TS Science

Copper indium sulfide (CuInS₂) exhibits strong visible light absorption and thus has the potential for good photocatalytic activity; however, rapid charge recombination limits its practical usage. An intriguing strategy to overcome this issue is to couple CuInS₂ with another semiconductor to form a heterojunction, which can improve the charge carrier separation and, hence, enhance the photocatalytic activity. In this study, photocatalysts comprising CuInS₂ with a secondary CuS phase (termed CuIn_xS_y) and CuIn_xS_y loaded with ZnS (termed ZnS@CuIn_xS_y) were synthesized via a microwave-assisted method. Structural and morphological characterization revealed that the ZnS@CuIn_xS_y photocatalyst comprised tetragonal CuInS₂ containing a secondary phase of hexagonal CuS, coupled with hexagonal ZnS. The effective band gap energy of CuIn_xS_y was widened from 2.23 to 2.71 as the ZnS loading increased from 0 to 30%. The coupling of CuIn_xS_y with ZnS leads to long-lived charge carriers and efficient visible-light harvesting properties, which in turn lead to a remarkably high activity for the photocatalytic degradation of brilliant green (95.6% in 5 h) and conversion of 4-nitrophenol to 4-nitrophenolate ions (95.4% in 5 h). The active species involved in these photocatalytic processes were evaluated using suitable trapping agents. Based on the obtained results, photocatalytic mechanisms are proposed that emphasize the importance of h⁺, O₂^•–, and OH⁻ in photocatalytic processes using ZnS@CuIn_xS_y.