Facile preparation of magnetic mesoporous MnFe 2 O 4 @SiO 2 -CTAB composites for Cr(VI) adsorption and reduction.

Chromium-contaminated water is regarded as one of the biggest threats to human health. In this study, a novel magnetic mesoporous MnFe2 O4 @SiO2 -CTAB composite was prepared by a facile one-step modification method and applied to remove Cr(VI). X-ray diffraction, scanning electron microscopy, transmission electron microscopy, specific surface area, and vibrating sample magnetometer were used to characterize MnFe2 O4 @SiO2 -CTAB composites. The morphology analysis showed that the composites displayed a core-shell structure. The outer shell was mesoporous silica with CTAB and the core was MnFe2 O4 nanoparticles, which ensured the easy separation by an external magnetic field. The performance of MnFe2 O4 @SiO2 -CTAB composites in Cr(VI) removal was far better than that of bare MnFe2 O4 nanoparticles. There were two reasons for the effective removal of Cr(VI) by MnFe2 O4 @SiO2 -CTAB composites: (1) mesoporous silica shell with abundant CTA+ significantly enhanced the Cr(VI) adsorption capacity of the composites; (2) a portion of Cr(VI) was reduced to less toxic Cr(III) by MnFe2 O4 , followed by Cr(III) immobilized on MnFe2 O4 @SiO2 -CTAB composites, which had been demonstrated by X-ray photoelectron spectroscopy results. The adsorption of Cr(VI) onto MnFe2 O4 @SiO2 -CTAB followed the Freundlich isotherm model and pseudo-second-order model. Tests on the regeneration and reuse of the composites were performed. The removal efficiency of Cr(VI) still retained 92.4% in the sixth cycle. MnFe2 O4 @SiO2 -CTAB composites exhibited a great potential for the removal of Cr(VI) from water.