Biomedical Engineering Reference
In-Depth Information
by small hexagonal nanosheets or nanorods generated during the hydrothermal
process, with the mechanism of formation being proposed rationally.
Recently, a solvothermal method has been developed in which the reaction was
carried out in organic media such as alcohols, amines and ionic liquids, instead
of an aqueous solution. When using organic complexes such as a metal carbonyl
and acetylacetonate as feedstocks, the solvothermal method demonstrates clear
advantages over its hydrothermal counterpart, as these compounds are either
insoluble or are decomposed in water, with the result being an unsuccessful reac-
tion. Similar 3-D, fl owerlike Co hierarchical microspheres were obtained in ethyl-
ene glycol solution with either CTAB [72] or PVP as stabilizer [73]. The microspheres
produced consisted of nanoplatelets of approximately 20 nm and 50 nm in thick-
ness, respectively. By using Ru as heterogeneous seeds, and dual-function 1,2-
propanediol as the solvent and reducing agent, a straightforward approach has
been explored to synthesize 1-D Co nanostructures such as nanowires, nanorods,
and nanonails in the presence of steric acid [74]. Meanwhile, 1-D CoPt nanowires
have been prepared in high yields by using Co
2
(CO)
8
and Pt(AcAc)
2
as the starting
materials. In this case ethylene diamine, when used as the solvent, may act as a
bidentate ligand and play a key role in directing the growth of CoPt nanowires at
the minimum required high temperature [75]. Later, Yu
et al.
demonstrated a novel
solvothermal approach for preparing stable, bracelet- like Ni - Co magnetic alloy
fl ux-closure nanorings with tunable dimensions and lengths. Here, a high con-
centration of PVP could be used to stabilize the intermediate short Ni- Co nano-
chains, while magnetic dipole interaction favored self-assembly of the fi nal
nanorings and chains [76].
16.3.3.3.5
Nonhydrolytic Organometallic Thermolysis
In 1993, Bawendi and
coworkers demonstrated a nonhydrolytic liquid phase method for preparing semi-
conductor nanocrystallites, in which the organometallic precursors and other
reagents were injected into high-boiling point solvent under an inert atmosphere
and over a temperature range of 120 to 300 ° C [77] . The as - obtained semiconductor
quantum dots (QDs) had advantages over other synthetic methods, such as a high
monodispersity and a good surface quality. Since that time, tremendous efforts
have been made to utilize this approach in the synthesis of myriad types of nano-
crystal, including as metal chalcogenides [78], metal oxides [79], and metals [80].
The sizes and morphologies of the fi nal nanocrystals were determined by the
monomer concentration, the nucleation ratio, and the crystallographic phase of
the material and capping agents [81].
A new crystal
-phase of cobalt nanoparticle was discovered following the
thermal decomposition of octacarbonyldicobalt Co
2
(CO)
8
at 110 ° C in solution, and
in the presence of trioctylphosphane oxide (TOPO) as coordinating ligand [3]. XRD
studies indicated different patterns compared to the standard fcc and hcp struc-
tures. Typically, the ligands and surfactants could be shown to play a critical role
in determining the resultant structure of the cobalt nanocrystals grown in solution
at low temperatures. In 2001, Alivosatos and coworkers reported an elaborate,
shape-controlled synthesis of cobalt nanocrystals via the rapid injection of Co
2
(CO)
8
ε
