JP2003126697A - Dispersion solution of fine particle of photocatalyst and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dispersion solution of fine particles of a photocatalyst, in which fine particle powders of the photocatalyst exist in the homogeneous dispersion state, and which exhibits photocatalyst activity by irradiation with visible radiation, and a manufacturing method therefor. SOLUTION: The dispersion solution of the fine particles of the photocatalyst is composed of titanium-containing oxynitride exhibiting a catalyst function and/or a hydrophilic property by irradiation with visible radiation. A surface of the fine particles of the photocatalyst is modified by a peroxo group.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a dispersion solution of photocatalyst fine particles in which photocatalyst fine particles exhibiting photocatalytic activity and / or hydrophilicity by irradiation with visible light are present in a uniformly dispersed state, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, there is a need for environment-purifying products having functions such as antibacterial, deodorant, and antifouling due to the growing interest in pollution control, health, comfort, and cleanliness. Attention has been paid. Above the "photocatalyst" refers to the absorption of light energy, the excited electrons are superoxide anion of reactive oxygen species by reducing oxygen (· O ₂ ^-) to generate a, active oxygen holes oxidize water It is a substance that oxidizes and decomposes organic substances and the like that come into contact with the surface of the photocatalyst by generating seed hydroxyl radicals (OH.

Further, when the photocatalyst is titanium oxide, it can exhibit superhydrophilicity of 5 ° or less at a contact angle of water. By utilizing this property, in outdoor use, anti-fouling treatment for oil, inorganic dust, carbon, etc., which are the main components of urban pollution, anti-fog treatment for ensuring visibility, and in indoor use, antibacterial / erasing Sanitary treatment such as odor can be performed.

The reaction in which the reactive oxygen species are generated occurs by photocatalysis.
The band gap energy of the medium is
Lugie (1.36eV (2.18 × 10^-19J)) just larger than
Sufficiently, the bottom of its conduction band and the top of the valence band are
O that produces volatile oxygen species₂/ O₂ ^-(-0.13 eV (-0.21 x 10
^-19J)) levels and O₂/ H₂O (1.23eV (1.97 × 10^-19J)) Quasi
You have to be in a position that sandwiches the position. This redox
Since the level is an equilibrium level, it causes the reactive oxygen species generation reaction.
It takes some overvoltage to rub it, so
Conduction is performed within the range where the band gap energy does not become excessive.
O at the bottom level of the belt₂/ O₂ ^-Position it on the negative side of the level,
Set the upper level of the valence band to O₂/ H₂Located on the positive side of the O level
It is desirable to let

However, since the anatase type titanium oxide which is currently put into practical use as a photocatalyst substance, the upper end level of the valence band is located on the positive side sufficiently deeper than the O ₂ / H ₂ O level, the The gap energy is as large as 3.2 eV (5.1 × 10 ⁻¹⁹ J), and the photocatalytic activity and the hydrophilic property cannot be exhibited by irradiation with visible light, and the above property can be exhibited only by irradiation with ultraviolet light.

For example, when sunlight or a fluorescent lamp is used as a light source, the spectral distribution spectrum of ultraviolet rays is at most 3
It is ~ 4%, and the intensity of near-ultraviolet light is 1-2 in daylight.
mW / cm ² is only about 1 μW / cm ^{2 for} indoor fluorescent lamps. Therefore, it is desired to develop a photocatalytic material capable of exhibiting photocatalytic activity and hydrophilic properties even when irradiated with visible light, in order to effectively utilize light energy and to exert a sufficient function even in a fluorescent lamp environment.

Therefore, the inventors of the present invention investigated a photocatalytic material capable of exhibiting photocatalytic activity and hydrophilicity even when irradiated with visible light. As a result, TiO was obtained by substituting a part of oxygen atoms constituting titanium oxide with nitrogen atoms. _2-x N _y (where x is 0 <
x <2, y is 0 <y <1), and Ti _1-x M _x O _{2- y in which} some of the titanium atoms are replaced with atoms of the transition metal element (M)
N _z (where x is 0 <x <1, y is 0 <y <2, and z is 0 <
It has been found that a material composed of titanium-containing oxynitride represented by z <1) is promising as a photocatalyst material capable of exhibiting photocatalytic activity and hydrophilicity by irradiation with visible light.

