JP2000334310A - Production of photocatalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a photocatalyst comprising titanium dioxide having a high content of an anatase type crystal structure. SOLUTION: A photocatalyst is produced by a first process for reacting a titanium alkoxide with a polycarboxylic acid, a second process for adding a polyol and a polyamine or either one of them to the reaction product of the titanium alkoxide and the polycarboxylic acid and a third process for baking the reaction product of the titanium alkoxide and the polycarboxylic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a photocatalyst comprising titanium dioxide. More specifically, the present invention relates to a method for producing a photocatalyst comprising titanium dioxide which contains a large amount of anatase crystals and has a high photocatalytic ability.

[0002]

2. Description of the Related Art In recent years, attention has been paid to the photocatalytic activity of titanium dioxide, and it is desired to increase the content of anatase-type crystal structure in titanium dioxide in order to effectively generate photocatalytic activity. Thus, for example, ilmenite to obtain sulfated titanium by a sulfuric acid method as a raw material, to produce a metatitanic acid (Ti (OH) ₂ or Ti0 ₂ · H ₂ O) the sulfated titanium heat decompose and further the A method of peptizing metatitanic acid with a monobasic acid such as nitric acid is known.

Further, titanium tetrachloride, (NH ₄ ) ₂ (TiO (C ₂ O ₄ ) ₂ ), isopropyl titanate, etc., which have been purified by repeating distillation, have been studied as titanium dioxide raw materials. For example, Reference 1: "Journal European Ceramic Society (J European Ceramic S
1988, 287-297 "describes a method for producing titanium dioxide powder from a precursor obtained by reacting isopropyl titanate or the like with triethanolamine and ethylene glycol.

Further, according to a recently developed sol-gel method, a titanium alkoxide such as isopropyl titanate is used as a starting material, and a regulator such as acetylacetonate is added thereto, followed by heating. A titanium compound (titanium oxide) such as a powder, a fiber, and a film can be obtained.

[0005]

However, the titanium sol obtained by the method using the sulfuric acid method is difficult to handle because it is a strong acid having a pH of about 1 to 2, and the production equipment becomes expensive. Was seen. Further, when the obtained titanium sol was formed into a film, there was also a problem that the adhesive strength to an adherend (substrate) was poor and the titanium sol was easily peeled off from the adherend. The titanium dioxide powder obtained by the method described in Document 1 has a rutile crystal structure of 10 to 15%.
% Is included in the range. Therefore, the content of the anatase crystal structure in titanium dioxide was still insufficient. Further, in the sol-gel method, a titanium sol (titanium sol solution) composed of titanium alkoxide has poor storage stability, and it has been difficult to obtain a titanium compound having stable and uniform properties. Furthermore, in the titanium dioxide obtained using the sol-gel method, the content of the anatase crystal structure was not sufficiently high even when a regulator was added.

Under such circumstances, the inventors have diligently studied the above-mentioned problem, and in a sol-gel method, a precursor is prepared by previously reacting a titanium alkoxide and a polycarboxylic acid, and the precursor is fired. The present inventors have found that an anatase crystal structure can be obtained at a high content, and have completed the present invention. That is, an object of the present invention is to provide a method for producing a photocatalyst comprising titanium dioxide having a high content of an anatase crystal structure and having high photocatalytic activity.

[0007]

The present invention is a method for producing a photocatalyst, which comprises, as a first step, a step of reacting a titanium alkoxide with a polycarboxylic acid. After reacting the titanium alkoxide with the polycarboxylic acid to obtain a reactant containing an ester bond (sometimes referred to as a precursor), the precursor is heated and calcined to be suitable as a photocatalyst. Titanium dioxide containing a large amount of an anatase-type crystal structure can be efficiently obtained.

In practicing the present invention, it is preferable to include a step of adding a polyol and / or a polyamine as a second step after the first step. By carrying out in this manner, the transparency of the obtained titanium dioxide can be improved, and the catalytic activity as a photocatalyst can be further improved.

In practicing the present invention, it is preferable to include a firing step as a third step after the second step. It has been found that a precursor obtained by reacting a titanium alkoxide and a polycarboxylic acid can obtain a predetermined photocatalytic effect without firing if heated in a temperature range of 140 to 200 ° C. However, by calcining in this way, it is possible to obtain titanium dioxide containing a large amount of an anatase crystal structure more suitable as a photocatalyst from a precursor which is a reaction product of titanium alkoxide and polycarboxylic acid.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment relating to a method for producing a photocatalyst according to the present invention will be specifically described.

