Synthesis and characterization of poly(HEA/MALA) hydrogel and its application in removal of heavy metal ions from water

A novel poly(Hydroxyethyl methacrylate/Maleamic acid) (p(HEA/MALA)) hydrogel was synthesized by 60Co-γ induced copolymerization, and used to remove Pb2+, Cd2+, Ni2+ and Cu2+ from aqueous solutions. The prepared copolymer was characterized by using the FTIR spectra, TGA analysis and XPS analysis. Batch equilibrium experiments were conducted to investigate the effects of pH, time, initial metal ion concentration and competition properties of the solutions on the adsorption of Pb2+, Cd2+, Ni2+ and Cu2+ ions. FTIR spectra and TGA analysis showed that the p(HEA/MALA) hydrogel was indeed a copolymer of HEA and Maleamic acid. Adsorption kinetics of Pb2+, Cd2+, Ni2+ and Cu2+ ions on p(HEA/MALA) followed pseudo-second-order kinetic model, and the adsorption rates followed the order Cd2+ > Pb2+ > Ni2+ > Cu2+. The isotherm experimental data fitted better to the Langmuir model (R2 > 0.99) than the Freundlich model, demonstrating that the Pb2+, Cd2+, Ni2+, Cu2+ on p(HEA/MALA) was removed through Langmuir monolayer adsorption. The XPS spectra of p(HEA/MALA) with and without chelate metal ions indicated that Pb2+, Cd2+, Ni2+ and Cu2+ were adsorbed via the chelation of NH2 groups and the ion-exchange of COOH groups. According to the competitive adsorption results, the priority order in multi-component adsorption was Pb2+ > Cu2+ > Ni2+ > Cd2+. These findings suggest that the hydrogel is a promising adsorbent to separate and recover the heavy metal ions from contaminated water.

• A novel poly(Hydroxyethyl methacrylate/Maleamic acid) hydrogel was synthesized.
• The adsorption kinetics and isotherms of metal ions on the hydrogel were studied.
• The adsorption of heavy metal ions on the copolymer was pH-dependent.
• The mechanisms are electrostatic interaction, chelation and ion-exchange.