The contamination of groundwater by 1,2,3-trichloropropane (TCP) has drawn significant attention due to its high toxicity to human, and low natural degradability in the environment. Pyrogenic carbonaceous matter (PCM), such as activated carbon and biochar, has drawn increasing attention in facilitating chlorinated solvent decay by synergistically interact with sulfide that naturally present in the environment. Previous work has highlighted the importance of nitrogenous functional groups in accelerating such reactions. However, the underlying mechanism of this PCM-sulfide synergy are still unclear due to structural complexity of PCM. In our study, a tunable platform, namely PCM-like polymer (PLPs), was employed as a PCM surrogate to delineate the role of different nitrogenous functional groups (i.e., quaternary ammonium (QA) and pyridinium cation (py⁺)) in accelerating TCP decay by sulfide. Our results suggest that two of the nitrogenous PLPs (i.e., PLP-QA and -py⁺) can facilitate the complete dechlorination of 1,2,3-trichloropropane (TCP) by sulfide, shortening the half-life of TCP to 16.91±1.17 and 0.98±0.15 days as compared to negligible decay in homogeneous solution. The experimentally determined activation energy for TCP decay is 63.6±6.1 and 51.9±4.9 kJ mol⁻¹ in the presence of PLP-QA and PLP-py⁺, respectively. The reactivity of PLPs is further increased as the density of the surface N group increased. We propose that the complete decay of TCP was resulted from a two-step dechlorination process through reductive ß-elimination followed by nucleophilic substitution by surface-bound nucleophile (C-Sn^–), which was formed covalently by the reaction between bisulfide and QA/py+ functional groups. The TCP decay kinetics was neither significantly affected by the presence of co-contaminants (i.e., 1,1,1-trichloroethane or trichloroethylene) nor 3 mg L^–1 Suwannee River natural organic matter (SRNOM). This work elucidates the N group identity on facilitating chlorinated solvent decay by sulfide, which provide important guidelines for design reactive PCM for groundwater remediation.

Jingdong Mao

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