Method for producing photocatalyst and method for producing hydrogen

Abstract

To provide a method for producing a photocatalyst with superior hydrogen generation efficiency, and a method for producing hydrogen with superior hydrogen generation efficiency.SOLUTION: The present invention provides a photocatalyst production method for decomposing water into hydrogen and oxygen, the method including the steps for: preparing particles containing oxide semiconductors; disposing gold nanoparticles on the surface of the particles; and disposing layers containing sulfide semiconductors on the surface of the particles by the chemical deposition technique.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a method for producing a photocatalyst and a method for producing hydrogen. [Background technology]

[0002] Hydrogen is expected to be used as an alternative energy source to fossil fuels. Known methods for producing hydrogen include extracting hydrogen from gas obtained by burning fossil fuels and extracting hydrogen from water by electrolysis. In order to realize a carbon-neutral society, there is a need to develop hydrogen production technologies that can replace existing methods that involve carbon dioxide emissions and large amounts of electricity consumption. Oxide semiconductors such as titanium dioxide are known as materials (photocatalysts) that decompose water into oxygen and hydrogen when irradiated with light. However, most oxide semiconductors have low photocatalytic activity when exposed to visible light, making it difficult to efficiently produce hydrogen using natural light.

[0003] As a photocatalyst capable of producing hydrogen using visible light, a Z-scheme photocatalyst has been proposed that combines a photocatalyst that produces oxygen and a photocatalyst that produces hydrogen. In the Z-scheme photocatalyst, it is important to efficiently transfer electrons from the photocatalyst that produces oxygen to the photocatalyst that produces hydrogen. For example, Patent Document 1 describes a Z-scheme photocatalyst in which particles of a photocatalyst that produces oxygen and particles of a photocatalyst that produces hydrogen are bonded via metal particles and organic groups to improve the transferability of electrons. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-150972 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide a method for producing a photocatalyst having excellent hydrogen production efficiency, and a method for producing hydrogen having excellent hydrogen production efficiency. [Means for solving the problem]

[0006] The present disclosure includes the following aspects. <1> A method for producing a photocatalyst for splitting water into hydrogen and oxygen, comprising the steps of: Preparing particles including an oxide semiconductor; disposing gold nanoparticles on a surface of the particle; and disposing a layer containing a sulfide semiconductor on the surface of the particle by a chemical deposition method. <2> The oxide semiconductor includes at least one selected from the group consisting of BiVO4, ZnO, WO3, and TiO2. <1> A method for producing the photocatalyst described in claim 1. <3> The sulfide semiconductor includes at least one selected from the group consisting of CdS, SnCdS, and ZnIn2S4, <1> A method for producing the photocatalyst described in claim 1. <4> The oxide semiconductor includes BiVO4, and the sulfide semiconductor includes CdS. <1> A method for producing the photocatalyst described in claim 1. <5> The average particle size of the particles containing the oxide semiconductor is 10 nm to 10 μm. <1> A method for producing the photocatalyst described in claim 1. <6> The thickness of the layer containing the sulfide semiconductor is within a range of 1 nm to 100 nm. <1> A method for producing the photocatalyst described in claim 1. <7> The content of the layer containing the sulfide semiconductor is 3% by mass to 15% by mass of the entire photocatalyst. <1> A method for producing the photocatalyst described in claim 1. <8> The content of the gold nanoparticles is 3% by mass to 20% by mass of the entire photocatalyst. <1> A method for producing the photocatalyst described in claim 1. <9> <1> ~ <8> Producing a photocatalyst by the method of A method for producing hydrogen, comprising decomposing water into hydrogen and oxygen using the photocatalyst. <10> The decomposition includes irradiating a photocatalyst with visible light. <9> The method for producing hydrogen according to claim 1. Effect of the Invention

[0007] An object of the present disclosure is to provide a method for producing a photocatalyst having excellent hydrogen production efficiency, and a method for producing hydrogen having excellent hydrogen production efficiency. [Brief description of the drawings]

[0008] [Figure 1] 1 is a SEM photograph of BiVO4 particles obtained in an example. [Diagram 2] 1 shows the results of XRD analysis of BiVO4 particles obtained in the examples. [Diagram 3] 1 is a SEM photograph of Au / BiVO4 particles obtained in an example. [Figure 4] FIG. 2 is a diagram showing the UV-Vis absorption spectrum of the Au / BiVO4 particles obtained in the examples. [Diagram 5] 1 is a SEM photograph of CdS / Au / BiVO4 particles obtained in an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In the numerical ranges described in the present disclosure in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In addition, in the numerical ranges described in the present disclosure, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.

