CN105451882A - Photocatalyst and photocatalyst dispersion using same, photocatalyst coating, photocatalyst film, and product - Google Patents

Abstract

The photocatalyst according to the embodiment includes tungsten oxide-based fine particles containing tungsten oxide in an amount ranging from 5% by mass to 100% by mass. In the Raman spectrum of the photocatalyst measured by Raman spectroscopy, the intensity X of the peak observed in the range of 920 cm ^-1 to 950 cm ^-1 is different from that observed in the range of 800 cm ^-1 to 810 cm ^-1 The peak intensity Y ratio (X/Y) ranges from more than 0 to less than 0.04.

Description

Photocatalyst, photocatalyst dispersion using same, photocatalyst coating, photocatalyst film and product

technical field

Embodiments of the present invention relate to a photocatalyst, a photocatalyst dispersion using the photocatalyst, a photocatalyst coating, a photocatalyst film, and a product.

Background technique

Titanium oxide is known as a photocatalytic material for antifouling and deodorizing applications. Photocatalyst materials are used in various fields such as indoor and outdoor building materials, home appliances such as lighting devices, air cleaners, and air conditioners, toilets, wash basins, mirrors, and bathrooms. However, titanium oxide causes excitation only in the ultraviolet region, and therefore, sufficient photocatalytic performance cannot be obtained in a room with less ultraviolet rays. Therefore, research and development of visible light-responsive photocatalysts that exhibit photocatalytic performance even under visible light are underway. In addition, in order to improve the visible light photocatalytic performance of ultraviolet-responsive titanium oxide, it is being studied to dope nitrogen or sulfur or to support other metals in titanium oxide.

Tungsten oxide is known as a visible light-responsive photocatalyst. A photocatalyst film using tungsten oxide is formed, for example, by applying a dispersion liquid containing tungsten oxide fine particles to the surface of a substrate of a product to be imparted with photocatalytic performance. As a photocatalyst dispersion liquid, for example, an aqueous dispersion liquid formed by dispersing tungsten oxide fine particles having an average primary particle diameter (D50) in the range of 1 to 400 nm in water or the like so that the pH thereof is in the range of 1.5 to 6.5 is known. . With such an aqueous dispersion liquid, the dispersibility of the tungsten oxide fine particles can be improved, and the formability of the film containing the tungsten oxide fine particles can be improved. Therefore, a photocatalyst film capable of stably exhibiting the photocatalytic performance of the tungsten oxide fine particles can be obtained.

The photocatalyst that can improve the visible light response performance of titanium oxide has a photocatalytic activity proportional to the amount of light. Therefore, sufficient photocatalytic performance cannot be obtained only with the amount of light under the illuminance of indoor lighting (about 1x to 3000lx). Therefore, in the living space where photocatalyst is expected to be applied, the effect can only be achieved in places near or directly below the lighting source. A conventional photocatalyst film containing tungsten oxide fine particles exhibits a gas decomposition rate of 5% or more in an environment where the illuminance of visible light is about 2000 lx, for example. However, considering the practicability of the photocatalyst film, since the performance of decomposing harmful gases such as acetaldehyde is not necessarily sufficient, it is required to improve the performance of decomposing gases under low illuminance. In addition, the conventional photocatalyst film containing tungsten oxide fine particles has a weak adsorption force to gas, so the decomposition rate of gas becomes slow in an environment with low gas concentration, which is a current problem. Therefore, it is demanded that visible light-responsive photocatalysts have high performance in decomposing gas.

prior art literature

patent documents

Patent Document 1: International Publication No. 2008/117655

Patent Document 2: International Publication No. 2009/031317

Patent Document 3: International Publication No. 2009/110234

Contents of the invention

The problem to be solved by the present invention is to provide a photocatalyst that exhibits good photocatalytic performance such as gas decomposition ability even in an environment with low illuminance of visible light or an environment with low gas concentration, and a photocatalyst using the photocatalyst. Catalyst dispersion, photocatalyst coating, photocatalyst film and products.

The photocatalyst according to the embodiment includes tungsten oxide-based fine particles containing tungsten oxide in the range of 5% by mass or more to 100% by mass or less. In the Raman spectrum of the photocatalyst measured by Raman spectroscopy, the intensity X of the peak observed in the range from 920 cm ^-1 to 950 cm ^-1 is the same as that observed in the range from 800 cm ^-1 to 810 cm ^-1 The ratio (X/Y) of the intensity Y of the peak is in the range of more than 0 to 0.04 or less.

Description of drawings

FIG. 1 is a graph showing Raman spectra of samples A (comparative example), sample D (example), and sample F (comparative example) in the production examples of tungsten oxide fine particles.

detailed description

Next, the photocatalyst, the photocatalyst dispersion liquid, the photocatalyst paint, the photocatalyst film, and the aspect of a product for carrying out this invention are demonstrated.

(catalyst of light)

The photocatalyst according to the embodiment includes tungsten oxide-based fine particles, and contains tungsten oxide within a range of 5 to 100% by mass. Examples of the tungsten oxide-based microparticles constituting the photocatalyst include single microparticles of tungsten oxide, or microparticles such as mixtures or composites of tungsten oxide and other metal elements. In the photocatalyst of the embodiment, the content of tungsten oxide is in the range of 5 to 100% by mass. If the content of tungsten oxide is less than 5% by mass, visible light-responsive photocatalytic performance based on tungsten oxide fine particles cannot be sufficiently obtained. The content of tungsten oxide is preferably 45% by mass or more.

The photocatalyst of the embodiment may contain metal elements other than tungsten (hereinafter referred to as "additional metal elements"). Examples of the metal element contained in the photocatalyst include transition metal elements other than tungsten, zinc group elements such as zinc, and earth group metal elements such as aluminum. Transition metal elements refer to elements with atomic numbers 21-29, 39-47, 57-79, and 89-109, and metal elements other than tungsten (atomic number 74) among these transition metals may be contained in the photocatalyst. Zinc group elements are elements with atomic numbers 30, 48, and 80, and earth group metal elements are elements with atomic numbers 13, 31, 49, and 81. These metal elements may also be contained in the photocatalyst. By making the photocatalyst contain an appropriate range of metal elements, the visible light-responsive photocatalytic performance of the photocatalyst can be improved.

In the photocatalyst, the content of the added metal element is preferably in the range of 0.001 to 50% by mass. If the content of the added metal element is less than 0.001% by mass, the effect of sufficiently improving the photocatalytic performance cannot be obtained. If the content of the added metal element is greater than 50% by mass, the content of tungsten oxide will be relatively reduced, which may reduce the photocatalytic performance based on the tungsten oxide particles. The content of the added metal element is more preferably in the range of 0.005 to 10% by mass. The photocatalytic performance of the photocatalyst of embodiment can be improved effectively by making a photocatalyst contain the added metal element in the said range.

The metal element (added metal element) that can be contained in the photocatalyst is preferably selected from titanium (Ti), zirconium (Zr), manganese (Mn), iron (Fe), ruthenium (Ru), nickel (Ni), palladium (Pd ), platinum (Pt), copper (Cu), silver (Ag), cerium (Ce) and aluminum (Al). The photocatalytic performance of the photocatalyst of embodiment can be improved more effectively by making a photocatalyst contain the said metal element in the range of 0.005-10 mass %.

