to a higher dye adsorption capacity due to the enhanced specific surface area when
some Si species are substituted by Al species. TiO 2 -supported photocatalyst have
been also obtained by using microporous supports such as zeolites. Mesoporous
TiO 2 -supported ZSM-5 zeolite with large specific surface area have been prepared
by a direct templating method with P123 as surfactant, 1,3,5-triisopropylbenzene
(TIPB) as swelling micelle agent (Znad et al. 2018). The inorganic component is
commercially and hydrothermally treated with P123/TIPB aqueous solution to form
a multilamellar mesoporous TiO 2 /ZSM-5 that is photocatalytically active for the
total and fast degradation of methyl orange dye under solar light irradiation in
aqueous media. Moreover, the regeneration and the reuse of the photocatalyst
were demonstrated. The high photocatalytic efficiency seems to be due in large
part to the high specific surface area; however, in this paper the structural and
textural characteristics are not clearly exploited and discussed.
Porous titania-supported composites have been also synthesized with the highly
stable metal-organic framework (MOF) UiO-66 that has a high specific surface area
(Wang et al. 2017). Different amounts of commercial TiO 2 P25 were directly
introduced in the precursor solution of the UiO-66. The presence of UiO-66 allowed
greatly increasing the methyl orange and rhodamine B dye adsorption in aqueous
solutions, and the photocatalytic decomposition under visible light was faster with
increasing amount of TiO 2 . An optimal molar ratio TiO 2 /Zr (from UiO-66) of 49 was
found for the most efficient photocatalyst, which correspond to the nanocomposite
with the most reduced band gap and recombination of electron-hole pairs. Moreover,
the reusability of these TiO 2 /MOF photocatalyst has been demonstrated.
Other problems that meet TiO 2 nanoparticles are related to their small size and
very active surface that make them prone to deformation and agglomeration during
reactions, leading to the loss of their catalytic activity. Besides dispersing TiO 2
nanoparticles on the surface of a solid matrix, another approach consisting in coating
them of a mesoporous SiO 2 (mSiO 2 ) layer. A 3D network of core shell P25@mSiO 2
has been prepared by a simple surfactant-assisted sol-gel method (Gong et al. 2017).
The resulting nanocomposite has shown improved photocatalytic activity for the
degradation of methyl orange due to the presence of the mSiO 2 coating that stabilizes
the nanosized photocatalysts, increases dye adsorption capacity, and binds TiO 2
particles, providing mechanical reinforcement of the nanocomposite. Moreover, it
was suggested that hydroxyl radicals (ÁOH) play a major role in enhancing the
performance of P25@mSiO 2 . A mechanism for the ÁOH radical generation and
transport in these nanocomposites has been proposed.
Interestingly, since powder materials are difficult to manipulate and to recover
from liquid suspension, the introduction of iron oxide phase was realized in TiO 2 /
SiO 2 composites to allow easy magnetic removal of the catalyst from water after
reaction (Fisli et al. 2017). Fe 3 O 4 /SiO 2 /TiO 2 composite has been prepared by the
heteroagglomeration method. Fe 3 O 4 magnetite nanoparticles were coprecipitated
with SiO 2 that forms an amorphous coating. A suspension of commercial TiO 2
nanoparticles dispersed in ammonium sulfate aqueous solution was added to the
obtained Fe 3 O 4 /SiO 2 suspension. TiO 2 nanoparticles are a mixture of anatase and
rutile phase. The photocatalytic activity of the Fe 3 O 4 /SiO 2 /TiO 2 composite was
2 Dyes Depollution of Water Using Porous TiO 2 -Based Photocatalysts
59
some Si species are substituted by Al species. TiO 2 -supported photocatalyst have
been also obtained by using microporous supports such as zeolites. Mesoporous
TiO 2 -supported ZSM-5 zeolite with large specific surface area have been prepared
by a direct templating method with P123 as surfactant, 1,3,5-triisopropylbenzene
(TIPB) as swelling micelle agent (Znad et al. 2018). The inorganic component is
commercially and hydrothermally treated with P123/TIPB aqueous solution to form
a multilamellar mesoporous TiO 2 /ZSM-5 that is photocatalytically active for the
total and fast degradation of methyl orange dye under solar light irradiation in
aqueous media. Moreover, the regeneration and the reuse of the photocatalyst
were demonstrated. The high photocatalytic efficiency seems to be due in large
part to the high specific surface area; however, in this paper the structural and
textural characteristics are not clearly exploited and discussed.
Porous titania-supported composites have been also synthesized with the highly
stable metal-organic framework (MOF) UiO-66 that has a high specific surface area
(Wang et al. 2017). Different amounts of commercial TiO 2 P25 were directly
introduced in the precursor solution of the UiO-66. The presence of UiO-66 allowed
greatly increasing the methyl orange and rhodamine B dye adsorption in aqueous
solutions, and the photocatalytic decomposition under visible light was faster with
increasing amount of TiO 2 . An optimal molar ratio TiO 2 /Zr (from UiO-66) of 49 was
found for the most efficient photocatalyst, which correspond to the nanocomposite
with the most reduced band gap and recombination of electron-hole pairs. Moreover,
the reusability of these TiO 2 /MOF photocatalyst has been demonstrated.
Other problems that meet TiO 2 nanoparticles are related to their small size and
very active surface that make them prone to deformation and agglomeration during
reactions, leading to the loss of their catalytic activity. Besides dispersing TiO 2
nanoparticles on the surface of a solid matrix, another approach consisting in coating
them of a mesoporous SiO 2 (mSiO 2 ) layer. A 3D network of core shell P25@mSiO 2
has been prepared by a simple surfactant-assisted sol-gel method (Gong et al. 2017).
The resulting nanocomposite has shown improved photocatalytic activity for the
degradation of methyl orange due to the presence of the mSiO 2 coating that stabilizes
the nanosized photocatalysts, increases dye adsorption capacity, and binds TiO 2
particles, providing mechanical reinforcement of the nanocomposite. Moreover, it
was suggested that hydroxyl radicals (ÁOH) play a major role in enhancing the
performance of P25@mSiO 2 . A mechanism for the ÁOH radical generation and
transport in these nanocomposites has been proposed.
Interestingly, since powder materials are difficult to manipulate and to recover
from liquid suspension, the introduction of iron oxide phase was realized in TiO 2 /
SiO 2 composites to allow easy magnetic removal of the catalyst from water after
reaction (Fisli et al. 2017). Fe 3 O 4 /SiO 2 /TiO 2 composite has been prepared by the
heteroagglomeration method. Fe 3 O 4 magnetite nanoparticles were coprecipitated
with SiO 2 that forms an amorphous coating. A suspension of commercial TiO 2
nanoparticles dispersed in ammonium sulfate aqueous solution was added to the
obtained Fe 3 O 4 /SiO 2 suspension. TiO 2 nanoparticles are a mixture of anatase and
rutile phase. The photocatalytic activity of the Fe 3 O 4 /SiO 2 /TiO 2 composite was
2 Dyes Depollution of Water Using Porous TiO 2 -Based Photocatalysts
59