Water-Recyclable Chitosan-Based Ion-Imprinted Thermoresponsive Hydrogel for Rare Earth Metal Ions Accumulation

Abstract

The demand for rare earth metal increases rapidly in the modern high-tech industry and therefore the accumulation of rare earth metal ions from an aqueous environment becomes a significant concern worldwide. In this paper, a water-recyclable chitosan-based La3+-imprinted thermoresponsive hydrogel (CLIT) was prepared to accumulate La3+ from solution. The CLIT was characterized by DSC, FITR, Raman spectroscopy, XPS, and SEM, which revealed obvious reversible thermosensitivity and imprinted sites of La3+ ions. An adsorption capacity of 112.21 mg/g to La3+ ions was achieved on CLIT under its optimum adsorption conditions (pH 5, 50 °C, 60 min). The adsorption could be well illustrated by second-order kinetics and Freundlich isotherm models. The La3+-adsorbed CLIT could be recycled only by rinsing with 10 °C cold water, with a desorption rate of 96.72%. After ten cycles of adsorption-desorption, CLIT retained good adsorption capability. In the solution containing six ions, the adsorption coefficients kLa3+/Mn+ of CLIT were 2.04–3.51 times that of non-imprinted hydrogel, with kLa3+/Y3+, kLa3+/Gd3+, kLa3+/Al3+, kLa3+/Fe3+ and kLa3+/Cu2+ being 1.67, 2.04, 3.15, 2.72 and 4.84, respectively.