Metal oxides are mentioned as a representative example of the form in which the metal element is added to the photocatalyst. The photocatalyst preferably contains an oxide of an added metal element other than tungsten oxide. In the photocatalyst, the content of the oxide of the added metal element is preferably in the range of 0.01 to 70% by mass. By making the photocatalyst contain the oxide of the added metal element within this range, the photocatalytic performance of the photocatalyst can be further improved. The oxide to which the metal element is added is more preferably at least one selected from zirconium oxide, titanium oxide, and ruthenium oxide. By making the photocatalyst contain such a metal oxide, photocatalytic performance can be improved more effectively. The content of metal oxides other than tungsten oxide in the photocatalyst is more preferably in the range of 0.02 to 55% by mass.

In the photocatalyst of the embodiment, the additional metal element may be contained in various forms. The photocatalyst may contain the added metal element in the form of a single substance of the added metal element, a compound such as an oxide, or a composite compound with tungsten oxide. Adding a metal element may form a composite oxide from two or more metal elements. Furthermore, simple substances or compounds of added metal elements may be supported on tungsten oxide. Alternatively, tungsten oxide may be supported on a compound or the like to which a metal element is added.

Specific examples of tungsten oxide-based particles containing added metal elements include mixtures of tungsten oxide particles and elemental particles (metal particles) or compound particles of added metal elements, simple substances or compounds of tungsten oxide and added metal elements, etc. Formed mixture particles, alloy particles formed by tungsten oxide and simple substances or compounds of added metal elements, composite compound particles formed by tungsten oxide and simple substances or compounds of added metal elements, tungsten oxide and simple substances or compounds of added metal elements, etc. carrier particles, etc. These fine particles are merely examples of tungsten oxide-based fine particles, and the photocatalyst of the embodiment is not limited thereto.

When the photocatalyst of the embodiment contains an additional metal element, there is no particular limitation on the method of combining tungsten oxide and the additional metal element. When mixing or compounding tungsten oxide and added metal elements, the method of mixing tungsten oxide powder with elemental powder (metal powder) or compound powder (such as metal oxide powder) of added metal elements can be used to make at least one Solutions, dispersions, sols, etc. are further mixed, impregnated, supported, and other mixing or compounding methods. For example, when the metal oxide to be added is zirconia, zirconia in various shapes can be used, but the primary particle is preferably rod-shaped. It is preferable to mix a zirconia sol having particles of rod-shaped primary particles aggregated with tungsten oxide fine particles or a dispersion obtained by dispersing them in water or the like.

The photocatalyst of the embodiment may contain metal elements and the like as trace impurities. The content of metal elements as impurity elements is preferably 2% by mass or less. Examples of impurity metal elements include elements generally contained in tungsten ores, or contamination elements mixed in when producing tungsten compounds used as raw materials, and the like. Examples of impurity metal elements include Fe, Mo, Mn, Cu, Ti, Al, Ca, Ni, Cr, Mg, and the like. However, when using these elements as an additive metal element, it is not limited to this.

The photocatalyst according to the embodiment has the following characteristics when the fine structure such as crystallinity and surface state is analyzed by Raman spectroscopy. In the Raman spectrum as a result of measuring the photocatalyst by Raman spectroscopy, the intensity X of the peak observed in the range of 920 to 950 cm ^-1 and the intensity of the peak observed in the range of 800 to 810 cm ^-1 The ratio of Y (X/Y) is in the range of 0<X/Y≦0.04. When the photocatalyst has the intensity ratio (X/Y) of the Raman peak, the photocatalytic performance such as the ability to decompose gas of the photocatalyst based on the tungsten oxide fine particles can be improved. Specifically, even in an environment with low illuminance of visible light or an environment with low gas concentration, good photocatalytic performance such as decomposing ability to gas can be obtained.

That is, the tungsten oxide fine particles exhibit photocatalytic performance such as the ability to decompose gas under the irradiation of visible light. However, in an environment with low visible light illumination, the photocatalytic performance of tungsten oxide cannot be fully exerted. Furthermore, as the gas concentration gradually decreases from the initial concentration, the rate of decomposition of gas by tungsten oxide becomes slower. This is considered to be due to the decrease in the decomposition performance of tungsten oxide for intermediate substances generated when gas is decomposed, and the decrease in the adsorption capacity of tungsten oxide for gas in an environment with low gas concentration. The inventors of the present invention have found that if it is necessary to improve the decomposition ability of tungsten oxide to gas and the decomposition performance of tungsten oxide to intermediate substances under the irradiation of low-illuminance visible light, and the adsorption force of tungsten oxide to gas at low concentrations, the Raman spectrum It is effective to set the peak intensity ratio (X/Y) in the range of 0<X/Y≤0.04.

The peak intensity ratio (X/Y) in the Raman spectrum indicates the crystallinity of the tungsten oxide-based fine particles, the state of surface defects, and the like. By controlling the peak intensity ratio (X/Y) in the range of greater than 0 to less than 0.04, the photocatalytic activity of the photocatalyst (tungsten oxide-based microparticles) can be effectively improved. When the peak intensity ratio (X/Y) is zero, even if the crystallinity of the tungsten oxide fine particles is improved, the surface of the tungsten oxide fine particles can hardly be brought into a state of oxygen deficiency or the like. In this state, a high gas decomposition ability cannot be obtained. The peak intensity ratio (X/Y) is more preferably 0.001 or more. If the peak intensity ratio (X/Y) is greater than 0.04, the amount of surface defects such as oxygen deficiency increases too much, and the photocatalytic activity decreases instead, so high gas decomposition performance cannot be obtained. The peak intensity ratio (X/Y) is more preferably 0.03 or less.

When the intensity ratio (X/Y) of the Raman peak of the photocatalyst is in the range of greater than 0 to less than 0.04, the crystallization state or surface state (existence of surface defects, etc.) of the tungsten oxide-based particles can be controlled as state suitable for photocatalysis. Therefore, the gas decomposition performance of the tungsten oxide-based microparticles under the condition of low-illuminance visible light can be improved. Furthermore, in a state where the gas concentration is low, the decomposition performance of the tungsten oxide-based fine particles for intermediate substances and the adsorption force for gas can be improved. According to the photocatalyst of the embodiment, even in an environment with low illuminance of visible light and an environment with low gas concentration, high gas decomposition performance can be exhibited. In addition, the photocatalyst of the embodiment exhibits its gas decomposition performance even in an ultraviolet irradiation environment. According to the photocatalyst of the embodiment, it is possible to exhibit its gas decomposition performance under a wider range of conditions than conventional photocatalysts. Thereby, the photocatalyst which can improve practicality can be provided.

The intensity ratio (X/Y) of the Raman peak of the above-mentioned photocatalyst can be obtained by controlling the heat treatment conditions, such as heat treatment atmosphere and heat treatment temperature, etc. after the production of tungsten oxide-based fine particles. Furthermore, since the surface state and the like of the tungsten oxide-based fine particles vary with the ambient temperature and the like in the storage state, by adjusting these conditions, the intensity ratio (X/Y) of the Raman peak can be maintained in an appropriate range. As will be described in detail later, the temperature of the heat treatment performed after the production of the tungsten oxide-based fine particles is preferably in the range of 200 to 800°C. Furthermore, in order to adjust the crystallinity and surface state of the tungsten oxide-based fine particles to an appropriate state, it is preferable to control the rate of temperature increase and rate of temperature decrease during the heat treatment.

