Comparison of NQR of O2, N2 and CO on Surface of Single-walled Carbon Nanotubes and Chemisorption of Oxygen-doped on the Surface of Single-walled Carbon Nanotubes: A DFT and Computational NMR Study

The discovery of carbon nanotubes produced by graphite, first reported by Iijima in 1991(S. Iijima & T. Ichihasi 1993), ushered in a new and very amazing research field in compacting gases by physisorption methods. The changes in electrical resistance, by adsorption of certain gas molecules are considerable, for example by adsorption of O2, N2, NH3 and H2 (H. Chang et al. 2001). Figure 1 depicts a C72H16 tube modeling an armchair (4, 4) SWCNTs which demonstrates the stated effect on the electronic structure of single-walled carbon nanotubes (SWCNTs). Comparing the adsorption of gases on the surface, using computational methods substantially reduces costs and thus NQR were used in related investigations. Even at low concentration, due to the charge transfer between gases and tube, gas physisorption can change the conductivity of CNTs. Electronic properties of SWCNT have been studied in a number of theoretical works (H. van C. Houten et al., 1992; H. Aijki & T. Ando, 1993; J. W. G. Wildoer et al., 1998; A. Bezryadin, 1998) and optimized forms of nanotube can be designed by a precise positioning of various gases on considered carbon atoms. Theoretical studies have found that this single-walled carbon nanotube has novel electronic properties, which can be semiconducting, depending on their radius or chiralities (T. Hertel et al., 1998; J. W. Mintmire et al., 1992; N. Hamada et al., 1992; R. Saito et al., 1992; M. Rao et al., 1997; H. Kataura et al., 1999). According to the electron-transmission mechanism on the surface of CNTs, the detected gas can be classified into reducing and oxidizing gaseous species. The electrical resistance of CNTs was found to increase when exposed to reduce gaseous species as N2 (J. Zhao et al., 2002), whereas being exposed to oxidizing ones as O2 (P. G. Collins et al., 2000) decreased. A new SWCNT gas sensor would be fulfilled by utilizing such electrical