(311b) Effect of Pore Size, Open Metal Sites, and Functionalized Ligands on Adsorption of Small Molecules In Metal-Organic Frameworks

Metal-organic frameworks represent a new direction in porous materials research that could lead to the creation of designer-specific multifunctional materials for adsorption applications. The rich field of coordination chemistry provides a versatile platform from which these materials may be assembled from an almost infinite set of building blocks. The key to developing these materials for use in adsorption separations and gas storage is to obtain a fundamental understanding of their adsorption properties.

In this work, we examine the effect of pore size, unsaturated metal sites, and functionalized ligands on the adsorption of carbon dioxide, carbon monoxide, and methane at various temperatures. The specific objective here is to determine the governing structure/property relationships for MOFs that contribute to favorable adsorption properties for polar and nonpolar molecules. Three MOFs were synthesized, and adsorption isotherms were measured. The first material, Cu-BTC, possesses open metal sites and interconnected pores. The other two MOFs were synthesized from a mixed-ligand system of benzene-dicarboxylic acid and triethylenediamine. From this system, we formed a zinc MOF (1) and an isostructural copper MOF (2), which possess two interconnected channels with dimensions of 7.5 x 7.5 angstrom and 4.8 x 3.2 angstrom. In this paper, we will discuss MOF synthesis methods and adsorption equilibrium measurements for CO2, CO, and CH4. We will also compare our findings with previously reported MOF results to strengthen the development of structure/property relationships. Recommendations for design of MOFs for trace contaminate applications will be discussed.