JP2024004698A - Photocatalyst film-coated body and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photocatalyst film-coated body which can achieve high levels of transparency and photocatalytic activity simultaneously across a broad spectrum from ultraviolet to visible light, and a method for producing the same.

SOLUTION: A photocatalyst film-coated body includes metal oxides with a bandgap energy between the valence band and conduction band of 0.1 eV-5.5 eV, wherein the photocatalyst film has a light transmittance of 80% or more across the wavelength range of 200 nm-800 nm, and the photocatalyst film has a thickness of 0.5 nm-200 nm. There is also provided a method for producing the same.

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

TECHNICAL FIELD The present invention relates to a photocatalytic membrane coating and a method for manufacturing the same.

Generally, when a photocatalyst is irradiated with light having an energy higher than its band gap, electrons are excited in the conduction band and holes are generated in the valence band. The excited electrons reduce surface oxygen and generate superoxide anions (・O ₂ ⁻ ), and the holes oxidize surface hydroxyl groups to generate hydroxyl radicals (・OH), and these reactions It is known that active oxygen species exhibit a strong oxidative decomposition function and have photocatalytic properties that decompose organic substances attached to the surface of a photocatalyst film with high efficiency.

The photocatalytic properties of photocatalysts have been applied to, for example, deodorization, antifouling, antibacterial, and sterilization, as well as the decomposition and removal of various substances that pose environmental pollution problems in wastewater and waste gas. ing.

It is also known that, as another function of the photocatalyst, when the photocatalyst is photoexcited, the surface of the photocatalyst film becomes superhydrophilic with a water contact angle of 10° or less. The superhydrophilic function of photocatalysts can be applied to, for example, soundproof walls on expressways, road reflectors, and various other products for the purpose of providing anti-fog, drip-proof, anti-fouling, anti-frost, and snow-sliding properties. Reflectors, street lights, vehicle body coats, side mirrors, and window films for automobiles and other vehicles, building materials including window glass, road signs, roadside signboards, refrigerator and freezer showcases, various lenses and sensors, and light sources. The use of photocatalytic films is being considered.

For example, Patent Document 1 describes that the practicality of a glass plate coated with a titanium oxide thin film having a photocatalytic function is improved by a specific method. Specifically, a thin film containing titanium element is formed on the surface of a glass substrate whose surface compressive stress is below a specific value, and the thin film surface is heated to a specific temperature and cooled under specific conditions to produce titanium oxide. It is described that the surface compressive stress of a thin film coated glass plate is improved and the friction resistance is improved.

Japanese Patent Application Publication No. 2003-112949

A photocatalytic film formed on the surface of a substrate such as glass or plastic that requires transparency is also required to have a high level of transparency of the photocatalytic film itself. Since a photocatalyst absorbs light with an energy higher than its band gap, in order to ensure a high level of transparency, it is necessary to control the film thickness and reduce the amount of photocatalyst that is not exposed on the surface.
However, in the glass plate coated with a titanium oxide thin film described in Patent Document 1, the thickness of the titanium oxide film having a photocatalytic function was not sufficiently thin with respect to the particle size of the titanium oxide particles used. Therefore, it is difficult to use the glass plate coated with a titanium oxide thin film described in Patent Document 1 in applications that have high transparency in a wide range from ultraviolet to visible light.
Until now, there has been no known photocatalytic film coating that can simultaneously achieve high levels of transparency and photocatalytic properties in a wide range from ultraviolet to visible light.

In view of the above-mentioned problems, the present invention aims to provide a photocatalytic membrane coating that can simultaneously achieve high levels of transparency and photocatalytic properties in a wide range from ultraviolet to visible light, and a method for manufacturing the same.

The above-mentioned problems are solved by the photocatalytic membrane coating and the manufacturing method thereof of the present invention. Specifically, the above problem is solved by forming the photocatalytic film of the present invention on the surface of a base material on which the film is to be formed.
That is, the gist of the present invention is the following [1] to [9].
[1] A photocatalytic film coating having a photocatalytic film containing a metal oxide whose band gap energy in the valence band and conduction band is 0.1 eV to 5.5 eV, wherein the photocatalytic film has a light beam at a wavelength of 200 nm to 800 nm. A photocatalytic membrane coating having a transmittance of 80% or more and a thickness of the photocatalytic membrane ranging from 0.5 nm to 200 nm.
[2] The metal oxide is zirconium, titanium, cerium, indium, tin, zinc, aluminum, magnesium, silicon, iron, lead, copper, tungsten, niobium, chromium, strontium, indium, ruthenium, cadmium, gallium, antimony. , tellurium, selenium, and hafnium.
[3] The [1 ] or the photocatalytic membrane coating according to [2].
0.5≦X≦200...(1)
1.0≦Y/X≦3.0...(2)
[4] The photocatalytic film coating according to any one of [1] to [3], wherein the photocatalytic film has a light transmittance of 90% or more at a wavelength of 200 nm to 800 nm.
[5] The photocatalytic film coating according to any one of [1] to [4] above, wherein the photocatalytic film has a thickness of 0.5 nm to 100 nm.
[6] [1] to [5] above, wherein the time required for the water contact angle on the surface of the photocatalytic film to become 20° or less as measured in accordance with JIS R 1703-1:2020 is 48 hours or less. The photocatalytic membrane coating according to any one of the above.
[7] The method for producing a photocatalyst film coated body according to any one of [1] to [6] above, wherein the metal oxide particle dispersion is applied to a base material, dried and aged, and then a solvent is added. A method for producing a photocatalyst membrane covering, which comprises washing at a temperature of 0°C to 1000°C and sintering at a temperature of 0°C to 1000°C.
[8] The method for producing a photocatalytic membrane coating according to [7] above, wherein the metal oxide particles have a mode diameter of 200 nm or less.
[9] The photocatalytic film coated body according to any one of [1] to [6] above, further comprising a light source that irradiates light with a spectrum having a peak at a wavelength of 10 nm to 400 nm.

According to the present invention, it is possible to provide a photocatalytic film covering that can simultaneously achieve high levels of transparency and photocatalytic properties in a wide range from ultraviolet to visible light, and a method for manufacturing the same.

1 is a graph showing the measurement results of light transmittance at wavelengths of 200 nm to 400 nm of base materials with metal oxide thin films obtained in Example 1 and Comparative Example 1. 2 is a graph showing the measurement results of the light transmittance at wavelengths of 400 nm to 800 nm of the base materials with metal oxide thin films obtained in Example 1 and Comparative Example 1. 2 is a graph showing the measurement results of the light transmittance at wavelengths of 200 nm to 400 nm of the base materials with metal oxide thin films obtained in Example 2 and Comparative Example 2. 2 is a graph showing the measurement results of the light transmittance at wavelengths of 400 nm to 900 nm of the base materials with metal oxide thin films obtained in Example 2 and Comparative Example 2. This is a graph showing the measurement results of the water contact angle of the thin film side surface of the base material with the metal oxide thin film obtained in Example 1 and Comparative Example 1 and the base material with the thin film obtained in Comparative Example 5. be.

In this specification, a numerical range expressed using "~" includes the numbers at both ends of "~".
In this specification, the lower and upper limits described in stages for preferred numerical ranges (for example, ranges of content, etc.) can be independently combined. For example, from the description "preferably 10 to 90, more preferably 30 to 60", the "preferable lower limit (10)" and "more preferable upper limit (60)" are combined to become "10 to 60". You can also do that.
Hereinafter, a photocatalyst membrane covering according to an embodiment of the present invention will be described.

"Photocatalytic membrane coating"
The photocatalytic membrane coating of the present invention has the photocatalytic membrane shown below.
It is preferable that the photocatalyst membrane coating further includes a light source shown below.
From the viewpoint that the photocatalytic property acts on the outermost surface, it is preferable that the photocatalytic film coating has a photocatalytic film on the outermost surface.
The photocatalytic film is formed, for example, on a substrate described below. That is, one embodiment of the photocatalyst film covering preferably includes a base material and a photocatalyst film formed on the base material, and more preferably further includes a light source in addition to these.

<Photocatalyst film>
The photocatalytic film includes a metal oxide whose valence band and conduction band have band gap energies of 0.1 eV to 5.5 eV.
In the present invention, the photocatalytic film means a thin film containing a metal oxide (hereinafter also referred to as a "metal oxide thin film").
In the present invention, the valence band refers to an energy band filled with electrons existing in the outermost shell of the electrons bound around the nucleus of an insulator or semiconductor, that is, valence electrons. .
In the present invention, the conduction band means an empty band immediately above the band gap in a system with a band gap.
In the present invention, band gap energy means the energy difference between the highest part of the valence band and the lowest part of the conduction band.

The thickness of the photocatalytic film is 0.5 nm to 200 nm, preferably 0.5 nm to 100 nm, more preferably 0.8 nm to 75 nm, even more preferably 1.0 nm to 18 nm. If the thickness of the photocatalyst film is within the above range, high transparency and mechanical strength can be maintained.
In the present invention, the film thickness of the photocatalyst film is measured by the method described in the Examples.

The light transmittance of the photocatalytic film at a wavelength of 200 nm to 800 nm is 80% or more, preferably 90% or more. If the light transmittance in the wavelength range is 80% or more, sufficient transparency suitable for various uses can be obtained. That is, it means that the photocatalyst film and the photocatalyst film covering are transparent.
In the present invention, "the light transmittance in the wavelength range of Anm to Bnm is C% or more" means that the light transmittance is C% or more in the entire wavelength range of Anm to Bnm.
In the present invention, the light transmittance of the photocatalyst film and the photocatalyst film coating means a value expressed as a relative value with respect to the spectral characteristics of the quartz glass substrate.

