Crystalline tungsten oxide is tungsten oxide powder of crystal grain, which is the largest particle in tungsten oxide powder, light yellow (yellow tungsten oxide) or blue (blue tungsten oxide) or brown (tungsten dioxide) or violet (violet tungsten oxide) in color.
The crystal size has a very important effect on the material properties of tungsten oxide, such as photocatalytic material properties. If the particle size of tungsten oxide powder is smaller than the thickness of space charge layer, the time for the photon-generated carrier to diffuse to the tungsten oxide surface will shorten as the particle size decreases, thereby greatly increasing the utilization of photo-induced carrier. 
At the same time, the reduction of particle size in tungsten oxide will increase the specific surface area. Thereby increasing the active sites of tungsten oxide and the adsorption capacity of target. In addition, the size decrease of tungsten oxide will widen the forbidden band width. This means that the oxidation-reduction ability of tungsten oxide is enhanced so that its photocatalytic reactivity can be enhanced.
From the size of the structure unit, we can study arrangement rules and crystal size of tungsten oxide.
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