Junction photocatalyst

Abstract

Provided is a junction photocatalyst exhibiting higher catalytic activity and greater freedom in molecular design than conventional junction photocatalysts. The junction photocatalyst has a solid mediator between an oxygen generating photocatalyst and a hydrogen generating photocatalyst including an organic semiconductor, wherein the hydrogen generating photocatalyst and the solid mediator are bonded together, and the oxygen generating photocatalyst and the solid mediator are bonded together.

Description

Bonded photocatalyst

[0001] The present invention relates to a junction-type photocatalyst having a solid mediator between a hydrogen-generating photocatalyst containing an organic semiconductor and an oxygen-generating photocatalyst, a photocatalytic composite having the junction-type photocatalyst on a substrate, a method for producing hydrogen, and a method for producing the junction-type photocatalyst.

[0002] In recent years, technology for producing hydrogen and oxygen by splitting water using a photocatalyst and sunlight has been attracting attention. When splitting water using a photocatalyst, it is preferable to use a photocatalyst that catalyzes both the reduction reaction of water (reduction reaction of protons) and the oxidation reaction of water.

[0003] Non-Patent Document 1 discloses the use of covalent organic frameworks (COFs) in a proton reduction reaction to generate hydrogen. However, it has been reported that hydrogen generation is possible only in the presence of a specific sacrificial reagent such as ascorbic acid. Non-Patent Document 2 discloses the use of COFs as a hydrogen-generating photocatalyst and BiFeO as an oxygen-generating photocatalyst. ３ The water splitting reaction using

[0004] Furthermore, Patent Document 1 proposes a photocatalytic layer including first photocatalytic particles of a visible light responsive type for generating hydrogen, second photocatalytic particles of a visible light responsive type for generating oxygen, and conductive particles that are provided between the first photocatalytic particles and the second photocatalytic particles and that are capable of storing electrons and holes and have a Fermi level that is more negative than the electronic energy level of the upper end of the valence band of the first photocatalytic particles and more positive than the electronic energy level of the lower end of the conduction band of the second photocatalytic particles, wherein the conductive particles are arranged so as to be connected to the first photocatalytic particles and the second photocatalytic particles.

[0005] Patent Document 2 discloses a bonded photocatalyst having a solid mediator between a hydrogen-generating photocatalyst and an oxygen-generating photocatalyst, a photocatalyst composite having the bonded photocatalyst on a substrate, a method for producing the bonded photocatalyst, and a method for producing hydrogen using the bonded photocatalyst or the photocatalyst composite.

[0006] JP 2017-124394 A International Publication No. 2022 / 045283 Pamphlet

[0007] Chunzhi Li et al., Nature Communications, 2022, 13, 2357M. L. Xu et al., Angew. Chem. Int. Ed., 2022, 61, e202210700

[0008] Junction-type photocatalysts, in which a hydrogen-generating photocatalyst and an oxygen-generating photocatalyst are joined together, and junction-type photocatalysts, in which a hydrogen-generating photocatalyst and an oxygen-generating photocatalyst are joined together via a metal or metal oxide, have a very simple structure and exhibit catalytic activity in the decomposition reaction of water, etc., under visible light irradiation. In recent years, there has been a demand for even higher catalytic activity.

[0009] Furthermore, conventional junction-type photocatalysts include hydrogen-generating photocatalysts that use inorganic semiconductors containing inorganic compounds. However, it is not easy to design molecules that can exhibit the required performance. For example, it has been found that there are many constraints when designing inorganic compounds with a small band gap and a wide light absorption range.

[0010] On the other hand, if a so-called organic semiconductor such as COF can be used as a hydrogen generating photocatalyst, the degree of freedom in molecular design will be high, and it will be possible to narrow the band gap and increase catalytic activity.

[0011] However, organic semiconductors have low affinity with inorganic semiconductors, metals, or metal oxides, making them difficult to bond, and manufacturing bonded photocatalysts is not easy. As a result, hydrogen-generating photocatalysts using organic semiconductors have rarely been used.

[0012] The present invention has been made in view of the above circumstances, and provides a junction-type photocatalyst that exhibits higher catalytic activity and offers greater freedom in molecular design than conventional junction-type photocatalysts.

[0013] As a result of extensive research, the present inventors have found that the above problems can be solved by the following junction-type photocatalyst.

[0014] That is, the present invention relates to the following 1. to 4.: 1. A bonded photocatalyst having a solid mediator between a hydrogen generating photocatalyst containing an organic semiconductor and an oxygen generating photocatalyst, the hydrogen generating photocatalyst and the solid mediator being bonded together, and the oxygen generating photocatalyst and the solid mediator being bonded together. 2. A photocatalyst composite having the bonded photocatalyst on a substrate. 3. A method for producing hydrogen, comprising irradiating the bonded photocatalyst or the photocatalyst composite with light in the presence of water or alcohol. 4. A method for producing the bonded photocatalyst, comprising using an ionic polymer as a bonding agent to bond the hydrogen generating photocatalyst and the solid mediator and / or to bond the oxygen generating photocatalyst and the solid mediator.

[0015] The junction-type photocatalyst of the present invention is useful because the hydrogen-generating photocatalyst contains an organic semiconductor, making it possible to obtain a junction-type photocatalyst containing a hydrogen-generating photocatalyst with excellent freedom in molecular design.In addition, the catalytic activity for water-splitting reactions is improved, and water can be split into oxygen and hydrogen with high water-splitting reaction efficiency.

[0016] A schematic diagram of a layer structure formed by a hexagonal COF. ４ FIG. 1 is an SEM image of the COF used in Example 1. FIG. 2 is an SEM image of the COF used in Example 1. FIG. 3 is an SEM image of the COF used in Example 1. FIG. 4 is an SEM image of the COF used in Example 1. FIG. 5 is an SEM image of the COF used in Example 5. FIG. 6 is an SEM image of the COF used in Example 5. FIG. 7 is an SEM image of the COF used in Example 5.

[0017] The present invention will be described in detail below.

[0018] <Joint-type photocatalyst> The joint-type photocatalyst of the present invention has a solid mediator between a hydrogen-generating photocatalyst containing an organic semiconductor and an oxygen-generating photocatalyst, and the hydrogen-generating photocatalyst and the solid mediator are joined together, and the oxygen-generating photocatalyst and the solid mediator are joined together.

[0019] Specifically, the hydrogen generating photocatalyst containing the organic semiconductor is directly or indirectly bonded to another part of the solid mediator. The oxygen generating photocatalyst is directly or indirectly bonded to a part of the solid mediator. Furthermore, the hydrogen generating photocatalyst and the oxygen generating photocatalyst are bonded via at least the solid mediator. Examples of bonding agents that can be used for bonding include ionic polymers that utilize ionic bonds.

[0020] Furthermore, it is preferable that the solid mediator and the hydrogen generating photocatalyst are bonded via an ionic polymer, and it is also preferable that the solid mediator has an ionic group, and that the solid mediator and the hydrogen generating photocatalyst are bonded via an ionic polymer having a charge opposite to that of the ionic group possessed by the solid mediator (preferably an ionic group introduced into the solid mediator).

[0021] One embodiment of the bonded photocatalyst of the present invention is, for example, one in which the solid mediator has an ionic group, the hydrogen generating photocatalyst has the ionic polymer having an opposite charge to the charge of the ionic group, and the solid mediator and the hydrogen generating photocatalyst are bonded together by an ionic bond between the ionic group and the ionic polymer.

[0022] Furthermore, one embodiment of the bonded photocatalyst of the present invention is, for example, a solid mediator having an ionic group, a hydrogen generating photocatalyst having an ionic polymer A and, via the ionic polymer A, an ionic polymer B having a charge opposite to that of the ionic group, and the solid mediator and the hydrogen generating photocatalyst are bonded together by an ionic bond between the ionic group and the ionic polymer B.

[0023] Furthermore, one embodiment of the bonded photocatalyst of the present invention is one in which the solid mediator has an ionic group and, via the ionic group, an ionic polymer B having a charge opposite to that of the ionic group, and the hydrogen generating photocatalyst has an ionic polymer A, and the solid mediator and the hydrogen generating photocatalyst are bonded together by an ionic bond between the ionic polymer B and the ionic polymer A.

[0024] When the ionic group of the solid mediator is an anionic group, the ionic polymer A is an anionic polymer, and the ionic polymer B is a cationic polymer.

[0025] When the ionic group of the solid mediator is a cationic group, the ionic polymer A is a cationic polymer, and the ionic polymer B is an anionic polymer.

[0026] In the present invention, "bonding" refers to a state in which the oxygen generating photocatalyst and the solid mediator, the hydrogen generating photocatalyst and the solid mediator, or the oxygen generating photocatalyst and the hydrogen generating photocatalyst are integrated by ionic bonds, hydrogen bonds, electrostatic attraction, van der Waals forces, or the like to such an extent that they do not separate when a photocatalytic reaction is carried out. Here, when at least one of the oxygen generating photocatalyst and the solid mediator has an ionic group, the state in which the oxygen generating photocatalyst and the solid mediator are integrated via the ionic group is also referred to as "(indirect) bonding" between the oxygen generating photocatalyst and the solid mediator. Similarly, when either the hydrogen generating photocatalyst and the solid mediator or the oxygen generating photocatalyst and the hydrogen generating photocatalyst has an ionic group, the respective states in which they are integrated via the ionic group are also referred to as "bonding" between the hydrogen generating photocatalyst and the solid mediator, and "bonding" between the oxygen generating photocatalyst and the hydrogen generating photocatalyst. In addition, the state in which they are integrated via a bonding agent is also referred to as "bonding" between the oxygen generating photocatalyst and the solid mediator, "bonding" between the hydrogen generating photocatalyst and the solid mediator, and "bonding" between the oxygen generating photocatalyst and the hydrogen generating photocatalyst, respectively.

[0027] In the present invention, the term "electron collecting surface" refers to an exposed crystal surface in the various structures of the oxygen generating photocatalyst where excited electrons are most likely to collect.

[0028] (Hydrogen-generating photocatalyst) The hydrogen-generating photocatalyst contains an organic semiconductor. By containing the organic semiconductor, titanium oxide (TiO ２ Compared to inorganic semiconductors containing metal oxides such as ZnO, it is possible to obtain hydrogen-generating photocatalysts with excellent molecular design freedom, which is useful.

[0029] The hydrogen generating photocatalyst is not particularly limited as long as it contains an organic semiconductor, but it is particularly preferred that the organic semiconductor is a covalent organic framework (COF).

[0030] The COF is a crystalline organic polymer with two- or three-dimensional periodicity formed by covalent bonds. Compared to conventional hydrogen-generating photocatalysts containing inorganic semiconductors, the combination of organic molecules makes molecular design (structural control) easier, and a structure that satisfies the required performance can be achieved.

[0031] For example, by adopting a long conjugated structure in the molecular structure of COF, the energy gap (energy difference) between the HOMO energy and LUMO energy of the molecule can be reduced, and the band gap becomes narrower (smaller), resulting in a hydrogen-generating photocatalyst with a wide light absorption range.

[0032] The two-dimensional COF is represented by the symmetric unit C ２ , C ３ , C ４ , and C ６ By linking or bonding these, it is possible to provide diversity in the topology and pore shape of the two-dimensional COF.

[0033] Here, Ar represents a bond, an element, or a skeleton of benzene or an aromatic compound (hereinafter, also simply referred to as skeleton Ar). ｘ represents a substituent. ｘExamples of the substituent Rx include a boronic acid group, an amidoborane group, an amino group, a hydroxy group, a hydrazide group, an orthothioaniline group, a cyano group, a cyanomethyl group, a ketone group, a carboxylic acid anhydride group, a carboxylic acid halide group, an aldehyde group, and a halogen group. Note that these substituents Rx may contain an aromatic compound. Examples include an aromatic amino group and an aromatic aldehyde group.

[0034] The topology diagrams that make up a two-dimensional COF include the following: (1) hexagonal type, (2) tetragonal type, (3) rhombus type, and (4) triangle type.

[0035] Among these, the (1) hexagonal type is preferable from the viewpoint of improving crystallinity and photocatalytic activity, because the conjugated system (conjugation length) in the COF can be extended in the in-plane (horizontal) direction of the COF and / or, when the COF forms a layer structure, in the stacking (vertical) direction (see FIG. 1 ).

[0036] Furthermore, in the case of the (1) hexagonal COF, the hexagonal pores tend to have uniform pore sizes. Furthermore, because the pore sizes are uniform, it tends to be easier to control the adsorption and desorption behavior of the sacrificial reagent and water molecules used as reactants in the synthesis of the COF, as well as the hydrogen molecules generated as a product when the COF functions as a hydrogen generating photocatalyst. Furthermore, the hydrogen generating photocatalyst obtained using the COF can achieve both a small band gap and high photocatalytic activity.

[0037] The three-dimensional COFs require precursor compounds with three-dimensional branched structures that are all covalently linked, and like two-dimensional COFs, they can have a variety of topologies and pore shapes.

[0038] The three-dimensional COF is composed of the symmetric unit and the tetrahedral unit (hereinafter referred to as "T") that contributes to the three-dimensional network. ｄ By linking or combining the COFs with other COFs, it is possible to provide a variety in the topology and pore shape of the three-dimensional COFs.

[0039] The topology diagrams that make up three-dimensional COFs include the following: (5) dia type, (6) dia type, ctn type, (7) bor type, ctn type, srs type, (8) pts type, and (9) dia type, pts type.

