solid mediator between a hydrogen generating photocatalyst and an oxygen generating photocatalyst, wherein the solid mediator has an ionic group and an ionic polymer B, the ionic group is bonded to the ionic polymer B, the hydrogen generating photocatalyst has an ionic polymer A having an opposite charge to that of the ionic polymer B, and the solid mediator and the hydrogen generating photocatalyst are bonded by an ionic bond between the ionic polymer B possessed by the solid mediator and the ionic polymer A possessed by the hydrogen generating photocatalyst. This means that the ionic polymer contained in the hydrogen generating photocatalyst is ionic polymer A, the solid mediator has the ionic group and ionic polymer B having an opposite charge to that of ionic polymer A, the ionic group is bonded to ionic polymer B, and the solid mediator and the hydrogen generating photocatalyst are joined by an ionic bond between the ionic polymer B contained in the solid mediator and the ionic polymer A contained in the hydrogen generating photocatalyst. When the ionic group is an anionic group, the ionic polymer A is an anionic polymer and the ionic polymer B is a cationic polymer. When the ionic group is a cationic group, the ionic polymer A is a cationic polymer and the ionic polymer B is an anionic polymer.

[0087] The ionic polymer may be the anionic polymer or the cationic polymer described in the second embodiment.

[0088] In steps 3 and 3', the ionic polymer is preferably contained (mixed) in an amount of 5 parts by mass or more, more preferably 20 parts by mass or more, relative to 100 parts by mass of the hydrogen generating photocatalyst, from the viewpoint of enhancing catalytic activity, and from the same viewpoint, it is preferably 500 parts by mass or less, more preferably 100 parts by mass or less, and preferably 5 parts by mass or more and 500 parts by mass or less, more preferably 20 parts by mass or more and 100 parts by mass or less.

[0089] Step 4: This step involves mixing the oxygen-generating photocatalyst to which the solid mediator having ionic groups obtained in Step 2 has been bonded (supported) with the hydrogen-generating photocatalyst to which the ionic polymer has been introduced obtained in Step 3.

[0090] Step 4': This is a step of mixing the oxygen generating photocatalyst to which the solid mediator having the ionic polymer obtained in step 2' has been bonded with the hydrogen generating photocatalyst to which the ionic polymer has been introduced obtained in step 3'.

[0091] In step 4 or step 4', the oxygen generating photocatalyst to which the solid mediator having an ionic group has been bonded (supported) is mixed with the hydrogen generating photocatalyst to which the ionic polymer obtained in step 3 or step 3' has been introduced, thereby making it possible to bond the oxygen generating photocatalyst and the hydrogen generating photocatalyst via the solid mediator. For example, when using an oxygen-generating photocatalyst bonded (supported) to a solid mediator into which an anionic group has been introduced, it is sufficient to use a hydrogen-generating photocatalyst into which a cationic group originating from a cationic polymer has been introduced; and when using an oxygen-generating photocatalyst bonded (supported) to a solid mediator into which a cationic group has been introduced, it is sufficient to use a hydrogen-generating photocatalyst into which an anionic group originating from an anionic polymer has been introduced.

[0092] In step 4, the mixing mass ratio (hydrogen generating photocatalyst into which the ionic polymer obtained in step 3 has been introduced / oxygen generating photocatalyst into which the solid mediator having an ionic group obtained in step 2 has been bonded (supported)) is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.07 or more, from the viewpoint of enhancing catalytic activity; and from the same viewpoint, it is preferably 10 or less, more preferably 5 or less, and even more preferably 1 or less, preferably 0.01 or more and 10 or less, more preferably 0.05 or more and 5 or less, and even more preferably 0.07 or more and 1 or less.

[0093] Furthermore, in step 4', the mixing mass ratio (hydrogen generating photocatalyst incorporating the ionic polymer obtained in step 3' / oxygen generating photocatalyst grafted with a solid mediator having the ionic polymer obtained in step 2') is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.07 or more, from the viewpoint of enhancing catalytic activity, and from the same viewpoint, is preferably 10 or less, more preferably 5 or less, and even more preferably 1 or less, preferably 0.01 or more and 10 or less, more preferably 0.05 or more and 5 or less, and even more preferably 0.07 or more and 1 or less.

[0094] By adjusting the mixing mass ratio in step 4 or step 4', the solid mediator and the hydrogen generating photocatalyst are bonded together via the ionic polymer in both mode 1 and mode 2. The ionic polymer mediates a strong electrostatic interaction, and the hydrogen generating photocatalyst and the oxygen generating photocatalyst are not separated but are bonded together via the solid mediator, improving catalytic activity and enabling water to be decomposed into oxygen and hydrogen with high water-splitting reaction efficiency.

[0095] (Solid mediator coverage and selectivity in junction-type photocatalysts and oxygen-evolving photocatalysts) In the bonded photocatalyst of the present invention and / or the oxygen-generating photocatalyst of the present invention, the coverage rate of the solid mediator relative to the electron collection surface area of ​​the oxygen-generating photocatalyst is 40% or more, preferably 50% or more, more preferably 55% or more, and even more preferably 58% or more, from the viewpoint of enhancing catalytic activity, and the upper limit is preferably 100% or less, and from the viewpoint of improving the adhesion and light transmittance of the fixed mediator, it is more preferably 95% or less, more preferably 90% or less. In the bonded photocatalyst and / or the oxygen generating photocatalyst, the coverage of the solid mediator relative to the electron collection surface area of ​​the oxygen generating photocatalyst is preferably 40% or more and 100% or less, more preferably 50% or more and 95% or less, and even more preferably 55% or more and 90% or less, from the viewpoint of increasing catalytic activity and improving the adhesion and light transmittance of the fixed mediator. By using the manufacturing method of step 1, i.e., at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation using an organic carboxylic acid compound and a solid mediator or a precursor thereof, the coverage can be increased to 40% or more. For example, the coverage can be further increased by increasing the content of the organic carboxylic acid compound relative to the solid mediator or a precursor thereof or by extending the light irradiation time in the photoelectrodeposition method.

