Density Functional Theory Study of the Effects of Diameter and Orientation on the Adsorption of Methane and Tetrafluoromethane on the Zigzag Single-Walled Carbon Nanotubes

The adsorption of gaseous molecules on single wall carbonnanotubes (SWCNT) have been investigated by many researchers[1,2]. This is due to the importance of the role of gas-SWCNTinteraction in various areas as nanotubes production [3], sensorsfabrication [1], fuel cells [2], and drug delivery [4]. In the presentwork, we study the adsorption of methane (CH4) andtetrafluoromethane (CF4) molecules on the inside and outside ofzigzag SWCNTs. Our interest on the CH4 and CF4 rely on the factthat they are top symmetric molecules with different chemicalbehaviours. It is expected that new aspects of gas-nanotubeinteraction are revealed by comparison the adsorption behaviour ofCH4 and CF4 molecules on the SWCNTs. Although several articleshave investigated, theoretically, the adsorption of methane onSWCNTs and graphite, in the case of CF4 there is little attempt toinvestigate its interaction with SWCNTs. Investigation of thediffusion of methane inside SWCNTs employing Lennard-Jonepotentials has been determined that the (11,0) tube has the optimaldiameter to perfectly fit methane [5]. Bausclicher and Ricca studiedthe adsorption of methane on graphite and (9,0) SWCNT employinga cluster model and MP2 methodologies [6]. Their results were ingood agreement with experiment. The work of Agraw et al. is one ofthe few works that considered the intern adsorption of methane andgave results that were in good agreement with experiment [7]. In thepresent work, we have studied the external and internal adsorptionsof CH4 and CF4 on SWCNTs to understand the effect of orientationand size of SWCNT on the adsorption process of these molecules.