How to explain the mechanism of nano-semiconductor catalytic treatment of wastewater

Photocatalysis is one of the unique properties of nano-semiconductors. As far as anatase nano-TiO _ 2 photocatalyst is concerned, the energy band structure of its particles consists of a low-energy valence band filled with electrons and an empty high-energy conduction band, and there is a forbidden band between the valence band and the conduction band. When the photon energy is equal to or greater than the forbidden band energy (3.2eV) of TiO2 _ 2, especially under ultraviolet irradiation, electrons in the valence band will be excited to transition to the conduction band, thus generating highly active photogenerated holes (h+) and photogenerated electrons (e-) in the valence band and the conduction band respectively. Photogenerated holes are oxidizing, while photogenerated electrons are reducing. At this time, there are two possibilities for h+ and e-. One is that they combine to release absorbed light energy in the form of heat, which reduces the photocatalytic efficiency. Second, under the action of external electric field, h+ and e- are separated and migrated to different positions on the particle surface, and the absorbed light energy is converted into chemical energy. Experiments show that O2 adsorbed on the surface of TiO2 _ 2 can absorb e- reaction and produce peroxide ion free radicals. At ph value