Facile Cross-Link Method To Synthesize Magnetic Fe3O4@SiO2–Chitosan with High Adsorption Capacity toward Hexavalent Chromium

The magnetic Fe3O4@SiO2–chitosan (MFSC) with an extremely high adsorption capacity of 336.7 mg g–1 toward toxic Cr(VI) was synthesized successfully by a simple cross-link method. The physicochemical properties of the Fe3O4, Fe3O4@SiO2, and MFSC were characterized comparatively via X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, N2 adsorption–desorption, X-ray photoelectron spectroscopy analysis, and vibrating sample magnetometer. Their adsorption processes are well-fitted by the pseudo-second-order kinetic model; their equilibrium isotherms are better matched with the Langmuir isotherm. Further recycling experiments of MFSC show that its adsorption capacity of 78.6 mg g–1 still remains 81.7% of the original value (96.2 mg g–1), even after five times reuse. The interference adsorption experiments show that MFSC has stronger affinity for Cr(VI) in the solution containing Cr(VI), Cd(II), Cu(II), Zn(II), and Ni(II). The high adsorption capacity, good selectivity, and easy separation of MFSC clearly indicate that it is a potential recyclable adsorbent for Cr(VI) removal from wastewater.