JP6170352B2 - Method for producing photocatalyst material - Google Patents

Description

  The present invention relates to a method for producing a photocatalyst material in which a photocatalyst capable of water photolysis by visible light is fixed on a conductive substrate.

  A visible light responsive photocatalyst is a photocatalyst that can use visible light contained in a large amount of sunlight. This visible light responsive photocatalyst is expected to be applied to hydrogen production by photolysis of organic substances and water. Among these, a photocatalyst for water splitting for the purpose of producing hydrogen has attracted attention as a photocatalyst used in a method for producing hydrogen using renewable energy. As a result, the demand for a photocatalyst for water splitting that provides high activity is increasing year by year.

Rhodium-doped strontium titanate (Rh—SrTiO ₃ ) is known to have a very high ability to generate hydrogen by photolysis of water as a photocatalyst for water splitting having visible light response. Moreover, the Z scheme type system combining the photocatalyst particles for oxygen generation and the Rh-SrTiO ₃ particles irradiates the aqueous suspension in which these two particles are aggregated with each other by pH control, It is known to generate hydrogen and oxygen in a complete water splitting reaction with a high energy conversion efficiency of 0.1% or more (Sasaki et al., J. Phys. Chem. C 17536-17542, 2009 (non- Patent Document 1)).

Conventionally, the Rh—SrTiO ₃ is produced by a solid-phase reaction method or a hydrothermal synthesis method, and in these methods, it is known to perform a high crystallization treatment by baking at about 1000 ° C. The Rh—SrTiO ₃ particles thus obtained have a primary particle size of about several hundred nm to several μm, and are known to exhibit high hydrogen generation ability under visible light irradiation. Meanwhile, in order to further highly activate Rh-SrTiO ₃ particles, increasing the specific surface area of the Rh-SrTiO ₃ particles, that is, Rh-SrTiO ₃ particles of fine crystal has been demanded.

  Japanese Patent Application Laid-Open No. 2012-187520 (Patent Document 2) discloses a water splitting photocatalyst immobilization product having a photocatalyst layer on a substrate, wherein the photocatalyst layer includes Ga, Zn, Ti, La, Ta, and Visible light responsive optical semiconductor that is a nitride or oxynitride containing Ba atom, at least one hydrophilicity selected from the group consisting of a cocatalyst supported on the optical semiconductor, silica, alumina, and titanium oxide A photocatalyst immobilized product for water splitting containing an inorganic material is described. According to this document, the coexistence of the visible light responsive photocatalyst and the hydrophilic inorganic material in the photocatalyst layer allows water to penetrate not only near the surface of the photocatalyst layer but also into the interior during the water splitting reaction. As a result of the product surface becoming difficult to adhere to the photocatalyst layer due to the hydrophilic surface, diffusion of the product gas into the gas phase is promoted.

  On the other hand, as a technique for immobilizing photocatalyst particles on a substrate, a technique is known in which photocatalyst particles are adhered to a substrate by electrophoresis and immobilized (Japanese Patent Application Laid-Open No. 2012-050913 (patent). Document 3)), Japanese Patent Application Laid-Open No. 2011-131170 (Patent Document 4)).

JP 2012-056947 A JP 2012-187520 A JP2012-050913A JP 2011-131170 A

Sasaki et al. Phys. Chem. C 17536-17542, 2009

  The present inventors have recently established a method for producing visible light responsive photocatalyst particles that achieve both high crystallinity and finer primary particles, and further, on an electroconductive substrate by an immobilization method based on electrophoresis. As a result of fixing the fine photocatalyst particles, the inventors have obtained knowledge that an excellent photocatalyst material can be obtained. The present invention is based on such knowledge.

  Accordingly, the object of the present invention is to provide a method for producing a photocatalyst material having a high hydrogen generating ability, in which visible light responsive photocatalyst particles having both high crystallinity and primary particle miniaturization are immobilized on a substrate. It is said.

  And the manufacturing method of the photocatalyst material by this invention is a manufacturing method of the photocatalyst material by which rhodium dope strontium titanate particle is fix | immobilized on the electroconductive base material, Comprising: The rhodium dope titanium whose primary particle diameter is 100 nm or less Preparing strontium acid particles, attaching the rhodium-doped strontium titanate particles onto the conductive substrate by electrophoresis, and rhodium-doped strontium titanate particles deposited on the conductive substrate And a step of immobilizing the particles on the base material.

  According to the method for producing a photocatalyst material of the present invention, a photocatalyst material capable of water splitting that exhibits high hydrogen generation activity under irradiation with visible light can be obtained.

It is a schematic diagram of the photocatalyst material cross section obtained by the manufacturing method by this invention. It is the photograph by the scanning electron microscope observation of the photocatalyst material surface obtained by the manufacturing method by this invention. It is the photograph by the scanning electron microscope observation of the photocatalyst material cross section obtained by the manufacturing method by this invention.

Definitions In this specification, “visible light” means electromagnetic waves (light) having a wavelength that can be visually recognized by human eyes. Preferably, it means light containing visible light having a wavelength of 380 nm or longer, more preferably light containing visible light having a wavelength of 420 nm or longer. In addition, as light including visible light, sunlight, condensed sunlight with increased energy density by condensing, 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, it is possible to use sunlight that has been poured infinitely on the earth as a light source. Thereby, visible light occupying 60% or more of the sunlight can be used, so that it is possible to increase the energy conversion efficiency as an index for extracting hydrogen and oxygen from water.

Preparation of rhodium-doped strontium titanate particles In the method for producing a photocatalyst material according to the present invention, rhodium-doped strontium titanate particles having a primary particle diameter of 100 nm or less are first prepared.

  The rhodium-doped strontium titanate particles used in the production method according to the present invention have high crystallinity and a fine primary particle diameter.

Crystallinity of rhodium-doped strontium titanate particles The inventors of the present invention have a higher light absorption rate derived from Rh ⁴⁺ in the crystal and oxygen defects present in the crystal than conventional rhodium-doped strontium titanate particles. It has been found that particles having a low light absorptance derived from the above have high crystallinity and high photocatalytic activity. In Rh—SrTiO ₃ , it is difficult to achieve both high crystallinity and a large specific surface area, that is, a fine crystal. That is, Rh—SrTiO ₃ is a substance that is difficult to grow to be a crystal having high crystallinity while remaining as a fine crystal during crystal growth. In such Rh—SrTiO ₃ particles, by using the light absorptance derived from Rh ⁴⁺ in the crystal and the light absorptance derived from oxygen defects present in the crystal as an index, a fine crystal and a high crystal It became possible to obtain a crystal having the property.

  Usually, the generation of oxygen defects can be considered as one of the factors that lower the crystallinity of the metal oxide. That is, as the number of oxygen site defects in the metal oxide increases, that is, the number of oxygen defects increases, the periodicity of the crystal is disturbed, so that the crystallinity of the metal oxide decreases, that is, the crystallinity decreases.

