JPH08164334A - Titanium dioxide coating film forming composition for photocatalyst and its production - Google Patents

Abstract

PURPOSE: To obtain the composition from which a titanium dioxide coating film can firmly be formed by using titanium dioxide having a specified average particle size, a hydrolyzate of a hydrolyzable silicon compound represented by a specific formula and a solvent as the components of the composition and adjusting the weight ratio of titanium to silicon and the total solid content of the composition to specified values respectively. CONSTITUTION: This composition consists of powdery titanium dioxide having a 0.001 to 0.5μm average particle size, a hydrolyzate of a hydrolyzable silicon compound represented by the formula (wherein: (n) is 0 or a whole number of 1 to 8; X is a halogen atom or alkoxyl group having 1 to 8 carbon atoms, which atoms or groups are the same or different) and a solvent. In the composition, the weight ratio of titanium to silicon is (30 to 96):(70 to 4) expressed in terms of TiO2 and SiO2 respectively (the total is 100) and the total solid content is <=30wt.%. By using this composition, the fine-powdery titanium dioxide that has a catalytic function capable of oxidizing or reducing organic matter through irradiating it in the presence of the titanium dioxide with light can firmly be stuck to the surface of a substrate so as to cover the surface of the substrate with it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composition capable of forming a titanium oxide-containing coating used as a photooxidation catalyst and a method for producing the composition, which comprises glass, metal, cement,
The present invention relates to a base material applied to the surface of wallpaper, gypsum board, stone material, ceramics, plastic or the like.

[0002]

2. Description of the Related Art Titanium oxide is itself an optical semiconductor, and when it is irradiated with light having an energy larger than its band gap, for example, ultraviolet rays, electrons are accumulated in the conduction band and holes ( Hole). It is known that the photocatalytic activity of decomposing organic substances in the atmosphere by the redox action based on the electron transfer generated by the accumulated electrons and holes and exhibiting a bactericidal effect, and various attempts have been made to industrially utilize this activating action. It is being appreciated.

It is difficult to form a titanium dioxide layer having a high photocatalytic activity on the surface of a substrate. One of the conventional methods is to form a titanium oxide film by air-oxidizing or anodizing the surface of a pure titanium plate, but it is difficult to obtain a good function although the oxidation method is difficult. .
As another method, titanium oxide is vapor-deposited on the surface of the base material by a CVD method or plasma spraying is performed (Japanese Patent Laid-Open No. 6-210).
170 gazette) is also known, but both are expensive,
It cannot be applied depending on the type of base material. Attempts have also been made to attach titanium dioxide powder to a substrate via an adhesive called a binder, but the photocatalytic action of titanium dioxide causes the binder to be oxidatively decomposed and fall off from the substrate after a few months, making it suitable for industrial applications. I can't stand it.

Recently, a method of forming a titanium dioxide thin film on the surface of a glass tube by a sol-gel method from titanium alkoxide has been announced. In this method, a solution obtained by adding a certain organic polymer to an alcohol solution of alkoxide is applied to a substrate, the organic polymer is thermally decomposed and removed by heat treatment, and titanium oxide is crystallized. The problem remains that it is expensive and that heat treatment at high temperature is essential.

[0005]

Various attempts have been made to purify air pollution and wastewater by utilizing the photocatalytic action of titanium oxide, but all have problems, and a definitive method has not yet been found. The current situation is not. The present invention is intended to provide a titanium oxide coating film-forming composition for a photocatalyst, which is economically widely applicable to various uses.

[0006]

The present invention is 0.001-
Titanium oxide having an average particle size of 0.5 μm, the following general formula (1)

[0007]

Embedded image

It comprises a hydrolyzate of a hydrolyzable silicon compound represented by and a solvent, and the weight ratio of titanium and silicon is 30 to 96: 7 in terms of conversion into TiO ₂ and SiO ₂ , respectively.
The titanium oxide coating film moldable composition for a photocatalyst and the method for producing the same are characterized in that the solid content concentration is 0 to 4 (total 100) and the total solid content concentration is 30% by weight or less. Further, the present invention provides a substrate or member having photocatalytic activity, which comprises coating and drying the composition to form a composite coating film of titanium oxide and silicon oxide having a thickness of 0.1 to 3 μm on the surface of a solid substrate. is there.

