Ultrastable and Robust Free-Standing COF Fiber Composite Membrane Enabled by Hydrogen Bonding for Selective Chromium(VI) Adsorption.

Covalent organic frameworks (COFs) are widely used due to their high structural order, tunable pore size, and large specific surface area. However, COFs are typically bulk solid microcrystalline powders that are insoluble and challenging to process, which significantly impacts their application prospects. We report a method for the in situ growth of COF-COOH on the surface of polyacrylonitrile (PAN) fibers by using electrospinning. COFs were synthesized via a solvothermal method suitable for most COF materials. Nitrogen atoms in the nitrile groups of the PAN macromolecular chain form hydrogen bonds with the hydrogen atoms of the monomer 2,5-diamino-terephthalic acid (DABDA). This interaction facilitates the effective mixing of PAN and DABDA, resulting in the uniform growth of COF-COOH, which adheres firmly to the fiber surface. The resulting PAN@COF-COOH fiber membrane exhibits remarkable structural stability. It has obvious adsorbability to chromium(VI) (Cr(VI)) in aqueous solution under acidic conditions and also for cationic dyes such as Rhodamine B and methylene blue. It is revealed that COF materials exhibit selective adsorption due to pore size limitations. The integration of the electrospinning method with COF materials allows for the large-scale production of COF fiber membranes, which holds significant importance and offers broad application prospects in this field.