Fly ash catalysed synthesis of CNFs for use in a photocatalytic CNF-TiO2 hybrid
Date
2016
Authors
Moya, Arthur Ndumiso
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Abstract
This study has explored the CVD synthesis of carbon nanofibres (CNFs) using Eskom’s
waste coal fly ash as a catalyst with acetylene and hydrogen as the carbon source and
carrier gas, respectively. In the process, a possible growth mechanism for these carbon
nanofibres was sought. CNFs were successfully synthesised from fly ash and were found to
have an average diameter of 22±7 nm.
The growth mechanism of these CNFs was studied using EDS, TEM and laser Raman
spectroscopy. It was observed that CNFs grew via root growth on spherical particles of fly
ash and by tip growth on irregular-shaped metal oxide agglomerates. Both of these were
found, through EDS analysis, to be Fe-rich.
CNFs were functionalised between 2-12 h under reflux at 110 °C using a 3:1 (v/v)
combination of HNO3 and H2SO4 in order to introduce functional groups onto their surfaces
to act as anchors for hydrophilic reactants. The functionalisation of these CNFs was studied
using TEM, laser Raman spectroscopy, ATR-FTIR spectroscopy, PXRD, BET, XRF and TGA.
ATR-FTIR spectroscopy showed that some carbonyl functional groups were present on the
surfaces of these CNFs after functionalisation.
The functionalised CNFs (fCNFs) were then treated using a simple hydrothermal method to
deposit 10% (m/m) of TiO2 nanoparticles onto their surface. This hydrothermal method
employed the drop-wise addition of TiCl4 to a cold water-fCNFs mixture, which was then
refluxed at 115 °C for 2-12 h. Laser Raman spectroscopy confirmed the presence of both
TiO2 (phase pure anatase) and CNFs. ATR-FTIR spectroscopy provisionally revealed the
presence of covalent Ti-O-C bonds.
Studies where the duration of exposure to TiCl4 and the functionalisation time of CNFs
were examined showed that the particle size and agglomeration of the TiO2 nanoparticles
did not affect the surface area of the CNF-TiO2 hybrids significantly. However, CNF-TiO2
hybrids which were shown by TGA to have high fly ash content were observed to have low
surface areas. fCNFs functionalised at 2 h had the highest surface area, at all fixed durations
of exposure to TiCl4 by comparison with fCNFs which had been functionalised for longer
periods.
Description
A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2016.
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Citation
Moya, Arthur Ndumiso (2016) Fly ash catalysed synthesis of CNFs for use in a photocatalytic CNF-TiO2 hybrid, University of Witwatersrand, Johannesburg, <http://wiredspace.wits.ac.za/handle/10539/21237>