Suitability of a diamine functionalized metal–organic framework for direct air capture

Abstract

The increase in the atmospheric carbon dioxide level is a significant threat to our planet, and therefore the selective removal of CO₂ from the air is a global concern. Metal–organic frameworks (MOFs) are a class of porous materials that have shown exciting potential as adsorbents for CO₂ capture due to their high surface area and tunable properties. Among several implemented technologies, direct air capture (DAC) using MOFs is a promising strategy for achieving climate targets as it has the potential to actively reduce the atmospheric CO₂ concentration to a safer levels. In this study, we investigate the stability and regeneration conditions of N,N′-dimethylethylenediamine (mmen) appended Mg₂(dobpdc), a MOF with exceptional CO₂ adsorption capacity from atmospheric air. We employed a series of systematic experiments including thermogravimetric analysis (TGA) coupled with Fourier transformed infrared (FTIR) and gas chromatography mass spectrometer (GCMS) (known as TGA-FTIR-GCMS), regeneration cycles at different conditions, control and accelerated aging experiments. We also quantified CO₂ and H₂O adsorption under humid CO₂ using a combination of data from TGA-GCMS and coulometric Karl-Fischer titration techniques. The quantification of CO₂ and H₂O adsorption under humid conditions provides vital information for the design of real-world DAC systems. Our results demonstrate the stability and regeneration conditions of mmen appended Mg₂(dobpdc). It is stable up to 50% relative humidity when the adsorption temperature varies from 25–40 °C and the best regeneration condition can be achieved at 120 °C under dynamic vacuum and at 150 °C under N₂.