[First Embodiment] In a first embodiment, a first step is a reaction step between a titanium alkoxide and a polycarboxylic acid, and a third step is a reaction step between a titanium alkoxide and a polycarboxylic acid. And baking the product. Hereinafter, reaction raw materials, reaction conditions, and the like for carrying out the first embodiment will be specifically described.

(1) Titanium alkoxide The titanium alkoxide used in the first embodiment is defined as a compound in which at least one alkoxy group is bonded to a titanium atom. preferable. The compound represented by the general formula (1) may contain a hydrolyzable group other than an alkoxy group or a non-hydrolyzable group. In the present invention, such a case may be used. , Titanium alkoxide. Further, a compound in which a part of the alkoxy group represented by the general formula (1) has already been hydrolyzed is also included in the titanium alkoxide.

Ti (OR ¹ ) ₄ (1) [In the general formula (1), R ¹ represents an alkyl group, an aryl group or an acyl group. ]

Here, R ¹ in the general formula (1) is preferably at least one selected from the group consisting of an alkyl group, an aryl group and an acyl group. This is because such a functional group can be easily hydrolyzed to efficiently obtain a titanium dioxide crystal.

Preferred examples of R ¹ in the general formula (1) include alkyl groups such as methyl group, ethyl group, propyl group, i-propyl group, n-butyl group and i-butyl group. . Similarly, as a preferred aryl group,
Examples include a phenyl group, a benzyl group and a naphthyl group.
More preferred acyl groups include formyl, acetyl, propionyl and the like. In addition, since a precursor having more excellent storage stability can be obtained, the general formula (1)
R ¹ in the formula is more preferably a linear or branched alkyl group, and particularly preferably a branched alkyl group, for example, an i-propyl group.

Specific examples of the titanium alkoxide represented by the general formula (1) include tetramethoxytitanium, tetraethoxytitanium, tetrapropoxytitanium, tetraisopropoxytitanium, tetrabutoxytitanium, and the like. Combinations. Particularly, tetraisopropoxytitanium is more preferable because a precursor having excellent storage stability can be obtained.

(2) Polycarboxylic acid The polycarboxylic acid used in the first embodiment is:
Although defined as a compound having a carboxyl group in one molecule, for example, a compound represented by the general formula (2) is preferable.

X- (COOH) _n (2) [In the general formula (2), X is a substitutable n-valent hydrocarbon group, and n is an integer of 1-10. ]

Specific examples of such polycarboxylic acids include monocarboxylic acids such as lactic acid, dicarboxylic acids such as citric acid, tartaric acid, oxalic acid, oxydiacetic acid, phthalic acid and maleic acid, and tetracarboxylic acids such as pyrrolitic acid. One type of carboxylic acid and the like or a combination of two or more types may be mentioned. In particular, it is preferable to use citric acid since titanium dioxide containing a large amount of anatase crystal structure can be obtained. It is also preferable to use hydrates of these polycarboxylic acids. By using such a hydrate of a polycarboxylic acid, compatibility and reactivity with a titanium alkoxide are further improved.

(3) Reaction conditions between titanium alkoxide and polycarboxylic acid The reaction between titanium alkoxide and polycarboxylic acid is preferably carried out in the presence of water or an organic solvent. By reacting in the presence of these solvents, the reaction between the titanium alkoxide and the polycarboxylic acid can be more uniformly caused. In addition, since titanium alkoxide has hydrolyzability, it is preferable to use a part of the organic solvent as an anhydrous organic solvent, dissolve the titanium alkoxide in this, and then react with the polycarboxylic acid for the purpose of improving the reaction. When water is used as the solvent, it is desirable to stir quickly when mixing the titanium alkoxide and the polycarboxylic acid. Preferred organic solvents include, for example, alcohol compounds of monoalcohol, diol and triol. Alternatively, it is also preferable to use an excess amino alcohol as the organic solvent from the viewpoint of preventing gelation.

