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 kobs 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.