Environmental Engineering Reference
In-Depth Information
7.2.2.6 Hydrothermal Method
Hydrothermal method includes diverse wet-chemical technologies for crystalliza-
tion of substances mixture in a close system (autoclave). Hydrothermal method is
successfully used when an increase of iron oxide nanoparticle crystals is desired.
Synthesis of iron oxide magnetic nanoparticles requires high temperatures
(above 200
C) and high pressures (0.3-4 MPa), using two main routs: hydrolysis
and oxidation or neutralization of metallic hydroxides mixture. The most important
parameters of the process are the solvent, temperature, and reaction time [
78
].
Chen and Xu [
78
] demonstrated that the size of Fe
3
O
4
particles are increasing as
the reaction time increases.
Zheng et al. [
79
] obtained Fe
3
O
4
particles using the hydrothermal method, with
particle size of 27 nm, using sodium bis(2-ethylhexyl)sulfosuccinate as surfactant.
The magnetite nanoparticles obtained are endowed with superparamagnetic behav-
ior at room temperature.
Wang et al. [
80
] present obtaining of Fe
3
O
4
nanoparticles with high crystalline
feature. The nanoparticles size obtained using this method at 140
C for 6 h was
40 nm, saturation magnetization was 85.8 emu/g, hardly decreased compared to
bulk Fe
3
O
4
bulk (92 emu/g).
Daou et al. [
81
] reported obtaining monodispersed magnetite nanoparticles of
39 nm in size, synthesized first by co-precipitation method at 70
C, followed by a
second synthesis phase—hydrothermal treatments at 250
C. Magnetite nanoparticles
obtained by co-precipitation method were 12 nm in size, being oxidized in contact
with air.
7.2.2.7 Sonochemical Method
Sonochemical method was largely used in generation of new materials with unusual
properties. Chemical effects of ultrasounds seem to be acoustic cavitation, which
means that the bubbles are forming, grow, and are implosively falling into fluid,
which generates a localized hot spot, as gaseous phase. This method was applied in
synthesis of nanocomposites, and its versatility was demonstrated in case of
preparing the iron oxide nanoparticles [
55
]. Vijayakumar et al. [
82
] reported
obtaining of magnetite nanoparticles using the sonochemical method by sonication
of iron acetate in water, in absence of air. Particles obtained by this method were
10 nm in size, presenting superparamagnetic behavior and very low saturation
magnetization at room temperature (below 1.25 emu/g).
Pinkas et al. [
83
] obtained amorphous iron oxide with very large specific surface
using sonochemical method. They sonicated Fe(acac)
3
in small amount of water, in
argon atmosphere. Organic content and specific surface of Fe
2
O
3
can be controlled
by water amount within the reaction mixture. Thus, nanoparticles of 48 m
2
/g
specific surfaces were obtained for using a solvent and 260 m
2
/g when working
within humid argon atmosphere.
