Thermochemistry of Fluorinated Single Wall Carbon Nanotubes

Abstract

The gradient corrected Perdew−Burke−Ernzerhof density functional in conjunction with a 3-21G\nbasis set and periodic boundary conditions was employed to investigate the geometries and energies of C₂F\nfluorinated armchair single wall carbon nanotubes (F−SWNT's) with diameters ranging from 16.4 to 4.2 Å\n[(12,12) to (3,3)] as well as a C₂F graphene sheet fluorinated on one side only. Using an isodesmic equation,\nwe find that the thermodynamic stability of F−SWNT's increases with decreasing tube diameter. On the other\nhand, the mean bond dissociation energies of the C−F bonds increase as the tubes become thinner. The C−F\nbonds in the (5,5) F−SWNT's are about as strong as those in graphite fluoride (CF)<i>_n</i> and are also covalent\nalbeit slightly (<0.04 Å) stretched. Whereas a fluorine atom is found not to bind covalently to the concave\nsurface of [60]fullerene, endohedral covalent binding is possible inside a (5,5) SWNT despite a diameter similar\nto that of the C₆₀ cage.