Selective Recovery of Uranyl Ions From Sea Water Using Covalent Organic Framework Membranes

The selective recovery of uranyl ions from aqueous environments is important for both uranium resource utilization and environmental remediation. However, achieving high ionic selectivity in membrane-based separations without compromising water permeability remains a significant challenge. Herein, we employ molecular dynamics simulations to elucidate how covalent organic framework (COF) membranes can be engineered for selective uranyl rejection. Slipped TpPa-1 and TpPa-F4 membranes exhibit complete rejection of ${\mathrm{UO}}_2^{2+}$ while allowing the passage of competing ions, whereas TpBpy and Tp-Azo exhibit only partial rejection. Both TpPa-1 and TpPa-F4 suppresses the transport of other divalent ions, such as ${\mathrm{Ca}}^{2+}$ and ${\mathrm{Mg}}^{2+}$ , pointing to a broader selectivity against multivalent species. Free energy calculations reveal that this selectivity originates from an energetic barrier of 3.6 kcal ${\mathrm{mol}}^{-1}$ imposed by the bilayer pore environment, which selectively impedes ${\mathrm{UO}}_2^{2+}$ ions without hindering the transport of water or monovalent ions. This mechanism remains effective in multilayer TpPa-1 membranes, demonstrating its robustness with increasing thickness. Collectively, these findings establish a clear structure-transport relationship in COF membranes and position slipped architectures as a viable route for uranium resource recovery and for mitigating uranium contamination in aquatic environments.