Computational Screening of Alkali, Alkaline Earth, and Transition Metals Alkoxide-Functionalized Metal-Organic Frameworks for CO2 Capture

Carbon dioxide capture from flue gas and natural gas are important industrial processes. As an energy-efficient alternative of the traditional cryogenic method, equilibrium-based CO2 capture by solid porous materials, that is, metal-organic frameworks (MOFs), has shown great potential for CO2 separation. In this work, the CO2 adsorption ability of a UiO-type MOFs, UiO-67, is dramatically tuned by incorporating various metal ions, including alkali metals (Li, Na, and K), alkaline earth metals (Be, Mg, and Ca), and first-row transition metals (Sc to Cu), into the framework. Specifically, the binding energies of CO2 on Be, Ca, Ti, V, Mn, and Fe alkoxide-functionalized ligands exceed that of Li alkoxide-functionalized ligand. Grand canonical Monte Carlo simulations show clear CO2 adsorption enhancements at 298 K and pressure up to 5000 kPa for the functionalized MOF, especially at a low pressure range. Ti alkoxide-functionalized MOFs show the highest uptake amount of CO2 at low pressures. Additionally, the extension of organic linkers leads to lower CO2 adsorption capacity at a low pressure range because of lower adsorption heat but higher CO2 adsorption capacity at high pressure range resulting from the increase of pore volume. Metal alkoxide functionalization is an efficient approach for enhancing CO2 capture.