The determination of these complex reaction mechanism is very difficult, and
their estimation is restricted to identifying the dissipation of primary pollutant, in
combination with a reduced total organic carbon. Therefore, the oxidation rate and
kinetic of the process are usually evaluated (Malato et al. 2009).
11.8 Factors Affecting Solar Photocatalysis
11.8.1 Solar Irradiance
In case of solar photocatalysis, the reaction rate increases with increase in solar
irradiance, and beyond a certain point, the rate of reaction depends as the square of
the solar irradiance which is due to higher recombination rate of electron-hole pair.
Furthermore, at high solar irradiance, the effect is negligible, and the rate remains
constant. Such condition appears due to the deficiency of electron scavengers or
excess of products conquering the catalyst surface which implies the lesser contact of
catalyst with the effluent (Silva et al. 2007; Spasiano et al. 2015).
11.8.2 Oxygen Concentration
The degradation of organic pollutant present in wastewater can be summarized by
Eq. 11.2 which concludes that in the absence of oxygen, there is no
photodegradation.
Organic pollutant þ Oxygen ! mineral acids þ carbon dioxide þ water ð11:2Þ
The availability of oxygen in water not only serves as an electron acceptor but
also leads to the formation of oxidative species (Malato et al. 2009).
11.8.3 Potential of Hydrogen
Usually, solar photocatalysis indicates a strong potential of hydrogen dependency,
and with the variation in potential of hydrogen, the valence and conduction band
edges of a photocatalyst move by 0.059 per unit potential of hydrogen, which makes
electrons of valence band more effective, and holes of conduction band less effective
(Hoffmann et al. 1995). Another notable characteristic of solar photocatalysis
generally not taken into consideration during water decontamination is the formation
of intermediate compounds which may respond divergently depending on potential
of hydrogen.
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their estimation is restricted to identifying the dissipation of primary pollutant, in
combination with a reduced total organic carbon. Therefore, the oxidation rate and
kinetic of the process are usually evaluated (Malato et al. 2009).
11.8 Factors Affecting Solar Photocatalysis
11.8.1 Solar Irradiance
In case of solar photocatalysis, the reaction rate increases with increase in solar
irradiance, and beyond a certain point, the rate of reaction depends as the square of
the solar irradiance which is due to higher recombination rate of electron-hole pair.
Furthermore, at high solar irradiance, the effect is negligible, and the rate remains
constant. Such condition appears due to the deficiency of electron scavengers or
excess of products conquering the catalyst surface which implies the lesser contact of
catalyst with the effluent (Silva et al. 2007; Spasiano et al. 2015).
11.8.2 Oxygen Concentration
The degradation of organic pollutant present in wastewater can be summarized by
Eq. 11.2 which concludes that in the absence of oxygen, there is no
photodegradation.
Organic pollutant þ Oxygen ! mineral acids þ carbon dioxide þ water ð11:2Þ
The availability of oxygen in water not only serves as an electron acceptor but
also leads to the formation of oxidative species (Malato et al. 2009).
11.8.3 Potential of Hydrogen
Usually, solar photocatalysis indicates a strong potential of hydrogen dependency,
and with the variation in potential of hydrogen, the valence and conduction band
edges of a photocatalyst move by 0.059 per unit potential of hydrogen, which makes
electrons of valence band more effective, and holes of conduction band less effective
(Hoffmann et al. 1995). Another notable characteristic of solar photocatalysis
generally not taken into consideration during water decontamination is the formation
of intermediate compounds which may respond divergently depending on potential
of hydrogen.
376
A. Tripathi and S. Narayanan