The amount of oxygen defects in the rhodium-doped strontium titanate particles used in the present invention can be quantitatively evaluated by measuring diffuse reflection spectra in the ultraviolet, visible, and near-infrared light regions of the powder composed of rhodium-doped strontium titanate particles. It is possible to evaluate using A (= 1-spectral reflectance R) as an index. Oxygen defects present in a metal oxide, for example, titanium oxide, in the band structure of titanium oxide, in a region of electron energy lower by about 0.75 to 1.18 eV from the lower end of the conduction band composed of Ti-3d orbitals, The donor level which consists of Ti3 ⁺ produced ^| generated by an oxygen defect is produced. Further, it is known that the absorption spectrum of titanium oxide having oxygen defects has a broad light absorption band in a wide range from the visible light region to the near infrared region (Cronemeyer et al., Phys. Rev. 113, 1222). ~ 1225 pages, 1959). Now, by measuring the diffuse reflection spectrum of rhodium-doped strontium titanate particles, the present inventors have produced a broad light absorption band from visible light to near-infrared light region, similar to titanium oxide. It was confirmed. Furthermore, it was confirmed that the light absorptance decreased in this near-infrared light region by increasing the firing temperature. From these facts, it was found that the improvement in crystallinity accompanying the increase in the firing temperature can be quantified by measuring the light absorption in the near infrared region from the visible light.

In addition, in the rhodium-doped strontium titanate particles having high photocatalytic activity, the present inventors also consider the rhodium state, and light absorption derived from tetravalent rhodium (Rh ⁴⁺ ) in the strontium titanate crystal. It was found that the larger the value, the higher the crystallinity. Regarding the influence of the valence of rhodium on the crystallinity, the following mechanism is expected, but the present invention is not limited to this mechanism.

Usually, the valence of rhodium is known as bivalent, trivalent, tetravalent and pentavalent. Among rhodiums having these valences, trivalent rhodium (Rh ³⁺ ) is most stable at room temperature and in the atmosphere. When starting materials containing trivalent rhodium are used, when strontium titanate (SrTiO ₃ ) is fired at high temperature and crystallized, the site of tetravalent titanium (Ti ⁴⁺ ) is known to be doped with rhodium. ing. At this time, when Rh ³⁺ is substituted and dissolved in a crystal site of Ti ⁴⁺ , oxygen defects are generated in order to maintain electrical neutrality. Therefore, in order to reduce the oxygen vacancies, the present inventors need to substitute Rh ⁴⁺ capable of maintaining the electrical neutrality of the crystal into a solid solution of Ti ⁴⁺ , thereby forming particles. It has been found that the crystallinity of is improved.

  Therefore, the present inventors have found that the optical property parameters of the rhodium-doped strontium titanate particles having high photocatalytic activity of the present invention can be clarified by measuring the particles by the following method.

As a method for measuring the optical properties of the rhodium-doped strontium titanate particles used in the present invention, for example, an ultraviolet-visible near-infrared spectrophotometer (“V-670” manufactured by JASCO Corporation) equipped with an integrating sphere unit is used. It is possible to use. Specifically, an integrating sphere unit (manufactured by JASCO Corporation, “ISV-722”) is attached to the ultraviolet visible near infrared spectrophotometer. Here, alumina sintered pellets are used for the baseline measurement. In addition, the diffuse reflectance spectrum when 30 mg of the particle powder was packed in the window (φ5 mm) of the micro-powder cell (manufactured by JASCO Corporation, “PSH-003”) so that the filling rate was 50% or more. By measuring, the spectral reflectance R can be measured. The optical properties of the rhodium-doped strontium titanate particles are shown by measuring a diffuse reflection spectrum in the wavelength range of 200 to 2500 nm using this apparatus. The rhodium-doped strontium titanate particles used in the present invention have an optical absorptance A ₃₁₅ (= 1-R ₃₁₅ [spectral reflectance at a wavelength of 315 nm]) at a wavelength of 315 nm in the range of 0.86 to 0.87. Under such conditions, the light absorption A ₅₇₀ (= 1-R ₅₇₀ [spectral reflectance at a wavelength of 570 nm]) at a wavelength of 570 nm, which is attributed to the light absorption derived from Rh ⁴⁺ in the strontium titanate crystal, The optical absorptance A _{1800 at a} wavelength of ₁₈₀₀ nm (= 1−R ₁₈₀₀ [spectral reflectance at a wavelength of ₁₈₀₀ nm]), which is 0.6 or more and is attributed to light absorption derived from oxygen defects in the crystal, is 0. .7 or less. According to a preferred embodiment, the light absorption rate A _{570 at} a wavelength of 570 nm is 0.6 or more and less than 0.8. According to another preferred embodiment, the light absorption ratio _{A 1800} at a wavelength of 1800nm is 0.3 to 0.7.

The primary particle diameter present invention by the manufacturing method rhodium doped strontium titanate particles used in rhodium-doped strontium titanate particles have a fine primary particle size. The primary particle diameter is preferably 70 nm or less. Thereby, the rhodium-doped strontium titanate particles can have a high specific surface area. Moreover, the surface area which can contact with water per unit weight becomes large. Thereby, the reduction reaction site of water increases, and as a result, highly efficient hydrogen generation becomes possible. A preferable primary particle diameter is 50 nm or less. A more preferable primary particle diameter is 30 nm or more and 70 nm or less. An even more preferable primary particle size is 30 nm or more and 50 nm or less.

  Further, the advantage of the rhodium-doped strontium titanate particles having a fine particle size is that the distance that the excited electrons and excited holes generated in the particles diffuse to the particle surface by irradiation with visible light is short. As a result, a hydrogen generation reaction by reduction of water on the particle surface where the excited electrons are diffused can occur with high efficiency.

  As an evaluation method of the primary particle diameter of rhodium-doped strontium titanate particles, for example, observation with a scanning electron microscope (manufactured by Hitachi, Ltd., “S-4100”, hereinafter also referred to as “SEM”) at a magnification of 40000 times. It is possible to define the average value by circular approximation of 50 crystal grains.

Structure of rhodium-doped strontium titanate particles The rhodium-doped strontium titanate particles used in the production method according to the present invention have a large specific surface area. In the present invention, by using the R _SP value of rhodium-doped strontium titanate particles as an index, rhodium-doped strontium titanate particles having a large surface area or a highly porous powder (secondary particles) in which they are aggregated are used. It became possible to show.

