Photocatalyst plate, photocatalyst particle structure, and manufacturing method thereof

Abstract

To provide a photocatalyst plate which can highly efficiently express water decomposition activity under irradiation with light including visible light, and preferably, a photocatalyst plate which is hard, is excellent in transportability, storability and workability, and has a resin base material and a photocatalyst particle structure layer, in a photocatalyst particle structure.SOLUTION: A photocatalyst plate includes a photocatalyst particle layer including visible light responsive photocatalyst particles for hydrogen generation and visible light responsive photocatalyst particles for oxygen generation satisfying a particle diameter requirement in a specific range, and conductive carbon, and a resin base material, in which the photocatalyst particle layer and the resin base material are preferably bonded to each other by applying a pressurization load thereto. The photocatalyst plate has high water decomposition activity and suitable film strength.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present invention relates to a photocatalyst plate having visible light responsive water decomposition ability, which includes visible light responsive photocatalyst particles for generating hydrogen, visible light responsive photocatalyst particles for generating oxygen, a carbon compound, and a substrate, and to a photocatalyst particle structure including visible light responsive photocatalyst particles for generating hydrogen, visible light responsive photocatalyst particles for generating oxygen, and a carbon compound, and methods for manufacturing the same. [Background technology]

[0002] In recent years, there has been a great demand for the establishment of clean energy systems as a means of resolving environmental problems such as the depletion of fossil fuels and global warming, which are becoming increasingly serious. One such clean energy system that has attracted attention is "solar hydrogen production technology," which produces hydrogen by effectively utilizing solar energy to split water, and active development is underway on visible light-responsive photocatalysts, which are the key to this hydrogen production technology.

[0003] The method of using a photocatalyst fixed to a substrate as a form of water splitting does not require a stirring device, stirring energy, or a large container, compared to the method of using an aqueous solution in which photocatalyst particles are suspended, and is therefore suitable for enlarging the area of ​​hydrogen production equipment. From this perspective, it is important to develop a simple, low-cost technique for immobilizing photocatalyst particles.

[0004] Patent Document 1 and Patent Document 2 exemplify photocatalyst sheets including photocatalyst particles for hydrogen generation, photocatalyst particles for oxygen generation, conductive particles, and a substrate. In Patent Document 1, a baking process at 300°C is required to form a film and to exhibit good water splitting activity, which limits the photocatalysts and substrates that can be used. In fact, the photocatalysts used are limited to metal oxide photocatalysts, and there is no mention of the use of metal sulfide photocatalysts that have a wide absorption band in the visible light region. In this example, glass is used as the substrate because the baking process is included, and no embodiment using a lightweight and flexible resin substrate is disclosed. The tests performed on the strength of the film are limited to non-contact tests even in Patent Document 2, which includes a peeling prevention part, and no mention is made of contact tests such as scratching.

[0005] Patent Document 3 exemplifies a photocatalyst sheet that includes photocatalyst particles for hydrogen generation, photocatalyst particles for oxygen generation, and a conductive substrate, and is formed by roll pressing. In this example, the substrate is a conductive material, so this is limited to materials such as Ti and In that have specific work functions, making the sheet expensive.

[0006] Non-Patent Documents 1 and 2 exemplify photocatalyst sheets using a particle transfer method that includes photocatalyst particles for hydrogen generation and photocatalyst particles for oxygen generation, and a process of depositing a conductive material onto these. In this example, since it includes a vacuum process, it becomes expensive for large areas.

[0007] Non-Patent Document 3 exemplifies a photocatalyst sheet containing a total water-splitting photocatalyst, an inorganic binder (nanosilica), and a substrate. In this example, a baking process at 350°C is required to form a film and to achieve good water-splitting activity, and glass is used as the substrate. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 6073520 [Patent Document 2] JP 2018-122214 A [Patent Document 3] JP 2017-217623 A [Non-patent literature]

[0009] [Non-Patent Document 1] Nature Mater.,15,6,p.611(2016),K.Domen et al. [Non-Patent Document 2] J.Am.Chem.Soc.,139,4,p.1675(2017),K.Domen et al. [Non-Patent Document 3] Joule, 2, 3, p. 509 (2018), K. Domen et al. Summary of the Invention [Problem to be solved by the invention]

[0010] In order to generate hydrogen on a large scale by decomposing water with light, it is important to arrange a photocatalyst particle layer in a plate shape and simplify the transportation, storage, processing, and installation of the plate. Therefore, the light weight and flexibility of the plate and the adhesion between the photocatalyst particle layer and the plate substrate are important. When manufacturing a plate provided with a photocatalyst particle layer made of inorganic material, it is difficult to use an organic binder or an inorganic binder used in general film formation in order to obtain adhesion to the substrate. When a general organic binder is used, it may adhere to the surface of the photocatalyst particle and block the reactive active points on the surface of the photocatalyst particle, hindering the progress of the water decomposition reaction. When a general inorganic binder is used, it may also be a factor that covers the surface of the photocatalyst particle. For example, in a configuration in which an inorganic binder is used in the photocatalyst particle layer for Z-scheme water decomposition, it may be a factor that hinders contact between particles and contact between these particles and a conductive material. In this specification, "plate" or "plate-like" includes those that are not flexible and those that are flexible (including sheets and sheet-like).

[0011] For this reason, it is important to develop a technology for fixing a highly adherent photocatalytic particle layer onto an organic material substrate, including an organic material such as an inexpensive, lightweight, and flexible resin, without impairing the photocatalytic activity. However, there tends to be a trade-off between forming a highly adherent photocatalytic particle layer onto an organic material substrate and photocatalytic activity, and it is not currently known how to achieve both.

[0012] If the photocatalyst plate has a highly adherent photocatalyst particle layer, several photocatalyst plates can be stacked directly on top of each other in a rod-like form, or a large-area, long photocatalyst plate can be rolled up, making it easy to transport and store.

[0013] In addition, in a practical environment, it is problematic that the photocatalyst particle layer easily peels off due to friction when touching. In order to avoid friction, it is necessary to keep a space above the photocatalyst particle layer at all times during transportation, storage, processing, and installation. In such a case, it is particularly an obstacle to increasing the area of ​​the hydrogen production device.

[0014] In addition, high adhesion between the photocatalyst particle layer and the substrate is useful for maintaining the photocatalyst particle layer stable for a long period of time even when performing a water splitting reaction in water. In particular, if it becomes possible to provide a highly adhesive photocatalyst particle layer on a substrate such as PET, which is inexpensive, lightweight, flexible, and recyclable as a resource, it will be extremely beneficial for increasing the area of ​​hydrogen production equipment.

[0015] In order to provide a photocatalyst particle layer on a substrate, a non-heating process technology is required to fix the photocatalyst particle layer at a temperature lower than the heat resistance temperature of the substrate. Organic substrates such as resins generally have a lower heat resistance temperature than inorganic substrates, so fixing the photocatalyst particle layer tends to be difficult.

[0016] If it becomes possible to manufacture photocatalyst plates at low temperatures, the options for photocatalyst materials that make up the photocatalyst particle layer can be expanded. In particular, metal sulfide photocatalysts, which have a wide and strong absorption band in the visible light region, are at risk of undergoing oxidation and deterioration under high temperature conditions, so if a manufacturing method at low temperatures becomes possible, the options for photocatalyst materials can also be expanded.

[0017] Therefore, the problem that the present invention aims to solve is to provide a photocatalyst particle composition and photocatalyst plate that can efficiently carry out a visible light responsive Z-scheme type water splitting reaction by combining photocatalyst particles for hydrogen generation and photocatalyst particles for oxygen generation, on an organic material substrate such as a resin that is economical, lightweight and flexible, and that has a stable structure and excellent transportability, storability and processability. Another objective of the present invention is to provide a technology for manufacturing photocatalyst plates using materials such as metal sulfide photocatalyst-based photocatalyst materials and resin substrates that have a wide absorption band in the visible light region, without requiring a process in a highly controlled environment such as a vacuum or a low-temperature environment. [Means for solving the problem]

[0018] As a result of the investigations conducted by the present inventors to solve the above problems, it was found that the above problems can be solved by a photocatalyst particle structure including visible light responsive photocatalyst particles for generating hydrogen with a specific particle size, visible light responsive photocatalyst particles for generating oxygen, and carbon fine powder with a specific content relative to the visible light responsive photocatalyst particles for generating oxygen, a photocatalyst plate including the structure layer and an organic material substrate, and a method for manufacturing the same, and the present invention was completed. More specifically, the present invention has the following configuration.

[0019] [1] A photocatalyst particle structure including visible light responsive photocatalyst particles for generating hydrogen, visible light responsive photocatalyst particles for generating oxygen, a photocatalyst particle structure including carbon fine powder, and an organic material substrate; The primary particle size of the visible light responsive photocatalyst particles for generating hydrogen and the visible light responsive photocatalyst particles for generating oxygen is 0.05 μm or more and 50 μm or less, A photocatalyst plate in which the abundance ratio of the carbon fine powder is 0.1 wt % or more and 30 wt % or less with respect to visible light responsive photocatalyst particles for generating oxygen. [2] The photocatalyst plate according to [1], wherein the carbon fine powder is reduced graphene oxide (RGO). [3] The photocatalyst plate according to [1] or [2], wherein the visible light responsive photocatalyst particles for hydrogen generation include photocatalyst particles containing metal sulfide. [4] The photocatalyst plate according to any one of [1] to [3], wherein the visible light responsive photocatalyst particles for generating hydrogen contain a co-catalyst. [5] The primary particle size of the visible light responsive photocatalyst particles for oxygen generation is 0.05 μm or more and 5 μm or less, The photocatalyst plate according to any one of [1] to [4], wherein the primary particle size of the visible light responsive photocatalyst particles for generating hydrogen is 2 μm or more and 50 μm or less, and is 1.5 times or more and 500 times or less the primary particle size of the visible light responsive photocatalyst particles for generating oxygen. [6] The photocatalyst plate according to any one of [1] to [5], wherein a weight ratio of the visible light responsive photocatalyst particles for generating hydrogen to the visible light responsive photocatalyst particles for generating oxygen is 10 / 90 to 80 / 20. [7] A photocatalyst particle construct comprising visible light responsive photocatalyst particles for generating hydrogen, visible light responsive photocatalyst particles for generating oxygen, and carbon fine powder; The visible light responsive photocatalyst particles for hydrogen generation are 1.1 μm or more and 50 μm or less, The primary particle size of the visible light responsive photocatalyst particles for generating oxygen is 0.05 μm or more and 50 μm or less, The carbon fine powder is present in an amount of 0.1 wt % or more and 30 wt % or less relative to the visible light responsive photocatalyst particles for generating oxygen. [8] A method for producing a photocatalyst particle construct, comprising a step of contacting the visible light responsive photocatalyst particles for generating hydrogen described in [7], the visible light responsive photocatalyst particles for generating oxygen, and carbon fine powder, and then applying pressure. [9] A method for manufacturing a photocatalyst plate, comprising a step of contacting visible light responsive photocatalyst particles for generating hydrogen according to any one of [1] to [6], visible light responsive photocatalyst particles for generating oxygen, carbon fine powder, and a substrate, followed by applying pressure.

[10] The method for producing a photocatalyst plate according to [9], wherein the substrate is a resin substrate.

[11] The method for producing a photocatalyst plate according to [9], wherein the substrate is a resin substrate containing an inorganic compound layer. Effect of the Invention

[0020] The photocatalyst plate of the present invention, which is formed by including a layer containing photocatalyst particles and an organic material substrate, includes a layer of a photocatalyst particle structure containing visible light responsive photocatalyst particles for generating oxygen and visible light responsive photocatalyst particles for generating hydrogen with specific particle sizes, and a specific weight ratio of carbon fine powder. The carbon fine powder can, for example, function as a conductive material and, in the pressurizing process, as a binding material between particles and between the particle and the substrate.

[0021] These effects are particularly prominent when reduced graphene oxide (hereinafter sometimes referred to as RGO) is used as the carbon fine powder. For example, even without a high-temperature environment, the binding strength between reduced graphene oxide (RGO) and photocatalyst particles is improved by the pressurization process, which results in high activation of the water splitting reaction due to improved conductivity and a robust photocatalyst plate including the photocatalyst particle construct. This is one of the preferred embodiments.

[0022] In addition, for example, the photocatalyst plate obtained by the above method can exhibit high performance, even if it is a metal sulfide photocatalyst that has a high response to light in a wide visible light range, because it can exert its potential without losing its potential. In addition, the above organic material substrate is generally inexpensive, has excellent processability, and has characteristics that make it easy to apply to continuous processes such as roll-to-roll, so it can often be made into an easy-to-handle photocatalyst plate. The photocatalyst particle structure is naturally the main site for realizing the high water splitting reaction efficiency as described above, and therefore can realize the high water splitting performance by light as described above. [Brief description of the drawings]

[0023] [Figure 1A] Schematic diagram of photocatalyst particle structure [Figure 1B] Schematic diagram of photocatalyst particle structure [Figure 1C] Schematic diagram of photocatalyst particle structure [Figure 1D] Schematic diagram of photocatalyst particle structure [Figure 2A] Schematic diagram of photocatalyst plate [Figure 2B] Schematic diagram of photocatalyst plate [Figure 2C] Schematic diagram of photocatalyst plate [Figure 2D] Schematic diagram of photocatalyst plate [Diagram 3] Example of the arrangement of each part during the pressing process in the photocatalyst plate manufacturing process and explanation after pressing [Figure 4] Evaluation of photocatalytic function of photocatalytic plate using closed circulation system [Diagram 5] Example of arrangement of each part during the pressurizing process in the process of producing a photocatalyst particle structure and explanation after pressing [Figure 6] Evaluation of photocatalyst plate and photocatalyst particle composition using a closed circulation system [Figure 7A] Spectrum of Example 1 [Figure 7B] Spectrum of Example 1 [Figure 8] Photo of catalyst particles from Example 1 [Figure 9] Graph of water splitting reaction in Example 1 [Figure 10] Photocatalyst plate photo of Example 1 [Figure 11] Schematic diagram of the photocatalyst plate of Example 1 [Figure 12] Graph of water splitting reaction in Example 2 and photocatalyst plate surface photograph [Figure 13A] Photograph of catalyst particles from Example 3 [Figure 13B] Graph of water splitting reaction of catalyst particles and photocatalyst plate of Example 3 [Figure 13C] Photo of the photocatalyst plate of Example 3 [Figure 14A] Graph of water splitting reaction in Example 4 [Figure 14B] Photo of catalyst particles from Example 4 [Figure 15A] Diffuse reflectance spectrum, X-ray diffraction spectrum, and catalyst particle photograph of Example 5 [Figure 15B] Graph of water splitting reaction in Example 5, photo of photocatalyst plate and schematic diagram [Figure 16] Graph of water splitting reaction in Example 6 [Figure 17A]Photo of catalyst particles from Example 8 [Figure 17B] Graph of water splitting reaction in Example 8 [Figure 17C] Photocatalyst plate surface photograph of Example 8 [Figure 18] Graph of water splitting reaction in Example 9 [Figure 19] Photocatalyst plate surface photograph of Example 9 [Figure 20] Diffuse reflectance spectrum of catalyst particles of Example 11 [Figure 21] Diffuse reflectance spectrum of catalyst particles of Example 12 [Figure 22] Graph of diffuse reflectance spectrum and water splitting reaction of visible light responsive photocatalyst particles for hydrogen generation of Example 13 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The present invention will be described in detail below. The photocatalyst plate of the present invention includes visible light responsive photocatalyst particles for hydrogen generation having a specific particle size range, visible light responsive photocatalyst particles for oxygen generation having a specific particle size range, and carbon fine powder in a specific weight ratio, and preferably includes these members including a layer including a particle structure bound by pressure, and an organic material substrate. Reduced graphene oxide (RGO) is particularly suitable as the carbon fine powder. In this configuration, reduced graphene oxide (RGO) is a good conductive material and preferably functions as a binding material between the visible light responsive photocatalyst particles for hydrogen generation and the visible light responsive photocatalyst particles for oxygen generation, by applying pressure. This makes it possible to provide a state in which the photocatalyst particles are bound together even when they are suspended in a solvent, which facilitates electron transfer between the particles, which is necessary for a Z-scheme water splitting reaction, and ultimately makes it possible to form a photocatalyst particle construct that exhibits high water splitting activity.

