Adsorption of gases and large polycyclic organic molecules in metal-organic frameworks

Metal-organic frameworks (MOFs) are a class of porous materials with unique properties, including size tunable pores and cavities that allow for high surface areas and high levels of porosity. These properties make MOFs appealing for a number of traditional processes such as separations and catalysis, and for areas of current interest such as gas storage. The implementation of these frameworks into these areas first requires an understanding of the adsorbene-adsorbent interactions. For this reason, the adsorption behavior of CH4, N2, and CO2 (298 K, 30 bar) in a series of isoreticular MOFs (IRMOFs) was investigated by Raman spectroscopy. The data were marked by different shifts to the normal vibrational modes of the gases, depending on the IRMOF to which they were adsorbed. These shifts arise due to interactions within the framework pores, and not with the outer crystal surface. In all cases, Raman spectra at pressures up to 30 bar showed that saturation of the sorption sites does not occur. The observed shifts of the vibrational modes for each gas indicate different chemical environments within different IRMOFs, pointing to the important role the linkers play in the adsorption of gases.; Despite the fact that MOFs possess surface areas that exceed those of other porous materials, no method of determining the upper limit in surface area for a material had yet been determined. Here, a general strategy is presented that has allowed for the realization of a structure that has one of the highest surface areas reported to date. The design and inclusion properties of crystalline Zn4O(1,3,5-benzenetribenzoate)2, a framework with a surface area measured to exceed 4,500 m2/g, is reported. This framework, named MOF-177, combines this exceptional level of surface area with an ordered structure that has extra-large pores capable of binding polycyclic organic guest molecules, that include C60 and several dyes. Size and isomer selectivity may also be achieved with MOF-177, as observed with a series of bromo arenes. The inclusion of solvatochromic dyes allowed for investigations involving vapor sensing, with the crystals changing colors upon exposure to solvent vapors with different chemical functionalities.