JP6883799B2 - A method for producing a metal compound, a method for producing a photocatalyst, and a method for producing a photocatalyst complex. - Google Patents

Description

The present invention relates to a method for producing a metal compound, a method for producing a photocatalyst, and a method for producing a photocatalyst complex.

The practical application of light energy conversion systems that use solar energy has become increasingly important in recent years from the perspective of curbing global warming and breaking away from dependence on depleting fossil resources. Among them, the technology to decompose water using solar energy to produce hydrogen is not only the current oil refining technology, the raw material supply technology for ammonia and methanol, but also hydrogen in the future hydrogen energy society based on fuel cells. It is seen as a promising supply technology.

In addition, the technology for producing hydrogen from water using light energy is regarded as a technology for converting light energy into chemical energy, but it is not easy to store the generated electric energy in photovoltaic power generation, which has been in practical use for a long time. Therefore, while advances in energy storage technology are desired, chemical energies such as hydrogen are expected to become superior energies in energy storage, transportation, and the amount of energy per unit.

Hydrogen is attracting attention as a clean fuel in that it reacts with oxygen in combustion and fuel cell type reactions to generate only water. However, industrial hydrogen production is mainly carried out by steam reforming of natural gas, and not only depends on fossil resources, but also carbon dioxide is emitted in the production process. Therefore, using hydrogen as a fuel does not solve the problems of fossil resource depletion and global warming caused by carbon dioxide.

If hydrogen can be produced from water as a raw material using solar energy, it will not only consume fossil resources but also emit no carbon dioxide, which will contribute to solving global environmental problems and energy problems.

There are two types of photocatalysts that generate hydrogen and oxygen by water decomposition, one for hydrogen generation and the other for oxygen generation. Among them, various metal sulfides have been proposed as photocatalysts capable of decomposing water to generate hydrogen.

Patent Document 1 reports on a composite metal sulfide represented by _{the composition formula Zn 1-2 x} (CuGa) _x In ₂ S ₄ as an effective photocatalyst for hydrogen generation. Further, Patent Document 2 reports on a photocatalyst composed of a sulfide solid solution in which a part of Cu or In of _{CuInS 2} is replaced with Ag or Ga as an effective photocatalyst for hydrogen generation. Further, Patent Document 3 reports on a visible light active sulfide solid solution represented by _{the composition formula (CuAg) x} In _{2 x} Zn _{2 (1-2x)} S ₂ as an effective photocatalyst for hydrogen generation.

In Non-Patent Document 1, similarly, as a photocatalyst effective for hydrogen generation, a metal sulfide represented _{by the composition formula Cu 0.8} Ga _0.8-x In _x Zn _0.4 S _{2 synthesized by the solid phase method.} Photocatalysts have been reported.
In Non-Patent Document 2, the solid synthesized formula in phase _{(CuGa) x Zn 2 (1} -x) metal sulfide photocatalyst represented by S ₂ is, similarly, to be effective in hydrogen generation It is shown.
Even in non-patent document 3, reported to exhibit combined formula in solution method _{(CuIn) x Zn 2 (1} -x) metal represented by S ₂ sulfide photocatalyst hydrogen generation activity using hydrogen sulfide gas Has been done.

Further, Non-Patent Document 4 reports _{that the photocatalyst CuGaS 2} effective for hydrogen generation is synthesized by a flux method using a metal chloride as a flux agent and its photocatalytic properties. _{However, it has been shown that the hydrogen production activity of the CuGaS 2} photocatalyst synthesized by the flux method is lower than that of the conventional solid phase method.

JP-A-2009-066529 Japanese Unexamined Patent Publication No. 2006-167652 Japanese Unexamined Patent Publication No. 2005-199222

The 92nd Annual Meeting of the Chemical Society of Japan (2012) 1G1-43 "Solar hydrogen production using a mixed sulfide photocatalyst of Cu0.8Ga0.8-xInxZn0.4S2" The 91st Annual Meeting of the Chemical Society of Japan (2011) 3B4-17 "Hydrogen production reaction of novel sulfide photocatalyst (CuGa) xZn2 (1-x) S2 under visible light irradiation J. Phys. Chem. B, Vol. 109, No. 15, 2005. "Photocatalytic H2 Evolution under Visible-Light Irradiation over Band-Structure-Control (CuIn) xZn2 (1-x) S2 Solid Solutions" Catalyst debate Autumn 2012 (Kyushu Univ.) "Solar hydrogen generation using metal composite sulfide prepared with chloride flux"

As a band structure of metal sulfide, it is known that the valence band is occupied by the 3p orbital of sulfur, and the conduction band is occupied by the sp orbital of metal. Since the sulfur 3p orbital is located on the base side of the oxygen 2p orbital, the metal sulfide generally has a narrower bandgap structure than the metal oxide and can therefore absorb light of a longer wavelength. This is the reason why metal sulfide is expected as a material for utilizing solar energy.

In fact, among the various metal sulfides proposed as photocatalysts that can decompose water to generate hydrogen using visible light, chalcopyrite, which is a sulfide containing copper, is a solar cell. Many of them are useful as photoresponsive materials, including CIGS (Cu-In-Ga-Se), which is used as a photocatalyst. However, the photocatalytic and photoelectrochemical properties of these sulfide materials used for water splitting under visible light irradiation are not yet sufficient.

Although the conventional CGIZS (Cu-Ga-In-Zn-S) photocatalyst has excellent performance as a photocatalyst suitable for hydrogen generation by water decomposition, it is necessary to improve the hydrogen production activity. It was also expected that the CGIZS photocatalyst would be applied to a photocatalyst electrode and that the photoelectrochemical properties of the photocatalyst electrode would be improved.

In addition, photocatalysts are still generally synthesized using the conventional solid phase method, but -2-valent sulfur is easily oxidized, and in order to prevent oxidation by oxygen in the air, vacuumed quartz ampoule tubes are used. It had to be sealed or heated at a high temperature of over 800 ° C. for a long time in an atmosphere of an inert gas such as nitrogen. From an industrial point of view, it was considered that it was desirable to be able to produce in the atmosphere rather than in a vacuum process or an inert gas atmosphere, and it was desirable that the heating conditions were lower temperature and shorter time.

In view of the present situation, the present invention describes the hydrogen production activity of a metal compound having a calcopylite type crystal structure or a photocatalyst containing the metal compound under visible light irradiation, and a photocatalyst electrode using the same (in the present specification, "photocatalyst electrode". (Sometimes referred to as).) Production of the metal compound, which can improve the photoelectrochemical properties and can be produced in the air at a lower temperature and for a shorter time than the conventional solid phase method. It is an object of the present invention to provide a method, a method for producing a photocatalyst, a method for producing a photocatalyst composite, a photocatalyst electrode, and a method for producing the photocatalyst electrode.

When water is decomposed under visible light irradiation using a photocatalyst or a photocatalyst electrode using the same, solar energy conversion efficiency is generally used as an index showing the activity. In order to improve the solar energy conversion efficiency, it is important to lengthen the response wavelength and improve the quantum yield. The former is related to the physical properties of the photocatalyst itself, such as the composition of the photocatalyst, and the latter is the crystal state of the photocatalyst to be produced, such as lattice defects, the physical state such as particle size and specific surface area, and surface modification. A wide variety of factors are involved, such as the state of the active point due to the photocatalyst.

In order to solve the above problems, the present inventors need to improve the quality of the photocatalyst itself, which can be realized by improving the method for producing a CGIZS photocatalyst and the method for producing a photocatalyst electrode using the same. The present invention has been completed.

Specifically, the present inventors have developed a method called a flux method, in which heat treatment is performed in the presence of a flux agent (metal chlorinated product, etc.) at a relatively low temperature of 400 ° C. to 800 ° C. in the atmosphere. It has been found that the photocatalytic performance can be significantly improved by using it. Conventionally, as a method for synthesizing a CGIZS photocatalyst, a predetermined amount of each sulfide Cu ₂ S, Ga ₂ S ₃ , In ₂ S ₃ , Zn S is mixed, and the temperature is 600 ° C. to 1000 ° C. under a vacuum or an inert gas atmosphere. A solid-phase method of firing at a high temperature of about 2 has been known, but the present invention is industrially advantageous in that it can be heat-treated in the air at a relatively low temperature as compared with such a solid-phase method.

By using a method of obtaining crystals at a low temperature by the flux method instead of the conventional solid-phase method, a high-quality photocatalyst could be obtained, and as a result, high-performance photowater decomposition activity was obtained. Conceivable. Furthermore, it has also been found that a photoelectrode using the photocatalyst also exhibits high-performance water splitting activity and photoelectrochemical properties.