[0025] The photocatalyst particle structure of the present invention includes visible light responsive photocatalyst particles for hydrogen generation having a specific particle size range, visible light responsive photocatalyst particles for oxygen generation having a specific particle size range, and carbon fine powder in a specific weight ratio. Reduced graphene oxide (RGO) is preferable as the carbon fine powder. The efficacy of such carbon fine particles is as described above.

[0026] The configurations of the photocatalyst plate and the photocatalyst particle structure and the manufacturing methods thereof will be described in detail below.

[0027] <Visible light responsive photocatalyst particles for hydrogen generation> The visible light responsive photocatalyst particles for generating hydrogen in the present invention are photocatalyst particles that, in response to irradiation with visible light in an aqueous solvent such as water in which visible light responsive photocatalyst particles for generating oxygen and carbon fine powder such as reduced graphene oxide (RGO) are present, generate oxygen on the visible light responsive photocatalyst particles for generating oxygen, for example, by exhibiting a hydrogen generation reaction associated with Z-scheme water decomposition.

[0028] The visible light responsive photocatalyst particles for generating hydrogen contained in the photocatalyst plate of the present invention may be any metal photocatalyst particles as long as they exhibit a hydrogen generating reaction. Representative examples of the visible light responsive photocatalyst particles for generating hydrogen according to the present invention include photocatalysts containing metal compounds, such as metal oxide photocatalysts, metal sulfide photocatalysts, metal oxysulfide photocatalysts, metal nitride photocatalysts, and metal oxynitride photocatalysts. It is also preferable that the metal photocatalyst particles contain a co-catalyst.

[0029] More specifically, suitable examples of visible light responsive photocatalyst particles for generating hydrogen in the present invention include photocatalysts and combinations of photocatalysts and co-catalysts for which hydrogen generation is recognized in Tables 4, 6, 8, and 9 in the literature Chem. Soc. Rev., 38, 1, p. 253 (2009), Y. Miseki, A. Kudo et al., photocatalysts and combinations of photocatalysts and co-catalysts for which hydrogen generation is recognized in Tables 1 and 2 in the literature Faraday Discussions, 215, p. 313 (2019), A. Kudo et al., and photocatalysts exemplified as photocatalysts on the hydrogen generation side in the section on the form for carrying out the invention in JP2016-55279A, but are not limited to these. The visible light responsive photocatalyst particles for generating hydrogen used in the present invention may be of a single component or may be of a combination of multiple types of photocatalysts.

[0030] <Visible light responsive metal sulfide photocatalyst for hydrogen generation> The visible light responsive photocatalyst particles for hydrogen generation in the present invention are preferably photocatalyst particles containing a metal sulfide. Visible light responsive photocatalyst particles for hydrogen generation that are metal sulfides tend to have a wide and strong light absorption band in the visible light region, and also tend to have excellent responsiveness. In addition to the above-mentioned literature, specific examples include Cu3MS4 (M = V, Nb, Ta) and its solid solution reported in literature ChemSusChem, 12, p. 1977 (2019), A. Kudo et al., and (CuGa) reported in literature J. Phys Chem. Lett., 6, 6,, p. 1042 (2015), A. Kudo et al. 1-x Zn2xS2, reported in Sustainable Energy Fuel, 2, p. 2016 (2018), A. Kudo et al. (CuGa 1-y In y ) 1-x Zinc 2x S2, Chem. Mater., 18, 7, p. 1969 (2006), A. Kudo et al. (CuAg) x In 2x Zinc 2(1-2x)S2, Cu reported in J. Mater. Chem. A, 3, p. 21815 (2015), A. Kudo et al. 1-x Ag x GaS2, and the names of the compounds described in the Examples. Such compounds can be synthesized not only by methods according to the above-mentioned documents, but also by combining the methods of these documents. They are capable of exhibiting high hydrogen generation reaction in response to visible light, and are therefore desirable as the visible light responsive metal sulfide photocatalyst for hydrogen generation in the present invention. The visible light responsive metal sulfide photocatalyst particles for hydrogen generation used in the present invention may be a single component or a combination of multiple types of photocatalysts. They may also be combined with photocatalyst particles that do not contain metal sulfide in their structure.

[0031] The primary particle size of the visible light responsive photocatalyst particles for hydrogen generation of the present invention is 0.05 μm or more and 50 μm or less. The preferred lower limit is 0.1 μm, more preferably 0.5 μm, even more preferably 1 μm, particularly preferably 1.1 μm, and especially preferably 2 μm. On the other hand, the preferred upper limit is 40 μm, more preferably 35 μm, even more preferably 30 μm, and particularly preferably 25 μm. The smaller the primary particle size, the larger the contact area between water and the photocatalyst, which increases the number of active sites for the water splitting reaction due to light irradiation, but if it is less than 0.05 μm, the crystallinity of the photocatalyst may decrease and sufficient pores may not be obtained between the particles, which may hinder the generation of gas. On the other hand, the larger the primary particle size, the better the crystallinity of the photocatalyst and the easier it is to obtain sufficient pores between the particles, but if it exceeds 50 μm, the surface area of ​​the photocatalyst particles may decrease and the film formation state may deteriorate when the photocatalyst particle layer is formed, which may reduce the catalytic activity.

[0032] Furthermore, the visible light responsive photocatalyst particles for hydrogen generation of the present invention have a primary particle size in the range of 2 μm to 50 μm, and is desirably 1.5 to 500 times the primary particle size of the visible light responsive photocatalyst particles for oxygen generation described later. In this case, the preferred lower limit of the primary particle size is 2.5 μm, more preferably 3 μm, even more preferably 3.5 μm, and particularly preferably 4 μm. On the other hand, the preferred upper limit is 40 μm, more preferably 35 μm, even more preferably 30 μm, and particularly preferably 25 μm. In addition, the preferred lower limit of the size of the visible light responsive photocatalyst particles for oxygen generation relative to the primary particle size is 2.5 times, while the preferred upper limit is 400 times, more preferably 300 times, even more preferably 250 times, and particularly preferably 200 times. In some cases, the primary particle size of the visible light responsive photocatalyst particles for hydrogen generation that is relatively larger than that of the visible light responsive photocatalyst particles for oxygen generation described later is more likely to obtain good water splitting activity. In the present invention, the primary particle size of the photocatalyst particles is measured using SEM images at 2000 to 20000 times magnification depending on the particle size, and the primary particle sizes of about 30 photocatalyst particles are measured and averaged to determine the primary particle size in the specification. If the particle size is visually determined to be uniform to a certain extent so that it is clearly within the scope of the claims of the present invention, the value of the primary particle size is determined by visually observing the SEM image and comparing it with the gauge on the image.

[0033] <Visible light responsive photocatalyst particles for oxygen generation> The visible light responsive photocatalyst particles for generating oxygen of the present invention are photocatalyst particles that exhibit an oxygen generation reaction, preferably involving Z-scheme water decomposition, in response to irradiation with visible light in an aqueous solvent in which carbon fine particles, preferably reduced graphene oxide (RGO), are present, and that generate hydrogen on the visible light responsive photocatalyst particles for generating hydrogen.

[0034] Typical compositions of visible light responsive photocatalyst particles for generating oxygen are BiVO4 and TiO2, with BiVO4 being particularly typical. However, any composition of metal photocatalyst particles that exhibit an oxygen generating reaction when configured as visible light responsive photocatalyst particles for generating oxygen in the photocatalyst plate of the present invention or in the photocatalyst particle construct described below may be used, and examples of such metal photocatalyst particles include BiVO4:Mo, which is Mo-doped BiVO4, and TiO2 doped with titanium elements Rh and Sb. In addition, it is a preferred embodiment that the visible light responsive catalyst particles for generating oxygen of the present invention are used in combination with a co-catalyst. The activity of the water splitting reaction may be improved by combining with a co-catalyst. A specific example of the above combination is a preferred embodiment in which a co-catalyst is supported on the visible light responsive catalyst particles for generating oxygen. In addition, in the present invention, the embodiment in which the visible light responsive catalyst particles for generating hydrogen or the visible light responsive catalyst particles for generating oxygen are combined with a co-catalyst may be referred to as metal photocatalyst particles or photocatalyst particles.

[0035] More specifically, examples of visible light responsive photocatalyst particles for generating oxygen include, but are not limited to, combinations of photocatalysts and co-catalysts for which oxygen generation is recognized in Tables 4, 6, 8, and 9 in the literature Chem. Soc. Rev., 38, 1, p. 253 (2009), Y. Miseki, A. Kudo et al., combinations of photocatalysts and co-catalysts for which oxygen generation is recognized in Tables 1 and 2 in Faraday Discussions, 215, p. 313 (2019), A. Kudo et al., and photocatalysts exemplified as photocatalysts on the oxygen generation side in the section on the form for implementing the invention in JP 2016-55279 A. The visible light responsive photocatalyst particles for generating oxygen used in the present invention may be a single component or a mixture of multiple types of photocatalysts.

[0036] The primary particle size of the visible light responsive photocatalyst particles for oxygen generation of the present invention is 0.05 μm or more and 50 μm or less. The lower limit is preferably 0.07 μm, more preferably 0.1 μm, even more preferably 0.15 μm, and particularly preferably 0.17 μm. On the other hand, the upper limit is preferably 40 μm, more preferably 35 μm, even more preferably 33 μm, particularly preferably 30 μm, and especially preferably 25 μm. The smaller the primary particle size, the larger the contact area between water and the photocatalyst, which increases the number of active sites for the water splitting reaction caused by light irradiation, but if it is below 0.05 μm, the crystallinity of the photocatalyst may decrease and sufficient pores may not be obtained between the particles, which may hinder the generation of gas. On the other hand, the larger the primary particle size, the better the crystallinity of the photocatalyst and the easier it is to obtain sufficient pores between the particles, but if it exceeds 50 μm, it may result in a decrease in the surface area of ​​the photocatalyst particles and a deterioration in the film formation state when forming the photocatalyst particle layer.

[0037] In the present invention, there is no particular limitation on the weight ratio of the visible light responsive photocatalyst particles for hydrogen generation and the visible light responsive photocatalyst particles for oxygen generation. The ratio can be selected according to the performance of each catalyst particle. The specific preferred weight ratio range is as follows. The weight ratio of the visible light responsive photocatalyst particles for generating hydrogen to the visible light responsive photocatalyst particles for generating oxygen is preferably in the range of 10 / 90 to 80 / 20. The lower limit is more preferably 15 / 85, and even more preferably 20 / 80. On the other hand, the upper limit is more preferably 70 / 30, even more preferably 65 / 35, and particularly preferably 60 / 40.

[0038] <Carbon fine powder, reduced graphene oxide (RGO)> The carbon particles used in the present invention are not particularly limited, but are preferably reduced graphene oxide (RGO). RGO is a conductive material obtained by reducing graphene oxide (hereinafter, sometimes referred to as GO), in which functional groups such as epoxy groups, carboxyl groups, carbonyl groups, and hydroxyl groups are bonded to a monolayer of graphite. The graphene oxide (GO) used as the raw material can be produced by a method described in J. Am. Chem. Soc., 80, p. 1339 (1958), W.S. Shummers et al., but is not limited thereto.

[0039] Examples of commercially available graphene oxide (GO) include, but are not limited to, powders such as Rap dGO (TQ-11) manufactured by Nishina Materials, 796034 manufactured by Sigma-Aldrich, and G0443 manufactured by Tokyo Chemical Industry Co., Ltd., and aqueous dispersions of the powder such as Rap GO (TQ-2), Rap GO (TQ-2pure), Rap GO (TQ-11), Rap eGO (TQ-11), Rap bGO (TQ-11), 777676 manufactured by Sigma-Aldrich, and G0444 manufactured by Tokyo Chemical Industry Co., Ltd.

[0040] The reduced graphene oxide (RGO) used in the present invention can be produced by a method such as that described in Chem. Soc. Rev., 43, 1, p. 291 (2014), M. Pumera et al., but is not limited thereto. Commercially available reduced graphene oxide (RGO) powders include, but are not limited to, Rap rGO (TQ-11) manufactured by Nishina Materials Co., Ltd., and 777684, 805424, and 805084 manufactured by Sigma-Aldrich.

[0041] The reduced graphene oxide (RGO) used in the present invention may be a pre-produced product that is combined with the visible light responsive photocatalyst particles for hydrogen generation or the visible light responsive photocatalyst particles for oxygen generation. Alternatively, as described in the examples of the present invention, a method may be used in which the photocatalyst particles constituting a photocatalyst particle construct or a photocatalyst plate described later and graphene oxide (GO) are suspended in a medium and irradiated with light to prepare reduced graphene oxide (RGO) in the photocatalyst particles by photoreduction.

[0042] In the present invention, the carbon fine particles are contained in the visible light responsive photocatalyst particles for oxygen generation at a ratio of 0.1 wt% to 30 wt%. The lower limit is preferably 0.5 wt%, more preferably 0.8 wt%, and even more preferably 1.0 wt%. On the other hand, the upper limit is preferably 25 wt%, more preferably 20 wt%, even more preferably 17 wt%, and particularly preferably 15 wt%. If the content is less than 0.1 wt%, the electrical conductivity and binding properties described below may be insufficient, while if it exceeds 30 wt%, the proportion of visible light absorbed by RGO increases, and the water splitting reactivity may be insufficient. In this specification, specific examples of "carbon fine powder" include RGO, as described above. In addition, it may be fine powder made of not only carbon (C) but also carbon compounds containing carbon and heteroatoms such as oxygen. In this specification, "carbon fine powder" may be referred to as carbon particles, carbon fine particles, etc.