[0096] In the bonded photocatalyst and / or the oxygen generating photocatalyst, the bond selectivity of the solid mediator relative to the electron collecting surface area of ​​the oxygen generating photocatalyst is preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and even more preferably 90% or more from the viewpoint of enhancing catalytic activity, and is 100% or less, preferably 99.5% or less from the viewpoint of production. The bond selectivity can be improved, for example, by the type of production method in step 1, and it is preferable to use a photoelectrodeposition method.

[0097] The coverage and bonding selectivity can be determined by the method of the following examples.

[0098] <Method of manufacturing oxygen-generating photocatalyst> The method for producing the oxygen generating photocatalyst is the same as step 1 of the method for producing the junction-type photocatalyst.

[0099] <Photocatalytic composite> The photocatalyst composite of the present invention comprises the above-mentioned junction-type photocatalyst on a substrate.

[0100] The substrate is not particularly limited as long as it can immobilize the bonded photocatalyst on its surface, and examples thereof include ceramic substrates such as alumina; glass substrates such as soda lime glass and borosilicate glass; quartz substrates; metal substrates such as titanium, copper, tin, iron, aluminum, and stainless steel; organic substrates such as methacrylic resin, acrylic resin, urethane resin, phenolic resin, melamine resin, urea resin, polyester resin, polycarbonate resin, fluororesin, polyethylene, polypropylene, polystyrene, polyamide, polyimide, polyacetal, polyvinyl chloride, and polyvinylidene chloride; fibrous substrates such as glass fiber and carbon fiber; and natural substrates such as paper, bamboo, and wood.

[0101] The substrate preferably has pores, more preferably has interconnected pores, which allows hydrogen gas produced by a water-splitting reaction on the surface of the junction-type photocatalyst to reach the outside through the pores, thereby enabling more efficient production of hydrogen gas.

[0102] The method for producing the photocatalyst composite is not particularly limited, and examples thereof include: (1) a method in which a dispersion liquid containing the bonded photocatalyst is applied to a substrate, dried, and optionally fired to immobilize the bonded photocatalyst on the substrate; and (2) a method in which a dispersion liquid containing the oxygen-generating photocatalyst is applied to a substrate, dried, and optionally fired to immobilize the oxygen-generating photocatalyst on the substrate, and then the solid mediator is bonded to the surface of the oxygen-generating photocatalyst in the same manner as above, and then the hydrogen-generating photocatalyst is bonded to the surface of the solid mediator.

[0103] <Applications of bonded photocatalysts and photocatalyst composites> The junction-type photocatalyst and photocatalyst composite of the present invention can be used not only as a photocatalyst that catalyzes the decomposition reaction of water or alcohol, but also as a photocatalyst that catalyzes the decomposition reaction of organic matter, and can be used, for example, as an environmental purification agent, antibacterial / sterilizing agent, deodorizing agent, or antifouling agent for neutralizing harmful organic compounds, bacteria, and malodorous substances, as well as inorganic compounds (ammonium ions, ammonia, nitrate ions, nitrite ions, etc.).

[0104] <Hydrogen production methods> The method for producing hydrogen using the junction-type photocatalyst or the photocatalyst composite of the present invention is not particularly limited, and examples thereof include a method for producing hydrogen including a step of irradiating the junction-type photocatalyst or the photocatalyst composite with light in the presence of water or alcohol to cause a decomposition reaction of water or alcohol to generate at least hydrogen.

[0105] The light to be irradiated may be either sunlight or artificial light (such as a fluorescent lamp, UV lamp, LED, mercury lamp, xenon lamp, metal halide lamp, sodium lamp, or halogen lamp). From the viewpoint of promoting the decomposition reaction, the wavelength of the light is preferably 180 to 1000 nm, more preferably 300 to 800 nm. From the viewpoint of promoting the decomposition reaction, the irradiance of the light irradiation is preferably 1 μW / m 2 More than 1mW / m 2 The decomposition reaction temperature is preferably 0°C or higher, more preferably 15°C or higher, from the viewpoint of accelerating the decomposition reaction.

[0106] The amount of hydrogen generated using the junction-type photocatalyst or the photocatalyst composite of the present invention (per 55 mg of catalyst) is preferably 0.05 (μmol h -1 ) or more, more preferably 0.1 (μmol h -1 ) or more, more preferably 0.20 (μmol h -1 ) or more, and there is no particular upper limit, but it is preferably 1 (mol h -1 ) is as follows.

