(523c) Thermal Analysis and Heat Capacity Study of Metal Organic Frameworks Using Differential Scanning Calorimetry
Metal-organic frameworks are quickly becoming established as a new class of porous materials with potential applications in adsorption separations. Pure-component adsorption isotherms of light gases and alkanes in a variety of MOFs are becoming prevalent in the literature. To a lesser extent, mixture adsorption and breakthrough studies are also beginning to appear. Because of the exothermic nature of physisorption, heat effects in fixed-bed adsorption processes are often significant. Two important parameters in such systems are heats of adsorption and heat capacities of the adsorbent. Isosteric heats have been determined for a variety of sorbate-MOF systems, but heat capacities of the hybrid materials are unknown. This information is essential if MOFs are to be effectively used in non-isothermal fixed-bed systems. Differential scanning calorimetry (DSC) is an effective analytical tool to characterize the thermal properties of materials. In this work, a thermal gravimetric analyzer coupled with DSC was employed to determine the heat capacities of typical MOF materials, covering both types with or without open metal sites, including CuBTC, IRMOF-1, and UMCM-1. The heat capacity of MOFs is very important thermodynamic data not only for characterizing adsorbent material itself, but also for optimizing adsorption process. The impact of the coordination environment and metal content and type on the heat capacity values will be discussed, and comparisons will be made with heat capacities of traditional porous materials.