inorganic precursor or hydrolysis controlling agents, such as acetylacetone or hydrogen peroxide (Tian et al. 2002; Tian et al. 2003; Li et al. 2008). For example, in 1995
Antonelli and Ying have reported the first example of mesoporous titania by using
tetradecyl phosphate as surfactant and titanium acetylacetonate trisisopropoxide as
Ti source. Acetylacetone acts as a hydrolysis controlling agent of the titanium
precursor (Antonelli and Ying 1995). The obtained material adopts a hexagonal
pore ordering, but the structure partially collapses after the pores are freed from the
surfactant by calcination at 350
C. More recently, we have developed a synthesis
procedure of ordered mesoporous materials, having semicrystalline framework and
with high specific surface area (>250 m
2 /g). Our strategy is based on the
evaporation-induced self-assembly method, usually used for the preparation of the
mesoporous films and on the liquid crystal templating mechanism (Zimny et al.
2010). The obtained mesostructured TiO 2 materials with semicrystalline framework
are effective photocatalyst for dyes degradation such as methyl orange (Zimny et al.
2012; Assaker et al. 2015). The efficiency of the process depends on the working
conditions, and the optimal conditions are 1 hour of dark adsorption, a TiO 2
concentration of 0.5 g/L, and a methyl orange concentration of 15 mg/L at acidic
pH (pH ¼ 4) with an incident light intensity of 10
–5 Einstein L
À1 s
À1 . The rates of
methyl orange decomposition follow Langmuir-Hinshelwood kinetics. The dependence of the reaction rate on the incident light intensity is first order. No change in
the activity of the catalyst is observed at the first four cycles, which indicates that the
TiO 2 is able to use repeatedly (Blin et al. 2012). We have also succeeded in
introducing a second level of porosity, and we have shown that thanks to the
synergic effect of the presence of the two mesopore networks, the dual mesoporous
titania are more efficient for the photodegradation of methyl orange, used as model
dye, than the mono-modal ones (Naboulsi et al. 2017). However, one main drawback
still persists: it concerns the limitation of the crystallization temperature around
400
C, which is far under the required temperature (550
C) to completely transform amorphous TiO 2 into anatase.
Another dual-templating approach has been reported to produce hierarchical
macro-/mesoporous TiO 2 by a bi-template interface-directed deposition mechanism
based on a combination of soft-templating with P123 surfactant for mesoporous
network and hard-templating with macroporous carbon gabarit (Zhao et al. 2016).
Macroporous carbon gabarit was first synthesized and immersed in the precursor
solution of the mesoporous TiO 2 network. The resulting hierarchical macro-/
mesoporous TiO 2 material presents a regular array of macropores surrounded by
ordered mesoporous titania walls composed of well-crystallized anatase
nanocrystals. Due to its high specific surface area, high porosity, well-connected
channels, and abundant hydroxyl groups, a high capacity of adsorption toward
rhodamine B dye was observed. Under stimulated sunlight the rhodamine B was
fully decomposed in the presence of this hierarchical macro-/mesoporous TiO 2 in
8 min. The photodecomposition of rhodamine B was slower with two reference
catalysts: TiO 2 hollow microsphere arrays and commercial Degussa P25 TiO 2 .
Macroporosity was also generated by an interesting approach derived from
particle-stabilized emulsions to produce macrostructure-controlled titania ceramics
2 Dyes Depollution of Water Using Porous TiO 2 -Based Photocatalysts
53
Antonelli and Ying have reported the first example of mesoporous titania by using
tetradecyl phosphate as surfactant and titanium acetylacetonate trisisopropoxide as
Ti source. Acetylacetone acts as a hydrolysis controlling agent of the titanium
precursor (Antonelli and Ying 1995). The obtained material adopts a hexagonal
pore ordering, but the structure partially collapses after the pores are freed from the
surfactant by calcination at 350
C. More recently, we have developed a synthesis
procedure of ordered mesoporous materials, having semicrystalline framework and
with high specific surface area (>250 m
2 /g). Our strategy is based on the
evaporation-induced self-assembly method, usually used for the preparation of the
mesoporous films and on the liquid crystal templating mechanism (Zimny et al.
2010). The obtained mesostructured TiO 2 materials with semicrystalline framework
are effective photocatalyst for dyes degradation such as methyl orange (Zimny et al.
2012; Assaker et al. 2015). The efficiency of the process depends on the working
conditions, and the optimal conditions are 1 hour of dark adsorption, a TiO 2
concentration of 0.5 g/L, and a methyl orange concentration of 15 mg/L at acidic
pH (pH ¼ 4) with an incident light intensity of 10
–5 Einstein L
À1 s
À1 . The rates of
methyl orange decomposition follow Langmuir-Hinshelwood kinetics. The dependence of the reaction rate on the incident light intensity is first order. No change in
the activity of the catalyst is observed at the first four cycles, which indicates that the
TiO 2 is able to use repeatedly (Blin et al. 2012). We have also succeeded in
introducing a second level of porosity, and we have shown that thanks to the
synergic effect of the presence of the two mesopore networks, the dual mesoporous
titania are more efficient for the photodegradation of methyl orange, used as model
dye, than the mono-modal ones (Naboulsi et al. 2017). However, one main drawback
still persists: it concerns the limitation of the crystallization temperature around
400
C, which is far under the required temperature (550
C) to completely transform amorphous TiO 2 into anatase.
Another dual-templating approach has been reported to produce hierarchical
macro-/mesoporous TiO 2 by a bi-template interface-directed deposition mechanism
based on a combination of soft-templating with P123 surfactant for mesoporous
network and hard-templating with macroporous carbon gabarit (Zhao et al. 2016).
Macroporous carbon gabarit was first synthesized and immersed in the precursor
solution of the mesoporous TiO 2 network. The resulting hierarchical macro-/
mesoporous TiO 2 material presents a regular array of macropores surrounded by
ordered mesoporous titania walls composed of well-crystallized anatase
nanocrystals. Due to its high specific surface area, high porosity, well-connected
channels, and abundant hydroxyl groups, a high capacity of adsorption toward
rhodamine B dye was observed. Under stimulated sunlight the rhodamine B was
fully decomposed in the presence of this hierarchical macro-/mesoporous TiO 2 in
8 min. The photodecomposition of rhodamine B was slower with two reference
catalysts: TiO 2 hollow microsphere arrays and commercial Degussa P25 TiO 2 .
Macroporosity was also generated by an interesting approach derived from
particle-stabilized emulsions to produce macrostructure-controlled titania ceramics
2 Dyes Depollution of Water Using Porous TiO 2 -Based Photocatalysts
53