[0043] <Visible light responsive photocatalyst particles for oxygen generation with added reduced graphene oxide (RGO)> As an example, the photocatalyst plate of the present invention and the photocatalyst particle construct described later preferably include preformed visible light responsive photocatalyst particles for oxygen generation, including reduced graphene oxide (RGO), as a component. The method of combining reduced graphene oxide (RGO) with visible light responsive photocatalyst particles for oxygen generation is not particularly limited, but a preferred example is an addition method that utilizes a generation reaction of reduced graphene oxide (RGO) by irradiating a suspension of visible light responsive photocatalyst particles for oxygen generation and graphene oxide (GO) with light in the presence of a sacrificial reagent as described in the examples of the present invention. The addition method of reduced graphene oxide (RGO) to visible light responsive photocatalyst particles for oxygen generation BiVO4 is reported in the literature J.Am.Chem.Soc.,133,29,p.11054(2011), A.Iwase,A.Kudo et al.

[0044] <Organic material base material> The organic material substrate used in the present invention is not particularly limited as long as it does not impair the photocatalytic function when used in combination with photocatalytic particles, and does not impair the object of the present invention. Preferably, it has one or more of the following functions: it is not broken in the pressurizing process described below, it has affinity with the photocatalytic particle structure, and it has flexibility that allows roll-to-roll processing. Furthermore, it is self-evident that it is preferable for the material to be inexpensive and lightweight. If an inexpensive, lightweight, and flexible resin substrate is used, it is advantageous in terms of transportation, storage, processing, etc., and it is possible to provide a photocatalytic plate that is economical in terms of the problem of large area. The organic material substrate as described above is preferably a resin substrate, and specifically, polyethylene terephthalate (PET), polycarbonate (PC), polyethylene (PE), polypropylene (PP), polyethylene naphthalate (PEN), polyester (PEs), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), acrylic (PMMA), polystyrene (PS), fluororesin (PTFE), polyimide (PI), polyamide (PA), ABS resin, etc. are given as preferred examples. The organic material substrate preferably has a layer of a conductive material. Examples of the conductive material include gold, silver, conductive carbon, ITO, and FTO layers. In addition, a preferred embodiment includes a peel-prevention layer on the surface of the organic material substrate. Specific examples of the peel-prevention layer include an adhesive resin layer and a matte finish (matte finish). In addition, a layer of a material with a low melting point or glass transition temperature, a layer of a material with a high polarity, or a layer of a material with a low elastic modulus can be formed to function as a fusion, welding, or pressure-bonding layer.

[0045] <Co-catalyst> As described above, it is preferable to use a co-catalyst in the visible light responsive photocatalyst particles for hydrogen generation and the visible light responsive photocatalyst particles for oxygen generation of the present invention. As such a co-catalyst, a known co-catalyst component can be used without any restrictions. Specifically, for the visible light responsive photocatalyst particles for hydrogen generation, term table For visible light responsive photocatalyst particles for oxygen generation, such as metal components of Groups 8 to 11, term tableExamples of the oxides include oxides of metals in Groups 8 to 11 of the above. The weight ratio of the visible light responsive photocatalyst particles for generating hydrogen and the visible light responsive photocatalyst particles for generating oxygen is not particularly limited as long as it is within a known range. Specific examples of suitable co-catalysts for visible light responsive photocatalyst particles for generating hydrogen include components containing ruthenium, platinum, gold, rhodium, nickel, etc. Most preferred is ruthenium. Specific examples of suitable co-catalysts for visible light responsive photocatalyst particles for generating oxygen include metal oxides such as cobalt oxide, iridium oxide, iron oxide, and manganese oxide. The particle size of the promoter used in the present invention is preferably smaller than the particle size of the visible light responsive photocatalyst particles for generating hydrogen and the visible light responsive photocatalyst particles for generating oxygen.

[0046] <Photocatalyst particle composition and its manufacturing method> The photocatalyst particle structure in the present invention is a structure containing visible light responsive photocatalyst particles for hydrogen generation, visible light responsive photocatalyst particles for oxygen generation, and carbon fine powder. For example, a preferred embodiment is a particle structure in which these three members are bonded by pressure, and a more preferred embodiment is a particle structure in which the visible light responsive photocatalyst particles for hydrogen generation, the visible light responsive photocatalyst particles for oxygen generation, and the carbon fine powder are contacted and then bonded by pressure. The visible light responsive photocatalyst particles for hydrogen generation, the visible light responsive photocatalyst particles for oxygen generation, and the carbon fine powder are the same as the materials introduced in the photocatalyst plate. However, the photocatalyst particle structure preferably has a lower limit of the particle diameter of the visible light responsive photocatalyst particles for hydrogen generation of 1.1 μm. In addition, as described above, reduced graphene oxide (RGO) is particularly suitable as the carbon fine powder. In this specification, the "photocatalyst particle structure" may be referred to as a photocatalyst particle structure, a photocatalyst particle structure layer, a photocatalyst particle structure layer, a photocatalyst particle layer, etc.

[0047] A preferred application of the photocatalyst particle structure of the present invention is the photocatalyst particle structure layer in the above-mentioned photocatalyst plate. However, the application is not limited to the above, and for example, the photocatalyst particle structure alone can be used as a water splitting catalyst. In this case, one example is to use it in the form of a tablet using a tablet molding method as described below. In the above-mentioned bonding method using visible light responsive photocatalyst particles for generating hydrogen, visible light responsive photocatalyst particles for generating oxygen, and carbon fine powder, there is no particular restriction on the order in which the components are brought into contact with each other, for example, mixed, and the photocatalyst particle construct may be formed by pressing a mixture of these three components together at once, or a process in which the components are formed in order may be used. One example is a process in which reduced graphene oxide (RGO) is added to form visible light responsive photocatalyst particles for oxygen generation, and then visible light responsive photocatalyst particles for hydrogen generation are brought into contact with the particles, e.g., mixed, and then pressurized to form a photocatalyst particle construct.

[0048] The pressure in the pressurizing step may be any pressure, but is preferably 0.1 to 10 ton f / cm 2 A more preferable lower limit is 0.2 ton f / cm 2 , and more preferably 0.3 tonnes f / cm 2 On the other hand, a more preferable upper limit is 7 ton f / cm 2 , and more preferably 5 tonnes f / cm 2 , particularly preferably 4 tonnes f / cm 2 If the pressure is too low, the binding strength of each component may be insufficient, resulting in insufficient strength of the structure. On the other hand, if the pressure is too high, various catalyst component particles may collapse, and when an organic material substrate is used in combination, the substrate may be damaged.

[0049] The method of pressurization is not particularly limited, but includes a method using a hydraulic press and a tablet molding machine. After filling a tablet molding machine with a mixture of the above three components, pressurize it with a hydraulic press, and then crush the contents with a mortar or the like to produce a photocatalyst particle construct. In this case, if a process is added in which a paste in which the three components are dispersed in a dispersion medium is prepared and then coated and dried on a suitable substrate to form a photocatalyst particle layer, a photocatalyst particle construct in which each component is homogeneously mixed can be easily formed. As the dispersion medium used in preparing the paste, any known medium can be used without limitation within a range that does not impair the functions of the present invention, which are the visible light responsive photocatalyst particles for generating hydrogen, the visible light responsive photocatalyst particles for generating oxygen, and the carbon fine powder. Specifically, examples of the dispersion medium include alcohols such as methanol, ethanol, propanol, butanol, and hexanol, ethers such as diethyl ether and dibutyl ether, ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, liquid hydrocarbons such as hexane, heptane, octane, and decane, and commercially available silicones. Among these, polar compounds having a heteroatom are preferred, alcohols are more preferred, and ethanol and butanol are particularly preferred.

[0050] The composition of the paste is preferably 1 to 50 grams / liter (g / L) as a ratio of the weight of the components constituting the photocatalyst particles including the visible light responsive photocatalyst particles for generating hydrogen, the visible light responsive photocatalyst particles for generating oxygen, and the carbon fine powder to the volume of the medium. A more preferred lower limit is 2 g / L, even more preferred is 4 g / L, and particularly preferred is 5 g / L, while a more preferred upper limit is 40 g / L, even more preferred is 35 g / L, and particularly preferred is 20 g / L.

[0051] Furthermore, during this process, it is preferable to apply pressure to the photocatalyst particle layer via a release film. For example, a resin film coated with an inorganic compound such as ITO is used as the release film, and the method of applying pressure by contacting this coated surface with the photocatalyst particle layer is effective because it does not transfer the photocatalyst particles to the pressure-applied surface.

[0052] FIG. 5 shows an example of the arrangement of each member during the pressurizing step in the process of producing a photocatalyst particle structure, and an explanation of the state after pressing.

[0053] Schematic diagrams corresponding to the photocatalyst particle construct of the present invention are shown in Figs. 1A to 1D (Fig. 1-1) to (Fig. 1-22). (Figure 1-1) is a schematic diagram of a photocatalyst particle construct in which reduced graphene oxide (RGO) is evenly distributed and aggregated in photocatalyst particles for hydrogen generation and photocatalyst particles for oxygen generation with equivalent primary particle size. (Figure 1-2) is a schematic diagram of a photocatalyst particle construct in which reduced graphene oxide (RGO) is unevenly distributed and aggregated around the photocatalyst particles for oxygen generation, when the photocatalyst particles for hydrogen generation and the photocatalyst particles for oxygen generation have the same primary particle size. (Figure 1-3) is a schematic diagram of a photocatalyst particle construct in which reduced graphene oxide (RGO) is unevenly distributed and aggregated around the photocatalyst particles for hydrogen generation and oxygen generation, respectively, for photocatalyst particles for hydrogen generation and photocatalyst particles for oxygen generation of equivalent primary particle size. (Figure 1-4) is a schematic diagram of a photocatalyst particle construct in which reduced graphene oxide (RGO) is evenly distributed and aggregated among photocatalyst particles for hydrogen generation with a small primary particle size and photocatalyst particles for oxygen generation with a large primary particle size. (Figure 1-5) is a schematic diagram of a photocatalyst particle construct in which reduced graphene oxide (RGO) is evenly distributed and aggregated among photocatalyst particles for hydrogen generation with a large primary particle size and photocatalyst particles for oxygen generation with a small primary particle size. (Figure 1-6) is a schematic diagram of a photocatalyst particle structure in which reduced graphene oxide (RGO) is unevenly distributed around the photocatalyst particles for hydrogen generation, while the photocatalyst particles for oxygen generation have a large primary particle size and are aggregated together. (Figure 1-7) is a schematic diagram of a photocatalyst particle structure in which reduced graphene oxide (RGO) is unevenly distributed around the photocatalyst particles for oxygen generation, which are aggregated with photocatalyst particles for hydrogen generation that have a large primary particle size and photocatalyst particles for oxygen generation that have a small primary particle size. (Figure 1-8) is a schematic diagram of a photocatalyst particle composition in which reduced graphene oxide (RGO) is unevenly distributed and aggregated around the photocatalyst particles for hydrogen generation, which have a small primary particle size, and the photocatalyst particles for oxygen generation, which have a large primary particle size. (Figure 1-9) is a schematic diagram of a photocatalyst particle composition in which reduced graphene oxide (RGO) is unevenly distributed and aggregated around the photocatalyst particles for oxygen generation, which have a large primary particle size and a small primary particle size, respectively. (Figure 1-10) is a schematic diagram of a photocatalyst particle composition in which reduced graphene oxide (RGO) is unevenly distributed and aggregated around the photocatalyst particles for oxygen generation, with the photocatalyst particles for hydrogen generation having a small primary particle size and the photocatalyst particles for oxygen generation having a large primary particle size. (Figure 1-11) is a schematic diagram of a photocatalyst particle composition in which reduced graphene oxide (RGO) is unevenly distributed and aggregated around the photocatalyst particles for hydrogen generation, which have a large primary particle size, and the photocatalyst particles for oxygen generation, which have a small primary particle size. (Figure 1-12) is a schematic diagram of a photocatalyst particle construct in which reduced graphene oxide (RGO) is evenly distributed and aggregated for two types of photocatalyst particles for hydrogen generation and two types of photocatalyst particles for oxygen generation with equivalent primary particle size. (Figure 1-13) is a schematic diagram of a photocatalyst particle structure in which reduced graphene oxide (RGO) is unevenly distributed around the photocatalyst particles for oxygen generation, and the photocatalyst particles for oxygen generation preferentially aggregate, for photocatalyst particles for hydrogen generation and photocatalyst particles for oxygen generation of equivalent primary particle size. (Figure 1-14) is a schematic diagram of a photocatalyst particle structure in which reduced graphene oxide (RGO) is unevenly distributed around the photocatalyst particles for hydrogen generation and photocatalyst particles for oxygen generation of equivalent primary particle size, and the photocatalyst particles for hydrogen generation preferentially aggregate. (Figure 1-15) is a schematic diagram of a photocatalyst particle structure in which reduced graphene oxide (RGO) is evenly distributed on isolated photocatalyst particles for oxygen generation with a large primary particle size to which photocatalyst particles for hydrogen generation with a small primary particle size are attached. (Figure 1-16) is a schematic diagram of a photocatalyst particle structure in which reduced graphene oxide (RGO) is evenly distributed on an isolated photocatalyst particle for hydrogen generation with a large primary particle size to which photocatalyst particles for oxygen generation with a small primary particle size are attached. (Figure 1-17) is a schematic diagram of a photocatalyst particle structure in which reduced graphene oxide (RGO) is unevenly distributed and aggregated around the small primary particle size of the photocatalyst particles for hydrogen generation, while the large primary particle size of the photocatalyst particles for oxygen generation are isolated. (Figure 1-18) is a schematic diagram of a photocatalyst particle structure in which reduced graphene oxide (RGO) is unevenly distributed and aggregated around the small primary particle size photocatalyst particles for oxygen generation, while the large primary particle size photocatalyst particles for hydrogen generation are isolated. (Figure 1-19) is a schematic diagram of a photocatalyst particle structure in which reduced graphene oxide (RGO) is unevenly distributed around the photocatalyst particle for hydrogen generation, while an isolated photocatalyst particle for oxygen generation with a large primary particle size is attached to the photocatalyst particle for hydrogen generation with a small primary particle size. (Figure 1-20) is a schematic diagram of a photocatalyst particle structure in which reduced graphene oxide (RGO) is unevenly distributed around an isolated photocatalyst particle for hydrogen generation with a large primary particle size to which photocatalyst particles for oxygen generation with a small primary particle size are attached. (Figure 1-21) is a schematic diagram of a photocatalyst particle structure in which reduced graphene oxide (RGO) is unevenly distributed on isolated photocatalyst particles for oxygen generation with large primary particle size, and photocatalyst particles for hydrogen generation with small primary particle size are attached to the particles. (Figure 1-22) is a schematic diagram of a photocatalyst particle structure in which reduced graphene oxide (RGO) is unevenly distributed on isolated photocatalyst particles for hydrogen generation with large primary particle size, and photocatalyst particles for oxygen generation with small primary particle size are attached to the particles.

