Metal-organic framework (MOF) membranes have significant potential for use in efficient gas separation. However, fabricating polymer substrate-supported ultra-thin MOF membranes with no defects remains a challenge. Herein, we proposed an in situ interface self-repair strategy for fabricating ultra-thin and defect-free ZIF-67 membranes for the first time. This was realized by preparing a polyvinyl alcohol (PVA)-Co 2+ interfacial layer containing a Co 2+ ion layer and a PVA-Co 2+ complex layer. The PVA-Co 2+ interfacial layer released Co 2+ ions and acted as a metal source to form ZIF-67 membranes by reducing the coordination rate of Co 2+ ions with 2-methylimidazole. The embedded Co 2+ ions functioned as anchor sites for the nucleation of ZIF-67 membrane assisted by the interface-enhanced deprotonation of 2-methylimidazole. Especially, the slow release of Co 2+ ions from the PVA-Co 2+ interfacial layer facilitated self-repair of defects to form a continuous and dense MOF layer. ZIF-67 membranes, 80-280 nm thick, were successfully synthesized and demonstrated unprecedented CO 2 permeance and good CO 2 /N 2 selectivity. This work provides a promising strategy for the fabrication of ultra-thin and defect-free MOF membranes on polymeric support layers for use in practical applications.
Zeolitic imidazolate framework-67 (ZIF-67) membranes hold great promise in efficiently separating propene/propane mixtures. However, achieving highly permselective ZIF-67 membranes remains challenging due to unruly crystal nucleation and poor grain boundary structure. Herein, a magnetic-field-driven approach is reported to fabricating high-quality ZIF-67 membranes on anodized aluminum oxide substrates at room temperature. The presence of a magnetic field increases the nucleation rates by shortening the induction period, facilitates the orderly and rapid migration of Co 2+ ions, optimizes the nucleation of ZIF-67 crystallites on the substrate, and inhibits the excessive crystal growth of ZIF-67 grains. These factors collectively contribute to improving the grain boundary structure and suppressing inter-grain defects in MOF membranes. The resulting ZIF-67 membranes, with a thickness of less than 480 nm, exhibit a superior propylene/propane separation performance, featuring a separation factor of 135 and a propylene permeance of 2.3 × 10 −8 mol m −2 s −1 Pa −1 . The magnetic-field-driven approach is expected to greatly promote the development of MOF membranes for highly efficient and energy-saving separations.
A novel microporous ZIF-67 membrane coating on paper-like stainless steel fibers (ZIF-67 membrane/PSSF) was successfully synthesized by a wet layup papermaking-sintering method followed by the seed-induced growth method. The effects of key factors such as crystallization temperature , synthesis time and Hmim/Co 2+ (2-methylimidazole/cobalt chloride) molar ratio on the morphology structure of the samples were studied by the modern characterization techniques including SEM, EDX , TEM, XRD , BET, FTIR and TGA, respectively. The experimental result indicated that the as-synthesized ZIF-67 membrane/PSSF was extremely compact with the average membrane thickness of 4.8 μm. And the sample exhibited high BET surface area (440.9 m 2 /g), uniform pore size (1.881 nm) and large pore volume (0.2096 cm 3 /g). The adsorption breakthrough experiment of toluene was performed on different bed reactors filled with ZIF-67 membrane/PSSF and granular ZSM-5 zeolites , respectively. The experiment data was well fitted by Yoon–Nelson model, where the values of rate constant in the fixed bed with ZIF-67 membrane/PSSF increased by 32.2% compared with that of commercial ZSM-5 zeolites at the flow rate of 100 mL/min. And the bed pressure drop and length of unused bed (LUB) were dramatically reduced by 39.6% and 16.8% in 3 cm ZIF-67 membrane/PSSF fixed bed. In conclusion, mass transfer efficiency was significantly enhanced based the structured ZIF-67 membrane/PSSF fixed bed, and this new material is a promising adsorptive material for VOCs removal.
Metal–organic frameworks (MOFs) show great potential in various separation applications. However, fast nucleation rate and crystallization of MOFs, produce non-uniform and uncontrollable sized crystals, which are not suitable for the formation of MOF-based membranes. Herein, we propose the concept of utilizing protein polyphenol nanoassemblies (PPNs) as the building blocks for the confined growth of MOFs to fabricate zeolitic imidazolate frameworks (ZIF-67)-based membranes. We first demonstrated that colloidal PPNs as modulators in solution enables the formation of ZIF-67 MOFs with uniform and controllable crystal sizes. Subsequently, we utilized the metal salt coordinated PPNs (Co 2+ @PPN) as the precursor layer matrix deposited on porous polymeric support to fabricate ZIF-67 membranes via in-situ growth strategy at room temperature. The resultant membrane features a robust heterogeneous and well-integrated ZIF-67-reinforced PPN (ZIF-67@PPN) microporous networks. Benefiting from the rigid and multidimensional micropores of ZIF-67, the optimized ZIF-67@PPN1 composite membrane with improved water stability exhibited good water permeance (45.68 L m −2 h −1 bar −1 ), excellent dye desalination performance (Na 2 SO 4 /Congo red selectivity of 1271.47), and good antibiotic desalination performance (NaCl/Erythromycin selectivity of 21.46). The findings in this work provide important engineering concepts for the development of MOF-based membranes using sustainable nature-derived building blocks for emergent environment-relevant desalination applications in the chemical process industry.
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