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anticipated that incorporating mesoporous coatings on a magnetic core could
increase the specific surface area of the resultant magnetic particles drastically
without sacrificing magnetization characteristics. Mesoporous magnetic nano-
composite particles of sufficiently high specific surface area formed in this way
could be easily separated from a multiphase complex system by magnetic
separation and effectively recycled or reused.
6.4.4.1 The Synthesis Process of Mesoporous Silica-Coated Magnetic Particles
The concept of template-based synthesis of mesoporous magnetic nanocompo-
site particles is illustrated in Fig. 6.7. In this synthesis, a thin silica layer is
deposited on the surface of magnetite particles of desired sized (I). The purpose
of silica layer is to protect the magnetic core from being leached into the mother
system under severe industrial conditions. The resultant silica surface also
facilitates the assembly of structured surfactant templates. With a negatively
charged silica surface, cationic surfactant micelles self-assemble on the nega-
tively charged silica layer (II), forming the desired structure. This step is highly
dependent on micelle solution concentration and solvent quality [109]. The
mesoporous silica network on the magnetic core (III) is formed by filling the
spaces among the assembled micelle templates using the conventional sol-gel
process [90, 110]. During sol-gel reaction, the positive nature of molecular
templates promotes the formation of silica precipitates within the voids
among the templates, resulting in a three-dimensional continuous silica net-
work. After calcinations at desired temperatures to remove the surfactant
templates from the formed silica network, pores are left on the surface (IV).
The silica surface of the so-formed mesoporous magnetic nanocomposite par-
ticles allows a variety of surface functionalities to be obtained by versatile
silanation chemistry (V), which enables ''molecular recognition'' in numerous
applications [6, 111, 112].
The prepared mesoporous magnetic nanocomposite particles have the fol-
lowing important attributes: strong magnetization for efficient magnetic
separation; large specific surface area for high loading capacity; well-sealed
silica coatings to prevent the substrate materials from leaching into the mother
Fig. 6.7 Illustration of the proposed synthesis process for the preparation of mesoporous
magnetic nanocomposite particles: dense-liquid-silica coating (I), molecular templating (II),
sol-gel process (III), calcination (IV), and functionalization (V). [122]
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