Preparation of a cyclodextrin metal-organic framework (CD-MOF) membrane for chiral separation

Due to their unique properties, the efficient separation of racemic mixtures remains a great challenge. Recently, membrane separation has been demonstrated as a promising chiral separation technique with the advantages of continuous operation, high throughput, and cost effectiveness. In this work, a cyclodextrin-metal-organic framework (CD-MOF) was prepared and then composited with polyvinylidene fluoride (PVDF) polymer by the phase inversion via immersion precipitation method to form a CD-MOF/PVDF composite membrane for chiral amino acid separation for the first time. The composite membranes prepared under different conditions were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) thermogravimetric analysis (TGA)and differential scanning calorimetry (DSC). The effects of preparation conditions including CD-MOF load, polymer concentration, and casting solution temperature on the hydrophilicity, water flux, bovine serum albumin (BSA) rejection and chiral separation performance of the membrane were investigated. It is found that the composite membrane (V-5%−12) prepared with the CD-MOF load of 5%, polymer concentration of 12%, and casting solution of 70 ℃ shows the best performance with the water flux of 466.4 L/m2∙h, BSA rejection rate of 24.3% and stable 100% separation efficiency for phenylalanine (Phe) enantiomers for 4 h. The interaction energies between the CD-MOF and D-Phe and L-Phe were calculated using the Gaussian 09 program package and the chiral separation mechanism of the composite membrane was proposed at the molecular level. Our work demonstrates great development potentials of the CD-MOF/PVDF composite membrane in the chiral separation of drugs.