Preparation of Tungsten Trioxide as Photocatalysis Material

Photocatalysis is a main measure to control environmental pollution in the future. Since the first use of titanium dioxide photocatalyst by the Japanese in 1972, the field of photocatalysis has experienced nearly half a century of development. At present, photocatalyst materials can be used in various fields and can be used for sewage treatment, air treatment, home environment purification, and even power generation.

It is well known that titanium oxide would only be excited in the ultraviolet environment; sufficient photocatalytic performance cannot be obtained in an indoor field that receives a small amount of ultraviolet light. Thus, tungsten oxide becomes another popular photocatalyst material other than titanium oxide. 

Among the tungsten oxides, tungsten trioxide (WO3) and tungsten trioxide-based tungstate are main materials for photocatalysts because of their excellent photocatalytic properties and are stable in air at normal temperature. However, WO3 has a complicated crystal structure including monoclinic, rhombic, triclinic, hexagonal, cubic, and tetragonal, and the crystal structure is easily changed even if a small pressure is applied thereto. Therefore, the photocatalytic performance of tungsten trioxide is unstable.

Although the crystal structure of the WO3 powder produced by heating ammonium metatungstate or the like in air is mainly monoclinic when the tungsten trioxide WO3 powder is treated to make it finer and improve the photocatalytic performance, the tungsten trioxide WO3 The crystal structure of the fine powder becomes mainly three oblique due to the pressure applied by the depolymerization treatment. Further, the finer the fine particles of the photocatalyst, the larger the specific surface area, and the more remarkable the effect. However, although the tungsten oxide powder particles can be ground to some extent by the depolymerization treatment, the effect of the conventional heating ammonium metatungstate method to produce tungsten trioxide WO3 powder particles does not seem to be satisfactory.

For this reason, the process of preparing tungsten trioxide for photocatalysis is different from the process of preparing ordinary tungsten oxide powder. It is understood that the production methods include: sublimation step, inductively coupled plasma treatment, arc discharge treatment, laser treatment and electrons. Beam processing and heat treatment steps.

Preparation of photocatalysis material is as follows:

A tungsten metal powder having an average particle diameter of 1 μm was prepared as a raw material powder. In the sublimation step, while the atmosphere (air) was used as the carrier gas, the raw material powder was sprayed into the R plasma to adjust the average flow rate to 2 m/s, and the raw material powder was sublimated while performing the oxidation reaction. The tungsten trioxide powder is thus obtained by the sublimation step.

Then, the obtained tungsten trioxide powder was subjected to a heat treatment step of 600 ° C for 2 hours under an air atmosphere. Thus, a tungsten trioxide powder for a photocatalyst was obtained.

The obtained tungsten trioxide powder for photocatalyst was measured and the following results were obtained: a BET specific surface area of ​​14 m 2 /g and a particle size distribution (D90 - D10) / D50 of 0.93. Further, it has been found that the crystal phase is composed only of a monoclinic crystal, an orthorhombic crystal, and a slant crystal, and can be used as a photocatalyst material.

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