Metal-sulfide-based heterojunction photocatalysts: Principles, impact, applications, and in-situ characterization

Semiconductor photocatalysis is a new sustainable development technology that has demonstrated remarkable potential in the fields of energy-production and environmental-protection. However, a single photocatalyst usually does not possess both strong redox and fast charge-separation properties, greatly limiting photocatalysis efficiency. Heterojunction photocatalysts can perfectly solve this problem by providing multiple reactive sites and fast charge separation and migration, elevating photocatalytic efficiency to a new higher level. Metal sulfides are a family of compounds composed of metals and sulfur (e.g., CdS, CuS, MoS2, In2S3, ZnIn2S4, and ZnxCd1–xS) that are preferred choices for heterojunction photocatalysts due to their narrow bandgaps, broad visible-light absorption ranges, and convenient preparation methods. This review article introduces the characteristics of metal sulfides, summarizes methods for their synthesis, and discusses various types of metal-sulfide-based heterojunctions. The use of such photocatalysts in energy and environmental-remediation applications is subsequently discussed. In addition, the roles of charge separation and transfer in heterojunction photocatalysts are demonstrated using in-situ characterization techniques. Finally, we discuss some application prospects and challenges concerning metal-sulfide-based heterojunction photocatalysts.