Synthesis of single- and multi-wall carbon nanotubes over supported catalysts

Catalytic synthesis and some characterization of multi- and single-wall carbon nanotubes are presented. Supported transition-metal catalysts were prepared by different methods and were tested in the production of nanotubes by decomposition of hydrocarbons at 700 degrees C, using a fixed-bed flow reactor. The quantities of deposited carbon were measured and the quality of the nanotubes was characterized by means of transmission electron microscopy and scanning tunneling microscopy. The inner and outer diameters of the nanotubes were also measured and the diameter distribution histograms were established. The multi-wall straight and coiled nanotubes were found to be quite regular with an average inner (outer) diameter of 4-7 nm (15-25 nm) and with lengths up to 50 mu m. The walls contain concentric cylindrical graphene sheets separated by the graphitic interlayer distance. The single-wall nanotubes were found as bundles of hundreds of aligned straight 1-nm-diameter nanotubes with lengths up to 1-mu m. The influence of various parameters such as the method of catalyst preparation, the nature and the pore size of the support, the nature of the metal, the quantity of catalyst active particles, and the reaction conditions on the nanotubes formation were studied. The numbers and dimensions of the catalyst active particles dispersed on the support were found to be of importance in regulating the shape of the produced nanotubes. Following these results, a model of growth mechanism was suggested for the nanotubes obtained by this method.