JP3094102B1 - Photocatalyst precursor solution, photocatalyst and method for producing the same - Google Patents

Abstract

Kind Code: A1 A photocatalyst precursor solution capable of forming a film under atmospheric humidity, forming a sufficient film thickness even with a small number of dip coatings, and providing a highly active photocatalyst, and a transparent solution obtained therefrom. Provided is a titanium dioxide thin film photocatalyst. A photocatalyst precursor solution containing (a) a titanium alkoxide having diethylene glycol monoalkyl ether and polyethylene glycol as ligands and (b) terpineol, and a calcined product of the photocatalyst precursor solution are formed into a thin film on the surface of a support. Titanium dioxide thin film photocatalyst fixed in a shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a titanium dioxide thin film photocatalyst useful as a catalyst for decomposing and removing various harmful substances, a catalyst for synthesizing various organic compounds, and a precursor solution thereof.

[0002]

2. Description of the Related Art Recently, catalysts for decomposing and removing various harmful substances,
As a catalyst for synthesizing various organic compounds, a titanium dioxide thin-film photocatalyst has attracted attention. This photocatalyst is usually made of titanium alkoxide as a precursor, which is applied and baked on a support such as a glass substrate by a dip coating method, a spin coating method, a spray pyrolysis or a pyrosol method using a sol-gel method, and fixed. It has been prepared by a method of In the case of the former sol-gel method, after a titanium alkoxide is hydrolyzed and chemically changed to titanium dioxide, and bonded to a hydroxyl group present on the surface of a support such as a glass substrate, a strong titanium dioxide thin film photocatalyst is formed. On the other hand, the latter, spray pyrolysis or pyrosol method, involves thermally decomposing titanium alkoxide and sintering and fixing titanium dioxide on a support such as a glass substrate.

[0003] Incidentally, titanium alkoxide, which is a precursor, is extremely liable to react with atmospheric moisture and is an unstable substance. Therefore, a compound such as acetylacetone or diethanolamine is conventionally coordinated to easily react with atmospheric moisture. After doing so, dip coating or spin coating method, spray pyrolysis method,
The film is formed by the pyrosol method.

However, a catalyst obtained from a titanium alkoxide precursor solution to which acetylacetone or diethanolamine is coordinated has a low catalytic activity, and when the film thickness is increased to obtain a required catalytic activity, a high transparency is obtained. There was a disadvantage that it could not be obtained.

In order to solve such disadvantages, the present inventors have previously proposed a photocatalyst precursor solution in which a titanium alkoxide having diethylene glycol monoalkyl ether and polyethylene glycol as ligands is dissolved in ethanol (J .Mater.Sci., 33 (1998) 5789, J. Mate
r. Lett., 38 (1999) 150, J. Mater. Sci. Lett., 18 (1
999) 515. The photocatalyst obtained from this photocatalyst precursor solution shows the same catalytic activity as a commercial product and has high transparency,
In the preparation, since volatile ethanol is used as a solvent, it is difficult to form a film under atmospheric humidity, and in the case of dip coating, the number of coatings must be increased. There was a problem.

As described above, the conventional photocatalyst synthesis method using a titanium alkoxide as a precursor solution can obtain a certain photocatalytic activity, but has a problem that a complicated operation such as control of a low humidity atmosphere is required. there were. Also, in order to obtain a highly active titanium dioxide photocatalyst, it is necessary to form a titanium dioxide having as small a particle size as possible and having a high crystallinity of a titanium dioxide anatase structure. It has been extremely difficult to obtain a highly active photocatalyst by simultaneously controlling both the crystal structure and the ultrafine structure of titanium. Furthermore, in the dip coating method, there is a film thickness at which the maximum photocatalytic activity is obtained, and it is necessary to repeat dip coating until the film thickness reaches the film thickness. There is a need for a way to obtain it.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems all at once, and it is possible to form a film under atmospheric humidity and to obtain a sufficient film thickness even if the number of times of dip coating is reduced. It is an object of the present invention to provide a photocatalyst precursor solution that can be formed and provides a highly active transparent titanium dioxide thin film photocatalyst, and a titanium dioxide thin film photocatalyst obtained from the same.