The R _SP value is an index that correlates with the amount of water molecules adsorbed on the particle surface, and is an index that depends on the surface area of particles dispersed in water that are in contact with water. Since the rhodium-doped strontium titanate particles used in the present invention are used as a photocatalyst for water splitting, the particles are used in contact with water. In this case, water diffuses into the gaps between the primary particles or the pores in the secondary particles, and the water comes into contact with the surface of the particles. Therefore, in the rhodium-doped strontium titanate particles used in the present invention, it is possible to accurately measure the surface area of the particles adsorbed with water using the R _SP value as an index, thereby obtaining particles having a large specific surface area. Effective above. As a method for measuring the specific surface area of particles, BET analysis based on nitrogen adsorption / desorption measurement, which is the mainstream in the past, can be mentioned. However, in this BET analysis, nitrogen is used as a probe, and the molecular diameter of nitrogen is small. Nitrogen is adsorbed on the pore surfaces where water cannot diffuse. Therefore, the specific surface area measurement method based on BET analysis lacks effectiveness when it is intended for particles on which water is adsorbed.

The R _SP value is represented by the following formula. The R _SP value can be measured by a pulse NMR particle interface evaluation apparatus (for example, “Acorn area”, manufactured by Nippon Luft).
R _SP = (R _b −R _av ) / R _b (1)
Here, R _av is an average relaxation time constant. The relaxation time constant is the reciprocal of the relaxation time of water that is in contact with or adsorbing to the surface when the particles are dispersed in water. The average relaxation time constant is a value obtained by averaging the obtained relaxation time constants.
R _b is the relaxation time constant of blank water containing no particles.

The larger the _Rsp value, the greater the interaction between the particle surface and water. That is, the area where the particles and water are in contact is large, and the specific surface area of the particles is large.

The R _SP value of the rhodium-doped strontium titanate particles used in the present invention is preferably 0.86 or more. More preferably, it is 0.88 or more. The R _SP value is preferably 10 or less.

Composition of rhodium-doped strontium titanate The composition of rhodium-doped strontium titanate used in the production method according to the present invention can be represented by SrTi _1-x Rh _x O ₃ . The molar ratio of rhodium-doped strontium titanate particles represented by M (rhodium) / M (titanium + rhodium) is preferably 0.001 to 0.03, and more preferably 0.01 to 0.03. It is. By setting the molar ratio within this range, an increase in the amount of oxygen defects in the crystal can be suppressed and high photocatalytic activity can be realized.

  As described above, the rhodium-doped strontium titanate particles used in the present invention can exhibit high photocatalytic activity by achieving both the above-described light absorption rate and the fine primary particle shape measured by SEM. Become.

As a method for producing rhodium-doped strontium titanate particles used in the process according to the production method the present invention of a rhodium-doped strontium titanate particles, strontium ions, titanium ions, pyrolysis method using an aqueous solution containing rhodium ions (aqueous pyrolysis ) Can be preferably used. "Aqueous solution pyrolysis method" uses a metal-containing precursor as a raw material, and heats an aqueous solution containing this metal-containing precursor, thereby dehydrating polycondensation of metal-containing precursors with the evaporation of water as a solvent. It is a method of causing a reaction. In the sol-gel method using a metal compound (for example, metal alkoxide or metal chloride) in which a hydrolysis reaction with water occurs rapidly, a metal hydroxide is generated by hydrolysis of metal-containing precursors, Since these dehydration polycondensation occurs rapidly, crystal nuclei are likely to be coarsened. On the other hand, in the aqueous solution thermal decomposition method, stable dissolution in water is possible by using a metal-containing precursor, which has a mild hydrolysis reaction, as a raw material. In addition, by heating an aqueous solution containing such a metal-containing precursor, a dehydration polycondensation reaction between the metal-containing precursors can occur gradually with the evaporation of water as a solvent. This slows down the generation rate of crystal nuclei during pyrolysis, and as a result, miniaturization of crystal nuclei becomes possible.

  According to one embodiment of the method for producing rhodium-doped strontium titanate particles, a rhodium-doped strontium titanate precursor is contained by mixing a titanium compound, a strontium compound, a rhodium compound and a hydrophobic complexing agent and dissolving them in water. It is preferable to prepare an aqueous solution (the aqueous solution thus obtained is hereinafter referred to as an aqueous solution A). Here, “rhodium-doped strontium titanate precursor” means a compound having a six-membered ring structure formed by coordination of a hydrophobic complexing agent to titanium ions generated by dissociation of a titanium compound, and strontium It is a mixture of strontium ions generated by dissociating compounds and rhodium ions generated by dissociating rhodium compounds. In the method for preparing the aqueous solution A, first, an aqueous solution containing a water-soluble titanium complex is prepared by mixing a titanium compound and a hydrophobic complexing agent (the aqueous solution thus obtained is hereinafter referred to as an aqueous solution B). This aqueous solution B is mixed with a strontium compound and a rhodium compound to prepare an aqueous solution containing the rhodium-doped strontium titanate precursor, that is, an aqueous solution A. Here, the water-soluble titanium complex is one in which a hydrophobic complexing agent is coordinated to titanium ions generated by dissociation of a titanium compound.

In the method for producing rhodium-doped strontium titanate particles, it is preferable to add a hydrophobic complexing agent in addition to the titanium compound as a raw material as a method for water-solubilizing a titanium compound containing Ti ⁴⁺ which is inherently poorly water-soluble. By coordinating the hydrophobic complexing agent to titanium ions and complexing the titanium ions, hydrolysis can be suppressed. Here, as the titanium compound, an alkoxide of titanium or a chloride of titanium can be used. As titanium alkoxide, titanium tetramethoxide, titanium tetraethoxide, titanium tetra n-propoxide, titanium tetraisopropoxide, titanium tetra n-butoxide and the like can be used. As the chloride of titanium, titanium tetrachloride, titanium tetrafluoride, titanium tetrabromide, or the like can be used.

The hydrophobic complexing agent used in the method for producing rhodium-doped strontium titanate particles is capable of coordinating to titanium ions, and the hydrophobic part is exposed on the solvent phase side when coordinated to titanium ions. As such a hydrophobic complexing agent, for example, diketones and catechols can be preferably used. Examples of diketones include diketones represented by the general formula: Z ₁ —CO—CH ₂ —CO—Z ₂ (wherein Z ₁ and Z ₂ are each independently an alkyl group or an alkoxy group). Can be preferably used. As the diketones represented by the general formula, acetylacetone, ethyl acetoacetate, propyl acetoacetate, butyl acetoacetate and the like can be preferably used. As catechols, ascorbic acid, pyrocatechol, tert-butylcatechol and the like can be preferably used. Even more preferably, acetylacetone or ethyl acetoacetate having a very high complexing ability in an aqueous solution of titanium can be used. Thereby, it is possible to suppress intermolecular polymerization due to intermolecular dehydration polycondensation that occurs when a hydroxyl group that is a hydrophilic portion is exposed on the solvent phase side. Therefore, it is possible to refine crystal nuclei and to refine particles after the pyrolysis reaction during pyrolysis.

