Effect of adding nickel to iron–alumina catalysts on the morphology of as-grown carbon nanotubes Original Research Article

The synthesis of carbon nanotubes (CNTs) from ethylene decomposition by Fe/Al2O3 and Fe/Ni/Al2O3 catalysts (Fe:Ni=10:1) is studied. A small amount of nickel introduced into the catalyst can significantly increase the yield of CNTs, but the nanotubes change from straight tubes with concentric parallel carbon sheets to helical tubes of the fish-bone type. Raman characterization of CNTs prepared at 823 and 1023 K and CNTs annealed at 2473 K shows that CNTs deposited on the Fe/Ni/Al2O3 catalyst have poor crystallinity, as compared with that on the Fe/Al2O3 catalyst. These differences are explained by a mechanism of formation of helical tubes of the fish bone type that takes into consideration the differences in the chemical nature of the catalyst with and without nickel.