Doctor of Philosophy
Metal-organic frameworks are porous organic-inorganic materials that have attracted enormous attention due to their promising capabilities for several technologies, including carbon dioxide capture and storage, gas separation, and heterogeneous catalysis. The performance of MOFs for these applications is directly linked to their properties and, by extension, structures. Therefore, it is essential to understand the structure – property relationship. Solid-state NMR (SSNMR) spectroscopy is a technique that provides complementary information to X-ray diffraction-based techniques. SSNMR can provide short-range information around the NMR-active nucleus of interest. Furthermore, SSNMR can provide additional information regarding host-guest interactions and dynamics of adsorbed molecules, which play a crucial role in the adsorption capacity of materials.
Herein, we investigate the structure and properties of several reprehensive MOFs via SSNMR. An introduction about the definitions and nomenclature of MOFs is given in Chapter 1, and a brief introduction to SSNMR is provided in Chapter 2. In Chapter 3, we demonstrate that the acquisition of ultra-high resolution 17O SSNMR spectra can be acquired at an ultrahigh magnetic field of 35.2 T. This allowed us to obtain important information regarding the subtle changes in the structure of MOFs upon activation, phase transition, host- guest interactions, etc. In Chapter 4, we investigate the structural changes of the flexible MIL-53(Al) MOF upon activation and hydration. 17O SSNMR experiments carried out at 35.2 T provided further insights into the intermolecular interaction governing the crystal structure. In Chapter 5, we describe the 17O NMR studies of MIL-121, a MOF with free carboxylic acid groups in the pores. The sensitivity of the 17O NMR achieved at high magnetic fields allowed us to further investigate the MOFs exchanged with different metal ions. In Chapter 6, we demonstrate that the co-adsorption of water and CO2 can be investigated using multinuclear SSNMR spectroscopy. The dynamics, adsorption sites, and intermolecular interaction were studied. Furthermore, this approach has also allowed to investigate the effect of water on the adsorption of carbon dioxide in ZnAtzOx.
Summary for Lay Audience
Metal-organic frameworks (MOFs) are porous materials that have found application in several technologies, including carbon capture and storage, catalysis, as gas separation. Understanding the structure and physicochemical properties of MOFs is crucial for development of new materials with real applications. Herein, we demonstrate how SSNRM spectroscopy can provide complementary information regarding the structure and properties of MOFs. Oxygen is a key element in the synthesis and properties of MOFs. We demonstrate that by performing 17O SSNMR experiments at ultra-high field can provide unprecedented information that is complimentary to X-ray crystallography. The ultra-high resolution allowed us to get information on the structure, host-guest interactions, activation process, phase transition, and structural flexibility. Furthermore, we show that SSNMR can be used to study the behavior of adsorbed CO2 in an ultramicroporous MOF under humid conditions.
Martins, Vinicius, "Solid State NMR Spectroscopic Characterization of Metal Organic Frameworks" (2022). Electronic Thesis and Dissertation Repository. 8413.
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