Specifically, the present invention provides the following.
[1]
A mixture of metal sulfides containing cuprous sulfide (Cu ₂ S), gallium sulfide (Ga ₂ S ₃ ), indium sulfide (In ₂ S ₃ ), and zinc sulfide (Zn S) in the presence of metal chloride. , A method for producing a metal compound having a chalcopyrite type crystal structure represented by the following general formula, which comprises heat treatment at 400 ° C. or higher and 800 ° C. or lower.
General formula: Cu _x Ga _{x-y + k} In _{y + j} Zn _{2 (1-x) + mA 2 + n}
(In the above formula, x, y, k, j, m and n satisfy the following conditions, and A represents S or Se.
0 <x <1, 0 ≦ y ≦ 1, x> y, 0 ≦ k ≦ 0.2, 0 ≦ j ≦ 0.2,
0 ≦ m ≦ 0.2, 0 ≦ n ≦ 0.8, n = 3 / 2k + 3 / 2j + m)
(In the present specification, the above general formula may be referred to as a "specific general formula".)
[2]
The production method according to [1], wherein the metal chloride is at least one metal chloride selected from the group consisting of an alkali metal chloride and an alkaline earth metal chloride.
[3]
The production method according to [1] or [2], wherein the metal chloride contains lithium chloride and potassium chloride.
[4]
The production method according to [3], wherein the molar ratio of lithium chloride to potassium chloride is 40:60 to 80:20.
[5]
The production method according to any one of [1] to [4], wherein the molar ratio of the metal chloride to the mixture of the metal sulfide is 1 or more and 20 or less.
[6]
The metal constituting the metal chloride is a metal other than Cu, Ga, In and Zn.
Any one of [1] to [5], wherein the amount of impurities made of a metal derived from the metal chloride is less than 100 ppm of the mass of the metal compound having a chalcopyrite type crystal structure represented by the general formula. The manufacturing method described in the section.

[7]
A method for producing a photocatalyst containing a metal compound having a chalcopyrite type crystal structure represented by the following general formula.
A method for producing a photocatalyst, wherein the metal compound is produced by the production method according to any one of [1] to [6].
General formula: Cu _x Ga _{x-y + k} In _{y + j} Zn _{2 (1-x) + mA 2 + n}
(In the above formula, x, y, k, j, m and n satisfy the following conditions, and A represents S or Se.
0 <x <1, 0 ≦ y ≦ 1, x> y, 0 ≦ k ≦ 0.2, 0 ≦ j ≦ 0.2,
0 ≦ m ≦ 0.2, 0 ≦ n ≦ 0.8, n = 3 / 2k + 3 / 2j + m)

[8]
A method for producing a photocatalyst complex containing a photocatalyst containing a metal compound having a chalcopyrite crystal structure represented by the following general formula, and at least one selected from the group consisting of a cocatalyst and a surface modifier.
The photocatalyst is produced by the production method according to [7].
The co-catalyst is at least one selected from the group consisting of ruthenium, platinum, iridium, palladium and gold, and is supported on the metal compound.
The surface modifier, CdS, comprising at least one selected from the group consisting of ZnS and an In ₂ S _3, and modifying the surface of the metal compound,
A method for producing a photocatalytic complex.
General formula: Cu _x Ga _{x-y + k} In _{y + j} Zn _{2 (1-x) + mA 2 + n}
(In the above formula, x, y, k, j, m and n satisfy the following conditions, and A represents S or Se.
0 <x <1, 0 ≦ y ≦ 1, x> y, 0 ≦ k ≦ 0.2, 0 ≦ j ≦ 0.2,
0 ≦ m ≦ 0.2, 0 ≦ n ≦ 0.8, n = 3 / 2k + 3 / 2j + m)

[9]
A metal compound having a chalcopyrite-type crystal structure represented by the general formula, which is produced by the production method according to any one of [1] to [6].
A photocatalyst electrode in which a photocatalyst containing the metal compound or a photocatalyst composite containing the photocatalyst and at least one selected from the group consisting of a co-catalyst and a surface modifier is laminated on a current collecting conductor layer.
The co-catalyst is at least one selected from the group consisting of ruthenium, platinum, iridium, palladium and gold, and is supported on the metal compound.
The surface modifier, CdS, comprising at least one selected from the group consisting of ZnS and an In ₂ S _3, and modifying the surface of the metal compound,
Photocatalytic electrode.
[10]
The current collector layer contains at least one current collector selected from the group consisting of Au and carbon.
The photocatalyst electrode according to [9], wherein the photocatalyst composite is laminated on the current collector conductor layer.
[11]
The photocatalytic electrode according to [9] or [10], which is used for hydrogen generation.

[12]
A metal compound having a calcopyrite crystal structure represented by the following general formula, a photocatalyst containing the metal compound, or a photocatalyst complex containing the photocatalyst and at least one selected from the group consisting of a cocatalyst and a surface modifier. Is a method for manufacturing a photocatalyst electrode, which comprises laminating a photocatalyst electrode on a current collecting conductor layer.
The metal compound is produced by the production method according to any one of [1] to [6].
The photocatalyst is produced by the production method according to [7].
The photocatalyst complex is produced by the production method according to [8].
A method for manufacturing a photocatalytic electrode.
[13]
The current collector layer contains at least one current collector selected from the group consisting of Au and carbon.
The method for producing a photocatalyst electrode according to [12], wherein the photocatalyst composite is laminated on a current collector conductor layer.
[14]
The photocatalytic electrode according to [12] or [13], which is used for hydrogen generation.

According to the present invention, the hydrogen generation activity of a metal compound having a calcopylite type crystal structure represented by the above-mentioned specific general formula or a photocatalyst containing the metal compound under visible light irradiation and the photoelectricity of the photocatalyst electrode using the same. A method for producing the metal compound, a method for producing a photocatalyst, and a method for producing a photocatalyst complex, which can improve chemical properties and can be produced under heating conditions at a lower temperature and for a shorter time than the conventional solid phase method and also in the atmosphere. A manufacturing method, a photocatalytic electrode, and a method for manufacturing the photocatalytic electrode can be provided.

Since the above-mentioned metal compound or photocatalyst thus obtained exhibits high activity in the hydrogen generation reaction by water decomposition under visible light irradiation, high-performance water decomposition performance can be expected and the photocatalytic performance of the CGIZS photocatalyst can be improved. .. In particular, when such a photocatalyst is used as a photoelectrode for hydrogen generation, it exhibits high hydrogen generation activity in water splitting under visible light irradiation, improves the photoelectrochemical properties of the photoelectrode, and improves the performance of the photoelectrode. be able to.
Further, the manufacturing method of the present invention can be said to be a simpler and lower energy process than the conventional solid phase method from the viewpoint of an industrial manufacturing method.

XRD measurement results of the CGIZS photocatalyst synthesized by the flux method in Examples 1 to 6 XRD measurement results of CGIZS photocatalyst synthesized by the solid phase method in Comparative Examples 1 to 6 DRS measurement results of CGIZS photocatalyst synthesized in Examples 1 to 6 and Comparative Examples 1 to 6 Hydrogen production activity measured in Examples 1-6 and Comparative Examples 1-6 Hydrogen production activity measured in Examples 7-12 and Comparative Example 7 XRD measurement results of the CGIZS photocatalyst synthesized in Example 13 and Comparative Example 7 DRS measurement results of the CGIZS photocatalyst synthesized in Example 13 and Comparative Example 7 Photoelectrochemical property evaluation results measured in Example 14 Hydrogen production activity evaluation result measured in Example 14 XRD measurement results of the CGIZS photocatalyst synthesized by the flux method in Examples 15 to 19. DRS measurement results of the CGIZS photocatalyst synthesized by the flux method in Examples 15 to 19. Photoelectrochemical characterization results measured in Examples 15-19

Hereinafter, a specific form will be shown.
A method for producing a metal compound or a photocatalyst represented by the above-mentioned specific general formula using the flux method, a method for cocatalyst / surface modification, a method for producing a photocatalyst electrode, and a method for producing hydrogen by water splitting will be described in order.

1. 1. Composition of Photocatalyst The composition of the metal compound constituting the photocatalyst in the present invention is the following general formula Cu _x Ga _{xy + k} In _{y + j} Zn _{2 (1-x) + mA 2 + n}
(0 <x <1, 0 ≦ y ≦ 1, x> y, 0 ≦ k ≦ 0.2, 0 ≦ j ≦ 0.2,
0 ≦ m ≦ 0.2, 0 ≦ n ≦ 0.8, n = 3 / 2k + 3 / 2j + m, A = S or Se)
It is represented by. It is important that the metal compound or the photocatalyst containing the metal compound in the present invention has a chalcopyrite type crystal structure, and the metal compound having a composition defined by this general formula and each component range is a chalcopyrite type. The crystal structure can be easily formed. In the present specification, such "a metal compound having a chalcopyrite type crystal structure represented by a general formula" may be abbreviated as "a metal compound represented by a specific general formula", "the metal compound" and the like. In the present specification, when both the metal compound and the photocatalyst containing the metal compound are applicable, the term “photocatalyst” may be simply used for description. Further, in the present specification, the metal compound represented by the above general formula or a photocatalyst containing the metal compound may be referred to as "CGIZS photocatalyst" or "CGIZS".