Regarding the crystallinity of tungsten oxide, the higher the crystallinity, the more the photocatalytic performance can be improved. However, if the heat treatment is performed under conditions that excessively increase the crystallinity of tungsten oxide, the crystal grains of tungsten oxide will grow and the specific surface area of the fine particles will decrease. Furthermore, if the crystallinity of tungsten oxide is too high, the surface of the fine particles will be in a state where there are almost no surface defects such as oxygen deficiency. These are the main factors that degrade the photocatalytic performance of the photocatalyst. Taking this into consideration, by controlling the intensity ratio (X/Y) of the Raman peak of the photocatalyst in the range of more than 0 to less than 0.04, the crystallinity of tungsten oxide, the surface state of the particles, and the particle size can be adjusted to an appropriate level. status. Therefore, it is possible to provide a photocatalyst which is excellent in photocatalytic performance, such as the ability to decompose gas, and whose practicality is further improved.

In the tungsten oxide-based microparticles constituting the photocatalyst of the embodiment, the peak intensity ratio (X/Y) of the Raman spectrum is in the range of greater than 0 to 0.04 or less. In addition, it is preferable that the Raman spectrum of the photocatalyst has a range of 268 to 274 cm. The first peak (the peak with the largest peak intensity ratio) in the range of ^-1 , the second peak (the peak with the second largest peak intensity ratio) in the range of 630 to 720 cm ^-1 , and the peak in the range of 800 to 810 cm ^- The 3rd peak (the peak with the 3rd largest peak intensity ratio) existing in the range of ¹ .

Furthermore, the half width of the first peak is preferably in the range of 8 to 25 cm ⁻¹ . The half width of the second peak is preferably in the range of 15 to 75 cm ⁻¹ , and the half width of the third peak is preferably in the range of 15 to 50 cm ⁻¹ . These Raman peaks show that the crystal structure of tungsten oxide crystals includes at least one kind selected from monoclinic crystals, triclinic crystals, and orthorhombic crystals, and the crystals shown are especially suitable for visible light-responsive photocatalysts. structure. The use of tungsten oxide-based microparticles having such a crystal structure can stably exhibit excellent photocatalytic performance.

The Raman spectrum of the embodiment is measured using an Ar ion laser with a wavelength of 514.5 nm under conditions of a temperature of 20 to 30° C. and a humidity of 30 to 70%. For the peak intensity of the Raman spectrum, the peak intensity X is the zero point of the straight line drawn from the spectral value with a wavenumber of 900cm ^-1 and the spectral value of 1000cm ^-1 , and the peak intensity Y is the zero point with a spectral value of 1000cm ^-1 , set as the intensity from these two zeros to the apex of the peak. Specifically, the intensity X to the maximum peak apex existing in the range of 920 to 950 cm ^-1 and the intensity Y to the maximum peak apex existing in the range of 800 to 810 cm ^-1 are measured, and the intensity X and intensity Y are obtained from these The intensity ratio (X/Y) of the peak.

Tungsten oxide constituting the photocatalyst is preferably composed mainly of WO ₃ (tungsten trioxide). Although tungsten oxide is preferably basically composed of WO ₃ , other tungsten oxides (WO ₂ , WO, W ₂ O ₃ , W ₄ O ₅ , W ₄ O ₁₁ , etc.). The average particle diameter (D50) of the tungsten oxide-based fine particles is preferably 1 nm or more and 30 μm or less. The average particle diameter (D50) of the tungsten oxide-based fine particles is more preferably 50 nm or more and 1 μm or less. Regarding the particle size distribution of the tungsten oxide-based fine particles, the D90 diameter is preferably 0.05 to 10 μm. The BET specific surface area of the tungsten oxide-based fine particles is preferably 4.1 to 820 m ² /g, more preferably 10 to 300 m ² /g.

The photocatalyst dispersion liquid can be produced by mixing tungsten oxide-based fine particles with an aqueous dispersion medium as described later, and dispersing it with an ultrasonic disperser, wet jet mill, ball mill, or the like. In the photocatalyst dispersion thus obtained, the photocatalyst including the tungsten oxide-based fine particles contains aggregated particles formed by aggregating primary particles. When aggregated particles are included and the particle size distribution is measured by a wet-type laser diffraction particle size distribution meter, etc., if the D50 diameter in the cumulative particle size based on volume is 1 nm or more and 30 μm or less, a good dispersion state and uniformity can be obtained. And stable film formability, as a result, high photocatalytic performance can be obtained.

If the D50 diameter of the tungsten oxide-based fine particles exceeds 30 μm, sufficient properties as a photocatalyst dispersion cannot be obtained. When the D50 diameter of the tungsten oxide-based fine particles is less than 1 nm, the particles are too small, the handleability of the photocatalyst is poor, and the practicability of the photocatalyst and the dispersion liquid using the photocatalyst decreases. Furthermore, when the D90 diameter of the tungsten oxide-based fine particles is less than 0.05 μm, the dispersibility of the tungsten oxide-based fine particles decreases. Therefore, it is difficult to obtain uniform dispersions and coatings. If the D90 diameter is larger than 10 μm, it will be difficult to form a uniform and stable film using a dispersion or a paint, and the photocatalytic performance cannot be sufficiently exhibited. Furthermore, in order to improve the photocatalytic performance when the photocatalyst is formed into a film, it is preferable not to deform the fine particles too much in the dispersion treatment when preparing the dispersion liquid.

The photocatalyst according to the embodiment preferably has a catalyst color in which a* is 10 or less, b* is -5 or more, and L* is 50 or more when the color is represented by the L*a*b* colorimetric system. The L*a*b* colorimetric system is a method for expressing the color of an object, standardized by the International Commission on Illumination (CIE) in 1976, and Japan in accordance with JISZ-8729. By forming a photocatalyst film using a photocatalyst having such a color and using a dispersion obtained by dispersing it in an aqueous dispersion medium, not only good photocatalytic performance can be obtained, but also the color tone of the substrate can not be damaged. Therefore, in addition to the original characteristics and quality of the product having the photocatalyst film, the photocatalytic performance by the photocatalyst film can be exhibited stably.

The tungsten oxide fine particles mainly constituting the photocatalyst of the embodiment are preferably produced by the method described below. However, the method of producing the tungsten oxide-based fine particles is not particularly limited. The tungsten oxide-based fine particles are preferably produced by a sublimation process. Furthermore, it is preferable to combine a heat treatment process with a sublimation process. The tungsten oxide-based microparticles produced by this method can stably realize the aforementioned Raman peak intensity ratio (X/Y) and the crystal state, crystal structure, and average particle size based on the intensity ratio.

First, the sublimation process is described. The sublimation step is a step of obtaining tungsten oxide particles by sublimating metal tungsten powder, tungsten compound powder, or tungsten compound solution in an oxygen atmosphere. Sublimation is a phenomenon caused by a change of state from a solid phase to a gas phase or from a gas phase to a solid phase without passing through the liquid phase. Tungsten oxide in a particulate state can be obtained by oxidizing metal tungsten powder, tungsten compound powder, or tungsten compound solution as a raw material while sublimating.

