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

Abstract

The large amount of uranium in seawater makes the development of effective extraction technologies particularly important. In this work, an efficient and selective adsorbent for uranyl ions, CS@Fe₃O₄ NPs@PCN-333, was synthesized by in situ assembling metal-organic frameworks on magnetic chitosan microspheres, possessing nano-pockets 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 maintained consistent high adsorption capacity over multiple cycles, and its magnetism provided 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-pockets constructed by amino, ortho-hydroxyl, and carboxyl groups formed a more stable coordination structure with UO₂²⁺ with high binding energy, and multiple coordinated adsorption sites facilitated 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.