Chiral metal-organic cage modified polyvinylidene fluoride membrane via metal phenolic networks for enantioseparation

High-performance chiral membrane materials hold great promise for the separation of pharmacological enantiomers. The key to achieving high-enantioselective chiral membrane separation is the development of suitable chiral membrane materials. However, traditional chiral separation membranes still face several limitations, including the main problem of the permeability-selectivity trade-off. In this study, a kind of novel chiral metal–organic cage (MOC) modified polyvinylidene fluoride (PVDF) membrane, namely PVDF@TA-Zn@MOC, was fabricated successfully by growing the chiral MOC [Zn3L2] onto the surface of PVDF substrate membranes induced by tannic acid (TA)-Zn2+ (TA-Zn) networks. In brief, ultrathin TA-Zn2+ metal-phenolic network coating was first adhered onto the surface of PVDF substrate membranes, followed with the in-situ growth of chiral MOC [Zn3L2] that was triggered by the coordination-enabled adhesion of Zn2+. A series of chiral PVDF@TA-Zn@MOC membranes were prepared with different hydrophilic properties and MOC loading by adjusting the concentrations of TA and metal/ligand. The transport and separation performances of these membranes were investigated for the mandelic acid (MA) enantiomers, and as a result, when the addition of TA was 1 mg and the metal ion concentration was 3.125 × 10-3 mol·L-1, the chiral membrane PVDF@TA-Zn@MOC-2 exhibited the most extraordinary entrapment ability in both permeability and selectivity for D-MA with an enantiomeric excess value of up to 71 % at a feed solution concentration of 300 ppm for 6 h under the neutral conditions. This method allows for the construction of the chiral hydrophilic MOC nanocoating membranes, which has the potential to broaden the applications of chiral MOC.