Page 66 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

52 Principles and Methods

Figure 3.12 TEM image of 4 nm Fe 3 O 4 nanoparticles prepared from the
thermal decomposition of Fe(acac) 3 .
distribution. By this method, highly uniform nanoparticles can be obtained
(see Figure 3.12).
In addition to simple metal oxides (M x O y ) a range of mixed metal oxides
can also be prepared. For example, nanospheres and nanocubes of cobalt
ferrite can be obtained from cobalt and iron acetylacetonates, Co(acac) 2
and Fe(acac) 3 in solution in phenylether and hexadecanediol in the pres-
ence of oleic acid and oleylamine [64]. Heating at 260 C forms CoFe 2 O 4
spherical nanocrystals with a diameter of 5 nm. These nanocrystals serve
as seeds for a new growth as the second step of the synthesis, giving per-
fect nanocubes from 8 to 12 nm, depending on the conditions. Nanocubes
in the 8 nm range can also be used as seeds to obtain spheres (Figure 3.13).
The tuning of the shape of ferrite nanocrystals is managed by the param-
eters of growth, such as heating rate, temperature, reaction time, ratio
of seed to precursors, and ratio of oleic acid, acting as surfactant stabilizing
the nanocrystal, to oleylamine providing basic conditions needed for the
formation of spinel oxide. Variations in the morphology of numerous
oxide nanocrystals, including nanocrystals of Fe, Co, Mn ferrites, Co 3 O 4 ,
Cr 2 O 3 , MnO, NiO, ZnO, and others, have been obtained by pyrolysis
of metal carboxylates in the presence of different fatty acids (oleic,
myristic) [65–67].