Interfacial micro-structure and properties of TiO 2 /SnO 2 heterostructures with rutile phase: A DFT calculation investigation

Composite photocatalyst with heterostructure is often recognized as an effective strategy to achieve efficient charge separation and increase carrier concentration. In this study, the (1 1 0) and (1 0 1) surfaces of TiO2 and SnO2 were chosen to construct the abrupt and graded TiO2/SnO2 hetero-structures. The interface properties and band offsets of four heterostructures are calculated and analyzed in detail. It was found that the graded heterostructures are more stable and easier to preparation than the abrupt heterostructures, the charge depletion and accumulation occur at both ends of the transition layer. The interfacial electric field caused by this effect allows the photo-generated electron-hole pairs to be easily separated and transferred in the opposite direction at the interface, which is important for improving the photocatalytic activity. In addition, the intrinsic mechanism of the four hetero-structures is discussed according to the analysis of the band offset, which belongs to the type II heterostructures. For TiO2/SnO2-(1 1 0) heterostructure, the photo-generated electrons transfer from the conduction band of TiO2 to the conduction band of SnO2, while the photo-generated holes transfer from the SnO2 to the valence band of TiO2. This phenomenon leads to the accumulation of the photo-generated electrons in the conduction band of TiO2, accumulation of the photo-generated holes in the valence band of SnO2. In short, the graded heterostructure has more favorable effects to enhance the photocatalytic activity than that of the abrupt heterostructure. The internal electric field at the TiO2/SnO2 interface acts as a selector for photo-generated carriers, which may lead to higher photocatalytic quantum efficiency and carrier concentration under the same external conditions. These intrinsic photocatalytic mechanisms and the interpretation of the interfacial microscopic properties of heterostructure can be used as a basis for the design of the sensing devices and composite photocatalysts with heterostructures.