JP2001130928A - Article with photocatalytic activity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an article free from various limitations when a titanium oxide film as photocatalytic film highly active to organic matter decomposition reaction is applied onto the uppermost surface thereof. SOLUTION: This article with photocatalytic activity is obtained by laminating the surface of a substrate with a photocatalytic film of titanium oxide and an overcoating film consisting of an n-type oxide semiconductor in this order.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an article coated with a photocatalyst film, and more particularly to an article coated with a photocatalyst film having functions such as harmful substance decomposition, antifouling property and antifogging property.

[0002]

2. Description of the Related Art Various articles have been developed for environmental purification technology for decomposing harmful substances by using a thin film of titanium oxide having a photocatalytic function, and for obtaining antifouling properties by decomposing organic dirt and making the surface hydrophilic. Attempts have been made to apply it to

Since the photocatalytic reaction is a surface reaction between electrons and holes excited by light irradiation in a titanium oxide film, a titanium oxide film is generally used as the outermost surface.

[0004] For applications such as anti-fog glass utilizing a photocatalytic function, a method of improving hydrophilicity retention by providing a hydrophilic film made of silicon dioxide on the surface has been disclosed (for example, Japanese Unexamined Patent Application Publication No. Hei 9 (1994)). -57912, JP-A-10-
57817).

[0005]

In the above prior art, when a titanium oxide film is used on the outermost surface, various characteristics are determined by the characteristics of the titanium oxide in the surface layer, and may not be practically desirable. For example, the titanium oxide surface easily loses hydrophilicity and easily adsorbs organic substances, and titanium oxide is a solid acid, so it is inferior in adsorption of acidic gas,
Because the refractive index of titanium oxide is large, if the outermost surface is titanium oxide, the reflectance of the article tends to increase.

In the above-mentioned prior art, the method of providing a hydrophilic film on the surface can improve the adsorptivity of the surface of the article, but reduces the activity of the surface for the decomposition reaction of organic substances.

[0007] An object of the present invention is to provide an article coated with a photocatalytic film having a high activity against an organic substance decomposition reaction.

[0008]

According to the present invention, a substrate is provided with
This is an article having photocatalytic activity in which a photocatalytic film made of titanium oxide and an overcoat film made of an n-type oxide semiconductor are laminated in this order.

When the photocatalyst film is irradiated with light, electron-hole pairs are generated in the photocatalyst film. Of these electrons and holes, those that have moved to the article surface contribute to photocatalytic activity.

In the present invention, since an overcoat film, which is an n-type semiconductor, is laminated on the photocatalyst film, the transfer of electrons and holes from the photocatalyst film to the surface of the article is hardly hindered. Therefore, even if the thickness of the overcoat film is increased, the photocatalytic activity is not significantly impaired, and the catalytic activity for a specific reaction is increased by utilizing the crystallinity of the overcoat film and the acid-base property of the surface, It has become possible to increase the degree of freedom in designing optical characteristics.

In the present invention, a titanium oxide (TiO ₂ ) oxide semiconductor film (band gap: 3.0 eV for a rutile structure, 3.2 e for an anatase structure) is used as a photocatalytic film.
V). Instead of the titanium oxide film, fine particles of titanium oxide may be dispersed in, for example, a silicon dioxide film.

[0012] If a non-oxide semiconductor is used as the overcoat film, a structural distortion occurs at the interface with the titanium oxide layer, which hinders the movement of electrons and holes from the titanium oxide layer to the overcoat layer. I do. In the overcoat film of a p-type semiconductor, p-type is formed at the interface with the n-type titanium oxide layer.
An n-junction effect appears and hinders the transfer of electrons from the titanium oxide layer to the overcoat layer.

Among the n-type oxide semiconductors of the overcoat layer in the present invention, those having an energy band gap of less than 4 eV are preferable. When the energy band gap is 4 eV or more, the energy band structure is lower because the upper end position of the valence band is lower than that of the titanium oxide layer, which hinders the movement of holes from the titanium oxide layer to the overcoat layer. Absent.

