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.