Chemistry Reference
In-Depth Information
Fig. 37 SEM images of aligned carbon nanotubes.
Left
: CNT-column array;
right
: higher
magnification on the CNT-columns. Reprinted from [
156
], Copyright 2012, with permission
from Elsevier
reaction and localized them both at the tips and at the sidewalls. In a similar
approach,
tert
-butyl groups could be clearly visualized by STM [
113
].
A mapping study of functionalized carbon nanotubes, showing the possibility
of combining STM topography to tunneling conductance mapping was reported,
in order to highlight
the dependence of functionalization on crystallographic
orientation [
159
].
5.2.5 Thermogravimetric Analysis
The employment of thermogravimetric analysis (TGA) for CNTs characterization
is so widespread that it deserves a separate section for its description.
This technique is fundamental for the evaluation of the functionalization
degree of a sample according to the weight loss that occurs after heating up to
1,000
C[
90
].
Owing to the different thermal stability between the nanotube carbonaceous
skeleton and the volatile chemical species appended on the sidewalls, it is possible
to evaluate the amount of functionalities introduced on the tubes, which are usually
expressed in
mol/g.
Generally the instrument is composed of a high-precision balance with a pan,
commonly made of platinum, on which the samples are placed. The pan is loaded
into an electrically heated oven equipped with a thermocouple, which accurately
measures the variation of temperature inside the chamber. The measurement can be
carried out in an inert gas, such as N
2
, He, or Ar, or in oxygen atmosphere.
Thermogravimetric analysis could be exploited to characterize nanotubes at
the raw stage, after purification and when chemically processed. When the pristine
material is analyzed in the presence of oxygen, it is possible to obtain information
about its residual mass and the oxidation temperature T
0
, whereas under an inert
atmosphere the carbon structure is maintained and the weight
μ
loss indicates
unequivocally the amount of organic material.
