JP6901718B2 - Photocatalytic material and its manufacturing method - Google Patents

Description

The present invention relates to a photocatalyst material in which a photocatalyst layer containing hydrogen-generating photocatalyst particles and oxygen-evolving photocatalyst particles capable of photodecomposing water with visible light is immobilized on a substrate, and a method for producing the same.

The visible light responsive photocatalyst is a photocatalyst capable of utilizing visible light contained in a large amount in sunlight. This visible light responsive photocatalyst is expected to be applied to photodecomposition of organic substances and hydrogen production by photodecomposition of water. Among them, a photocatalyst for water decomposition for the purpose of producing hydrogen is attracting attention as a photocatalyst used in a hydrogen production method using renewable energy. Then, there is a demand for a photocatalyst for water decomposition that can obtain high activity.

According to WO2014 / 046305, a photocatalyst material including a base material and a photocatalyst layer immobilized on the base material, wherein the photocatalyst layer has a primary particle size of 100 nm or less for hydrogen generation. Those including visible light responsive photocatalyst particles and visible light responsive photocatalyst particles for oxygen evolution are exemplified. In this example, the visible light responsive photocatalyst particles for hydrogen generation and the visible light responsive photocatalyst particles for oxygen generation are in contact with each other. According to WO2014 / 046305, it is reported that this photocatalytic material has a high hydrogen generating ability, but further improvement in the hydrogen generating ability of the photocatalytic material is required.

Japanese Patent Application Laid-Open No. 2012-187520 describes a photocatalyst immobilized product for water splitting having a photocatalyst layer on a substrate, and a visible light responsive photosemiconductor whose photocatalyst layer is a nitride or an oxynitride, and a visible light response. A photocatalyst immobilized product containing a cocatalyst supported on a type photosemiconductor and a hydrophilic inorganic material is exemplified.

Japanese Unexamined Patent Publication No. 2001-219073 describes a photooxidation catalyst in which a photocatalyst carrying a co-catalyst is fixed on a substrate using a binder such as silica, and the blending ratio of the photocatalyst is 20 to 60 with respect to the binder. It is stated that it is preferably about% by weight.

WO2014 / 046305 Japanese Unexamined Patent Publication No. 2012-187520 Japanese Unexamined Patent Publication No. 2001-21907

Photocatalytic particles having high crystallinity can be obtained by firing at a high temperature using a solid phase method or the like. Due to the high temperature firing, the particle size of these particles is relatively large (several hundred nm). Water decomposition activity has been confirmed by irradiating a suspension in which these particles are dispersed in water with light while stirring. For practical use, it is necessary to prepare a photocatalyst sheet in which photocatalyst particles are fixed to a base material. When particles having such a large particle size are arranged and fixed on the substrate, it is preferable to provide a certain amount of pores in order to increase the contact area with water. However, in this case, for example, running water or the like tends to cause threshing of these particles. On the other hand, when a binder is used as in the conventional case, the contact area between the photocatalyst particles and water is reduced, and the water decomposition performance is deteriorated.

The present invention has made it possible to suppress both shedding and a decrease in photocatalytic activity by devising the pore diameter and the thickness of the peeling prevention portion. That is, the photocatalytic material according to the present invention is
With the base material
The photocatalyst layer provided on the base material and
It is a photocatalytic material containing
The photocatalyst layer is
A plurality of first photocatalytic particles of the visible light responsive type for hydrogen generation,
A plurality of visible light responsive second photocatalytic particles for oxygen evolution,
Between the plurality of first photocatalyst particles, between the plurality of second photocatalyst particles, between the plurality of first photocatalyst particles and the plurality of second photocatalyst particles, the plurality of first photocatalyst particles. A peeling prevention portion provided at least in a part between the photocatalyst particles of the above and the base material, and between the plurality of second photocatalyst particles and the base material.
The pores provided between the plurality of first photocatalyst particles, the plurality of second photocatalyst particles, and the peeling prevention portion, and the like.
Including
The average primary particle diameter of the first photocatalyst particles and the second photocatalyst particles is 100 nm or more and 5000 nm or less.
The pore diameter is 20 nm or more and 500 nm or less.
The peeling prevention portion contains at least one selected from the group consisting of metal hydroxides, oxides and phosphates.
The average thickness of the peeling prevention portion is 50 nm or less.

According to the photocatalytic material according to the present invention, both shedding and a decrease in photocatalytic activity can be suppressed.

It is a schematic cross-sectional view which shows the photocatalyst material by this invention. It is a schematic cross-sectional view which shows the photocatalyst material by this invention. It is a schematic cross-sectional view which shows the photocatalyst material by this invention. It is an SEM image of the photocatalyst layer by this invention. It is a TEM image of the photocatalyst layer by this invention. This is the result of XPS measurement of the photocatalytic material according to the present invention.

Definition In the present specification, "visible light" means an electromagnetic wave (light) having a wavelength that can be visually recognized by the human eye. It preferably means light containing visible light having a wavelength of 380 nm or more, and more preferably light containing visible light having a wavelength of 420 nm or more. As the light including visible light, sunlight, condensed sunlight whose energy density is increased by condensing it, or an artificial light source such as a xenon lamp, a halogen lamp, a sodium lamp, a fluorescent lamp, or a light emitting diode is used as a light source. It is possible. Preferably, the inexhaustible amount of sunlight falling on the earth is used as a light source. As a result, visible light that occupies about 52% of the sun's rays can be used, and hydrogen and oxygen can be efficiently extracted from water.

In the present specification, the "visible light responsive photocatalytic particle for hydrogen generation" means a photocatalytic particle capable of generating hydrogen by a photocatalytic reaction of water with visible light, and is "visible light responsive photocatalytic particle for oxygen generation". Means photocatalytic particles capable of generating oxygen by the photocatalytic reaction of water with visible light.

As used herein, the term "couple" of particles means at least a state in which a plurality of particles are arranged so that holes and / or electrons can move between the particles. For example, it also includes an embodiment in which particles are not physically in contact with each other but are arranged so that holes and / or electrons can move. On the other hand, "contact" between particles means a state in which some of the particles are arranged in contact with each other. In the "contact" mode of particles, a state in which holes and / or electrons can move between the particles by contacting a part of the particles, that is, the particles are in contact with each other. Includes electrically connected states. Further, the term "bind" of particles means a state in which particles are arranged in contact with each other more firmly than in the case of "contact". "Joining" includes, for example, a chemically bonded state.

Photocatalytic material The overall configuration of the photocatalytic material according to the present invention will be described with reference to FIG.
The photocatalyst material 100 includes a base material 90 and a photocatalyst layer 70 immobilized on the base material 90. The photocatalyst layer 70 includes a first photocatalyst particle 10 of a visible light responsive type for hydrogen generation (hereinafter, also simply referred to as “first photocatalyst particle”) and a second photocatalyst particle 20 of a visible light responsive type for oxygen generation (hereinafter, also simply referred to as “first photocatalyst particle”). Hereinafter, it is also simply referred to as “second photocatalytic particle”), and includes a peeling prevention portion 60 and pores 71. In this example, the peeling prevention unit 60 includes a plurality of colloidal particles 61. In the photocatalyst layer 70, the peeling prevention unit 60 is used between the first photocatalyst particles 10 and between the second photocatalyst particles 20, between the first photocatalyst particles 10 and the second photocatalyst particles 20, and first. It is arranged at least a part between the photocatalyst particles 10 and the base material 90, and between the second photocatalyst particles 20 and the base material 90. The pores 71 are arranged between the first photocatalyst particles 10, the second photocatalyst particles 20, and the peeling prevention portion 60. Since the photocatalytic material according to the present invention has the above-mentioned structure, it can exhibit high photocatalytic activity under visible light irradiation, can photodecompose water with high efficiency, and generates extremely high hydrogen. It has the ability and can suppress granulation.

Base material The base material 90 contained in the photocatalyst material according to the present invention may be any material capable of immobilizing the photocatalyst layer 70 on its surface. Specific examples of such a base material 90 include an organic base material and an inorganic base material. Examples of the organic base material include a plastic base material. Examples of the inorganic base material include a ceramic base material such as an alumina substrate, a glass base material such as soda lime glass and borosilicate glass, and a quartz base material. For example, a base material that is not easily decomposed by heating at 250 ° C. or higher or 300 ° C. or higher is more preferable. A base material having light transmission may be used.

Further, a metal base material may be used as the base material 90. Specific examples of the metal include titanium, aluminum, iron, stainless steel and the like. Practically, the above organic or inorganic substances are preferable to metals.

In the photocatalyst material according to the present invention, an insulating base material can be used as the base material 90.

The base material 90 may have a shape such that the photocatalyst layer 70 can be immobilized on the surface thereof by drying or firing. Specific examples of such a base material 90 include a flat plate having a smooth surface (for example, a glass substrate, an alumina substrate, etc.), a flat plate having a porous surface (for example, anodized alumina), and a porous body (for example, porous ceramics). A fiber body (for example, glass fiber, carbon fiber) or the like can be preferably used. More preferably, glass fiber having high light transmission can be used as the fiber body. As a result, light can be transmitted to the inside of the layer rather than the light-irradiated surface of the fiber body, and an increase in the amount of light absorption can be expected. Further, the surface shape of the base material 90 may be a wavy shape, a comb shape, a fibrous shape, or a mesh shape.

The base material 90 may have a plurality of pores. The diameter of each pore is preferably 0.1 to 30 μm, for example. These pores are preferably arranged as continuous pores. As a result, for example, the hydrogen gas generated by the water splitting reaction on the surfaces of the photocatalyst particles 10 and 20 arranged inside the photocatalyst layer 70 diffuses the pores 71 inside the photocatalyst layer 70, and then, for example, the pores. It becomes possible to reach the outside of the photocatalyst layer 70 through these pores having an opening larger than 71, and more efficient hydrogen gas generation becomes possible.

Photocatalyst layer In the present invention, the photocatalyst layer 70 may be a dense continuous layer. The photocatalyst layer 70 may have, for example, a discontinuous portion. For example, the photocatalyst layer 70 may be discretely present on the surface of the base material 90 in an island shape. The photocatalyst layer 70 may be in a wavy, comb-shaped, fibrous, mesh-like state or the like.