From the viewpoint of further improving transparency, the light transmittance (1) of the photocatalytic film at a wavelength of 400 to 800 nm is preferably 80% or more, more preferably 90% or more.
From the viewpoint of further improving transparency, the light transmittance (2) of the photocatalyst film at a wavelength of 280 to 400 nm is preferably 80% or more, more preferably 90% or more.
From the viewpoint of further improving transparency, the light transmittance (3) of the photocatalytic film at a wavelength of 200 to 280 nm is preferably 80% or more, more preferably 90% or more.
The photocatalyst film preferably has light transmittances (1) to (3) of 80% or more, more preferably 90% or more.

From the viewpoint of further improving transparency, the light transmittance of the photocatalyst film in the entire visible light region is 80% or more, preferably 90% or more. Note that the visible light region means a wavelength region of 400 nm or more and 780 nm or less.
From the viewpoint of further improving transparency, the light transmittance of the photocatalyst film in the entire UV-A region is 80% or more, preferably 90% or more. Note that the UV-A region means a wavelength region of 315 nm or more and less than 400 nm.
From the viewpoint of further improving transparency, the light transmittance of the photocatalyst film in the entire UV-B region is 80% or more, preferably 90% or more. Note that the UV-B region means a wavelength region of 280 nm or more and less than 315 nm.
From the viewpoint of further improving transparency, the light transmittance of the photocatalytic film in the entire UV-C region is 80% or more in the region of 200 nm or more, preferably 90% or more. Note that the UV-C region means a wavelength region of 100 nm or more and less than 280 nm.
By increasing the light transmittance in the ultraviolet region in each of the wavelength ranges mentioned above, the photocatalytic film and the substrate coated with it, that is, the photocatalytic film coating, can also be used for applications such as protective covers for ultraviolet irradiation equipment. Can be done.

From the viewpoint of easily ensuring transparency suitable for various uses, the light transmittance of the photocatalytic film should be 80% or more in the range from 200 nm to 800 nm, and the light transmittance in the range from 100 nm to 900 nm should be 80% or more. is more preferable.
Note that the haze of the photocatalyst film is not particularly limited.

From the viewpoint of easily imparting high transparency to the photocatalytic film, specifically, from the viewpoint of easily controlling the light transmittance of 80% or more in the wavelength range of 200 nm to 800 nm, the minimum particle size of the metal oxide in the photocatalytic film is It is preferable that the following formula (1) and the following formula (2) be satisfied, where Xnm is the thickness of the metal oxide thin film and Ynm is the thickness of the metal oxide thin film.
0.5≦X≦200...(1)
1.0≦Y/X≦3.0...(2)

X will be described later.
From the viewpoint of maintaining sufficient mechanical properties and durability, Y/X is 1.0 or more, preferably 1.1 or more, and more preferably 1.2 or more. Moreover, Y/X is 3.0 or less, preferably 2.5 or less, and more preferably 2.0 or less, from the viewpoint of better maintaining sufficient light transmittance.

Although the water contact angle in the air on the surface of the photocatalytic film is not particularly limited, the present invention provides a photocatalytic film coating that can simultaneously achieve higher levels of transparency and photocatalytic properties in a wide range from ultraviolet to visible light. From the viewpoint of being able to do this, the angle is preferably 10° or less, more preferably 9.0° or less, and even more preferably 8.5° or less.
In this specification, the water contact angle in the atmosphere on the surface of the photocatalytic film is determined according to JIS R 1703-1:2020 (Fine Ceramics - Self-cleaning performance test method for photocatalyst materials Part 1: Water contact angle) described in Examples. Measured using a method that complies with

Although the contact angle of oil droplets in water on the surface of the photocatalytic membrane is not particularly limited, the present invention provides a photocatalytic membrane coating that can simultaneously achieve higher levels of transparency and photocatalytic properties in a wide range from ultraviolet to visible light. From the viewpoint of possible bending, the angle is preferably 100° or more, more preferably 110° or more, and even more preferably 115° or more.
In this specification, the contact angle of oil droplets in water on the surface of a photocatalytic film is determined according to JIS R 1703-1:2020 (Fine Ceramics - Self-cleaning performance test method for photocatalyst materials Part 1: Water contact) described in Examples. angle measurements).

The time required for the water contact angle on the surface of the photocatalyst film to become 20 degrees or less (hereinafter also referred to as "water contact angle reduction time") is preferably 72 hours or less, more preferably 48 hours or less. The shorter the water contact angle reduction time, the better the photocatalytic property.
In the present invention, the water contact angle on the surface of the photocatalytic film was determined in accordance with JIS R 1703-1:2020 (Fine Ceramics - Self-cleaning performance test method for photocatalytic materials Part 1: Measurement of water contact angle) described in Examples. Measured by method.

The surface roughness (Ra) of the photocatalyst film is preferably 200 nm or less, more preferably 100 nm or less, even more preferably 70 nm or less, even more preferably 50 nm or less, and particularly preferably 30 nm or less, from the viewpoint of increasing the uniformity of the photocatalyst film. , 15 nm or less is more particularly preferred, 10 nm or less is even more particularly preferred, 5 nm or less is most preferred, and 3 nm or less is especially most preferred. In addition, the surface roughness (Ra) of the photocatalyst film is preferably 0.01 nm or more, more preferably 0.03 nm or more, even more preferably 0.05 nm or more, and 0.07 nm or more, from the viewpoint of increasing hydrophilicity and antifogging property. The thickness is particularly preferably 0.1 nm or more, and most preferably 0.1 nm or more.

The maximum value (Rmax) of the surface roughness of the photocatalyst film is preferably 500 nm or less, more preferably 300 nm or less, even more preferably 150 nm or less, even more preferably 100 nm or less, and 50 nm or less, from the viewpoint of increasing the uniformity of the photocatalyst film. The following is particularly preferable, 30 nm or less is more particularly preferable, 20 nm or less is even more particularly preferable, and 15 nm or less is most preferable. Further, the maximum value (Rmax) of the surface roughness of the photocatalyst film is preferably 0.05 nm or more, more preferably 0.1 nm or more, and even more preferably 0.5 nm or more, from the viewpoint of increasing hydrophilicity and antifogging property. Particularly preferably 0.7 nm or more, and most preferably 1.0 nm or more.

<Metal oxide>
Metal oxides include zirconium, titanium, cerium, indium, tin, zinc, aluminum, magnesium, silicon, iron, lead, copper, tungsten, niobium, chromium, strontium, indium, ruthenium, cadmium, gallium, antimony, tellurium, and selenium. The metal oxide is preferably a metal oxide containing one or more metal elements selected from the group consisting of and hafnium.
From the viewpoint of further increasing transparency, the metal oxide is more preferably a metal oxide containing one or more metal elements selected from the group consisting of titanium, zirconium, hafnium, zinc, and tin. More preferably, it is a metal oxide containing.
From the viewpoint of photocatalytic properties, it is preferable that the metal oxide constitutes the photocatalytic film.
Preferably, the metal oxide is in particulate form. Hereinafter, particulate metal oxides will also be referred to as "metal oxide particles."
The minimum particle diameter (X) and mode diameter of the metal oxide will be described later.

<Base material>
Although the base material is not particularly limited, examples thereof include inorganic base materials such as glass, polymer film base materials such as polyethylene terephthalate, polyimide, polycarbonate, and polyethylene naphthalate.
The base material may be subjected to a surface treatment to improve the adhesion of the metal oxide thin film. Examples of the surface treatment liquid include silane coupling agents, organic metals, and the like. Examples of the silane coupling agent include vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, tris(2-methoxyethoxy)vinylsilane, γ-glycidoxypropyltrimethoxysilane, γ-(methacryloxypropyl)trimethoxysilane, Examples include methoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and γ-aminopropyltriethoxysilane. Examples of the organic metal include organic titanium, organic aluminum, and organic zirconium. Silane coupling agent or organic metal diluted with an organic solvent such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, etc. to a concentration of 0.1 to 5% by mass. You can also use Surface treatment can be achieved by uniformly applying this surface treatment liquid onto a substrate using a spinner or the like and then drying it.

<Light source>
From the viewpoint that photocatalytic properties can be expressed by irradiating light with a wavelength having an energy greater than or equal to the band gap energy of the metal oxide constituting the photocatalytic film, the photocatalytic film coating has a spectrum having a peak in the wavelength range of 10 nm to 400 nm. It is preferable to have a light source that irradiates light.
From the viewpoint of further increasing transparency, it is preferable that the photocatalyst membrane covering has a light source on the base material side.
The light source is not particularly limited, but includes, for example, an incandescent lamp using radiant heat, a halogen lamp, a mercury lamp using discharge emission, a fluorescent lamp, electroluminescence using electroluminescence, a light emitting diode, an excimer laser using laser emission, and the like.

<Effect>
The reason why the photocatalyst membrane coating of the present invention exhibits the effects of the present invention can be inferred as shown in (i) below, although it is not limited to the following.
(i) In a photocatalytic film coating having a photocatalytic film containing a metal oxide whose band gap energy in the valence band and conduction band is 0.1 eV to 5.5 eV, the light transmittance of the photocatalytic film at a wavelength of 200 nm to 800 nm is 80% or more, and the film thickness of the photocatalytic film is 0.5 nm to 200 nm, so that the photocatalytic film coating has high light transmittance over a wide range of wavelengths of 200 nm to 800 nm, more preferably, over a wide range of wavelengths of 200 nm to 900 nm. can be granted. That is, since excellent transparency can be imparted to the photocatalytic membrane coating, even if the photocatalytic membrane is formed on a transparent base material, the transparency of the photocatalytic membrane coating is unlikely to be impaired.
For the above reasons, it is presumed that the photocatalytic membrane coating of the present invention can simultaneously achieve high levels of transparency and photocatalytic properties in a wide range from ultraviolet to visible light.

