Synergistic Isoreticular Diversification and Subambient Direct Air CO2 Capture in Anion-Pillared Metal–Organic Frameworks

Abstract

Advancing sorbent materials is vital to enable the adsorptive removal of trace carbon dioxide (CO2) in the air. Anion-pillared metal–organic frameworks (APMOFs) have shown opportunities for this type of application. Nonetheless, their design modularity is limited even in the presence of an extra building unit, namely inorganic anionic pillars, compared to other classes of MOFs. It is also noteworthy that while ambient air is treated as a feed stream in many cases, feed air adsorption at subambient temperatures makes such physisorbents more viable by lowering absolute humidity, which almost always hinders atmospheric CO2 adsorption, and by enhancing equilibrium CO2 uptake at reduced temperatures. Here, we conducted large-scale molecular simulations of a well-established computation-ready database of APMOFs for the adsorption of 400 ppm of CO2, referring to direct air capture (DAC) of CO2, under ambient and subambient conditions in accordance with global implementation. We identified chemically plausible materials, by substituting fluorometallate pillars of SnF62– and ZrF62– within an isoreticular APMOF platform, several of these have been less examined for DAC, that are compatible with existing benchmarks in equilibrium capacity as well as other adsorbent evaluation metrics. Our results allow us to probe how altering anionic pillars affects the electrostatic nature of fine-tuned ultramicropores, forming electronegative “sweet spots” for CO2, and could thus contribute to a Coulomb interaction-dominant affinity for ultralow CO2 concentrations. We also reassessed the adsorbent evaluation metrics that can be adapted when optimized for direct air CO2 sorption at 253 K using a number of adsorbents that consist of GaF52– and InF52– pillars, for instance. Our predictions imply synergistic effects of diversifying APMOFs mainly through pillar substitution and expanding their utilization in subambient CO2 adsorption, which reconfigures the electrostatic landscape.