Enantiomeric Separation of Chiral Hyper-Crosslinked Polymer Based Nanotube Membranes

Abstract

The separation of racemic mixtures remains a great challenge due to the similar physicochemical properties of enantiomers in an achiral environment. Currently, membrane-based separations often face a trade-off between permeability and enantioselectivity. In this study, a uniquely fibrous nanotube membrane, derived from a chiral hyper-crosslinked polymer (CHCP), was constructed and used to separate racemates, motivated by the need for more efficient and scalable separation methods. The results show that such the CHCP-based nanotube membrane exhibits a 2~4 orders of magnitude increase in flux compared to conventional chiral separation membranes and a ca. one order of magnitude improvement relative to GO-based membranes, while maintaining the superior enantioselectivity. This can be attributed to the CHCP-based nanotube that is rich in the micropore and mesopore, thereby resulting in the ultimate membrane that is characteristic of the hierarchically porous structure and the high porosity. Moreover, this membrane displays a great stability, which offers a significant potential for scalable and continuous operations. Experimental studies, combined with density functional theory calculations, substantiate that this membrane follows the retarded transport mechanism, having a great promise in resolving the inherent trade-off. Our findings suggest that this CHCP-based nanotube can find applications in various fields, e.g., separation, catalysis, etc., due to its intrinsic porosity, good processability and ease of synthesis and modifiability.

Keywords: Hyper-crosslinked polymers, Enantioseparation, Membranes, Retarded transport, High flux