Furthermore, it is presumed that due to the following (ii), the photocatalytic membrane coating has excellent antifogging properties and antifouling properties in addition to transparency and photocatalytic properties.
(ii) If the surface roughness (Ra) of the photocatalytic film is moderately small, specifically 200 nm or less, fine irregularities with uniform heights on the nano-order are formed, increasing the hydrophilicity of the photocatalytic film. can do. Therefore, the base material can be given the following functions: it is hard to fog even under high humidity, has high anti-fog properties, is hard to attract organic substances in water, and has high antifouling properties.
For the above reasons, it is presumed that by appropriately reducing the surface roughness (Ra) of the photocatalyst film, the photocatalyst film coating will have excellent transparency, antifogging properties, and antifouling properties.

Furthermore, due to the following (iii) and (iv), it is presumed that the photocatalytic membrane coating can simultaneously achieve high levels of mechanical properties and durability in addition to transparency and photocatalytic properties.
(iii) Since a photocatalyst film generally has high hardness, by providing a photocatalyst film on a base material, the base material can be made less likely to be damaged.
(iv) The photocatalytic film can also be formed as a film made essentially only of metal oxides. Therefore, if the photocatalytic film is made of substantially only metal oxides, the possibility that impurities etc. will leach out from the photocatalytic film and adversely affect the surrounding area during use of the photocatalytic film or photocatalytic film coating will be greatly reduced. obtain.
For the above reasons, it is inferred that the photocatalytic membrane coating can simultaneously achieve high levels of mechanical properties and durability.

<Application>
By exhibiting the effects inferred in (i) to (iv) above, the photocatalytic membrane coating of the present invention can be used for surface treatment of optical glass and optical plastic, for medical use, for metals for ultraviolet irradiation equipment, It is extremely useful as a film for coating the surfaces of glass, plastics, etc.
To give a specific example, when the photocatalytic film is provided on the surface of an endoscope lens, a lens that is hard to be damaged, hard to fog, and hard to get dirty can be obtained even after repeated use. Therefore, it is possible to improve the accuracy of endoscopic observation and surgery. Additionally, by using a photocatalytic film that consists essentially only of metal oxides, it is extremely unlikely that impurities will be eluted from the metal oxide film during use, which will greatly reduce the impact on the human body. Can be done.

<Method for manufacturing photocatalyst membrane coating>
The method for producing the photocatalyst membrane coating is not particularly limited, but for example, a metal oxide particle dispersion having a predetermined particle size is applied to a substrate (coating step), and the resulting coating film is dried and aged. After that (drying and aging process), the coating film is washed with a solvent (cleaning process), and the washed coating film is sintered at 0°C to 1000°C (sintering process) to produce a photocatalyst film coated body. can do. That is, it is preferable that the method for manufacturing a photocatalyst film coated body includes a coating step, a drying and aging step, a washing step, and a sintering step.
As the metal oxide particles, it is preferable to use metal oxide particles synthesized by the method described below.
From the viewpoint of uniformly applying the metal oxide particle dispersion to the substrate, the metal oxide particle dispersion is preferably a dispersion in which metal oxide particles are stabilized by dispersion in an organic solvent using a dispersant. preferable.

In addition, in the method for manufacturing a photocatalyst film coated body, it is thought that some kind of interaction occurs between the metal oxide particles and the surface of the base material. This is one of the factors that makes it possible to produce a photocatalytic film coating that can simultaneously achieve high levels of transparency and photocatalytic properties in a wide range from ultraviolet to visible light.

[Preparation of metal oxide particle dispersion]
By adding metal oxide particles and a dispersant described below into an organic solvent, or by adding a dispersant such as carboxylic acids to the reaction solution when producing metal oxide particles as described later. By allowing the metal oxide particles to disperse in the organic solvent, a stable metal oxide particle dispersion (hereinafter also simply referred to as "dispersion") can be prepared. In metal oxide particles, additives such as dispersants that bind to or modify metal oxides are solvated by organic solvents, so it is difficult to add other special dispersants or perform special operations. A stable dispersion can be prepared by adding the particles into a commonly used organic solvent without the need for additional solvents.

Any organic solvent can be used as long as it can disperse metal oxide particles, and it can be used alone or in combination of several types.
Examples of organic solvents include aromatic hydrocarbons such as toluene, xylene, mesitylene, and nitrobenzene; aliphatic hydrocarbons such as hexane, octane, cyclohexane, and decahydronaphthalene; acetone, methyl ethyl ketone, diethyl ketone, acetylacetone, and methyl isobutyl. Ketones such as ketones, cyclopentanone, cyclohexanone, N-methylpyrrolidone; amides such as formamide, N,N-dimethylformamide, N,N-dimethylacetamide; diethyl ether, tetrahydrofuran, dioxane, methoxyethanol, ethoxyethanol, etc. ethers; chlorinated aliphatic hydrocarbons such as dichloromethane, chloroform, and 1,2-dichloroethane; alcohols such as methanol, ethanol, and isopropyl alcohol; ethyl acetate, butyl acetate, amyl acetate, propylene glycol monomethyl ether acetate (PGMEA) Examples include acetate esters such as. From the viewpoint of increasing the dispersion stability of metal oxide particles, hexane, cyclohexane, chloroform, diethyl ether, toluene, decahydronaphthalene, butyl acetate, and propylene glycol monomethyl ether acetate (PGMEA) are preferable as the organic solvent.

The amount of the organic solvent used in the dispersion is not particularly limited, but from the viewpoint of being able to prepare an economically stable dispersion, it is preferably 80% by mass or more, based on the total mass of the metal oxide particles and the organic solvent. It is more preferably at least 90% by mass, and even more preferably at least 90% by mass. Further, it is preferably 99.7% by mass or less, more preferably 99.5% by mass or less, and even more preferably 99% by mass or less.

As a dispersant, any compound can be used as long as it has the ability to disperse metal oxide particles, such as caprylic acid, acrylic acid, methacrylic acid, tiglic acid, propionic acid, methylbutyric acid, and hexane. Acid, nonanoic acid, o-toluic acid, p-toluic acid, benzoic acid, pt-butylbenzoic acid, 4-trifluoromethylbenzoic acid, phenylthioacetic acid, oleic acid, behenic acid, stearic acid, myristic acid, palmitic acid. Examples include carboxylic acids such as acids. One type of these may be used alone, or two or more types may be used in combination in any combination and ratio. As the dispersant, caprylic acid, acrylic acid, and 4-trifluoromethylbenzoic acid are preferred.

The amount of dispersant used in the dispersion is not particularly limited, but from the viewpoint of being able to prepare an economically stable dispersion, it is preferably 10 parts by mass or more, and 20 parts by mass, based on 100 parts by mass of metal oxide particles. The above is more preferable, and 30 parts by mass or more is still more preferable. Further, it is preferably 70 parts by mass or less, more preferably 65 parts by mass or less, and even more preferably 60 parts by mass or less.

The metal oxide particle dispersion further contains a low molecular dispersant other than carboxylic acid, a polymer dispersant such as a binder resin, a thickener, a surfactant, an antifoaming agent, an ultraviolet absorber, an emulsifier, etc. You can.

[Coating process]
The method for applying the metal oxide particle dispersion onto the base material can be freely selected depending on the material and shape of the base material. For example, if the base material has a flat plate shape with a diameter or long side of 300 mm or less, spin coating is possible. If the base material is in the form of a wide film, it is also possible to apply it continuously in a roll-to-roll manner using a gravure roll, lip roll, reverse roll, or the like. Furthermore, if the surface is three-dimensional and has a complex shape, it is also possible to apply by dip coating or spray coating.
Examples of the base material include those mentioned above. Furthermore, a surface-treated base material may be used.
In this specification, a metal oxide particle dispersion applied to a substrate is also referred to as a "coating film."

[Drying and aging process]
Drying of the coating film (drying step) is performed to reduce the amount of organic solvent in the coating film to a certain amount or less. Therefore, the drying temperature and time are determined by the amount of residual organic solvent required for the coating film and the type of organic solvent. Drying conditions after application are arbitrary.
Further, the drying atmosphere is not particularly limited, and may be air, nitrogen atmosphere, reduced pressure, or the like. Specifically, the temperature for drying the coating film is preferably 20°C to 300°C, more preferably 25°C to 200°C. The time for drying the coating film is preferably 1 second to 1800 seconds, more preferably 2 seconds to 1200 seconds. By drying the coating film, the amount of organic solvent in the coating film can be reduced to 50% by mass or less based on the mass of the applied dispersion.

Aging of the coating film (aging process) is performed to reduce defects in the metal oxide thin film obtained through the cleaning process and sintering process described below, and to improve the mechanical strength of the metal oxide thin film. It is thought that the aging of the coating film causes aggregation of the metal oxide particles and non-covalent bonds or the like with the base material, and this is thought to be the reason for achieving the above objective. In order to achieve this purpose, the conditions for aging the coating film are set arbitrarily. Specifically, the temperature for aging the coating film is preferably 5°C to 300°C, more preferably 10°C to 200°C. The time for aging the coating film is preferably 0.01 minutes to 180 minutes, more preferably 0.02 minutes to 60 minutes.
Note that the aging step may be performed after the drying step, or may be performed together with the drying step. That is, the aging process may also serve as a drying process.

