Zn-vacancy mediated electron-hole separation in ZnS/g-C3N4 heterojunction for efficient visible-light photocatalytic hydrogen production

Abstract

Vacancy defects play an important role in modifying the electronic structure and the properties of photoexcited charge carriers by introducing additional energy levels and consequently enhanced the photocatalytic activity of photocatalyst. In this work, we report a ZnS/g-C3N4 heterostructure with abundant zinc vacancy defects on the surface of ZnS to emphasis the synergistic promotion on charge separation. The ZnS/g-C3N4 heterostructured photocatalyst possesses low over-potential, extended absorption in the visible light region, and promoted photoinduced electron-hole separation capability. Fluorescence emission spectra and XPS results confirm that existence of abundant zinc vacancies on ZnS. VZn-rich CZV20 (g-C3N4/ZnS-20 wt%) heterojunction exhibits more than 30 times higher photocatalytic H2 evolution rate (713.68 μmol h−1 g−1) than that of pure g-C3N4 (24.09 μmol h−1 g−1) under visible light irradiation and high stability during the prolonged photocatalytic operation. The enhanced photocatalytic performance can be attributed to the intimate interfacial contact between g-C3N4 and ZnS nanoparticles, increasing the light-absorbing capacity and charge separation efficiency of ZnS/g-C3N4 heterojunction. And more importantly, the visible-light photocatalytic H2 production activity can be ascribed to the two-photo excitation in the middle band gap of ZnS. This work demonstrates that appropriate Zn vacancy defects modified ZnS/g-C3N4 heterojunction can be used for highly efficient visible-light photocatalysis.