By the way, as a method for forming a photocatalyst material as a film, a wet method in which a coating solution is applied and dried to form a film is suitable as a method which requires little equipment investment and can be easily used.

As a coating solution for forming a film of anatase-type titanium oxide, which is a photocatalytic material, by the wet method, for example, peroxotitanic acid is prepared by adding peroxide to a liquid in which titanium oxide or the like is dispersed. After being dissolved as a solution, the peroxotitanic acid solution is heat-treated to generate microcrystals of anatase-type titanium oxide having a peroxo group. A coating solution in which an inorganic binder of titanium oxide is mixed in an arbitrary ratio is proposed in Japanese Patent No. 2875993.

However, the coating solution described in the above publication is a method in which titanium oxide or the like is once dissolved in an amorphous state and the anatase type titanium oxide particles crystallized by heat treatment are precipitated and dispersed in the solution. It is not a technique for dispersing quality powder. Further, there is no known document disclosing a sol solution in which titanium-containing oxynitride fine particles are uniformly dispersed and a coating solution using the sol solution.

[0011]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional techniques, an object of the present invention is to provide a photocatalyst containing photocatalyst fine particle powder which exhibits photocatalytic activity and / or hydrophilicity by irradiation with visible light in a dispersed state. It is to provide a dispersion solution of fine particles and a method for producing the same.

[0012]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made TiO 2 in which a part of oxygen atoms constituting titanium oxide are replaced with nitrogen atoms.
_2-x N _y (where x is 0 <x <2, y is 0 <y <1),
In addition, some of the titanium atoms are atoms of transition metal elements (M).
Ti _1-x M _x O _2-y N _z (where x is 0 <x <1, y
Is a photocatalyst material composed of titanium-containing oxynitride represented by 0 <y <2, and z <0 <z <1), which exhibits photocatalytic activity and / or hydrophilicity under visible light irradiation and further has abrasion resistance, Focusing on the improvement in corrosion resistance, studies were conducted to develop a method capable of advantageously producing a thin film made of such a photocatalytic material. As a result, by using the powder of the photocatalyst fine particles made of titanium-containing oxynitride and mixing with the hydrogen peroxide-containing solution within the range in which the powder of the photocatalyst fine particles is not dissolved, the hydroxyl groups existing on the surface of the photocatalyst fine particles are peroxidized. As a result of easily reacting with hydrogen to modify the surface with a peroxo group and dissociating secondary agglomeration of the powder of the photocatalyst particles, the photocatalyst particles are stably and uniformly dispersed in the solution. The inventors have found out what can be done and have completed the present invention. Furthermore, it was also found that secondary aggregation is further dissociated by adding an appropriate amount of ammonia to the hydrogen peroxide-containing solution.

That is, the gist of the present invention is as follows. (1) A dispersion solution of photocatalyst fine particles composed of titanium-containing oxynitride, wherein the surface of the photocatalyst fine particles is modified with a peroxo group (first invention).

(2) A dispersion solution of photocatalyst fine particles, wherein the dispersion solution described in (1) above contains an inorganic binder.

(3) A powder of photocatalyst fine particles made of titanium-containing oxynitride and a hydrogen peroxide-containing solution are mixed, the surface of the photocatalyst fine particles is modified with a peroxo group, and the photocatalyst fine particles are dispersed in the solution. A method for producing a dispersion solution of photocatalyst fine particles (second invention).

(4) The hydrogen peroxide-containing solution further contains ammonia, and the ammonia content is 0.3 or less in mass ratio with respect to the hydrogen peroxide content. A method for producing a dispersion solution of the photocatalyst fine particles as described above.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. The photocatalytic anatase-type titanium oxide currently in practical use cannot express a photocatalytic activity by irradiation with visible light, but can express a photocatalytic activity only by irradiation with ultraviolet rays. This is because the upper level of the valence band of an oxide mainly composed of 2p orbits of oxygen is the oxidation level of water O ₂ /
Since it is located deeper on the positive side than H ₂ O,
The cause is that the band gap energy becomes large.

Therefore, as a method of exhibiting a photocatalytic activity by irradiation with visible light, oxynitride obtained by doping an oxide photocatalyst with a nitrogen element is drawing attention. When the oxygen site of the oxide is doped with nitrogen element, N _{2p, which} has a higher energy level than oxygen O _2p, is also used for the configuration of the conduction band, and as a result, the upper level of the conduction band is on the negative side. It is considered that visible light can be absorbed as a result of shifting to and narrowing the band gap.