[0054] <Photocatalyst plate and its manufacturing method> As described above, the photocatalyst plate of the present invention includes a substrate in addition to visible light responsive photocatalyst particles for hydrogen generation, visible light responsive photocatalyst particles for oxygen generation, and reduced graphene oxide (RGO). A preferred manufacturing method is a method in which these four components are bonded by pressure to form a photocatalyst plate. The preferred range of pressure when pressurized is as described above. There is no particular restriction on the order of bonding, and the photocatalyst plate may be formed by pressing the assembled body of these four members together at once, or a process of forming them in order may be used.

[0055] Further, a second or more photocatalyst particle layers are added to the surface of the photocatalyst particle layer of the photocatalyst plate formed in this step, and the resulting structure is pressed to form a photocatalyst plate. In this case, the additional photocatalyst particle layer may be composed of photocatalyst particles having a different composition or form from the other photocatalyst particle layers.

[0056] One example is a process in which visible light responsive photocatalyst particles for oxygen generation are first formed by adding reduced graphene oxide (RGO), and then visible light responsive photocatalyst particles for hydrogen generation are mixed in, and the mixture is then formed into a photocatalyst particle layer on the surface of a substrate, and pressure is applied to the resulting structure to form a photocatalyst plate.

[0057] Another example is a process in which only visible light responsive photocatalyst particles for hydrogen generation are first formed as a photocatalyst particle layer on the surface of a substrate, and then visible light responsive photocatalyst particles for oxygen generation are formed as a photocatalyst particle layer on the surface of the substrate, and the resulting structure is pressurized to form a photocatalyst plate.Furthermore, the process is repeated multiple times to form a film and pressurize to form a photocatalyst plate.

[0058] When forming a photocatalyst plate in which multiple photocatalyst particle layers are stacked and formed, pressure may be applied sequentially as each layer is formed, or pressure may be applied all at once after all layers have been formed.

[0059] The photocatalyst particle layer may be disposed on only one side of the substrate, or on both sides. When the photocatalyst particle layer is disposed on both sides, the composition type, weight, and pressure load of each layer may be different.

[0060] The method of applying pressure in the production of the photocatalyst plate of the present invention is not particularly limited, but examples thereof include a method of applying pressure to a base material on which a photocatalyst particle layer is arranged using a press, and a method of applying pressure by roll-to-roll pressing.

[0061] By adding a step of preparing a paste in which the components that form the photocatalyst particle layer are dispersed in a solvent, and applying and drying the paste on the substrate, it becomes easier to form a photocatalyst particle layer in which the components are homogeneously mixed. As an example, a method using a hydraulic press and a tablet molding machine is tentatively given. The tablet molding machine is filled with a base material on which a photocatalyst particle layer is arranged, and the base material is pressed with the hydraulic press to produce a photocatalyst plate.

[0062] Furthermore, during this process, it is preferable to apply pressure to the photocatalyst particle layer via a release film. For example, a resin film coated with an inorganic compound such as ITO is used as the release film, and the method of applying pressure by contacting this coated surface with the photocatalyst particle layer is effective because it does not transfer the photocatalyst particles to the pressure-applied surface.

[0063] An example of the arrangement of each part during the pressing step in the process of making a photocatalyst plate and an explanation of the part after pressing are shown in FIG.

[0064] Schematic diagrams corresponding to the photocatalyst plate of the present invention are shown in Figs. 2A to 2D (Fig. 2-1) to (Fig. 2-15). FIG. 2-1 is a schematic diagram of a photocatalyst plate having a photocatalyst particle layer on one side of a substrate. (Figure 2-1-1) is a schematic diagram of a photocatalyst plate having photocatalyst particles for hydrogen generation and photocatalyst particles for oxygen generation with equivalent primary particle sizes, and a photocatalyst particle layer in which reduced graphene oxide (RGO) is unevenly distributed around the photocatalyst particles for oxygen generation, as an example of (Figure 2-1). (Figure 2-1-2) is a schematic diagram of a photocatalyst plate having a photocatalyst particle layer configured as an example of (Figure 2-1), in which photocatalyst particles for hydrogen generation with a large primary particle size are aggregated with photocatalyst particles for oxygen generation with a small primary particle size, and reduced graphene oxide (RGO) is unevenly distributed around the photocatalyst particles for oxygen generation. (Figure 2-1-3) is a schematic diagram of a photocatalyst plate, as an example of (Figure 2-1), having a photocatalyst particle layer configured with photocatalyst particles for hydrogen generation with a large primary particle size, photocatalyst particles for oxygen generation with a small primary particle size, and reduced graphene oxide (RGO) unevenly distributed around the photocatalyst particles for oxygen generation. FIG. 2-2 is a schematic diagram of a photocatalyst plate having two photocatalyst particle layers on one side of a substrate, the layers differing in composition, primary particle size, distribution, and other configurations. FIG. 2-3 is a schematic diagram of a photocatalyst plate having photocatalyst particle layers on both sides of a substrate. FIG. 2-4 is a schematic diagram of a photocatalyst plate having photocatalyst particle layers with different compositions, primary particle diameters, distributions, etc. on both sides of a substrate. FIG. 2-5 is a schematic diagram of a photocatalyst plate having a photocatalyst particle layer for generating hydrogen on one side of a substrate, and a photocatalyst particle layer for generating oxygen on the upper layer. FIG. 2-6 is a schematic diagram of a photocatalyst plate having a layer of photocatalyst particles for oxygen generation on one side of a substrate, and a layer of photocatalyst particles for hydrogen generation on the upper layer. (Figure 2-5-1) is a schematic diagram of a photocatalyst plate having a layer of photocatalyst particles for hydrogen generation with large primary particle size, photocatalyst particles for oxygen generation with small primary particle size aggregated on the upper layer, and reduced graphene oxide (RGO) unevenly distributed around the photocatalyst particles for oxygen generation, as an example of (Figure 2-5). FIG. 2-7 is a schematic diagram of a photocatalyst plate having a layer of photocatalyst particles for generating hydrogen on one side of a substrate, and a layer of photocatalyst particles for generating oxygen on the upper layer. (Figure 2-8) is a schematic diagram of a photocatalyst plate having a first photocatalyst particle layer for hydrogen generation on one side of a substrate, a first photocatalyst particle layer for oxygen generation on the layer above that, a photocatalyst particle layer for hydrogen generation different in composition, primary particle size, distribution, etc. from the first photocatalyst particle layer for hydrogen generation on the layer above that, and a photocatalyst particle layer for oxygen generation different in composition, primary particle size, distribution, etc. from the first photocatalyst particle layer for oxygen generation. (Figure 2-9) is a schematic diagram of a photocatalyst plate having a photocatalyst particle layer for hydrogen generation on one side of a substrate and a photocatalyst particle layer for oxygen generation on the back side of the substrate (the substrate is porous). (Figure 2-10) is a schematic diagram of a photocatalyst plate having a photocatalyst particle layer for hydrogen generation on one side of the substrate, a photocatalyst particle layer for oxygen generation on the upper layer thereof, a photocatalyst particle layer for oxygen generation on the back side of the substrate, and a photocatalyst particle layer for hydrogen generation on the upper layer thereof. FIG. 2-11 is a schematic diagram of a photocatalyst plate having a photocatalyst particle layer for generating hydrogen on each side of a substrate, and a photocatalyst particle layer for generating oxygen on each of the layers above that. (Figure 2-12) is a schematic diagram of a photocatalyst plate having a photocatalyst particle layer for hydrogen generation on one side of a substrate, a photocatalyst particle layer for oxygen generation on the upper layer, a photocatalyst particle layer for oxygen generation on the back side of the substrate whose composition, primary particle size, distribution, etc. differ from that of the front side, and a photocatalyst particle layer for hydrogen generation on the upper layer whose composition, primary particle size, distribution, etc. differ from that of the front side. (Figure 2-13) is a schematic diagram of a photocatalyst plate having a photocatalyst particle layer on one side of a substrate with a reduced graphene oxide (RGO) layer interposed therebetween. (Figure 2-13-1) is a schematic diagram of a photocatalyst plate having a photocatalyst particle layer configured as an example of (Figure 2-13), in which photocatalyst particles for hydrogen generation with large primary particle size and photocatalyst particles for oxygen generation with small primary particle size aggregated therewith, and reduced graphene oxide (RGO) is unevenly distributed around the photocatalyst particles for oxygen generation and at the interface between the substrate and the photocatalyst particles for hydrogen generation. (Figure 2-14) is a schematic diagram of a photocatalyst plate having a photocatalyst particle layer for hydrogen generation on one side of a substrate, a reduced graphene oxide (RGO) layer, and a photocatalyst particle layer for oxygen generation on the upper layer. (Figure 2-15) is a schematic diagram of a photocatalyst plate having a photocatalyst particle layer for hydrogen generation on one side of a substrate, with a reduced graphene oxide (RGO) layer sandwiched between the photocatalyst particle layer for oxygen generation and a photocatalyst particle layer on top of that. (Figure 2-14-1) is a schematic diagram of a photocatalyst plate having a photocatalyst particle layer for hydrogen generation and a photocatalyst particle layer for oxygen generation of equivalent primary particle size as an example of (Figure 2-14), and a photocatalyst particle layer in which reduced graphene oxide (RGO) is unevenly distributed at the interface between the photocatalyst particle layer for hydrogen generation and the photocatalyst particles for oxygen generation. EXAMPLES

[0065] The present invention will be described below based on examples, but the present invention is not limited thereto.

[0066] Example 1 (Example 1: Examining the effect of the presence or absence of reduced graphene oxide (RGO) and the effect of pressure load during film formation on water splitting activity and film strength in a photocatalyst plate containing Cu3VS4 for hydrogen generation and BiVO4 for oxygen generation as visible light responsive photocatalyst particles)

[0067] Example 1-1 (Preparation of visible light responsive photocatalyst particles for hydrogen generation) Ru-loaded Cu3VS4 (Ru / Cu3VS4) was prepared as a visible light responsive photocatalyst particle for hydrogen generation containing metal sulfide in its structure as follows.

[0068] (Synthesis of photocatalyst particles Cu3VS4) The synthesis of photocatalyst particles Cu3VS4 was in accordance with the synthesis method described in ChemSusChem, 12,9, p.1977 (2019), A.Kudo et al. and JP2018-58732A. The raw materials CuS, V2S3, and S were mixed in a ratio of 3 / 1.1 / 8 (V element 10% excess, S element 100% excess condition), and the target product was obtained by solid-phase synthesis in a degassed sealed ampoule at 650°C for 10 hours. The DRS (diffuse reflectance spectrum), XRD pattern, and SEM observation image of the photocatalyst obtained by this synthesis method are shown in Figures 7A to 7B (Figure 101-1-1), (Figure 101-2-1), and Figure 8 (Figure 101-3-1), respectively. DRS (diffuse reflectance spectrum) shows that the photocatalyst particles Cu3VS4 have an absorption band over the entire visible light range up to a wavelength of 800 nm. SEM observation images show that the primary particle size of the synthesized photocatalyst particles Cu3VS4 is about 5 to 10 μm.

[0069] (Preparation of photocatalyst particles Ru-loaded Cu3VS4 (Ru / Cu3VS4)) The photocatalyst particles Cu3VS4 were supported with Ru as a promoter, and the Ru-supported Cu3VS4 was prepared as follows. An aqueous solution of ruthenium chloride (manufactured by Tanaka Kikinzoku Co., Ltd.) was prepared in an amount equivalent to a weight ratio of 0.75% of metal Ru to Cu3VS4. 100 mg of Cu3VS4 was added to 50 ml of water prepared in an Erlenmeyer flask, and after ultrasonic dispersion treatment, the aqueous solution of ruthenium chloride was added dropwise while stirring. While continuing to stir, the mixture was heated to 65°C and held for 30 minutes, after which it was filtered through a membrane filter, washed with an appropriate amount of water and ethanol, and then dried at room temperature to obtain the target product. This is referred to as Ru (0.75 wt%) / Cu3VS4.

[0070] (Preparation of visible light responsive photocatalyst particles for oxygen generation) Reduced graphene oxide (RGO)-doped CoOx-supported BiVO4 (RGO-CoOx / BiVO4) was prepared as a visible light-responsive photocatalyst particle for oxygen evolution as follows.

[0071] (Synthesis of photocatalyst particles BiVO4) The synthesis of photocatalyst particles BiVO4 was performed according to the synthesis method described in J.Solar Energy Engineering, 132, 2, 021106, (2010), A.Kudo et al., and J.Am.Chem.Soc., 121, 49, p.11459 (1999), A.Kudo et al., to obtain the target product. The DRS (diffuse reflectance spectrum), XRD pattern, and SEM observation image of the photocatalyst in this synthesis are shown in Figures 7A to 7B (Figure 101-1-2), (Figure 101-2-2), and Figure 8 (Figure 101-3-2). From the DRS (diffuse reflectance spectrum), it can be seen that the photocatalyst particles BiVO4 have an absorption band in the visible light up to a wavelength of 520 nm. From the SEM observation image, it can be seen that the primary particle size of the synthesized photocatalyst particles BiVO4 is around 1 μm. In some examples, Mo-doped BiVO4:Mo obtained by adding MoO3 to the synthesis raw material to replace 0.05 to 0.25% of vanadium element was used instead of BiVO4.

[0072] (Preparation of photocatalyst particles CoOx-supported BiVO4 (CoOx / BiVO4)) The preparation of CoOx-supported BiVO4, in which CoOx is supported as a cocatalyst on BiVO4 photocatalyst particles, was carried out in accordance with the method described in J. Am. Chem. Soc., 138, 32, p. 10260 (2016), A. Kudo et al., to obtain the target product (the composition ratio of oxygen to metal Co is uncertain). As the raw material for the cocatalyst, an aqueous solution of cobalt nitrate (divalent) (Wako Pure Chemical Industries, Ltd.) was prepared in an amount equivalent to a weight ratio of metal Co to BiVO4 of 0.5%. This is referred to as CoOx (0.5 wt%) / BiVO4.

