Sustainable Uranium Extraction via Reversible Uranyl Carbonate Capture-Release Cycling Stemming from Weak Interaction...

Extracting abundant uranium resources from the ocean would contribute greatly to the sustainable development of nuclear energy. In this work, it is found that the imine N, phenol-bidentate chelation groups from imine-Covalent-Organic Frameworks (COFs) are superior sites for the weak complexation with uranyl carbonate species. The surprisingly low binding energy of -13.36 kcal mol^-1 originating from the weak coordination bond and hydrogen bond benefits to the readily spontaneous decomplexation of the chelated uranyl carbonate species by CO₃ ^2- ions. Through the rational design of three COFs with uniform imine N, phenol-bidentate sites but varied amine monomer geometry, i.e., pyrene COF (Py-COF), 1,3,5-Triazine COF (TTA-COF) and porphyrin COF (TAPP-COF), it's found that the abundantly available imine N, phenol-bidentate sites ensured by the high specific surface area and strong hydrophilicity of Py-COF and TTA-COF result in the highly reversible uranyl capture-release during the cycled extraction of uranyl carbonate from seawater and mild elution with 2.0 mM Na₂CO₃ solution. With the 3.0 × 3.0 cm² self-supported plate fabricated by Py-COF growth on carbon cloth, a record high uranium extraction capacity of 45 mg g^-1 (i.e., 3.0 mg g^-1 day^-1) from seawater is achieved within 15 days' capture-release cycles.