2.7 Conclusions
Because of their potential toxic effects on human health, water pollution by dyes is a
major issue, and many efforts are devoted to solve it. Among the different methods
considered to remove dye, photodegradation is one of the most promising methods
since it leads to the complete mineralization of the organic pollutants to CO 2 , water,
and mineral acids. In addition, such process avoids the production of solid wastes,
and only mild temperature and pressure conditions are required. Thanks to its
properties, titania has been widely considered as photocatalyst for dyes removal,
and many efforts have been devoted to increase the specific surface area since this
parameter is crucial for the photocatalytic activity.
Various types of porous TiO 2 nanomaterials such as powder mesostructured
titania, nanoparticles, nanotubes, or nanorods have been successfully used for dyes
photodegradation such as methylene blue, rhodamine B, or methyl orange. However, up to now, these materials are barely incorporated in a process, and most of the
tests are performed at the laboratory scale. Many efforts are devoted to their shape
modeling to integrate these materials in processes, and formation of films and the
immobilization of TiO 2 on support such as membrane disks have been considered.
Properties of titania and in peculiar the specific surface area can also be tuned by
associating it with another material to get nanocomposites. By the way both the
specific surface area and the thermal stability are increased. As a consequence, in
comparison with the performances of commercial titania such as P25, the
photocatalytic efficiency of the composites is enhanced. Coupling TiO 2 with another
material can also induce a decrease of the band gap, which allows enhancing the
activity under the visible light. This can also be achieved by doping, which limits the
electron/hole recombination and therefore favors the photocatalytic activity.
Up to now, membrane-based photocatalytic process is one of the most studied
techniques to remove dyes from water at a large scale. Nevertheless, micro-reactors
also appear as a promising technology for wastewater treatment. The main challenge
that still persists is to implant the porous titania in these processes and to develop
them at the industrial scale.
References
Abramian L, El-Rassy H (2009) Adsorption kinetics and thermodynamics of azo-dye Orange II
onto highly porous titania aerogel. Chem Eng J 150:403–410. https://doi.org/10.1016/j.cej.
2009.01.019
Ahmed S, Rasul MG, Martens WN, Brown R, Hashib MA (2010) Heterogeneous photocatalytic
degradation of phenols in wastewater: a review on current status and developments. Desalination 261:3–18. https://doi.org/10.1016/j.desal.2010.04.062
Ajmal A, Majeed I, Malik RN, Idriss H, Nadeem MA (2014) Principles and mechanisms of
photocatalytic dye degradation on TiO 2 based photocatalysts: a comparative overview. RSC
Adv 4:37003–37026. https://doi.org/10.1039/c4ra066584
2 Dyes Depollution of Water Using Porous TiO 2 -Based Photocatalysts
77
Because of their potential toxic effects on human health, water pollution by dyes is a
major issue, and many efforts are devoted to solve it. Among the different methods
considered to remove dye, photodegradation is one of the most promising methods
since it leads to the complete mineralization of the organic pollutants to CO 2 , water,
and mineral acids. In addition, such process avoids the production of solid wastes,
and only mild temperature and pressure conditions are required. Thanks to its
properties, titania has been widely considered as photocatalyst for dyes removal,
and many efforts have been devoted to increase the specific surface area since this
parameter is crucial for the photocatalytic activity.
Various types of porous TiO 2 nanomaterials such as powder mesostructured
titania, nanoparticles, nanotubes, or nanorods have been successfully used for dyes
photodegradation such as methylene blue, rhodamine B, or methyl orange. However, up to now, these materials are barely incorporated in a process, and most of the
tests are performed at the laboratory scale. Many efforts are devoted to their shape
modeling to integrate these materials in processes, and formation of films and the
immobilization of TiO 2 on support such as membrane disks have been considered.
Properties of titania and in peculiar the specific surface area can also be tuned by
associating it with another material to get nanocomposites. By the way both the
specific surface area and the thermal stability are increased. As a consequence, in
comparison with the performances of commercial titania such as P25, the
photocatalytic efficiency of the composites is enhanced. Coupling TiO 2 with another
material can also induce a decrease of the band gap, which allows enhancing the
activity under the visible light. This can also be achieved by doping, which limits the
electron/hole recombination and therefore favors the photocatalytic activity.
Up to now, membrane-based photocatalytic process is one of the most studied
techniques to remove dyes from water at a large scale. Nevertheless, micro-reactors
also appear as a promising technology for wastewater treatment. The main challenge
that still persists is to implant the porous titania in these processes and to develop
them at the industrial scale.
References
Abramian L, El-Rassy H (2009) Adsorption kinetics and thermodynamics of azo-dye Orange II
onto highly porous titania aerogel. Chem Eng J 150:403–410. https://doi.org/10.1016/j.cej.
2009.01.019
Ahmed S, Rasul MG, Martens WN, Brown R, Hashib MA (2010) Heterogeneous photocatalytic
degradation of phenols in wastewater: a review on current status and developments. Desalination 261:3–18. https://doi.org/10.1016/j.desal.2010.04.062
Ajmal A, Majeed I, Malik RN, Idriss H, Nadeem MA (2014) Principles and mechanisms of
photocatalytic dye degradation on TiO 2 based photocatalysts: a comparative overview. RSC
Adv 4:37003–37026. https://doi.org/10.1039/c4ra066584
2 Dyes Depollution of Water Using Porous TiO 2 -Based Photocatalysts
77