Environmental Engineering Reference
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coated, and uniform-size magnetic nanoparticles, Santra
et al.
performed
water-in-oil microemulsion mediated sonochemical synthesis of super-
paramagnetic iron oxide nanoparticles in nonionic surfactants [80]. h e
magnetic core was coated by a thin layer of silica for stabilization of mag-
netic nanoparticles. h e synthesized magnetic nanoparticles have diam-
eters as small as 1-2 nm, and the thickness of the silica coating is as thin
as 1-2 nm.
Vestal and Zhang have used normal and reverse micelle microemulsion
methods to synthesis single-phase CoCrFeO
4
nanoparticles with a con-
trolled size range of 6-16 nm [81]. Results obtained in this study showed
that microemulsion methods provide a synthetic approach that allows for
high-quality nanoparticles with a narrow size distribution. h is method
can be utilized for the synthesis of magnetic nanoparticles of various mor-
phologies. However, this method needs large amounts of solvents and the
yield is low.
11.5.4 h
ermal Decomposition
Magnetic nanoparticles with smaller size and dif erent morphology can
be synthesized through the thermal decomposition of organometal-
lic compounds in high-boiling organic solvents containing stabilizing
surfactants [66, 82]. Iron oxide magnetic nanoparticles can also be syn-
thesized by the thermal decomposition method. In thermal decomposi-
tion, two dif erent approaches have been used for this purpose. h e i rst
approach is thermal decomposition of metal carbonyl precursors fol-
lowed by an oxidation step using air, or oxidation by using an oxidant at
elevated temperatures. h e second is decomposition of precursors with a
cationic metal center in the absence of reducing agents. h e presence of
reducing agents leads to metal nanoparticles even by the use of cationic
precursors.
h e thermal decomposition route appears to be the best synthesizing
method for controlling size and morphology of magnetic nanoparticles.
It gives scalable and high production yield. Although, one of the major
disadvantages of this method is the production of organic soluble nanoma-
terials which limit the extent of application uses of them in biological and
environmental i elds, besides which surface treatment is needed at er syn-
thesis; also, thermal decomposition methods usually lead to complicated
processes or require relatively high temperatures. However, success in
precise particle size control of Fe
3
O
4
nanoparticle has only been achieved
through thermal decomposition using large quantities of toxic and expen-
sive precursors and surfactants in organic solvent [83].
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