Sulfide transformation by biochar for trichloroethylene dechlorination: Mechanistic insights into the fate of sulfur species and electron transfer.

This study demonstrates that biochar carbon materials (BCs) derived from biomass effectively catalyze the dechlorination of trichloroethylene (TCE) in sulfide-containing aqueous solutions. Unlike the complex product profiles typically observed with common iron-based reducing agents, approximately 99 % of TCE was converted to acetylene as the sole dechlorination product within 144 h, achieving a reaction rate constant (kobs) of 0.026 h⁻¹ . The performance of the BCs-sulfide system is contingent upon the generation of reducing sulfur species (S22-), which can be facilitated by the quinone functional groups and mesoporous structure of the BCs. The reactive S₂²⁻ electrostatically adsorbs onto electron-deficient carbon atoms adjacent to nitrogen species on biochar as an electron donor, while the sp²-hybridized carbon conductive zone critically enhances electron transfer for TCE dechlorination, evidenced by the strong positive correlation between electrical resistance and kobs. Furthermore, the proposed MWBC900-sulfide system exhibits highly efficient TCE degradation (>90 % dechlorination) in groundwater samples. These findings provide a fundamental basis for the development of an alternative remediation technique for chlorinated solvent-contaminated groundwater using sulfide-mediated processes.