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

In this study, biochar supported iron sulfide (Fe_xS_y) composite (Fe_xS_y@biochar) was synthesized and utilized as a persulfate (PS) activator for benzene removal from contaminated groundwater. The Fe_xS_y@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 Fe_xS_y@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 Fe_xS_y@biochar was mainly attributed to the free radicals (i.e., SO₄^•−,·OH) generated from PS activation induced by Fe_xS_y particles on biochar, followed by the possible activation by oxygen-containing groups. The as-prepared Fe_xS_y@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 Fe_xS_y@biochar/PS system, as strong signals were observed in the Fe_xS_y@biochar/PS system even after 24 h. The Fe_xS_y@biochar could be an alternative to existing activators of in-situ chemical oxidation for contaminated groundwater remediation.