The present invention will be described in detail below. Titanium oxide used in the present invention shows a catalytic action for redox of an organic substance by irradiation with light having a specific energy, and in addition to pure titanium oxide, hydrous titanium oxide,
It includes what are called hydrated titanium oxide, metatitanic acid, orthotitanic acid, and titanium hydroxide. Titanium dioxide or one in a lower oxidation state than titanium dioxide is particularly preferably used. The crystal form of titanium dioxide may be any of anatase type, rutile type, flukite type, and a mixture thereof.

These titanium dioxides are in the form of fine powder,
The particle size is 0.001 to 0. 0 in view of the strength of photocatalytic activity.
A fine particle of about 05 μm is preferable, but a particle size up to about 0.5 μm, which is larger than this, can be used. This fine powder may be used as a powder in a dry state, but it is desirable to prepare it in advance as a dispersion in order to uniformly disperse it with a silica binder derived from a hydrolyzable silicon compound described later. Whether or not titanium dioxide is well dispersed in the composition of the present invention greatly affects the photocatalytic function when a coating film is formed.

Titanium oxide is produced by various known methods. For example 1. 1. A method of hydrolyzing a titanium compound such as titanyl sulfate, titanium chloride, or an organic titanium compound in the presence of a nucleating species, if necessary. 2. A method in which an alkali is added to a titanium compound such as titanyl sulfate, titanium chloride, or an organic titanium compound in the presence of a nucleus-forming seed, if necessary, to neutralize it. 3. A method of vapor-phase oxidizing titanium chloride, an organic titanium compound, etc. Examples thereof include a method of firing the titanium oxide obtained by the above methods 1 and 2. In particular, titanium oxide obtained by the above methods 1 and 2 is preferable because it has a high photocatalytic function. In order to further improve the photocatalytic function, the titanium oxide surface may be coated with a metal such as platinum, gold, silver, copper, palladium, rhodium or ruthenium, or a metal oxide such as ruthenium oxide or nickel oxide.

These titanium oxides are used by being highly dispersed in a solvent such as water. In order to place titanium oxide in the form of ultrafine particles in a uniformly dispersed state with a solvent such as water without secondary agglomeration, it is preferable to store the titanium oxide in an acidic or alkaline state. When placed under acidic conditions, pH 0.5-
4, especially 1 to 3.5 is preferable. As the dispersion medium, a mixture of water and alcohol may be used in addition to water.

The hydrolyzable silicon compound represented by the above general formula (1) used in the present invention is an alkyl silicate, a silicon halide and a partial hydrolyzate thereof. As the alkyl silicate, methyl, ethyl, isopropyl silicate or the like is used. All of these silicates also used in the form of oligomers produced by monomeric or partially hydrolyzed, as the oligomer general formula _{Si n O n-1 (OR} ) 2n + 2 ( where n is 2
An alkyl silicate condensate represented by 6, R is a C1-4 alkyl group) is particularly preferable. These oligomers are also used in mixtures.

As a catalyst for the partial hydrolysis, an acid,
Any of the alkalis can be used. When the titanium oxide dispersion is acidic, an acid-hydrolyzed alkyl silicate is preferred. The dispersion solvent of the hydrolyzed liquid has water or a carbon number of 1 to
Alcohol of 4 is used. Esters such as ethyl acetate are not preferable because they destabilize the composition liquid. The silicon compound and its partial hydrolyzate used in the present invention are used for the purpose of binding titanium oxide, and hence are referred to as silica binders hereinafter.

The titanium oxide and the silica binder can be appropriately mixed, but as an example, a predetermined amount of titanium dioxide aqueous dispersion under acidic condition is kept at a liquid temperature of 10 to 50 ° C. and weighed. The alkyl silicate or partial hydrolyzate is added dropwise over a period of time. After the dropping is completed,
A composition liquid is prepared by reacting with stirring for 1 to 5 hours. When the alkyl silicate or the partial hydrolyzate is added, its hydrolysis catalyst may be added at the same time, or the hydrolysis may be promoted by utilizing the acid component present in the titanium dioxide dispersion. When an alcohol-based medium is used as the dispersion medium, a water / alcohol mixed medium dispersion liquid of titanium dioxide and a liquid obtained by hydrolyzing 50 to 1500% of an alkyl silicate or a partial hydrolyzate in an alcohol medium are mixed with stirring. Then, the present composition can be obtained.

