Boosting photocatalytic water oxidation reactions over strontium tantalum oxynitride by structural laminations

Perovskite oxynitrides often own a poor photocatalytic activity under normal conditions, being incommensurate to their strong visible light absorbance. This is particularly true for SrTaO 2 N which undergoes self-oxidative decompositions even under protection of a hole scavenger. In this work, we laminate the crystal structure of SrTaO 2 N by inserting extra layers of SrO to form a Ruddlesden-Popper (RP) compound Sr 2 TaO 3 N. This structural modification not only improves the light absorption of SrTaO 2 N but also effectively suppresses the defect formation such as Ta 4+ species etc. More importantly, Sr 2 TaO 3 N is able to drive photocatalytic water oxidation reactions under visible light illumination (λ ≥ 420 nm) without the aid of a cocatalyst and self-oxidative decompositions found for SrTaO 2 N are largely inhibited. Further analysis suggests that the presence of extra SrO layers positively shifts the valence band edge and stabilizes N species in the structure according to Pauling’s second rule. Theoretical calculations indicate that Sr 2 TaO 3 N has typical 2D charge transportation properties which are associated with the structural laminations. Its conduction band minimum (CBM) and valence band maximum (VBM) are found to be located within TaN 2 O 2 square planes which favors efficient charge transportations.