Any of metal tungsten powder, tungsten compound powder, or tungsten compound solution can be used as the raw material (tungsten raw material) in the sublimation step. Examples of tungsten compounds used as raw materials include tungsten trioxide (WO ₃ ), tungsten dioxide (WO ₂ ), tungsten oxides such as lower oxides, tungsten carbide, ammonium tungstate, calcium tungstate, and tungstic acid.

By performing the sublimation process of the tungsten raw material as described above in an oxygen atmosphere, the metal tungsten powder and/or tungsten compound powder are instantly changed from solid phase to gas phase, and then the metal tungsten vapor that has become gas phase is oxidized to obtain tungsten oxide particles. Even in the case of using a solution, it becomes a gaseous phase through a tungsten oxide or compound. Thus, tungsten oxide fine particles can be obtained by utilizing the oxidation reaction in the gas phase. Furthermore, the crystal structure and the like of the tungsten oxide fine particles can be controlled.

As the raw material of the sublimation step, in order to make the tungsten oxide fine particles sublimated in an oxygen atmosphere less likely to contain impurities, at least one selected from metal tungsten powder, tungsten oxide powder, tungsten carbide powder, and ammonium tungstate powder is preferably used. Since metal tungsten powder and tungsten oxide powder do not contain harmful substances (substances other than tungsten oxide) formed as by-products in the sublimation process, they are particularly preferable as raw materials for the sublimation process.

As the tungsten compound used as a raw material, a compound containing tungsten (W) and oxygen (O) as its constituent elements is preferable. When W and O are contained as constituent components, it is easy to sublimate instantaneously when inductively coupled plasma treatment or the like described later is used in the sublimation step. Examples of such tungsten compounds include WO ₃ , W ₂₀ O ₅₈ , W ₁₈ O ₄₉ , WO ₂ and the like. In addition, tungstic acid, ammonium p-tungstate, ammonium metatungstate solutions or salts are also effective.

In the case of producing complex particles formed of tungsten oxide and a simple substance or compound of an added metal element, in addition to the tungsten raw material, transition metal elements or earth group metals can also be added in the form of metals, oxide-containing compounds, and composite compounds. Elements and other metal elements are mixed. By treating tungsten oxide and other metal elements at the same time, composite compound particles such as composite oxides formed of tungsten oxide and other metal elements can be obtained. Composite fine particles can also be obtained by mixing and supporting tungsten oxide fine particles with simple particles or compound particles of other metal elements. The method for combining tungsten oxide and other metal elements is not particularly limited, and various known methods can be used.

The average particle size of the metal tungsten powder and/or the tungsten compound powder as a tungsten raw material is preferably in the range of 0.1 to 100 μm. The average particle size of the tungsten raw material is more preferably in the range of 0.3 μm to 10 μm, still more preferably in the range of 0.3 μm to 3 μm, and desirably in the range of 0.3 μm to 1.5 μm. When metal tungsten powder and/or tungsten compound powder having an average particle diameter within the above-mentioned range is used, sublimation easily occurs. When the average particle size of the tungsten raw material is less than 0.1 μm, the raw material powder is too fine, so the raw material powder must be sorted in advance, otherwise the workability will be reduced and the price will be increased, which is industrially disadvantageous of. If the average particle diameter of the tungsten raw material is larger than 100 μm, it is difficult to cause a uniform sublimation reaction. Even if the average particle size is large, a uniform sublimation reaction can be caused by treating with a large amount of energy, but it is industrially unpreferable.

As a method of sublimating the tungsten raw material in an oxygen atmosphere in the sublimation step, at least one treatment selected from the group consisting of inductively coupled plasma treatment, arc discharge treatment, laser treatment, electron beam treatment, and gas burner treatment can be mentioned. . Among them, the laser treatment or the electron beam treatment is a process of performing sublimation by irradiating laser light or electron beams. Since the irradiation spot diameter of laser or electron beam is small, it takes a long time to process a large amount of raw materials at one time, but it is not necessary to strictly control the particle size of the raw material powder and the stability of the supply amount, which is an advantage of this method.

In inductively coupled plasma processing and arc discharge processing, it is necessary to adjust the generation area of plasma and arc discharge, but it is possible to oxidize a large amount of raw material powder in an oxygen atmosphere at one time. In addition, it is also possible to control the amount of raw materials that can be processed at one time. The power cost of gas burner treatment is relatively cheap, but it is difficult to process raw material powder and raw material solution in large quantities. Therefore, the productivity of gas burner processing is poor. It should be noted that the gas burner treatment is not particularly limited as long as it has enough energy to sublimate the raw material. A propane gas burner, an acetylene gas burner, etc. can be used.

When the inductively coupled plasma treatment is applied to the sublimation step, a method of generating plasma using argon or oxygen gas and supplying metal tungsten powder and/or tungsten compound powder to the plasma is generally employed. As a method of supplying the tungsten raw material into the plasma, for example, a method of blowing metal tungsten powder and/or tungsten compound powder together with a carrier gas, dispersing metal tungsten powder and/or tungsten compound powder in a predetermined liquid dispersion The method of blowing into the dispersion liquid in the medium, etc.

When blowing metal tungsten powder and/or tungsten compound powder into plasma, examples of the carrier gas used include air, oxygen, and an inert gas containing oxygen. Among them, air is preferably used because of its low cost. In the case of blowing a reactive gas containing oxygen in addition to the carrier gas, or when the tungsten compound powder is tungsten oxide, etc., when there is enough oxygen in the reaction area, an inert gas such as argon or helium can also be used. gas as carrier gas. As the reaction gas, oxygen or an oxygen-containing inert gas or the like is preferably used. When using an oxygen-containing inert gas, it is preferable to set the amount of oxygen so that the necessary amount of oxygen can be sufficiently supplied to the oxidation reaction.

The crystal structure of tungsten oxide particles can be easily controlled by blowing metal tungsten powder and/or tungsten compound powder together with carrier gas, while adjusting the gas flow rate or the pressure in the reaction vessel. Specifically, at least one kind selected from monoclinic and triclinic crystals (monoclinic, triclinic, or mixed crystals of monoclinic and triclinic), or mixed with triclinic Tungsten oxide particles with a square crystal structure. The crystal structure of tungsten oxide particles is preferably a mixed crystal structure of monoclinic and triclinic crystals, a mixed crystal structure of monoclinic and orthorhombic crystals, a mixed crystal structure of triclinic and orthorhombic crystals, monoclinic crystals, and triclinic crystals. Any of the crystalline structures in which crystals and orthorhombic crystals are mixed.

Examples of the dispersion medium for producing a dispersion liquid of metal tungsten powder and/or tungsten compound powder include a liquid dispersion medium having an oxygen atom in the molecule. When a dispersion liquid is used, the handling of the raw material powder becomes easy. As the liquid dispersion medium having an oxygen atom in the molecule, for example, a liquid dispersion medium containing at least 20% by volume of at least one selected from water and alcohol can be used. As the alcohol used as the liquid dispersion medium, for example, at least one selected from the group consisting of methanol, ethanol, 1-propanol and 2-propanol is preferable. Since water or alcohol is easily volatilized by the heat of the plasma, it does not hinder the sublimation reaction and oxidation reaction of the raw material powder, and since the molecule contains oxygen, it is easy to promote the oxidation reaction.

