Enhanced adsorption of humic acid on amine functionalized magnetic mesoporous composite microspheres

Fe3O4@mesoporous SiO2 core–shell composite microspheres (MS), synthesized by a typical solvothermal reaction and PEI functionalized MS (MS-PEI), have been investigated for humic acid (HA) adsorption. The structure of microspheres was characterized using scanning electron microscope, transmission electron microscope, energy dispersive X-ray, N2 adsorption–desorption, zeta potential measurements, X-ray diffraction and vibrating sample magnetometer. The high saturation magnetization (31.9 emu/g) made them easier and faster to be separated from water under an external magnetic field. Batch adsorption tests indicated that MS-PEI exhibited high adsorption affinity to aqueous HA with a maximum adsorption capacity of 128.64 mg/g. The Freundlich model could fit the adsorption isotherm of HA on MS and MS-PEI very well, implying that adsorption processes are heterogeneous. HA adsorption on MS and MS-PEI could be well described by the pseudo-second-order kinetics. Adsorption of HA on the adsorbents was found to be strongly dependent on pH. HA loaded MS-PEI can be effectively desorbed in 0.1 M NaOH, and the regenerated microspheres can be recycled. So, it can be used as a promising adsorbent for the adsorptive HA removal in water treatment process.