N-type oxide used for overcoat film
As a semiconductor, niobium oxide (Nb _TwoO_Five: 3.4e
V), tin oxide (SnO)_Two: 3.5 eV) and zinc oxide
(ZnO: 3.3 eV) selected from the group consisting of metal oxides
It is preferable to use at least one kind of oxide semiconductor film.
Good.

The thickness of the photocatalyst film is preferably at least 30 nm, more preferably at least 50 nm. If the thickness is less than 30 nm, light is not sufficiently absorbed. On the other hand, the upper limit of the thickness is 2000
nm or less, and more preferably 1000 nm or less. Even when the thickness exceeds 2000 nm, the effect of improving the photocatalytic activity is small, and when the thickness is 1000 nm.
This is because, if it exceeds, optical haze tends to occur.

The thickness of the overcoat film is required to be a certain thickness in order to improve optical characteristics and improve crystallinity, and is preferably 5 nm or more, more preferably 50 nm or more. On the other hand, the upper limit of the thickness is preferably 500 nm or less so as not to hinder the movement of the electric charge, and not to hinder the transmission of light when light enters from the opposite side of the substrate using a transparent substrate. , 20
More preferably, it is 0 nm or less.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail based on examples and comparative examples. FIG. 1 is a sectional view of an embodiment of the article having photocatalytic activity of the present invention. The article 1 having photocatalytic activity is obtained by laminating a silicon dioxide film 3 as an alkali diffusion preventing film, a titanium oxide film 4 as a photocatalytic film, an overcoat film 5, and a hydrophilic film 6 on the surface of a glass plate 2 as a substrate. I have. Of these, the photocatalytic film 4 and the overcoat film 5 are essential films, and the alkali diffusion preventing film 3
And the hydrophilic film 6 are films appropriately provided as necessary.

The substrate used in the present invention is not particularly limited. Optically, a transparent body or an opaque body is used, and as a material, metal, ceramics, glass, plastic, or the like is used. By using a transparent silicate glass plate as the substrate, for example, a glass plate manufactured by a float manufacturing method, a window glass having an environmental purification action and a stain prevention effect can be obtained.

The silicate glass often contains an alkali component such as sodium, potassium or the like for the purpose of normally securing the melting property and forming into a plate shape. When an alkali component is contained in the glass plate, it is preferable to prevent the alkali component from diffusing by interposing an alkali diffusion preventing film between the glass plate and the photocatalytic film. As such an alkali diffusion preventing film, the thickness is 5 to 5.
A 300 nm silicon dioxide film, a silicon nitride film, a silicon oxynitride film and the like can be exemplified. Other metal oxide films can also be used.

When the above-mentioned alkali diffusion preventing film is coated, when the glass substrate is heated to form the photocatalyst film, the alkali component in the substrate diffuses into the photocatalyst film to impair its crystallinity, Disturbing the electronic structure of the film is prevented. As described above, the coating of the alkali diffusion preventing film can further prevent the photocatalytic activity from lowering.

In the present invention, a hydrophilic film can be formed on the surface of the article to impart antifogging property and antifouling property. By coating with a hydrophilic film, the surface can be made more hydrophilic. The thickness of the hydrophilic film is
It is preferable that the thickness be such that the transfer of the charge from the photocatalytic film or the overcoat film to the surface is not hindered.
It is good to be 0 nm or less, preferably 10 nm or less, more preferably 5 nm or less. The hydrophilic film may be coated so as to cover the entire article, or may be coated so as to cover a part thereof. As a material of the hydrophilic film, a film such as silicon oxide can be exemplified as a preferable material.

Further, in order to enhance photocatalytic activity and hydrophilicity, any one of an alkali diffusion preventing film, a photocatalytic film, an overcoat film, and a hydrophilic film is formed to have an uneven surface, and the surface of the article is formed. May be provided with irregularities.

[Examples 1 to 3] A soda lime silicate glass plate was floated on a surface of a soda lime glass plate by a sol-gel method.
100 nm silicon dioxide film as alkali diffusion prevention film
The titanium oxide film as a photocatalyst film was coated with a thickness of 90 nm, and the overcoat film was coated with a thickness of 60 nm.