The photocatalyst layer 70 has, for example, pores 71 into which water, hydrogen, and oxygen gas can diffuse. The pores 71 are arranged, for example, between the first photocatalyst particles 10, the second photocatalyst particles 20, and the peeling prevention portion 60. Through the pores 71, not only the surface of the photocatalyst layer 70 but also the photocatalyst particles located inside the photocatalyst layer 70 can come into contact with water and light. The pore diameter is 20 nm or more and 500 nm or less, preferably 20 nm or more and 100 nm or less.

In the present invention, the thickness of the photocatalyst layer 70 is preferably 0.1 μm or more and 50 μm or less. A more preferable thickness of the photocatalyst layer 70 is 0.2 μm or more and 30 μm or less.
Here, the thickness of the photocatalyst layer 70 can be determined, for example, by observing a cross section of the photocatalyst material with a scanning electron microscope. Specifically, it is the distance from the horizontal tangent at a point on the surface of the substrate 90 to the top of the photocatalyst layer 70 at a perpendicular to this tangent. For example, when the base material 90 is a flat plate as shown in FIG. 1, the thickness of the photocatalyst layer 70 is the distance from the surface of the base material 90 to the uppermost portion of the photocatalyst layer 70 in the vertical direction. When the surface of the base material 90 is like a fiber, the thickness of the photocatalyst layer 70 is the distance from the horizontal tangent at a certain point on the surface of the fiber to the top of the photocatalyst layer 70 in the perpendicular to this tangent. Is.

As shown in FIG. 2, in the photocatalyst material 101, the photocatalyst layer 70 may contain conductive particles 40. In this case, the conductive particles 40 are in contact with both the first photocatalyst particles 10 and the second photocatalyst particles 20 at arbitrary parts (points, surfaces, etc.) on the surface thereof. In the photocatalyst layer 70, the surface of the conductive particles 40 has a first region, a second region, and a third region. In the first region, the conductive particles 40 are in physical contact with the first photocatalytic particles 10. In the second region, the conductive particles 40 are in physical contact with the second photocatalytic particles 20. The third region is a region other than the first region and the second region on the surface of the conductive particles 40. That is, in the third region, the conductive particles 40 do not come into contact with either the first photocatalyst particles 10 or the second photocatalyst particles 20.

In the photocatalyst layer 70, since the first photocatalyst particles 10 and the second photocatalyst particles 20 are electrically connected via the conductive particles 40, they are generated in the valence band of the first photocatalyst particles 10. The degree of electrical connection between the excited holes and the excited electrons generated in the conduction band of the second photocatalytic particle 20 via the conductive particles 40 becomes stronger. Therefore, in the photocatalytic material 101, a charge recombination reaction occurs between the photoexcited holes and the photoexcited electrons in the conductive particles 40. As a result, the photocatalytic activity of the photocatalyst layer 70 can be further enhanced, and the hydrogen generating ability of the photocatalyst layer 70 is further improved.

Visible light responsive photocatalytic particles for hydrogen generation (first photocatalytic particles)
The first photocatalyst particle 10 is a semiconductor particle having an optical bandgap. When the first photocatalyst particles 10 absorb visible light, electron transitions such as band-to-band transitions in the first photocatalyst particles 10 generate excitation electrons at the electron acceptor level existing in the conduction band or band gap. In addition, excited holes are generated at the electron donor level existing in the valence band or band gap. The first photocatalyst particle 10 is a photocatalyst material in which each of the excited electrons and the excited holes can reduce and oxidize the reaction target. That is, the first photocatalyst particle 10 is a photocatalyst material in which excited electrons generated by irradiating visible light can reduce water to generate hydrogen. The electron acceptor level existing in the conduction band or band gap of the first photocatalyst particle 10 is located at a position negative from the reduction potential of water (0 V vs. NHE (standard hydrogen electrode potential) at pH = 0), for example. is there. Further, the electron donor level existing in the valence band or band gap of the first photocatalyst particle 10 is, for example, at a position more positive than the conduction band position of the second photocatalyst particle.

Preferred examples of the first photocatalyst particles 10 include Rh-doped _{SrTIO 3} (SrTi _1-x Rh _x O ₃ : x = 0.002-0.1), Ir-doped SrTiO ₃ (SrTi _1-x Ir _x O3:). x = 0.002-0.1), Cr-doped _{SrTIO 3} (SrTi _1-x Cr _x O ₃ : x = 0.002-0.1), Cr and Ta-doped _{SrTIO 3} (SrTi _1-x-y Cr) _{x T y} O ₃ : x = 0.002 to 0.1, y = 0.002 to 0.1), La and Rh-doped SrTIO ₃ (Sr _1-x La _x Ti _1-y Rh _y O ₃ : x = 0.005 to 0.2, y = 0.005 to 0.2) and other transition metals or noble metals doped with perovskite type SrTiO ₃ , Cu ₂ O, CuO, CaFe ₂ O ₄ , NiO , Bi ₂ O ₃ , BiOX (X = Cl, Br, I), GaN-ZnO solid solution, LaTIO ₂ N, BaTaO ₂ N, BaNbO ₂ N, TaON, Ta ₃ N ₅ , Ge ₃ N _4, etc. Acid nitrides or nitrides containing typical metals, CuGaS ₂ , CuInS ₂ , Cu (Ga, In) S ₂ , CuGaSe ₂ , CuInSe ₂ , Cu (Ga, In) Se ₂ , Cu ₂ ZnSnS ₄ (CZTS), Copper selenide containing typical metals such as Ga, In, Al such as Cu ₂ ZnSn (S, Se) _{4 , copper sulfide, or copper composite sulfur selenide, La 5} Ti ₂ CuS ₅ O ₇ , La ₅ Ti ₂ One or more selected from the group consisting of acid sulfide selenium products such as AgS ₅ O ₇ , La ₅ Ti ₂ CuSe ₅ O ₇ , La ₅ Ti ₂ AgSe ₅ O _{7 and acid sulfides such as metal-doped compounds thereof.} Be done.

More preferred examples of the first photocatalyst particles 10 are Rh-doped _{SrTIO 3} (SrTi _1-x Rh _x O ₃ : x = 0.005-0.05), Ir-doped SrTiO ₃ (SrTi _1-x Ir _x O3). : X = 0.005-0.05), Cr-doped _{SrTIO 3} (SrTi _1-x Cr _x O ₃ : x = 0.002-0.1), Cr and Ta-doped _{SrTIO 3} (SrTi _{1-x-y) cr x Ta y O 3: x} = 0.002~0.1, y = 0.002~0.1), La and Rh-doped _{SrTiO 3 (Sr 1-x La} x Ti 1-y Rh y O 3: _{Perovskite-type SrTiO 3} , Cu ₂ O, Cu O, CaFe ₂ O ₄ , doped with at least one of transition metals or noble metals such as x = 0.005 to 0.2, y = 0.005 to 0.2), NiO, Bi ₂ O ₃ , BiOX (X = Cl, Br, I), GaN-ZnO solid solution, LaTIO ₂ N, BaTaO ₂ N, BaNbO ₂ N, TaON, Ta ₃ N ₅ , Ge ₃ N ₄ , CuGaS ₂ , CuInS ₂ , Cu (Ga, In) S ₂ , CuGaSe ₂ , CuInSe ₂ , Cu (Ga, In) Se ₂ , Cu ₂ ZnSnS ₄ (CZTS), Cu ₂ ZnSn (S, Se) _4, La ₅ Ti ₂ CuS One or more selected from the group consisting of acid sulfides such as ₅ O ₇ and its metal-doped compound, La ₅ Ti ₂ AgS ₅ O _{7 and its metal-doped compound and the like can be mentioned.}

The most preferable examples of the first photocatalytic particle 10 are Rh-doped _{SrTIO 3} (SrTi _1-x Rh _x O ₃ : x = 0.01 to 0.04) and Cr-doped _{SrTIO 3} (SrTi _1-x Cr _x O). _3: x = _0.002~0.1), Cr and Ta-doped _{SrTiO 3 (SrTi 1-x-} y Cr x Ta y O 3: x = 0.002~0.1, y = 0.002~0 .1), La and Rh-doped _{SrTiO 3 (Sr 1-x La} x Ti 1-y Rh y O 3: x = 0.005~0.2, y = 0.005~0.2) transition metal such Alternatively precious metal of at least one-doped perovskite _{SrTiO 3, TaON, Ta 3 N} 5, 1 or more selected from the group consisting of and the like.

Average primary particle size of the first photocatalyst particles The average primary particle size of the first photocatalyst particles 10 is 100 nm or more and 5000 nm or less. Having such a small particle size increases the surface area of the first photocatalyst particles 10 per unit weight that can come into contact with water. As a result, the number of reduction reaction sites of water increases, and as a result, highly efficient hydrogen generation becomes possible. The preferred lower limit of the average primary particle size of the first photocatalyst particles 10 is 100 nm, and the preferred upper limit is 1000 nm.

Visible light responsive photocatalytic particles for oxygen evolution (second photocatalytic particles)
The second photocatalyst particle 20 is a semiconductor particle having an optical bandgap. When the second photocatalyst particles 20 absorb visible light, excited electrons are generated in the conduction band and excited holes are generated in the valence band due to electron transitions such as band-to-band transitions in the second photocatalyst particles 20. The second photocatalyst particle 20 is a photocatalyst material in which each of the excited electrons and the excited holes can reduce and oxidize the reaction object. That is, the second photocatalyst particle 20 is a photocatalyst material in which excited holes generated by irradiating visible light can oxidize water to generate oxygen. The valence band of the second photocatalyst particle 20 is located at a position more positive than, for example, the oxidation potential of water (+1.23 V vs. NHE (standard hydrogen electrode potential) at pH = 0). Further, the conduction band of the second photocatalyst particles 20 is located at a position more negative than the valence band position of the first photocatalyst particles, for example.

