Flame synthesis of carbon nanotubes using catalyst particles prepared by laser ablation

Flame synthesis of carbon nanotubes using catalyst particles prepared by laser ablation was studied. A greater yield of nanofibers of greater length were produced with the CO/C₂H₂ based gas mixture than with C₂H₂ alone. The reactivity of nickel towards C₂H₂ (at the same concentration) in the absence of CO increased, where fewer nanofibers, of shorter lengths were produced (along with encapsulated particles). Ultrasmall Ni particles (< 4 nm) might not be particularly active towards catalyzing C₂H₂ dissociation. Fe exhibited selective reactivity towards CO. Moreover, the absence of nanofibers of MWNT suggested a decline in reactivity with increasing particle size for Fe nanoparticles, in contrast to nickel. In a metal nanoparticle, the density of electronic states is finite and the traditional conduction and valence bands are absent due to the small number of constituent atoms.