JP3794067B2 - Method for producing photocatalyst composition - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a photocatalyst composition capable of effectively utilizing light energy such as sunlight and the like by imparting stain decomposability, antifogging property, deodorizing property, antifungal property, and antibacterial property to various substrate materials such as glass and tile. It relates to a manufacturing method.
[0002]
[Prior art]
As environmental problems become more prominent, anti-fouling properties and anti-fouling properties of indoor and outdoor building materials such as glass and tiles are required in addition to deodorizing properties in indoor spaces. As a prior art for this, a semiconductor photocatalyst represented by TiO ₂ is formed on the substrate surface by spray coating method, dip coating method, spin coating method, sputtering method, fixing with a binder, etc., so as to decompose, deodorize and prevent fouling. It has been proposed to provide a function (Japanese Patent Laid-Open No. Hei 6-278241).
[0003]
However, the photocatalyst layer formed by the prior art is not satisfactory from a practical viewpoint because the catalyst activity is insufficient, the strength of the photocatalyst is low, and the photocatalyst layer is scratched or cracked during use.
[0004]
[Problems to be solved by the invention]
The present invention provides a method for producing a photocatalyst composition having sufficient catalytic activity and high strength.
[0005]
[Means for Solving the Problems]
The present invention provides a method for producing a photocatalyst composition , characterized in that a silica sol formed by hydrolyzing an organoalkoxysilane in the presence of a basic catalyst is dispersed in a semiconductor photocatalyst sol and then heat-treated .
[0006]
The band gap value E ₁ of the photocatalyst composition of the present invention is 0.05 eV or more compared to the band gap value E ₂ of the semiconductor photocatalyst alone, that is, E ₁ −E ₂ ≧ 0.05 (eV). It is preferable. When the band gap becomes so high, the redox power increases and the decomposition rate of organic substances increases.
[0007]
The semiconductor photocatalyst is selected from the group consisting of TiO ₂ , Bi ₂ O ₃ , In ₂ O ₃ , WO ₃ , ZnO, SrTiO ₃ , Fe ₂ O ₃ and SnO ₂ from the viewpoint of chemical stability and photocatalytic activity. One or more are preferable.
[0008]
The organoalkoxysilane is preferably a tetraalkoxysilane that can be easily hydrolyzed to obtain a stable silica sol.
[0009]
The basic catalyst is preferably one or more selected from the group consisting of ammonia, amine and tetraalkylammonium hydroxide because it is thermally decomposed and does not adversely affect the semiconductor photocatalyst. When an alkali metal or alkaline earth metal hydroxide is used as the basic catalyst, the metal ions may adversely affect the semiconductor photocatalyst.
[0010]
The dispersion ratio of the silica is preferably 10 to 80% by weight with respect to the total of the semiconductor photocatalyst and silica. When the dispersion ratio of silica is less than 10% by weight, the photocatalytic activity is not different from that of the semiconductor photocatalyst alone, and the strength is insufficient. On the other hand, when the amount is more than 80% by weight, the absolute amount of the semiconductor photocatalyst itself is lowered, so that the photocatalytic activity tends to be lowered. In particular, it is preferably 15 to 70% by weight.
[0011]
The photocatalyst composition of the present invention can be obtained by dispersing a silica sol formed by hydrolyzing an organoalkoxysilane in the presence of a basic catalyst in a semiconductor photocatalyst sol, followed by heat treatment.
[0012]
Further, the photocatalyst composition of the present invention is obtained by dispersing a silica sol formed by hydrolyzing an organoalkoxysilane in the presence of a basic catalyst in a metal complex salt solution that is a precursor of a semiconductor photocatalyst, and then performing a heat treatment. It is done.
[0013]
The form of the photocatalyst composition of the present invention can take various forms such as a film form, a bulk form, a fine powder, and an ultrafine particle.
[0014]
As a method for obtaining a film-like photocatalyst composition of the present invention, a solution in which a silica sol formed by hydrolyzing an organoalkoxysilane with a basic catalyst is dispersed on a semiconductor photocatalyst sol (hereinafter simply referred to as a sol mixed solution) is used. the) that it was applied, and a method of heat treatment under appropriate conditions.
