Effects of Nitrogen Based Anions on CO₂ Binding and Proton Affinity

The anion appears to be the one of the most important factors when selecting an ionic liquid for the capture of CO₂. Experiments have also shown that the anion has the ability to re-protonate due to water content in the system, which would limit CO₂ binding. To further examine this issue the binding enthalpies have been studied for a variety of anions that include two or three nitrogens in the bicyclic structure. A trend was found between the binding of CO₂ and the proton affinity to determine which anion would be most successful at binding CO₂ while not binding a proton. Five-member rings showed a greater performance to CO₂ binding, when compared to the six membered side of the structure. A positive correlation was also observed between the charge of the CO₂ in the system and the bond length associated with CO₂ binding to a nitrogen site on the anion.