Abstract
Two-dimensional (2D) Nb-based oxynitrides are promising visible-light-responsive photocatalysts for the water splitting reaction, but their photocatalytic activity is degraded by the formation of reduced Nb(5+) species and O(2-) vacancies. To understand the influence of nitridation on the formation of crystal defects, this study synthesized a series of Nb-based oxynitrides through the nitridation of LaKNaNb(1-x)Ta(x)O(5) (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0). During nitridation, K and Na species volatilized, which helped transform the exterior of LaKNaNb(1-x)Ta(x)O(5) into a lattice-matched oxynitride shell. Ta inhibited defect formation, yielding Nb-based oxynitrides with a tunable bandgap between 1.77 and 2.12 eV, straddling the H(2) and O(2) evolution potentials. After loading with Rh and CoO(x) cocatalysts, these oxynitrides exhibited good photocatalytic activity for H(2) and O(2) evolution in visible light (650-750 nm). The nitrided LaKNaTaO(5) and LaKNaNb(0.8)Ta(0.2)O(5) delivered the maximum H(2) (19.37 μmol h(-1)) and O(2) (22.81 μmol h(-1)) evolution rates, respectively. This work provides a strategy for preparing oxynitrides with low defect densities and demonstrates the promising performance of Nb-based oxynitrides for water splitting.