Ionic liquid functionalization – an effective way to tune carbon dioxide adsorption properties of carbon nanotubes

Abstract

In this research, the influence of non-covalent functionalization by ionic liquids on carbon dioxide (CO₂) adsorption–desorption properties of multi-walled carbon nanotubes (MWNTs) and partially exfoliated MWNTs (PEMWNTs) has been studied. In addition, the effect of polymerization of the ionic liquid on CO₂ adsorption–desorption properties has also been studied at low pressures (<100 kPa) and at different temperatures. The thermodynamic parameters were also determined. It was found that ionic liquid functionalization significantly improved the adsorption capacity through weak CO₂ complex formation with the substituted nitrogen of the imidazolium cation. Furthermore, the adsorption isotherm analysis suggested that the residual functional groups were more affine compared to the ionic liquid moieties. The heat of adsorption behaves differently upon polymerization of the ionic liquid on both substrates. The influence of polymerization on the entropy change was much more significant with the MWNTs substrate, whereas it was negligible with PEMWNTs.