Due to its properties, titania has been widely studied in the water treatment processes. However, to be implanted at a large scale, the photocatalytic activity still
needs to be enhanced, especially in the visible domain. One way to reach this goal
consists in increasing the specific surface area of the photocatalyst. From this point
of view, porous TiO 2 are excellent candidates to be considered in the water treatment
technologies.
Here we review the use of porous titania-based nanomaterials for the
photocatalytic degradation of dyes contained in wastewater, since this process is
the most promising. First a short presentation of common dyes used in the industry
and their classification is given. The main information concerning TiO 2 as potential
good photocatalyst for dye removal from wastewater is then given to remind its
structures and properties, describe the mechanisms proposed for pollutant
photodegradation, and present the parameters affecting its photoactivity efficiency.
These aspects are the bases that orient researches in the synthesis of performant
nanostructured TiO 2 photocatalysts. Recent advances related to this topic are
reviewed including the shaping and preparation of TiO 2 -based (nano)composites
materials that have been developed to favor their use and/or integration in a process
for potential industrial use. The last part is devoted to the progress of two most
promising process for the implementation of viable system to remove dyes from
wastewater at a large scale. Finally some patents and the interest of titania and
photocatalysis in industry are reviewed.
Keywords Photodegradation · Titania · Nanomaterials · Doping · Membrane
process · Flow reactor · Azo dyes
2.1 Introduction
There are several different types of substances that may pollute water, and contamination of surface water, groundwater, and soil is a major problem (Dror et al. 2012).
Because of their potential carcinogenic and toxic effects on human health, among the
different pollutants such as detergents, fertilizers, volatile organic compounds
(VOC), halogenated organic compounds (HOCs), and dyes are a major environmental concern (Kolpin et al. 2002; Chen et al. 2011). Dyes are mainly discharged
from pharmaceutics, printing, food coloring, cosmetics, paper, textiles, and many
other industries, involving an environmental pollution. Dyes can change the color of
water, impact light penetration, and reduce the solubility of gases such as oxygen,
and some of them are toxic, which further affect the ecology in the water (Epolito
et al. 2005; Nandi et al. 2009). Over 7 Â 10
5 tons of dyes and pigments comprising
more than 10,000 different molecules are produced annually worldwide (Dutta et al.
2014). Among the different kinds of dyes, the ones belonging to the azo family
(Forgacs et al. 2004) are carcinogenic, resistant to biodegradation, highly toxic, and
mutagenic to both human beings and aquatic life (Cai et al. 2017). Because of this
toxicity for human health, many efforts have been devoted to remove dyes in
36
B. Lebeau et al.
needs to be enhanced, especially in the visible domain. One way to reach this goal
consists in increasing the specific surface area of the photocatalyst. From this point
of view, porous TiO 2 are excellent candidates to be considered in the water treatment
technologies.
Here we review the use of porous titania-based nanomaterials for the
photocatalytic degradation of dyes contained in wastewater, since this process is
the most promising. First a short presentation of common dyes used in the industry
and their classification is given. The main information concerning TiO 2 as potential
good photocatalyst for dye removal from wastewater is then given to remind its
structures and properties, describe the mechanisms proposed for pollutant
photodegradation, and present the parameters affecting its photoactivity efficiency.
These aspects are the bases that orient researches in the synthesis of performant
nanostructured TiO 2 photocatalysts. Recent advances related to this topic are
reviewed including the shaping and preparation of TiO 2 -based (nano)composites
materials that have been developed to favor their use and/or integration in a process
for potential industrial use. The last part is devoted to the progress of two most
promising process for the implementation of viable system to remove dyes from
wastewater at a large scale. Finally some patents and the interest of titania and
photocatalysis in industry are reviewed.
Keywords Photodegradation · Titania · Nanomaterials · Doping · Membrane
process · Flow reactor · Azo dyes
2.1 Introduction
There are several different types of substances that may pollute water, and contamination of surface water, groundwater, and soil is a major problem (Dror et al. 2012).
Because of their potential carcinogenic and toxic effects on human health, among the
different pollutants such as detergents, fertilizers, volatile organic compounds
(VOC), halogenated organic compounds (HOCs), and dyes are a major environmental concern (Kolpin et al. 2002; Chen et al. 2011). Dyes are mainly discharged
from pharmaceutics, printing, food coloring, cosmetics, paper, textiles, and many
other industries, involving an environmental pollution. Dyes can change the color of
water, impact light penetration, and reduce the solubility of gases such as oxygen,
and some of them are toxic, which further affect the ecology in the water (Epolito
et al. 2005; Nandi et al. 2009). Over 7 Â 10
5 tons of dyes and pigments comprising
more than 10,000 different molecules are produced annually worldwide (Dutta et al.
2014). Among the different kinds of dyes, the ones belonging to the azo family
(Forgacs et al. 2004) are carcinogenic, resistant to biodegradation, highly toxic, and
mutagenic to both human beings and aquatic life (Cai et al. 2017). Because of this
toxicity for human health, many efforts have been devoted to remove dyes in
36
B. Lebeau et al.