JP2000126613A - Production of photocatalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a photocatalyst body which does not cause deterioration in the photocatalytic activity with time by sputtering method. SOLUTION: Titanium oxide is used for a target 2 and a mixture gas of argon and oxygen is used as a gas to be introduced into a sputtering device. The pressure of the introduced gas is controlled to >10 mTorr, and a film of titanium oxide is produced by the mixture gas plasma. Or, metal titanium is used as the target 2, and the mixture gas of argon and oxygen is used as the gas to be introduced into the sputtering device. The pressure of the introduced gas is controlled to >10 mTorr and a film of anatase-type crystalline titanium oxide is formed by reactive sputtering by the mixture gas plasma.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a photocatalyst in which a photocatalyst such as titanium oxide is formed in a film on a substrate.

[0002]

2. Description of the Related Art The use of photocatalysts as catalysts for decomposing, purifying, or disinfecting odorous substances, harmful substances, oils, and the like generated in daily living environments has been studied. Practical application is underway. The photocatalyst can obtain a very strong decomposition action by active species generated by light irradiation. Since titanium oxide, which is a typical photocatalyst material, can obtain a stronger oxidizing action than chlorine and ozone, it can decompose hardly decomposable organic substances such as trihalomethane.

That is, 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. Due to the strong reducing power of electrons and the strong oxidizing power of holes generated by this photoexcitation, it decomposes and purifies organic substances, decomposes water, removes nitrogen oxides, etc., and exhibits a hydrophilic function that does not repel water. .

Although such a photocatalyst has a strong decomposing power, its decomposition rate is low. In order to increase the decomposition rate, studies have been made to increase the surface area of a photocatalyst formed and to combine the photocatalyst with an adsorbent such as zeolite and activated carbon.
Further, in order to increase the catalytic activity, support of metal fine particles and the like have been studied.

[0005] Therefore, at first, the photocatalyst was considered to be applied in the form of powder from the viewpoint of securing a sufficient contact area with the decomposed material and problems in production. However, when the photocatalyst is a powder, it is necessary to remove the photocatalyst powder again after mixing with a system such as air or water for purification to purify. Therefore, studies for practical use have been mainly conducted on film-like titanium oxide.

As a main method of forming a titanium oxide photocatalyst into a film, powdery titanium oxide is mixed with a substance having an adhesive property, for example, a binder, applied to a substrate, and then cured by heating or at room temperature. And a photocatalytic film. Silica-based materials and fluororesin materials are used as binder materials having adhesive performance.

As a general method of forming a photocatalytic material directly into a film without using a binder, there is a method of forming a titanium oxide film using a sol-gel method. After the raw material liquid is applied to the substrate and dried, baking is performed at a high temperature of 500 ° C. or more to form a photocatalytic film.

However, in the case of the binder method, a large amount of the photocatalyst is buried in the adhesive substance, which has a disadvantage that the original catalytic action of the photocatalyst is impaired.
Further, by using a porous material as the adhesive substance, a decrease in catalytic action can be suppressed, but there is a problem that adhesion to a substrate is reduced. In addition, the sol-gel method generally has a drawback that it cannot be formed on a substrate having low heat resistance since the raw material liquid is heated to a high temperature of 500 ° C. or higher after application, and thus its use is limited.

Further, as a method for improving the activity of the photocatalyst, there are a method of supporting fine metal particles on titanium oxide, a method of performing a reduction treatment in hydrogen or alcohol gas, and the like. However, when reducing the photocatalyst, it is necessary to heat in a combustible gas, which poses a safety problem.
In addition, since the treatment is performed at a high temperature of 300 ° C. or more, it is not suitable for a substrate having low heat resistance. Moreover, each of these methods is performed after the formation of the photocatalytic film, and has a disadvantage that the number of manufacturing steps increases.

[0010]

Therefore, there is a sputtering method as another method of forming a photocatalytic film which is neither the binder method nor the sol-gel method. For example, JP-A-8-30920
As disclosed in Japanese Patent Application Publication No. 4 (1993) -4, a photocatalytic film of a metal oxide is formed by sputtering. in this case,
The type of substrate on which the photocatalytic film is formed is not limited. The photocatalyst obtained by this method has better photocatalytic activity than the photocatalyst obtained by the sol-gel method.

