Environmental Engineering Reference
In-Depth Information
applications. The superparamagnetic domains present in the akaganeite
nanoparticles make them important for pharmaceutical and biomedical applications
like targeted drug delivery.
12.4.2 Nanomaterials Based on ZnO
Nanomaterials based on ZnO have attracted significant attention due to their
possible applications in electro-optical devices, transparent ultraviolet protection
films, and spintronic devices [
15
,
16
]. Zinc oxide exhibits ferromagnetism when
doped with most of the transition metals [
17
]. Misra et al. [
18
] have investigated the
mechanism of ferromagnetism in the Zn
1-x
Fe
x
O system. As the nanosamples
possess different surface structure/groups depending on the solvent used for syn-
thesis, authors prepared two sets of iron-doped zinc oxide nanosamples using
similar chemical hydrolysis methods, one in diethylene glycol, and another in
denatured ethanol solutions and EMR spectra were recorded at X and Q-band.
Authors have reported coexistence of ferromagnetic and paramagnetic states in
diethylene glycol prepared samples. They could further discuss that ferromagne-
tism occurs in the regions, which are rich in oxygen vacancies whereas in some
regions Fe ions are not bound together through exchange interactions due to lack of
oxygen vacancies and such localized Fe ions are responsible for paramagnetic
signal.
Sibera et al. [
19
] have performed EMR studies of the iron doped zinc oxide for
different concentration of the dopant. Very intense and broad EMR line centered at
effective g value near 2 is reported (Fig.
12.1
). Resonance field and line width were
not found to depend significantly on the concentration of Fe
2
O
3
, while the intensity
strongly increases with increasing concentrations of Fe
2
O
3
. They could conclude
that dipole-dipole interaction depends essentially on concentration of magnetic
nanoparticles.
Antibacterial and anticancerous activities of ZnO nanoparticles have also been
reported in literature. Lipovsky et al. [
20
] have performed EMR coupled with the
spin-trapping technique to demonstrate the formation of hydroxyl radicals and
singlet oxygen in a water suspension of ZnO nanoparticles. Authors reported that
level of oxy radicals increased considerably when the suspension was irradiated
with visible light (Fig.
12.2
). They have suggested that the production of OH and
singlet oxygen radicals by ZnO is responsible for the cellular damage leading to its
bactericidal activity.
12.4.3 TiO
2
Nanoparticles
Titanium dioxide is a very important material, intensely investigated due to its
various technological applications, especially in the nanoparticles form [
21
-
