CO2 Capture from Ambient Air by Crystallization with a Guanidine Sorbent

Abstract Carbon capture and storage is an important strategy for stabilizing the increasing concentration of atmospheric CO 2 and the global temperature. A possible approach toward reversing this trend and decreasing the atmospheric CO 2 concentration is to remove the CO 2 directly from air (direct air capture). Herein we report a simple aqueous guanidine sorbent that captures CO 2 from ambient air and binds it as a crystalline carbonate salt by guanidinium hydrogen bonding. The resulting solid has very low aqueous solubility ( K sp =1.0(4)×10 −8 ), which facilitates its separation from solution by filtration. The bound CO 2 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 CO 2 separation from air requires minimal energy and chemical input, and offers the prospect for low‐cost direct air capture technologies.