Gate Opening Transition of Zeolitic Imidazolate Framework--8 in Xenon adsorption and Carbon Monoxide Adsorption.

DINUKA H GALLABA ; ALDO D MIGONE ; KARIM SAPAG ; JHONNY VILLAROEL

BULLETIN OF THE AMERICAN PHYSICAL SOCIETY

American Physical Society

Año: 2016

0003-0503

Zeolitic Imidazolate Framework? 8 (ZIF-8) is a porous metal-organic framework material that shows flexibilityin adsorbing larger molecules. We have investigated Xe adsorption on ZIF-8 fortemperatures in the range between 95K and 157.5 K and we are exploring COadsorption between 80K and 110K. ZIF-8 is known to undergo a structural (?gateopening?)transition when sorbent loading increases. We report on this gate-openingphenomenon for Xe and CO on ZIF-8. The gate-opening transition appears as asub-step at higher loadings in the adsorption isotherm data. For Xe the sub-stepdisappeared for temperatures above 145 K. All isotherms below this temperatureclearly show the extra step. Gate-opening occurs as a result of the re-orientation ofthe organic linkers in ZIF-8. This re-orientation increases the size of the aperturesin the structure, consequently allowing more molecules or atoms to adsorb into theZIF -8 (which produces the additional sub-step). The isosteric heat of adsorption asa function of loading, and, the energy associated with the structural transition weredetermined from the adsorption data. We also report on the kinetics of sorption forXe on ZIF-8: there are two rates that dominate the sorption kinetics on ZIF-8. Wereport on the values of the rates as a function of sorbent loading.