Date of Award
Doctor of Philosophy (PhD)
Nuclear magnetic resonance (NMR) has proven to be a versatile and powerful analytical tool to study many areas of interest to the scientific community, such as molecular dynamics and structural characterization. In this dissertation, NMR was used as a probe for CO2 dynamics in metal-organic frameworks. Variable temperature (VT) NMR was used to determine molecular dynamics of CO2, going as low as 8 K. In the fast motion regime, where the CO2 hopping rate is fast compared to the NMR experiment time, 13CO2 inside of Mg-MOF-74 still exhibits a chemical shift anisotropy (CSA) powder pattern. However, there is a certain loading of CO2 inside the framework (~ 1 CO2 molecule per 1 open metal site) the results in a symmetric Gaussian lineshape where it appears that the CSA is motionally averaged. This is not the case though, the CO2 molecules adopt an average orientation inside the channels of the framework as a function of CO2 loading. This average orientation manifests itself in the CSA lineshape and can be explained using the Legendre polynomial, P2. Additionally, 27Al magic-angle spinning (MAS) NMR was performed to characterize aluminum carbide (Al4C3) and its related derivatives. Multiple-quantum magic-angle spinning of Al4C3 revealed accurate values for the quadrupolar tensor, and elucidated the presence of additional sites likely to be from an oxycarbide unit (Al4(C,O)3). Extracting accurate values for the quadrupolar tensor was critical in the understanding and deconvolution of MIL-53(Al) derived from aluminum carbide. 27Al NMR is uniquely qualified to identify the presence of -, -, and -coordinate amorphous aluminum oxide species that would otherwise be unseen in techniques such as powder X-ray diffraction (PXRD). The formation of this aluminum oxide layer appears to be a necessary step to the formation of MIL-53(Al).
Chair and Committee
Sophia E. Hayes
Richard Axelbaum, Alexander Barnes, Julio D'Arcy, Erik Henriksen,
Marti, Robert M., "An NMR Study of CO2 Dynamics and Structural Characterization of Porous Materials" (2018). Arts & Sciences Electronic Theses and Dissertations. 1638.