Synthesis, doping and functionalization of carbon nanotubes
Date
2011-03-11
Authors
Maubane, Manoko Stephina
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Abstract
This study reports the synthesis of carbon nanotubes (CNTs) incorporated into polymeric
materials for potential use in photovoltaic solar cells. Both undoped (CNTs) and nitrogendoped
(N-CNTs) materials were made using the chemical vapor deposition (CVD), catalytic
CVD and floating catalyst CVD methods. The procedures produced CNTs with an average
yield of 1151 % using a 10 % Fe/Co catalyst supported on CaCO3. This is about three times
that produced using 5 % Fe/Co catalyst (average 409 %). Morphology studies showed that the
synthesized materials had an average diameter of 30 nm. CNTs were successfully incorporated
into polythiophenes (PTh) using an in situ chemical oxidative polymerization method. TEM
images showed that the functionalized CNTs in polythiophene, f-CNT/PTh, were thicker
(average 192 nm) as compared to pristine CNTs (30 nm). TGA analysis then revealed that the
new materials (f-CNT/PTh) were more thermally stable as compared to the pure polymer.
N-CNTs were synthesized by the floating catalyst CVD method using toluene, ferrocene and
tetramethylethylenediamine. Functionalization of the N-CNTs was then achieved using 3-
thiophenecarboxaldehyde and sarcosine in 1,2-dichlorobenzene (Prato reaction). Elemental
analysis showed nitrogen incorporation (1.8%) into the N-CNTs and this value tripled after
functionalization with the nitrogen donor reagents. Morphology studies showed that the amount
of monomer used in forming the N-CNT/PTh nanostructures had an influence on the average
diameters of the materials. Different ratios of nanotubes to thiophene monomer by weight were
used (1:3, 1:10 and 1:20). It was found that when the amount of thiophene monomer was
increased, the overall diameter of the materials increased as did the thickness of the polymer
attached onto the N-CNTs. Similar studies were undertaken in order to evaluate the influence of
time on the formation of f-N-CNT/PTh nanostructures. Polymerization reactions were carried
out for 1 h, 12 h and 24 h and it was found that when the polymerization time increased, the
average diameter of the f-N-CNT/PTh also increased, as did the thickness of the polymer attached onto the f-N-CNTs.