[0040] The topology diagram of the COF is largely determined by the geometric shape (the symmetric unit) of the precursor compound, which is the raw material for synthesizing the COF, and the geometric shape of the precursor compound also affects the physical properties of the COF.

[0041] The geometric shape of the precursor compound is preferable, for example, when the molecular skeleton of the COF is planar and the COF forms a layer structure, since the conjugated system (conjugation length) can be extended in the stacking (vertical) direction, and a COF having a narrow (small) band gap and improved mobility of excited electrons and holes tends to be obtained.

[0042] Specific examples based on the topology diagram of the COF include COFs formed by combining multiple symmetric units as shown below. These COF topology diagrams may be used alone or in combination of two or more.

[0043] (Symmetric unit (geometric shape of precursor compound)) The symmetric unit C used in the synthesis of the COF ２ The skeleton Ar is a single bond, and the substituent R Ｘ a compound in which the skeleton Ar is an aromatic skeleton and two substituents R are bonded to each other at an angle of 180° from the aromatic skeleton; Ｘ The compound having an aromatic skeleton may have, for example, a substituent R Ｘ The aromatic skeleton is a benzene skeleton, a biphenyl skeleton, an anthracene skeleton, a triazine skeleton, a porphyrin skeleton, etc. Specific examples include hydrazine, p-phenylenediamine-containing compounds, and 4,4'-diaminobiphenyl-containing compounds.

[0044] Symmetric unit C used in the synthesis of the COF３ The skeleton Ar is an aromatic skeleton, and three substituents R Ｘ The compound may have, for example, substituents R Ｘ Examples of the aromatic skeleton include a benzene skeleton, a triazine skeleton, a porphyrin skeleton, a naphthalene skeleton, a triphenylbenzene skeleton, a triphenyltriazine skeleton, a triphenylamine skeleton, a triphenylphosphine skeleton, etc. Specific examples include 1,3,5-triformylbenzene-containing compounds, tris(4-formylphenyl)amine-containing compounds, and 2,4,6-tris(4-aminophenyl)triazine-containing compounds.

[0045] Symmetric unit C used in the synthesis of the COF ４ The skeleton Ar is an aromatic skeleton, and four substituents R Ｘ The compound may have, for example, substituents R Ｘ Examples of aromatic compounds include those having a benzene skeleton, a biphenyl skeleton, an anthracene skeleton, a triazine skeleton, a porphyrin skeleton, etc. Specific examples include 5,10,15,20-tetrakis(4-aminophenyl)porphyrin, 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin, and 2,3,9,10,16,17,23,24-octakis(amino)phthalocyanine.

[0046] Symmetric unit C used in the synthesis of the COF ６ The skeleton Ar is an aromatic skeleton, and six substituents R are attached to the aromatic skeleton on a plane at angles of 60° to each other. Ｘ Specific examples include hexa(4-formylphenyl)benzene, hexa(4-formylphenyl)-perylhexabenzocoronene, and the like.

[0047] The tetrahedral unit T contributes to the three-dimensional network used in the synthesis of the COF. ｄThe compound has a central skeleton and four substituents R Ｘ Specific examples include tetrakis(4-boronylphenyl)methane, tetrakis(4-aminophenyl)methane, and tetrakis(4-formylphenyl)methane.

[0048] Examples of the combination of the symmetric units include the combination shown in Chemical Formula 2. Examples of the combination of the symmetric unit and the tetrahedral unit include the combination shown in Chemical Formula 4.

[0049] The COF is a structure having periodicity obtained by self-organizing polycondensation of organic molecules having symmetry such as linear, equilateral triangular, or regular tetrahedral symmetry.

[0050] The structure of the structure is a structure obtained by polycondensation of a single molecule or a structure obtained by polycondensation of two or more types of molecules, and the molecular design (structural control) and physical properties such as electronic conductivity can be controlled by combining the molecules. In addition, a crystalline structure with two-dimensional periodicity is preferable from the viewpoints of suppressing charge recombination between electrons and holes and charge mobility (mobility).

[0051] Furthermore, when the topology is a two-dimensional topology diagram, the conjugated system (conjugation length) can be extended in the in-plane (horizontal) direction of the COF and / or in the stacking (vertical) direction when the COF forms a layer structure. Therefore, a COF with high crystallinity tends to be obtained, which is preferable.

[0052] In the synthesis of the COF, a COF having a desired structure and physical properties can be obtained in view of the bonding mode and / or topology diagram of the COF.

[0053] Examples of the bonding type of the COF include (10) boroxine type, (11) boronate ester type, (12) borazine type, (13) imide type, (14) amide type, (15) dioxin type, (16) imine type, (17) hydrazone type, (18) azine type, (19) oxazole type, (20) thiazole type, (21) squaraine type, (22) triazine type, (23) phenazine type, (24) amino type, and (25) olefin type, as shown in the following structural formulas.

[0054] The (16) imine type may have a keto-enamine structure. Among these, the bonding mode of the COF is preferably one or more of the (16) imine type and the (24) amino type, and more preferably the (16) imine type, from the viewpoint of improving crystallinity and photocatalytic activity.

[0055]

[0056]

[0057] The molecular skeletons of the bonding modes shown in (10) to (25) all have a benzene skeleton. The bonding mode of the COF may also have a skeleton of an aromatic compound such as a biphenyl skeleton, a triphenylamine skeleton, a triphenylphosphine skeleton, a naphthalene skeleton, an anthracene skeleton, or a triazine skeleton.

[0058] Specific examples based on the bonding mode of the COF include COFs formed by a polycondensation reaction of precursor compounds shown below. These bonding modes of the COF may be used alone or in combination of two or more.

[0059] Although it is possible to form a COF using one precursor compound that can be polycondensed alone, from the viewpoint of obtaining a hydrogen-generating photocatalyst with a small band gap and a wide light absorption range and from the viewpoint of enhancing photocatalytic activity, it is preferable to form a COF with a long conjugated structure by a polycondensation reaction of two or more precursor compounds. By adopting a long conjugated structure in the molecular structure of the COF, it is possible to reduce the energy gap (energy difference) between the HOMO energy and LUMO energy of the molecule, and by narrowing (reducing) the band gap, it is possible to obtain a hydrogen-generating photocatalyst with a wide light absorption range.

[0060] (Precursor Compound) The precursor compound used for synthesizing the COF may be one that can contribute to a polycondensation reaction. Specific examples include boronic acid-containing compounds, amidoborane-containing compounds, hydrazide-containing compounds, orthothioaniline-containing compounds, cyano group-containing compounds, acetonitrile-containing compounds, aromatic boronic acids, aromatic amidoboranes, aromatic amines, aromatic catechols, aromatic hydrazides, aromatic orthothioanilines, aromatic nitriles, aromatic acetonitriles, aromatic quinones, and hydrazines. These compounds may be partially substituted with amino groups or hydroxyl groups.

[0061] Examples of COFs obtained by polycondensation of two or more different precursor compounds include the following (a) to (n): (a) a COF having (11) a boronic acid ester type among the above-mentioned bonding modes, obtained by a dehydration condensation reaction between an aromatic boronic acid and an aromatic catechol; (b) a COF having (13) an imide type among the above-mentioned bonding modes, obtained by a dehydration condensation reaction between an aromatic amine and an aromatic carboxylic anhydride; (c) a COF having (14) an amide type among the above-mentioned bonding modes, obtained by an amidation reaction between an aromatic amine and an aromatic carboxylic acid halide; (d) a COF having (15) a dioxin type among the above-mentioned bonding modes, obtained by an oxidation reaction between an aromatic catechol and an aromatic halide; and (e) a COF having (16) an imine type among the above-mentioned bonding modes, obtained by a condensation reaction between an aromatic amine and an aromatic aldehyde. (f) A COF having (17) a hydrazone type among the above bonding modes, obtained by a condensation reaction between an aromatic hydrazide and an aromatic aldehyde. (g) A COF having (18) an azine type among the above bonding modes, obtained by a condensation reaction between a hydrazine and an aromatic aldehyde. (h) A COF having (19) an oxazole type among the above bonding modes, obtained by a dehydration condensation reaction between an aromatic catechol and an aromatic aldehyde. (i) A COF having (20) a thiazole type among the above bonding modes, obtained by a desulfurization reaction between an aromatic orthothioaniline and an aromatic aldehyde. (j) A COF having (21) a squaraine type among the above bonding modes, obtained by a dehydration condensation reaction between an aromatic amine and an oxocarbonic acid. (k) A COF having (22) a triazine type among the above bonding modes, obtained by a dehydration condensation reaction between an aromatic amidine and an aromatic aldehyde. (l) A COF having (23) a phenazine type among the above bonding modes, obtained by a condensation reaction between an aromatic quinone and an aromatic diamine. (m) A COF having (24) an amino type among the above bonding modes, obtained by a substitution reaction between an aromatic amine and an aromatic halide. (n) A COF having (25) an olefin type among the above bonding modes, obtained by a condensation reaction between an aromatic acetonitrile and an aromatic aldehyde.

[0062] Among these, from the viewpoint of extending the conjugation length of the COF and narrowing the band gap, the bonding type of the COF is preferably any one selected from (16) imine type, (17) hydrazone type, (19) oxazole type, (20) thiazole type, (21) squaraine type, (22) triazine type, and (24) amino type.

[0063] The COF is formed by combining one or more of the precursor compounds described above. The precursor compounds form a pair (donor-acceptor) of a compound having an electron-donating group (donor) and a compound having an electron-withdrawing group (acceptor). The COF obtained by combining these compounds can have high mobility of excited electrons and holes, thereby improving photocatalytic activity.

[0064] Examples of the electron-donating group include a hydroxy group, an alkoxy group, a dialkylamino group, an alkyl group, an aryl group, and a halogen group.

[0065] Examples of the electron-withdrawing group include a cyano group, a nitro group, a ketone group, an amide group, an ester group, and a trifluoromethyl group.

[0066] As a method for synthesizing the COF, for example, a method for synthesizing an imine-type COF, which is one of the bonding modes of the COF, will be exemplified below.

[0067] (Method for synthesizing imine-type COF) The method for synthesizing the imine-type COF is not particularly limited, and examples thereof include a solvothermal method, a hydrothermal synthesis method, a reflux method, a microwave synthesis method, a mechanochemical method, etc. Among these, from the viewpoint of enhancing crystallinity and photocatalytic activity, one selected from the solvothermal method and the reflux method is preferred.

[0068] The imine-type COF can be synthesized, for example, by the following steps based on the solvothermal method.

[0069] Synthesis step: In a reaction vessel, the aromatic amine and the aromatic aldehyde (the two precursor compounds capable of polycondensation), a solvent, a catalyst, etc. are mixed to obtain a mixture (reaction solution). The resulting reaction solution is degassed and then heated for a certain period of time to dehydrate and condense the two precursor compounds capable of polycondensation. Once the reaction is complete, the COF-containing liquid is removed from the reaction vessel.

[0070] Washing step: The removed COF-containing liquid is washed with a solvent, and then the washed COF-containing liquid is filtered to recover the precipitate.

[0071] Drying step: The recovered precipitate is dried by maintaining it at a temperature equal to or higher than the boiling point of the solvent used for washing.

[0072] Pulverization step: The dried product is pulverized using a pulverizer and, if necessary, using a pulverization medium and a solvent.

[0073] Synthesis confirmation method: To confirm that the pulverized product obtained by the above process is a COF, a scanning electron microscope (SEM), powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), or an ultraviolet-visible spectrophotometer can be used to confirm the synthesis of the COF. XRD can be used as a method for confirming the crystallinity of the COF. FT-IR can be used as a method for confirming the degree of polymerization of the COF.

[0074] In addition, by increasing the crystallinity of the COF, the mobility of excited electrons and holes is improved, and the photocatalytic activity of the hydrogen generating photocatalyst obtained from the COF is improved, which is useful.

[0075] In addition, increasing the degree of polymerization of the COF is useful because it forms a highly ordered framework, which improves chemical stability and thermal stability.Furthermore, increasing the degree of polymerization of the COF forms a highly ordered framework, which improves the crystallinity of the COF and the photocatalytic activity of the resulting junction-type photocatalyst, which is useful.

[0076] Examples of catalysts used in the synthesis include acetic acid, lactic acid, malic acid, citric acid, sulfuric acid, nitric acid, hydrochloric acid, trifluoroacetic acid, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, and ammonia. These may be used alone or in combination of two or more, or may be salts formed from an acid and a base. Among these, acetic acid is preferred from the viewpoint of increasing the degree of polymerization and crystallinity of the COF.

[0077] The amount of catalyst used in the synthesis is preferably 100 parts by mass or more, more preferably 200 parts by mass or more, and even more preferably 400 parts by mass or more, relative to 100 parts by mass of the raw materials used, from the viewpoint of the degree of polymerization and crystallinity of the resulting COF. Also, from the viewpoint of improving the degree of polymerization and crystallinity of the resulting COF, the amount of catalyst used is preferably 1,000 parts by mass or less, more preferably 800 parts by mass or less, and even more preferably 600 parts by mass or less, relative to 100 parts by mass of the raw materials used.

[0078] Examples of solvents used in the synthesis include mesitylene, 1,4-dioxane, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, γ-butyrolactone, paratoluenesulfonic acid, toluene, piperidine, pyridine, tetrahydrofuran, acetone, and water. These may be used alone or in combination of two or more. Among these, from the viewpoint of increasing the degree of polymerization and crystallinity of COF, one or more selected from mesitylene and 1,4-dioxane are preferred, and a mixed solvent of mesitylene and 1,4-dioxane is more preferred.

