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].