Zeolitic imidazolate frameworks in mixed matrix membranes for boosting phenol/water separation: Crystal evolution and preferential orientation

The treatment of phenolic wastewater has become a critical but challenging issue for growing concerns over human health and the environment. In this study, the highly permeable mixed matrix membranes (MMMs) were fabricated by embedding structure- and morphology-tailored zeolitic imidazolate frameworks (ZIFs) in poly(ether-block-amide) (PEBA) bulk for pervaporation (PV) separation of phenol/water mixture. The crystal evolution from rhombic dodecahedral ZIF-8 particles to anisotropic ZIF-L nanosheets (ZLNs) was achieved by varying precursor concentration in aqueous system, and the morphology of ZIFs was precisely adjusted. Using a spin-coating method, the horizontally-oriented ZLNs constructed a typical brick-and-mortar architecture in the polymer matrix, suggesting their excellent interfacial compatibility. The high aspect-ratio ZLNs created preferential pathways for phenol but limited water transport in the membrane. Notably, the ZLNs/PEBA MMMs exhibited ultra-high phenol permeance of 4.96 × 10⁵ GPU and phenol/water selectivity of 32.5 in separation of 1000 ppm phenol aqueous solution at 60 °C, which surpassed the overall performance of other phenol-selective membranes. Besides, the presence of ZLNs endowed the MMMs with good thermal and mechanical properties, guaranteeing long-term stability in realistic conditions. These findings of regulating morphology and preferential orientation of two-dimensional metal-organic framework fillers might have significant implications in designing high-performance membranes for various applications.