JP2000218161A - Photocatalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable activity when using tungsten oxide which can be activated by irradiation with visible light as a photocatalyst. SOLUTION: A mixture of tungsten oxide and a solid acid such as alumina, a silicon-aluminum composite oxide, and a composite oxide of tungsten and zirconium, which has a higher ability to adsorb by-products generated when deodorizing odor, is mixed. To prepare a coating solution. This is applied to the surfaces of the carriers 1 and 2 formed in a honeycomb shape and fired to form the photocatalyst film 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocatalyst having high activity or activity with visible light and suitable for deodorization and removal of harmful substances.

[0002]

2. Description of the Related Art When a photocatalyst is irradiated with light having a wavelength having energy equal to or greater than the band gap, electrons are generated in a conduction band and holes are generated in a valence band by photoexcitation. The strong reducing power of electrons generated by this photoexcitation and the strong oxidizing power of holes are considered for use in decomposing and purifying organic matter, decomposing water, removing nitrogen oxides, decomposing and fixing carbon dioxide, etc. In the field of antibacterial and purification, some of them are being put to practical use.

[0003] The most typical material for the photocatalyst is titanium oxide. Titanium oxide is highly active and also has excellent chemical stability, and its activity as a photocatalyst is maintained semipermanently. In addition, it is harmless to the human body, abundant in resources, and inexpensive.

In order to activate titanium oxide, which is a type of n-type semiconductor, as a catalyst, it is necessary to irradiate light energy exceeding the band gap. Among various crystal structures of titanium oxide, anatase crystal has a large activity, and has a band gap of about 3.2 eV. Therefore, it is necessary to irradiate ultraviolet light of 380 nm or less in order to obtain the activity. For example, an air purifier using a titanium oxide photocatalyst incorporates a black light or a germicidal lamp that emits ultraviolet light in order to deodorize odor components due to tobacco or the like in the air.

Further, when natural light such as white fluorescent light, daylight fluorescent light, sunlight or the like is irradiated on titanium oxide, it is possible to obtain a slight activity with a small amount of ultraviolet light. Practical use is progressing. Also, N
Examination of purification of Ox is also in progress.

[0006] As one of measures against the energy problem, a method of decomposing water with a photocatalyst to obtain hydrogen and oxygen,
As a countermeasure against global warming, a method of converting carbon dioxide into alcohol or the like using a photocatalyst has been studied.

[0007]

The photocatalyst has a strong oxidizing / reducing power capable of decomposing hardly decomposable chemical substances, but has a disadvantage that its decomposition rate is low. In addition, in order to activate titanium oxide, it is necessary to irradiate light in an ultraviolet region. When a general-purpose light source such as sunlight or a fluorescent lamp is used as an excitation light source, only a very small amount of ultraviolet light is used. And have the disadvantages of low activity and poor energy efficiency. Therefore, a special light source such as a black light or an ultraviolet lamp for sterilization is generally used in order to efficiently and highly activate titanium oxide.

Various studies have been conducted since the 1970's to obtain photocatalytic activity with visible light in order to eliminate such disadvantages of titanium oxide. Fe2 O3, CdS, CdSe, GaP and the like have been studied as materials other than titanium oxide that absorb visible light. However, Fe203 has almost no activity and Cd
Since S, CdSe, and GaP have poor stability even if they are initially activated, there are problems of reduced activity and dissolution in water.
WO3 (tungsten oxide) is also active in visible light, but generally has poor stability and is said to have a problem in reliability. Further, a method using a potassium niobate-based composite oxide has been studied, but the activity by visible light is small and has not been put to practical use.

On the other hand, doping of titanium oxide with various materials has been studied. However, when doping is performed, visible light can be absorbed, but there is a problem that the catalytic activity is lost. In recent years, attention has been paid to doping by ion implantation as a method for obtaining activity with visible light without losing the activity due to doping. This method is disclosed in
As disclosed in JP-A-262482, metal ions are implanted into titanium oxide, and then 400 to 500 ° C.
And visible light activity can be obtained without impairing the activity of titanium oxide. However, since this method uses an ion implantation method, it is difficult to continuously treat a titanium oxide photocatalyst formed on a substrate having a large area, and the mass productivity is poor, so that it has not been put to practical use.

