Fisissorção do etanol em nanotubos de carbono de borda aberta

Abstract

Carbon nanotubes (NTC) are considered promising candidates to act as filtration elements for azeotropic solutions, especially water-ethanol mixtures. Nanochannels formed by NTC with diameters of approximately 1 nanometer show a pronounced affinity with ethanol molecules, exhibiting an energetic stabilization. Further, van der Waals forces are relevant interactions when the ethanol molecule is at the entrance of NTC. However, there are open questions regarding the chemical and physical interactions between ethanol molecules and the NTC structure. The present study used the Density Functional Theory (DFT), including van der Waals corrections, to evaluate the interaction of ethanol molecules with open-edge carbon nanotubes. The considered NTC presents H-passivated edges and exhibits 8.44 Å in diameter and 16.64 Å in length. On the gas phase, the NTC shows C-C bonds with 1.38 Å and 1.42 Å at the edge and centre of the carbon nanotube structure, respectively. The ethanol molecule shows a C-O bond with 1.44 Å, with an angle of 108.5 degrees between the C-O-H atoms. Results also show that a weak force attracts the ethanol molecule into the NT. Further, the ethanol C-C bond is oriented along the NTC central axis, while the molecule is approximately in the centre of the structure. A stabilization of around 0.4 eV was noted when ethanol was moved from the edge to the centre of the carbon nanotube, with this energy reduction due to the contribution of van der Waals forces. Such results indicate an ethanol physisorption on the NTCs. On the other hand, it was found that the chemical interaction, through charge exchange (covalent character reinforcement), is more intense at the edge of the nanotube. The information presented helps us understand the interaction between ethanol molecules and carbon nanotubes and can serve as a basis for future studies involving ethanol nanofilters based on nanostructures.