Removal of toxic metals using superabsorbent polyelectrolytic hydrogels

Because of the presence of carboxylic acid moieties, poly(acrylic acid) possesses a unique ability to form stable complexes with divalent metal ions. However, its practical use for the removal of heavy metals from aqueous solutions is restricted because of its inherent water solubility. To address this issue, crosslinking of this polymer has been attempted to synthesize hydrogel, which is stable in aqueous medium over a wide range of pH values. The hydrogels, prepared by redox polymerization of acrylic acid in the presence of polyethylene glycol diacrylate as the crosslinker, were characterized by Fourier transform infrared spectrometry, elemental analysis, thermal analysis, and swelling studies. This chelating hydrogel‐bearing O, O donor groups exhibited high‐metal sorption capacity of 41.1, 58.2, 43.1, and 81.2 mg/g for Cr6+, Ni2+, Cu2+, and Pb2+, respectively, under optimum conditions. The effect of parameters including pH, concentration, and interference of common ions on metal uptake was also investigated. Langmuir and Freundlich adsorption isotherms have been used to validate the metal uptake data. High recovery (>97%) was achievable for all metal ions with 1N HCl as eluting agent, and the regeneration tests revealed that the sorbent could be used repeatedly for at least 10 cycles without any loss in chelating efficiency.