Carbon−Chlorine Bond Scission in Li-Doped Single-Walled Carbon Nanotubes: Reaction of CH3Cl and Lithium

The doping of single-walled carbon nanotubes (SWNTs) under ultrahigh vacuum by Li atoms has been explored experimentally and theoretically. The chemical effect of Li in breaking the C−Cl bond in chloromethane has been observed. Temperature programmed desorption (TPD) experiments show that at low coverage CH 3 Cl is physisorbed to the undoped SWNT sample, exhibiting a desorption process near 178 K. The CH 3 Cl desorption peak shifts to about 240 K for lithiated SWNTs, indicating an increase in binding energy of about 0.16 eV. More importantly, the integrated intensity of the CH 3 Cl desorption peak is dramatically reduced in the lithiated SWNT case, and CH 3, C 2 H 6, or related species are not observed in significant quantities in the TPD experiments up to a temperature of 500 K. This strongly indicates that CH 3 Cl reacts on lithiated SWNTs to produce an irreversibly bound species. Products LiCl and Li 2 Cl 2 are observed to desorb near 700 K. Density functional theory calculations present possible reaction mechanisms and clues to the fate of the reacted CH 3 Cl. Our calculations show that at least two Li atoms are required to dissociate CH 3 Cl through a low-energy pathway. The products of the reaction are LiCl and CH 3 . The CH 3 is chemically bound to defect sites on the nanotubes, and CH 3 + CH 3 radical recombination is suppressed. The second Li atom acts catalytically to lower the reaction energy required to break the C−Cl bond in CH 3 Cl. Furthermore, the CH 3 bound to SWNT defect sites is observed to dehydrogenate at high temperatures in molecular dynamics simulations. This study indicates the potential for Li doping of SWNTs and other high surface area carbons to produce highly dispersed reaction centers for the destruction of toxic materials containing carbon−chlorine bonds.