Furthermore, potential of hydrogen also affects the surface charge of a
photocatalyst which could affect the efficiency of photocatalysis process (Spasiano
et al. 2015). Hence, potential of hydrogen is one of the most important parameters
which must be considered during the study of any photocatalytic process.
11.8.4 Temperature
Due to the photonic activation, the photocatalysis systems do not require heating and
can be operated at ambient conditions. Many studies concludes that at temperature
below 0
C, the rate-limiting step is controlled by the final product desorption, and at
this point the apparent activation energy increases (Malato et al. 2009; Nan et al.
2010). While at temperature above 80
C the exothermic adsorption of reactants
becomes rate-limiting step, the apparent activation energy becomes negative. Furthermore, at higher temperature, recombination of electron-hole pairs increases and
demonizes the adsorption of organic compounds onto the photocatalyst surface
(Malato et al. 2009; Nan et al. 2010).
In addition, the solubility of oxygen decreases with increased temperature and
affects the photocatalytic kinetics. Hence for the photocatalysis system, 20 and 80
C
temperature range is considered as optimum (Malato et al. 2009; Nan et al. 2010).
11.8.5 Catalysis Load
Catalysis load and solar photocatalytic reactor diameter are interconnected reactor
design parameters. In the case of slurry reactors, the rate of reaction is proportional to
the load of catalyst, but after a specific dose due to particle agglomeration and poor
penetration of sunlight, the photocatalytic activity decreases (Assano and Alfano
1998; Silva et al. 2007). Hence optimization of the photocatalyst dose for a better
efficiency is required; various reports conclude that 25–50 mm must be the ideal
diameter of a solar photocatalytic slurry reactor. Lesser than this range may result in
operating pressure loss (Dillert et al. 1999; Guillard et al. 1999).
In immobilized photocatalytic reactor system, the film thickness plays an important role which depends on photocatalyst deposition technique, optical and physical
properties of the material used and the nature of light wavelength. When the film
thickness is very low (<1 μm), the photons will absorb on the photocatalyst surface,
whereas the thick film gives rise to an unreactive “dark zone” (Chen et al. 2000;
Camera-Roda and Santarelli 2007).
11 Solar Photocatalytic Treatment of Tannery Effluents
377
photocatalyst which could affect the efficiency of photocatalysis process (Spasiano
et al. 2015). Hence, potential of hydrogen is one of the most important parameters
which must be considered during the study of any photocatalytic process.
11.8.4 Temperature
Due to the photonic activation, the photocatalysis systems do not require heating and
can be operated at ambient conditions. Many studies concludes that at temperature
below 0
C, the rate-limiting step is controlled by the final product desorption, and at
this point the apparent activation energy increases (Malato et al. 2009; Nan et al.
2010). While at temperature above 80
C the exothermic adsorption of reactants
becomes rate-limiting step, the apparent activation energy becomes negative. Furthermore, at higher temperature, recombination of electron-hole pairs increases and
demonizes the adsorption of organic compounds onto the photocatalyst surface
(Malato et al. 2009; Nan et al. 2010).
In addition, the solubility of oxygen decreases with increased temperature and
affects the photocatalytic kinetics. Hence for the photocatalysis system, 20 and 80
C
temperature range is considered as optimum (Malato et al. 2009; Nan et al. 2010).
11.8.5 Catalysis Load
Catalysis load and solar photocatalytic reactor diameter are interconnected reactor
design parameters. In the case of slurry reactors, the rate of reaction is proportional to
the load of catalyst, but after a specific dose due to particle agglomeration and poor
penetration of sunlight, the photocatalytic activity decreases (Assano and Alfano
1998; Silva et al. 2007). Hence optimization of the photocatalyst dose for a better
efficiency is required; various reports conclude that 25–50 mm must be the ideal
diameter of a solar photocatalytic slurry reactor. Lesser than this range may result in
operating pressure loss (Dillert et al. 1999; Guillard et al. 1999).
In immobilized photocatalytic reactor system, the film thickness plays an important role which depends on photocatalyst deposition technique, optical and physical
properties of the material used and the nature of light wavelength. When the film
thickness is very low (<1 μm), the photons will absorb on the photocatalyst surface,
whereas the thick film gives rise to an unreactive “dark zone” (Chen et al. 2000;
Camera-Roda and Santarelli 2007).
11 Solar Photocatalytic Treatment of Tannery Effluents
377