Co-incorporation of C and S into zero-valent iron to enhance trichloroethylene dechlorination: Kinetics, electron efficiency, and dechlorination capacity

Zero-valent iron (ZVI) technology has become prevalent for the in situ dechlorination of trichloroethylene (TCE) widely found in soils and groundwater. Nevertheless, ZVI technology still encounters several severe bottlenecks, including inadequate reactivity, poor selectivity, and unelucidated mechanism. Herein, we report that a C&S-mZVI^bm material, with the Co-incorporation of C and S into Zero-Valent Iron, could significantly improve the degradation efficiency of ZVI, while simultaneously inhibiting the hydrogen evolution reaction (HER), thereby enhancing the electron selectivity in the TCE dechlorination. Comprehensive characterization techniques have demonstrated that the Co-incorporation of C and S into ZVI leads to better TCE affinity, faster electron transfer and lower charge-transfer resistances. In addition, novel FeS_x and Fe₃C species emerged as new active sites, resulting in two distinct reaction pathways. Specifically, when the C weight percentage is below 2 %, the cumulative quantity of hydrocarbon products surpasses that of DCE, indicating the dominant β-elimination pathway. Conversely, when the weight percentage of C exceeds 2 %, the overall hydrocarbon products fall short of DCE, suggesting that the TCE hydrogenolysis dechlorination reaction becomes the primary pathway. These insights can benefit not only the development of ZVI-based materials but also enhance the broad application of these materials in remediation of groundwater with chlorinated hydrocarbons.