Water Sorption on Isoreticular CPO-27-Type MOFs: From Discrete Sorption Sites to Water-Bridge-Mediated Pore Condensation
Pore engineering is commonly used to alter the properties of metal–organic frameworks. This is achieved by incorporating different linker molecules (<i>L</i>) into the structure, generating isoreticular frameworks. CPO-27, also named MOF-74, is a prototypical material for this approach,...
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2024-11-01
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| author | Marvin Kloß Lara Schäfers Zhenyu Zhao Christian Weinberger Hans Egold Michael Tiemann |
| author_facet | Marvin Kloß Lara Schäfers Zhenyu Zhao Christian Weinberger Hans Egold Michael Tiemann |
| author_sort | Marvin Kloß |
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| description | Pore engineering is commonly used to alter the properties of metal–organic frameworks. This is achieved by incorporating different linker molecules (<i>L</i>) into the structure, generating isoreticular frameworks. CPO-27, also named MOF-74, is a prototypical material for this approach, offering the potential to modify the size of its one-dimensional pore channels and the hydrophobicity of pore walls using various linker ligands during synthesis. Thermal activation of these materials yields accessible open metal sites (i.e., under-coordinated metal centers) at the pore walls, thus acting as strong primary binding sites for guest molecules, including water. We study the effect of the pore size and linker hydrophobicity within a series of Ni<sup>2+</sup>-based isoreticular frameworks (i.e., Ni<sub>2</sub><i>L</i>, <i>L</i> = dhtp, dhip, dondc, bpp, bpm, tpp), analyzing their water sorption behavior and the water interactions in the confined pore space. For this purpose, we apply water vapor sorption analysis and Fourier transform infrared spectroscopy. In addition, defect degrees of all compounds are determined by thermogravimetric analysis and solution <sup>1</sup>H nuclear magnetic resonance spectroscopy. We find that larger defect degrees affect the preferential sorption sites in Ni<sub>2</sub>dhtp, while no such indication is found for the other materials in our study. Instead, strong evidence is found for the formation of water bridges/chains between coordinating water molecules, as previously observed for hydrophobic porous carbons and mesoporous silica. This suggests similar sorption energies for additional water molecules in materials with larger pore sizes after saturation of the primary binding sites, resulting in more bulk-like water arrangements. Consequently, the sorption mechanism is driven by classical pore condensation through H-bonding anchor sites instead of sorption at discrete sites. |
| format | Article |
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| spelling | doaj-art-374b5cbaf20b4d94af35fc3ea0b2849b2025-08-20T02:48:06ZengMDPI AGNanomaterials2079-49912024-11-011422179110.3390/nano14221791Water Sorption on Isoreticular CPO-27-Type MOFs: From Discrete Sorption Sites to Water-Bridge-Mediated Pore CondensationMarvin Kloß0Lara Schäfers1Zhenyu Zhao2Christian Weinberger3Hans Egold4Michael Tiemann5Department of Chemistry, Paderborn University, 33098 Paderborn, GermanyDepartment of Chemistry, Paderborn University, 33098 Paderborn, GermanyDepartment of Chemistry, Paderborn University, 33098 Paderborn, GermanyDepartment of Chemistry, Paderborn University, 33098 Paderborn, GermanyDepartment of Chemistry, Paderborn University, 33098 Paderborn, GermanyDepartment of Chemistry, Paderborn University, 33098 Paderborn, GermanyPore engineering is commonly used to alter the properties of metal–organic frameworks. This is achieved by incorporating different linker molecules (<i>L</i>) into the structure, generating isoreticular frameworks. CPO-27, also named MOF-74, is a prototypical material for this approach, offering the potential to modify the size of its one-dimensional pore channels and the hydrophobicity of pore walls using various linker ligands during synthesis. Thermal activation of these materials yields accessible open metal sites (i.e., under-coordinated metal centers) at the pore walls, thus acting as strong primary binding sites for guest molecules, including water. We study the effect of the pore size and linker hydrophobicity within a series of Ni<sup>2+</sup>-based isoreticular frameworks (i.e., Ni<sub>2</sub><i>L</i>, <i>L</i> = dhtp, dhip, dondc, bpp, bpm, tpp), analyzing their water sorption behavior and the water interactions in the confined pore space. For this purpose, we apply water vapor sorption analysis and Fourier transform infrared spectroscopy. In addition, defect degrees of all compounds are determined by thermogravimetric analysis and solution <sup>1</sup>H nuclear magnetic resonance spectroscopy. We find that larger defect degrees affect the preferential sorption sites in Ni<sub>2</sub>dhtp, while no such indication is found for the other materials in our study. Instead, strong evidence is found for the formation of water bridges/chains between coordinating water molecules, as previously observed for hydrophobic porous carbons and mesoporous silica. This suggests similar sorption energies for additional water molecules in materials with larger pore sizes after saturation of the primary binding sites, resulting in more bulk-like water arrangements. Consequently, the sorption mechanism is driven by classical pore condensation through H-bonding anchor sites instead of sorption at discrete sites.https://www.mdpi.com/2079-4991/14/22/1791metal–organic frameworksMOF-74IRMOF-74open metal siteswater vapor sorptionhydrophobicity |
| spellingShingle | Marvin Kloß Lara Schäfers Zhenyu Zhao Christian Weinberger Hans Egold Michael Tiemann Water Sorption on Isoreticular CPO-27-Type MOFs: From Discrete Sorption Sites to Water-Bridge-Mediated Pore Condensation Nanomaterials metal–organic frameworks MOF-74 IRMOF-74 open metal sites water vapor sorption hydrophobicity |
| title | Water Sorption on Isoreticular CPO-27-Type MOFs: From Discrete Sorption Sites to Water-Bridge-Mediated Pore Condensation |
| title_full | Water Sorption on Isoreticular CPO-27-Type MOFs: From Discrete Sorption Sites to Water-Bridge-Mediated Pore Condensation |
| title_fullStr | Water Sorption on Isoreticular CPO-27-Type MOFs: From Discrete Sorption Sites to Water-Bridge-Mediated Pore Condensation |
| title_full_unstemmed | Water Sorption on Isoreticular CPO-27-Type MOFs: From Discrete Sorption Sites to Water-Bridge-Mediated Pore Condensation |
| title_short | Water Sorption on Isoreticular CPO-27-Type MOFs: From Discrete Sorption Sites to Water-Bridge-Mediated Pore Condensation |
| title_sort | water sorption on isoreticular cpo 27 type mofs from discrete sorption sites to water bridge mediated pore condensation |
| topic | metal–organic frameworks MOF-74 IRMOF-74 open metal sites water vapor sorption hydrophobicity |
| url | https://www.mdpi.com/2079-4991/14/22/1791 |
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