JPH08252461A - Preparation of photocatalyst - Google Patents

Abstract

PURPOSE: To provide an easy method for preparing a photocatalyst which is strong and has high catalytic activity. CONSTITUTION: Metal or alloy containing titanium as a main component and 0-20wt.% of transition metal as a subordinate component, after being acid- treated with an inorganic acid, is heat-treated. The transition metal is selected from chromium, manganese, iron, cobalt, nickel, copper, zinc, rubidium and palladium; the inorganic acid is selected from hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, hydrofluoric acid, and hydrochloric acid; the heat treatment is conducted in air at 200-400 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a photocatalyst, and in particular, an organic chlorine compound represented by trichloroethylene or PCB, a humic acid, an agricultural chemical, heavy oil, a persistent organic compound such as benzene, NOx, NH ₃ , Alternatively, it relates to a simple method for producing a photocatalyst used for decomposing various substances such as malodorous components.

[0002]

2. Description of the Related Art A photocatalyst decomposes various organic substances by holes and electrons generated on the catalyst when it is irradiated with light including ultraviolet rays, and widely treats the environment regardless of the liquid phase or gas phase. Is used for. A typical composition of a photocatalyst having high catalytic activity is titanium oxide, and a general manufacturing method thereof is a sol-gel method. The sol-gel method is a method in which a titanium alkoxide solution is applied as it is or applied to a carrier material, dried, and then baked in air at 400 to 700 ° C., but application drying is required to form a photocatalyst layer having a predetermined thickness. Alternatively, the firing process needs to be repeated many times, which is a technique that requires a lot of labor and energy.

This photocatalyst has the following problems. When trying to increase the catalytic activity, the particle size becomes extremely small, which makes handling difficult. The cost of reagents used in the sol-gel method is high, the manufacturing process is complicated, and the energy consumption is large. On the other hand, for practical use of the powdery photocatalyst, it is necessary to separate the fine catalyst itself. In particular, when the target substance is in the liquid phase, membrane separation or the like is required, and the treatment process becomes complicated. Therefore, the immobilization of the catalyst is important. As an immobilization method, addition to a carrier,
Although coating, sintering, thermal spraying, and the like have been tried, there are problems in maintaining the catalytic activity of the immobilization layer, peeling resistance, abrasion resistance, and the like.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and provides a photocatalyst which is strong and has high catalytic activity.
It is an object to provide a simple manufacturing method.

[0005]

In order to solve the above problems, in the present invention, titanium is the main component and 0 to 20% wt.
In the method for producing a photocatalyst, the metal or alloy containing the transition metal as a subcomponent is acid-treated with an inorganic acid and then heat-treated. Next, the present invention will be described in detail. The composition of the titanium metal used in the present invention does not need to have an extremely high purity, and there may be other metals capable of forming an intermediate product similar to titanium by acid treatment. In some cases, it is possible to add a plurality of second components to form an alloy and enhance the catalytic ability. A transition metal is preferably used as the additive component from the viewpoint of affinity with titanium and reactivity with acid, and the addition amount thereof is preferably 0 to 20% by weight, and particularly preferably 2 to 10% by weight with respect to titanium. .

Transition metals include chromium, manganese,
Iron, cobalt, nickel, copper, zinc, rubidium and palladium can be appropriately selected. These components are mixed and dissolved in the matrix to form holes on the photocatalyst surface.
Promotes production. It is also possible to use a composite material in which such a material is carried on the surface of another type of carrier (for example, various metals, glass plates, etc.). It should be considered that the role of the acid treatment in the present invention is not the cleaning of the metal surface (removal of oxides, exposure of clean metal surface) but the production of another intermediate component. Therefore, a corrosive and oxidizing strong acid is used. An organic acid, which is a milder acid than an inorganic acid, has a weak oxidizing power, so that the titanium surface cannot be changed and a predetermined effect cannot be obtained even if it takes time. The details of the mechanism of acid treatment are not clear, and the optimum conditions have not been determined yet, but experimentally, hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, hydrofluoric acid,
One or more chloric acids may be used. The hydrofluoric acid and nitric acid-based etching agents used in the production of semiconductor electrodes are preferably used alone or in combination.

Higher acid treatment temperature (becomes a thermal inorganic acid)
Is preferable because the reaction rate is high and the processing time is short, but if it is too high, energy is consumed, so that it is usually preferable that the temperature is around room temperature. The acid treatment time is not too long and does not adversely affect the catalyst performance, but it is not economical because it results in dissolution loss of the metal component. On the other hand, if it is too short, the modification of the surface state is insufficient and there is an appropriate time. That time is
Depending on the composition of titanium, the type of acid, the temperature of the acid, etc.,
Since there is no standard for determining the optimum state, it is economically decided. Under normal conditions, it takes about 1 to 60 minutes. Although the heat treatment step in the present invention does not oxidize the surface of the clean metal with oxygen, oxygen interference is not particularly considered. Therefore, it is not necessary to strictly limit the heat treatment atmosphere, and the heat treatment step can be performed in air. Care must be taken because the composition / capacity of the resulting catalyst layer changes depending on the heat treatment temperature. In particular, there is a limit value on the high temperature side, and at 500 ° C. or higher, only products with low performance can be obtained. It takes a long time to oxidize at low temperature. Usually 200 ~
400 ° C is suitable. As general heat treatment conditions,
In air, at 300 ° C. for about 3 hours.

