Nonporous hydrophobic organic crystals for carbon dioxide capture via chain-melting phase transition

An efficient carbon capture and release system necessitates rapid CO2 transport to and from active sites, a property typically associated with permanently porous materials featuring large surface areas. Here, we present hydrophobic organic crystals of alkylated monoethanolamine that, despite their nonporous nature, undergo a rapid and reversible solid-to-solid phase transition upon CO₂ uptake and release. Exposure to CO2 triggers a thermodynamically favored structural rearrangement, enabling quantitative CO2 capture and forming a stable carbamate, aided by intermolecular interactions involving the long side chains. This process is fully reversible under practical flue-gas CO2 capture conditions (>0.6% CO2, 0-100% relative humidity) and enables low-temperature desorption using CO2 itself as a stripping gas (65 °C at 1 atm CO2). Structural analysis through in situ XRPD, solid-state NMR spectroscopy, electron diffraction, and Raman analysis confirms that these hydrophobic absorbents selectively uptake CO2 to form an anhydrous ammonium carbamate pair in the solid state. The non-hygroscopic nature of these organic crystals is exemplified by a representative C10-MEA in the presence of CO2, resulting in a desorption process with a minimal temperature swing (ΔTabs-des = 30 °C), offering an energy-efficient (>1.2 GJ/t of captured CO₂) and economically viable alternative for carbon capture applications.