New insight into the activation mechanism of hydrogen peroxide by greigite (FeS) for benzene removal: The combined action of dissolved and surface bounded ferrous iron.

Iron sulfides have attracted growing concern in heterogeneous Fenton reaction. However, the structure of iron sulfides is different from that of iron oxides and how the structures affect the activation property of hydrogen peroxide (HO) remains unclear. This study investigated benzene removal through the activation of HO by the synthesized magnetite (FeO) and greigite (FeS). The structures of FeO and FeS were characterized by XRD and EPR, the electron transfer properties of FeO and FeS were analyzed by electrochemical workstation, XPS and DFT. It is revealed that the effective benzene removal rate of 88.86％ in the FeS/HO was achieved, which compared to 15.58％ obtainable from the FeO/HO, with the apparent rate constant in the FeS/HO being approximately 65 times over that in the FeO/HO. The better HO activation by FeS was attributed to the significant roles of S (-II) and S vacancies in regulating the dissolution of ferrous iron ions, thus generating abundant free •OH radical. In addition, surface bounded ferrous iron of FeS could transfer more electrons to HO and O to generate more surface bounded •OH and •O. This study revealed the combined action of dissolved and surface bounded ferrous iron of greigite on HO activation, and provides an efficient heterogeneous HO activator for the remediation of organic contaminants in groundwater.