[0073] (Preparation of photocatalyst particles RGO-CoOx-supported BiVO4 (RGO-CoOx / BiVO4)) The preparation of RGO-added CoOx-supported BiVO4, in which reduced graphene oxide (RGO) was added as a conductive material to the CoOx-supported BiVO4 photocatalyst particles, was carried out in accordance with the method described in J. Am. Chem. Soc., 133, 29, p. 11054 (2011), A. Iwase, A. Kudo et al. The target product was obtained by preparing an aqueous dispersion of graphene oxide (Rap GO (TQ-11) manufactured by Nishina Materials Co., Ltd.) in an amount equivalent to a weight ratio of RGO of 5% relative to CoOx (0.5 wt%) / BiVO4.

[0074] Specifically, 20 ml of a water-soluble solvent (water) was filled into a 50 ml glass tube bottle, 1 ml of Rap GO(TQ-11)-10 (aqueous dispersion of graphene oxide (GO) at a concentration of 10 mg / ml) was added and ultrasonically treated, after which 200 mg of CoOx (0.5 wt%) / BiVO4 was ultrasonically dispersed, 20 ml of methanol was added, and nitrogen flow was performed for 30 minutes while stirring. After this, the mixture was irradiated with light from a 300 W xenon lamp from a close distance for 3 hours while continuing this flow. The solid matter that had become easily precipitated was then filtered off and air-dried to obtain the desired product. This is denoted as RGO(5wt%)-CoOx(0.5wt%) / BiVO4.

[0075] (Primary particle size measurement of photocatalyst particles) The primary particle size of the photocatalyst particles was measured using SEM images magnified 2000 to 20000 times depending on the particle size, and the primary particle sizes of about 30 photocatalyst particles were measured and averaged to obtain the primary particle size in the specification. When the particle size was clearly within the range of the requirements of the claims of the present invention, the SEM image was visually observed and the value of the primary particle size was obtained by comparing it with the gauge on the image.

[0076] (Preparation of photocatalyst dispersion paste for drop cast film formation) In order to form and arrange a photocatalyst particle layer on the surface of a substrate, a paste is prepared by dispersing a mixture of the photocatalysts to be used in a solvent, and a drop casting process is carried out in which this paste is dropped onto the substrate surface and dried repeatedly to form a film. A photocatalyst dispersion paste for drop-casting film formation was prepared as follows.

[0077] The visible light responsive photocatalyst particles for hydrogen generation were Ru (0.75 wt%) / Cu3VS4, and the visible light responsive photocatalyst particles for RGO-added oxygen generation were RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4. The total weight of the photocatalyst particles was 1.6 mg / cm. 2 In this embodiment, the area is 12 cm 2 The photocatalyst particles were weighed out in an amount of 19.2 mg per photocatalyst plate, so that the photocatalyst particle weight ratio was 1:1 in the order listed. This was mixed in 2.5 ml of ethanol and dispersed ultrasonically for 10 minutes to obtain the desired photocatalyst dispersion paste.

[0078] (Preparation of photocatalyst plate) The photocatalyst plate of the present invention is produced by arranging visible light responsive photocatalyst particles for hydrogen generation, visible light responsive photocatalyst particles for oxygen generation, and reduced graphene oxide (RGO) on the surface of a substrate to form a photocatalyst particle layer, and bonding these together under pressure.

[0079] A photocatalyst plate containing Ru (0.75 wt%) / Cu3VS4 as visible light responsive photocatalyst particles for hydrogen generation containing metal sulfide in its structure, RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4 as visible light responsive photocatalyst particles for oxygen generation with added reduced graphene oxide (RGO), and a substrate was prepared as follows.

[0080] (Preparation of PET substrate) In the pressing process for producing the photocatalyst plate, a tablet press with a pressing surface diameter of 20 mm was used. The substrate that could fit inside the press was prepared as follows. A transparent polyethylene terephthalate (PET) substrate with a thickness of 0.5 mm was punched to a surface area of ​​3 cm 2 We cut out four circular plates with an area of ​​12 cm. 2 The substrate for the photocatalytic plate was 12 cm2. 2 If the value deviates from the above, the water decomposition activity value in the examples is corrected according to formula 1. 2 was used as the activity value of the photocatalyst plate (* indicates multiplication and / indicates division).

[0081] Area 12cm 2 Photocatalyst plate activity value = measured activity value * (12cm 2 / actual substrate area) Equation 1

[0082] (Formation of photocatalyst particle layer by drop casting method) Using the prepared photocatalyst dispersion paste, a photocatalyst particle layer was formed by drop casting as follows. The photocatalyst dispersion paste was dropped into the four prepared PET substrates in appropriate amounts using a pipetter, and the photocatalyst particle layer was formed by repeating the process of drying. During the process, the photocatalyst dispersion paste was redispersed with ultrasonic waves as necessary. Specifically, the photocatalyst dispersion paste was dropped at about 70 μl per PET substrate and then dried, and the desired photocatalyst particle layer was formed by repeating this process.

[0083] (Preparation of photocatalytic plates by pressure) By applying pressure to the photocatalyst particle layer formed on the PET substrate, the visible light responsive photocatalyst particles for hydrogen generation, the visible light responsive photocatalyst particles for oxygen generation, reduced graphene oxide (RGO), and the substrate are bonded to produce the photocatalyst plate of the present invention. A photocatalytic plate using pressure was prepared as follows.

[0084] For the pressure application, a hydraulic press "Hand Press SSP-10A" (manufactured by Shimadzu Corporation) and a tablet molding machine for 20 mm diameter tablets (manufactured by the same company) were used. Four PET substrates with photocatalyst particle layers formed on them were stacked and placed inside the tablet molding machine with each photocatalyst particle layer facing up. Four pieces of release film cut to the same shape as the PET substrate were placed on each substrate to cover the surface of the photocatalyst particle layer. The release film was a low-resistance ITO-PEN film "PECF-IP" (Pexel Technologies) with a thickness of 0.125 mm, and was placed so that the ITO surface was in contact with the photocatalyst particle layer.

[0085] FIG. 3 shows an example of the arrangement of each part during the pressing step in the process of producing a photocatalyst plate, and an explanatory diagram after pressing.

[0086] By using a release film coated with this inorganic compound, the photocatalyst particle layer can be prevented from being transferred to the release film side, and a homogeneous photocatalyst plate can be formed without loss of the photocatalyst raw material.

[0087] After placing the tablet in the tablet forming machine, pressure was applied to the tablet using a hydraulic press until the gauge indicated 1.5 tons, and this pressure was maintained for 2 minutes. 2 So, this pressure load is 0.5 ton / cm 2 It was decided. After pressure treatment, the contents are removed from the tablet forming machine and the release film is removed to give a total area of ​​12 cm 2 The desired photocatalyst plate was obtained.

[0088] (Evaluation of the photocatalytic function of photocatalytic plates) The photocatalytic function of the obtained photocatalyst plate was evaluated by measuring the amount of hydrogen (hydrogen gas) generated as the hydrogen generation activity of the obtained photocatalyst plate and the amount of oxygen (oxygen gas) generated as the oxygen generation activity of the obtained photocatalyst plate using a closed circulation system as shown in Figure 4. In Fig. 4, 201 is a reaction tube, 202 is a cutoff filter, 203 is a vacuum line for exhausting generated hydrogen and oxygen gases connected to a vacuum pump, 204 is an argon gas supply line for a gas chromatograph, 205 is a thermostatic bath, 206 is a stirrer, 207 is a stirring bar, 208 is a photocatalyst plate (fixed on a support in the aqueous solvent), 209 is the liquid level of the aqueous solvent, 210 is a circulator, 211 is a pressure gauge, 212 is a gas chromatograph, 213 is a Liebig condenser, and L1 is a light source. The aqueous solvent is water.

[0089] Specifically, in the closed circulation system shown in Fig. 4, a reaction tube 201, the inside of which is an argon gas atmosphere, was filled with 120 ml of water, and a photocatalyst plate was fixed to a support stand and placed at the position shown in Fig. 4. The water surface and the photocatalyst plate were irradiated from the top of the reaction tube 201 with light emitted from a light source L1 consisting of a 300 W xenon lamp "CERMA X LX-300" (manufactured by ILC Technology) with light having a wavelength longer than 420 nm, through a cutoff filter 202 consisting of a cutoff filter "HOYA L42" (manufactured by HOYA) that cuts off light with a wavelength of 420 nm or less. The water splitting activity consisting of the hydrogen generation activity and the oxygen generation activity was measured by quantifying the generated hydrogen (hydrogen gas) and oxygen (oxygen gas) using a gas chromatograph 212 consisting of a gas chromatograph "GC-8A" (manufactured by Shimadzu Corporation; MS-5A column; TCD; Ar carrier). Quantitative analysis was performed every hour, and the measured values ​​during the period when the generation rate was stable were averaged and then measured on a 12cm photocatalyst plate. 2 The measured value of water splitting activity was used as a measurement value of water splitting activity in the presence of 100 mM NaCl.

[0090] (Comparison of measured values ​​within the same example and comparison between examples) The measured values ​​of water splitting activity in the examples are also influenced by the condition of the photocatalyst particle construct made of a plurality of materials and the materials of the photocatalyst plate, such as the finish and storage history of each material. Therefore, even if the photocatalyst plate and photocatalyst particle structure are described as having the same material composition, the measured value of the water splitting activity may differ for each measurement occasion. The measured values ​​of the water splitting activity in this specification are obtained on the same measurement occasion within the same table, so that comparison between examples is valid, but it is not necessarily valid between different tables.

[0091] (Photocatalyst plate photocatalyst particle layer film strength evaluation 1) The film strength of the photocatalyst particle layer of the obtained photocatalyst plate was evaluated by a pencil hardness test in accordance with JIS K5600-5-4, and the film strength was evaluated on a 22-level scale from 10H to 10B.

[0092] (Photocatalyst plate photocatalyst particle layer film strength evaluation 2) The photocatalyst plate of the present invention has improved film strength of the photocatalyst particle layer by applying pressure. The photocatalyst particle layer without applying pressure has a significantly weak film strength, and can be easily rubbed off with the pad of a finger to expose the substrate surface, so it is difficult to express the difference in film strength between the presence and absence of pressure by the pencil hardness method alone. Therefore, the following film strength evaluation of the photocatalyst particle layer was performed.

[0093] (Membrane strength evaluation 2 test method) The photocatalyst plate test piece was fixed on the balance pan of the upper pan balance with double-sided tape or the like so that the photocatalyst particle layer side was facing up, and the surface of the photocatalyst particle layer was rubbed once with the pads of the fingers wearing latex powder-free gloves "Navi Roll Gloves 0-5905-22" (manufactured by AS ONE Corporation) at a strength that indicated 100 g on the balance. If the photocatalyst particle layer was rubbed off by this operation and at least a part of the substrate surface was exposed, the evaluation was △, and if not, it was ◯.

[0094] The pressure load and the evaluation results are shown in Table 1.

[0095] Furthermore, after this evaluation, a test was conducted in which one of the four photocatalyst plates was bent using finger pressure so that the PET substrate was on the outside. The results showed that the photocatalyst particle layer was adhered closely to the PET substrate and would not peel off. A photograph of the photocatalyst plate that underwent the bending test is shown in Figure 10 (Figure 101-7-2).

[0096] [Examples 1-2 and 1-3] The pressure load in Example 1-1 was 1 ton / cm 2 , 2ton / cm 2 A photocatalyst plate was obtained in the same manner as in Example 1-1, except that the above-mentioned change was made. The pressure load and the evaluation results are shown in Table 1.

[0097] [Examples 1-4] A photocatalyst plate was obtained in the same manner as in Example 1-1, except that no pressure load was applied. The pressure load and the evaluation results are shown in Table 1.

[0098] Comparative Example 1 A photocatalyst plate was obtained in the same manner as in Example 1-1, except that reduced graphene oxide (RGO) was not added to the photocatalyst particles for oxygen generation in Example 1-1. The pressure load and the evaluation results are shown in Table 1.

[0099] [Table 1]

[0100] The time course of the water splitting activity corresponding to Table 1 is shown in FIG. 9 (FIG. 101-4), and the pressure load dependence of the hydrogen production rate and the oxygen production rate corresponding to Examples 1-1 to 1-3 and 1-4 is shown in FIG. 9 (FIG. 101-7-1).

[0101] (Summary of Example 1) The water splitting activity of the photocatalyst plates of Examples 1-1 to 1-4 was improved compared to the Comparative Example. The water splitting activity of the photocatalyst plate obtained by the method including the pressurizing step in Example 1 was superior, and the optimal pressurizing load in this experiment was 0.5 ton / cm in Example 1-1. 2 Furthermore, the film strength of the photocatalyst particle layer was significantly improved by the process of applying a pressure load. In the comparative example that did not contain reduced graphene oxide (RGO), the water splitting activity significantly decreased, and the film strength also decreased. (This shows that RGO functions as a binder.)

[0102] The changes that the pressure load brings to the photocatalyst particle layer are as follows: the bonding between the visible light responsive photocatalyst particles for hydrogen generation, the visible light responsive photocatalyst particles for oxygen generation, and reduced graphene oxide (RGO) becomes stronger, facilitating the electron transfer between the particles required for the Z-scheme water splitting reaction and promoting the water splitting reaction; and the voids in the photocatalyst particle layer decrease, which becomes a factor that hinders gas generation. It is believed that there is an optimal pressure load that balances both factors (Figure 9 (Figure 101-7-1)). In the configuration of this embodiment, which uses visible light responsive photocatalyst particles for hydrogen generation (5 to 10 μm) with a larger primary particle size than the visible light responsive photocatalyst particles for oxygen generation (approximately 1 μm), the photocatalyst particles with a large primary particle size function as a spacer against compression in the pressurizing process, and are thought to contribute to ensuring an appropriate amount of voids in the photocatalyst particle layer. Note that in this specification, a larger primary particle size is sometimes referred to as "large primary particle size," and a smaller primary particle size is sometimes referred to as "small primary particle size."

[0103] A schematic diagram of a photocatalyst plate corresponding to Example 1-1 is shown in FIG. 11 (FIG. 101-7-3). This photocatalyst plate is made up of a resin substrate, large primary particle size visible light responsive metal sulfide photocatalyst particles for hydrogen generation, small primary particle size visible light responsive photocatalyst particles for oxygen generation, and a photocatalyst particle layer made of conductive reduced graphene oxide (RGO) bonded together by applying a pressure load, and has high water splitting activity and robust film strength. This configuration is considered to correspond to the configuration of (FIG. 2-1-2) or (FIG. 2-1-3) in the schematic diagrams of the photocatalyst plates of FIGS. 2A to 2D.

[0104] Example 2 (Example 2: Observing the effect of pressure load during film formation on water splitting activity and film strength in a photocatalyst plate containing Cu3VS4 for hydrogen generation and BiVO4 for oxygen generation as visible light responsive photocatalyst particles)

[0105] Example 2-1 A photocatalyst plate was obtained in the same manner as in Example 1-1, except that the photocatalyst particle weight ratio of the visible light responsive photocatalyst particles for hydrogen generation Ru (0.75 wt%) / Cu3VS4 and the RGO-added visible light responsive photocatalyst particles for oxygen generation RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4 in Example 1-1 was changed to 1:2. The pressure load and the evaluation results are shown in Table 2.

