Synthesis of a Visible-Light-Responsive Perovskite SmTiO2 N 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 SmTiO2 N from the layered NaSmTiO4 precursor is demonstrated to exhibit wide visible-light response with a bandgap of ≈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 SmTiO2 N 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 RTiO2 N (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.