In the case of preparing a dispersion liquid by dispersing metal tungsten powder and/or tungsten compound powder in a dispersion medium, it is preferable to contain metal tungsten powder in the range of 10 to 95 mass %, more preferably 40 to 80 mass % in the dispersion liquid and/or tungsten compound powder. By making the dispersion ratio in the dispersion liquid within this range, the metal tungsten powder and/or the tungsten compound powder can be uniformly dispersed in the dispersion liquid. When uniformly dispersed, the sublimation reaction of the raw material powder tends to proceed uniformly. If the content in the dispersion liquid is less than 10% by mass, the amount of raw material powder will be too small, and efficient production will not be possible. If it is more than 95% by mass, since the dispersion liquid is small, the viscosity of the raw material powder increases and the powder tends to stick to the container, resulting in poor handleability.

The crystal structure of tungsten oxide fine particles can be easily controlled by employing a method of blowing metal tungsten powder and/or tungsten compound powder into a dispersion liquid into plasma. Specifically, tungsten oxide fine particles whose crystal structure is at least one selected from monoclinic crystals and triclinic crystals, or in which orthorhombic crystals are mixed can be easily obtained. Furthermore, by using a tungsten compound solution as a raw material, the sublimation reaction can be uniformly advanced, and the controllability of the crystal structure of the tungsten oxide fine particles can be further improved. The method using the above-mentioned dispersion liquid can also be applied to the arc discharge treatment.

When performing the sublimation process by irradiating laser beams or electron beams, it is preferable to use metal tungsten or a tungsten compound in the form of pellets as a raw material. Since the irradiation spot diameter of laser light or electron beam is small, it is difficult to supply metal tungsten powder or tungsten compound powder, but it can be efficiently sublimated by using granular metal tungsten or tungsten compound powder. The laser is not particularly limited as long as it has enough energy to sublimate metal tungsten or a tungsten compound, but CO ₂ laser is preferable because it has high energy.

When irradiating the particles with laser light or electron beams, moving at least one of the irradiation source of the laser light or the electron beams or the particles can effectively sublimate the entire surface of the particles having a certain size. Thereby, tungsten trioxide powder having a crystal structure in which orthorhombic crystals are mixed with at least one selected from monoclinic crystals and triclinic crystals can be obtained. The above-mentioned particles can also be suitably used for inductively coupled plasma treatment or arc discharge treatment.

The photocatalyst according to the embodiment can be obtained with high reproducibility by heat-treating the tungsten oxide-based fine particles obtained in the above sublimation step. In the heat treatment step, the tungsten oxide-based fine particles obtained in the sublimation step are heat-treated at a predetermined temperature and time in an oxidizing atmosphere. The heat treatment step is preferably performed in air or in an oxygen-containing gas. Oxygen-containing gas refers to an inert gas containing oxygen. The heat treatment temperature is preferably in the range of 200 to 800°C, more preferably in the range of 340 to 650°C. The heat treatment time is preferably in the range of 10 minutes to 5 hours, more preferably in the range of 30 minutes to 2 hours. By setting the temperature and time of the heat treatment step within the above ranges, the crystallinity of the tungsten oxide-based fine particles, the amount of surface defects, and the like can be brought into a state suitable for photocatalysts.

When the heat treatment temperature is lower than 200° C., there is a possibility that the oxidation effect of turning the powder that has not been turned into tungsten trioxide into tungsten trioxide cannot be sufficiently obtained in the sublimation step. Furthermore, the crystallinity of the tungsten trioxide obtained in a sublimation process cannot fully be improved. If the heat treatment temperature is higher than 800° C., the crystallinity of tungsten oxide is too high, and the surface of the fine particles tends to have almost no surface defects such as oxygen deficiency. In either case, the photocatalytic activity of the tungsten oxide-based fine particles cannot be sufficiently enhanced. Furthermore, the crystallinity and surface state of the tungsten oxide-based fine particles can be reproducibly controlled to a state suitable for photocatalysis by adjusting the heating rate and cooling rate during the heat treatment within an appropriate range. In the heat treatment step, it is preferable to put the tungsten oxide powder into a furnace heated to a set temperature, and after a predetermined time, take the tungsten oxide powder out of the furnace and cool it down to room temperature. The temperature increase rate during heat treatment is preferably in the range of 80 to 800°C/min, and the temperature drop rate is preferably in the range of -800 to -13°C/min.

(Photocatalyst dispersion, photocatalyst coating, photocatalyst film and products)

Next, the photocatalyst dispersion liquid and photocatalyst coating material of embodiment, the photocatalyst film produced using them, and the product provided with the photocatalyst film are demonstrated. The photocatalyst dispersion liquid of the embodiment is obtained by dispersing the photocatalyst of the embodiment in an aqueous dispersion medium so that the particle concentration is in the range of 0.001 to 50% by mass. If the particle concentration is less than 0.001% by mass, the content of the photocatalyst is insufficient and desired performance cannot be obtained. If the particle concentration exceeds 50% by mass, the fine particles of the photocatalyst in film formation will exist in a state of being too close together, and a surface area for sufficiently exhibiting the photocatalytic performance cannot be obtained. Therefore, not only the performance cannot be fully exhibited, but also the cost is increased in order to contain more than necessary photocatalyst. The concentration of the photocatalyst is more preferably in the range of 0.01 to 20% by mass.

In the photocatalyst dispersion liquid according to the embodiment, the pH of the dispersion liquid is preferably in the range of 1-9. By setting the pH of the photocatalyst dispersion liquid in the range of 1 to 9, since the zeta potential becomes a negative value, the dispersed state of the photocatalyst can be improved. As long as this dispersion liquid or the paint made from it is used, it can be thinly and uniformly coated on the substrate. If the pH of the photocatalyst dispersion liquid is less than 1, since the zeta potential approaches zero, the dispersibility deteriorates. When the pH of the photocatalyst dispersion liquid exceeds 9, tungsten oxide becomes easy to dissolve. In order to adjust the pH of the photocatalyst dispersion liquid, an aqueous acid or alkali solution such as hydrochloric acid, sulfuric acid, tetramethylammonium hydroxide (TMAH), ammonia, and sodium hydroxide may be added as necessary.

The pH of the photocatalyst dispersion liquid is more preferably in the range of 2.5 to 7.5. Thereby, the photocatalytic performance (gas decomposition performance) of a film formed using a dispersion liquid or a paint can be further improved. After coating and drying the photocatalyst dispersion with a pH in the range of 2.5 to 7.5, when the surface state of the particles was observed by FT-IR (Fourier Transform Infrared Spectroscopy), it was observed that there were hydroxyl groups around 3700 cm ^-1 absorb. By using this film as a photocatalyst film, excellent organic gas decomposition performance can be obtained. When the photocatalyst dispersion adjusted to pH 8 is applied and dried, the absorption of hydroxyl groups decreases, and the gas decomposition performance tends to deteriorate. When the pH of the photocatalyst dispersion was adjusted to 1.5, although hydroxyl groups existed, the zeta potential was close to 0, so the dispersibility and gas decomposition performance were slightly lowered.

The photocatalyst dispersion liquid of the embodiment can be obtained by dispersing the photocatalyst of the embodiment in an aqueous dispersion medium. The photocatalyst dispersed in the aqueous dispersion medium is not limited to the above-mentioned individual fine particles of tungsten oxide, and may be fine particles such as a mixture or composite of tungsten oxide and other metal elements. Tungsten oxide and other metal elements can be dispersed in the aqueous dispersion medium in a pre-mixed or composite state, or as a mixture or composite in the aqueous dispersion medium. The types and forms of metal elements other than tungsten are as described above.

