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

FeNX in Fe single-atom catalysts can be the active site for adsorption and activation of reactants. In addition, FeNX 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 FeNX 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-mZVIbm) dechlorinated TCE at higher rates than bare mZVIbm (about 3.5-fold) due to facilitated electron transfer through (or around) the surface layer of iron oxides by the newly formed Fe–NX(C). N–C-mZVIbm gave higher kTCE (0.4–1.14 day–1) than mZVIbm (0–0.4 day–1) over a wide range of pH values (4–11). Unlike most ZVI systems, kTCE for N–C-mZVIbm increased with increasing pH values. This is because the oxide layer that passivates Fe0 at a high pH is disrupted by Fe–NX(C) formed on N–C-mZVIbm, thereby allowing TCE dechlorination and HER under basic conditions. Serial respike experiments gave no evidence of decreased performance of N–C-mZVIbm, showing that the advantages of this material might remain under field applications.