JP4437695B2 - Method for producing nitrogen-containing metal oxide photocatalyst - Google Patents

Description

  The present invention relates to a method for producing a nitrogen-containing metal oxide photocatalyst.

  Metal oxide semiconductors are known as photocatalysts that exhibit oxidation resolution and hydrophilicity when irradiated with light.

  In recent years, metal oxide semiconductors have attracted attention for their photocatalytic action, and are used in various applications such as purification of air and water, antibacterial properties, and antifouling.

  However, metal oxide semiconductors that stably exhibit high photocatalytic activity in the natural environment have a large band gap, so that they exhibit photocatalytic activity when irradiated with ultraviolet light, but light emitted by fluorescent lamps and the like that emit very little ultraviolet light. Irradiation shows little photocatalysis. Therefore, when a metal oxide semiconductor is used as a catalyst for indoor use, there is a problem that a special light source that emits ultraviolet light must be provided separately.

  In order to solve this problem, visible light responsive photocatalysts that exhibit photocatalytic action not only by ultraviolet light but also by visible light irradiation have already been proposed (see, for example, Patent Documents 1 and 2).

Patent Document 1, by making oxygen defects by processing the oxide semiconductor with a hydrogen gas plasma or rare gas element plasma, how to grant visible light response has been proposed. However, this method is industrially disadvantageous because the amount that can be processed at one time is small.

  Patent Document 2 proposes a method of imparting visible light responsiveness by mixing nitrogen with urea and heating the oxide to cause nitrogen to enter the oxide. This method is industrially advantageous because a large amount of treatment is possible at one time.

Republished patent WO00 / 10706 JP 2002-154823 A

  However, when the effect of the catalytic action of the visible light responsive photocatalyst produced by the method of Patent Document 2 was confirmed, almost no catalytic action was exhibited by fluorescent lamp irradiation. This is presumably because nitrogen has not effectively penetrated into the oxide. In addition, it was confirmed that the ultraviolet light characteristics were significantly deteriorated. This is presumably because crystal growth was promoted by heat treatment and the specific surface area was reduced.

  An object of the present invention is to produce a nitrogen-containing metal oxide photocatalyst that exhibits high activity even when irradiated with a fluorescent lamp.

  Another object of the present invention is to produce a nitrogen-containing metal oxide photocatalyst excellent in ultraviolet light characteristics in addition to exhibiting high activity even when irradiated with a fluorescent lamp.

The method for producing a nitrogen-containing metal oxide photocatalyst according to claim 1 includes a step of mixing at least amorphous zinc hydroxide and urea, and a step of heating the mixture .

According to a second aspect of the invention, the method for producing nitrogen-containing metallic oxide photocatalyst according to claim 1, carried out within the heating of the mixture was cut off the outside air from entering the space.

According to the first aspect of the present invention, by heating a mixture of at least amorphous zinc hydroxide and urea, the amorphous zinc hydroxide is decomposed into amorphous zinc oxide and water and generated. As a result of the reaction with water, urea is decomposed to generate ammonia. Generated ammonia uniformly adsorbed in amorphous zinc oxide, drift around the amorphous zinc oxide become the excess ammonia that was not adsorbed ammonia gas, amorphous in such a ammonia atmosphere Since zinc oxide crystallizes, nitrogen effectively penetrates into the zinc oxide crystal during the crystallization process. Thereby, the nitrogen-containing metal oxide photocatalyst which shows high activity by fluorescent lamp irradiation is obtained .

Further, according to the first aspect of the invention, in order to penetrate the crystallized simultaneously with nitrogen from the amorphous state, unlike the case already is entering the nitrogen by heating zinc oxide is crystallized, excessive crystal Reduction of the specific surface area due to growth can be avoided, and the ultraviolet light characteristic which is the catalytic performance by ultraviolet light is maintained.

According to the second aspect of the present invention, when a mixture of at least amorphous zinc hydroxide and urea is heated, the atmosphere around the amorphous zinc oxide is surely an ammonia atmosphere, and the zinc oxide crystal enters. Increases the nitrogen penetration effect.

An embodiment will be described. First, an amorphous metal hydroxide and urea are prepared. The amorphous metal hydroxide can be produced by a wet method. A commercially available urea can be used.

  Next, an amorphous metal hydroxide and urea are mixed. The mixing ratio is not particularly limited, but when the amount of urea is small, the amount of ammonia generated is small, so that the amount of nitrogen entering the metal oxide described later becomes insufficient. Conversely, if the amount of urea is large, urea cannot be completely decomposed and remains as an impurity. Therefore, it is desirable to set the mixing ratio in consideration of the amount of water required for complete decomposition of urea and the amount of water generated from the amorphous metal hydroxide by heating.

