ncluding pristine CNT are shown in Figure 3. This figure and the data of the strongest vibrational modes represented in Table 3 reveal that IR vibrational frequencies do not depend too much on the positions on the surface of CNT. Onlysmall shifts are seen in the O-H stretching andbending vibrational modes. The higher O-H vibrational frequency belongs to the structure A where it is the most stable structure among A-D structures. Other vibrational frequencies such as C=C stretching and bending modes do not strongly depend on the position of hydroxyl group on the surface. However, the intensities of some of these modes do depend on the position of hydroxyl group, as the dipole moments and the polarization of normal modes are not equivalent for all these structures.
In this study, the structure of different hydroxylated CNTs has been studied using
Figure 3. IR spectra of structure A-D and the CNT obtained using UB3LYP/6-31G(d) theory level. Dominated number relate to the vibrational frequencies of O-H and C-H stretching modes. The notation ν is used for stretching and δ for bending vibrational normal modes.
Table 3. The strongest vibrational mode of structure A-D and the pristine structure in cm−1. The notation ν is used for stretching and δ for bending vibrational normal modes. δ(C-H) ┴ represents the bending vibrational model of C-H groups which vibrate in perpendicular to the longitude side of CNT. * represents the most intensive frequency among the frequencies in the mentioned ranges.
UB3LYP/6-31G(d) theory level. For this purpose, a (5, 0) zigzag CNT with 60 C atoms has been used. The optimized structures of four isomers of HO-C60H10 show that the geometry and all the other molecular properties such as dipole moments, energies and the shape of frontier molecular orbitals strongly depend on the position of hydroxyl group on the surface and only one of these isomers is thermodynamically stable in STP condition. All these structure have higher band gap with respect to the pristine CNT. Thus, a hydroxylated CNT is less conductive than the pristine one.
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