Thermoresponsive‐interpenetrating polymer network hydrogels for heavy metal ion recovery

ABSTRACT Thermoresponsive‐interpenetrating polymer network (TR‐IPN) hydrogels containing a large number of chelating groups were synthesized; the aim was to ensure the recovery of large amounts of heavy metal ions through temperature cycling across volume phase transition temperature of the hydrogel. The TR‐IPN hydrogels were synthesized from poly(N‐isopropylacrylamide) and alginate, and the ability of these hydrogels to adsorb a heavy metal ion, Cu(II), was investigated at different temperatures. In the experiment, the hydrogels were prepared using various alginate and crosslinker concentrations. Despite the incorporation of a large number of chelating groups, the TR‐IPN hydrogels exhibited a large thermoresponsive volume change regardless of the presence of Cu(II). The Cu(II) adsorption experiment showed that the saturated adsorption amount of the hydrogels was larger at 50 than at 10 °C. In addition, we demonstrated that the difference between the amounts adsorbed at 10 and 50 °C, which we consider to be the amount of Cu(II) that the TR‐IPN hydrogels can recover through temperature cycling, was greater than those obtained by other conventional copolymerized thermoresponsive hydrogels. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46701.