method proposed by Zhang et al. [31]. It was found that the 15% SiO 2 -dopped
mesoporous TiO 2 exhibited much higher photoactivity than P25, attributing to the
high anatase crystallinity, large specific surface area, abundant preserved surface
hydroxyl groups, and mesoporous channels. In 2010, N and F co-doped TiO 2
microspheres were prepared by ethanol solvothermal method, using tetrabutyl titanate as precursor, urea as a nitrogen source, and ammonium fluoride as a fluorine
source [32]. Then Zhang and his group reported that the synergetic effect of nitrogen
and fluorine doping is responsible for the enhancement of photodegradation activity
of AO7 under the irradiation of visible light. Later, Zhang et al. [33] synthesized N,
B, Si-tridoped mesoporous TiO 2 photocatalyst through a modified sol–gel method.
In this process, dodecylamine not only acted as a pore template but also as a nitrogen
dopant, and H 3 BO 3 acted as a boron dopant. Moreover, it showed a strong absorption in the visible light region because the doping of N and B narrowed the bandgap.
Besides doping of either metal or nonmental elements, the co-doping of metal and
nonmetal element is another effective way of modification. For instance, Zhang et al.
[34] obtained the iron (III) and nitrogen co-doped mesoporous TiO2 for the first time
by the modified sol–gel method. Ma et al. [35] synthesized well-ordered mesoporous
TiO 2 co-doped with nitrogen and ytterbium by an evaporation-induced self-assembly process.
The merits of mesoporous TiO 2 have been listed aforementioned. And we have
summarized various preparation methods reported in existing literature as well. By
doping modification of TiO 2 , the photoactivity of corresponding catalysts can be
enhanced to some extent; however, the fast recombination of electron–hole pairs and
scarce adsorptive sites undermined the further research. According to some reported
literatures, the composition of Si or porous MOFs with the TiO 2 may be a feasible
way in enhancing the separation of electrons and holes.
3.2.3 Mesoporous TiO 2 –Graphene Materials
Graphene (GR) possesses large specific surface area, excellent conductive, mechanical, and hydrophobic properties, which allow it to be multifunctional materials with
excellent capacity for carrying and conducting electrons and holes. Especially, threedimensional (3D) graphene aerogels (GAs) compounded with mesoporous TiO 2
composites are ultralight massive catalysts, which display hydrophobic properties
and facilitate photocatalytic recyclings. In 2014, Qiu et al. [36] studied TiO 2 –
graphene composites as solar light photocatalysts and electrode materials for
lithium–ion batteries (LIBs). They used a one-step hydrothermal method to prepare
3D-structured TiO 2 /GA composites. In this process, Ti(SO 4 ) 2 was firstly dissolved
in aqueous solution to form crystal seeds before a known amount of glucose was
adsorbed on the seeds, followed by fixation of the seeds on the surface of graphene
oxides. The presence of glucose results in the exposure of (001) facets in the
nanocrystals up to 50% (inset of Fig. 3.3b), achieving the sizes ranging from 15 to
20 nm and realizing mesoporous interface between TiO 2 and the GR (in Fig. 3.3c).
3.2 The Development of Mesoporous TiO 2 in Photocatalysis
51
mesoporous TiO 2 exhibited much higher photoactivity than P25, attributing to the
high anatase crystallinity, large specific surface area, abundant preserved surface
hydroxyl groups, and mesoporous channels. In 2010, N and F co-doped TiO 2
microspheres were prepared by ethanol solvothermal method, using tetrabutyl titanate as precursor, urea as a nitrogen source, and ammonium fluoride as a fluorine
source [32]. Then Zhang and his group reported that the synergetic effect of nitrogen
and fluorine doping is responsible for the enhancement of photodegradation activity
of AO7 under the irradiation of visible light. Later, Zhang et al. [33] synthesized N,
B, Si-tridoped mesoporous TiO 2 photocatalyst through a modified sol–gel method.
In this process, dodecylamine not only acted as a pore template but also as a nitrogen
dopant, and H 3 BO 3 acted as a boron dopant. Moreover, it showed a strong absorption in the visible light region because the doping of N and B narrowed the bandgap.
Besides doping of either metal or nonmental elements, the co-doping of metal and
nonmetal element is another effective way of modification. For instance, Zhang et al.
[34] obtained the iron (III) and nitrogen co-doped mesoporous TiO2 for the first time
by the modified sol–gel method. Ma et al. [35] synthesized well-ordered mesoporous
TiO 2 co-doped with nitrogen and ytterbium by an evaporation-induced self-assembly process.
The merits of mesoporous TiO 2 have been listed aforementioned. And we have
summarized various preparation methods reported in existing literature as well. By
doping modification of TiO 2 , the photoactivity of corresponding catalysts can be
enhanced to some extent; however, the fast recombination of electron–hole pairs and
scarce adsorptive sites undermined the further research. According to some reported
literatures, the composition of Si or porous MOFs with the TiO 2 may be a feasible
way in enhancing the separation of electrons and holes.
3.2.3 Mesoporous TiO 2 –Graphene Materials
Graphene (GR) possesses large specific surface area, excellent conductive, mechanical, and hydrophobic properties, which allow it to be multifunctional materials with
excellent capacity for carrying and conducting electrons and holes. Especially, threedimensional (3D) graphene aerogels (GAs) compounded with mesoporous TiO 2
composites are ultralight massive catalysts, which display hydrophobic properties
and facilitate photocatalytic recyclings. In 2014, Qiu et al. [36] studied TiO 2 –
graphene composites as solar light photocatalysts and electrode materials for
lithium–ion batteries (LIBs). They used a one-step hydrothermal method to prepare
3D-structured TiO 2 /GA composites. In this process, Ti(SO 4 ) 2 was firstly dissolved
in aqueous solution to form crystal seeds before a known amount of glucose was
adsorbed on the seeds, followed by fixation of the seeds on the surface of graphene
oxides. The presence of glucose results in the exposure of (001) facets in the
nanocrystals up to 50% (inset of Fig. 3.3b), achieving the sizes ranging from 15 to
20 nm and realizing mesoporous interface between TiO 2 and the GR (in Fig. 3.3c).
3.2 The Development of Mesoporous TiO 2 in Photocatalysis
51