JP7077550B2 - Titanium oxide airgel particles, method for producing titanium oxide airgel particles, composition for forming a photocatalyst, photocatalyst, and structure. - Google Patents

Description

The present invention relates to titanium oxide airgel particles, a method for producing titanium oxide airgel particles, a composition for forming a photocatalyst, a photocatalyst, and a structure.

Patent Document 1 includes a granular material formed of a porous material having micropore to mesopore pores, and a thermal spray coating formed by spraying a thermal spray material containing photocatalyst particles onto the outer surface of the granular material. It is determined that a gap larger than the pores is formed between the photocatalyst particles that have been spray-attached to the outer surface of the granular material and the outer surface of the granular material, and between the photocatalyst particles that have been sprayed and adhered to each other. Characteristic adsorbents are disclosed.

Patent Document 2 describes an adsorbent-photocatalyst hybrid deodorizing material for coating containing a titanium oxide nanodisperse, an adsorbent, an inorganic compound dispersion, a silica compound and metal fine particles, wherein the inorganic compound dispersion contains an inorganic compound. A adsorbent-photocatalyst hybrid deodorizing material is disclosed, which comprises 0.02 to 0.2 by weight with respect to the amount of the adsorbent.

Patent Document 3 discloses an ammonia decomposition catalyst having metal particles having ammonia decomposing ability and a porous material having pores having a diameter smaller than the particle size of the metal particles and in contact with the metal particles. ing.

Patent Document 4 is a titanium-containing powder for a raw material of a honeycomb-shaped exhaust gas treatment catalyst containing at least one of titanium dioxide and a titanium composite oxide, which comprises the following (a) to (c). (Excluding those containing vanadium oxide) are disclosed.
(A) Phosphorus is contained as P ₂ O ₅ in an amount of 0.03 to 0.5% by mass.
(B) The crystallite diameter of the anatase-type crystal (101) plane is in the range of 12 to 40 nm when the titanium-containing powder (1) contains only titanium dioxide, and (2) contains a titanium composite oxide. In some cases, it should be in the range of 10 to 38 nm.
(C) Sulfuric acid root should be contained in the range of 0.4 to 4.0% by mass.

Patent Document 5 describes titanium dioxide having a ratio D _top / D ₅₀ of the maximum particle size D _top and the average particle size D ₅₀ of the primary particles observed with an electric field radiation scanning electron microscope of 1 or more and 3 or less. Is disclosed.

Patent Document 6 describes a composite formed of visible light responsive photocatalyst titanium oxide and porous silica, having a BET specific surface area of 200 to 1000 m ² / g and a pore volume of 0.10 to 1.0 cm ³ . A photocatalyst characterized by / g and a pore diameter of 1 to 10 nm is disclosed.

Patent Document 7 describes a first coat layer (21) and a second coat layer composed of a porous base material (10) and oxide particles sequentially laminated on the surface of the porous base material (10). The particle size of the oxide particles comprising (22) and the catalyst component (30) provided on the second coat layer (22) and constituting the first coat layer (21) is determined. A catalyst body characterized by having a particle size larger than that of the oxide particles constituting the second coat layer (22) is disclosed.

Patent Document 8 discloses a porous complex characterized in that nanoscale metal ultrafine particles are immobilized on a carrier containing a metal oxide in a dispersed state.

Japanese Unexamined Patent Publication No. 2017-0356445 Japanese Unexamined Patent Publication No. 2016-22147 Japanese Unexamined Patent Publication No. 2016-064407 JP-A-2015-142917 Japanese Unexamined Patent Publication No. 2011-057552 Japanese Unexamined Patent Publication No. 2009-131760 Japanese Unexamined Patent Publication No. 2006-281155 Japanese Unexamined Patent Publication No. 2006-247524

Titanium oxide particles, which are widely used as photocatalytic materials, exhibit a photocatalytic function by absorbing ultraviolet light. Therefore, the titanium oxide particles can exhibit the photocatalytic function in the daytime on a sunny day when sufficient ultraviolet light can be secured, but the photocatalytic function tends to decrease at night or in the shade. For example, when titanium oxide particles are used as the outer wall material, the stain resistance performance may differ between the sun and the shade. Further, when the titanium oxide particles are used in an air purifier, a water purifier, or the like, it may be necessary to install a black light or the like as a light source of ultraviolet rays inside the device. In view of the above circumstances, there is a demand for a photocatalytic material that exhibits a photocatalytic function even in the visible light region.

On the other hand, as a technique for increasing the specific surface area that exhibits a photocatalytic function, a photocatalytic material in which photocatalytic particles are attached to the pore surface of a porous material made of a microporous material such as zeolite or silica gel or a mesoporous material is known. However, in this photocatalytic material, the photocatalytic function may not necessarily be improved because the photocatalyst particles block the pore inlet of the porous material or the inside of the fine pores is not exposed to light.

The present invention has been made under the above circumstances.

INDUSTRIAL APPLICABILITY The present invention exhibits a higher photocatalytic function even in the visible light region and has excellent dispersibility as compared with titanium oxide particles which have absorption only at a wavelength of less than 450 nm in the visible absorption spectrum and have a BET specific surface area of less than 120. An object of the present invention is to provide titanium aerogel particles.

Specific means for solving the above-mentioned problems include the following aspects.

The invention according to < 1 > is
The BET specific surface area is 120 m ² / g or more and 1000 m ² / g or less, has absorption at wavelengths of 450 nm and 750 nm in the visible absorption spectrum, and a metal atom having a hydrocarbon group is bonded to the surface via an oxygen atom. Titanium oxide aerogel particles having an elemental ratio C / Ti of carbon C and titanium Ti on the surface of 0.3 or more and 1.5 or less.

The invention according to < 2 > is
When the titanium airgel particles are irradiated with ultraviolet rays having a wavelength of 352 nm and an irradiation intensity of 1.3 mW / cm ² for 20 hours, the amount of decrease in C / Ti on the surface of the titanium airgel particles is 0.01 or more and 0.3 or less. The titanium oxide airgel particles according to < 1 > .

The invention according to < 3 > is
The titanium oxide airgel particles according to < 1 > or < 2 > , which have absorption in the entire range of wavelengths of 400 nm or more and 800 nm or less in the visible absorption spectrum.

The invention according to < 4 > is
The titanium oxide airgel particles according to any one of < 1 > to < 3 > , wherein the volume average particle size is 0.1 μm or more and 3 μm or less, and the volume particle size distribution is 1.5 or more and 10 or less.

The invention according to < 5 > is
The titanium oxide airgel particles according to any one of < 1 > to < 4 > , wherein the primary particles contained in the titanium oxide airgel particles have an average diameter of 1 nm or more and 120 nm or less.

The invention according to < 6 > is
The titanium oxide airgel particles according to any one of < 1 > to < 5 > , wherein the metal atom is a silicon atom.

The invention according to < 7 > is
Any one of < 1 > to < 6 > , wherein the hydrocarbon group is a saturated or unsaturated aliphatic hydrocarbon group having 1 or more and 20 or less carbon atoms or an aromatic hydrocarbon group having 6 or more and 20 or less carbon atoms. The titanium oxide aerogel particles described in the section.

The invention according to < 8 > is
The titanium oxide airgel particles according to < 7 > , wherein the hydrocarbon group is a saturated aliphatic hydrocarbon group having 1 or more carbon atoms and 20 or less carbon atoms.

The invention according to < 9 > is
The titanium oxide airgel particles according to < 8 > , wherein the hydrocarbon group is a saturated aliphatic hydrocarbon group having 4 or more and 10 or less carbon atoms.

The invention according to < 10 > is
A step of granulating porous particles containing titanium oxide by a sol-gel method to prepare a dispersion liquid containing the porous particles and a solvent, and a step of removing the solvent from the dispersion liquid using supercritical carbon dioxide. The step of surface-treating the porous particles after removing the solvent with a metal compound having a metal atom and a hydrocarbon group in supercritical carbon dioxide, and heating the porous particles after the surface treatment. The method for producing titanium oxide airgel particles according to any one of < 1 > to < 9 > , which comprises a step of treating.

The invention according to < 11 > is
It is a composition for forming a photocatalyst containing the titanium oxide airgel particles according to any one of < 1 > to < 9 > , and at least one compound selected from the group consisting of a dispersion medium and a binder.

The invention according to < 12 > is
A photocatalyst containing or consisting of titanium oxide airgel particles according to any one of < 1 > to < 9 > .

The invention according to < 13 > is
It is a structure having the titanium oxide airgel particles according to any one of < 1 > to < 9 > .