The term "hydrolysis rate" as used herein is calculated from the amount of water used, assuming that the rate of hydrolysis is 100% when 1 mole of alkyl silicate is used and 2 moles of water is used. When a partial hydrolyzate in the form of the general formula Si _n O _n-1 (OR) _{2n + 2} is used, the hydrolysis rate is 1 when 1 mole of this condensate is used and n + 1 mole of water is used.
It was calculated as 00%.

The proportion of titanium and silica in the composition of the present invention must be 96/4 to 30/70 in terms of weight ratio (TiO ₂ / SiO ₂ ) converted to titanium dioxide and silicon dioxide, respectively. is there. When the proportion of silica exceeds 70%, the photocatalytic function of titanium oxide becomes small and the practicality becomes poor. It is considered that this is because the proportion of silica covering the surface of the titanium oxide particles is increased, which hinders the contact between the titanium oxide and the substance to be oxidatively decomposed. On the other hand, if the mixing ratio of silica is 4% or less, the adhesive strength between the base material and titanium oxide is not sufficient, and it easily falls off due to finger touch or vibration, making it difficult to industrially use as a coating film. . The preferable ratio of silica is 10 to 50%.

The solid content concentration in the composition of the present invention is 3 by weight.
0% or less. Here, the solid content refers to the total amount of titanium oxide and silica in the entire composition. Titanium oxide is titanium dioxide, and silica is the alkyl silicate in the composition or silicon (Si) content in the oligomer thereof is SiO ₂ . The converted value is used. Other components are mainly composed of water and / or an organic solvent, and should be substantially removed by applying the composition onto the surface of the substrate and then drying. A preferable solid content concentration is 5 to 20%, and when it is 5% or less, the adhesiveness to the base material becomes strong, but the thickness of the coating film, that is, the amount of titanium dioxide is insufficient, and the photocatalytic function can be sufficiently exhibited. Cannot be formed. It is possible to increase the coating thickness by two-layer coating or three-layer coating, but normally, the merit of the two-layer coating, in which the solid content concentration is purposely lowered, is troublesome, does not appear. However, it can be used for special applications such as when a strong thin coating film is required even if the photocatalytic function is sacrificed.

On the other hand, when the solid content concentration exceeds 30%, the dispersibility of the solid matter in the composition is deteriorated, the storage stability of the composition is remarkably lowered, and gelation easily occurs in a few days.
Further, at such a high concentration, the film-forming property is poor, the adhesiveness of the formed film to the substrate is significantly reduced, and the film is peeled off when rubbed with a finger, which is not preferable.

A small amount of titanium alkoxide or titanium tetrachloride may be added to the composition of the present invention. Further, titanium or a silane coupling agent may be added. Further, various surfactants may be added to secure the stability of the composition and improve the wetting property. Further, a small amount of alkylsilane or hydrosilane containing two or more alkoxy groups may be added, but these titanium and silane compounds are added in terms of silica when calculating the solid content.

The composition of the present invention is applied to the surface of a substrate, dried and optionally baked at low temperature to form a coating film. As the coating method, spin coating, spray coating, bar coating, dip method, etc. are appropriately used depending on the shape of the substrate to be coated. The thickness of the coating film is 0.1-3 μm,
Particularly, 0.3 to 2 μm is suitable. Although the photocatalytic activity of titanium dioxide is related to the amount of titanium dioxide that can come into contact with the compound to be exposed and oxidatively decomposed on the surface, the thickness of the coating film is not originally related, but in reality, it is not related to the thickness of the coating film. There is uniformity,
Also, the dispersion of particles does not always achieve the desired uniformity,
If it is too thin, the amount of titanium dioxide on the surface of the coating film is small and the photocatalytic activity is not sufficient, so it is preferable to set the thickness to the above range. With such a thickness, the coating film can be made transparent, and a photoactive coating film can be formed on the surface of the substrate without impairing various structures and designs of the substrate.

The base material to which the coating film moldable composition of the present invention is applied is glass, metal, cement concrete, slate, gypsum board, stone material, wood, ceramics, plastic tube, tubular, plate-like or lattice-like. , Spherical, honeycomb-shaped members or molded products from these members,
After coating, it is preferable to dry sufficiently to remove solvent, water and the like.

