Improving Carbon Dioxide Storage Capacity of Metal Organic Frameworks by Lithium Alkoxide Functionalization: A Molecular Simulation Study

Metal organic frameworks (MOFs) represent a new kind of porous solid and have shown promising potential for carbon dioxide (CO2) capture and separation. In this work, grand canonical Monte Carlo simulations were performed to explore lithium alkoxide functionalization for improving CO2 adsorption capacity in HKUST-1, MOF-143, and MOF-399. The results show that lithium alkoxide functionalization remarkably improves the CO2 uptake ability in all three kinds of MOFs at 298 K, especially at the low-pressure range. The CO2 uptake amount in lithium-functionalized HKUST-1 increased more than 1700% compared with its unfunctionalized form at 1 kPa. Furthermore, the extension of organic linkers leads to lower CO2 adsorption capacity at the low-pressure range due to the lower isosteric heat, but higher CO2 adsorption capacity at the high-pressure range resulting from the increase of total free volume. Specifically, the incorporation of Li atoms onto the frameworks induced a shift of preferential adsorption sites for CO2. The CO2 molecules were first adsorbed around the Li atoms in the three lithium-functionalized MOFs.