To understand the confinement effect of carbon nanotubes (CNTs) on energetic compounds, the encapsulation and thermal decomposition of nitromethane (NM) confined inside finite armchair (5,5) single-walled CNTs of various lengths (C30+10nH20) were investigated on the basis of ONIOM calculations. It was found that NM was not encapsulated by CNT(5,5) of n ≤ 5, while CNT(5,5) of n≥ 6 were able to encapsulate NM. The NM confined inside the CNT(5,5) displayed different structural characteristics in contrast to the isolated NM. The activation energy barriers of the C-N thermal decomposition for the confined NM were found to be about 5˜15 kcal/mol lower than that of the isolated NM, suggesting that CNT confinement enabled the C-N thermal decomposition of NM to take place more easily. In addition, our computations showed that a distinct oscillation of the activation energy barriers was correlated to tube length increase, especially when n≤ 10. This indicated that the energy barrier was highly dependent on CNT length.
Keywords: Carbon nanotube, Nitromethane, Thermal decomposition, Confinement effect, Bond dissociation energy, Ab initio, encapsulation, ONIOM calculation, energetic compounds, energy barrier