According to < 1 > , it exhibits a higher photocatalytic function even in the visible light region and has dispersibility as compared with titanium oxide particles having absorption only at a wavelength of less than 450 nm in the visible absorption spectrum and having a BET specific surface area of less than 120. Excellent titanium oxide airgel particles are provided.
According to < 2 > , the amount of decrease in C / Ti on the surface of the titanium oxide airgel particles when the titanium oxide airgel particles are irradiated with ultraviolet rays having a wavelength of 352 nm and an irradiation intensity of 1.3 mW / cm ² for 20 hours is 0. Titanium oxide airgel particles that exhibit higher photocatalytic function even in the visible light region are provided as compared to the case where it is less than 01 or more than 0.3.
According to the invention according to < 3 > , oxidation exhibiting a higher photocatalytic function even in the visible light region as compared with titanium oxide aerogel particles having absorption only in a part of the wavelength range of 400 nm or more and 800 nm or less in the visible absorption spectrum. Titanium aerogel particles are provided.
According to the invention according to < 4 > , the photocatalyst is higher in the visible light region than when the volume average particle size is less than 0.1 μm or more than 3 μm, or the volume particle size distribution is less than 1.5 or more than 10. Titanium oxide airgel particles that exhibit their function are provided.
According to the invention according to < 5 > , titanium oxide airgel particles exhibiting a higher photocatalytic function in the visible light region than when the average diameter of the primary particles is less than 1 nm or more than 120 nm are provided.
According to the invention according to < 6 > , titanium oxide airgel particles exhibiting a higher photocatalytic function in the visible light region as compared with the case where the metal atom is an aluminum atom or a titanium atom are provided.
According to the invention according to < 7 > , titanium oxide airgel particles exhibiting a higher photocatalytic function in the visible light region as compared with the case where the hydrocarbon group has more than 20 carbon atoms are provided.
According to the invention according to < 8 > , a higher photocatalytic function is exhibited in the visible light region and the dispersibility is superior as compared with the case where the hydrocarbon group is an aromatic hydrocarbon group having 6 or more carbon atoms and 20 or less carbon atoms. Titanium oxide aerogel particles are provided.
According to the invention according to < 9 > , titanium oxide exhibits a higher photocatalytic function in the visible light region and is superior in dispersibility as compared with the case where the saturated aliphatic hydrocarbon group has 1 or more and 3 or less carbon atoms. Aerogel particles are provided.

According to the invention according to < 10 > , there is provided a method for producing titanium oxide airgel particles which exhibits a high photocatalytic function even in the visible light region as compared with the case where the step of removing the solvent from the dispersion liquid is performed in the atmosphere. ..
According to the invention according to < 11 > , < 12 > or < 13 > , the visible light region has absorption only at a wavelength of less than 450 nm in the visible absorption spectrum, as compared with titanium oxide particles having a BET specific surface area of less than 120. Also provided are a photocatalyst forming composition, a photocatalyst or a structure using titanium oxide aerogel particles exhibiting a high photocatalytic function.

It is a schematic diagram which shows the titanium oxide airgel particles which concerns on this embodiment.

Hereinafter, embodiments of the invention will be described. These explanations and examples are illustrative of embodiments and do not limit the scope of the invention.

When referring to the amount of each component in the composition in the present disclosure, if a plurality of substances corresponding to each component are present in the composition, unless otherwise specified, the plurality of species present in the composition. It means the total amount of substances.

In the present disclosure, the term "process" is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes.

<Titanium oxide airgel particles>
The titanium oxide aerogel particles according to the present embodiment have a BET specific surface area of 120 m ² / g or more and 1000 m ² / g or less, have absorption at wavelengths of 450 nm and 750 nm in the visible absorption spectrum, and a metal atom having a hydrocarbon group is oxygen. It is bonded to the surface via an atom, and the elemental ratio C / Ti of carbon C and titanium Ti on the surface is 0.3 or more and 0.5 or less.

Here, a schematic diagram of titanium oxide airgel particles according to this embodiment is shown in FIG. As shown in FIG. 1, the titanium oxide airgel particles according to the present embodiment have an airgel structure in which the primary particles aggregate while forming a porous structure.
The term "airgel" refers to a structure in which primary particles are aggregated while forming a porous structure. The inside of the airgel particles has a three-dimensional network-like fine structure, and has a cluster structure in which spherical bodies of several nm are bonded.

The titanium oxide airgel particles according to the present embodiment exhibit a high photocatalytic function even in the visible light region and have excellent dispersibility due to the above configuration. The reason for this is presumed as follows.

First, usually, untreated titanium oxide particles as a photocatalyst exert a photocatalytic function (photocatalytic activity) by absorbing ultraviolet light. For this reason, the untreated titanium oxide particles exhibit a photocatalytic function during the daytime on a sunny day when sufficient ultraviolet light can be secured, but cannot exhibit a sufficient function at night or in the shade. For example, when untreated titanium oxide particles are used as the outer wall material, the stain resistance tends to decrease in the sun and shade. Further, when untreated titanium oxide particles are used in an air purifier, a water purifier, or the like, an installation space may be required, such as installing a black light or the like as a light source of ultraviolet rays inside the device.

In recent years, titanium oxide particles that exhibit a photocatalytic function (photocatalytic activity) by absorbing visible light are also known. For example, such visible light absorption type titanium oxide particles include titanium oxide airgel particles in which dissimilar metals (iron, copper, tungsten, etc.) are adhered to titanium oxide, and titanium oxide particles doped with element nitrogen, element sulfur, and the like. Etc. are known. On the other hand, when the photocatalyst function is enhanced, there are problems such as decomposition of a binder such as an organic resin for immobilizing the photocatalyst material on the surface of the base material and deterioration of the base material itself.

In addition, since most of the titanium oxide-based photocatalytic materials known so far are hydrophilic, they tend to have a low affinity with the organic / inorganic binder used for immobilizing the material, and the particles agglomerate. It was easy to do, and problems such as deterioration of photocatalytic performance and desorption from the binder were likely to occur. There is a method of treating the surface of the material with a surface treatment agent or the like to solve this problem. Although this method improves particle aggregation and dispersibility in the binder, the surface treatment agent covers the surface of the photocatalyst material to provide photocatalytic performance. May decrease.

Therefore, there is a demand for photocatalytic particles that exhibit a high photocatalytic function even in the visible light region, have low particle cohesiveness, and have good dispersibility in a binder.

On the other hand, the BET specific surface area is 200 m ² / g or more and 1000 m ² / g or less, has absorption at wavelengths of 450 nm and 750 nm in the visible absorption spectrum, and a metal atom having a hydrocarbon group is bonded to the surface via an oxygen atom. The element ratio C / Ti of carbon C and titanium Ti on the surface is set to 0.3 or more and 1.5 or less.

The titanium oxide aerogel particles having an element ratio C / Ti on the surface of the particles of 0.3 or more and 1.5 or less are ordinary titanium oxide particles surface-treated with a metal-containing compound having a hydrocarbon group or untreated titanium oxide particles. Compared with, it shows an appropriate C / Ti.
When the C / Ti on the surface of the titanium oxide aerogel particles is 0.3 or more and 1.5 or less, the amount of carbon such as hydrocarbon groups on the surface of the titanium oxide aerogel particles is appropriate, and sufficient absorption is performed at wavelengths of 450 nm and 750 nm. It has a high photocatalytic function in the visible light region. Further, due to the appropriate amount of carbon such as hydrocarbon groups on the surface of titanium oxide airgel particles, the particle agglomeration property is small and the dispersibility in the binder is improved.
When the C / Ti is less than 0.3, the amount of carbon on the surface of the titanium oxide airgel particles is small, so that sufficient absorption cannot be obtained at wavelengths of 450 nm and 750 nm, the photocatalytic function in the visible light region is inferior, and the particle aggregation Poor property and dispersibility in binder. Further, when the C / Ti element ratio exceeds 1.5, the amount of hydrocarbon groups on the surface of the titanium oxide airgel particles is large, so that the exposure amount of the photocatalytically active portion such as titania on the surface of the titanium oxide airgel particles is reduced. The photocatalytic function in the visible light region is inferior.

Further, in general, untreated titanium oxide particles have a low degree of freedom in controlling the particle size, particle size distribution, and particle shape, and tend to have high particle agglomeration. For this reason, the dispersibility of titanium oxide particles in the resin and liquid is poor, and 1) it is difficult to exert the photocatalytic function, 2) the transparency of the film and the like, and the uniformity of the coating film of the coating liquid tend to deteriorate. There is.
However, in the titanium oxide airgel particles according to the present embodiment, since the metal atom bonded to the surface of the mother particle via an oxygen atom has a hydrocarbon group, the dispersibility of the primary particles in the coating film is also ensured. Has been done. Therefore, a nearly uniform coating film can be formed, and the titanium oxide airgel particles are efficiently exposed to light, and the photocatalytic function is easily exhibited. In addition, the transparency of the film and the like and the uniformity of the coating film of the coating liquid are improved, and the design is maintained. As a result, for example, when a paint containing titanium oxide airgel particles is applied to the surface of an outer wall material, a plate, a pipe, or a non-woven fabric (a non-woven fabric such as ceramic), aggregation and coating defects of the titanium oxide aerogel particles are suppressed for a long period of time. The photocatalytic function is easily exhibited.

Further, since the titanium oxide aerogel particles according to the present embodiment have many pores and voids in the particles, the BET specific surface area (120 m ² ) is higher than that of the conventional non-porous titanium oxide particles for the particle size. It has a BET specific surface area (/ g or more and 1000 m ² / g or less), and has absorption at wavelengths of 450 nm and 750 nm in the visible absorption spectrum due to the fact that the organic metal compound is bonded to the surface via oxygen atoms. That is, it is presumed that the titanium oxide aerogel particles exhibit a photocatalytic function (that is, high visible light responsiveness) even in the visible light region and have excellent dispersibility.

From the above, it is presumed that the titanium oxide airgel particles according to the present embodiment have excellent particle dispersibility and exhibit a high photocatalytic function even in the visible light region due to the above configuration.

Hereinafter, the details of the titanium oxide airgel particles according to this embodiment will be described.