[Washing process]
The coating film is washed after the drying and aging steps in order to reduce the amount of metal oxide particles in the coating film to 50% by mass or less based on the mass of metal oxide particles applied to the substrate. As the solvent used for cleaning the coating film after the drying and aging steps (hereinafter also referred to as "cleaning solvent"), the organic solvent used in the production of the dispersion can be used. Furthermore, an ester solvent may be used as a cleaning solvent. As the ester solvent, for example, a monocarboxylic acid ester solvent such as butyl acetate, a partial ether carboxylate solvent of a polyhydric alcohol such as propylene glycol monomethyl ether acetate (PGMEA), or a carbonate solvent such as diethyl carbonate may be used. Can be done.

The method for cleaning the coating film is arbitrarily selected depending on the type and shape of the substrate. From the viewpoint that it is possible to obtain a coating film with a desired thickness by optimizing the cleaning conditions, the temperature of the cleaning solvent for cleaning the coating film is preferably 0°C to 80°C, and preferably 5°C. -60°C is more preferred. The amount of cleaning solvent to be used is not particularly limited as long as a coating film of desired thickness can be obtained.

By providing both a drying step and a washing step, for example, high boiling point solvents and the like that cannot be sufficiently removed in the drying step can be sufficiently removed in the washing step.
By providing a cleaning process after the drying process and the aging process, the mechanical strength of the coating film is improved by agglomeration of metal oxide particles and formation of bonds with the base material, and excess metal oxide particles are removed. Therefore, the transmittance can also be improved at the same time.

The thickness of the coating film after cleaning is not particularly limited, but from the viewpoint of creating a photocatalytic film coating that can simultaneously achieve a higher level of transparency and photocatalytic properties in a wide range from ultraviolet to visible light. , preferably 0.5 nm to 600 nm, more preferably 0.5 nm to 300 nm, even more preferably 1.0 nm to 150 nm, even more preferably 1.0 nm to 100 nm, particularly preferably 1.5 nm to 50 nm, and particularly preferably 1.5 nm to 300 nm. 25 nm is particularly preferred, 2.0 nm to 15 nm is even more particularly preferred, and 2.0 nm to 10 nm is most preferred.

[Sintering process]
The sintering process of the coating film after cleaning is a necessary process to improve the mechanical strength of the resulting metal oxide thin film, but the temperature and time depend on the metal oxide particle dispersion used. Determined by the type of The sintering process firmly binds the metal oxide particles and develops the desired mechanical strength. The conditions for the sintering process may be determined by taking into consideration the heat resistance of the base material.
By optimizing the cleaning and sintering processes, the thickness of the resulting metal oxide thin film is determined, and the surface of the photocatalytic film has a nano-level fine uneven structure derived from the size of the metal oxide particles. is formed.

By going through the above-mentioned coating process, drying and aging process, cleaning process, and sintering process, a photocatalytic film, which is a thin film of metal oxide, is provided on the surface of the base material, and by covering the surface of the base material with the photocatalytic film, , a photocatalytic membrane coating, which is a thin film coating of metal oxide, is obtained.

<Metal oxide particles>
Examples of the metal oxide particles include particles of the same metal oxide as the metal oxide described above. Specific examples of metal oxide particles include particles of zirconium oxide, titanium oxide, cerium oxide, indium oxide, tin oxide, aluminum oxide, silicon oxide, hafnium oxide, zinc oxide, and the like. Among these, from the viewpoint of obtaining a transparent dispersion, particles of one or more metal oxides from titanium oxide, zirconium oxide, hafnium oxide, zinc oxide, and tin oxide are preferable, and particles of titanium oxide are more preferable. .
However, the metal oxide constituting the metal oxide particles is not limited to those exemplified here. One type of metal oxide may constitute metal oxide particles alone, or two or more types may constitute metal oxide particles in any combination and ratio.

From the viewpoint of increasing the scratch resistance of the photocatalytic film, the metal oxide particles are preferably metal oxide nanoparticles, and more preferably crystalline metal oxide nanoparticles.
In this specification, metal oxide particles, crystalline metal oxide particles, metal oxide nanoparticles, and crystalline metal oxide nanoparticles having a particle size larger than nanosize are collectively referred to as "metal oxide". sometimes referred to as "particles".

Although the minimum particle size (X) of the metal oxide particles is arbitrary, specifying the minimum particle size (X) of the metal oxide particles can be done by, for example, This is important for dispersion.
The minimum particle size (X) of the metal oxide, in other words, the minimum particle size (X) of the metal oxide contained in the metal oxide thin film coating is preferably 0.5 nm or more, more preferably 1.0 nm or more. . Further, the minimum particle size (X) of the metal oxide is preferably 200 nm or less, more preferably 100 nm or less, even more preferably 50 nm or less, and particularly preferably 10 nm or less. If the minimum particle size (X) of the metal oxide is equal to or larger than the lower limit, an appropriate fine uneven structure is likely to be formed when a thin film is formed, and hydrophilicity will be easily developed. If the minimum particle size (X) of the metal oxide is below the above-mentioned upper limit, the metal oxide particles can be easily dispersed transparently, and a rough surface uneven structure can be avoided when a thin film is formed. , a thin film having a fine uneven structure having a surface roughness (Ra) within the above-mentioned range is easily formed, and hydrophilicity is easily developed.
Note that the minimum particle size (X) of the metal oxide can be measured using an atomic force microscope (AFM). In this specification, the particle diameters of the primary particles of a plurality of particles are measured according to the procedure described in Examples, and the smallest value among the particle diameters is defined as the minimum particle diameter (X).

In addition, the minimum particle size (X) of the metal oxide is calculated using the following Scherrer formula (formula (3)) from the peak half-width of the (111) plane near 2θ = 30° in X-ray diffraction measurement. be able to.
[Scherrer style]
Crystallite size (D) = K・λ/(β・cosθ) (3)
Here, K is a Scherrer constant, K=0.9, and the X-ray (CuKα1) wavelength (λ)=1.54056 Å (1 Å=1×10 ⁻¹⁰ m). Further, the Bragg angle (θ) and half-width (βo) derived from the CuKα ray are calculated by a profile fitting method (Peason-XII function or Pseud-Voigt function). Further, the half-width β used in the calculation is corrected using the following formula (4) from the device-derived half-width (βi) determined in advance using standard Si.
β=(βo ² -βi ² ) ^1/2 ...(4)

The mode diameter of the metal oxide, in other words, the mode diameter of the metal oxide contained in the metal oxide thin film coating is not particularly limited, but it is possible to form a uniform fine uneven structure and keep the surface roughness (Ra) within a predetermined range. From the viewpoint of being able to achieve this, the thickness is preferably 0.1 nm or more, more preferably 0.5 nm or more, and even more preferably 1.0 nm or more. In addition, the mode diameter of the metal oxide is preferably 300 nm or less, more preferably 250 nm or less, still more preferably 200 nm or less, particularly preferably 150 nm or less, from the viewpoint of making the surface roughness (Ra) within a predetermined range. , 100 nm or less is most preferable. In particular, the mode diameter of the metal oxide particles is preferably 200 nm or less, from the viewpoint of facilitating the formation of a thin film having a fine uneven structure having a surface roughness (Ra) within the above-mentioned range.
Note that the mode diameter of the metal oxide is the mode particle diameter of the particle size distribution measured by a dynamic light scattering method. In this specification, the mode diameter is determined by measuring the volume-based particle size distribution of the primary particles of a plurality of particles using the procedure described in the Examples.

In addition, in the method for producing metal oxide particles described below, when carboxylic acids are used as additives in the reaction liquid raw material, or when carboxylic acids are not added as additives and carboxylic acids are added after collecting metal oxide particles. When used, carboxylic acids are adsorbed on the surface of each particle. In this case, the dispersibility of each particle in the organic solvent is further improved. The amount of carboxylic acids adsorbed on each particle is arbitrary, and a desired amount may be adsorbed depending on the intended use. Note that it can be confirmed by infrared absorption spectroscopy (IR) that carboxylic acids are adsorbed on the metal oxide particles.

<Method for manufacturing metal oxide particles>
Metal oxide particles, typified by crystalline metal oxide nanoparticles, can be produced by, for example, processing a metal oxide precursor by a solvothermal method using an organic solvent having an oxygen atom in the molecule in the presence of amines. Synthesize.

[Solvothermal method]
The solvothermal method is a method of producing particles in a closed container in a high-temperature environment in the presence of a predetermined solvent, and is carried out under a pressure depending on the solvent used and the synthesis temperature.
Usually, a reaction solution is prepared by coexisting a metal oxide precursor, an organic or aqueous solvent having an oxygen atom in its molecule, and, if necessary, a predetermined amount of amines. Note that the reaction solution may contain other components. For example, the reaction solution may contain additives other than amines (hereinafter also referred to as "other additives"), if necessary. As a result, this reaction solution has a metal oxide precursor and, if necessary, one or more of amines and other additives dissolved or dispersed in an organic solvent having an oxygen atom in the molecule or an aqueous solvent. It is prepared as a composition.

[Metal oxide precursor]
Any substance can be used as the metal oxide precursor as long as desired metal oxide particles can be obtained. Therefore, an appropriate metal can be arbitrarily selected and used from simple metals and metal compounds containing the metal element contained in metal oxide particles such as crystalline metal oxide nanoparticles to be synthesized. .
Examples of metal oxide precursors include metal chlorides, metal acetates, metal alkoxides, and metal hydroxides. Among these, metal alkoxides, metal acetates, and metal hydroxides are preferred from the viewpoint of suppressing the generation of by-product impurities (for example, chlorides, etc.).

