JP2000302442A - Production of titanium oxide thin film photocatalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily obtain the subject thin film photocatalyst without causing such problems as operational safety and corrosion by coating a substrate with an aqueous solution of hydroxy(hydroxycarboxylato)titanium followed by baking through heating from room temperature to a specific temperature range to conduct a baking. SOLUTION: This thin film photocatalyst is obtained by coating a substrate with an aqueous solution of hydroxy(hydroxycarboxylato)titanium followed by baking through gradually heating from room temperature to 600-700 deg.C to conduct a baking at 600-700 deg.C; wherein the hydroxy(hydroxycarboxylato)titanium is prepared by reaction, at room temperature to about 100 deg.C, of a solution made by mixing an alkoxytitanium with the corresponding hydroxycarboxylic acid in the weight ratio of about (1:0.1) to (1:10); in this case, the alkoxytitanium to be used is e.g. tetramethoxytitanium, tetraethoxytitanium, while the hydroxycarboxylic acid to be used is e.g. glycolic acid, lactic acid, α- hydroxybutyric acid or the like, gluconic acid, galactaric acid or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a titanium precursor used as a raw material for producing a titanium oxide thin film, and a method for producing a titanium oxide thin film photocatalyst using the same. Titanium oxide can be used as a photocatalyst to remove odors and harmful substances in the air, or to perform wastewater treatment, water purification treatment, antibacterial treatment, and the like. In addition, there is a use as an antifogging, easy cleaning, and self-cleaning material utilizing the superhydrophilicity of the photocatalytic titanium oxide.

[0002]

2. Description of the Related Art Conventionally, as a technique for forming a titanium oxide thin film on a substrate, Japanese Patent Publication Nos.
No. 2,636,158 and JP-A-9-227161, a titania sol is spray-coated on a substrate surface, a dip coating method, a flow coating method,
There is a method of applying and baking by a method such as a spin coating method and a roll coating method. As an organic titanate method, titanium alkoxide (tetraethoxytitanium, tetramethoxytitanium, tetrapropoxytitanium,
Organic titanates such as tetrabutoxytitanium, titanium acetate, titanium chelate, etc.
Ethylamine) and alcohol (ethanol,
After dilution with a non-aqueous solvent such as propanol, butanol, etc., the mixture is applied and dried with partial or complete hydrolysis.
By drying, the hydrolysis of the organic titanate is completed to produce titanium hydroxide, and a layer of amorphous titanium oxide is formed on the surface of the base material by dehydration-condensation polymerization of the titanium hydroxide. afterwards,
There is a method in which baking is performed at a temperature equal to or higher than the crystallization temperature of anatase to cause a phase transition from amorphous titanium oxide to anatase titanium oxide. As a method of transforming amorphous titanium oxide into anatase type titanium oxide, besides the thermal treatment of calcination, as described in JP-A-6-166501 and JP-A-9-157855, light in the ultraviolet region is irradiated by using a mercury lamp or laser. Irradiation. However, in the method of applying a titania sol or an organic titanate to a substrate that has been carried out so far, in order to maintain the stability and transparency of the titania sol or the organic titanate as described above, an organic solvent is used, such as hydrochloric acid or nitric acid. It was necessary to add a highly corrosive acid.
Therefore, there are drawbacks such as the harmfulness of the organic solvent becomes a problem from the viewpoint of work safety, and the production equipment becomes expensive due to the corrosiveness. Also, it is not possible to increase the weight percent of the titanium element contained in the solution to ensure the stability and transparency of the titania sol and organic titanate. To obtain the required film thickness, apply and bake several times. It was necessary to repeat such processing operations.

[0003]

SUMMARY OF THE INVENTION In view of the above, the present invention provides a simple method for producing a titanium oxide thin film photocatalyst using a water-soluble titanium complex as a precursor which does not cause problems in work safety and corrosiveness. It is the purpose.

