The rapid rise in atmospheric CO₂ concentration and consequent warming climate have resulted in the increased frequency of disastrous weather events and irreversible damage to various ecosystems, posing a significant threat to societal wellbeing. The removal of greenhouse gases from the atmosphere or preemptive capture of industrially produced gases could potentially mitigate this concerning trend. Such mitigation could potentially be accomplished by direct-air capture (DAC) and sorption of CO₂ in porous materials.
Metal-organic frameworks (MOFs) are porous coordination polymers that have emerged as promising DAC sorbents thanks to their high stability, porosity, and tunability. An extensive library of MOFs has been developed from a variety of components comprising inorganic nodes and organic bridging linkers. From this library, some MOFs have exhibited superior CO₂ sorption performance resulting from the properties of their internal pore surface. While many of these depend on physisorption interactions, the introduction of platforms for chemisorption in MOFs has led to significant improvement in gas capture. Proper understanding of the mechanisms operative during chemisorption can inform the further logical design and development of materials for use in DAC processes.
While previous studies assumed that the capping carboxylate modulator groups at MOF nodes were static and prevented direct chemisorption of gases to open metal sites, recent reports have explored the dynamic nature of the bonds between nodes and bridging carboxylate linkers. Presumably, carboxylate modulators could be similarly labile, exposing open metal sites for direct sorption. Described here is a mechanistic investigation of the dynamic role of node-capping modulator in controlling CO₂ sorption, insights from which can potentially lead to the development of enhanced DAC sorbents.

Seryeong Lee

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