Role of surface termination in forming type-II photocatalyst heterojunctions: the case of TiO/BiVO.

In this work we investigate TiO and BiVO nanostructures by means of density functional theory (DFT) calculations, to provide an estimate of the band alignment in TiO/BiVO interfaces, highly active in photo-electrochemistry and photocatalytic water splitting. Calculations were carried out with both DFT range separated and self-consistent dielectric dependent hybrid functionals (HSE06 and PBE0). The impact of systems' size has been investigated. The converged electronic levels of TiO and BiVO surfaces have been used to predict the band alignment in TiO/BiVO heterostructures. Results indicated that when TiO (101) surface is matched with BiVO (110), a type-II alignment is obtained, where the band edges of BiVO are higher in energy that those of TiO. This picture is favorable for charge-carriers separation upon photoexcitation, where electrons move toward TiO and holes toward BiVO. On the contrary, if TiO (101) is interfaced to BiVO (010) the offset between the band edges is negligible, thus reducing the driving force toward separation of charge carriers. These results rationalize the dependence on the facet's exposure of the observed photocatalytic performances of TiO/BiVO composites, where the TiO (101)/BiVO (110) interface outperforms the TiO (101)/BiVO (010) one.