Calixarene-Based Porous Coordination Cages for Ultrafast Extraction of Uranium From Seawater

The design and synthesis of porous framework materials with strong affinity and selectivity for uranyl ion are extremely appealing for the efficient extraction of uranium from seawater. Herein, rectangular porous framework cage(denoted as Co16) is prepared by using p-tert-butylsulfonylcalix［4］arene, CoCl2·6H2O and 1,3-bis(2H-tetrazol-5-yl)benzene (H2L) ligands under solvothermal conditions. Further, the Co16 is used for uranium extraction. As the result, the Co16 exhibits short adsorption equilibrium time(≈90 min) and is in accordance with the pseudo-second-order kinetic model. Robust framework and active U(Ⅵ) adsorption in the wide pH range are displayed. Besides, Co16 adsorbents exhibit high U(Ⅵ) uptake capacity(547.31 mg/g) and well fit the Langmuir model. Adsorption thermodynamics research has clearly demonstrated that the adsorption process is endothermic and spontaneous. Furthermore, Co16 achieves a high uranium adsorption capacity(4.88 mg/g) after immersing in real seawater for 20 days. Overall, these advantages of Co16 adsorbents highlight the potential candidate for the selective capture of U(Ⅵ) from seawater.