Flexible High-Aspect-Ratio COF Nanofibers: Defect-Engineered Synthesis, Superelastic Aerogels, and Uranium Extraction Applications

The lack of macro-continuity and mechanical strength of covalent organic frameworks (COFs) has significantly limited their practical applications. Here, we propose an "alcohol-triggered defect cleavage" strategy to precisely regulate the growth and stacking of COF grains through a moderate reversed Schiff base reaction, realizing the direct synthesis of COF nanofibers (CNFs) with high aspect ratio (L/D = 103.05) and long length (> 20 μm). An individual CNF exhibits a biomimetic scale-like architecture, achieving superior flexibility and fatigue resistance under dynamic bending via a multiscale stress dissipation mechanism. Taking advantages of these structural features, we engineer CNF aerogels (CNF-As) with programmable porous structures (e.g., honeycomb, lamellar, isotropic) via directional ice-template methodology. CNF-As demonstrate 100% COF content, high specific surface area (396.15 m² g^-1) and superelasticity (~ 0% elastic deformation after 500 compression cycles at 50% strain), outperforming most COF-based counterparts. Compared with the conventional COF aerogels, the unique structural features of CNF-A enable it to perform outstandingly in uranium extraction, with an 11.72-fold increment in adsorption capacity (920.12 mg g^-1) and adsorption rate (89.9%), and a 2.48-fold improvement in selectivity (U/V = 2.31). This study provides a direct strategy for the development of next-generation COF materials with outstanding functionality and structural robustness.