[0010] In the present disclosure, each component may contain multiple types of corresponding substances. When referring to the amount of each component in a composition in the present disclosure, if multiple substances corresponding to each component are present in the composition, the total amount of the multiple substances present in the composition is meant unless otherwise specified.

[0011] <Photocatalyst manufacturing method> The method for producing the photocatalyst according to the present disclosure includes: A method for producing a photocatalyst for splitting water into hydrogen and oxygen, comprising the steps of: Preparing particles including an oxide semiconductor; disposing gold nanoparticles on a surface of the particle; and disposing a layer containing a sulfide semiconductor on the surface of the particle by a chemical deposition method.

[0012] In the photocatalyst produced by the method of the present disclosure, the oxide semiconductor functions as a photocatalyst that generates oxygen when irradiated with light, and the sulfide semiconductor functions as a photocatalyst that generates hydrogen when irradiated with light. The photocatalyst produced by the method of the present disclosure is not one in which an oxide semiconductor as a photocatalyst for generating oxygen and a sulfide semiconductor as a photocatalyst for generating hydrogen are dispersed in a medium, but rather one in which a layer containing a sulfide semiconductor is disposed on the surface of a particle containing an oxide semiconductor. Therefore, compared to a case in which an oxide semiconductor and a sulfide semiconductor are dispersed in a medium, the two semiconductors are in closer proximity to each other, and electrons are transferred more efficiently between the two semiconductors.

[0013] The photocatalyst produced by the method of the present disclosure has gold nanoparticles arranged on the surface of particles containing an oxide semiconductor. The gold nanoparticles function as an electron transfer agent that transfers electrons between the oxide semiconductor and the sulfide semiconductor, making the transfer of electrons between the two semiconductors more efficient. Furthermore, as shown in the results of the Examples described later, the absorption of visible light is increased by arranging gold nanoparticles on the surface of particles containing an oxide semiconductor, improving the efficiency of visible light utilization by the photocatalyst.

[0014] Furthermore, as shown in the results of the Examples described later, it was found that the efficiency of hydrogen production by photocatalysis is affected by the method of disposing a layer containing a sulfide semiconductor on the surface of a particle containing an oxide semiconductor. Specifically, it was found that when a layer containing a sulfide semiconductor is disposed on the surface of a particle containing an oxide semiconductor by a chemical deposition method, the efficiency of hydrogen production by photocatalysis is significantly improved compared to when a layer containing a sulfide semiconductor is disposed by other methods. Such findings have not been reported before.

[0015] Hereinafter, preparing particles containing an oxide semiconductor is also referred to as "step 1," disposing gold nanoparticles on the surfaces of particles containing an oxide semiconductor is also referred to as "step 2," and disposing a layer containing a sulfide semiconductor on the surfaces of particles containing an oxide semiconductor by a chemical deposition method is also referred to as "step 3."

[0016] (Step 1: Preparation of particles containing oxide semiconductor) In this step, particles containing an oxide semiconductor are prepared. The oxide semiconductor used in this step is not particularly limited as long as it is a substance that causes a water oxidation reaction (oxygen generation reaction) when irradiated with light, and is preferably a substance that causes a water oxidation reaction when irradiated with visible light (for example, light having a wavelength λ of 360 nm or more).

[0017] From the viewpoint of the efficiency of hydrogen production by photocatalysis, it is preferable to select the oxide semiconductor contained in the particle and the sulfide semiconductor contained in the layer disposed on the surface of the particle so that the potential of the conduction band bottom (CBM) of the oxide semiconductor is more negative than the potential of the valence band top (VBM) of the sulfide semiconductor, and it is more preferable that the potential difference be 0.1 V or more.

[0018] From the viewpoint of the efficiency of using visible light by a photocatalyst, it is preferable that the band gap of the oxide semiconductor is small, for example, 4.0 eV or less, or 3.0 eV or less.

