Abstract
Coiled multiwall carbon nanotubes (MWCNTs) were prepared on Fe, Co, and Ni metal oxides supported on alpha-Al2O3 using urea as fuel and catalyst surface modifying agent by catalytic chemical vapour deposition (CCVD). The shape of the nanotubes was influenced by the addition of urea, where coiled and uncoiled tubes were obtained in the presence and absence of urea, respectively. The MWCNTs were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and nitrogen adsorption analysis. The coiling/uncoiling of the nanotubes was visualized from the SEM and TEM images of the prepared specimens. The XRD data showed the characteristic peaks of the nanotubes. BET analysis of the coiled tubes revealed 85.57 m(2) g(-1) surface area with a pore diameter 102.2-110.8 angstrom. A mechanism for the nanotubes coiling is suggested.