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Electric field mediated separation of water-ethanol mixture in carbon-nanotubes integrated to nanoporous graphene membrane


We investigate the influence of an applied electric field on the separation of water-ethanol solution inside a carbon nanotube (CNT) using a series of molecular dynamics simulations. The electric field is applied at an angle with respect to the axis of the CNT. The study uncovers that with the application of a ‘small-angle’ electric field (e.g. smaller ), the water molecules exhibit preferential occupancy inside the CNT, whereas application of the same at a ‘wide-angle’ mode (e.g. higher ) fills the CNT with ethanol molecules in place of water. Remarkably, the direction of the electric field plays a pivotal role because the field exerts a contrasting influence on the behaviours of the water and ethanol molecules. The water dipoles are favourably aligned at small values of creating an ordered water structure inside the CNT. Increasing disrupts the water dipole orientation and leads to preferential occupancy of the CNT by ethanol molecules. An in-depth analysis on the simulated systems unveil that, at lower values of , multiple layers of water molecules are physically adsorbed near the CNT walls, which is found to diminish as is increased. In comparison, at higher magnitudes of , the ethanol molecules are preferentially adsorbed inside the CNT. The average interaction energy per ethanol (water) molecule is found to enhance (reduce) when is monotonically increased, which can be ascribed to the promotion (reduction) of intermolecular hydrogen bonding capacity of the ethanol (water) molecules at larger values of . Consequently, inside the CNT, the average occupancy of water molecules decreases and ethanol molecules increases, as is monotonically increased, leading to the separation of ethanol-water mixture. The proposed methodology can convert an equimolar mixture (1:1) of ethanol-water into a concentrated one (14:1) when the electric field is applied orthogonal to the axis of the CNT. The separation efficiency is found to improve with the increase in intensity of the externally applied electric field.

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Publication details

The article was received on 12 Feb 2018, accepted on 16 Apr 2018 and first published on 16 Apr 2018

Article type: Paper
DOI: 10.1039/C8FD00027A
Citation: Faraday Discuss., 2018, Accepted Manuscript
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    Electric field mediated separation of water-ethanol mixture in carbon-nanotubes integrated to nanoporous graphene membrane

    M. P. Borthakur, D. Bandyopadhyay and G. Biswas, Faraday Discuss., 2018, Accepted Manuscript , DOI: 10.1039/C8FD00027A

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