The oxynitride photocatalyst is anatase type TiO _2-x N _y (where x is 0 <x <2 and y is 0 <y.
<1) or titanium, niobium, tantalum perovskite or layered perovskite materials such as LaTaON ₂ , CaT
aON ₂ , SrTaON ₂ , BaTaON ₂ , LaTiO ₂ N, Ca _1-x La _x TiO
_{3-x N x, CaNbON 2} , SrNbON 2, BaNbON 2, although such LiLaTaNO ₆ are known, in practice, the cost, safety, in view of stability, the photocatalyst fine particles used in the present invention powder Is a TiO _2-x N _y (where x is 0 <x <2 and y is 0) in which a part of oxygen atoms constituting titanium oxide is replaced with nitrogen atoms.
<Y <1) and Ti _1-x M _x O _{2 -y} N _z (where x is 0 <x <1, y Is a fine particle powder of titanium-containing oxynitride represented by 0 <y <2, z is 0 <z <1), and preferably titanium-based oxynitride. The term "titanium base" as used herein means a compound in which the proportion of titanium element in the transition metal element forming the conduction band is 50 atom% or more.

As a method for synthesizing the powder of titanium-containing oxynitride fine particles, for example, titanium oxide or a precursor substance thereof is used in an atmosphere such as ammonia gas, ammonia mixed gas, nitrogen gas, or mixed gas of nitrogen gas and hydrogen gas. By heat-treating under 400-1200 ° C for 1-120 minutes, preferably 5-60 at 500-1000 ° C under an atmosphere of ammonia gas or a mixed gas of nitrogen gas and hydrogen gas.
It can be synthesized by heat treatment for minutes.

If the powder of titanium-containing oxynitride fine particles thus synthesized can be dispersed in a solution to form a sol solution, a photocatalytic film can be simply formed by a wet method in which the sol solution is applied onto a substrate and dried. It is desirable because it can be formed into a film. However, when the powder of titanium-containing oxynitride fine particles is added to the solution, it is generally difficult to uniformly disperse the powder in the solution because the powder is secondarily aggregated. In fact, there is no known literature that discloses a sol solution in which the powder is uniformly dispersed in the solution.

Therefore, in the present invention, the surface of the photocatalyst fine particles is prepared by using the above-synthesized titanium-containing oxynitride fine powder and mixing the photocatalyst fine powder with the hydrogen peroxide-containing solution within a range that does not dissolve the powder. The hydroxyl groups present in the above readily react with hydrogen peroxide to modify the surface with peroxo groups, and as a result of dissociating the secondary agglomeration of the powder of the photocatalyst fine particles, the photocatalyst fine particles become stable in the solution. We have developed a sol solution that exists in a uniformly dispersed state. Then, by using this sol solution, the photocatalytic coating can be easily formed at low cost.

The oxide powder, which is a raw material for producing the photocatalyst fine particles composed of titanium-containing oxynitride used in the present invention, has a primary particle diameter or a crystallite diameter of 200 nm or less in order to improve dispersibility in a solution. Is preferably, and more preferably 100 nm or less. The oxide powder is modified into photocatalyst fine particles made of titanium-containing oxynitride which responds to visible light irradiation by the nitriding treatment.

Then, the titanium-containing oxynitride powder and the hydrogen peroxide-containing solution are mixed to convert the hydroxyl groups on the powder surface into peroxo groups, and at the same time, the secondary agglomeration of the titanium-containing oxynitride powder is dissociated and dispersed. Use as a solution. This peroxo group is polarized in the solution and an electric repulsive force acts between the particles, so that the dispersibility of the particles is improved, and as a result, the photocatalyst particles can be uniformly dispersed in the solution.

Further, it is preferable to mix ammonia into the hydrogen peroxide-containing solution because it promotes the dissociation of the secondary-aggregated titanium-containing oxynitride powder.

However, if the mixing ratio of ammonia in the hydrogen peroxide-containing solution becomes excessive, the dissolution reaction of the titanium-containing oxynitride powder proceeds and the amorphous peroxotitanic acid is changed. When mixing ammonia in the hydrogen peroxide-containing solution, the ammonia content in the hydrogen peroxide-containing solution may be 0.3 or less by mass ratio to the hydrogen peroxide content, preferably 0.05 to 0.20. is necessary.