[0010] In view of the above, an object of the present invention is to provide a photocatalyst that can stably obtain an activity by using tungsten oxide that can obtain an activity with visible light.

[0011]

The object of the present invention is to provide a photocatalyst using tungsten oxide which can absorb visible light to obtain an activity and further mixing a solid acid as a photocatalyst. Titanium oxide, which is a general photocatalyst, has to be irradiated with ultraviolet light in order to obtain the activity, and has a disadvantage that a large photocatalytic activity cannot be obtained with natural light or a general-purpose light source. Tungsten oxide, which can be activated by visible light, is generally said to have poor stability and reliability problems, but as a result of the study of the present inventors, when a solid acid is added to tungsten oxide, the activity is reduced. Can prevent the drop,
It became clear that stable activity could be maintained.

Although the details of this mechanism are not yet clear, the following mechanism is conceivable. Tungsten oxide is more likely to produce by-products due to photocatalysis than titanium oxide. For example, when acetaldehyde, which is a kind of malodorous substance, is decomposed by a tungsten oxide photocatalyst, acetic acid is generated as a by-product, and the acetic acid adheres to the tungsten oxide photocatalyst. Since acetic acid is harder to decompose than acetaldehyde, the adhesion area of acetic acid reduces the contact area with acetaldehyde, hinders the decomposition of acetaldehyde, and greatly reduces the activity. However, when a solid acid is mixed with tungsten oxide, a decrease in activity can be suppressed. In other words, solid acids have the effect of attracting polar molecules or electrons and anions.Accordingly, acetic acid, which has a slow decomposition rate, adsorbs to solid acids, and acetic acid adhering to the surface of tungsten oxide is greatly reduced, maintaining a highly active state. can do.

Therefore, the photocatalyst obtained by mixing the tungsten oxide and the solid acid has a large activity by natural light such as white fluorescent lamp, daylight fluorescent lamp and sunlight without irradiating ultraviolet light, utilizing the characteristics of tungsten oxide. Can be obtained for a long period of time, and stable activity can be obtained by eliminating adhesion of by-products.

Here, the solid acid may be any as long as it has a higher by-product adsorption performance than tungsten oxide, that is, alumina, a composite oxide of tungsten and zirconium, and a silicon-aluminum composite oxide. Are suitable. Alumina is industrially mass-produced, easily available, and relatively inexpensive, yet has an effect of preventing acetic acid from adhering to tungsten oxide, and is excellent in cost performance. In addition, since it is white, when mixed with tungsten oxide powder, irregular reflection is repeated when irradiated with excitation light, the light absorption efficiency of tungsten oxide is increased, the efficiency of light irradiation on the photocatalyst is improved, and a large photocatalytic activity is obtained. There is an advantage.

Since the composite oxide of tungsten and zirconium has a strong adsorption performance, a large effect of preventing acetic acid from adhering to tungsten oxide can be obtained. Further, since it is white like alumina, mixing with tungsten oxide powder has the advantage that the irradiated excitation light repeats irregular reflection and the efficiency of light irradiation on the tungsten oxide is improved.

The silicon-aluminum composite oxide is a so-called zeolite, has higher adsorption performance than alumina, and has a large effect of preventing acetic acid from adhering to tungsten oxide. In addition, it has the advantage of being cheap and easy to obtain.

In order to further enhance the effect of preventing by-products from adhering to tungsten oxide, it is preferable to mix tungsten oxide with a solid acid carrying fine metal particles. Here, as the metal fine particles, fine particles of platinum, gold, silver, palladium or the like are used, and ultrafine particles having a particle diameter of 2 nm or less are suitable. By adding a solid acid supported by a metal to tungsten oxide, by-products such as acetic acid generated by photocatalysis, which have a low decomposition rate, are adsorbed by the solid acid and the adhesion to tungsten oxide is suppressed, so that a large photocatalytic activity is obtained. Maintained for a long time.

