Enhanced Atomic Hydrogen Pathway for Contaminant Degradation in an S-nZVI/Epigallocatechin Gallate System: A Synergistic Enhancement Strategy

Sulfidized nanoscale zerovalent iron (S-nZVI) has been recognized as a promising reductant for treating trichloroethylene-contaminated groundwater. However, its superior reductive capacity appears to be contaminant-specific, showing limited efficacy toward other chlorinated and nitroaromatic compounds. In this study, epigallocatechin gallate (EGCG), a representative natural polyphenol, was combined with S-nZVI to amplify the atomic hydrogen (H*) pathway for decontamination. The S-nZVI/EGCG system demonstrated enhanced reduction reactivity for chloramphenicol (CAP) degradation, with the <i>k</i>_obs value exhibiting obvious enhancement (4.9-10 times) compared with that of the control systems (i.e., nZVI, S-nZVI, and nZVI/EGCG). Mechanistic investigations using fluorescence spectroscopy and cyclic voltammetry substantiated the sustained generation of H* in the system. Scavenging experiments and kinetic isotope effect (KIE) analysis (KIE = 23.98) confirmed H* as the predominant reactive species. The enhanced performance originated from the synergistic mechanism that oxidized EGCG derivatives served as an electron shuttle, promoting electron transfer from Fe⁰ to accelerate water dissociation and the subsequent H* formation. Additionally, sulfidation played a crucial role in the retention of transient H*, effectively facilitating H* for contaminant reduction rather than the undesirable H₂ evolution reaction. Herein, the S-nZVI/EGCG system exhibited great potential for reduction remediation, providing an environmentally sustainable strategy to broaden the applicability of S-nZVI in groundwater remediation.