Moderately Crystalline Azine-Linked Covalent Organic Framework Membrane for Ultrafast Molecular Sieving

Covalent organic frameworks are potential candidates for the preparation of advanced molecular separation membranes due to their porous structure, uniform aperture, and chemical stability. However, the fabrication of continuous COF membranes in a facile and mild manner remains a challenge. Herein, a continuous, defect-free, and flexible azine-linked ACOF-1 membrane was prepared on a hydrolyzed polyacrylonitrile (HPAN) substrate via in situ interfacial polymerization (IP). A moderately crystalline COF ultrathin selective layer enabled ultrafast molecular sieving. The effect of synthesis parameters including precursor concentration, catalyst dosage, and reaction duration on the dye separation performance was investigated. The optimized membrane displayed an ultrahigh water permeance of 142 L m^-2 h^-1 bar^-1 together with favorable rejection (e.g., 99.2% for Congo red and 96.3% for methyl blue). The water permeance is 5-12 times higher than that of reported membranes with similar rejections. In addition, ACOF-1 membranes demonstrate outstanding long-term stability together with organic solvent and extreme pH resistance. Meanwhile, the membrane is suitable for removing dyes from salt solution products owing to their nonselective permeation for hydrated salt ions (<10.6%). The superior performance and the excellent chemical stability render the ACOF-1 membrane a satisfactory system for water purification.