Spatially confined coordination platform in covalent organic framework for selective uranium adsorption from aqueous solutions

The use of covalent organic frameworks (COFs) to remove uranium from nuclear wastewater, especially capture uranium by well-defined nanopores and customizable groups, is highly desired. The development of an ideal binding site with optimal balance between adsorption capacity and selectivity has remained an attractive challenge. Herein, a staggered stacking self-assembly approach was adapted to control the pore size and confine space of dioxin-linked COF-316 with modified functional groups to achieve higher capture efficiency. EXAFS analysis suggested that COF-316-COOH and COF-316-AO both have high affinities toward U(VI) owing to inner-sphere surface complexation by two or three atoms, DFT calculations further revealed that the uranyl cation was coordinated by = NOH or –COOH groups from two adjacent COF layers. The synergistic coordination in multi-confined interlaminar position provides an ideal spatial coordination platform for uranium, and the merits of capacity, selectivity and stability underscore the potential application of COF-316-AO for efficient uranium removal.