Although a number of electron acceptors, such as H 2 O 2 , (NH 4 ) 2 S 2 O 8 ), and
KBrO 3 , have been explored to trounce this limitation, mineralization photo efficiency is still lower. The modification of TiO 2 via doping or alloying has proven to
be an effective approach to improve the photo efficiency. For instance, noble metaldecorated TiO 2 has been demonstrated to have enhanced photo efficiency. The
electrons present in the conduction band can be excited and moved to the decorated
metal having narrower band gap to shun the recombination of electrons and holes,
resulting in the efficient separation of charges and high rates of photocatalytic
reaction (Ni et al. 2007). The doping of transition-metal ions and rare-earth metal
ions into TiO 2 lattice has also been shown to enhance its photocatalytic performance.
The doping of non-metallic species, such as nitrogen, fluorine, carbon, and sulfur,
has also been investigated to obtain improved photo efficiency in the full solar
spectrum (Malato et al. 2009).
Another important photocatalytic material that is broadly investigated for the
treatment of wastewater is ZnO. ZnO is non-toxic, cost-effective, and chemically
stable. Although TiO 2 is regarded as the most active photodegradation catalyst, ZnO
exhibits even better photocatalytic performance in certain situations (Khan et al.
2019a; Khan et al. 2019b; Yu and Yu 2008). Moreover, it can work in the broader
solar window than TiO 2 , so it is the most appropriate catalyst for the
photodegradation of organics under sunlight illumination. There are many reports
demonstrating ZnO as a photocatalyst for the degradation of organic pollutants and
colored dyes, such as kraft black liquor, 2-phenylphenol fungicide, phenols, lignin,
and many other azo dyes. Furthermore, photocatalytic degradation of few antibiotics, such as sulfamethoxazole, amoxicillin, ampicillin, cloxacillin, and lincomycin,
has also been reported (Elmolla and Chaudhuri 2010; Farzadkia et al. 2014).
Owing to low band gap of 2.2 eV and n-type semiconducting nature of Fe 2 O 3 , it
becomes an appropriate candidate for photocatalytic degradation of organic dyes and
pollutants. Several Fe
3+ species have been used for the treatment of organic
dye-polluted water, such as α-Fe 2 O 3 , γ-Fe 2 O 3 , α-FeOOH, β-FeOOH, and
γ-FeOOH. Highly efficient photocatalytic degradation of Congo red using iron
oxide nanoparticles has been demonstrated (Khedr et al. 2009). Moreover, this
type of photocatalyst is stable and found to have the best performance even after
several cycles. The limitation of such nanomaterials is the fast electron–hole recombination. To surmount this issue, different noble metal particles can be deposited on
their surface and may be used as a support. For instance, Au/Fe 2 O 3 has been
employed for the photodegradation of water-dispersed azo dye, i.e., blue 79. The
Au nanoparticles here are regarded as electron accumulation sites, thus can assist
their transfer from the surface. Better charge separation imparts improved
photocatalytic performance.
Many metal chalcogenides and nitrides have also been designed as catalysts for
the photodegradation of pollutant to treat wastewater. For example the 2.42 eV band
gap of CdS allows the easy transfer of electrons from valance band to the conduction
band by light having a wavelength of less than 495 nm (Yang et al. 2013). Recently,
semiconductor CdS nanoparticles have attracted much attention as photocatalysts to
treat wastewater polluted with organic dyes owing to their distinct chemical and
18 Nanomaterials for Textile Waste Treatment
671
KBrO 3 , have been explored to trounce this limitation, mineralization photo efficiency is still lower. The modification of TiO 2 via doping or alloying has proven to
be an effective approach to improve the photo efficiency. For instance, noble metaldecorated TiO 2 has been demonstrated to have enhanced photo efficiency. The
electrons present in the conduction band can be excited and moved to the decorated
metal having narrower band gap to shun the recombination of electrons and holes,
resulting in the efficient separation of charges and high rates of photocatalytic
reaction (Ni et al. 2007). The doping of transition-metal ions and rare-earth metal
ions into TiO 2 lattice has also been shown to enhance its photocatalytic performance.
The doping of non-metallic species, such as nitrogen, fluorine, carbon, and sulfur,
has also been investigated to obtain improved photo efficiency in the full solar
spectrum (Malato et al. 2009).
Another important photocatalytic material that is broadly investigated for the
treatment of wastewater is ZnO. ZnO is non-toxic, cost-effective, and chemically
stable. Although TiO 2 is regarded as the most active photodegradation catalyst, ZnO
exhibits even better photocatalytic performance in certain situations (Khan et al.
2019a; Khan et al. 2019b; Yu and Yu 2008). Moreover, it can work in the broader
solar window than TiO 2 , so it is the most appropriate catalyst for the
photodegradation of organics under sunlight illumination. There are many reports
demonstrating ZnO as a photocatalyst for the degradation of organic pollutants and
colored dyes, such as kraft black liquor, 2-phenylphenol fungicide, phenols, lignin,
and many other azo dyes. Furthermore, photocatalytic degradation of few antibiotics, such as sulfamethoxazole, amoxicillin, ampicillin, cloxacillin, and lincomycin,
has also been reported (Elmolla and Chaudhuri 2010; Farzadkia et al. 2014).
Owing to low band gap of 2.2 eV and n-type semiconducting nature of Fe 2 O 3 , it
becomes an appropriate candidate for photocatalytic degradation of organic dyes and
pollutants. Several Fe
3+ species have been used for the treatment of organic
dye-polluted water, such as α-Fe 2 O 3 , γ-Fe 2 O 3 , α-FeOOH, β-FeOOH, and
γ-FeOOH. Highly efficient photocatalytic degradation of Congo red using iron
oxide nanoparticles has been demonstrated (Khedr et al. 2009). Moreover, this
type of photocatalyst is stable and found to have the best performance even after
several cycles. The limitation of such nanomaterials is the fast electron–hole recombination. To surmount this issue, different noble metal particles can be deposited on
their surface and may be used as a support. For instance, Au/Fe 2 O 3 has been
employed for the photodegradation of water-dispersed azo dye, i.e., blue 79. The
Au nanoparticles here are regarded as electron accumulation sites, thus can assist
their transfer from the surface. Better charge separation imparts improved
photocatalytic performance.
Many metal chalcogenides and nitrides have also been designed as catalysts for
the photodegradation of pollutant to treat wastewater. For example the 2.42 eV band
gap of CdS allows the easy transfer of electrons from valance band to the conduction
band by light having a wavelength of less than 495 nm (Yang et al. 2013). Recently,
semiconductor CdS nanoparticles have attracted much attention as photocatalysts to
treat wastewater polluted with organic dyes owing to their distinct chemical and
18 Nanomaterials for Textile Waste Treatment
671