JPH10113563A - Photocatalyst and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively use light energy such as solar light and sufficiently provide stain decomposing and hazing-preventive properties to various kinds of substrates such as glass, tiles, etc., by forming a solid acid on a semiconductive photocatalyst surface. SOLUTION: This catalyst having excellent stain-proof, hazing-preventive, mildewproof, deodorizing, and anti-bacterial properties is produced by forming a solid acid on a semiconductive photocatalyst surface and the semiconductor photocatalyst is preferably an oxide semiconductor and especially one or more substances selected from TiO2 , Bi2 O3 , In2 O3 , WO3 , ZnO, SrTiO3 , etc., are used. Also, the solid acid to be used consists of oxides as a carrier (carrier oxides) and oxides (deposited oxides) deposited on the surface of the carrier and as the carrier oxides, one or more oxides selected fromZrO2 , SrTiO3 , Fe2 'O3 , HfO2 , SiO2 , etc., are preferable and as the deposited oxides, one or more oxides selected from SO4 , WO3 , MoO3 , and B2 O3 are preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a photocatalyst and a method for producing the same.

[0002]

2. Description of the Related Art As environmental problems have become more prominent, there has been a demand for not only deodorization properties in indoor spaces, but also antifouling properties and antifungal properties of building materials such as glass and tiles in and out of rooms. Conventionally, a semiconductor photocatalyst represented by TiO ₂ is formed on a substrate surface by a spray coating method, a dip coating method, a spin coating method, a sputtering method, fixing with a binder, or the like,
It has been proposed to impart stain resolution, deodorizing property, and antifungal property (Japanese Patent Application Laid-Open No. Hei 6-278241).

[0003]

However, the photocatalyst layer formed by the conventional technique has insufficient catalytic activity and is not satisfactory from a practical viewpoint.

[0004] The present invention provides a photocatalyst and a method for producing the same, which can effectively utilize light energy such as sunlight and can practically sufficiently impart stain resolution and anti-fog properties to various substrates such as glass and tiles. .

[0005]

The present invention provides a photocatalyst characterized by forming a solid acid on the surface of a semiconductor photocatalyst.

[0006] The photocatalyst of the present invention is P-25 (fine powder T manufactured by Nippon Aerosil Co., Ltd.), which is conventionally considered to have the highest activity.
It has antifouling property, antifogging property, antifungal property, deodorant property and antibacterial property exceeding iO ₂ ).

The semiconductor photocatalyst used in the present invention is preferably an oxide semiconductor in view of chemical stability and photocatalytic activity. In particular, TiO ₂ , Bi ₂ O ₃ , In ₂ O ₃ , WO
₃ , ZnO, SrTiO ₃ , Fe ₂ O ₃ and SnO ₂
The photocatalyst is preferably at least one selected from the group consisting of

[0008] The solid acid in the present invention has a chemical composition different from that of the semiconductor photocatalyst surface. The solid acid used in the present invention includes an oxide as a carrier (hereinafter, referred to as a carrier oxide) and an oxide supported on the surface thereof (hereinafter, referred to as a supported oxide). When the carrier oxide and the semiconductor photocatalyst have the same composition, a solid acid is formed only by the supported oxide.

As carrier oxides, ZrO ₂ , SrTi
O ₃ , TiO ₂ , Fe ₂ O ₃ , SnO ₂ , HfO ₂ , S
One or more oxides selected from the group consisting of iO ₂ and Al ₂ O ₃ are preferred. As the supported oxide, a strongly acidic one is obtained, and good results are obtained.
₄ , one or more oxides selected from the group consisting of WO ₃ , MoO ₃ and B ₂ O ₃ are preferred. In the solid acid, the supported amount of the supported oxide on the surface of the carrier oxide is 0.2%.
-20% by weight is suitable.

Since the photocatalytic activity can be further improved, Fe, Mn, Pt, Os, Ir, R
It is preferable to add at least one metal selected from the group consisting of u, Pd and Rh or a compound containing the metal. Examples of the metal-containing compound include chlorides and oxides.

