Chemical Bond Bridging across Two Domains: Generation of Fe(II) and In Situ Formation of FeS on Zerovalent Iron.

Sulfidation of zerovalent iron (SZVI) can strengthen the decontamination ability by promoting the electron transfer from inner Fe to external pollutants by iron sulfide (FeS). Although FeS forms easily, the mechanism for the FeS bonding on the ZVI surface through a liquid precipitation method is elusive. In this work, we demonstrate a key pathway for the sulfidation of ZVI, namely, the in situ formation of FeS on ZVI surface, which leads to chemical bonding across two domains: the pristine ZVI and the newly formed FeS phase. The two chemically bridged heterophases display superior activity in electron transportation compared to the physically coated SZVI, eventually bringing about the better performance in reducing Cr(VI) species. It is revealed that the formation of chemically bonded FeS requires balancing the rates for the two processes of Fe(II) release and sulfidation, which can be achieved by tuning the pH and S(-II) concentration. This study elucidates a mechanism for surface generation of FeS on ZVI, and it provides new perspectives to design high-quality SZVI for environmental applications.