[0107] In relation to the above-described embodiment, the present invention further discloses the following aspects. [1] A method for producing a bonded photocatalyst having a solid mediator between the hydrogen generating photocatalyst and the oxygen generating photocatalyst, the method comprising bonding a solid mediator to a surface of an oxygen generating photocatalyst, and then bonding a hydrogen generating photocatalyst to the surface of the solid mediator, the method comprising: A method for producing a junction-type photocatalyst, comprising the following step 1: Step 1: A step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation using an organic carboxylic acid compound and a solid mediator or a precursor thereof. [2] The method for producing a bonded photocatalyst according to [1], wherein the solid mediator and the hydrogen generating photocatalyst are bonded via an ionic polymer. Process [3] The method for producing a bonded photocatalyst according to [1] or [2], wherein the solid mediator has an ionic group, and the solid mediator and the hydrogen generating photocatalyst are bonded via an ionic polymer having an opposite charge to that of the ionic group. [4] The method for producing a junction-type photocatalyst according to any one of [1] to [3], further comprising the step of irradiating a dispersion containing an oxygen-generating photocatalyst in addition to the organic carboxylic acid compound and the solid mediator or a precursor thereof with light when the photoelectrodeposition method is used in step 1. [5] The method for producing a junction-type photocatalyst according to any one of [1] to [4], wherein the organic carboxylic acid compound is at least one selected from the group consisting of ether carboxylates, fatty acids, hydroxymonocarboxylic acids, and polycarboxylic acids. [6] the organic carboxylic acid compound comprises an ether carboxylate; The method for producing a junction type photocatalyst according to any one of [1] to [5], wherein the solid mediator contains gold. [7] A method for producing a junction-type photocatalyst having a solid mediator between a hydrogen generating photocatalyst and an oxygen generating photocatalyst, comprising: the solid mediator has an ionic group; the hydrogen generating photocatalyst has the ionic polymer having an opposite charge to the charge of the ionic group; the solid mediator and the hydrogen generating photocatalyst are bonded together by an ionic bond between the ionic group and the ionic polymer; A method for producing a junction-type photocatalyst, comprising the following step 1, wherein the solid mediator contains gold. Step 1: A step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of a photoelectrodeposition method, an impregnation method, and a precipitation method using an organic carboxylic acid compound containing an ether carboxylate and a solid mediator or a precursor thereof. [8] A method for producing a junction-type photocatalyst having a solid mediator between a hydrogen generating photocatalyst and an oxygen generating photocatalyst, comprising: the solid mediator has an ionic group; The hydrogen generating photocatalyst comprises an ionic polymer A and The polymer further includes, via the ionic polymer A, an ionic polymer B having an opposite charge to the charge of the ionic group, the solid mediator and the hydrogen generating photocatalyst are bonded together by an ionic bond between the ionic group and the ionic polymer B, A method for producing a junction-type photocatalyst, comprising the following step 1, wherein the solid mediator contains gold. Step 1: A step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of a photoelectrodeposition method, an impregnation method, and a precipitation method using an organic carboxylic acid compound containing an ether carboxylate and a solid mediator or a precursor thereof. [9] A method for producing a junction-type photocatalyst having a solid mediator between a hydrogen generating photocatalyst and an oxygen generating photocatalyst, comprising: the solid mediator has an ionic group and, via the ionic group, an ionic polymer B having a charge opposite to that of the ionic group; the hydrogen generating photocatalyst contains the ionic polymer A, the solid mediator and the hydrogen generating photocatalyst are joined together by an ionic bond between the ionic polymer B contained in the solid mediator and the ionic polymer A contained in the hydrogen generating photocatalyst, A method for producing a junction-type photocatalyst, comprising the following step 1, wherein the solid mediator contains gold. Step 1: A step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of a photoelectrodeposition method, an impregnation method, and a precipitation method using an organic carboxylic acid compound containing an ether carboxylate and a solid mediator or a precursor thereof.

[10] The method for producing a junction-type photocatalyst according to any one of [1] to [9], further comprising the following steps 2 to 4, provided that steps 2 and 3 can be performed in any order. Step 2: A step of introducing an ionic group into the solid mediator to obtain an oxygen-generating photocatalyst to which the solid mediator having the ionic group is bonded. Step 3: introducing an ionic polymer having an opposite charge to the charge of the ionic group into the hydrogen generating photocatalyst. Step 4: Mixing the oxygen generating photocatalyst obtained in step 2 to which the solid mediator having an ionic group has been bonded with the hydrogen generating photocatalyst obtained in step 3 to which the ionic polymer has been introduced.

[11] The method for producing a junction-type photocatalyst according to any one of [1] to [9], further comprising the following steps 2', 3', and 4', provided that steps 2' and 3' can be performed in any order. Step 2': A step of introducing an ionic group into the solid mediator, and then reacting the ionic group with an ionic polymer having an opposite charge to that of the ionic group, to obtain an oxygen-generating photocatalyst bonded to the solid mediator having the ionic polymer. Step 3': introducing an ionic polymer having an opposite charge to the charge of the ionic polymer into the hydrogen generating photocatalyst. Step 4': A step of mixing the oxygen generating photocatalyst obtained in step 2' to which the solid mediator having the ionic polymer has been bonded, with the hydrogen generating photocatalyst obtained in step 3' to which the ionic polymer has been introduced.

[12] The method for producing a junction-type photocatalyst according to any one of [1] to

[11] , wherein the solid mediator is a transition metal or a compound thereof, and preferably contains a transition metal selected from gold, silver, copper, nickel, titanium, manganese, rhodium, palladium, ruthenium, and iridium, more preferably gold or silver, and even more preferably gold.

[13] The method for producing a junction-type photocatalyst according to any one of [1] to

[12] , wherein the hydrogen generating photocatalyst is a metal oxide, preferably TiO2, SrTiO3, La2Ti2O7, SnNb2O6, or a compound thereof doped with one or more of the metals Cr, Sb, Ta, Ir, and La, more preferably SrTiO3.

[14] The method for producing a junction-type photocatalyst according to any one of [1] to

[13] , wherein the oxygen-generating photocatalyst is a metal oxide, preferably BiVO4, TiO2, WO3, SrTiO3, Ag3PO4, SnNb2O6, Bi2WO6, Fe2TiO5, Fe2O3, Bi2MoO6, or a compound thereof doped with one or more metals such as Cr, Ni, Sb, Nb, Th, Mo, and W, more preferably BiVO4.

[15] The method for producing a junction-type photocatalyst according to any one of [1] to

[14] , wherein in step 1, the organic carboxylic acid compound is preferably used in an amount of 100 parts by mass or more and 100,000 parts by mass or less, more preferably 500 parts by mass or more and 50,000 parts by mass or less, and even more preferably 1,000 parts by mass or more and 20,000 parts by mass or less, relative to 100 parts by mass of the solid mediator or its precursor (metal salt).

[16] The method for producing a junction-type photocatalyst according to any one of [1] to

[15] , wherein in step 1, the amount of the solid mediator or its precursor (metal salt) relative to 100 parts by mass of the oxygen-generating photocatalyst is preferably 0.1 parts by mass or more and 1000 parts by mass or less, more preferably 1 part by mass or more and 500 parts by mass or less, and even more preferably 5 parts by mass or more and 100 parts by mass or less.

[17] The method for producing a junction-type photocatalyst according to any one of

[10] to

[16] , wherein a thiol compound having an ionic group is used in introducing an ionic group into the solid mediator in the step 2 or the step 2'.

[18]

[17] The method for producing a bonded photocatalyst according to

[17] , wherein in the introduction of an ionic group into the solid mediator in step 2 or step 2', the thiol compound having the ionic group is reacted in an amount of preferably 0.1 parts by mass or more and 100 parts by mass or less, more preferably 1 part by mass or more and 50 parts by mass or less, with respect to 100 parts by mass of the oxygen generating photocatalyst bonded (supported) with the solid mediator.

