work of Honda and Fujishima [54], they obtained the photo-assisted production of
H 2 and O 2 from water with a photoelectrochemical cell consisting of a Pt and TiO 2
electrodes under a small electric bias. Moreover, TiO 2 photocatalysts with incorporated Ti-oxide species anchored onto supports such as SiO 2 , glass, and zeolite
exhibited selective photoactivity. The Ti-oxide species prepared within the supports,
for example, SiO 2 , glass, and zeolite, have revealed a unique local structure as well
as high selectivity in the oxidation of organic substances with hydrogen peroxide.
Ti–Si binary oxide powders with a low TiO 2 content prepared by sol–gel methods
have been reported to include the fourfold coordinated Ti-oxide species highly
dispersed within the SiO 2 matrices, showing a unique and characteristic
photocatalytic performance for the hydrogenation of unsaturated hydrocarbons
with H 2 O; the decomposition of NO into N 2 , O 2 , and N 2 O; as well as the reduction
of CO 2 with H 2 O to produce CH 3 OH and CH 4 under UV light irradiation [74–
79]. Moreover, many reports have mentioned that the specific photocatalytic reactivity of those catalysts was much higher than that for TiO 2 powder, which may be
attributed to the tetrahedrally coordinated titanium oxide moieties. Thus, we will
discuss it comprehensively in this section.
3.5.1 The Preparation of Ti–SiO 2 Mesoporous Materials
Many reports have been published on preparation of Ti–SiO 2 mesoporous materials,
such as ionized cluster beam (ICB) method [76, 80], ion-exchange method [79, 81],
anchored on substrate [74, 78, 82, 83], CVD method [84], hydrothermal synthesis
method [85], solvent evaporation method [86], and metal ion implantation [87].
3.5.2 The Application of Ti–SiO 2 Mesoporous Materials
in Photocatalysis
3.5.2.1 CO 2 Photoreduction
In 1992, Anpo et al. [82] prepared highly dispersed titanium oxide anchored onto
Vycor glass through a facile reaction between surface OH groups of Vycor and
TiCl 4 . It was investigated that the photoreduction of CO 2 with H 2 O should be linked
to the high reactivity of the charge-transfer excited state, i.e., (Ti
3+ -O
À )
* , owing to
the presence of well-dispersed homogeneous titanium oxide species on the surface.
Ti-MCM-41 and Ti-MCM-48 mesoporous zeolite catalysts synthesized by hydrothermal method exhibited high and unique photocatalytic reactivity for the reduction
of CO 2 with H 2 O to produce CH 4 and CH 3 OH in the gas phase [74]. Keita Ikeue
et al. [86] also prepared self-standing porous silica thin films with different pore
structures by a solvent evaporation method. From 2002 to 2003, Anpo and his
coworkers reported many works about photocatalytic reduction of CO 2 on
64
3 Titanium-Based Mesoporous Materials for Photocatalysis
H 2 and O 2 from water with a photoelectrochemical cell consisting of a Pt and TiO 2
electrodes under a small electric bias. Moreover, TiO 2 photocatalysts with incorporated Ti-oxide species anchored onto supports such as SiO 2 , glass, and zeolite
exhibited selective photoactivity. The Ti-oxide species prepared within the supports,
for example, SiO 2 , glass, and zeolite, have revealed a unique local structure as well
as high selectivity in the oxidation of organic substances with hydrogen peroxide.
Ti–Si binary oxide powders with a low TiO 2 content prepared by sol–gel methods
have been reported to include the fourfold coordinated Ti-oxide species highly
dispersed within the SiO 2 matrices, showing a unique and characteristic
photocatalytic performance for the hydrogenation of unsaturated hydrocarbons
with H 2 O; the decomposition of NO into N 2 , O 2 , and N 2 O; as well as the reduction
of CO 2 with H 2 O to produce CH 3 OH and CH 4 under UV light irradiation [74–
79]. Moreover, many reports have mentioned that the specific photocatalytic reactivity of those catalysts was much higher than that for TiO 2 powder, which may be
attributed to the tetrahedrally coordinated titanium oxide moieties. Thus, we will
discuss it comprehensively in this section.
3.5.1 The Preparation of Ti–SiO 2 Mesoporous Materials
Many reports have been published on preparation of Ti–SiO 2 mesoporous materials,
such as ionized cluster beam (ICB) method [76, 80], ion-exchange method [79, 81],
anchored on substrate [74, 78, 82, 83], CVD method [84], hydrothermal synthesis
method [85], solvent evaporation method [86], and metal ion implantation [87].
3.5.2 The Application of Ti–SiO 2 Mesoporous Materials
in Photocatalysis
3.5.2.1 CO 2 Photoreduction
In 1992, Anpo et al. [82] prepared highly dispersed titanium oxide anchored onto
Vycor glass through a facile reaction between surface OH groups of Vycor and
TiCl 4 . It was investigated that the photoreduction of CO 2 with H 2 O should be linked
to the high reactivity of the charge-transfer excited state, i.e., (Ti
3+ -O
À )
* , owing to
the presence of well-dispersed homogeneous titanium oxide species on the surface.
Ti-MCM-41 and Ti-MCM-48 mesoporous zeolite catalysts synthesized by hydrothermal method exhibited high and unique photocatalytic reactivity for the reduction
of CO 2 with H 2 O to produce CH 4 and CH 3 OH in the gas phase [74]. Keita Ikeue
et al. [86] also prepared self-standing porous silica thin films with different pore
structures by a solvent evaporation method. From 2002 to 2003, Anpo and his
coworkers reported many works about photocatalytic reduction of CO 2 on
64
3 Titanium-Based Mesoporous Materials for Photocatalysis