Specifically, preferred monoalcohols include alcohol compounds represented by the formula R ² OH. R ^{2 in} this formula is a linear or branched alkyl group having 1 to 10 carbon atoms or a linear or branched alkyl group having 1 to 10 carbon atoms having an oxygen bond. Therefore, specific examples of preferred monoalcohols include methanol, ethanol, isopropanol, butanol and the like. Also, as a diol, the compound of the formula HO (R ³ )
And an alcohol compound represented by OH. R ^{3 in} this formula is a linear or branched alkylene group having 1 to 10 carbon atoms. Therefore, specific examples of preferred diols include ethylene glycol, propylene glycol, 1,2-butanediol, 1,3-butanediol, hexamethylenediol and the like.
Further, specific examples of preferred triols include glycerin, 1,2,6-hexanetriol, and the like.

The reaction ratio between the titanium alkoxide and the polycarboxylic acid is not particularly limited. For example, the molar ratio of the titanium element (Ti) to the carboxyl group (C) (Ti: C )
The value is preferably in the range of 1:10 to 10: 1, more preferably in the range of 1: 5 to 5: 1, and in the range of 1: 2 to 2: 1. More preferably,

The reaction temperature between the titanium alkoxide and the polycarboxylic acid is not particularly limited, but specifically, the reaction temperature is preferably in the range of -20 to 100 ° C. . The reason for this is that if the reaction temperature is lower than −20 ° C., the reactivity between the titanium alkoxide and the polycarboxylic acid may be significantly reduced. On the other hand, if the reaction temperature exceeds 100 ° C., these reactions may occur. This is because it may be difficult to control.
Therefore, the reaction temperature between the titanium alkoxide and the polycarboxylic acid is more preferably set to a value in the range of 0 to 90 ° C, and even more preferably to a value in the range of 20 to 80 ° C. The reaction time has a relationship with the reaction temperature, but is preferably in the range of 5 minutes to 40 hours, more preferably in the range of 10 minutes to 10 hours. Further, the reaction pressure is not particularly limited, but is preferably a value within a range of 0.01 to 1.0 atm, more preferably a value within a range of 0.01 to 0.2 atm. That is.

(4) Conditions for calcining the reaction product of titanium alkoxide and polycarboxylic acid As described above, the reaction product (precursor) of titanium alkoxide and polycarboxylic acid partially
Although a predetermined photocatalytic effect can be exerted by heating in a temperature range of 140 to 200 ° C., it is preferable to calcine a reaction product of a titanium alkoxide and a polycarboxylic acid in a range of 200 to 1000 ° C. The reason for this is that if the firing temperature of the precursor is lower than 200 ° C., it may be difficult to obtain titanium dioxide having an anatase crystal structure, while if the firing temperature of titanium dioxide exceeds 1000 ° C., it may be excessively high. This is because it may be difficult to obtain titanium dioxide having an anatase crystal structure by oxidation. Therefore, the firing temperature of the precursor is set to 300 to 80.
The temperature is more preferably set to a value in the range of 0 ° C, most preferably to a temperature in the range of 400 to 700 ° C.

The method for calcining titanium dioxide is not particularly limited, but more specifically, a precursor (including a precursor solution or a sol obtained therefrom) is applied on a substrate. After forming the coating film by heating, it is preferable to heat. By employing this method, titanium dioxide having a high content of the anatase crystal structure can be easily formed on the substrate. More specifically, the content of the anatase crystal structure can be 80% by weight or more, and the content of the anatase crystal structure can be adjusted to 90% by weight or more by adjusting the heating conditions and the like. be able to. Further, the titanium dioxide thus obtained has a feature that, even when it is heated to 650 ° C. or more for a long time, the anatase type crystal structure is maintained and the titanium dioxide is not converted to the rutile type crystal structure.

The substrate on which titanium dioxide (thin film) is formed is not particularly limited. For example, glass such as soda glass and quartz glass, ceramics such as zirconia and titania, and metals such as iron and stainless steel And the like. Therefore, when formed on glass, for example, it can be widely used as glass for vehicles such as automobiles, glass for houses, and glass for buildings such as glass for buildings. The method for forming the precursor on the substrate is not particularly limited, and for example, a dipping method, a casting method, a roll coating method, a spin coating method, or the like can be used.

[Second Embodiment] In a second embodiment, a reaction between a titanium alkoxide and a polycarboxylic acid is performed as a first step, and a reaction between a titanium alkoxide and a polycarboxylic acid is performed as a second step. Adding a polyol and a polyamine or either compound to the product,
A third step of calcining a reaction product of the titanium alkoxide and the polycarboxylic acid. Hereinafter, the polyol and polyamine used for carrying out the second step, the reaction conditions, and the like will be specifically described. The first step and the third step are the same as those in the first embodiment. The detailed description here is omitted.

