Band-Engineered Bismuth Titanate Pyrochlores for Visible Light Photocatalysis

Abstract

A density functional theory (DFT) study on stoichiometric bismuth titanate pyrochlore (Bi2Ti2O7−BTO) is presented. Pseudopotential plane wave calculations were carried out to determine band gaps, density of states (DOS), and partial density of states (PDOS) of BTO. The theoretically determined optical property of BTO with a direct band gap of 2.6 eV corresponds to a red shift of 70 nm in absorption activity compared to titanium dioxide (TiO2). A rationale has been developed to determine various possibilities of adding impurity elements within the BTO structure to enhance the visible light absorption. Mainly the effects of 3d element (Fe, Ni, Cr, Mn, and V) substitution in the crystal structure of BTO at the titanium position have been the focus of this study. The substitution of these elements shows the formation of different midgap states which indicates the flexibility of the BTO structure to tunability. Among the elements studied, Fe substitution showed a shift in the valence band toward the conduction band. This band gap reduction may facilitate a better electron transfer process. These theoretical results suggest that BTO can be a promising candidate for photocatalytic applications, such as solar-assisted water splitting reactions.