Functionalized polyarylether-based COFs for rapid and selective extraction of uranium from aqueous solution

Selective uranium extraction from aqueous solution is critical for both radioactive contamination remediation and uranium recovery from seawater. Herein, amidoxime (−AO) and carboxyl (–COOH) groups are equipped on a polyarylether-based covalent organic framework (COF) for fabrication of post-modified adsorbents, JUC-505-AO and JUC-505-COOH. The maximum adsorption capacities (Qm) of JUC-505-AO and JUC-505-COOH are 395 mg⋅g−1 and 464 mg⋅g−1, respectively. JUC-505-COOH shows preponderant uranium extraction efficiencies of 36–95% at low pH 2–4, and its removal performances are almost unaffected at high temperature ranging from 25 to 80 °C. Whereas, JUC-505-AO exhibits an impressive adsorption kinetics with the adsorption process equilibrates within 20 min (C0 = 20 mg⋅L-1), and marked sorption selectivity toward uranium against coexisting metal ions. JUC-505-AO also capable of extracting uranium with fast kinetics and capacity (Qm = 4604 μg⋅g−1) from real seawater. U L3 edge X-ray absorption spectra analysis reveals that uranyl ions in JUC-505-AO are anchored by coordinating with O and N from the oxime groups by η2 mode with the coordination numbers of 5 or 6. Meanwhile, HOH⋅⋅⋅O hydrogen bonds between the coordinated water of the hydrated uranyl ions and the oxygen atoms on the skeleton of JUC-505-AO were observed by density functional theory simulations.