The hydrogen peroxide solution to be mixed with the titanium-containing oxynitride powder may be 1 to 500 g of 1% of the titanium-containing oxynitride powder in the case of 30% by mass of hydrogen peroxide solution. It is more preferably 10 to 200 g.

When the titanium-containing oxynitride powder is mixed with the hydrogen peroxide-containing solution, in order to promote the reaction of converting hydroxyl groups on the surface of the titanium-containing oxynitride powder into peroxo groups and dissociation of aggregation. It is preferable to go through the dispersion step.

As the dispersing means used in the dispersing step, stirring with stirring blades or stirrers, homogenizer, ultrasonic waves, etc. can be usually used, but not limited thereto.

The stirring time is usually about 1 hour to 1 week, but the stirring time can be appropriately changed depending on the state of the powder. After the dispersion process of the titanium-containing oxynitride powder is completed, in order to remove excess hydrogen peroxide, it is allowed to stand at room temperature or higher for 1 day to 1 week, and further to remove precipitated large-sized particles. The dispersion solution of the present invention is obtained by collecting the supernatant. This dispersion solution does not show sedimentation even after standing for 1 month or more, and can maintain a highly dispersed state.

When the dispersion solution of titanium-containing oxynitride fine particles is used alone, a photocatalytic coating can be formed by heating at 500 ° C. or higher. Further, if an inorganic binder is mixed with this dispersion solution at an arbitrary ratio to prepare a dispersion solution of photocatalyst fine particles, it can be used as a coating solution capable of forming a photocatalyst film even at a low temperature.

The solid content concentration when the coating solution is used is preferably 0.2 to 10% by mass, more preferably 0.5 to 3% by mass.

The mixing ratio of the inorganic binder is preferably 10 to 90% by mass with respect to the solid content, more preferably
It is 30 to 70% by mass. Examples of the inorganic binder include, but are not limited to, amorphous titanium oxide, amorphous silica, and a mixture thereof.

The aqueous solution of amorphous titanium oxide is orthotitanic acid, peroxotitanic acid, a hydrolyzate of titanium alkoxide, or a mixture thereof, but is not particularly limited thereto.

Orthotitanic acid can be obtained by hydrolyzing and dialyzing a titanium salt solution such as titanium sulfate.
Peroxotitanic acid can be obtained by treating titanium chloride with aqueous ammonia or by dissolving titanium hydroxide obtained by hydrolyzing titanium alkoxide in aqueous hydrogen peroxide.

The aqueous solution of amorphous silica is a solution containing a polymer derived from an alkali silicate, a quaternary ammonium silicate, or a mixture thereof.
It is not particularly limited to these.

[0037]

EXAMPLES Next, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

Example 1 Photocatalytic anatase type titanium oxide powder STOl (manufactured by Ishihara Sangyo: primary particle diameter 7 nm, surface area 300)
The m ² / g) was placed in a furnace placed in an alumina crucible, NH ₃
Nitrogen treatment was performed at 600 ° C. for 30 minutes while flowing gas at 100 ml / min to obtain titanium oxynitride powder.
This powder had a pale yellow color. After weighing 10 g of this powder in a 1-liter separable flask,
500 g of a mixed solution of ammonia water / 30% by mass hydrogen peroxide = 0.05% by mass was added and vigorously stirred with a Teflon (R) stirrer for one day. After stirring, the solution was allowed to stand for 1 day, only the supernatant of the solution was taken out, ion-exchanged water was further added, and the concentration was adjusted so that the solid content was 1% by mass to obtain a dispersion solution. Next, 150 g of a 1% by mass amorphous titanium oxide solution was mixed with 350 g of this dispersion solution to obtain a coating solution. Then, the adjusted coating solution was sprayed onto the enamel substrate, dried and cured at 300 ° C. to form a photocatalytic film on the enamel substrate. At this time, the adhered amount of the solid content was 0.5 g / m ² . The characteristics of the photocatalytic coating were measured and evaluated by the methods described below. The evaluation results are shown in Table 1.