There is no particular limitation on the method of mixing or compounding tungsten oxide and other metal elements in a dispersion medium. Typical compounding methods are described below. As a method of compounding with ruthenium, there is a method of adding an aqueous solution of ruthenium chloride to an aqueous dispersion liquid in which tungsten oxide fine particles are dispersed. As a method of compounding with platinum, there is a method of mixing platinum powder into an aqueous dispersion liquid containing tungsten oxide fine particles. Furthermore, the compounding method with copper using an aqueous solution of copper nitrate or copper sulfate or an ethanol solution, the compounding method with iron using an aqueous solution of ferric chloride, the compounding method with silver using an aqueous solution of silver chloride, and the compounding method using an aqueous solution of chloroplatinic acid A composite method with platinum, a composite method with palladium using an aqueous solution of palladium chloride, and the like are also effective. In addition, an oxide sol such as titanium oxide sol or alumina sol may be used to composite tungsten oxide and a metal element (oxide). Various compounding methods other than those described above may also be employed.

As the photocatalyst dispersion liquid according to the embodiment, an aqueous dispersion medium can be used. Water is mentioned as a representative example of an aqueous dispersion medium. The aqueous dispersion medium may contain less than 50% by mass of alcohol in addition to water. As alcohol, methanol, ethanol, 1-propanol, 2-propanol, etc. can be used, for example. If the content of alcohol exceeds 20% by mass, the photocatalyst may aggregate, so the content of alcohol is more preferably 20% by mass or less. The content of alcohol is more preferably 10% by mass or less. The photocatalyst of the embodiment may be dispersed in a water-based dispersion medium such as water or alcohol in a state of being mixed with a material having adsorption properties such as activated carbon or zeolite, supported, and impregnated. The photocatalyst dispersion liquid may contain the photocatalyst in such a state.

The photocatalyst dispersion of the embodiment can be used as a film-forming material in its original state. It is also possible to mix the photocatalyst dispersion liquid and the binder component to prepare a paint, and use the paint as a film-forming material. The paint contains an aqueous dispersion and at least one binder component selected from inorganic binders and organic binders. The content of the binder component is preferably in the range of 5 to 95% by mass. If the content of the binder component exceeds 95% by mass, desired photocatalytic performance may not be obtained. When the content of the binder component is less than 5% by mass, sufficient adhesive force may not be obtained, and film properties may decrease. By applying such a coating, the strength, hardness, adhesion to the substrate, and the like of the film can be adjusted to a desired state.

As the inorganic binder, for example, products obtained by decomposing hydrolyzable silicon compounds such as alkyl silicates (esters), silicon halides, and their partial hydrolyzates, organopolysiloxane compounds and polycondensates thereof, Silica, colloidal silica, water glass, silicon compounds, phosphates such as zinc phosphate, metal oxides such as zinc oxide and zirconia, polyphosphate, cement, gypsum, lime, enamel frit, etc. As the organic binder, for example, fluororesins, silicone resins, acrylic resins, epoxy resins, polyester resins, melamine resins, polyurethane resins, alkyd resins and the like can be used.

By applying the above-mentioned photocatalyst dispersion liquid or photocatalyst coating to a substrate, a photocatalyst-containing film can be stably and uniformly formed. As a base material for forming the photocatalyst film, resins such as glass, ceramics, plastics, and acrylic resins, paper, fiber, metal, wood, and the like can be used. The film thickness is preferably in the range of 2 to 1000 nm. If the film thickness is less than 2 nm, a state in which tungsten oxide-based fine particles are uniformly present may not be obtained. When the film thickness exceeds 1000 nm, the adhesion force of the photocatalyst film to the substrate will decrease. The film thickness is more preferably in the range of 2 to 400 nm.

The photocatalyst film of the embodiment exhibits photocatalytic performance not only under visible light but also under ultraviolet irradiation. Generally speaking, visible light refers to light with a wavelength in the range of 380-830nm, which is generally illuminated by sunlight, white fluorescent lamps, white LEDs, bulbs, halogen lamps, xenon lamps, or blue light-emitting diodes, blue lasers, etc. illuminated light. Ultraviolet light refers to light with a wavelength in the range of 10 to 400 nm, including light irradiated by the sun and mercury lamps. The photocatalyst film according to the embodiment can exhibit photocatalytic performance not only in a normal indoor environment, but also can exhibit photocatalytic performance under irradiation of ultraviolet rays. The photocatalytic performance means that a pair of electrons and holes corresponding to one photon are excited by absorbing light, and the excited electrons and holes activate the hydroxyl and oxygen (acid) on the surface through oxidation and reduction. The active oxygen generated acts to oxidize and decompose organic gases, etc., and to exert hydrophilicity and antibacterial/sterilizing properties.

The product of the embodiment includes a film formed by using the above-mentioned photocatalyst dispersion or photocatalyst coating. Specifically, it is a product in which a photocatalyst dispersion liquid or a photocatalyst coating is applied on the surface of a substrate constituting the product to form a film. The film formed on the surface of the substrate may contain zeolite, activated carbon, porous ceramics, and the like. Under the irradiation of visible light, the photocatalyst film and products equipped with the photocatalyst film have excellent decomposition performance to organic gases such as acetaldehyde and formaldehyde, and especially show high activity under low illumination. In addition, compared with conventional visible light-responsive photocatalysts, the products of the embodiments have high photocatalytic performance even under ultraviolet irradiation, and can expand the use environment. The photocatalyst film of the embodiment shows hydrophilicity in the measurement of the contact angle of water. Furthermore, in the evaluation of the antibacterial activity against Staphylococcus aureus and Escherichia coli under irradiation with visible light, a high antibacterial effect was exhibited.

Specific examples of products equipped with the photocatalyst film of the embodiment include air conditioners, air cleaners, fans, refrigerators, microwave ovens, dish washer dryers, rice cookers, pots, pot lids, IH heaters, washing machines, vacuum cleaners, and lighting. Equipment (light bulbs, lamp bodies, lampshades, etc.), sanitary products, toilets, washbasins, mirrors, bathrooms (walls, ceilings, floors, etc.), building materials (interior walls, ceiling materials, floors, exterior walls, etc.), interior products (curtains) , carpets, tables, chairs, sofas, shelves, beds, bedding, etc.), glass, window frames, railings, doors, handles, clothes, filters for home appliances, stationery, kitchen supplies, and automotive interiors Spatial components, etc. By providing the photocatalyst film of the embodiment, a photocatalytic effect can be imparted to a product. Examples of suitable substrates include glass, ceramics, plastics, acrylic resins, paper, fibers, metals, wood, and the like.

In the case of using fibers as the base material, synthetic fibers such as polyester, nylon, and acrylic, regenerated fibers such as rayon, natural fibers such as cotton, wool, and silk, and their blended, woven, and blended fibers can be used as the fiber material. goods etc. The fibrous material may be loose hairy. The fiber may have any form such as woven fabric, knitted fabric, or non-woven fabric, and may be subjected to usual dyeing or printing. When applying the photocatalyst dispersion liquid to a fiber material, the method of using the photocatalyst of embodiment together with a resin binder, and fixing it to a fiber material is convenient.

