Bifunctional PEI/SA Hydrogel With Phosphate‐Amidoxime Groups for Enhanced Uranium Extraction From Seawater

ABSTRACT Efficient uranium capture from seawater could alleviate terrestrial uranium scarcity. The key challenge is developing advanced adsorbents with excellent adsorption capacity and environmental stability. In this work, a novel polyethyleneimine/sodium alginate (PEI/SA) hydrogel bifunctionalized with phosphate and amidoxime groups is fabricated by covalent, ionic, and hydrogen‐bond cross‐linking (PSP‐AOAM). The multi‐crosslinked network and various functional groups impart this spongy hydrogel with good structural stability and abundant accessible binding sites. PSP‐AOAM demonstrates an ultra‐high adsorption capacity of 501.04 mg·g −1 in an 8 mg·L −1 uranium solution. The adsorption kinetic data are well fitted by the pseudo‐second‐order and the Weber‐Morris model. Moreover, it shows excellent selectivity for UO 2 2+ over various competing ions while maintaining a large adsorption amount of 386.31 mg·g −1 with an elution efficiency of 85.3% after five cycles. It also achieves a uranium uptake of 6.1 mg·g −1 from natural seawater within 30 days. XPS analysis and DFT calculations reveal that the phosphate, amidoxime, carboxyl, and amino groups in PSP‐AOAM capture uranyl ions through the synergistic coordination effect. Our study offers a valuable approach to designing adsorbents with synergy among multiple functional groups.