[0004]

Means for Solving the Problems The present inventor has conducted intensive studies to achieve the above object, and as a result, coated an aqueous solution of hydroxy (hydroxycarboxylato) titanium on a substrate, and (1) gradually reduced the temperature from room temperature. 600 ° C to 700
The present inventors have found that a thin film photocatalyst can be produced by heating and raising the temperature to ℃ and firing (2) light of 350 nm or less at an energy density of 50 to 100 mJ / cm ² , and completed this study. The aqueous solution of hydroxy (hydroxycarboxylato) titanium used in this reaction is obtained by dissolving the titanium complex in water. This complex can also be synthesized by reacting a titanium halide such as titanium tetrachloride with a hydroxycarboxylic acid in a non-aqueous solvent system, but is easily synthesized from alkoxytitanium and hydroxycarboxylic acid with good yield. The following formula shows a synthesis example using a reaction formula.

[0005]

Embedded image

As the alkoxytitanium, tetramethoxytitanium, tetraethoxytitanium, tetra-n-propoxytitanium, tetraisopropoxytitanium, tetra-n-butoxytitanium and the like can be used. The alkoxy may be a combination of 2 to 4 types of components instead of a single component.
The hydroxycarboxylic acid is not particularly limited as long as it is a compound having a hydroxyl group and a carboxyl group in the same molecule, and a compound having a plurality of hydroxyl groups and carboxyl groups in one molecule cannot be used. The number of carbon atoms is not particularly limited, but is determined as appropriate from the solubility of the complex in water and the titanium content. Such compounds include glycolic acid, lactic acid, α-hydroxybutyric acid, α-hydroxyisobutyric acid, β
-Hydroxypropionic acid, β-hydroxybutyric acid, β-
Hydroxyisobutyric acid, γ-hydroxybutyric acid, glyceric acid, tertronic acid, malic acid, tartaric acid, meso-tartaric acid, and citric acid can be suitably used, and they may be used alone or as a mixture of two or more hydroxycarboxylic acids. Further, gluconic acid, galactaric acid, mannaric acid, etc. obtained by oxidizing a saccharide having 6 carbon atoms can also be suitably used.

As a method for synthesizing hydroxy (hydroxycarboxylato) titanium from alkoxytitanium and hydroxycarboxylic acid, a solvent capable of dissolving each compound is used. Specifically, the same alkoxy group as the alkoxy group of the alkoxytitanium used is used. It is preferred to use an alcohol containing alcohol. For example, when using tetraisopropoxytitanium, isopropanol is preferred. In addition to this, various alcohols, ethers, esters, hydrocarbons,
Water or the like can also be used. Conditions for producing hydroxy (hydroxycarboxylato) titanium are room temperature to 100 ° C, preferably room temperature to 50 ° C. The mixing ratio of alkoxytitanium and hydroxycarboxylic acid is 1:
0.1 to 1:10, preferably 1: 0.2 to 1: 4
It is. From hydroxycarboxylic acids having one hydroxyl group and one carboxyl group in the molecule, such as glycolic acid, lactic acid, α-hydroxybutyric acid, and α-hydroxyisobutyric acid, dihydroxybis (titanium and hydroxycarboxylic acid have a composition ratio of 1: 2) (Hydroxycarboxylato) titanium is synthesized. When a hydroxycarboxylic acid having a plurality of hydroxyl groups or carboxyl groups in one molecule is used, an arbitrary complex is synthesized depending on the mixing ratio with titanium and the number of hydroxyl groups and carboxyl groups, but water solubility is maintained. If so, the structure is not limited. By mixing a solution of alkoxytitanium and hydroxycarboxylic acid and distilling off the solvent, a solid powder of hydroxy (hydroxycarboxylato) titanium can be easily obtained.

