Functionalization of the Single-walled Carbon Nanotubes by Sulfur Dioxide and Electric Field Effect, a Theoretical Study on the Mechanism

In this study, kinetics and mechanism of the sulfur dioxide adsorption on the single-walled carbon nanotubes (CNT) are investigated. Three single-walled carbon nanotubes, including the armchair (6,6), chiral (6,5) and zigzag (6,0) CNTs were chosen as the models and the different orientations of SO2 molecule relative to the CNT axis were considered. The B3LYP functional within the 6-31G(d) basis set was used for the theoretical calculations. For all orientations, reaction Gibbs free energies (ΔG˚) were calculated and the transition state structures were investigated for the spontaneous reactions. Chiral single-walled carbon nanotube (6,5) showed the least activation energy (11.72 kcal mol-1) while the armchair model showed the highest one (17.93 kcal mol-1). Natural bond orbital analysis showed that the electronic charge is transferred from CNT to sulfur dioxide. Topological analysis confirmed the C-S bond formation at the transition state. Density of states analysis showed that Fermi level energy is increased in armchair model. The application of the external electric field indicated that the CNTs stability and the functionalization energies are improved. Based on the obtained data, by using the electric field, it is possible to elevate the conductivity of CNT and the functionalization rate of SWCNT for industrial applications.