Abstract-We report reactivity of silicon doped single walled carbon nanotube (Si-CNT) towards the small atmospheric gas molecules O 2 , CO 2 , SO 2 and NO 2 using density functional theory based on the numerical basis set method. The reactivity of gas molecules is explained with binding energy, band structure, charge density, and density of states. We found that the substitutional doping of silicon atom in CNT increases the binding energy as compared with pure CNT. The charge density analysis reveals the formation of sigma (σ) bonds between silicon and carbon atoms. Further, the band structure and density of states clearly illustrate the creation of extra state near the Fermi level and reduction in the band gap, which acts as a reactive center for adsorption of the molecules on Si-CNT. We have observed that the large value of adsorption energy shows the chemisorption between molecules and Si-CNT. Mulliken population analysis clearly reveals the charge-induced dipole interactions between the Si-CNT and molecules, which are responsible for chemisorption for gas molecules. The donor like impurity state generated in energy gap almost disappears after adsorption of all gas molecules excluding NO 2 . We further note that molecules accept the electronic charge from nanotubes and have significant influence on electronic structure near the Fermi level and are responsible for the increase in the p-type conductivity of tubes.
Density functional theory is used to investigate the adsorption properties of O2, CO2, SO2 and NO2 gas molecules on pristine carbon nanotube (CNT) and Si-doped carbon nanotube (Si-CNT). All molecules except NO2 are physisorbed, with essentially no charge transfer between the CNT and molecules. The electronic properties of CNT are sensitive to the adsorption of NO2 because of its chemisorption, while they are insensitive to the O2, CO2 and SO2 molecules. The weak binding of these molecules on CNT is due to formation of charge-dipole interactions. In case of Si-CNT, all molecules are chemisorbed to the Si-C bonds with appreciable adsorption energy and significant charge transfer. The density of state analysis shows that the additional state near the Fermi level due to doping of silicon is responsible for chemisorption of the molecules. Further, our theoretical results suggest that molecule-induced modification of the density of states close to the Fermi level might significantly affect the transport properties of nanotubes.
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