Moreover, according to the preferable aspect of the manufacturing method of rhodium dope strontium titanate particle | grains, in addition to a hydrophobic complexing agent, a hydrophilic complexing agent can be used. As the hydrophilic complexing agent, a carboxylic acid can be preferably used, and more preferably a carboxylic acid represented by the formula R ¹ —COOH (wherein R ¹ is a C _1-4 alkyl group), or A C1-C6 hydroxy acid or dicarboxylic acid can be used. Specific examples of such a hydrophilic complexing agent include water-soluble carboxylic acids such as acetic acid, lactic acid, citric acid, butyric acid and malic acid. Even more preferred water-soluble carboxylic acid is acetic acid or lactic acid. Thereby, it becomes possible to suppress the hydrolysis reaction of the titanium compound and improve the solubility in water.

  Moreover, although the solvent for complex formation may be water, according to another preferable aspect, you may use a water-soluble organic solvent as a solvent. Thereby, the solubility of a transition metal compound can be improved. Specific examples of the water-soluble organic solvent include methanol, ethanol, n-propanol, isopropanol, cellosolve solvent, and carbitol solvent.

According to a preferred embodiment of the present invention, the water-soluble titanium complex described in JP 2012-056947 A can be used. Specifically, a titanium complex having a coordination number of 6 with respect to a titanium ion, which is coordinated with the titanium ion, is represented by the general formula: Z ₁ —CO—CH ₂ —CO—Z ₂ (wherein , Z ₁ and Z ₂ are each independently an alkyl group or an alkoxy group.), A first ligand that functions as a bidentate ligand and a second coordination that is a carboxylate A third ligand and a fourth ligand each independently selected from the group consisting of an alkoxide and a hydroxide ion, and a fifth ligand that is H ₂ O A titanium complex consisting of can be used.

Moreover, as a strontium compound containing Sr ²⁺ , a compound that is water-soluble and does not leave an anionic component as a residue upon heat crystallization is preferable. For example, strontium nitrate, strontium acetate, strontium chloride, strontium bromide, strontium lactate, strontium citrate and the like are preferably used.

The rhodium compound containing Rh ³⁺ is preferably water-soluble and does not leave an anionic component as a residue during heat crystallization. As the rhodium compound, for example, rhodium nitrate, rhodium acetate, rhodium chloride, rhodium bromide, rhodium lactate, rhodium citrate and the like are preferably used. Further, a molecule containing Rh ⁴⁺ may be used as the rhodium compound. In order to improve the solubility of the strontium compound or rhodium compound in water, a hydrophilic complexing agent such as lactic acid, butyric acid or citric acid may be used.

  In the production of rhodium-doped strontium titanate particles used in the production method according to the present invention, the preferable mixing ratio of various raw materials in the aqueous solution A is as follows. -0.2 mol, more preferably 0.02-0.1 mol, the strontium compound is 1-1.1 times the molar amount of the titanium compound containing 1 atom of titanium, the rhodium compound is The desired doping amount, the hydrophobic complexing agent is 0.005-0.4 mol, more preferably 0.015-0.15 mol, and the hydrophilic complexing agent is 0.01-0. It is preferable that it is 2 mol, More preferably, it is 0.025-0.15 mol. By mixing at this ratio, the titanium compound becomes water-soluble satisfactorily, and the particles after thermal decomposition can be highly crystallized and refined. Further, the molar ratio of the hydrophobic complexing agent to the titanium compound is preferably 0.5 to 2 mol, more preferably 0.8 to 1 with respect to 1 mol of the titanium compound containing 1 atom of titanium. .2 moles. Within this range, it is possible to suppress the progress of the hydrolysis reaction of the titanium compound and the decrease in water solubility due to the improved hydrophobicity of the molecule. In addition, the molar ratio of the hydrophilic complexing agent to the titanium compound is preferably 0.2 to 2 mol, more preferably 0.3 to 1 with respect to 1 mol of the titanium compound containing 1 atom of titanium. .5 moles. Within this range, the progress of the hydrolysis reaction of the titanium compound can be suppressed, and the solubility of the titanium compound in water can be improved. In the aqueous solution A, the pH at which the stability of each ion in the aqueous solution can be maintained and the particles after crystallization can be refined is preferably 2 to 6, more preferably 3 to 5. By setting it as this range, the coarsening of the crystal | crystallization by acceleration | stimulation of hydrolysis polycondensation by a strong acid or strong alkali atmosphere can be suppressed.

  In addition, in the production of rhodium-doped strontium titanate particles used in the production method according to the present invention, it is preferable to add water-dispersed organic polymer particles to the aqueous solution A (the aqueous solution-dispersed organic polymer solution obtained thereby). Hereinafter, the polymer particles added are referred to as a dispersion.) Moreover, the powder which consists of rhodium dope strontium titanate particle | grains can be obtained by heating and crystallizing this dispersion. By adding water-dispersed organic polymer particles to aqueous solution A, the degree of aggregation of rhodium-doped strontium titanate particles is reduced, and the porosity and porosity of powders composed of rhodium-doped strontium titanate particles are improved. Is possible.

  As the water-dispersed organic polymer particles, spherical latex particles or oil-in-water dispersed (O / W) emulsions can be used. By adding the water-dispersed organic polymer particles, fine rhodium-doped strontium titanate particles are obtained, and secondary particles in which such particles are aggregated are porous. The mechanism by which fine primary particles are obtained as a result and the porosity of the aggregated secondary particles is considered as follows, but the present invention is not limited to this mechanism. . By adding the water-dispersed organic polymer particles, water-soluble titanium complexes, strontium ions and rhodium ions, which are also polar molecules, are adsorbed on the surface of the polymer particles having polarity in water. In the heating and crystallization process, the titanium complex on the surface of the polymer particles is hydrolyzed to produce rhodium-doped strontium titanate crystal nuclei. Here, since the crystal nuclei on the surface of the polymer particles exist with a physical distance from each other, there are few opportunities for bonding between the crystal nuclei, and the crystal growth is considered to proceed slowly. As a result, it is considered that the primary particle diameter of the rhodium-doped strontium titanate particles becomes fine. Furthermore, the resulting rhodium-doped strontium titanate particles bind to each other as the polymer particles disappear due to thermal decomposition, but the presence of the polymer particles suppresses aggregation of the rhodium-doped strontium titanate particles, and as a result, It is considered that the porosity of the secondary particles becomes higher, that is, the porosity becomes higher.

