Trends in CO$_{2}$-MOF Binding from First Principles: Implications for Gas Separations

Metal-organic frameworks (MOFs) are a class of highly ordered, highly customizable nanoporous materials that are attractive for use in energy-relevant gas separations. MOF-253 Al(OH)(bpydc) can be post-synthetically modified by introduction of metal cations and charge-stabilizing anions [1]. These post-synthetically modified MOF-253 samples have been shown to exhibit enhanced CO$_{2}$-N$_{2}$ selectivity over the unmodified framework [1]. Here we use van der Waals-corrected density functional theory (DFT) to study CO$_{2}$ binding energy trends in this series of modified frameworks. Particular focus is paid to examining the predictive power of our calculations on modified bipyridine fragments as a proxy for the full framework, as well as the suitability of binding energy trends to predict measured gas selectivity trends [1]. We focus on the following series of 10 post-synthetic modifications: CoCl$_{2}$, CuCl$_{2}$, FeCl$_{2}$, NiCl$_{2}$, PdCl$_{2}$, Co(BF$_{4})_{2}$, Cu(BF$_{4})_{2}$, Fe(BF$_{4})_{2}$, Ni(BF$_{4})_{2}$, Pd(BF$_{4})_{2}$.\\[4pt] [1] E. Bloch, et. al, J. Am. Chem. Soc., 132, 14382-14384, 2010.