The titanium oxide airgel particles according to the present embodiment have a BET specific surface area of 120 m ² / g or more and 1000 m ² / g or less. When the BET specific surface area is 120 m ² / g or more, the surface area is large with respect to the amount, the area where the photodegradable object can be adsorbed becomes large, and the photocatalytic object is easily adsorbed, so that the photocatalytic function is enhanced. When the BET specific surface area is 1000 m ² / g or less, the proportion of coarse particles (particles having a particle size of more than 20 μm) is small, and the particle dispersibility is improved and high in the photocatalyst forming composition, photocatalyst or structure described later. The photocatalytic function is easy to develop. For the above reasons, when the BET specific surface area of the titanium oxide airgel particles is set within the above range, it becomes easy to develop a high photocatalytic function in the visible light region.
From the above viewpoint, the BET specific surface area of the titanium oxide airgel particles is 120 m ² / g or more and 1000 m ² / g or less, more preferably 150 m ² / g or more and 900 m ² / g or less, and 180 m ² / g or more and 800 m ² / g. It is more preferably g or less.

The BET specific surface area of the titanium oxide airgel particles is determined by a gas adsorption method using nitrogen gas. The detailed measurement method is as described in [Example] described later.

The volume average particle size of the titanium oxide airgel particles according to this embodiment is preferably 0.1 μm or more and 3 μm or less. When the volume average particle size is 0.1 μm or more, a porous structure is easily formed, the specific surface area is large, and the adsorptivity of the photodegradable object is easily improved. As a result, a high photocatalytic effect is likely to be exhibited. When the volume average particle size is 3 μm or less, the number of coarse particles (particles having a particle size exceeding 20 μm) is small, and the dispersibility of the titanium oxide airgel particles is improved in the photocatalyst forming composition, photocatalyst or structure described later, and the photocatalyst function is improved. Will increase. For the above reasons, when the volume average particle size of the titanium oxide airgel particles is within the above range, it becomes easy to develop a high photocatalytic function in the visible light region.
From the above viewpoint, the volume average particle size of the titanium oxide airgel particles is more preferably 0.3 μm or more and 2.8 μm or less, and further preferably 0.5 μm or more and 2.5 μm or less.

The particle size of the titanium oxide airgel particles is the particle size (aggregation diameter) of the aggregated particles. The volume average particle size of the titanium oxide airgel particles is a particle size of 50% cumulative from the small diameter side in the volume-based particle size distribution.

The volume particle size distribution of the titanium oxide airgel particles according to this embodiment is preferably 1.5 or more and 10 or less. When the volume particle size distribution is 1.5 or more, a porous structure is easily formed, the specific surface area is large, and the adsorptivity of the photodecomposition object is easily improved. As a result, a high photocatalytic effect is likely to be exhibited. When the volume particle size distribution is 10 or less, the number of coarse particles (particles having a particle size exceeding 20 μm) is small, the dispersibility of the titanium oxide airgel particles is improved in the photocatalyst forming composition, photocatalyst or structure described later, and the photocatalyst function is improved. It will increase. For the above reasons, when the volume particle size distribution of the titanium oxide airgel particles is within the above range, it becomes easy to develop a high photocatalytic function in the visible light region.
From the above viewpoint, the volume particle size distribution of the titanium oxide airgel particles is preferably 1.5 or more and 10 or less, more preferably 2 or more and 9 or less, and further preferably 3 or more and 7 or less.

In this embodiment, the volume particle size distribution of titanium oxide airgel particles is defined as (D90v ÷ D10v) ^1/2 . Here, D90v has a cumulative particle size of 90% from the small diameter side in the volume-based particle size distribution, and D10v has a cumulative 10% particle size from the small diameter side in the volume-based particle size distribution.

The titanium oxide airgel particles according to the present embodiment preferably have an average primary particle diameter (average primary particle diameter) of 1 nm or more and 120 nm or less from the viewpoint of exhibiting a high photocatalytic function even in the visible light region. When the average diameter of the primary particles is 1 nm or more, the pore diameter on the surface of the aggregated particles becomes an appropriate size, and the adsorptivity of the photodegradable object is improved, so that the photocatalytic function in the visible light region is likely to be exhibited. When the average diameter of the primary particles is 120 nm or less, the primary particles tend to aggregate while forming a porous structure, and the aggregated particles tend to exhibit a high photocatalytic function in the visible light region.
From the above viewpoint, the average diameter of the primary particles is preferably 1 nm or more and 120 nm or less, more preferably 5 nm or more and 100 nm or less, and further preferably 10 nm or more and 90 nm or less.

The titanium oxide airgel particles according to the present embodiment have absorption at wavelengths of 450 nm and 750 nm in the visible absorption spectrum.

The titanium oxide aerogel particles according to the present embodiment preferably have absorption at wavelengths of 450 nm, 600 nm and 750 nm in the visible absorption spectrum, and have a wavelength of 450 nm or more in the visible absorption spectrum, from the viewpoint of exhibiting a high photocatalytic function even in the visible light region. It is more preferable to have absorption in the entire range of 750 nm or less, and it is particularly preferable to have absorption in the entire range of wavelengths of 400 nm or more and 800 nm or less in the visible absorption spectrum.

The titanium oxide aerogel particles according to the present embodiment have an absorbance at a wavelength of 450 nm of 0.02 or more when the absorbance at a wavelength of 350 nm is 1 in the ultraviolet-visible absorption spectrum from the viewpoint of exhibiting a high photocatalytic function even in the visible light region. (More preferably 0.1 or more, still more preferably 0.2 or more), and the absorbance at a wavelength of 600 nm is 0.02 or more (more preferably 0.1 or more, still more preferably 0.2 or more). It is preferable that the absorbance at a wavelength of 750 nm is 0.02 or more (more preferably 0.1 or more, still more preferably 0.2 or more).

The ultraviolet visible absorption spectrum of the titanium oxide aerogel particles is obtained by measuring the diffuse reflection spectrum in the wavelength range of 200 nm to 900 nm and theoretically obtaining the absorbance at each wavelength from the diffuse reflection spectrum by Kubelka-Munk conversion.
The ultraviolet-visible absorption spectrum is measured by the following method.
First, titanium oxide airgel particles to be measured are dispersed in tetrahydrofuran, then coated on a glass substrate and dried in the air at 24 ° C. The measurement was performed with a diffuse reflection arrangement, and the absorbance was theoretically determined by the Kubelka-Munk conversion. The diffuse reflection spectrum is measured by a spectrophotometer (Measured by Hitachi High-Technologies Co., Ltd .: U-4100) [Measurement conditions; scan speed: 600 nm, slit width: 2 nm, sampling interval: 1 nm, measured in total reflectance measurement mode]. The wavelength range of 200 nm or more and 900 nm or less is measured by the reflectance, and Kubelka-Munk conversion is performed to obtain a visible absorption spectrum.

The titanium oxide aerogel particles according to the present embodiment have an element ratio C / Ti on the surface of 0.3 or more and 1.5 or less, and have a wavelength of 352 nm and an irradiation intensity of 1.3 mW / cm ² with respect to the titanium oxide aerogel particles. The amount of decrease in C / Ti on the surface of the titanium oxide aerogel particles before and after the irradiation with ultraviolet rays for 20 hours is 0.01 or more from the viewpoint of exhibiting a high photocatalytic function even in the visible light region. It is preferably 3 or less, more preferably 0.02 or more and 0.25 or less, and particularly preferably 0.03 or more and 0.2 or less.
The titanium oxide airgel particles according to the present embodiment are C / Ti on the surface of the titanium oxide airgel particles before and after the ultraviolet irradiation when irradiated with ultraviolet rays having a wavelength of 352 nm and an irradiation intensity of 1.3 mW / cm ² for 20 hours. Those having a reduction amount of 0.01 or more and 0.3 or less can be obtained. Although the reason for this is not clear, it is presumed that the titanium oxide airgel particles in the present embodiment have a porous body structure, so that the surface element C is not destroyed even when irradiated with ultraviolet rays, and the structural change becomes small before and after irradiation with ultraviolet rays. Ru.
From the viewpoint of exhibiting a high photocatalytic function even in the visible light region, the titanium oxide airgel particles preferably have an element ratio C / Ti on the surface of 0.3 or more and 1.5 or less, preferably 0.4 or more and 1.3. It is more preferably 0.5 or more and 1.2 or less, and particularly preferably 0.6 or more and 1.0 or less.

The element ratio C / Ti on the surface of the titanium oxide airgel particles is measured by the following method. First, for the titanium oxide aerogel particles to be measured, an X-ray photoelectron spectroscopy (XPS) analyzer (JPS-9000MX manufactured by JEOL Ltd.) is used, and MgKα rays are used as an X-ray source to control the acceleration voltage. The emission current is set to 10 kV and the emission current is set to 20 mA for measurement, and C / Ti is calculated from the peak intensity of each element.

The surface of the titanium oxide airgel particles is irradiated with ultraviolet rays having a wavelength of 352 nm and an irradiation intensity of 1.3 mW / cm ² . The temperature of the titanium oxide airgel particles at the start of irradiation with ultraviolet rays shall be 15 ° C. or higher and 30 ° C. or lower, and the irradiation time shall be 20 hours.
After the irradiation with the ultraviolet rays, C / Ti is measured by the above method, and the amount of decrease in C / Ti before and after the irradiation with the ultraviolet rays is calculated.

In the titanium oxide airgel particles according to the present embodiment, untreated titanium oxide airgel particles are surface-treated with a metal compound having a metal atom and a hydrocarbon group, and a part of the hydrocarbon group is oxidized or heat-treated. It is preferably carbonized titanium oxide airgel particles. In the present disclosure, titanium oxide airgel particles that have not been surface-treated with an organometallic compound are referred to as "untreated titanium oxide airgel particles". In the present disclosure, a metal compound having a metal atom and a hydrocarbon group is referred to as an "organic metal compound".

[Untreated titanium oxide airgel particles]
The untreated titanium oxide airgel particles are titanium oxide airgel particles that have not been surface-treated with an organometallic compound, and do not exclude other surface treatments. The untreated titanium airgel particles in the present embodiment are preferably titanium oxide airgel particles that have not been surface-treated with an organic metal compound or other surface treatments.