However, the photocatalyst obtained by the above sputtering method has a relatively large photocatalytic activity immediately after film formation, but has a problem that the activity decreases with time. That is, even if a photocatalytic film is simply formed by a sputtering method, it is inevitable that the photocatalytic activity deteriorates with time unless proper film forming conditions are used.

In view of the above, an object of the present invention is to produce a photocatalyst in which the photocatalytic activity does not deteriorate with time by finding appropriate film forming conditions in the sputtering method.

[0013]

The object of the present invention is to provide a method of forming a photocatalytic film made of a metal oxide on a substrate by sputtering.
rr. Examples of the metal oxide having a photocatalytic action include titanium oxide, zinc oxide, tungsten oxide, vanadium oxide, and zirconium oxide. Titanium oxide has high photocatalytic activity, is stable without being decomposed itself, and is inexpensive. Is most often used.

As described above, when the photocatalyst is formed by the sputtering method, by performing the film formation at a high gas pressure higher than 10 mTorr, the photocatalytic activity hardly deteriorates with time, and the film can be formed at a low gas pressure. A larger photocatalytic activity can be obtained as compared with the case where it is performed. In addition, unlike the case where the fine particle photocatalyst is fixed with an adhesive substance to form a film, the photocatalyst is not buried in the adhesive substance and the photocatalytic activity is not impaired. Further, unlike the case where a film is formed by a sol-gel method, high-temperature sintering is not required, and formation on a substrate having low heat resistance becomes possible. Further, a larger photocatalytic activity can be obtained as compared with a photocatalytic film formed by a general sol-gel method.

As described above, when forming a titanium oxide film by sputtering, if the film is formed at a high gas pressure, the activity does not deteriorate and the activity becomes high, but the reason is not clear. However, the following can be considered.

That is, when the crystal states of the titanium oxide film formed at a low gas pressure and the titanium oxide film formed at a high gas pressure are examined from the peak intensities by X-ray diffraction, respectively, It was found that titanium had a higher peak intensity than titanium oxide formed at a high gas pressure. Therefore, it is considered that titanium oxide at a low gas pressure has larger crystals and fewer crystal defects. On the other hand, it is considered that titanium oxide formed at a high gas pressure has smaller crystals and more crystal defects.

For example, in a platinum catalyst, it is known that a kink or a step, which is a defective portion on a crystal surface, becomes an active site. It is considered that a similar phenomenon occurs in a titanium oxide photocatalyst. When the film is formed at a low gas pressure, there is almost no kinks or steps, and the number of active sites is extremely small. On the other hand, when the film is formed at a high gas pressure, it is considered that the active deterioration hardly occurs because of many kinks and steps. Also,
In a film formed at a high gas pressure, a small crystal grain size and a large surface area are presumed to be factors that further increase the activity.

As a specific manufacturing method, titanium oxide is formed by a mixed gas plasma using titanium oxide as a target material, a mixed gas of argon and oxygen as a mixed gas into a sputtering apparatus. Alternatively, titanium oxide is formed by reactive sputtering using mixed gas plasma using metal titanium as a target material, a mixed gas of argon and oxygen as a mixed gas into a sputtering apparatus.

When titanium oxide is used as a target material, a photocatalytic film having photocatalytic activity can be formed under a wider range of film forming conditions than when titanium metal is used as a target material. There is an advantage that the characteristics do not change significantly even if the values vary. for that reason,
Known sputtering apparatuses and film forming conditions can be adopted.

However, when titanium oxide is used as the target material, the target material is reduced due to insufficient oxygen partial pressure during film formation, and the composition ratio of titanium and oxygen in the target material is likely to change. On the other hand, using metal titanium as a target has the advantage that the target material does not change. Moreover, the titanium metal target
Harder to crack and higher thermal conductivity than titanium oxide target. For this reason, even if the target surface is exposed to plasma during sputtering and the temperature increases, cracks due to thermal expansion hardly occur. Therefore, there is an advantage that maintenance is easier than when a titanium oxide target is used, and no crack is generated in the target even when the power during film formation is increased.

Here, in forming a titanium oxide film using a titanium metal target, it is necessary to form an anatase type crystal titanium oxide in order to form a highly active photocatalytic film. As a result of investigations by the inventors, it has been found that when titanium oxide is formed using a metal titanium target, titanium oxide of anatase type crystal can be formed only under limited film forming conditions.

