such as of Fenton mechanism (iron/H 2 O 2 ), ozonation (O 3 ), electrochemical oxidation, ultra-violet (UV), heterogeneous photocatalysis, or the blend of all the stated
applications) (Bedia et al. 2019).
10.3 Photocatalysis
10.3.1 Background
It is well known that HP is regarded as an emerging vehicle for water detoxification
in the removal of various dyes (Ribeiro et al. 2015; Singh et al. 2013; Carp et al.
2004; Ahmed 2018; Hopfield 1961; Chong et al. 2010; Babu et al. 2015). HP process
involves an irradiation of photocatalyst with UV light to separate charges followed
by development of the ROS (Carp et al. 2004; Ahmed 2018; Babu et al. 2015). The
material which is used in HP is known as a photocatalyst. It is a semiconductor that
posseses the valence band (i.e. highest occupied molecular orbital) level and conduction band (i.e. lowest unoccupied molecular orbital) level. The distance between
the levels is called the energy band gap (E g ) (Hopfield 1961; Chong et al. 2010).
During the irradiation of a semiconductor with the UV light, the semiconductor
absorbs light with energy which is equivalent to its E g (Bedia et al. 2019). The
electrons are promoted from the valence band to the conduction band for generation
of photons of charges and create an electron hole, h
+ behind (Chong et al. 2010;
Babu et al. 2015). There are several pathways that photogenerated charges can take
at an excited state. These include recombination, the release of the excitation energy
as heat, migration to the surface of the photocatalyst or production of the reactive
oxygen species (Bedia et al. 2019). Lastly, ÁOH is produced through oxidation of
water which is accomplished by the h
+
, whereas superoxide radical anions (O 2 Á
À
) is
generated via adsorbed oxygen reduction mechanism. On the other hand, it was seen
that the protonation process may take place to oxidize this O 2 Á
À to hydroperoxyl
radicals (HO 2 Á
À ) (Bedia et al. 2019; Babu et al. 2015). These oxidants together with
a direct oxidation by h
+ are responsible for the mineralization of the organic dye to
CO 2 and H 2 O (Bedia et al. 2019; Deng and Zhao 2015; Ribeiro et al. 2015; Singh
et al. 2013; Carp et al. 2004; Ahmed 2018; Hopfield 1961; Chong et al. 2010; Babu
et al. 2015).
10.3.2 Photocatalysts for Wastewater Treatment
The fast growing interests in the area of photocatalysis for wastewater treatment has
risen in the manufacture of various photocatalysts such as metal oxide and metal
sulfides (Kumar and Rao 2017; Lee et al. 2016; Fagan et al. 2016; Mondal et al.
2015; Wang et al. 2015). A number of photocatalysts in water (Bedia et al.
2019; Kumar and Rao 2017; Lee et al. 2016). Nonetheless, the application of
10 Photocatalytic Degradation of Dyes in Wastewater Using Metal Organic Frameworks 265
applications) (Bedia et al. 2019).
10.3 Photocatalysis
10.3.1 Background
It is well known that HP is regarded as an emerging vehicle for water detoxification
in the removal of various dyes (Ribeiro et al. 2015; Singh et al. 2013; Carp et al.
2004; Ahmed 2018; Hopfield 1961; Chong et al. 2010; Babu et al. 2015). HP process
involves an irradiation of photocatalyst with UV light to separate charges followed
by development of the ROS (Carp et al. 2004; Ahmed 2018; Babu et al. 2015). The
material which is used in HP is known as a photocatalyst. It is a semiconductor that
posseses the valence band (i.e. highest occupied molecular orbital) level and conduction band (i.e. lowest unoccupied molecular orbital) level. The distance between
the levels is called the energy band gap (E g ) (Hopfield 1961; Chong et al. 2010).
During the irradiation of a semiconductor with the UV light, the semiconductor
absorbs light with energy which is equivalent to its E g (Bedia et al. 2019). The
electrons are promoted from the valence band to the conduction band for generation
of photons of charges and create an electron hole, h
+ behind (Chong et al. 2010;
Babu et al. 2015). There are several pathways that photogenerated charges can take
at an excited state. These include recombination, the release of the excitation energy
as heat, migration to the surface of the photocatalyst or production of the reactive
oxygen species (Bedia et al. 2019). Lastly, ÁOH is produced through oxidation of
water which is accomplished by the h
+
, whereas superoxide radical anions (O 2 Á
À
) is
generated via adsorbed oxygen reduction mechanism. On the other hand, it was seen
that the protonation process may take place to oxidize this O 2 Á
À to hydroperoxyl
radicals (HO 2 Á
À ) (Bedia et al. 2019; Babu et al. 2015). These oxidants together with
a direct oxidation by h
+ are responsible for the mineralization of the organic dye to
CO 2 and H 2 O (Bedia et al. 2019; Deng and Zhao 2015; Ribeiro et al. 2015; Singh
et al. 2013; Carp et al. 2004; Ahmed 2018; Hopfield 1961; Chong et al. 2010; Babu
et al. 2015).
10.3.2 Photocatalysts for Wastewater Treatment
The fast growing interests in the area of photocatalysis for wastewater treatment has
risen in the manufacture of various photocatalysts such as metal oxide and metal
sulfides (Kumar and Rao 2017; Lee et al. 2016; Fagan et al. 2016; Mondal et al.
2015; Wang et al. 2015). A number of photocatalysts in water (Bedia et al.
2019; Kumar and Rao 2017; Lee et al. 2016). Nonetheless, the application of
10 Photocatalytic Degradation of Dyes in Wastewater Using Metal Organic Frameworks 265