[0019] The oxide semiconductor may include at least one selected from the group consisting of an oxide semiconductor containing vanadium, an oxide semiconductor containing zinc, an oxide semiconductor containing tungsten, an oxide semiconductor containing titanium, an oxide semiconductor containing tantalum, an oxide semiconductor containing iron, and an oxide semiconductor containing copper. In the following compound names, "XY" means an oxide semiconductor Y doped with an element X.

[0020] Specific examples of oxide semiconductors containing vanadium include BiVO4, V2O5, Ag3VO4, AgVO3, and Bi4V2O 11 , CuV2O6, Fe2VO4, Cu3V2O8, FeV2O4, etc.

[0021] Specific examples of oxide semiconductors containing zinc include ZnO and ZrO2.

[0022] Specific examples of oxide semiconductors containing tungsten include WO3 and CaWO4.

[0023] Specific examples of oxide semiconductors containing titanium include TiO2, M-TiO2 (wherein M is N, S, F, Ni, Ru, Rh, Fe, Cu, or Co), SrTiO3, M-SrTiO3 (wherein M is Cr, Mn, Ru, Rh, or Ir), CaTiO3, Sr3Ti2O7, Sr4Ti3O7, and K2La2Ti3O. 10 , Rb2La2Ti3O 10 , Cs2La2Ti3O 10 , CsLaTi2NbO 10 , La2TiO5, La2Ti3O9, La2Ti2O7, Na2Ti6O 13 , K2Ti6O 13 , KTiNbO5, etc.

[0024] Specific examples of oxide semiconductors containing tantalum include Ta2O5, N-Ta2O5, TaON, CaTaO2N, SrTaO2N, BaTaO2N, LaTaO2N, Y2Ta2O5N, InTaO4, and Ni-TaO4.

[0025] Specific examples of oxide semiconductors containing iron include Fe2O3, M-Fe2O3 (M is N, Zn, Cu, Ni, Ti, Si, or Nb), CaFe2O4, CuFe2O4, CuFeO2, ZnFe2O4, and BiFeO3.

[0026] Specific examples of oxide semiconductors containing copper include Cu2O, CuO, and CuBi2O4.

[0027] From the viewpoint of the efficiency of hydrogen production by photocatalysis, the oxide semiconductor preferably contains at least one selected from an oxide semiconductor containing vanadium, an oxide semiconductor containing zinc, an oxide semiconductor containing tungsten, and an oxide semiconductor containing titanium, more preferably contains at least one selected from BiVO4, ZnO, WO3, and TiO2, and further preferably contains BiVO4 (band gap: 2.4 eV).

[0028] The size of the particles containing an oxide semiconductor is not particularly limited and can be selected in consideration of the efficiency of hydrogen production, etc. For example, the average particle size of the particles containing an oxide semiconductor may be within a range of 10 nm to 10 μm, 10 nm to 1 μm, or 10 nm to 500 nm. The average particle size of the particles containing an oxide semiconductor is the average value of particle sizes of 30 particles arbitrarily selected from an image obtained by observation with an electron microscope, etc. The particle size of each particle is the average value of the long diameter and the short diameter. As the electron microscope, for example, a scanning electron microscope (SEM) can be used.

[0029] The particles containing an oxide semiconductor prepared in this step may be of one type or a mixture of two or more types having different components. The oxide semiconductor particles used in this step may be commercially available or may be synthesized. When synthesizing the oxide semiconductor particles, the synthesis method is not particularly limited and may be selected from known methods.

[0030] (Step 2: Arrangement of gold nanoparticles on the surface of particles containing oxide semiconductor) In this step, gold nanoparticles are disposed on the surfaces of particles containing an oxide semiconductor.

[0031] The method for disposing gold nanoparticles on the surface of the oxide semiconductor-containing particles is not particularly limited and can be selected from known methods. From the viewpoint of disposing gold nanoparticles of a desired size on the surface of the particles, it is preferable to dispose the gold nanoparticles by a photoprecipitation method.

[0032] In the present disclosure, the photodeposition method refers to a method in which metal ions or metal complexes are reduced by utilizing photoexcited electrons of a semiconductor, thereby depositing a metal on the semiconductor. A specific example of a method for disposing gold nanoparticles on particles containing an oxide semiconductor by photoprecipitation is a method in which particles containing an oxide semiconductor are dispersed in a solution in which a metal salt containing gold is dissolved, and then irradiated with light to reduce the metal salt and precipitate gold nanoparticles on the surface of the particles.