As the resin binder, water-soluble, water-dispersed, or solvent-soluble resins can be used. Specifically, melamine resin, epoxy resin, urethane resin, acrylic resin, fluororesin, etc. can be used, but not limited thereto. In the case of using the photocatalyst dispersion liquid of the embodiment to fix the photocatalyst to the fiber material, for example, the photocatalyst dispersion liquid is mixed with a water-dispersible or water-soluble resin binder to prepare a resin liquid, and the resin liquid impregnate the fibrous material, and then roll it with a liquid roller to dry it. By increasing the viscosity of the resin liquid, it can be coated on one surface of the fiber material with a known device such as a knife coater. It is also possible to use a gravure roll to attach the photocatalyst to one side or both sides of the fiber material.

When the photocatalyst is attached to the surface of the fiber using a photocatalyst dispersion, if the amount of adhesion is too small, the photocatalytic performance such as gas decomposition performance and antibacterial performance of tungsten oxide cannot be fully exhibited. If the adhesion amount is too much, although the performance of tungsten oxide can be exerted, the hand feeling as a fiber material will often be deteriorated. Therefore, it is preferable to select an appropriate adhesion amount according to the material and application. Clothes and housewares on which the photocatalyst-attached fibers contained in the photocatalyst dispersion liquid are attached to the surface exhibit excellent deodorizing effects and antibacterial effects under visible light irradiation in an indoor environment. In addition, photocatalytic performance can be exhibited even when ultraviolet rays are irradiated.

Example

Next, specific examples of the present invention and evaluation results thereof are described. In addition, as the manufacturing method of the powder in the following Example, the method which applied the inductive coupling type plasma process in a sublimation process was used, However, this invention is not limited to this.

(Example 1, Comparative Example 1)

As raw material powder, tungsten trioxide powder with an average particle diameter of 0.5 μm was prepared. This raw material powder was sprayed into RF plasma together with carrier gas (Ar), and further, argon gas was flowed at a flow rate of 40 L/min, and oxygen gas was flowed at a flow rate of 40 L/min as reaction gas. In this way, tungsten oxide powder is produced through a sublimation step in which an oxidation reaction proceeds while sublimating the raw material powder. A tungsten oxide powder that has not been heat-treated is designated as sample A (comparative example). Samples B to E (Examples) were prepared by heat-treating the above-mentioned tungsten oxide powder in air at temperatures of 300°C, 500°C, 575°C, and 600°C. In addition, the same tungsten oxide powder was heat-treated in the air at a temperature of 1000° C., thereby preparing Sample F (comparative example). The heat treatment time was all 1 hour. In addition, in the process of producing samples B to E, the temperature was rapidly raised to a predetermined temperature during the heat treatment, and after 1 hour, they were taken out from the furnace and cooled down to room temperature.

The average primary particle diameter (D50) and BET specific surface area of samples A to F (tungsten oxide powder) were measured. The average primary particle size is measured by image analysis of TEM photographs. In TEM observation, using H-7100FA manufactured by Hitachi Corporation, image analysis was performed on enlarged photographs, 50 or more particles were extracted, the cumulative particle diameter based on volume was obtained, and the D50 diameter was calculated. The measurement of the BET specific surface area was performed using a specific surface area measuring device Macsorb 1201 (trade name) manufactured by Mountec Corporation. The pretreatment was carried out under the conditions of 200° C.×20 minutes in nitrogen gas. Table 1 shows the measurement results of the average primary particle diameter (D50 diameter) and the BET specific surface area of samples A to F.

Next, Raman spectroscopic analysis of samples A to F (tungsten oxide powder) was performed. The Raman spectroscopic analysis of each sample was measured in an environment with a temperature of 25° C. and a humidity of 50% using a spectrograph PDP-320 (trade name) manufactured by Photon Desin Corporation. The measurement conditions are: the measurement mode is micro-Raman, the measurement magnification is 100 times, the beam diameter is less than 1 μm, the light source is Ar ⁺ laser with a wavelength of 514.5nm, the laser power in the tube is 0.5mW, and the diffraction grating is a single 600gr/mm , the cross slit (crossslit) is 100 μm, and the slit is 100 μm, and the detector is a 1340-channel CCD manufactured by Japanese ローパーー. The measurement range of the Raman shift is 100 to 1500 cm ^-1 . Raman spectra as the measurement results of Sample A, Sample D, and Sample F are shown in FIG. 1 . In the Raman spectrum of each sample, the first peak that exists in the range of 268 to 274 cm ^-1 , the second peak that exists in the range of 630 to 720 cm ^-1 , and the third peak that exists in the range of 800 to 810 cm ^-1 are considered. Each wave number of the peak. Furthermore, the ratio (X/Y) of the peak intensity X to the peak intensity Y existing in the range from 920 cm ⁻¹ to 950 cm ⁻¹ was calculated. These results are shown in Table 1.

[Table 1]

Next, the tungsten oxide powders of samples A to F were dispersed in water so that the particle concentration became 10% by mass to prepare photocatalyst dispersion liquids, respectively. The obtained photocatalyst dispersion liquid was used for the characteristic evaluation mentioned later.

(Example 2, Comparative Example 2)

Using the tungsten oxide powders of samples A to F similar to those in Example 1 and Comparative Example 1, a photocatalyst dispersion liquid was produced as follows. First, tungsten oxide powder was dispersed in water to a concentration of 10% by mass. A dispersion obtained by dispersing tungsten oxide powder in water and an aqueous dispersion obtained by dispersing zirconia powder with an average primary particle diameter (D50) of 70 nm in water were mixed, and the zirconia relative to the total of tungsten oxide and zirconia The proportion of the amount was 33% by mass. The mixed dispersion liquid was adjusted with hydrochloric acid and ammonia so that the pH of the mixed dispersion liquid was in the range of 6.5 to 5.5. The dispersion treatment was performed using a ball mill. The particle concentration of the photocatalyst dispersion thus obtained was 10% by mass.

(Example 3, Comparative Example 3)

Using the tungsten oxide powders of samples A to F similar to those in Example 1 and Comparative Example 1, a photocatalyst dispersion liquid was produced as follows. Tungsten oxide powder was dispersed in water to a concentration of 10% by mass. A dispersion obtained by dispersing tungsten oxide powder in water was mixed with a ruthenium chloride solution so that the ratio of ruthenium oxide to the total amount of tungsten oxide and ruthenium oxide was 0.02% by mass. Ammonia was added dropwise to the mixture to adjust the pH to 7. Furthermore, an aqueous dispersion obtained by dispersing zirconia powder having an average particle diameter (D50) of 70 nm in water was dropped into the mixed liquid, and the pH was adjusted to a range of 6.5 to 5.5. Regarding the mixing ratio of tungsten oxide, ruthenium oxide, and zirconia in the dispersion liquid, the ratio of ruthenium oxide was about 0.017% by mass and the ratio of zirconia was about 33% by mass based on their total amount. The particle concentration of the obtained photocatalyst dispersion liquid was 13 mass %.

(Example 4, Comparative Example 4)

Using the tungsten oxide powders of samples A to F similar to those in Example 1 and Comparative Example 1, a photocatalyst dispersion liquid was produced as follows. Tungsten oxide powder was dispersed in water to a concentration of 10% by mass. Platinum particles with an average particle diameter of 2 nm were mixed into a dispersion obtained by dispersing tungsten oxide powder in water so that the ratio of platinum to the total amount of tungsten oxide and platinum was 0.02% by mass to prepare a photocatalyst dispersion.

