Sulfhydryl functionalized hydrogel with magnetism: Synthesis, characterization, and adsorption behavior study for heavy metal removal

• A novel Fe3O4-poly(l-cysteine/2-hydroxyethyl acrylate) hydrogel was synthesized.
• The adsorption kinetics and isotherms of metal ions on the hydrogel were studied.
• The adsorption mechanisms were a combined reaction of chelation and ion-exchange.

In this study, functionalized hydrogel with sulfhydryl group was initially synthesized by 60Co-γ induced copolymerization and then loaded with Fe3O4 nanoparticles by in situ coprecipitation method. The prepared magnetic hydrogel, Fe3O4-poly(l-cysteine/2-hydroxyethyl acrylate) (Fe3O4-P(Cys/HEA)), was used to remove Pb2+, Cd2+, Ni2+ and Cu2+ from aqueous solutions, and was characterized by various methods including scanning electron microscope, FTIR spectroscopy, X-ray diffraction, vibrating sample magnetometer, and X-ray photoelectron spectroscopy. The FTIR spectra analysis identified its functional groups featured of –NH2 and –SH, indicating that the magnetic hydrogel was indeed a copolymer of 2-hydroxyethyl acrylate and l-cysteine. The saturation magnetization and superparamagnetic properties of the hydrogel were also measured, laying a foundation for the separation of Fe3O4-P(Cys/HEA) hydrogel from the environment when adsorption completed. The performance of the sulfhydryl modified magnetic hydrogel for heavy metal ions removal was evaluated by changing four process variables: pH, temperature, initial heavy metal concentration and the contact time of adsorbent and heavy metal solutions. Results showed that the hydrogel was pH sensitive but barely affected by temperature, and the adsorption process followed a pseudo-second-order rate equation and better fitted Langmuir monolayer adsorption. X-ray photoelectron spectroscopy analysis of the magnetic hydrogel further revealed that the adsorption mechanisms of Pb2+, Cd2+, Cu2+ and Cr3+ on Fe3O4-P(Cys/HEA) could be a combined reaction of chelation and ion-exchange between functional groups and metal ions. Moreover, Fe3O4-P(Cys/HEA) was regenerated with an efficiency of greater than 90% using 0.1 M ethylene diamine tetraacetic acid.