By dissolving the obtained solid powder in water, an aqueous hydroxy (hydroxycarboxylato) titanium solution is obtained. The solubility in water is determined by the type of hydroxycarboxylic acid used in the synthesis, but the solubility can be significantly improved by adding ammonia, organic amine, and urea to the aqueous solution and controlling the pH of the solution. The hydroxy (hydroxycarboxylato) titanium aqueous solution is a transparent solution, but when left in the air at room temperature, turbidity or precipitation may occur depending on the type and concentration of the hydroxycarboxylic acid used over time. Add ammonia, organic amine, urea to the aqueous solution
By controlling H, this turbidity or precipitation does not occur, and the stability of the aqueous solution can be ensured. PH of aqueous solution of hydroxy (hydroxycarboxylato) titanium
Is 2.0 or less, but the stability of the aqueous solution is improved by adding ammonia, organic amine, and urea to adjust the pH to 2.0 or more. But ammonia,
When the pH is increased to more than 8.0 by adding too much organic amine or urea, the stability of the aqueous solution is again reduced, and turbidity or precipitation occurs. As the pH control of the aqueous solution, 2.0 to 8.0 is preferable. Ammonia and urea are water-soluble and can be added as such or as an aqueous solution. The organic amine is not particularly limited, but is preferably a water-soluble compound. Such compounds include monoethanolamine, diethanolamine, triethanolamine, N
Alcohol amines such as -methyldiethanolamine, N-ethyldiethanolamine, N, N-dimethyldiaminoethanol, diisopropanolamine, alkylamines having a relatively small number of carbon atoms such as monomethylamine, dimethylamine, trimethylamine, and ethylamine; ethylenediamine; Chelating amines. In addition, in addition to these, a water-soluble organic polymer compound such as polyvinyl alcohol, polyethylene glycol, polyacrylamide or carboxymethyl cellulose is added to adjust the viscosity of the solution or adjust the surface area of the resulting thin film. That doesn't matter at all.

The titanium oxide thin film photocatalyst of the present invention is obtained by coating the thus obtained aqueous solution of hydroxy (hydroxycarboxylato) titanium on a substrate by dip coating, spin coating, coating, spraying, etc., and then gradually increasing the temperature from room temperature. By heating and raising the temperature, drying is performed while partially promoting hydrolysis. The hydrolysis is completed by drying to produce titanium hydroxide, and an amorphous titanium oxide layer is formed on the surface of the base material by dehydration-condensation polymerization of titanium hydroxide. At this time, the remaining organic hydroxycarboxylic acid can be removed by washing with water. In the present invention using a water-soluble titanium complex, an organic solvent such as an alcohol or a hydrocarbon is not used, so that no organic solvent vapor is generated and the work environment is remarkably improved. Further, since a highly corrosive mineral acid such as hydrochloric acid or nitric acid is not used as a hydrolysis inhibitor, there is an advantage that there is no corrosion of the apparatus and a low capital investment is required. Then, it is calcined at a temperature equal to or higher than the crystallization temperature of anatase, and the amorphous titanium oxide undergoes a phase transition to the anatase titanium oxide. The final temperature of the heating and the firing temperature are 6
00-700 degreeC is preferable. Firing directly at a temperature of 600 to 700 ° C, firing temperature lower than 600 ° C,
When the temperature is higher than 700 ° C., only a rutile-type titanium oxide or a titanium oxide thin film mixed with amorphous can be obtained as a photocatalyst. In addition, in the titania sol method and the organic titanate method, only those having a low ratio of titanium content can be prepared due to the stability of the sol and the solubility of the organic titanate, but the titanium content is increased in the aqueous solution of the titanium complex of the present invention. be able to. Therefore, conventionally, in order to obtain a durable and high-performance titanium oxide thin film, a titania sol or an organic titanate is applied thinly and fired, and this operation is repeated to obtain a thick and durable titanium oxide film. On the other hand, an aqueous solution of a titanium complex has the advantage that the number of repetitive operations can be reduced. The substrate used for producing the titanium oxide thin film photocatalyst of the present invention may be any material as long as it can withstand firing at a temperature of 600 to 700 ° C., such as glass, ceramics, concrete, and metal. good. There is no problem even if a layer such as silica or alumina is applied or molded on the surface of these substrates. The shape is not limited.