[0079] The amount of solvent used in the synthesis is preferably 300 parts by mass or more, more preferably 500 parts by mass or more, even more preferably 1000 parts by mass or more, and even more preferably 1200 parts by mass or more, relative to 100 parts by mass of the raw materials used, from the viewpoint of increasing the degree of polymerization and crystallinity of the COF. Also, from the viewpoint of increasing the degree of polymerization and crystallinity of the COF, the amount of solvent used is preferably 50000 parts by mass or less, more preferably 10000 parts by mass or less, even more preferably 5000 parts by mass or less, and even more preferably 3000 parts by mass or less, relative to 100 parts by mass of the raw materials used.

[0080] From the viewpoint of increasing the degree of polymerization of COF, the reaction temperature is preferably 40° C. or higher, more preferably 80° C. or higher, and even more preferably 100° C. or higher. From the viewpoint of increasing the photocatalytic activity of COF, the reaction temperature is preferably 300° C. or lower, more preferably 200° C. or lower, and even more preferably 150° C. or lower.

[0081] The reaction time is preferably 3 hours or more, more preferably 24 hours or more, and even more preferably 72 hours or more from the viewpoint of increasing the degree of polymerization of the COF, and is preferably 1,000 hours or less, more preferably 300 hours or less, and even more preferably 200 hours or less from the viewpoint of increasing the productivity of the COF.

[0082] Examples of solvents used in the washing step include mesitylene, 1,4-dioxane, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, γ-butyrolactone, paratoluenesulfonic acid, toluene, piperidine, pyridine, tetrahydrofuran, acetone, and water. These may be used alone or in combination of two or more. Among these, from the viewpoint of enhancing the photocatalytic activity of COF, one or more selected from dimethylformamide, tetrahydrofuran, and acetone are preferred.

[0083] The COF obtained by the synthesis method described above functions as a hydrogen generating photocatalyst containing an organic semiconductor, and is excellent in the degree of freedom in molecular design of hydrogen generating photocatalysts and junction-type photocatalysts containing the same, catalytic activity, and the like.

[0084] The junction-type photocatalyst of the present invention is a junction-type photocatalyst having a solid mediator between a hydrogen-generating photocatalyst containing an organic semiconductor and an oxygen-generating photocatalyst, and therefore, of the excited electrons and holes generated in the organic semiconductor by light irradiation, the holes are consumed by recombining with excited electrons generated on the oxygen-generating photocatalyst side via the solid mediator. Meanwhile, the excited electrons generated in the organic semiconductor can contribute to hydrogen generation in the hydrogen-generating photocatalyst, thereby efficiently promoting hydrogen generation.

[0085] Furthermore, when using a hydrogen-generating photocatalyst containing an organic semiconductor alone, it is not a junction-type photocatalyst with an oxygen-generating photocatalyst via a solid mediator, so the use of a sacrificial reagent is required to generate hydrogen. However, the junction-type photocatalyst of the present invention does not require a sacrificial reagent, and uses only water, which is inexhaustible, as a raw material, making it highly economical. A sacrificial reagent may also be used in the junction-type photocatalyst of the present invention.

[0086] (Oxygen-generating photocatalyst) The oxygen-generating photocatalyst is not particularly limited, and examples thereof include BiVO ４ , TiO ２ , W.O. ３ , SrTiO ３ , Ag ３ P.O. ４ , SnNb ２ O ６ , Bi ２ WO ６ , Fe ２ TiO ５ , Fe ２ O ３ , Bi ２ MoO ６ and compounds thereof doped with one or more metals selected from Cr, Ni, Sb, Nb, Th, Mo, and W; ３ N ５ , and Ge ３ N ４ Metal nitrides such as LaTiO ２ N, BaTaO ２ N, BaNbO ２ and metal oxynitrides such as N and TaON. These may be used alone or in combination of two or more. From the viewpoint of enhancing catalytic activity, the oxygen generating photocatalyst is preferably one or more oxides selected from oxides containing elements selected from elements belonging to Group 14 and Group 15 of the periodic table, more preferably one or more oxides selected from oxides containing elements selected from Bi, Pb, Sb, and Sn, even more preferably one or more oxides selected from oxides containing Bi, and even more preferably BiVO ４ and even more preferably BiVO ４ is.

[0087] The electron collecting surface of the oxygen generating photocatalyst depends on the composition and crystal system of the material. For example, a method for identifying the electron collecting surface includes contacting semiconductor crystal particles, which are the material of the oxygen generating photocatalyst, with a precursor solution of a metal such as Pt, Au, or Ag, allowing the metal particles to be deposited by photoprecipitation, and then confirming the crystal surface on which the metal particles are deposited using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0088] The crystal planes on which the metal particles are deposited can be identified by, for example, determining the crystal plane spacing to which the particles belong from lattice fringes observed under a TEM.

[0089] The electron collecting surface of the oxygen generating photocatalyst is, for example, BiVO ４ In the case of monoclinic scheelite crystals, the {010} plane or the {040} plane, TiO ２ (rutile crystal) has {110} plane, TiO ２ (anatase crystal) has {101} plane, WO ３ (monoclinic crystal) {002} plane, SrTiO ３ (perovskite crystal) {110} plane, Ag ３ P.O. ４ In the case of a cubic crystal, it is the {110} plane.

[0090] The hydrogen generating photocatalyst and the oxygen generating photocatalyst preferably have a co-catalyst on their surfaces. Furthermore, the hydrogen generating photocatalyst preferably contains an organic semiconductor, and the organic semiconductor is preferably a covalent organic framework, and the covalent organic framework more preferably contains the co-catalyst. By containing the co-catalyst, reduction and oxidation reactions of water and the like are promoted, improving the efficiency of generating hydrogen and oxygen.

[0091] The co-catalyst of the hydrogen generating photocatalyst may be, for example, a transition metal such as Pt, Pd, Ru, Ni, Au, Fe, Ir, or Rh; NiO, RuO ２ , IrO ２ , and Rh ２ O ３ Metal oxides such as NiS, and MoS ２and metal sulfides such as those mentioned above; Cr-Rh composite oxides; and the like. These may be used alone or in combination of two or more. Of these, from the viewpoint of hydrogen production efficiency, preferably one or more selected from transition metals, more preferably one or more selected from metals belonging to groups 8 to 10 of the periodic table, even more preferably one or more selected from metals belonging to the iron group and platinum group, even more preferably one or more selected from metals belonging to the platinum group, and even more preferably Ru. Examples of metals belonging to the iron group include Fe, Co, and Ni, and examples of metals belonging to the platinum group include Pt, Pd, Ru, Rh, Os, and Ir.

[0092] Examples of the co-catalyst for the oxygen generating photocatalyst include transition metals such as Mn, Fe, Co, Ir, Ru, Rh, Ni, Sb, Nb, Th, and Cr; oxides and hydroxides of the transition metals; and the like. These may be used alone or in combination of two or more. Among these, from the viewpoint of improving the oxygen generation efficiency, one or more selected from oxides of transition metals are preferred.

[0093] Examples of methods for supporting the co-catalyst on the surface of the hydrogen generating photocatalyst or the oxygen generating photocatalyst include photoelectrodeposition, impregnation, adsorption, precipitation, hydrogen reduction, and electroless plating.

[0094] The impregnation method and the adsorption method are methods in which the photocatalyst is dispersed in a solution in which a co-catalyst precursor is dissolved, and the co-catalyst precursor is adsorbed onto the surface of the photocatalyst. Examples of the co-catalyst precursor include chlorides, nitrates, and amine salts of the transition metals.

[0095] It is preferable to reduce the co-catalyst precursor after supporting it on the surface of the photocatalyst. By reducing the co-catalyst precursor to a metallic state, the activity increases. Examples of methods for reducing the co-catalyst precursor include photoreduction and chemical reduction.

[0096] The photoreduction method is a method in which the co-catalyst precursor adsorbed on the photocatalyst is reduced by excited electrons generated in the photocatalyst upon irradiation of the photocatalyst with ultraviolet light or visible light.

[0097] The chemical reduction method is a method of reducing a co-catalyst precursor in a hydrogen gas stream at 400° C. or less, preferably 300° C. or less. The co-catalyst supported on the surface of the photocatalyst is in the form of particles, and the amount of the co-catalyst supported may be adjusted as appropriate.

[0098] (Solid Mediator) The solid mediator is a material that can store excited electrons generated by the oxygen generating photocatalyst that do not contribute to the reduction of water, etc., and positive holes generated by the hydrogen generating photocatalyst that do not contribute to the oxidation of water, etc., and can cause a charge recombination reaction between the excited electrons and the positive holes.

[0099] Examples of the solid mediator include transition metals such as Au, Ag, Cu, Ni, Ti, Mn, Rh, Pd, Ru, and Ir; transition metal compounds such as oxides, nitrides, and carbides of the transition metals; and doped metal oxides such as tin-doped indium oxide (ITO), metal (B, Al, Ga)-doped zinc oxide, fluorine-doped tin oxide, and antimony-doped tin oxide. These may be used alone or in combination of two or more. Among these, from the viewpoint of enhancing catalytic activity, preferably one or more selected from transition metals or compounds thereof, more preferably one or more selected from transition metals containing elements belonging to Group 11 of the periodic table and compounds thereof, even more preferably one or more selected from Au and Ag, and even more preferably one containing Au.

[0100] The hydrogen generating photocatalyst can be bonded to the solid mediator and the oxygen generating photocatalyst, and from the viewpoint of obtaining high catalytic activity, it is preferable that the hydrogen generating photocatalyst is selectively bonded to the solid mediator (that is, more of the hydrogen generating photocatalyst is bonded to the solid mediator than to the oxygen generating photocatalyst).

[0101] <Method for manufacturing a bonded photocatalyst> The method for manufacturing a bonded photocatalyst of the present invention is, for example, a method for manufacturing a bonded photocatalyst having a solid mediator between the hydrogen generating photocatalyst and the oxygen generating photocatalyst, by bonding a solid mediator to the surface of an oxygen generating photocatalyst and then bonding a hydrogen generating photocatalyst containing an organic semiconductor to the surface of the solid mediator, and the method includes the following step 1:

[0102] Step 1: A step of bonding the solid mediator onto the oxygen-generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation using an organic carboxylic acid compound and a solid mediator or a precursor thereof. Specifically, the following production methods (I) and (II), which further include steps 2, 3, and 4 or steps 2', 3', and 4', are preferred.

[0103] In the method for producing a bonded photocatalyst of the present invention, it is preferable to bond the hydrogen generating photocatalyst and the solid mediator and / or the oxygen generating photocatalyst and the solid mediator using an ionic polymer as a bonding agent. By using an ionic polymer as the bonding agent, the hydrogen generating photocatalyst and the solid mediator and / or the oxygen generating photocatalyst and the solid mediator can be bonded by ionic bonds via the ionic polymer of the binder, and an integrated "bonded" photocatalyst can be formed, which is preferable.

[0104] A preferred example of the method for producing a junction-type photocatalyst of the present invention is (I) a method for producing a junction-type photocatalyst including the following steps 1 to 4. However, the order of steps 2 and 3 is not critical. Step 3 may be performed after step 2, or step 2 may be performed after step 3, or they may be performed simultaneously.

[0105] Step 1: A step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation, which is a method using an organic carboxylic acid compound and a solid mediator or a precursor thereof.

[0106] Step 2: A step of introducing an ionic group into the solid mediator (hereinafter referred to as "Mode 1") to obtain an oxygen generating photocatalyst to which the solid mediator having the ionic group is bonded.

[0107] Step 3: introducing an ionic polymer having an opposite charge to the charge of the ionic group into the hydrogen generating photocatalyst.

[0108] Step 4: Mixing the oxygen generating photocatalyst obtained in step 2 to which the solid mediator having an ionic group has been bonded with the hydrogen generating photocatalyst obtained in step 3 to which the ionic polymer has been introduced.

[0109] Furthermore, the method for producing a junction-type photocatalyst of the present invention is preferably, for example, (II) a method for producing a junction-type photocatalyst including the following steps 1, 2', 3', and 4'. However, the order of steps 2' and 3' is not critical. Step 3' may be performed after step 2', or step 2' may be performed after step 3', or they may be performed simultaneously.

[0110] Step 1: A step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation using an organic carboxylic acid compound and a solid mediator or a precursor thereof.

[0111] Step 2': A step of introducing an ionic group into the solid mediator, and then reacting the ionic group with an ionic polymer having an opposite charge to that of the ionic group (hereinafter referred to as "mode 2") to obtain an oxygen generating photocatalyst bonded to a solid mediator having the ionic polymer.

[0112] Step 3': A step of introducing an ionic polymer having an opposite charge to the charge of the ionic polymer into the hydrogen generating photocatalyst.

[0113] Step 4': A step of mixing the oxygen generating photocatalyst obtained in step 2' to which the solid mediator having the ionic polymer has been bonded and the hydrogen generating photocatalyst obtained in step 3' to which the ionic polymer has been introduced.

[0114] <Explanation of Each Step> Each step in the method for producing the junction-type photocatalyst of the present invention will be explained below.

[0115] <Step 1> The method for bonding (supporting) the solid mediator on the surface of the oxygen generating photocatalyst is not particularly limited, but it is preferable to use, for example, at least one method selected from the group consisting of a photoelectrodeposition method, an impregnation support method, and a precipitation method.

