Hydroxyl-directed phosphorylated cationic metal-organic framework for enhanced uranium adsorption from aqueous solutions

The targeted immobilization of high-affinity functional groups within robust porous frameworks is crucial for developing selective adsorbents for uranium extraction from wastewater. A nickel-based cationic metal-organic framework (MOF) is first synthesized and subsequently phosphorylated via the modification of its ligand hydroxyl groups, producing an efficient uranium adsorbent (NiBTAB-PO 3 H 2 ). The adsorption performance of NiBTAB-PO 3 H 2 for U(VI) is systematically evaluated under various conditions, including pH, initial concentration, contact time, and the presence of competing ions. Owing to the strong coordination of the grafted phosphate groups with UO 2 2+ , NiBTAB-PO 3 H 2 exhibits an enhanced maximum adsorption capacity of 166.6 mg/g at pH = 5. The adsorption process is well-fitted by the Langmuir isotherm and the pseudo-second-order kinetic model. NiBTAB-PO 3 H 2 demonstrates exceptional selectivity for U(VI), almost maintaining its adsorption capacity in multiple competing ions. This work highlights NiBTAB-PO 3 H 2 as a highly effective adsorbent for uranium recovery, primarily due to its engineered phosphate functionality.