[19] The method for producing a junction-type photocatalyst according to any one of

[10] to

[18] , wherein in step 3 and step 3', the ionic polymer is preferably contained (mixed) in an amount of 5 parts by mass or more and 500 parts by mass or less, more preferably 20 parts by mass or more and 100 parts by mass or less, per 100 parts by mass of the hydrogen generating photocatalyst.

[20] The method for producing a junction-type photocatalyst according to any one of

[10] and

[12] to

[19] , wherein in step 4, the mixing mass ratio (hydrogen generating photocatalyst into which the ionic polymer obtained in step 3 has been introduced / oxygen generating photocatalyst to which the solid mediator having an ionic group obtained in step 2 has been junctioned (supported)) is preferably 0.01 or more and 10 or less, more preferably 0.05 or more and 5 or less, and even more preferably 0.07 or more and 1 or less. [twenty one] The method for producing a junction-type photocatalyst according to any one of

[11] to

[19] , wherein in step 4', the mixing mass ratio (hydrogen generating photocatalyst into which the ionic polymer obtained in step 3' has been introduced / oxygen generating photocatalyst into which a solid mediator having the ionic polymer obtained in step 2' has been junctioned) is preferably 0.01 or more and 10 or less, more preferably 0.05 or more and 5 or less, and even more preferably 0.07 or more and 1 or less. [twenty two] The method for producing a junction-type photocatalyst according to any one of [1] to

[21] , wherein the coverage of the solid mediator with respect to the electron collection surface area of ​​the oxygen generating photocatalyst is 40% or more, preferably 40% or more and 100% or less, more preferably 50% or more and 95% or less, and even more preferably 55% or more and 90% or less. [twenty three] A junction-type photocatalyst having a solid mediator between a hydrogen generating photocatalyst and an oxygen generating photocatalyst, A bonded photocatalyst in which the coverage of the solid mediator with respect to the electron collection surface area of ​​the oxygen generating photocatalyst is 40% or more, preferably 40% or more and 100% or less, more preferably 50% or more and 95% or less, and even more preferably 55% or more and 90% or less. [twenty four] The bonded photocatalyst according to

[23] , wherein the bond selectivity of the solid mediator to the electron collection surface of the oxygen generating photocatalyst is 60% or more, preferably 60% or more and 100% or less, more preferably 80% or more and 100% or less, and even more preferably 90% or more and 99.5% or less. [twenty five] The bonded photocatalyst according to

[23] or

[24] , wherein the solid mediator and the hydrogen generating photocatalyst are bonded via an ionic polymer.

[26] the solid mediator has an ionic group; The conjugated photocatalyst according to

[23] or

[24] , wherein the solid mediator and the hydrogen generating photocatalyst are conjugated via an ionic polymer having an opposite charge to that of the ionic group.

[27] the solid mediator has an ionic group; the hydrogen generating photocatalyst has the ionic polymer having an opposite charge to the charge of the ionic group; The bonded photocatalyst according to

[23] or

[24] , wherein the solid mediator and the hydrogen generating photocatalyst are bonded together by an ionic bond between the ionic group and the ionic polymer.

[28] the solid mediator has an ionic group; The hydrogen generating photocatalyst comprises an ionic polymer A and The ionic polymer B further has an opposite charge to the charge of the ionic group via the ionic polymer A, The conjugated photocatalyst according to

[23] or

[24] , wherein the solid mediator and the hydrogen generating photocatalyst are conjugated via an ionic bond between the ionic group and the ionic polymer B.

[29] the solid mediator has an ionic group and, via the ionic group, an ionic polymer B having a charge opposite to that of the ionic group; the hydrogen generating photocatalyst contains an ionic polymer A, The solid mediator and the hydrogen generating photocatalyst are joined by an ionic bond between the ionic polymer B contained in the solid mediator and the ionic polymer A contained in the hydrogen generating photocatalyst.

[30] The junction type photocatalyst according to any one of

[26] to

[29] , wherein the ionic group is an anionic group or a cationic group.

[31] The conjugated photocatalyst according to

[30] , wherein the anionic group is preferably a sulfonic acid group, a phosphonic acid group, a phosphoric acid group, or a carboxy group, more preferably a sulfonic acid group or a carboxy group, and the cationic group is a quaternary ammonium group.

[32] the ionic group is an anionic group, the ionic polymer A is an anionic polymer, The junction-type photocatalyst according to

[28] or

[29] , wherein the ionic polymer B is a cationic polymer.

[33] the ionic group is a cationic group, the ionic polymer A is a cationic polymer, The junction-type photocatalyst according to

[28] or

[29] , wherein the ionic polymer B is an anionic polymer.

[34] The conjugated photocatalyst according to

[32] or

[33] , wherein the anionic polymer preferably comprises a polymer having a sulfate group, a sulfonic acid group, a phosphonic acid group, a phosphoric acid group, or a carboxy group, more preferably a polymer having a sulfonic acid group (sulfonic acid-based polymer) or a polymer having a carboxy group (carboxylic acid-based polymer).

[35] The junction type photocatalyst according to any one of

[32] to

[34] , wherein the cationic polymer is preferably a polymer having a quaternary ammonium group, more preferably one or more selected from the group consisting of a cationized polysaccharide, a diallyl quaternary ammonium salt polymer or copolymer thereof, a (meth)acryloyloxyethyl quaternary ammonium salt polymer or copolymer thereof, a (meth)acrylamidopropyl quaternary ammonium salt polymer or copolymer thereof, and a dimethylamine epichlorohydrin polymer, and even more preferably at least one selected from the group consisting of (a) cationized cellulose, (b) cationized guar gum, (c) diallyl quaternary ammonium salt polymer and diallyl quaternary ammonium salt / acrylamide copolymer, (d) a (meth)acryloyloxyethyl quaternary ammonium salt polymer, a (meth)acryloyloxyethyl quaternary ammonium salt / acrylamide copolymer, or (e) a dimethylamine epichlorohydrin polymer.