[0033] In order to fully exert the effect of the arrangement of gold nanoparticles, the average particle size of the gold nanoparticles is preferably within the range of 5 nm to 200 nm, 5 nm to 100 nm, or 5 nm to 50 nm. The average particle size of gold nanoparticles is the average value of the particle sizes of 30 particles randomly selected from images obtained by electron microscope observation, etc. The particle size of each particle is the average value of the long diameter and the short diameter. As the electron microscope, for example, a scanning electron microscope (SEM) can be used.

[0034] In order to fully exert the effect of the arrangement of gold nanoparticles, the content of gold nanoparticles is preferably 3% by mass to 20% by mass, and more preferably 5% by mass to 15% by mass, of the entire photocatalyst.

[0035] (Step 3: Arranging a layer containing a sulfide semiconductor on the surface of a particle containing an oxide semiconductor) In this step, a layer containing a sulfide semiconductor is disposed on the surface of a particle containing an oxide semiconductor.

[0036] The type of sulfide semiconductor used in this step is not particularly limited as long as it is a substance that causes a water reduction reaction (hydrogen production reaction) when irradiated with light, and is preferably a substance that causes a water reduction reaction when irradiated with visible light (for example, light with a wavelength λ of 360 nm or more).

[0037] From the viewpoint of the efficiency of using visible light by a photocatalyst, it is preferable that the band gap of the sulfide semiconductor is small, for example, 4.0 eV or less, or 3.0 eV or less.

[0038] Specific examples of sulfide semiconductors include sulfides of metals such as Cd, Zn, Bi, Sb, Sn, Pb, ZnCd, ZnIn, CuGa, CuIn, AgIn, CuAl, AgGa, CuZn, CuGaZn, CuInZn, AgInZn, etc. The sulfide may be in a solid solution state.

[0039] From the viewpoint of the efficiency of hydrogen production by photocatalysis, the sulfide semiconductor preferably contains a sulfide containing at least one of Cd and Zn, more preferably contains at least one selected from the group consisting of CdS, SnCdS, and ZnIn2S4, and further preferably contains CdS (band gap: 2.42 eV).

[0040] In this step, the deposition of the layer containing a sulfide semiconductor is carried out by chemical deposition. A photocatalyst manufactured by depositing a layer containing a sulfide semiconductor by a chemical deposition method has a higher hydrogen production efficiency than a photocatalyst manufactured by depositing a layer containing a sulfide semiconductor by other methods (such as a photodeposition method).

[0041] In the present disclosure, chemical deposition refers to a method in which a precursor complex is reacted with other chemicals with the aid of heat, ultrasound or other energy to form a desired material. A specific example of a method for forming a layer containing a sulfide semiconductor on particles containing an oxide semiconductor by chemical precipitation includes a method in which particles containing an oxide semiconductor are dispersed in a solution in which a raw material for the sulfide semiconductor is dissolved, and the raw material and the particles are chemically reacted without light irradiation.

[0042] The thickness of the layer containing a sulfide semiconductor disposed on the surface of the particle containing an oxide semiconductor is not particularly limited. From the viewpoint of the efficiency of hydrogen production by photocatalysis, the thickness of the layer containing a sulfide semiconductor is preferably within the range of 1 nm to 100 nm. The thickness of the layer containing a sulfide semiconductor is measured from an image obtained by observation using an electron microscope or the like. From the viewpoint of efficiency of hydrogen production by the photocatalyst, the content of the layer containing the sulfide semiconductor is preferably 3 mass % to 15 mass %, and more preferably 4 mass % to 10 mass %, of the entire photocatalyst.

[0043] In the present disclosure, the order of performing step 2 and step 3 is not particularly limited, and either may be performed first. From the viewpoint of efficiently mediating the transfer of electrons from the oxide semiconductor to the sulfide semiconductor through the gold nanoparticles, it is preferable to perform step 3 after step 2.

[0044] <Hydrogen production methods> The method for producing hydrogen according to the present disclosure includes producing the above-described photocatalyst, A method for producing hydrogen includes decomposing water into hydrogen and oxygen using the photocatalyst.