Examples of metal oxide precursors include titanium methoxide, titanium ethoxide, titanium di-n-butoxide (bis-2,4-pentanedionate), titanium diisopropoxide (bis-2,4 -pentanedionate), titanium-diisopropoxide (bisethylacetoacetate), titanium-2-hexoxide, titanium-n-butoxide, titanium tetraisopropoxide, titanium methoxypropoxide, titanium-n-nonyloxide, titanium oxide (bistetramethylpentanedionate), titanium-n-propoxide, titanium stearyl oxide, titanium triisostearyl isopropoxide, titanium trimethyl siloxide, zirconium-n-butoxide, zirconium-t-butoxide, zirconium-di-n -butoxide (bis-2,4-pentanedionate), zirconium-diisopropoxide (bis-2,2,6,6-tetramethyl-3,5-heptanedioate), zirconium ethoxide, zirconium propoxide , zirconium-2-ethylhexanoate, zirconium-2-ethylhexoxide, zirconium isopropoxide, zirconium-2-methyl-2-butoxide, zirconium-2,4-pentanedionate, zirconium-n-propoxide , zirconium-2,2,6,6-tetramethyl-3,5-heptanedionate, zirconium trimethyl siloxide, zirconyl propionate, hafnium-n-butoxide, hafnium-t-butoxide, hafnium ethoxide, hafnium- 2,4-pentanedionate, hafnium tetramethylheptanedionate, cerium (III) acetate hydrate, cerium-t-butoxide, cerium-2-ethylhexanoate, cerium isopropoxide, cerium methoxyethoxide, cerium -2,4-pentanedionate hydrate, cerium-2,2,6,6-tetramethylheptanedioate, cerium hydroxide, tin(IV) chloride pentahydrate, and the like.

One type of metal oxide precursor may be used alone, or two or more types may be used in combination in any combination and ratio.
The metal oxide precursor may be present in any state in the reaction solution. However, it is usually preferable that the metal oxide precursor exists in a dissolved state in an organic solvent or an aqueous solvent having an oxygen atom in its molecule.

[Organic solvent with oxygen atom in molecule]
Organic solvents having oxygen atoms in their molecules function as reaction solvents for reactions in which metal oxide precursors are transformed into metal oxide particles such as crystalline metal oxide nanoparticles, and also serve as reaction solvents for reactions in which metal oxide precursors are transformed into metal oxide particles such as crystalline metal oxide nanoparticles. It also functions as an oxygen source that supplies oxygen to the precursor. As the organic solvent having an oxygen atom in its molecule, any organic solvent containing oxygen can be used without any other limitations. The carbon number of the organic solvent having an oxygen atom in the molecule is arbitrary as long as it does not significantly impair the effects of the present invention, but from the viewpoint of increasing the reactivity of the reaction and oxygen supply performance, it is preferably 1 or more and 30 or less, and 20 or more. The following is more preferable, and 10 or less is still more preferable.
The molecular weight of the organic solvent having an oxygen atom in the molecule is arbitrary as long as it does not significantly impair the effects of the present invention, but from the viewpoint of increasing the reactivity of the reaction and oxygen supply performance, it is preferably 32 or more, and more preferably 50 or more. Preferably, 70 or more is more preferable. Further, the molecular weight of the organic solvent having an oxygen atom in the molecule is preferably 500 or less, more preferably 400 or less, and still more preferably 300 or less.
The boiling point of the organic solvent having an oxygen atom in the molecule is arbitrary as long as it does not significantly impair the effects of the present invention, but from the viewpoint of solvent volatility, it is preferably 50°C or higher, more preferably 70°C or higher, and 100°C or higher. The temperature is more preferably 150° C. or higher, particularly preferably 150° C. or higher. Further, the boiling point of the organic solvent having an oxygen atom in the molecule is preferably 300°C or lower, more preferably 270°C or lower, and even more preferably 250°C or lower.

Examples of organic solvents having an oxygen atom in the molecule include alcohols, ketones, aldehydes, ethers, esters, and siloxanes. Further, the number of oxygen atoms contained in one molecule of the organic solvent having oxygen atoms in these molecules is not particularly limited as long as it is one or more.
Examples of organic solvents having an oxygen atom in the molecule include ethanol, methanol, 1-octanol, benzyl alcohol, methoxyethanol, ethylene glycol, diethylene glycol, methylethanolamine, diethanolamine, acetone, benzaldehyde, cyclohexanone, acetophenone, diphenyl ether, and hexane. Examples include methyldisiloxane. Among these, benzyl alcohol and methoxyethanol are preferred from the viewpoint of excellent oxygen supply performance.
Note that the organic solvents having an oxygen atom in the molecule may be used alone or in combination of two or more in any combination and ratio.

Although there is no limit to the amount of the organic solvent having an oxygen atom in the molecule, the concentration of the metal oxide precursor in the organic solvent having an oxygen atom in the molecule is preferably 0.1 mol/L or more, and 0.1 mol/L or more. It is more preferably 3 mol/L or more, and even more preferably 0.5 mol/L or more. Further, the concentration of the metal oxide precursor in the organic solvent having an oxygen atom in the molecule is preferably 1.0 mol/L or less, more preferably 0.8 mol/L or less, and even more preferably 0.6 mol/L or less. preferable. When the amount of the organic solvent having an oxygen atom in the molecule is within the above range, gelation is less likely to occur and the yield of metal oxide particles is less likely to decrease.

[Water solvent]
Although there is no limit to the amount of the water solvent used, the concentration of the metal oxide precursor in the water solvent is preferably 0.1 mol/L or more, more preferably 0.3 mol/L or more, and 0.5 mol/L or more. is even more preferable. Further, the concentration of the metal oxide precursor in the aqueous solvent is preferably 1.0 mol/L or less, more preferably 0.8 mol/L or less, and even more preferably 0.6 mol/L or less. When the amount of the water solvent used is within the above range, gelation is less likely to occur and the yield of metal oxide particles is less likely to decrease.

[Amines]
As the amines, any of primary amines, secondary amines, and tertiary amines may be used. However, if tertiary amines are used, the effect of using amines in the method for producing metal oxide particles may be reduced, so one or more of primary amines and secondary amines may be used. It is preferable. Among these, primary amines are preferred from the viewpoint of less coloring due to oxidative deterioration.
Further, as the amines, aliphatic amines are preferable from the viewpoint of high action as a particle stabilizer during synthesis. In particular, it is preferable to use one or more types of aliphatic amines among primary and secondary aliphatic amines from the viewpoint of their high effectiveness as particle growth promoters or inhibitors.
The carbon number of the amine is arbitrary as long as it does not significantly impair the effects of the present invention, but is preferably 8 or more, more preferably 14 or more, and even more preferably 16 or more. Further, the number of carbon atoms in the amine is preferably 24 or less, more preferably 20 or less, and even more preferably 18 or less. If the carbon number of the amine is within the above range, it is easy to remove the amine that has been modified at high temperatures, and it is easy to ensure the effect as a stabilizer for particles during synthesis.
Examples of amines include, among primary amines, aliphatic amines such as oleylamine and octylamine. Examples of aromatic amines include aniline. Among secondary amines, examples of aliphatic amines include dioctylamine, methylethanolamine, diethanolamine, and the like.
One type of amine may be used alone, or two or more types may be used in combination in any combination and ratio.

The amount of amines used is preferably 0.5 times or more, more preferably 1.0 times or more, and still more preferably 1.5 times or more, based on the total number of moles of the metal oxide precursor. The amount of amines used is preferably 10 times or less, more preferably 6.0 times or less, and even more preferably 4.0 times or less, based on the total number of moles of the metal oxide precursor. If the amount of amines used is above the lower limit value, it will be easier to ensure the effect of using amines, the particle size of the obtained metal oxide particles will be less likely to increase, and the crystallinity of the obtained metal oxide particles will be improved. It becomes easier to improve. Moreover, if the amount of amines used is below the above-mentioned upper limit, the generation of impurities is suppressed in the above-mentioned manufacturing method, and it becomes easy to improve the quality of the obtained metal oxide particles.

Note that amines can act as crystal growth promoters and crystal growth inhibitors.
For example, when synthesizing zirconium oxide as metal oxide particles, crystal growth is promoted by the use of amines. Therefore, by using a synthesis method involving such amines, it becomes easier to synthesize metal oxide particles at a lower temperature and in a shorter time than conventional methods. That is, by appropriately adjusting the addition of amines to the metal oxide precursor, synthesis temperature, synthesis time, organic solvent or aqueous solvent having oxygen atoms in the molecule, etc., the crystallinity of the metal oxide particles and the particle size can be improved. Mode diameter etc. can be controlled.

[Other additives]
In addition to the metal oxide precursor, an organic or aqueous solvent having an oxygen atom in its molecule, and amines, other additives may be present in the reaction solution.
Examples of other additives include carboxylic acids, solvents other than organic solvents having an oxygen atom in the molecule (hereinafter also referred to as "other solvents"), phosphines, and the like.

(carboxylic acids)
Carboxylic acids are compounds for modifying metal oxide particles such as crystalline metal oxide nanoparticles with carboxylic acids. By allowing carboxylic acids to coexist in an organic solvent or an aqueous solvent having an oxygen atom in the molecule, metal oxide particles having carboxylic acids on the surface can be obtained. Therefore, it becomes possible to improve the dispersibility of metal oxide particles in an organic solvent or an aqueous solvent. Metal oxide particles may be synthesized by coexisting carboxylic acids in an organic solvent or aqueous solvent having an oxygen atom in the molecule, or metal oxide particles may be synthesized without carboxylic acids coexisting, and then carboxylic acids may be synthesized. An acid may be applied to the metal oxide particles. From the viewpoint of preventing side reactions during synthesis and contamination of impurities, it is preferable to allow carboxylic acids to act on the metal oxide particles after preparing them. If the method involves coexisting carboxylic acids in an organic solvent or aqueous solvent having an oxygen atom in the molecule, the step of adding carboxylic acids or a dispersant after synthesis of metal oxide particles can be omitted.

