Magnetic ion-imprinted microspheres for the removal of heavy metal ions from aqueous solution

Magnetic ion-imprinted microspheres (IIM) with core-shell structure were successfully prepared by reverse emulsion polymerization and applied to adsorb heavy metal ions from sewage. The semi-interpenetrating polymer network composed of cross-linked polyacrylamide (PAM) and linear chitosan (CTS) was used as the microgel shell of microspheres, which can not only fully retain the active sites of CTS but also tightly encapsulate magnetic particle nuclei. In addition, ion imprinting technology was used to further improve the adsorption capacity. In this study, the effects of PAM to CTS ratio on the thermal stability, magnetic properties, and microstructure of microspheres were investigated. Adsorption studies showed that IIM exhibited excellent selective adsorption of Cu(II), and the effects of initial concentration of metal ions, adsorption time, adsorbent dosage, pH, ionic strength, and cycle times on adsorption of Cu(II) by IIM-2 were also studied. In addition, it was revealed that pseudo-second-order kinetic model and Langmuir isotherm model could better simulate the adsorption kinetic and isotherm of IIM-2 for Cu(II), respectively. At 30 degrees C and pH 5.0, the theoretical maximum adsorption capacities for Cu(II) by IIM-2 were 151.13 mg/g. X-ray photoelectron spectroscopy and Zeta potential study showed that the adsorption mechanism of IIM-2 was a combination of electrostatic interaction and ion exchange.