Sulfidation of zerovalent iron (SZVI) can strengthen the decontamination ability by promoting the electron transfer from inner Fe0 to external pollutants by iron sulfide (FeS x ). Although FeS x forms easily, the mechanism for the FeS x 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 x on ZVI surface, which leads to chemical bonding across two domains: the pristine ZVI and the newly formed FeS x 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 x 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 x on ZVI, and it provides new perspectives to design high-quality SZVI for environmental applications.

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