Effect by Elemental Doping on Band Structure of Tungsten Trioxide

Tungsten trioxide photocatalysts are widely used in various fields because of their good photosensitivity, good electron transport properties, and excellent photostability.

However, due to the lower band gap of tungsten trioxide, the utilization of visible light is not high. In addition, since tungsten trioxide has a lower conduction band bottom, it is not possible to photo catalytically decompose water to water using tungsten trioxide. For photocatalytic degradation, the lower conduction band will lead to the photoelectron single electron reduction oxygen reaction is subject to certain restrictions. So that the consumption of photogenerated electrons is hindered, thereby reducing the utilization rate of photogenerated holes. Studies have shown that for tungsten trioxide, the photoelectron will undergo two competing four-electron oxygen reduction processes.

In this regard, doping with other elements to adjust the energy band structure of tungsten trioxide to make its conduction band and valence band to meet the required potential has become a potentially effective method. At the same time, it is also noticed that due to the doping, the crystal lattice of tungsten trioxide will be distorted, and the change of the crystal structure will also cause the change of the energy band structure of the material.

Doping elements are mainly divided into metal doping, non-metallic doping and metal - non-metallic doping, three for the tungsten trioxide band structure has a different impact. For the equivalent Mo or Cr to replace the lattice W, tungsten trioxide conduction band position down. When S is substituted for O, S forms a localized occupation state at the top of the valence band of tungsten trioxide, resulting in narrowing of the bandgap of tungsten trioxide and upward shift of the conduction band of tungsten trioxide.

It is therefore possible to increase the photocatalytic activity of tungsten trioxide. When W is replaced by Ti, Zr or Hf in the lower valence state, the forbidden band width of tungsten trioxide becomes wider and the conduction band position shifts up. However, substitution of W with a lower valent ion will form a compensation defect. For example, oxygen vacancy formation energy of Hf-doped tungsten trioxide may be negative, so oxygen vacancies will be formed. This will cause both the conduction band and the valence band of tungsten trioxide to move in the direction of high energy and their band gap will be reduced.

• < Prev
• Next >