Geoscience Reference
In-Depth Information
Figure 10.29 Electron microscopy images of selectively doped TiO
2
and ZnO
nanomaterials: (a) manganese doped TiO
2
with caprylic acid as surfactant; (b) neodymium-
doped TiO
2
with n-butylamine as surfactant; (c) tungsten-doped TiO
2
with caprylic acid as
surfactant; (d) ZnO with caprylic acid as surfactant; (e) indium-doped ZnO without
surfactant; and (f) indium-doped ZnO with n-butylamine as surfactant.
Source: From the works of K. Byrappa.
properties insist on a precise control of properties such as particle size, shape, and
variables that affect these properties are the focus of attention among researchers.
It is also very important that the particles be superparamagnetic for DDS. In tar-
geted drug delivery, a drug is bound to the surface of a coated nanoparticle and an
external magnetic field is applied to attract the particle to a specific site in the
body. At the site, the chemical unbinds from the nanoparticle due to specific chem-
ical interactions. The external magnetic field is then turned off and the nanoparticle
freely circulates throughout the body until it is naturally eliminated. Therefore, it is
important to know the biocompatibility of the particles and possible coating materi-
als
[129,130]
. Currently, paramagnetic metal ion complexes, such as Gd-EDTA,
are used as contrast agents. However, the superparamagnetic nanoparticles offer
higher molar relaxivities, which would enhance image contrast
[131]
. Magnetic
nanoparticles in hyperthermia involve heating certain tissues or organs to between
41
C and 46
C for cancer therapy
[132]
. Hence, the synthesis of magnetic nanopar-
ticles is an important subject of study in nanomaterials science and technology.
Several magnetic nanoparticles based on ferrites and perovskites (such as manga-
nates) are in use for such applications, among them iron oxide (
α
γ
-Fe
2
O
3
),
cobalt oxide and cobalt iron oxide are the most important ones. The present authors
discuss these materials in more detail in this review.
Amyn Teja and coworkers have done an extensive work on the synthesis of a
variety of magnetic nanoparticles using continuous hydrothermal
-Fe
2
O
3
,
system