Preferred examples of the second photocatalyst particles 20 are BiVO ₄ , X-doped BiVO ₄ (X: Mo, W), SnNb ₂ O ₆ , WO ₃ , Bi ₂ WO ₆ , Fe _{2 thio 5} , Fe ₂ O ₃ , From oxynitrides or nitrides containing transition metals or main group _{elements such as Bi 2} MoO ₆ , GaN-ZnO solid solution, LaTIO ₂ N, BaTaO ₂ N, BaNbO ₂ N, TaON, Ta ₃ N ₅ , Ge ₃ N ₄ One or more selected from the group of

More preferred examples of the second photocatalytic particle 20 are BiVO ₄ , X-doped BiVO ₄ (X: Mo, W), SnNb ₂ O ₆ , WO ₃ , Bi ₂ WO ₆ , Bi ₂ MoO ₆ , Fe ₂ O ₃ , GaN-ZnO solid solution, LaTIO ₂ N, BaTaO ₂ N, BaNbO ₂ N, TaON, Ta ₃ N ₅ , Ge ₃ N ₄ or more selected from the group.

The most preferable example of the second photocatalytic particle 20 is selected from the group consisting of _{BiVO 4} , Mo-doped BiVO ₄ , WO ₃ , SnNb ₂ O ₆ , Bi ₂ WO ₆ , BaTaO ₂ N, and Fe ₂ O _3. More than seeds can be mentioned.

Average primary particle size of the second photocatalyst particles The average primary particle size of the second photocatalyst particles 20 is 100 nm or more and 5000 nm or less. Having such a small particle size increases the surface area of the second photocatalyst particles 20 per unit weight that can come into contact with water. This increases the number of oxidation reaction sites in water, resulting in highly efficient oxygen evolution. The preferable lower limit of the average primary particle diameter of the second photocatalyst particles 20 is 100 nm, and the preferable upper limit is 1000 nm or less.

Evaluation Method of Average Primary Particle Size of First and Second Photocatalyst Particles As an evaluation method of the average primary particle size of the first photocatalyst particles 10 and the second photocatalyst particles 20, for example, a scanning electron microscope (Hitachi Co., Ltd.) According to "S-4100" manufactured by Mfg. Co., Ltd., hereinafter also referred to as "SEM"), it is possible to define the average value by circular approximation of 50 crystal particles when observed at a magnification of 40,000 times.

Conductive particles (definition)
In the present invention, the conductive particle 40 is a position negative from the electron energy level at the upper end of the valence band of the first photocatalyst particle 10 and from the electron energy level at the lower end of the conduction band of the second photocatalyst particle 20. Is also a conductive particle that has a Fermi level in the positive position and can store electrons and holes. By having such a specific Fermi level in the conductive particles 40, it is possible to improve the photodecomposition of water by the photocatalytic material 101. The Fermi level of the conductive particle can be expressed by using the potential as a reference instead of the electron energy level. In this case, the conductive particle 40 is the upper end of the valence band of the first photocatalyst particle 10. It has a more negative potential and has a Fermi level at a positive potential than the lower end of the conduction band of the second photocatalyst particle 20.

(material)
Examples of preferable materials for the conductive particles 40 include metals such as gold, silver, copper, nickel, rhodium and palladium, carbon materials, nitrides such as TiN, carbides such as TiC, and manganese oxides (MnO ₂ , AmnO _3). (A: Ca or Sr), B-doped AmnO ₃ (A: Ca or Sr, B: La ³⁺ , Y ³⁺ , Bi ³⁺ , Nb ⁵⁺ , or Ta ⁵⁺ )), tin-doped indium oxide (ITO) , Metal (B, Al, Ga) -doped zinc oxide, fluorine-doped tin oxide, antimony-doped tin oxide, ruthenium oxide, iridium oxide, rhodium oxide, spinel-type oxide AB ₂ O ₄ (A = Fe, Ni, Mn, Co. , Zn, etc., B = Fe, Co, Mn, etc., A = B, A ≠ B, etc.), etc., and one or more selected from the group consisting of conductive metal oxides can be mentioned. Among these, select from the group consisting of gold, carbon materials, ITO, and conductive metal oxides such as metal (B, Al, Ga) -doped zinc oxide, ruthenium oxide, iridium oxide, and magnetite (Fe ₃ O _4). It is more preferable that one or more of them are used. As the carbon material, for example, carbon black, ketjen black, acetylene black, channel black, furnace black, thermal black, lamp black and the like can be used.

When the materials of the conductive particles and the photocatalyst particles are both metal oxides, the photocatalyst particles and the conductive particles are metal oxides, so that the conductive particles can obtain an excellent binder effect and are conductive. The contact between the particles and the photocatalyst particles can be strengthened. When an inorganic substance such as glass or alumina, especially a metal oxide, is used as the material of the base material and the material of the conductive particles is also a metal oxide, a metal-oxygen bond is formed between the base material and the conductive particles. Will be done. Therefore, the adhesion between the conductive particles and the base material is improved. As a result, it is possible to improve the mechanical strength of the entire photocatalyst material. Further, as the conductive particles made of a metal oxide as a material, those having a crystal structure are preferable to those having an amorphous structure. This provides high conductivity and high stability to redox.

Barium, cesium, and sodium, which are generally known as conductive materials, have a small work function and do not have the above-mentioned Fermi level. Therefore, these materials are not included in the conductive particles 40 in the present invention.

(Shape and particle state)
The conductive particles 40 may be in any particle state. As shown in FIG. 2, even if the conductive particles 40 are so-called primary particles, and the first photocatalyst particles 10 and the second photocatalyst particles 20 are in contact with one conductive particle 40, for example. Good. Alternatively, as the conductive particles 40, for example, so-called secondary particles in which the primary particles are aggregated are used, and the first photocatalyst particles 10 and the second photocatalyst particles 20 are connected by an aggregate of a plurality of conductive particles 40. You may. Further, the conductive particles 40 may be in a state in which a plurality of primary particles and / or a single or a plurality of secondary particles are bonded by, for example, heating. Each of the above aspects is included in a state in which the conductive particles 40, the first photocatalyst particles 10 and the second photocatalyst particles 20 are connected via the same conductive particles 40.

In the present invention, the conductive particles 40 may have any shape. The shape of the conductive particles 40 is, for example, an isotropic shape (spherical shape, approximately polygonal shape, etc.) or an anisotropic shape (columnar shape, rod shape, plate shape, flaky shape, etc.). As the anisotropically shaped particles, for example, a conductive wire can be used. Examples of conductive wires include particles having a rod-like or needle-like shape.

(Average primary particle size)
In the present invention, the average primary particle size of the conductive particles 40 is preferably smaller than the average primary particle size of each of the first photocatalyst particles 10 and the second photocatalyst particles 20. As a result, in the photocatalyst layer 70, for example, the first and second photocatalyst particles 10 and 20 can be effectively irradiated with light. When the average primary particle size of the conductive particles 40 is smaller than the average primary particle size of each of the first photocatalyst particles 10 and the second photocatalyst particles 20, the base material 90 and the photocatalyst layer 70 are formed. The number of contact points per unit area with particles can be increased. Therefore, the adhesion between the photocatalyst layer 70 and the base material 90 can be improved.

Further, the average primary particle size of the conductive particles 40 can be appropriately selected within a range in which light irradiation of the first photocatalyst particles 10 and the second photocatalyst particles 20 is ensured in the photocatalyst layer 70. For example, when light-transmitting particles are used as the conductive particles 40, those having a relatively large particle size can be used. On the other hand, when the conductive particles 40 are particles having no light transmittance, it is preferable to use particles having a smaller particle size.

The average primary particle diameter of the conductive particles 40 is, for example, preferably 1 nm or more and 1000 nm or less, more preferably 5 nm or more and 500 nm or less, and even more preferably 5 nm or more and 200 nm or less. As a result, in the photocatalyst layer 70, the first photocatalyst particles 10 and the second photocatalyst particles 20 can be effectively irradiated with visible light. Further, in the photocatalyst layer 70, for example, the conductive particles 40 and the photocatalyst particles 10 and 20 can be brought into good contact with each other. In addition, suitable pores 71 can be formed in the photocatalyst layer 70. Further, by making the average primary particle size of the conductive particles relatively large within the above range, the probability that a charge recombination reaction will occur between the first photocatalyst particles 10 and the second photocatalyst particles 20 is increased. Can be done. As a result, high water decomposition activity can be more reliably obtained in the photocatalytic material.

It is particularly preferable that the average primary particle diameter of the conductive particles 40 is 10 nm or more and 200 nm or less. By setting this particle size range, the conductive particles 40 can not only connect the first photocatalyst particles 10 and the second photocatalyst particles 20, but also exhibit an excellent function as a binder and photocatalyst. The adhesion between particles can be improved.

When the conductive particles 40 are isotropic particles, the average primary particle diameter is, for example, 1 nm or more and 1000 nm or less, more preferably 5 nm or more and 500 nm or less, further preferably 5 nm or more and 200 nm or less, and 10 nm or more and 200 nm or less. Is particularly preferable. Having such an average primary particle size enables efficient contact between the conductive particles 40 and the photocatalyst particles 10 and 20. Further, the conductive particles 40 suppress the interference of the photocatalyst particles 10 and 20 with light absorption. In the present invention, when the conductive particles 40 are particles having an isotropic shape, for example, the area of the conductive particles obtained by observing the conductive particles 40 by SEM or TEM is obtained by converting the area of the conductive particles into the area of a circle. The diameter to be obtained may be the average primary particle diameter thereof. Alternatively, the diameter of the maximum cross section of the conductive particles 40 may be the average primary particle diameter of the conductive particles 40.

When the conductive particles 40 are anisotropically shaped particles, the aspect ratio (major axis diameter / minor axis diameter) of the conductive particles 40 is preferably 5 or more and 1000 or less. With such an aspect ratio, the probability that the first photocatalyst particles 10 and the second photocatalyst particles 20 come into contact with the conductive wire can be sufficiently increased. Therefore, the charge recombination reaction described later is promoted. As a result, efficient photodecomposition of water is possible. Further, when the anisotropically shaped conductive particles 40 are used, the binder effect of the conductive particles 40 can be enhanced.

