Carbon capture and storage is an important strategy for stabilizing the increasing concentration of atmospheric CO2 and the global temperature. A possible approach toward reversing this trend and decreasing the atmospheric CO2 concentration is to remove the CO2 directly from air (direct air capture). Herein we report a simple aqueous guanidine sorbent that captures CO2 from ambient air and binds it as a crystalline carbonate salt by guanidinium hydrogen bonding. The resulting solid has very low aqueous solubility (Ksp=1.0(4)×10−8), which facilitates its separation from solution by filtration. The bound CO2 can be released by relatively mild heating of the crystals at 80–120 °C, which regenerates the guanidine sorbent quantitatively. Thus, this crystallization‐based approach to CO2 separation from air requires minimal energy and chemical input, and offers the prospect for low‐cost direct air capture technologies.
Out of thin air: A simple aqueous bis‐iminoguanidine ligand (PyBIG) was found to effectively scrub CO2 from ambient air and bind it as a crystalline carbonate salt via guanidinium hydrogen bonding. The CO2 gas can be released by relatively mild heating of the carbonate crystals, which regenerates the guanidine ligand quantitatively.