Skeleton engineering of rigid covalent organic frameworks to alter the number of binding sites for improved radionuclide extraction

Crystalline porous covalent frameworks (COFs) have been considered as a platform for uranium extraction from seawater and nuclear waste. However, the role of rigid skeleton and atomically precise structures of COFs is often ignored in the design of defined binding configuration. Here, a COF with an optimized relative position of two bidentate ligands realizes full potential in uranium extraction. Compared with the para-chelating groups, the optimized ortho-chelating groups with oriented adjacent phenolic hydroxyl groups on the rigid skeleton endow an additional uranyl binding site, thereby increasing the total number of binding sites up to 150%. Experimental and theoretical results indicate that the uranyl capture is greatly improved via the energetically favored multisite configuration and the adsorption capacity reaches up to 640 mg g-1, which exceeds that of most reported COF-based adsorbents with chemical coordination mechanism in uranium aqueous solution. This ligand engineering strategy can efficiently advance the fundamental understanding of designing the sorbent systems for extraction and remediation technology.

Automated summary

In this study, a COF with optimized relative position of two bidentate ligands is designed for uranium extraction. The optimized ortho-chelating groups with adjacent phenolic hydroxyl groups on the rigid skeleton provide additional uranyl binding sites, resulting in a 150% increase in total binding sites. Experimental and theoretical results demonstrate improved uranyl capture and higher adsorption capacity compared to other COF-based adsorbents in uranium aqueous solution. This ligand engineering strategy enhances the fundamental understanding of sorbent system design for extraction and remediation technology.