Co-catalysts, photocatalysts, dispersions, compositions, coatings, substrates

Abstract

The present invention provides a co-catalyst for visible light-responsive photocatalysts that exhibits higher activity against water oxidation compared to conventional Co oxide co-catalysts, a photocatalytic material containing the co-catalyst, a dispersion containing the photocatalytic material, a composition containing the dispersion, a coating film which is a dried product of the dispersion or a cured product of the composition, and a substrate having the coating film. [Solution] A co-catalyst for a visible light-responsive photocatalyst, comprising cobalt and at least one of iron and nickel. A photocatalytic material comprising iridium-doped strontium titanate particles and a co-catalyst supported on the strontium titanate particles.

Description

[Technical Field]

[0001] The present invention relates to a co-catalyst for visible light-responsive photocatalysts, a photocatalytic material containing the co-catalyst, a dispersion containing the photocatalytic material, a composition containing the dispersion, a coating film which is a dried product of the dispersion or a cured product of the composition, and a substrate having the coating film. [Background technology]

[0002] One technology attracting attention for hydrogen production is the decomposition of water using sunlight with photocatalysts. Common photocatalysts include semiconductor particles supported by co-catalysts. When semiconductor particles are irradiated with light having energy greater than their band gap, electrons in the valence band are excited to the conduction band in the semiconductor. For photocatalytic water decomposition to occur, the potential at the lower end of the conduction band of the semiconductor must be positive compared to the reduction potential of water, and the potential at the upper end of the valence band must be negative compared to the oxidation potential of water.

[0003] To obtain cost-competitive hydrogen, it is necessary for semiconductors to absorb visible light and for a high proportion of the absorbed light to be consumed in catalytic reactions (quantum yield). To improve the quantum yield, it is effective to suppress the recombination of excited electron-hole pairs, suppress the reverse reaction of water production from hydrogen and oxygen, and reduce the oxidation-reduction overpotential of water by supporting an appropriate co-catalyst.

[0004] Non-patent document 1 describes a photocatalyst in which SrTiO3 semiconductor particles, which have a cubic shape with the vertices cut off by planes, are treated in a SrCl2 flux with Al2O3 added, and Rh / Cr2O3 is supported as a hydrogen production co-catalyst and CoOOH as an oxygen production co-catalyst. This photocatalyst is made of a material that absorbs only ultraviolet light, but water splitting reaction occurs with a quantum yield of almost 100%. This is achieved because the electric field gradient inside the SrTiO3 separates excited electron-hole pairs and suppresses recombination, and the cut-off faces function as water oxidation sites and the cubic surfaces function as water reduction sites, and the reverse reaction is suppressed by core-shell type co-catalysts.

[0005] On the other hand, Non-Patent Document 2 describes that semiconductor particles doped with Ir and Sb in SrTiO3, forming impurity levels within the forbidden band, absorb visible light up to about 600 nm. However, Non-Patent Document 3 describes that a photocatalyst flux-treated using Ir,Sb-doped SrTiO3 in the same manner as in Non-Patent Document 1 absorbs visible light, yet exhibits lower water-splitting activity compared to the photocatalyst shown in Non-Patent Document 1. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Nature, 581, 411 (2020) [Non-Patent Document 2] 126th Catalyst Symposium, P058(2020) [Non-Patent Document 3] "Development of Process Technology for Manufacturing Basic Chemicals Using Carbon Dioxide as a Raw Material (Artificial Photosynthesis Project)" Results Report (2022) (https: / / www.nedo.go.jp / content / 100942691.pdf) [Overview of the project] [Problems that the invention aims to solve]

[0007] The factors contributing to the decreased activity described above include the impurities Ir and Sb themselves, and the fact that crystal defects caused by impurity doping acted as recombination centers for excited electron-hole pairs, resulting in a decrease in quantum yield. Additionally, holes with low oxidizing power generated at impurity levels located shallower than the valence band are less likely to oxidize water, which may also contribute to the decrease in quantum yield.

[0008] The present invention has been made in view of the above circumstances, and provides a cocatalyst for a visible light-responsive photocatalyst having high activity for water oxidation, a photocatalyst material containing the cocatalyst, a dispersion containing the photocatalyst material, a composition containing the dispersion, a coating film which is a dried product of the dispersion or a cured product of the composition, and a substrate having the coating film, as compared with a conventional Co oxide cocatalyst. **Means for Solving the Problems**

[0009] The present invention has the following aspects. [1] A cocatalyst for a visible light-responsive photocatalyst, comprising cobalt and at least one of iron and nickel. [2] A photocatalyst material, comprising strontium titanate particles doped with iridium and the cocatalyst according to [1] supported on the strontium titanate particles. [3] A photocatalyst material, comprising strontium titanate particles doped with iridium and antimony and the cocatalyst according to [1] supported on the strontium titanate particles. [4] A dispersion, comprising the photocatalyst material according to [2] or [3] and a solvent. [5] A composition, comprising the dispersion according to [4] and a binder. [6] A coating film which is a dried product of the dispersion according to [4]. [7] A coating film which is a cured product of the composition according to [5]. [8] A substrate having the coating film according to [6] or [7]. **Advantages of the Invention**

[0010] According to the present invention, it is possible to provide a cocatalyst for a visible light-responsive photocatalyst having high activity for water oxidation, a photocatalyst material containing the cocatalyst, a dispersion containing the photocatalyst material, a composition containing the dispersion, a coating film which is a dried product of the dispersion or a cured product of the composition, and a substrate having the coating film, as compared with a conventional Co oxide cocatalyst. **Modes for Carrying Out the Invention**

[0011] Embodiments of the co-catalyst, photocatalytic material, dispersion, composition, coating film, and substrate of the present invention will be described. This embodiment is provided to give a better understanding of the spirit of the invention and does not limit the present invention unless otherwise specified. Within the scope of the present invention, it is possible to change, omit, substitute, or add to numerical values, quantities, materials, types, times, temperatures, order, etc.

