CO2 capture by fluorinated-imidazolium based ionic liquids: a multiple minima hypersurfaces analysis.

Ionic liquids (ILs) are a promising alternative for CO2 capture, offering high stability, environmental friendliness, and scalability. The present theoretical study focused on the evaluation of 12 ILs for the capture of up to 5 CO2 molecules. The 12 ILs are based on imidazole and fluorine, [C8H4F13mim]+[BF4]-, [C8H4F13mim]+[TFO]-, [Dmim]+[BF4]-, [Dmim]+[TFO]-, [Hmim]+[FAP]-, [Dbim]+[FAP]-, [Hmim]+[methide]-, [Dbim]+[methide]-, [Hmim]+[(PFOc)SO3]-, [Omim]+[(PFOc)SO3]-, [Hmim]+[(PFBu)SO3]-, and [Omim]+[(PFBu)SO3]-. A stochastic dynamic search algorithm was used to generate the structure of the nCO2-IL clusters, with n = 1 to 5. The molecular clusters were then optimized using Density Functional Theory (DFT) calculations to describe the nature of the interactions between the 12 ILs and CO2. Results show that CO2 physisorps and preferentially interacts with anions, also fluorine substitution increasing CO2 affinity. Cluster formation is exothermic and favored at lower temperatures. The physisorption is driven by weak van der Waals interactions. The [Dbim]+[FAP]-, [C8H4F13mim]+[BF4]- and [C8H4F13mim]+[TFO]- ILs demonstrated the highest CO2 binding capacity but at the simulated conditions the process is not spontaneous. These findings are useful for designing efficient CO2 capture materials based on ILs.