Developing efficient adsorbents for uranium enrichment is of great significance for resource sustainability and environmental safety. This study presents a facile and adaptable post-synthetic strategy to prepare highly efficient uranium adsorbents via engineering the π-conjugated skeletons of homocoupled conjugated microporous polymers (HCMPs). Taking advantage of the diyne units in the π-conjugated skeletons, bis-amidoxime uranophiles, one of the state-of-the-art ligands of uranyl ions, were introduced to the frameworks of HCMPs. The functionalized HCMPs preserved the interconnected 3D microporous networks and rigid conjugated skeletons with abundant bis-amidoxime ligands uniformly distributed in the pore channels. Such structural advantages of the adsorbents afforded very fast adsorption kinetics within 15 min to reach the equilibrium and high capacity of uranium (450 mg/g). Moreover, DFT calculation suggests a synergistic coordination as the most energetically favored coordination mode of the uranyl/bis-amidoxime complexes. This study contributes new insights into the underlying mechanism responsible for the highly efficient adsorption ability of the bis-amidoxime-functionalized HCMPs toward uranium. Meanwhile, the synthetic methodology established here could be extended to task-specific design and skeleton engineering of more functional HCMPs for broadened applications.
Keywords: adsorption; amidoxime; density functional theory (DFT); homocoupled conjugated microporous polymer (HCMP); uranium.