[0008]

Means for Solving the Problems In a process for producing a transparent titanium dioxide thin film photocatalyst using a titanium alkoxide as a precursor, the present inventors have studied how to reduce the size of crystallites of titanium dioxide, As a result of intensive studies on whether a thin film having a sufficient thickness can be obtained with a small number of dip coatings, it has been found that it is effective to use a specific high-viscosity solvent as a solvent, and the present invention has been completed. That is, according to the present invention, first, there is provided a photocatalyst precursor solution containing (a) a titanium alkoxide having diethylene glycol monoalkyl ethers and polyethylene glycols as ligands and (b) terpineols. Secondly, there is provided a titanium dioxide thin-film photocatalyst, wherein the calcined product of the photocatalyst precursor solution according to the first aspect is fixed on a surface of a support in a thin film form. Third, the photocatalyst precursor solution according to the above-described first is applied on a support, and is heated at 400 to 500 ° C. in an air atmosphere.
The titanium dioxide thin-film photocatalyst according to the second aspect, wherein the photocatalyst is fired at a temperature of:

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As the titanium alkoxide used in the present invention, any conventionally known titanium alkoxide such as titanium tetraethoxide, titanium tetrabutoxide and titanium tetraisopropoxide can be used.

The diethylene glycol monoalkyl ether used as the ligand and the polyethylene glycol are those represented by the following structural formulas. In this case, examples of the alkyl group of diethylene glycol monoalkyl ether include a methyl group, an ethyl group, and a butyl group, and the molecular weight of polyethylene glycol is preferably about 300 to 2,000.

## STR1 ## RO- (CH ₂ CH ₂ —O) nH (R: alkyl group)

HO- (CH ₂ -CH ₂ ) n-OH (n: an integer of 1 or more)

The titanium alkoxide (a) having diethylene glycol monoalkyl ether and polyethylene glycol as the ligand according to the present invention may be obtained by directly mixing the above tetraalkoxide with the ligand diethylene glycol monoalkyl ether and polyethylene glycol or in an appropriate amount. Obtained by diluting and mixing with an alcohol solvent.

The component (b) according to the present invention is terpineol. Specific examples of this terpineol include α-
Terpineol, β-terpineol, γ-terpineol and the like can be mentioned, but α-terpineol is preferably used. These terpineols have excellent affinity with titanium tetraalkoxide, diethylene glycol monoalkyl ether and polyethylene glycol as ligands, exhibit low volatility and high viscosity, and have excellent adhesion to a support such as glass. Things. Therefore,
(B) A photocatalyst precursor solution obtained by dissolving (a) titanium alkoxide having diethylene glycol monoalkyl ether and polyethylene glycol as ligands in terpineol is low in volatility and hardly volatilizes even in an open system. Can be formed into a film, and because of its excellent adhesion to the support and high viscosity, it does not cause dripping or cracking or peeling in the baking process, and can be formed into a desired film in a remarkably small number of times. Can be achieved. Such an effect is a surprising fact discovered by the present inventors for the first time, and is extremely specific. This shows that the photocatalyst precursor solution using ethanol in place of terpineol has low viscosity and takes several times as long as the present invention to obtain a desired film thickness. It is clear from the description.

There is no particular limitation on the amount of the terpineol used as the component (b), but (a) a volume ratio of 2 to 5 with respect to a titanium alkoxide having diethylene glycol monoalkyl ether and polyethylene glycol as a ligand.
It is appropriate to double. In addition, another solvent can be used in combination with the component (b) as long as the action of terpineol is not inhibited. As such a solvent, any solvent may be used as long as terpineol and titanium alkoxide are soluble, but alcohols forming an alkoxide component of titanium alkoxide are preferably used.

To prepare the photocatalyst precursor solution according to the present invention, (i) (a) a titanium alkoxide having diethylene glycol monoalkyl ether and polyethylene glycol as ligands and (b) terpineol, if necessary, Mixing in the presence of an organic solvent of (i)
i) A mixing method such as a method of mixing titanium alkoxide, diethylene glycol monoalkyl ether as a ligand, polyethylene glycol, terpineol, and another organic solvent as necessary may be employed.

The titanium dioxide thin film photocatalyst according to the present invention is characterized in that the calcined product of the photocatalyst precursor solution is fixed on the surface of the support in a thin film form. Such a photocatalyst can be preferably synthesized by applying the photocatalyst precursor solution on a support and calcining the solution at a temperature of 400 to 500 ° C. in an air atmosphere.

The support is not particularly limited, but inorganic materials such as glass and ceramics, and metal materials such as stainless steel and aluminum are preferably used. In order to deposit the photocatalyst precursor solution on the support, a coating method such as dip coating or spin coating may be used.

