Preparation of hydrogels based on pectin with different esterification degrees and evaluation of their structure and adsorption properties

In this study, pectin (Pe) with different esterification degrees was used as raw materials to prepared hydrogel adsorbents via free radical polymerization. The effect of Pe esterification degree on hydrogel structure and adsorption performance was studied by FTIR, SEM and XPS characterization and copper ion adsorption experiment. The results demonstrated that the carboxyl group in the hydrogels was bonded to Cu2+ through electrostatic force and coordination, which was an important factor in its adsorption capacity. The hydrogels prepared from Pe with low esterification degree had finer pores and higher carboxyl content, so the adsorption capacity on both water and Cu2+ was stronger. The preparation of hydrogels from low-ester Pe was more conducive to the adsorption of copper ions. Besides, the adsorption behavior of the hydrogels on Cu2+ was investigated through the adsorption thermodynamics and kinetics. The results indicated that the adsorption kinetics of the hydrogels was in accordance with the quasi-second-order model. The adsorption of Cu2+ by hydrogels was the result of physical and chemical adsorption, which was endothermic under natural condition, and a higher temperature will result in more favorable spontaneous adsorption.