CO₂ Adsorption in MOF-808, MOF-808-GLY, and MOF-808-DL-LYS: Enhanced Capture via Amine Functionalization

Metal-organic frameworks (MOFs) have been shown to be promising materials for tackling challenges within our climate like excess CO₂ emissions. MOFs do this using use their adsorption capabilities to adsorb small molecules like CO₂. MOFs utilize their physisorptive interactions between atoms on the MOFs pore and the gas molecules for adsorption however, there has been great interest in highlighting key structural attributes of MOFs that not only promote CO₂ affinity but can also utilize chemisorption interactions between CO₂ and the MOF framework. To study this, we investigate CO₂ adsorption in MOF-808, as well as amine functionalized MOFs MOF-808-Glycine (MOF-808-GLY), and MOF-808-DL-Lysine (MOF-808-DL-LYS), which are two amine functionalized MOFs that have shown to have higher CO₂ adsorption compared to their pristine counterpart. Molecular dynamics simulations were performed to calculate several thermodynamic and dynamical properties of CO₂ in MOF-808, MOF-808-GLY, and MOF-808-DL-LYS, as a function of absolute pressure from the initial adsorption step to full pore filling. At low pressures, MOF-808-GLY and MOF-808-DL-LYS showcase stronger interactions with the framework compared to MOF-808. One of the contributing factors is the presence of amine groups which not only attract CO₂ to pockets where the amine groups are located. Quantum Mechanic (QM) calculations were also performed on a cluster of MOF-808-GLY to study and highlight the reaction pathways and transition states of CO₂ binding to the amine sites on the framework to form carbamate. This work is crucial in identifying amine groups that promote the highest CO₂ adsorption.