[0012] [Assistant catalyst] The co-catalyst of this embodiment comprises cobalt (Co) and at least one of iron (Fe) and nickel (Ni). The co-catalyst of this embodiment is used in a photocatalyst that responds to visible light (visible light-responsive photocatalyst).

[0013] The co-catalysts of this embodiment are specifically a composite oxide of Co and Fe, a composite oxide of Co and Ni, and a composite oxide of Co, Fe, and Ni.

[0014] When the co-catalyst in this embodiment is a composite oxide of Co and Fe, the blending ratio of Fe to Co (Fe / Co) is preferably 0.05 to 0.95 by mass, more preferably 0.1 to 0.9, and even more preferably 0.2 to 0.8. If the mass ratio is above the lower limit, the effect of improving activity due to the composite of Co and Fe becomes insufficient.

[0015] When the co-catalyst in this embodiment is a composite oxide of Co and Ni, the mixing ratio of Ni to Co (Ni / Co) is preferably 0.05 to 0.95 by mass, more preferably 0.1 to 0.9, and even more preferably 0.2 to 0.8. If the mass ratio is outside the above range, the effect of improving activity due to the composite of Co and Ni will be insufficient.

[0016] In this embodiment, when the co-catalyst is a composite oxide of Co, Fe, and Ni, the Fe / Co ratio to Co is preferably 0.05 to 0.95 by mass, more preferably 0.1 to 0.9, and even more preferably 0.2 to 0.8. If the mass ratio is outside this range, the effect of improving activity due to the composite of Co, Fe, and Ni will be insufficient. Similarly, the Ni / Co ratio to Co is preferably 0.05 to 0.95 by mass, more preferably 0.1 to 0.9, and even more preferably 0.2 to 0.8. If the mass ratio is outside this range, the effect of improving activity due to the composite of Co, Fe, and Ni will be insufficient.

[0017] The co-catalyst in this embodiment may contain impurities other than Co, Fe, and Ni. Examples of impurities include alkali metals such as Na and K, alkaline earth metals such as Mg and Ca, and transition metals such as Mn, Ru, and Ir.

[0018] The impurity content is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.3% by mass or less, relative to the total mass (100% by mass) of the co-catalyst. When the impurity content is below the above upper limit, the decrease in the activity of the co-catalyst due to the impurities is negligibly small.

[0019] The co-catalyst in this embodiment preferably has a particle size of 1 nm to 30 nm as measured by a secondary electron image obtained by a scanning electron microscope, more preferably 1 nm to 25 nm, and even more preferably 1 nm to 20 nm. When the particle size is within the above range, the photocatalytic activity is high, and the decrease in stability due to dissolution can be suppressed.

[0020] The co-catalyst of this embodiment provides a co-catalyst for visible light-responsive photocatalysts that has higher activity against water oxidation compared to conventional Co oxide co-catalysts.

[0021] [Photocatalyst material] (First embodiment) The photocatalytic material of this embodiment includes iridium (Ir)-doped strontium titanate (SrTiO3) particles and the co-catalyst of the above-described embodiment supported on the strontium titanate particles.

[0022] In Ir-doped SrTiO3 particles, the amount of Ir doping is preferably 0.01 moles to 5 moles per 100 moles of SrTiO3, more preferably 0.01 moles to 3 moles, and even more preferably 0.01 moles to 2 moles. If the amount of Ir doping is above the lower limit, visible light can be absorbed sufficiently. If the amount of Ir doping is below the upper limit, the frequency of recombination of excited electron-hole pairs will not be excessive.

[0023] (Method for measuring Ir doping levels) The amount of Ir doping can be measured by mixing it with a flux such as lithium tetraborate or sodium tetraborate, heating it in a platinum crucible above the melting point of the flux to dissolve the semiconductor particles in the flux, and then quantifying the solution dissolved in nitric acid after cooling by ICP emission spectroscopy.

[0024] The amount of co-catalyst supported on Ir-doped SrTiO3 particles is preferably 0.1 parts by mass or more and 1 part by mass or less, more preferably 0.1 parts by mass or more and 0.5 parts by mass or less, and even more preferably 0.1 parts by mass or more and 0.3 parts by mass or less, per 100 parts by mass of Ir-doped SrTiO3 particles. If the amount of co-catalyst supported is above the lower limit, the co-catalyst will have the effect of improving photocatalytic activity. If the amount of co-catalyst supported is below the upper limit, it will be absorbed by the co-catalyst, and the reduction in the amount of light irradiated to the semiconductor particles will be negligibly small.