[0008]

The mechanism and mechanism of action of the present invention are often unclear because identification of intermediate products and final products is difficult and incomplete.
At present, it can be considered as follows. That is, the surface of titanium metal is modified by acid treatment to produce an intermediate product, which is changed by heat treatment to form a final product which is considered to be titanium oxide. This is because it is said that metallic titanium does not change in air and is oxidized into titanium dioxide at 610 ° C. or higher in oxygen for the first time (physical chemistry dictionary). In the present invention, the catalyst layer is heat-treated in air at about 300 ° C. Is generated, and metallic titanium is oxidized by nitric acid to become metatitanic acid (TiO ₂ · H ₂ O) (physical chemistry dictionary).

[0009]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Example 1 Process comparison (combination of acid treatment and heat treatment) As metal titanium, a pure titanium plate manufactured by Toho Tech Co., Ltd. (length 75 mm, width 25 mm, thickness 1 mm) was used as a test piece. The acid treatment was carried out by adding 1 part of the test piece to 100 ml of a mixture (composition, water: hydrofluoric acid: nitric acid = 50: 1: 1) at room temperature.
It was carried out by immersing the sheet for 25 minutes.

The firing treatment was carried out in air at 300 ° C. for 3 hours. Insert the test piece stored at room temperature into the electric furnace that reached the temperature of 300 ° C, and take it out of the furnace after a predetermined time,
It was cooled with room temperature air. The catalytic activity was evaluated by the photolytic ability of gaseous trichlorethylene (TCE) obtained by the following method. That is, diameter 35 mm, length 150 mm,
The test piece was placed in a cylindrical glass cell having a capacity of 144 ml with flanges at both ends, and the TCE concentration was 10 in the cell.
Air of 00 ppm was introduced, and a black light (8 20 W lamps) was irradiated from the surroundings while maintaining a distance of 60 mm. The TCE concentration after a predetermined time (10 minutes) was measured by FTIR and gas chromatography. The test piece was exchanged and the same experiment was conducted. The results are shown in Table 1 below.

[0011]

[Table 1] * A titanium plate supported by the sol-gel method on a glass plate of the same size as the test piece. (Coating / drying cycles, 20 times)

From the above results, the test piece manufactured by this method has photocatalytic activity (decomposition of TCE is not observed without irradiation with black light), and does not have catalytic activity unless both acid treatment and heat treatment are performed. It can be seen that the catalytic activity is equal to or higher than that produced by the sol-gel method. Separately from the above test, the peel resistance and abrasion resistance of the test piece were examined, and good results were obtained.

Example 2 (Influence of Acid Composition and Acid Treatment Time) A test piece was prepared under the condition that the acid composition and the treatment time were different from those of Example 1, and the catalytic ability was evaluated by the same evaluation method as in Example 1. evaluated. The results are shown in Table 2.

[Table 2] * A titanium plate supported by the sol-gel method on a glass plate of the same size as the test piece. (The number of times of coating / drying is repeated 20 times) From these results, the acid composition used is a corrosive or oxidizing strong acid (hydrofluoric acid, nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, chloric acid).
It is clear that even if the concentration is low, it takes a long time even if the concentration is low. Further, it can be seen that the catalytic ability is equal to or higher than that of the conventional method (glass plate-supported titanium oxide by the sol-gel method).

Example 3 (Influence of heat treatment temperature) A test piece was prepared under the condition that only the heat treatment temperature was different from that of Example 1, and its catalytic ability was evaluated by the same evaluation method as in Example 1. Table 3 shows the results.

[Table 3] * A titanium plate supported by the sol-gel method on a glass plate of the same size as the test piece. (Repeating / repeating times, 20 times) From these results, it is understood that the heat treatment temperature is preferably 200 to 400 ° C. Further, it can be seen that the catalytic ability is equal to or higher than that of the conventional method (glass plate-supported titanium oxide by the sol-gel method).

Example 4 Operating Conditions (Titanium Composition) A test piece was prepared under the condition that only the composition of the titanium plate was different from that of Example 1, and its catalytic ability was evaluated by the same evaluation method as in Example 1. The results are shown in Table 4.

