Rigidity‐Flexibility Regulation and Hard‐Soft Donor Combination: Dual Strategies in Covalent Organic Frameworks Construction for Actinides/lanthanides Separation

Separating actinides from lanthanides is essential for managing nuclear waste and promoting sustainable nuclear energy development. The recycling of transuranium elements (TRUs: Np, Pu, Am) is also significant for various nuclear technology applications. In this study, a dual strategy is introduced to designing covalent organic frameworks (COFs) that skillfully combines molecular rigidity with flexibility, integrating both hard and soft donor atoms in the synthesis of monomers. This results in a specialized COF that efficiently and selectively captures TRUs from acidic aqueous solutions. By utilizing the topological arrangement of rigid ligands to influence the twisting and stretching of flexible ligands, coordination environment featuring nitrogen and oxygen is created, which enhances the separation of transuranium in various oxidation states over lanthanides. In 0.5 m HNO