The amount of addition of the metal or the metal-containing compound (in terms of metal) is preferably 0.5 to 10% by weight based on the supported oxide (in terms of oxide). If the addition amount is less than 0.5% by weight, the effect of the addition is not sufficient,
If the amount is more than the percentage by weight, the ratio of the surface of the solid acid covered with metal increases, and the activity tends to decrease.

Various forms such as powder, fine powder, and thin film can be used as the form of the photocatalyst in the present invention. When the photocatalyst of the present invention is formed on a substrate, the substrate is not particularly limited, and can be applied to glass, ceramics, metal, other inorganic materials, and the like.

The surface of the substrate may be the surface of the substrate itself, such as the surface of a surface-treated layer of a surface-treated glass (eg, a surface provided with a sol-gel film, a sputter film, a CVD film, a vapor deposition film, etc.). May be surfaces of different materials. The shape of the base is not particularly limited. For example, it may be flat, such as one having a full or partial curvature,
Any shape depending on the purpose may be used.

According to the present invention, a semiconductor photocatalyst layer formed on a substrate is coated with a precursor solution of an oxide which forms a solid acid, and then subjected to a heat treatment to allow the semiconductor photocatalyst to carry the oxide acid. A method for producing a photocatalyst is provided.

As an example of the production method, an oxide precursor solution for forming a solid acid carrier oxide is applied and baked on a semiconductor photocatalyst layer formed on a substrate, and then a solid acid-carrying oxide is applied. Impregnation with the oxide precursor solution to be formed and heat treatment are performed.

Examples of the method of applying the oxide precursor solution for forming the carrier oxide include a spray coating method, a dip coating method, a flexographic printing method, a screen printing method, and a spin coating method. The oxides described above are suitable as the carrier oxide and the supported oxide.

The semiconductor photocatalyst layer is preferably formed by applying 1) a semiconductor photocatalyst sol solution or 2) a semiconductor photocatalyst precursor solution to a substrate. Examples of the coating method include the above-described methods.

1) As a semiconductor photocatalyst sol solution, Sr
A sol solution of at least one oxide selected from the group consisting of TiO ₃ , TiO ₂ , Fe ₂ O ₃ and SnO ₂ , 2) as a semiconductor photocatalyst precursor solution, SrTiO ₃ , TiO
₂ , a precursor solution of one or more oxides selected from the group consisting of Fe ₂ O ₃ and SnO ₂ .

As the semiconductor photocatalytic sol, it is preferable to use a semiconductor photocatalytic sol in which the particle diameter of oxide particles in the semiconductor photocatalytic sol is 20 nm or less. After applying the semiconductor photocatalyst sol solution to the substrate, it is preferable to form a semiconductor photocatalyst layer by performing a heat treatment under a heat treatment condition in which the crystallite diameter of the oxide in the semiconductor photocatalyst layer becomes 20 nm or less.

In particular, ZrO ₂ , Sr
TiO ₃ , TiO ₂ , Fe ₂ O ₃ , SnO ₂ , HfO
_When one or more oxides selected from the group consisting of SiO ₂ and Al ₂ O ₃ are formed by heat treatment, it is preferable to use heat treatment conditions in which the crystallite diameter of these oxides is 20 nm or less. If it exceeds 20 nm, even if one or more oxides selected from the group consisting of SO ₄ , WO ₃ , MoO _3, and B ₂ O ₃ suitable as a supported oxide are formed on the surface of the carrier oxide, the super-strong acidity may not be maintained. Difficult to develop.

The semiconductor photocatalyst layer can be formed by a sputtering method, a CVD method or a vapor deposition method. in this case,
For the same reason as described above, it is preferable to form the semiconductor photocatalyst layer under the condition that the crystallite diameter in the semiconductor photocatalyst layer is 20 nm or less.

In the present invention, if the carrier oxide and the semiconductor photocatalyst are oxides having the same composition, the production of the photocatalyst becomes very easy, and the supporting oxide is supported on the surface of the semiconductor photocatalyst. A photocatalyst is obtained.

