The study of bicyclic amidine-based ionic liquids as promising carbon dioxide capture agents

Abstract

Abstract CO2 capture by ionic liquids has been successfully achieved, indicating that the adsorption of CO2 plays an important role in the activation and transformation of CO2. In this work, highly efficient capture of CO2 is investigated with several novel ILs, which were prepared from bicyclic amidine (DBN) with pyrazole derivatives. Among the kinds of DBN-based ILs, it is found that the optimal absorption capacity (0.93 mol CO2/mol IL) can be achieved by [DBNH][3-MethylPyr] at 40 °C and atmospheric pressure. In view of analysis, the significant increase in CO2 capacity was affected by the reactivity of activated nitrogen, steric hindrance and the type of substituents. On the basis of the spectroscopic investigation and Density Functional Theory (DFT) calculation, the absorption mechanism was illustrated, it was verified that anions can react with CO2 to form carbamates. Meanwhile, charge analysis reasonably elucidated the diversity of absorption capacity in various ILs. It suggested that electric-charge distribution of activated nitrogen in pyrazole ring system can play an important role in determining the reaction of ILs with CO2. Consequently, DBN-based ILs can be excellent candidates for CO2 capture.