Rational Construction of Defects in Covalent Organic Frameworks for Highly Selective Uranium Extraction

Through rational defect design, engineering covalent organic frameworks (COFs) to overcome the issues of insufficient active sites and poor selectivity is an effective strategy. In this study, we successfully constructed a molecular unit-induced defect-engineered COF using a stoichiometric control strategy for efficiently capturing radioactive uranium from rare earth tailings wastewater. The rational introduction of a molecular unit-induced defect can alter the charge density of the COF, thereby enhancing the adsorption performance of the synthesized materials. Especially, the synergistic effect of carboxyl functional groups and defects effectively reduces the hydrophobicity of COF materials, alters the adsorption environment of the pores, and enhances the selectivity for uranyl ions. Impressively, the tailored defect COF exhibits a remarkable uranium adsorption capacity (551.8 mg/g) under pH 6. Furthermore, the selectivity of the defect COF remains as high as 94.5%, and the Kd value can reach up to 6.1 × 104 mL/g under actual rare earth tailings wastewater. These results demonstrate that the rational construction of defect engineering can markedly enhance the efficiency and selectivity of uranium adsorption on COFs. This work demonstrates that the rational construction of defect engineering in COFs provides an effective route for enhanced uranium sequestration.