  The dispersed particle diameter of the water-dispersed organic polymer particles in water is preferably 10 to 1000 nm, and more preferably 30 to 300 nm. By setting the dispersed particle diameter within this range, the physical distance between the crystal nuclei of rhodium-doped strontium titanate can be increased. Therefore, it becomes possible to refine the rhodium-doped strontium titanate particles after heat crystallization. The material of the water-dispersed organic polymer particles is preferably a material that does not leave a residue such as amorphous carbon, which is a heated residue of the organic polymer particles, after heat crystallization at 600 ° C. or higher. For example, those obtained by polymerizing monomer units such as styrene, acrylic, urethane, and epoxy, or those containing a plurality of types of monomer units are preferably used. And the addition amount of the water-dispersed organic polymer particles is preferably 1 to 20 times, more preferably 3 to 15 times the amount of rhodium-doped strontium after high temperature crystallization. By adding an amount of polymer particles to the aqueous solution A, aggregation of particles after crystallization can be suppressed, and the primary particle diameter of the particles can be reduced.

  As a method for producing rhodium-doped strontium titanate particles from the dispersion in the method for producing rhodium-doped strontium titanate particles, the following method is preferably used. The dispersion is first dried at a low temperature of 200 ° C. or lower to obtain a dry powder. By firing this dried powder for crystallization, rhodium-doped strontium titanate particles can be produced. Moreover, you may perform the drying and baking process of this dispersion continuously. The calcination temperature at the time of crystallization of rhodium-doped strontium titanate is more than 800 ° C. and less than 1100 ° C., more preferably 900 ° C. or more and 1050 ° C. or less. By adjusting to this temperature range, it is possible to highly crystallize high-purity rhodium-doped strontium titanate particles while thermally decomposing the water-dispersed organic polymer particles.

According to a preferred embodiment of the co-catalyst carrying the present invention into the rhodium-doped strontium titanate particles, when generating hydrogen by photolysis of water using a rhodium-doped strontium titanate particles used in the process according to the invention, A promoter is supported on the surface of the rhodium-doped strontium titanate particles. Thereby, generation of hydrogen occurs promptly.

  As the co-catalyst for hydrogen generation, at least one selected from metal particles such as platinum, ruthenium, iridium and rhodium, or a mixture of these metal particles can be preferably used. More preferably, platinum and ruthenium metal particles can be used. By supporting the promoter in the form of particles on the surface of the photocatalyst particles for hydrogen generation, it becomes possible to reduce the activation energy in the reduction reaction of water, so that hydrogen can be generated promptly.

Attachment of rhodium-doped strontium titanate particles to a substrate by electrophoresis In the production method according to the present invention, rhodium-doped strontium titanate particles having a primary particle diameter of 100 nm or less prepared as described above are used as a conductive substrate. It is attached to the top by electrophoresis. By using the electrophoresis method, it is possible to easily attach the photocatalyst particles to various conductive substrates.

  Specific examples of the procedure for depositing rhodium-doped strontium titanate particles on a conductive substrate by electrophoresis include the following procedures. That is, a step of preparing a dispersion slurry containing the prepared rhodium-doped strontium titanate particles, a step of adding this slurry to a solvent to prepare a solution for electrophoresis, and a surface of the rhodium-doped strontium titanate particles in this solution It is possible to use a procedure including a step of adding a compound that imparts a charge to the substrate, a step of immersing the conductive substrate in the obtained solution, and a step of applying a voltage between the conductive substrates.

Preparation of slurry containing rhodium-doped strontium titanate particles The slurry containing rhodium-doped strontium titanate particles used in the production method according to the present invention can disperse rhodium-doped strontium titanate particles having a primary particle diameter of 100 nm or less in a solvent. Any wet dispersion method can be used. As such a wet dispersion method, kneading methods such as mechanical kneading and manual kneading; mechanical milling methods such as ball mill, bead mill and planetary mill; ultrasonic irradiation; and stirring can be preferably used.

  As the solvent capable of dispersing the rhodium-doped strontium titanate particles, both an organic solvent and an aqueous solvent can be used. Specific examples of the organic solvent include solvents that do not undergo electrolysis even when a voltage of about 10 V is applied. For example, ketone solvents such as acetone, acetylacetone, and methyl ethyl ketone, alcohol solvents such as ethanol and isopropyl alcohol, acetonitrile, and α-terpineol. An organic vehicle solvent such as can be used. Specific examples of the aqueous solvent include water and a water-soluble organic solvent. When water is used as the aqueous solvent, hydrogen and oxygen are generated by electrolysis, and the generated hydrogen and oxygen are present between the rhodium-doped strontium titanate particles, so that voids are formed between the particles and the slurry becomes porous. It is possible to be in a state. As a result, aggregation of rhodium-doped strontium titanate particles in the slurry can be suppressed.

  Further, a dispersant may be added to the solvent. As a dispersant that can be added when an organic solvent is used as the solvent, a vehicle binder polymer such as polyvinyl butyral or ethyl cellulose can be used. Examples of the dispersant that can be added when an aqueous solvent is used include polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyvinyl pyrrolidone, carboxymethyl cellulose, carboxypropyl cellulose, and triblock copolymers (for example, polyethylene oxide-polypropylene oxide-polyethylene oxide). Etc. can be used.

  In this way, the dispersibility of the rhodium-doped strontium titanate particles in the solvent can be improved. In this way, it is possible to realize a state in which the rhodium-doped strontium titanate particles are uniformly dispersed in a form close to primary particles and are stably mixed. As a result, aggregation of rhodium-doped strontium titanate particles can be suppressed. Therefore, rhodium-doped strontium titanate particles can exist at a close distance from each other, and the rhodium-doped strontium titanate particles have a high density due to volatilization of the solvent component during or after the adhesion to the conductive substrate and subsequent firing. Can be obtained.

Preparation of Electrophoresis Solution The electrophoresis solution used in the production method according to the present invention is prepared by adding a slurry in which rhodium-doped strontium titanate particles are dispersed to a solvent. As a solvent, what was mentioned above as a solvent which can disperse | distribute this particle | grain at the time of preparation of the slurry containing rhodium dope strontium titanate particle | grains can be used.

Concentration of rhodium-doped strontium titanate The concentration of rhodium-doped strontium titanate contained in the electrophoresis solution is preferably 0.01 to 50% by weight, more preferably 0.1 to 20% by weight. By setting this concentration range, the relative distance between the surface of the charged electrode (conductive substrate) and the charged rhodium-doped strontium titanate particles contained in the solution can be reduced. As a result, a sufficient amount of rhodium-doped strontium titanate migrating particles can be secured, and the adhesion and deposition of particles on the electrode surface can be made sufficient. In addition, the viscosity of the electrophoresis solution can be controlled, that is, the viscosity resistance in the solution can be lowered, and the charged rhodium-doped strontium titanate particles can be easily migrated. Here, the rhodium-doped strontium titanate concentration is determined by the following equation.
Rhodium-doped strontium titanate concentration (% by weight) = (weight of rhodium-doped strontium titanate particles contained in the solution) ÷ (total weight of the solution) × 100

Charge imparting to rhodium-doped strontium titanate particles A compound that imparts charge to the surface of rhodium-doped strontium titanate particles is added to the electrophoretic solution used in the production method according to the present invention. As a result, the surface of the rhodium-doped strontium titanate particles becomes charged and has a surface charge, which enables migration to an electrode having an opposite charge by electrostatic force, and the particles are placed on the electrode by electrophoresis. Can be moved. As the compound imparting electric charge, a halogen molecule can be preferably used. As the halogen molecule, iodine or bromine can be preferably used.

