Enhancing zerovalent iron-based Fenton-like chemistry by copper sulfide: Insight into the active sites for sustainable Fe(II) supply

Zerovalent iron (ZVI)-based Fenton-like processes have been widely applied in degrading organic contaminants. However, the surface oxyhydroxide passivation layer produced during the preparation and oxidation of ZVI hinders its dissolution and Fe(III)/Fe(II) cycling, and restricts the generation of reactive oxygen species (ROS). In this study, copper sulfide (CuS) was found to effectively enhance the degradation of diverse organic pollutants in the ZVI/H2O2 system. Moreover, the degradation performance for the actual industrial wastewater (i.e., dini-trodiazophenol wastewater) in the ZVI/H2O2 system was impressively improved by 41% with CuS addition, and the COD removal efficiency could reach 97% after 2 h of treatment. Mechanism investigation revealed that the introduction of CuS accelerated the sustainable supply of Fe(II) in the ZVI/H2O2 system. Specifically, Cu(I) and reductive sulfur species (i.e., S2-, S22-, Sn2- and H2S (aq)) from CuS directly induced efficient Fe(III)/Fe(II) cycling. The iron-copper synergistic effect between Cu(II) from CuS and ZVI expedited Fe(II) generation from ZVI dissolution and Fe(III) reduction by formed Cu(I). This study not only elucidates the promotion effects of CuS on ZVI dissolution and Fe(III)/Fe(II) cycling in ZVI-based Fenton-like processes, but also provides a sustainable and high-efficiency iron-based oxidation system for removal of organic contaminants.