There is no restriction on the specific type of carboxylic acids, and any compound can be used as long as it can bind to metal oxide particles. From the viewpoint of less coloring, aliphatic carboxylic acids are preferred as the carboxylic acids.
Further, the number of carbon atoms in the carboxylic acids is arbitrary as long as it does not significantly impair the effects of the present invention, but it is preferably 2 or more, and more preferably 3 or more. Further, the number of carbon atoms in the carboxylic acids is preferably 24 or less, more preferably 20 or less, and even more preferably 18 or less. By setting the number of carbon atoms in the carboxylic acid within the above range, it becomes easier to remove the carboxylic acid that has been modified at high temperatures, and it becomes easier to ensure the effect as a modifier.
Examples of carboxylic acids include acrylic acid, methacrylic acid, tiglic acid, propionic acid, caprylic acid, methylbutyric acid, hexanoic acid, nonanoic acid, o-toluic acid, p-toluic acid, benzoic acid, and pt-butylbenzoic acid. Examples include phenylthioacetic acid, oleic acid, behenic acid, stearic acid, myristic acid, palmitic acid, and the like.
One type of carboxylic acids may be used alone, or two or more types may be used in combination in any combination and ratio.

There is no limit to the amount of carboxylic acids used, but it is preferably 0.1 times or more, more preferably 0.75 times or more, and 1.0 times or more based on the total number of moles of the metal oxide precursor. is even more preferable. The amount of carboxylic acids used is preferably 5.0 times or less, more preferably 3.0 times or less, and even more preferably 2.0 times or less, based on the total number of moles of the metal oxide precursor. Preferably, 1.5 times the mole or less is particularly preferable. By setting the amount of carboxylic acids to be used below the upper limit value, it becomes easier to obtain the effects of using carboxylic acids. In addition, by setting the amount of carboxylic acids to be equal to or more than the lower limit value, generation of gel is suppressed in the method for producing metal oxide particles, and the quality of the obtained metal oxide particles can be easily improved.
In addition, when using amines and carboxylic acids in combination, the amount of carboxylic acids used is preferably 0.5 times or less based on the total number of moles of amines, from the viewpoint of suppressing gel formation. , more preferably 0.25 times the mole or less.

Note that when carboxylic acids are used as additives when producing metal oxide particles, the carboxylic acids also adsorb to the surface of the metal oxide particles in the same way as the amines mentioned above, and the metal oxide particles and organic Improves affinity with solvents. This prevents the metal oxide particles from strongly attracting each other, so when carboxylic acids are used, aggregation of the metal oxide particles is further suppressed.

(Other solvents)
The reaction solution may contain an organic solvent having an oxygen atom in its molecule or a solvent other than the water solvent. One type of other solvents may be used alone, or two or more types may be used in combination in any combination and ratio.
Examples of other solvents include aromatic hydrocarbons such as toluene, xylene, and mesitylene, aliphatic hydrocarbons such as hexane, octane, cyclohexane, and decahydronaphthalene, formamide, N,N-dimethylformamide, N,N -Amides such as dimethylacetamide, chlorinated aliphatic hydrocarbons such as dichloromethane, chloroform, and 1,2-dichloroethane, and the like.
One type of other solvents may be used alone, or two or more types may be used in combination in any combination and ratio.

[Preparation method of reaction solution]
The method for preparing the reaction solution for producing metal oxide particles such as crystalline metal oxide nanoparticles is not particularly limited and is arbitrary. Further, the order in which the metal oxide precursor, the organic solvent or aqueous solvent having an oxygen atom in the molecule, and the amines and other additives used as necessary are mixed is not particularly limited and may be arbitrary. However, many metal oxide precursors react quickly with moisture in the air. Therefore, it is preferable to mix in an inert gas such as a nitrogen atmosphere that does not contain moisture. For example, a method in which an organic solvent having an oxygen atom in its molecule is bubbled with nitrogen for a predetermined period of time, a predetermined amount of a metal oxide precursor is mixed and stirred, and then a predetermined amount of amines and additives are mixed as necessary. can be mentioned.

[Reaction process]
The reaction solution is maintained under predetermined reaction conditions, the reaction is allowed to proceed, and metal oxide particles are obtained in the reaction solution.
The reaction conditions are shown below.

(reaction temperature)
The reaction temperature (here, it means the temperature of the reaction solution) is not particularly limited, and is arbitrary as long as desired metal oxide particles such as crystalline metal oxide nanoparticles can be obtained. However, one of the advantages is that metal oxide particles can be obtained at a relatively low temperature, and the reaction temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 160°C or higher. Further, the reaction temperature is preferably 240°C or lower, more preferably 220°C or lower, and even more preferably 200°C or lower. If the reaction temperature is within the above range, it is easy to obtain crystalline metal oxide nanoparticles, the amount of by-products due to the decomposition of organic matter is less likely to increase, and the quality of the crystalline metal oxide nanoparticles is good. becomes. Note that the reaction temperature may be constant or may vary. Further, the temperature of the reaction solution may be continuously within the above reaction temperature range, or may be intermittently within the range of the reaction temperature. Furthermore, the temperature within the reaction solution may be uniform or non-uniform. Therefore, as long as metal oxide particles are obtained, for example, a part of the reaction solution may be outside the reaction temperature range.

(reaction pressure)
The pressure conditions under which the reaction proceeds are not particularly limited, and may be arbitrary as long as desired metal oxide particles such as crystalline metal oxide nanoparticles can be obtained. However, the pressure condition is usually lower than the autogenous pressure. Note that the autostatic pressure herein refers to the vapor pressure at the above temperature of an organic solvent or an aqueous solvent having an oxygen atom in its molecule.

(reaction time)
The reaction time is not particularly limited, and is arbitrary as long as desired metal oxide particles such as crystalline metal oxide nanoparticles can be obtained. However, in the method for producing metal oxide particles, by coexisting a metal oxide precursor, an organic solvent or aqueous solvent having an oxygen atom in the molecule, and, if necessary, amines in the reaction system, One of the advantages is that metal oxide particles can be obtained in a shorter time than conventional methods. Therefore, the reaction time is preferably 48 hours or less, more preferably 24 hours or less, and even more preferably 18 hours or less. Moreover, the reaction time is preferably 1 hour or more, more preferably 4 hours or more, and even more preferably 8 hours or more.

(Atmosphere during reaction)
The atmosphere during the reaction is not particularly limited and may be arbitrary as long as desired metal oxide particles such as crystalline metal oxide nanoparticles can be obtained. However, the reaction is preferably carried out under an inert atmosphere. This is because many metal oxide precursors quickly react with moisture in the air. Note that the inert atmosphere here means that none of the metal oxide precursor, the organic solvent or water solvent having an oxygen atom in the molecule, and the amines react with the atmosphere.
Examples of the atmospheric gas constituting the inert atmosphere include nitrogen, argon, and helium. In addition, a single inert gas may be used for the inert atmosphere, or two or more types of inert gases may be used.
In order to satisfy the above reaction conditions, for example, the reaction solution may be maintained at the above predetermined reaction temperature in a closed container. For example, the reaction solution may be sealed in an airtight container such as an autoclave container under an inert atmosphere, heated within the airtight container, and maintained at the predetermined reaction temperature.

(Process during reaction)
Preparation of the reaction solution and progress of the reaction can also be performed as a series of steps. For example, in an environment where predetermined reaction conditions have been prepared, a metal oxide precursor, an organic solvent or aqueous solvent having an oxygen atom in the molecule, and one or more of amines and additives as necessary. By mixing the two, it becomes possible to carry out the preparation of the reaction solution and the progress of the reaction as a series of steps that are not distinguished from each other.
Desired metal oxide particles, such as crystalline metal oxide nanoparticles, can be obtained by such a synthesis method, but metal oxide particles are primary particles (metal oxide crystal particles formed by other particles). It is obtained as a slurry in a state of (meaning a single particle not in contact with other particles) or a weakly agglomerated state.

[Other processes]
In the method for producing metal oxide particles, steps other than the above-mentioned reaction step may be performed as necessary.
For example, a recovery step may be performed after the reaction step. In the recovery step, metal oxide particles such as crystalline metal oxide nanoparticles obtained in the reaction step are isolated and recovered. The recovery method is arbitrary, but for example, by mixing a composition (reaction solution) containing metal oxide particles with a poor solvent, precipitation can easily occur, and the metal oxide particles can be separated into precipitates. It can be recovered as Here, the term "poor solvent" refers to a solvent for metal oxide particles to which one or more of amines and carboxylic acids have been adsorbed. Examples of poor solvents include alcohols. Note that the use of a poor solvent also makes it possible to wash the metal oxide particles.
Furthermore, centrifugation, filter filtration, and other conventional recovery methods can be used to recover the precipitated metal oxide particles.

Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

[Production Example 1: Production of metal oxide particles 1]
Put 45.90 mL of 1-octanol (an organic solvent having an oxygen atom in the molecule) into a 200 mL beaker, add 22.78 g of oleic acid, and 1.5 mL of titanium tetraisopropoxide (number of moles = 5 mmol), and stir for 30 minutes. A reaction solution was prepared by bubbling nitrogen while stirring. This reaction solution was sealed in a stainless steel sealed container and heated at 140° C. for 7 hours. After the reaction was completed, a large excess of acetone was added to the resulting reaction solution to generate a precipitate, and the precipitate was collected by centrifugation. The precipitate was washed three times with ethanol, collected, and dried to obtain 0.24 g of crystalline titanium oxide (metal oxide nanocrystals). This was designated as metal oxide particle 1.
Regarding metal oxide particles 1, the mode diameter (most frequent diameter) of the particle size distribution was confirmed using a particle size measurement system (manufactured by Otsuka Electronics Co., Ltd., "ELSZ-2000") based on dynamic light scattering method. , 8 nm.

