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Abstract
New temperature-responsive hydrogels containing various composition of N-acryloyl morpholine (AM) and N-isopropyl acrylamide (NIPAM) were prepared by free-radical solution polymerization using poly(ethyleneglycol) diacrylate (PEGDA) as the chemical crosslinker. The gels were responsive to changes in external temperature, and exhibited the volume phase transition phenomenon. The gels swelled extensively in water at 23°C, with water-uptake of more than 90% at swelling equilibrium. The influence of molecular heterogeneity of the gels in terms of co-monomer and crosslinker composition on the swelling capacity and equilibrium water uptake was evaluated. The dye adsorption capacity of the gels at room temperature was studied using Congo red as a model dye. The gels displayed significant adsorption capacity of the dye, and the adsorption capacity was found to be dependent on the hydrophilic character of the gel. The characteristic adsorption parameters were determined using the Langmuir isotherm model. The value of equilibrium binding constant was below 1 which indicated favorable adsorption of dye by the hydrogels. The dye release behavior was studied below and above the volume phase transition temperature of the gels. The dye release from the gels was about 95% at temperatures above the volume phase transition temperature of the gels. These gels can be used as reversible sorbents in the efficient removal of Congo red from waste water.