The coating film from the composition of the present invention can form a fairly strong coating film which is not easily peeled off even if it is rubbed with a nail by drying at 100 ° C., but the silica binder is dried at a temperature of 100 ° C. or more. Since a stronger coating film can be formed, it may be dried at 100 to 300 ° C. or baked at a low temperature, if necessary. However, the catalytic activity of ultrafine particulate titanium dioxide begins to gradually decrease when it is dried at 150 ° C or higher, and may rapidly decrease when it exceeds 400 ° C. Therefore, the drying temperature should be adjusted according to the need for coating strength. However, in any case, drying at 480 ° C. or lower or low temperature firing is preferable.

The substrate or member on which the coating film of the present invention is formed is used in a wide variety of applications. For example, a plate-shaped or lattice-shaped member made of metal or plastics is used as a sound insulation member for highways, and it is used for decomposing and removing organic substances and microorganisms attached to the plate. Alternatively, a ceramic honeycomb covered with a substance is used as a catalyst for decomposing a harmful substance by bringing a gas or liquid containing a harmful substance such as hydrogen sulfide into contact therewith. Also, when it is applied to a plastic decorative plate made of vinyl chloride or the like, it exerts the function of automatically purifying the wall surface when it is used as a wall material, and can be used in hospitals and the like as having a sterilizing effect. Those attached to spherical glass, pumice stone, ceramics, etc. can be used as a purification agent for wastewater. In a conference room or the like, it can be used for decomposing cigarette smoke simply by placing a member made of a base material coated with the composition of the present invention and dried, such as an ashtray or a screen. Furthermore, it can be applied to the inside of a water tank and used for algae control.

[0025]

EXAMPLES In the examples, the photocatalytic activity decomposition rate was determined by applying the composition of the present invention to a glass plate by the following method and using a test piece on which a film was formed, which was irradiated with light while being in vapor phase contact with acetaldehyde. It is measured by the decomposition rate of acetaldehyde.

1. Preparation of test piece (application condition of composition liquid) Application piece: glass plate 100 × 50 × 2 t (mm) Application method: Meyer bar # 3, # 5 Drying condition: 100 ° C., 1 hour

2. Photocatalytic activity decomposition rate measurement method (1) Gas phase decomposition reaction device A three-neck separable flask is assembled and set sideways so that the test piece can be placed inside. (2) Light source Two black lights 4W manufactured by Toshiba Corp. are installed at a distance of about 8 cm from the coating surface of the test piece so that the light quantity (light intensity) is 1 mW / cm ² . (3) Circulating device An air pump is used to connect the inside of the flask and the sampling three-way cock with a Tygon tube so as to circulate at 1 liter / min. (4) Detector tube for introduction of acetaldehyde and concentration measurement A test piece is placed, and a silicone W cap is attached to one of the three necks of a flask filled with normal air, and acetaldehyde is introduced by a microsyringe. Introduction amount is 4
It should be 0 to 200 ppm. One of the three-way cocks for sampling is provided with a gas detector tube for measuring acetaldehyde concentration so that the concentration can be measured. (5) Pretreatment of test piece and measurement of acetaldehyde decomposition rate Prior to measuring the photocatalytic activity of the test piece, pretreatment was performed with acetaldehyde. The pretreatment of the test piece is performed because when the residual organic matter is present in the coating film of the test piece, the organic matter is decomposed before or together with the decomposition of acetaldehyde, and it becomes difficult to measure the correct decomposition rate of the introduced acetaldehyde. This is done to minimize the impact. In the pretreatment, about 100 ppm of acetaldehyde is introduced into the flask, the circulating device is operated without irradiating light, and after circulating for 10 minutes, the concentration is measured with a gas detection tube. Then, the light source switch is turned on, and the acetaldehyde concentration is measured every 30 minutes after the start of light irradiation for a maximum of 3 hours. The decomposition rate was determined as that the reduced acetoaldehyde was decomposed, and the pretreatment of the test piece was completed when the decomposition rate reached 85% or more or when light irradiation for 3 hours was performed. With respect to the test piece on which the pretreatment was completed, the decomposition rate was measured from the change of the acetaldehyde concentration before and after the light irradiation by the following calculation formula in the same manner as the pretreatment, and used for the evaluation of the photocatalytic activity of the coating film.

