The interactions of simple and Al, B, N, S, P and Si-doped carbon nanotubes with three sulfur-containing molecules (H2S, SO2 and thiophene) have been investigated to assess their adsorption potencies and sensor abilities. DFT calculations were used to calculate the adsorption energies and NBO parameters. Besides, Population analyses were performed to calculate the energy gaps and reactivity parameters and to obtain DOS plots. The results showed an exothermic interaction of H2S, SO2 and thiophene with simple and doped CNTs while the maximum negative adsorption energies were belonged to Al and B containing complexes. Furthermore, evaluation of second order perturbation energies (obtained from NBO calculations) confirmed that the highest energies were related to B and Al containing intramolecular interactions. The results revealed the favourability of adsorption of SO2 by nanotubes (B and Al doped carbon nanotubes, in particular), in comparing with the other examined adsorbates.

In this work, geometries, stabilities and electronic properties of carbon monoxide (CO) molecule as an adsorbent on simple carbon nanotube (CNT) and N, B, S-doped carbon nanotubes (NCNT, BCNT and SCNT) with parallel and perpendicular configurations are fully considered using ONIOM, natural bond orbital (NBO), and quantum theory of atom in molecule (QTAIM) calculations. The adsorption energies (Ead) demonstrate that CO molecule could be adsorbed on the surface of the simple carbon nanotube with parallel configuration (CNT-p) and N-doped carbon nanotube with perpendicular configuration (NCNT-d) in exothermic process. QTAIM calculations are showed the close-shell (non-covalent) interactions between CO molecule and CNT or N, B, S-doped CNTs. Also, the energy gap (Eg) values between the highest occupied molecular orbital and the lowest unoccupied molecular orbital are calculated. In accordance to the results of energy gap, simple and N-doped carbon nanotubes could be used as CO-sensors.