Abstract
Ph.D.
This work presents a detailed study of the synthesis of carbon nanotubes and
nanospheres by nebulised spray pyrolysis. This method has been used by other
workers mainly for preparation of sub-micron particles and the deposition of thin
films on various substrates. The effect of various synthesis parameters including
the temperature, choice of the carbon source and the metal precursor as well as
the carrier gas flow rate on the selectivity of the reaction and the properties of the
carbon nanotubes produced was investigated. A major part of this work was
devoted to a study of the effects of the addition of small quantities of oxygencontaining
compounds (alcohols, esters and aldehydes) to the reaction mixture.
The products were analysed using various methods including TEM, SEM, Laser-
Raman spectroscopy and HRTEM.
Furthermore, the possible use of carbon nanotubes and carbon nanospheres as
supports for palladium in the hydrogenation of ethylene was investigated.
Nebulised spray pyrolysis proved to be a suitable technique for the synthesis of
well graphitized carbon nanotubes and carbon nanospheres with uniform diameters
and it was demonstrated that good control of the carbon nanotube properties could
be achieved by controlling the synthesis parameters. Better graphitization of the
carbon nanotubes was observed at higher temperatures. Ferrocene, iron
pentacarbonyl, nickelocene and cobaltocene were successfully used in carbon
nanotube synthesis with the last two producing carbon nanotubes with diameters
close to those on single-walled carbon nanotubes. Toluene (with and without
acetylene as a supplementary carbon source), benzene, mesitylene, xylene and nhexane
were successfully used to produce carbon nanotubes with a high degree of
alignment while no success was achieved with ethanol. The poor yields obtained
with ethanol appear to be a consequence of chemical changes in the ethanol
induced by exposure to ultrasound irradiation.
On the other hand, low concentrations of methyl acetate and ethyl acetate appear
to enhance the production of carbon nanotubes.
It was demonstrated that carbon nanotubes and nanospheres are suitable for use
as supports for palladium in the hydrogenation of ethylene. Pd particles of uniform
size were obtained and the conversion rates were slightly higher when the carbon
nanotubes were pre-treated with a mixture of sulphuric acid and nitric acid.