[Production Example 2: Production of metal oxide particles 2]
37.Pour 32 mL of benzyl alcohol (an organic solvent having an oxygen atom in the molecule) into a 200 mL beaker, add 1.75 g of tin(IV) chloride pentahydrate (number of moles = 5 mmol), and stir for 30 minutes. A reaction solution was prepared by bubbling nitrogen. This reaction solution was sealed in a stainless steel sealed container and heated at 130° C. for 3 hours. After the reaction was completed, a large excess of acetone was added to the resulting reaction solution to generate a precipitate, and the precipitate was collected by centrifugation. The precipitate was washed three times with ethanol, collected, and dried to obtain 0.4 g of crystalline tin oxide (metal oxide nanocrystals). This was designated as metal oxide particle 2.
Regarding metal oxide particles 2, we checked the mode diameter (most frequent diameter) of the particle size distribution measured with a particle size measurement system (manufactured by Otsuka Electronics Co., Ltd., "ELSZ-2000") based on the dynamic scattering method. It was 8 nm.

[Production Example 3: Production of metal oxide particles 3]
500 mL of benzyl alcohol (an organic solvent having an oxygen atom in the molecule) was placed in a 1 L three-necked flask, and nitrogen bubbling was carried out for 30 minutes. While bubbling with nitrogen, 116.7 g of a 70% by mass 1-propanol solution of zirconium isopropoxide (number of moles of zirconium isopropoxide = 0.25 mol) was added as a metal oxide precursor, and the mixture was stirred for 30 minutes. 100.3 g of oleylamine (amines = 0.375 mol) was added to the mixture, and the mixture was further stirred for 30 minutes to prepare a reaction solution. This reaction solution was sealed in a stainless steel sealed container and heated at 200° C. for 48 hours. After the reaction was completed, a large excess of ethanol was added to the resulting milky white slurry reaction solution to form a precipitate, and the precipitate was collected by centrifugation. The precipitate was washed three times with ethanol, collected, and dried to obtain 20 g of crystalline zirconium oxide (metal oxide nanocrystals). This was designated as metal oxide particle 3.
Regarding metal oxide particles 3, 100 particles were observed based on an image observed at 2 million times (acceleration voltage 200 kV) using a transmission electron microscope (manufactured by JEOL Ltd., "JEM-ARM200F"). The size (primary particle diameter) was measured and the average particle diameter was determined by arithmetic averaging, which was 5 nm.

[Production Example 4: Production of metal oxide particles 4]
Put 135 g of pure water in a 300 mL beaker, add 3.52 g of cerium (III) acetate hydrate (number of moles = 10.50 mmol), drop 15 mL of 5 mol/L NaOH aqueous solution while stirring, and stir for 1 hour. did. Thereafter, the gel was collected by centrifugation, washed six times with pure water, and 75 g of pure water was added to obtain a precursor solution. Next, 35 g of a 39.84 mmol/L Na oleate aqueous solution was put into a 100 mL beaker, and 15 g of the precursor solution was added while stirring to prepare a reaction solution. This reaction solution was sealed in a stainless steel sealed container and heated at 180° C. for 6 hours. After the reaction was completed, a large excess of pure water was added to the resulting reaction solution, and the mixture was centrifuged to collect the precipitate. The precipitate was washed three times with methanol, collected, and dried to obtain 0.38 g of crystalline cerium oxide (metal oxide nanocrystals). This was designated as metal oxide particle 4.
Regarding the metal oxide particles 4, we checked the mode diameter (most frequent diameter) of the particle size distribution measured with a particle size measurement system (manufactured by Otsuka Electronics Co., Ltd., "ELSZ-2000") based on the dynamic scattering method. It was 8 nm.

[Production Example 5: Preparation of metal oxide particle dispersion 3]
0.3 g of crystalline zirconium oxide (metal oxide particles 3) obtained in Production Example 3 was added to 28.5 g of butyl acetate, an organic solvent, and while loosening the precipitated crystalline zirconium oxide, Dispersion was performed using a sonic cleaner for 60 minutes. After that, 0.09 g of caprylic acid and 0.06 g of acrylic acid were added as dispersants (total of dispersants were 50% by mass based on the crystalline zirconium oxide), and further dispersed in an ultrasonic cleaner for 60 minutes to make the crystal clear. A metal oxide particle dispersion liquid 3 was prepared.

[Production Example 6: Preparation of metal oxide particle dispersion 1]
Instead of metal oxide particles 3, the crystalline titanium oxide (metal oxide particles 1) obtained in Production Example 1 was used, and the dispersants were 60% by mass of 4-trifluoromethylbenzoic acid and 40% by mass of acrylic acid. % (total 100% by mass of the dispersant based on the crystalline zirconium oxide), a transparent metal oxide particle dispersion 1 was prepared in the same manner as in Production Example 5.

[Production Example 7: Preparation of metal oxide particle dispersion 2]
Instead of metal oxide particles 3, the crystalline tin oxide (metal oxide particles 2) obtained in Production Example 2 was used, and the organic solvent was replaced with propylene glycol monomethyl ether acetate (hereinafter also referred to as PGMEA). A transparent metal oxide particle dispersion 2 was prepared in the same manner as in Production Example 5, except that only caprylic acid was used as the dispersant (the total amount of the dispersant was 100% by mass based on the crystalline tin oxide).

[Production Example 8: Preparation of metal oxide particle dispersion liquid 4]
Instead of metal oxide particles 3, the crystalline cerium oxide (metal oxide particles 4) obtained in Production Example 4 was used, the organic solvent was replaced with PGMEA, and the dispersant was 4-trifluoromethylbenzoic acid. A transparent metal oxide particle dispersion liquid 4 was prepared in the same manner as in Production Example 5 except that the dispersant was replaced with only 100% by mass of the dispersant based on the crystalline cerium oxide.

[Example 1: Formation of photocatalyst film 1]
1 mL of metal oxide particle dispersion 1 was dropped onto a quartz glass substrate (thickness: 1 mm) with a diameter of 25 mm as a base material using a dropper, and was applied onto the base material by rotating at a speed of 3000 rpm for 20 seconds (coating process ). Thereafter, it was prebaked at 80° C. for 60 seconds using a hot plate to form a coating film on the substrate (drying and aging step).
Next, the coated surface was cleaned by immersing the base material on which the coating film was formed in butyl acetate as a cleaning solvent for 1 minute (cleaning step).
After the cleaning process, the substrate with the coating film was heated from room temperature to 800°C over 4 hours, held at 800°C for 30 minutes, and then allowed to cool to sinter the coating film (sintering process). ), a photocatalytic film 1 made of a thin film of a metal oxide was formed on a base material to obtain a base material (photocatalyst film coated body) with a thin film of a metal oxide.

[Example 2: Formation of photocatalyst film 2]
By performing the same operation as in Example 1 except for replacing metal oxide particle dispersion 1 with metal oxide particle dispersion 2 and using PGMEA instead of butyl acetate as the cleaning solvent, the base material A photocatalytic film 2 made of a thin film of metal oxide was formed thereon to obtain a base material (photocatalyst film coated body) with a thin film of metal oxide.

[Example 3: Formation of photocatalyst film 3]
In the sintering process, the same procedure as in Example 1 was performed except that instead of high-temperature sintering at 800°C, photosintering was performed using a Xe excimer lamp at room temperature of 25°C. A photocatalytic film 3 made of a thin film of metal oxide was formed to obtain a base material (photocatalyst film coating) with a thin film of metal oxide.

[Comparative Example 1: Formation of metal oxide thin film C1]
1 mL of metal oxide particle dispersion 1 was dropped onto a quartz glass substrate (thickness: 1 mm) with a diameter of 25 mm as a base material using a dropper, and was applied onto the base material by rotating at a speed of 1000 rpm for 20 seconds (coating process ). Thereafter, it was prebaked at 80° C. for 60 seconds using a hot plate to form a coating film on the substrate (drying and aging step).
After the drying and aging process, the substrate with the coated film is heated from room temperature to 800°C over 4 hours, held at 800°C for 30 minutes, and then allowed to cool to sinter the coated film. Bonding step), a metal oxide thin film C1 was formed on the base material to obtain a base material with a metal oxide thin film.

[Comparative Example 2: Formation of metal oxide thin film C2]
A thin film C2 of metal oxide was formed on the substrate by performing the same operation as in Comparative Example 1 except that metal oxide particle dispersion 2 was used instead of metal oxide particle dispersion 1. , a substrate with a thin film of metal oxide was obtained.

[Comparative Example 3: Formation of metal oxide thin film C3]
A thin film C3 of metal oxide was formed on the substrate by performing the same operation as in Comparative Example 1 except that metal oxide particle dispersion 3 was used instead of metal oxide particle dispersion 1. , a substrate with a thin film of metal oxide was obtained.

[Comparative Example 4: Formation of metal oxide thin film C4]
A thin film C4 of metal oxide was formed on the substrate by performing the same operation as in Comparative Example 1 except that metal oxide particle dispersion 4 was used instead of metal oxide particle dispersion 1. , a substrate with a thin film of metal oxide was obtained.

