Role of surface termination in forming type-II photocatalyst heterojunctions: the case of TiO2/BiVO4

In this work we investigate TiO2 and BiVO4 nanostructures by means of density functional theory (DFT) calculations, to provide an estimate of the band alignment in TiO2/BiVO4 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(DD)). The impact of systems' size has been investigated. The converged electronic levels of TiO2 and BiVO4 surfaces have been used to predict the band alignment in TiO2/BiVO4 heterostructures. Results indicated that when TiO2 (101) surface is matched with BiVO4 (110), a type-II alignment is obtained, where the band edges of BiVO4 are higher in energy that those of TiO2. This picture is favorable for charge-carriers separation upon photoexcitation, where electrons move toward TiO2 and holes toward BiVO4. On the contrary, if TiO2 (101) is interfaced to BiVO4 (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 TiO2/BiVO4 composites, where the TiO2 (101)/BiVO4 (110) interface outperforms the TiO2 (101)/BiVO4 (010) one.