Tuning Pore Chemistry of Metal-Organic Frameworks Using Anionic Pillars for Humid-Tolerant CO2 Capture

Abstract

Reducing global CO2 emissions is a critical challenge, and metal-organic frameworks (MOFs) have emerged as promising physisorbents for capturing trace amounts of CO2 from wet flue gas and humid ambient air. The tunability of the MOF pore chemistry through functional moieties enables selective CO2 capture over H2O. In this study, 18 hypothetical MOFs (hMOFs) were rationally designed by integrating chemical moieties previously explored for trace CO2 capture. Anionic pillars (SiF6 2- and SO4 2-), known to induce strong interactions with electrophilic CO2, were incorporated into template MOFs (CALF20, CALF20-met-w, and CALF20-met-e) that have demonstrated efficacy in post-combustion CO2 capture. These anionic pillars create nucleophilic pore environments that enhance the selectivity of CO2 under humid conditions. Among the candidates, CALF20-SiF6-met-w, composed of Zn metal, methyl-triazolate, and SiF6 2- anionic pillars, theoretically maintained CO2 uptake efficiency above 92.4% across the entire relative humidity range, outperforming its template MOF and benchmark materials. To evaluate its practical applicability, we integrated this material into a temperature-vacuum swing adsorption (TVSA) process simulation. Parametric analysis revealed that it offers a more favorable trade-off between productivity and energy consumption than the template MOF, primarily attributable to its higher working capacity and lower H2O uptake under varying humidity conditions. This study demonstrates the potential of anion pillar engineering in MOFs to achieve efficient CO2 capture under humid conditions.