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CO2 Adsorption in M-IRMOF-10 (M = Mg, Ca, Fe, Cu, Zn, Ge, Sr, Cd, Sn, Ba)

Borycz, Joshua, Tiana, Davide, Haldoupis, Emmanuel, Sung, Jeffrey C., Farha, Omar K., Siepmann, J. Ilja, Gagliardi, Laura
The Journal of Physical Chemistry C 2016 v.120 no.23 pp. 12819-12830
adsorption, barium, cadmium, calcium, carbon dioxide, coordination polymers, copper, dicarboxylic acids, electrons, flue gas, germanium, ions, iron, magnesium, oxygen, quantum mechanics, strontium, surface area, tin, zinc
Metal–organic frameworks (MOFs) have been studied extensively for application in flue gas separation because of their tunability, structural stability, and large surface area. M-IRMOF-10 (M = transition metal or main-group atom) is a well-studied series of structures and is composed of saturated tetrahedral Zn₄O nodes and dicarboxylate linkers that form a cubic unit cell. We report the results of a computational study on the effects that changing the metal atoms within IRMOF-10 has on the affinity of the material towards CO₂. Force fields were parametrized using quantum mechanical calculations to systematically compare the effects of different metal centers on CO₂ adsorption at high and low pressure. Two different methods for the determination of partial charges (DDEC and CM5) and force field parameter sets (TraPPE and UFF) were employed. TraPPE parameters with fitted metal–CO₂ interactions and CM5 charges resulted in isotherms that were closer to experiment than pure UFF. The results indicate that exchanging the Zn²⁺ ions in the IRMOF-10 series with metals that have larger ionic radii (Sn²⁺ and Ba²⁺) can lead to an increase in CO₂ affinity due to the increased exposure of the positive metal charge to the oxygen atoms of CO₂ and the increased interaction from the more diffuse electrons.