  Next, the mixture (a mixture of amorphous metal hydroxide and urea) is heated. The heating temperature should just be more than the temperature which a metal oxide crystallizes. However, if the heating temperature is too low, urea remains as impurities without being decomposed. On the other hand, if the heating temperature is too high, the crystal grain size of the metal oxide increases and the specific surface area decreases. Therefore, the heating temperature is preferably in the range of 300 to 800 ° C.

  The heating method is not particularly limited, but it is preferable to heat in a space where oxygen does not enter. The reason is to prevent ammonia and oxygen from reacting to generate harmful nitrogen oxides. Although heating may be performed while supplying an inert gas or ammonia gas into the space, the manufacturing cost increases. Therefore, in consideration of prevention of generation of nitrogen oxides and production costs, it is preferable to heat in a sealed space. Furthermore, in consideration of safety, it is desirable to provide a check valve in the direction in which the gas generated inside is exhausted.

  The heating time depends on the heating temperature and cannot be limited. However, if the heating time is short, the amount of nitrogen entering the metal oxide becomes insufficient. Conversely, if the heating time is long, the crystal grain size of the metal oxide Increases and the specific surface area decreases. Therefore, the heating time is preferably several minutes to several hours.

  The reaction when a mixture of amorphous metal hydroxide and urea is heated will be described. By mixing and heating the amorphous metal hydroxide and urea, first, the amorphous metal hydroxide is decomposed into an amorphous metal oxide and water. By reaction with the generated water, urea is completely decomposed and ammonia is efficiently generated. The generated ammonia is uniformly adsorbed on the amorphous metal oxide. Excess ammonia that has not been adsorbed becomes a gas (ammonia gas) and drifts into the space, and amorphous metal oxides crystallize in such an ammonia atmosphere, so nitrogen is oxidized into metal during the crystallization process. It can effectively penetrate into the crystal of the object.

  Furthermore, since nitrogen is introduced at the same time as crystallization, a reduction in specific surface area due to excessive crystal growth can be avoided unlike in the case where nitrogen is introduced by heating an already crystallized oxide.

  Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

<Example 1>
1 g of amorphous zinc hydroxide prepared by a wet method and 0.5 g of commercially available urea are mixed and stirred on a ceramic dish, and heated at 500 ° C. for 1 hour in an electric furnace where oxygen intrusion is blocked. A photocatalyst (nitrogen-containing metal oxide photocatalyst) was obtained.

  0.2 g of the catalyst (nitrogen-containing metal oxide photocatalyst) obtained in this way was laid flat and uniformly in a case of 15 mm × 40 mm, and it was placed in a quartz tube with a diameter of 20 mm and a length of 200 mm to emit light. A NO gas decomposition test was conducted by irradiating and diluting NO gas with a concentration of 1 ppm at 0.8 liters per minute for 1 hour. As a light source, a 100 W UV lamp and a 27 W fluorescent lamp were used, and a chemiluminescent nitrogen oxide concentration measuring device (APNA-360 manufactured by Horiba, Ltd.) was used for reaction gas measurement.

<Comparative Example 1>
1 g of amorphous zinc hydroxide prepared by a wet method was placed on a ceramic dish and heated at 500 ° C. for 1 hour in an electric furnace where oxygen intrusion was blocked to obtain a photocatalyst.

  Using 0.2 g of the photocatalyst thus obtained, a NO gas decomposition test was performed in the same manner as in Example 1.

<Comparative example 2>
Using 0.2 g of commercially available zinc oxide, a NO gas decomposition test was performed in the same manner as in Example 1.

<Comparative Example 3>
1 g of commercially available zinc oxide and 0.5 g of commercially available urea were stirred and mixed on a ceramic dish, and heated at 500 ° C. for 1 hour in an electric furnace where oxygen intrusion was blocked to obtain a photocatalyst.

  Using 0.2 g of the photocatalyst thus obtained, a NO gas decomposition test was performed in the same manner as in Example 1.

  Table 1 shows the test results obtained in Example 1 and Comparative Examples 1 to 3. The test results are shown as the ratio of NOx converted to the total amount of NO gas supplied in the one hour test.

  In the case of Comparative Example 3, the result of Comparative Example 2 that was used without treatment with commercially available zinc oxide was compared with Comparative Example 3 in which commercial zinc oxide and urea were mixed and heat-treated. It can be seen that there is a problem that the catalytic action in the lamp irradiation is not exhibited and the ultraviolet light characteristics are deteriorated as compared with those before the heat treatment.

In contrast, in the case of the nitrogen-containing metal oxide photocatalyst of the present invention shown in Example 1, it can be seen that the catalytic action in the fluorescent lamp irradiation is expressed and the ultraviolet light characteristics are maintained.

Claims (2)

Mixing at least amorphous zinc hydroxide and urea ;
Heating the mixture ;
A method for producing a nitrogen-containing metal oxide photocatalyst comprising : The process according to claim 1 nitrogen-containing metal oxide photocatalyst according performed in the space heating blocked the entry of outside air in the mixture.