(112d) CH3Cl Dissociation On Li-Doped Single Walled Carbon Nanotubes

Single walled carbon nanotubes (SWNTs) have been extensively studied as adsorbents for gases. However, relatively little work has been done involving SWNTs as a platform for chemical reactions. We present experimental and theoretical work on adsorption and dissociation of CH3Cl on lithium-doped SWNTs. CH3Cl was dosed onto Li-doped and undoped samples of SWNT in an ultrahigh vacuum chamber. Temperature programmed desorption (TPD) was used to monitor the fate of CH3Cl during the experiments. CH3Cl was observed to desorb from undoped nanotubes. However, almost no CH3Cl or CHn fragments desorbed from Li-doped SWNTs. Instead, a small amount of LiCl was detected to desorb from doped nanotubes, indicating that the CH3Cl has been consumed by chemical reaction. We have used plane-wave density functional theory (DFT) to study the physical and chemical interactions of CH3Cl with Li-doped and undoped SWNTs. We found that CH3Cl is first adsorbed on Li atoms on SWNTs. CH3Cl dissociation and binding of CH3 groups occurs at defective sites on the SWNT, but our calculations indicate that this process it not likely on pristine nanotubes. The CH3 radicals generated from the reaction readily attach to the dangling bonds at the defective sites, and eventually incorporate in the nanotube sidewall. We have used DFT molecular dynamics to observe initial incorporation of the CH3 radical into the nanotube on a time-scale of only 3 picoseconds. Our calculations provide insights into possible reaction pathways of other species on Li-doped SWNTs.