Conductive base material The base material used in the production method according to the present invention must be capable of adhering and depositing rhodium-doped strontium titanate particles by electrophoresis, and therefore must have electrical conductivity. As such a base material, when the metal or the base material itself is not conductive, the base material may be made conductive by providing a thin film that imparts conductivity to the surface. For example, glass or resin (PET, PEN, polyimide, or the like) provided with a conductive film on the surface can be preferably used. In addition, as the conductive film, a known conductive film can be used without limitation, for example, when performing photodecomposition of water by irradiating visible light from the side opposite to the side where the photocatalytic layer of the substrate is supported, When the photocatalyst layer is fixed over the entire periphery of the substrate, the conductive film is preferably transparent. Here, examples of the transparent conductive film include fluorine-doped tin oxide, tin-doped indium oxide, aluminum-doped zinc oxide, gallium-doped zinc oxide, niobium-doped titanium oxide, and tantalum-doped titanium oxide, and preferably fluorine-doped tin oxide and tin-doped. Indium oxide is mentioned. As the metal, titanium, aluminum, stainless steel or the like is used, and preferably titanium or aluminum is used. Moreover, there is no restriction | limiting in particular as a shape of a base material, However, Flat shape, fiber shape, mesh shape, etc. can be mentioned.

The voltage applied in the applied voltage electrophoresis method is preferably 1 V or more and 20 V or less, more preferably 5 V or more and 15 V or less. Thereby, electrolysis of the solvent does not occur, and a sufficient potential difference can be secured for depositing charged particles in the slurry on the substrate surface. The voltage applying device can be used without particular limitation as long as it can provide a desired potential difference between the electrodes, but a potentiostat, a DC voltage generator, an electrometer, or the like is preferably used. it can.

  The time for applying the voltage is preferably 10 seconds to 30 minutes. This makes it possible to attach and deposit a sufficient amount of photocatalytic particles on the electrode. The temperature of the electrophoresis solution during electrophoresis can be controlled in consideration of the boiling point of the solvent to be used, but is preferably 10 to 80 ° C.

Immobilization of rhodium-doped strontium titanate particles on substrate
Firing In the production method according to the present invention, the dried aggregate of rhodium-doped strontium titanate particles is then fired. Thereby, the aggregate | assembly of the rhodium dope strontium titanate particle | grains adhering and deposited on the base material is stuck firmly on this base material. The firing temperature is equal to or higher than the thermal decomposition temperature of a solvent, a dispersant and the like, and is preferably a temperature at which sintering of the base material, rhodium-doped strontium titanate particles and rhodium-doped strontium titanate particles can be promoted. Specifically, it is 200 ° C. or higher and 700 ° C. or lower, and more preferably 300 ° C. or higher and 600 ° C. or lower. By firing at a temperature in this range, it is possible to suppress the generation of impurities due to the reaction between the base material and the rhodium-doped strontium titanate particles and the decrease in strength of the aggregate of particles due to insufficient adhesion. In addition, it is possible to obtain a photocatalyst material having high adhesion between the substrate and the particles and high binding property between the particles. As a result, it is possible to obtain a photocatalyst material capable of hydrogen generation by water decomposition that is stable for a long time under visible light irradiation. The drying time is preferably 5 minutes to 10 hours.

Drying In the production method according to the present invention, the aggregate of rhodium-doped strontium titanate particles adhered to and deposited on the substrate by electrophoresis is preferably heated and dried before firing. . Thereby, evaporation of the solvent used for electrophoresis can be promoted, and a stable aggregate of particles can be obtained by baking performed after drying. The drying temperature is preferably a low temperature of 10 to 120 ° C.

Photocatalyst material The photocatalyst material obtained by the production method according to the present invention comprises a base material and rhodium-doped strontium titanate particles having a primary particle diameter of 100 nm or less immobilized on the base material. The photocatalyst supported on this photocatalyst material contains rhodium-doped strontium titanate having a fine structure with a small primary particle diameter, and exists as an aggregate formed by aggregation of these fine particles (hereinafter also referred to as “photocatalyst layer”). .) For this reason, the porosity of this photocatalyst layer becomes high, that is, the porosity becomes high, and the specific surface area of the photocatalyst layer becomes large. As a result, the photocatalytic activity of the photocatalytic layer formed by aggregation of rhodium-doped strontium titanate particles that originally have high photocatalytic activity is exhibited as low as possible.

  Further, the photocatalyst material obtained by the production method according to the present invention is formed by agglomerating rhodium-doped strontium titanate particles having a small primary particle diameter, and thus the contact between the particles and the substrate. The area becomes larger. Thereby, it becomes possible to obtain a photocatalyst material having high adhesion between the substrate and the photocatalyst layer.

  Further, since the photocatalyst material obtained by the production method according to the present invention is an aggregate of fine rhodium-doped strontium titanate particles, the binding property between the particles is good. As a result, the particles can form a photocatalytic layer with uniformity. In addition, the photocatalyst layer thus formed can be in a thick state in which rhodium-doped strontium titanate particles are deposited.

  Such a state of the photocatalyst layer includes, for example, a partially film-like state in addition to a complete film shape as long as the photocatalyst particles are present on the substrate surface. Moreover, the photocatalyst layer may exist discretely in an island shape on the substrate surface. In addition to the so-called film state, the photocatalyst layer may be in a wave shape, a comb shape, a fiber shape, a mesh shape, or the like. In the present invention, the “photocatalyst layer” means an aggregate of photocatalyst particles present on the base material in the above-described state.

  The thickness of the photocatalyst layer carried on the photocatalyst material obtained by the production method according to the present invention is preferably 0.1 μm or more and 100 μm or less. A more preferable thickness of the photocatalyst layer is 0.2 μm or more and 30 μm or less.

  Further, the photocatalyst material obtained by the production method according to the present invention carries an aggregate of fine rhodium-doped strontium titanate particles, so that per unit area of the fine rhodium-doped strontium titanate particles and the substrate. There are many contact points. Thereby, the mechanical strength between the substrate and the particles and between the particles and the particles is improved, and the adhesion between the substrate and the rhodium-doped strontium titanate particles and the binding property between the rhodium-doped strontium titanate particles are improved. It becomes possible. Thereby, it becomes possible to prevent rhodium-doped strontium titanate particles from being detached from the base material or segregating on the base material. As a result, the photocatalyst material obtained by the production method according to the present invention can maintain a stable hydrogen production function for a long time.