By-products such as acetic acid adsorbed on the surface of a solid acid are gradually decomposed by the photocatalytic action of tungsten oxide. However, when a high-concentration odor component is treated with a photocatalyst for a long period of time, by-products are produced. Since the accumulation rate of the substances exceeds the decomposition rate, the surface of the solid acid reaches adsorption saturation, and by-products such as acetic acid start covering the tungsten oxide surface. In order to prevent this phenomenon, a photocatalyst made of tungsten oxide and a solid acid carrying a metal is periodically heated. Then, by-products such as acetic acid are promptly decomposed and removed by the catalytic action of the metal fine particles on the solid acid, the tungsten oxide is regenerated, and high activity can be maintained without impairing the photocatalytic activity of the tungsten oxide. . In addition, the activity can be obtained for a long time by irradiation with visible light.

Further, by using a porous solid acid, the effect of preventing by-products from adhering to tungsten oxide can be further enhanced. That is, the porous solid acid acts as an adsorbent. For example, when a high-concentration odorant is treated with a photocatalyst for a long time, by-products are adsorbed on the solid acid, and the by-products are deposited on the tungsten oxide surface. And high photocatalytic activity can be obtained for a long period of time. Here, as the porous solid acid, the above-mentioned alumina and the silicon-aluminum composite oxide are suitable, but any porous material may be used, for example, activated carbon. When metal particles such as platinum, gold, silver, and palladium, preferably ultra-fine particles having a particle size of 2 nm or less are supported on a porous solid acid, the photocatalyst is periodically heated to be adsorbed on the solid acid. By-products can be quickly decomposed and removed, and high activity can be maintained.

Then, rather than simply mixing the tungsten oxide and the solid acid, the solid acid is supported on the tungsten oxide in the form of islands, or the tungsten oxide is supported on the solid acid in the form of islands. And the other is dispersed. As a result, the solid acid adheres to the surface of the tungsten oxide, or the tungsten oxide adheres to the surface of the solid acid, and by-products such as acetic acid generated by active species such as OH radicals and O 2 -radicals near the tungsten oxide. The substance is quickly adsorbed on the solid acid without being adsorbed on the tungsten oxide. In addition, since the distance between the solid acid and the tungsten oxide is short, an effect is obtained that by-products adsorbed on the surface of the solid acid are easily decomposed by active species generated by the tungsten oxide.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION A photocatalyst according to one embodiment of the present invention is a mixture of tungsten oxide capable of absorbing visible light to obtain an activity and a solid acid. Solid acid has a function of adsorbing by-products such as acetic acid generated by the photocatalysis of tungsten oxide, alumina,
A composite oxide of tungsten and zirconium and a silicon-aluminum composite oxide are used. Note that one of these may be used alone, or a combination thereof may be used. Furthermore, a metal having a catalytic action such as platinum, gold, silver, and palladium can be supported on the solid acid.

As the form of the photocatalyst, a mixture of tungsten oxide powder and solid acid powder is supplied in powder form. Alternatively, a tungsten oxide powder and a solid acid powder are mixed to form a slurry, and the slurry is applied or immersed in a carrier and fired to be supported as a photocatalytic film. By doing so, a photocatalyst unit is formed, and handling of the photocatalyst body is facilitated.

Further, a solid acid may be dispersed and provided on the surface of the tungsten oxide, and the solid acid is distributed in an island shape. Specifically, tungsten oxide is formed in a flaky shape, mixed with a solid acid and crushed with a ball mill or the like, so that the solid acid is supported on the surface of the tungsten oxide in an island shape. Or,
Tungsten is formed on a substrate by a sputtering method to form a tungsten oxide film, on which solid acid powder is dispersed and bonded. When tungsten is formed on an alumina substrate by a sputtering method, tungsten oxide is dispersed and formed in an island shape.

