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The role of non-covalent interaction for the adsorption of CO2 and hydrocarbons with per-hydroxylated pillar[6]arene: A Computational Study

Abstract

A systematic study has been performed with DFT calculations for the physisorption of CO2, CH4, and n-butane gases by the pillar[6]arene (PA[6]) in gas phase. The DFT(B3LYP)-D3 calculations showed that CO2 and n-butane could be adsorbed efficiently inside the cavity of PA[6] compared to CH4 molecule. The order of the binding energies of the adsorbed gases by PA[6] is n-butane > CO2 > CH4 at 1 atm and 298K. The hydroquinone units of PA[6] are playing the important role for the adsorption of the gas molecules. The strong cooperative binding of n-butane compared to CO2 and CH4 inside the cavity of PA[6] facilitates the higher adsorption of n-butane inside the PA[6] cavity. The structural analysis of the gas adsorbed PA[6] shows that the carbon atom of CO2 is in close proximity to the aromatic hydroquinone ring of PA[6] and the oxygen atom of CO2 is in close contact to the hydrogen atom of the hydroxyl group of the hydroquinone unit of PA[6]. Similarly, the hydrogen atoms of the hydrocarbon (methane and n-butane) are closely interacting with the aromatic Pi-electron walls of the hydroquinone ring of PA[6] and the electronegative oxygen (O) atoms of the hydroxyl group (-OH) belong to the hydroquinone unit of the PA[6]. The calculated results show that four CO2, four CH4, and two n-butane molecules can reside inside the cavity of PA[6]. The atoms in a molecule (AIM) analyses performed with the adsorbed CO2, CH4 and n-butane inside the cavity of PA[6] show that the strong ‘closed shell’ type interactions for n-butane to hold inside the PA[6] cavity. Beside the adsorption, the desorption of the CO2, CH4, and n-butane from the PA[6] was also accounted with the desorption enthalpies (∆HDE) calculated per gas molecule, that indicates that both adsorption and desorption are feasible in nature. The DFT studies of PA[6] with the CO2, CH4, and n-butane gases may help to understand the development of new design materials which can efficiently capture and separate such gases. The (B3LYP-D3) computed results corroborate the experimental observations that n-butane can better adsorb with PA[6] compared to CH4 gas molecules. The associative butane-butane interactions seem to be superior over the CO2-CO2 interactions inside the PA[6] cavity that promote the higher adsorption of the hydrocarbon.

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Publication details

The article was received on 19 May 2017, accepted on 07 Sep 2017 and first published on 07 Sep 2017


Article type: Paper
DOI: 10.1039/C7NJ01744H
Citation: New J. Chem., 2017, Accepted Manuscript
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    The role of non-covalent interaction for the adsorption of CO2 and hydrocarbons with per-hydroxylated pillar[6]arene: A Computational Study

    D. Sahu, K. Jana and B. Ganguly, New J. Chem., 2017, Accepted Manuscript , DOI: 10.1039/C7NJ01744H

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