Nitrogen-Doped Carbon Materials as Metal-Free Catalyst for the Dechlorination of Trichloroethylene by Sulfide

A new method for trichloroethylene (TCE) dechlorination is proposed using sulfide (HS^- and S^2-) as reductant under the mediation of nitrogen-doped carbon materials (NCMs). About 99% of the TCE was converted to acetylene after 200 h using this method. Dechlorination of TCE in the NCMs-sulfide system (NCSS) followed pseudo-first-order kinetics. Pyridinic N (N6) on surface of the NCMs appeared to play a critical role in NCSS as shown by the good linear relationship between the surface content of N6 and k_obs. Nucleophilic substitution was suggested as the first step in TCE dechlorination, and the nucleophilic reagent was identified as a sulfur intermediate with C-S-S-H as the functional group. The generation of C-S-S-H could be ascribed to the interaction between positively charged carbon atoms in N6 and negative charged sulfide. This work is the first to demonstrate that sulfide combined with NCMs can produce active substances that are effective in TCE dechlorination and the findings will assist in the development of strategies that use natural sulfide as reductant for detoxicating organic chloroethene contaminants.