Biology Reference
In-Depth Information
the type, quantity, and bonding of these functional groups in the
structure. Heteroatoms distributed randomly in the core of the car-
bon matrix may be nonreactive due to their inaccessibility. How-
ever, the heteroatoms can also be concentrated at the exposed
surface of carbons or presented as an “active” dislocation of the
microcrystalline structure. Much of the research being carried out
is focused not only on the identification and characterization of
oxygen-containing functional groups in oxidized carbon surfaces,
such as carboxyl, phenolic, quinonic, and lactones, but also in the
changes that take place in the carbon surface under different oxida-
tion treatments.
The electrochemical oxidation pretreatment was found to
improve the electrochemical behavior by introducing more active
edge sites on the treated carbon surface. The effect of oxidation
on the chemical composition is related to the increased concentra-
tion of strong and weak acidic groups found upon electrochemi-
cal oxidation of the graphite surface [65]. The acidity of carboxylic
groups on the oxidized carbon surface could be stronger than that
of a carboxylic resin. The weight increase after electrochemical pre-
treatment was attributed to the formation of the oxidized graphite
and the intercalation of solvent molecules and anions into graphitic
material.
Regarding the CNTs, the growing methods provide not only
the CNT product, but also different contaminants (mainly amor-
phous carbon and catalyst metallic particles) which are commonly
removed by treatment with oxidizing acids, for example, HNO
3
,
which results in ends largely decorated with carboxyl groups [66].
However, defects in the sidewalls can also be introduced under
such drastic conditions. Functionalization or modification of CNTs
has become a major activity within the interdisciplinary fields of
nanoscience, nanotechnology, bioengineering, and bionanotechnol-
ogy, as it promises to be the best approach for improving the sol-
ubility and compatibility of CNTs. Defects in SWNTs are important
in the covalent chemistry of the tubes because they can serve as
anchorgroupsforfurtherfunctionalization,andthereforeapromis-
ing starting point for the development of the covalent chemistry of
SWNTs [67].