[0116] The photoelectrodeposition method is a method in which a dispersion containing a photocatalyst, a metal salt (a precursor of a solid mediator), and an organic carboxylic acid compound is irradiated with light to reduce the metal salt and deposit and bond (support) metal particles or metal compound particles (a solid mediator) to the surface of the photocatalyst. Examples of the precursor of the solid mediator include ion salts of mediators such as silver nitrate and gold halide (tetrachloroauric acid).

[0117] The impregnation support method is a method in which a photocatalyst is mixed with a solution or dispersion in which a metal salt (a precursor of a solid mediator) and an organic carboxylic acid compound are dissolved or dispersed; thereafter, the solvent is removed by solid-liquid separation such as filtration, decantation, or centrifugation, or by heating or distilling off the solvent under reduced pressure, thereby supporting the metal salt on the surface of the photocatalyst; and then the metal salt is calcined or reduced, thereby bonding (supporting) metal particles or metal compound particles (solid mediator) to the surface of the photocatalyst.

[0118] The precipitation method is a method in which metal particles or metal compound particles (solid mediator) obtained by reducing a metal salt (a precursor of a solid mediator) in a solution containing an organic carboxylic acid compound are mixed with a photocatalyst, thereby bonding (supporting) the metal particles or metal compound particles (solid mediator) to the surface of the photocatalyst.

[0119] The photoelectrodeposition method is preferred from the viewpoint of increasing the coverage of the solid mediator with respect to the electron-collecting surface area of ​​the oxygen-generating photocatalyst.

[0120] The photoelectrodeposition method is a method in which a dispersion containing an oxygen-generating photocatalyst, an organic carboxylic acid compound, and a solid mediator or its precursor is irradiated with light to bond (support) the solid mediator onto the oxygen-generating photocatalyst. At this time, excited electrons and holes are generated in the photocatalyst by the light irradiation, and it is thought that the excited electrons cause the reduction and precipitation of the solid mediator, and the holes cause the oxidation of water, etc.

[0121] The solvent used for the dispersion is preferably water. In addition, a lower alcohol having 1 to 5 carbon atoms, such as methanol, ethanol, or 2-propanol, may be used as an auxiliary (sacrificial reagent) in the solvent to promote the consumption of holes.

[0122] The organic carboxylic acid compound is presumed to contribute to the reduction of the metal salt (precursor of the solid mediator) and also acts as an auxiliary agent for bonding (supporting) the solid mediator on the oxygen-generating photocatalyst.

[0123] The use of the organic carboxylic acid compound improves the coverage of the solid mediator on the electron collection surface of the oxygen generating photocatalyst. ４ In the case of monoclinic scheelite crystals, the selectivity to the {010} plane, which is the electron collection surface, is improved, and the solid mediator can be densely bonded to the oxygen generating photocatalyst, thereby improving catalytic activity.

[0124] From the viewpoint of densely bonding the solid mediator onto the oxygen-generating photocatalyst, the organic carboxylic acid compound preferably contains one or more compounds selected from the group consisting of ether carboxylates, fatty acids, hydroxymonocarboxylic acids, and polycarboxylic acids, and more preferably contains ether carboxylates. Specific examples include the following organic carboxylic acid compounds 1) to 4):

[0125] 1) Ether Carboxylate Examples of the ether carboxylate include those represented by the following general formula (1): １ -O-(EO) ｎ -CH ２ COOH (1)

[0126] In the general formula (1), R 1 is preferably a linear or branched alkyl or alkenyl group having 4 to 22 carbon atoms, more preferably a linear or branched alkyl or alkenyl group having 8 to 18 carbon atoms, and even more preferably a linear or branched alkyl group having 8 to 18 carbon atoms (alkyl ether carboxylate), from the viewpoints of water solubility and the ability to exert the function of the auxiliary. Furthermore, the average number of moles n of EO (ethyleneoxy group) added is preferably 1 to 25, more preferably 2 to 12, and even more preferably 3 to 8, from the viewpoints of water solubility and the ability to exert the function of the auxiliary.

[0127] The ether carboxylate may be, for example, polyoxyethylene (4.5) lauryl ether acetic acid, or the like, and may be a potassium salt, a sodium salt, or an ammonium salt thereof.

[0128] 2) Fatty Acids Preferred examples of the fatty acids include those represented by the following general formula (2): ２ -COOH (2)

[0129] In the general formula (2), R ２ From the viewpoints of water solubility and exhibiting the function of the auxiliary, is preferably a linear or branched alkyl or alkenyl group having 4 to 22 carbon atoms, more preferably a linear or branched alkyl or alkenyl group having 8 to 22 carbon atoms, and even more preferably a linear or branched alkyl or alkenyl group having 12 to 18 carbon atoms.

[0130] The fatty acid may be, for example, oleic acid, and may be a potassium salt, a sodium salt, or an ammonium salt thereof.

[0131] 3) Hydroxymonocarboxylic Acid From the viewpoint of water solubility and exhibiting the function of an auxiliary, the hydroxymonocarboxylic acid preferably has a hydrocarbon group having from 2 to 12 carbon atoms, and more preferably has a hydrocarbon group having from 3 to 8 carbon atoms.

[0132] Examples of the hydroxymonocarboxylic acid include glycolic acid, lactic acid, glyceric acid, gluconic acid, and pantothenic acid.

[0133] 4) Polycarboxylic Acid From the viewpoint of water solubility and exhibiting the function of an auxiliary, the polycarboxylic acid preferably has a hydrocarbon group having from 2 to 12 carbon atoms, and more preferably has a hydrocarbon group having from 3 to 8 carbon atoms.

[0134] The polycarboxylic acid is preferably a dicarboxylic acid, such as malic acid, tartaric acid, oxalic acid, malonic acid, maleic acid, succinic acid, or glutaric acid, and the tricarboxylic acid is preferably citric acid.

[0135] The organic carboxylic acid compounds 1) to 4) above may be used alone or in combination of two or more.

[0136] In step 1, in a dispersion liquid containing a photocatalyst, a metal salt (a precursor of a solid mediator), and an organic carboxylic acid compound, the amount of the organic carboxylic acid compound used relative to 100 parts by mass of the solid mediator or its precursor (metal salt) is preferably 100 parts by mass or more, more preferably 500 parts by mass or more, and even more preferably 1,000 parts by mass or more, from the viewpoint of increasing the coverage of the solid mediator on the oxygen-generating photocatalyst and improving catalytic activity. Also, from the same viewpoint, it is preferably 100,000 parts by mass or less, more preferably 50,000 parts by mass or less, and even more preferably 20,000 parts by mass or less, and is preferably 100 parts by mass or more and 100,000 parts by mass or less, more preferably 500 parts by mass or more and 50,000 parts by mass or less, and even more preferably 1,000 parts by mass or more and 20,000 parts by mass or less.

[0137] In step 1, the amount of the solid mediator or its precursor (metal salt) used in the dispersion liquid relative to 100 parts by mass of the oxygen-generating photocatalyst is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 5 parts by mass or more, from the viewpoint of increasing the coverage of the solid mediator on the oxygen-generating photocatalyst and improving catalytic activity. From the same viewpoint, the amount is preferably 1,000 parts by mass or less, more preferably 500 parts by mass or less, and even more preferably 100 parts by mass or less, and is preferably 0.1 parts by mass or more and 1,000 parts by mass or less, more preferably 1 part by mass or more and 500 parts by mass or less, and even more preferably 5 parts by mass or more and 100 parts by mass or less.

[0138] The light to be irradiated (irradiation light) may be either sunlight or artificial light (fluorescent lamp, UV lamp, LED, mercury lamp, xenon lamp, metal halide lamp, sodium lamp, halogen lamp, etc.).

[0139] The wavelength of the light is preferably 180 to 1000 nm, more preferably 300 to 800 nm, from the viewpoint of increasing the coverage of the solid mediator on the oxygen generating photocatalyst.

[0140] The intensity of the irradiation light is preferably 1 mW / cm from the viewpoint of increasing the coverage of the solid mediator on the electron collecting surface of the oxygen generating photocatalyst. ２ More preferably, 5 mW / cm ２ More preferably, 20 mW / cm ２ From the same viewpoint, it is preferable that the light intensity is 1000 mW / cm ２ or less, more preferably 500 mW / cm ２ More preferably, 200 mW / cm or less ２ The following is the result.

[0141] <Step 2> To introduce an ionic group into the solid mediator (Mode 1), a compound containing an ionic group and a group having affinity for the solid mediator may be used. Specifically, when the solid mediator contains gold (atom), silver, or platinum, from the viewpoint of improving affinity with the metal, the compound is preferably one or more compounds selected from a thiol compound having an ionic group and a selenium compound having an ionic group, and more preferably a thiol compound having an ionic group.

[0142] The thiol compound having an ionic group has at least one ionic group (ionic substituent).

[0143] Among the ionic groups, examples of the anionic groups include a sulfonic acid group, a phosphonic acid group, a phosphoric acid group, and a carboxy group.

[0144] Among the ionic groups, an example of the cationic group is an ammonium group.

[0145] Among the ionic groups, thiol compounds having an ammonium group or a carboxy group are particularly preferred from the viewpoint of enhancing catalytic activity.

[0146] From the same viewpoint, the ionic group is more preferably an anionic group, and even more preferably a carboxylate anion (carboxy group).

[0147] From the viewpoint of enhancing catalytic activity, the thiol compound having an ionic group preferably has an alkylene group having 1 or more carbon atoms, more preferably 2 or more carbon atoms. From the same viewpoint, the alkylene group preferably has 18 or less carbon atoms, more preferably 14 or less carbon atoms, and even more preferably 8 or less carbon atoms.

[0148] From the viewpoint of enhancing catalytic activity, the thiol compound having an ionic group preferably has two or less thiol groups, and more preferably has one thiol group.

[0149] When the thiol compound having an ionic group has an acidic group, it may be an acid, a salt, or a mixture thereof.

[0150] The thiol compound having an ionic group is preferably one or more selected from the group consisting of thiomalic acid, 3-mercaptopropionic acid (MPA), thioglycolic acid, and (11-mercaptoundecyl)trimethylammonium.

[0151] In step 2, the amount of the thiol compound having an ionic group used relative to 100 parts by mass of the oxygen-generating photocatalyst bonded (supported) with the solid mediator is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of enhancing catalytic activity. Also, from the same viewpoint, it is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, preferably 0.1 parts by mass or more and 100 parts by mass or less, more preferably 1 part by mass or more and 50 parts by mass or less.

[0152] <Step 2'> As in the above-described embodiment 1, an ionic group is introduced into the solid mediator, and then the ionic group is reacted (ionic bonded) with an ionic polymer having an opposite charge to that of the ionic group (embodiment 2), thereby obtaining an oxygen generating photocatalyst bonded to a solid mediator having an ionic group resulting from the ionic polymer introduced therein.

[0153] Examples of the cationic modification method for introducing an ionic group into the solid mediator and then reacting (ionically bonding) an ionic polymer having an opposite charge to that of the ionic group with the ionic group include (i) a method in which an oxygen-generating photocatalyst bonded (supported) to a solid mediator is mixed and reacted with a thiol compound having an anionic group to introduce an anionic group into the solid mediator, and then a polymer having a cationic group having an opposite charge to that of the anionic group (hereinafter simply referred to as a "cationic polymer") is mixed and reacted with the thiol compound to introduce an anionic group into the solid mediator (ionically bonding).

[0154] Another method is (ii) an anion modification method in which an oxygen-generating photocatalyst bonded (supported) to a solid mediator is reacted with a thiol compound having a cationic group to introduce a cationic group into the solid mediator, and then a polymer having an anionic group having an opposite charge to the cationic group (hereinafter also simply referred to as an "anionic polymer") is mixed and reacted (ionic bonded) with the solid mediator.

[0155] By these methods, the solid mediator has an ionic group and an ionic polymer, and the ionic group is ionically bonded to the ionic polymer.

[0156] The ionic polymer refers to a cationic polymer or an anionic polymer, and as will be described later, the terms ionic polymer A and ionic polymer B are used for convenience to distinguish the ionicity of the ionic polymers. That is, when ionic polymer A is a cationic polymer, it means that ionic polymer B is an anionic polymer, and when ionic polymer A is an anionic polymer, it means that ionic polymer B is a cationic polymer.

[0157] The cationic polymer may be, for example, a polymer having a quaternary ammonium group, from the viewpoint of enhancing catalytic activity.Specifically, it is preferably a polymer having a quaternary ammonium group, more preferably one or more selected from the group consisting of cationized polysaccharide, a diallyl quaternary ammonium salt polymer or copolymer thereof, a (meth)acryloyloxyethyl quaternary ammonium salt polymer or copolymer thereof, a (meth)acrylamidopropyl quaternary ammonium salt polymer or copolymer thereof, and a dimethylamine epichlorohydrin polymer, and more preferably (a) cationized cellulose, (b) cationized guar gum, (c) one or more selected from the group consisting of a diallyl quaternary ammonium salt polymer and a diallyl quaternary ammonium salt / acrylamide copolymer, (d) a (meth)acryloyloxyethyl quaternary ammonium salt polymer and a (meth)acryloyloxyethyl quaternary ammonium salt / acrylamide copolymer, or (e) a dimethylamine epichlorohydrin polymer.The above (c) is particularly preferred. The quaternary ammonium group also includes a tertiary amine having a proton added thereto.

[0158] (a) Cationized cellulose: The degree of cation substitution of the cationized cellulose is 0.01 to 1, i.e., the average value per anhydroglucose unit is preferably 0.01 to 1, more preferably 0.02 to 0.5, from the viewpoint of enhancing catalytic activity. The weight-average molecular weight of the cationized cellulose is preferably about 100,000 to 8,000,000, from the viewpoint of enhancing catalytic activity.

