and promotes the development of depletion layer between both semiconductors in
sunlight. Secondly, the greater electronic diffusion between these two forms a
distinct junction. This heterojunction facilitates the transportation of charge carriers.
Further, the tuning between the band gap energies resulted into the overall low
difference between valence and conduction gap of the nanocomposite. In addition to
the functionalization widen the visible light absorption area and enhance the redox
reaction on surface of the catalyst (Subramanian et al. 2019). Involvement of metalbased nanocatalysts has been seen to be more in these degradation processes as
described above. This is due to the unique nature of semiconductors oxides. The
outermost electrons are mostly in the d orbitals, which are partially filled and permit
the alteration of electronic properties to enable these in visible/solar light (Bouzid
et al. 2015). Generation of defects in the semiconductors, through their
functionalization, results into the trapping of electrons and holes, which result into
the generation of superoxide and hydroxyl radical (Ani et al. 2018).
5.7 Other Factors Affecting Degradation
5.7.1 Concentration
The initial concentration of polycyclic aromatic hydrocarbons has high effect on the
degradation ability of the functionalized catalyst. Rise in concentration results into
the blocking of the active sites on the catalyst surface for further adsorption as well
as lowers the contact between polycyclic aromatic hydrocarbon molecules and the
catalyst owing to the restricted active sites. Moreover, the fall in the path length of
photons lowers the photocatalytic activity of the catalyst (Shanker et al. 2017a, b).
The influence of initial number of molecules of chrysene upon iron oxide@zinc
hexacyanoferrate was studied by Rachna and Shanker (2018) under sunlight. The
polycyclic aromatic hydrocarbon molecules also interacted with the absorbed photons and, hence, reduced the access of photons for the catalyst that initiates the
reactive radicals (Rachna and Shanker 2018).
5.7.2 Catalyst Loading
Economical aspect of a degradation technology is one of the important factors to be
focused on. Dosage of a photocatalyst plays a vital role in the removal of polycyclic
aromatic hydrocarbons owing to the interaction between its number of molecules
and the number of active sites. Generally it has been noticed that the activity of
functionalized nanocatalysts rises with the rise in its dosage (Rani and Shanker
2018a), but after a particular mount, the activity decreases (Rani and Shanker
2018b). This is because as the catalyst amount increases, the photon energy is
interrupted by the excess catalyst, thus declining in overall activity. After a certain
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Rachna et al.
sunlight. Secondly, the greater electronic diffusion between these two forms a
distinct junction. This heterojunction facilitates the transportation of charge carriers.
Further, the tuning between the band gap energies resulted into the overall low
difference between valence and conduction gap of the nanocomposite. In addition to
the functionalization widen the visible light absorption area and enhance the redox
reaction on surface of the catalyst (Subramanian et al. 2019). Involvement of metalbased nanocatalysts has been seen to be more in these degradation processes as
described above. This is due to the unique nature of semiconductors oxides. The
outermost electrons are mostly in the d orbitals, which are partially filled and permit
the alteration of electronic properties to enable these in visible/solar light (Bouzid
et al. 2015). Generation of defects in the semiconductors, through their
functionalization, results into the trapping of electrons and holes, which result into
the generation of superoxide and hydroxyl radical (Ani et al. 2018).
5.7 Other Factors Affecting Degradation
5.7.1 Concentration
The initial concentration of polycyclic aromatic hydrocarbons has high effect on the
degradation ability of the functionalized catalyst. Rise in concentration results into
the blocking of the active sites on the catalyst surface for further adsorption as well
as lowers the contact between polycyclic aromatic hydrocarbon molecules and the
catalyst owing to the restricted active sites. Moreover, the fall in the path length of
photons lowers the photocatalytic activity of the catalyst (Shanker et al. 2017a, b).
The influence of initial number of molecules of chrysene upon iron oxide@zinc
hexacyanoferrate was studied by Rachna and Shanker (2018) under sunlight. The
polycyclic aromatic hydrocarbon molecules also interacted with the absorbed photons and, hence, reduced the access of photons for the catalyst that initiates the
reactive radicals (Rachna and Shanker 2018).
5.7.2 Catalyst Loading
Economical aspect of a degradation technology is one of the important factors to be
focused on. Dosage of a photocatalyst plays a vital role in the removal of polycyclic
aromatic hydrocarbons owing to the interaction between its number of molecules
and the number of active sites. Generally it has been noticed that the activity of
functionalized nanocatalysts rises with the rise in its dosage (Rani and Shanker
2018a), but after a particular mount, the activity decreases (Rani and Shanker
2018b). This is because as the catalyst amount increases, the photon energy is
interrupted by the excess catalyst, thus declining in overall activity. After a certain
156
Rachna et al.