[0106] Example 2-2 The pressure load in Example 2-1 was 2 ton / cm 2 A photocatalyst plate was obtained in the same manner as in Example 2-1, except that the above-mentioned change was made. The pressure load and the evaluation results are shown in Table 2.

[0107] Example 2-3 A photocatalyst plate was obtained in the same manner as in Example 2-1, except that no pressure load was applied. The pressure load and the evaluation results are shown in Table 2.

[0108] [Table 2]

[0109] The change over time in water splitting activity corresponding to Table 2 is shown in FIG. 12 (FIG. 102-4), and SEM observation images of the photocatalyst plate surface corresponding to each example are shown in FIG. 12 (FIG. 102-5).

[0110] (Summary of Example 2) In the case of a photocatalyst particle weight ratio of 1:2, consisting of visible light responsive photocatalyst particles for hydrogen generation Ru (0.75 wt%) / Cu3VS4 and visible light responsive photocatalyst particles for RGO-added oxygen generation RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4, the optimal pressure load for water splitting activity was 0.5 ton / cm in Example 2-1, as in Example 1. 2 The water splitting activity of the photocatalyst plate to which a pressure load was applied was higher than that of the comparative example to which no pressure load was applied, and the film strength of the photocatalyst particle layer was significantly improved. From the SEM observation image of the photocatalyst plate surface, it can be seen that the higher the applied pressure, the more densely the particles tend to be packed. From this result and the result of Example 2-1 above, it can be seen that the performance as a catalyst is important to have an appropriate balance between moderate adhesion and porosity.

[0111] Example 3 (Example of observing the effect of particle size change of each photocatalyst on water splitting activity in a photocatalyst plate containing Cu3VS4 for hydrogen generation and BiVO4 for oxygen generation as visible light responsive photocatalyst particles) We investigated the combination of large and small primary particle sizes of visible light responsive photocatalyst particles for hydrogen generation and visible light responsive photocatalyst particles for oxygen generation in the photocatalyst plate.

[0112] [Examples 3-1 to 3-4] As visible light responsive photocatalyst particles for hydrogen generation having a primary particle size, metal sulfide photocatalyst particles synthesized and prepared under the same conditions as Ru(0.75wt%) / Cu3VS4 in Example 1-1 were used. For visible light responsive photocatalyst particles for hydrogen generation with a small primary particle size, Cu3VS4 was synthesized at a temperature of 500°C for 10 hours, and other photocatalyst particles were used under the same synthesis and preparation conditions as Ru (0.75 wt%) / Cu3VS4 in Example 1-1. A comparison of SEM images of Cu3VS4 synthesized with large and small primary particle sizes is shown in Figure 13A (Figure 103-3-1).

[0113] As visible light responsive photocatalyst particles for oxygen generation having a primary particle size, metal oxide photocatalyst particles were synthesized using a microwave-assisted urea synthesis method in accordance with the synthesis method described in Catal. Lett., 144, p. 1962 (2014), A. Kudo et al., and other photocatalyst particles prepared as RGO (5 wt%)-CoOx (0.3 wt%) / BiVO4 in the same manner as in Example 1-1 were used. As visible light responsive photocatalyst particles for oxygen generation with a small primary particle size, photocatalyst particles synthesized and prepared under the same conditions as RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4 in Example 1-1 were used. A comparison of SEM images of BiVO4 synthesized with large and small primary particle sizes is shown in Figure 13A (Figure 103-3-2).

[0114] The photocatalyst particle weight ratio of the visible light responsive photocatalyst particles Ru (0.75 wt%) / Cu3VS4 for hydrogen generation and the visible light responsive photocatalyst particles RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4 for RGO-added oxygen generation in Example 1-1 was changed to 1:2, and the pressure load was changed to 2 ton / cm. 2 The other conditions were the same as in Example 1-1. Table 3 shows the relationship between the primary particle size of the photocatalyst particles and the evaluation results.

[0115] [Table 3]

[0116] The change over time in water splitting activity corresponding to Table 3 is shown in FIG. 13B (FIG. 103-4), and the SEM observation image of the photocatalyst plate surface is shown in FIG. 13C (FIG. 103-5).

[0117] (Summary of Example 3) All photocatalyst plates showed robust film strength. The water splitting activity of the photocatalyst plate varies greatly depending on the primary particle size relationship of the constituent visible light responsive photocatalyst particles for hydrogen generation and visible light responsive photocatalyst particles for oxygen generation, and the combination of Ru (0.75 wt%) / Cu3VS4 with a large primary particle size (approximately 2-10 μm) and RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4 with a small primary particle size (approximately 1 μm) showed the highest water splitting activity (Example 3-3). This combination corresponds to the photocatalyst plate configuration in the first and second embodiments.

[0118] Example 4 (Example of the effect of pressure load on water splitting activity in a photocatalyst particle composition containing Cu3VS4 for hydrogen generation and BiVO4 for oxygen generation as visible light responsive photocatalyst particles, and comparing it with a powder of a composition in which the same photocatalyst particles are simply blended together)

[0119] Example 4-1 (Preparation of photocatalyst dispersion paste for drop cast film formation) The preparation of photocatalyst particles and the measurement of particle size were carried out in the same manner as in Example 1-1. The preparation of the photocatalyst dispersion paste for drop-cast film formation was the same as in Example 1-1, but the total weight of the photocatalyst particles was changed to 120 mg, and the amount of ethanol used was changed to 6 ml, to obtain the desired photocatalyst dispersion paste.

[0120] (Preparation of photocatalyst particle structure) The photocatalyst particle structure of the present invention is produced by bonding visible light responsive photocatalyst particles for generating hydrogen, visible light responsive photocatalyst particles for generating oxygen, and reduced graphene oxide (RGO) under pressure.

[0121] A photocatalyst particle composite containing Ru (0.75 wt%) / Cu3VS4 as a visible light responsive photocatalyst particle for hydrogen generation containing metal sulfide in its structure, and RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4 as a visible light responsive photocatalyst particle for oxygen generation with added reduced graphene oxide (RGO) was prepared as follows.

[0122] (Formation of photocatalyst particle layer by drop casting method) Using half of the prepared photocatalyst dispersion paste, a photocatalyst particle layer was formed on a release film by the drop casting method in the same manner as in Example 1-1, except that the PET substrate in Example 1-1 was replaced with a release film, as follows: Four release films equivalent to those used in Example 1-1 were prepared, and a photocatalyst particle layer was formed on the ITO surface of each film.

[0123] (Preparation of photocatalyst particle structure by pressure) By applying pressure to the photocatalyst particle layer formed on the ITO surface of the release film, the visible light responsive photocatalyst particles for hydrogen generation, the visible light responsive photocatalyst particles for oxygen generation, and reduced graphene oxide (RGO) are bonded together, and then the bonded particles are peeled off from the release film to produce the photocatalyst particle structure of the present invention. A photocatalyst particle structure was prepared by pressing as follows.

[0124] Using the same hydraulic press and tablet molding machine as in Example 1-1, four sheets of the release film with photocatalyst particle layers formed on the ITO surface were stacked in the tablet molding machine so that each photocatalyst particle layer was on top. At that time, four newly prepared release films were alternately placed on the surface of each of the four photocatalyst particle layers so that their ITO surfaces were in contact with each photocatalyst particle layer. In other words, each of the four photocatalyst particle layers was sandwiched between the ITO surfaces and placed in the tablet molding machine.

[0125] FIG. 5 shows an example of the arrangement of each member during the pressurizing step in the process of producing a photocatalyst particle structure, and an explanatory diagram after pressing.

[0126] By using a release film coated with the inorganic compound, the photocatalyst particle layer can be prevented from being transferred to the release film side, and a homogeneous photocatalyst particle construct can be formed without loss of the photocatalyst raw material.

[0127] After placing the tablet in the tablet forming machine, pressure was applied to the tablet using a hydraulic press until the gauge indicated 3 tons, and this pressure was maintained for 2 minutes. 2So this pressure load is 1 ton / cm 2 It was decided.

[0128] After the pressure treatment, the contents were taken out of the tablet molding machine, the release film was removed, and the pressed photocatalyst particle layer was collected on an agate mortar and lightly crushed to obtain the desired photocatalyst particle composition.

[0129] (Evaluation of photocatalytic function of photocatalytic particle components) The photocatalytic function of the obtained photocatalyst particle composition was evaluated by measuring the amount of hydrogen (hydrogen gas) generated as the hydrogen generation activity of the obtained photocatalyst plate and the amount of oxygen (oxygen gas) generated as the oxygen generation activity using a closed circulation system as shown in Figure 6. In FIG. 6, 301 is a reaction tube, 302 is a cutoff filter, 303 is a vacuum line for exhausting generated hydrogen and oxygen gases connected to a vacuum pump, 304 is an argon gas supply line for a gas chromatograph, 305 is a thermostatic bath, 306 is a stirrer, 307 is a stirring bar, 309 is the liquid surface of the photocatalyst particle constituent suspension, 310 is a circulator, 311 is a pressure gauge, 312 is a gas chromatograph, 313 is a Liebig cooling tube, and L1 is a light source.

[0130] Specifically, a reaction tube 301 in a closed circulation system shown in Fig. 6, the inside of which is an argon gas atmosphere, was filled with 120 ml of water in advance, and 100 mg of the photocatalyst particle construct was dispersed therein, and the suspension was placed so as to form the photocatalyst particle construct as shown in Fig. 5. The liquid surface was irradiated from the top of the reaction tube 301 with light emitted from a light source L1 consisting of a 300 W xenon lamp "CERMA X LX-300" (manufactured by ILC Technology) with light having a wavelength longer than 420 nm, via a cutoff filter 302 consisting of a cutoff filter "HOYA L42" (manufactured by HOYA) that cuts off light having a wavelength of 420 nm or less. The generated hydrogen (hydrogen gas) and oxygen (oxygen gas) were quantified using a gas chromatograph 312 consisting of a gas chromatograph "GC-8A" (Shimadzu Corporation; MS-5A column; TCD; Ar carrier) to measure the water splitting activity consisting of the hydrogen generation activity and oxygen generation activity. Since the ratio of the hydrogen generation rate to the oxygen generation rate tended to deviate significantly from the quantitative water splitting reaction immediately after the start of the reaction, a re-evacuation process was performed in which the reaction vessel was once evacuated 3 to 5 hours after the start of the reaction and then the reaction was resumed. Quantification was performed every hour after the re-evacuation, and the measured values ​​during the period when the generation rate was stable were averaged, and this was used as the measured value of the water splitting activity in the photocatalyst particle constituent suspension. The pressure load and the evaluation results are shown in Table 4.

[0131] [Examples 4-2 and 4-3] The pressure load in Example 4-1 was 0.5 and 0.1 ton / cm 2 A photocatalyst particle structure was obtained in the same manner as in Example 4-1, except that the above-mentioned change was made. The pressure load and the evaluation results are shown in Table 4.

[0132] [Example 4-4] The pressure load in Example 4-1 is 0 ton / cm 2A photocatalyst particle construct of 100 mg was produced and evaluated under the above conditions. In other words, the photocatalyst particle layer was formed by the drop casting method, and the photocatalyst particle layer was peeled off from the release film without carrying out the pressurizing step, thereby obtaining a photocatalyst particle construct. The pressurizing load and the results are shown in Table 4.

[0133] [Table 4]

[0134] The change over time in water splitting activity corresponding to Table 4 is shown in FIG. 14A (FIG. 104-4), and optical microscope images of the photocatalyst particle component suspensions corresponding to Examples 4-1 and 4-4 are shown in FIG. 14B (FIG. 104-6-J1) and (FIG. 104-6-J4).

[0135] (Summary of Example 4) The suspension of the photocatalyst particle structure obtained through the process of forming the photocatalyst particle layer and the process of applying a pressurized load showed a tendency for the water activity to improve when the pressurized pressure was increased within the range of the results of this study. 2 The treatment conditions were optimal for water splitting activity (Example 4-1).

[0136] In the optical microscope image, a structure in which the photocatalyst particles are three-dimensionally assembled as secondary particles is observed in Example 4-1 (within the dashed line). Such a structure is not observed in Example 4-4, and the water splitting activity is inferior to that of Example 4-1. Therefore, the "structure in which the photocatalyst particles are three-dimensionally assembled as secondary particles" is considered to be one of the preferable structures for a photocatalyst.

[0137] Example 5 (CuGa) 0.5 Example of observing the effect of pressure load during film formation on water splitting activity and film strength in a photocatalyst plate containing ZnS2 for hydrogen generation and BiVO4 for oxygen generation as visible light responsive photocatalyst particles)

[0138] [Examples 5-1 and 5-2] In Example 1-1, the metal sulfide photocatalyst particles Cu3VS4 were (CuGa 0.5 A photocatalyst plate was obtained by the same process as in Example 1-1, except that ZnS2 was used instead and the pressure load was changed.

[0139] (Photocatalyst particles (CuGa) 0.5 Synthesis of ZnS2 Photocatalyst particles (CuGa) 0.5 The synthesis of ZnS2 was performed according to the synthesis method described in J. Phys. Chem. Lett., 6, 6, p. 1042 (2015), A. Kudo et al. The raw materials Cu2S, Ga2S3, and ZnS were mixed in a ratio of 0.5 / 0.6 / 1 (Ga element 20% excess condition), and the target product was obtained by solid-phase synthesis in a degassed sealed ampoule at 800℃ for 10 hours.

[0140] The DRS (diffuse reflectance spectrum), XRD pattern, and SEM observation image of the photocatalyst synthesized by this synthesis method are shown in Figure 15A (Figure 105-1), (Figure 105-2), and (Figure 105-3), respectively. Photocatalyst particles (CuGa) synthesized by SEM observation image 0.5 It can be seen that the primary particle size of ZnS2 is about 2 to 3 μm.

[0141] In Example 1-1, the visible light responsive photocatalyst particles for hydrogen generation were Ru(0.5wt%) / (CuGa) 0.5 The visible light responsive photocatalyst particles for oxygen generation were replaced with RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4:Mo (0.05%), and the total weight of the photocatalyst particles was 2 mg / cm. 2 The photocatalyst particle weight ratio was 1:1 (12 mg each) in the order listed, and the pressure load during the pressing process was 0 to 2 ton / cm 2 The photocatalyst plate was prepared by changing the temperature within the range of 1. The Ru promoter was adsorbed and supported under the same conditions as in Example 1-1, except that heating was not performed. The rest of the process was the same as in Example 1-1 to obtain a photocatalyst plate. The pressure load and the evaluation results are shown in Table 5.