[0159] Examples of commercially available products of (a) include "Poise C-80H" (manufactured by Kao Corporation) and "Polymer JR-400" (manufactured by Dow Chemical Company).

[0160] (b) Cationized Guar Gum: From the viewpoint of enhancing catalytic activity, the degree of cation substitution of the cationized guar gum is preferably 0.01 to 1, and more preferably 0.02 to 0.5, of cationic groups introduced into the sugar units.

[0161] An example of the commercially available product of (b) is "Jaguar C-13C" (manufactured by Rhodia).

[0162] (c) Diallyl quaternary ammonium salt polymer and diallyl quaternary ammonium salt / acrylamide copolymer: From the viewpoint of enhancing catalytic activity, the weight-average molecular weight (Mw) of the diallyl quaternary ammonium salt polymer is preferably about 30,000 to 1,000,000, and the weight-average molecular weight of the diallyl quaternary ammonium salt / acrylamide copolymer is preferably about 30,000 to 2,000,000, more preferably about 1,000,000 to 2,000,000, from the viewpoint of enhancing catalytic activity.

[0163] Examples of commercially available products of (c) include "Merquat 100 Polymer" (manufactured by Lubrizol Corporation) and "Merquat 550 Polymer" (manufactured by Lubrizol Corporation).

[0164] (d) (meth)acryloyloxyethyl quaternary ammonium salt polymer and (meth)acryloyloxyethyl quaternary ammonium salt / acrylamide copolymer: The weight-average molecular weight of the methacryloyloxyethyl quaternary ammonium salt / acrylamide copolymer is preferably about 100,000 to 10,000,000, and more preferably about 2,000,000 to 6,000,000, from the viewpoint of enhancing catalytic activity.

[0165] (e) Dimethylamine epichlorohydrin polymer (poly-2-hydroxypropyldimethylammonium chloride): The weight average molecular weight (Mw) of the dimethylamine epichlorohydrin polymer is preferably about 1,000 to 100,000, and more preferably about 3,000 to 10,000, from the viewpoint of enhancing catalytic activity.

[0166] An example of a commercially available product of (e) is "Catiomaster PD-7" (manufactured by Yokkaichi Chemical Co., Ltd.).

[0167] The anionic polymer is preferably a polymer having a sulfate group, a sulfonic acid group, a phosphonic acid group, a phosphoric acid group, or a carboxy group, and among these, from the viewpoint of enhancing catalytic activity, a polymer having a sulfonic acid group (sulfonic acid-based polymer) or a polymer having a carboxy group (carboxylic acid-based polymer) is preferred.

[0168] The sulfonic acid group-based polymer is preferably poly(sodium styrene sulfonate).

[0169] The carboxylic acid polymer is preferably a carboxylic acid polymer having a constituent unit derived from an anionic group-containing monomer selected from acrylates, methacrylates, and maleates.

[0170] The carboxylic acid polymer is preferably a polymer composed of the anionic group-containing monomer, but may also be a copolymer of the anionic group-containing monomer and a monomer other than the anionic group-containing monomer.

[0171] Examples of monomers other than the anionic group-containing monomer include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate and ethyl (meth)acrylate; N-substituted (meth)acrylamides such as N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, isopropyl (meth)acrylamide, and tert-butyl (meth)acrylamide; vinyl ethers such as methyl vinyl ether and butyl vinyl ether; and olefinic hydrocarbons such as styrene, ethylene, propylene, and isobutylene. These may be used alone or in combination of two or more. Among these, (meth)acrylic acid alkyl esters such as methyl (meth)acrylate and ethyl (meth)acrylate are preferred.

[0172] In this specification, "(meth)acrylic" means "acrylic or methacrylic".

[0173] From the viewpoint of enhancing catalytic activity, the weight average molecular weight (Mw) of the carboxylic acid polymer is preferably 1,000 or more, more preferably 5,000 or more, and even more preferably 10,000 or more, and from the same viewpoint, is preferably 500,000 or less, more preferably 100,000 or less, even more preferably 50,000 or less, and still more preferably 35,000 or less.

[0174] From the viewpoint of enhancing catalytic activity, the weight average molecular weight (Mw) of the polymer having sulfonic acid groups is preferably 10,000 or more, more preferably 50,000 or more, and even more preferably 100,000 or more. From the same viewpoint, it is preferably 5,000,000 or less, more preferably 2,000,000 or less, even more preferably 1,000,000 or less, and still more preferably 600,000 or less.

[0175] In this specification, the weight average molecular weight (Mw) of the cationic polymer and the anionic polymer is a value determined by gel permeation chromatography (GPC) using polystyrene as a standard substance.

[0176] In step 2', the amount of the ionic polymer used relative to 100 parts by mass of the oxygen-generating photocatalyst bonded (supported) with the solid mediator having an ionic group introduced therein is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, from the viewpoint of enhancing catalytic activity. From the same viewpoint, the amount is preferably 500 parts by mass or less, more preferably 100 parts by mass or less.

[0177] <Step 3> To introduce an ionic polymer having an opposite charge to the charge of the ionic group into the hydrogen generating photocatalyst, for example, if the ionic group of the solid mediator in step 2 is an anionic group, the hydrogen generating photocatalyst may be mixed and dispersed with a polymer having a cationic group to introduce the ionic polymer having the opposite charge.

[0178] Furthermore, the hydrogen generating photocatalyst may be mixed and dispersed with a polymer having an anionic group, and then remixed and redispersed with a polymer having a cationic group to introduce an ionic polymer having an opposite charge.

[0179] That is, it is a bonded photocatalyst having a solid mediator between a hydrogen generating photocatalyst and an oxygen generating photocatalyst, wherein the solid mediator has an ionic group, the hydrogen generating photocatalyst has an ionic polymer B having an opposite charge to that of the ionic group via an ionic polymer A, and the solid mediator and the hydrogen generating photocatalyst are bonded by an ionic bond between the ionic group and the ionic polymer B. In this bonded photocatalyst, the ionic polymer contained in the hydrogen generating photocatalyst is ionic polymer A, and the hydrogen generating photocatalyst has an ionic polymer B having an opposite charge to that of the ionic group via the ionic polymer A, and the solid mediator and the hydrogen generating photocatalyst are bonded by an ionic bond between the ionic group and the ionic polymer B.

[0180] When the ionic group is an anionic group, the ionic polymer A is an anionic polymer, and the ionic polymer B is a cationic polymer. When the ionic group is a cationic group, the ionic polymer A is a cationic polymer, and the ionic polymer B is an anionic polymer.

[0181] <Step 3'> To introduce an ionic polymer having an opposite charge to the charge of the ionic group into the hydrogen generating photocatalyst, for example, if the ionic group of the solid mediator in step 2' is an anionic group, the solid mediator may further contain a cationic polymer by mixing and dispersing the solid mediator with a polymer having a cationic group, and the hydrogen generating photocatalyst may be mixed and dispersed with a polymer having an anionic group to introduce an ionic polymer having an opposite charge.

[0182] Furthermore, the hydrogen generating photocatalyst may be mixed and dispersed with a polymer having a cationic group, and then remixed and redispersed with a polymer having an anionic group to introduce an ionic polymer having an opposite charge.

[0183] That is, it is a bonded photocatalyst having a solid mediator between a hydrogen generating photocatalyst and an oxygen generating photocatalyst, wherein the solid mediator has an ionic group and an ionic polymer B, the ionic group is bonded to the ionic polymer B, the hydrogen generating photocatalyst has an ionic polymer A having an opposite charge to that of the ionic polymer B, and the solid mediator and the hydrogen generating photocatalyst are bonded by an ionic bond between the ionic polymer B possessed by the solid mediator and the ionic polymer A possessed by the hydrogen generating photocatalyst. This means that the ionic polymer contained in the hydrogen generating photocatalyst is ionic polymer A, the solid mediator has the ionic group and ionic polymer B having an opposite charge to that of ionic polymer A, the ionic group is bonded to ionic polymer B, and the solid mediator and the hydrogen generating photocatalyst are joined by an ionic bond between the ionic polymer B contained in the solid mediator and the ionic polymer A contained in the hydrogen generating photocatalyst.

[0184] When the ionic group is an anionic group, the ionic polymer A is an anionic polymer, and the ionic polymer B is a cationic polymer. When the ionic group is a cationic group, the ionic polymer A is a cationic polymer, and the ionic polymer B is an anionic polymer.

[0185] The ionic polymer may be the anionic polymer or the cationic polymer described in the second embodiment.

[0186] In Step 3 and Step 3', the amount of the ionic polymer used relative to 100 parts by mass of the hydrogen generating photocatalyst is preferably 5 parts by mass or more, more preferably 20 parts by mass or more, from the viewpoint of enhancing catalytic activity. Also, from the same viewpoint, the amount is preferably 500 parts by mass or less, more preferably 100 parts by mass or less, preferably 5 parts by mass or more and 500 parts by mass or less, more preferably 20 parts by mass or more and 100 parts by mass or less.

[0187] <Step 4> and <Step 4'> In Step 4 or Step 4', the oxygen generating photocatalyst to which the solid mediator having an ionic group has been bonded (supported) is mixed with the hydrogen generating photocatalyst to which the ionic polymer obtained in Step 3 or Step 3' has been introduced, thereby making it possible to bond the oxygen generating photocatalyst and the hydrogen generating photocatalyst via the solid mediator.

[0188] For example, when using an oxygen-generating photocatalyst bonded (supported) with a solid mediator having an anionic group introduced therein, a hydrogen-generating photocatalyst having a cationic group derived from a cationic polymer introduced therein may be used.Furthermore, when using an oxygen-generating photocatalyst bonded (supported) with a solid mediator having a cationic group introduced therein, a hydrogen-generating photocatalyst having an anionic group derived from an anionic polymer introduced therein may be used.

[0189] In step 4, the mixing mass ratio (hydrogen generating photocatalyst into which the ionic polymer obtained in step 3 has been introduced / oxygen generating photocatalyst to which the solid mediator having an ionic group has been bonded (supported) obtained in step 2) is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.07 or more, from the viewpoint of enhancing catalytic activity. Also, from the same viewpoint, it is preferably 10 or less, more preferably 5 or less, even more preferably 1 or less, preferably 0.01 or more and 10 or less, more preferably 0.05 or more and 5 or less, and even more preferably 0.07 or more and 1 or less.

[0190] In step 4', the mixing mass ratio (hydrogen generating photocatalyst into which the ionic polymer obtained in step 3' has been introduced / oxygen generating photocatalyst to which the solid mediator having the ionic polymer obtained in step 2' has been bonded) is preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.07 or more, from the viewpoint of enhancing catalytic activity. Also, from the same viewpoint, it is preferably 10 or less, more preferably 5 or less, and even more preferably 1 or less, preferably 0.01 or more and 10 or less, more preferably 0.05 or more and 5 or less, and even more preferably 0.07 or more and 1 or less.

[0191] By adjusting the mixing mass ratio in step 4 or step 4', the solid mediator and the hydrogen generating photocatalyst are bonded together via the ionic polymer in both mode 1 and mode 2. The ionic polymer mediates a strong electrostatic interaction, and the hydrogen generating photocatalyst and the oxygen generating photocatalyst are not separated but are bonded together via the solid mediator, improving catalytic activity and enabling water to be decomposed into oxygen and hydrogen with high water-splitting reaction efficiency.

[0192] (Coverage of solid mediator relative to electron-collecting surface area of ​​oxygen-generating photocatalyst) From the viewpoint of enhancing catalytic activity, the coverage of the solid mediator relative to the electron-collecting surface area of ​​the oxygen-generating photocatalyst is preferably 40% or more, more preferably 50% or more, even more preferably 55% or more, and still more preferably 58% or more. The upper limit is preferably 100% or less, and from the viewpoint of improving the adhesiveness and light transmittance of the solid mediator, it is more preferably 95% or less, even more preferably 90% or less.

[0193] The coverage of the solid mediator relative to the electron collection surface area of ​​the oxygen generating photocatalyst is preferably 40% or more and 100% or less, more preferably 50% or more and 95% or less, and even more preferably 55% or more and 90% or less, from the viewpoint of increasing catalytic activity and improving the adhesiveness and light transmittance of the fixed mediator.

[0194] The coverage can be increased to 40% or more by using the production method in step 1, i.e., at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation using an organic carboxylic acid compound and a solid mediator or a precursor thereof. The coverage can be further increased by, for example, increasing the content of the organic carboxylic acid compound relative to the solid mediator or a precursor thereof, or by extending the light irradiation time in the photoelectrodeposition method.

[0195] (Selectivity of bonding of solid mediator to electron collecting surface of oxygen generating photocatalyst) From the viewpoint of enhancing catalytic activity, the selectivity of bonding of the solid mediator to the electron collecting surface of the oxygen generating photocatalyst is preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and even more preferably 90% or more. From the viewpoint of production, it is 100% or less, preferably 99.5% or less. The bonding selectivity can be improved, for example, by the type of production method in step 1. Specifically, it is preferable to use a photoelectrodeposition method.

[0196] The coverage and bonding selectivity can be determined by the method of the following examples.

[0197] <Method for producing oxygen-generating photocatalyst> The method for producing the oxygen-generating photocatalyst is the same as step 1 of the method for producing the junction-type photocatalyst.

