Environmental Engineering Reference
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Fig. 3 a Schematics of the sol-gel fabrication procedure of a TiO
2
inverse opal via a template-
assisted method. SEM images of SU8 templates (b) and TiO
2
inverse opal (c). (Reprinted with
permission from Ref. a [
92
], b, c [
72
]. Copyright Wiley-VCH and American Chemical
Society)
In the past decade, mesoporous TiO
2
materials have attracted considerable
interest for many applications due to their continuous particle framework, which
contain nanoparticles distributed throughout structures of adjustable pore size and
high specific surface area. Mesoporous TiO
2
materials with tailored pore size, high
specific surface area, and well-defined crystalline structure in particular have
potential applications in solar cells, photocatalysis, and water splitting [
75
,
76
]. In
photocatalytic applications, a tunable pore size can facilitate the diffusion rate of
reactants toward adsorption sites, while a high surface area can maximize the
interface between the reactant and the catalyst surfaces [
77
]. For DSSCs, meso-
porous TiO
2
can enhance light harvesting within the electrodes without sacrificing
the accessible surface for dye loading [
78
].
Generally, the sol-gel process using organic surfactants as assisting templates
represents the most widely used route for the synthesis of mesoporous TiO
2
and
involves a complicated mechanism called evaporation-induced self-assembly
(EISA) [
79
]. The EISA process produces an ideal grid-like morphology consisting
of a continuous, ordered network of anatase TiO
2
with a high surface area by
condensation of a titanium precursor around self-organized organic templates in a
gel phase, followed by removal of the templates via heat treatment. This simple
process uses a wide range of surfactants as structure directing agents to prepare
ordered mesoporous TiO
2
. The structure directing agent in this method is an
amphiphilic macromolecule (block copolymer) which microphase-separates into
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