Modulating the doping state of transition metal ions in ZnS for enhanced photocatalytic activity

Transition metal ions (M = Ag⁺, Cu²⁺, Co²⁺, and Cr³⁺) are surface or homogeneously doped into ZnS via facile cation-exchange reaction, and while Ag⁺ and Cu²⁺ doping does not induce sulphur vacancies (V_s) or zinc vacancies (V_Zn), Co²⁺ and Cr³⁺ doping induces V_s. The surface doped catalysts exhibit greatly higher activity than the ZnS and homogenous doped catalysts for H₂ evolution and CO₂ reduction. The important role of the doping state on affecting the photo-absorption, carrier separation efficiency, and photoreaction kinetics has been systemically investigated and proposed. This work sheds light on the future design and fabrication of high-performance photocatalysts by element doping.