The above photocatalyst is applied to a deodorizing device or a harmful substance removing device. In this case, a photocatalyst film in which tungsten oxide and a solid acid are mixed is formed on a carrier, and formed into a predetermined shape by bending and laminating to form a photocatalyst unit, which may be used for a desired device. The tungsten oxide and the solid acid are fixed on a carrier with, for example, an alumina or silica-based binder.

Specifically, as shown in FIGS. 1 and 2, the chromated aluminum is cut into a band-shaped carrier 1 having a predetermined width, and a part of the band-shaped carrier 1 is pressed to form a corrugated carrier 2.
To Next, these carriers 1 and 2 are adhered to each other with an adhesive to form a honeycomb-shaped carrier 3.

The photocatalyst coating liquid is prepared by the following method. To a silica sol (Snowtex O manufactured by Nissan Chemical Co., Ltd.), a tungsten oxide powder (WO3 manufactured by Kanto Chemical Co.) and an alumina powder carrying platinum (Pt-Al203 manufactured by Okitsumo) are added. However, the content of tungsten oxide was 25%, the content of platinum-supported alumina was 25%, and the content of silica was 50% in terms of solid content weight.
Set to be. After immersing the honeycomb-shaped carrier 3 in the coating solution thus adjusted, the honeycomb-shaped carrier 3 is pulled up, the above-mentioned coating material for a photocatalyst body is applied, and then fired at 200 ° C. for 30 minutes,
The photocatalyst film 4 is formed on the surfaces of the carriers 1 and 2. This dip coating to baking is repeated two more times to form a total of three photocatalyst films, thereby completing the honeycomb-shaped photocatalyst unit.

For example, when the above-mentioned photocatalyst unit is used as a cylindrical rotor 5 of a deodorizing device as shown in FIG. 3, the rotor 5 is rotated by a motor or the like via a rotating shaft 6. When air containing odor is blown into the rotor 5 by a blower or the like, acetaldehyde, which is one of the harmful substances, is decomposed by the tungsten oxide photocatalyst while passing through the gap 7 of the rotor 5, and deodorized air is blown out. . At this time, acetic acid is generated as a by-product and adheres to the surface of the photocatalyst. However, acetic acid is selectively adsorbed on the surface of the solid acid, and little acetic acid adheres to the surface of the tungsten oxide. Therefore, tungsten oxide can exhibit a stable photocatalytic action over a long period of time.
Then, when the photocatalyst unit is irradiated with visible light from a light source 8 such as a white fluorescent lamp or a daylight fluorescent lamp, or from sunlight or the like,
The photocatalyst can maintain a high active state.

When a high concentration of odor is deodorized for a long period of time, by-products such as acetic acid having a low decomposition rate adhere to the surface of the tungsten oxide and its activity is reduced. By doing so, by-products are decomposed by the catalytic action of platinum supported on the solid acid, the surface of the photocatalytic unit can be refreshed, and high activity can be obtained again.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that many modifications and changes can be made to the above-described embodiment within the scope of the present invention.

[0030]

The present invention will be described below based on examples and comparative examples.

(Example 1) 0.5 g of WO3 / ZrO2 composite oxide (manufactured by Daiichi Kagaku Kagaku Kogyo) was mixed with 0.5 g of tungsten oxide powder (WO3 manufactured by Kanto Kagaku).

Example 2 0.5 g of tungsten oxide powder (WO3 manufactured by Kanto Chemical) and alumina powder (AL manufactured by Showa Light Metal Co., Ltd.)
(-150SG) 0.5 g.

Example 3 0.5 g of zeolite (manufactured by Nissan Gardler) was mixed with 0.5 g of tungsten oxide powder (WO3 manufactured by Kanto Kagaku).

(Example 4) Silica sol (Snowtex O manufactured by Nissan Chemical Co., Ltd.) was added to tungsten oxide powder (W
O3) and alumina powder (AL-150S made by Showa Light Metal)
G) was added. However, the content of tungsten oxide was set to 25%, the content of alumina was set to 25%, and the content of silica was set to 50% in terms of solid content weight. The coating solution thus prepared was dip-coated on a 3 cm × 12 cm 3 chromate-treated aluminum substrate and baked at 200 ° C. for 30 minutes. Immersion, coating and baking are repeated twice more, for a total of 3
A layer of photocatalytic film was formed.

