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. Effective carbon capture requires rapid gas transport to active sites, challenging to achieve without permanent porosity. Here, the authors report the development of hydrophobic organic crystals that undergo phase transition on exposure to carbon dioxide, allowing efficient carbon capture.