[0045] In the hydrogen production method of the present disclosure, water decomposition is carried out by irradiating a medium containing a photocatalyst with light. The type of light is not particularly limited, and natural light or various light sources can be used. The hydrogen production method of the present disclosure is suitable for a method using visible light (for example, light with a wavelength λ of 360 nm or more) because it uses the above-mentioned photocatalyst.

[0046] As the medium, an aqueous medium such as water may be used. If necessary, the medium may contain an electron transfer agent such as Fe ions. Since the photocatalyst of the present disclosure exhibits excellent catalytic activity even without the use of an electron transfer agent, the medium does not need to contain an electron transfer agent. If necessary, the medium may contain a promoter, such as platinum, palladium, ruthenium, rhodium, silver, copper, or iridium. The promoter may be used alone or in combination of two or more kinds. If necessary, the medium may contain a sacrificial agent, specifically, Na2S, Na2SO3, etc. EXAMPLES

[0047] Hereinafter, the embodiments of the present disclosure will be described in more detail based on examples, but the present disclosure is not limited to these examples.

[0048] <Example 1> (1) Synthesis of particles containing oxide semiconductors A solution was obtained by dissolving 0.25 mg of Bi(NO3)5H2O and 7% by weight of oleic acid and oleylamine in 10 mL of octadecene. At a temperature of 170°C, 12 mL of NH4VO3 / HNO3 solution was poured into the above solution under stirring, resulting in the formation of plate-like BiVO4 particles. The obtained BiVO4 particles were washed several times with EtOH / Hexane by centrifugation. FIG. 1 shows an SEM photograph of the obtained BiVO4 particles, and FIG. 2 shows the results of XRD analysis of the obtained BiVO4 particles.

[0049] (2) Arrangement of gold nanoparticles (photodeposition method) A mixed solution was obtained by injecting 100 μL of an aqueous solution containing 1 mass% HAuCl4 into an aqueous dispersion containing 2 mg of the BiVO4 particles synthesized in (1) above. After irradiating the mixed solution with light from a 300 W Xe lamp for 10 minutes, the BiVO4 particles were collected by centrifugation. An SEM photograph of the BiVO4 particles after collection is shown in Figure 3. As shown in Figure 3, it was confirmed that nano-sized gold particles were precipitated on the surface of the BiVO4 particles. The UV-Vis absorption spectrum of the BiVO4 particles after recovery and, for comparison, the UV-Vis absorption spectrum of BiVO4 particles that were not subjected to step (2) are shown in Figure 4. As shown in Figure 4, the BiVO4 particles with gold nanoparticles precipitated on their surfaces (Au / BiVO4 particles) showed increased absorbance in the visible range of light.

[0050] (3) Arrangement of layers containing sulfide semiconductors (chemical deposition method) The process of forming a layer containing CdS on the surface of BiVO4 particles with gold nanoparticles arranged on the surface was carried out by chemical deposition. Specifically, a mixture of thiourea and cadmium acetate dihydrate (0.026 mg) was mixed in deionized water to obtain a precursor solution. Next, this precursor solution was poured into an aqueous dispersion (10 mL) containing 2 mg of Au / BiVO4 particles while stirring, and reacted at 90°C for 1 hour. The product was then washed with water several times by centrifugation. Figure 5 shows an SEM image of the product after washing. As shown in Figure 5, Au / BiVO4 particles with CdS precipitated on the surface (CdS / Au / BiVO4 particles) were confirmed.

[0051] <Example 2> Example 2 was prepared by using CdS / Au / BiVO4 particles obtained in the same manner as in Example 1, except that the amounts of gold nanoparticles and CdS arranged on the surface of the BiVO4 particles were changed.

[0052] <Comparative Example 1> In Example 1, the BiVO4 particles were obtained in the same manner as in step (1), but no gold nanoparticles were arranged on them, and a layer containing CdS was formed by the chemical precipitation method described in step (3) to obtain CdS / BiVO4 particles, which were used as Comparative Example 1.

[0053] <Comparative Example 2> Comparative Example 2 was prepared by using CdS / Au / BiVO4 particles obtained in the same manner as in Example 1, except that the layer containing the sulfide semiconductor in step (3) was disposed by the photoprecipitation method described below instead of the chemical deposition method.

