Review on charge transfer and chemical activity of TiO2: Mechanism and applications

Charge separation and transfer at the interface between two materials play a significant role in various atomic-scale processes and energy conversion systems. In this review, we present the mechanism and outcome of charge transfer in TiO₂, which is extensively explored for photocatalytic applications in the field of environmental science. We list several experimental and computational methods to estimate the amount of charge transfer. The effects of the work function, defects and doping, and employment of external electric field on modulating the charge transfer are presented. The interplay between the band bending and carrier transport across the surface and interface consisting of TiO₂ is discussed. We show that the charge transfer can also strongly affect the behavior of deposited nanoparticles on TiO₂ through built-in electric field that it creates. This review encompasses several advances of composite materials where TiO₂ is combined with two-dimensional materials like graphene, MoS₂, phosphorene, etc. The charge transport in the TiO₂-organohalide perovskite with respect to the electron-hole separation at the interface is also discussed.