Environmental Engineering Reference
In-Depth Information
Polyethylene glycol (PEG) is a hydrophilic polymer, water-soluble, biocompat-
ible, which can be used in synthesis of biocompatible nanoparticles with increased
resistance within blood circulation [
105
].
Another alternative for magnetite particles coating is represented by use of
co-polymers, which conduct to particles core-shell, which possible applications in
drug transport and delivery (drug vector).
Kumagai et al. [
106
] developed a simple method for nanoparticles synthesis,
followed by their treatment with copolymer block polyethylene glycole-
polyaspartic acid. The nanoparticles obtained by this method are endowed with
increased stability and solubility in aqueous solutions and biological media.
Koneracka et al. [
107
] synthesized double-layer coated magnetite nanoparticles
for further dispersion in water. Primary surfactant was sodium oleate
(C
17
H
33
COONa), while secondary surfactant was polyethylene glycol which is a
biocompatible surfactant. Magnetic nanofluid is used in generation of polymeric
nanospheres containing cytostatic drugs.
Moeser et al. [
108
] prepared magnetite nanoparticles covered with a bifunctional
polymer composed of polypropylene oxide, as primary surfactant, and polyacrylic
acid anchored with polyethylene oxide chains, as secondary surfactant.
Nanoparticles obtained by this method were used in separation of organic com-
pounds from aqueous media.
Utilization of inorganic compounds, such as gold, silver, silica gel, carbon, as
surfactants, not only that provides a good stability of the particles, but also allows
functionalization of their surface due to engraftment of certain biological ligands.
Silica gel is the most used compound for preparation of iron oxide nanoparticles
with functionalized surface, because has few advantages: excellent biocompatibil-
ity, hydrophilic ability, integration of other functional groups on its surface, stabi-
lization of iron oxide magnetic nanoparticles in solutions, prevents interactions
between particles and their agglomeration, thus providing a better encapsulation
[
109
,
110
].
The most common method for synthesis in obtaining magnetic nanoparticles
covered with silica is St¨ber method [
111
].
Generally, silica layer increases particle size, so that magnetic properties will be
changed. However, the thickness of silica layer can be adjusted by changing TEOS:
water ratio, ammonium concentration, hydrolysis time [
111
].
Many studies described the role of functional groups, which control reactivity
and colloidal properties of magnetic suspension, as well as the influence of alkaline
reagents, concentration of coated nanoparticles, water/alcohol ratio, or concentra-
tion of TEOS on final morphological aspect of these nanostructures [
92
,
93
,
112
,
113
].
Magnetic nanoparticles using gold as surfactant seem to be ideal, due to its
decreased reactivity; however, direct coating of magnetic nanoparticles with gold is
very difficult, due to different characteristics of the two surfaces [
114
-
116
].
Good coating with carbon layers provides an effective barrier against oxidation
and acid erosion of magnetic nanoparticles. So that, it is possible to synthesize
magnetic nanoparticles covered with carbon, which are stable from the thermal and