[36] The junction-type photocatalyst according to any one of

[23] to

[35] , wherein the hydrogen generating photocatalyst is a metal oxide.

[37] The metal oxide is preferably TiO2, SrTiO3, La2Ti2O7, SnNb2O6, or a compound thereof doped with one or more of the metals Cr, Sb, Ta, Ir, and La, more preferably SrTiO3.

[36] The junction-type photocatalyst according to claim 1, wherein the metal oxide is TiO2, SrTiO3, LaTiO3, SnNb2O6 ...

[38] The junction-type photocatalyst according to any one of

[23] to

[37] , wherein the oxygen-generating photocatalyst is a metal oxide.

[39] The metal oxide is preferably BiVO4, TiO2, WO3, SrTiO3, Ag3PO4, SnNb2O6, Bi2WO6, Fe2TiO5, Fe2O3, Bi2MoO6, or a compound thereof doped with one or more metals such as Cr, Ni, Sb, Nb, Th, Mo, and W, more preferably BiVO4.

[38] The junction-type photocatalyst according to

[40] The junction type photocatalyst according to any one of

[23] to

[39] , wherein the solid mediator is a transition metal or a compound thereof.

[41] The solid mediator preferably contains a transition metal selected from gold, silver, copper, nickel, titanium, manganese, rhodium, palladium, ruthenium, and iridium, more preferably gold or silver, and even more preferably gold. The junction-type photocatalyst according to any one of

[23] to

[40] .

[42] The bonded photocatalyst according to any one of

[23] to

[41] , wherein the solid mediator is bonded onto the oxygen generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation using an organic carboxylic acid compound and a solid mediator or a precursor thereof.

[43] An oxygen generating photocatalyst to which a solid mediator is bonded, An oxygen generating photocatalyst to which a solid mediator is bonded, wherein the coverage of the solid mediator relative to the electron collection surface area of ​​the oxygen generating photocatalyst is 40% or more, preferably 40% or more and 100% or less, more preferably 50% or more and 95% or less, and even more preferably 55% or more and 90% or less.

[44]

[43] The oxygen generating photocatalyst to which a solid mediator is bonded, as described in

[43] , wherein the selectivity of bonding of the solid mediator to the electron collecting surface is 60% or more, preferably 60% or more and 100% or less, more preferably 80% or more and 100% or less, and even more preferably 90% or more and 99.5% or less.

[45] The oxygen generating photocatalyst having a solid mediator bonded thereto according to

[43] or

[44] , wherein the solid mediator is bonded onto the oxygen generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation using an organic carboxylic acid compound and a solid mediator or a precursor thereof.

[46] A method for producing an oxygen generating photocatalyst to which the solid mediator according to any one of

[43] to

[45] is bonded, comprising: A method for producing an oxygen generating photocatalyst having a solid mediator bonded thereto, comprising the step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation, using an organic carboxylic acid compound and a solid mediator or a precursor thereof.

[47]

[46] A method for producing an oxygen-generating photocatalyst having a solid mediator bonded thereto, comprising the step of irradiating a dispersion containing the organic carboxylic acid compound, the solid mediator or a precursor thereof, and the oxygen-generating photocatalyst with light, when the photoelectrodeposition method is used.

[48] The method for producing an oxygen generating photocatalyst having a solid mediator bonded thereto according to

[46] or

[47] , wherein the organic carboxylic acid compound is at least one selected from the group consisting of ether carboxylates, fatty acids, hydroxymonocarboxylic acids, and polycarboxylic acids.

[49] the organic carboxylic acid compound comprises an ether carboxylate; The method for producing an oxygen generating photocatalyst having a solid mediator bonded thereto according to any one of

[46] to

[48] , wherein the solid mediator contains gold.

[50] The method for producing an oxygen generating photocatalyst to which a solid mediator is bonded according to any one of

[46] to

[49] , wherein the organic carboxylic acid compound is preferably used in an amount of from 100 to 100,000 parts by mass, more preferably from 500 to 50,000 parts by mass, and even more preferably from 1,000 to 20,000 parts by mass, relative to 100 parts by mass of the solid mediator or its precursor (metal salt).

[51] The method for producing an oxygen generating photocatalyst having a solid mediator bonded thereto according to any one of

[46] to

[50] , wherein the amount of the solid mediator or its precursor (metal salt) relative to 100 parts by mass of the oxygen generating photocatalyst is preferably 0.1 parts by mass or more and 1000 parts by mass or less, more preferably 1 part by mass or more and 500 parts by mass or less, and even more preferably 5 parts by mass or more and 100 parts by mass or less.

[52] A photocatalyst composite having the bonded photocatalyst according to any one of

[23] to

[42] on a substrate.

[53] Use of the bonded photocatalyst according to any one of

[23] to

[42] as a photocatalyst for water splitting or an organic matter decomposing photocatalyst.

[54] A method for producing hydrogen by irradiating light on the bonded photocatalyst according to any one of

[23] to

[42] or the photocatalyst composite according to

[52] in the presence of water or alcohol.

Examples

[0108] Hereinafter, the present invention will be specifically described based on examples. Unless otherwise specified, reagents manufactured by Fujifilm Wako Pure Chemical Corporation were used.

[0109] (Example 1) <Preparation of Bismuth Vanadate (BiVO4)> 6.06 g of bismuth nitrate pentahydrate and 1.46 g of ammonium vanadate were dissolved in 50 mL of 2 mol / L nitric acid. Then, aqueous ammonia was added dropwise until the pH reached 2.0, and 0.12 g of sodium chloride was added to obtain a yellow-orange dispersion. The dispersion was transferred to a fluororesin container and reacted at 170 °C for 24 hours in an autoclave. After the reaction, the precipitate was separated by suction filtration, and the obtained precipitate was washed with deionized water, filtered, and dried under reduced pressure. The sample obtained after drying was fired in an electric furnace at 500 °C for 2 hours to obtain yellow powder BiVO4. The prepared BiVO4 particles were confirmed to have an icosahedral structure with the {010} plane as the basal plane by SEM (manufactured by JEOL Ltd., JSM-IT500HR) observation. Also, from powder X-ray diffraction measurement (manufactured by Rigaku Corporation, MiniFlex II diffractometer), it was confirmed that the crystal system was monoclinic scheelite crystal.

