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.
Wang et al. (Tue,) studied this question.