That is, the film forming temperature and the ratio of oxygen in the mixed gas are related. When a film is formed at a substrate temperature lower than 350 to 360 ° C. as a film forming condition, the proportion of oxygen in the mixed gas is increased. When the film is formed at a substrate temperature higher than 350 to 360 ° C.,
Reduce the proportion of oxygen in the gas mixture. As a result, highly active anatase-type crystal titanium oxide is obtained. At this time, unless the total gas pressure is set to 10 mTorr or more, the photocatalytic activity deteriorates with time as described above.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a film forming apparatus used for manufacturing a photocatalyst according to an embodiment of the present invention. This is a magnetron sputtering device, 1 is a vacuum chamber, 2 is a target, 3 is an RF power supply or DC power supply, 4 is an exhaust port,
Reference numeral 5 denotes a gas inlet, and reference numeral 6 denotes a conductive holder for holding the substrate 7.

Then, a substrate 7 such as glass, aluminum whose surface is oxidized, or a film of polyester, polyethylene or the like is fixed to the holder 6, and the inside of the vacuum chamber 1 is evacuated. After heating the substrate 7 to a predetermined temperature, a mixed gas of an inert gas such as argon and helium and oxygen is introduced. At this time, the exhaust valve and the flow rate of the introduced gas are adjusted so that the partial pressure ratio between the inert gas and oxygen in the introduced gas becomes a predetermined value. Next, a high-frequency voltage or a DC voltage is applied to the target 2 made of titanium oxide or metal titanium, and a film of titanium oxide is formed on the substrate 7. Thus, a photocatalytic film made of titanium oxide is formed on the substrate 7. When a metal corresponding to a metal oxide such as zinc oxide, tungsten oxide, vanadium oxide, or zirconium oxide is used for the target 2, a photocatalytic film made of the sputtered metal oxide is formed.

When the film is formed by the sputtering method, if the gas pressure of the mixed gas is 10 mTorr or less, the photocatalytic activity deteriorates with time.
By setting it higher than orr, the photocatalytic activity hardly deteriorates with time, and the photocatalytic activity is also improved. If the pressure is at least 20 mTorr or more, the deterioration can be surely prevented, and a large photocatalytic activity can be obtained.

When titanium oxide is used as the target, anatase-type crystal titanium oxide can be obtained irrespective of the temperature and the mixed gas, except for high gas pressure as a film forming condition. On the other hand, when metal titanium is used as the target, in order to obtain anatase-type crystal titanium oxide, the temperature during film formation and the oxygen partial pressure of the mixed gas must be regulated. As the film forming conditions, the substrate temperature during film formation was set to 35
0 ° C. or less, the proportion of oxygen in the mixed gas is 30% or more, or the substrate temperature is 360 ° C. or more, and the proportion of oxygen in the mixed gas is 35% or less. It was confirmed that a highly active anatase-type crystal titanium oxide can be obtained by using any of these film forming conditions.

[0027]

The present invention will be described below in more detail with reference to examples and comparative examples. In each of the examples and comparative examples, the substrate size was set to 6 cm × 6 cm, and the film formation time was adjusted so that the film thickness became 0.6 μm.

[0028]

[Table 1]

(Example 1) Barium borosilicate alkali-free glass having a smooth surface as a substrate and RF as a film forming apparatus
A titanium oxide film was formed using a magnetron sputtering apparatus, titanium oxide having a purity of 99.9% or more as a target material, and a mixed gas of argon and oxygen as an introduction gas. Table 1 shows the film forming conditions.

First, the inside of the vacuum chamber to which the substrate was attached was evacuated, the substrate was heated to 300 ° C., and a mixed gas of argon and oxygen was introduced. The exhaust valve and the flow rate of the introduced gas were adjusted so that the partial pressure ratio of argon and oxygen in the mixed gas was 89/11. A high-frequency voltage was applied to the target, and a film was formed at a total gas pressure of 20 mTorr and an RF power of 200 W.

(Example 2) Titanium oxide was formed in the same manner as in Example 1 under the film forming conditions shown in Table 1. However, the oxygen partial pressure was set to 50% higher than in Example 1.

Example 3 A film of titanium oxide was formed in the same manner as in Example 1 under the film forming conditions shown in Table 1. However, the substrate temperature was set to 400 ° C. higher than that in Example 1, and the oxygen partial pressure was set to 50
%.

