Theoretical Study On Interaction Mechanism Between Ionic Liquid And Carbon Nanotubes

In recent years,ionic liquids have attracted wide interest in applications such as the controllable preparation and energy storage of carbon nanotubes due to their excellent properties.However,the mechanism of interaction between ionic liquid and carbon nanotubes is not clear.Therefore,in this paper,the structural and corresponding properties of improtonated aprotic imidazole ionic liquids and protic ethylamine nitrate ionic liquids at the interface of carbon nanotubes are systematically investigated by density functional theory.The specific studies are as follows:1.Three imidazole-based cations（[C₂MIM]⁺,[C₄MIM]⁺and[C₆MIM]⁺）and four anions（[BF₄]^-,[Cl]^-,[NO₃]^-and[PF₆]^-）were selected to systematically investigate their structures,orientations,binding energies and infrared spectral properties at the interfaces of carbon nanotubes with three tube diameters.Our calculations demonstrated that the interfacial cations display two different orientations（cations paralleling and perpendicular to the carbon nanotubes surface）irrespective of the diameters of carbon nanotubes,alkyl length of imidazolium cations,as well as types of anions.The calculated results indicated that the E_binding values of cations paralleling to the carbon nanotubes surface are somewhat larger than those perpendicular to the carbon nanotubes,indicating that cations paralleling to the carbon nanotubes surface are thermodynamically much more stable.We found that there is significantly difference for the infrared spectra of the ion-pair on the carbon nanotubes surface.Therefore,with the infrared spectra,the specific orientations of imidazolium cations on surface of carbon nanotubes can be further understood.Finally,the interaction region indicator as well as the symmetry-adapted perturbation theory analysis were further employed to deep understanding of non-covalent interactions between imidazolium-based ILs and carbon nanotubes.Our results show that the paralleling cations is stabilized on the carbon nanotubes surface by the dispersion（especially for theπ-πstacking）interactions.However,for the cations perpendicular to the carbon nanotubes surface,electrostatic,induction as well as the dispersion interactions are all very important.2.Three sizes of ethylamine nitrate clusters（（[C₂H₅NH₃][NO₃]）_n,n=1,2,3）were selected to investigate their properties such as structure,charge and infrared spectra in carbon nanotubes of four tube diameters.Our calculations demonstrated that the nitrate ethylamine ionic liquids showed two stable structures inside the carbon nanotubes:near the side of the carbon nanotubes and in the middle of the carbon nanotubes.Our results indicated that the-NH₃⁺group was always close to NO₃^-in the form most favorable for-NH₃⁺-NO₃^-hydrogen bond formation,indicating that hydrogen bonding is an important factor affecting the structure of the nitrate ethylamine cluster inside the carbon nanotubes.Our results demonstrated that ethylamine nitrate ionic liquids cluster size and carbon nanotube tube diameter have little effect on charge transfer and a large effect on infrared spectra.The nitrate ethylamine clusters and their interactions within carbon nanotubes were investigated in depth by interaction region indicator.It is shown that there are obvious hydrogen bonding and van der Waals interactions between nitrate ethylamine clusters,and the main interaction between nitrate ethylamine clusters and carbon nanotubes is van der Waals interaction.