(Example 2) Primary particle diameter 20 nm, surface area 50 m ²
/ G of anatase titanium oxide powder "P25 instead of STOl
(Made by Nippon Aerosil: primary particle size 20 nm, surface area 50 m ² /
g) ”, but in the same manner as in Example 1,
A photocatalytic coating was formed on a enamel substrate. At this time, the adhered amount of solid content was 0.6 g / m ² . The characteristics of the photocatalytic coating are shown in Table 1.

Example 3 Titanium oxynitride powder obtained by nitriding treatment was weighed in an amount of 10 g in a 1-liter separable flask, and then 30% by mass ammonia water / 30% by mass hydrogen peroxide solution = 0.05. A photocatalytic film was formed on the enamel substrate in the same manner as in Example 1 except that 500 g of 30% by mass hydrogen peroxide solution alone was added instead of the mixed solution having the mass ratio. At this time, the amount of solids attached is 0.6 g
Was / m ² . The characteristics of the photocatalytic coating are shown in Table 1.

Example 4 A photocatalytic film was formed on a enamel substrate in the same manner as in Example 1 except that titanium-tantalum oxynitride powder was used instead of titanium oxynitride powder. At this time, the amount of solid matter attached was 0.6 g / m ² . The characteristics of the photocatalytic coating are shown in Table 1. As the titanium-tantalum oxynitride powder, a powder obtained by mixing anatase type titanium oxide (ST01) and tantalum pentoxide at a molar ratio of 9: 1 was placed in an alumina crucible and placed in a furnace, and NH ₃ gas was supplied. It was obtained by performing a nitriding treatment at 600 ° C. for 30 minutes while flowing at 100 ml / min. This titanium-tantalum oxynitride was of anatase type.

Example 5 In the same manner as in Example 1 except that titanium-strontium oxynitride powder was used instead of titanium oxynitride powder,
A photocatalytic coating was formed on a enamel substrate. At this time, the adhesion amount of the solid content was 0.5 g / m ² . The characteristics of the photocatalytic coating are shown in Table 1. The titanium-strontium oxynitride powder is anatase type titanium oxide (ST01).
Powder containing strontium carbonate and strontium carbonate mixed at 1: 1 (molar ratio) is placed in an alumina crucible and placed in a furnace, and nitriding treatment is performed at 600 ° C for 30 minutes while flowing NH ₃ gas at 100 ml / min. Obtained by. This titanium-strontium oxynitride was a perovskite type.

(Comparative Example 1) Anatase type titanium powder STOl
A photocatalyst coating was formed on the enamel substrate in the same manner as in Example 1 except that the nitriding treatment was not performed. At this time, the adhesion amount of the solid content was 0.5 g / m ² . The characteristics of the photocatalytic coating are shown in Table 1.

Comparative Example 2 Titanium oxynitride powder obtained by nitriding treatment was weighed in an amount of 10 g in a 1 liter separable flask, and then 30% by mass ammonia water / 30% by mass hydrogen peroxide solution = 0.05. A photocatalytic film was formed on the enamel substrate in the same manner as in Example 1 except that 500 g of ion-exchanged water was added instead of the mixed liquid having the mass ratio. At this time, the adhered amount of solid content was 0.7 g / m ² . The characteristics of the photocatalytic coating are shown in Table 1.

(Test Method) [Adhesion] The adhesion was evaluated by a cross-cut cellophane tape test (cross-cut number 100) based on JIS K 5400 8.20 (general paint test). That is, each test material was immersed in boiling ion-exchanged water for 2 hours, the appearance was observed, and a cross-cut peeling test was performed. In the cross-cut peeling test, after making a cut with a cutter to a depth reaching the substrate (base material) of the test material, a cell spacing of 1 mm and a cellophane tape on the grid of 100 squares, and peeling off the tape momentarily The number of cross-cuts of the coating film remaining on the sample material was counted, and the adhesiveness was evaluated by the counted number.