[0198] <Photocatalytic Composite> The photocatalytic composite of the present invention comprises the above-mentioned junction-type photocatalyst on a substrate.

[0199] The substrate is not particularly limited as long as it can immobilize the conjugated photocatalyst on its surface, and examples thereof include ceramic substrates such as alumina; glass substrates such as soda lime glass and borosilicate glass; quartz substrates; metal substrates such as titanium, copper, tin, iron, aluminum, and stainless steel; organic substrates such as methacrylic resin, acrylic resin, urethane resin, phenolic resin, melamine resin, urea resin, polyester resin, polycarbonate resin, fluororesin, polyethylene, polypropylene, polystyrene, polyamide, polyimide, polyacetal, polyvinyl chloride, and polyvinylidene chloride; fibrous substrates such as glass fiber and carbon fiber; and natural substrates such as paper, bamboo, and wood.

[0200] The substrate preferably has pores, more preferably continuous pores. This promotes the supply of water at the interface between the substrate and the junction-type photocatalyst, and allows hydrogen gas generated by a water-splitting reaction on the surface of the junction-type photocatalyst to reach the outside through the pores, resulting in more efficient production of hydrogen gas. The substrate is also preferably transparent, more preferably having a transmittance of 50% or more in the visible light range. This allows the junction-type photocatalyst to absorb light from a light source incident on the substrate surface, resulting in more efficient production of hydrogen gas.

[0201] The method for producing the photocatalyst composite is not particularly limited, and examples thereof include: (1) a method in which a dispersion liquid containing the conjugated photocatalyst is applied to a substrate, dried, and optionally calcined to immobilize the conjugated photocatalyst on the substrate; and (2) a method in which a dispersion liquid containing the oxygen-generating photocatalyst is applied to a substrate, dried, and optionally calcined to immobilize the oxygen-generating photocatalyst on the substrate, and then the solid mediator is bonded to the surface of the oxygen-generating photocatalyst in the same manner as above, and then the hydrogen-generating photocatalyst is bonded to the surface of the solid mediator.

[0202] <Uses of Junction-Type Photocatalyst and Photocatalyst Composite> The junction-type photocatalyst and photocatalyst composite of the present invention can be used not only as a photocatalyst that catalyzes the decomposition reaction of water or alcohol, but also as a photocatalyst that catalyzes the decomposition reaction of organic matter. For example, they can be used as an environmental purification agent, antibacterial agent, disinfectant, deodorizer, or antifouling agent for detoxifying harmful organic compounds, bacteria, and malodorous substances, and for detoxifying inorganic compounds (ammonium ions, ammonia, nitrate ions, nitrite ions, etc.).

[0203] <Method for Producing Hydrogen> The method for producing hydrogen using the junction-type photocatalyst or the photocatalyst composite of the present invention is not particularly limited. For example, the method for producing hydrogen includes a step of irradiating the junction-type photocatalyst or the photocatalyst composite with light in the presence of water or alcohol to cause a decomposition reaction of the water or alcohol to generate at least hydrogen.

[0204] The light to be irradiated may be either sunlight or artificial light (such as a fluorescent lamp, a UV lamp, an LED, a mercury lamp, a xenon lamp, a metal halide lamp, a sodium lamp, or a halogen lamp).

[0205] The wavelength of the light is preferably 180 to 1000 nm, more preferably 300 to 800 nm, from the viewpoint of promoting the decomposition reaction.

[0206] The irradiance of the light irradiation is preferably 1 μW / m from the viewpoint of promoting the decomposition reaction. ２ More preferably, 1 mW / m ２ That's all.

[0207] The temperature of the decomposition reaction is preferably 0° C. or higher, more preferably 15° C. or higher, from the viewpoint of accelerating the decomposition reaction.

[0208] The amount of hydrogen generated using the junction-type photocatalyst or the photocatalyst composite of the present invention (per 55 mg of catalyst) is preferably 0.05 (μmol h －１ ) or more, more preferably 0.1 (μmol h －１ ) or more, more preferably 0.15 (μmol h －１ ) or more, and there is no particular upper limit, but it is preferably 1 (mol h －１ ) is as follows.

[0209] With respect to the above-described embodiments, the present invention further discloses the following aspects. [1] A junction-type photocatalyst having a solid mediator between a hydrogen generating photocatalyst containing an organic semiconductor and an oxygen generating photocatalyst, the hydrogen generating photocatalyst and the solid mediator being junctioned together, and the oxygen generating photocatalyst and the solid mediator being junctioned together. [2] The junction-type photocatalyst according to [1], in which the solid mediator is junctioned to the electron collecting surface of the oxygen generating photocatalyst. [3] The junction-type photocatalyst according to [1] or [2], in which the junction selectivity of the solid mediator to the electron collecting surface of the oxygen generating photocatalyst is 60% or more. [4] The junction-type photocatalyst according to any one of [1] to [3], in which the coverage of the solid mediator with respect to the electron collecting surface area of ​​the oxygen generating photocatalyst is 40% or more. [5] The junction-type photocatalyst according to any one of [1] to [4], in which the organic semiconductor is a covalent organic framework. [6] The junction type photocatalyst according to [5], wherein the topology diagram constituting the covalent organic framework is preferably one or more types selected from (1) a hexagonal type, (2) a tetragonal type, (3) a rhombus type, and (4) a triangle type, and more preferably (1) a hexagonal type. [7] The covalent organic framework preferably has one or more bonding modes selected from (10) boroxine type, (11) boronate ester type, (12) borazine type, (13) imide type, (14) amide type, (15) dioxin type, (16) imine type, (17) hydrazone type, (18) azine type, (19) oxazole type, (20) thiazole type, (21) squaraine type, (22) triazine type, (23) phenazine type, (24) amino type, and (25) olefin type, more preferably has one or more bonding modes selected from (16) imine type and (24) amino type, and even more preferably has (16) imine type bonding mode. [8] The hydrogen generating photocatalyst according to any one of [1] to [7], further comprising a cocatalyst.[9] The co-catalyst is preferably one or more selected from transition metals, more preferably one or more selected from metals belonging to groups 8 to 10 of the periodic table, even more preferably one or more selected from metals belonging to the iron group and the platinum group, even more preferably one or more selected from metals belonging to the platinum group, and even more preferably Ru.

[10] The oxygen-generating photocatalyst is preferably one or more selected from oxides containing elements selected from elements belonging to groups 14 and 15 of the periodic table, more preferably one or more selected from oxides containing elements selected from Bi, Pb, Sb, and Sn, even more preferably one or more selected from oxides containing Bi, and even more preferably BiVO. ４ and even more preferably BiVO ４

[11] The junction type photocatalyst according to any one of [1] to [9], wherein the solid mediator is preferably one or more selected from transition metals or compounds thereof, more preferably one or more selected from transition metals containing elements belonging to Group 11 of the periodic table or compounds thereof, even more preferably one or more selected from Au and Ag, and even more preferably Au.

[12] The hydrogen generating photocatalyst contains a covalent organic framework, and the topology diagram constituting the covalent organic framework is one or more types selected from (1) a hexagonal type, (2) a tetragonal type, (3) a rhombus type, and (4) a triangle type, and the covalent organic framework has one or more types of bonding modes selected from (10) a boroxine type, (11) a boronate ester type, (12) a borazine type, (13) an imide type, (14) an amide type, (15) a dioxin type, (16) an imine type, (17) a hydrazone type, (18) an azine type, (19) an oxazole type, (20) a thiazole type, (21) a squaraine type, (22) a triazine type, (23) a phenazine type, (24) a amino type, and (25) a olefin type, The junction-type photocatalyst according to any one of [1] to

[11] , wherein the oxygen-generating photocatalyst is one or more oxides selected from oxides containing elements selected from elements belonging to Group 14 and Group 15 of the periodic table, and the solid mediator is one or more selected from one or more transition metals selected from Au, Ag, Cu, Ni, Ti, Mn, Rh, Pd, Ru, and Ir, one or more transition metal compounds selected from oxides, nitrides, and carbides of the transition metals, and one or more doped metal oxides selected from tin-doped indium oxide (ITO), metal (B, Al, Ga)-doped zinc oxide, fluorine-doped tin oxide, and antimony-doped tin oxide.

[13] The junction type photocatalyst according to any one of [1] to

[11] , wherein the hydrogen generating photocatalyst contains a covalent organic framework, and the topology diagram constituting the covalent organic framework is one or more types selected from (1) a hexagonal type, (2) a tetragonal type, (3) a rhombus type, and (4) a triangle type, and the covalent organic framework has one or more types of bonding modes selected from (16) an imine type and (24) an amino type, and the hydrogen generating photocatalyst has a co-catalyst, and the co-catalyst of the hydrogen generating photocatalyst is one or more types selected from metals belonging to Groups 8 to 10 of the periodic table and compounds thereof, the oxygen generating photocatalyst is one or more types selected from oxides containing an element selected from Bi, Pb, Sb, and Sn, and the solid mediator is one or more types selected from transition metals containing an element belonging to Group 11 of the periodic table or compounds thereof.

[14] The junction type photocatalyst according to any one of [1] to

[11] , wherein the hydrogen generating photocatalyst contains a covalent organic framework, and the topology diagram constituting the covalent organic framework is one or more types selected from (1) a hexagonal type, (2) a tetragonal type, (3) a rhombus type, and (4) a triangle type, and the covalent organic framework has one or more types of bonding modes selected from (16) an imine type and (24) an amino type, and the hydrogen generating photocatalyst has a co-catalyst, and the co-catalyst of the hydrogen generating photocatalyst is one or more types selected from Pt, Pd, Ru, Ni, Fe, Ir, Rh, and compounds thereof, and the oxygen generating photocatalyst is one or more types selected from oxides containing Bi, and the solid mediator comprises one or more types selected from transition metals containing elements belonging to Group 11 of the periodic table or compounds thereof.

[15] The junction type photocatalyst according to any one of [1] to

[11] , wherein the hydrogen generating photocatalyst contains a covalent organic framework, and the topology diagram constituting the covalent organic framework is one or more types selected from (1) a hexagonal type, (2) a tetragonal type, (3) a rhombus type, and (4) a triangle type, and the covalent organic framework has one or more types of bonding modes selected from (16) an imine type and (24) an amino type, and the hydrogen generating photocatalyst has a co-catalyst, and the co-catalyst of the hydrogen generating photocatalyst is one or more types selected from Pt, Pd, Ru, Ni, Fe, Ir, Rh, and compounds thereof, and the oxygen generating photocatalyst is one or more types selected from oxides containing Bi, and the solid mediator comprises one or more types selected from transition metals containing elements belonging to Group 11 of the periodic table or compounds thereof.

[16] The hydrogen generating photocatalyst contains a covalent organic framework, the topology diagram constituting the covalent organic framework is (1) hexagonal, the covalent organic framework has a (16) imine type bonding pattern, the hydrogen generating photocatalyst has a co-catalyst, the co-catalyst of the hydrogen generating photocatalyst contains Ru, and the oxygen generating photocatalyst is BiVO. ４wherein the solid mediator contains Au.

[17] A photocatalyst composite having the junction type photocatalyst according to any one of [1] to

[16] on a substrate.

[18] A method for producing hydrogen, comprising irradiating the junction type photocatalyst according to any one of [1] to

[16] or the photocatalyst composite according to

[17] with light in the presence of water or alcohol.

[19] A method for producing the junction type photocatalyst according to any one of [1] to

[16] , wherein the hydrogen generating photocatalyst and the solid mediator are bonded together and / or the oxygen generating photocatalyst and the solid mediator using an ionic polymer as a bonding agent.

[20] A method for producing the junction type photocatalyst according to

[19] , comprising the following steps 1 to 4, wherein steps 2 and 3 can be performed in any order. Step 1: A method using an organic carboxylic acid compound and a solid mediator or a precursor thereof, wherein the solid mediator is bonded to an oxygen generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation, and precipitation. Step 2: A step of introducing ionic groups into the solid mediator to obtain an oxygen generating photocatalyst bonded to the solid mediator having the ionic groups. Step 3: A step of introducing an ionic polymer having an opposite charge to that of the ionic groups into the hydrogen generating photocatalyst. Step 4: A step of mixing the oxygen generating photocatalyst bonded to the solid mediator having ionic groups obtained in step 2 with the hydrogen generating photocatalyst obtained in step 3 to which the ionic polymer has been introduced.

[21] A preferred example of the method for producing a bonded photocatalyst according to

[19] includes the following steps 1, 2', 3', and 4'. However, steps 2' and 3' may be performed in any order.Step 1: A step of bonding the solid mediator onto the oxygen generating photocatalyst by at least one method selected from the group consisting of photoelectrodeposition, impregnation support, and precipitation using an organic carboxylic acid compound and a solid mediator or a precursor thereof. Step 2': A step of introducing an ionic group into the solid mediator, and further reacting the ionic group with an ionic polymer having an opposite charge to that of the ionic group, thereby obtaining an oxygen generating photocatalyst bonded to a solid mediator having the ionic polymer. Step 3': A step of introducing an ionic polymer having an opposite charge to that of the ionic polymer into the hydrogen generating photocatalyst. Step 4': A step of mixing the oxygen generating photocatalyst bonded to the solid mediator having the ionic polymer obtained in step 2' with the hydrogen generating photocatalyst obtained in step 3'.

[22] A method for producing a bonded photocatalyst according to

[20] or

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

[23] The method for producing a junction-type photocatalyst according to

[22] , wherein the anionic group is a sulfonic acid group, a phosphonic acid group, a phosphoric acid group, or a carboxy group, and the cationic group is an ammonium group.

