Synthesis of a Visible-Light-Responsive Perovskite SmTiO2N Bifunctional Photocatalyst via an Evaporation-Assisted Layered-Precursor Strategy

Development of visible-light-responsive oxynitride photocatalysts has been highly inspired for promising solar-to-chemical conversion, but the number of Ti-based oxynitrides is scarce because of the relatively low thermal stability of Ti4+ ions under ammonia flow. Here, the feasible synthesis of a novel perovskite SmTiO2N from the layered NaSmTiO4 precursor is demonstrated to exhibit wide visible-light response with a bandgap of approximate to 2.1 eV and to show effective water reduction and oxidation functionalities under visible-light irradiation. The successful preparation mainly results from the synergistic effect of the layered structure of NaSmTiO4 and the evaporation spillover of Na+ ions, both of which are favorable for ammonia diffusion to accelerate the substitution of nitrogen to oxygen atoms and to shorten the nitridation time. The thermodynamic and kinetic feasibility of SmTiO2N for water splitting are investigated in detail, and its optimal apparent quantum efficiency (AQE) of water oxidation reaches 16.7% at 420 +/- 10 nm, higher by far than that of most previous visible-light-responsive photocatalysts. Interestingly, a series of oxynitrides RTiO2N (R = La, Pr, Nd) are similarly synthesized by the alkali-metal evaporation-assisted layered-precursor strategy, demonstrating its generality to prepare visible-light-responsive (oxy)nitride photocatalysts containing reducible metals for solar energy conversion.