Adsorption of NH3 and NO2 molecules on carbon nanotubes

Adsorption of ${\mathrm{NH}}_{\mathrm{3}}$ and ${\mathrm{NO}}_{\mathrm{2}}$ molecules on semiconducting single-walled carbon nanotubes is investigated using density functional theory. Both ${\mathrm{NH}}_{\mathrm{3}}$ and ${\mathrm{NO}}_{\mathrm{2}}$ molecules are found to bind to carbon nanotubes via physisorption. Electron charge transfer is found to be a major mechanism determining the conductivity change in carbon nanotubes upon exposure to ${\mathrm{NH}}_{\mathrm{3}}$ and ${\mathrm{NO}}_{\mathrm{2}}$ molecules. The calculated density of states is also considered to elucidate the differences in the ${\mathrm{NO}}_{\mathrm{2}}$ and ${\mathrm{NH}}_{\mathrm{3}}$ gas detection mechanism of carbon nanotubes.