Isothermal Capture and Release of Carbon Dioxide with a Porous Molecular Hexaamine

The decarbonization of fossil fuel combustion streams and air is imperative to achieve negative carbon emissions and requires discovery of new materials that exhibit high CO2 capacities, long-term stability, and minimal energy input for the release of pure CO2. Numerous candidate sorbents have been reported, but none meet all of these requirements simultaneously. Our strategy for creating a material that does is centered on designing a crystalline molecular polyamine that retains porosity throughout CO2 absorption and desorption while achieving a high CO2 uptake capacity, thereby enabling meaningful CO2 capture and release under mild conditions. Here, we show that porous crystals of 2,3,6,7,14,15-hexakis(aminomethyl)triptycene (C20H8(CH2NH2)6, TriptH) capture CO2 from flue gas or air to form a porous ammonium carbamate network solid. The reversibility of the transformation is monitored in situ using powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, and solid-state nuclear magnetic resonance spectroscopy. Breakthrough analyses reveal that TriptH achieves a high CO2 capacity of 5.3 mmol/g under humid conditions, long-term oxidative and thermal stability through the course of 660 absorption-desorption cycles, and an unprecedented ability to capture CO2 from humid, low-concentration streams and release it with little or no temperature change and vacuum pressures as high as 100 mbar.