Comparative Example 1 A film of titanium oxide was formed in the same manner as in Example 1 under the film forming conditions shown in Table 1. However, the total gas pressure was set to 8 mTorr lower than that in Example 1, but the oxygen partial pressure was the same.

[0034]

[Table 2]

Example 4 A barium borosilicate alkali-free glass having a smooth surface was used as a substrate, and DC was used as a film forming apparatus.
A titanium oxide film was formed by reactive sputtering using a magnetron sputtering apparatus, titanium metal having a purity of 99.9% or more as a target material, and a mixed gas of argon and oxygen as an introduction gas. Table 2 shows the film forming conditions.

First, the inside of the vacuum chamber to which the substrate was attached was evacuated, the substrate was heated to 300 ° C., and a mixed gas of argon and oxygen was introduced. The exhaust valve and the flow rate of the introduced gas were adjusted so that the partial pressure ratio of argon and oxygen in the mixed gas became 60/40. A DC voltage was applied to the target, and a film was formed at a total gas pressure of 20 mTorr and a DC power of 100 W.

(Comparative Example 2) Under the film forming conditions shown in Table 2, a titanium oxide film was formed in the same manner as in Example 4. However,
Although the oxygen partial pressure was lower than in Example 4, the total gas pressure was the same.

(Comparative Example 3) Under the film forming conditions shown in Table 2, a titanium oxide film was formed in the same manner as in Example 4. However,
The total gas pressure was lower than in Example 4, but the oxygen partial pressure was the same.

[0039]

[Table 3]

Example 5 A titanium oxide film was formed under the film forming conditions shown in Table 3 using a titanium target in the same manner as in Example 4. However, set the substrate temperature as high as 400 ° C,
The ratio of the oxygen partial pressure was reduced to 8%.

(Comparative Example 4) Under the film forming conditions shown in Table 3, a titanium target was used and the substrate temperature was 400
The temperature was raised to a temperature of ° C., and a film of titanium oxide was formed. However, the ratio of the oxygen partial pressure was set as high as 40%.

Comparative Example 5 Titanium alkoxide was applied on a barium borosilicate alkali-free glass having a smooth surface and fired (500 ° C., 1 hr) to form a titanium oxide film. Coating and firing were repeated until the film thickness became 0.6 μm. The substrate used was 6 cm × 6 cm, similarly to the sample on which titanium oxide was formed by the sputtering method.
(36 cm ² ).

The photocatalyst samples obtained in Examples 1 to 5 and Comparative Examples 1 to 5 were separately placed in a 27-liter container, and acetaldehyde, one of the malodorous substances, was injected to a concentration of 120 ppm. Next, using a 6 W black light, the photocatalyst on the sample surface was irradiated with ultraviolet rays, and the time required for the acetaldehyde concentration to decrease to 10 ppm was measured. The evaluation of each sample was started within 2 hours of film formation, and was evaluated again 14 days after film formation. Further, the crystal state of each sample was examined with an X-ray diffractometer. Table 4 shows the above results.

[0044]

[Table 4]

In the samples of Comparative Examples 1 and 3 in which the gas pressure during film formation was low, acetaldehyde could be decomposed immediately after film formation.
Almost no activity was found in the measurement 14 days after the film formation, and acetaldehyde could not be decomposed.
On the other hand, in all of the samples of Examples 1 to 5 in which the gas pressure during film formation was high, the ability to decompose acetaldehyde did not decrease even after 14 days of film formation. That is, deterioration of the photocatalytic activity was not observed. Further, acetaldehyde was decomposed in half the time as compared with the sample of Comparative Example 5 in which a titanium oxide film was formed from a titanium alkoxide by a sol-gel method.

Using a titanium oxide target, 10 mTo
In the samples of Examples 1 to 3 in which film formation was performed at a high gas pressure exceeding rr, the oxygen partial pressure in the mixed gas of argon and oxygen was changed to 11% and 50%, and the substrate temperature was changed to 300 ° C and 400 ° C. Also crystallized into anatase type under any conditions, and high activity was obtained.

