# Combined Experimental and Computational Study on the Structure–Property Relationships of Mono- and Dicationic Imidazolium Ionic Liquids for CO2 Capture

## TL;DR

This study explores how dicationic ionic liquids can capture CO2 more effectively than monocationic ones, combining experiments and computational analysis.

## Contribution

The study introduces dicationic ionic liquids as superior CO2 capture materials, supported by computational and experimental validation.

## Key findings

- Dicationic ionic liquids showed higher CO2 sorption capacity than monocationic ones.
- The trans conformation of [E(MIM)2]2+ was found to be the most energetically favorable.
- DIL [E(MIM)2][2Cl] demonstrated high CO2 selectivity and stability over multiple cycles.

## Abstract

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.