Structural Stability of Metal-Organic Frameworks Under Humid Conditions

Wednesday, November 10, 2010: 2:10 PM
254 B Room (Salt Palace Convention Center)
Paul M. Schoenecker, Cantwell Carson and Krista S. Walton, Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA

The field of metal-organic framework (MOF) synthesis and characterization has grown exponentially in recent years. Reports on gas storage (hydrogen/methane) and carbon dioxide separation from flue gas or natural gas have dominated much of the adsorption investigations for MOFs. While MOFs clearly have the potential for selective gas adsorption with high capacities, sensitivity to water vapor is widely considered to be a critical weakness from an applications perspective. The water sensitivity of certain MOFs has been well-documented, but a variety of MOFs have been reported in recent years that do not lose structural integrity in the presence of water. An understanding of MOF performance in humid environments is of paramount importance for elevating MOFs to the applied level. However, few studies on the coadsorption of humid gases have been reported. A pattern, though incomplete, is beginning to emerge in which MOFs connected through nitrogen-bearing ligands show greater water stability than materials constructed solely through carboxylic acid groups. MOFs constructed using metals with higher coordination numbers have also shown excellent structural integrity upon exposure to water. In this work, we present water adsorption isotherms and carbon dioxide isotherms measured under humid conditions in several MOFs at room temperature. X-ray diffraction is performed for each sample after exposure to water. Recyclability is also examined. Results will be discussed for a wide range of MOFs including open metal sites, closed metal sites, functionalized ligands, nitrogen-based ligands, 4-coordinated metals, and 8-coordinated metals. The results of this study suggest design criteria that may be used to synthesize MOFs possessing high water stability.

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