JP2001089142A - Method of producing titanium oxide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a titanium oxide film acting as a photocatalyst used for removal, etc., of organic substances and inorganic ions in water and capable of exhibiting a high decomposition rate when used as the photocatalyst at the time of applying a hydrolyzed sol prepared from a tetra-lower alkoxytitanium to the surface of a heat-resistant substrate, heating and baking the resultant film and producing the titanium oxide film. SOLUTION: A hydrolyzed sol for forming a titanium oxide film prepared from a solution of a tetra-lower alkoxytitanium in ethanol or isopropanol or an ethylene glycol mono-lower alkyl ether is applied to the surface of a heat- resistant substrate, then heated and baked to form a titanium oxide thin film having <=100 nm film thickness. The film-forming operations are repeated to form a laminated film of the titanium oxide thin film. When the solution in the ethylene glycol lower alkyl ether is used, polyvinylpyrrolidone can be added into the hydrolyzed sol for forming the titanium oxide film for use to remarkably raise the decomposition rate of the photocatalyst structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a titanium oxide thin film. More specifically, the present invention relates to a method for producing a titanium oxide thin film acting as a photocatalyst used for removing organic substances and inorganic ions in water.

[0002]

2. Description of the Related Art Environmental problems such as water pollution, air pollution, and soil pollution are becoming more important year by year, and adversely affect human-originated chemical substances, particularly contaminants such as organic solvents, pesticides, and surfactants, and the human body. It is desired to remove viruses, bacteria, and the like, which cause harm. In order to remove these contaminants and pathogenic bacteria, ozone treatment using an ultraviolet lamp is often used. However, since ozone remains after the treatment, a technique for further removing ozone is required. In addition, there is concern about the production of substances that adversely affect the human body, including environmental hormones.

On the other hand, the method of decomposing and removing the above-mentioned chemical substances using a photocatalyst represented by titanium oxide is clean because it does not use chemicals and the like, and can use light energy such as sunlight. This is an environmental purification method that is currently attracting attention.

[0004] In such a photocatalytic decomposition method, it is difficult to separate the photocatalyst after the treatment, particularly in a liquid phase decomposition treatment such as an aqueous solution treatment. In order to solve these problems, a method using a film-shaped photocatalyst is currently being studied.
Although the problem of the separation of the photocatalyst has been solved, there is a disadvantage that the efficiency of the film-shaped photocatalyst is low.

[0005] In order to obtain a titanium oxide thin film, a method is generally employed in which a titanium-containing hydrolyzed sol obtained by hydrolyzing tetra-lower alkoxytitanium is adhered to the surface of a base material and heated and fired. . Hydrolysis of tetra-lower alkoxytitanium is carried out by adding diethanolamine, acetic acid, hydrochloric acid to an ethanol solution of tetra-lower alkoxytitanium,
It is performed by a method in which a hydrolysis catalyst such as nitric acid is added, and water is further added and mixed under stirring conditions.

However, when the titanium-containing hydrolyzed sol prepared as described above is adhered to the surface of a base material and heated and calcined, the titanium oxide thin film, when used as a photocatalyst, has a decomposition rate. There is a problem of being slow.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to deposit a hydrolyzed sol for forming a titanium oxide film obtained by hydrolyzing tetra-lower alkoxytitanium on the surface of a heat-resistant substrate, and heat and sinter the resultant. It is an object of the present invention to provide a method for producing a titanium oxide film which exhibits a high decomposition rate when used as a photocatalyst when producing a titanium oxide film.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
A hydrolysis sol for forming a titanium oxide film obtained by hydrolyzing an ethanol or isopropanol solution of tetra-lower alkoxytitanium or an ethylene glycol mono-lower alkyl ether solution is adhered to the surface of a heat-resistant base material, which is heated and fired to form a film. This is achieved by forming a titanium oxide thin film having a thickness of 100 nm or less, repeating such a film forming operation a plurality of times, and forming a titanium oxide thin film by forming a laminated film of the titanium oxide thin film. When an ethylene glycol lower alkyl ether solution is used, if polyvinyl pyrrolidone is added to the hydrolysis sol for forming a titanium oxide film, the decomposition rate of the photocatalyst structure obtained can be further increased.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As the tetra-lower alkoxytitanium, for example, tetramethoxytitanium, tetraethoxytitanium, tetra-n-propoxytitanium, tetraisopropoxytitanium, tetra-n-butoxytitanium, tetraisobutoxytitanium and the like can be used in an amount of about 0.01 to 0.01. 2 molar, preferably about 0.1-
It is used as a 1 molar solution of ethanol or isopropanol or a solution of ethylene glycol mono-lower alkyl ether such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether.