[0025] (Method for measuring the amount of co-catalyst supported) The amount of co-catalyst supported can be measured by mixing semiconductor particles supporting the co-catalyst with an acid that has oxidizing power to dissolve only the co-catalyst without dissolving the semiconductor particles, such as aqua regia. The resulting solution can then be quantified by ICP emission spectroscopy.

[0026] In this embodiment, the photocatalytic material preferably has a particle size D50 (D50) of 0.1 μm or more and 10 μm or less when the cumulative volume percentage of the dry particle size distribution is 50%, more preferably 0.1 μm or more and 5 μm or less, and even more preferably 0.1 μm or more and 3 μm or less. When D50 is within the above range, the effects of light loss due to scattering can be reduced, and the settling of the photocatalyst in the photocatalyst dispersion can be suppressed.

[0027] The above D50 can be measured in the same way as the co-catalyst.

[0028] The specific surface area of ​​the photocatalytic material in this embodiment is 1 m². 2 / g or more 30m 2 Preferably less than / g, 1m 2 / g or more 20m 2 It is more preferable that it be less than or equal to / g, 1m 2 / g or more 15m 2 It is even more preferable that the value is less than or equal to / g. If the specific surface area of ​​the photocatalytic material is greater than or equal to the lower limit, a sufficient reaction field necessary for the photocatalytic reaction occurring on the particle surface can be obtained. If the specific surface area of ​​the photocatalytic material is less than or equal to the upper limit, the particle size becomes sufficient to generate the four electrons necessary for the decomposition of water within the same particle, and high catalytic activity can be obtained.

[0029] Specific surface area of ​​photocatalytic material (unit: m²) 2 / g) refers to the BET specific surface area calculated using the BET method. The specific surface area of ​​the photocatalytic material can be measured in the same way as that of the co-catalyst.

[0030] The method for producing the photocatalytic material of this embodiment will now be described. The method for producing the photocatalytic material of this embodiment comprises the steps of: obtaining Ir-doped SrTiO3 particles by a method for producing Ir-doped SrTiO3 particles; and supporting a co-catalyst on the Ir-doped SrTiO3 particles (method for supporting the co-catalyst).

[0031] (Method for manufacturing Ir-doped SrTiO3 particles) The method for producing Ir-doped SrTiO3 particles in this embodiment will be described. Titanium tetraisopropoxide (Ti(iPrO)4) is added to pure water while stirring, and the resulting slurry is filtered under reduced pressure to obtain a white cake. Next, a predetermined amount of the white cake as titanium is added to the reaction vessel, followed by a predetermined amount of strontium hydroxide octahydrate (Sr(OH)2·8H2O) and a predetermined amount of iridium chloride (IrCl3) aqueous solution, and then pure water is added until the total volume reaches a predetermined amount.

[0032] Next, the reaction vessel is heated in an autoclave to a temperature between 120°C and 240°C and maintained for between 1 hour and 48 hours, then allowed to cool naturally to room temperature to obtain an Ir-doped SrTiO3 slurry. Next, the obtained Ir-doped SrTiO3 slurry is subjected to repeated solid-liquid separation and addition of pure water using a centrifuge until the conductivity of the liquid phase is 100 μS / cm or less, and the solid phase is dried to obtain Ir-doped SrTiO3 particles.

[0033] Next, the obtained SrTiO3 particles doped with a predetermined amount of Ir, a predetermined amount of aluminum oxide powder (Al2O3), and a predetermined amount of strontium chloride (SrCl2·6H2O) are mixed in an alumina mortar and pestle, and the mixture is placed in an alumina vessel with a purity of 99.9%. The mixture is then heated in an electric furnace to a temperature between 1000°C and 1200°C for a period of 1 to 6 hours, and held for 1 to 48 hours for flux treatment. An appropriate amount of pure water is added to an aluminium vessel cooled to room temperature to dissolve SrCl2, and the mixture is filtered through a membrane filter. The filtrate is then washed with pure water repeatedly until the conductivity of the filtrate is 100 μS / cm or less.

[0034] (Method for supporting the co-catalyst: photoelectrodeposition) This invention describes a method for supporting a co-catalyst on Ir-doped SrTiO3 particles. A predetermined amount of flux-treated particles and a predetermined amount of pure water are added to a cylindrical container equipped with two branch tubes to suspend and prepare a suspension. Next, while irradiating the suspension with light using a xenon lamp or the like, a predetermined amount of RhCl3 aqueous solution is added to the suspension, then a predetermined amount of K2CrO4 aqueous solution is added, and further, for example, a solution of a predetermined amount of Co(NO3)2 aqueous solution and a predetermined amount of FeSO4 is added to support the co-catalyst on the Ir-doped SrTiO3 particles. This method of loading materials is called photoelectrodeposition.

