Environmental Engineering Reference
In-Depth Information
The methods used to prepare the magnetic particles can be divided into two
general types [30]. The first method involves the coating of an existing magnetic
material. Representative examples of this type are adsorption of proteins onto
nickel microspheres [31], coupling of functionalized polymeric silane on mag-
netite [32, 33], adsorption of serum albumin onto aggregates of magnetite or
other magnetic metal oxides during or immediately after ultrasonic disruption
of the aggregates [34, 35], polymerization of monomers in the presence of
magnetite [36, 37], encapsulation of iron oxide by emulsion polymerization
[38, 39], and adsorption of Protein A to magnetite [40]. The second method
involves the generation of the magnetic material in the presence of the coating
material. Representative examples are precipitation of magnetite in the pre-
sence of dextran [41], serum albumin [42], and arabinogalactan [43]. A related
method is the precipitation of magnetite in the pores or on the surface of an
existing particle as magnetic tags [44].
In magnetic composite synthesis, magnetite is the most commonly used mag-
netic material since particles prepared from freshly precipitated magnetite are
claimed to be superparamagnetic [45], a property which facilitates re-suspension
of the particles after magnetic separation. Other magnetic materials, such as
g-Fe
2
O
3
, metallic iron, cobalt, and nickel, are also used. In a recent review [46],
Li et al. elaborated the synthesis, properties, and environmental applications
of nanoscale iron-based materials. Different physical and chemical methods
used for synthesizing nanoiron-based particles with desired size, structure, and
surface properties were reported. The applications of this kind of particles include
degradation of chlorinated organic compounds (such as trichloroethane (TCA),
trichloroethene (TCE), tetrachloroethene, or carbon tetrachloride), removal of
metallic ions (such as arsenic (As), lead (Pb), mercury (Hg), and chromium (Cr))
and inorganic contaminants (such as selenium (Se), denitrification and reduction
of carbon monoxide (CO)). A key mechanism of these applications is oxidative
nature of iron.
Lu et al. [47], on the other hand, provided a detailed report on the special
features, synthesis, protection/stabilization, functionalization, and application
of magnetic nanoparticles. Substantial progress in the size and shape control
of magnetic nanoparticles has been made by developing methods such as
co-precipitation, thermal decomposition and/or reduction, and molecular
template or hydrothermal synthesis. Protection of magnetic particles against
corrosion remains a major challenge. Therefore suitable protection strategies,
for example, surfactant/polymer coating, silica coating, and carbon coating of
magnetic nanoparticles or embedment of nano magnetic particles in a matrix/
support have been emphasized. Properly protected magnetic nanoparticles can
be used as building blocks for the fabrication of various functional systems and
applied to catalysis and biotechnology.
It is evident that the application of magnetic nanocomposite particles to
separation science and technology offers great flexibility. A key-and-lock rela-
tionship shown in Fig. 6.2 [48] can be developed to describe various applications
of magnetic nanocomposites. The lock varies from metals or toxic species as in