When manufacturing a titanium oxide thin film photocatalyst on a substrate which cannot withstand firing at a temperature of 600 to 700 ° C., for example, a plastic surface, or forming a titanium oxide thin film photocatalyst on glass or ceramic surface without firing In this case, light having a wavelength of 350 nm or less and an energy density of 50 to 1
Irradiation at 00 mJ / cm ² is possible. As an operation method, first, an amorphous titanium oxide layer is formed on the surface of the base material, similarly to the firing method. In this case, when a plastic having a low heat-resistant temperature is used as the substrate, it is preferable to carry out the process at a temperature lower than the glass transition temperature of the plastic used. There is no particular problem with substrates such as glass, ceramics, and concrete. An aqueous solution of a water-soluble titanium complex is applied to a substrate and hydrolyzed while drying water as a solvent to form a water-insoluble gel film and an amorphous titanium oxide layer. At this time, the remaining organic hydroxycarboxylic acid can be removed by washing with water. When the amorphous titanium oxide layer is formed on the surface of the substrate, the wavelength of the thin film becomes 35 nm.
Irradiation with ultraviolet light of 0 nm or less is performed. Any type of ultraviolet light source can be used as long as it can emit ultraviolet light having a wavelength of 350 nm or less. For example, high-pressure mercury lamp, low-pressure mercury lamp, excimer lamp, ArF excimer laser, KrF excimer laser, YAG laser 4
Harmonic waves, synchrotron radiation and the like are used. Also,
It is also possible to use two or more of these light sources in combination. When irradiating the thin film with ultraviolet light, the substrate may be heated, the substrate may be placed under reduced pressure, or may be placed in an oxidizing atmosphere or a reducing atmosphere. The irradiation intensity and the number of shots of ultraviolet light are selected as appropriate according to the type and composition of the thin film of the metal oxide gel.However, when manufacturing a titanium oxide thin film photocatalyst, the irradiation intensity is anatase-type titanium oxide which is highly active on the photocatalyst. Is preferably 50 to 100 mJ / cm ² . 5
0 mJ / The lower energy density than cm ² produced an anatase phase is not observed, also become increasingly produce photoactive low rutile phase at higher energy density than 100 mJ / cm ^2. In the present invention, the substrate is coated with an aqueous solution of hydroxy (hydroxycarboxylato) titanium, and (1) the temperature is gradually increased from room temperature to 600 ° C. to 7 ° C.
An operation of heating to 00 ° C. and firing, and (2) 350
nm or less with an energy density of 50-100 mJ / c
It is also possible to perform both the operation of irradiating with m ² . Hereinafter, embodiments to which the present invention is specifically applied will be described.

[0011]

EXAMPLE 1 Synthesis of Water-Soluble Titanium Complex α-Hydroxyisobutyric acid 7 was added to 100 g of isopropanol.
4 g is dissolved, and tetraisopropoxy titanium 1
00 g was slowly added dropwise. The ratio between the added α-hydroxyisobutyric acid and tetraisopropoxytitanium is 2: 1 in molar ratio. After completion of the dropwise addition, the mixture was stirred as it was at room temperature. When a white suspension was formed, the stirring was stopped, and the solvent was distilled off using a rotary evaporator. The amount of the obtained white powder was 126 g. The weight abundance of Ti measured by ICP was 17.3%. From elemental analysis, C was 33.0% and H was 5.4% (theoretical value T).
i: 16.6%, C: 33.3%, H: 5.6%). The white powder obtained from this was identified as dihydroxybis (hydroxyisobutyrate) titanium. 26.5 g of this compound was collected, 100 g of water was added thereto, and the mixture was stirred to obtain a colorless and transparent water-soluble titanium aqueous solution.

Examples 2 to 17 and Comparative Examples 1 to 4 Using hydroxytetracarboxylic acid and various hydroxycarboxylic acids, hydroxy (hydroxycarboxylato) titanium was synthesized in the same manner as in Example 1, and an aqueous solution was prepared. The pH of the solution was measured, and the storage stability at 25 ° C. was examined. In addition, when ammonia, organic amine, and urea were added, the pH of the solution was measured to examine the storage stability. The results are summarized in Table 1. The aqueous solution of hydroxy (hydroxycarboxylato) titanium alone has a pH of 2.0
At lower levels, there were some that did not completely turn into a solution, and those that became turbid or precipitated over time. In addition, ammonia, organic amine, and urea are added too much, and the pH of the solution becomes 8.
When it was larger than 0, turbidity and precipitation occurred over time. By adjusting the pH of the solution to 2.0 to 8.0, such a problem did not occur and the storage stability was improved.