[0035] (Method of supporting the co-catalyst: Impregnation method) This invention describes a method for supporting a co-catalyst on Ir-doped SrTiO3 particles. A predetermined amount of flux-treated particles and a predetermined amount of pure water are added to a cylindrical container equipped with two branch tubes to suspend and prepare a suspension. Next, while irradiating with light from a xenon lamp or the like, a predetermined amount of RhCl3 aqueous solution is added to the suspension, and then a predetermined amount of K2CrO4 aqueous solution is added. Subsequently, a predetermined amount of powder, filtered through a membrane filter and dried at room temperature, is mixed with a predetermined amount of Co(acac)3 solution prepared using a 10% by mass acetic acid / ethanol solution as a solvent, and a predetermined amount of Ni(acac)2 solution prepared using a 10% by mass acetic acid / ethanol solution as a solvent. This slurry is then dried on a hot plate while being mixed with a glass rod. Next, the dried powder is heat-treated at a temperature of 200°C to 500°C for 0.5 hours to 3 hours to support the co-catalyst. This method of loading is called impregnation.

[0036] (Second embodiment) The photocatalytic material of this embodiment includes iridium (Ir) and antimony (Sb) doped strontium titanate (SrTiO3) particles, and the co-catalyst of the above-described embodiment supported on the strontium titanate particles.

[0037] In SrTiO3 particles doped with Ir and Sb, the amount of Ir doping is preferably 0.01 moles to 5 moles, more preferably 0.01 moles to 3 moles, and even more preferably 0.01 moles to 2 moles, per 100 moles of SrTiO3. If the amount of Ir doping is above the lower limit, visible light can be absorbed sufficiently. If the amount of Ir doping is below the upper limit, the frequency of recombination of excited electron-hole pairs will not be excessive.

[0038] (Method for measuring Ir doping levels) The method for measuring the amount of Ir doping is the same as in the first embodiment.

[0039] (Method for measuring the amount of Sb doping) The method for measuring the amount of Sb doping is the same as the method for measuring the amount of Ir doping.

[0040] The ratio of the amount of Sb doped to the amount of Ir doped (Sb / Ir) is preferably 1 to 5 in molar ratio, more preferably 1 to 4, and even more preferably 1 to 3. When the mass ratio is within the above range, the charge mismatch caused by Ir doping can be balanced, and catalytic activity is improved.

[0041] The amount of co-catalyst supported on Ir and Sb-doped SrTiO3 particles is preferably 0.1 parts by mass or more and 1 part by mass or less, more preferably 0.1 parts by mass or more and 0.5 parts by mass or less, and even more preferably 0.1 parts by mass or more and 0.3 parts by mass or less, per 100 parts by mass of Ir and Sb-doped SrTiO3 particles. If the amount of co-catalyst supported is above the lower limit, the co-catalyst will have the effect of improving photocatalytic activity. If the amount of co-catalyst supported is below the upper limit, it will be absorbed by the co-catalyst, and the reduction in the amount of light irradiated to the semiconductor particles will be negligibly small.

[0042] (Method for measuring the amount of co-catalyst supported) The method for measuring the amount of co-catalyst supported is the same as in the first embodiment.

[0043] In the photocatalyst material of this embodiment, the particle diameter D50 (D50) when the cumulative volume percentage of the dry particle size distribution is 50% is preferably 0.1 μm or more and 10 μm or less, more preferably 0.1 μm or more and 5 μm or less, and even more preferably 0.1 μm or more and 3 μm or less. When D50 is within the above range, the influence of light loss due to scattering can be reduced, and sedimentation of the photocatalyst in the photocatalyst dispersion can be suppressed.

[0044] The above D50 can be measured in the same manner as the cocatalyst.

[0045] The specific surface area of the photocatalyst material of this embodiment is 2 1 m 2 / g or more and 30 m 2 / g or less, preferably 1 m 2 / g or more and 20 m 2 / g or less, and more preferably 1 m 2 / g or more and 15 m

[0046] The specific surface area of the photocatalyst material (unit: m 2 / g) refers to the BET specific surface area determined by the BET method. The specific surface area of the photocatalyst material can be measured in the same manner as the cocatalyst.

[0047] The manufacturing method of the photocatalyst material of this embodiment will be described. The manufacturing method of the photocatalyst material of this embodiment includes a step of obtaining SrTiO3 particles doped with Ir and Sb by a method for manufacturing SrTiO3 particles doped with Ir and Sb, and a step of supporting a cocatalyst on the SrTiO3 particles doped with Ir and Sb (cocatalyst supporting method).

[0048] (Method for manufacturing SrTiO3 particles doped with Ir and Sb) This invention describes a method for producing Ir and Sb-doped SrTiO3 particles. Titanium tetraisopropoxide (Ti(iPrO)4) is added to pure water while stirring, and the resulting slurry is filtered under reduced pressure to obtain a white cake. Next, a predetermined amount of the white cake as titanium is placed in the reaction vessel, followed by a predetermined amount of strontium hydroxide octahydrate (Sr(OH)2·8H2O), a predetermined amount of iridium chloride (IrCl3) aqueous solution, and a predetermined amount of potassium hexahydroxoantimonate (K[Sb(OH)6]) aqueous solution, after which pure water is added until the total volume reaches a predetermined amount.

[0049] Next, the reaction vessel is heated in an autoclave to a temperature between 120°C and 240°C and maintained for 1 hour to 48 hours, then allowed to cool naturally to room temperature to obtain an Ir and Sb-doped SrTiO3 slurry. Next, the obtained Ir and Sb-doped SrTiO3 slurry is subjected to repeated solid-liquid separation and addition of pure water using a centrifuge until the conductivity of the liquid phase is 100 μS / cm or less, and the solid phase is dried to obtain Ir and Sb-doped SrTiO3 particles.

