Capture-reduction mechanism for promoting Cr(VI) removal by sulfidated microscale zerovalent iron/sulfur-doped graphene-like biochar composite

Abstract

The application of microscale zerovalent iron (mZVI) in the removal of Cr(VI) from water is plagued with the readily formation of oxide passivation layer. In this study, we propose a “capture-reduction” mechanism to enhance the Cr(VI) removal performance of mZVI under anaerobic condition through dual modification, i.e., sulfidation and construction of composite with sulfur-doped graphene like biochar (SGB). The S-mZVI/SGB has a Cr(VI) removal capacity of 70.2 mg·g− 1 at circumneutral pH, which is 56 times of that of mZVI. The 1,10-phenanthroline shielding experiments indicate that the contribution of Fe(II) to Cr(VI) removal is only 17.6%. Density-theory-functional (DFT) calculation results indicate that sulfur doping could significantly promote the adsorption of Cr(VI) on SGB nanosheets. The mechanism study confirmed the “capture-reduction” Cr(VI) removal mechanism, whereby the SGB nanosheets capture Cr(VI) ions and receive electrons from Fe0 to reduce Cr(VI) to Cr(III). Considering its advantages such as low cost and easy preparation, the S-mZVI/SGB composite is a promising green material for the removal of Cr(VI) from water. Graphical Abstract: [Figure not available: see fulltext.]