Chemistry Reference
In-Depth Information
RBM
Radial breathing modes
SDBS
Sodium dodecylbenzene sulfonate
SDS
Sodium dodecylsulfate
SEM
Scanning electron microscopy
STM
Scanning tunneling microscopy
SWCNTs
Single walled carbon nanotubes
TEM
Transmission electron microscopy
TGA
Thermogravimetric analysis
THF
Tetrahydrofuran
1
Introduction
Diamond and graphite are the two main allotropic forms of carbon. In diamond,
each sp
3
hybridized carbon atom is arranged in the corresponding tetrahedral
configuration, giving an extended and highly ordered three-dimensional network,
where the motif is represented by the chair conformation of cyclohexane. Graphite
is made by planar sheets where sp
2
carbon atoms are disposed following the
benzene ring motif and giving a honeycomb arrangement.
A third carbon structure, fullerene or buckminsterfullerene, was discovered in
1985 and added to the family of carbon allotropes [
1
]. The best known fullerene,
C
60
, consists of sp
2
hybridized carbon atoms combined together in hexagons
and pentagons to form a truncated icosahedral-shaped molecule that reminds a
soccer ball.
The first evidence of carbon nanotubes dates back to 1952, when the Russian
scientists Radushkevich and Lukyanovich published some transmission electron
micrographs of carbon filaments with 50 nm diameters [
2
]. However, the first time
that carbon nanotubes were significantly introduced to scientific imagery was only
in 1990, at a carbon composite workshop, when Rick Smalley envisioned a fourth
carbon tubular structure, formed by the elongation of a C
60
molecule.
One year later, experimental evidence of nanotube existence and synthesis was
reported by Iijima, who, by means of a high-resolution transmission electron
microscope (HR-TEM), observed fullerene tubular needles in the soot produced
by an arch discharge between two graphite electrodes [
3
]. The powder analyzed
was made of multi-walled carbon nanotubes (MWCNTs), up to several tens of
hollow concentric cylinders of graphene, capped on the edges by fullerene-type
hemispheres (Fig.
1
).
In 1993, Iijima, Ichihashi, and Bethune reported the existence of a similar single-
walled construction (SWCNTs), whose structure was investigated and elucidated in
order to confirm the fundamental properties of the tubes [
4
-
8
].
According to a widely known definition, it is sufficient to cut a strip of graphene
from an infinite two-dimensional sheet and roll it up to form a nanotube. However,
the deceptively simple idea of rolling up a graphene sheet brings about different
