Efficient and selective extraction of uranyl ions from seawater by nano-pocket structures with multiple coordinated sites

The several hundred times higher uranium concentration in seawater than that in on land makes the development of effective technologies for extracting uranium from seawater particularly important. In this work, an efficient and selective uranyl ions adsorbent, CS@Fe3O4 NPs@PCN-333, was synthesized by in situ assembling metal-organic frameworks on magnetic chitosan microsphere, possessing nano-pocket with multiple adsorption sites. The uncoordinated carboxyl groups enhanced the stability of as synthesized materials in acidic media and significantly improved their adsorption capacity for UO22+. The material maintains consistent high adsorption capacity over multiple cycles, and its magnetism provides the possibility of rapid separation from seawater. A maximum adsorption capacity of 785.48 mg g-1 was achieved for UO22+ with high selectivity. The characterization and DFT calculation results showed that nano pocket constructed by amino, ortho-hydroxyl, and carboxyl groups forms a more stable coordination structure with UO22+ with high binding energy, and multiple coordinated adsorption sites facilitated the effective UO22+ enrichment through high binding energy. Consequently, this work provides a promising material for the highly efficient extraction of uranyl ions from natural seawater.