[0015]
Also, a solution in which a silica sol formed by hydrolyzing an organoalkoxysilane with a basic catalyst is dispersed in a metal complex salt solution that is a precursor of a semiconductor photocatalyst (hereinafter simply referred to as a sol-dispersed complex salt solution) is applied to the substrate. The method of heat-processing on suitable conditions is mentioned .
[0016]
Examples of the coating method include spray coating, flexographic printing, dip coating, screen printing, and spin coating.
The heat treatment conditions are preferably a temperature of 400 to 700 ° C. and a time of 5 minutes to 2 hours, and the temperature profile can be appropriately selected.
[0017]
As another method for obtaining a film-like photocatalytic composition of the present invention, a sol mixed solution or a sol-dispersed complex salt solution is applied to a substrate heated to an appropriate temperature by a spray coating method. In this case, the heating temperature of the substrate is preferably in the range of 100 to 800 ° C.
[0018]
The substrate used in the present invention is not particularly limited, and examples thereof include glass, ceramics, metal, and other inorganic materials.
The surface of the substrate may be subjected to a surface treatment, for example, a substrate itself such as a glass surface treatment layer surface (for example, a surface provided with a sol-gel film, a sputtered film, a CVD film, a vapor deposition film, etc.) May be surfaces of different materials.
Further, the shape of the substrate is not particularly limited, and the substrate can be used in any shape depending on the purpose, such as a flat surface, a surface having a partial curvature or the like.
[0019]
[Action]
Since the photocatalyst composition of the present invention has a large band gap value and greatly improved strength, it is more resistant than P-25 (fine powder TiO ₂ manufactured by Nippon Aerosil Co., Ltd.), which has been considered to have the highest activity. A photocatalyst composition having high soil strength, antifogging properties, antifungal properties, deodorizing properties and antibacterial properties can be obtained.
[0020]
In the present invention, the mechanism by which the dispersion of silica obtained from a silica sol formed by hydrolyzing an organoalkoxysilane with an alkali catalyst in a semiconductor photocatalyst improves the photocatalytic activity is considered as follows.
[0021]
When a sol mixed solution or sol-dispersed complex salt solution is applied onto a substrate and heat-treated, the crystal growth of the oxide semiconductor is moderately suppressed during the heat-treatment, resulting in hydrolysis of organoalkoxysilane in the presence of an alkali catalyst. The crystallites of the semiconductor photocatalyst are smaller than when silica obtained from the silica sol is not dispersed.
[0022]
This phenomenon means that the degeneration is partially removed by the miniaturization of semiconductor particles, the band structure is changed, and the band gap value is increased, that is, the position of the valence band is lowered electrochemically. Means that the oxidation-reduction potential in the valence band becomes noble and the oxidizing power increases, and the photocatalytic activity of the semiconductor is improved in terms of reaction. This can be verified from the fact that the absorption of ultraviolet light in the photocatalyst composition of the present invention shifts to a shorter wavelength side than the semiconductor photocatalyst alone.
[0023]
On the other hand, in the photocatalyst composition in which silica sol formed by hydrolyzing organoalkoxysilane with an acidic catalyst is dispersed, the above phenomenon is not observed, and the ultraviolet light absorption characteristics are almost the same as those of the semiconductor photocatalyst alone.
[0024]
In the photocatalyst composition of the present invention, the photocatalytic activity is improved, but in a system using silica obtained from a silica sol formed by hydrolyzing organoalkoxysilane with an acidic catalyst, the photocatalytic activity is not improved but rather lowered. Although the cause is not clear, it is considered that the shape and chemical reactivity of silica sol are greatly different.
[0025]
The reason why the photocatalyst composition of the present invention has antifogging properties can be explained as follows. That is, when the photocatalyst composition of the present invention is irradiated with light, holes are generated in the valence band. Since these holes have a strong oxidizing power as described above, they oxidize moisture in the air and generate many OH radicals on the surface of the photocatalyst. For this reason, the wettability of a surface improves and antifogging property is expressed. Moreover, the dirt adhering to the surface is decomposed and removed by the above-mentioned OH radical having a very strong oxidizing power, and the wettability will be maintained for a long time.
