(708h) Systematic Investigation of the Influence of Metal Sites On Water Stability and Carbon Monoxide Adsorption

MOF-74 is a well-known metal-organic framework consisting of one-dimensional channels with coordinately unsaturated metal centers desirable for adsorption, providing discrete, regularly-spaced active sites.    The variety of metal centers that can be included with relative ease creates a favorable system for investigating the role of open metal sites in adsorption in metal-organic frameworks.  Specifically, these materials are promising for breathing air purification, removing toxic chemicals such as carbon monoxide.  A series of MOF-74 isostructures were synthesized and investigated for water stability and carbon monoxide capacity.  Activation conditions were evaluated to minimize the impact of varying amounts of unevacuated solvent between samples to isolate the influence of the open metal site.  The water capacity of the examined materials is greater than or equal to that previously reported, with Co-MOF-74 being the least sensitive to pre-experimental conditions.  Like Mg-MOF-74 reported previously, Co-MOF-74 and Zn-MOF-74 retain some crystallinity as determined via PXRD, but cannot be fully regenerated, as determined by porosity characterization after water exposure.   Co-MOF-74 and Ni-MOF-74 were found to interact strongly with carbon monoxide, and Co-MOF-74 was found to have a higher CO capacity than any previously reported material at 25°C and 1 bar, making this a promising material for further investigation into air purification.  Heats of adsorption for CO were calculated for each analog and found to be comparable to previous predictions or measurements.