A New Type of Metal-Organic Framework Films
The research led by Prof. Kevin C.-W. Wu at National Taiwan University and Prof. Yusuke Yamauchi at Nagoya University reveals a new and scalable strategy for fabricating continuous mesoporous amorphous metal-organic framework (aMOF) films, specifically demonstrated using amorphous ZIF-90 (aZIF-90). The work focuses on overcoming the difficulties of forming uniform MOF films, which typically suffer from grain boundaries, cracks, and poor mechanical integrity due to their crystalline nature. The study is published in Advanced Materials.
The team of scientists developed a solvent‐evaporation–induced micelle assembly method, employing block copolymer micelles as soft templates. By carefully optimizing the co-solvent system (THF/MeOH) and the ratio of metal ions and organic linkers, they enabled the cooperative self-assembly of polymeric micelles with MOF precursors during solvent evaporation.
This approach yielded thin films with continuous mesoporous architectures (15–20 nm pores), smooth surfaces (Ra ≈ 0.5 nm), and excellent uniformity across different substrates. The optimal solvent condition was 20 vol% methanol in THF, balancing micellization and film formation rates. Both spin-coating and spray-coating techniques were demonstrated to be effective, highlighting the method’s adaptability for large-scale production.
Comprehensive characterization, including SEM, AFM, GISAXS, XRD, FTIR, solid-state NMR, and XAS, confirmed the amorphous structure and chemical consistency of aZIF-90 with its crystalline counterpart. Despite lacking long-range order, aZIF-90 retained similar local Zn-N coordination while offering interconnected mesopores beneficial for mass transport. Density-functional theory (DFT) simulations clarified the role of solvent composition: methanol facilitated linker deprotonation and coordination, while THF favored kinetic trapping and amorphization.
Finally, the mesoporous aZIF-90 film was applied to uric acid sensing, showing higher sensitivity and lower detection limits than crystalline ZIF-90 due to its open, accessible pore network. This work establishes a general, time-efficient route for fabricating uniform mesoporous aMOF films suitable for electrochemical, catalytic, or sensing applications.
"This work establishes a new benchmark for the development of high-performance aMOF films. By overcoming the typical limitations of crystalline MOFs, such as grain boundaries and poor film continuity, our evaporation-induced strategy opens pathways for their broader integration into advanced functional devices, including practical biosensing applications,” says Prof. Kevin C.-W. Wu, corresponding author of the study.
“Furthermore, this work demonstrates the successful scientific cooperation between Taiwan (National Taiwan University) and Japan (Nagoya University)."
Norman Chu-Ren Chen, Ph.D. candidate in the International Graduate Program of Molecular Science and Technology (TIGP-MST) at National Taiwan University, was the study’s first author.
Prof. Kevin C.-W. Wu's email address: [email protected]
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