Enhanced adsorption of heavy metal ions onto simultaneous interpenetrating polymer network hydrogels synthesized by UV irradiation

Simultaneous interpenetrating polymer network (IPN) hydrogels have been prepared by UV-initiated polymerization of a mixture of 2-acrylamido-2-methyl-1-propansulfonic acid (AMPS) and triethylene glycol divinyl ether (DVE-3) with enhanced adsorption properties for heavy metal ion removal. The swelling ratio of the IPN hydrogels determined by gravimetric method increased with the AMPS content in the formulation. The IPN hydrogels were used to remove heavy metal ions from aqueous solution. The effects of pH value of the feed solution and AMPS content in the formulation on the adsorption capacity were investigated. The results indicated that the adsorption capacity increased with the pH values and AMPS content in the formulation. Furthermore, the synergistic complexation of metal ions with two polymer networks in the IPN was found in the adsorption studies. The adsorption isotherm of the IPN hydrogels can be well fitted to the Freundlich model. The adsorption kinetics on IPN hydrogels clearly followed an initial transport-controlled adsorption process, but transited to an attachment-controlled adsorption kinetics in the later stage. Thermodynamic parameters such as the Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) for the adsorption were estimated. Results suggested that the adsorption process was a spontaneous, exothermic process that had positive entropy.