[0050] Next, the obtained SrTiO3 particles doped with a predetermined amount of Ir and Sb, a predetermined amount of aluminum oxide powder (Al2O3), and a predetermined amount of strontium chloride (SrCl2·6H2O) are mixed in an alumina mortar and pestle, placed in an alumina vessel with a purity of 99.9%, and heated in an electric furnace to a temperature of 1000°C to 1200°C for 1 to 6 hours, and held for 1 to 48 hours for flux treatment. An appropriate amount of pure water is added to an aluminium vessel cooled to room temperature to dissolve SrCl2, and the mixture is filtered through a membrane filter. The filtrate is then washed with pure water repeatedly until the conductivity of the filtrate is 100 μS / cm or less.

[0051] (Method of supporting the co-catalyst) Using the electrodeposition or photoelectrodeposition method described above, a co-catalyst is supported on Ir and Sb-doped SrTiO3 particles.

[0052] In this embodiment, the photocatalytic material has superior activity against water oxidation compared to conventional Co oxide cocatalysts, because the cocatalyst of the above embodiment is supported on Ir-doped SrTiO3 particles.

[0053] [Dispersion] The dispersion of this embodiment includes the photocatalytic material of the above embodiment and a solvent. The dispersion of this embodiment also includes a paste-like dispersion with high viscosity.

[0054] The content of the photocatalytic material in relation to the total mass of the dispersion in this embodiment is not particularly limited and can be arbitrarily selected, but for example, it is preferably 1% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 40% by mass or less, and even more preferably 1% by mass or more and 30% by mass or less. If the content of the photocatalytic material in the above dispersion is within the above range, it is possible to reduce the amount of dispersion solvent used and suppress aggregation of the photocatalytic material at the same time.

[0055] The dispersion medium is selected appropriately depending on the application of the dispersion. Suitable dispersion mediums are exemplified below, but the dispersion medium in this embodiment is not limited to these. The dispersion mediums listed below may be used individually or in combination from the examples below. Examples of dispersion media include alcohols such as water, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, octanol, and glycerin; esters such as ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, and γ-butyrolactone; and ethers such as diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, and diethylene glycol monoethyl ether. These are preferably used. These dispersion media may be used individually or in combination of two or more.

[0056] Other dispersion media include, for example, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, and cyclohexanone; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; cyclic hydrocarbons such as cyclohexane; amides such as dimethylformamide, N,N-dimethylacetacetamide, and N-methylpyrrolidone; and linear polysiloxanes such as dimethylpolysiloxane, methylphenylpolysiloxane, and diphenylpolysiloxane. These are suitably used. These dispersion media may be used individually or in combination of two or more.

[0057] Furthermore, other dispersion media that can be suitably used include, for example, cyclic polysiloxanes such as octamethylcyclotetrasiloxane, cyclopentasiloxane, and dodecamethylcyclohexasiloxane; and modified polysiloxanes such as amino-modified polysiloxane, polyether-modified polysiloxane, alkyl-modified polysiloxane, and fluorine-modified polysiloxane. These dispersion media may be used individually or in combination of two or more.

[0058] Other dispersion media different from those mentioned above include, for example, hydrocarbon oils such as liquid paraffin, squalane, isoparaffin, branched light paraffin, petrolatum, and ceresin; ester oils such as isopropyl myristate, cetyl isooctanoate, and glyceryl trioctanoate; silicone oils such as cyclopentasiloxane, dimethylpolysiloxane, and methylphenylpolysiloxane; higher fatty acids such as lauric acid, myristic acid, palmitic acid, and stearic acid; and higher alcohols such as lauryl alcohol, cetyl alcohol, stearyl alcohol, hexyldodecanol, and isostearyl alcohol. These dispersion media may be used individually or in combination of two or more.

[0059] The dispersion of this embodiment may contain commonly used additives, to the extent that it does not impair its properties. Examples of additives include dispersants, surfactants, stabilizers, water-soluble binders, thickeners, oil-soluble preservatives, UV absorbers, oil-soluble drugs, oil-soluble dyes, oil-soluble proteins, vegetable oils, animal oils, and the like. These additives may be included in amounts that can be selected at will.

[0060] The dispersion in this embodiment can be an aqueous dispersion containing the photocatalytic material of the above embodiment and an aqueous dispersion containing water. The aqueous dispersion of this embodiment may optionally contain additives commonly used in aqueous cosmetics, such as surfactants, dispersants, stabilizers, water-soluble binders, thickeners, alcohols, chelating agents, and solvents. For example, the aqueous dispersion may contain ethylenediaminetetraacetic acid (EDTA) in an amount of 0.01% to 1.0% by mass, relative to the total mass, as a pH stabilizer. Furthermore, the aqueous dispersion of this embodiment may also contain a nonionic surfactant.

[0061] The method for producing the dispersion of this embodiment is not particularly limited, but one example is to mechanically disperse the photocatalytic material of the above embodiment and the dispersion medium using a known dispersion apparatus. Examples of dispersion devices include agitators, orbital mixers, homomixers, ultrasonic homogenizers, sand mills, ball mills, and roll mills.

[0062] The dispersion of this embodiment can be preferably used for the formation of a coating film (photocatalytic film) having photocatalytic function.