Specifically, the photocatalyst of the present invention can be obtained by impregnating the semiconductor photocatalyst layer with a precursor solution of the supported oxide) and performing a heat treatment to support the solid acid on the semiconductor photocatalyst. As described above, as the supported oxide, SO ₄ , W
One or more oxides selected from the group consisting of O ₃ , MoO ₃ and B ₂ O ₃ are preferred.

SO ₄ , WO ₃ , MoO ₃ and B ₂ O ₃
As precursors of sulfuric acid (H ₂ SO ₄ ), ammonium sulfate [(NH ₄ ) ₂ SO ₄ ], ammonium metatungstate [(NH ₄ ) ₆ (H ₂ W ₁₂ O ₄₀ )], ammonium paratungstate 5 Hydrate [(NH ₄ ) ₁₀ W ₁₂ O
₄₁ · 5H ₂ O], molybdate [H ₂ MoO _4], ammonium molybdate _{[(NH 4) 6 Mo 7} O 24 · 4H
₂ O], trimethoxyborane [(CH ₃ O) ₃ B] and the like, and their aqueous solutions and organic solvent solutions can be used as appropriate.

According to the present invention, a powdery photocatalyst is also obtained. Specifically, the semiconductor photocatalyst powder is impregnated with a precursor solution of an oxide that forms a solid acid (only a supported oxide may be used), and heat treatment is performed to support the solid acid on the semiconductor photocatalyst. Is obtained. It is preferable to use a powder having a crystallite diameter of 20 nm or less as the semiconductor photocatalyst powder for the same reason as described above.

The solid acid in the present invention is preferably a super strong acid. In the present invention, a super strong acid is defined as an acid having an acid strength higher than 100% sulfuric acid. In terms of Hammett's acidity constant (H ₀ ), 100% sulfuric acid is H ₀ = -11.9.
The one having an acid strength of H ₀ ≦ −1.93 is a super strong acid, and the smaller the value of H ₀ , the stronger the acid. As the solid acid used in the present invention, an acid exhibiting an acidity stronger than 100% sulfuric acid, that is, a solid superacid is preferable.

The reason why the photocatalytic activity is greatly improved by forming a solid superacid on the surface of the semiconductor photocatalyst in the present invention is considered as follows.

Even on an organic substance which does not react under ordinary conditions, on a solid superacid, a carbocation such as pentacoordinated CH ₅ ⁺ to which a proton has been added or H ⁻ is extracted by the catalytic action of the solid superacid. It is known that this produces carbenium ions such as CH ₃ ⁺ . Since these reaction intermediates are thermodynamically unstable, electrons and holes generated when the photocatalyst of the present invention is irradiated with light easily react with the reaction intermediates and are decomposed. It is considered that the activity is greatly improved. That is, by forming a solid superacid on the surface of the semiconductor photocatalyst, the decomposition and removal of the organic matter progresses remarkably.

Further, Fe, Mn, Pt, Os, Ir, R
The reason why the addition and removal of one or more metals selected from the group consisting of u, Pd and Rh or the metal-containing compound facilitates the decomposition and removal of organic substances is that these elements serve as cocatalysts. Can be

By using the photocatalyst in the present invention, a remarkable stain resolution, deodorizing property, and antifungal property can be imparted as compared with a conventional photocatalyst represented by TiO ₂ .

In the present invention, the mechanism for exhibiting anti-fogging properties can be explained as follows. The irradiation of the photocatalyst of the present invention with light generates holes in the valence band. Since these holes have a strong oxidizing power, they oxidize moisture in the air to generate a large number of OH radicals on the photocatalyst surface. Therefore, the wettability of the surface is improved, and the antifogging property is exhibited. Further, the dirt adhering to the surface is decomposed and removed by the above-described solid acid and the OH radical having a very strong oxidizing power generated on the photocatalyst surface, so that the wettability is maintained for a long time.

[0032]

EXAMPLES The present invention will be specifically described below with reference to Examples (Example 1, Examples 3 to 7) and Comparative Examples (Example 2), but the present invention is not limited to Examples.

