A COMPARISON OF GAS ADSORPTION ON METALORGANIC FRAMEWORKS USING A STICKING FACTOR CONCEPT.

A study was done to determine how a new parameter denoted sticking factor would correlate with gas adsorption by MOFs. The adsorptions of hydrogen, carbon dioxide and methanegaseson a variety of MOFs werecompared at low and high pressures. It was found that, at low pressures, sticking factorcorrelated better with gas adsorption capacity than did surface area. At higher pressures, surface area correlated better with the gas adsorption capacity than did sticking factor for the adsorption of hydrogen and carbon dioxide on MOFs. However, the sticking factor correlated better with methane gas uptake at both low and higher pressures than did surface area. The most likely reason for this is that, under the conditions used,the isotherms for methane did not show saturation at higher pressures whereas those for hydrogen and carbon dioxide did. This demonstrates that it is saturation not pressure that determines whether a correlation will exist between sticking factor and gas uptake. So in general it can be stated that, when saturation has occurred, gas adsorption capacity will be proportional to the surface area, but prior to saturationthe adsorption capacity will be proportional to the sticking factor.Since MOFs are relatively complex materials with various functional groups, open coordination sites, etc., it is truly remarkable that a simple parameter such as the sticking factor is able to correlate so well with gas uptake prior to saturation.