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

- Thermal treatment in Ethylene glycol effectively removes defects.
- Structure lamination results in anisotropic charge migration.
- Inter-layer charge recombination is prevented in layered perovskites.
- Defects removal and structure lamination boost photocatalytic activity.

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 (≥250 nm). The highest activity under full range irradiation belongs to Sr2FeTaO6, which gives an average hydrogen production rate ∼107 μmol/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.

Ethylene glycol serves as an effective reducing agent to remove the high oxidation state Fe defects in double perovskite compound Sr2FeTaO6 and its layered derivatives - Ruddlesden-Popper (RP) compounds Sr3FeTaO7 and Sr4FeTaO8. Structural lamination by inserting additional SrO layers into double perovskite structure results in anisotropic charge migration phenomenon which prevents inter-layer charge recombination. The defects removal and structural lamination are responsible for the high photocatalytic activity observed.182