Nitrogen-doped layered oxide Sr5Ta4O15−xNx for water reduction and oxidation under visible light irradiation

Abstract

Development of a photocatalyst with wide visible light absorption is of vital importance in solar-chemical energy conversion. In this work, we introduce a new nitrogen-doped layered oxide, Sr5Ta4O15−xNx, which exhibits a significantly extended absorption edge compared with the undoped oxide Sr5Ta4O15. The extension of the visible light absorption has been ascribed to the substitution of nitrogen for oxygen atoms as well as the formation of Ta–N bonds, which was confirmed by X-ray diffraction (XRD) patterns, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Judged by the first principle calculation, the N 2p states mixed with pre-existing O 2p states shift the valence band maximum upward and result in wide visible light absorption. Band structure analysis combined with UV-Vis diffuse reflectance spectrum (DRS) and Mott–Schottky (M–S) measurement shows that the conduction and valence bands of Sr5Ta4O15−xNx are sufficient for water reduction and oxidation, respectively. The photocatalytic water splitting performances of Sr5Ta4O15−xNx are strongly related to the deposited cocatalyst. With an optimized cocatalyst, the Sr5Ta4O15−xNx shows both H2 and O2 evolution activities under visible light irradiation using CH3OH and AgNO3 as scavengers respectively. Following the optimized cocatalyst deposition of the Sr5Ta4O15−xNx, the cocatalyst-modified nitrogen-doped tantalum-based layered oxides Sr2Ta2O7−xNx and Ba5Ta4O15−xNx also exhibit activities for both the water splitting half reactions. This work demonstrates that the nitrogen-doped tantalum-based layered oxides may be a new type of potential photocatalyst with wide visible light absorption for solar water splitting.