Mechanism of biochar functional groups in the catalytic reduction of tetrachloroethylene by sulfides

In recent years, biochar has become of considerable interest for environmental applications, it can be used as a catalyst for sulfides reduction of perchloroethylene, but the crucial role of biochar properties played in catalyzing dechlorination remained ambiguous investigation. To pinpoint the critical functional groups, the modified biochars were respectively produced by HNO3, KOH and H2O2 with similar dimensional structures but different functional groups. Combined with the adsorption and catalytic results of different biochars, the acid-modified biochar had the best catalytic performance (99.9% removal) due to the outstanding specific surface area and ample functional groups. According to characterization and DFT results, carboxyl and pyridine nitrogen exhibited a positive correlation with the catalytic rate, indicating that their contribution to catalytic performance. Customizing biochar with specific functional groups removed depth demonstrated that the carboxyl was essential component. Further, alkaline condition was conducive to catalytic reduction, while tetrachloroethylene cannot be reduced under acidic conditions, because HS- and S2- mainly existed in alkaline environment and the sulfur-containing nucleophilic structure formed with biochar was more stable under this condition. Overall, this study opens new perspectives for in situ remediation by biochar in chlorinated olefin polluted anoxic environment and promotes our insight of modifying for biochar catalyst design.