and synthesis conditions. Those novel TiO 2 –SiO 2 materials not only take advantages
of both TiO 2 (an n-type semiconductor and an active catalytic support) and SiO 2
(high thermal stability and excellent mechanical strength) but also extend their
applications through the generation of new catalytic active sites based on the
interactions between TiO 2 and SiO 2 [39]. Hence, it is indeed a promising and new
catalytic material in many research areas.
3.3.1 The Preparation of TiO 2 –SiO 2 Mesoporous Materials
There are various methods of preparing TiO 2 –SiO 2 mesoporous materials, such as
sol–gel method [38, 40–42], hydrothermal method [43, 44], chemical vapor deposition [45], precipitation method [46], liquid phase deposition [47], microwave
irradiation method [48], impregnation method [49, 50], and evaporation-induced
self-assembly (EISA) method [51].
For instance, TiO 2 –SiO 2 nanocomposite can be prepared by sol–gel method.
Commonly, the first step is to formulate sol with all kinds of ingredients, and then
the gelation process, and at last removal of the surfactant to obtain mesoporous
materials. In 2003, titania–silica mixed oxides were prepared by the sol–gel method
from tetraethylorthosilicate (TEOS) and titanium (IV) isopropoxide (TTIP) as precursors by Elizabeth et al. [42]. Li et al. [43] also obtained silica-modified titanium
dioxides by a hydrothermal method. There was strong interaction between SiO 2 and
TiO 2 , and Ti–O–Si bonds formed during the hydrothermal process. In addition, He
et al. [51] synthesized highly ordered bicontinuous cubic mesoporous titania–silica
binary oxides via an evaporation-induced self-assembly (EISA) method. As illustrated in Scheme 3.1, TTIP and TEOS hydrolyzed simultaneously with the existence
of HCl, then the condensation and polymerization of TTIP were slowed down, and
later the hydrolysis of TEOS was accelerated owing to the large amount of HCl. In
the aging section, titanium species and silica species co-assembly with F127, and
ordered mesostructures were formed. In the calcination process, titanate oligomers
and silicate oligomers can be cross-linked with each other through the Ti–O–Si
bonds. Under this circumstance, silica acts as glue between TiO 2 nanocrystals; thus,
the thermal stability of the mesostructures can be improved. Moreover, Li et al. [49]
successfully introduced benzopyrylium salt S-2(2,4-diphenyl-5,6,7,8-tetrahedro-1benzopyrylium perchlorate) into the channels of mesoporous molecular sieves
Ti-HMS with different Ti content by impregnation method.
3.3 The Development of TiO 2 –SiO 2 Mesoporous Materials
53
of both TiO 2 (an n-type semiconductor and an active catalytic support) and SiO 2
(high thermal stability and excellent mechanical strength) but also extend their
applications through the generation of new catalytic active sites based on the
interactions between TiO 2 and SiO 2 [39]. Hence, it is indeed a promising and new
catalytic material in many research areas.
3.3.1 The Preparation of TiO 2 –SiO 2 Mesoporous Materials
There are various methods of preparing TiO 2 –SiO 2 mesoporous materials, such as
sol–gel method [38, 40–42], hydrothermal method [43, 44], chemical vapor deposition [45], precipitation method [46], liquid phase deposition [47], microwave
irradiation method [48], impregnation method [49, 50], and evaporation-induced
self-assembly (EISA) method [51].
For instance, TiO 2 –SiO 2 nanocomposite can be prepared by sol–gel method.
Commonly, the first step is to formulate sol with all kinds of ingredients, and then
the gelation process, and at last removal of the surfactant to obtain mesoporous
materials. In 2003, titania–silica mixed oxides were prepared by the sol–gel method
from tetraethylorthosilicate (TEOS) and titanium (IV) isopropoxide (TTIP) as precursors by Elizabeth et al. [42]. Li et al. [43] also obtained silica-modified titanium
dioxides by a hydrothermal method. There was strong interaction between SiO 2 and
TiO 2 , and Ti–O–Si bonds formed during the hydrothermal process. In addition, He
et al. [51] synthesized highly ordered bicontinuous cubic mesoporous titania–silica
binary oxides via an evaporation-induced self-assembly (EISA) method. As illustrated in Scheme 3.1, TTIP and TEOS hydrolyzed simultaneously with the existence
of HCl, then the condensation and polymerization of TTIP were slowed down, and
later the hydrolysis of TEOS was accelerated owing to the large amount of HCl. In
the aging section, titanium species and silica species co-assembly with F127, and
ordered mesostructures were formed. In the calcination process, titanate oligomers
and silicate oligomers can be cross-linked with each other through the Ti–O–Si
bonds. Under this circumstance, silica acts as glue between TiO 2 nanocrystals; thus,
the thermal stability of the mesostructures can be improved. Moreover, Li et al. [49]
successfully introduced benzopyrylium salt S-2(2,4-diphenyl-5,6,7,8-tetrahedro-1benzopyrylium perchlorate) into the channels of mesoporous molecular sieves
Ti-HMS with different Ti content by impregnation method.
3.3 The Development of TiO 2 –SiO 2 Mesoporous Materials
53