Chemistry Reference
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Fig. 3.7
Schematic illustration of
a
hard- and
b
soft-templating methods to synthesized
mesoporous materials
has received increasing attention in the last few decades, due to the periodically
aligned pore systems, uniform pore size in the mesoscale range, high surface area,
controllable mesophase, and abundant framework compositions, and has found
diverse applications in the fields of adsorption, separation, catalysis, biosensing,
and energy storage and conversion [
34
,
35
]. The surfactant-induced route for the
formation of mesopores can be classified into two types (Fig.
3.7
). The first ones
are termed as hard templates or nanocasting, which are the prepared mesoporous
materials with solid frameworks, including carbons, polymer beads, and silicas.
However, the prepared materials often have a wider pore size distribution than
that of the pristine replicas, and multiple preparation procedures with costly hard
templates make it expensive, complicated, and consequently unsuitable for large-
scale production and industrial applications. Meanwhile, the template removal
always involves the use of strong acids, bases, and high-temperature calcination,
which cause it to be favorable for the synthesis of special mesoporous materi-
als, for instance, metal sulfides and oxides [
36
,
37
], carbons [
38
,
39
], and silicon
carbides [
40
], while not suitable for the cases of hybrid materials. The soft-tem-
plating methodology, which is usually referred to as “soft” molecules including
cationic surfactants C
n
H
2
n
+
1
N(CH
3
)
3
Br (
n
=
8-22) and nonionic surfactants
of amphiphilic poly(alkylene oxide) triblock copolymers [e.g., PEO-PPO-PEO
(PEO
=
poly(ethylene oxide), PPO
=
poly(propylene oxide))] and oligomeric
alkylethylene oxides, has received much attention. In comparison with the nano-
casting method, the entire procedure of soft-templating is low costing, facile, con-
venient, effective, and promising for large-scale production. More importantly, the
mesophase formation depends on the temperature, type of solvent, ionic strength
and pH, and the nature of the template molecules (hydrophobic/hydrophilic vol-
ume ratio, hydrophobic length, etc.), which make the pore structure and surface
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