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Mesoporous Cages in Chemically Robust MOFs Created by a Large Number of Vertices with Reduced Connectivity
Summary:
The authors from the Key Laboratory of Biomedical Polymers-Ministry of Education, College of Chemistry and Molecular Sciences, Wuhan University, and other institutions developed two metal−organic frameworks (MOFs), MOF-818 and MOF-919, with permanent porosity and large mesoporous cages. These MOFs achieved significant results in the application of biomolecule inclusion and catalysis.
Background:
1. To address the problem of limited pore sizes in traditional MOFs, previous researchers conducted work on extending cage sizes from micropores to mesopores, achieving success in gas storage and separation. However, challenges remained in constructing large mesoporous cages with small organic linkers.
2. The authors proposed an innovative method using a small ditopic organic linker, 1H-pyrazole-4-carboxylic acid (H2PyC), and multiple metal-containing second building units (SBUs) to create large mesoporous cages. They obtained three unprecedented polyhedra with diameters of 3.8, 4.9, and 6.0 nm.
Research Content:
1.Synthesis:
The authors synthesized MOF-818 and MOF-919 using ZrOCl2, Cu(NO3)2, and H2PyC in DMF under ultrasound and heating conditions. The as-synthesized MOFs were activated by solvent exchange and supercritical CO2 drying.
2.Characterizations:
1) BET surface area measurements showed values of 2050 m²/g for MOF-818 and 2740 m²/g for MOF-919-Sc. Pore size distribution analysis revealed mesopores of 3.7 nm for MOF-818 and 2.0, 3.9, and 6.0 nm for MOF-919-Sc.
2) SEM/TEM tests showed the particle size of MOF-818 to be around 400 nm and MOF-919-Sc to be around 4 μm.
3) X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectra (XAS) confirmed the oxidation states of the metals in the MOFs.
3.Application:
The MOFs were tested for biomolecule inclusion. MOF-818 successfully encapsulated vitamin B12 (4.4 nmol/mg) and insulin (2.8 nmol/mg), while MOF-919-Sc encapsulated insulin (3.79 nmol/mg).
4.Mechanism:
The reduction in connectivity of vertices in the polyhedra was found to be an effective way to create large cages. The [2-c, 3-c] connectivity used in this study resulted in the largest cage size to linker size ratio of 15, allowing for the successful inclusion of large biomolecules.
Outlook:
This research achieved significant progress in designing large mesoporous cages using small organic linkers, demonstrating their potential for biomolecule inclusion and catalysis. The findings provide a new strategy for constructing large cages in MOFs and supramolecules.
Mesoporous Cages in Chemically Robust MOFs Created by a Large Number of Vertices with Reduced Connectivity
Authors: Qi Liu, Yinyin Song, Yanhang Ma, Yi Zhou, Hengjiang Cong, Chao Wang, Jorryn Wu, Gaoli Hu, Michael O’Keeffe, Hexiang Deng
DOI: 10.1021/jacs.8b11230
Link: https://pubs.acs.org/doi/10.1021/jacs.8b11230
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