Defect Control via Compositional Engineering of Zn-Cu-In-S Alloyed QDs for Photocatalytic HO Generation and Micropollutant Degradation: Affecting Parameters, Kinetics, and Insightful Mechanism.

Photocatalytic HO production and recalcitrant pollutant degradation are regarded as promising clean technology toward achieving sustainable solar-to-chemical energy conversion. Herein, nonstoichiometric Zn-Cu-In-S (ZCIS) quaternary alloyed quantum dots (QDs) are rationally fabricated via a reflux method toward HO generation and ciprofloxacin degradation under visible light irradiation. The optimum catalyst (ZCIS-2) exhibits a notable HO production of 1685.2 μmole h g (solar-to-chemical conversion efficiency (SCC), 0.19%), which is 5.3 times higher than that of CuInS (CIS), and a ciprofloxacin (CIP) degradation efficiency of 96% in 2 h. The observed improvement in activity corresponds to optimized exciton separation/transfer, broad photon absorption, tunable band alignment, and effective adsorption/activation. In addition, oxygen reduction goes through both direct two-electron single-step reduction and single-electron two-step superoxide radical pathways, whereas CIP degradation proceeds via direct O and indirect OH radical pathways, as confirmed by scavenger experiments. An appropriate amount of defects improves the adsorption/activation of O toward HO and active oxygen species generation that facilitates CIP degradation. The effect of operational parameters, such as pH, surrounding environment, presence of ions, sacrificial agent, etc., on both HO formation and CIP removal is vividly studied. Hence, the current study will provide an in-depth insight into O photoreduction and micropollutant removal, which encourages further advancement of potent alloyed quantum dot-oriented photocatalytic systems.