[0054] Deposition of layers containing sulfide semiconductors (photodeposition method) A 0.6M Na2S aqueous solution (500μL) was added to 10mL of an aqueous dispersion containing Au / BiVO4 particles (2mg). Then, a 1% cadmium acetate aqueous solution (400μL) was added to the above aqueous dispersion to obtain a mixed solution. This mixed solution was irradiated with light from a Xe lamp (15A) for 2 hours. The product was then washed with an ethanol aqueous solution to obtain CdS / Au / BiVO4 particles with CdS precipitated on the surface.

[0055] <Photocatalyst composition> Table 1 shows the compositions (mass %) of the photocatalysts obtained in the examples and comparative examples.

[0056] <Photocatalyst experiment> The following experiment was carried out to examine the hydrogen production rate of the photocatalysts obtained in the examples and comparative examples. The experiment was carried out using a Pyrex glass reactor (wavelength of transmitted light > 300 nm) in combination with a closed circulation system. The photocatalyst (2.5 mg) obtained in the examples or comparative examples was dispersed in a 5 mM H2PtCl6 aqueous solution (25 μL) as a Pt source, which is a promoter, and a 0.15 M mixed aqueous solution of Na2S and Na2SO3 (80 mL) as a sacrificial agent (the amount of the sacrificial agent was about 0.1% by mass relative to the photocatalyst). The irradiation light source used was a 300 W Xe lamp (Eagle Lamphouse R300-3J, Cermax, Excelitas Technology). The reactor, equipped with a half-skinned aluminum jacket, was placed on a cooling plate (set at 20°C) under stirring and then irradiated from the side of the reactor. Hydrogen gas evolution was analyzed using a gas chromatograph (Agilent Tech. 7890B) equipped with a pulsed discharge helium ionization detector (PDHID). The results are shown in Table 1.

[0057] [Table 1]

[0058] As shown in Table 1, the photocatalysts of Examples 1 and 2, in which gold nanoparticles and a CdS layer were arranged on the surface of BiVO4 particles and the CdS layer was arranged by a chemical deposition method, showed a superior hydrogen production rate compared to Comparative Example 1, in which a CdS layer was arranged on the surface of BiVO4 particles but no gold nanoparticles were arranged, and Comparative Example 2, in which gold nanoparticles and a CdS layer were arranged on the surface of BiVO4 particles but the CdS layer was arranged by a photodeposition method. The above results suggest that the placement of gold nanoparticles together with a CdS layer on the surface of BiVO4 particles, and the placement of the CdS layer by chemical deposition, contribute to improving the hydrogen production rate.

Claims

1. A method for producing a photocatalyst for splitting water into hydrogen and oxygen, comprising the steps of: Preparing particles including an oxide semiconductor; disposing gold nanoparticles on a surface of the particle; and disposing a layer containing a sulfide semiconductor on the surface of the particle by a chemical deposition method.

2. The oxide semiconductor is BiVO ４ , ZnO, WO ３ and TiO ２ The method for producing a photocatalyst according to claim 1, comprising at least one selected from the group consisting of:

3. The sulfide semiconductors are CdS, SnCdS and ZnIn ２ S ４ The method for producing a photocatalyst according to claim 1, comprising at least one selected from the group consisting of:

4. The oxide semiconductor is BiVO ４ The method for producing a photocatalyst according to claim 1 , wherein the sulfide semiconductor comprises CdS.

5. The method for producing a photocatalyst according to claim 1, wherein the average particle size of the particles containing the oxide semiconductor is 10 nm to 10 μm.

6. The method for producing a photocatalyst according to claim 1, wherein the layer containing the sulfide semiconductor has a thickness in the range of 1 nm to 100 nm.

7. 2. The method for producing a photocatalyst according to claim 1, wherein the content of the layer containing the sulfide semiconductor is 3 mass % to 15 mass % of the entire photocatalyst.

8. The method for producing a photocatalyst according to claim 1, wherein the content of the gold nanoparticles is 3% by mass to 20% by mass of the entire photocatalyst.

9. Producing a photocatalyst by the method of any one of claims 1 to 8; A method for producing hydrogen, comprising decomposing water into hydrogen and oxygen using the photocatalyst.

10. The method for producing hydrogen according to claim 9 , wherein the decomposition comprises irradiating a photocatalyst with visible light.

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