Mechanochemical integration of vitamin B12 with zero-valent iron for enhanced reductive dechlorination: The critical role of FexN species.

Mechanochemical integration of vitamin B12 (B12) with microscale zero-valent iron (mZVI) (i.e., B12-mZVIbm) markedly enhances reductive dechlorination, but the origin of this enhancement remains unclear. Here we show that the performance gain of B12-mZVIbm arises from interfacial restructuring rather than immobilization alone. Systematic characterization revealed that mechanochemical synthesis immobilized B12 on mZVI via the formation of abundant FexN species, including γ'-Fe4N and ε-Fe2+xN, while preserving the structural integrity of B12 and shifting the cobalt center toward the catalytically active Co(II) state. Electrochemical analyses further indicated that these iron nitride species promote electron transfer from the Fe⁰ core to surface-bound B12 catalytic sites, thereby enhancing the reaction performance. B12-mZVIbm remained effective across a wide pH range, at elevated contaminant concentrations, and in real groundwater and wastewater, and retained its dechlorination performance after 270 days of aging with less than 9% B12 leaching. The economic feasibility and environmental impact analyses further confirm the practical application prospects of B12-mZVIbm. These findings will assist in the development of efficient bio-inspired systems for environmental remediation, and for industrial catalysis.