Very high chemical stability and mechanical strength have made carbon nanotubes a very important material in nanotechnology. The most active research area using carbon nanotubes includes applications in nanodevices, field emitters, gas sensors, hydrogen storage in fuel cells, and DNA recognition technology. Due to the fact that studies related to adsorptions of various gases on carbon nanotubes have explored different aspects of nanotube adsorbate interactions, an important aspect of the properties of single walled carbon nanotubes (SWNTs) is related to the nanotube-gas interaction. In addition to its effect on the carbon gasification processes, carbon monoxide has an important role in different synthetic approaches of carbon nanotubes. In all of the processes, CO is primarily physisorbed on SWNT. Therefore, to understand the effect of CO on the electronic and transport properties of carbon nanotubes, we theoretically studied adsorption of CO molecules on SWNTs. In this work, the density functional theory (DFT) calculations were used to study adsorption of carbon monoxide on the (5, 0), (7, 0), and (10, 0) SWNTs. In order to provide further insights on adsorptions of CO molecules on the outside and inside of the SWNTs, we carried out calculations at the angles 0o, 45o, 90o, 135o, and 180o between the molecular axis and the x-axis of the tubes. In the case of zigzag nanotubes with diameters lower than 7.0 Å, rotation of the CO molecules inside the tubes was limited by the nanotube walls, and thus only the 90o angle was investigated. The equilibrium geometries, adsorption energies, charge transfers, and electronic properties were calculated using the Gaussian 2003 package. This information is important for researchers trying to understand the electronic properties of these materials and how it might be exploited for sensor and membrane applications.