(1) Polyol and Polyamine By adding a polyol and / or a polyamine, it is possible to improve the transparency of the obtained titanium dioxide and also to improve the catalytic activity as a photocatalyst. Can be.

Here, preferred polyols include ethylene glycol, propylene glycol, 1,2-butanediol, hexatylenediol, glycerin,
One kind of 1,2,6-hexanetriol, triethanolamine and the like may be used alone or in combination of two or more kinds. In addition, examples of the polyamine include ethylenediamine, hexamethylenediamine, p-phenylenediamine, aminodiphenylpropane, and the like, alone or in combination of two or more.

The amount of the polyol and the polyamine to be added is not particularly limited, but the reaction product (precursor) of the titanium alkoxide and the polycarboxylic acid (precursor) 10
It is preferable that the addition amount of the polyol and the polyamine be a value within the range of 10 to 500 parts by weight per 0 parts by weight. The reason for this is that if the added amount of the polyol and polyamine is less than 10 parts by weight, the effect of addition may not be exhibited. On the other hand, if the added amount exceeds 500 parts by weight, titanium dioxide having an anatase crystal structure may be used. This is because it may be difficult to obtain Therefore, the addition amount of the polyol and the polyamine is more preferably set to a value within the range of 50 to 300 parts by weight, and more preferably within a range of 80 to 200 parts by weight, per 100 parts by weight of the reaction product of the titanium alkoxide and the polycarboxylic acid. Is more preferable.

(3) Additives In the second step, it is preferable to add additives such as PVA (polyvinyl alcohol), silica particles, and calcium. For example, PVA is 10 to 10
By adding it in the range of 15% by weight, the transparency of the obtained titanium dioxide can be remarkably improved, and the catalytic activity can be also improved. In addition, PVA can also specifically improve the catalytic activity when used in combination with 1 to 10% by weight of polyethylene glycol. Further, by adding silica particles (SiO ₂ ) within the range of 0.1 to 10% by weight based on the total amount, the catalytic activity of the obtained titanium dioxide can be improved. Further, it is preferable to add calcium in the range of 0.1 to 10% by weight based on the total amount. By adding calcium in this way,
The catalytic activity of the obtained titanium dioxide can be further improved.

[0032]

The present invention will be further described below with reference to examples. However, needless to say, the scope of the present invention is not limited to the description of the examples.

Example 1 (1) Preparation of precursor sol In a round bottom flask having a capacity of 500 ml, 56.8 g of titanium tetraisopropoxide dissolved in 20 ml of anhydrous isopropanol as titanium alkoxide and polycarboxylic acid were used. 100 ml of heated isopropanol
And 42 g of citric acid monohydrate dissolved therein. Thereafter, the mixture was stirred for 30 minutes using a stirrer to cause an ester reaction between the titanium alkoxide and the polycarboxylic acid to obtain a precursor solution containing a reactant. This precursor solution was 80 T at room temperature using a rotary evaporator.
The pressure was gradually reduced to orr, and the temperature in the round-bottom flask was increased to 80 ° C. using a heater to volatilize isopropanol as a solvent to obtain a white solid of titanium dioxide. However, in order to dry without lowering the yield, the rotation of the rotary evaporator was stopped, and the internal pressure was reduced to 20 Torr. Then, the obtained white solid (about 63 g) was heated at 50 ° C. and 50 ° C.
It was dissolved in water of ml, and water was added until the volume finally reached 100 ml to obtain a titanium sol having a concentration of 2M.

(2) Preparation of Coating Solution Next, an aqueous surfactant Briji 98 (trade name) having a concentration of 2% by weight was added to 10 g of the obtained 2M titanium sol.
1 g was added and stirred uniformly. Further, 10 g of glycerol was added thereto, and the mixture was stirred until the solution became uniform. If necessary, the solution was filtered to prepare a coating solution.

(3) Preparation of Titanium Dioxide Thin Film A coating solution is spin-coated on the surface of a glass substrate (rotational speed: 4
00 rpm) and 30 ° C. in an oven at 140 ° C.
After heating and drying for a minute, a coating film containing an ester bond was obtained. Next, the resultant was baked at a temperature of 600 ° C. for a time of 6 minutes to obtain a transparent titanium dioxide thin film having a thickness of 0.61 μm.

