Coordinatively Unsaturated Reduced Iron Sites Enable Hemin-Catalyzed Electrochemical Dechlorination of Trichloroethylene

Abstract

Metal porphyrin structure is believed to be the active site for microbiological reductive dechlorination. In this work, a biomimetic Hemin catalyst was used for the electrochemical dechlorination of trichloroethylene (TCE). Cyclic voltammetric analysis demonstrates the high electrochemical reactivity of Hemin toward reductive dechlorination of TCE, which is further confirmed by controlled potential electrolysis. TCE can be fully dechlorinated to acetylene, ethylene, and ethane. Density functional theory calculations show the appearance of unpaired electron spins on coordinatively unsaturated Fe sites. The breakage of the Fe–Cl bond in Hemin with the formation of coordinatively unsaturated FeII sites shows reactivity toward TCE-to-dichloroethylene (DCE) conversion, but FeII sites with the coordination to Cl atoms have no reactivity. Lowering the applied potential to −2.1 V generates coordinatively unsaturated FeI sites, showing much higher reactivity toward TCE reduction compared with FeII sites. The energy barrier involving complete dechlorination of TCE was decreased from 1.83 eV by FeII sites to 0.86 eV by FeI sites. FeI sites can continue to contribute to TCE dechlorination in electrochemical systems. Our study provides a novel biomimetic electrochemical approach for the dechlorination of TCE in groundwater.