Alcohothermal synthesis of sulfidated zero-valent iron for enhanced Cr(VI) removal

Sulfidation of zero-valent iron (ZVI) has attracted broad attention in recent years for improving the sequestration of contaminants from water. However, sulfidated ZVI (S-ZVI) is mostly synthesized in the aqueous phase, which usually causes the formation of a thick iron oxide layer on the ZVI surface and hinders the efficient electron transfer to the contaminants. In this study, an alcohothermal strategy was employed for S-ZVI synthesis by the one-step reaction of iron powder with elemental sulfur. It is found that ferrous sulfide (FeS) with high purity and fine crystallization was formed on the ZVI surface, which is extremely favorable for electron transfer. Cr(VI) removal experiments confirm that the rate constant of S-ZVI synthesized by the alcohothermal method was 267.1- and 5.4-fold higher than those of un-sulfidated ZVI and aqueous-phase synthesized S-ZVI, respectively. Systematic characterizations proved that Cr(VI) was reduced and co-precipitated on S-ZVI in the form of a Fe(III)/Cr(III)/Cr(VI) composite, suggesting its environmental benignancy.