Construction of Zn vacancy mediated ZnS/Cu2−xS heterostructure via cation exchange reactions for broadband photocatalytic water splitting

Abstract

Vacancy engineering has attracted great attention as the construction of defects can modify bandstructure and enhance photoabsorption ability by introducing additional vacancy energy levels, thereby achieving efficient photocatalytic H2 evolution activity. In this work, zinc-vacancy ZnS/Cu2−xS (ZnS-VZn/Cu2−xS) photocatalyst was successfully prepared by surface modification of ZnS-VZn. The presence of zinc vacancies endows visible light responsiveness of ZnS, which can be attributed to the two-photon absorption mechanism and demonstrated by the upward PL spectra. Cu2−xS would tightly anchor the surface of ZnS-VZn after the cation exchange reaction, which is good for the efficient transfer of charge carriers. Furthermore, Cu2−xS broadens the light absorption range of the ZnS-VZn/Cu2−xS composite and can generate more photoexcited charge carriers under visible light irradiation, resulting in outstanding photocatalytic H2 generation activity. As a result, the optimum photocatalytic H2 generation rate of 642.30 μmol g−1 h−1 was obtained over ZnS-VZn/Cu2−xS, which is 10.34 times higher than the pure ZnS-VZn. Additionally, ZnS-VZn/Cu2−xS composite exhibits excellent photostability over four cycles totaling 16 h and the charge transfer route is further confirmed by the in-situ XPS. The present work deepens the understanding of vacancy defects and provides a feasible method to rationally establish a semiconductor photocatalyst for efficient H2 generation from water splitting.