[0013]

[Table 1]

Example 18 10 wt% of dihydroxybis (α-hydroxyisobutyrate) titanium synthesized from α-hydroxyisobutyric acid and tetraisopropoxytitanium in the same manner as in Example 1.
Ammonia was added to the aqueous solution to prepare an aqueous solution having a pH of 6.2 (titanium concentration: 1.7%). Diameter 10mm,
A quartz glass tube having a length of 60 mm and a thickness of 1 mm was immersed in this solution, pulled up and dried, and then gradually heated from room temperature to 630 ° C. and fired. This operation was repeated twice to produce a 0.2 μm titanium oxide film on the surface of the quartz glass tube.
As a result of examining the crystal structure of the obtained titanium oxide film by X-ray diffraction, it was found to be an anatase crystal. Photodecomposition experiment of tetrachloroethylene was performed using this titanium oxide thin film. 10
15 mL of an aqueous solution of tetrachloroethylene having a concentration of 0 ppm was placed in a test tube made of Pyrex, a quartz glass tube formed with a titanium oxide thin film catalyst was immersed in the above surface, and irradiated with light from a xenon lamp of 300 W for 3 hours while bubbling oxygen. After the reaction, the product liquid was analyzed by gas chromatography, and the amount of tetrachloroethylene was below the detection limit.

Comparative Example 5 Tetraisopropoxytitanium was diluted with isopropanol, and hydrochloric acid and diisopropanolamine were added with stirring to prepare a sol solution (titanium concentration: 0.5%). A quartz glass tube having a diameter of 10 mm, a length of 60 mm, and a thickness of 1 mm was immersed in the sol solution, pulled up and dried, and then heated and gradually heated from room temperature to 630 ° C. for firing. At this time, the used organic solvents isopropanol and hydrochloric acid were generated as steam during the drying and baking steps. This operation had to be repeated seven times to produce a 0.2 μm titanium oxide film on the surface of the quartz glass tube. As a result of examining the crystal structure of the obtained titanium oxide film by X-ray diffraction, it was found to be an anatase crystal. Further, it had the same photocatalytic activity as in Example 1.

Example 19 In the same manner as in Example 1, 10 wt% of dihydroxybis (α-hydroxyisobutyrate) titanium synthesized from α-hydroxyisobutyric acid and tetraisopropoxytitanium
Ammonia was added to the aqueous solution to prepare an aqueous solution having a pH of 6.2 (titanium concentration: 1.7%). 40mm length and width
A 1 mm square quartz glass plate was immersed in this solution, pulled up and dried at 120 ° C. The UV / VIS spectrum of the gel film formed on the quartz glass plate was 700 to 185 nm.
As a result, absorption was observed at 350 nm or less. Using KrF excimer laser, wavelength 248n
m laser light at an energy density of 90 mJ / cm ²
Irradiated with 00 shots. When the X-ray diffraction of this film was measured, a peak due to an anatase crystal showing photocatalytic activity was observed. Photodecomposition experiment of tetrachloroethylene was performed using this titanium oxide thin film. 15 mL of a 100 ppm aqueous solution of tetrachloroethylene was placed in a square test cell made by Pyrex, a quartz glass plate formed with a titanium oxide thin film catalyst was immersed in the above surface, and irradiated with light from a xenon lamp of 300 W for 3 hours while bubbling oxygen. After the reaction, the product liquid was analyzed by gas chromatography, and the amount of tetrachloroethylene was below the detection limit.

[0017]

By using the water-soluble titanium of the present invention as a precursor for producing a titanium oxide thin film, problems such as work safety and corrosiveness have been solved, and the operation has been simplified.

Claims (3)

[Claims] 1. After coating an aqueous solution of hydroxy (hydroxycarboxylato) titanium on a substrate, the substrate is gradually heated from room temperature to 600 ° C. to 700 ° C., and then fired at 600 ° C. to 700 ° C. Of producing a titanium oxide thin film photocatalyst. 2. After coating the substrate with an aqueous solution of hydroxy (hydroxycarboxylato) titanium,
0 nm or less light with an energy density of 50-100 mJ /
A method for producing a titanium oxide thin film photocatalyst, which comprises irradiating with a cm ² . 3. Hydroxy (hydroxycarboxylato) titanium is produced from tetraalkoxytitanium and hydroxycarboxylic acid, wherein the hydroxycarboxylic acid is glycolic acid, lactic acid, α-hydroxybutyric acid, α-hydroxyisobutyric acid, β-hydroxypropionic acid, β-hydroxybutyric acid, β-hydroxyisobutyric acid, γ-hydroxybutyric acid, glyceric acid, tartronic acid, malic acid, tartaric acid,
The method for producing a titanium oxide thin film photocatalyst according to claim 1 or 2, wherein the photocatalyst is at least one selected from mesotartaric acid and citric acid.