Adsorption of Nitrogen in Carbon Nanotube Arrays

Abstract

Grand canonical Monte Carlo molecular simulations have been carried out for adsorption of nitrogen at 77 K on square arrays of open and closed single-wall carbon nanotubes with diameters of 6-30 Å and nanotube separations of 4-30 Å. Exohedral spaces for arrays of closed nanotubes with small tube separations are microporous. For large separations, two-stage adsorption occurs, corresponding to monolayer formation followed by a condensation step. Filling of the exohedral space is dominated by geometrical factors that allow the calculation of adsorbate molecular packing factors, which are close to that for liquid nitrogen. The amounts adsorbed in arrays of open nanotubes are higher than for closed tube arrays, as expected. The highest increase is for arrays with small tube separations and large tube diameters, where endohedral adsorption dominates; for wider tube separations the increase in amount adsorbed is less because exohedral adsorption becomes important. Arrays of single-wall carbon nanotubes have the potential to develop very high adsorptive capacities, to which the interstitial spaces between the nanotubes make significant contributions. The adsorptive capacity can be optimized when exohedral adsorption dominates, that is, with arrays of narrow single-wall nanotubes with wide spacings between them.

Simple model of adsorption on external surface of carbon nanotubes—a new analytical approach basing on molecular simulation data

“…Moreover, on experimental data we do not observe a plateau around saturation and in fact on simulated data this plateau also vanishes on isotherms obtained for large distances between tubes. It is interesting that this plateau is usually observed on nitrogen isotherms simulated in different simulation boxes for example for square array of tubes (Yin et al 1999). Summing up, in our opinion the experimental data obtained for the studied systems show that adsorption process can be dominated by adsorption on those fragments of bundles, where the tubes are at relatively large distances and they behave almost independently.…”

“…The probability of attempts of changing a system state by creation, annihilation, and rotation and displacement (the latter one is connected with the change in angular orientation) were equal to: 1/3, 1/3, 1/6 and 1/6. Simulation studies of nitrogen adsorption in carbon nanotubes can be performed assuming a spherical model (Alain et al 2000;Kotsalis et al 2004;Kowalczyk et al 2005;Maddox and Gubbins 1995;Ohba and Kaneko 2002;Ohba et al 2007;Wongkoblap et al 2009;Yin et al 1999) but if nitrogen molecules are confined in nanotubes the assumed shape of molecules is important and nitrogen should be modeled as a diatomic molecule (Arab et al 2004;Arora et al 2004;Arora and Sandler 2005, 2007a, 2007bJiang and Sandler 2003;Khan and Ayappa 1998;Müller 2008;Paredes et al 2003;Wongkoblap et al 2009;Zhang et al 2008). To test the importance of molecular shape, both potential models (spherical and diatomic) were used by Wongkoblap et al (2009) in computer simulation.…”

“…It should be noted that more and more complicated models reproducing the structure of real carbon nanotubes (i.e. from ideal cylinders (Arora et al 2004;Arora and Sandler 2005;Gauden et al 2009;Harris 2009;Khan and Ayappa 1998;Kotsalis et al 2004;Kowalczyk et al 2005;Maddox and Gubbins 1995;Müller 2008;Ohba and Kaneko 2002;Terzyk et al 2008;Zhang et al 2008) to bundles (Alain et al 2000;Arab et al 2004;Furmaniak et al 2008aFurmaniak et al , 2009aHarris 2009;Sandler 2003, 2004;Paredes et al 2003;Wongkoblap et al 2009;Yin et al 1999) and tubes with defects Sandler 2007a, 2007b;Furmaniak et al 2009a;Gauden et al 2009;Harris 2009;Terzyk et al 2008;Zhang et al 2008)) have been applied. On the other hand, despite the complex structure of carbon nanotubes confirmed by the analysis of experimental data (mutual position of nanotubes in the bundle, defects, an unavoidable by-products of a typical nanotube growth process i.e.…”

“…It should be noted that other mixtures were also studied (N 2 (single LJ model)-H 2 O) (Kotsalis et al 2004). Yin et al (1999) studied adsorption of nitrogen (single LJ model) on square arrays of open and closed single-walled nanotubes with different diameters. They concluded that adsorption isotherms, in closed tubes with small tube separations, are of type I.…”

Production of Carbon Nanofibers Using a CVD Method with Lithium Fluoride as a Supported Cobalt Catalyst

“…Since their discovery in 1991 [1], carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have attracted a deal of interests due to their own unique characteristics and potential applications such as separation, gas sensing, catalyst support, energy storage, and environmental protection [4][5][6]. On the other hand, graphitic carbon nanofibers (GCNFs) represent a class of nanostructured carbon fibers with atomic structures uniquely different from that of carbon nanotubes.…”