In this general formula, k, j, m, n are not included, and the general formula Cu _x Ga _x-y In _y Zn _{2 (1-x)} A ₂ (0 <x <1, 0 ≦ y ≦ 1, x> The photocatalyst having the composition represented by y, A = S or Se) shows the composition showing the conventional chalcopyrite type, and x and y show the complementary quantitative relationship of Cu, Ga, In and Zn. It is a thing.

Further, the general formula Cu _x Ga _{x−y + k} In _{y + j} Zn _{2 (1-x) + mA 2 + n} (0 <x <1, 0 ≦ y ≦ 1, x> y, 0 ≦ k ≦ 0.2, of the present invention, 0 ≦ j ≦ 0.2, 0 ≦ m ≦ 0.2, 0 ≦ n ≦ 0.8, n = 3 / 2k + 3 / 2j + m, A = S or Se), in addition to the above x and y, k , J, m, n. These k, j, m, and n indicate excess amounts of each component of Ga, In, Zn, and S, respectively, and in the present invention, the performance of the photocatalyst is achieved by using these components in an appropriate excess. Can be improved over that of the conventional composition. k, j, m, and n are 0 ≦ k ≦ 0.2, 0 ≦ j ≦ 0.2, 0 ≦ m ≦ 0.2, 0 ≦ n ≦, respectively, as described in the above-mentioned specific general formula. Although it is 0.8, it may be 0.02 ≦ k ≦ 0.16, 0.02 ≦ j ≦ 0.16, 0.02 ≦ m ≦ 0.16, 0.08 ≦ n ≦ 0.64. It is preferable that 0.04 ≦ k ≦ 0.12, 0.04 ≦ j ≦ 0.12, 0.04 ≦ m ≦ 0.12, and 0.16 ≦ n ≦ 0.48.

Further, in the present invention, 0 <x <1, 0 ≦ y ≦ 1, x> y, but 0.4 ≦ x ≦ 0.8, 0.2 ≦ y ≦ 0.8 is preferable. More preferably, 0.4 ≦ x ≦ 0.8 and 0.3 ≦ y ≦ 0.6. It is known that the light absorption characteristics and the photoelectrochemical characteristics change by changing these x and y, but if x and y are within the above range, the obtained photocatalyst has excellent hydrogen production activity. Can have.

2. Method for producing photocatalyst In the method for producing a CGIZS photocatalyst in the present invention, a high-quality photocatalyst crystal can be grown at a relatively low temperature by using a production method called a flux method. Specifically, the method for producing a metal compound of the present invention or a photocatalyst containing the metal compound uses cuprous sulfide (Cu ₂ S), gallium sulfide (Ga ₂ S ₃ ), and indium sulfide (In _{2) as starting materials.} Metallic sulfides such as S ₃ ) and zinc sulfide (ZnS), or cuprous _{serene (Cu 2} Se), gallium selenide (Ga ₂ Se ₃ ), indium selenide (In ₂ Se ₃ ), and selenization. It includes heat treatment at 400 ° C. or higher and 800 ° C. or lower in the presence of a flux agent composed of metal chloride using a metal selenide such as zinc (ZnSe). By such a manufacturing method, a high-performance CGIZS photocatalyst can be obtained.

Crystal growth can be classified into liquid phase method, vapor phase method and solid phase method. In order to grow a large crystal, it is advantageous to go through the liquid phase because of the ease of rearranging the constituent atoms and the like. Crystal growth from the liquid phase can be divided into a melt method and a solution method.

The solution method is a crystal growth method from a liquid phase having exactly the same composition as the chemical composition of the target crystal. Since supercooling is the driving force for crystal growth, the cooling method is devised to grow crystals.
On the other hand, the solution method using a solvent includes an aqueous solution method, a hydrothermal method and a flux (melting agent) method, and supersaturation due to slow cooling of the solution or evaporation of the solvent is the driving force for crystallization. In the aqueous solution method, water is used as a solvent to grow crystals at a temperature close to room temperature. In the hydrothermal method, crystals are grown under high temperature and high pressure conditions using water exceeding 100 ° C. as a solvent. In the case of the aqueous solution method or the hydrothermal method, the constituent components of the target crystal are first dissolved in water and then crystallized under predetermined conditions.

Even when water is not used as a solvent, inorganic compounds (oxides, halides, etc.), metals, etc. can be used as a solvent by melting at a high temperature. These solvents are called flux or flux agent, and the crystal growth method using the flux is the flux method. The solute is dissolved in the flux, and crystals are grown using the change in supersaturation due to the cooling of the solution and the evaporation of the flux as the driving force.

The advantages of the flux method are that the crystal grows at a temperature much lower than the melting point of the substance (solute), and that the device has a self-shaped structure surrounded by a flat crystal plane that reflects the crystal structure while growing. It is simple and easy to operate. The automorphic form is the original form of the crystal. By growing a crystal using a flux method capable of having an automorphic shape, it is possible to easily specify the crystal orientation.

Specific examples of the metal sulfide used as a starting material include cuprous sulfide (Cu ₂ S), gallium sulfide (Ga ₂ S ₃ ), indium sulfide (In ₂ S ₃ ), and zinc sulfide (Zn S). Use a mixture of metal sulfides containing.

In the flux method, it is important to select an appropriate flux agent. The flux method is crystal growth from a solution and always goes through the processes of dissolution and precipitation. Since the flux is required to have the ability to dissolve the solute and then crystallize from the supersaturated solution, it is necessary to have properties such as sufficiently dissolving the solute and stably precipitating the crystal. Further, it is desirable that the flux has a low melting point, and it is also a requirement that the flux is not mixed into the crystal as an impurity.

In this embodiment, the substance used as the flux agent is not particularly limited, but is limited to metal chlorides, for example, alkali metal chlorides such as lithium chloride, sodium chloride, potassium chloride and cesium chloride, calcium chloride, strontium chloride and barium chloride. Alkaline earth metal chlorides such as, among others, lithium chloride, sodium chloride, potassium chloride, and cesium chloride are more preferable, and eutectic molten salts composed of a mixture of two or more of such metal chlorides are further preferable. preferable.

For example, a mixture of lithium chloride (melting point 605 ° C.) and potassium chloride (melting point 770 ° C.) forms a eutectic molten salt with a melting point of 352 ° C. in a molar ratio of 59.5: 40.5. A mixture of sodium chloride (melting point 801 ° C.) and cesium chloride (melting point 645 ° C.) is also a eutectic molten salt having a melting point of 486 ° C. at a molar ratio of 35:65.

As the metal chloride, a combination of lithium chloride and potassium chloride is particularly preferable. The mixed composition of lithium chloride and potassium chloride preferably has a molar ratio of lithium chloride to potassium chloride of 40:60 to 80:20, preferably 50:50 to 70:30, in terms of lowering its melting point. Is more preferable, and 59.5: 40.5 is particularly preferable in that the melting point is the lowest. In this embodiment, as the metal chloride, a mixture of lithium chloride and potassium chloride having a molar ratio of about 59.5: 40.5 is preferably used.

The amount of the flux agent used, that is, the metal chloride is not particularly limited, but is preferably 1 or more and about 20 or less in terms of molar ratio with respect to the amount of the mixture of the metal sulfide as the raw material, and usually 5 or more and about. 10 times or less is preferable. Within such a range, the heat treatment in the method for producing a metal compound or photocatalyst represented by the above-mentioned specific general formula of the present embodiment can be easily lowered to a low temperature, and the component range of the above-mentioned specific general formula can be easily achieved. Can be done.

The heat treatment in this embodiment, that is, the temperature at the time of flux is preferably 400 ° C. or higher and 800 ° C. or lower, and more preferably 450 ° C. or higher and 750 ° C. or lower.
The heat treatment time is preferably 0.5 hours or more and 50 hours or less, more preferably 1 hour or more and 30 hours or less, and further preferably 2 hours or more and 20 hours or less.
The rate of temperature rise in the heat treatment is preferably 0.5 ° C./min or more and 20 ° C./min or less, and more preferably 1 ° C./min or more and 15 ° C./min or less.

