Tailoring chelating sites in two-dimensional covalent organic framework nanosheets for enhanced uranium capture

In this study, we intricately designed and synthesized two isoreticular two-dimensional covalent organic framework nanosheets, namely TAPA-COF-1 and TAPA-COF-2, distinguished by their unique spatial arrangement of hydroxyl groups. These precisely engineered nanosheets were employed as a tailored platform for the selective capture of uranium, due to their tunable chelating sites and characteristic sheet-like morphology. Notably, TAPA-COF-1, featuring ortho-hydroxyl groups, demonstrated a significantly enhanced adsorption capacity for uranium capture originating from the additional oriented adjacent phenolic hydroxyl chelating sites in comparison to TAPA-COF-2 with para-hydroxyl groups, which was proved by theoretical calculation. The impressive features of TAPA-COF-1, including its notable selectivity, rapid adsorption kinetics, and high uptake capacity (657.2 mg g-1), endow it as a highly promising candidate for uranium capture. Two isoreticular two-dimensional covalent organic framework nanosheets are elaborately designed and synthesized, showcasing distinctive U(vi) capture performance attributed to the varied spatial arrangement of chelating sites.