Condensed-Matter Physics & Materials Science Seminar

Selective adsorption and sequestration of carbon dioxide from sources of anthropogenic emissions is important to mitigate the growing level of the atmospheric CO2. Solid state adsorbents, such as metal organic frameworks (MOFs), are proposed as an alternative to the currently used toxic and corrosive alkanolamine solutions. Experimental gas sorption studies of MOFs usually focus on gas isotherms measurements that, while providing the necessary information on the overall gas uptake and framework behavior upon gas loading, yield limited information on the mechanism of the gas adsorption. Molecular level understanding of gas adsorption in MOFs is an important problem and the most detailed structural models necessary to elucidate the adsorbate-adsorbent interaction can be obtained with the crystallographic techniques. This talk will present the recent exciting discoveries of CO2 and hydrocarbon adsorption in MOFs. In contrast to current trends in the design of MOFs, we discovered the unique mechanism responsible for a high CO2/N2 adsorption selectivity in a Ca-based MOF: Ca(sdb), (sdb: 4,4'-sulfonyldibenzoate), even in the presence of water in the gas stream. Single crystal XRD (SCXRD) experiments of gas loaded samples revealed that the v-shaped linker provides a "pi-pocket" formed by two phenyl rings, and that CO2 locate between the rings, resulting in a high heat of adsorption. To determine the gas adsorption performance in situ in the presence of water, we used differential scanning calorimetry technique (XRD-DSC) that allows for measuring enthalpy while collecting X-ray diffraction patterns, to evaluate the structural response during the gas adsorption. The XRD-DSC technique and single crystal diffraction were further used to evaluate the CO2 adsorption in a Cd-analog of Ca(sdb), hydrocarbon adsorption in two Ca-based MOFs and gate opening mechanism in a Mn-based MOF. The knowledge acquired can promote the directed synthetic search for novel