The amount (thickness) of the photocatalyst precursor solution needs to be set so that the catalytic activity of the photocatalyst after calcination is maximized, but usually 100 to 250 nm (dip coating). (After baking).
In the present invention, as described above, it is difficult to volatilize even in an open system, that is, since titanium alkoxide hardly comes into contact with moisture in the air, it is possible to form a film even under atmospheric humidity, and furthermore, it is possible to form a film with a support. Since the precursor solution which has excellent adhesion and high viscosity is used, the desired film thickness can be obtained with a remarkably small number of dipping times without causing cracking in the firing step, whitening or peeling due to hydrolysis of titanium alkoxide. It can be.

After the desired film formation, the photocatalyst precursor solution attached to the support is fired. The firing temperature is 400-500 ° C, preferably around 450 ° C. According to the present invention, (a) titanium alkoxide having diethylene glycol monoalkyl ether and polyethylene glycol as ligands is thermally decomposed at about 330 ° C., and the crystallization temperature of titanium oxide obtained by this pyrolysis is about 420 ° C. . Therefore,
When the film is baked at a temperature of 400 to 500 ° C., a titanium oxide thin film having a uniform particle size and almost no crystal growth can be obtained. Further, at a low firing temperature of 400 to 500 ° C., the pore structure generated by the combustion of the organic substance is preserved, and a thin film having fine pores of several nm or less and having a high surface area is obtained. Further, since the temperature of 400 to 500 ° C. is generally equal to or lower than the softening point of glass as a typical support, a highly active titanium oxide thin film is formed on a glass support by using such a precursor solution. be able to.

Titanium alkoxide, whose ligand is only polyethylene glycol, can form a uniform thin film, but cracks occur partially during firing, and titanium dioxide aggregates precipitate on the thin film. May be. On the other hand, the titanium alkoxide in which the ligand is only diethylene glycol monoalkyl ether does not separate from the solvent but has a very low viscosity, and it is difficult to form a thin film having a uniform thickness.
As the component (a), it is essential to use a titanium alkoxide having both diethylene glycol monoalkyl ether and polyethylene glycol as ligands.

The thickness of the fired photocatalyst according to the present invention is usually 0.5 to 1.5 microns, preferably 1 micron.

The photocatalyst according to the present invention is a harmful substance such as NO
x, SOx, CFCs, ammonia, hydrogen sulfide, aldehydes, amines, mercaptans, etc., as a catalyst for decomposition and removal, or as a synthesis catalyst for organic compounds by photoreduction of carbon dioxide, It is useful as a photoelectrochemical device or the like in which a sex dye is immobilized.

[0022]

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

Example 1 0.34 mol of titanium tetraisopropoxide (TPOT) was added to a mixed solution of 2.12 mol of α-terpineol (TPO), 1.96 mol of isopropanol (PrOH), and 0.74 mol of diethylene glycol monoethyl ether (EEE). Mix and add 0.
19 mol of polyethylene glycol 600 (PEG) was added and mixed at room temperature to prepare a photocatalyst precursor solution. The solution viscosity was approximately 11.3 cP as measured using a Brookfield viscometer. This solution was used as a dip coating solution, and the rate of increase in the film thickness as the number of coatings increased was measured in the following manner. The result is shown in FIG. The method of measuring the film thickness is described in the literature (J. Mater. Sci., 33
(1988) 5789).
The process of dip coating → firing was repeated until the film thickness became 1 μm.

Comparative Example 1 A comparative photocatalyst precursor solution was prepared in the same manner as in Example 1 except that ethanol (EtOH) was used instead of α-terpineol (TPO). The solution viscosity was approximately 3.8 cP as measured using a Brookfield viscometer. This solution was used as a dip coating solution, and the rate of increase in the film thickness as the number of coatings increased was measured in the same manner as in Example 1. The result is shown in FIG.

FIG. 1 shows that the viscosity of the photocatalyst precursor solution of Example 1 of the present invention was higher than that of Comparative Example 1;
It can also be seen that a sufficient film thickness can be formed with a small number of dips.

