Synergistic Enhancement of Lindane Removal by Biochar-Supported Sulfidated Nano Zero-Valent Iron: Elucidating Core-Shell Reactivity Mechanism

Abstract

Nano zero-valent iron (nZVI) has demonstrated significant efficacy in the remediation of organochlorine contaminants. However, enhancing its reactivity and mitigating its aging rate remains a critical challenge. This study developed a biochar-supported sulfidated nZVI (S-nZVI/BC) with a distinctive core-shell structure to synergistically enhance the degradation efficiency of lindane (γ-HCH). Systematic characterization revealed that modulating the S/Fe molar ratio (optimal at 0.077) precisely controlled sulfur speciation distribution between core and shell regions, optimized surface hydrophobicity, and improved electron transfer efficiency, achieving nearly complete removal of 5 mg/L γ-HCH within 24 h.  Unlike conventional supports, biochar demonstrated dual functionality: its electron shuttle effect increased Fe0 utilization compared to unsupported counterparts, while its conductive aromatic structures facilitated long-range electron transfer, significantly enhancing dechlorination performance. Mechanistic investigations revealed that core properties rather than shell characteristics dominated the material’s reactivity, challenging conventional surface-centric theories. The synergistic mechanism involves sulfur doping suppressing hydrogen recombination side reactions to strengthen atomic hydrogen-mediated reduction, while biochar simultaneously inhibits nZVI agglomeration through physical dispersion and optimizes reaction kinetics as an electron conductor. These findings provide a theoretical framework for designing high-performance engineered carbon-iron materials for organochlorine-contaminated site remediation and highlight critical considerations for field-scale implementation.

Keywords: biochar, Sulfidated nano zero-valent iron, Lindane, dechlorination, Core-shell structure