(Example 1) An aqueous solution (6% by weight) of a titanium oxide sol containing titanium oxide particles having an average particle diameter of 15 nm is spin-coated on quartz glass and then heat-treated at 400 ° C. for 1 hour to form a TiO ₂ film. Was formed. The thickness of this film is about 100 nm, and the crystallite diameter of TiO ₂ is 17n.
m.

Next, this TiO ₂ coated quartz glass was
Immerse in a specified sulfuric acid solution for 5 minutes, and then
Quartz glass to which a photocatalyst in which a solid acid was formed on the surface of the semiconductor photocatalyst by baking for a minute was obtained.

In order to evaluate the photocatalytic activity of this photocatalyst,
The photodegradation kinetics of acetaldehyde, the main component of tobacco odor, was evaluated. In the experiment, a 5 cm square sample was placed in a 3 liter quartz square reaction tube, acetaldehyde vapor was introduced into the reaction tube, and ultraviolet light (365 nm) on the photocatalyst surface was used.
The sample was irradiated with black light from the outside so that the irradiation intensity was 1.8 mW / cm ² . The reduction amount of acetaldehyde was measured by gas chromatography, and the reaction rate of acetaldehyde decomposition was determined. The photodegradation reaction was considered to be of zero order based on the change over time in the amount of decrease in acetaldehyde, and the reaction rate k was calculated. As a result, the reaction rate k was 150 μg /
hr · cm ² .

(Example 2) The photocatalytic activity of only the quartz glass with a TiO ₂ coating in Example 1 (that is, without immersion in a 1N sulfuric acid solution) was evaluated in the same manner as in Example 1. As a result, the reaction rate k was 18 μg / hr. - it was cm ^2.

Example 3 A quartz glass with a TiO ₂ coating was obtained in the same manner as in Example 1, and then immersed in a 1% aqueous solution of ammonium metatungstate [(NH ₄ ) ₆ (H ₂ W ₁₂ O ₄₀ )]. After drying at 100 ° C., the mixture was calcined at 700 ° C. for 20 minutes to obtain a photocatalyst supporting WO ₃ on TiO ₂ . As a result of evaluation in the same manner as in Example 1, the reaction rate k was 120 μg / hr · cm.
^{Was 2} .

(Example 4) A TiO ₂ film was formed in the same manner as in Example 1 except that a toluene solution (5% by weight) of titanium 2-ethylhexanoate, which is a precursor of titanium oxide, was used instead of the titanium oxide sol of Example 1. To obtain a quartz glass. The thickness of the film was about 100 nm, and the crystallite diameter of TiO ₂ was 7 nm.

Next, molybdic acid [H ₂ MoO ₄ ] obtained by dissolving the quartz glass with the TiO ₂ coating in ammonia was used.
%, Dried at 100 ° C., and calcined at 700 ° C. for 20 minutes to obtain a photocatalyst supporting MoO ₃ on TiO ₂ . As a result of evaluation in the same manner as in Example 1, the reaction rate k was 140.
μg / hr · cm ² .

[0040] (Example 5) in place of the toluene solution of 2-ethylhexanoic acid titanium Example 4, as a toluene solution (SrTiO ₃ which is the precursor of the SrTiO ₃ 2-ethylhexanoic acid titanium and strontium 2-ethylhexanoate 2
% By weight) except that SrTiO _{3 was used.}
A quartz glass with a coating was obtained. The film thickness is about 100 nm
And the crystal form of SrTiO ₃ was amorphous.

Next, the SrTiO ₃ coated quartz glass was immersed in a 1% aqueous solution of molybdic acid [H ₂ MoO ₄ ] dissolved in ammonia in the same manner as in Example 4, and MoO ₃ was changed to S
A photocatalyst supported on rTiO ₃ was obtained. As a result of evaluation in the same manner as in Example 1, the reaction rate k was 150 μg / hr · cm ² .

