Comparison of Photocatalytic Properties of Nanometer Tungsten Oxide

Nanotungsten trioxide is a typical N-type semiconductor functional material with large specific surface area, stable chemical properties, and wide band gap (2.2 ~ 2.8eV), can be said that tungsten trioxide is a natural beauty of photocatalytic material in the near-ultraviolet and visible light region has a strong absorption capacity, and good stability.

It can be known from the photocatalytic reaction mechanism that the photocatalytic reaction is a redox reaction between a strongly polar hydroxyl radical (-OH) generated by the reaction of photogenerated electrons or holes on the surface of a catalyst with a substance adsorbed on the surface of the catalyst. For photogenerated electrons and holes, the energy level due to oxygen vacancies can serve as the electron trapping level, which can reduce the recombination of photogenerated electrons and holes to a certain extent, so as to enhance the catalytic effect of the semiconductor photocatalyst. It is well known that the real chemical expression of tungsten oxide is WO₃-X, and tungsten oxide has three common chemical types: tungsten, blue tungsten and violet tungsten.

Yellow tungsten oxide, blue tungsten oxide and purple tungsten oxide were prepared by hydrogen reduction. By SEM scanning, we can see that WO_2.9 and WO_2.72 have larger specific surface area than WO₃. In the photocatalytic reaction under the same conditions, the contact area between them and organic pollutants is greater, and the photocatalytic effect is further improved.

Taking photocatalytic methylene blue solution as an example, we found that the color depth of methylene blue solution varies with the change of tungsten oxide concentration. The greater the concentration is, the deeper the color is. The efficiency of photodecomposition of methylene blue by photocatalyst can be characterized by measuring the decolorization rate after a certain period of photocatalysis. The results showed that photocatalytic activity of methylene blue with WO_2.9 nanopowder and W_2.72 nanopowder with obvious oxygen deficiency was significantly higher than that of WO₃ with stoichiometry, under the same conditions, the order of photocatalytic activity of the three kinds of tungsten oxide nano / micro structure on methylene blue solution is: WO_2.72 nanoparticles> WO_2.9 nanoparticles> WO₃ micro particles.

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