Reduced sulfur accelerates Fe(III)/Fe(II) recycling in FeS₂ surface for enhanced electro-Fenton reaction

FeS₂ is well-known for its role in redox reactions. However, the mechanism within heterogeneous electron-Fenton (Hetero-EF) systems remains unclear. In this study, a novel FeS₂ based three-dimensional system (GF/Cu-FeS₂) with self-generation of H₂O₂ was investigated for Hetero-EF degradation of sulfamethazine (SMZ). The results revealed that SMZ could be completely removed in 1.5 h, accompanying with the mineralization efficiency of 96% within 4 h. This system performed excellent stability, evidenced by consistently eliminated 100% of SMZ within 2 h over 4 cycles. The generated Reactive Oxygen Species (ROS) of •OH and •O₂^- in every degradation cycle were quantitatively measured to confirm the stability of the GF/Cu-FeS₂ system. Additionally, the redox reaction mechanism on the surface of FeS₂ was thoroughly analyzed in detail. The accelerated reduction of Fe(III) to Fe(II), triggered by S₂^2- on the surface of FeS₂, promoted the iron cycling, thereby quickening the Fenton process. Density Functional Theory (DFT) results illustrated the process of S₂^2- to be oxidized to in detail. Therefore, this work provides deeper insight into the mechanistic role of S₂^2- in FeS₂ for environmental remediation.