Ball-milled S-Ni-mZVI for trichloroethylene removal: Mechanism of sulfur-nickel synergy

Co-doping with non-metallic and metallic elements offers an effective strategy to address the inherent limitations of zero-valent iron (ZVI) materials, including low reactivity and selectivity towards target contaminants and surface passivation. This study synthesized high-performance sulfur-nickel co-doped microscale ZVI (S-Ni-mZVI) through a facile and cost-effective one-step ball milling method to achieve high dehalogenation activity. A comprehensive comparative analysis between mZVI, S-mZVI, and Ni-mZVI revealed the superior trichloroethylene (TCE) degradation kinetics, electron efficiency, pH tolerance, and long-term activity of S-Ni-mZVI. Specifically, S-Ni-mZVI achieved a pseudo-first-order TCE degradation rate constant of 1.05 h −1 (>97 % removal in 4 h), outperforming mZVI by 150.9-fold, and exhibited an electron efficiency of 70.7 %. Mechanistically, S (FeS) effectively suppressed hydrogen evolution (up to 99.3 % inhibition) and passivated Ni-induced hydrogenolysis, and Ni (Ni-Fe galvanic couple) augmented the electron cloud density of sulfur and synergistically promoted electron transfer in conjunction with FeS, resulting in a 6.4-fold rate acceleration. Furthermore, the co-doping of S and Ni induced Fe⁰ lattice contraction, significantly enhancing the material’s corrosion resistance. Additionally, S-Ni-mZVI exhibited broadened pH adaptability and sustained long-term degradation performance, maintaining a TCE removal rate exceeding 98 % over 13 days. Moreover, the leaching concentration of Ni remained consistently below 0.2 mg·L −1 , confirming the environmental friendliness of the material. Electrochemical analysis and kinetic isotope effect studies further revealed that Ni-mZVI degraded TCE primarily via hydrogenolysis. In contrast, S-mZVI and S-Ni-mZVI mainly employed direct electron transfer ( β -elimination). This work offers a pragmatic and scalable strategy for engineering highly active, electron-efficient, and durable ZVI-based materials for efficient remediation of chlorinated hydrocarbons.