Zn defect-mediated Z-scheme electron-hole separation in AgIn5S8/ZnS heterojunction for enhanced visible-light photocatalytic hydrogen evolution

Abstract

Exploring high-efficiency Z-scheme heterojunction photocatalyst has been regarded as an effective approach for promoting photocatalytic hydrogen production efficiency. In this study, a novel direct Z-scheme heterojunction composed of AgIn5S8 (denoted as AIS) and Zn-defective ZnS (denoted as D-ZnS) was fabricated via two-step hydrothermal method. The AIS/D-ZnS heterojunction exhibited improved visible light harvesting capability, prolonged charge lifetime and promoted charge separation efficiency, thus contributing to the remarkably enhanced photocatalytic activity as well as stability. The photocatalytic H2 evolution rate of the optimized (0.10:1)AIS/D-ZnS reached 932.76 μmol·h−1 g−1, which was 12 times higher than that of bare D-ZnS (75.13 μmol·h−1 g−1) under visible light irradiation, and an optimal apparent quantum yield of 3.7% was achieved at λ = 420 nm. TEM, XPS, EPR and PL results confirmed the appropriate concentration of Zn defects is conducive to the separation of photogenerated carriers. DMPO-EPR and PL probe experiments for determining O2− and OH active radicals further proved that the transfer and separation of electrons and holes followed Z-scheme mechanism. This work not only presents an alternative strategy for the construction of highly efficient Z-scheme heterojunction photocatalysts, but also provides new insights into the role of defects in mediating the separation and migration of charge carriers.