Polyethylenimine-functionalized poly(vinyl alcohol) magnetic microspheres as a novel adsorbent for rapid removal of Cr(VI) from aqueous solution

A novel adsorbent, polyethylenimine-functionalized poly(vinyl alcohol) (PVA-PEI) magnetic microspheres, was prepared by a process involving: (1) synthesis of magnetic poly(vinyl acetate) microspheres (PVAc) using modified suspension polymerization, (2) preparation of PVA magnetic microspheres by methanolysis of PVAc and (3) two-step reaction with epichlorohydrin and polyethylenimine to yield amino groups. Magnetic measurement illustrated that the PVA-PEI microspheres were superparamagnetic, with a high saturated magnetization of 36.7 emu/g. Once generated, the PVA-PEI microspheres were used as adsorbent to remove Cr(VI) from an aqueous solution. The results demonstrated that the optimized pH value was observed at 2.0. The adsorption rate was extremely fast and the equilibrium was reached within 8 min. The adsorption isotherms of the adsorbent were preferably fitted to the Langmuir model, with the maximum adsorption capacity of 88.4 mg/g at 25 °C. Thermodynamic parameters indicated the spontaneous and exothermic nature of adsorption. In addition, the Cr(VI) ions were successfully eluted by a 0.1 mol/L NaOH solution, with the desorption efficiency of over 99%, and the adsorbent exhibited a good reusability. These results implied that the PVA-PEI microspheres should be considered as a potential adsorbent to remove Cr(VI) from wastewater.