[Comparative Example 5: Formation of thin film C5]
A thin film C5 was formed on the base material by performing the same operation as in Example 1 except that the metal oxide particle dispersion liquid 1 was not applied, and a base material with a thin film was obtained.

[Comparative Example 6: Formation of metal oxide thin film C6]
In the sintering process, the same operation as in Comparative Example 1 was performed except that instead of high-temperature sintering at 800°C, photosintering was performed using a Xe excimer lamp at room temperature of 25°C. A metal oxide thin film C6 was formed to obtain a base material with a metal oxide thin film.

The physical property values of the thin films obtained in each Example and Comparative Example were measured and evaluated using the following procedure.

[Measurement of physical properties of metal oxide thin film]
(Measurement of primary particle diameter (minimum particle diameter (X)) in AFM surface observation of metal oxide particles)
The minimum particle size (X) of the metal oxide particles was measured using an atomic force microscope (AFM) "NanoScope V/Dimension Icon" manufactured by Bruker AXS. The AFM measurement conditions were such that the measurement mode was tapping mode, the measurement range was 1 μm×1 μm, and the number of measurement points was 512×512. Among the observed metal oxide particles on the surface, the one with the smallest particle size was taken as the measured value of the primary particle size (minimum particle size (X)). The results are shown in Table 1.

(Measurement of film thickness of metal oxide thin film)
The thickness of the metal oxide thin film after sintering was measured using a "Spectroscopic Ellipsometer RC2" manufactured by JA Woollam Japan Co., Ltd., and the thickness of the metal oxide thin film (film thickness (Y)). The results are shown in Table 1.

(Measurement of water contact angle and evaluation of hydrophilicity)
In order to evaluate the hydrophilicity of the base material with the metal oxide thin film obtained in Examples 1 and 2 and Comparative Examples 1 to 4 and the base material with the thin film obtained in Comparative Example 5, JIS R 1703-1:2020 (Fine Ceramics - Self-cleaning Performance Test Method for Photocatalytic Materials Part 1: Measurement of Water Contact Angle), the water contact angle on the surface of the thin film side was measured according to the following procedure.
In the atmosphere, 1 μL of pure water was dropped onto the surface of the thin film using a pipette, and after 0.1 seconds, a photograph was taken from the side, and the contact angle was measured based on the photographed image for evaluation. Specifically, if the water contact angle was 10 degrees or less, it was evaluated that the hydrophilicity was sufficiently high, and if the water contact angle exceeded 10 degrees, it was evaluated that the hydrophilicity was insufficient. The results are shown in Table 1.

(Measurement of light transmittance and evaluation of transparency)
The substrates with the metal oxide thin films obtained in Examples 1 to 3 and Comparative Examples 1 to 4, and 6, and the substrate with the thin film obtained in Comparative Example 5 were tested using a spectrophotometer manufactured by Ocean Optics. The light transmittance in the wavelength range from 200 nm to 800 nm on the surface of the thin film was measured using a 2000-nm USB-4000. If it shows a light transmittance of 80% or more in all wavelength regions, it is judged to be sufficiently transparent and is evaluated as "A", and if the light transmittance in any wavelength region is 70% or more and less than 80%. It was evaluated as "B", and the case where the light transmittance was less than 70% in any wavelength region was evaluated as "C". The results are shown in Table 1.
In addition, graphs of the light transmittance of the base materials with thin films of metal oxides obtained in Example 1 and Comparative Example 1 are shown in FIGS. Graphs of the light transmittance of the base material with the thin film are shown in FIGS. 3 and 4. The solid line is the measurement result of the light transmittance of the base material with the metal oxide thin film obtained in Example 1 and Example 2, and the broken line is the measurement result of the metal oxide thin film obtained in Comparative Example 1 and Comparative Example 2. These are the measurement results of the light transmittance of the base material with the attached. The measurement results of the light transmittance shown in FIGS. 1 to 4 are shown as relative values to the light transmittance of a single quartz glass substrate measured using the same procedure, and when the light transmittance is 100%, This means that the light transmittance is equal to that of a quartz glass substrate.

[Evaluation of photocatalytic property]
Regarding the base material with the thin film of metal oxide obtained in Examples 1 to 3 and Comparative Examples 1 to 4, and 6, and the base material with the thin film obtained in Comparative Example 5, 2.5 μg was applied to the surface of the thin film side. 5 mL of methylene blue aqueous solution with a concentration of /mL was added dropwise, and ultraviolet rays were irradiated for 5 minutes using a handy type UV lamp (HLR100T-2) with an ultraviolet illuminance of 170 mW/cm ² to visually evaluate the fading state of the methylene blue aqueous solution. If the methylene blue aqueous solution has faded to a colorless level to the extent that the color cannot be visually distinguished, it is judged that sufficient photocatalytic properties have been expressed and is evaluated as "A". A case where the color of the methylene blue aqueous solution could be clearly distinguished by visual observation without fading was evaluated as "B". The results are shown in Table 1.

[Self-cleaning evaluation]
Regarding the base material with the metal oxide thin film obtained in Example 1 and Comparative Example 1 and the base material with the thin film obtained in Comparative Example 5, JIS R 1703-1:2020 (Fine Ceramics - Photocatalyst Materials) The water contact angle was measured while irradiating the surface of the thin film with ultraviolet rays in accordance with Self-cleaning Performance Test Method Part 1: Measurement of Water Contact Angle. Specifically, the surface of the thin film before irradiation with ultraviolet rays and 1 hour, 2 hours, 4 hours, 6 hours, 24 hours, 28 hours, and 48 hours after the start of ultraviolet irradiation. Water contact angle was measured. Table 1 shows the time required for the water contact angle to become 20° or less. In addition, a case where the water contact angle did not become 20° or less even after 48 hours was evaluated as "x". Moreover, the measurement results of the water contact angle before irradiation with ultraviolet rays and at each elapsed time are shown in FIG.

As is clear from the results in Table 1 and Figures 1 to 4, the metal oxide thin film-covered substrates obtained in Examples 1 and 2 were superior to a single quartz glass substrate in the entire wavelength range of 200 nm to 800 nm. It showed the same high transparency, the transmittance did not easily decrease, and it was sufficiently transparent.
On the other hand, in the base materials with thin metal oxide films obtained in Comparative Examples 1 and 2, there was a wavelength range in which the transmittance was 80% or less in the wavelength range of 200 nm to 800 nm.

Furthermore, as is clear from the results in Table 1, the base materials with the metal oxide thin films obtained in Examples 1 to 3 had a metal oxide on the surface on the thin film side that had a bandgap energy that absorbed light in the ultraviolet region. By having an oxide nanostructure, it had excellent transparency and photocatalytic properties. Further, the base material with the metal oxide thin film obtained in Example 1 also had excellent self-cleaning properties.
On the other hand, in the base materials with the metal oxide thin film obtained in Comparative Examples 1 to 4 and Comparative Example 6, in which the coating film was sintered without solvent cleaning, the minimum particle size (X) of the metal oxide The film thickness (Y) of the thin film was not sufficiently thin, and there was a wavelength region with poor transparency. In particular, the base material with the metal oxide thin film obtained in Comparative Example 4 was also poor in photocatalytic properties.
In the base material with a thin film obtained in Comparative Example 5, the thin film did not contain a metal oxide and had poor photocatalytic properties and self-cleaning properties.

According to the present invention, it is possible to provide a photocatalytic film covering that can simultaneously achieve high levels of transparency and photocatalytic properties, and a method for producing the same. It is extremely important industrially because it can be suitably used in a wide range of fields such as irradiation equipment.

Claims (9)

A photocatalytic film coating having a photocatalytic film containing a metal oxide having a band gap energy of valence band and conduction band of 0.1 eV to 5.5 eV,
The light transmittance of the photocatalytic film at a wavelength of 200 nm to 800 nm is 80% or more,
A photocatalytic film coating, wherein the photocatalytic film has a thickness of 0.5 nm to 200 nm. The metal oxide is zirconium, titanium, cerium, indium, tin, zinc, aluminum, magnesium, silicon, iron, lead, copper, tungsten, niobium, chromium, strontium, indium, ruthenium, cadmium, gallium, antimony, tellurium, The photocatalytic membrane coating according to claim 1, containing one or more metal elements selected from the group consisting of selenium and hafnium. According to claim 1 or 2, the metal oxide in the photocatalytic film satisfies the following formula (1) and the following formula (2) when the minimum particle size of the metal oxide is X nm and the film thickness of the photocatalyst film is Y nm. The photocatalytic membrane coating described above.
0.5≦X≦200...(1)
1.0≦Y/X≦3.0...(2) The photocatalytic film coating according to claim 1 or 2, wherein the photocatalytic film has a light transmittance of 90% or more in a wavelength range of 200 nm to 800 nm. The photocatalytic film coating according to claim 1 or 2, wherein the photocatalytic film has a thickness of 0.5 nm to 100 nm. The photocatalytic film coating according to claim 1 or 2, wherein the time required for the water contact angle on the surface of the photocatalytic film to become 20° or less as measured in accordance with JIS R 1703-1:2020 is 48 hours or less. body. A method for producing a photocatalytic membrane coating according to claim 1 or 2, comprising:
A method for producing a photocatalyst film coated body, comprising applying the metal oxide particle dispersion to a substrate, drying and aging, washing with a solvent, and sintering at 0° C. to 1000° C. The method for producing a photocatalytic membrane coating according to claim 7, wherein the metal oxide particles have a mode diameter of 200 nm or less. The photocatalytic membrane coating according to claim 1 or 2, further comprising a light source that irradiates light with a spectrum having a peak in a wavelength range of 10 nm to 400 nm.

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