As a hydrolysis catalyst, an inorganic acid such as hydrochloric acid or nitric acid or an organic acid such as acetic acid is used as the above-mentioned various organic solvent solutions. This hydrolysis catalyst solution is placed in a tetra lower alkoxytitanium solution at room temperature to about 80 ° C.
When added and mixed under stirring conditions at a temperature of ° C., a transparent and stable hydrolysis sol capable of forming a titanium oxide film uniform at the molecular level can be obtained.

In the case of a titanium oxide film-forming hydrolytic sol using ethylene glycol mono-lower alkyl ether, it is not more than about 30% by weight, preferably about 3 to 3% by weight.
Polyvinylpyrrolidone is used at an addition rate of 15% by weight. If used at a higher ratio, the viscosity of the titanium oxide film-forming hydrolyzable sol increases, making film formation difficult. The average molecular weight and K value of the polyvinylpyrrolidone used are not particularly limited, but preferably have an average molecular weight of about 5,000 to 15,000, and a K value of about 10 to 20.
It is about. Addition of polyvinylpyrrolidone, when the formed titanium oxide film was used as a photocatalyst structure,
It shows a higher decomposition rate.

The hydrolytic sol for forming a titanium oxide film using various organic solvents as described above is subjected to a dipping method, a spraying method, a spin coating method, or the like to form a plate-like, rod-like, tubular, or bead-like heat-resistant base material surface. To form a gel film,
When this is heat-treated at a temperature of about 300 to 700 ° C., preferably about 400 to 700 ° C. for about 10 minutes to about 3 hours, a titanium oxide thin film is formed on the surface of the heat-resistant base material. The titanium oxide thin film thus formed must have a thickness of 100 nm or less, and such a thickness, preferably about 10 to 100 n
The formation of a titanium oxide thin film of m
A titanium oxide film composed of a laminated film having a thickness of 0.02 to 10 μm, preferably about 0.05 to 3 μm is formed. The formed titanium oxide laminated film is made of quartz glass, soda glass,
The adhesiveness to ceramics and the like is also good, and it is so small that it does not peel off even with the tape peeling test method.

The titanium oxide film supported on the surface of the heat-resistant substrate is effectively used as a photocatalyst structure for decomposing and removing organic substances or inorganic ions in water. For example, when used for decomposition treatment or sterilization treatment of organic substances in water such as isopropanol and sodium dodecylbenzenesulfonate contained in factory wastewater, general organic solvents, organic chlorine compounds, dyes, oils, surfactants, etc. The decomposition reaction proceeds smoothly on the surface of the titanium oxide film irradiated with light such as ultraviolet light. The same applies to the case of inorganic ions in water.

[0014]

According to the present invention, when a photocatalyst is used to decompose organic substances and inorganic ions contained in water, the titanium oxide powder generally has a (110) plane occupying most of the external surface in the rutile type, which has poor photocatalytic properties, whereas the anatase type. Then, the (001) plane occupies a large amount of the outer surface and shows an excellent photocatalyst.

In the present invention, by using a specific organic solvent to form a titanium oxide film-forming hydrolytic sol, only a structure near the surface of the anatase powder having excellent photocatalytic activity is formed on the surface of the substrate. Moreover, the decomposition rate is improved by using the titanium oxide thin film formed thereon as a laminated film.

When ethylene glycol lower alkyl ether is used as an organic solvent for forming a titanium oxide film-forming hydrolytic sol, polyvinylpyrrolidone is added thereto, and when polyvinylpyrrolidone is added thereto, heat-resistant base material is formed. The decomposition rate of organic substances such as sodium dodecylbenzenesulfonate by the photocatalyst structure comprising the titanium oxide film formed on the substrate can be further improved.

The photocatalyst structure on which such a titanium oxide film is formed is composed of inorganic ions in water, such as ammonium ion, nitrite ion, nitrate ion, bromine ion, bromate ion, sulfite ion, sulfate ion, and phosphate ion. It is also effectively used for decomposing and removing ions and the like, and water may further contain organic substances.

[0018]

Next, the present invention will be described with reference to examples.

EXAMPLE 1 0.42 ml of 10% by weight hydrochloric acid was added to 10.58 ml of ethanol in 20 ml of a 0.4 molar concentration of tetraisopropoxytitanium in ethanol.
Was mixed under stirring conditions to prepare a hydrolysis sol for forming a titanium oxide film. The gel film formed by applying this sol to the surface of a quartz glass substrate by dipping is heated to 500 ° C. at a rate of 1 ° C./min.
Heat treatment was performed for a time to form a titanium oxide thin film having a thickness of 80 nm. The formation of the titanium oxide thin film by such a method was further performed three times to obtain a titanium oxide laminated film having a thickness of 320 nm.

The photocatalyst structure on which the titanium oxide laminated film is formed is immersed in 2.5 ml of a 100 ppm aqueous solution of sodium dodecylbenzenesulfonate [DBS] in a quartz glass cell. (6W)
When the DBS decomposition rate is determined from the change in absorbance of the UV absorption spectrum of the solution, the decomposition rate is
1.6 × 10 ^-7 mol / m ² · sec.

