Chitosan/polyethyleneimine magnetic hydrogels for adsorption of heavy metal ions

Various adsorption materials are widely used in the treatment of heavy metal wastewater and dye wastewater because of their good adsorption properties. Here, polyethyleneimine (PEI)-modified chitosan magnetic hydrogels were prepared through a chemical co-precipitation method using glutaraldehyde as the cross-linking agent. The functional groups and structures of the hydrogels were characterized by Fourier-transform infrared spectroscopy and X-ray diffraction phase analysis, respectively. The surface structures were characterized by scanning electron microscopy. The magnetic parameters including hysteresis loops of the hydrogel were measured. Heavy metal adsorption experiments showed that the synthesized magnetic hydrogel had good adsorption properties for heavy metals, and saturated adsorption of Pb 2+ , Ni 2+ , and Cu 2+ reached 100.32, 105.98, and 128.96 mg g −1 , respectively. Studies of isothermal adsorption and adsorption kinetics showed that the adsorption process follows a pseudo-second-order kinetics model adsorption, as the Langmuir isothermal adsorption. Selective adsorption of heavy metal ions by a magnetic hydrogel showed that Pb 2+ , Ni 2+ , and Cu 2+ had obvious competitive adsorption (on the order of Cu 2+ > Ni 2+ > Pb 2+ ). The cyclic adsorption of metal ions showed that the magnetic hydrogel could be reused by 0.02 mol L −1 EDTA-2Na desorption. The hydrogel retained its good adsorption properties, and the removal rate of Pb 2+ , Ni 2+ , and Cu 2+ was still more than 85% after 4 cycles. The PEI-modified chitosan magnetic hydrogel adsorbent thus had broad application prospects for the treatment of heavy metal wastewater. Graphical abstract