Coincorporation of N and S into Zero-Valent Iron to Enhance TCE Dechlorination: Kinetics, Electron Efficiency, and Dechlorination Capacity

Sulfidated zero-valent iron (S-ZVI) enhances the degradation of chlorinated hydrocarbon (CHC) in contaminated groundwater. Despite numerous studies of S-ZVI, a versatile strategy to improve its dechlorination kinetics, electron efficiency (ε_e), and dechlorination capacity is still needed. Here, we used heteroatom incorporation of N(C) and S by ball-milling of microscale ZVI with melamine and sulfur via nitridation and sulfidation to synthesize S-N(C)-mZVI^bm particles that contain reactive Fe-N_X(C) and FeS species. Sulfidation and nitridation synergistically increased the trichloroethene (TCE) dechlorination rate, with reaction constants k_SA of 2.98 × 10^-2 L·h^-1·m^-2 by S-N(C)-mZVI^bm, compared to 1.77 × 10^-3 and 8.15 × 10^-5 L·h^-1·m^-2 by S-mZVI^bm and N(C)-mZVI^bm, respectively. Data show that sulfidation suppressed the reductive dissociation of N(C) from S-N(C)-mZVI^bm, which stabilized the reactive Fe-N_X(C) and reserved electrons for TCE dechlorination. In addition to lowering H₂ production, S-N(C)-mZVI^bm dechlorinated TCE to less reduced products (e.g., acetylene), contributing to the material's higher ε_e and dechlorination capacity. This synergistic effect on TCE degradation can be extended to other recalcitrant CHCs (e.g., chloroform) in both deionized and groundwater. This multiheteroatom incorporation approach to optimize ZVI for groundwater remediation provides a basis for further advances in reactive material synthesis.