[0028]

[Equation 1]

The evaluation of the coating film-forming composition surface obtained in each example is shown in the table, and the hardness in the table is a measured value relating to the strength of the coating film, which is indicated according to the following criteria. The degree to which the coating film is destroyed by finger touch The degree to which the coating film is peeled off when rubbed with a nail The degree to which scratches are caused when rubbed with a nail Between the above and the following To the extent that no scratches are left Also, the reaction rate constants in the table are calculated assuming that the decomposition of acetaldehyde is linearly proportional to time,
The unit is min ^-1 . In the examples, "parts" means parts by weight.

Example 1 An aqueous dispersion of titanium dioxide having an average particle size of 0.006 μm was adjusted to pH 1.5, and a predetermined amount of ethyl silicate was added dropwise with stirring while maintaining this at 30 ° C. The ratio of titanium and silica was adjusted as shown in Table 1 so that the solid content concentration was 10%. Water (ion exchanged water) was used for concentration adjustment. Nothing was added as a hydrolysis catalyst. After completion of the dropping, the mixture was stirred and reacted at 30 ° C. for 3 hours, and the obtained liquid was used to form a film on the glass plate of the test piece so as to have a film thickness of 0.75 μm using Meyer bar # 5. After drying at 100 ° C. for 1 hour, the appearance and hardness of the coating film and the photocatalytic activity were measured according to the method described above. The results are shown in Table 1. from this result,
It can be seen that even if the proportion of SiO ₂ exceeds 50%, it still has the ability to decompose acetaldehyde.

[0031]

[Table 1]

Example 2 (1) Preparation of Hydrolyzed Liquid of Silicon Compound In a separable flask equipped with a stirrer, thermometer and reflux condenser, 223.5 parts of methyl alcohol, 40 parts of ethyl silicate (5 parts of ethyl silicate) were prepared. Charge 30 parts of body equivalent, Colcoat Co., Ltd., trade name, and stir evenly 3
Keep at 0 ° C. To this, a mixed solution of 45 parts of ion-exchanged water and 1.5 parts of 60% nitric acid was added all at once so that the hydrolysis rate was about 1000%, and hydrolysis was performed at 30 ° C. for 5 hours. The solid content concentration of the hydrolyzed liquid thus prepared is S
It was 4% as iO ₂ .

(2) Mixing method with TiO ₂ dispersion A separable flask equipped with a stirrer, a thermometer and a reflux condenser was charged with 12.5 parts of the above hydrolysis solution and 55.8 parts of isopropyl alcohol and homogenized. Stir to maintain at 30 ° C. A predetermined amount of a TiO ₂ dispersion having a particle size of 0.006 μm was added thereto, and the mixture was stirred at 30 ° C. for 1 hour. The TiO ₂ / SiO ₂ ratio of the obtained liquid is as shown in Table 2,
The solid content concentration was adjusted to 10%.

(3) Film formation and photoactivity measurement The composition liquid obtained by the above mixing was applied to a test piece using Meyer bar # 3, dried at 100 ° C. as in Example 1, and calculated. To form a coating film having a film thickness of 0.45 μm. The photocatalytic activity of the obtained test piece was measured. Table 2 shows the results
Shown in The film thickness on the test piece used here is an extremely thin film from an actual point of view, and even if it is such a thin film, it shows photocatalytic activity, and in practical use it will be thicker than it is practical. Will be things.

[0035]

[Table 2]

[Example 3] The composition having a total solid content concentration of 10% obtained in Example 2 was applied to a test piece using Meyer bar # 5, and the coating was dried at 150 ° C for 30 minutes. ,
A coating film having a calculated film thickness of 0.75 μm was formed. The photocatalytic activity of the obtained test piece was measured. The results are shown in Table 3. When the coating film is dried at a high temperature, the hardness of the coating film is slightly improved, but the catalytic effect on the decomposition of acetaldehyde is not decreased, and it can be seen that the decomposition rate is increased as the film thickness is increased.

[0037]

[Table 3]

Example 4 A composition of the present invention was prepared by using a silica binder prepared by the following method instead of the hydrolyzing solution of the silicon compound used in Example 2. A separable flask equipped with a stirrer, a thermometer, and a reflux condenser was charged with 230.4 parts of methyl alcohol, 23.4 parts of methyl silicate 51 (equivalent to a methyl silicate tetramer, a product name of Colcoat Co., Ltd.). , Stir uniformly and maintain at 30 ° C. The hydrolysis rate is about 1000%
44.7 parts of ion-exchanged water and 60% nitric acid 1.
5 parts of the mixed solution was added all at once and hydrolyzed at 30 ° C. for 5 hours. The hydrolyzed liquid thus prepared had a solid content concentration of 4% as SiO ₂ .