[0110] <Preparation of Au-BiVO4> Add 150 mg of the prepared BiVO4 to a glass container, disperse it in 20 mL of deionized water, add 18.8 mg of chloroauric acid tetrahydrate and 7.76 mL of AKYPO RLM-45NV (manufactured by Kao Corporation, sodium polyoxyethylene (4.5) lauryl ether acetate, active ingredient 24%), and irradiate with light for 5 minutes using a 300 W solar simulator (manufactured by PECCELL, PEC-L01, current value 7.5 A) while stirring with a stirrer chip to cause a reaction. From a light power meter (manufactured by Hioki Electric Co., Ltd., H3664), the irradiation light intensity at a wavelength of 435 nm set value was 40 mW / cm 2 was obtained. After the reaction was completed, the precipitate was separated by suction filtration, and the obtained precipitate was washed with deionized water, followed by filtration and drying under reduced pressure to obtain green powder Au-BiVO4. When the prepared Au-BiVO4 particles were observed by SEM, as shown in Fig. 1, an image in which an Au layer was selectively formed on the {010} plane of BiVO4 was obtained. When the obtained observation image was analyzed by ImageJ, the bonding selectivity of Au to the {010} plane with respect to the BiVO4 surface was calculated to be 99%, and the coverage rate of Au on the {010} plane was 60%.

[0111] <Preparation of MPA-treated Au-BiVO4> Add 50 mg of the prepared Au-BiVO4 to a glass container, disperse it in 5 mL of deionized water, add 12 μL of 3-mercaptopropionic acid (MPA), and stir with a stirrer chip for 2 hours. After the reaction was completed, the precipitate was separated by suction filtration, and the obtained precipitate was washed with deionized water, followed by filtration and drying under reduced pressure to obtain green powder MPA-treated Au-BiVO4.

[0112] <Preparation of cation-modified Au-BiVO4> 50 mg of the prepared MPA-treated Au-BiVO₄ was added to a glass container and dispersed in 1 mL of a 0.8 mass% aqueous solution of Merquat 100 (manufactured by Lubrizol), a cationic polymer (8.0 mg of pure polymer), and stirred with a stirrer chip for 2 hours. Then, the precipitate was separated by suction filtration, and the obtained precipitate was washed with deionized water, followed by filtration and drying under reduced pressure to obtain cation-modified Au-BiVO₄ as a green powder. When the volume particle size distribution of the obtained cation-modified Au-BiVO₄ in water was evaluated by laser diffraction scattering measurement (LA960 manufactured by Horiba, Ltd.), it was as shown in Figure 3.

[0113] <Preparation of Ru-Supported SrTiO₃> 120 mg of SrTiO₃ (manufactured by High-Purity Chemical Research Institute) was added to a glass container, dispersed in 160 mL of deionized water, 2.2 mg of ruthenium chloride n-hydrate was added, and ultrasonic dispersion treatment was performed for 15 minutes. 20 mL of methanol was added to the obtained dispersion, and while bubbling argon gas at 20 mL / min for 60 minutes, light irradiation was performed with a 300 W xenon lamp for 120 minutes to cause a reaction and support Ru on SrTiO₃. After the reaction was completed, the precipitate was separated by suction filtration, and the obtained precipitate was washed with deionized water, followed by filtration and drying under reduced pressure to obtain Ru-supported SrTiO₃ as a gray powder.

[0114] <Preparation of Anion-Modified Ru-Supported SrTiO₃> 100 mg of the prepared Ru-supported SrTiO₃ was added to a glass container and dispersed in 1.13 mL of a 4 mass% aqueous solution of Poiz 520 (weight average molecular weight: 21,000, copolymer of sodium acrylate / sodium maleate, manufactured by Kao Corporation) (0.05 g of pure polymer), and ultrasonic irradiation was applied for 30 minutes. Then, the dispersion was filtered by suction, and the solid matter was recovered. The recovered product was washed with deionized water, followed by filtration and drying under reduced pressure to obtain anion-modified Ru-supported SrTiO₃ as a gray powder. When the volume particle size distribution of the obtained anion-modified Ru-supported SrTiO₃ in water was evaluated, it was as shown in Figure 3.

[0115] <Preparation of a Composite Photocatalyst> 50 mg of the prepared cation-modified Au-BiVO4 and 5 mg of anion-modified Ru-loaded SrTiO3 were placed in a glass container and dispersed in 1 mL of deionized water. After stirring for 30 minutes, the dispersion was allowed to stand. All particles in the dispersion were observed to settle. The volumetric particle size distribution of the resulting particles was measured, as shown in Figure 3. No separate fine particles originating from Ru-loaded SrTiO3 were present, confirming 100% composite formation of Au-BiVO4 and Ru-loaded SrTiO3. The particles (bonded particles) were applied to a silicon substrate and dried. SEM observation revealed that Ru-loaded SrTiO3 was formed on the Au layer on the {010} plane of BiVO4, as shown in Figure 2. Analysis of the image using ImageJ revealed that the bonding selectivity of Au to the {010} plane of BiVO4 was 99%, and the coverage of the Au layer on the {010} plane was 60%.

[0116] <Evaluation of water splitting activity of junction-type photocatalysts> The resulting bonded particles were added to 180 mL of water, and argon gas was bubbled through at 20 mL / min for 30 minutes. The mixture was then irradiated with light from a 300 W xenon lamp. The generated gas was analyzed using a gas chromatograph with a TCD detector. Light irradiation was continued for 5 hours, and the average hydrogen generation rate was calculated. The results are shown in Table 1.

