be removed completely through adsorption, particularly when they are in low
concentrations. Thus, an efficient strategy should be developed to handle the contaminants present in trace amount in order to reduce their accretion.
18.3 Concurrent Adsorption and Degradation
18.3.1 Photocatalytically Active Inorganic Nanomaterials
During the last few years, the semiconductor photoactive nanomaterial-catalyzed
heterogeneous oxidation of organics has attained special interest due to its costeffective, eco-friendly, and sustainable treatment technology for wastewater treatment. This strategy involves the degradation of aqueous contaminants at ambient
conditions to more biodegradable and less-toxic components that may not be the
cause of secondary pollution (García-Ripoll et al. 2007). The hydroxyl radicals
(
•
OH) produced during this process are transferred into organic compounds. The
ultraviolet–visible light is the driving force for the production of such an oxidant,
depending on the nature of photocatalysts. Under light illumination, photons having
energies higher than the semiconductor band gap energy (ΔE) can result in the
excitation of electrons from the valence band, thus accelerating the reactions. In the
case of absorbed photons with lesser energies (lesser than ΔE), the energy in the heat
form dissipates. The absorption of sufficient energy by photocatalyst results in the
formation of a positive hole (h
+
) in the valance band and an electron (e
À ) in the
conduction band (Fig. 18.3). The generated h
+ can react with organic species or
water to produce hydroxyl radicals (
• OH), whereas the oxygen adsorbed on the
catalyst is reduced by the electrons present in the conduction band.
The following steps demonstrate the ultraviolet–visible light-assisted activation
of photocatalysts and the redox reaction of organic moieties.
Photoactivation:
Photocatalyst þ light illumination ! e
À
þ h
þ
ð18:1Þ
e
À
þ O 2 ! O 2
ÀÁ
ð18:2Þ
Oxidation:
h
þ
þ Pollutant ! CO 2
ð18:3Þ
h
þ
þ H 2 O!
Á OH þ H
þ
ð18:4Þ
Reductive reaction:
Á OH þ organics ! CO 2
ð18:5Þ
18 Nanomaterials for Textile Waste Treatment
669
concentrations. Thus, an efficient strategy should be developed to handle the contaminants present in trace amount in order to reduce their accretion.
18.3 Concurrent Adsorption and Degradation
18.3.1 Photocatalytically Active Inorganic Nanomaterials
During the last few years, the semiconductor photoactive nanomaterial-catalyzed
heterogeneous oxidation of organics has attained special interest due to its costeffective, eco-friendly, and sustainable treatment technology for wastewater treatment. This strategy involves the degradation of aqueous contaminants at ambient
conditions to more biodegradable and less-toxic components that may not be the
cause of secondary pollution (García-Ripoll et al. 2007). The hydroxyl radicals
(
•
OH) produced during this process are transferred into organic compounds. The
ultraviolet–visible light is the driving force for the production of such an oxidant,
depending on the nature of photocatalysts. Under light illumination, photons having
energies higher than the semiconductor band gap energy (ΔE) can result in the
excitation of electrons from the valence band, thus accelerating the reactions. In the
case of absorbed photons with lesser energies (lesser than ΔE), the energy in the heat
form dissipates. The absorption of sufficient energy by photocatalyst results in the
formation of a positive hole (h
+
) in the valance band and an electron (e
À ) in the
conduction band (Fig. 18.3). The generated h
+ can react with organic species or
water to produce hydroxyl radicals (
• OH), whereas the oxygen adsorbed on the
catalyst is reduced by the electrons present in the conduction band.
The following steps demonstrate the ultraviolet–visible light-assisted activation
of photocatalysts and the redox reaction of organic moieties.
Photoactivation:
Photocatalyst þ light illumination ! e
À
þ h
þ
ð18:1Þ
e
À
þ O 2 ! O 2
ÀÁ
ð18:2Þ
Oxidation:
h
þ
þ Pollutant ! CO 2
ð18:3Þ
h
þ
þ H 2 O!
Á OH þ H
þ
ð18:4Þ
Reductive reaction:
Á OH þ organics ! CO 2
ð18:5Þ
18 Nanomaterials for Textile Waste Treatment
669