The BET specific surface area of the untreated titanium oxide airgel particles is preferably 120 m ² / g or more and 1000 m ² / g or less, more preferably 150 m ² / g or more and 900 m ² / g or less, and 180 m from the viewpoint of exhibiting a high photocatalytic function. More preferably, it is ² / g or more and 800 m ² / g or less.

The volume average particle size of the untreated titanium oxide airgel particles is preferably 0.1 μm or more and 3 μm or less, more preferably 0.3 μm or more and 2.8 μm or less, and 0.5 μm or more, from the viewpoint of exhibiting a high photocatalytic function. 5 μm or less is more preferable.

The untreated titanium oxide airgel particles are preferably aggregated particles in which titanium oxide particles (primary particles) are aggregated while forming a porous structure from the viewpoint of exhibiting a high photocatalytic function. In this case, the average diameter of the titanium oxide particles (primary particles) is preferably 1 nm or more and 120 nm or less, more preferably 5 nm or more and 100 nm or less, and further preferably 10 nm or more and 90 nm or less.

The method for producing untreated titanium oxide airgel particles is not particularly limited, but a sol-gel method using titanium alkoxide as a material is preferable from the viewpoint of controlling the range of the BET specific surface area to the above range. The titanium oxide airgel particles produced by the sol-gel method form secondary particles having a porous structure in which the primary particles are aggregated in the dispersion liquid, and the BET specific surface area in the above range can be realized.

The untreated titanium oxide airgel particles are preferably made of a hydrolyzed condensate of titanium alkoxide. However, some of the alkoxy groups of the titanium alkoxide may remain unreacted in the particles.

The untreated titanium oxide airgel particles may contain a small amount of metal elements other than titanium such as silicon and aluminum. When the untreated titanium oxide airgel particles contain silicon, the silicon content of silicon to titanium element ratio Si / Ti up to 0.05 means that the titanium oxide airgel particles exhibit high photocatalytic function in the visible light region. There is no effect on.

The crystal structure of the primary particles constituting the untreated titanium oxide aerogel particles may be any of a brucite type, anatase type, and rutile type, and may have a single crystal structure of these, or a mixed crystal structure in which these coexist. You may have. The crystal structure of the primary particles constituting the titanium oxide airgel particles can be controlled by adjusting the temperature of the heat treatment.

[Organometallic compounds]
An organometallic compound is bonded to the surface of the titanium oxide airgel particles according to the present embodiment via oxygen atoms. The organic metal compound is preferably a metal compound consisting only of a metal atom, a carbon atom, a hydrogen atom and an oxygen atom from the viewpoint of more easily exhibiting visible light responsiveness.

The organic metal compound is bonded to the surface of the titanium oxide aerogel particles via the oxygen atom O directly bonded to the metal atom M in the organic metal compound from the viewpoint of more easily exhibiting visible light responsiveness. , MO-Ti, preferably bonded to the surface of titanium oxide aerogel particles by a covalent bond.

As the organometallic compound, an organometallic compound having a metal atom M and a hydrocarbon group directly bonded to the metal atom M is preferable from the viewpoint of more easily exhibiting visible light responsiveness. The organometallic compound is preferably bonded to the surface of titanium oxide aerogel particles via an oxygen atom O directly bonded to the metal atom M in the organometallic compound. That is, on the surface of the titanium oxide aerogel particles, from the viewpoint of more easily exhibiting visible light responsiveness, a hydrocarbon group, a metal atom M, an oxygen atom O, and a titanium atom Ti are sequentially linked in a covalent bond. It is preferable that (hydrocarbon group-MO-Ti) is present.

When the organometallic compound has a plurality of hydrocarbon groups, it is preferable that at least one hydrocarbon group is directly bonded to the metal atom in the organometallic compound.

The chemical bond state between atoms in an organometallic compound can be known by performing high-resolution analysis (narrow scan analysis) of XPS.

As the metal atom of the organometallic compound, silicon, aluminum or titanium is preferable, silicon or aluminum is more preferable, and silicon is particularly preferable.

The hydrocarbon group contained in the organic metal compound has 1 or more and 40 or less carbon atoms (preferably 1 or more and 20 or less carbon atoms, more preferably 1 or more and 18 or less carbon atoms, still more preferably 4 or more and 12 or less carbon atoms, and particularly preferably. Saturated or unsaturated aliphatic hydrocarbon groups having 4 or more and 10 or less carbon atoms, or 6 or more and 27 or less carbon atoms (preferably 6 or more and 20 or less carbon atoms, more preferably 6 or more and 18 or less carbon atoms, still more preferable. Examples thereof include aromatic hydrocarbon groups having 6 or more and 12 or less carbon atoms, particularly preferably 6 or more and 10 or less carbon atoms.

The hydrocarbon group contained in the organic metal compound is preferably an aliphatic hydrocarbon group, more preferably a saturated aliphatic hydrocarbon group, and more preferably an alkyl group, from the viewpoint of exhibiting a high photocatalyst function and improving dispersibility. Is particularly preferable. The aliphatic hydrocarbon group may be linear, branched or cyclic, but is preferably linear or branched from the viewpoint of dispersibility. The number of carbon atoms of the aliphatic hydrocarbon group is preferably 1 or more and 20 or less, more preferably 1 or more and 18 or less, further preferably 4 or more and 12 or less, and particularly preferably 4 or more and 10 or less.

As the organometallic compound, a silane compound having a hydrocarbon group is particularly preferable. Examples of the silane compound having a hydrocarbon group include a chlorosilane compound, an alkoxysilane compound, and a silazane compound (hexamethyldisilazane and the like).

The silane compound having a hydrocarbon group used for the surface treatment of titanium oxide airgel particles is a compound represented by the formula (1): R ¹ _n SiR ² _m from the viewpoint of exhibiting a high photocatalytic function and improving dispersibility. Is preferable.

Formula (1): In R ¹ _n SiR ² _m , R ¹ represents a saturated or unsaturated aliphatic hydrocarbon group having 1 or more and 20 or less carbon atoms or an aromatic hydrocarbon group having 6 or more and 20 or less carbon atoms. ² represents a halogen atom or an alkoxy group, n represents an integer of 1 or more and 3 or less, m represents an integer of 1 or more and 3 or less, where n + m = 4. When n is an integer of 2 or 3, the plurality of R ^1s may be the same group or different groups. When m is an integer of 2 or 3, the plurality of R ^2s may be the same group or different groups.

The aliphatic hydrocarbon group represented by R ¹ may be linear, branched or cyclic, but is preferably linear or branched from the viewpoint of dispersibility. The carbon number of the aliphatic hydrocarbon group is preferably 1 or more and 20 or less, more preferably 1 or more and 18 or less, and 4 or more and 12 or less carbons, from the viewpoint of exhibiting a high photocatalyst function and improving dispersibility. More preferably, the number of carbon atoms is 4 or more and 10 or less, which is particularly preferable. The aliphatic hydrocarbon group may be saturated or unsaturated, but a saturated aliphatic hydrocarbon group is preferable, and an alkyl group is more preferable, from the viewpoint of exhibiting a high photocatalyst function and improving dispersibility.

Saturated aliphatic hydrocarbon groups include linear alkyl groups (methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, dodecyl group and hexadecyl group. , Icosyl group, etc.), branched chain alkyl group (isopropyl group, isobutyl group, isopentyl group, neopentyl group, 2-ethylhexyl group, tertiary butyl group, tertiary pentyl group, isopentadecyl group, etc.), cyclic alkyl group ( Cyclopropyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, tricyclodecyl group, norbornyl group, adamantyl group, etc.) and the like can be mentioned.

Examples of the unsaturated aliphatic hydrocarbon group include an alkenyl group (vinyl group (ethenyl group), 1-propenyl group, 2-propenyl group, 2-butenyl group, 1-butenyl group, 1-hexenyl group, 2-dodecenyl group, (Pentenyl group, etc.), alkynyl group (ethynyl group, 1-propynyl group, 2-propynyl group, 1-butynyl group, 3-hexynyl group, 2-dodecynyl group, etc.) and the like.

Aliphatic hydrocarbon groups also include substituted aliphatic hydrocarbon groups. Examples of the substituent that can be substituted with the aliphatic hydrocarbon group include a halogen atom, an epoxy group, a glycidyl group, a glycidoxy group, a mercapto group, a methacryloyl group, an acryloyl group and the like.

The aromatic hydrocarbon group represented by ^R1 preferably has 6 or more and 20 or less carbon atoms, more preferably 6 or more and 18 or less carbon atoms, still more preferably 6 or more and 12 or less carbon atoms, and particularly preferably 6 or more and 10 carbon atoms. It is as follows.

Examples of the aromatic hydrocarbon group include a phenylene group, a biphenylene group, a terphenylene group, a naphthalene group, an anthracene group and the like.

Aromatic hydrocarbon groups also include substituted aromatic hydrocarbon groups. Examples of the substituent that can be substituted with the aromatic hydrocarbon group include a halogen atom, an epoxy group, a glycidyl group, a glycidoxy group, a mercapto group, a methacryloyl group, an acryloyl group and the like.

Examples of the halogen atom represented by R ² include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom and the like. As the halogen atom, a chlorine atom, a bromine atom, or an iodine atom is preferable.

