Tailoring S-vacancy concentration changes the type of the defect and photocatalytic activity in ZFS

Abstract

Defect engineering is crucial in the development of semiconductor catalyst activity. However, the influence of defect/vacancy density and states on catalysis remains vague. Thus, the optimized sulfur vacancy (S_V) state is achieved among Fe-ZnS models (ZFS) via a chemical etching strategy for photocatalytic degradation (PD). As the S_V concentration (ρS_V) increases, the predominant state of vacancies changes from isolated defects－a state to a combination of a state and vacancy clusters－e state, as verified by positron annihilation and X-ray absorption fine structure spectra. However, the two types of defect states activated the intrinsic activity of the crystal via radically different mechanisms and exerted different degrees of influence on PD activity, as revealed by first-principles calculations and quantitative structure-activity relationship. Our results suggest that the S_V activity is strongly influenced by its concentration in the ZFS crystal, while the vacancy concentration is not a control parameter for the PD activity, but a defect form. The underlying essence of atomic defects behavior affecting crystal catalytic activity at the atomic level is also revealed in this paper. Uncovering these structural relationships provide a theoretical basis for designing effective catalysts.

Keywords: Photocatalytic degradation; Sulphur vacancy; Vacancy concentration; Vacancy state.