  The aggregate of fine rhodium-doped strontium titanate particles supported on the photocatalyst material obtained by the production method according to the present invention has a structure with a high degree of porosity in which interparticle voids form pores. Allows efficient diffusion of water into the film and desorption of hydrogen and oxygen produced in the film out of the film. Thereby, the photocatalyst material can generate hydrogen efficiently by water splitting reaction with high efficiency. According to a preferred embodiment of the present invention, the pore diameter of the photocatalyst material obtained by the production method according to the present invention is preferably 10 nm or more and 200 nm or less, and more preferably 20 nm or more and 100 nm or less.

  In the present invention, the pore diameter of the photocatalyst layer means the pore diameter of the pores existing between the photocatalyst particles contained in the photocatalyst layer. The pore diameter can be measured by pore distribution measurement by nitrogen gas adsorption / desorption, and is determined by analysis by the BJH method. Specifically, for example, the adsorption / desorption isotherm of nitrogen gas is measured using a gas adsorption pore distribution measuring device (“BELSORP-mini”, manufactured by Nippon Bell), and the pore diameter is obtained by analysis by the BJH method. . The pore volume distribution is obtained by plotting the Log differential pore volume against the obtained pore diameter. In this pore volume distribution, the pore diameter at the peak position is defined as the pore diameter.

  A schematic diagram of a cross section of a photocatalyst material obtained by the production method according to the present invention is shown in FIG. In FIG. 1, the photocatalyst material is formed by fixing a photocatalyst layer having an interparticle void 2 and a film thickness 4, which is made of an aggregate of fine rhodium-doped strontium titanate particles 1, on a conductive substrate 3.

  The following examples further illustrate the present invention. The present invention is not limited to these examples.

Examples 1-4
Synthesis of rhodium-doped strontium titanate particles Add 0.02 mol (2.003 g) of acetylacetone (Wako Pure Chemical) to a 20 mL glass sample tube and stir at room temperature. Titanium tetraisopropoxide (Wako Pure Chemical) 0.02 Mol (5.684 g) was added to prepare a solution containing a yellow water-soluble titanium-acetylacetone complex. The solution containing this water-soluble titanium-acetylacetone complex was added to 50 mL of a 0.32 mol / L acetic acid aqueous solution with stirring at room temperature. After the addition, the mixture was stirred at room temperature for about 1 hour, and further stirred at 60 ° C. for about 1 hour to prepare an aqueous solution containing a yellow transparent water-soluble titanium complex.

  Next, 10 g of an aqueous solution containing the water-soluble titanium complex prepared above was collected (Ti content: 3.41 mmol). Also, in order to compensate for the decrease in sublimable strontium during high-temperature firing, strontium acetate 0.5 hydrate (Wako Pure Chemical Industries, Ltd.) was used so that the molar amount of Sr was 1.07 times that of Ti. ) 3.75 mmol (0.84 g) and 0.70 g of lactic acid (manufactured by Wako Pure Chemical Industries) were dissolved in 3.16 g of distilled water to prepare a Sr-containing aqueous solution. Next, the Sr-containing aqueous solution was gradually added to the collected aqueous solution containing the water-soluble titanium complex. Further, a 5 wt% aqueous solution of rhodium trichloride (manufactured by Wako Pure Chemical Industries, Ltd.) was gradually added so that Rh was 0.02 mol% with respect to Ti, followed by stirring at room temperature for 3 hours. As a result, an orange transparent 2 mol% rhodium-doped strontium titanate precursor aqueous solution was obtained.

  Furthermore, an acrylic-styrene-based O / W emulsion (manufactured by DIC, “EC-”) was added to the aqueous solution so that the solid content was 5 times the weight of the rhodium-doped strontium titanate obtained after firing. 905EF ”, dispersed particle diameter 150 nm, pH: 9, solid content concentration 50 wt%) was added to prepare a dispersion.

  The dispersion prepared as described above was dried at 80 ° C. for 1 hour and then calcined at 500 ° C. for 2 hours. The powder was collected from the glass substrate and further fired at 1000 ° C. for 10 hours to obtain a powder composed of rhodium-doped strontium titanate particles. Observation with a scanning electron microscope (S-4100, manufactured by Hitachi, Ltd.) confirmed that the powder composed of rhodium-doped strontium titanate particles has a porous structure composed of fine particles having a primary particle diameter of about 50 nm. It was.

Support of promoter on rhodium-doped strontium titanate particles 1 g of the powder containing the obtained rhodium-doped strontium titanate particles contains 1 wt% of chloroplatinic acid hexahydrate (manufactured by Wako Pure Chemical Industries) as a promoter material. After adding to 1.32 g of aqueous solution, it was suspended and dispersed by ultrasonic irradiation. Thereafter, the dispersion was kneaded for 30 minutes using a mortar, and concentrated while drying water to obtain a paste. Then, this paste was dried at room temperature for 2 hours, and after collecting the powder, it was calcined at 400 ° C. for 30 minutes to produce rhodium-doped strontium titanate particles carrying 0.5 wt% of platinum as a promoter. .

Production of a dispersion slurry containing rhodium-doped strontium titanate particles A slurry in which rhodium-doped strontium titanate particles carrying a cocatalyst were highly dispersed in a solvent was produced using a planetary mill. Specifically, rhodium-doped strontium titanate fine particle powder in which a cocatalyst is supported in a zirconia-coated container (with a content of 45 ml) using a high-speed planetary ball mill (Fritsch, “Premium Line P-7”) 1 g each of 0.1 mmφ zirconia beads and 4 g of ethanol were added, and milling was performed at 700 rpm for 30 minutes. Next, a slurry (solid content: 20 wt%) in which rhodium-doped strontium titanate particles were dispersed was obtained by filtering the slurry liquid after treatment under reduced pressure using a resin sieve and collecting zirconia beads. .

Preparation of a photocatalyst material in which rhodium-doped strontium titanate particles are immobilized on a substrate by electrophoresis The rhodium-doped strontium titanate particles are immobilized by electrophoresis according to the following procedure. First, the dispersion slurry containing the rhodium-doped strontium titanate particles was added to acetone in a 100 mL beaker to prepare a solution for electrophoresis. Under the present circumstances, 50 mL of each reaction liquid for electrophoresis (Examples 1-4) was prepared so that the density | concentration of the rhodium dope strontium titanate particle | grains contained in a solution might become the density | concentration shown in Table 1. Further, 10 mg of iodine was added to this solution for the purpose of imparting electric charge to the particle surface, and ultrasonic dispersion was performed for 1 minute.

Then, _two pieces of glass with F-doped SnO ₂ film (hereinafter also referred to as “FTO substrate”, “U film” manufactured by AGC Fabrytec, substrate thickness: 1 mm, sheet resistance: 15Ω / □, size: 5 × 5 cm), With the conductive surfaces facing each other, it was immersed in a beaker so that the electrode take-out portion was 1 × 4 cm (distance between electrodes: 1 cm).

