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

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 La(3+)-imprinted thermoresponsive hydrogel (CLIT) was prepared to accumulate La(3+) from solution. The CLIT was characterized by DSC, FITR, Raman spectroscopy, XPS, and SEM, which revealed obvious reversible thermosensitivity and imprinted sites of La(3+) ions. An adsorption capacity of 112.21 mg/g to La(3+) 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 La(3+)-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 k(La3+/Mn+) of CLIT were 2.04–3.51 times that of non-imprinted hydrogel, with k(La3+/Y3+), k(La3+/Gd3+), k(La3+/Al3+), k(La3+/Fe3+) and k(La3+/Cu2+) being 1.67, 2.04, 3.15, 2.72 and 4.84, respectively.