(4) Evaluation of Titanium Dioxide Thin Film When the obtained titanium dioxide thin film was irradiated with X-rays having a diffraction angle of 2θ (output condition: 400 kv × 100 mA · CuK wavelength), the diffraction peak shown in FIG. 1 was obtained. . The symbol A in FIG. 1 indicates the peak intensity of the anatase crystal structure,
Symbol R represents the peak intensity of the rutile crystal structure, respectively. The peak intensity (anatase type crystal structure) at 2θ = 25.3 to 25.5 is defined as Ia, and 2θ = 2
Peak intensity of 7.5 to 27.9 (rutile type crystal structure Ti
O2) was defined as Ir, and the content (f) of the anatase crystal structure in the obtained titanium dioxide was determined from the following formula. f = 1 / (1 + 1.265 × Ir / Ia) As a result, it was confirmed that the content of the anatase crystal structure in the obtained titanium dioxide thin film was substantially 100%.

Comparative Example 1 (1) Preparation of Coating Solution A solution of 5% by weight of an isopropanol solution of 80% by weight of diisopropoxytitanium bis (triethanolamine) (manufactured by Matsumoto Pharmaceutical Co., Ltd.) was dissolved in 10 ml of absolute ethanol to obtain a titanium solution. And While stirring the obtained titanium solution, 10 ml of 50% by weight aqueous ethanol was dropped to form a sol. While stirring this sol, 3 ml of 28% by weight aqueous ammonia was added dropwise thereto, and the mixture was aged at 70 ° C. for 1 hour and gelled to prepare a coating solution.

(2) Preparation and Evaluation of Titanium Dioxide Thin Film The obtained coating solution was spin-coated in the same manner as in Example 1, air-dried for 12 hours, and further heated and dried at 80 ° C. for 2 hours. Thereafter, the temperature was raised from room temperature to 500 ° C. at a rate of 5 ° C./min, and kept at 500 ° C. for 15 minutes. Next, the temperature was further increased from 500 ° C. to 650 ° C. at a rate of 5 ° C./min, and the temperature was maintained at 650 ° C. for 5 minutes to obtain a titanium dioxide thin film. When the obtained titanium dioxide thin film was subjected to X-ray diffraction measurement in the same manner as in Example 1, the diffraction peak shown in FIG. 2 was obtained. Then, the content of the anatase crystal structure was similarly determined to be 72.5%.

[0039]

According to the method for producing a photocatalyst of the present invention, by reacting a titanium alkoxide with a polycarboxylic acid, a precursor from which titanium dioxide having a high content of anatase type crystal structure can be efficiently produced, Moreover, it has become possible to obtain it stably. Therefore, by firing this precursor, titanium dioxide excellent in photocatalytic ability can be easily obtained. Therefore, a product containing titanium dioxide having a high content of the anatase type crystal structure as a photocatalyst has excellent photocatalytic ability and hydrophilicity, and is preferably used for applications such as surface modification of buildings and vehicle parts. There is expected. Further, according to the method for producing a photocatalyst of the present invention, not only a particulate photocatalyst but also a photocatalyst comprising a thin-film titanium dioxide having a uniform thickness can be efficiently obtained. Therefore, it is expected to be more suitably used for the above-mentioned surface modification use and the like.

[Brief description of the drawings]

FIG. 1 is an X-ray analysis spectrum of titanium dioxide obtained in Example 1.

FIG. 2 is an X-ray analysis spectrum of titanium dioxide obtained in Comparative Example 1.

Continued on the front page (72) Inventor Al Salim Naja New Zealand Lower Hat Lo Pataku Crescent 4B (72) Inventor Toshio Ono 2--11-11 Tsukiji, Chuo-ku, Tokyo F-term in JSR Corporation (reference) 4D048 AA22 BA07X BA41X BB03 EA01 4G069 AA08 AA09 BA04A BA04B BA04C BA48A BA48C CA01 CA07 CA10 CA11 CA17 DA06 EA11 FB08 FB30 FC02

Claims (3)

[Claims] 1. A method for producing a photocatalyst, comprising a step of reacting a titanium alkoxide with a polycarboxylic acid as a first step. 2. The method for producing a photocatalyst according to claim 1, further comprising a step of adding a polyol and / or a polyamine as a second step after the first step. 3. The method for producing a photocatalyst according to claim 1, further comprising a baking step as a third step after the second step.