[0117] (Comparative Example 1) When preparing Au-BiVO4, 0.36 mL of methanol was added as a Hall sacrificial reagent (auxiliary agent) instead of AKYPO RLM-45NV. Furthermore, when preparing the junction-type photocatalyst, the Au-BiVO4 was not treated with 3-mercaptopropionic acid or subjected to cation modification, and the Ru-loaded SrTiO3 was not subjected to anion modification. Otherwise, the sample was prepared using the same procedures as in Example 1. Figure 4 shows the volumetric particle size distribution of the mixed sample of Ru-loaded SrTiO3 and Au-BiVO4. The particle size distribution of Au-BiVO4 shows a distribution in the 1-5 μm range, which is not observed in the volumetric particle size distribution of Au-BiVO4, indicating that the mixed sample was not uniformly composited and that some of the Ru-loaded SrTiO3 was floating.

[0118] Example 2 The junction-type photocatalyst was prepared in the same manner as in Example 1, except that the Au-BiVO4 was not treated with 3-mercaptopropionic acid or subjected to cation modification, and the Ru-supported SrTiO3 was not subjected to anion modification.

[0119] Example 3 A junction-type photocatalyst was prepared in the same manner as in Example 1, except that when preparing Au-BiVO4, 1.55 mL of potassium oleate FR-14 (manufactured by Kao Corporation) was added instead of AKYPO RLM-45NV.

[0120] Example 4 <Preparation of cation-modified Ru-supported SrTiO3> 50 mg of anion-modified Ru-supported SrTiO3 powder prepared in the same manner as in Example 1 was dispersed in 1 mL of a 0.8 mass% aqueous solution of Merquat 100 (Lubrizol Corporation) cationic polymer (8.0 mg pure polymer content) and stirred for 10 minutes with a stirrer tip. After the reaction was completed, the precipitate was separated by suction filtration. The resulting precipitate was washed with deionized water and then dried under reduced pressure to obtain a gray powder of cation-modified Ru-supported SrTiO3.

[0121] <Preparation of Bonded Photocatalyst> As in Example 1, 50 mg of the prepared MPA-treated Au-BiVO4 and 5 mg of cation-modified Ru-supported SrTiO3 were added to a glass container, dispersed in 1 mL of deionized water, and stirred for 30 minutes to prepare a junction-type photocatalyst.

[0122] Example 5 A junction-type photocatalyst was prepared in the same manner as in Example 1, except that when preparing Au-BiVO4, light irradiation was carried out at a current value of 8.0 A for 8 minutes.

[0123] Example 6 <Preparation of cation-modified Ru-supported SrTiO3> 50 mg of Ru-supported SrTiO3 powder prepared in the same manner as in Example 1 was dispersed in 1 mL of a 0.8 mass% aqueous solution (8.0 mg pure polymer content) of Merquat 100 (Lubrizol Corporation), a cationic polymer, and ultrasonic irradiation was performed for 30 minutes. The dispersion was then suction filtered to recover the solid. The recovered material was washed with deionized water, filtered, and dried under reduced pressure to obtain a gray powder of cation-modified Ru-supported SrTiO3.

[0124] <Preparation of Bonded Photocatalyst> As in Example 1, 50 mg of the prepared MPA-treated Au-BiVO4 and 5 mg of cation-modified Ru-supported SrTiO3 were added to a glass container, dispersed in 1 mL of deionized water, and stirred for 30 minutes to prepare a junction-type photocatalyst.

[0125] Example 7 When preparing Au-BiVO4, light irradiation was carried out for 3 minutes at a current value of 8.0 A. Otherwise, a junction-type photocatalyst was prepared in the same manner as in Example 6.

[0126] For Examples 1 to 7 and Comparative Example 1, Table 1 shows the calculation of the bonding selectivity of Au to the {010} plane relative to the BiVO4 surface, the coverage of Au on the {010} plane, and the evaluation results of water splitting activity.

[0127] The obtained SEM images were analyzed using the following procedure: FIJI, a package developed based on ImageJ (National Institutes of Health, USA), was used as image analysis software.

[0128] Calculation method for the bonding selectivity of Au to the {010} plane of BiVO4 surface 1. Ten areas corresponding to the {010} plane are randomly cropped from the SEM image, and ten cropped image data are obtained. 2. Ten areas corresponding to the {110} and {011} planes are randomly cropped from the SEM image, and ten cropped image data are obtained. 3. Run the Trainable Weka Segmentation (TWS) function on all image data and specify three regions: Au, BiVO4, and the background. 4. Learn three classifications using TWS. 5. After classification is complete, 10 images of {010} faces, 10 images of {110} faces, and 10 images of {011} faces are output. 6. The Au coverage area on the {010} plane and the Au coverage areas on the {110} and {011} planes are calculated from the Area value in the Analyze Particles function using the image data of the Au region output by the TWS classification. 7. Bonding selectivity (%) = Au coverage area on {010} plane / (Au coverage area on {010} plane + Au coverage area on {110} and {011} planes) × 100, and the average value of 10 images is obtained.

[0129] Calculation method for the coverage on the Au {010} plane 1. Ten areas corresponding to the {010} plane are randomly cropped from the SEM image, and ten cropped image data are obtained. 2. Run the Trainable Weka Segmentation (TWS) function on all image data and specify three regions: Au, BiVO4, and the background. 3. Learn three classifications using TWS. 4. Output 10 images of image data after classification is completed. 5. The area of ​​the {010} plane is calculated from the Area value in the Analyze Particles function of the cropped image data, and the Au-covered area is calculated from the Area value in the same function using the image data of the Au region output by TWS classification. 6. Coverage rate (%) = Au coverage area / {010} plane area × 100, and obtain the average value of 10 images.

[0130] [Table 1]

[0131] The evaluation results in Table 1 above confirm that the use of an organic carboxylic acid compound can increase the coverage of the solid mediator relative to the electron-collecting surface area of ​​the oxygen-generating photocatalyst, and that the bonded photocatalysts of Examples 1 to 7, in which the coverage of the solid mediator relative to the electron-collecting surface area of ​​the oxygen-generating photocatalyst is 42 to 98%, have superior water-splitting activity compared to the bonded photocatalyst of Comparative Example 1, in which the coverage is 7%. [Industrial Applicability]

[0132] The junction-type photocatalyst of the present invention is useful as a photocatalyst for water decomposition or organic matter decomposition.

