Combined Experimental and Computational Study on the Structure-Property Relationships of Mono- and Dicationic...

The present study investigates the potential of dicationic ionic liquids (DILs) and monocationic ionic liquids (MoIL), with and without metal in the anion, for CO₂ capture applications. The structures of the samples were confirmed by FTIR, ¹H NMR spectroscopy, and Raman spectroscopy, while their physicochemical properties, density, viscosity, and thermal stability were evaluated. A series of computational simulations were conducted by using density functional theory (M11/def2-TZVP) to ascertain the multiplicity of the ground state of the magnetic anion [FeCl₄]^-. These simulations determined the multiplicity to be a sextet and furthermore identified the trans conformation as the most energetically favorable for cation [E(MIM)₂]²⁺. This finding demonstrates a correlation between the structural conformations and the experimental Raman spectra. The findings of CO₂ sorption and kinetic tests, conducted under postcombustion conditions (40 °C, 4 bar), indicated that DILs exhibited superior performance in comparison to MoILs. The DIL [E(MIM)₂][2Cl] exhibited the highest sorption capacity (110.20 μmol/g), which is almost three times higher than that of the best MoIL (BMIM FeCl₄). These enhancements can be ascribed to reduced viscosities and an augmented number of active interaction sites in the dicationic structures. Furthermore, [E(MIM)₂][2Cl] exhibited a high degree of selectivity for CO₂ over N₂ and demonstrated stability over five recycling cycles, suggesting the potential of DILs as candidates for the development of CO₂ capture technologies.