[0026]
The reason why the photocatalyst composition of the present invention is high in strength is considered to be that silica sol serves as a binder to produce a strong adhesion with the oxide semiconductor microcrystals.
[0027]
【Example】
Hereinafter, the present invention will be specifically described with reference to Examples (Example 1, Example 4, Example 5, Example 6, Example 7) and Comparative Examples (Example 2, Example 3), but the present invention is not limited thereto. .
[0028]
(Example 1)
Silica sol prepared by hydrolyzing tetraethoxysilane with 1% by weight aqueous ammonia in isopropyl alcohol solvent to isopropyl alcohol solution (6% by weight) of titanium oxide sol by weight ratio of TiO ₂ / SiO ₂ = 80/20 A dispersed solution was prepared. Next, this solution was applied onto quartz glass by a spin coating method, and then heat treated at 550 ° C. for 1 hour to obtain quartz glass (sample) on which a film-like photocatalytic composition was formed.
[0029]
As a result of measuring the ultraviolet light transmittance of this sample, rapid absorption was observed from 370 nm to a short wavelength, and it was found that the band gap of this photocatalyst composition was about 3.35 eV.
[0030]
In order to evaluate the photocatalytic activity of this photocatalytic composition, the photodegradation reaction rate of acetaldehyde, which is the main component of tobacco malodor, was evaluated.
[0031]
In the experiment, first, a 5 cm square sample was placed in a ³ dm ³ quartz square reaction tube, and acetaldehyde vapor was introduced into the reaction tube. Next, the sample was irradiated with black light from the outside so that the irradiation intensity of ultraviolet rays (365 nm) on the sample surface was 1.8 mW / cm ^2, and the amount of acetaldehyde decreased was measured with a gas chromatograph. The reaction rate was determined. The photodegradation reaction was considered to be zero-order from the time-dependent change in the decrease in acetaldehyde, and the acetaldehyde decomposition reaction rate was 44 μg / h · cm ² .
[0032]
Next, the coating strength of the photocatalyst composition was evaluated by a Taber abrasion test. Although the load was 500 g and the test was performed 1000 times, almost no wear was observed.
[0033]
(Example 2)
Using only the isopropyl alcohol solution (6% by weight) of the titanium oxide sol shown in Example 1, samples were prepared in the same manner as in Example 1, and the ultraviolet light transmittance, photocatalytic activity, and coating strength were evaluated.
[0034]
As a result of measuring the transmittance of ultraviolet light, abrupt absorption was observed from 393 nm to a short wavelength, and it was found that the band gap of this photocatalyst was about 3.16 eV. The acetaldehyde decomposition reaction rate was 10 μg / h · cm ² . As a result of evaluating the film strength by the Taber abrasion test in the same manner as in Example 1, the film was severely worn after 1000 times, and the substrate was completely exposed.
[0035]
(Example 3)
Instead of the silica sol used in Example 1, a silica sol prepared by hydrolyzing tetraethoxysilane with a 1% by weight aqueous solution of nitric acid in an isopropyl alcohol solvent was used at a weight ratio of TiO ₂ / SiO ₂ = 80/20. Samples were prepared in the same manner as in Example 1, and ultraviolet light transmittance, photocatalytic activity, and coating strength were evaluated.
[0036]
As a result of measuring the transmittance of ultraviolet light, rapid absorption was observed from 390 nm to a short wavelength, and it was found that the band gap of this photocatalyst was about 3.16 eV. The acetaldehyde decomposition reaction rate was 5 μg / h · cm ² . As a result of evaluating the film strength by the Taber abrasion test, the film was hardly worn after 1000 times.
[0037]
(Example 4)
Instead of the silica sol used in Example 1, a silica sol prepared by hydrolyzing tetramethoxysilane with a 0.5% by weight aqueous solution of triethanolamine in an isopropyl alcohol solvent was used in a weight ratio of TiO ₂ / SiO ₂ = 75/25. Samples were prepared in the same manner as in Example 1 except that they were used in Example 1, and ultraviolet light transmittance, photocatalytic activity, and coating strength were evaluated.
