A first-principles study of anionic (S) and cationic (V/Nb) doped Sr2Ta2O7 for visible light photocatalysis

Abstract

In order to effectively utilize the visible solar light to catalyze and decompose water into hydrogen and oxygen, the ultraviolet light responsive photocatalyst Sr₂Ta₂O₇ is engineered via co-doping of the anionic (S) and cationic (V/Nb) to shift the VBM (valence band maximum) upward and CBM (conduction band minimum) downward by approximately 1 eV, respectively. By first principles study (GGA-PBE), it is discovered that the VBM of (S, V) co-doped Sr₂Ta₂O₇ is shifted upward by 1.14 eV while the CBM of this system is shifted downward by 0.68 eV, which is due to the appearance of impurity states near the VBM and CBM, respectively. For (S, Nb) co-doped Sr₂Ta₂O₇, the VBM is shifted upward by 0.74 eV and the CBM is shifted downward by 0.63 eV. No impurity states of Nd are created, neither near the CBM nor in the band gap for (S, Nb) co-doped case, probably because the Sr₂Ta₂O₇ is essentially isostructural with Sr₂Nb₂O₇. For these two systems mentioned above, it could be a feasible way for Sr₂Ta₂O₇ photocatalyst on water splitting under UV irradiation to convert into the visible light-utilizing material without introducing extra electrons or holes.