[Antibacterial Test] The antibacterial activity was evaluated according to the light irradiation film adhesion method of the Antibacterial Product Technology Council. 5cm x 5cm
Bacteria solution with a bacterial concentration of 1.5 × 10 ⁶ cells / ml was added to the size of the test material.
After inoculating 1 ml, cover it with a polyethylene film to make it adhere, set it in a transparent petri dish, and keep the temperature at 25 ° C.
Cover with a relative humidity of 90% or more and use a white fluorescent lamp to
Illuminate the visible light of Lux for 4 or 8 hours, or
It was left in the dark for 4 hours or 8 hours. After that, the surviving bacteria were washed out from the test material with physiological saline, and the NA medium was used at 35 ° C for 24 hours.
After culturing for a period of time, the viable cell count was measured. For the antibacterial activity, the number of viable bacteria was less than 10 when the number of viable bacteria was 1 per test material. The bacterium is Staphylococcus aureus I
F0 12732 is used, and the white fluorescent lamp is equipped with an ultraviolet cut film (trade name "ObicC" manufactured by King Manufacturing Co., Ltd.) and the ultraviolet intensity is 0.1 μW / cm ² or less (the ultraviolet intensity is 36
(Measured with a 5 nm ultraviolet sensor).

[Contact Angle] 20 μL of ion-exchanged water was dropped onto the test material using a microsyringe, and the water droplets on the test material were image-processed contact angle meter (Kyowa Interface Science Co., Ltd.,
CA-X) was used to measure the contact angle of water by the three-point method.
The contact angle was similarly measured in the initial state before irradiation with visible light and after irradiation with visible light of 1000 lux for 8 hours using the white fluorescent lamp.

[Appearance Observation] The appearance of the sample was visually observed.

[0049]

[Table 1]

From the results shown in Table 1, all the Examples
It can be seen that the appearance is good, the adhesiveness is excellent, and the irradiation of visible light for 8 hours has excellent antibacterial activity, a small contact angle, and exhibits high levels of both photocatalytic activity and hydrophilicity. Moreover, the coating liquid used in the examples did not cause precipitation even when left at room temperature for one month.

[0051]

INDUSTRIAL APPLICABILITY According to the present invention, a dispersion solution capable of advantageously forming a photocatalytic film made of titanium-containing oxynitride exhibiting photocatalytic activity and / or hydrophilicity not only by ultraviolet irradiation but also by visible light irradiation. (Coating solution) can be provided. Further, by using the dispersion solution (coating solution) of the present invention, a photocatalytic film can be formed without using an expensive apparatus, and
It can also be formed on a large-area substrate. further,
The composite member formed with the photocatalytic coating according to the present invention can be used as, for example, an interior material that requires an environment purifying or anticorrosion function, a scenic material such as a sidewall material, and an outer wall material. The photocatalyst coating made of titanium-containing oxynitride constituting the composite material is superior in wear resistance and corrosion resistance as compared with the photocatalyst coating made of oxides such as titanium oxide.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tatsuya Nobuzawa             1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Made in Kawasaki             Technical Research Institute of Iron Co., Ltd. (72) Inventor Shigeru Takano             1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Made in Kawasaki             Technical Research Institute of Iron Co., Ltd. (72) Inventor Hirohiko Murakami             Tokodai 5-9-7 Stock Association, Tsukuba City, Ibaraki Prefecture             ULVAC Tsukuba Institute for Supermaterials (72) Inventor Chizuru Ogane             Tokodai 5-9-7 Stock Association, Tsukuba City, Ibaraki Prefecture             ULVAC Tsukuba Institute for Supermaterials F-term (reference) 4G069 AA02 AA05 AA08 BA48A                       BB01C BB20 BC50A BD01C                       BD02C BD06C EA01X EA01Y                       FA01 FB80 FC04 FC08                 4J038 AA011 HA216 HA306 HA316                       HA446 JC38

Claims (4)

[Claims] 1. A dispersion solution of photocatalyst fine particles composed of titanium-containing oxynitride, wherein the surface of the photocatalyst fine particles is modified with a peroxo group. 2. A dispersion solution of photocatalyst fine particles, wherein the dispersion solution according to claim 1 contains an inorganic binder. 3. A powder of photocatalyst fine particles made of titanium-containing oxynitride and a hydrogen peroxide-containing solution are mixed,
The surface of the photocatalyst fine particles is modified with a peroxo group,
A method for producing a dispersion solution of photocatalyst particles, which comprises dispersing the photocatalyst particles in a solution. 4. The hydrogen peroxide-containing solution further contains ammonia, and the ammonia content is 0.3 or less in a mass ratio with respect to the hydrogen peroxide content. A method for producing a dispersion solution of photocatalyst fine particles.