Green remediation of benzene contaminated groundwater using persulfate activated by biochar composite loaded with iron sulfide minerals

•FexSy@biochar was utilized as persulfate activator for benzene removal.•SEM, XRD and FTIR analysis revealed the FexSy@biochar characteristics.•Effects of catalyst dosage, persulfate dosage and benzene levels were assessed.•Cycled tests and EPR analysis showed the sustainable release of reactive species.•FexSy@biochar could be an alternative to existing activators of ISCO. In this study, biochar supported iron sulfide (FexSy) composite (FexSy@biochar) was synthesized and utilized as a persulfate (PS) activator for benzene removal from contaminated groundwater. The FexSy@biochar/PS system exhibited excellent performance in benzene adsorption and subsequent degradation. The optimal conditions for benzene removal in this study were found to be 1 g L-1 FexSy@biochar dosage and 3 mM PS concentration (removal rate 99.8%), with no reversible desorption of benzene concentrations in a long-time interval. The high catalytic performance of FexSy@biochar was mainly attributed to the free radicals (i.e., SO4•−,·OH) generated from PS activation induced by FexSy particles on biochar, followed by the possible activation by oxygen-containing groups. The as-prepared FexSy@biochar also showed long-term effectiveness for PS activation as confirmed by the 4 test cycled tests. The EPR not only demonstrated the presence of •OH and SO4•− free radicals but also indicated the sustainable release effect of reactive species from FexSy@biochar/PS system, as strong signals were observed in the FexSy@biochar/PS system even after 24 h. The FexSy@biochar could be an alternative to existing activators of in-situ chemical oxidation for contaminated groundwater remediation.