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

[19] to

[23] , wherein the ionic polymer is a cationic polymer or an anionic polymer.

[25] The method for producing a junction-type photocatalyst according to

[24] , wherein the cationic polymer is preferably a polymer having a quaternary ammonium group, more preferably one or more selected from the group consisting of cationized polysaccharides, diallyl quaternary ammonium salt polymers or copolymers thereof, (meth)acryloyloxyethyl quaternary ammonium salt polymers or copolymers thereof, (meth)acrylamidopropyl quaternary ammonium salt polymers or copolymers thereof, and dimethylamine epichlorohydrin polymers, and more preferably one or more selected from the group consisting of (a) cationized cellulose, (b) cationized guar gum, (c) diallyl quaternary ammonium salt polymers, and diallyl quaternary ammonium salt / acrylamide copolymers, and further preferably one or more selected from the group consisting of (d) (meth)acryloyloxyethyl quaternary ammonium salt polymers, (meth)acryloyloxyethyl quaternary ammonium salt / acrylamide copolymers, or (e) dimethylamine epichlorohydrin polymers.

[26] The method for producing a junction-type photocatalyst according to

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

[0210] The present invention will be specifically described below with reference to examples. Unless otherwise specified, reagents used were manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. The following polymers were used: Anionic polymer 1: Poise 520, manufactured by Kao Corporation, sodium acrylate / sodium maleate copolymer Cationic polymer 1: Merquat 100 Polymer, manufactured by Lubrizol Corporation, polydiallyldimethylammonium chloride

[0211] [Powder X-ray Diffraction (XRD)] Powder X-ray diffraction (XRD) of COF was performed using a MiniFlex II (manufactured by Rigaku Corporation) as a powder X-ray diffractometer under the following conditions, and the chemical formula (structure) of COF was confirmed based on the XRD pattern. (Measurement Conditions) X-ray source: Cu-Kα, voltage: 30 kV, current: 15 mA, sampling width: 0.02, divergence slit: 1.25°, scattering slit: open, receiving slit: 0.15 mm, scanning range: 2θ = 2 to 40°, scanning speed: 10° / min, using a continuous scan method.

[0212] (Example 1) [Production of oxygen generating photocatalyst] <Bismuth vanadate (BiVO ４ Preparation of Bismuth nitrate pentahydrate (6.06 g) and ammonium vanadate (1.46 g) were dissolved in 50 mL of 2 mol / L nitric acid. Then, ammonia water was added dropwise until the pH reached 2.0, and 0.88 g of sodium chloride was added to obtain a yellow-orange dispersion. The dispersion was transferred to a fluororesin container and reacted in an autoclave at 170°C for 24 hours. After the reaction was completed, the precipitate was separated by suction filtration, and the obtained precipitate was washed with deionized water, filtered, and dried under reduced pressure. The sample obtained after drying was fired in an electric furnace at 500°C for 2 hours to obtain a yellow powder of BiVO4. ４ The produced BiVO ４ The particles were confirmed to have a decahedral structure with the {010} plane as the basal plane by SEM (JSM-IT500HR, manufactured by JEOL Ltd.) observation (magnification 2000 times). Furthermore, powder X-ray diffraction measurement (MiniFlex II diffractometer, manufactured by Rigaku Corporation) confirmed that the crystal system was monoclinic scheelite crystal.

[0213] <Au-BiVO ４ Production of BiVO ４50 mg of the above was added to a glass container and dispersed in 4 mL of deionized water, followed by the addition of 4.8 mg of tetrachloroauric acid tetrahydrate and 1.55 mL of AKYPO RLM-45NV (Kao Corporation, polyoxyethylene (4.5) lauryl ether sodium acetate, active ingredient 24%). While stirring with a stirrer tip, the mixture was irradiated with light for 5 minutes using a 300 W solar simulator (PECCELL Corporation, PEC-L01, current value 7.5 A) to allow the reaction to proceed. An optical power meter (Hioki E.E. Corporation, H3664) measured the irradiated light intensity at a wavelength of 435 nm at 150 mW / cm. ２ After the reaction was completed, the precipitate was separated by suction filtration, washed with deionized water, filtered, and dried under reduced pressure to obtain a green powder of Au—BiVO4. ４ The produced Au-BiVO ４ When the particles were observed under SEM, as shown in FIG. ４ The image showed that an Au layer was selectively formed on the {010} plane of BiVO4. ４ The bonding selectivity to the {010} plane relative to the surface was calculated to be 99%, and the coverage of Au on the {010} plane was calculated to be 90%.

[0214] <MPA-treated Au-BiVO ４ Manufacture of > Manufactured Au-BiVO ４ 50 mg of the above was added to a glass container and dispersed in 5 mL of deionized water, and 12 μL of 3-mercaptopropionic acid (MPA) was added and stirred with a stirrer tip for 2 hours. After the reaction was completed, the precipitate was separated by suction filtration, and the precipitate was Au-BiVO4 doped with MPA. ４ (MPA-treated Au-BiVO ４ ) was obtained.

[0215] <Cation-modified Au-BiVO ４ The obtained precipitate (MPA-treated Au-BiVO ４) was washed with deionized water, dispersed in 1 mL of a 50 mmol / L aqueous solution of cationic polymer 1, and stirred for 2 hours with a stirrer tip. After the reaction was completed, the precipitate was separated by suction filtration. The resulting precipitate was washed with deionized water and then dried under reduced pressure to obtain a green powder of Au-BiVO4 incorporating a cationic polymer, which is an oxygen-generating photocatalyst. ４ (Cation-modified Au-BiVO ４ In Table 1, Merquat 100 Polymer (cationic polymer 1) is shown as binder 2 (polymer supported on solid mediator).

[0216] [Preparation of Hydrogen-Generating Photocatalyst] <Preparation of COF (COF1)> 168 mg of 2,4,6-triformylphloroglucinol (Tokyo Chemical Industry Co., Ltd.) and 281 mg of 4,4'-diamino-[1,1'-biphenyl]-3,3'-dicarbonitrile (BLD Pharmatech) were added to a pressure-resistant test tube, dispersed in 8.0 mL of a 1:1 mixture of 1,4-dioxane and mesitylene, and subjected to ultrasonic treatment for 10 minutes. Subsequently, 2 mL of 6 mol / L acetic acid was added, and ultrasonic dispersion treatment was performed for 10 minutes. Dissolved oxygen was removed by freeze-degassing. The test tube was transferred to an oil bath and heated at 120°C for three days under a nitrogen atmosphere. After completion of the reaction, the precipitate was washed with dimethylformamide, acetone, and tetrahydrofuran, in that order, purified by Soxhlet extraction with tetrahydrofuran, and dried under reduced pressure at 120°C. 150 mg of the dried powder was transferred to a plastic container, filled with zirconia balls (φ2 mm), and pulverized for 30 minutes using a rotary mixer (MIX ROTOR VMR-5) to obtain an orange powder of COF (COF1). Figure 3 shows an SEM image of COF (COF1) observed after drying, and Figure 4 shows its powder X-ray diffraction (XRD) pattern. A peak was observed near 2θ = 3.5°, confirming that the synthesized COF (COF1) was a hexagonal crystal. The estimated structure of COF1 is shown in the following chemical formula.

[0217] <Production of Ru-supported COF (Ru-supported COF1)> 40 mg of the obtained COF was added to a glass container and dispersed in 3 mL of deionized water. 0.72 mg of ruthenium chloride n-hydrate (0.7 mass% / COF) was added, and ultrasonic dispersion treatment was performed for 15 minutes. The dispersion was irradiated with light for 120 minutes using a solar simulator (manufactured by Pexel Technologies) while stirring, and Ru was supported on the COF. After completion of the reaction, the precipitate was separated by suction filtration. The obtained precipitate was washed with deionized water and then dried under reduced pressure to obtain an orange powder of Ru-supported COF (Ru-supported COF1).

[0218] <Preparation of anion-modified Ru-supported COF> 20 mg of the prepared Ru-supported COF (Ru-supported COF1) was placed in a glass container and dispersed in 5 mL of a 480 mmol / L aqueous solution of anionic polymer 1. Ultrasonic irradiation was performed for 30 minutes. After the reaction was completed, the precipitate was separated by suction filtration. The resulting precipitate was washed with deionized water and then dried under reduced pressure to obtain anion-modified Ru-supported COF as an orange powder, which served as a hydrogen-generating photocatalyst. Note that Poise 520 (anionic polymer 1) was listed as bonding agent 1 (the polymer supported on the hydrogen-generating photocatalyst) in Table 1.

[0219] <Production of Bonded Photocatalyst> Cation-modified Au-BiVO4 prepared in a glass container ４ 50 mg of the above and 5 mg of anion-modified Ru-supported COF were added and dispersed in 1 mL of deionized water and stirred for 30 minutes. After stirring, the dispersion was allowed to stand, and all of the particles in the dispersion were observed to settle. These particles were applied to a silicon substrate to obtain a junction-type photocatalyst. An SEM image of this junction-type photocatalyst is shown in Figure 5.

[0220] <Evaluation of water splitting activity of the bonded photocatalyst> The particles (bonded particles) obtained above were added to 180 mL of water, and argon gas was bubbled through at 20 mL / min for 30 minutes, followed by light irradiation using a 300 W xenon lamp. The generated gas was analyzed using a gas chromatograph with a TCD detector. Light irradiation was continued for 4 hours, and the average hydrogen generation rate (μmol h －１ The results are shown in Table 1.

[0221] Example 2 Production of a cation-modified Ru-supported COF 20 mg of Ru-supported COF (Ru-supported COF1) produced in the same manner as in Example 1 was added to a glass container, dispersed in 1 mL of a 0.8% by mass aqueous solution of cationic polymer 1 (8.0 mg pure polymer content), and subjected to ultrasonic irradiation for 30 minutes. After completion of the reaction, the precipitate was separated by suction filtration. The obtained precipitate was washed with deionized water and then dried under reduced pressure to obtain an orange powder of Ru-supported COF (cation-modified Ru-supported COF) into which the cationic polymer had been introduced.

[0222] <Production of Bonded Photocatalyst> MPA-treated Au—BiVO4 was produced in the same manner as in Example 1. ４ The junction-type photocatalyst was produced by adding 50 mg of the above and 5 mg of the cation-modified Ru-supported COF to a glass container, dispersing them in 1 mL of deionized water, and stirring for 30 minutes. The results are shown in Table 1.

[0223] Example 3 A junction-type photocatalyst was produced and evaluated in the same manner as in Example 2, except that 15 mg of anion-modified Ru-supported COF was added when producing the junction-type photocatalyst. The results are shown in Table 1.

[0224] Example 4 Production of Anion-Modified COF (Anion-Modified COF1) 20 mg of COF (COF1) produced in the same manner as in Example 1 was added to a glass container, dispersed in 5 mL of a 480 mmol / L aqueous solution of anionic polymer 1, and subjected to ultrasonic irradiation for 30 minutes. After completion of the reaction, the precipitate was separated by suction filtration. The obtained precipitate was washed with deionized water and then dried under reduced pressure to obtain an orange powder COF (anion-modified COF1) into which an anionic polymer, a hydrogen-generating photocatalyst, had been introduced.

[0225] <Production of Bonded Photocatalyst> MPA-treated Au—BiVO4 was produced in the same manner as in Example 1. ４ 50 mg of the above and 5 mg of anion-modified COF were added to a glass container, dispersed in 1 mL of deionized water, and stirred for 30 minutes to produce a junction-type photocatalyst, which was then evaluated. The results are shown in Table 1.

[0226] Example 5 [Production of Hydrogen-Generating Photocatalyst] <Production of COF (COF2)> 71 mg of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)trianiline (Tokyo Chemical Industry Co., Ltd.) and 66 mg of tris(4-formylphenyl)amine (Fujifilm Wako Pure Chemical Industries, Ltd.) were placed in a pressure-resistant test tube and dispersed in 6.0 mL of a 1:1 mixture of 1,4-dioxane and mesitylene. 0.3 mL of 6 mol / L acetic acid was added, and the mixture was subjected to ultrasonic dispersion treatment for 60 minutes. Dissolved oxygen was then removed by freeze-degassing. The test tube was transferred to an oil bath and heated at 120°C for three days under a nitrogen atmosphere. After the reaction was completed, the precipitate was washed with acetone and dried at 80°C. An SEM image of the COF (COF2) observed after drying is shown in Figure 6, and a powder X-ray diffraction (XRD) pattern is shown in Figure 7. Since a peak was observed around 2θ=4.3°, it was confirmed that the synthesized COF (COF2) was a hexagonal crystal. The estimated structure of COF2 is shown in the chemical formula below.

[0227] <Production of Anion-Modified COF (Anion-Modified COF2)> 20 mg of the produced COF (COF2) was placed in a glass container, dispersed in 5 mL of a 480 mmol / L aqueous solution of Anionic Polymer 1, and ultrasonic irradiation was performed for 30 minutes. After the reaction was completed, the precipitate was separated by suction filtration. The obtained precipitate was washed with deionized water and then dried under reduced pressure to obtain a yellow powder of anion-modified COF (anion-modified COF2), which is a hydrogen-generating photocatalyst.

[0228] <Production of Bonded Photocatalyst> A cation-modified Au—BiVO4 was produced in the same manner as in Example 1. ４ 50 mg of the above and 5 mg of anion-modified COF2 were added to a glass container, dispersed in 1 mL of deionized water, and stirred for 30 minutes to produce a junction-type photocatalyst. The SEM image of this junction-type photocatalyst is shown in Figure 8, and the evaluation results are shown in Table 1.

