Homogeneous nitrogen-doped (111)-type layered Sr₅Nb₄O_15−xN_x as a visible-light-responsive photocatalyst for water oxidation

The development of visible-light-responsive photocatalysts for promoting solar-driven oxygen (O₂) production from water splitting is a potentially attractive but still a challenging scheme. In the present work, a (111)-type layered perovskite oxynitride, Sr₅Nb₄O_15−xN_x, was synthesized via the nitridation treatment of the disk-like oxide precursor under the ammonia flow, which was fabricated using a flux method. The homogeneous dispersion of nitrogen (N) dopant in N-doped Sr₅Nb₄O₁₅ was ascertained by energy-dispersive X-ray spectroscopy characterization, and the Sr₅Nb₄O_15−xN_x was found to be a direct semiconductor with a light absorption edge of approximately 640 nm. Density functional theory investigation implies that the hybridization between the outmost N 2p orbitals and O 2p orbitals upshifts the original valence band maximum of Sr₅Nb₄O₁₅ and endows its visible-light-responsive characteristics. Loading with cobalt oxide (CoO_x) as cocatalyst, the as-prepared Sr₅Nb₄O_15−xN_x exhibited an enhanced photocatalytic O₂ evolution activity from water splitting under visible-light illumination (λ > 420 nm). Moreover, another homogeneous N-doped layered perovskite-type niobium (Nb)-based oxynitride, Ba₅Nb₄O_15−xN_x, was also developed and investigated for the visible-light-actuated O₂ production, highlighting the versatility of the present approach for exploring novel visible-light-responsive photocatalysts.