Nitrogen and Oxygen Mixture Adsorption on Carbon Nanotube Bundles from Molecular Simulation

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• 作者：Jianwen Jiang and Stanley I. Sandler
• 刊名：Langmuir
• 出版年：2004
• 出版时间：December 7, 2004
• 年：2004
• 卷：20
• 期：25
• 页码：10910 - 10918
• 全文大小：351K
• 年卷期：v.20,no.25(December 7, 2004)
• ISSN：1520-5827

文摘

The adsorption of a nitrogen and oxygen mixture (air) on two types of single-walled carbon nanotubebundles at both sub- and supercritical temperatures is studied using grand canonical Monte Carlo molecularsimulation. On an infinite periodic hexagonal bundle without an external surface, adsorption at a subcriticaltemperature is of type I. With increasing pressure, nitrogen adsorption first increases and then decreasesuntil saturation; oxygen adsorption continues increasing, displacing nitrogen, until saturation. Both nitrogenand oxygen first form annuli inside the nanotubes, then with increased coverage they occupy the nanotubecenters, and at the highest coverage some oxygen also adsorbs in the interstitial channels between thenanotubes. The selectivity of nitrogen over oxygen decreases with increasing pressure and reaches aconstant near saturation. Adsorption at a supercritical temperature is also of type I, with both nitrogenand oxygen adsorption increasing with increasing pressure, though the selectivity of nitrogen to oxygenfirst increases slightly and then decreases with increasing pressure. On a small isolated hexagonal bundlewith an external surface, adsorption at a subcritical temperature is of type II. With increasing pressure,nitrogen adsorption first increases, then decreases, and finally increases again due to wetting by liquidair, while oxygen adsorption increases continually. Both nitrogen and oxygen adsorb first at the internalannuli and at the grooves, and with increasing pressure, they then adsorb at the ridges and at the nanotubecenters; at higher pressures, only oxygen adsorbs in the interstitial channels, and multilayer adsorptionand wetting occur on the external surface as the bulk phase approaches saturation. The selectivity, likethat of subcritical temperature adsorption on the infinite periodic bundle, decreases with increasing pressureand reaches a constant upon wetting. Adsorption at a supercritical temperature is of type I, with bothnitrogen and oxygen adsorption increasing with increasing pressure. The selectivity of nitrogen to oxygen,like that of supercritical temperature adsorption on the infinite periodic bundle, first increases slightlyand then decreases with increasing pressure. These results indicate that the adsorption selectivity stronglydepends on temperature but only weakly depends on the type of the bundle and that a nitrogen-oxygenmixture (air) might be separated by competitive adsorption on the carbon nanotube bundles.