[Table 4] * A titanium plate supported by the sol-gel method on a glass plate of the same size as the test piece. (The number of times of coating and drying is repeated, 20 times) From these results, it is found that the titanium plate composition to be used preferably has titanium as a main component and one or more transition metals as sub-components. Further, it can be seen that the catalytic ability is equal to or higher than that of the conventional method (glass plate-supported titanium oxide by the sol-gel method).

Example 5 Object to be Treated (Odor) Using the test piece manufactured in Example 1, the same experiment was conducted by changing only the object sample to air containing 20 ppm of acetaldehyde. The results are shown in Table 5.

[Table 5] * A titanium plate supported by the sol-gel method on a glass plate of the same size as the test piece. (Repeating / repeating times, 20 times) From these results, the catalyst of the present invention is effective for acetaldehyde, which is a representative of malodorous substances, and its ability is
It can be seen that it is equivalent to or better than that of the conventional method.

Example 6 Object to be Treated (Liquid Phase, Trichlorethylene) Using the test piece prepared in Example 1, the same experiment was conducted by changing only the object sample to groundwater containing 100 ppm of trichlorethylene. Table 6 shows the results.

[Table 6] * A titanium plate supported by the sol-gel method on a glass plate of the same size as the test piece. (Repeating / repeating times, 20 times) From these results, the catalyst of the present invention is effective for trichlorethylene, which is a representative substance of groundwater pollution, and its ability is equal to or higher than that of the conventional method. Recognize.

Example 7 Treatment Target (Liquid Phase, Microbial Sterilization) Using the test piece prepared in Example 1, the same experiment was conducted by changing only the target sample to groundwater containing 1,000 bacteria / ml of general bacteria. The results are shown in Table 7.

[Table 7] * A titanium plate supported by the sol-gel method on a glass plate of the same size as the test piece. (Repeating and drying times, 20 times) From these results, the catalyst according to the present invention is effective against general bacteria, which is a representative substance of microbial contamination, and its ability is equal to or higher than that of the conventional method. I understand.

Example 8 Usage form (liquid phase, trough, easy processing) The titanium plate manufactured under the conditions of Example 1 was gutter-shaped (width 300 m).
m, depth 200 mm, length 5 m) and used for the water collecting part of the coagulating sedimentation device used in water purification plants. As a target, a titanium plate processed to the same size was used. Table 8 shows the observation results after the outdoor installation for 3 months, and it was found that the catalyst according to the present invention has an effect of suppressing the generation of adherent microorganisms. Moreover, the production was easy, and no problems such as peeling occurred during use for several months.

[Table 8]

Example 9 Usage pattern (gas phase, catalyst plate shape, corrugated plate) From a titanium plate manufactured under the conditions of Example 1, corrugated plate (wave depth 2
0mm, pitch 20mm, length 500mm),
This corrugated plate was installed so as to surround a black light fluorescent lamp, and a cylindrical reactor (outer diameter 80 mm, length 600 mm)
Was configured. Five sets of this reactor were provided, the gas in the road tunnel was ventilated in series, and the NOx concentration was measured. An apparatus using a titanium plate was used as a comparative example. The results are shown in Table 9, and it was found that the catalyst according to the present invention has an effect of decomposing NOx. Moreover, the production was easy, and no problems such as peeling occurred when used for several months.

[Table 9]

[0021]

According to the present invention, a strong and high-performance photocatalyst can be provided at low cost. In addition to being practically applicable as a photocatalyst material, it can be used as it is as a semiconductor electrode for decomposing and sterilizing organic substances.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/02 ZAB B01J 23/34 ZABM 23/06 ZAB 23/44 ZABM 23/16 ZAB 23/70 ZABM 23/34 ZAB 23/72 ZABM 23/44 ZAB 37/08 23/70 ZAB B01D 53/36 J 23/72 ZAB ZABG 23/745 102D 23/755 B01J 23/74 301M 37/08 321M (72) Invention Author Koki Ito 156 Tokiwadai, Hodogaya-ku, Yokohama-shi, Kanagawa Yokohama National University (72) Inventor Go Yamanaka 156 Tokiwadai, Hodogaya-ku, Yokohama-shi, Kanagawa Yokohama National University

Claims (4)

[Claims] 1. A method for producing a photocatalyst, which comprises subjecting a metal or an alloy containing titanium as a main component and 0 to 20% by weight of a transition metal as a subcomponent to an acid treatment using an inorganic acid and then performing a heat treatment. Method. 2. The transition metal is chromium, manganese,
The method for producing a photocatalyst according to claim 1, which is one or more metals selected from iron, cobalt, nickel, copper, zinc, rubidium, and palladium. 3. The inorganic acid is one or more strong acids selected from corrosive or oxidizing hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, hydrofluoric acid or chloric acid. 1. The method for producing a photocatalyst according to 1 or 2. 4. The heat treatment is performed in air at 200 to 400.
The method according to claim 1, 2 or 3, which is carried out at a temperature of a predetermined temperature.
A method for producing the photocatalyst described.