Regarding the synthetic methods discussed above, we have listed some advantages and disadvantages among them. Sol–gel method exhibits good properties in
terms of synthesized materials, such as low cost, high purity, good uniformity, and
easy to be doped. In this part, organic and inorganic titanium precursors can be used
to obtain photocatalysts, for example, TTIP and TiCl 4 . Hydrothermal methods can
prepare materials with high crystallinity; meanwhile, it can save time. In this method,
there are various options of titanium precursors, such as TiOSO 4 , TBOT, and TTIP.
Compared with the previous two synthesis methods, the advantage of atmospheric
liquid phase method is that it merely requires simple experimental equipment; thus it
can achieve the possibility of industrialization. Adding the template agent during the
reaction, and then stripped by heating or other methods to remove template, is a
general method for the preparation of mesoporous materials. As a result, the heat
treatment will significantly influence the products’ structures, and inorganic skeleton
is prone to collapse. Additionally, this process takes several hours, greatly extends
the reaction time, and increases energy consumption. Hence, the adverse effect of
template removal method is obvious. Moreover, the experimental conditions are not
only harsh but also cumbersome. As to the radio frequency magnetron sputtering
deposition method (RF-MS), the general way is using the TiO 2 plate, and then the
depositions are carried out in a mixture of Ar and O 2 . The thin films can be deposited
on metal substrates such as Al, Fe, Ti, Zr, Pd, and Pt. Analyzing these methods, it is
interesting to find the samples prepared by RF-MS methods have much smaller BET
areas than those samples prepared by other three methods; therefore, each kind of
catalysts has unique applications owing to their special properties.
3.2.2 Doping Modification on Mesoporous TiO 2
Since the discovery of mesoporous silica M41S, a variety of mesoporous materials
have been synthesized [2]. These mesoporous materials exhibit widely potential
applications in the industrial catalytic reactions, because they have high surface area,
large pore size, and multidimensional framework and they are easy to be recycled.
However, the widespread technological use of mesoporous TiO 2 is always to some
extent constrained by its wide bandgap (3.2 eV), which requires ultraviolet irradiation for photocatalytic activation. And TiO 2 only absorbs 5% of the spectrum of the
sunlight in the near ultraviolet region, which greatly limits its efficient application.
To achieve efficient photocatalytic activity in the visible light range, one strategy is
to reduce the bandgap of TiO 2 . Doping of metal and nonmetal elements seems to be
an effective method to enhance the photoactivity of mesoporous TiO 2 .
In 2001, the metal ion implantation of TiO 2 with metal ions (V
+
, Mn
+
, Fe
+ ) at
high energy acceleration was prepared by Yamashita et al. [25]. These catalysts
exhibited photocatalytic reactivity for degradation of 2-propanol diluted in water
under visible light irradiation (λ > 450 nm). After then, Zhang et al. [10] obtained the
large mesoporous microspheres of titania and WO 3 /TiO 2 composites by using
TiOSO 4 as an inorganic precursor and P123 as structure directing agent via
3.2 The Development of Mesoporous TiO 2 in Photocatalysis
49
terms of synthesized materials, such as low cost, high purity, good uniformity, and
easy to be doped. In this part, organic and inorganic titanium precursors can be used
to obtain photocatalysts, for example, TTIP and TiCl 4 . Hydrothermal methods can
prepare materials with high crystallinity; meanwhile, it can save time. In this method,
there are various options of titanium precursors, such as TiOSO 4 , TBOT, and TTIP.
Compared with the previous two synthesis methods, the advantage of atmospheric
liquid phase method is that it merely requires simple experimental equipment; thus it
can achieve the possibility of industrialization. Adding the template agent during the
reaction, and then stripped by heating or other methods to remove template, is a
general method for the preparation of mesoporous materials. As a result, the heat
treatment will significantly influence the products’ structures, and inorganic skeleton
is prone to collapse. Additionally, this process takes several hours, greatly extends
the reaction time, and increases energy consumption. Hence, the adverse effect of
template removal method is obvious. Moreover, the experimental conditions are not
only harsh but also cumbersome. As to the radio frequency magnetron sputtering
deposition method (RF-MS), the general way is using the TiO 2 plate, and then the
depositions are carried out in a mixture of Ar and O 2 . The thin films can be deposited
on metal substrates such as Al, Fe, Ti, Zr, Pd, and Pt. Analyzing these methods, it is
interesting to find the samples prepared by RF-MS methods have much smaller BET
areas than those samples prepared by other three methods; therefore, each kind of
catalysts has unique applications owing to their special properties.
3.2.2 Doping Modification on Mesoporous TiO 2
Since the discovery of mesoporous silica M41S, a variety of mesoporous materials
have been synthesized [2]. These mesoporous materials exhibit widely potential
applications in the industrial catalytic reactions, because they have high surface area,
large pore size, and multidimensional framework and they are easy to be recycled.
However, the widespread technological use of mesoporous TiO 2 is always to some
extent constrained by its wide bandgap (3.2 eV), which requires ultraviolet irradiation for photocatalytic activation. And TiO 2 only absorbs 5% of the spectrum of the
sunlight in the near ultraviolet region, which greatly limits its efficient application.
To achieve efficient photocatalytic activity in the visible light range, one strategy is
to reduce the bandgap of TiO 2 . Doping of metal and nonmetal elements seems to be
an effective method to enhance the photoactivity of mesoporous TiO 2 .
In 2001, the metal ion implantation of TiO 2 with metal ions (V
+
, Mn
+
, Fe
+ ) at
high energy acceleration was prepared by Yamashita et al. [25]. These catalysts
exhibited photocatalytic reactivity for degradation of 2-propanol diluted in water
under visible light irradiation (λ > 450 nm). After then, Zhang et al. [10] obtained the
large mesoporous microspheres of titania and WO 3 /TiO 2 composites by using
TiOSO 4 as an inorganic precursor and P123 as structure directing agent via
3.2 The Development of Mesoporous TiO 2 in Photocatalysis
49