Adsorption pathways of singlet ${\mathrm{O}}_2$ on $4\mathrm{\AA }$ carbon nanotubes

Using density functional calculations and the nudged elastic band method, we investigate the adsorption pathways of singlet ${\mathrm{O}}_2$ on $4\mathrm{\AA }$ single-wall carbon nanotubes, which have been recently fabricated using a templating method. We find that the reaction barriers for these ultrasmall-radius tubes are lower than those previously reported for larger-diameter tubes. Moreover, another chemisorbed product is identified for the (3,3) tube, and the reaction path is very different from those reported for larger armchair tubes.

Figure 1

(Color online) The minimum-energy path from physisorption (site I) to chemisorption (site I) of singlet ${\mathrm{O}}_2$ on tube (5,0). The average $\mathrm{C}\mathrm{O}$ distance is taken as reaction coordinate, and the energy of physisorbed product is set at zero.

Figure 2

(Color online) The minimum-energy path from physisorption (site II) to the cycloaddition and epoxy state of singlet ${\mathrm{O}}_2$ on tube (5,0). The average $\mathrm{C}\mathrm{O}$ distance is taken as reaction coordinate, and the energy of physisorbed product is set at zero.

Figure 3

(Color online) The minimum-energy path from physisorption to chemisorption of singlet ${\mathrm{O}}_2$ on tube (3,3) at site II. The average $\mathrm{C}\mathrm{O}$ distance is taken as reaction coordinate, and the energy of physisorbed product is set at zero.

Figure 4

(Color online) The minimum-energy path from physisorption to the cycloaddition and epoxy state of singlet ${\mathrm{O}}_2$ on tube (3,3). An intermediate chemisorbed state is found between them. The average $\mathrm{C}\mathrm{O}$ distance is taken as reaction coordinate, and the energy of physisorbed product is set at zero.

Figure 5

(Color online) Top and side views of the intermediate chemisorbed product of tube (3,3).

Figure 6

Molecular dynamics results of the $\mathrm{C}\mathrm{C}$ and $\mathrm{C}\mathrm{O}$ distance for the intermediate chemisorbed product of tube (3,3).