When a conductive wire is used as the anisotropically shaped conductive particles 40, the average primary particle diameter thereof is, for example, preferably 1 nm or more and 1000 nm or less, and preferably 5 nm or more and 200 nm or less. Here, the average primary particle diameter of the conductive wire means the diameter of the conductive wire when the cross section having the minimum cross-sectional area is approximately circularly approximated.
The length of the long axis of the conductive wire is not particularly limited, but is preferably 10 nm or more and 10000 nm or less. Having such a shape and size makes it possible to efficiently bring the conductive wire into contact with the photocatalyst particles 10 and 20. Further, the conductive particles 40 suppress the interference of the photocatalyst particles 10 and 20 with light absorption. In addition, the binder effect of the conductive particles 40 can be enhanced.

When a conductive plate having a plate-like or flaky shape is used as the anisotropic conductive particles 40, the major axis diameter of the plate surface or flakes is preferably 20 nm or more and 1000 nm or less. The average primary particle size of the plate surface or flakes is preferably 1 nm or more and 1000 nm or less. Here, the average primary particle diameter of the conductive plate means, for example, the diameter of the conductive plate when the cross section having the maximum cross-sectional area is approximately circularly approximated. The aspect ratio (major axis diameter / minor axis diameter) of the conductive plate is, for example, preferably 3 or more and 5000 or less, and more preferably 10 or more and 1000 or less. By using the conductive plate having such a shape and size as the conductive particles 40, it is possible to efficiently bring the photocatalytic particles 10 and 20 into contact with the conductive particles 40. Further, the conductive particles 40 suppress the interference of the photocatalyst particles 10 and 20 with light absorption. In addition, the binder effect of the conductive particles 40 can be enhanced.

(Conductivity / volume resistivity)
The conductivity of the conductive particles 40 ^{is preferably 0.1 Scm-1} or more. The volume resistivity of the conductive particles 40 is preferably 10 Ωcm or less, for example.

(Content)
In the present invention, the photocatalyst material preferably contains an amount of conductive particles 40 capable of increasing the number of electrical connection points between the first photocatalyst particles 10 and the second photocatalyst particles 20. Further, the photocatalyst material preferably contains the conductive particles 40 in an amount that does not interfere with the light absorption of the first photocatalyst particles 10 and the second photocatalyst particles 20. The content thereof can be appropriately set in consideration of the average primary particle diameter of the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40, or the specific gravity of the conductive particles 40. The content thereof is preferably set appropriately within a range in which pores 71 can be formed in the photocatalyst layer 70, for example. For example, it is preferable that the conductive particles 40 are contained in an amount of 1 wt% or more and 99 wt% or less with respect to the total content of the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40. The ratio of the content of the conductive particles 40 is more preferably 5 wt% or more and 60 wt% or less, and 5 wt% or more and 50 wt% or less.
By irradiating with visible light, the excited holes generated in the valence band of the first photocatalyst particles 10 diffuse to the surface of the first photocatalyst particles 10 and are negative from the electron energy level at the upper end of the valence band. It is believed that it moves into the conductive particles 40 having the Fermi level at the position. Further, by irradiating the visible light, the excited electrons generated in the conduction band of the second photocatalyst particle 20 are diffused on the surface of the second photocatalyst particle 20, and the position is more positive than the electron energy level at the lower end of the conduction band. It is considered that the particles move into the conductive particles 40 having the Fermi level. Then, the photoexcited holes generated in the valence band of the first photocatalyst particles 10 stored in the conductive particles 40 react with the photoexcited electrons generated in the conduction band of the second photocatalyst particles 20, and the charge is charged. It is considered that the recombination reaction occurs and these two excitation carriers disappear. This charge recombination reaction efficiently produces photoexcited holes and photoexcited electrons that have not been involved in the photocatalytic reaction of water in the past, but rather tended to reduce the photocatalytic activity of individual particles in the photolytic reaction of water. It is thought that it can be extinguished, which makes it possible for the photodecomposition reaction of water to occur efficiently. As a result, it is considered that the first photocatalytic particles 10 and the second photocatalytic particles 20 electrically connected by the conductive particles 40 can exhibit high photocatalytic activity, and the hydrogen generating ability can be improved. Be done.

(Work function)
In the present invention, the Fermi level of the conductive particle 40 can be estimated using a work function which is an energy difference between the vacuum level and the Fermi level. The work function can be determined, for example, by measuring the potential using a Kelvin probe force microscope (KPFM).

Peeling prevention unit In the present invention, the photocatalyst layer 70 of the photocatalyst material 100 is formed between the first photocatalyst particles, between the second photocatalyst particles, between the first photocatalyst particles and the second photocatalyst particles, and so on. It further includes a peeling prevention portion 60 provided at least in a part between the photocatalyst particles of 1 and the base material, and between the photocatalyst particles of 1 and the base material. Further, when the photocatalyst layer 70 contains the conductive particles 40, the peeling prevention portion 60 may be provided in at least a part of the third region of the conductive particles 40. Since the photocatalyst layer 70 has the peeling prevention portion 60, it is possible to prevent the photocatalyst particles 10 and 20 from peeling from the base material.
In the photocatalytic material of the present invention, water can be decomposed to generate hydrogen and oxygen by irradiating with visible light. At this time, hydrogen and oxygen gas generated by the water splitting reaction in water react on the surface of the conductive particles using the conductive particles as a catalyst, so that a reverse reaction to generate water occurs, and the hydrogen produced. And there is a problem that the amount of oxygen decreases. When the conductive particles are metal particles such as gold, the metal particles tend to act as a catalyst for the reverse reaction and promote the reverse reaction. On the other hand, for example, by performing water decomposition in a reduced pressure state, a reverse reaction can be prevented, but a method that is simpler in practice is preferable. In the present invention, the peeling prevention portion 60 provided on the conductive particles 40 diffuses hydrogen or oxygen molecules generated by water decomposition into the third region 40c, which is the outer surface of the conductive particles 40, and on the surface of the conductive particles 40. It has been found that it is possible to prevent the generation of water associated with the reverse reaction of hydrogen and oxygen. Therefore, the reverse reaction can be effectively prevented with a simple configuration, and the decrease in hydrogen production ability can be suppressed.

The photocatalytic material according to the present invention is exposed to running water or the like for a long period of time during use. Therefore, it is important that the photocatalyst layer 70 does not peel off from the base material 90. In order to provide practically sufficient adhesion between the photocatalyst layer 70 and the base material 90, for example, it is conceivable to bake the photocatalyst layer 70 onto the base material at a high temperature. However, in order to mass-produce and reduce the cost, it is preferable that sufficient adhesion can be ensured even without firing or even at low temperature firing.
In the present invention, in the photocatalyst layer 70, between the first photocatalyst particles, between the second photocatalyst particles, between the first photocatalyst particles and the second photocatalyst particles, the first photocatalyst particles and the base material. By providing the peeling prevention portion 60 between the photocatalyst particles and at least a part between the second photocatalyst particles and the base material, the peeling of the photocatalyst particles 10 and 20 can be suppressed. The peeling prevention portion 60 can be formed by using particles that function as a filler that enhances the adhesion between the photocatalyst layer 70 and the base material 90, for example.

In the present invention, the peeling prevention unit 60 contains at least one of metal hydroxides, oxides or phosphates. The peeling prevention unit 60 preferably contains a hydroxide, oxide or phosphate of one metal selected from iron, silicon, chromium, titanium, zirconium, tantalum, niobium, aluminum, magnesium, lanthanum and cerium. .. The peeling prevention unit 60 is more preferably diiron trioxide (Fe ₂ O ₃ ), silica (SiO ₂ ), zirconium oxide (ZrO ₂ ), tantalum oxide (Ta ₂ O ₅ ), cerium oxide (CeO ₂ ), or Contains titanium dioxide (TiO ₂ ). The thickness t60 of the peeling prevention portion 60 can be appropriately selected within a range that does not impair the water decomposition performance. For example, the average thickness of the peeling prevention portion is 50 nm or less. Preferably, the average thickness of the peeling prevention portion 60 is 2.5 nm or more and 20 nm or less. By setting the thickness of the peeling prevention portion 60 within such a range, the photocatalytic reaction is not hindered and the reverse reaction suppressing effect can be obtained. Here, the reverse reaction means a reaction in which hydrogen and oxygen gas generated by a water splitting reaction in water react on the surface of the conductive particles using the conductive particles as a catalyst to generate water. When the peeling prevention portion 60 is formed of colloidal particles, it is preferably a single particle film.

Further, the peeling prevention portion 60 can be formed by using, for example, glass frit or fine particles of an inorganic oxide. As the glass frit, a low melting point glass frit is preferably used. As the inorganic oxide, for example, materials such as silica, alumina, ZrO ₂ , and TiO ₂ are preferably used. The average primary particle size of the glass frit or the inorganic oxide fine particles is preferably 100 nm or less. Within this particle size range, water, hydrogen, and oxygen gas can be smoothly diffused into the photocatalyst layer without lowering the photocatalytic activity.

In the present invention, the state of the peeling prevention portion 60 may be, for example, a continuous layer or a discontinuous island-like structure. The peeling prevention unit 60 may support the colloidal particles in the third region of the conductive particles 40. Further, the peeling prevention portion 60 may be formed of, for example, a dense continuous layer. The peeling prevention unit 60 can be analyzed by observing the fracture surface of the photocatalyst material with a transmission electron microscope (TEM) at high magnification.

A specific example of the peeling prevention unit 60 will be described in more detail with reference to FIGS. 2 and 3. 2 and 3 are schematic cross-sectional views for explaining the photocatalytic material according to the present invention. As a first example, the photocatalyst material 101 is shown. As shown in FIG. 2, in the photocatalyst material 101, the photocatalyst layer 70 contains conductive particles 40. In this example, the peeling prevention unit 60 includes a plurality of colloidal particles 61. In the photocatalyst material 101, a plurality of colloidal particles 61 are arranged on the outer surfaces of the first and second photocatalyst particles 10, 20 and the conductive particles 40. Here, the "outer surface" refers to a portion (first region, second region) other than the portion (first region, second region) of the surface of the target particle that is in physical contact with the particles contained in the photocatalyst layer 70 other than the target particle. Third area).

