Reaching beyond the sulfided surface: Doping of copper cation to expand the pH tolerance range for SZVI

Sulfidation of zero-valent iron (SZVI) is an important means to greatly inhibit the formation of inert hydr/oxide and improve the overall reactivity in pollutant removal reactions, which is mainly benefiting from the formation of FeS x layer on surface of the zero-valent iron (ZVI). However, FeS x phase can act as reducing reagent in the treatment of pollutants, resulting in inevitable consumption. Considering that, copper cation was introduced to the FeS x phases to prepare copper-doped sulfides with improved durability. In this study, we successfully prepared copper-doped SZVI (Cu-SZVI). The composition and structure have been clearly confirmed by a combination of several techniques, including Raman spectroscopy and X-ray powder diffraction. Cu-SZVI exhibits a superior sequestration reaction to remove Cr(VI) with higher removal capacity of 82.93 mg/g, with the comparison of SZVI (57.54 mg/g) and ZVI (8.23 mg/g). Moreover, Cu-SZVI possesses better operational pH tolerance and longer lifetime of usage, which makes it particularly attractive to large-scale environmental applications. This work proposes a new way to modify SZVI by doping a secondary cation, which can be used to further explore new SZVI materials based on specific needs.