Examples of the alkoxy group represented by ^R2 include an alkoxy group having 1 or more and 10 or less carbon atoms (preferably 1 or more and 8 or less, more preferably 3 or more and 8 or less). Examples of the alkoxy group include a methoxy group, an ethoxy group, an isopropoxy group, a t-butoxy group, an n-butoxy group, an n-hexyloxy group, a 2-ethylhexyloxy group, a 3,5,5-trimethylhexyloxy group and the like. Be done. Alkoxy groups also include substituted alkoxy groups. Examples of the substituent that can be substituted with the alkoxy group include a halogen atom, a hydroxyl group, an amino group, an alkoxy group, an amide group, a carbonyl group and the like.

The compound represented by the formula (1): R ¹ _n SiR ² _m is preferably a compound in which R ¹ is a saturated aliphatic hydrocarbon group from the viewpoint of expressing a high photocatalytic function and improving dispersibility. In particular, in the compound represented by the formula (1): R ¹ _n SiR ² _m , R ¹ is a saturated aliphatic hydrocarbon group having 1 or more carbon atoms and 20 or less carbon atoms, and R ² is a halogen atom or an alkoxy group. It is preferable that n is an integer of 1 or more and 3 or less, m is an integer of 1 or more and 3 or less, and n + m = 4.

Formula (1): Examples of the compound represented by R ¹ _n SiR ² _m include vinyltrimethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, and hexyltrimethoxysilane. n-octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, vinyltriethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, butyltriethoxysilane, hexyltriethoxysilane, decyltriethoxysilane, dodecyltriethoxysilane Silane, phenyltrimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, phenyltriethoxysilane, benzyltriethoxysilane, decyltrichlorosilane, phenyltrichlorosilane (above, n = 1, m = 3). );
Didimethyldimethoxysilane, dimethyldiethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, dimethyldichlorosilane, dichlorodiphenylsilane (above, n = 2, m = 2);
Trimethylmethoxysilane, trimethylethoxysilane, trimethylchlorosilane, decyldimethylchlorosilane, triphenylchlorosilane (above, n = 3, m = 1);
3-Glysidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane , Γ- (2-Aminoethyl) Aminopropyltrimethoxysilane, γ- (2-Aminoethyl) Aminopropylmethyldimethoxysilane, γ-glycidyloxypropylmethyldimethoxysilane (above, R ¹ substituted aliphatic hydrocarbons) Compounds that are hydrogen groups or substituted aromatic hydrocarbon groups);
Examples thereof include silane compounds such as. The silane compound may be used alone or in combination of two or more.

The hydrocarbon group in the silane compound represented by the formula (1) is preferably an aliphatic hydrocarbon group, preferably a saturated aliphatic hydrocarbon group, from the viewpoint of exhibiting a high photocatalyst function and improving dispersibility. Is more preferable, and an alkyl group is particularly preferable. The hydrocarbon group in the silane compound is preferably a saturated aliphatic hydrocarbon group having 1 or more and 20 or less carbon atoms, and a saturated aliphatic hydrocarbon having 1 or more and 18 or less carbon atoms, from the viewpoint of exhibiting a high photocatalyst function and improving dispersibility. A hydrogen group is more preferable, a saturated aliphatic hydrocarbon group having 4 or more and 12 or less carbon atoms is further preferable, and a saturated aliphatic hydrocarbon group having 4 or more and 10 or less carbon atoms is particularly preferable.

Examples of the compound in which the metal atom of the organometallic compound is aluminum include aluminum chelates such as di-i-propoxyaluminum and ethylacetoacetate; and aluminate-based coupling agents such as acetoalkoxyaluminum diisopropyrate; ..

Examples of the compound in which the metal atom of the organic metal compound is titanium include titanium-based coupling agents such as isopropyltriisostearoyl titanate, tetraoctylbis (ditridecylphosphite) titanate, and bis (dioctylpyrophosphate) oxyacetate titanate; Di-i-propoxybis (ethylacetate acetate) titanium, di-i-propoxybis (acetylacetonate) titanium, di-i-propoxybis (triethanolaminate) titanium, di-i-propoxytitanium diacetate, di -Titanium chelate such as i-propoxytitanium dipropionate; and the like.
The organometallic compound may be used alone or in combination of two or more.

Titanium oxide airgel particles having an organometallic compound bonded to the surface are advantageous from the following viewpoints in addition to exhibiting a high photocatalytic function even in the visible light region.

In general, titanium oxide particles do not have good dispersibility in a resin or a solvent, and therefore, the uniformity of the coating film is low, and the photocatalytic function tends to be difficult to be exhibited.
On the other hand, the titanium oxide aerogel particles having the organometallic compound bonded to the surface have good dispersibility in the resin or the solvent because the surface has a hydrocarbon group derived from the organometallic compound. Therefore, a nearly uniform coating film can be formed, and the titanium oxide airgel particles are efficiently exposed to light, and the photocatalytic function is easily exhibited. Further, when a paint containing titanium oxide airgel particles is applied to the surface of an outer wall material, a plate, a pipe, a non-woven fabric, etc., aggregation or coating defects of the titanium oxide airgel particles are suppressed, and the photocatalytic function is likely to be exhibited for a long period of time.

Further, the titanium oxide airgel particles according to the present embodiment preferably contain carbon from the viewpoint of photocatalytic function in the visible light region. For example, titanium oxide airgel particles surface-treated with a metal-containing compound having a hydrocarbon group are produced by oxidatively decomposing a part of the hydrocarbon groups by a treatment such as heating. In such titanium oxide aerogel particles, hydrocarbon groups, those in which hydrocarbon groups are oxidized, and carbon in which hydrocarbon groups are carbonized are present inside the pores of the titanium oxide aerogel particles, that is, titanium oxide. It is considered that hydrocarbon groups, oxidized hydrocarbon groups, and carbon carbonized by hydrocarbon groups are incorporated from the surface layer to the inside of the aerogel particles.
On the other hand, the incorporated carbon has light absorption of visible light together with ultraviolet light, and is considered to function as a charge separating substance and a co-catalyst.

<Manufacturing method of titanium oxide airgel particles>
The method for producing titanium oxide airgel particles according to this embodiment is not particularly limited. For example, it is obtained by obtaining porous particles containing titanium oxide by a sol-gel method and surface-treating the porous particles with an organometallic compound. In this case, it is preferable that the porous particles are heat-treated after the surface treatment to obtain the titanium oxide airgel particles according to the present embodiment.

Hereinafter, an example of a method for producing titanium oxide airgel particles according to the present embodiment will be described.

The method for producing titanium oxide airgel particles preferably contains at least the following (1), (2) and (3), and more preferably contains (4).
(1) A step of granulating porous particles containing titanium oxide by a sol-gel method to prepare a dispersion liquid containing the porous particles and a solvent (dispersion liquid preparation step).
(2) A step of removing the solvent from the dispersion liquid using supercritical carbon dioxide (solvent removal step).
(3) A step of surface-treating the porous particles after removing the solvent with a metal compound having a metal atom and a hydrocarbon group (surface treatment step). Preferably, the porous particles after removing the solvent are surface-treated with a metal compound having a metal atom and a hydrocarbon group in supercritical carbon dioxide.
(4) A step of heat-treating the porous particles after the surface treatment (heat treatment step).

[(1) Dispersion liquid preparation step]
In the dispersion preparation step, for example, titanium alkoxide is used as a material to cause a reaction (hydrolysis and condensation) of titanium alkoxide to produce titanium oxide, and a dispersion in which porous particles containing titanium oxide are dispersed in a solvent is prepared. This is the process of obtaining.

Specifically, the dispersion liquid preparation step is, for example, the following step.
Titanium alkoxide is added to alcohol, and an acid aqueous solution is dropped therein under stirring to react titanium alkoxide to produce titanium oxide, and a dispersion liquid in which porous particles containing titanium oxide are dispersed in alcohol (porous particle dispersion). Liquid).

The particle size of the primary particles and the particle size of the porous particles can be controlled by the amount of titanium alkoxide added in the dispersion preparation step, and the larger the amount of titanium alkoxide added, the larger the particle size of the primary particles and the particle size of the porous particles. growing. The amount of titanium alkoxide added is preferably 4 parts by mass or more and 65 parts by mass or less, and more preferably 10 parts by mass or more and 50 parts by mass or less in terms of 100 parts by mass of alcohol.

Examples of the titanium alkoxy used in the dispersion preparation step include tetraalkoxytitanium such as tetramethoxytitanium, tetraethoxytitanium, tetrapropoxytitanium, and tetrabutoxytitanium, di-i-propoxybis (ethylacetoacetate) titanium, and di-i-. Examples thereof include an alkoxytitanium chelate obtained by chelating a part of an alkoxy group such as propoxy-bis (acetylacetonate) titanium. These may be used alone or in combination of two or more.

The porous particles may contain a small amount of metal elements other than titanium such as silicon and aluminum. Materials used in the dispersion preparation step to contain silicon or aluminum include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, methyltrimethoxysilane, methyltriethoxysilane, and ethyl. Examples thereof include alkyltrialkoxysilanes such as triethoxysilane, alkyldialkoxysilanes such as dimethyldimethoxysilane and dimethyldiethoxysilane, and aluminum alkoxydos such as aluminumisopropoxide. When the porous particles contain an element of silicon, the material used in the dispersion preparation step is preferably used so that the element ratio Si / Ti of silicon and titanium is in the range of 0 or more and 0.05 or less.

Examples of the alcohol used in the dispersion preparation step include methanol, ethanol, propanol, butanol and the like. These may be used alone or in combination of two or more.

Examples of the acid of the aqueous acid solution used in the dispersion preparation step include oxalic acid, acetic acid, hydrochloric acid, nitric acid and the like. The acid concentration of the aqueous acid solution is preferably 0.001% by mass or more and 1% by mass or less, and more preferably 0.005% by mass or more and 0.01% by mass or less.

