Heat of Adsorption of Butane on Multiwalled Carbon Nanotubes

Abstract

We report the isosteric heats of adsorption, q st , for butane on multiwalled carbon nanotubes (MWNTs) over a range of surface loadings at temperatures below the normal boiling point. Butane is a nonspherical, nonpolar molecule that may exhibit different orientations in multilayer adsorption. The morphology of our MWNTs is such that only surface adsorption or capillary condensation can occur: no interstitial sites between nanotubes are available to butane. For these nanotubes, exterior surface adsorption is the principal mechanism measured by gravimetric analysis as the internal pores are only a small volume fraction of the total solid volume. The isosteric heat of adsorption varied with the surface coverage, θ, defined as the ratio of adsorbed butane to the MWNT butane monolayer capacity. The initial heat of adsorption was in the region ∼22-26 kJ/mol, which is approximately 1 / 3 lower than the corresponding value for various graphite-butane systems. At θ ) 1, q st displays a minima (13.5-15.9 kJ/mol). The isosteric heat of adsorption approaches the butane heat of condensation for θ > 2.5, suggesting that the surface film is similar to a bulk phase. The isosteric heat of adsorption of butane on MWNTs can be related to the morphology of the MWNTs. The higher heats of adsorption at low coverages are likely related to the presence of surface defects. The minima in q st near the monolayer coverage relates to a high self-association of butane. At high loadings, the butane surface film is similar to a bulk phase.

Adsorption behavior of epirubicin hydrochloride on carboxylated carbon nanotubes

“…On the other hand, Gotovac et al (2007) find that the external surface of SWNTs is the main area for naphthalene adsorption, but the inner pore sites are not due to the dimensional restriction. The reason for the unavailable interstitial sites is that the organic molecules are too large to fit into this area (Hilding and Grulke, 2004). EPI molecular structure is relatively larger, thus, we infer that external surface area is the most important factor dominating EPI adsorption on CNTs.…”

Coordination chemistry on carbon surfaces

“…In graphene-based materials, each defect has certain mobility parallel to the graphene plane. Several studies have indicated that defective sites are of great importance to the adsorption process [41][42][43][44][45][46]. The presence of these defects in the structure creates highly reactive sites for the adsorption of various species.…”

Adsorption–desorption equilibrium investigations of n-butane on nanocrystalline sulfated zirconia thin films

“…The second and subsequent layers may not necessarily be considered as condensation, as such a state has been reported to occur only after 2.5 monolayers for butane on multiwalled carbon nanotubes (which have lower initial heats of adsorption than sulfated zirconia). [64] …”