Example 5 15 g of tungsten oxide powder (WO3, manufactured by Kanto Chemical Co.) was added to 100 ml of alumina sol (520, manufactured by Nissan Chemical) whose solid content was adjusted to 5%, and the mixture was stirred and coated on a glass substrate. Fired. After firing, the coating on the glass substrate was scraped off with a spatula, and crushed with an alumina ball mill for 10 hours to produce tungsten oxide in which alumina was dispersed and supported.

Comparative Example 1 Only 0.5 g of tungsten oxide powder (WO3 manufactured by Kanto Chemical Co.) was used as a sample.

Comparative Example 2 Only 0.5 g of anatase type titanium oxide powder (ST-01 manufactured by Ishihara Sangyo) was used as a sample.

Comparative Example 3 0.5 g of WO3 / ZrO2 composite oxide (manufactured by Daiichi Kagaku Kagaku Kogyo) was used as a sample.

(Comparative Example 4) 0.5 g of tungsten oxide powder (WO3 manufactured by Kanto Chemical Co.) was added to activated carbon (manufactured by Cataler Industry).
0.5 g was mixed.

Comparative Example 5 0.5 g of zeolite (manufactured by Nissan Gardler) was mixed with 0.5 g of anatase type titanium oxide powder (ST-01 manufactured by Ishihara Sangyo).

(Comparative Example 6) Silica sol (Snowtex O manufactured by Nissan Chemical Co.) was added to tungsten oxide powder (W
O3) was added. However, the content was set such that the content of tungsten oxide was 25% and the content of silica was 75% in terms of solid content weight. 3cm ×
It was immersed and applied to a 12 cm chromate treated aluminum substrate and baked at 200 ° C. for 30 minutes. The dipping / coating / firing was repeated twice more to form a total of three photocatalyst films.

(Comparative Example 7) Titanium oxide powder (ST-0, manufactured by Ishihara Sangyo) was added to silica sol (Snowtex O, manufactured by Nissan Chemical Industries, Ltd.).
1) was added. However, the content was set so that the content of titanium oxide was 25% and the content of silica was 75% in terms of solid content weight. The coating solution adjusted in this way is 3 cm × 12 cm
Dipped and coated on the chromated aluminum substrate
It was baked at 00 ° C. for 30 minutes. The dipping / coating / firing was repeated twice more to form a total of three photocatalyst films.

The samples of the photocatalysts described above were separately placed in a styrene dish having an area of 8.4 cm × 5.4 cm and a depth of 1.3 cm, and each was individually placed in a 5-liter container. Next, acetaldehyde, one of the malodorous substances, was injected in an amount to give a concentration of 100 ppm. Thereafter, the sample was irradiated with light using a 6 W daylight fluorescent lamp, and the time required for the acetaldehyde concentration to decrease to 1 ppm was measured. Table 1 shows the results.

[0044]

[Table 1] The sample of Example 1 in which the tungsten oxide and the WO3 / ZrO2 composite oxide were mixed was about 60% shorter in time than the sample of Comparative Example 1 using only tungsten oxide and the sample of Comparative Example 2 using titanium oxide. Decomposes acetaldehyde. The WO3 / ZrO2 composite oxide alone has almost no activity of decomposing acetaldehyde as shown in Comparative Example 3. Therefore, it is considered that the activity of tungsten oxide was enhanced by adding WO3 / ZrO2 composite oxide to tungsten oxide.

The sample of Example 2 in which tungsten oxide and alumina were mixed further decomposed acetaldehyde at a high speed, and the sample of Comparative Examples 1 and 2 could decompose acetaldehyde in less than half the time. The sample of Example 5 in which alumina was dispersed on the surface of tungsten oxide can also efficiently decompose acetaldehyde.