The amount of the aqueous acid solution dropped in the dispersion preparation step is preferably 0.001 part by mass or more and 0.1 part by mass or less with respect to 100 parts by mass of titanium alkoxide.

The porous particle dispersion obtained in the dispersion preparation step preferably has a solid content concentration of 1% by mass or more and 30% by mass or less.

[(2) Solvent removal step]
The solvent removing step is a step of bringing the supercritical carbon dioxide into contact with the dispersion liquid containing the porous particles and the solvent to remove the solvent. The solvent removal treatment using supercritical carbon dioxide is less likely to cause the pores of the porous particles to be crushed or clogged than the solvent removal treatment by heating. Since the solvent removing step is a step of removing the solvent with supercritical carbon dioxide, titanium oxide airgel particles having a BET specific surface area of 120 m ² / g or more can be obtained.

Specifically, the solvent removing step is performed by, for example, the following operation.
After charging the porous particle dispersion into the closed reactor and then introducing liquefied carbon dioxide, the closed reactor is heated and the pressure inside the closed reactor is increased by a high-pressure pump to make the carbon dioxide in the closed reactor supercritical. Make it a state. Then, the liquefied carbon dioxide is made to flow into the closed reactor, and the supercritical carbon dioxide is discharged from the closed reactor, so that the supercritical carbon dioxide is circulated in the porous particle dispersion in the closed reactor. While the supercritical carbon dioxide flows through the porous particle dispersion, the solvent dissolves in the supercritical carbon dioxide, and the solvent is removed along with the supercritical carbon dioxide flowing out of the closed reactor.

The temperature and pressure inside the closed reactor are the temperature and pressure that bring carbon dioxide into a supercritical state. Where the critical point of carbon dioxide is 31.1 ° C / 7.38 MPa, for example, the temperature and pressure are set to a temperature of 50 ° C. or higher and 200 ° C. or lower / a pressure of 10 MPa or higher and 30 MPa or lower.

[(3) Surface treatment process]
The surface treatment step is a step of reacting a metal compound having a metal atom and a hydrocarbon group (also referred to as “organic metal compound” in the present disclosure) with the surface of the porous particles. In the surface treatment step, the reactive group (for example, a hydrolyzable group such as a halogeno group or an alkoxy group) in the organic metal compound reacts with the reactive group (for example, a hydroxyl group) existing on the surface of the porous particles. , The surface of the porous particles is treated. The surface treatment step can be performed in the air or in a nitrogen atmosphere. In the surface treatment step, by performing the surface treatment step in supercritical carbon dioxide, the organic metal compound reaches deep into the pores of the porous particles, and the surface treatment is performed deep into the pores of the porous particles. Therefore, it is preferable to carry out in supercritical carbon dioxide.

The surface treatment step is performed, for example, by mixing an organometallic compound and porous particles in supercritical carbon dioxide under stirring and reacting them. In addition, the surface treatment step is performed, for example, by preparing a treatment liquid obtained by mixing an organic metal compound and a solvent, and mixing the porous particles and the treatment liquid in supercritical carbon dioxide with stirring. .. In order to maintain the pore structure of the porous particles and increase the specific surface area, the organic metal compound is continuously added to the supercritical carbon dioxide after the completion of the step (2), and the organic metal compound is added to the supercritical carbon dioxide. It is preferable to react with the surface of the porous particles.

The temperature and pressure of the surface treatment step shall be the temperature and pressure that bring carbon dioxide into a supercritical state. For example, the surface treatment step is performed in an atmosphere having a temperature of 50 ° C. or higher and 200 ° C. or lower / a pressure of 10 MPa or higher and 30 MPa or lower. The duration of stirring is preferably 10 minutes or more and 24 hours or less, more preferably 20 minutes or more and 120 minutes or less, and even more preferably 30 minutes or more and 90 minutes or less.

The organometallic compound used for the surface treatment is as described above. The organometallic compound may be used alone or in combination of two or more.

When a treatment liquid obtained by mixing an organic metal compound and a solvent is used, the solvent used for preparing the treatment liquid is not particularly limited as long as it is a chemical substance compatible with the organic metal compound. As the solvent used for preparing the treatment liquid, alcohols such as methanol, ethanol, propanol and butanol, and organic solvents such as toluene, ethyl acetate and acetone are preferable.

In the treatment liquid, the amount of the organic metal compound is preferably 10 parts by mass or more and 200 parts by mass or less, more preferably 20 parts by mass or more and 180 parts by mass or less, and 50 parts by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the solvent. The following is more preferable.

The amount of the organometallic compound used for the surface treatment is preferably 10 parts by mass or more and 200 parts by mass or less, more preferably 20 parts by mass or more and 180 parts by mass or less, and 30 parts by mass or more and 150 parts by mass with respect to 100 parts by mass of the porous particles. Less than a portion is more preferable. When the amount of the organometallic compound is 10 parts by mass or more, a high photocatalytic function is more likely to be exhibited even in the visible light region, and the dispersibility is also enhanced. When the amount of the organometallic compound is 200 parts by mass or less, the amount of carbon derived from the organometallic compound present on the surface of the porous particles is suppressed from becoming excessive, and the deterioration of the photocatalytic function due to the excess carbon is suppressed. ..

After the surface treatment, a drying treatment may be performed for the purpose of removing excess organometallic compounds and residues such as a solvent of the treatment liquid. As the drying treatment, known methods such as spray drying and shelf drying can be used, but a step of removing the solvent from the dispersion liquid containing the porous particles using supercritical carbon dioxide is preferable, and the step of (3) is preferable. After the surface treatment step is completed, a step of circulating supercritical carbon dioxide in supercritical carbon dioxide to remove the solvent is more preferable. The specific operation may be the same as the operation described in (2) above.

[(4) Heat treatment step]
The heat treatment step further improves the photocatalytic function of the titanium oxide airgel particles in visible light. Although the detailed mechanism is unknown, some of the hydrocarbon groups of the organic metal compounds bonded to the particle surface and pores are oxidized by heat treatment, so that they are absorbed by visible light. It is considered that the photocatalyst function is exhibited by the photocharge separation function working by the light absorption of visible light as well as the ultraviolet light. This indicates that the titanium oxide airgel particles have absorption at wavelengths of 450 nm and 750 nm in the visible absorption spectrum. That is, the oxidized hydrocarbon groups present on the surface and pores of the titanium oxide airgel particles act to selectively capture electrons by absorbing visible light together with ultraviolet light. As a result, the probability that electrons and holes generated by light absorption are recombined is reduced, and charge separation is efficiently promoted, and this promotion of charge separation enhances the visible light responsiveness of titanium oxide airgel particles. Guessed.

From the viewpoint of improving the photocatalytic function, the temperature of the heat treatment is preferably 180 ° C. or higher and 500 ° C. or lower, more preferably 200 ° C. or higher and 450 ° C. or lower, and further preferably 250 ° C. or higher and 400 ° C. or lower. From the viewpoint of improving the photocatalytic function, the heat treatment time is preferably 10 minutes or more and 24 hours or less, more preferably 20 minutes or more and 300 minutes or less, and further preferably 30 minutes or more and 120 minutes or less.

By setting the temperature of the heat treatment to 180 ° C. or higher and 500 ° C. or lower, titanium oxide airgel particles exhibiting a high photocatalytic function even in the visible light region can be efficiently obtained. When heat-treated at 180 ° C or higher and 500 ° C or lower, the hydrocarbon groups derived from the organic metal compounds present on the surface of the titanium oxide aerogel particles are appropriately oxidized, and some of the CC bonds of the hydrocarbon groups are C-. It is presumed to change to O bond or C = O bond.

The heat treatment is preferably performed in an atmosphere having an oxygen concentration (% by volume) of 1% or more and 21% or less. By performing the heat treatment in this oxygen atmosphere, the hydrocarbon group derived from the organometallic compound existing on the surface of the titanium oxide airgel particles can be appropriately and efficiently oxidized. The oxygen concentration (% by volume) is more preferably 3% or more and 21% or less, and further preferably 5% or more and 21% or less.

The method of heat treatment is not particularly limited, and is, for example, heating by an air furnace, a firing furnace (roller harskin, shuttle kiln, etc.), a radiant heating furnace, a hot plate, etc .; by laser light, infrared rays, UV, microwaves, etc. Heating; A known heating method such as heating is applied.

Through the above steps, titanium oxide airgel particles according to the present embodiment can be obtained.

<Composition for forming a photocatalyst>
The composition for forming a photocatalyst according to the present embodiment contains titanium oxide airgel particles according to the present embodiment and at least one compound selected from the group consisting of a dispersion medium and a binder.

Examples of the photocatalyst-forming composition according to the present embodiment include, for example, a dispersion liquid containing the titanium oxide airgel particles and the dispersion medium according to the present embodiment; the titanium oxide airgel particles and the organic or inorganic binder according to the present embodiment. Compositions; and the like. The dispersion liquid may be in the form of a paste having a high viscosity.

As the dispersion medium, water, an organic solvent and the like are preferably used. Examples of water include tap water, distilled water, pure water and the like. The organic solvent is not particularly limited, and examples thereof include a hydrocarbon solvent, an ester solvent, an ether solvent, a halogen solvent, and an alcohol solvent. From the viewpoint of dispersion stability and storage stability, the dispersion liquid preferably contains at least one compound selected from the group consisting of dispersants and surfactants. Known chemical substances are used as the dispersant and the surfactant. The dispersion may contain a binder as an emulsion.

