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magnetization and smaller size. Nitrogen passes during the precipitation,
and protects oxidation of the Fe
3
O
4
nanomaterials but also reduces the par-
ticle size when compared to methods without oxygen removal. Magnetic
nanoparticles, Fe
3
O
4
or
γ-
Fe
2
O
3,
prepared under alkaline condition of
NH
4
OH, can be suitably stabilized with silica to form well-dispersed mag-
netic silica nanospheres. It gives several advantages over other stabiliza-
tion materials. h e change in the SiO
2
/Fe
3
O
4
ratio controls the particle size
distribution.
11.5.2 Hydrothermal Synthesis
Several scientists have reported the hydrothermal synthesis of magnetic
nanoparticles for a wide range of applications [71, 72, 73]. Hydrothermal
reactions are performed in aqueous solutions at high temperature and
pressure. h e reaction conditions, such as solvent, temperature, and time,
usually have important ef ects on the products synthesized by the hydro-
thermal method. h ere are mainly two routes for the synthesis of mag-
netic nanoparticles via hydrothermal conditions: hydrolysis and oxidation
or neutralization of mixed metal hydroxides. h e hydrothermal method
of ers high production yields with reduced production costs and is envi-
ronmentally friendly as a result of the simple equipment, readily available
source materials, absence of explosive or corrosive gases, and use of only
deionized water as the reaction medium [72]. Wan
et al.
[73] have suc-
cessfully synthesized Fe
3
O
4
nanostructures with dif erent morphologies
such as Fe
3
O
4
nanoparticles, nanorods and nanowire bundles via a devel-
oped hydrothermal route. h e Fe
3
O
4
nanoparticles with uniform size and
relatively better monodispersity were synthesized at room temperature.
h ey have reported that the synthesized product was mainly composed
of uniform Fe
3
O
4
nanoparticles with the average diameter of about 20
nm. h e selected area electron dif raction (SAED) pattern indicated the
good crystalline nature of the nanoparticles. It is worthwhile to note that
the complexation between the surfactant molecules and ferrites leads to
an improvement in the uniformity of crystallite size and morphology. As
a result, the prepared Fe
3
O
4
nanoparticles showed uniform size and rela-
tively better monodispersity.
Cao
et al.
[74]
reported a new reaction route to obtain rice- and cube-
shaped single-crystalline α-Fe
2
O
3
nanostructures via a reaction between
Fe(NO
3
)
3
·9H
2
O and NH
3
·H
2
O in ethylene glycol at 200 and 280
C, respec-
tively. h e morphology of the products was studied using transmission
electron microscopy and high-resolution TEM. h e average size of a rice-
shaped α-Fe
2
O
3
nanocrystal along its major axis was approximately 84.9
°
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