The Gibbs free energy differences (∆Grela) of interaction CO molecule with CNT and DNTs with p and d configurations are shown in Table 2. As shown in table 2, the difference of energy between CNT-d and CNT-p is 53.54 kcal/mol in the gas phase, so the p configuration is more stable than d configuration in simple CNT. Also, the p configuration of SCNT is more stable than d configuration, 9.35 kcal/mol. In contrast, the d configuration of NCNT is more stable than the p configuration, 53.89 kcal/mol. The ∆Grela of BCNT complexes is very low and the CO molecule could be perpendicular (d) or parallel (p) on the surface of BCNT. The results of ΔGrela in three solvents were obtained from Gibbs free energies of solvation in the solvents. The instructions of ΔGrela in the solvents were similar to the gas phase, and it is observed that the solvents did not change the stability of the CO molecule at the surface of CNT.