The sample of Example 3 in which tungsten oxide and zeolite were mixed decomposed acetaldehyde in about 1/3 the time of the sample of Comparative Example 4 in which tungsten oxide and activated carbon were mixed. In addition, it was decomposed in 1/4 time as compared with the sample of Comparative Example 5 in which titanium oxide and zeolite were mixed. It should be noted that even a mixture of tungsten oxide and activated carbon decomposed acetaldehyde in a shorter time than the sample of Example 1.

The sample of Example 4 in which a mixed powder of tungsten oxide and alumina was fixed with a silica binder was used in Comparative Example 6 in which the tungsten oxide powder was fixed without using alumina.
Acetaldehyde was decomposed in half the time as compared with the sample of No. 1. Acetaldehyde was decomposed in less than half the time compared to the sample of Comparative Example 7 in which titanium oxide powder was fixed with a silica binder, and when irradiated with a daylight fluorescent lamp containing a large amount of visible light, tungsten oxide and alumina were decomposed. The sample of Example 4 in which is mixed shows higher activity than titanium oxide.

Example 6 Tungsten was formed on three 6 cm × 6 cm alumina substrates by ion beam sputtering. The substrate temperature during film formation was room temperature, and the set film thickness was 20 °. Next, the resultant was fired at 500 ° C. for 2 hours in a firing furnace to produce an alumina substrate having tungsten oxide formed in an island shape.

Comparative Example 8 Tungsten was formed on three 6 cm × 6 cm quartz glass substrates by ion beam sputtering. The substrate temperature during film formation was room temperature, and the set film thickness was 20 °. Next, the glass substrate was fired in a firing furnace at 500 ° C. for 2 hours to form tungsten oxide in an island shape.

Then, each of the three samples prepared in Example 6 and Comparative Example 8 was placed in a 5 liter container. Next, acetaldehyde, which is one of the malodorous substances, was injected until the concentration reached 100 ppm. Then 6
Using a daylight fluorescent lamp of W, the sample was irradiated with light, and the time required for the acetaldehyde concentration to decrease to 1 ppm was measured. Table 2 shows the results.

[0051]

[Table 2] In the sample of Example 6 in which tungsten oxide was formed in an island shape on an alumina substrate, acetaldehyde was decomposed in 9.3 hours, whereas in the sample of Comparative Example 8 in which tungsten oxide was formed in an island shape on a glass substrate. In the sample, the decomposition time of acetaldehyde was 15 hours, and the decomposition time was about 1.
6 times as long.

Example 7 0.5 g of tungsten oxide powder (WO3 manufactured by Kanto Kagaku) and 0.5 g of alumina powder carrying platinum (Pt-Al2O3 manufactured by Okitsumo) were mixed.

Then, a hot plate was placed in a 5 liter container, and an aluminum area of 8.4 cm × 5.
A 4 cm, 1.3 cm deep dish was placed on a hot plate. The samples of Examples 2 and 7 were individually placed in an aluminum dish, and one of the malodorous substances, acetaldehyde, was added to the dish.
Injection was performed until the concentration reached 00 ppm. Next, the sample was irradiated with light using a 6 W daylight fluorescent lamp for 3.5 hours. After repeating this 9 times, the concentrations of acetaldehyde and acetic acid were measured 3.5 times after irradiation with a daylight fluorescent lamp at the 10th time.

Next, a second embodiment is performed by using a hot plate.
After heating each of the samples of Example 7 and 250 ° C. for 2 hours, 100 ppm of acetaldehyde was injected again, and the concentrations of acetaldehyde and acetic acid were measured 3.5 hours after irradiation with a daylight fluorescent lamp. Table 3 shows the results.

[0055]

[Table 3] When the injection of acetaldehyde and the irradiation of a daylight fluorescent lamp were repeated 10 times, both the sample of Example 2 and the sample of Example 7 did not decompose acetaldehyde to 1 ppm,
It remains at a high concentration of ppm. Also, acetic acid as a by-product remains at a high concentration of 9 ppm. Next, 250
After heating each sample for 2 hours at 100 ° C., 100 ppm of acetaldehyde was injected again, and after irradiating with a daylight fluorescent lamp for 3.5 hours, the measurement was carried out. Acetic acid is 0.1
ppm and acetaldehyde is 1p
Decomposed to a low concentration of pm. On the other hand, in the sample of Example 2 using alumina not carrying platinum,
The acetic acid concentration is as high as 12 ppm, and the amount of acetic acid produced does not decrease even after heating at 250 ° C. Acetaldehyde is 4pp
m and remains at a high concentration.

