Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

68j 2 Carbon Nanotube–Metal Nanocomposites
Figure 2.21 Schematic representation of spark plasma sintering
system. Reproduced with permission from [83]. Copyright Ó
(2007) Elsevier.
2.7.3
Molecular Level Mixing
An important step procedure for forming metal nanocomposites at molecular level
is functionalization of CNTs. This strategy is often employed to prepare polymer-CNT
nanocomposites since CNTs have poor compatibility with most polymers [6, 85].
CNTs can be functionalized covalently by oxidizing nanotubes in nitric and sulfuric
acids in order to induce carboxylic or hydroxyl groups on the end-caps or defect sites
of CNTs. These acids disrupt the aromatic ring arrangement at the caps of CNTs,
leading to the incorporation of functional groups at the open ends. This acid
treatment also results in shortening of CNTs as described in Chapter 1. To form
nanocomposites, functionalized CNTs act as adsorption centers that strongly
interact with metal ions or hydration molecules in aqueous phase. In other words,
functionalized CNTs react with metal ions of selected metal salt and organic ligand in
a solution at the molecular level to form metal complexes which act as the building
blocks for metal-matrix nanocomposites.
Hong and coworkers synthesized the Cu/MWNT nanocomposites using a
molecular level mixing process [86–89]. The synthesis involves several steps:
(a) functionalization of MWNTs and their dispersion in ethanol; (b) addition of
copper acetate monohydrate [Cu(CH 3COO)2.H2O] to CNT suspension under
sonication; (c) dissolution of copper salt and attachment of Cu ions to the functional