Sulfur Dioxide Internal and External Adsorption on the Single-Walled Carbon Nanotubes: DFT Study

Density functional theory is used to investigate sulfur dioxide physisorption inside and outside of single-walled carbon nanotube (SWCNT) of (5,0) and (5,5). This study is conducted at B3LYP/6-31G* level of theory. Sulfur dioxide molecule is studied with axis oriented parallel or perpendicular to the nanotube wall. Both internal and external adsorption on nanotubes are increased with the angle of interaction being at maximum of 90° to the tube axis. The harmonic frequencies are computed from analytical derivatives for all species in order to define the minimum energy structures. The lowest values of HOMO and LUMO energies are obtained in the process of the adsorption on the external wall of (5,5) nanotube. The dipole moment of the SWCNTs-SO2 system is highly increased and is more than that of SWCNTs- H2S and SWCNTs- CO2. The lowest ΔGtot for SO2 on the outside wall of (5,0) is obtained while this quantity is positive and is not a favorable adsorption process for H2S on the nanotubes. The NBO analysis shows the change in the electronic structure of nanotubes could be suitable for fabricating sensors.