UNC-CH Physics and Astronomy Thesis Proposal Presentation

Yao An

“Experimental and Simulation Approaches of in-situ NMR for Studying Thermodynamics and Kinetics of Metal-organic Frameworks UiO-66”

To gain insight into the role of topology and defects in molecular accessibility, diffusivity, and reactivity, which will lead to design rules of metal-organic frameworks (MOFs), studying their kinetics and thermodynamics properties are necessary but challenging. Here we propose to use in situ nuclear magnetic resonance-detected (NMR-detected) techniques for studies of well-characterized UiO-66. This new set up successfully captures the kinetics and thermodynamics information of only several milligrams of MOF by loading isopropanol and water. The distinguishable kinetics of approaching equilibrium, together with the different width of spectra, the nucleus-independent chemical shift, and simulation results and this supports the defective UiO-66 filling order as a reaction on defect site, physisorption in tetrahedral cage, and then the octahedral cage. Dissociated water on defect sites has been detected. Defects are found to be one of the key factors controlling the thermodynamic properties. Furthermore, competitive adsorption indicates the hydration will lower the transport rate of guest molecule but it will not affect the gas storage capacity at vapor pressure. The expulsion of pre-adsorbed water when introducing isopropanol gives us a direction for optimizing functionalities.