The temperature lowering rate in the heat treatment in the present embodiment is preferably 0.5 ° C./min or more and 20 ° C./min or less, and more preferably 1 ° C./min or more and 15 ° C./min or less. In particular, since the temperature drop has a large effect on crystal growth, it may be effective not only to lower the temperature at a constant rate but also to maintain the temperature at a constant temperature in the middle or change the temperature drop rate in the middle. Specifically, after lowering the temperature at a temperature lowering rate of 1 ° C./min or higher and 15 ° C./min or lower, the temperature is maintained at a constant temperature of 300 ° C. or higher and 600 ° C. or lower for 30 minutes or longer and 300 minutes or lower, and then 1 ° C. Examples thereof include a method of lowering the temperature to near room temperature at a temperature lowering rate of / min or more and 15 ° C./min or less.

The heat treatment in this embodiment can be carried out in the atmosphere and is usually carried out at a pressure of 0.1 × 10 ⁵ Pa or more and 2000 × 10 ⁵ Pa or less, for example, 1 × 10 ⁵ Pa or more and 1000 × 10 ⁵ Pa or less. It can be carried out. Such heat treatment can be performed, for example, in a closed reaction vessel. Therefore, the heat treatment in the present embodiment does not need to be heat-treated under vacuum, and the metal sulfide as a raw material and the metal chloride as a flux agent are used as a closed reaction vessel such as a quartz glass tube or a quartz ampol tube. Although it is not necessary to heat-treat the inside, the atmosphere at the time of heat treatment or flux in the present embodiment is not particularly limited, and any atmosphere under the atmosphere or an inert gas atmosphere, and usually under reduced pressure or vacuum. It is applicable and heat treatment may be performed in a closed reaction vessel. The atmosphere during the heat treatment or flux in this embodiment is preferably in the apparatus, under an inert gas atmosphere, or under vacuum, and more preferably under vacuum.

After the heat treatment (flux) is performed, it is preferable to wash with water to remove the flux agent. Since the metal sulfide and CGIZS are insoluble in water and the metal chloride is soluble in water, the metal chloride which is a flux agent can be effectively removed by washing with water.
The amount of water used for washing, the number of washings, the washing time, and the like are not particularly limited, and the usual index is until chlorine is no longer detected in the washing water. As a method of washing with water, for example, using water having a volume 2 to 20 times the volume of solid matter per washing, the number of washings is usually 3 times or more, and the washing time is 5 minutes or more / time. Be done. Usually, within such a range, the number of washings can be 6 times or less, and the washing time can be 60 minutes or less / time.

After washing, the CGIZS photocatalyst is usually dried. The drying method is not particularly limited, but it is desirable to remove the moisture without applying a large heat load. It is preferable to dry at room temperature to about 50 ° C. under normal pressure or reduced pressure.

The amount of flux impurities remaining in the metal compound or photocatalyst represented by the above-mentioned specific general formula obtained by the above production method is preferably 100 ppm or less with respect to the mass of the metal compound or photocatalyst. Specifically, with respect to the mass of the metal compound or the photocatalyst, the metal component derived from the metal chloride used in the flux is preferably 500 ppm or less, more preferably less than 200 ppm, still more preferably 100 ppm or less. The chlorine derived from is preferably 50 ppm or less, more preferably 10 ppm or less.

Further, the CGIZS photocatalyst thus produced can also be used as a photocatalyst by mixing a plurality of types having different compositions. In order for electrons and holes generated by being excited by light irradiation to move in the photocatalyst without recombination, it is better to mix and use a photocatalyst having a non-uniform composition than a homogeneous photocatalyst having a constant composition. May show performance. In that case, it is desirable to heat-treat at a predetermined temperature within the range of 150 to 600 ° C. under an atmosphere of an inert gas containing no oxygen or under reduced pressure. By promoting the compatibility of particles with each other by heating, the conduction resistance due to the potential barrier at the grain boundaries is relaxed.

The metal compound or photocatalyst represented by the above-mentioned specific general formula produced by the production method of the present embodiment can be suitably used as a photocatalyst for a photowater decomposition reaction. In that case, the form of the photocatalyst to be subjected to the photowater decomposition reaction is not particularly limited, and for example, a form in which the photocatalyst is dispersed in water, a form in which the photocatalyst is used as a molded body and the molded body is placed in water, and a substrate A layer containing a photocatalyst is provided in the water to form a laminate, and the laminate is installed in water. A photocatalyst is immobilized on a current collector to form a photocatalyst electrode for a photocatalyst decomposition reaction, and the laminate is installed in water together with a counter electrode. The latter form of the photocatalytic electrode is preferable. The photocatalytic electrode will be described later.
The water in which the photocatalyst is installed may be liquid or gaseous. Moreover, you may use an aqueous electrolyte solution as the said water.

3. 3. Supporting co-catalyst and surface modification This sulfide catalyst uses photoexcited electrons to reduce water to produce hydrogen, and the co-catalyst functions as its active site. At that time, it is considered that the photoexcited electrons donate electrons to the water molecules on the surface of the co-catalyst to generate hydrogen molecules.

Therefore, in order for the photocatalyst used for photowater decomposition to effectively exert its photowater decomposition activity, it is preferable to support and use an auxiliary catalyst that promotes hydrogen generation on the surface of the photocatalyst. In addition, the photocatalyst is used to efficiently separate the charge of the photoexcited electrons and move them to the co-catalyst supported on the surface of the catalyst, or to alleviate the deterioration of the photocatalyst itself due to contact with water over time. It is desirable to modify the surface of the surface to improve performance and impart stability.

In the present embodiment, the co-catalyst loading and / or the surface modification of the photocatalyst is performed, for example, before laminating the metal compound represented by the above-mentioned specific general formula or the photocatalyst containing the metal compound and the current collector described later. This may be done, but it may be done after laminating with the current collector.
In the present embodiment, the co-catalyst may be supported and the surface of the photocatalyst may not be modified, or conversely, the surface of the photocatalyst may be modified and the co-catalyst may not be supported. It is preferable to perform both surface modifications.
When both the co-catalyst support and the photocatalyst surface modification are performed, either of them may be performed first. For example, the co-catalyst support may be performed and then the photocatalyst surface modification may be performed, or conversely. After surface modification of the photocatalyst, such a co-catalyst may be supported.

When the photocatalyst to be subjected to the photowater decomposition reaction is provided, for example, in the form of dispersing the photocatalyst in water, it is preferable to carry the cocatalyst. The photocatalyst to be subjected to the photocatalyst decomposition reaction is, for example, a form in which the photocatalyst is used as a molded body and the molded body is installed in water. When the photocatalyst is immobilized on the current collector to serve as a photocatalyst electrode for a photocatalyst decomposition reaction and is provided in water together with a counter electrode, it is preferable to modify the surface of the photocatalyst, and the surface modification of the photocatalyst and the auxiliary catalyst It is more preferable to carry it.

In the present specification, a photocatalyst complex obtained by carrying at least one selected from the group consisting of supporting a cocatalyst and surface modification on a photocatalyst containing a metal compound represented by the above-mentioned specific general formula is referred to as a "photocatalyst complex". Sometimes. That is, such a photocatalytic complex comprises a photocatalyst and at least one selected from the group consisting of co-catalysts and surface modifiers. In such a photocatalyst composite, specifically, the co-catalyst is supported on the metal compound represented by the above-mentioned specific general formula, and the surface modifier modifies the surface of the metal compound.

As the co-catalyst in this embodiment, noble metals such as platinum, ruthenium, iridium, palladium, and gold (Pt, Ru, Ir, Pd, Au) are preferably used. In particular, Pt, Ir, and Ru are more preferable. Two or more kinds of co-catalysts may be used, but usually, even if only one kind is used, the function of the co-catalyst can be sufficiently exhibited.

The form of supporting the co-catalyst is not particularly limited, but a state in which the co-catalyst is supported as particles on the surface of the catalyst is preferable. The co-catalyst is preferably nano-sized fine particles having an average diameter of 0.1 to 10 nm.
The method for supporting the co-catalyst is not particularly limited, and examples thereof include general methods such as impregnation, photoelectric adhesion, electrophoresis, sputtering, and drop casting. The amount carried is not particularly limited, and is preferably 0.1 to 10% by mass, more preferably 0.5 to 3% by mass, of the metal compound represented by the above-mentioned specific general formula or the photocatalyst.

The metal compound represented by the above-mentioned specific general formula, which carries a co-catalyst of the present embodiment, can have excellent hydrogen-producing activity under visible light irradiation. Specifically, for example, the quantitative value of the number of moles of hydrogen generated per unit time when irradiating with pseudo-sunlight under the following conditions can be ^{set to 3 mL · h -1 or more by an online gas chromatograph.} The upper limit of the quantitative value is not particularly limited, but can be, for example, 150 mL · h ^-1 or less.
Conditions: 0.2 g of powder carrying 2% by mass of Ru co-catalyst with respect to the metal compound, 200 ml of an aqueous solution containing _{0.50 mol / L K 2} SO ₃ and 0.10 mol / L Na _{2 S.} Suspended in, put into an upper irradiation type reaction cell connected to a closed circulation type reaction device, and irradiated with pseudo-sunlight using a solar simulator (AM1.5G) at a reaction temperature of 20 ° C. and a reaction pressure of 5 kPa, with an irradiation intensity of 100 mW / Irradiate to cm ^2.