[0063] [Composition] The composition of this embodiment comprises the dispersion of the above-described embodiment and a binder.

[0064] The content of the dispersion relative to the total mass of the composition of this embodiment may be adjusted as appropriate to suit the desired properties. The content of the dispersion is preferably, for example, 1% by mass or more and 80% by mass or less, more preferably 5% by mass or more and 70% by mass or less, and even more preferably 10% by mass or more and 70% by mass or less. By keeping the content of the dispersion within the above range relative to the total mass of the above composition, it is possible to achieve both a sufficient amount of photocatalytic material to obtain the desired film thickness and adhesion by the binder.

[0065] The binder is not particularly limited as long as it is a resin commonly used in industrial applications, but examples include acrylic resin, epoxy resin, urethane resin, polyester resin, silicone resin, and water-soluble polymers. The binder content in the composition of this embodiment is not particularly limited and can be adjusted as appropriate depending on the desired properties of the composition.

[0066] The composition of this embodiment may contain commonly used additives, to the extent that they do not impair its properties. Examples of additives include polymerization initiators, dispersants, and preservatives.

[0067] The method for producing the composition of this embodiment is not particularly limited, but one example is to mechanically mix the dispersion of the above-described embodiment and a binder using a known mixing device. Examples of mixing devices include agitators, self-rotating mixers, homomixers, and ultrasonic homogenizers.

[0068] [coating film] (First embodiment) The coating film in this embodiment is the dried product of the dispersion liquid of the above-described embodiment.

[0069] The thickness of the coating film in this embodiment is preferably 0.1 μm to 100 μm, preferably 1 μm to 50 μm, and more preferably 5 μm to 30 μm. By having the coating film thickness in this embodiment within the above range, it is possible to achieve both sufficient absorption of irradiated light and suppression of excessive use of photocatalytic material.

[0070] (Method for measuring coating thickness) The thickness of the coating can be measured from images observed using a transmission electron microscope (TEM). Alternatively, the thickness of the coating film in this embodiment may be determined by measuring the film thickness at five locations in the TEM image observing the film thickness and taking the arithmetic mean of those measurements. Preferably, the five measurement locations are one point each in areas with thick film thickness, one point in areas with thin film thickness, and three points in areas with medium film thickness.

[0071] (Method for forming a coating film) The coating film of this embodiment can be formed by applying the dispersion liquid of the above embodiment to an object such as a substrate, and then drying the dispersion liquid applied to the object. Methods for applying the dispersion include, for example, roll coating, flow coating, spray coating, screen printing, brush coating, and immersion.

[0072] Methods for drying the dispersion applied to the object include, for example, a box-type dryer, a hot-air box-type dryer, a conveyor-type dryer, a conveyor-type microwave dryer, and the like.

[0073] The coating film of this embodiment can be used as a photocatalytic film.

[0074] (Second embodiment) The coating film of this embodiment is a cured product of the composition of the above-described embodiment.

[0075] The thickness of the coating film in this embodiment is preferably 0.1 μm to 100 μm, preferably 1 μm to 50 μm, and more preferably 5 μm to 30 μm. By having the coating film thickness in this embodiment within the above range, it is possible to achieve both sufficient absorption of irradiated light and suppression of excessive use of photocatalytic material.

[0076] (Method for measuring coating thickness) The thickness of the coating can be measured from images observed using a transmission electron microscope (TEM). Alternatively, the thickness of the coating film in this embodiment may be determined by measuring the film thickness at five locations in the TEM image observing the film thickness and taking the arithmetic mean of those measurements. Preferably, the five measurement locations are one point each in areas with thick film thickness, one point in areas with thin film thickness, and three points in areas with medium film thickness.

[0077] (Method for forming a coating film) The coating film of this embodiment can be formed by applying the composition of the above-described embodiment to an object such as a substrate, and then curing the composition applied to the object. Methods for applying the composition include, for example, roll coating, flow coating, spray coating, screen printing, brush coating, and immersion.

[0078] Methods for curing a composition applied to an object include, for example, heat treatment and ultraviolet irradiation.

[0079] The coating film of this embodiment can be used as a photocatalytic film.

[0080] [Base material] The substrate of this embodiment has the coating film of the embodiment described above. In other words, the substrate of this embodiment has a base substrate and a coating film formed on one main surface of the base substrate.

[0081] The base material is not particularly limited, but examples include plastic substrates such as polyester film, metal substrates made of various metals, and glass substrates.

[0082] The thickness of the base material can be adjusted as appropriate depending on the application of the material.

[0083] The thickness of the coating film is preferably 0.1 μm to 100 μm, preferably 1 μm to 50 μm, and more preferably 5 μm to 30 μm. By having the coating film thickness in this embodiment within the above range, it is possible to achieve both sufficient absorption of irradiated light and suppression of excessive use of photocatalytic material.

[0084] The thickness of the coating film on the substrate in this embodiment can be measured in the same way as the coating film in the embodiments described above.

[0085] The coating film on the substrate in this embodiment can be formed in the same manner as the coating film in the embodiments described above.