The "outer surface of the first photocatalyst particles 10" means physical contact with particles contained in the photocatalyst layer 70, such as the conductive particles 40 and the second photocatalyst particles 20, on the surface of the first photocatalyst particles 10. It refers to the part other than the part that is being used. The surface of the first photocatalyst particle 10 has a first region, a second region, and a third region. In the first region, the first photocatalyst particles 10 come into contact with the second photocatalyst particles 20. In the second region, the first photocatalytic particles 10 come into contact with the conductive particles 40. In the first photocatalyst particle 10, the third region is a region other than the first region and the second region. The third region corresponds to the outer surface of the first photocatalyst particle 10.

The "outer surface of the second photocatalyst particles 20" means physical contact with particles contained in the photocatalyst layer 70, such as the conductive particles 40 and the first photocatalyst particles 10, on the surface of the second photocatalyst particles 20. It refers to the part other than the part that is being used. The surface of the second photocatalyst particle 20 has a first region, a second region, and a third region. In the first region, the second photocatalyst particles 20 come into contact with the first photocatalyst particles 10. In the second region, the second photocatalytic particles 20 come into contact with the conductive particles 40. In the second photocatalyst particle 20, the third region is a region other than the first region and the second region. The third region corresponds to the outer surface of the second photocatalyst particle 20.

In the photocatalyst material 101, since a plurality of colloidal particles 61 are arranged as peeling prevention portions 60 on the outer surface (third region) of the conductive particles 40, the strength of the photocatalyst layer 70 is increased and the durability is improved. To do.

As a method for forming the peeling prevention portion 60 including the plurality of colloidal particles 61, for example, after forming a layer containing the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40 on the substrate, peeling prevention is performed. A method of adsorbing the dispersion liquid containing the colloidal particles 61 to be part 60 on the surface of the layer can be used. Alternatively, a method of directly depositing colloids on the surface of the conductive particles 40 by a chemical reduction method, a photoreduction method, or the like may be used. Further, a method may be used in which a layer containing the first photocatalyst particles 10, the second photocatalyst particles 20, the conductive particles 40, and the colloidal particles 61 to be the peeling prevention portion 60 is formed on the base material 90. In this case, by reducing the compounding ratio (weight ratio) of each particle in the order of photocatalyst particles, colloidal particles, conductive particles, or in the order of photocatalyst particles, conductive particles, colloidal particles, for example, a highly efficient photocatalyst It can be a characteristic. Alternatively, the primary particle size may be reduced in the order of the photocatalyst particles, the colloidal particles, and the conductive particles, or in the order of the photocatalyst particles, the conductive particles, and the colloidal particles.

As a second example, the photocatalyst material 102 is shown. As shown in FIG. 3, in the photocatalyst material 102, the peeling prevention portion 60 is composed of a continuous coating layer 62. The coating layer 62 is arranged so as to cover the outer surfaces of the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40, respectively. In this example, the coating layer 62 has a substantially continuous layer structure, but may have a part of the discontinuous portion. In the photocatalyst material 102, the strength of the photocatalyst layer 70 is increased and the durability is also improved. The coating layer 62 may be any of an amorphous phase, a crystalline phase, and a hydroxide phase.

As a method for forming the coating layer 62, for example, a raw material containing a monomer, an oligomer or a polymer-like metal is adsorbed on the surfaces of the conductive particles 40 and / and the photocatalytic particles 10 and 20, and in some cases, by heating or a chemical reaction. A method of polymerizing the raw material on the surfaces of the conductive particles 40 and / and the photocatalytic particles 10 and 20 can be used. This makes it possible to form a coating layer. It is also possible to form a coating layer by a dry film forming method (sputtering method, thin film deposition method, CVD method, atomic layer deposition method, etc.), a chemical reduction method, a photoreduction method, or the like.
The photocatalyst material 100 may further include an intermediate layer 80 between the base material 90 and the photocatalyst layer 70. The intermediate layer 80 is arranged between the base material 90 and the photocatalyst layer 70, and is connected to each of the base material 90 and the photocatalyst layer 70. Thereby, for example, the adhesion between the base material 90 and the photocatalyst layer 70 can be improved. Examples of the material used for the intermediate layer 80 include conductive particles 40 and non-conductive particles having a small aspect ratio, which will be described later. The intermediate layer 80 formed by using the conductive particles 40 is excellent in the photodecomposition performance of water. The intermediate layer 80 formed by using non-conductive particles having a small aspect ratio functions as a binder, and the photocatalyst layer 70 can be firmly adhered to the base material 90. When the photocatalyst material 100 includes the intermediate layer 80, the thickness of the intermediate layer 80 can be evaluated by observing the fracture surface of the layer with a scanning electron microscope.

Other Particles According to a preferred embodiment of the present invention, the photocatalyst layer 70 of the photocatalyst material 100 may further contain other particles other than the photocatalyst particles 10 and 20 and the conductive particles 40.

Further, in the present invention, the other particles are preferably particles that do not cover the surfaces of the photocatalyst particles 10 and 20. As a result, it is possible to suppress a decrease in the photocatalytic activity of the photocatalytic material 100. Preferred examples of other particles include particles having a small aspect ratio. Further, as the other particles, it is preferable to use particles having a small absorption in the visible light region. As a result, it is possible to suppress the inhibition of light absorption of the photocatalytic particles 10 and 20.

Cocatalyst of photocatalyst particles In the present invention, when water is photodecomposed using the first photocatalyst particles 10 and the second photocatalyst particles 20, an cocatalyst can be supported on the surface of these photocatalyst particles. This promotes the reduction and oxidation reactions of water and improves the efficiency of hydrogen and oxygen production. The co-catalyst is provided, for example, in a third region of the first photocatalyst particles 10 and / or a part of a third region of the second photocatalyst particles 20.

The cocatalyst of the first photocatalyst particles 10 is one or more selected from the group consisting of metal particles such as platinum, ruthenium, iridium, and rhodium, or from the group consisting of oxide particles such as ruthenium oxide and nickel oxide. One or more selected ones, a mixture of these metal particles or oxide particles, or a composite hydroxide or composite oxide containing rhodium and chromium can be preferably used. More preferably, metal particles of platinum or ruthenium, or a composite hydroxide or composite oxide containing rhodium and chromium can be used. By supporting this co-catalyst on the surface of the first photocatalyst particles 10 in the form of particles, it is possible to reduce the activation energy in the reduction reaction of water, so that hydrogen can be rapidly generated.

In the present invention, it is also possible to cover at least a part of the co-catalyst surface of the first photocatalyst particles 10 other than the part in physical contact with the first photocatalyst particles 10 with another layer. is there. As a result, it is possible to suppress the formation of water molecules due to the reverse reaction of hydrogen and oxygen molecules on the surface of the co-catalyst of the first photocatalyst particles 10. This separate layer preferably comprises an amorphous oxide or hydroxide, oxide crystals, or phosphate containing at least one selected from silicon, chromium, titanium, zirconium, tantalum, niobium, aluminum, magnesium. .. The material forming another layer covering the co-catalyst is preferably amorphous. As a result, it is possible to suppress the diffusion of protons and water molecules onto the surface of the co-catalyst. In addition, hydrogen gas and oxygen gas can be suppressed from entering the co-catalyst. The thickness of the other layer is preferably 1 nm or more and 50 nm or less, more preferably 2 nm or more and 20 nm or less.

The cocatalyst of the second photocatalyst particles 20 is one or more selected from the group consisting of metals such as Mn, Fe, Co, Ir, Ru, and Ni, or a metal oxide obtained by mixing these metals. Particles made of metal hydroxide or metal phosphate can be preferably used. More preferably, metal oxide particles or metal hydroxide particles containing one or more selected from Mn, Co, and Ru can be used.

The average primary particle size of these co-catalysts is preferably less than 10 nm, more preferably 5 nm or less. By reducing the average primary particle size, it can efficiently function as an active site for hydrogen and oxygen evolution reactions, and it becomes possible to exert a sufficient function as a co-catalyst. When the average primary particle size of the co-catalyst is 10 nm or more, the number of active points per supported weight decreases as water reduction or oxidation reaction sites, so that efficient water decomposition may be suppressed.

As a method for supporting the co-catalyst, an impregnation method, an adsorption method and the like are preferably mentioned. The impregnation method or the adsorption method is a method in which the photocatalyst particles 10 and 20 are dispersed in a solution in which the photocatalyst precursors are dissolved, and the photocatalyst precursors are adsorbed on the surfaces of the photocatalyst particles 10 and 20. Examples of the co-catalyst precursor include chlorides of metals such as platinum, ruthenium, iridium, rhodium, and nickel, nitrates, ammine salts, and the like.

Further, when the co-catalyst precursor is supported on the surface of the photocatalyst particles 10, the activity is increased by making the photocatalyst precursor in a metallic state. Therefore, it is preferable that the co-catalyst precursor is reduced on the surface of the photocatalyst particles 10 and precipitated in a state containing a metal. As a method for reducing the co-catalyst precursor, a photoreduction method, a chemical reduction method, or the like is preferably used. The photoreduction method is a method of reducing the cocatalyst precursor adsorbed on the photocatalyst particles 10 by excited electrons generated in the photocatalyst particles 10 by irradiating the photocatalyst particles with ultraviolet light or visible light. The chemical reduction method is a method of reducing the co-catalyst precursor under a hydrogen gas stream of 400 ° C. or lower, preferably 300 ° C. or lower. The co-catalyst supported in this way is in the form of particles. By supporting the co-catalyst on the surface of the first photocatalyst particles 10, it is possible to reduce the activation energy in the reduction reaction of water, so that hydrogen can be rapidly generated.

The amount of the co-catalyst supported on the surface of the photocatalyst particles can be appropriately determined within a range in which the irradiation light to the photocatalyst particles is not blocked by the presence of the co-catalyst. The amount of co-catalyst is preferably small.

Method for Producing Photocatalyst Material As a method for producing photocatalyst materials 100 to 102 according to the present invention, a first photocatalyst particle 10, a second photocatalyst particle 20, a peeling prevention portion 60, and a pore 71 are formed on a base material 90. A method capable of forming the above structure by immobilizing the photocatalyst layer 70 containing the above can be used.