Further, as the surface modification, first, it is preferable to laminate or support a substance to be an n-type semiconductor on the metal compound or photocatalyst represented by the above-mentioned specific general formula. A pn junction is formed by laminating or supporting an n-type semiconductor on the surface of CGIZS, which is a p-type semiconductor, whereby excited electrons are effectively transferred from the p-type semiconductor CGIZS to an n-type semiconductor and further to a cocatalyst. Will be carried to. At that time, it is also expected to suppress the recombination of excited electrons and vacancies, so that efficient charge separation can be realized.

As the n-type semiconductor suitably used in the present embodiment, CdS, ZnS, include metal sulfides such as _In 2 _{S 3,} CdS, ZnS is more preferably used. As the n-type semiconductor or metal sulfide, two or more kinds may be used, but usually, even if only one kind is used, the function can be sufficiently exhibited. In the present specification, an n-type semiconductor or metal sulfide that surface-modifies a metal compound or photocatalyst represented by the above-mentioned specific general formula may be referred to as a “surface modifier”.

The form of supporting these n-type semiconductor metal sulfides is not particularly limited, but a state in which they are laminated as a film or supported as particles on the surface of a metal compound represented by the above-mentioned specific general formula or a photocatalyst is preferable. The thickness of the layer in the case of is usually 0.1 nm or more and 500 nm or less, preferably 1 nm or more and 200 nm or less, and the particle size in the case of carrying is usually 1 nm or more and 200 nm or less, preferably 2 nm or more in average diameter. , 100 nm or less is preferable.

The method for supporting the n-type semiconductor metal sulfide is not particularly limited, and for example, an impregnation method, a chemical solution precipitation method (CBD method, Chemical Bath Deposition), photoelectric adhesion, electrophoresis, sputtering and the like are preferably used. Be done. In particular, the chemical solution precipitation method is more preferable.

A case where CdS is supported by the chemical solution precipitation method will be described. A Cd salt such as cadmium sulfate or cadmium acetate is preferably used as the Cd source, thiourea is preferably used as the sulfur source, and aqueous ammonia is preferably used as the neutralizing agent. Specifically, the CGIZS photocatalyst electrode is immersed in an aqueous solution containing a Cd salt, thiourea, and aqueous ammonia while being heated to 40 to 80 ° C. Since CdS is deposited on the electrode surface, it is immersed for a predetermined time, then taken out and washed with water.
Further, as a surface treatment for imparting stability, it is preferable to laminate an oxide such _{as TiO 2 on the electrode surface as a film.}

4. Photocatalyst electrode In the following description of the photocatalyst electrode, it is preferable to use the above-mentioned photocatalyst complex as the photocatalyst.
The photocatalyst electrode for the photocatalytic reaction using the metal compound represented by the above-mentioned specific general formula or the photocatalyst in the above-described embodiment can be produced, for example, by a known method. For example, general methods such as a drop casting method, a particle transfer method, a physical film forming method, a roll press method, and an electrophoresis method are preferably used.

The particle transfer method (Chem. Sci., 2013, 4, 1120-1124) is a preferred method, and a high-performance photocatalytic electrode can be easily produced. That is, a photocatalyst is placed on a first base material such as glass to obtain a laminate of the photocatalyst layer and the first base material layer. A conductive layer (current collector, current collector conductor) is provided on the surface of the photocatalyst layer of the obtained laminate by vapor deposition or the like. Here, the photocatalyst on the surface layer on the conductive layer side of the photocatalyst layer is immobilized on the conductive layer. Then, the second base material is adhered to the surface of the conductive layer, and the conductive layer and the photocatalyst layer are peeled off from the first base material layer. Since a part of the photocatalyst is immobilized on the surface of the conductive layer, it is peeled off together with the conductive layer, and as a result, an electrode for photowater decomposition reaction having a photocatalyst layer, a conductive layer, and a second base material layer is obtained. Can be done.

Further, an electrode for photowater decomposition reaction may be obtained by applying a slurry in which a photocatalyst is dispersed to the surface of a current collector and drying it, or the photocatalyst and the current collector are integrally formed by pressure molding or the like. The electrode for photowater decomposition reaction may be obtained by the conversion. Alternatively, the current collector may be immersed in a slurry in which the photocatalyst is dispersed, a voltage may be applied, and the photocatalyst may be integrated on the current collector by electrophoresis.

The metal compound represented by the above-mentioned specific general formula or a photocatalyst containing the metal compound is usually obtained as a powder, but when the powder is laminated on the current collector, the liquid in which the powder is suspended is applied to the current collector. It can be done by doing. The suspension of the powder of the metal compound or the photocatalyst is not particularly limited, but for example, a liquid using an alcohol such as ethanol, 2-propanol, or t-butanol as a dispersion medium is preferable.

As the current collector, Au or carbon, or a transparent conductive film or glass such as ITO or FTO is preferably used. The method for producing the current collector of Au or carbon is not particularly limited, but it is preferable to carry it on a laminated surface by physical means such as thin film deposition or sputtering.

Further, when a photocatalyst electrode is produced using a CGIZS photocatalyst, a current collector layer containing at least one current collector conductor selected from the group consisting of Au and carbon, preferably a current collector made of Au or carbon. conductor layer, and, CdS, ZnS, and _in 2 surface treatment with any one or more of sulfide selected from _{S 3, Pt, Au, Ir} , Ru, and any one or more auxiliaries selected from Pd The performance of the photocatalyst electrode is fully exhibited by applying the three factors of carrying the catalyst.
For the production of the CGIZS photocatalyst electrode, various production methods such as a drop casting method, a particle transfer method, and a physical film forming method can be applied using the CGIZS photocatalyst. The particle transfer method is more preferred.

5. Method for Producing Hydrogen by Photo-Water Decomposition A metal compound represented by the above-mentioned specific general formula or a photocatalyst containing the metal compound, or the above-mentioned photocatalyst electrode produced by the present embodiment is immersed in water or an aqueous electrolyte solution. Hydrogen can be produced by irradiating the photocatalyst or the photocatalyst electrode with light to perform photoaqueous decomposition. In this case, it is preferable to use the above-mentioned photocatalyst complex as the above-mentioned metal compound or photocatalyst.

For example, as described above, a photocatalyst is immobilized on a current collector composed of a conductor to obtain a photocatalyst electrode for oxygen generation and a photocatalyst electrode for hydrogen generation, and the electrodes are connected with a conductive material such as an electric wire. After that, the water is irradiated with light while supplying liquid or gaseous water to allow the water splitting reaction to proceed. The water splitting reaction can be promoted by providing a potential difference between the electrodes as needed.
On the other hand, the water decomposition reaction may proceed by irradiating a fixed product in which a photocatalyst is immobilized on an insulating base material or a molded product in which a photocatalyst is pressure-molded with water while supplying water. Alternatively, the photocatalyst may be dispersed in water or an aqueous electrolyte solution, and light may be irradiated therein to allow the water splitting reaction to proceed. In this case, the reaction can be promoted by stirring as necessary.

The reaction conditions at the time of producing hydrogen are not particularly limited, but for example, the reaction temperature, the reaction pressure, and the like can be selected. The reaction temperature can be, for example, 0 ° C. or higher and 200 ° C. or lower, preferably 10 ° C. or higher and 150 ° C. or lower, more preferably 15 ° C. or higher and 100 ° C. or lower. The reaction pressure can be, for example, 2 MPa (G) or less, preferably 1 MPa (G) or less, more preferably 0.5 MPa (G) or less, still more preferably 0.2 MPa (G) or less, and such a range. If it is within, it is preferably 0.001 MPa (G) or more, and more preferably 0.005 MPa (G) or more.

Visible light having a wavelength of 900 nm or less can be preferably used as the irradiation light, although it depends on the type of photocatalyst. Examples of the light source of the irradiation light include, in addition to the sun, a lamp capable of irradiating sunlight-approximate light or pseudo-sunlight such as a xenon lamp and a metal halide lamp, a mercury lamp, and an LED.

