TITLE: INVESTIGATING MULTI-SCALE THERMAL PROPERTIES OF A METAL-ORGANIC FRAMEWORK (MOF) ADSORBENT FOR THE DIRECT AIR CAPTURE (DAC) OF CARBON DIOXIDE ( CO2 )

ABSTRACT: To address the need to limit global warming to l.5°C or less, CO2 must actively be removed from the atmosphere through the direct air capture (DAC) of CO2• Current research utilizes a solid "cooperative" metal-organic framework (MOF) adsorbent with high capacity, but the regeneration of these materials is thermally expensive at the system level. However, the thermal properties of MOFs are critically understudied experimentally, thus there exists a lack of understanding of how they interact with stimuli in real-world environments. This doc­toral research aims to experimentally study hierarchical thermal transport of MOFs through a multi-scale approach to investigate changes in thermal properties as a function of scale, structure, and environment. The first section discusses the theory and sample preparation required for various thermal property measurement techniques. The MOF material of inter­est is then introduced, detailing current work in the literature regarding thermal properties. With this background, we move into the proposed project where we consider as-synthesized MOF and MOF that is post-synthetically modified with amines and polymers. In the sec­ond section, we consider a variety of environments including inert conditions, CO2 and H2O loading, and ambient lab conditions. This focus will provide the understanding of how the gaseous conditions of the system interact with the MOF adsorbent to alter its thermal properties and phonon vibrational spectra. The multi-scale approach is introduced through the use of Transient Plane Source (Hot Disk) method, Thermal Wave Sensing (TWS), and Frequency Domain Thermoreflectance (FDTR) techniques to obtain thermal property mea­surements. Finally, thermal modeling is discussed, primarily the thermal transfer functions and effective thermal conductivity models, allowing for better parameter selection during experiments and data comparison across scales. By utilizing a multi-scale approach, the intrinsic, or single crystal, and effective, or bulk, thermal properties can be understood. The intrinsic properties will elucidate how phonons traverse within MOF adsorbents, while the bulk properties introduce crystal interactions into the picture, providing a deeper under­standing of contributors to thermal properties in MOFs in real world systems. Therefore, this fundamental research aims to not only understand thermal transport in MOFs across scales, structures, and environments but, also, to eliminate some current unknowns in critical DAC of CO2 systems.

COMMITTEE: ADVISOR/CHAIR Professor Sean Lubner, ME/MSE; Professor Joerg Werner, ME/MSE; Professor Emily Ryan, ME/MSE