Interfacial structure and properties of TiO2 phase junction studied by DFT calculations

Abstract Mixed-phase (i.e. phase junction) TiO2 has been widely used in commercial photocatalysis applications, because of its excellent photocatalytic performance. However, the interfacial composition, micro-structure, and properties of mixed-phase TiO2 are not fully understood so far. Consequently, the phase transition process TiO2 from anatase to rutile is still not entirely clear; and there is no consensus on the mechanism of mixed-phase enhancing photocatalytic performance of TiO2. In this article, 16 interface models for TiO2 phase junctions were constructed by the low-index surfaces of TiO2 with anatase and rutile phases. The interfacial energy, microstructure, electronic structure and properties have been systematically calculated and analyzed. Based on the interfacial formation energy and the configuration of [TiO6] octahedron at A/R interface, the phase transition of TiO2 is most likely to occur at the interface between anatase (110) plane and rutile (011) plane, owing to the favorable interface formation energy and the smallest deformation of [TiO6] octahedrons. However, because the migration direction of photo-generated carriers is opposite to the direction of the built-in electric field at the A/R interface in A(110)/R(011) phase junction, the hetero-direction migration of photo-generated electron-hole pairs will be prevented. Thereby, the existence of A(110)/R(011) phase junction is unfavorable to improve the photocatalytic performance. On the other hand, when the calcination temperature rises, the favorable phase junctions (such as A(110)/R(001) phase junction) gradually occupies the growth advantage, which can improve the photocatalytic performance of TiO2. This is a possible explanation for the excellent photocatalytic properties of Degussa P25 with mixed-phase.