[0038]
As a result of measuring the transmittance of ultraviolet light, abrupt absorption was observed from 375 nm to a short wavelength, and it was found that the band gap of this photocatalyst was about 3.32 eV. The acetaldehyde decomposition reaction rate was 38 μg / h · cm ² . As a result of evaluating the film strength by the Taber abrasion test, the film was hardly worn after 1000 times.
[0039]
(Example 5)
Using titanium triethanolamate [(HOCH ₂ CH ₂ ) ₃ N] ₂ Ti in an ethyl alcohol solution (5% by weight) as a precursor of titanium oxide, tetraethylammonium hydroxide is added in an amount of 1% by weight in an ethyl alcohol solvent. A solution was prepared by dispersing silica sol prepared by hydrolysis with a% aqueous solution so that TiO ₂ / SiO ₂ = 70/30 by weight ratio. Next, using this solution, a sample was prepared in the same manner as in Example 1, and ultraviolet light transmittance, photocatalytic activity, and coating strength were evaluated.
[0040]
As a result of measuring the transmittance of ultraviolet light, abrupt absorption was observed from 375 nm to a short wavelength, and it was found that the band gap of this photocatalyst was about 3.32 eV. The acetaldehyde decomposition reaction rate was 35 μg / h · cm ² . As a result of evaluating the film strength by the Taber abrasion test, the film was hardly worn after 1000 times.
[0041]
(Example 6)
Using the solution prepared in Example 1, the photocatalyst composition was formed by spray coating on quartz glass that had been heated to 500 ° C. in advance. Thereafter, the transmittance of ultraviolet light, photocatalytic activity, and coating strength were evaluated in the same manner as in Example 1.
[0042]
As a result of measuring the transmittance of ultraviolet light, abrupt absorption was observed from 372 nm to a short wavelength, and it was found that the band gap of this photocatalyst was about 3.33 eV. The acetaldehyde decomposition reaction rate was 42 μg / h · cm ² . As a result of evaluating the film strength by the Taber abrasion test, the film was hardly worn after 1000 times.
[0043]
(Example 7)
Using the solution prepared in Example 5, it was spray-coated on quartz glass that had been heated to 550 ° C. in advance to form a photocatalytic composition. Thereafter, the transmittance of ultraviolet light, photocatalytic activity, and coating strength were evaluated in the same manner as in Example 1.
[0044]
As a result of measuring the transmittance of ultraviolet light, abrupt absorption was observed from 375 nm to a short wavelength, and it was found that the band gap of this photocatalyst was about 3.32 eV. The acetaldehyde decomposition reaction rate was 36 μg / h · cm ² . As a result of evaluating the film strength by the Taber abrasion test, the film was hardly worn after 1000 times.
[0045]
【The invention's effect】
The photocatalyst composition of the present invention has sufficient catalytic activity and excellent strength.

Claims (7)

  A method for producing a photocatalyst composition, comprising: dispersing a silica sol formed by hydrolyzing an organoalkoxysilane in the presence of a basic catalyst;   A method for producing a photocatalyst composition, comprising: dispersing a silica sol formed by hydrolyzing an organoalkoxysilane in the presence of a basic catalyst in a metal complex solution that is a precursor of a semiconductor photocatalyst; The method for producing a photocatalyst composition according to claim 1 or 2 , wherein the band gap value of the photocatalyst composition is 0.05 eV or more larger than the band gap value of the semiconductor photocatalyst alone. The method of manufacturing a semiconductor photocatalyst, the photocatalyst composition according to any one of claims 1 to 3 is a TiO _2. The method for producing a photocatalyst composition according to any one of claims 1 to 4 , wherein the organoalkoxysilane is tetraalkoxysilane. Method for producing a basic catalyst, ammonia, amines and the photocatalytic composition as claimed in any one of claims 1 to 5 1 or more elements in a selected from the group consisting of tetraalkyl ammonium hydroxide. Dispersion ratio of the silica in the presence of a basic catalyst obtained from the silica sol organoalkoxysilane formed by hydrolysis, any claims 1-6 which is 10 to 80 wt% on the sum of the semiconductor photocatalyst and silica method for producing a photocatalyst composition according to any one of claims.