Study of Carbon Monoxide and Neon Adsorption on Zeolitic Imidazolate Framework -8 (ZIF-8)

Zeolitic Imidazolate frameworks (ZIFs) are porous Metal Organic Framework materials that have zeolite-like structures. We will present the results of an adsorption isotherm study of carbon monoxide in ZIF-8. The adsorption isotherms display multiple sub-steps. Similar substeps have been observed before with xenon and O2 in ZIF-8; they have been interpreted as indicating a pressure-induced structural transition or ``gate-opening'' of the ZIF-8 at low temperatures. We have conducted our measurements for CO on ZIF-8 at temperatures in the range between 72K and 105K. All the isotherms measured in this range have clear sub-steps (which reflect an increase in CO loading due to gate-opening transition). We have used the isotherm data to calculate the isosteric heat of adsorption as a function of loading for this system. We found a change in isoteric heat at the loading corresponding to the structural transition; a similar feature was observed in previous experiments conducted on Xe and on O2 in the same sorbent. We have preliminary results for the sorption of neon in ZIF-8. The isotherm data for neon will be presented and compared data for other gases.