Ligand-Assisted Enhancement of CO$_{2}$ Capture in Tunable MOFs: Balancing Electrostatic and van der Waals Interactions

Metal-organic frameworks (MOFs) are promising nanoporous materials for CO$_2$ separation technologies. Here, we use first-principles van der Waals (vdW)-corrected calculations to identify and understand how CO$_2$ binds to a novel ``BTT-type'' MOF [1] featuring open metal centers. Our study indicates that CO$_2$ binds to the open metal cation sites, but with an adsorption energy that can be enhanced by more than a factor of two depending on the choice of the bridging ligand. Judicious choices for metal cations and bridging ligands are shown to lead to a maximum binding energy of 0.67 eV for MgBTT. In all cases, the binding can be attributed to a combination of electrostatics and dispersion, both critically sensitive to the local environment, and contributing nearly equally to the overall binding strength. The possibility to independently tailor these energetics in a manner optimal for CO$_2$ capture is discussed in the context of recent experiments.