s-p orbital hybridization: a strategy for developing efficient photocatalysts with high carrier mobility

Photocatalysis has not only invigorated the field of energy conversion materials, but also is leading to bright prospects for application in the environmental purification field [1]. Akira Fujishima and Kenichi Honda [2] first reported photocatalytic water splitting on a TiO2 semiconductor electrode under ultraviolet (UV) light in 1972. In semiconductor photocatalysts, electrons are excited from valence band maximum (VBM) to conduction band minimum (CBM) under light irradiation, and then trigger the photocatalytic process [3]. Considering solar-light-driven photocatalysis, semiconductor photocatalysts should possess a narrow band gap and appropriate band positions [4]. It was also found that photoinduced charge generation, separation, and transportation determine activities of semiconductor photocatalysts. High mobility of charge carriers facilitates these processes, which can be achieved in the photocatalysts with highly dispersive bands, because their effective masses of charge carriers are small. Usually, the antibonding hybridization/coupling is predominantly responsible for the band dispersion, especially for oxides. For example, Sn-5s/O- 2p anti-bonding coupling in VBM of Sn2+ oxides, Cu-3d/O-2p anti-bonding coupling in VBM of Cu+ oxides and anti-bonding coupling in CBM of most of semiconductors [5-9]. Especially, s-p orbital hybridization is found to improve the performance of photocatalysts by affecting their band structures [10,11].