[0142] [Table 5]

[0143] The time course of the water splitting activity corresponding to Table 5 is shown in FIG. 15B (FIG. 105-4). A photograph of the photocatalyst plate of Example 5-2 on which writing was done with the pencil used in the film strength evaluation is shown in FIG. 15B (FIG. 105-7).

[0144] (Summary of Example 5) The photocatalyst plate of the embodiment showed robust film strength. The water splitting activity of the photocatalyst plate was improved by the process of applying a pressure load. However, compared to the cases of Example 1 and Example 2, in which visible light responsive photocatalyst particles for hydrogen generation with a large primary particle size (5 to 10 μm) were used, the configuration of this example, in which visible light responsive photocatalyst particles for hydrogen generation (2 to 3 μm) were used in comparison with the primary particle size of the visible light responsive photocatalyst particles for oxygen generation (around 1 μm), showed a gradual change in the improvement of water splitting activity with increasing pressurized load, and the optimum pressurized load was not recognized within the condition range of Example 5. Within the range of Example 5, a pressurized load of 2 ton / cm 2 The treatment conditions were optimal for water splitting activity (Example 5-2).

[0145] A schematic diagram of a photocatalyst plate corresponding to Example 5-2 is shown in FIG. 15B (FIG. 105-7-2). This photocatalyst plate is made of a resin substrate, visible light responsive metal sulfide photocatalyst particles for hydrogen generation, visible light responsive photocatalyst particles for oxygen generation, and a photocatalyst particle layer consisting of conductive reduced graphene oxide (RGO) bonded together by applying a pressure load, and has high water splitting activity and robust film strength. RGO is bonded onto the visible light responsive photocatalyst particles for oxygen generation. This configuration is considered to correspond to the configuration of (FIG. 2-1-1) in the schematic diagrams of the photocatalyst plate in FIGS. 2A to 2D.

[0146] Example 6 (CuGa) 0.5Example of observing the effect of heating on the water splitting activity of a photocatalyst plate containing ZnS2 for hydrogen generation and BiVO4 for oxygen generation as visible light responsive photocatalyst particles during co-catalyst adsorption and support treatment on the visible light responsive photocatalyst particles for hydrogen generation)

[0147] [Examples 6-1, 6-2, and 6-3] Visible light responsive photocatalyst particles Ru(0.5wt%) / (CuGa) for hydrogen generation 0.5 Visible light responsive photocatalyst particles for oxygen generation with ZnS2 and RGO added RGO (5wt%)-CoOx (0.5wt%) / BiVO4:Mo (0.25%) were used, and the total weight of the photocatalyst particles was 2mg / cm 2 The adsorption and loading of Ru co-catalyst onto visible light responsive photocatalyst particles for hydrogen generation was performed by changing the temperature conditions under which the photocatalyst particle weight ratio was 2:3 in the order listed (treatment time was 30 minutes in each case). The rest of the process was the same as in Example 5-2 to obtain a photocatalyst plate. The promoter supporting treatment temperature and the evaluation results are shown in Table 6.

[0148] [Table 6]

[0149] The time course of the water splitting activity corresponding to Table 6 is shown in FIG. 16 (FIG. 106-4).

[0150] (Summary of Example 6) All photocatalyst plates showed robust film strength. Visible light responsive photocatalyst particles (CuGa) for hydrogen generation 0.5 The water splitting activity of the photocatalyst plate using the Ru co-catalyst on ZnS2 tends to improve by heating in the adsorption and support process in a water solvent. Among the conditions in Example 6, the treatment condition of 65°C for 30 minutes was optimal for water splitting activity (Example 6-1).

[0151] Example 7 (CuGa) 0.5Example of observing the effect of changing the photocatalyst particle composition ratio (weight ratio) on water splitting activity in a photocatalyst plate containing ZnS2 for hydrogen generation and BiVO4 for oxygen generation as visible light responsive photocatalyst particles)

[0152] [Examples 7-1 to 7-5] Visible light responsive photocatalyst particles Ru(0.5wt%) / (CuGa) for hydrogen generation 0.5 The weight ratio of ZnS2 and RGO-doped visible light responsive photocatalyst particles for oxygen generation was changed between RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4:Mo (0.25%). (CuGa) 0.5 The synthesis conditions for ZnS2 were 700°C for 10 hours. The rest of the process was the same as in Example 6-1 to obtain a photocatalyst plate. The photocatalyst weight ratio and evaluation results are shown in Table 7.

[0153] [Table 7]

[0154] (Summary of Example 7) All photocatalyst plates showed robust film strength. Photocatalyst plate is made up of visible light responsive photocatalyst particles Ru(0.5wt%) / (CuGa) for hydrogen generation 0.5 The photocatalyst particle weight ratio of ZnS2 and RGO-added visible light responsive photocatalyst particles for oxygen generation RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4:Mo (0.25%), in the listed order, was optimal at 1:2, which showed the highest water splitting activity (Example 7-3).

[0155] Example 8 (Example of observing the effect of changing the particle size of Cu3VS4 on water splitting activity in a photocatalyst plate containing Cu3VS4 for hydrogen generation and BiVO4 for oxygen generation as visible light responsive photocatalyst particles) In relation to Example 3, the effect of changing the particle size of the visible light responsive photocatalyst particles for hydrogen generation in the photocatalyst plate was further investigated.

[0156] [Examples 8-1 to 8-4] Photocatalyst particles were used under the same synthesis and preparation conditions as those for Ru (0.75 wt%) / Cu3VS4 in Example 1-1, except that the temperature conditions during the synthesis of Cu3VS4 in Example 1-1 were changed. The synthesis was carried out at temperatures of 500, 580, 650 and 800°C for 10 hours each. A comparison of SEM images of Cu3VS4 synthesized under each temperature condition is shown in Figure 17A (Figure 108).

[0157] Other conditions were the same as in Example 1-1. The primary particle size and evaluation results of each Cu3VS4 are shown in Table 8.

[0158] [Table 8]

[0159] The change over time in water splitting activity corresponding to Table 8 is shown in FIG. 17B (FIG. 108-4), and the SEM observation image of the photocatalyst plate surface is shown in FIG. 17C (FIG. 108-5).

[0160] (Summary of Example 8) All photocatalyst plates showed robust film strength. The water splitting activity of the photocatalyst plate varied greatly by changing the synthesis temperature of the visible light responsive photocatalyst particles for hydrogen generation used to change the primary particle size. It can be said that the configuration using photocatalyst particles with a primary particle size of 5 to 10 μm obtained under conditions of a synthesis temperature of 650°C is a preferred embodiment that shows the highest water splitting activity (Example 8-3). The water splitting activity tends to decrease whether the primary particle size is greater or less than that, but it shows higher activity than Comparative Example 1. The combination of large and small primary particle sizes in Example 8-3 corresponds to the configuration of the photocatalyst plate in Examples 1 and 2.

[0161] Example 9 (Example of observing the effect of changing the composition ratio of photocatalyst particles on water splitting activity in a photocatalyst plate containing Cu3VS4 for hydrogen generation and BiVO4 for oxygen generation as visible light responsive photocatalyst particles)

[0162] [Examples 9-1 to 9-4] In relation to Example 7, the weight ratio of the photocatalyst particles, Ru(0.75wt%) / Cu3VS4 visible light responsive photocatalyst particles for hydrogen generation and RGO(5wt%)-CoOx(0.5wt%) / BiVO4 visible light responsive photocatalyst particles for oxygen generation with added RGO, was changed. The rest of the process was the same as in Example 1-1 to obtain a photocatalyst plate. The photocatalyst particle weight ratio and the evaluation results are shown in Table 9.

[0163] [Table 9] The change over time in water splitting activity corresponding to Table 9 is shown in FIG. 18 (FIG. 109-4), and the SEM observation image of the photocatalyst plate surface is shown in FIG. 19 (FIG. 109-5).

[0164] (Summary of Example 9) All photocatalyst plates showed robust film strength. The photocatalyst particle weight ratio of the hydrogen generating visible light responsive photocatalyst particles Ru (0.75 wt%) / Cu3VS4 and the RGO added oxygen generating visible light responsive photocatalyst particles RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4 constituting the photocatalyst plate is optimal at 1:1 in the listed order, and showed the highest water splitting activity in this Example 9 (Example 9-4). The water splitting activity also showed a tendency to decrease with the decrease in the content of the hydrogen generating photocatalyst particles (both are more active than Comparative Example 1). The optimum ratio is Ru(0.5wt%) / (CuGa). 0.5This is different from the photocatalyst particle ratio of 1:2, which was optimal in Example 7, in which ZnS2 was used as the visible light responsive photocatalyst particles for hydrogen generation. It is also possible that the effect of the photocatalyst particle weight ratio with the visible light responsive photocatalyst particles for oxygen generation on the water splitting reaction activity differs depending on the particle size of the visible light responsive photocatalyst particles for hydrogen generation (Cu3VS4 in Example 9 has a primary particle size of 5 to 10 μm, and (CuGa) in Example 7 has a primary particle size of 5 to 10 μm). 0.5 ZnS2 has a primary particle size of 2-3μm.

[0165] Example 10 (CuGa) 0.5 Example of observing the effect of the change in unit area membrane weight of the photocatalyst particle layer on water splitting activity in a photocatalyst plate containing ZnS2 for hydrogen generation and BiVO4 for oxygen generation as visible light responsive photocatalyst particles)

[0166] [Examples 10-1 to 10-6] Visible light responsive photocatalyst particles Ru(0.5wt%) / (CuGa) for hydrogen generation 0.5 Photocatalyst plates were prepared by varying the total photocatalyst weight per unit area (unit area film weight) under the condition that the photocatalyst particle weight ratio of ZnS2 and RGO-added visible light responsive photocatalyst particles for oxygen generation RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4:Mo (0.25%) prepared under the same conditions as in Example 7 was 1:2 in the order listed. Above (CuGa) 0.5 The synthesis conditions for ZnS2 were the same as those in Example 5, except that the synthesis was carried out in a degassed sealed ampoule at a temperature of 700° C. for 10 hours. The primary particle size of the obtained particles was 2 to 3 μm. Other than that, the same treatment as in Example 6-1 was carried out to obtain a photocatalyst plate. The membrane weight per unit area and the evaluation results are shown in Table 10.

[0167] [Table 10]

[0168] (Summary of Example 10) All photocatalyst plates showed robust film strength. Photocatalyst plate is made up of visible light responsive photocatalyst particles Ru(0.5wt%) / (CuGa) for hydrogen generation 0.5 Visible light responsive photocatalyst particles for oxygen generation with addition of ZnS2 and RGO. When the weight ratio of RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4:Mo (0.25%) is 1:2, the unit area film weight of the photocatalyst particles is 1.6 mg / cm, which is the maximum oxygen generation rate. 2 showed the optimum and best water splitting activity (Example 10-3). This shows that as the membrane weight per unit area decreases, the hydrogen production rate also tends to decrease (water splitting activity decreases). On the other hand, as the membrane weight per unit area increases, the hydrogen production rate increases, but the oxygen production rate tends to decrease preferentially. (All water splitting reaction activities are higher than in Comparative Example 1.)

[0169] Example 11 (Example of changing the type of visible light responsive photocatalyst particles for hydrogen generation and observing the water splitting activity in a photocatalyst plate containing BiVO4 as visible light responsive photocatalyst particles for oxygen generation)

[0170] [Examples 11-1 to 11-8] The metal sulfide photocatalyst particles Cu3VS4 in Example 1-1 were replaced with other visible light responsive photocatalyst particles for hydrogen generation, and a photocatalyst plate was obtained by the same process as in Example 1-1. The photocatalyst plate containing the metal sulfide photocatalyst particles Cu3VS4 was also evaluated for comparison.

[0171] (Synthesis of metal sulfide photocatalyst particles for hydrogen generation) The synthesis of each metal sulfide hydrogen generation photocatalyst particle (used in Examples 11-2 to 11-7) other than Cu3VS4 was carried out by mixing Cu2S, Ga2S3, Ag2S, In2S3, and ZnS as raw materials in the metal element ratio corresponding to each composition formula with reference to the synthesis method described in the literature Sustainable Energy Fuel, 2, p. 2016 (2018), A. Kudo et al., and solid-phase synthesis was carried out in a degassed sealed ampoule. At that time, the hydrogen generation photocatalyst particle requiring Ga element was mixed in 20% excess to the required composition formula ratio (Ga element 20% excess condition). In addition, for the synthesis condition in which excess sulfur content is mixed, a crushed product of sulfur (crystal; Kanto Chemical Co., Ltd.) was mixed so as to be 100% excess to the required composition formula ratio (S element 100% excess condition). The primary particle size of each metal sulfide hydrogen generating photocatalyst particle was about 3 to 5 μm (used in Example 11-3), about 2 to 5 μm (used in Example 11-4), about 6 to 12 μm (used in Example 11-5), about 0.1 to 3 μm (used in Example 11-6), and about 0.5 μm (used in Example 11-7). Cu3VS4 in Example 11-1 was about 0.1 to 3 μm (used in Example 11-2) and (CuGa) in Example 11-2. 0.5 ZnS2 was prepared under the same conditions as in Example 5.

[0172] (Synthesis of photocatalyst particles SrTiO3:Rh (1%)) (Used in Example 11-8) The photocatalytic particle SrTiO3:Rh (1%) was synthesized according to the synthesis method described in J. Phys. Chem. B, 108, p. 8992 (2004), A. Kudo et al. The primary particle size of the obtained particles was about 0.5 to 1 μm.

[0173] The DRS (diffuse reflectance spectrum) of each of the visible light responsive photocatalyst particles for hydrogen generation used in Examples 11-3 to 11-8 is shown in FIG. 20 (FIG. 111-1).

[0174] Visible light responsive photocatalyst particles for hydrogen generation and RGO added Visible light responsive photocatalyst particles for oxygen generation RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4 photocatalyst particle weight ratio was changed to 1:2 in Examples 11-6 and 11-7. The Ru promoter was supported on the photocatalyst particles SrTiO3:Rh (1%) by photoelectrodeposition using an aqueous solution of ruthenium chloride (Tanaka Kikinzoku Co., Ltd.) in a 10% methanol aqueous solution. Other than that, the same treatment as in Example 1-1 was carried out to obtain a photocatalyst plate. Table 11 shows the composition of the various visible light responsive photocatalyst particles for hydrogen generation used in each example, the solid phase synthesis conditions, and the evaluation results.

[0175] [Table 11]

[0176] (Summary of Example 11) All photocatalyst plates showed robust film strength. As a result of varying the type of visible light responsive photocatalyst particles for hydrogen generation constituting the photocatalyst plate, all showed water splitting activity in the configurations within the range of Example 11. Among these, the photocatalyst plate containing metal sulfide photocatalyst particles Cu3VS4, which corresponds to the same configuration as in Example 1-1, showed the highest water splitting activity.

