The influence of physicochemical reaction parameters on the synthesis of multi-walled carbon nanotubes for use as catalyst supports.
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Date
2012
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Abstract
Multi-walled carbon nanotubes (MWCNTs) and other shaped carbon nanomaterials (SCNMs) were
synthesized by the floating catalyst chemical vapour deposition (CVD) method, using either
ferrocene [1] as the catalyst at 2.5 or 5 wt.%, or a synthesized heteroatom-containing ferrocene
derivative, in toluene, in the range 750 to 950 °C. The derivatives used were ferrocenoyl
imidazolide [3] (a source of N and O) at 2.5 and 5 wt.%, (N-phenylcarbamoyl)ferrocene [4] (a
source of N and O) at 1.25 wt.% and S,S-bis(ferrocenylmethyl)dithiocarbonate [5] (a source of S
and O) at 2.5 wt.%, which was synthesized from ferrocenylmethanol [2]. These were characterized
by melting point, 1H- and 13C-NMR spectroscopy, IR spectroscopy and mass spectrometry (MS).
The effects of variations in the CVD physicochemical reaction parameters, namely temperature,
catalyst employed (and the effect of its heteroatoms, where applicable) and catalyst
concentration, on the CVD products were investigated. These materials were characterized by
transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive Xray
spectroscopy (EDX), Raman spectroscopy, thermogravimetric analysis (TGA) and some by the
Brunauer, Emmett and Teller method (BET).
The best temperature range, in terms of high yields of MWCNTs with relatively high thermal
stabilities and surface areas, in general, was identified as being 800 to 900 °C, from results
obtained with [1]. This temperature range was used for further experiments. Among other
results, it was shown that [1] and [3], at 2.5 wt.%, and at 800 and 850 °C respectively, produced
the best materials. Catalysts [4] and [5] produced primarily carbon spheres, however, in general,
all experiments using N-containing catalysts produced bamboo-shaped MWCNTs. For [3], at 2.5
wt.%, smaller bamboo compartment lengths correlated with decreasing temperature and
decreasing crystallinity, suggesting a larger incorporation of nitrogen with lowered temperature.
Catalyst [3] at 2.5 wt.% also produced very “clean” MWCNTs and this was attributed to optimal
levels of oxygen being able to convert amorphous carbons to gas. Certain MWCNT properties
were shown to be dependent on the combined, or synergistic, effects of catalyst concentration
and temperature.
The best undoped MWCNTs that were synthesized and commercially produced MWCNTs were
loaded with Pd nanoparticles using a metal organic CVD (MOCVD) method. Results revealed well
dispersed metal nanoparticles of narrow size distribution.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2012.
Keywords
Carbon nanotubes., Catalysts., Theses--Chemistry.