Example 2 In Example 1, when isopropanol was used instead of ethanol, the DB by the photocatalyst structure formed there was used.
The decomposition rate of S was 1.5 × 10 ⁻⁷ mol / m ² · sec.

Comparative Example 1 In Example 1, the decomposition rate of DBS by a photocatalyst structure having a 320 nm-thick titanium oxide single-layer film formed by one film forming operation was measured, and the value was 0.7 × 10 ^{− It was 7} mol / m ² · sec.

Comparative Example 2 In Example 2, the DBS decomposition rate of the photocatalyst structure having a 320 nm-thick titanium oxide single-layer film formed by one film forming operation was measured. The value was 0.7 × 10 ^{− It was 7} mol / m ² · sec.

Example 3 In Example 1, when ethylene glycol monomethyl ether was used instead of ethanol, the decomposition rate of DBS by the photocatalyst structure formed there was 1.8 × 10 ⁻⁷ mol / m ^2.
・ It was seconds.

Example 4 In Example 1, when ethylene glycol monoethyl ether was used instead of ethanol, the decomposition rate of DBS by the photocatalyst structure formed there was 1.9 × 10 ⁻⁷ mol / m ^2.
・ It was seconds.

Comparative Example 3 In Example 3, the decomposition rate of DBS by a photocatalyst structure having a 320 nm-thick titanium oxide single-layer film formed by one film-forming operation was measured. The value was 0.8 × 10 ^{− It was 7} mol / m ² · sec.

Comparative Example 4 In Example 4, the decomposition rate of DBS by a photocatalyst structure having a 320 nm-thick titanium oxide single-layer film formed by one film forming operation was measured. The value was 0.9 × 10 ^{−. It was 7} mol / m ² · sec.

Example 5 In Example 3, polyvinylpyrrolidone (average molecular weight: about 10,000, K value: 15) was added to the hydrolysis sol for forming a titanium oxide film.
The [PVP] With added as EGME solution as the addition rate is 3.4 wt%, there to a degradation rate of the formed DBS by the photocatalyst structure 1.8 × 10 ^-7 mol / m ² · sec there were.

Example 6 In Example 5, when the addition ratio of PVP was changed to 6.6% by weight,
The decomposition rate of DBS by the photocatalyst structure formed there is
2.1 × 10 ^-7 mol / m ² · sec.

Example 7 In Example 5, when the PVP addition rate was changed to 12.3% by weight, the decomposition rate of DBS by the photocatalyst structure formed there was 2.0 × 10 ^-7 mol / m ² · sec. .

Comparative Example 5 In Example 5, the decomposition rate of DBS by the photocatalyst structure in which a 320 nm-thick titanium oxide single-layer film was formed by one film forming operation was measured. The value was 1.1 × 10 ^{− It was 7} mol / m ² · sec.

Comparative Example 6 In Example 6, the decomposition rate of DBS by a photocatalyst structure having a 320 nm-thick titanium oxide single-layer film formed by one film forming operation was measured. The value was 1.3 × 10 ^{−. It was 7} mol / m ² · sec.

Comparative Example 7 In Example 7, the decomposition rate of DBS by the photocatalyst structure in which a 320 nm-thick titanium oxide single-layer film was formed by one film forming operation was measured. The value was 1.1 × 10 ^{− It was 7} mol / m ² · sec.

Claims (6)

[Claims] 1. A hydrolytic sol for forming a titanium oxide film, obtained by hydrolyzing an ethanol or isopropanol solution of tetra-lower alkoxytitanium, is adhered to the surface of a heat-resistant base material, and heated and calcined to a film thickness of 100 nm or less. A method for producing a titanium oxide film, comprising: forming a titanium oxide thin film as described above; and repeating such a film forming operation a plurality of times to form a laminated film of the titanium oxide thin film. 2. A hydrolysis sol for forming a titanium oxide film, obtained by hydrolyzing a solution of an ethylene glycol mono-lower alkyl ether of tetra-lower alkoxytitanium, is adhered to the surface of a heat-resistant substrate, and heated and fired to form a film. A method for producing a titanium oxide film, comprising forming a titanium oxide thin film having a thickness of 100 nm or less, and repeating such a film forming operation a plurality of times to form a laminated film of the titanium oxide thin film. 3. The method for producing a titanium oxide film according to claim 2, wherein polyvinylpyrrolidone is added to the hydrolysis sol for forming a titanium oxide film. 4. A photocatalyst structure having a titanium oxide film formed by the method according to claim 1, 2 or 3. 5. The photocatalyst structure according to claim 4, which functions as a photocatalyst used for decomposing and removing organic substances in water. 6. The photocatalyst structure according to claim 4, which functions as a photocatalyst used for decomposing and removing inorganic ions in water.