The silicon dioxide film is formed by applying a coating solution of tetraethoxysilane as a starting material by a spin coating method,
It was preliminarily dried at 0 ° C. for 5 minutes, and then fired at 500 ° C. for 1 hour to form a film. The titanium oxide film was obtained by adding 10.68 g of titanium isopropoxide to 7.53 of acetylacetone.
g and ethyl cellosolve at a rate of 41.79 g to prepare a coating solution, which was applied by spin coating, and preliminarily dried at 320 ° C. for 5 minutes. The overcoat film was formed by applying the following various coating solutions onto the pre-dried titanium oxide film by spin coating, pre-drying at 320 ° C. for 5 minutes, and then drying at 620 ° C., 6
Baking in minutes.

The coating solution for the overcoat film is as follows. Example 1 (Niobium oxide film)-Hydrolyzed solution of alkoxide of niobium (GIP-Nb04 manufactured by Giken Kagaku Co., Ltd.)
1). Example 2 (tin oxide)-a compound obtained by adding 1.59 g of acetylacetone and 25.62 g of ethyl cellosolve to 2.79 g of stannic chloride hydrate. Example 3 (zinc oxide)-8.92 g of zinc nitrate hexahydrate
7.80 g of ethyl acetoacetate and 44.31 g of ethyl cellosolve.

Comparative Examples 1 to 3 A soda lime silicate glass plate produced by a float process was coated with a silicon dioxide film as an alkali diffusion preventing film to a thickness of 100 nm by a sol-gel method. The films used were each coated with a thickness of 60 nm. The used coating solution, coating method, and heat treatment conditions are the same as in Examples 1 to 3.

Comparative Example 4 A soda lime silicate glass plate produced by a float process was coated by a sol-gel method with a silicon dioxide film having a thickness of 100 nm as an alkali diffusion preventing film and a titanium oxide film having a thickness of 90 nm as a photocatalytic film. . The used coating solution, coating method, and heat treatment conditions are the same as in Examples 1 to 3.

COMPARATIVE EXAMPLE 5 A soda lime silicate glass plate produced by a float process was overcoated with a silicon dioxide film having a thickness of 100 nm as an alkali diffusion preventing film and a titanium oxide film having a thickness of 90 nm as a photocatalytic film by a sol-gel method. A silicon dioxide film as a film was coated with a thickness of 60 nm. Example 1 used coating solution, coating method and heat treatment conditions
Same as ~ 3.

As for the photocatalytic activities of Examples 1 to 3 and Comparative Examples 1 to 5, acid blue 9 decomposition rate and acetaldehyde gas decomposition rate were measured as follows. Shown in

The acid blue 9 decomposition rate was determined by spin coating an aqueous solution of polyvinyl alcohol and acid blue 9 as an organic dye on the sample surface of each of the examples and comparative examples, and irradiating with a black light of 3 mW / cm ² for 10 minutes. The oxidative decomposition rate of Acid Blue 9 was measured from the difference in absorbance before and after. The results show that the decomposition reaction rate of Comparative Example 4 was 1.0
It is shown as a relative value when 0 is set.

The decomposition rate of acetaldehyde gas is determined by putting a sample and acetaldehyde gas into a closed 3 liter container, irradiating the sample with light from a high-pressure mercury lamp through a quartz glass window from outside the container, and irradiating air in the container. Withdraw 5 ml every 15 minutes from the start,
The acetaldehyde concentration was measured. The results are shown as relative values when the decomposition reaction rate in Comparative Example 4 was 1.00.

[0032]

[Table 1] Alkaline Alkali Diffusion Photocatalyst Over Acid Acid 9 Acetaldehyde Prevention film Membrane Coat film Decomposition rate (relative value) Decomposition rate (relative value) ───────────────────────────────── ─── Example 1 SiO ₂ TiO ₂ Nb ₂ O ₅ 1.71 1.01 Example 2 SiO ₂ TiO ₂ SnO ₂ 0.82 0.66 Example 3 SiO ₂ TiO ₂ ZnO 0.71 1.33 − −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Comparative Example 1 SiO ₂ Nb ₂ O ₅ − 0.00 − Comparative Example ₂ SiO 2 SnO 2 - 0.00 - Comparative example 3 SiO ₂ ZnO - 0.11 - Comparative example 4 SiO ₂ TiO ₂ - 1.00 1.00 Comparative example _{5 SiO 2 TiO 2 SiO 2 0.00} - ── ────────────────── ────────────────