The binder used in the composition is not particularly limited, but is a fluororesin, a silicone resin, a polyester resin, an acrylic resin, a styrene resin, an acrylonitrile / styrene copolymer resin, an acrylonitrile / butadiene / styrene copolymer (ABS) resin, and the like. Organic binders such as epoxy resin, polycarbonate resin, polyamide resin, polyamine resin, polyurethane resin, polyether resin, polysulfide resin, polyphenol resin, composites thereof, and resins obtained by silicone-modified or halogen-modified of these; glass, ceramic, Inorganic binders such as metal powder;

The composition for forming a photocatalyst according to the present embodiment may contain other components other than the above. As other components, known additives are used, and examples thereof include co-catalysts, colorants, fillers, preservatives, defoamers, adhesion improvers, and thickeners.

The composition for forming a photocatalyst according to the present embodiment may contain one kind of titanium oxide airgel particles according to the present embodiment alone, or may contain two or more kinds.

The content of the titanium oxide airgel particles according to the present embodiment in the photocatalyst forming composition according to the present embodiment is not particularly limited, and depends on various aspects such as a dispersion liquid and a resin composition, a desired photocatalyst amount, and the like. Then, it may be selected as appropriate.

The method for producing a photocatalyst or a structure having a photocatalyst using the photocatalyst forming composition according to the present embodiment is not particularly limited, and a known application method is used. Examples of the method for applying the photocatalyst forming composition according to the present embodiment include a spin coating method, a dip coating method, a flow coating method, a spray coating method, a roll coating method, a brush coating method, a sponge coating method, and a screen printing method. Inkjet printing method and the like can be mentioned.

<Photocatalyst, structure>
The photocatalyst according to the present embodiment contains the titanium oxide airgel particles according to the present embodiment, or is composed of the titanium oxide airgel particles according to the present embodiment. The structure according to the present embodiment has titanium oxide airgel particles according to the present embodiment.

The photocatalyst according to the present embodiment may be a photocatalyst composed of only the titanium oxide airgel particles according to the present embodiment, or may be a photocatalyst in which a cocatalyst is mixed with the titanium oxide airgel particles according to the present embodiment. It may be a photocatalyst in which the titanium oxide airgel particles according to the embodiment are hardened into a desired shape by an adhesive or a pressure-sensitive adhesive.

The structure according to the present embodiment preferably has titanium oxide airgel particles according to the present embodiment as a photocatalyst. From the viewpoint of photocatalytic activity, the structure according to the present embodiment preferably has titanium oxide airgel particles according to the present embodiment at least on the surface.

The structure according to the present embodiment may be a structure having titanium oxide airgel particles according to the present embodiment on at least a part of the surface of the base material, or may be a structure having at least a part of the surface of the base material of the present embodiment. It may be a structure formed by applying the composition for forming a photocatalyst according to the above. In the structure, the amount of the photocatalyst forming composition according to the present embodiment is not particularly limited and may be selected as desired.

In the structure according to the present embodiment, the titanium oxide airgel particles according to the present embodiment may be attached to the surface of the base material or may be immobilized, but from the viewpoint of the durability of the photocatalyst, they are immobilized. It is preferable that it is made. The immobilization method is not particularly limited, and a known immobilization method is used.

Examples of the base material used in the present embodiment include various materials regardless of whether they are inorganic materials or organic materials, and their shapes are not limited. Preferred examples of substrates are metals, ceramics, glass, plastics, rubber, stones, cement, concrete, fibers, fabrics, wood, paper, combinations thereof, laminates thereof, and at least one layer of coating on their surfaces. Examples include articles to have. Preferred examples of substrates from an application point of view are building materials, exterior materials, window frames, window glass, mirrors, tables, tableware, curtains, lenses, prisms, vehicle exteriors and paints, mechanical equipment exteriors, and article exteriors. , Dustproof covers and paints, traffic signs, various display devices, advertising towers, road sound insulation walls, railway sound insulation walls, bridges, guard rail exteriors and paints, tunnel interiors and paints, glass, solar cell covers, solar water heater heat collector covers, Examples include polymer films, polymer sheets, filters, indoor signs, outdoor signs, vehicle lighting covers, outdoor lighting fixtures, air purifiers, water purifiers, medical appliances, nursing care products, and the like.

Hereinafter, embodiments of the invention will be described in detail with reference to Examples, but the embodiments of the invention are not limited to these Examples. In the following description, all "parts" are based on mass unless otherwise specified.

<Example 1>
[Dispersion preparation process]
115.4 parts of methanol and 14.3 parts of tetrabutoxytitanium were charged and mixed in the reaction vessel. While stirring the mixture at 100 rpm (rotation / min) with a magnetic stirrer, 7.5 parts of a 0.009 mass% oxalic acid aqueous solution was added dropwise over 30 seconds. The mixture was kept as it was with stirring for 30 minutes to obtain 137.2 parts (solid content: 3.4 parts, liquid phase content: 133.9 parts) of the dispersion liquid (1).

[Solvent removal step]
137.2 parts of the dispersion liquid (1) was put into the reaction vessel, CO ₂ was added while stirring at 85 rpm, and the temperature was raised to 150 ° C./20 MPa. CO ₂ was introduced and discharged while stirring as it was, and 132 parts of the liquid phase was removed over 60 minutes.

[Surface treatment process]
A mixture of 3.4 parts of isobutyltrimethoxysilane and 3.4 parts of methanol was added to the solid phase remaining after removing the liquid phase over 5 minutes, and the mixture was stirred at 85 rpm for 30 minutes at 150 ° C./20 MPa. Retained. CO ₂ was introduced and discharged while stirring as it was, and 8.5 parts of the liquid phase was removed over 30 minutes. The pressure was reduced to atmospheric pressure over 30 minutes, and 3.7 parts of the powder was recovered.

[Heat treatment process]
0.5 part of the powder was weighed in a SUS container and placed on a hot plate. The temperature was raised to 380 ° C., held for 60 minutes, and then allowed to cool to 30 ° C., and 0.5 part of the powder (titanium oxide airgel particles) was recovered.

<Comparative Examples 1 to 7 and Examples 2 to 21>
Each titanium oxide airgel particle was prepared in the same manner as in Example 1 except that the material or treatment conditions were changed as shown in Table 1 or Table 2.

<Comparative Example 8>
Commercially available anatase-type titanium oxide particles (SSP-20, manufactured by Sakai Chemical Industry Co., Ltd., volume average particle size 12 nm) were used as they were as titanium oxide particles.

<Comparative Example 9>
Commercially available anatase-type titanium oxide particles (SSP-20, manufactured by Sakai Chemical Industry Co., Ltd., volume average particle size 12 nm) were heat-treated in an electric furnace at 400 ° C. for 60 minutes to obtain titanium oxide particles. ..

<Comparative Example 10>
100% by mass of isobutyltrimethoxysilane with respect to titanium oxide aerogel particles in a dispersion liquid in which commercially available anatase-type titanium oxide particles (SSP-20, manufactured by Sakai Chemical Industry Co., Ltd., volume average particle size 12 nm) are dispersed in methanol. Was dropped and reacted at 40 ° C. for 1 hour, and then spray-dried at an outlet temperature of 120 ° C. to obtain titanium oxide particles.

<Measurement of physical properties of titanium oxide airgel particles>
The physical characteristics of the titanium oxide airgel particles obtained in each example were measured according to the following measuring methods. The results are shown in Tables 1 to 3. In Tables 1 to 3, the "UV-Vis characteristic" is the absorbance at a wavelength of 450 nm, a wavelength of 600 nm, and a wavelength of 750 nm, respectively, when the absorbance at a wavelength of 350 nm is 1.

[BET specific surface area]
Using "Macsorb HMmodel-1201" manufactured by Mountech as a specific surface area measuring device, a 50 mg sample was pretreated at 30 ° C./120 minutes for degassing, and BET using nitrogen gas with a purity of 99.99% or higher. The BET specific surface area was determined by the multipoint method.

[Average diameter of primary particles (average primary particle diameter)]
100 parts of resin particles (styrene-butyl acrylate copolymer particles, copolymer ratio (mass ratio) 80:20, weight average molecular weight 130,000, glass transition temperature 59 ° C.) with a volume average particle size of 8 μm, and titanium oxide aerogel particles. 1.0 part was mixed with a sample mill (model SK-M2 type, manufactured by Kyoritsu Riko Co., Ltd.) at 13000 rpm for 2 minutes.
The titanium oxide airgel particles dispersed in the resin particles were observed with a scanning electron microscope (S-4100, manufactured by Hitachi, Ltd.) and an image was taken. At this time, as shown in FIG. 1, individual particles forming aggregated particles were used as primary particles, and a scanning electron microscope was adjusted to a magnification at which the primary particles could analyze the image, and an image was taken. The captured image is taken into an image analysis device (LUZEXIII, manufactured by Nireco Co., Ltd.), the area of each particle is obtained by image analysis of the primary particles, the circle equivalent diameter (nm) is calculated from the area, and the average of the circle equivalent diameters is averaged. The primary particle diameter (nm) was used (referred to as "Dp" in Tables 1 to 3). The average primary particle diameter was determined by analyzing about 10 to 50 primary particles.