Next, using the photocatalyst dispersion liquid produced in Examples 1-4 and Comparative Examples 1-4, the photocatalyst film was formed on the glass surface. The photocatalytic performance of the photocatalyst film under visible light irradiation was evaluated. The photocatalytic performance was evaluated by measuring the decomposition rate of acetaldehyde gas. Specifically, the gas decomposition rate was measured under the conditions shown below using the same flow-through apparatus as in JIS-R-1701-1 (2004) for evaluating the removal performance (decomposition ability) of nitrogen oxides.

The decomposition test of acetaldehyde gas was implemented as follows. The initial concentration of acetaldehyde was 10ppm, the gas flow rate was 140mL/min, and the sample volume was 0.2g. Conditioning of the samples was done by spreading the samples on a 5 x 10 cm glass plate and allowing to dry. Pretreatment was 12 hours of exposure under black light. A white fluorescent lamp (FL20SS·W/18 manufactured by Toshiba Laitec Co., Ltd.) was used as a light source, and a cut filter (Clarex N-169 manufactured by Nitto Jushi Kogyo Co., Ltd.) was used to filter wavelengths below 380 nm. Adjust the illumination to 1000lx. The light is not irradiated at first, and the light is irradiated only after the gas is no longer adsorbed and stabilized.

Light was irradiated under these conditions, and the gas concentration was measured 15 minutes later to obtain the gas decomposition rate. However, if the gas concentration is still unstable after 15 minutes has elapsed, the concentration measurement is continued until the concentration becomes stable. Let the gas concentration before light irradiation be A, and let the gas concentration after 15 minutes or more from light irradiation reach a stable state be B. ] The calculated value was taken as the gas decomposition rate (%). As a gas analyzer, a multi-gas monitor 1412 manufactured by INOVA was used. Table 2 shows the measurement results of the gas decomposition rate.

[Table 2]

As shown in Table 2, in the case of the photocatalyst films formed using the photocatalyst dispersion liquids of Examples 1 to 4, it was confirmed that the decomposition rate of acetaldehyde was fast and completely decomposed. This is considered to be because the crystal state and surface state of the tungsten oxide fine particles are in a state suitable for photocatalysis when the intensity ratio (X/Y) of the Raman peak is in the range of more than 0 to 0.04 or less. Therefore, even in an environment where the illuminance of visible light is low and the gas concentration is low, the gas decomposition performance of the photocatalyst film can be improved. Furthermore, the gas decomposition performance of the photocatalyst film can be further improved by utilizing zirconia to adsorb gas.

Next, mix the photocatalyst dispersions of Examples 1 to 4 and Comparative Examples 1 to 4 into an acrylic resin-based resin solution, and use the mixed solution (coating) to impregnate polyester with a mass per unit area of 150 g/m ² to prepare A flat fabric, from which polyester fibers attached with visible light-responsive photocatalysts were produced. Samples of 5×10 cm were cut from each fiber, and the photocatalytic performance under visible light irradiation was evaluated by the same method as above. As a result, it was confirmed that polyester fibers to which the photocatalysts of Examples 1 to 4 were adhered had a higher decomposition rate of acetaldehyde gas than fibers impregnated with coating materials using the photocatalyst dispersions prepared in Comparative Examples 1 to 4. Furthermore, 10 samples prepared in the same manner were prepared, and performance fluctuation was evaluated. As a result, it was confirmed that the dispersion liquid of the example had excellent dispersibility, and thus the amount of adhesion of the photocatalyst to the fiber was stable. It was also confirmed that the polyester fiber maintained a uniform texture.

Since the photocatalyst dispersion liquid of the above examples has excellent dispersibility, a uniform photocatalyst film can be obtained. In addition, based on the photocatalytic performance of the photocatalyst film, the performance of decomposing organic gases such as acetaldehyde can be stably obtained, and problems such as visually uneven color shades are not easy to occur. Therefore, it is suitable for parts used in the interior space of automobiles, building materials, interior materials, home appliances, etc. used in factories, stores, schools, public facilities, hospitals, welfare facilities, accommodation facilities, houses, etc. In addition, the photocatalysts of Examples can exhibit high gas decomposition performance even in an environment with low illuminance of visible light, an environment irradiated with ultraviolet rays in addition to visible light, and an environment with low gas concentration. Excellent deodorizing and deodorizing effects can be obtained by forming a photocatalyst film on indoor interior materials or interior decorations using a dispersion or paint containing such a photocatalyst. Such a film or product can be applied to various applications by making effective use of the characteristics of the photocatalyst of the example.

In addition, although some embodiment was demonstrated in this invention, these embodiment is presented as an example, and is not intended to limit the scope of this invention. These new embodiments can also be implemented in other various forms, and various omissions, substitutions, and changes can be made without departing from the gist of the present invention. These embodiments and modifications thereof are included in the scope and gist of the present invention, and are also included in the invention described in the claims and the equivalent scope thereof.

Claims (15)

1. A photocatalyst comprising tungsten oxide-based fine particles containing tungsten oxide in an amount ranging from 5% by mass to 100% by mass, In the Raman spectrum of the above-mentioned photocatalyst measured by Raman spectroscopy, the intensity X of the peak observed in the range of 920 cm ^-1 to 950 cm ^-1 is different from that observed in the range of 800 cm ^-1 to 810 cm ^-1 The peak intensity Y ratio (X/Y) is greater than 0 to less than 0.04. 2. The photocatalyst according to claim 1, wherein the tungsten oxide-based fine particles contain metal elements other than tungsten in a range of 0.001% by mass to 50% by mass. 3. The photocatalyst according to claim 2, wherein the metal element is at least one selected from the group consisting of titanium, zirconium, manganese, iron, ruthenium, nickel, palladium, platinum, copper, silver, cerium and aluminum. 4. The photocatalyst according to claim 3, wherein the content of the metal element is in a range from 0.005% by mass to 10% by mass. 5. The photocatalyst according to claim 1, wherein the tungsten oxide-based fine particles contain metal oxides other than tungsten oxide in a range of 0.01% by mass to 70% by mass. 6. The photocatalyst according to claim 5, wherein the metal oxide is at least one selected from the group consisting of zirconium oxide, titanium oxide, and ruthenium oxide. 7. The photocatalyst according to claim 1, wherein the average particle diameter (D50) of the tungsten oxide-based fine particles is not less than 1 nm and not more than 30 μm. 8. A photocatalyst dispersion comprising a dispersion medium and the photocatalyst according to claim 1 dispersed in the dispersion medium in a range of 0.001% by mass to 50% by mass. 9. The photocatalyst dispersion according to claim 8, wherein the dispersion medium is at least one selected from water and alcohol. 10. The photocatalyst dispersion according to claim 9, wherein the photocatalyst dispersion has a pH of 1 to 9. 11. A photocatalyst coating comprising the photocatalyst dispersion according to claim 8 and at least one binder component selected from inorganic binders and organic binders. 12. A photocatalyst film formed by applying the photocatalyst dispersion according to claim 8 to a substrate. 13. A photocatalyst film formed by applying the photocatalyst coating according to claim 11 to a substrate. 14. A product comprising the photocatalyst film according to claim 12. 15. A product comprising the photocatalyst film according to claim 13.