Sulfidation of ZVI by mechanochemical synthesis: Lattice doping and enhanced reactivity

Sulfur doping into the crystalline lattice of zero-valent iron (ZVI) enhances its electronic properties and local structure, improving its efficacy for transforming environmental contaminants. This study demonstrates a novel high-energy ball milling approach to initiate mechanochemical reactions for precise sulfur doping into the Fe⁰ lattice, addressing the hazards posed by hexavalent chromium (Cr(VI)) and trichloroethylene (TCE), two priority pollutants known to threaten public health and ecosystems. Mechanochemically sulfidized ZVI (SZVI, 0.182 %-5.698 % sulfur) exhibited Cr(VI) and TCE removal rates up to 20 and 7 times higher, respectively, than SZVI prepared by conventional solution chemistry with aqueous Na₂S, forming primarily surface-bound iron sulfides. By tuning milling time to control sulfur incorporation, removal capacities of 130.5 mg/g for Cr(VI) (S: 3.802 %) and 70.1 mg/g for TCE (S: 4.557 %) were achieved under environmentally relevant conditions mimicking groundwater matrices. Mechanical energy catalyzes in-situ iron sulfide (FeS_x) ieformation through lattice expansion and atomic-scale Fe-S interpenetration, as confirmed by FeS and FeS₂ crystalline phases, symmetric Fe-S bond vibrations, and rearrangement in the Fe coordination environment. These findings advance ZVI-based remediation strategies, mitigating risks from hazardous contaminants in environmental systems.