Environmental Engineering Reference
In-Depth Information
7.2.2 Methods for Synthesis of Magnetic Nanoparticles
In the last years numerous research were focused on the synthesis of magnetic
nanoparticles. Many scientific publications described efficient methods for synthe-
sis that allows the obtaining of single dispersed magnetic nanoparticles stable in
time and with controllable shape.
The synthesis of magnetic nanoparticles experienced substantial progress in the
last years but with all of these the high-quality magnetic nanoparticles with
controllable proprieties represent a continuous challenge.
The superparamagnetic nanoparticles synthesis is a complex process. First of all
an appropriate method of synthesis, that does not involve complicated purification
steps and that can be used on industrial scale, must be selected. The most important
stage of this process is represented by the establishment of experimental conditions
that can assure the obtaining of nanoparticles with proprieties specific for the
application domain.
From the iron oxides, magnetite (Fe
3
O
4
) and maghemite (
-Fe
2
O
3
) are the most
used in a variety of fields and can be considered superparamagnetic nanoparticles—
in certain synthesis conditions.
In Table
7.1
, some of the proprieties of the two oxides are presented [
10
,
12
,
13
]. Synthetic iron oxides can be obtained by a number of methods, such as
precipitation of iron salts [
14
-
22
], thermic decomposing of the organometallic
precursors [
23
-
28
], sol-gel method [
29
-
32
], microemulsion [
33
-
36
] laser pyrolysis
[
37
-
40
], combustion method [
41
-
46
], hydrothermal method [
47
-
52
],
sonochemical method [
53
-
56
], etc.; from all these methods the most common
and used is Fe
2+
and Fe
3+
salts precipitation method.
γ
7.2.2.1
Iron Salts Precipitation Method
The iron salts precipitation method is the most simple and efficient method for
obtaining magnetic particles, due to the large quantity of particles that can be
synthetized.
This method consists of mixing two salts Fe
3+
and Fe
2+
in 2:1 molar ratio, in
aqueous media, followed by precipitation of these salts using a precipitation agent
(a base) [
57
]. The chemical reaction equation for the formation of magnetite can be
described as follows:
Fe
2
þ
þ
2Fe
3
þ
þ
8OH
!
Fe
3
O
4
þ
4H
2
O
ð
7
:
1
Þ
