Role of oxygen vacancy in the adsorption and dissociation of the water molecule on the surfaces of pure and Ni-doped rutile (110): a periodic full-potential DFT study

Abstract

Ni atom is seen as a momentous impurity to extend the exciting response of TiO2 to the visible light and increase that photocatalytic reactivity. The impact of substituted nickel impurities in rutile (110) surface on the electronic structure, the formation energy of the oxygen vacancy defect, charge transfer and the energy of water adsorption in molecular and dissociated forms were successfully calculated by a full potential method based on density functional theory (DFT). Here, the pure, defective, Ni-doped and defective Ni-doped rutile TiO2 (110) surfaces were simulated. The analysis of partial DOS calculations of all surfaces showed that oxygen 2p and Ti 3d orbitals dominate the main contribution of the edge of the valence band maximum and the conduction band minimum respectively. By developing oxygen vacancy, the occupied defect states of 3d states of the nearest Ti atoms is pinned inside the conduction band. The nickel impurities create empty defect states appearing inside the band gap, one which is exactly above the valence band and the other in the middle, near the conduction band. The simultaneous effect of nickel impurity and O-vacancy is two occupied and one empty defect states inside the gap mainly corresponding to the Ni 3d orbitals. Ni impurity significantly not only reduces O-vacancy formation energy increases the water adsorption energy, especially in dissociated form. While the molecular adsorption is more favorable on the pure perfect rutile (110) surface, the dissociated form is preferred upon developing O-vacancy and Ni impurity. Both O-vacancy and Ni impurity expand the adsorption energy releasing a positive synergic effect on the reactivity of the rutile surface.