Methane storage in singlewalled carbon nanotube Molecular dynamics simulation

The discovery of multi-walled carbon nanotubes (MWCNTs) in 1991, and single-walled carbon nanotubes (SWCNTs) 2 years latter by Iijima, attracted enormous attention of many research groups. The special structures and unique properties of these novel forms of elemental carbon make them useful for a wide variety of applications ranging from electronics field emitters to nanodevices[1]. In particular, Kong et al. [2] and Jalili et al. [3] studied the use of carbon nanotubes (CNTs) as gas sensors based on results showing that electronic properties of CNTs change dramatically upon gas adsorption.Methane and krypton adsorption isotherms on SWNTs have been investigated using volumetric measurements and isothermal microcalorimetry [4]. Temperature programmed adsorption and other surface analytical tools have also been used to study the adsorption of Xe into both open and close SWCNTs [5]. Ulbricht and coworkers presented a study on the kinetics of Xe desorption from SWCNTs bundles using thermal desorption spectroscopy. It was found that opening the ends of the nanotube by chemical cutting increases both the kinetic rate and the saturation capacity of the nanotubes for rare gases [6]. Magnetic resonance (NMR) measurements had shown that the interior of SWCNTs becomes available for methane and ethane molecules after cutting of SWNTs [7].The grand canonical Monte Carlo (GCMC) simulations were used to study the adsorption of CH4 [8,9], Xe [8], Ar [8], and N2 [8,10] in SWCNTs bundles.In this paper, methane adsorptions on (10,10) SWCNTs have been investigated at different pressures using MD simulations. Adsorption coverage for exohedral (external surface of a single nanotube), and endohedral (internal surface of a single nanotube) were reported. Also, experimental studies of methane adsorption on a sample of open-ended SWCNT that was synthesized by CVD method were performed. We compare our simulation and experimental results.