[0086] The substrate of this embodiment can be used as a photocatalytic substrate. [Examples]

[0087] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0088] [Example 1] (Synthesis of Ir and Sb-doped SrTiO3 particles) A slurry obtained by adding 150g of titanium tetraisopropoxide (Ti(iPrO)4, manufactured by Kanto Chemical Co., Ltd.) to 1000g of pure water while stirring was subjected to vacuum filtration using a 90mm diameter filter paper (Advantec 5A) to obtain a white cake. Next, a white cake containing 0.45 moles of titanium was added to a 2000 ml container, along with 0.47 moles of strontium hydroxide octahydrate (Sr(OH)2·8H2O, manufactured by Kanto Chemical Co., Ltd.) and 4.5 × 10⁻¹⁶ iridium. -5 As moles (0.01 mol%) of titanium, an aqueous solution of iridium chloride (IrCl3, manufactured by Kanto Chemical Co., Ltd.) and 9.0 × 10⁻⁶ antimony are used. -5 An aqueous solution of potassium hexahydroxoantimonate (K[Sb(OH)6], manufactured by Nacalai Tesque) was added at a molar ratio (0.02 mol%) relative to titanium, and then pure water was added until the total volume reached 900 g. Next, the container was heated to 200°C in an autoclave (SR-200, manufactured by Suzuki Rika Seisakusho Co., Ltd.) and held for 8 hours, then naturally cooled to room temperature. The resulting Ir and Sb-doped SrTiO3 slurry was then subjected to repeated solid-liquid separation and addition of pure water using a centrifuge until the conductivity of the liquid phase was 100 μS / cm or less, and the solid phase was dried to obtain Ir and Sb-doped SrTiO3 particles. Next, 1 g of the obtained Ir and Sb-doped SrTiO3 particles, 0.011 g of aluminum oxide powder (Al2O3, manufactured by Wako Pure Chemical Industries, Ltd.), and 14.5 g of strontium chloride (SrCl2·6H2O, manufactured by Kanto Chemical Co., Ltd.) were mixed in an alumina mortar and pestle, and the mixture was placed in an alumina vessel with a purity of 99.9%. The mixture was then heated to 1150°C in an electric furnace for 3 hours and held for 10 hours for flux treatment. An appropriate amount of pure water was added to an aluminium vessel cooled to room temperature to dissolve SrCl2, and the mixture was filtered through a membrane filter. Washing with pure water was repeated until the conductivity of the filtrate was 100 μS / cm or less.

[0089] (Supporting of co-catalysts) A suspension was prepared by placing 0.2 g of flux-treated particles and 100 ml of pure water into a cylindrical container made of Pyrex® glass with an inner diameter of 65 mm and equipped with two branch tubes. Next, while irradiating with light from a 300W xenon lamp (Eagle Engineering CX-05E), a 0.02 mol / L RhCl3 aqueous solution was added, with an Rh equivalent of 2 × 10⁻⁶.-4 Add g, then add 1 / 30 mol / L K2CrO4 aqueous solution, which is 1 × 10 in terms of Cr. -4 g was added, and then a 0.02 mol / L Co(NO3)2 aqueous solution was added, which was converted to Co equivalent to 2 × 10⁻¹⁰ g. -5 g and 0.02 mol / L FeSO4 are converted to Fe equivalent to 8 × 10 -5 A solution mixed to a concentration of g was added to support the co-catalyst on Ir and Sb-doped SrTiO3 particles.

[0090] [Example 2] A 0.02 mol / L Co(NO3)2 aqueous solution is converted to 8 × 10⁻¹⁰ Co₀. -5 g and 0.02 mol / L FeSO4 are converted to Fe equivalent to 2 × 10 -5 A co-catalyst was supported on Ir and Sb-doped SrTiO3 particles in the same manner as in Example 1, except that a solution mixed to the ratio g was used.

[0091] [Example 3] A co-catalyst was supported on Ir-doped SrTiO3 particles in the same manner as in Example 1, except that Ir-doped SrTiO3 particles were prepared without the addition of antimony.

[0092] [Example 4] (Supporting of co-catalysts) A suspension was prepared by placing 0.3 g of flux-treated particles and 100 ml of pure water into a cylindrical container made of Pyrex® glass with an inner diameter of 65 mm and equipped with two branch tubes. Next, while irradiating with light from a 300W xenon lamp (Eagle Engineering CX-05E), a 0.02 mol / L RhCl3 aqueous solution was added, with a Rh equivalent of 3 × 10⁻⁶. -4 Add the amount to g, then add a 1 / 30 mol / L K2CrO4 aqueous solution, which is equivalent to 1.5 × 10 in terms of Cr. -4 g was added. Subsequently, 0.25 g of the powder, filtered through a membrane filter and dried at room temperature, was used as a solvent to prepare a solution of 10% by mass acetic acid / ethanol, yielding 2.5 × 10⁻⁶ CO equivalent. -5A solution of 0.02 mol / L of Co(acac)3 containing g of nitrogen was prepared using a 10% by mass acetic acid / ethanol solution as the solvent, resulting in a Ni equivalent of 1 × 10⁻⁶. -4 A slurry prepared by mixing g of Ni(acac) with a 0.02 mol / L Ni(acac)2 solution was dried on a hot plate while being stirred with a glass rod. Next, the dried powder was heat-treated at 400°C for 1 hour to support the co-catalyst on Ir and Sb-doped SrTiO3 particles.

