Abstract:

The molecular structure and thermal decomposition of nitromethane confined inside armchair (CNT(5,5), CNT(6,6), CNT(8,8)) and zigzag (CNT(9,0), CNT(10,0), CNT(11,0)) single-walled carbon nanotubes (CNTs) with different diameters were investigated using the ONIOM (B3LYP/6-311++G**:UFF) method. Results showed that the Cs symmetry of nitromethane confined inside CNT(5,5) and CNT(9,0) was destroyed and that the C—N bond was compressed slightly. Confinement in CNT(6,6), CNT(8,8), CNT(10,0), and CNT(11,0) had no evident influence on the molecular structure of nitromethane. By analyzing the potential energy surface along the C—N bond, we found that a transition state existed during the thermal decomposition of nitromethane confined inside CNT(5,5) and CNT(9,0). This was very different from the behavior of the nitromethane monomer as no transition state existed during C—N bond dissociation. The activation energy barriers of the thermal decomposition for nitromethane confined inside CNT(5,5) and CNT(9,0) were found to be lower by about 71 and 58 kJ·mol-1, respectively, compared with the bond dissociation energy of the nitromethane monomer. Confinement in CNT(6,6) and CNT(8,8) resulted in a slight decrease in the activation energy. Confinement in CNT(8,8) and CNT(11,0) did not affect the thermal decomposition of nitromethane. We concluded that the activation energy of nitromethane decomposition was significantly reduced by confinement in a carbon nanotube with a small diameter. Additionally, the activation energy was not influenced by the chirality of the carbon nanotube.

Key words: Carbon nanotube, Nitromethane, Thermal decomposition, Confinement effect, Ab initio