Interaction of hydrogen with vacancies in a (12,0) carbon nanotube

We perform detailed calculations for the chemical interaction of molecular and atomic hydrogen with single monovacancy and divacancy in a (12,0) carbon nanotube, in the framework of a tight-binding potential model. For the case of monovacancy, the dangling bond in the defect supplies a large cross section to capture either a hydrogen molecule or an atomic hydrogen nearby. The dangling bond site can be hydrogenated in either $s{p}^2$-like or $s{p}^3$-like hybridization. Our energetic calculations demonstrate that the void in a monovacancy is not an effective access for the penetration of either atomic or molecular hydrogen between the outer and inner sides of the tube wall, but it could be in a divacancy. These results are of importance in the application of defected carbon nanotubes in the future.

Figure 1

The adsorption energy of a ${\mathrm{H}}_2$ versus the distance between the DB site and its nearest hydrogen atom. (a) corresponds to the adsorption process of a ${\mathrm{H}}_2$ parallel to the tube axis, and (b) to the adsorption process of a ${\mathrm{H}}_2$ perpendicular to the tube axis. The total energy of initial configuration where there is no interaction between the hydrogen and the tube wall is taken as a reference.

Figure 2

A hydrogen molecule adsorbed on the DB site in a (12,0) carbon nanotube. (a) displays the final configuration for the dissociated hydrogen molecule adsorbed on the DB site and (b) for the adsorbed hydrogen molecule without dissociation.

Figure 3

Local structural configuration of the 5-1DB defect. (a) A top view of the 5-1DB defect and (b) a side view of the 5-1DB defect. The DB carbon atom is marked with ${\mathrm{C}}_1$. The dashed line in (a) stands for a symmetric plane.

Figure 4

Adsorption energy curve (a) and the stable configurations (b), (c), and (d) of a hydrogen atom on the DB site in the 5-1DB defect. The rotation angles range from $-180°\text{to}180°$. The three crosses labeled by $A^{\prime }$, $B^{\prime }$, and $C^{\prime }$ near the crosses in (a) stand for the resulting configurations without any constraint applied. The local structural features in $A^{\prime }$, $B^{\prime }$, and $C^{\prime }$ are plotted in (b), (c), and (d), respectively.

Figure 5

The local configuration (a) and energy curve (b) for kicking a hydrogen atom inside. The rotation angle is defined as that between the ${\mathrm{C}}_1–\mathrm{H}\left(2\right)$ bond and the radial direction outward at ${\mathrm{C}}_1$ in the tube wall.