The photocatalyst electrode using the metal compound or the photocatalyst represented by the above-mentioned specific general formula of the present embodiment can have excellent photoelectrochemical properties. Specifically, for example, when the photocatalyst electrode produced under the following conditions is irradiated with pseudo-sunlight under the following conditions, ^{the cathode current density of 1 mA / cm 2} or more is measured at an operating potential of 0.0 Vvs RHE. Can be done. In addition, the quantum efficiency of hydrogen generation in photo-water decomposition at that time shows a value of 90% or more. The upper limit of the cathode current density is not particularly limited, but can be, for example, 10 mA / cm ² or less.
Photocatalyst electrode preparation conditions: Au having a film thickness of 1 to 3 μm is laminated on a photocatalyst layer having a film thickness of 1 to 3 μm made of the metal compound, and the surface is modified with CdS having a film thickness of 2 to 20 nm. To obtain a photocatalytic electrode composed of Pt / CdS / CGIZS / Au.
Pseudo-sunlight irradiation conditions:
・ Light source Solar simulator AM1.5G (100mW / cm ² )
-Electrolytic solution 0.5M Na ₂ SO ₄ , 0.25M Na ₂ HPO ₄ , 0.25M NaH ₂ PO ₄ pH 6.3
・ Reference electrode Ag / AgCl, counter electrode Pt wire ・ Argon atmosphere

Hereinafter, the composite metal compound and the photocatalytic electrode of the present invention will be specifically described based on Examples, but the present invention is not limited to these Examples. In addition, Examples 11, 12, 15 to 17, 19 and 23 shall be read as Reference Examples 11, 12, 15 to 17, 19 and 23, respectively.

Example 1
<Photocatalytic synthesis, flux method, Cu _0.8 Ga _0.48 In _0.48 Zn _0.4 S _2.24 >
The photocatalyst was synthesized by the flux method. As raw materials, _{1.019 g (6.40 mmol) of Cu 2} S (manufactured by High Purity Chemical Laboratory Co., Ltd., purity 99.0%), Ga ₂ S ₃ (manufactured by High Purity Chemical Laboratory Co., Ltd., purity 99) 0.905 g (3.84 mmol), In ₂ S ₃ (manufactured by High Purity Chemical Laboratory Co., Ltd., purity 99.99%) 1.251 g (3.84 mmol), ZnS (Co., Ltd.) 0.748 g (7.68 mmol) of 99.999% pure, manufactured by High Purity Chemical Laboratory was used. This raw material preparation is performed by the general formula Cu _x Ga _{xy + k} In _{y + j} Zn _{2 (1-x) + mA 2 + n} (0 <x <1, 0 ≦ y ≦ 1, x> y, 0 ≦ k ≦ 0.2, For 0 ≦ j ≦ 0.2, 0 ≦ m ≦ 0.2, 0 ≦ n ≦ 0.8, n = 3 / 2k + 3 / 2j + m, A = S or Se), x = 0.8, y = It corresponds to 0.4, k = 0.08, j = 0.08, m = 0, n = 0.24. That is, _{it corresponds to Cu 0.8} Ga _0.48 In _0.48 Zn _0.4 S _2.24 , and Ga and In are each used in excess of 20 mol% of the stoichiometric value. Mixing the raw materials using a agate mortar, it was performed in a N ₂ glove box. As the flux agent, 4.070 g (48 mmol) of LiCl (manufactured by Kanto Chemical Co., Inc., purity 99.0%) and 4.771 g (32 mmol) of KCl (manufactured by Kanto Chemical Co., Inc., purity 99.5%) were used. .. The flux agent was mixed in the same manner as the mixing of the raw material metal sulfide. These mixtures were placed in a quartz sheath tube in the order of the raw material and the flux agent, and heat-treated in the air at 500 ° C. for 3 hours in a vertical tube furnace. In the heat treatment, the heating rate is 10 ° C./min. The temperature of the heat treatment was lowered at a temperature lowering rate of 5 ° C./min. The sample after the heat treatment was thoroughly washed with pure water to remove the flux component, and then the produced CGIZS powder was separated and recovered by suction filtration. Then, it was dried in the air at room temperature overnight.

Examples 2-6
A CGIZS photocatalyst was synthesized in the same manner as in Example 1 except that y = 0.4 was replaced with y = 0, 0.2, 0.5, 0.6, 0.8. That is, each of the obtained CGIZS photocatalysts corresponds to the following composition formula.
Example 2 (y = 0): Cu _0.8 Ga _0.88 In _0.08 Zn _0.4 S _2.24
Example 3 (y = 0.2): Cu _0.8 Ga _0.68 In _0.28 Zn _0.4 S _2.24
Example 4 (y = 0.5): Cu _0.8 Ga _0.38 In _0.58 Zn _0.4 S _2.24
Example 5 (y = 0.6): Cu _0.8 Ga _0.28 In _0.68 Zn _0.4 S _2.24
Example 6 (y = 0.8): Cu _0.8 Ga _0.08 In _0.88 Zn _0.4 S _2.24

Comparative Example 1
The CGIZS photocatalyst was synthesized by the solid phase method. Specifically, as the raw material metal sulfide, the same material as in Example 1 was used in the same amount, and a mixture thereof was placed in a quartz glass tube, sealed under a vacuum of 0.5 Pa, and then subjected to electricity. Heat treatment was performed at 800 ° C. for 10 hours in a furnace.

Comparative Examples 2 to 6
The CGIZS photocatalyst was synthesized by the same method as in Comparative Example 1 using the same raw material preparation as in Examples 2 to 6. That is, as the raw material metal sulfide, the same material as in Examples 2 to 6 was used in the same amount.

Examples 7-12
In Example 1, the catalyst was synthesized by the same operation except that the heat treatment temperatures were set to 400 ° C., 600 ° C., 650 ° C., 700 ° C., 750 ° C., and 800 ° C.

Example 13
<Photocatalytic synthesis, flux method, Cu _0.8 Ga _0.48 In _0.4 Zn _0.4 S _2.12 >
Except that the amount of raw material charged (mol) corresponding to x = 0.8, y = 0.4, k = 0.08, j = 0, m = 0, n = 0.12 was used. The photocatalyst CGIZS was synthesized by the same method as in Example 1. That is, _{it corresponds to Cu 0.8} Ga _0.48 In _0.4 Zn _0.4 S _2.12. , And Ga is used in an excess of 20%.

Comparative Example 7
<Photocatalytic synthesis, solid phase method, x = 0.8, y = 0.4>
Photocatalyst CGIZS was synthesized by the same method as in Comparative Example 1 except that Cu ₂ S, In ₂ S ₃ , and Zn S were stoichiometric values, and Ga ₂ S _{3 was 20 mol% excess.} did.

<Characterization by powder X-ray diffraction (XRD)>
Crystal structure analysis was performed on each sample obtained in Examples 1 to 13 and Comparative Examples 1 to 7 using powder X-ray diffraction (XRD). The results of each sample obtained in Examples 1 to 6 are shown in FIG. 1, the results of each sample obtained in Comparative Examples 1 to 6 are shown in FIG. 2, and the results obtained in Examples 13 and 7 are shown. The results of the sample are shown in FIG.

In the XRD measurement results of FIGS. 1 and 2, it was confirmed that crystals having a calcopalite structure were obtained in each of the samples.
Further, in the XRD measurement results of FIGS. 1 and 2, a low angle shift was observed as the y value increased, that is, as Ga decreased and In increased.
From FIG. 6, the XRD measurement results are substantially the same between the sample synthesized by the flux method in Example 13 and the sample synthesized by the conventional solid phase method in Comparative Example 7, and all the samples are crystals having a calcopalite structure. Was obtained.

<Characterization by diffuse reflection spectrum measurement (DRS)>
Diffuse reflection spectrum measurement (DRS) was performed on each of the samples obtained in Examples 1 to 6 and 13 and Comparative Examples 1 to 7 using a UV-VIS-NIR spectrophotometer. The results of each sample obtained in Examples 1 to 6 and Comparative Examples 1 to 6 are shown in FIG. 3, and the results of each sample obtained in Examples 13 and 7 are shown in FIG. 7.

In the DRS results of each catalyst in FIG. 3, it was confirmed that the absorption edge wavelength was shifted to the long wavelength side from 540 nm to about 900 nm as the y value increased, that is, as Ga decreased and In increased. It was. From this, it can be seen that the absorption edge wavelength can be controlled to the long wavelength side by decreasing Ga and increasing In.
Further, it can be seen from FIG. 7 that the absorption edge is substantially the same at about 670 nm.

[Supporting co-catalyst]
With respect to the CGIZS photocatalysts obtained in Examples 1 to 12 and Comparative Examples 1 to 6, 2% by weight of Ru was supported as a co-catalyst by the photoelectric adhesion method. Specifically, light irradiation with a 300 W xenon lamp was carried out for 3 hours in a state where 0.2 g of the CGIZS powder was suspended under stirring at room temperature in 200 mL of an aqueous solution containing 0.40 mmol of _{RuCl 3 and 20 mL of methanol.} .. Then, it was filtered, washed with water, and dried at room temperature overnight.

