image: Schematic illustration of air‒water interfacial synthesis and sequential water surface constriction process for MOF nanosheet membrane fabrication, showing a record high membrane fabrication efficiency
Credit: ©Science China Press
Ultrathin 2D metal-organic framework (MOF) membranes, with their highly tunable pore structures, ultrahigh pore density, and nanoscale thickness, are ideal materials for achieving both high selectivity and high permeance, promising to revolutionize industrial separation processes. However, their development is significantly hampered by existing preparation methods, which are complex and time-consuming (tens of hours or even weeks), resulting in extremely low efficiency.
To address this, the team of researchers from Dalian Institute of Chemical Physics, Chinese Academy of Sciences, developed a triggered air-water interfacial coordination assembly method. Using only microliter-scale organic ligand dosage, this method successfully produces ultrathin, large-sized, continuous and defect-free 2D MOF membranes within just 30 minutes, which enables highly accurate, permeable, and stable H2/CO2 separation for industrial scenarios like steam reforming gas product separation. It dramatically improves molecular sieve membrane preparation efficiency and cost-effectiveness. Furthermore, the method was successfully extended to various MOF systems, demonstrating its high versatility.
1. Rapid Molecular Sieve Membrane Synthesis
Guided by this triggered air-water interfacial coordination assembly method, researchers synthesized Zn-MOF nanosheets using zinc acetylacetonate and benzimidazole as an example. The resulting nanosheets possess micrometer-scale lateral dimensions and an ultrathin thickness of merely 7.7 nm (aspect ratio > 10,000), highlighting the effectiveness of this strategy for producing large-area, ultrathin nanosheets. The study also investigated the influence of reactant volume, reaction time, and external forces promoting coordination on nanosheet quality during the tailored interfacial synthesis. Subsequent water surface contraction caused the nanosheets to aggregate, forming a dense membrane layer. After transfer onto a support, scanning electron microscopy revealed a semi-transparent, silk-like nanosheet layer uniformly covering the surface. Driven by capillary forces from the porous support and the inherent flexibility of the MOF nanosheets, the layer adhered tightly to the rough substrate surface without observable pinholes, cracks, or wrinkles. Cross-sectional SEM imaging further confirmed its ultrathin nature.
2. Excellent Gas Separation Performance
Membranes formed with the optimal ligand dosage of 250 μL exhibited a densely packed nanosheet structure. This membrane configuration achieved remarkable H2/CO2 separation performance with a separation factor of 210 and a H2 permeance of 1862 GPU, demonstrating a good long-term stability even under a near real-work humid condition. This underscores the significant potential of the membrane for H2 purification and CO2 capture.
3. High Versatility
Leveraging the flexible combination of different metal ions and organic ligands, twelve distinct MOF nanosheets with varied framework structures and pore environments were successfully fabricated based on this method. All obtained nanosheets exhibited micrometer-scale lateral dimensions and characteristic 2D nanosheet flexibility. This result opens a new pathway for the tailored synthesis of MOF nanosheets and ultrathin 2D MOF membranes, enabling high-performance separation tailored to diverse application needs.
“This work not only provides a new strategy for efficiently customization of MOF nanosheets, but also expands the application potential of the ultrathin, flexible 2D materials with high-density, regular pore arrays in material science, device architecture design, catalyst and separation engineering,” said Prof. YANG.