Claims

1. A method for producing a junction-type photocatalyst having a solid mediator between a hydrogen generating photocatalyst and an oxygen generating photocatalyst, comprising: A method for producing a junction-type photocatalyst, comprising the following step 1: Step 1: A step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation using an organic carboxylic acid compound and a solid mediator or a precursor thereof.

2. 2. The method for producing a junction-type photocatalyst according to claim 1, wherein, when the photoelectrodeposition method is used in step 1, the method further comprises a step of irradiating a dispersion containing an oxygen-generating photocatalyst in addition to the organic carboxylic acid compound and the solid mediator or a precursor thereof with light.

3. 3. The method for producing a junction-type photocatalyst according to claim 1, wherein the organic carboxylic acid compound is at least one selected from the group consisting of ether carboxylates, fatty acids, hydroxymonocarboxylic acids, and polycarboxylic acids.

4. the organic carboxylic acid compound comprises an ether carboxylate; The method for producing a junction-type photocatalyst according to claim 1 or 2, wherein the solid mediator contains gold.

5. The method for producing a junction-type photocatalyst according to claim 1 or 2, further comprising the following steps 2 to 4, provided that steps 2 and 3 can be performed in any order: Step 2: A step of introducing an ionic group into the solid mediator to obtain an oxygen generating photocatalyst to which the solid mediator having the ionic group is bonded. Step 3: introducing an ionic polymer having an opposite charge to the charge of the ionic group into the hydrogen generating photocatalyst. Step 4: Mixing the oxygen generating photocatalyst to which the solid mediator having an ionic group obtained in Step 2 has been bonded with the hydrogen generating photocatalyst to which the ionic polymer has been introduced obtained in Step 3.

6. 3. The method for producing a junction-type photocatalyst according to claim 1 or 2, further comprising the following steps 2', 3', and 4', provided that steps 2' and 3' can be performed in any order. Step 2': A step of introducing an ionic group into the solid mediator, and further reacting the ionic group with an ionic polymer having an opposite charge to that of the ionic group, to obtain an oxygen generating photocatalyst bonded to a solid mediator having the ionic polymer. Step 3': A step of introducing an ionic polymer having an opposite charge to the charge of the ionic polymer into the hydrogen generating photocatalyst. Step 4': A step of mixing the oxygen generating photocatalyst obtained in step 2' to which the solid mediator having the ionic polymer has been bonded and the hydrogen generating photocatalyst obtained in step 3' to which the ionic polymer has been introduced.

7. 6. The method for producing a junction-type photocatalyst according to claim 5, wherein a thiol compound having an ionic group is used in the introduction of an ionic group into the solid mediator in the step 2 or the step 2'.

8. 3. The method for producing a junction-type photocatalyst according to claim 1, wherein the coverage of the solid mediator with respect to the electron-collecting surface area of ​​the oxygen-generating photocatalyst is 40% or more.

9. A junction-type photocatalyst having a solid mediator between a hydrogen generating photocatalyst and an oxygen generating photocatalyst, A bonded photocatalyst, wherein the coverage of the solid mediator with respect to the electron collection surface area of ​​the oxygen generating photocatalyst is 40% or more.

10. The junction-type photocatalyst according to claim 9 , wherein the junction selectivity of the solid mediator to the electron-collecting surface of the oxygen-generating photocatalyst is 60% or more.

11. The bonded photocatalyst according to claim 9 or 10, wherein the solid mediator and the hydrogen generating photocatalyst are bonded via an ionic polymer.

12. The bonded photocatalyst according to claim 9 or 10, wherein the solid mediator has an ionic group, and the solid mediator and the hydrogen generating photocatalyst are bonded via an ionic polymer having an opposite charge to that of the ionic group.

13. A method for producing an oxygen generating photocatalyst having a solid mediator bonded thereto, comprising the steps of: A method for producing an oxygen generating photocatalyst having a solid mediator bonded thereto, comprising the step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of a photoelectrodeposition method, an impregnation method, and a precipitation method using an organic carboxylic acid compound and a solid mediator or a precursor thereof.

14. 14. The method for producing an oxygen generating photocatalyst having a solid mediator bonded thereto according to claim 13, wherein the method uses the photoelectrodeposition method, and further comprises a step of irradiating a dispersion containing the organic carboxylic acid compound, the solid mediator or a precursor thereof, and the oxygen generating photocatalyst with light.

15. The method for producing an oxygen generating photocatalyst having a solid mediator bonded thereto according to claim 13 or 14, wherein the organic carboxylic acid compound is at least one selected from the group consisting of ether carboxylates, fatty acids, hydroxymonocarboxylic acids, and polycarboxylic acids.

16. the organic carboxylic acid compound comprises an ether carboxylate; 15. The method for producing a solid mediator-bonded oxygen generating photocatalyst according to claim 13 or 14, wherein the solid mediator comprises gold.

17. 15. The method for producing an oxygen generating photocatalyst having a solid mediator bonded thereto according to claim 13 or 14, wherein the coverage of the solid mediator with respect to the electron collecting surface area of ​​the oxygen generating photocatalyst is 40% or more.

18. An oxygen generating photocatalyst to which a solid mediator is bonded, An oxygen generating photocatalyst to which a solid mediator is bonded, wherein the coverage of the solid mediator with respect to the electron collecting surface area of ​​the oxygen generating photocatalyst is 40% or more.

19. 19. The oxygen generating photocatalyst having a solid mediator bonded thereto according to claim 18, wherein the selectivity of bonding of the solid mediator to the electron collecting surface is 60% or more.

20. A photocatalytic composite comprising the junction-type photocatalyst according to claim 9 or 10 on a substrate.

21. Use of the junction-type photocatalyst according to claim 9 or 10 as a photocatalyst for water splitting or a photocatalyst for organic matter decomposition.

22. A method for producing hydrogen, comprising irradiating the junction-type photocatalyst according to claim 9 or 10 or the photocatalyst composite according to claim 20 with light in the presence of water or alcohol.

Images