<Evaluation of hydrogen production activity of CGIZS photocatalyst (suspension system)>
For each of the CGIZS photocatalysts obtained in Examples 1 to 12 and Comparative Examples 1 to 6 carrying the Ru cocatalyst as described above, the photocatalytic activity of decomposing water to generate hydrogen is sulfite under pseudo-sunlight irradiation. It was evaluated by a hydrogen production reaction from an aqueous solution containing potassium and sodium sulfide. An upper irradiation type reaction cell connected to a closed circulation type reaction device was used for the evaluation. 0.2 g of the catalyst powder _{was suspended in 200 ml of an aqueous solution containing 0.50 mol / L K 2} SO ₃ and 0.10 mol / L Na ₂ S, and the mixture was stirred with a magnetic stirrer during the evaluation. The reaction conditions are a reaction temperature of 20 ° C. and a reaction pressure of 5 kPa. Pyrex® glass windows were used to irradiate pseudo-sunlight using a solar simulator (AM1.5G). The irradiation intensity was 100 mW / cm ² . The generated hydrogen was quantified by an online gas chromatograph (manufactured by Shimadzu Corporation; GC-8A, MS-5A, TCD, Ar carrier). The results of the Ru co-catalyst carrier of each CGIZS photocatalyst obtained in Examples 1 to 6 and Comparative Examples 1 to 6 are shown in FIG. 4, and the Ru of each CGIZS photocatalyst obtained in Examples 7 to 12 and Comparative Example 7 is shown in FIG. The results of the co-catalyst carrier are shown in FIG.

As is clear from FIG. 4, the photocatalyst produced by the flux method in Examples 1 to 6 over a wide range of x = 0.8 and y = 0 to 0.8 is more conventional in Comparative Examples 1 to 6. It was found that the photocatalyst produced by the solid phase method showed higher hydrolytic hydrogen production activity.
As is clear from FIG. 5, each photocatalyst obtained by the flux method at a flux temperature of 400 to 700 ° C. in Examples 7 to 10 has a higher hydrogen decomposition hydrogen than the photocatalyst obtained by the solid phase method in Comparative Example 7. It was found to show generative activity.

Example 14
[Preparation of CGIZS photocatalytic electrode, particle transfer method]
30 mg of the photocatalyst CGIZS obtained in Example 13 was suspended in 1 mL of 2-propanol, 200 μL of this suspension was dropped onto a glass substrate, and then drying was repeated three times to form a photocatalyst layer on the glass substrate. Formed. Next, Au, which is a current collector conductor layer, was laminated on the photocatalyst layer with a film thickness of about 2 μm by vapor deposition. As the vapor deposition apparatus, a vacuum vapor deposition apparatus (VPC-260F manufactured by ULVAC Kiko Co., Ltd.) was used. Then, another glass substrate was adhered from the top of the current collector layer using double-sided tape to remove the first attached glass substrate, and ultrasonically cleaned in pure water. Finally, a portion other than the photocatalyst layer is sealed with an epoxy resin, and the In conductor is further adhered to the current collector layer to obtain a CGIZS photocatalyst electrode composed of a photocatalyst layer / current collector conductor layer / glass substrate. It was.

[CdS surface modification and Pt co-catalyst support]
50 mL of water was heated to 70 ° C., and 0.28 g of cadmium sulfate, 0.4 mL of 28% ammonia water, and 1.4 g of thiourea were sequentially added under stirring at the same temperature, and then the above was obtained. The CGIZS photocatalyst electrode was immersed for 5 minutes. The taken-out photocatalyst electrode was washed with pure water and then dried overnight at room temperature to obtain a CGIZS photocatalyst electrode surface-modified with CdS. Next, Pt as an co-catalyst was supported in an amount corresponding to a thickness of about 1 nm using a multi-deposition apparatus. In this way, a photocatalytic electrode composed of Pt / CdS / CGIZS / Au as an electrode configuration was obtained.

<Evaluation of photoelectrochemical characteristics>
Using each photocatalytic electrode obtained in Example 14, the photoelectrochemical properties were examined under the following measurement conditions. The results are shown in FIG. As is clear from FIG. 8, the photoelectrode using the CGIZS photocatalyst synthesized by the flux method gave a high cathode current.
・ Light source Solar simulator AM1.5G (100mW / cm ² )
-Electrolytic solution 0.5M Na ₂ SO ₄ , 0.25M Na ₂ HPO ₄ , 0.25M NaH ₂ PO ₄ pH 6.3
・ Reference electrode Ag / AgCl, counter electrode Pt wire ・ Argon atmosphere

<Evaluation of water splitting hydrogen production activity>
Using the photocatalytic electrode obtained in Example 14, the hydrogen production activity due to water splitting was investigated under the following measurement conditions. The results are shown in FIG.
・ Light source Solar simulator AM1.5G (100mW / cm ² )
-Electrolytic solution 0.5M Na ₂ SO ₄ , 0.25M Na ₂ HPO ₄ , 0.25M NaH ₂ PO ₄ pH 6.3
・ Reference electrode Ag / AgCl, counter electrode Pt wire ・ Argon atmosphere

As shown in FIG. 9, the quantum is due to the relationship between hydrogen and oxygen being generated in a volume ratio of 2: 1 and the theoretical gas generation amount (dotted line part) calculated from the photocurrent value measured at that time. It was found that an efficiency of about 95% could be obtained.

Example 15
<Photocatalytic synthesis, flux method, Cu _0.8 Ga _0.48 In _0.4 Zn _0.4 S _2.12 >
A photocatalyst CGIZS with an excess of Ga 20% was synthesized by the same method as in Example 13 except that the heat treatment was carried out under a nitrogen stream at 750 ° C. for 3 hours.

Example 16
<Photocatalytic synthesis, flux method, Cu _0.8 Ga _0.4 In _0.48 Zn _0.4 S _2.12 >
The photocatalyst CGIZS was synthesized by the same method as in Example 15 except that there was no Ga excess and In 20% excess instead of the Ga 20% excess in Example 15.

Example 17
<Photocatalytic synthesis, flux method, Cu _0.8 Ga _0.4 In _0.4 Zn _0.48 S _2.12 >
The photocatalyst CGIZS was synthesized by the same method as in Example 15 except that there was no Ga excess and the Zn was 20% excess instead of the Ga 20% excess in Example 15.

Example 18
<Photocatalytic synthesis, flux method, Cu _0.8 Ga _0.52 In _0.4 Zn _0.4 S _2.18 >
The photocatalyst CGIZS was synthesized by the same method as in Example 15 except that the excess of Ga was 30% instead of the excess of 20% of Ga in Example 15 and the heat treatment was performed at 550 ° C. for 15 hours.

Example 19
<Photocatalytic synthesis, flux method, Cu _0.8 Ga _0.4 In _0.4 Zn _0.4 S ₂ >
The photocatalyst CGIZS was synthesized by the same method as in Example 15 except that there was no Ga excess in place of the Ga 20% excess in Example 15.

<Characterization by powder X-ray diffraction (XRD)>
Crystal structure analysis (XRD) was performed on each sample obtained in Examples 15 to 19 using powder X-ray diffraction (XRD). The results are shown in FIG.
From FIG. 10, it was confirmed that crystals having a calcopalite structure were obtained in all the samples.

<Characterization by diffuse reflection spectrum measurement (DRS)>
Diffuse reflection spectrum measurement (DRS) was performed on each sample obtained in Examples 15 to 19 using a UV-VIS-NIR spectrophotometer. The results are shown in FIG.

From FIG. 11, in Example 16 in which the excess amount of In is 20 mol%, in Example 17 in which the excess amount of Zn is 20 mol%, and in Example 19 in which there is no excess amount of Ga, In and Zn (0 mol%). It can be seen that the absorption end is around 700 nm, and in Example 15 in which the excess amount of Ga is 20 mol% and in Example 18 in which the excess amount of Ga is 30 mol%, the absorption end is around 660 nm.

[Preparation of CGIZS photocatalytic electrode, particle transfer method]
For each photocatalyst CGIZS obtained in Examples 15 to 19, a photocatalyst electrode was prepared by the same method as in Example 14.

[CdS surface modification and Pt co-catalyst support]
Further, by performing surface treatment and supporting the co-catalyst by the same method as in Example 14, a photocatalyst electrode composed of Pt / CdS / CGIZS / Au as an electrode configuration was obtained.

<Evaluation of photoelectrochemical characteristics>
Using the photocatalytic electrode obtained above, the photoelectrochemical properties were investigated under the following measurement conditions. The results of the photocatalyst electrode using each of the photocatalysts obtained in Examples 15 to 19 as described above are shown in FIG.
・ Light source Solar simulator AM1.5G (100mW / cm ² )
-Electrolytic solution 0.5M Na ₂ SO ₄ , 0.25M Na ₂ HPO ₄ , 0.25M NaH ₂ PO ₄ pH 6.3
・ Reference electrode Ag / AgCl, counter electrode Pt wire ・ Argon atmosphere

As is clear from FIG. 12, the photocatalyst electrode using the photocatalyst composite obtained by subjecting each of the photocatalysts obtained in Examples 15 to 19 to CdS surface modification and Pt cocatalyst support provided a high cathode current.