[0093] [Example 5] A 10% by mass acetic acid / ethanol solution was prepared as the solvent, resulting in a CO equivalent of 1 × 10⁻⁶. -4 g of 0.02 mol / L Co(acac)3 solution and 2.5 × 10 in terms of Ni equivalent -5 A co-catalyst was supported on Ir and Sb-doped SrTiO3 particles in the same manner as in Example 3, except that a 0.02 mol / L Ni(acac)2 solution prepared using a 10% by mass acetic acid / ethanol solution of g was mixed as the solvent.

[0094] [Example 6] A 10% by mass acetic acid / ethanol solution was used as the solvent, yielding 4.2 × 10⁻¹⁰ CO equivalent. -5 A solution of 0.02 mol / L of Co(acac)3 containing g of acetic acid was prepared using a 10% by mass acetic acid / ethanol solution as the solvent, resulting in a Ni equivalent of 4.2 × 10⁻⁶. -5 A 0.02 mol / L Ni(acac)2 solution containing g of iron was prepared using a 10% by mass acetic acid / ethanol solution as the solvent, yielding 4.2 × 10⁻⁶ Fe equivalents. -5 The co-catalyst was supported on Ir and Sb-doped SrTiO3 particles in the same manner as in Example 3, except that it was mixed with a 0.02 mol / L Fe(acac)3 solution of g.

[0095] [Comparative Example 1] 1 × 10 in CO equivalent -4 A co-catalyst was supported on Ir and Sb-doped SrTiO3 particles in the same manner as in Example 1, except that g of 0.02 mol / L Co(NO3)2 aqueous solution was added.

[0096] [Comparative Example 2] A 10% by mass acetic acid / ethanol solution was used as the solvent to prepare 1.3 × 10⁻¹⁰ CO equivalents. -4 The co-catalyst was supported on Ir and Sb-doped SrTiO3 particles in the same manner as in Example 3, except that g of 0.02 mol / L Co(acac)3 solution was mixed.

[0097] [Comparative Example 3] Except for preparing Ir-doped SrTiO3 particles without adding antimony, the co-catalyst was supported on Ir-doped SrTiO3 particles in the same manner as in Comparative Example 1.

[0098] [Comparative Example 4] A 10% by mass acetic acid / ethanol solution was used as the solvent, yielding 1.3 × 10⁻¹⁶ Fe equivalents. -4 The co-catalyst was supported on Ir and Sb-doped SrTiO3 particles in the same manner as in Example 3, except that g of 0.02 mol / L Fe(acac)3 solution was mixed.

[0099] [Comparative Example 5] A 10% by mass acetic acid / ethanol solution was used as the solvent to prepare a Ni equivalent of 1.3 × 10⁻⁶. -4 The co-catalyst was supported on Ir and Sb-doped SrTiO3 particles in the same manner as in Example 3, except that g of 0.02 mol / L Ni(acac)2 solution was mixed.

[0100] [Water splitting activity measurement] For Examples 1 and 2 and Comparative Example 1, after supporting the co-catalyst, an argon gas cylinder was connected to one end of the branch tube via a mass flow controller (CU-2130, Horiba, Ltd.), and the other end of the branch tube was connected to a gas chromatograph (GAS-5000, Yanaco Technical Science Co., Ltd.) to seal the cylindrical container. A mass flow controller was used to measure 50 mL·m³. -1 After removing dissolved nitrogen and oxygen from the water by passing adjusted argon gas through it for one hour, the hydrogen generated by irradiating it with light from a xenon lamp was quantified using a gas chromatograph. For Examples 3, 4, 5, and 6, and Comparative Examples 2, 3, 4, and 5, 0.2 g of particles supporting the co-catalyst and 100 ml of pure water were placed in a cylindrical container made of Pyrex® glass with an inner diameter of 65 mm and equipped with two branch tubes, and suspended. An argon gas cylinder was connected to one of the branch tubes via a mass flow controller (CU-2130, Horiba, Ltd.), and the other branch tube was connected to a gas chromatograph (GAS-5000, Yanaco Technical Science Co., Ltd.), and the cylindrical container was sealed. A mass flow controller was used to measure 50 mL·m³. -1 After removing dissolved nitrogen and oxygen from the water by passing adjusted argon gas through it for one hour, the hydrogen generated by irradiating it with light from a xenon lamp was quantified using a gas chromatograph. The results are shown in Table 1.

[0101] [Table 1]

[0102] The results shown in Table 1 confirm that the photocatalytic materials in Examples 1-6 had a higher hydrogen generation rate than the photocatalytic materials in Comparative Examples 1-5.

Claims

1. A co-catalyst for a visible light-responsive photocatalyst, comprising cobalt and at least one of iron and nickel.

2. A photocatalytic material comprising iridium-doped strontium titanate particles and the co-catalyst according to claim 1 supported on the strontium titanate particles.

3. A photocatalytic material comprising iridium and antimony-doped strontium titanate particles and the co-catalyst according to claim 1 supported on the strontium titanate particles.

4. A dispersion comprising the photocatalytic material according to claim 2 or 3 and a solvent.

5. A composition comprising the dispersion according to claim 4 and a binder.

6. A coating film which is a dried product of the dispersion described in claim 4.

7. A coating film which is a cured product of the composition described in claim 5.

8. A substrate having the coating film described in claim 6.

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