Cyclodextrin metal-organic framework-polymer composite membranes towards ultimate and stable enantioselectivity

Homochiral metal-organic framework (MOF)-based membranes are highly attractive for continuous and efficient chiral resolution, but the decline of membrane enantioselectivity with permeation time remains a common issue for their practical applications. In this work, ultrahigh and stable enantioselectivity is achieved by mixed-matrix membranes (MMMs) composed of cyclodextrin (CD)-MOF as a chiral selector and polyethersulfone (PES) as a matrix. The CD-MOF/PES MMM with a 20 wt% CD-MOF loading achieves a stable and nearly 100% enantioselectivity of R-(+)-1-phenylethanol over S-(−)-1-phenylethanol when non-polar n-hexane is used as the solvent, while the membrane enantioselectivity decreases with the permeation time when polar methanol and ethanol are used as solvents. It is found that the interaction of solvent with chiral molecules and MOF structure is a key factor for consideration in the design of homochiral MOF-based membranes in addition to the choice of membrane materials and fabrication process. This work provides a new strategy to develop enantioselective membranes with ultrahigh and stable selectivity using homochiral MOFs and common membrane polymers.