According to a preferred embodiment of the present invention, as a method for producing the photocatalyst materials 100 to 102 according to the present invention, a dispersion containing the first photocatalyst particles 10 and a solvent is applied to the base material 90 and dried. , A step of forming the first structural layer having pores 71, and applying a solution containing at least one selected from the group consisting of metal monomers, metal oligomers and metal polymers to the surface of the first structural layer. A method including a step of forming the peeling prevention portion 60 by drying can be used. Further, according to another preferred embodiment of the present invention, as a method for producing the photocatalyst materials 100 to 102 according to the present invention, a dispersion containing the first photocatalyst particles 10, the second photocatalyst particles 20, and a solvent is used as a base. A step of forming a first structural layer having pores 71 by applying to the material 90 and drying, and a solution containing at least one selected from the group consisting of metal monomers, metal oligomers and metal polymers. A method including a step of forming a peeling prevention portion 60 by applying it to the surface of the structural layer of 1 and drying it can be used. As the dispersion liquid, for example, a paste-like one can be used. Examples of the metal monomer include zirconium butoxide. Examples of the metal oligomer include a hydrolyzed polycondensate of zirconium butoxide. Examples of the metal polymer include a hydrolyzed polycondensate of zirconium butoxide. Examples of the drying conditions for forming the peeling prevention portion 60 include 30 minutes to 5 hours at 40 to 100 ° C.

The conductive particles 40 may be included in the dispersion liquid, or may be separately added, for example, later. Specifically, according to another preferred embodiment of the present invention, in the method for producing the photocatalytic materials 101 and 102 according to the present invention, a dispersion liquid in which the conductive particles 40 are wet-dispersed is dropped onto the first structural layer. Includes steps. At this time, with drying, for example, the conductive particles 40 move to the grain boundaries of the first and second photocatalyst particles 10 and 20. Thereby, the photocatalytic materials 101 and 102 can be obtained.

According to another preferred embodiment of the present invention, the method for producing the photocatalytic materials 101 and 102 according to the present invention previously carries the conductive particles 40 on the surface of either the first photocatalytic particles 10 or the second photocatalyst particles 20. A dispersion containing the first photocatalyst particles 10 or the second photocatalyst particles 20 carrying the conductive particles 40 and the solvent (furthermore, the other photocatalyst particles not carrying the conductive particles 40 (the first). This method includes a step of applying the first or second photocatalyst particles 10, 20)) to the base material 90 and drying the base material 90. At this time, the method of supporting the conductive particles 40 in advance on the surface of either the first photocatalyst particles 10 or the second photocatalyst particles 20 is the same as the method of supporting the cocatalyst on these photocatalyst particles (impregnation). Method, adsorption method, photoreduction method, chemical precipitation method, etc.) can be used.

In the above embodiment, glaze fine particles may be further added to the dispersion liquid. By heating the dispersion liquid to which the glaze fine particles are added to, for example, 300 ° C. or lower, each glaze fine particle adheres to the surface of the base material 90. Therefore, the adhesion of the photocatalyst layer 70 to the base material 90 can be improved. Further, since the glaze fine particles do not completely cover the surfaces of the photocatalytic particles 10 and 20, it is possible to suppress a decrease in the photocatalytic activity of the photocatalytic material.

Further, in the above embodiment, for example, an intermediate layer may be formed before applying the dispersion liquid containing the photocatalytic particles. The intermediate layer can be formed by applying, for example, a dispersion liquid containing conductive particles 40 or non-conductive particles having a small aspect ratio to the base material 90. After forming the intermediate layer, a dispersion liquid containing photocatalyst particles may be applied to form the photocatalyst layer 70. The photocatalyst layer 70 may be formed after the intermediate layer is formed and then dried. Alternatively, after forming a photocatalyst film containing the first photocatalyst particles, the second photocatalyst particles and the conductive particles on the first substrate, for example, a paste containing the conductive particles is further applied onto the photocatalyst film. It is dried and fired to further form a conductive particle film. Then, a second base material provided with an adhesive layer such as carbon tape is pressed against the conductive particle film to remove the first base material. In this way, it is possible to obtain a photocatalyst material in which a photocatalyst film is formed on the second base material via a conductive particle film (intermediate layer).

In the present invention, as a method of dispersing the particles 10, 20 and 40 in a solvent, a method of adsorbing a solvent such as water or an organic solvent or a dispersant on the surface of each particle can be preferably used. This makes it possible to realize a state in which each particle is stably mixed in a form close to that of a primary particle. That is, it is possible to suppress the aggregation of the first photocatalyst particles 10 to each other, the second photocatalyst particles 20 to each other, or the conductive particles 40 to each other. Therefore, in the photocatalyst layer 70, the first photocatalyst particles 10 and the second photocatalyst particles 20 can exist at a short distance via the conductive particles 40. Therefore, the water splitting reaction is promoted, and the hydrogen generation efficiency can be increased.

In the present invention, as the wet dispersion method, a mechanical dispersion method such as ultrasonic irradiation, a ball mill and a bead mill can be preferably used.

In the present invention, as the solvent, a solvent capable of dispersing the particles contained in the dispersion liquid can be used. According to a preferred embodiment of the present invention, as such a solvent, an organic solvent such as water or ethanol or an organic vehicle solvent such as α-terpineol can be used. Further, in order to improve the dispersibility of the particles in the solvent, a dispersant may be added to the solvent.

In the present invention, as a method for applying the dispersion liquid to the base material 90, a spin coating method, a dip coating method, a spray method, a doctor blade method, an electrophoresis method, a screen printing method and the like can be preferably used. Further, the coating method can be appropriately selected according to the shape and type of the base material 90.

In order to achieve the target layer thickness, the method for forming the photocatalyst layer 70 can be appropriately selected. For example, when the photocatalyst layer 70 having a thickness of 1 μm or less is obtained, it is preferable to use a spin coating method, a dip coating method, a spray method, or the like. Further, when the photocatalyst layer 70 having a thickness of 1 μm or more is obtained, it is preferable to use a screen printing method, a doctor blade method, an electrophoresis method or the like.

According to a preferred embodiment of the present invention, the method of dispersing the first photocatalyst particles 10 and the second photopolymer particles 20 in a liquid medium is such that the first photopolymer particles 10 and the second photopolymer particles 20 are each, for example. It comprises a step of dispersing in a solution containing polymers having different charges such as anionic polymer and cationic polymer to make the state close to monodisperse dispersed in the state of primary particles. After that, the obtained dispersion liquid is mixed, and the first photocatalyst particles 10 and the second photocatalyst particles 20 spontaneously generate each other by the Coulomb interaction between different charges of the polymers adsorbed on the surfaces of the photocatalyst particles 10 and 20, respectively. It is possible to adsorb the particles and bring them into close proximity or contact with each other. For example, the first photocatalyst particles 10 are dispersed in a solution containing an anionic polymer, and the second photocatalyst particles 20 are dispersed in a solution containing a cationic polymer. After that, by mixing these dispersions, it becomes possible to bring the primary particles into a state where they can be brought close to each other or in contact with each other at high density. After that, the primary particles are heated or fired in a state of being close to or in contact with each other at high density to remove the polymer, so that a highly active state can be realized as a photocatalyst material for visible light responsive water splitting.

In the present invention, the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40 are immobilized on the base material 90 by drying a dispersion containing them, preferably by drying and firing. To. The firing temperature is equal to or higher than the thermal decomposition temperature of the solvent, dispersant, etc., and further, the base material 90 and the first photocatalyst particles 10, the second photocatalyst particles 20 and the conductive particles 40, or the conductive particles 40 and the first It is preferable that the temperature is such that the firing of the photocatalyst particles 10 and the second photocatalyst particles 20 or the first photocatalyst particles 10, the second photocatalyst particles 20 and the conductive particles 40 can be promoted. Specifically, it is 100 ° C. or higher and 700 ° C. or lower, more preferably 200 ° C. or higher and 600 ° C. or lower, and further preferably 300 ° C. or higher and 400 ° C. or lower. By firing at a temperature in this range, it is possible to obtain a long-term stable photocatalyst material for visible light responsive water decomposition that has high adhesion to the base material 90 and adhesion between the particles 10, 20, and 40. Become. The firing atmosphere may be any of the atmosphere, nitrogen, and reducing gas (ammonia, hydrogen). An air or nitrogen atmosphere is preferred. As a result, the binder disappears efficiently during firing. Further, in firing in a nitrogen atmosphere, it is possible to suppress the oxidation of conductive particles. Therefore, it is possible to suppress a decrease in the conductivity of the conductive particles.

(Mixing ratio)
In the method for producing a photocatalyst material according to the present invention, the mixing ratio of the first photocatalyst particles and the second photocatalyst particles is a weight ratio of first photocatalyst particles: second photocatalyst particles = 10: 90 to 90:10. It is preferably, and more preferably 20:80 to 80:20. Mixing in this range makes it possible to promote the charge recombination reaction at the particle interface. As a result, it becomes possible to increase the water decomposition efficiency of the photocatalytic material.

Photocatalyst module for water decomposition The photocatalyst module for water decomposition according to the present invention includes the above-mentioned photocatalyst material. According to a preferred embodiment of the present invention, the photocatalyst module for water splitting according to the present invention has a substantially transparent photocatalytic surface and has a structure in which light is incident on a photocatalyst material installed inside the module. In addition, it has a closed panel shape that can be filled with water so that the photocatalyst material can always come into contact with water. Further, according to a more preferable aspect of the present invention, the photocatalyst module for water splitting according to the present invention further has a mechanism such as a water passage hole capable of sequentially additionally supplying water which is reduced due to the progress of the water splitting reaction. Is preferable. By using a water splitting photocatalyst module having such a configuration, it becomes possible to produce hydrogen that can be practically used.

Hydrogen production system The hydrogen production system according to the present invention includes the photocatalyst module for water splitting. According to a preferred embodiment of the present invention, the hydrogen production system according to the present invention comprises a water supply device, a filtration device for removing impurities in water to some extent, a water splitting photocatalyst module, a hydrogen separation device, and a hydrogen storage device. Is. By adopting a hydrogen production system having such a configuration, it is possible to realize a system capable of practically producing hydrogen from renewable energies such as sunlight and water.