[0042] to obtain a photocatalyst created in (Example 6) Example 1, 2% was immersed in chloroplatinic acid solution _{[H 2 PtCl 6 · 6H 2} O], followed photocatalyst added with Pt and dried at 100 ° C. Was. The amount of Pt-supported oxide relative to SO ₄ (as oxide) was 2% by weight in terms of metal. As a result of evaluation in the same manner as in Example 1, the reaction rate k was 650 μg / hr · cm.
^{Was 2} .

Example 7 The photocatalyst prepared in Example 5 was immersed in a 2% iridium chloride solution [IrCl ₃ ], and then
After drying at 00 ° C., a photocatalyst to which Ir was added was obtained. The addition amount of the supported oxide of Ir to MoO ₃ (in terms of oxide) was 5% by weight in terms of metal. As a result of evaluation in the same manner as in Example 1, the reaction rate k was 700 μg / hr · cm ² .

(Evaluation of antifogging property, antifogging durability and antifungal property) The photocatalysts obtained in Examples 1 to 7 were evaluated for antifogging property, antifogging durability and antifungal property by the following methods. Table 1 shows the results. The photocatalysts obtained in Examples 1 to 6 were also evaluated for deodorizing properties and antibacterial properties. As a result, practically sufficient performance was obtained with the light energy of sunlight.

The anti-fogging property was measured by measuring the time required until the fogging completely disappeared by blowing a breath on the sample. The test was performed three times and the average time was examined. The anti-fogging durability was determined by examining the anti-fogging property after immersion in 60 ° C. hot water for 3 days. The antifungal property was obtained by using the quartz glass with a photocatalyst obtained in Examples 1 to 7 in a bathroom (of a floor area of about 3.
A 3 m ² ) wall tile (30 cm above the floor) was attached with a ceramic adhesive. The bath was used for a total of two hours a day, almost every day. When the bath was used, a 20-W fluorescent lamp attached to the ceiling was turned on, and two months later, the surface of the sample was examined for the occurrence of mold.

[0046]

[Table 1]

[0047]

Industrial Applicability The photocatalyst of the present invention can effectively utilize the light energy of sunlight, is extremely excellent in dirt resolution and antifogging property, and has various practical properties such as antifungal property, deodorizing property and antibacterial property. Above is enough.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01J 23/34 B01J 23/34 M 23/652 23/84 ZABM 23/84 ZAB 23/85 ZABM 23/85 ZAB 23/89 ZABM 23/89 ZAB 27/053 ZABM 27/053 ZAB 37/02 301Z 37/02 301 C09D 5/14 C09D 5/14 5/16 5/16 E06B 7/12 E06B 7/12 B01J 23/64 103M

Claims (7)

[Claims] 1. A photocatalyst wherein a solid acid is formed on the surface of a semiconductor photocatalyst. 2. The method according to claim 1, wherein the semiconductor photocatalyst is TiO ₂ , Bi ₂ O
₃ , In ₂ O ₃ , WO ₃ , ZnO, SrTiO ₃ , Fe
₂ O ₃ and claim 1 of the photocatalyst comprising one or more semiconductor optical catalyst selected from the group consisting of SnO _2. 3. A solid acid formed on the surface of a semiconductor photocatalyst,
Fe, Mn, Pt, Os, Ir, Ru, Pd and Rh
The photocatalyst according to claim 1, wherein at least one metal selected from the group consisting of or a metal-containing compound is added. 4. The addition amount of said metal or said metal-containing compound is 0.5 to 10% by weight in terms of metal.
Photocatalyst. 5. A semiconductor photocatalyst layer formed on a substrate,
A method for producing a photocatalyst, comprising applying a precursor solution of an oxide that forms a solid acid, and then performing a heat treatment to support the solid acid on the semiconductor photocatalyst. 6. The method for producing a photocatalyst according to claim 5, wherein the semiconductor photocatalyst layer is formed under the condition that the crystallite diameter in the semiconductor photocatalyst layer is 20 nm or less. 7. A precursor solution of one or more oxides selected from the group consisting of SO ₄ , WO ₃ , MoO ₃ and B ₂ O ₃ as a precursor solution of an oxide forming a solid acid. Item 7. The method for producing a photocatalyst according to item 5 or 6.