Example 2 The photocatalyst precursor solution obtained in Example 1 was applied onto a silica-coated glass support by dip coating using the method described in Example 1 so that the final film thickness was 1 μm. A titanium dioxide thin film was formed. The crystal structure of the obtained titanium dioxide thin film photocatalyst was analyzed with an X-ray scattering device (XRD). As a result, the crystal structure of this thin film was formed only from the titanium dioxide anatase structure that was optimal as a photocatalyst, and the crystallite size of titanium dioxide anatase was determined from XRD observation results to be about 7 nm. In addition, when the surface structure of the thin film was measured by an atomic force microscope, it was found that crystals having the same size as the anatase crystallite size determined by XRD were coarsely accumulated as shown in FIG. Was done. Examination of the pore structure and specific surface area revealed that the pore size distribution was approximately 3n.
m, the specific surface area was found to be about 80 m ² / g.

Example 3 The photocatalytic activity of the titanium dioxide thin film photocatalytic film obtained in Example 2 was evaluated by photo-oxidation of NO. Chemiluminescent nitrogen oxide meter (NOx meter), purified air supply device, NO gas cylinder,
The titanium oxide thin film photocatalyst thin film (10 × 10 cm ×) obtained in Example 2 was placed in a Pyrex glass reaction vessel of a flow-type photocatalytic reaction evaluation device comprising a mass flow controller.
2). The light intensity was about 0.38 mW / cm ² . Dry air containing 1 ppm NO at room temperature 1.5 L / min per minute
In the above device. The NO concentration was monitored by a NOx meter. As a result, as shown in FIG. 3, immediately after light irradiation, a decrease in catalytic activity due to poisoning by the reaction product was observed, but thereafter, a stable catalytic activity was maintained, and the catalytic efficiency was 7%.
0% or more.

[0028]

The photocatalyst precursor solution according to claim 1 comprises (b)
Since terpineol contains (a) a titanium alkoxide having diethylene glycol monoalkyl ether and polyethylene glycol as ligands, it is low in volatility and hardly volatilizes even in an open system. Because it is difficult to contact with, it is possible to form a film even under atmospheric humidity, furthermore it has excellent adhesion to the support, and it has high viscosity, so it does not cause significant dripping or cracking or peeling in the firing process The desired film formation can be achieved with an extremely small number of times. Further, in the titanium dioxide thin film photocatalyst according to the second aspect, which provides a highly active transparent titanium dioxide thin film photocatalyst by firing, the fired product of the photocatalyst precursor according to the first aspect is fixed to the surface of the support in a thin film state. Therefore, the film thickness is constant, there is no cracking, the film is transparent and shows high catalytic activity. According to the method for producing a titanium dioxide thin film photocatalyst of the third aspect, cracking, whitening, and peeling in the liquid dripping and firing step occur in an open system (under atmospheric humidity) instead of a closed system, and with an extremely small number of dipping times. Thus, a titanium dioxide thin film photocatalyst can be synthesized. Further, since the film is baked at a temperature of 400 to 500 ° C. slightly higher than the crystallization temperature of titanium dioxide, a titanium oxide thin film having a uniform grain size and substantially no crystal growth can be obtained. 400 to 50
At a low firing temperature of 0 ° C., the pore structure generated by the organic fuel is preserved, and a thin film having fine pores of several nm or less and a high surface area is obtained. In addition, generally 400 to 5
Since the temperature of 00 ° C. is equal to or lower than the softening point temperature of glass, which is a typical support, according to this method, a highly active titanium oxide thin film can be easily formed on a glass support.

[Brief description of the drawings]

FIG. 1 is a graph showing a ratio of a film thickness increase with an increase in the number of dip coatings due to a difference in a photocatalyst precursor solution (Example 1 and Comparative Example 1).

FIG. 2 is a photograph taken by an atomic force microscope of a crystal structure of a transparent titanium dioxide thin film photocatalyst according to Example 2 and a state of the thin film.

FIG. 3 is a graph showing the removal characteristics of NO contained in dry air of the transparent titanium dioxide thin film photocatalyst according to Example 2.

Claims (3)

(57) [Claims] 1. A photocatalyst precursor solution comprising (a) a titanium alkoxide having diethylene glycol monoalkyl ether and polyethylene glycol as ligands and (b) terpineol. 2. A titanium dioxide thin film photocatalyst, wherein the photocatalyst precursor solution according to claim 1 is applied to a support under atmospheric humidity, and the calcined product is fixed on the surface of the support in a thin film form. . 3. A titanium dioxide thin film photocatalyst according to claim 2, wherein the photocatalyst precursor solution according to claim 1 is coated on a support and calcined at a temperature of 400 to 500 ° C. in an air atmosphere. Manufacturing method.