The present invention will be described in more detail with reference to the following examples. The present invention is not limited to these examples.

Raw Material The first photocatalyst particles, the second photocatalyst particles, and the conductive particles used as raw materials will be described.

Preparation of First Photocatalytic Particles (3% Rh Doped SrTIO ₃ Particles) 3% Rh Doped _{SrTIO 3} (SrTi _0.97 Rh _0.03 O ₃ ) particles were prepared by the solid phase method. Specifically, SrCO ₃ (manufactured by Wako Pure Chemical Industries, Ltd., 99.9%), TiO ₂ (manufactured by High Purity Chemical Laboratory, 99.99%), and Rh ₂ O ₃ (manufactured by Wako Pure Chemical Industries, Ltd.) are 1.05. The mixture was placed in an alumina mortar at a molar ratio of: 0.97: 0.03, methanol was added, and the mixture was mixed for 2 hours. Next, the obtained mixture was placed in an alumina crucible and calcined at 900 ° C. for 1 hour, and then fired at 1050 ° C. for 10 hours. After firing, the fired body was allowed to cool to room temperature and then crushed to prepare a powder composed of _{3% Rh-doped SrTIO 3} (SrTi _0.97 Rh _0.03 O _{3) particles.}

(Average primary particle size)
The average primary particle size of the 3% Rh-doped SrTiO ₃ particles (first photocatalytic particles) was calculated by SEM observation. Specifically, the average value obtained by circular approximation of 50 crystal particles when observed at a magnification of 40,000 times by SEM (manufactured by Hitachi, Ltd., "S-4100") was taken as the primary particle diameter. As a result, the average primary particle size of the 3% Rh-doped SrTiO _{3 particles was about 500 nm.}

(Band structure)
The band positions of the 3% Rh-doped SrTIO ₃ particles were considered as follows with reference to Wang et al., J. Catal. 305-315, 328 (2015).
Upper end of valence band: -6.6 eV (vs. vacuum level)
Lower end of conduction band: -4.1 eV (vs. vacuum level)
The upper end of the valence band in the 3% Rh-doped SrTiO ₃ particles is considered to be derived from the upper end of the donor orbit derived from the ^{doped Rh 3+} generated in the band gap of _{SrTiO 3.}

Preparation of Second Photocatalytic Particles (0.05% Mo-doped BiVO ₄ Particles) The 0.05% Mo-doped BiVO ₄ particles were prepared by the liquid solid phase method. Specifically, first, K ₂ CO ₃ (manufactured by Kanto Chemical Co., Ltd., 99.5%), V ₂ O ₅ (manufactured by Wako Pure Chemical Industries, Ltd., 99.0%) and MoO ₃ (manufactured by Kanto Chemical Co., Ltd., 99.5%). Was placed in a menor mortar so that K: V: Mo = 3.03: 4.9975: 0.0025 (mol ratio), ethanol (10 mL) was added, and the mixture was mixed for 30 minutes. The resulting mixture was then placed in a magnetic crucible and fired in an electric furnace at 450 ° C. for 5 hours. After firing, the fired body was allowed to cool to room temperature and then crushed.

The resulting powder, 100 ml of water and _{Bi (NO 3) 3 · 5H} 2 O ( Wako, 99.9%) was placed in the entered was 300mL Erlenmeyer flasks (Bi: (V + Mo) = 1: 1), 70 The mixture was stirred at 1500 rpm using a stirrer at ° C. for 10 hours. The obtained precipitate was collected by suction filtration, washed with water, and dried in a dryer at 60 ° C. for 12 hours to obtain a 0.05% Mo-doped BiVO ₄ powder.

(Average primary particle size)
The average primary particle size of 0.05% Mo-doped BiVO ₄ particles (second photocatalytic particles) was calculated by SEM observation. As a result, the average primary particle size was about 800 nm.

(Band structure)
The band positions of BiVO ₄ were considered as follows with reference to Wang et al., J. Catal. 305-315, 328 (2015).
Upper end of valence band: -6.8 eV (vs. vacuum level)
Lower end of conduction band: -4.6 eV (vs. vacuum level)

Preparation of Conductive Particles A 10 wt% ethanol dispersion of colloidal gold (manufactured by Shinko Kagaku Kogyo Co., Ltd.) was used. The average primary particle size of the gold colloidal particles was 20 nm. The average primary particle size is a value listed in the catalog as a value calculated by TEM observation. The electronic properties of the colloidal gold particles were work function: 5.1 eV, Fermi level: -5.1 eV (vs. vacuum level) (A. Sharma et al., Applied Physics letters, 93, 163308). (2008)).

Preparation of photocatalyst materials 1 to 10 (preparation of coating paste)
The first photocatalyst particles and the second photocatalyst particles were weighed by 0.125 g each. This was mixed with 0.75 g of an organic dispersion medium to disperse the photocatalytic particles. As the organic dispersion medium, α-terpineol (manufactured by Kanto Chemical Co., Ltd.), 2- (2-butoxyethoxy) ethanol (manufactured by Wako Pure Chemical Industries, Ltd.), and polyacrylic resin (SPB-TE1, manufactured by Soken Kagaku) are in this order. The mixture was used in a weight ratio of 62.5: 12.5: 25.0. Next, gold colloid (average particle size: 20 nm) was added to prepare a coating paste having a total solid content concentration of 25 wt% of the first photocatalyst particles, the second photocatalyst particles, and the conductive particles. ..

(Preparation of photocatalytic materials 1 to 10)
This coating paste is applied to a base material (synthetic quartz glass, size: 5 cm x 5 cm x thickness 1 mm) by a ^{screen printing method so that the coating thickness is 60 μm and the coating area is 6.25 cm 2} (2.5 cm square). It was applied. Then, after drying at 80 degreeC for 30 minutes, it was calcined at 300 degreeC for 30 minutes to prepare photocatalyst materials 1-10. The thickness of the photocatalyst layer after firing was 10 μm in each case.

(Preparation of photocatalytic materials 1 to 8 and 10 having a peeling prevention portion)
Peeling prevention portions were formed on the photocatalytic materials 1 to 8 and 10 using the materials shown in Table 1. The peeling prevention portion was arranged on the photocatalyst material according to the following procedure. First, in the photocatalyst materials 1 to 4, 7 and 8, 50 to 200 μL of the alcohol solution of the 20 mM metal monomer shown in Table 1 was evenly added dropwise to the surface of the photocatalyst layer. In the photocatalyst materials 5, 6 and 10, 50 to 200 μL of an alcohol dispersion of 0.4 wt% metal oxide colloid was evenly added dropwise. In the photocatalyst materials 1 to 4, a butanol solution of zirconium butoxide was used as the alcohol solution of the metal monomer. In the photocatalyst material 7, an ethanol solution of tetraethoxysilane was used as the alcohol solution of the metal monomer. In the photocatalyst material 8, a methanol solution of tantalum ethoxydo was used as the alcohol solution of the metal monomer. Then, it was dried at 100 ° C. for 30 minutes to form a peeling prevention portion on the surface of the photocatalyst layer. The photocatalyst material 9 did not form a peeling prevention portion.

In the photocatalyst material 5, _{as a diiron trioxide (Fe 2} O _{3 ) colloid sol, a mixed solution of α-Fe 2} O ₃ colloid having an average primary particle diameter of about 10 nm and ethanol (water: ethanol = 0.1: 99.9). Degree, solid content 0.4 wt%) was used.
In the photocatalyst material 6, as a cerium oxide (CeO _{2 ) sol, a mixed solution of water and ethanol of CeO 2} colloid having an average primary particle size of about 8 nm (water: ethanol = about 0.1: 99.9, solid content 0.4 wt%). ) Was used.
In the photocatalyst material 10, as a titanium oxide (TiO _{2 ) sol, a mixed solution of water and ethanol of TiO 2} colloid having an average primary particle diameter of about 10 nm (water: ethanol = about 0.1: 99.9, solid content 0.4 wt%). ) Was used.

Evaluation Structure of photocatalyst layer The structure of the photocatalyst layer was observed by SEM for the produced photocatalyst material. Representative results are shown in FIG. This surface observation image is an image obtained by observing a plane perpendicular to the stacking direction (Z-axis direction) from the base material to the photocatalyst layer.

As shown in FIG. 4, it was confirmed that the photocatalyst layer had pores 71. Further, in the photocatalyst layer, it was confirmed that the first photocatalyst particles and the second photocatalyst particles were in physical contact with the conductive particles.
In addition, the structure of the photocatalyst layer was TEM-observed with respect to the produced photocatalyst material. The result of the photocatalyst material 3 is shown in FIG. As shown in FIG. 5, it was confirmed that the peeling prevention portion 60 covered the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40. The thickness of the prepared peeling prevention portion was as shown in Table 1.
In addition, XPS measurement was performed on the produced photocatalyst material. The results of the photocatalytic material that does not form the separation preventing sections photocatalytic material having (photocatalytic material 9), and separation preventing sections (ZrO _X) (photocatalytic material 3) shown in FIG. As shown in FIG. 6, in the photocatalyst material having the peeling prevention portion as compared with the photocatalyst material not forming the peeling prevention portion, the first photocatalyst particles 10, the second photocatalyst particles 20, and the conductive particles 40 It was confirmed that the peak intensity derived from the peak decreased and the peak derived from Zr contained in the peeling prevention portion 60 was observed.

Peeling test A peeling test was conducted on the produced photocatalyst material. The peeling test was carried out according to the following procedure. 100 mL of pure water was placed in a glass cell manufactured by Pyrex (registered trademark). A photocatalyst material fixed with a glass jig was placed in this cell. Pure water was heated to 40 degrees using a hot stirrer and stirred at 1000 rpm for 3 hours. After stirring, the photocatalyst material was taken out of the cell and the water was dried at room temperature. After drying, the surface of the film was observed with a microscope to check the number of exposed points on the substrate. The results are shown in Table 1. As shown in Table 1, it was confirmed that the peeling was prevented by having the peeling prevention portion as compared with the photocatalyst material 9 having no peeling prevention portion.