[0229] Comparative Example 1 The water splitting activity of the photocatalyst was evaluated in the same manner as in Example 1, except that only the Ru-supported COF synthesized in Example 1 was used as the photocatalyst. The results are shown in Table 1.

[0230] (Comparative Example 2) When evaluating the water splitting activity of the photocatalyst, Ru-supported COF and Au-BiVO ４ The evaluation was carried out in the same manner as in Example 1, except that the mixture of the above was used. The results are shown in Table 1.

[0231] (Comparative Example 3) <MPA-treated BiVO ４ BiVO was produced in the same manner as in Example 1. ４ 50 mg of the above was added to a glass container and dispersed in 5 mL of deionized water, and 12 μL of 3-mercaptopropionic acid (MPA) was added and stirred with a stirrer tip for 2 hours. After the reaction was completed, the precipitate was separated by suction filtration, and the precipitate was BiVO4 containing MPA. ４ (MPA processed BiVO ４ ) was obtained.

[0232] <Cation-modified BiVO ４ The obtained precipitate (MPA-treated BiVO ４ After washing with deionized water, the mixture was dispersed in 1 mL of a 50 mmol / L aqueous solution of cationic polymer 1 and stirred for 2 hours using a stirrer tip. After the reaction was completed, the precipitate was separated by suction filtration. The resulting precipitate was washed with deionized water and then dried under reduced pressure to obtain a yellow powder of BiVO4 into which the cationic polymer had been introduced. ４ (cation-modified BiVO ４ ) was obtained.

[0233] <Production of Bonded Photocatalyst> Produced Cation-Modified BiVO ４ 50 mg of the above and 5 mg of the anion-modified Ru-supported COF were added to a glass container, dispersed in 1 mL of deionized water, and stirred for 30 minutes to produce a junction-type photocatalyst without a solid mediator. The results are shown in Table 1.

[0234] Regarding Example 1 etc., BiVO ４ Table 1 shows the calculation results of the Au bonding selectivity to the {010} plane relative to the surface, the Au coverage relative to the area of ​​the {010} plane, and the evaluation results of the water splitting activity.

[0235] The obtained SEM images were analyzed by the following procedure: FIJI, a package developed based on ImageJ (National Institutes of Health), was used as image analysis software.

[0236] (BiVO ４ (Method for calculating the bonding selectivity of Au to the {010} plane relative to the surface) 1. Randomly crop 10 areas corresponding to the {010} plane from the SEM image, and obtain 10 pieces of cropped image data. 2. Randomly crop 10 areas corresponding to the {110} plane and {011} plane from the SEM image, and obtain 10 pieces of cropped image data. 3. Activate the Trainable Weka Segmentation (TWS) function for all image data, and perform a segmentation of Au and BiVO. ４ and background areas. 4. TWS is used to learn the three classifications. 5. Ten images of the {010} plane and ten images of the {110} and {011} planes are output as classified image data. 6. The Au coverage area on the {010} plane and the Au coverage area on the {110} and {011} planes are calculated from the Area value in the Analyze Particles function using the image data of the Au regions output by TWS classification. 7. Bonding selectivity (%) is calculated as follows: Au coverage area on the {010} plane / (Au coverage area on the {010} plane + Au coverage area on the {110} and {011} planes) × 100, and the average value of the 10 images is obtained.

[0237] (Method for calculating the coverage of Au relative to the area of ​​the {010} plane) 1. Randomly crop 10 areas corresponding to the {010} plane from the SEM image, and obtain 10 cropped image data. 2. Activate the Trainable Weka Segmentation (TWS) function for all image data, and extract the Au and BiVO ４and background areas are specified. 3. Three classifications are learned using TWS. 4. Ten images of classified image data are output. 5. The area of ​​the {010} plane is calculated from the Area value in the Analyze Particles function of the cropped image data, and the Au-covered area is calculated from the Area value in the same function as above using the image data of the Au region output by TWS classification. 6. The coverage rate (%) is calculated as = Au-covered area / area of ​​the {010} plane x 100, and the average value of the 10 images is obtained.

[0238] (Note) "None (MPA)" in the table indicates that no carrier polymer was used as a binder, but MPA was used as a binder. AP1 indicates anionic polymer 1 (trade name: Poise 520), and CP1 indicates cationic polymer 1 (trade name: Merquat 100 Polymer).

[0239] From the evaluation results in Table 1 above, it was confirmed that in Examples 1 to 5, by using a junction-type photocatalyst having a solid mediator between the hydrogen-generating photocatalyst containing an organic semiconductor and the oxygen-generating photocatalyst, the hydrogen generation rate was high and the water decomposition activity was excellent.

[0240] On the other hand, from the evaluation results in Table 1 above, it was confirmed that in Comparative Example 1, although a hydrogen generating photocatalyst containing an organic semiconductor was used, it was not a bonded photocatalyst having a solid mediator between the hydrogen generating photocatalyst and the oxygen generating photocatalyst, and therefore hardly any hydrogen generation was observed, making it not at a practical level.

[0241] In Comparative Example 2, Ru-supported COF and Au-BiVO ４ As a result of using a mixture of these as the photocatalyst and not using a binder (support polymer), the hydrogen-generating photocatalyst and oxygen-generating photocatalyst do not form a "bonded" photocatalyst via a solid mediator, and almost no hydrogen generation was observed, confirming that this is not at a practical level.

[0242] Furthermore, in Comparative Example 3, Au equivalent to the solid mediator was not used, and the photocatalyst was a junction type photocatalyst without a solid mediator, so almost no hydrogen generation was observed, and it was confirmed that the photocatalyst was not at a practical level.

[0243] The junction-type photocatalyst of the present invention is particularly useful as a photocatalyst for use in water decomposition or organic matter decomposition, or as a photocatalyst for hydrogen production.

Claims

1. a solid mediator is provided between a hydrogen generating photocatalyst containing an organic semiconductor and an oxygen generating photocatalyst, the hydrogen generating photocatalyst and the solid mediator are bonded together, and the oxygen generating photocatalyst and the solid mediator are bonded together; The junction-type photocatalyst, wherein the organic semiconductor is a covalent organic framework.

2. The bonded photocatalyst according to claim 1 , wherein the solid mediator is bonded to the electron collecting surface of the oxygen generating photocatalyst.

3. 2. The junction-type photocatalyst according to claim 1, wherein the junction selectivity of the solid mediator to the electron-collecting surface of the oxygen-generating photocatalyst is 60% or more.

4. 2. The junction-type photocatalyst according to claim 1, wherein the coverage of the solid mediator with respect to the electron-collecting surface area of the oxygen-generating photocatalyst is 40% or more.

5. 2. The junction type photocatalyst according to claim 1, wherein the topology diagram constituting the covalent organic framework is one or more types selected from (1) a hexagonal type, (2) a tetragonal type, (3) a rhombus type, and (4) a triangle type, and preferably is (1) a hexagonal type.

6. The junction type photocatalyst according to claim 1, wherein the covalent organic framework has one or more bonding modes selected from (10) boroxine type, (11) boronate ester type, (12) borazine type, (13) imide type, (14) amide type, (15) dioxin type, (16) imine type, (17) hydrazone type, (18) azine type, (19) oxazole type, (20) thiazole type, (21) squaraine type, (22) triazine type, (23) phenazine type, (24) amino type, and (25) olefin type, preferably has one or more bonding modes selected from (16) imine type and (24) amino type, and more preferably has (16) imine type bonding mode.

7. The junction-type photocatalyst according to claim 1 , wherein the hydrogen generating photocatalyst comprises a co-catalyst.

8. The co-catalyst is one or more kinds selected from transition metals, preferably one or more kinds selected from metals belonging to groups 8 to 10 of the periodic table, more preferably one or more kinds selected from metals belonging to the iron group and the platinum group, even more preferably one or more kinds selected from metals belonging to the platinum group, and still more preferably Ru.

9. The oxygen generating photocatalyst is one or more oxides selected from oxides containing elements selected from elements belonging to Group 14 and Group 15 of the periodic table, preferably one or more oxides selected from oxides containing elements selected from Bi, Pb, Sb, and Sn, more preferably one or more oxides selected from oxides containing Bi, and even more preferably BiVO ４ and even more preferably BiVO ４ The junction-type photocatalyst according to claim 1, wherein

10. 2. The junction-type photocatalyst according to claim 1, wherein the solid mediator is one or more selected from transition metals or compounds thereof, preferably one or more selected from transition metals containing elements belonging to Group 11 of the periodic table or compounds thereof, more preferably one or more selected from Au and Ag, and even more preferably one containing Au.

11. the hydrogen generating photocatalyst contains a covalent organic framework, the topology diagram constituting the covalent organic framework is one or more types selected from (1) a hexagonal type, (2) a tetragonal type, (3) a rhombus type, and (4) a triangle type; The covalent organic framework has one or more bonding modes selected from (10) boroxine type, (11) boronate ester type, (12) borazine type, (13) imide type, (14) amide type, (15) dioxin type, (16) imine type, (17) hydrazone type, (18) azine type, (19) oxazole type, (20) thiazole type, (21) squaraine type, (22) triazine type, (23) phenazine type, (24) amino type, and (25) olefin type; the oxygen generating photocatalyst is one or more oxides selected from oxides containing elements selected from elements belonging to Group 14 and Group 15 of the periodic table, 11. The junction type photocatalyst according to claim 1, wherein the solid mediator comprises one or more metals selected from the group consisting of one or more transition metals selected from Au, Ag, Cu, Ni, Ti, Mn, Rh, Pd, Ru, and Ir, one or more transition metal compounds selected from oxides, nitrides, and carbides of the transition metals, and one or more doped metal oxides selected from the group consisting of tin-doped indium oxide (ITO), metal (B, Al, Ga)-doped zinc oxide, fluorine-doped tin oxide, and antimony-doped tin oxide.

12. the hydrogen generating photocatalyst contains a covalent organic framework, the topology diagram constituting the covalent organic framework is one or more types selected from (1) a hexagonal type, (2) a tetragonal type, (3) a rhombus type, and (4) a triangle type; The covalent organic framework has one or more bonding modes selected from (16) an imine type and (24) an amino type, the hydrogen generating photocatalyst has a co-catalyst, the co-catalyst of the hydrogen generating photocatalyst is one or more selected from metals belonging to Groups 8 to 10 of the periodic table and compounds thereof; the oxygen generating photocatalyst is one or more oxides selected from oxides containing elements selected from Bi, Pb, Sb, and Sn, The junction-type photocatalyst according to any one of claims 1 to 10, wherein the solid mediator comprises one or more selected from transition metals including elements belonging to Group 11 of the periodic table or compounds thereof.

13. the hydrogen generating photocatalyst contains a covalent organic framework, the topology diagram constituting the covalent organic framework is one or more types selected from (1) a hexagonal type, (2) a tetragonal type, (3) a rhombus type, and (4) a triangle type; The covalent organic framework has one or more bonding modes selected from (16) an imine type and (24) an amino type, the hydrogen generating photocatalyst has a co-catalyst, the co-catalyst of the hydrogen generating photocatalyst is one or more selected from Pt, Pd, Ru, Ni, Fe, Ir, Rh, and compounds thereof; the oxygen generating photocatalyst is one or more oxides selected from oxides containing Bi, The junction-type photocatalyst according to any one of claims 1 to 10, wherein the solid mediator comprises one or more selected from transition metals including elements belonging to Group 11 of the periodic table or compounds thereof.

14. the hydrogen generating photocatalyst contains a covalent organic framework, the topology diagram constituting the covalent organic framework is one or more types selected from (1) a hexagonal type, (2) a tetragonal type, (3) a rhombus type, and (4) a triangle type; The covalent organic framework has one or more bonding modes selected from (16) an imine type and (24) an amino type, the hydrogen generating photocatalyst has a co-catalyst, the co-catalyst of the hydrogen generating photocatalyst is one selected from Pt, Pd, Ru, Ni, Fe, Ir, Rh and compounds thereof; the oxygen generating photocatalyst is one or more oxides selected from oxides containing Bi, The junction-type photocatalyst according to any one of claims 1 to 10, wherein the solid mediator comprises one or more selected from transition metals including elements belonging to Group 11 of the periodic table or compounds thereof.

15. the hydrogen generating photocatalyst contains a covalent organic framework, The topology diagram constituting the covalent organic framework is (1) a hexagonal type, The covalent organic framework (16) has an imine-type bonding mode, the hydrogen generating photocatalyst has a co-catalyst, the co-catalyst of the hydrogen generating photocatalyst contains Ru, The oxygen generating photocatalyst is BiVO ４ and The junction-type photocatalyst according to any one of claims 1 to 10, wherein the solid mediator contains Au.

16. A photocatalytic composite comprising the junction-type photocatalyst according to any one of claims 1 to 10 on a substrate.

17. A method for producing hydrogen, comprising irradiating the junction-type photocatalyst according to any one of claims 1 to 10 with light in the presence of water or alcohol.

18. A method for producing hydrogen, comprising irradiating the photocatalytic complex described in claim 16 with light in the presence of water or alcohol.

19. A method for producing the junction-type photocatalyst according to any one of claims 1 to 10, A method for producing a bonded photocatalyst, wherein the hydrogen generating photocatalyst and the solid mediator are bonded together and / or the oxygen generating photocatalyst and the solid mediator are bonded together using an ionic polymer as a bonding agent.