Modification of Zero-valent Iron with Fe-N₄ Coordination Structure Enables Dechlorination of 1,2-Dichloroethane

Zero-valent iron (ZVI, Fe⁰) can effectively reduce a variety of chlorinated hydrocarbons. However, ZVI is incapable of dechlorinating 1,2-dichloroethane (1,2-DCA), a commonly found contaminant in groundwater, and the existing ZVI modification methods have little effect on this predicament. In this study, we prepared ZVI composites modified with Fe-N₄ coordination structure (Fe⁰@FeNC), which exhibited outstanding dechlorination performance toward 1,2-DCA. Fe⁰@FeNC (1 g/L) can degrade 94% of 1,2-DCA (10 mg/L) within 37 days, with an ethene selectivity of nearly 100%, whereas nanoscale ZVI (nZVI) or even Pd-doped nZVI and sulfidated ZVI cannot degrade 1,2-DCA. The results from X-ray diffraction patterns and Mössbauer spectra confirmed the presence of Fe⁰ and Fe-N₄ coordination structure in the Fe⁰@FeNC, which were proven to be the electron donor and dechlorination active center for 1,2-DCA dechlorination, respectively. Theoretical calculation reveals that the Fe-N₄ coordination structure can reduce the free energy required for 1,2-DCA reduction, thus allowing 1,2-DCA to utilize electrons provided by Fe⁰ to achieve dechlorination. These findings can guide the design of ZVI-based materials to achieve in situ abiotic remediation of 1,2-DCA-contaminated groundwater.