Abstract
Carbon nanofibers (CNFs), cylindrical nanostructures containing graphene, were synthesized directly from South African fly ash (a waste product formed during the combustion of coal). The CNFs (as well as other carbonaceous materials like carbon nanotubes (CNTs)) were produced by the catalytic chemical vapour deposition method (CCVD) in the presence of acetylene gas at temperatures ranging from 400°C to 700°C. The fly ash and its carbonaceous products were characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), laser Raman spectroscopy and Brunauer-Emmett-Teller (BET) surface area measurements. It was observed that as-received fly ash was capable of producing CNFs in high yield by CCVD, starting at a relatively low temperature of 400°C. Laser Raman spectra and TGA thermograms showed that the carbonaceous products which formed were mostly disordered. Small bundles of CNTs and CNFs observed by TEM and energy-dispersive spectroscopy (EDS) showed that the catalyst most likely responsible for CNF formation was iron in the form of cementite; X-ray diffraction (XRD) and Mössbauer spectroscopy confirmed these findings.
Highlights
The synthesis of carbon nanomaterials (CNMs) has received tremendous interest in the last two decades [1,2,3,4,5]
While the exact growth mechanism of carbon nanotubes (CNTs)/Carbon nanofibers (CNFs) formed from fly ash as a catalyst has not been fully ascertained, it appeared that tip growth could not be discounted
The smooth, glassy and inert surfaces of the South African coal fly ash were covered with irregularly shaped CNFs in the presence of acetylene and hydrogen at temperatures as low as 400°C
Summary
The synthesis of carbon nanomaterials (CNMs) has received tremendous interest in the last two decades [1,2,3,4,5]. Dunens et al [36] showed that CNTs and CNFs could be produced by Australian coal fly ash using the chemical vapour deposition (CVD) method In their case, multiple steps were followed, as iron (which was low in their fly ash,
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