Direct CO2 Capture from Air via Crystallization with a Trichelating Iminoguanidine Ligand

Effectively reducing the concentration of CO 2 in ambient air is essential to mitigate global warming. Existing carbon capture and storage technology can only slow down the carbon emissions of large point sources but cannot treat the already accumulated CO 2 in the environment. Herein, we demonstrated a simple direct CO 2 capture method from air via reactive crystallization with a new trichelating iminoguanidine ligand (BTIG). It could strongly bind CO 2 to form insoluble carbonate crystals that could be easily isolated. In the crystal, CO 2 was transformed to CO 3 2- and trapped in a dense hydrogen bonding network in terms of carbonate-water clusters. This capture process was reversible, and the BTIG ligand could be regenerated by heating the BTIG-CO 2 crystal at a mild temperature, which was much lower than the decomposition temperature of CaCO 3 (∼900 °C). Thermodynamic and kinetics analyses indicate that the crystallization process was exothermic with an enthalpy of -292 kJ/mol, and the decomposition energy consumption was 169 kJ per mol CO 2 . In addition, BTIG could also be employed for CO 2 capture from flue gas with a capacity of 1.46 mol/mol, which was superior to that of most of the reported sorbents.