Ruddlesden-Popper compounds in the double-perovskite family Sr2FeTaO6(SrO)n (n = 0, 1 and 2) and their photocatalytic properties

Abstract

Defects control and structural modifications are useful tools in tailoring the photocatalytic activity of a semiconductor. In this work, we demonstrate how defects removal and structural lamination control the photocatalytic performance of double perovskite Sr2FeTaO6 and its layered derivatives – Ruddlesden-Popper (RP) compounds Sr3FeTaO7 and Sr4FeTaO8. Our results show that high oxidation state Fe defects are involved during the high temperature synthesis of these compounds. A simple thermal treatment in the presence of ethylene glycol effectively removes these defects and turns their color from dark green to bright yellow while still maintaining their crystal structures and microstructures. Further experiments on photocatalysis reveal the critical role of thermal treatment in terms of boosting photocatalytic hydrogen production almost 3-fold for all samples under full range irradiation (≥250nm). The highest activity under full range irradiation belongs to Sr2FeTaO6, which gives an average hydrogen production rate ∼107μmol/h, corresponding to apparent quantum efficiency (AQE) ∼1.36%. More importantly, visible light photocatalytic hydrogen production was also realized after thermal treatment with the highest AQE ∼0.54% for Sr4FeTaO8. Theoretical calculations indicate the anisotropic feature of RP compounds for charge migrations and highlight the benefits of structural lamination by reducing inter-layer charge recombination. Our work here signifies the importance of defect control and offers some clues for the design of efficient photocatalysts by means of structural modifications.