Mei-Ling Feng,Debajit Sarma,Yu-Jie Gao,Xing-Hui Qi,Wei-An Li,Xiao-Ying Huang,Mercouri G. Kanatzidis
Unconventional ion exchangers can achieve efficient removal of [UO2]2+, Cs+, and Sr2+ ions from complex aqueous solutions and are of great interest for environmental remediation. We report two new gallium thioantimonates, [Me2NH2]2[Ga2Sb2S7]·H2O (FJSM-GAS-1) and [Et2NH2]2[Ga2Sb2S7]·H2O (FJSM-GAS-2), which present excellent ion exchange properties for [UO2]2+, Cs+, and Sr2+ ions. They exhibit high ion exchange capacities for [UO2]2+, Cs+, and Sr2+ ions (qmU = 196 mg/g, qmCs = 164 mg/g, and qmSr = 80 mg/g for FJSM-GAS-1, qmU = 144 mg/g for FJSM-GAS-2) and short equilibrium times for [UO2]2+ ion exchange (5 min for FJSM-GAS-1 and 15 min for FJSM-GAS-2, respectively). Both compounds display active ion exchange with [UO2]2+ in the pH range of 2.9–10.5. Moreover, the sulfide compounds could maintain high distribution coefficients KdU even in the presence of excess Na+, Ca2+, and HCO3–. The distribution coefficient KdU of 6.06 × 106 mL/g exhibited by FJSM-GAS-1 is the highest among the reported U adsorbents. The [UO2]2+-laden products can be recycled by conveniently eluting the uranium with a low-cost method. These advantages combined with facile synthesis, as well as β and γ radiation resistance, make FJSM-GAS-1 and FJSM-GAS-2 promising for selective separations in nuclear waste remediation.
A thermosensitive amidoxime-based hydrogel named PAOU was prepared from polyamidoxime through ion-imprinted polymerization, with UO 2 2+ 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 UO 2 2+ solution. The quasi-second-order kinetic equation and the Langmuir adsorption isotherm model were both followed by the adsorption of UO 2 2+ by PAOU. The thermodynamic parameters indicated that the adsorption process of PAOU was endothermic (Δ H θ = 27.04 kJ/mol) and spontaneous (Δ G θ = −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.
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