Environmental Engineering Reference
In-Depth Information
7.2.2.3 Microemulsion Method
A microemulsion is an isotopic thermodynamically stable dispersion of two liquids
that are immiscible (water and oil), in the presence of surfactant, which forms a film
at the interface between oil and water, having the hydrocarbon chain, non-polar,
dissolved in oil and the polar group in the aqueous phase [
66
].
Vidal-Vidal et al. [
67
] obtained spherical single dispersed maghemite particles
covered with oleilamine or oleic acid, which presents a narrow distribution of the
dimension between 0.6 and 3.5 nm, with magnetization saturation very high
(76.3 Am
2
/kg, for uncoated nanoparticles; 35.2 Am
2
/kg, for magnetic nanoparticles
coated with oleic acid, and 33.2 Am
2
/kg for magnetic nanoparticles coated with
oleilamine). The results demonstrated that oleilamine acts as a precipitation and
bonding agent. Chin and Yaacob [
68
] demonstrated that by the synthesis of the
nanoparticles of iron oxide using microemulsion method, nanoparticles under
10 nm can be obtained.
This method is difficult to control, and the efficiency is low compared with other
synthesis methods for magnetic nanoparticles, and the obtained particles are
polydispersed.
7.2.2.4 Laser Pyrolysis
Laser pyrolysis from gas phase was demonstrated to be an essential procedure in the
synthesis of uniformed iron nanoparticles, where the reactants are diluted, which
results in the obtaining of fine particles with narrow distributions for the dimension
of the particles and the controlled purity, without congesting them [
38
,
39
].
The method for obtaining the magnetic particles by laser pyrolysis was initiated
by Haggerty in 1981 for preparing ultrafine silicon powder [
69
].
The nanoparticles obtained by laser pyrolysis presents a core-shell structure of
Fe/FeO, in which the thickness of the shell is not dependent on initial conditions.
The mean diameter of the particles depends on the laser power and it varies
between 4 and 11 nm. In the case of FeO particles with the diameter between 9 and
11 nm, the saturation magnetization of the nanopowder reaches 80 Am
2
/kg [
70
].
Core-shell nanoparticles covered with carbon layer present a special interest for
biomedical utilization.
The laser pyrolysis synthesis method is one of the most promising with respect to
the industrial scale production of nanopowders with the diameter between 5 and
20 nm.
7.2.2.5 Combustion Method
Combustion method involves a strong exothermal redox reaction, between an
oxidant agent and diverse organic reducing agents. Initiation of combustion process
