Regulation of the microstructure of polyvinylidene fluoride membrane via incorporation of nano‐ZIF‐7 for improving hydrophobicity and antiwetting performance

Abstract

AbstractThe design and fabrication of a membrane with super hydrophobicity and antiwetting property is of great importance for improving membrane performance in distillation, desalination, gas absorption, and separation. In this work, polyvinylidene fluoride (PVDF) membranes were modified by Zeolitic Imidazolate Framework‐7 (ZIF‐7) nanocrystals to improve the hydrophobic property and antiwetting performance. ZIF‐7/PVDF hybrid membranes were prepared via the nonsolvent‐induced phase separation (NIPS) method. Different concentrations of ZIF‐7 nanocrystals (0, 0.5, 1, 2, 3, and 5 wt%) were introduced into the PVDF dope solution, and the physical structure of the resulting membranes were systematically characterized. Due to the hydrophobic nature of ZIF‐7 nanocrystals, the solvent–nonsolvent exchange rate had been regulated effectively during phase inversion. The morphology of top and bottom surfaces, together with the inner structures of the hybrid membrane, has been changed obviously, showing a more twisted finger‐like macrovoid layer and a thicker sponge‐like layer compared to pristine PVDF membrane. Furthermore, the hydrophobicity and antiwetting properties of these hybrid membranes improved obviously when the incorporated concentration of ZIF‐7 was higher than 1 wt%. The M(2) membrane, which possessed the highest surface roughness and water contact angles, showed the best antiwetting property and recovered gas permeance ratio (>95%) after being immersed in aqueous solution for 10 hr.