Abstract
The discovery of carbon nanotubes has stimulated intensive research on the synthesis, modification and physical properties of these novel carbon materials due to their unique and one dimensional pore structure, rolled graphitic layers as well as their potential application in sensors, separations, electronic devices, gas storage and quantum dots. Research has suggested that the role of nitrogen in the synthesis of carbon nanotubes could be either to enhance the formation of graphitic layers on the catalyst or to increase the separation of the graphitic layers from the catalyst. The studies further suggested that if nitrogen is incorporated into the structure then the presence of nitrogen in the pentagonal defects would induce the bending and distortion of the carbon nanotubes, whilst nitrogen in substitutional sites would not produce major distortion of the nanotubes.
Well-aligned carbon nanotubes were grown from the pyrolysis of ferrocene, toluene and small fractions of various amines, aromatic amines, diamines and amides by nebulized spray pyrolysis at temperature of 8500C. Transmission electron microscopy and scanning electron microscopy reveal that the carbon nanotubes possess bamboo-like-structures and that the nanotubes are well-aligned. The nanotubes ranged from 36 nm to 121 nm in diameter and 65 μm to 625 μm in length depending on the specific growth conditions such as concentration of various nitrogen containing hydrocarbons, growth time and flow rates of the carrier gasses.
Raman spectra show the characteristics bands at 1336 cm-1 (D-band) and 1583 cm-1 (G-band). The G-band modes are larger than the D-band modes, suggesting that the carbon nanotubes synthesized In the presence of nitrogen additives are more graphitic than those synthesized without nitrogen addition.
TGA analysis under static air environment, showed that the carbon nanotubes are stable within a temperature range of 40 – 5600C and in the at temperature range of 590 – 8000C, the mass loss of carbon nanotubes is constant. The residual metal content in the carbon nanotubes was found to be approximately 20%, when nanotubes were synthesized by the pyrolysis of toluene and ferrocene and about 7% after addition of nitrogen containing hydrocarbons to the catalyst.
Selected carbon nanotubes were purified using a microwave purification method. The mass loss between unpurified carbon nanotubes and purified nanotubes were found to be insignificant. The diameters of the carbon nanotubes were found to have been reduced drastically, which suggest that defects were removed during the purification process.
The data generated in this study revealed that nitrogen containing hydrocarbons acted as co-promoters of CNTs during the synthesis of carbon nanotubes.
Mr. L.M. Cele
Prof. N. Coville