Benignly-fabricated supramolecular poly(amidoxime)-alginate-poly(acrylic acid) beads synergistically enhance uranyl capture from seawater

Design of amidoxime-based adsorbents in a cooperative and synergistic manner together with a concept of facile and green fabrication is becoming highly desirable to harvest uranium from seawater. Herein, taking benefit of supramolecular ionic-crosslinking and hydrogen bonding interactions, we have reported a simple and environmentally benign approach to construct novel bifunctional poly(amidoxime)-alginate-poly(acrylic acid) (PAO-A-PAA) composite beads. As a result of synergistic uranyl binding, the PAO-A-PAA composite beads reached a high adsorption capacity of 735.1 mg g−1 for uranium aqueous solution (36 ppm), which is 2.24 and 1.46 times that of monofunctional Alg-PAA (328.1 mg g−1) and Alg-PAO (502.2 mg g−1), respectively. More importantly, the PAO-A-PAA exhibits excellent selectivity towards U(VI) in the presence of natural organic matter and multiple coexisting metal ions in simulated seawater. The XPS analysis reveals the utilization and coordination of both amidoxime and carboxylate ligands of PAO-A-PAA for uranyl binding, which results in energetically more stable synergistic uranyl complexes (Ebinding = −9.45 to −10.34 eV) as proved by the density functional theory study. The adsorption efficiency of PAO-A-PAA is further supported by its ability to extract µg L−1-level uranium in real seawater (94.7–99.5%). The PAO-A-PAA also demonstrates good mechanical and chemical stability over a wide pH range, as well as good reusability. These findings provide insight into the significance of designing efficient sorbent material for enhanced uranyl capture via a supramolecular strategy.