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 degree celsius (exothermic peak) and 39.64 degree celsius (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 degree celsius, 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 (Delta H-theta = 27.04 kJ/mol) and spontaneous (Delta G(theta) = -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 similar to 42.04. It outperformed its non-imprinted equivalent in terms of adsorption selectivity. The adsorbent also showed good uranium adsorption ability in natural seawater.