FeNX(C)-Coated Microscale Zero-Valent Iron for Fast and Stable Trichloroethylene Dechlorination in both Acidic and Basic pH Conditions

FeN_X in Fe single-atom catalysts can be the active site for adsorption and activation of reactants. In addition, FeN_X species have been shown to facilitate electron transfer between Fe and the carbon supports used in newly developed metal-air batteries. We hypothesized that the combination of FeN_X species with granular zero-valent iron (ZVI) might result in catalyzed reductive decontamination of groundwater contaminants such as trichloroethylene (TCE). Here, such materials synthesized by ball milling microscale ZVI with melamine and the resulting N species were mainly in the form of pyridinic, pyrrolic, and graphitic N. This new material (abbreviated as N-C-mZVI^bm) dechlorinated TCE at higher rates than bare mZVI^bm (about 3.5-fold) due to facilitated electron transfer through (or around) the surface layer of iron oxides by the newly formed Fe-N_X(C). N-C-mZVI^bm gave higher k_TCE (0.4-1.14 day^-1) than mZVI^bm (0-0.4 day^-1) over a wide range of pH values (4-11). Unlike most ZVI systems, k_TCE for N-C-mZVI^bm increased with increasing pH values. This is because the oxide layer that passivates Fe⁰ at a high pH is disrupted by Fe-N_X(C) formed on N-C-mZVI^bm, thereby allowing TCE dechlorination and HER under basic conditions. Serial respike experiments gave no evidence of decreased performance of N-C-mZVI^bm, showing that the advantages of this material might remain under field applications.