[Volume average particle size and volume particle size distribution of titanium oxide airgel particles]
100 parts of resin particles (styrene-butyl acrylate copolymer particles, copolymer ratio (mass ratio) 80:20, weight average molecular weight 130,000, glass transition temperature 59 ° C.) with a volume average particle size of 8 μm, and titanium oxide aerogel particles. 1.0 part was mixed at 13000 rpm for 2 minutes using a sample mill (model SK-M2, manufactured by Kyoritsu Riko Co., Ltd.).
Put 0.1 g of the mixed particles in a beaker, add 1.5 g of an aqueous surfactant solution obtained by diluting the anionic surfactant (Tayca Power BN2060, manufactured by TAYCA Corporation) with ion-exchanged water to a concentration of 12%, and mix. The particles were sufficiently wetted. Next, 5 g of pure water was added, and the mixture was dispersed in an ultrasonic disperser for 30 minutes. The resin particles were removed with a 5C filter paper to obtain a titanium oxide airgel particle dispersion. The particle size of the particles in the titanium oxide airgel particle dispersion was measured using a dynamic light scattering type particle size measuring device (Nanotrack UPA-ST, manufactured by Microtrac Bell) to obtain a volume-based particle size distribution. The particle size D50v having a cumulative total of 50% was obtained from the small diameter side, and D50v was defined as the volume average particle size (μm) (denoted as “Da” in Tables 1 to 3). Further, the particle size D10v having a cumulative 10% from the small diameter side and the particle size D90v having a cumulative 90% from the small diameter side were obtained, and the volume particle size distribution GSDv = (D90v ÷ D10v) ^1/2 was calculated.

[Ultraviolet-visible absorption spectrum]
After the titanium oxide airgel particles were dispersed in tetrahydrofuran, they were applied onto a glass substrate and dried in the air at 24 ° C. Using a spectrophotometer U-4100 (manufactured by Hitachi High-Technologies), the scan speed is set to 600 nm, the slit width is set to 2 nm, and the sampling interval is set to 1 nm. The spectrum was measured. From the diffuse reflection spectrum, the absorbance at each wavelength was theoretically obtained by Kubelka-Munk conversion, and an ultraviolet-visible absorption spectrum was obtained.

The titanium oxide airgel particles of Examples 1 to 21 had absorption in the entire range of a wavelength of 400 nm or more and 800 nm or less.

[Elemental ratio C / Ti]
Before and after irradiating the particle surface obtained in each example with ultraviolet rays having a wavelength of 352 nm and an irradiation intensity of 1.3 mW / cm ² at 25 ° C. for 20 hours at the start of irradiation, the element ratio C / Ti on the particle surface by XPS was as follows. The measurement was performed according to the conditions, and the amount of decrease in the element ratio C / Ti before and after the irradiation with the ultraviolet rays was calculated.

<Performance evaluation of titanium oxide airgel particles>
[Gas adsorption and gas decomposition]
As the activity of the titanium oxide airgel particles obtained in each example, the gas adsorptivity and the gas decomposability by visible light irradiation were evaluated as follows. The results are shown in Tables 1 to 3.

The titanium oxide airgel particles obtained in each example were dispersed in methanol so that the solid content concentration was 4% by mass. 0.25 g of the dispersion was applied to half of the glass plate for a microscope (area 10 cm ² ) and then sufficiently dried to prepare a test piece in which particles were uniformly adhered to the surface (half) of the glass plate. Two test pieces were prepared for each titanium oxide airgel particle of each example.

Immediately after making the test piece, put it in a tedler bag with a 1-mouth cock with a capacity of 1 L (one test piece was put in each tedler bag), extrude the air inside the tedler bag to seal it, and then put it in a dark place with the coating surface facing up. And stored until the performance evaluation test.

The performance evaluation test was performed according to the following procedure.
First, all the residual air inside was discharged from the cock of the tedler bag containing the test piece with a suction device, and then 800 ml of ammonia gas having a concentration of 100 ppm was injected. Next, visible light (6,500 LX (lux) on the surface of the test piece) is applied to one of the two tedler bags containing the test piece of the same type using a light emitting diode (LED) that irradiates visible light with a wavelength of 400 nm or more and 800 nm or less. Continuous irradiation was performed. The other of the two test pieces of the same type, the tedler bag, was placed in a dark box out of the light and stored for 1 hour.
Ammonia gas concentration in each tedler bag containing a test piece after continuous irradiation with visible light for 45 minutes and a tedler bag containing a test piece stored in a dark box for 45 minutes was measured using a detector tube (manufactured by Gastec). Then, the index ΔA of the ammonia gas adsorption property and the ammonia gas decomposition rate ΔS by irradiation with visible light were obtained from the following equations.

-S1 = Ammonia gas concentration (ppm) in the tedler bag after continuous irradiation with visible light for 1 hour.
・ S2 = Ammonia gas concentration (ppm) in the tedler bag after storage in a dark box for 1 hour
-Ammonia gas adsorption index ΔA (ppm) = 100-S2
Ammonia gas decomposition rate ΔS (%) = (S2-S1) ÷ S2 × 100

From the above values, the gas adsorptivity and gas decomposability were evaluated as follows.

-Gas adsorption-
G1 (◎): 90 ≦ ΔA, very good adsorptivity.
G2 (◯): 70 ≦ ΔA <90, good adsorptivity.
G3 (Δ): 50 ≦ ΔA <70, slightly good adsorptivity.
G4 (×): ΔA <50, poor adsorptivity.

-Gas degradability-
G1 (◎): 30 ≦ ΔS, very good decomposability.
G2 (◯): 15 ≦ ΔS <30, good decomposability.
G3 (Δ): 5 ≦ ΔS <15, slightly good in decomposability.
G4 (×): ΔS <5, poor decomposability.

[Amount of coarse particles (dispersity)]
A sieve having a mesh size of 20 μm was prepared, and the weight thereof was precisely weighed to the unit of 0.01 g. 1.00 g of titanium oxide airgel particles were passed through the sieve while being sucked by a dust collector. At that time, the agglomerates on the sieve were passed through the sieve while being crushed using a brush, and strong agglomerates that were not crushed were left on the sieve. The coarse particle index was calculated from the weight (g) of the sieve before and after passing the titanium oxide airgel particles by the following formula. The smaller the coarse particle index, the better the dispersibility. The results are shown in Tables 1 to 3.

Coarse particle index (%) = (weight of sieve after passing-weight of sieve before passing) ÷ 1.00 × 100

G1 (○): Coarse particle index is 1% or less.
G2 (△): Coarse particle index is more than 1% and less than 5%.
G3 (x): Coarse particle index is over 5%.

The details of some of the organometallic compounds shown in Tables 1 to 3 are as follows.
・ Acetalkoxyaluminum diisopropilate: manufactured by Ajinomoto Co., Inc., Plenact AL-M
-Isopropyltriisostearoyl titanate: Ajinomoto Co., Inc., Plenact TTS

From the results of the performance evaluations shown in Tables 1 to 3, it can be seen that this example is superior in photocatalytic activity in the visible light region and secures dispersibility as compared with the comparative example.

Claims (11)

The BET specific surface area is 120 m ² / g or more and 1000 m ² / g or less.
Has absorption at wavelengths of 450 nm and 750 nm in the visible absorption spectrum
A metal atom having a hydrocarbon group is bonded to the surface via an oxygen atom, and the metal atom is bonded to the surface.
The element ratio C / Ti of carbon C and titanium Ti on the surface determined by X-ray photoelectron spectroscopy is 0.3 or more and 1.5 or less.
The volume average particle size is 0.5 μm or more and 2.5 μm or less.
The volume particle size distribution is 2 or more and 9 or less,
The volume particle size distribution is defined as (D90v ÷ D10v) ^1/2 , D90v is a particle size of 90% cumulative from the small diameter side in the volume-based particle size distribution, and D10v is the small diameter side in the volume-based particle size distribution. Cumulative particle size from 10%
The average diameter of the primary particles contained in the titanium oxide airgel particles is 5 nm or more and 120 nm or less.
Titanium oxide airgel particles. Claimed that the amount of decrease in the element ratio C / Ti is 0.01 or more and 0.3 or less when the titanium oxide airgel particles are irradiated with ultraviolet rays having a wavelength of 352 nm and an irradiation intensity of 1.3 mW / cm ² for 20 hours. Item 2. The titanium oxide airgel particles according to Item 1. The titanium oxide airgel particle according to claim 1 or 2, which has absorption in the entire range of a wavelength of 400 nm or more and 800 nm or less in the visible absorption spectrum. The titanium oxide airgel particle according to any one of claims 1 to 3 , wherein the metal atom is a silicon atom. One of claims 1 to 4 , wherein the hydrocarbon group is a saturated or unsaturated aliphatic hydrocarbon group having 1 to 20 carbon atoms or an aromatic hydrocarbon group having 6 to 20 carbon atoms. The titanium oxide aerogel particles described in the section. The titanium oxide airgel particles according to claim 5 , wherein the hydrocarbon group is a saturated aliphatic hydrocarbon group having 1 or more carbon atoms and 20 or less carbon atoms. The titanium oxide airgel particles according to claim 6 , wherein the hydrocarbon group is a saturated aliphatic hydrocarbon group having 4 or more and 10 or less carbon atoms. A step of granulating porous particles containing titanium oxide by a sol-gel method to prepare a dispersion liquid containing the porous particles and a solvent, and
The step of removing the solvent from the dispersion liquid using supercritical carbon dioxide, and
A step of surface-treating the porous particles after removing the solvent with a metal compound having a metal atom and a hydrocarbon group in supercritical carbon dioxide.
The step of heat-treating the porous particles after the surface treatment and
The method for producing titanium oxide airgel particles according to any one of claims 1 to 7 , which comprises. The titanium oxide airgel particles according to any one of claims 1 to 7 .
At least one compound selected from the group consisting of a dispersion medium and a binder, and
A composition for forming a photocatalyst containing. A photocatalyst containing or comprising titanium oxide airgel particles according to any one of claims 1 to 7 . The structure having the titanium oxide airgel particles according to any one of claims 1 to 7 .

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