Further, a metal titanium target was used as a target material at the time of sputtering, and the substrate temperature was set at 30 ° C.
0 ° C, the partial pressure of oxygen in the mixed gas of argon and oxygen is 3
The sample of Comparative Example 2 set to less than 0% does not decrease in activity over time, but has a crystalline state of amorphous and has a slow rate of decomposing acetaldehyde as 9.2 hours. On the other hand, the sample of Example 4 in which only the oxygen partial pressure during film formation was increased to 30% or more under the same film formation conditions was an anatase type crystal, and the decomposition time of acetaldehyde was 1.5 hours, about 1 / Acetaldehyde could be decomposed in 6 hours.

As in the case of Example 4, a metal titanium target was used as a target material during sputtering, the substrate temperature was increased to 400 ° C., and the oxygen partial pressure in the mixed gas of argon and oxygen was set to 40% or more. Although the activity of the sample of Comparative Example 4 does not decrease with time, the crystalline state is amorphous, and the rate of decomposing acetaldehyde is as low as 8.7 hours. On the other hand, the sample of Example 5 in which only the oxygen partial pressure during film formation was reduced to 35% or less under the same film formation conditions was an anatase type crystal, and the decomposition time of acetaldehyde was 1.5 hours, about 1 / Acetaldehyde could be decomposed in 6 hours.

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.

[0050]

As is apparent from the above description, according to the present invention, the gas pressure at the time of performing sputtering is 10 mT.
Since it is higher than orr, a highly reliable photocatalyst without deterioration of photocatalytic activity with time can be obtained.

Further, by employing the sputtering method,
There are the following advantages. That is, in the binder method,
There is no problem that the photocatalyst is buried in the binder and the activity is reduced. When a binder is used, the film needs to be made porous so that the photocatalyst is not buried, but it becomes difficult to increase the adhesion. However, a large activity can be obtained even if a relatively dense film is formed by the sputtering method. Further, a film having a large photocatalytic activity can be formed as compared with the sol-gel method.

As a sputtering target material, titanium oxide or titanium metal can be used. However, when titanium oxide is used as a target material, a highly active photocatalyst can be obtained under a wide range of film forming conditions. In addition, the quality is stable even when the film forming conditions vary.

On the other hand, when metallic titanium is used as the target material, it can be produced by setting the film forming conditions in a specific range, and highly active anatase-type titanium oxide can be obtained. In addition, since cracks due to a temperature difference and a change in temperature are unlikely to occur, high power can be applied, a film formation time can be reduced, and manufacturing efficiency can be increased. In addition, since the composition of the target material does not easily change, maintenance is easy and a highly active photocatalyst can be stably manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a film forming apparatus used for manufacturing a photocatalyst according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Target 3 RF power supply or DC power supply 4 Exhaust port 5 Gas inlet 6 Holder 7 Substrate

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kuraichi Ogawa 2-7-1, Ayumino, Izumi City, Osaka Prefecture Inside the Osaka Prefectural Institute of Advanced Industrial Science and Technology (72) Tsutomu Yotsuya 2-7-1, Ayumino, Izumi City, Osaka Prefecture No. 1 Inside the Osaka Prefectural Institute of Industrial Science and Technology (72) Inventor Toshinori Nosaka 2-7-1, Ayumino, Izumi-shi, Osaka Prefecture F-term inside the Osaka Prefectural Institute of Industrial Science and Technology CA10 CA17 DA06 EA08 FB02 FC02 FC07 4K029 AA09 AA24 BA48 BB01 BD00 CA01 DC03 DC05

Claims (5)

[Claims] When a photocatalytic film made of a metal oxide is formed on a substrate by a sputtering method, an introduced gas is 10 mTo
A method for producing a photocatalyst, wherein the gas pressure is higher than rr. 2. The photocatalyst according to claim 1, wherein a titanium oxide is used as a target material, and a mixed gas of an inert gas and oxygen is used as an introduction gas to form a photocatalyst film made of titanium oxide. Production method. 3. A method of forming a photocatalytic film by using titanium as a target material, using a mixed gas of an inert gas and oxygen as an introduction gas, and generating titanium oxide having an anatase crystal structure by reactive sputtering. A method for producing a photocatalyst according to claim 1. 4. The method according to claim 1, wherein the substrate temperature during film formation is 350 ° C. or less.
The method for producing a photocatalyst according to claim 3, wherein the proportion of oxygen in the mixed gas is 30% or more. 5. The method according to claim 1, wherein the substrate temperature during the film formation is 360 ° C. or higher.
The method for producing a photocatalyst according to claim 3, wherein the proportion of oxygen in the mixed gas is 35% or less.