  Then, two FTO substrates are connected by potentiostat terminals (+,-) to form a bipolar electrolysis cell, and 10V is applied between the two electrodes, and the dispersed particles are electrophoresed for 3 minutes. It was. Further, the substrate after electrophoresis is taken out of the reaction solution, dried at room temperature for 1 minute, and then at 80 ° C. for 30 minutes, and then calcined at 450 ° C. for 30 minutes, so that a photocatalyst layer composed of rhodium-doped strontium titanate particles is formed on the substrate. Each photocatalyst material (Examples 1 to 4) immobilized on the substrate was prepared.

Comparative Examples 1 and 2
Synthesis of rhodium-doped strontium titanate particles The rhodium-doped strontium titanate was prepared by solid-phase reaction method. Specifically, each powder of strontium carbonate (manufactured by Kanto Chemical Co., Inc.), titanium oxide (manufactured by Soekawa Richemical Co., Ltd., rutile type), and rhodium oxide (Rh ₂ O ₃ : manufactured by Wako Pure Chemical Industries, Ltd.) was used. .07: 1-x: x (x: rhodium doping ratio = 0.02). Then, the obtained mixed powder was baked at 1000 ° C. for 10 hours to produce rhodium-doped strontium titanate powder. Observation by a scanning electron microscope (S-4100, manufactured by Hitachi, Ltd.) confirmed that the powder composed of rhodium-doped strontium titanate particles has a porous structure composed of fine particles having a primary particle diameter of about 500 nm. It was.

  Using the obtained particle powder, except that the concentration of rhodium-doped strontium titanate particles contained in the electrophoresis solution was changed to the concentration shown in Table 1, co-catalyst loading, dispersion slurry preparation, and electrophoresis The procedure for preparing the photocatalyst material was the same as in the example, and each photocatalyst material (Comparative Examples 1 and 2) was obtained. The production conditions and characteristics of the produced photocatalyst material are shown in Table 1.

Microstructure of a photocatalyst material in which rhodium-doped strontium titanate particles are immobilized on a substrate by electrophoresis . A photograph of the surface and cross-section of the photocatalyst material prepared in Example 4 above by scanning electron microscope is shown in FIG. 2 and FIG. 3 shows. From FIG. 2, it was confirmed that a porous membrane structure was obtained.

Measurement of the film thickness of the photocatalyst material by observation with a scanning electron microscope The film thickness was measured from a photograph (magnification: 2000 times) of the cross section of each photocatalyst material obtained by observation with a scanning electron microscope. Here, the film thickness was measured as the distance from the substrate surface to the top of the photocatalyst layer. In Example 4, it was confirmed from FIG. 3 that a 9 μm porous photocatalyst layer was obtained. The film thickness of each photocatalyst material other than Example 4 was as shown in Table 1.

Adhesion test between photocatalyst layer and base material In each of the photocatalyst materials of Examples 1 to 4 and Comparative Examples 1 and 2, a mending tape (Sumitomo 3M, thickness 63 μm) was pasted on the photocatalyst layer formed on the substrate. Then, the adhesion between the substrate and the photocatalyst layer was evaluated by a tape peeling test for peeling the tape. The evaluation method was as follows. That is, the mending tape was stuck on the photocatalyst layer, and the finger was slid 5 times while pressing the tape with the belly of the finger. After 10 seconds, the tape was peeled off at once. The criteria for determination were as follows.
○: The photocatalyst layer remained on the substrate after the tape was peeled x: The photocatalyst layer was completely peeled from the substrate after the tape was peeled off

  As a result, in each of the photocatalyst materials of Examples 1 to 4, the photocatalyst layer remained on the titanium substrate even after the tape was peeled, and strong substrate adhesion was confirmed. In the material, the photocatalyst layer was completely peeled from the substrate, and it was confirmed that the material had fragile substrate adhesion.

Hydrogen generation activity by water decomposition of photocatalyst material Each produced photocatalyst material is introduced into a separable glass flask with a window made of Pyrex (registered trademark), and 200 ml of an aqueous solution containing 10 vol% of methanol as a sacrificial reagent is added. did. The glass flask containing the reaction solution was attached to a closed circulation device, and the atmosphere in the reaction system was replaced with argon. Then, visible light was irradiated from the Pyrex (registered trademark) window side by a 300 W xenon lamp (manufactured by Cermax, PE-300BF) equipped with a UV cut filter (L-42, manufactured by HOYA). Then, the amount of hydrogen generated by reduction of water by the photocatalytic reaction is examined over time by a gas chromatograph (manufactured by Shimadzu Corporation, GC-8A, TCD detector, MS-5A column). Time evaluation was performed.

  The results were as shown in Table 1. In the photocatalyst materials of Examples 1 to 4, it was confirmed that hydrogen was favorably generated by the water splitting reaction by visible light irradiation. Further, it was confirmed that the photocatalyst layer was immobilized on the substrate in the same manner as the initial stage after the evaluation for 3 hours. On the other hand, in the samples of Comparative Examples 1 and 2, the generation of hydrogen by visible light irradiation was hardly observed, and the state of the sample was confirmed after 3 hours of evaluation, and the photocatalyst layer hardly remained on the substrate. It was confirmed that the photocatalyst layer diffused into the evaluation solution after peeling from the substrate during the evaluation.

1 Rhodium-doped strontium titanate particles 2 Interparticle voids 3 Conductive substrate 4 Film thickness

Claims (4)

A method for producing a photocatalytic material in which rhodium-doped strontium titanate particles are immobilized on a conductive substrate,
Primary particle diameter of Ri der than 100nm or less 50 nm, further, under conditions such that the light absorptance _{A 315} at a wavelength of 315nm is in the range of 0.86 to 0.87, the light absorption ratio _{A 570} at a wavelength of 570nm is 0 and at .6 or more and preparing a rhodium-doped strontium titanate particles light absorptivity _{a 1800} is Ru der 0.7 at a wavelength of 1800 nm,
Attaching the rhodium-doped strontium titanate particles onto the conductive substrate by electrophoresis;
And firing the rhodium-doped strontium titanate particles deposited on the conductive substrate to immobilize the particles on the substrate. The manufacturing method of Claim 1 whose primary particle diameters of the said rhodium dope strontium titanate particle are 50 nm or more and 70 nm or less.   The manufacturing method according to claim 1 or 2, wherein a voltage applied in the electrophoresis method is 1 V or more and 20 V or less.   The manufacturing method according to any one of claims 1 to 3, wherein the conductive substrate is one selected from titanium, aluminum, glass with a fluorine-doped tin oxide film, and glass with a tin-doped indium oxide film.

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