From the results, the following mechanism is estimated. When a large amount of acetaldehyde is decomposed with tungsten oxide, a large amount of acetic acid is generated as a by-product. Acetic acid is gradually decomposed by the photocatalytic action of tungsten oxide. However, if a high concentration of acetaldehyde is treated for a long time, the produced acetic acid is released into the air without being completely absorbed by alumina. Further, a part of acetic acid covers the surface of the tungsten oxide and inhibits the decomposition of acetaldehyde. Here, when alumina supporting platinum by heating to a high temperature is mixed with tungsten oxide, acetic acid is rapidly decomposed by the action of a platinum catalyst. For this reason, after the heat treatment, the ability to adsorb acetic acid is restored, and the adsorption of acetic acid on the surface of tungsten oxide is suppressed, so that the decomposition of acetaldehyde is not hindered and the activity is maintained.

[0057]

As is clear from the above description, according to the present invention, since tungsten oxide is mixed with a solid acid having a high ability to adsorb by-products, decomposition of acetic acid and the like generated by the photocatalytic action of tungsten oxide. It is possible to prevent by-products having a low rate from adhering to tungsten oxide, and to obtain stable activity. As a result, the activity of the tungsten oxide is prevented from lowering due to the adverse effect of the by-products, and the excellent properties of the tungsten oxide, that is, a large photocatalytic activity can be obtained even with visible light, can be greatly exhibited. Therefore, it is not necessary to use a special light source for irradiating ultraviolet light such as titanium oxide, and an inexpensive general-purpose light source or natural light can be used, so that the photocatalyst can be easily used in a deodorizing device or a harmful substance removing device. Value increases.

In particular, when metal fine particles having a catalytic action are carried on a solid acid, by-products such as acetic acid adsorbed and accumulated on the solid acid can be removed by heating. Therefore, the photocatalyst can be periodically refreshed, and the life can be extended.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a honeycomb-shaped photocatalytic unit according to an embodiment of the present invention.

FIG. 2 is a perspective view of the same.

FIG. 3 is a schematic diagram of a dehumidifier using a photocatalytic unit for a rotor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Band-shaped carrier 2 Wavy carrier 3 Honeycomb-shaped carrier 4 Photocatalytic film

 ────────────────────────────────────────────────── ─── Continued on front page F term (reference) 4G069 AA03 AA08 BA01A BA01B BA03A BA03B BA05A BA05B BA07B BA37 BA48A BB04A BB04B BB06A BC60A BC60B BC75B CA17 DA05 EA01X EA01Y EA07 FB02 FB13 FB30

Claims (7)

[Claims] 1. A photocatalyst comprising a mixture of tungsten oxide and a solid acid which prevents adhesion of by-products generated by decomposition of an organic substance by the tungsten oxide to the tungsten oxide. 2. The photocatalyst according to claim 1, wherein metal solid particles are supported on the solid acid. 3. The photocatalyst according to claim 1, wherein the solid acid is porous. 4. The photocatalyst according to claim 1, wherein one of the tungsten oxide and the solid acid is dispersed on the surface of the other. 5. The solid acid according to claim 1, wherein one of alumina, a silicon-aluminum composite oxide, and a composite oxide of tungsten and zirconium is used. Photocatalyst. 6. A photocatalyst film formed by mixing tungsten oxide and a solid acid that prevents adhesion of by-products generated by decomposition of an organic substance by the tungsten oxide to the tungsten oxide is formed on the carrier. Characteristic photocatalyst. 7. A plurality of carriers are combined to form a gap through which an organic substance can pass.
The photocatalyst according to the above.