[0177] Example 12 (Example of changing the type of visible light responsive photocatalyst particles for hydrogen generation and observing the water splitting activity in a photocatalyst plate containing TiO2:Rh (0.5%), Sb (1%) as visible light responsive photocatalyst particles for oxygen generation)

[0178] [Examples 12-1 to 12-3] The metal sulfide photocatalyst particles Cu3VS4 in Example 1-1 were replaced with other visible light responsive photocatalyst particles for hydrogen generation, and the RGO-added visible light responsive photocatalyst particles RGO(5wt%)-CoOx(0.5wt%) / BiVO4 for oxygen generation were replaced with RGO(5wt%)-TiO2:Rh(0.5%),Sb(1%), and the rest was treated in the same manner as in Example 1-1 to obtain a photocatalyst plate. The photocatalyst plate containing the metal sulfide photocatalyst particles Cu3VS4 was also evaluated for comparison.

[0179] (Synthesis of TiO2:Rh(0.5%),Sb(1%)) The synthesis of TiO2:Rh(0.5%),Sb(1%) was carried out according to the synthesis method described in the literature RSC Advances, 8,10,p.5331(2018), A.Kudo et al. The primary particle size of the obtained particles was about 0.5-1.5μm.

[0180] The DRS (diffuse reflectance spectrum) of the photocatalyst synthesized by this method is shown in Figure 21 (Figure 112-1).

[0181] A photocatalyst plate was obtained in the same manner as in Example 1-1, except that each visible light responsive photocatalyst particle for hydrogen generation and RGO-added visible light responsive photocatalyst particle for oxygen generation RGO (5 wt%)-TiO2:Rh (0.5%), Sb (1%) were used. Table 12 shows the composition of the various visible light responsive photocatalyst particles for hydrogen generation used in each example, the solid phase synthesis conditions, and the evaluation results.

[0182] [Table 12]

[0183] (Summary of Example 12) All photocatalyst plates showed robust film strength. As a result of carrying out an experiment using TiO2:Rh (0.5%), Sb (1%) as the visible light responsive photocatalyst particles for generating oxygen that constitute the photocatalyst plate, all of the configurations within the range of Example 12 showed water splitting activity.

[0184] Example 13 (Cu(Ga 1-y In y ) 0.8 Zinc 0.4 In a photocatalyst plate containing S2 for hydrogen generation and BiVO4 for oxygen generation as visible light responsive photocatalyst particles, the effect of changing the absorption wavelength of the visible light responsive photocatalyst particles for hydrogen generation on water splitting activity is observed by changing the y value in the composition formula.

[0185] [Examples 13-1 to 13-3] In Example 1-1, the metal sulfide photocatalyst particles Cu3VS4 (CuGa 1-y In y ) 0.8 Zinc 0.4 The y values ​​in the structural formula correspond to 0.3, 0.5, and 0.7, respectively. 0.8 Ga 0.56 In 0.24 Zinc 0.4 S2, Cu 0.8 Ga 0.4 In 0.4 Zinc 0.4 S2, Cu 0.8 Ga 0.24 In 0.56 Zinc 0.4 S2 was used. In addition, the visible light responsive photocatalyst particles Ru(0.5wt%) / (CuGa 1-y In y ) 0.8 Zinc 0.4 The weight ratio of the photocatalyst particles RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4, a visible light responsive photocatalyst particle for oxygen generation with added RGO, was changed to 1:2, and the GO used as the raw material for RGO was changed to Rap GO(TQ-2)-10 (aqueous dispersion of graphene oxide (GO) at a concentration of 10 mg / ml) manufactured by Nishina Materials Co., Ltd. Other than that, a photocatalyst plate was obtained by the same treatment as in Example 1-1.

[0186] (Photocatalytic particles (CuGa 1-y In y ) 0.8 Zinc0.4 Synthesis of S2) Photocatalytic particles (CuGa 1-y In y ) 0.8 Zinc 0.4 The synthesis of S2 was carried out in the same manner as the synthesis of the particles in Example 11-4. The raw materials Cu2S, Ga2S3, In2S3, ZnS, and S were mixed in an element ratio of Cu / Ga / In / Zn / S of 0.8 / ((1-y)*0.8)*1.2 / y*0.8 / 0.4 / 4 (Ga element 20% excess, S element 100% excess), and a solid-phase synthesis was carried out in a degassed sealed ampoule at 800℃ for 10 hours to obtain the target product (* indicates multiplication). The DRS (diffuse reflectance spectrum) of the photocatalyst particles synthesized by this method is shown in Figure 22 (Figure 113-1).

[0187] The absorption edge wavelength and evaluation results of each hydrogen generation photocatalyst particle are shown in Table 13.

[0188] [Table 13]

[0189] The time course of the water splitting activity corresponding to Table 13 is shown in Figure 22 (Figure 113-4).

[0190] (Summary of Example 13) All photocatalyst plates showed robust film strength. Visible light responsive photocatalyst particles for hydrogen generation, Ru(0.5wt%) / (CuGa 1-y In y ) 0.8 Zinc 0.4 The water splitting activity of the photocatalyst plate containing S2 was highest in the configuration containing photocatalyst particles having visible light responsive photocatalyst particles for hydrogen generation with a composition having an absorption edge on the shortest wavelength side among the photocatalyst particles in Example 13 (Example 13-1).

[0191] (Summary of all examples) A photocatalyst plate in which a photocatalyst particle layer consisting of a resin substrate, visible light responsive photocatalyst particles for hydrogen generation, visible light responsive photocatalyst particles for oxygen generation, and conductive reduced graphene oxide (RGO) was bonded by applying a pressure load showed high water splitting activity and robust film strength. The pressure load and reduced graphene oxide (RGO) promote the Z-scheme water splitting reaction by the photocatalyst particles for hydrogen generation and the photocatalyst particles for oxygen generation, and contribute to improving the film strength (Comparison with Example 1 and Comparative Example 1). It is believed that reduced graphene oxide (RGO) functions as a conductive material that facilitates electron transfer within the photocatalyst particle layer under pressure conditions, and as a binder material that improves the adhesion strength between photocatalyst particles and between the photocatalyst particles and the substrate.

[0192] This photocatalyst plate configuration can be applied to visible light responsive photocatalyst particles for hydrogen generation and visible light responsive photocatalyst particles for oxygen generation of various structural formulas (Examples 11, 12, and 13).

[0193] A photocatalyst plate configured by combining RGO-added visible light responsive photocatalyst particles for oxygen generation RGO (5 wt%)-CoOx (0.5 wt%) / BiVO4 with a primary particle size of approximately 1 μm with visible light responsive metal sulfide photocatalyst particles for hydrogen generation Ru (0.75 wt%) / Cu3VS4 with a large primary particle size of 5 to 10 μm has particularly excellent water splitting activity (Example 11). This water splitting activity may be significantly affected by the primary particle size of Cu3VS4, and for example, a primary particle size of 5 to 10 μm was found to be suitable in Example 8. One of the reasons for this is thought to be that if the primary particle size is too small, the voids in the photocatalyst particle layer may be reduced by compression due to pressure, which may hinder gas generation, and if the primary particle size is too large, the surface area of ​​the photocatalyst particles may be reduced, which may reduce the number of active photocatalyst species.

[0194] In addition, in Example 8, the configuration of the photocatalyst plate, which contains Cu3VS4 with a primary particle size of 5 to 10 μm, may contribute to ensuring an appropriate amount of voids within the photocatalyst particle layer by allowing the large particle size photocatalyst particles to function as spacers against compression during the pressurizing process. It was also suggested that the water splitting activity of the photocatalyst plate with this configuration was affected by the pressure during the pressurization step. For example, in the embodiments of Examples 1 and 2, the pressure was 0.5 ton / cm 2 The results are considered to be optimal, and it can be assumed that there is an optimal pressure value depending on the type of catalyst particle. On the other hand, if the pressure load is too large, the voids in the photocatalyst particle layer are reduced, and it is considered that the generation of gas as described above may become difficult to occur.

[0195] The optimal composition ratio (weight ratio) of the visible light responsive photocatalyst particles for hydrogen generation and the visible light responsive photocatalyst particles for oxygen generation varies depending on factors such as the primary particle size of the photocatalyst particles for hydrogen generation used, but it was suggested from Examples 7 and 9 that excellent water splitting activity is exhibited over a relatively wide range.

[0196] As for the combination of primary particles of photocatalyst particles, it is suggested from Example 3 that the photocatalyst particles for hydrogen generation tend to show higher water splitting activity when they are larger than the photocatalyst particles for oxygen generation. This may be because the arrangement of reduced graphene oxide (RGO) in the photocatalyst particle layer may not be suitable for electron transfer between the photocatalyst particles.

[0197] Furthermore, Example 6 suggests that a more suitable elemental technology for promoting the water splitting activity of a photocatalyst plate is to support a co-catalyst on the hydrogen generation photocatalyst particles and then to heat them during the support process.

[0198] Furthermore, it was suggested that a method of applying pressure through a release film having a release layer such as ITO during the pressure application process is an effective elemental technology for obtaining a homogeneous and highly active photocatalyst particle layer.

[0199] The results of Example 4, for example, suggest that the highly efficient water splitting activity of the photocatalyst plate according to the present invention is preferably achieved by forming a photocatalyst particle composition by a method including a pressurizing step of visible light responsive photocatalyst particles for generating hydrogen, visible light responsive photocatalyst particles for generating oxygen, and conductive reduced graphene oxide (RGO). [Industrial Applicability]

[0200] Photocatalyst particle compositions and photocatalyst plates that can efficiently exhibit water splitting activity when irradiated with visible light can be realized on a resin substrate that is economical, lightweight, and flexible, and provide photocatalyst plates that are robust and easy to transport, store, and process. This technology is necessary for increasing the area of ​​hydrogen production equipment in promoting energy systems that solve environmental problems. The present invention provides a photocatalyst plate including a resin substrate having a specific particle size range, visible light responsive photocatalyst particles for hydrogen generation, visible light responsive photocatalyst particles for oxygen generation, and a photocatalyst particle layer including conductive reduced graphene oxide (RGO) in a specific content range, and a technique for manufacturing the same, which will be an important device that can provide a large-area hydrogen production device with high water splitting activity, robustness, and economic efficiency. In addition, the performance of the photocatalyst plate is expected to be improved by using a pressurization process in combination. [Explanation of symbols]

[0201] 1. Reduced graphene oxide (RGO) 2. Photocatalyst particles for hydrogen generation 3. Photocatalyst particles for oxygen generation 4 Photocatalyst particles for hydrogen generation that differ from 2 in composition, primary particle size, etc. 5 Photocatalyst particles for oxygen generation that differ from 3 in composition, primary particle size, etc. 11 Base material 12 Photocatalyst particle layer 13 Photocatalyst particle layer with different composition, primary particle size, distribution, etc. from 12 21 Photocatalyst particle layer for hydrogen generation that may contain reduced graphene oxide (RGO) 22 Photocatalyst particle layer for oxygen generation that may contain reduced graphene oxide (RGO) 23 Photocatalyst particle layer for hydrogen generation that may contain reduced graphene oxide (RGO) with different composition, primary particle size, distribution, etc. from 21 24 Photocatalyst particle layer for oxygen generation that may contain reduced graphene oxide (RGO) with different composition, primary particle size, distribution, etc. from 22 31 Reduced graphene oxide (RGO) layer 201, 301 Reaction tube 202, 302 Cutoff Filter 203, 303 Vacuum line for exhausting hydrogen gas generated 204, 304 Argon gas supply line for gas chromatograph 205, 305 Constant temperature bath 206, 306 Stirrer 207, 307 Stirring bar 208 Photocatalyst plate (fixed on a support in a water solvent) 209 Water Solvent Liquid Level 309 Liquid surface of photocatalyst particle component suspension 210, 310 Cardiovascular system 211, 311 Pressure gauge 212, 312 Gas chromatograph 213, 313 Liebig cooling tube

Claims

1. The photocatalyst particle composition includes visible light responsive photocatalyst particles for generating hydrogen, visible light responsive photocatalyst particles for generating oxygen, a photocatalyst particle construct including carbon fine powder, and an organic material substrate, The visible light responsive photocatalyst particles for generating hydrogen and the visible light responsive photocatalyst particles for generating oxygen have a primary particle size of 0.05 μm or more and 50 μm or less, The primary particle size of the visible light responsive photocatalyst particles for generating hydrogen is 1.5 times or more and 500 times or less than the primary particle size of the visible light responsive photocatalyst particles for generating oxygen, A photocatalyst plate in which the carbon fine powder is present in an amount of 0.1 wt % or more and 30 wt % or less relative to the visible light responsive photocatalyst particles for generating oxygen.

2. A photocatalyst plate as described in claim 1, wherein the carbon micropowder is reduced graphene oxide (RGO).

3. 3. The photocatalyst plate according to claim 1, wherein the visible light responsive photocatalyst particles for hydrogen generation include photocatalyst particles containing a metal sulfide.

4. The photocatalyst plate according to any one of claims 1 to 3, wherein the visible light responsive photocatalyst particles for generating hydrogen contain a promoter which is a metal component of Groups 8 to 11 of the Periodic Table.

5. A photocatalyst plate according to any one of claims 1 to 4, wherein the primary particle size of the visible light responsive photocatalyst particles for hydrogen generation is 2 μm or more and 50 μm or less.

6. A photocatalyst plate according to any one of claims 1 to 5, wherein the weight ratio of the visible light responsive photocatalyst particles for hydrogen generation to the visible light responsive photocatalyst particles for oxygen generation is 10 / 90 to 80 / 20.

7. A photocatalyst particle structure including visible light responsive photocatalyst particles for generating hydrogen, visible light responsive photocatalyst particles for generating oxygen, and carbon fine powder, The visible light responsive photocatalyst particles for hydrogen generation have a size of 1.1 μm or more and 50 μm or less, The primary particle size of the visible light responsive photocatalyst particles for generating oxygen is 0.05 μm or more and 50 μm or less, The primary particle size of the visible light responsive photocatalyst particles for generating hydrogen is 1.5 times or more and 500 times or less than the primary particle size of the visible light responsive photocatalyst particles for generating oxygen, The carbon fine powder is present in an amount of 0.1 wt % or more and 30 wt % or less relative to the visible light responsive photocatalyst particles for generating oxygen.

8. A method for producing a photocatalyst particle construct, comprising a step of contacting the visible light responsive photocatalyst particles for generating hydrogen according to claim 7, the visible light responsive photocatalyst particles for generating oxygen, and the carbon fine powder, and then pressurizing the contacted particles.

9. A method for manufacturing a photocatalyst plate, comprising a step of contacting the visible light responsive photocatalyst particles for hydrogen generation according to any one of claims 1 to 6, the visible light responsive photocatalyst particles for oxygen generation, the carbon fine powder, and the organic material substrate, and then applying pressure.

10. The method for producing a photocatalyst plate according to claim 9, wherein the organic material substrate is a resin substrate.

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