From the comparison of the decomposition rates of Acid Blue 9 in Examples 1 to 3 and Comparative Examples 1 to 3, in Examples 1 to 3, electrons and holes excited by the titanium oxide film were exposed to the surface via the overcoat film. Indicates that acid blue has been decomposed. On the other hand, a comparison between Comparative Example 4 and Comparative Example 5 reveals that the activity is completely lost when silicon dioxide is used as the overcoat film.

In the comparison between Example 1 and Comparative Example 4, the decomposition activity of Acid Blue 9 is increased by coating with niobium oxide. As a result of X-ray diffraction analysis, niobium oxide on titanium oxide was preferentially oriented in the (100) plane of the crystal, which is considered to be the cause of showing excellent activity against acid blue 9 decomposition.

In the comparison between Example 2 and Comparative Example 4, although the photocatalytic activity was slightly lowered by coating with tin oxide, it was still at a practically sufficient level. Example 2 has better surface conductivity than Comparative Example 4.

In the comparison between Example 3 and Comparative Example 4, the activity of decomposing acetaldehyde gas is increased by coating with zinc oxide. This is probably because the surface of titanium oxide is acidic while the surface of zinc oxide is basic, and the amount of adsorption of acetaldehyde, which is an acidic gas, on the surface is increased.

[0037]

According to the present invention as described above,
By sequentially laminating a photocatalytic film made of titanium oxide and an overcoat film made of an n-type oxide semiconductor on the surface of the substrate, electrons generated in the titanium oxide film, without hindering the transfer of holes to the article surface, Utilizing the crystallinity of the overcoat film and the acid-base characteristics of the surface, it has become possible to increase the catalytic activity for a specific reaction and to expand the degree of freedom in designing the optical characteristics of the article.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

[Explanation of symbols]

 1: Article of the present invention 2: Glass plate 3: Alkali diffusion preventing film of silicon dioxide 4: Photocatalytic film of titanium oxide 5: Overcoat film 6: Hydrophilic film

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B01J 23/20 B01J 35/02 J35 / 02 B32B 9/00 A // B32B 9/00 B01D 53/36 J GF term (reference) 4D048 AA19 AB03 BA07X BA07Y BA16X BA16Y BA21X BA21Y BA24X BA24Y BB03 EA01 4F100 AA17C AA20 AA21 AA21B AA25C AA28C JA40C AG00A AR00B AR00C AR00E BA00 BA03 BA02BA03 JN01A YY00B YY00C 4G059 AA01 AC21 AC22 AC25 EA04 EA05 EB05 GA01 GA02 GA04 GA12 4G069 AA03 BA04A BA04B BA14A BA14B BA48A BC22A BC22B BC35A BC35B BC50A BC50B BC55A BC55B CA02 CA08 CA11 DA06

Claims (7)

[Claims] 1. An article having photocatalytic activity in which a photocatalytic film made of titanium oxide and an overcoat film made of an n-type oxide semiconductor are laminated on a substrate surface in this order. 2. The method according to claim 1, wherein the overcoat film comprises niobium oxide;
The article having photocatalytic activity according to claim 1, which is at least one kind of oxide semiconductor film selected from the group of metal oxides consisting of tin oxide and zinc oxide. 3. The photocatalytic film has a thickness of 30 to 2000 n.
The article having photocatalytic activity according to claim 1 or 2, which is m. 4. The thickness of the overcoat film is 5 to 50.
The article having photocatalytic activity according to any one of claims 1 to 3, which has a thickness of 0 nm. 5. The article having photocatalytic activity according to claim 1, wherein the substrate is a transparent glass plate. 6. An alkali diffusion preventing film for preventing an alkali component contained in the glass plate from diffusing between the glass plate and the photocatalytic film.
Item having photocatalytic activity according to 1. 7. The article having photocatalytic activity according to claim 1, wherein the article having photocatalytic activity has a hydrophilic film on the outermost surface.