Computational Screening of MOFs and Zeolites for Direct Air Capture of Carbon Dioxide under Humid Conditions

With rising CO2 levels, it is important to develop new methods to capture CO2 directly from air. Currently, most direct air capture (DAC) adsorbents, such as amines, rely on chemisorption. However, finding materials with weaker, reversible adsorption could improve the regenerability of these adsorbents. The low concentration of CO2 relative to other components of air and the presence of humidity limit the effectiveness of physisorbent materials for DAC. In this work, we screened the 2014 computation-ready, experimental metal-organic framework (CoRE MOF) database along with silica zeolites, aluminophosphate (AlPO) zeolites, and gallophosphate (GaPO) zeolites for DAC under humid conditions based on heat of adsorption criteria. After the initial assessment, AlPO and GaPO zeolites appeared to be promising adsorbents for DAC. To assess the accuracy of these initial predictions, we compared adsorbate-adsorbent interaction energies predicted by the force field used in screening (UFF) and dispersion-corrected density functional theory. To improve the accuracy of these predictions, first-principles force fields were fit for AlPO and GaPO zeolites. More accurate CO2 and H2O heats of adsorption and adsorption isotherms were computed and showed that AlPO and GaPO zeolites are not suitable for DAC applications.