Improving the Chemical Reactivity of Single-Wall Carbon Nanotubes with Lithium Doping

The effect of lithium doping on the reactivity of single-wall carbon nanotubes (SWCNTs) was studied by means of first principle calculations. Two prototype reactions were considered, the 1,3 dipolar cycloaddition and the attachment of free radicals. The results obtained employing the PBE, M06L, and M06-2X functionals indicated that lithium significantly increases the reaction energies. Although this effect is slightly increased upon diameter enlargement, it decreases when the distance between the functional group and lithium is augmented. We observed a stronger enhancement of reactivity for semiconducting SWCNTs as compared with the metallic ones. Regarding the endohedral and exohedral lithium dopings, both increase the binding energies, although for some functional groups the latter doping is far less effective because exohedral lithium can remove the fluorine atoms or hydroxyl or thiol groups from the tube walls. Therefore, endohedral lithium is expected to be more useful to enhance the reactions performed onto SWCNTs, whereas in some cases exohedral lithium may have a negative effect depending on the affinity that lithium has with the functional groups attached to the SWCNTs. If the lithium–functional group interaction is stronger than the binding energy between the nanotube and the functional group, the perfect sp 2 framework of the nanotube will be restored. All of the functionals employed gave the same results from a qualitative standpoint, but important quantitative differences were observed in the magnitude of the reactivity enhancement.