CO₂ Capture from Ambient Air by Crystallization with a Guanidine Sorbent

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 (K_sp =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.