Pressure induced reactivity change on the side-wall of a carbon nanotube: A case study on the addition of singlet O2

Using the addition of an O₂ to a (10, 0) tube as a model case, the link between pressure and the reactivity of a carbon nanotube is examined by first principles calculations. Attaching functional groups to nanotube side-walls have been envisioned as a method to produce desired structural and electronic properties, although challenges remain for activating and controlling such reactions, especially for tubes with large diameters. Upon pressure, the circular section of a nanotube is flattened and differentiation in chemical reactivity is induced, with the bent section more reactive than the flat section. In the reaction with singlet O₂, both the adsorption energy and the activation barrier for the crucial initial step of cyclo-addition become more favorable on the bent sections, as higher pressure is applied. These values are also found to be linearly correlated with the pyramidalization angle θ_p, which can be further related to external pressure. The estimate shows that it is easier to activate tubes with larger diameters by applying pressure, since such tubes are easier to deform. Our results indicate that pressure, as an easily controlled macroscopic variable, can be used for both selective adsorption and chemical activation.