Molecular selectivity due to adsorption properties in nanotubes

Abstract

The adsorption of small molecules (N 2 ,O 2 , CO, CO 2 ,H 2 O, and HF͒ in model ropes of carbon nanotubes has been studied to determine the main parameters ͑stable adsorption sites, potential barriers, ...) which define the ability of carbon nanotubes to select small molecules through their different behavior in the diffusion mechanism. When the polarization of the nanotubes is taken into account in the semiempirical potentials, it has a significant influence on the adsorption of polar species. Examination of the potential maps along the ropes shows that the nature and the stability of the adsorption sites are strongly dependent on the molecular species and on the diameter of the tubes. For a small rope formed with ͑10,10͒ single-wall nanotubes, different trapping sites are favored by the molecules considered. Furthermore the corresponding trapping well depths are sufficiently selective to discriminate the species. Improving the size homogeneity of the ropes and judiciously calibrating their diameter would provide an efficient mean of selecting molecular species.

Adsorption Dynamics of Alkanes on Single-Wall Carbon Nanotubes: A Molecular Beam Scattering Study

“…1 Material science applications (at ambient pressures) such as compositematerials, 2 sensors, 3,4 gascapture, 5,6 andnanoelectronics [7][8][9] have been extensively studied. However, rather little attention has been paid to applications in heterogeneous catalysis, [10][11][12] particularly in ultrahigh vacuum (UHV) surface chemistry model studies, although the advantages of CNTs as supports for fuel cells 13,14 and the Fischer-Tropsch 15,16 synthesis have been demonstrated.…”

“…Thus, no bulky parts have been used in designing the sample holder. Helium gas has been bubbled through the liquid N 2 , reducing the sample temperature to 85-90 K. 42 (3) For most of the measurements, the alkanes have been dosed on the sample with the molecular beam system, keeping the background pressure while dosing the gas below 2 × 10 -8 mbar. The beam flux has been estimated by comparing the area of the TDS peaks obtained by backfilling the chamber with the TDS peak areas detected by molecular beam dosing.…”

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

“…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.…”

“…The results discussed by Jiang and Sandler demonstrate the important role of the external surface of a nanotube bundle in the character of the adsorption isotherm, and provide a substantial physical explanation for the difference between experimental observation and previous theoretical predictions. The results published by Arab et al (2004) show that (i) including polarization effects in the interaction potential is required for the case of interaction with polar molecules, (ii) the sieving properties of SWNT depend strongly on the radius of the tubes and four domains of behavior regarding the most stable site can be found depending on the radius values, and (iii) the groove sites are more favorable energetically for N 2 . Wongkoblap et al (2009) used homogeneous (hexagonal) nanotube bundles to investigate adsorption of N 2 (1LJ or 2LJ models, GCMC) and Ar.…”

“…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.…”