Among these four, the degradation of the OCDD was considered to be best by the
nZVZ because of its property of dechlorination under the ambient conditions
(Lu et al. 2016).
12.5.2 Metal Oxides Nanoparticles
12.5.2.1 TiO 2 Nanoparticles
TiO 2 Nanoparticles is most extensively used as the semiconductor electrode for the
electrochemical photolysis of water by the process of photocatalytic degradation. As
this photocatalytic degradation technology is considered to be the best for the
contaminant degradation present in the waste water (Fujishima and Honda 1972).
In this process by the use of the catalyst and in the presence of the light the
contaminant will get broken into some low molecular weight intermediate products
and later get converted into CO 2 , H 2 O, and some anions (Liu and Li 2014). As the
TiO 2 catalyst is considered as the best catalyst as compared to the other catalysts
such as the metal oxide or sulfide semiconductors because of its unique properties
which includes high photocatalytic activity, reasonable cost, photostability, and
chemical-biological stability (Vedrine 2017). Along with the best it is considered
as the most exceptional catalyst due to its large energy gap band i.e., 3.2 eV because
of which it requires ultraviolet excitation for the charge separation within the
particles. Therefore, when the TiO 2 NPs comes in contact with the UV radiations
they start producing the reactive oxygen species (ROS) As a result, when these TiO 2
NPs are irradiated with the UV radiations, TiO 2 will produce the reactive oxygen
species (ROS) which will degrade the contaminants in a short time period (Credico
et al. 2015). The other reason for considering it the best is its selectivity which makes
it suitable for all the contaminants degradation such as chlorinated organic
compounds, polycyclic aromatic hydrocarbons, dyes, phenols, pesticides, arsenic,
cyanide, and heavy metals. TiO 2 NPs also have the property of producing the
hydroxyl radicals which will damage the structure of several cells. Also as they
show the photocatalytic properties, therefore with the help of this they destroy the
number of microorganisms which includes both Gram-negative, Gram-positive
bacteria as well as fungi, algae, protozoa, and viruses (Yin et al. 2012).
For the degradation of the contaminants the TiO 2 NPs is used with the membrane
technology by incorporating these NPs in the membranes such as poly (vinylidene
fluoride), polyethersulfone, polymethyl methacrylate, and poly (amide-imide). For
example—by the photocatalysis of the TiO 2 NPs methylene blue can be removed
successfully (Dagher et al. 2018). Also these TiO 2 NPs can be easily removed from
the system by the simple filteration because of their coupling with the polymeric
membranes.
12.5.2.2 ZnO Nanoparticles
In the treatment of wastewater the ZnO nanoparticles are used because of their
photocatalytic properties. Sometimes these nanoparticles are used in place of TiO 2
nanoparticles as they both exhibit the same energy bands (Lu et al. 2016). These
12 Management of Waste Using Nanotechnology
265
nZVZ because of its property of dechlorination under the ambient conditions
(Lu et al. 2016).
12.5.2 Metal Oxides Nanoparticles
12.5.2.1 TiO 2 Nanoparticles
TiO 2 Nanoparticles is most extensively used as the semiconductor electrode for the
electrochemical photolysis of water by the process of photocatalytic degradation. As
this photocatalytic degradation technology is considered to be the best for the
contaminant degradation present in the waste water (Fujishima and Honda 1972).
In this process by the use of the catalyst and in the presence of the light the
contaminant will get broken into some low molecular weight intermediate products
and later get converted into CO 2 , H 2 O, and some anions (Liu and Li 2014). As the
TiO 2 catalyst is considered as the best catalyst as compared to the other catalysts
such as the metal oxide or sulfide semiconductors because of its unique properties
which includes high photocatalytic activity, reasonable cost, photostability, and
chemical-biological stability (Vedrine 2017). Along with the best it is considered
as the most exceptional catalyst due to its large energy gap band i.e., 3.2 eV because
of which it requires ultraviolet excitation for the charge separation within the
particles. Therefore, when the TiO 2 NPs comes in contact with the UV radiations
they start producing the reactive oxygen species (ROS) As a result, when these TiO 2
NPs are irradiated with the UV radiations, TiO 2 will produce the reactive oxygen
species (ROS) which will degrade the contaminants in a short time period (Credico
et al. 2015). The other reason for considering it the best is its selectivity which makes
it suitable for all the contaminants degradation such as chlorinated organic
compounds, polycyclic aromatic hydrocarbons, dyes, phenols, pesticides, arsenic,
cyanide, and heavy metals. TiO 2 NPs also have the property of producing the
hydroxyl radicals which will damage the structure of several cells. Also as they
show the photocatalytic properties, therefore with the help of this they destroy the
number of microorganisms which includes both Gram-negative, Gram-positive
bacteria as well as fungi, algae, protozoa, and viruses (Yin et al. 2012).
For the degradation of the contaminants the TiO 2 NPs is used with the membrane
technology by incorporating these NPs in the membranes such as poly (vinylidene
fluoride), polyethersulfone, polymethyl methacrylate, and poly (amide-imide). For
example—by the photocatalysis of the TiO 2 NPs methylene blue can be removed
successfully (Dagher et al. 2018). Also these TiO 2 NPs can be easily removed from
the system by the simple filteration because of their coupling with the polymeric
membranes.
12.5.2.2 ZnO Nanoparticles
In the treatment of wastewater the ZnO nanoparticles are used because of their
photocatalytic properties. Sometimes these nanoparticles are used in place of TiO 2
nanoparticles as they both exhibit the same energy bands (Lu et al. 2016). These
12 Management of Waste Using Nanotechnology
265