High Performance Enantioselective Separation Facilitated by Charged Chiral Covalent Organic Framework Membrane

To date, the application of chiral covalent organic frameworks (CCOFs) as membranes has encountered considerable challenges in attaining high enantioselectivity. In this study, a pair of charged CCOFs, constructed from pyridinium units serving as the framework linkages, was synthesized via a bottom-up synthetic strategy. The incorporation of these irreversible bonds confers substantial stability, particularly under aqueous conditions. These porous chiral materials were subsequently incorporated into a polytetrafluoroethylene membrane, which functioned as the supporting substrate for membrane separation. The resulting membrane exhibited pronounced enantioselectivity toward mandelic acid, tryptophan, and phenylalanine. Enantioseparation analyses revealed that the (S)-CCOF possessed a strong affinity for l-enantiomers, facilitated by multiple intermolecular interactions. Notably, the ionic-pairing effect enhanced the retention of l-enantiomers within the membrane's cavity channels, thereby allowing d-enantiomers to permeate more readily through the porous structure. This separation strategy achieved a maximum enantiomeric excess of 96.2 ± 0.5%. Furthermore, the membrane demonstrated satisfactory reproducibility. In brief, these findings underscore the considerable potential of charged CCOFs to enhance functional performance in membrane-based enantioseparation processes.