Thiophene adsorption on Single Wall Carbon Nanotubes and graphene

We investigated the adsorption of thiophene inside and outside Single Wall Carbon Nanotubes (SWCNTs) and onto graphene, employing periodic boundary conditions and the VDW-DF and LDA methodologies. The results indicate that thiophene adopts a nearly parallel configuration with respect to the graphene plane. The sulfur atom is 3.7 angstrom above the sheet, whereas the two hydrogen atoms located in carbon atoms not bonded to sulfur are 3.45 angstrom above it. The adsorption energy for this configuration is 8.9 kcal/mol, smaller a value than the one determined for benzene. For the T-shaped configurations the potential energy surface is very flat showing different orientations with similar interaction energies. When two hydrogen atoms are positioned over a CC bond the binding energy is 5.2 kcal/mol. However, when the sulfur atom is over a hexagon, the interaction energy reaches its minimum value. The vibrational frequencies of thiophene are red-shifted when it is adsorbed on graphene being the intensity of the most prominent peak in the IR spectra increased by 34% and red-shifted by 14 cm(-1). For the adsorption on carbon nanotubes, the internal adsorption energies are larger than the external ones, although the former decreases rapidly as the tube radius is increased. The orientation of the thiophene molecule inside a SWCNT strongly depends on the diameter of the tube. The charge transfer between thiophene and the carbon nanostructures is minimal thus the electronic properties are not affected by the adsorption. (C) 2010 Elsevier BM. All rights reserved.