Temperature-sensitive amidoxime-based hydrogels for fast and efficient adsorption of uranium ions

A thermosensitive amidoxime-based hydrogel named PAOU was prepared from polyamidoxime through ion-imprinted polymerization, with UO22+ as the template ions and N-isopropylacrylamide as the monomer. The PAOU was characterized by DSC, FTIR, SEM/EDS, XPS and Raman spectroscopy. PAOU expressed phase transition at 29.76 °C (exothermic peak) and 39.64 °C (endothermic peak), respectively, and still maintained good reversible thermosensitivity after five cycles of heating and cooling. The maximum adsorption capacity of PAOU (dry weight 10 mg) was 856.47 mg/g after adsorption for 50 min at 50 °C, pH 4.5, 80 mL 0.5 mg/mL UO22+ solution. The quasi-second-order kinetic equation and the Langmuir adsorption isotherm model were both followed by the adsorption of UO22+ by PAOU. The thermodynamic parameters indicated that the adsorption process of PAOU was endothermic (ΔHθ= 27.04 kJ/mol) and spontaneous (ΔGθ= −19.17 kJ/mol). After five cycles of adsorption–desorption experiments on PAOU under optimal adsorption conditions, the adsorption capacity of PAOU was 704.32 mg/g, being 82.23 % of the first adsorption capacity. The adsorption selectivity coefficients of PAOU in seven kinds of mixed metal ion solutions were 1.61 ∼ 42.04. It outperformed its non-imprinted equivalent in terms of adsorption selectivity. The adsorbent also showed good uranium adsorption ability in natural seawater.