Mixed matrix composite membranes comprising nanocage-like hollow ZIF-71(h) polyhedral nanocrystals in poly(ether-block-amide) membranes for phenol/water separation

Organophilic pervaporation (PV) mixed matrix membranes (MMMs) have enormous potential for organic wastewater treatment due to their environmental friendliness and high efficiency. However, developing a high-flux PV membrane remains challenging. In this work, the nanocage-like hollow ZIF-71(h) (HZIF-71(h)) polyhedral nanocrystals were synthesized by heteroepitaxial growth of a ZIF-71(h) shell and successive excavation of a ZIF-67 core. The resultant HZIF-71(h) nanocrystals were blended with poly (ether block amide) (PEBA) matrix to fabricate MMMs for phenol/water separation. Results from several characterization techniques confirmed the successful preparation and formation mechanism of HZIF-71(h). Further, a series of experiments were conducted using the composite membranes to explore the impact of filler type, filler loading, operating temperature, and feed concentration on the separation performance. The incorporation of ZIFs facilitated phenol permeation while limited water transport, thereby resulting in increased separation factor. Notably, the HZIF-71(h)/PEBA-21 MMM exhibits a higher phenol flux in comparison to ZIF-71/PEBA-21 and ZIF-67/PEBA-21 MMMs, indicating the importance of the low-resistance hollow structure. The HZIF-71(h)/PEBA-21 MMM exhibits outstanding pervaporation performance with a separation factor of 15.86 and a phenol flux of 17.32 g·m −2 ·h −1 , respectively, displaying an improvement of 41.2 % and 6.4 % compared to the PEBA/PVDF membrane. Furthermore, this composite membrane demonstrated outstanding durability during continuous testing for 84 h, implying a promising potential for phenol separation.