Various composition liquids obtained by using the above silica binder were applied to a test piece by using Meyer bar # 5, and dried at 150 ° C. for 30 minutes as in Example 3 (however,
Sample No. No. 14 was dried at 200 ° C. for 30 minutes) to form a coating film having a calculated film thickness of 0.75 μm. The photocatalytic activity of the obtained test piece was measured. The results are shown in Table 4. The coating film using methyl silicate 51 tends to have high hardness as a whole.

[0040]

[Table 4]

[0041]

INDUSTRIAL APPLICABILITY The composition of the present invention is capable of firmly coating and adhering titanium dioxide fine powder having a catalytic function for redox of organic substances by irradiation of light onto the surface of a substrate, and adhering it with an organic binder. It is possible to form a coating film having a high photoactivity, which does not decrease the adhesive force with the lapse of time due to the decomposition of organic substances. A transparent film can be formed by selecting the ratio of the film thickness and the silica binder, and it can be applied to a wide range of applications.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masanori Tomonari 5-9-15 Hirai, Kusatsu-shi, Shiga (72) Inventor Takeshi Koreto 1-20-5 Sanno, Sakura-shi, Chiba

Claims (6)

[Claims] 1. A titanium oxide having an average particle size of 0.001 to 0.5 μm, represented by the following general formula (1): Which comprises a hydrolyzate of a hydrolyzable silicon compound represented by and a solvent, and the weight ratio of titanium and silicon is 30 to 96:70 to 4 (total 100) in terms of conversion to TiO ₂ and SiO ₂ , respectively. Solid content concentration in the composition is 30% by weight
A titanium oxide coating film-forming composition for a photocatalyst, characterized in that: 2. The solvent is substantially water and the hydrolyzable silicon compound is of the general formula Si _n O _n-1 (OR) _{2n + 2} (where n
Is a lower alkyl silicate condensate represented by 2 to 6 and R is a C1 to C4 alkyl group, and has a pH of 0.5 to 4
The coating film-forming composition according to claim 1, which is 3. The solvent is an alcohol having substantially 1 to 4 carbon atoms, and the hydrolyzable silicon compound is represented by the general formula Si _n O _n-1.
(OR) _{2n + 2} (where n is 2 to 6 and R is a C1 to C4 alkyl group) is an alkyl silicate condensate, which is further hydrolyzed to a hydrolysis rate of 50 to 1500%. The coating film-forming composition of claim 1, which is 4. An acidic aqueous dispersion containing 4 to 50% by weight of titanium oxide having an average particle size of 0.001 to 0.5 μm and having a pH of 4 or less is maintained at 10 to 50 ° C. A lower alkyl silicate or a lower oligomer thereof is added with stirring and reacted for 1 hour or more, and the weight ratio of titanium and silicon is 30 to 30 in terms of TiO ₂ and SiO ₂ , respectively.
It is 96: 70-4 (total 100), and the manufacturing method of the titanium oxide coating film forming composition for photocatalysts whose total solid content concentration in a composition is 30 weight% or less. 5. An aqueous dispersion containing 4 to 50% by weight of a titanium oxide having an average particle size of 0.001 to 0.5 μm and a lower alkyl silicate or silicon tetrachloride in an alcohol of 50 to 1500%. The alcoholic silica sol obtained by hydrolysis is added and mixed at 10 to 50 ° C., and the weight ratio of titanium and silicon is 30 to 96:70 to 4 (total 100) in terms of conversion to TiO ₂ and SiO ₂ , respectively. And a method for producing a titanium oxide coating film-forming composition for a photocatalyst, wherein the total solid content concentration in the composition is 30% by weight or less. 6. A titanium oxide having an average particle size of 0.001 to 0.5 μm, represented by the following general formula (1): Which comprises a hydrolyzate of a hydrolyzable silicon compound represented by and a solvent, and the weight ratio of titanium and silicon is 30 to 96:70 to 4 (total 100) in terms of conversion to TiO ₂ and SiO ₂ , respectively. Solid content concentration in the composition is 30% by weight
A substrate having a photocatalytic function, which comprises coating the following titanium oxide and silicon oxide-containing composition and drying it to form a coating film of titanium oxide and silicon oxide having a thickness of 0.1 to 3 μm on the surface.