Example 20
<Photocatalyst synthesis and fabrication of photocatalyst electrodes, catalyst composition: Cu _0.8 Ga _0.44 In _0.4 Zn _0.4 S _2.06, synthesis method: flux method, heat treatment temperature: 450 ° C.>
CGIZS photocatalyst by the same method as in Example 1 except that only Ga was 10% excessive and heat treatment was performed in an electric furnace at 450 ° C. for 3 hours in a quartz glass tube sealed under a vacuum of 0.5 Pa. Was synthesized. Further, by performing the photocatalyst electrode, the support catalyst, and the surface modification by the same method as in Example 14, a photocatalyst electrode composed of Pt / CdS / CGIZS / Au as an electrode configuration was obtained.

Example 21
<Photocatalyst synthesis and photocatalyst electrode fabrication, catalyst composition: same as above, synthesis method: same as above, heat treatment temperature: 550 ° C>
A CGIZS photocatalyst was synthesized by the same method as in Example 20 except that the heat treatment temperature was changed to 550 ° C., and further, a photocatalyst electrode composed of Pt / CdS / CGIZS / Au was obtained in the same manner.

Example 22
<Photocatalyst synthesis and photocatalyst electrode fabrication, catalyst composition: same as above, synthesis method: same as above, heat treatment temperature: 650 ° C>
A CGIZS photocatalyst was synthesized by the same method as in Example 20 except that the heat treatment temperature was changed to 650 ° C., and further, a photocatalyst electrode composed of Pt / CdS / CGIZS / Au was obtained in the same manner.

Example 23
<Photocatalyst synthesis and photocatalyst electrode fabrication, catalyst composition: same as above, synthesis method: same as above, heat treatment temperature: 750 ° C>
A CGIZS photocatalyst was synthesized by the same method as in Example 20 except that the heat treatment temperature was changed to 750 ° C., and further, a photocatalyst electrode composed of Pt / CdS / CGIZS / Au was obtained in the same manner.

Comparative Example 8
<Photocatalyst synthesis and photocatalyst electrode fabrication, catalyst composition: same as above, synthesis method: same as above, heat treatment temperature: 350 ° C>
A CGIZS photocatalyst was synthesized by the same method as in Example 20 except that the heat treatment temperature was changed to 350 ° C., and further, a photocatalyst electrode composed of Pt / CdS / CGIZS / Au was obtained in the same manner.

Comparative Example 9
<Photocatalyst synthesis and photocatalyst electrode fabrication, catalyst composition: same as above, synthesis method: same as above, heat treatment temperature: 850 ° C>
A CGIZS photocatalyst was synthesized by the same method as in Example 20 except that the heat treatment temperature was changed to 850 ° C., and further, a photocatalyst electrode composed of Pt / CdS / CGIZS / Au was obtained in the same manner.

<Evaluation of photoelectrochemical characteristics>
Using the photocatalytic electrode obtained above, the photoelectrochemical properties were investigated under the following measurement conditions. Table 1 shows the results of the photocatalyst electrodes using the photocatalysts obtained in Examples 20 to 23 and Comparative Examples 8 to 9 as described above.
・ Light source Solar simulator AM1.5G (100mW / cm ² )
-Electrolytic solution 0.5M Na ₂ SO ₄ , 0.25M Na ₂ HPO ₄ , 0.25M NaH ₂ PO ₄ pH 6.3
・ Reference electrode Ag / AgCl, counter electrode Pt wire ・ Argon atmosphere

As is clear from Table 1, the cathode current densities at 0.0 vs RHE by each photocatalytic electrode obtained in Examples 20 to 23 showed a high value of ^{1.0 mA / cm 2 or more.} On the other hand, the cathode current densities in Comparative Examples 8 and 9 were as low as less than ^{1 mA / cm 2.} From these, it can be seen that the photoelectrochemical properties are good when the heat treatment temperature is 450 ° C. to 750 ° C.

Claims (11)

A mixture of metal sulfides containing cuprous sulfide (Cu ₂ S), gallium sulfide (Ga ₂ S ₃ ), indium sulfide (In ₂ S ₃ ), and zinc sulfide (Zn S) in the presence of metal chloride. , 400 ° C. or higher, and heat-treated at 700 ° C. or less is dissolved in the metal chloride saw including a Rukoto grown crystals, melting point of the metal chloride is lower than the temperature of the heat treatment is represented by the following general formula A method for producing a metal compound having a sulfur pyrite type crystal structure.
General formula: Cu _x Ga _{x-y + k} In _{y + j} Zn _{2 (1-x) + mA 2 + n}
(In the above formula, x, y, k, j, m and n satisfy the following conditions (excluding those in which k = j = m = n = 0) , and A represents S or Se.
0 <x <1, 0 ≦ y ≦ 1, x> y, 0 ≦ k ≦ 0.2, 0 ≦ j ≦ 0.2,
0 ≦ m ≦ 0.2, 0 ≦ n ≦ 0.8, n = 3 / 2k + 3 / 2j + m) The production method according to claim 1, wherein k, j, m, and n satisfy at least one of the following requirements (α) to (δ).
(Α) 0.02 ≦ k ≦ 0.16
(β) 0.02 ≤ j ≤ 0.16
(γ) 0.02 ≤ m ≤ 0.16
(δ) 0.08 ≤ n ≤ 0.64 The production method according to claim 1 or 2, wherein the metal chloride is a eutectic molten salt composed of a mixture of two or more kinds. Claim that the metal chloride is a eutectic molten salt composed of a mixture of two or more selected from the group consisting of lithium chloride, sodium chloride, potassium chloride, cesium chloride, calcium chloride, strontium chloride, and barium chloride. The production method according to any one of 1 to 3. The metal chloride is at least one metal chloride selected from the group consisting of a eutectic molten salt composed of a mixture of lithium chloride and potassium chloride and a eutectic molten salt composed of a mixture of sodium chloride and cesium chloride. , The manufacturing method according to any one of claims 1 to 4. The production method according to any one of claims 1 to 5, wherein the metal chloride contains lithium chloride and potassium chloride. The production method according to claim 6 , wherein the molar ratio of lithium chloride to potassium chloride is 40:60 to 80:20. The production method according to any one of claims 1 to 7 , wherein the molar ratio of the metal chloride to the mixture of the metal sulfide is 1 or more and 20 or less. The metal constituting the metal chloride is a metal other than Cu, Ga, In and Zn.
The amount of impurities made of a metal derived from the metal chloride is less than 100 ppm of the mass of the metal compound having a chalcopyrite type crystal structure represented by the general formula, according to any one of claims 1 to 8. The manufacturing method described. A method for producing a photocatalyst containing a metal compound having a chalcopyrite type crystal structure represented by the following general formula.
A method for producing a photocatalyst, wherein the metal compound is produced by the production method according to any one of claims 1 to 9.
General formula: Cu _x Ga _{x-y + k} In _{y + j} Zn _{2 (1-x) + mA 2 + n}
(In the above formula, x, y, k, j, m and n satisfy the following conditions (excluding those in which k = j = m = n = 0) , and A represents S or Se.
0 <x <1, 0 ≦ y ≦ 1, x> y, 0 ≦ k ≦ 0.2, 0 ≦ j ≦ 0.2,
0 ≦ m ≦ 0.2, 0 ≦ n ≦ 0.8, n = 3 / 2k + 3 / 2j + m) A method for producing a photocatalyst complex containing a photocatalyst containing a metal compound having a chalcopyrite crystal structure represented by the following general formula, and at least one selected from the group consisting of a cocatalyst and a surface modifier.
The photocatalyst is produced by the production method according to claim 10.
The co-catalyst is at least one selected from the group consisting of ruthenium, platinum, iridium, palladium and gold, and is supported on the metal compound.
The surface modifier, CdS, comprising at least one selected from the group consisting of ZnS and an In ₂ S _3, and modifying the surface of the metal compound,
A method for producing a photocatalytic complex.
General formula: Cu _x Ga _{x-y + k} In _{y + j} Zn _{2 (1-x) + mA 2 + n}
(In the above formula, x, y, k, j, m and n satisfy the following conditions (excluding those in which k = j = m = n = 0) , and A represents S or Se.
0 <x <1, 0 ≦ y ≦ 1, x> y, 0 ≦ k ≦ 0.2, 0 ≦ j ≦ 0.2,
0 ≦ m ≦ 0.2, 0 ≦ n ≦ 0.8, n = 3 / 2k + 3 / 2j + m)

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