Microwave-assisted synthesis of ZnS@CuInS for photocatalytic degradation of coloured and non-coloured pollutants.

Copper indium sulfide (CuInS) 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 CuInS 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 CuInS with a secondary CuS phase (termed CuInS) and CuInS loaded with ZnS (termed ZnS@CuInS) were synthesized via a microwave-assisted method. Structural and morphological characterization revealed that the ZnS@CuInS photocatalyst comprised tetragonal CuInS containing a secondary phase of hexagonal CuS, coupled with hexagonal ZnS. The effective band gap energy of CuInS was widened from 2.23 to 2.71 as the ZnS loading increased from 0 to 30%. The coupling of CuInS 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, O, and OH in photocatalytic processes using ZnS@CuInS.