Identifying UiO‐67 Metal‐Organic Framework Defects and Binding Sites through Ammonia Adsorption

Ammonia is a widely used toxic industrial chemical that can cause severe respiratory ailments. Therefore, understanding and developing materials for its efficient capture and controlled release is necessary. One such class of materials is 3D porous metal‐organic frameworks (MOFs) with exceptional su...

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Published in:ChemSusChem 2022-01, Vol.15 (1), p.e202102217-n/a
Main Authors: Swaroopa Datta Devulapalli, Venkata, McDonnell, Ryan P., Ruffley, Jonathan P., Shukla, Priyanka B., Luo, Tian‐Yi, De Souza, Mattheus L., Das, Prasenjit, Rosi, Nathaniel L., Karl Johnson, J., Borguet, Eric
Format: Article
Language:English
Subjects:
Adsorption
Ammonia
Band theory
Binding Sites
Controlled release
defects
Density functional theory
Hydrogen bonding
Infrared spectroscopy
Mass spectrometry
Metal-Organic Frameworks
Porous materials
Sorption
Structural analysis
Ultrahigh vacuum
Zirconium
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Summary:Ammonia is a widely used toxic industrial chemical that can cause severe respiratory ailments. Therefore, understanding and developing materials for its efficient capture and controlled release is necessary. One such class of materials is 3D porous metal‐organic frameworks (MOFs) with exceptional surface areas and robust structures, ideal for gas storage/transport applications. Herein, interactions between ammonia and UiO‐67‐X (X: H, NH2, CH3) zirconium MOFs were studied under cryogenic, ultrahigh vacuum (UHV) conditions using temperature‐programmed desorption mass spectrometry (TPD‐MS) and in‐situ temperature‐programmed infrared (TP‐IR) spectroscopy. Ammonia was observed to interact with μ3−OH groups present on the secondary building unit of UiO‐67‐X MOFs via hydrogen bonding. TP‐IR studies revealed that under cryogenic UHV conditions, UiO‐67‐X MOFs are stable towards ammonia sorption. Interestingly, an increase in the intensity of the C−H stretching mode of the MOF linkers was detected upon ammonia exposure, attributed to NH−π interactions with linkers. These same binding interactions were observed in grand canonical Monte Carlo simulations. Based on TPD‐MS, binding strength of ammonia to three MOFs was determined to be approximately 60 kJ mol−1, suggesting physisorption of ammonia to UiO‐67‐X. In addition, missing linker defect sites, consisting of H2O coordinated to Zr4+ sites, were detected through the formation of nNH3⋅H2O clusters, characterized through in‐situ IR spectroscopy. Structures consistent with these assignments were identified through density functional theory calculations. Tracking these bands through adsorption on thermally activated MOFs gave insight into the dehydroxylation process of UiO‐67 MOFs. This highlights an advantage of using NH3 for the structural analysis of MOFs and developing an understanding of interactions between ammonia and UiO‐67‐X zirconium MOFs, while also providing directions for the development of stable materials for efficient toxic gas sorption. Toxic gas sorption: In‐situ temperature‐programmed infrared spectroscopy and mass spectrometry coupled with computational studies reveal NH3 binding sites in UiO‐67 metal‐organic frameworks (MOFs), including missing linker defects, and monitor their evolution as a function of MOF activation temperature.
ISSN:1864-5631
1864-564X
DOI:10.1002/cssc.202102217