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.
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