Photocatalytic activity of photocatalytic material (water decomposition activity)
Relationship between the material of the peeling prevention part and the hydrogen production activity (reverse reaction prevention rate based on the hydrogen production rate) A test was conducted to confirm the reverse reaction prevention effect as follows. First, the production rates of hydrogen and oxygen were measured under reduced pressure so that the reverse reaction would not easily occur. Then, the atmospheric pressure was raised to semi-normal pressure, and the hydrogen and oxygen production rates were measured in an environment where a reverse reaction could occur. The production rates of hydrogen and oxygen were evaluated by the following methods. A photocatalytic material and 100 ml of ultrapure water were placed in a glass flask manufactured by Pyrex (registered trademark) with a window for upward irradiation to prepare a reaction solution. A glass flask containing this reaction solution was attached to a closed circulation device (manufactured by Makuhari Rikagaku), and the atmosphere in the reaction system was replaced with argon. Visible light was irradiated from the Pyrex (registered trademark) window side by a 300 W xenon lamp (Cermax, PE-300BF) equipped with a UV cut filter (L-42, manufactured by HOYA). Gas chromatograph (manufactured by Shimadzu Corporation, GC-8A, TCD detector, MS-) shows the amount of hydrogen produced by reducing water and the amount of oxygen produced by oxidizing water for 3 hours after light irradiation. 5A column) was examined over time, and the production rate was calculated. Here, the decompression environment was set to 80 torr, and the semi-atmospheric pressure environment was set to 380 torr. Then, as shown in the following formula, the percentage of the production rate under semi-normal pressure (380 torr) with respect to the production rate under reduced pressure (80 torr) was calculated as the reverse reaction prevention rate (%). That is, when the reverse reaction is completely prevented by the formation of the peeling prevention portion, the hydrogen and oxygen generation rates under reduced pressure and semi-normal pressure are the same values, and the reverse reaction prevention rate is 100%.
Reverse reaction prevention rate (%) = formation rate under semi-normal pressure (380 torr) / formation rate under reduced pressure (80 torr) x 100

Hydrogen production rate (μmol / hr) under reduced pressure (80 torr) and hydrogen under semi-normal pressure (380 torr) of multiple photocatalytic materials that commonly contain Au colloidal particles as conductive particles and have different materials for the peeling prevention part. The production rate (μmol / hr) and the reverse reaction prevention rate (%) are shown in Table 1. All of the photocatalyst materials 1 to 8 show a higher reverse reaction prevention rate than the photocatalyst material 9 having no peeling prevention portion, and are ferric trioxide (Fe ₂ O ₃ ), silica (SiO _X ), and zirconium oxide. It was confirmed that when (ZrO ₂ ), tantalum oxide (Ta ₂ O ₅ ), and cerium oxide (CeO ₂ ) were used as the peeling prevention part, the reverse reaction prevention effect on the Au particle surface was obtained. The reverse reaction prevention rate of the photocatalyst materials 1 to 8 was as high as 65% or more, and the reverse reaction prevention rate of the photocatalyst material 3 was higher than 80%. From this, it was confirmed that when zirconium oxide (ZrO ₂ ) was used as the material of the peeling prevention portion, a high reverse reaction prevention effect could be obtained. Further, it was confirmed that the photocatalyst materials 5, 1 and 2 had a higher hydrogen generation rate under reduced pressure than the photocatalyst material 9, and that these photocatalyst materials originally had excellent hydrogen production ability. Since the reverse reaction is unlikely to occur under reduced pressure, it is considered that the photocatalytic material originally has excellent hydrogen producing ability because the hydrogen production rate under reduced pressure is high. From the above, when diiron trioxide (Fe ₂ O ₃ ) and zirconium oxide (ZrO ₂ ) are used as the material of the peeling prevention part, a high reverse reaction prevention effect can be obtained and a high hydrogen growth ability can be obtained. It was confirmed that.

Relationship between the material of the peeling prevention part and the oxygen generation activity (reverse reaction prevention rate based on the oxygen generation rate) Au colloidal particles are commonly contained as conductive particles by the same method as the above-mentioned method for evaluating hydrogen production activity. Oxygen growth rate (μmol / hr) under reduced pressure (80torr), oxygen growth rate (μmol / hr) under semi-normal pressure (380torr), and vice versa of multiple photocatalyst materials with different materials for the peel prevention part. The reaction prevention rate (%) was determined. The results are shown in Table 1. All of the photocatalyst materials 1 to 8 show a higher reverse reaction prevention rate than the photocatalyst material 9 having no peeling prevention portion, and are ferric trioxide (Fe ₂ O ₃ ), silica (SiO ₂ ), and zirconium oxide. It was confirmed that when (ZrO ₂ ), tantalum oxide (Ta ₂ O ₅ ), and cerium oxide (CeO ₂ ) were used as the material of the peeling prevention part, the reverse reaction prevention effect on the Au particle surface was obtained. .. It was confirmed that the reverse reaction prevention rates of the photocatalyst materials 1 and 3 were particularly high, _{and that a high reverse reaction prevention effect was obtained when zirconium oxide (ZrO 2} ) was used as the material of the peeling prevention portion. Further, it was confirmed that the photocatalyst materials 5 and 2 had a higher oxygen generation rate under reduced pressure than the photocatalyst material 9, and that these photocatalyst materials originally had excellent oxygen generation ability. Since the reverse reaction is unlikely to occur under reduced pressure, it is considered that the photocatalytic material originally has excellent oxygen producing ability because the oxygen generation rate under reduced pressure is high. From the above, when diiron trioxide (Fe ₂ O ₃ ) and zirconium oxide (ZrO ₂ ) are used as the material of the peeling prevention part, a high reverse reaction prevention effect can be obtained and a high oxygen generation ability can be obtained. Was confirmed.

In the photocatalyst material 9 not including the peeling prevention portion, as shown in Table 1, the amount of hydrogen produced under reduced pressure was 2.88 μmol / hr, whereas the reverse reaction prevention rate was 54%. It was low.

On the other hand, in the case of photocatalyst materials 1 to 4 containing Au colloidal particles as conductive particles and having different thicknesses of the zirconium oxide peeling prevention portion, when the thickness of the peeling prevention portion is 10 nm or less, the pressure is reduced. The hydrogen generation rate did not decrease so much, but when the thickness was increased to 20 nm, the hydrogen generation rate decreased significantly. Further, when the thickness of the peeling prevention portion was up to 10 nm, the reverse reaction prevention rate increased according to the thickness. On the other hand, when the thickness of the peeling prevention portion was as thick as 20 nm, the reverse reaction prevention rate decreased. From the above, it was confirmed that when the peeling prevention portion is formed of a metal monomer, the thickness thereof is preferably 50 nm or less.

In the photocatalyst material 9 not including the peeling prevention portion, as shown in Table 1, the amount of oxygen produced under reduced pressure was 1.26 μmol / hr, whereas the reverse reaction prevention rate was 56%. It was low.

On the other hand, in the case of photocatalyst materials 1 to 4 containing Au colloidal particles as conductive particles and having different thicknesses of the zirconium oxide peeling prevention portion, when the thickness of the peeling prevention portion is 10 nm or less, the pressure is reduced. The oxygen production rate did not decrease so much, but when the thickness was increased to 20 nm, the oxygen production rate decreased significantly. Further, when the thickness of the peeling prevention portion was up to 10 nm, the reverse reaction prevention rate was generally increased according to the thickness. On the other hand, when the thickness of the peeling prevention portion was as thick as 20 nm, the reverse reaction prevention rate decreased. From the above, it was confirmed that when the peeling prevention portion is formed of a metal monomer, the thickness thereof is preferably 50 nm or less.

Claims (6)

With the base material
The photocatalyst layer provided on the base material and
It is a photocatalytic material containing
The photocatalyst layer is
A plurality of first photocatalytic particles of the visible light responsive type for hydrogen generation,
A plurality of visible light responsive second photocatalytic particles for oxygen evolution,
Between the plurality of first photocatalyst particles, between the plurality of second photocatalyst particles, between the plurality of first photocatalyst particles and the plurality of second photocatalyst particles, the plurality of first photocatalyst particles. A peeling prevention portion provided at least in a part between the photocatalyst particles of the above and the base material, and between the plurality of second photocatalyst particles and the base material.
The pores provided between the plurality of first photocatalyst particles, the plurality of second photocatalyst particles, and the peeling prevention portion, and the like.
Including
The average primary particle diameter of the first photocatalyst particles and the second photocatalyst particles is 100 nm or more and 5000 nm or less.
The pore diameter is 20 nm or more and 500 nm or less.
The peeling prevention portion contains at least one selected from the group consisting of metal hydroxides, oxides and phosphates.
The average thickness of the peeling prevention portion is 50 nm or less.
The photocatalyst layer further contains a plurality of conductive particles that electrically connect the first photocatalyst particles and the second photocatalyst particles.
The surface of the conductive particles is
A first region that is in physical contact with the first photocatalytic particles,
A second region that is in physical contact with the second photocatalytic particle,
A third region that does not come into contact with any of the first and second photocatalytic particles,
Have at least
The peeling prevention portion is a coating layer provided on at least a part of the third region.
Photocatalytic material. The photocatalytic material according to claim 1, wherein the peeling prevention portion contains at least one selected from the group consisting of _{Fe 2} O ₃ , CeO ₂ , ZrO ₂ , SiO ₂ , Ta ₂ O ₅ and TiO _2. The photocatalytic material according to claim 1 or 2, wherein the average thickness of the peeling prevention portion is 2.5 nm or more and 20 nm or less. The peeling prevention portion according to any one of claims 1 to 3 , wherein the peeling prevention portion is arranged so as to cover the outer surfaces of the first photocatalyst particles, the second photocatalyst particles, and the conductive particles. Photocatalytic material. The method for producing a photocatalytic material according to any one of claims 1 to 4.
A step of applying the dispersion liquid containing the first photocatalytic particles and the solvent to the base material and then drying the dispersion to form the first structural layer having the pores.
A step of applying a solution containing at least one selected from the group consisting of a metal monomer, a metal oligomer, and a metal polymer to the surface of the first structural layer and then drying the solution to form the peeling prevention portion.
A method for producing a photocatalytic material, including. The production method according to claim 5, wherein the dispersion liquid further contains conductive particles.

Images