Adsorption and reduction of hexavalent chromium on magnetic greigite (Fe3S4)-CTAB: leading role of Fe(ii) and S(−ii)

Abstract

In this study, a facile one-step route was used to synthesize a novel magnetic mesoporous greigite (Fe₃S₄)-CTAB composite, which was utilized to remove hexavalent chromium (Cr(VI)). The optimized Fe₃S₄-CTAB_0.75 composite with a CTAB dosage of 0.75 g possessed the maximum specific surface, showing the highest Cr(VI) adsorption capacity of 330.03 mg g⁻¹. The mechanism analysis revealed that Fe(II) and S(−II) were critical for the reduction of Cr(VI). CTAB can promote the removal of Cr(VI) by Fe₃S₄-CTAB composites, possibly due to increased S(−II) concentration, better dispersion of nanoparticles, and greater zeta potential. Besides, there is mild effect of Fe⁰ on Cr(VI) removal, which is confirmed by the disappearance of the Fe⁰ peak from the XPS analysis. The pseudo-second-order kinetic model could explain the Cr(VI) removal processes well. The adsorption of Cr(VI) at different initial concentrations was more consistent with a Langmuir isotherm. The existence of H⁺ was beneficial for Cr(VI) removal by Fe₃S₄-CTAB_0.75. Our work confirmed that the obtained Fe₃S₄-CTAB_0.75 composites exhibit considerable potential for Cr(VI) removal from aqueous solution.