O 2 þ e
À
ÀÀÀÀ! O 2
• À
ð1:6Þ
O 2
• À
þ H
þ
ÀÀÀÀ! HO 2
•
ð1:7Þ
2 HO 2
•
ÀÀÀÀ! H 2 O 2
ð1:8Þ
H 2 O 2 þ hν ÀÀÀ À!
• OH
ð1:9Þ
H 2 O 2 þ O 2
À
ÀÀÀ À!
• OH þ
À OH þ O 2
ð1:10Þ
H 2 O 2 þ e
À
ÀÀÀ À!
• OH þ
À OH
ð1:11Þ
The generated hydroxyl radicals are the main oxidizing and reactive species with
the very short lifetime and having the oxidation potential of 2.8 V. Hence, these
produced hydroxyl radicals react with the substrate organic compounds and dye
molecules very rapidly to mineralize them completely in a very nonselective manner
as shown in Fig. 1.2.
1.4 Influence of Different Parameters on the Degradation
of Pollutants
The parameters like pH of the reaction solution, surface area of the catalyst,
concentration of the contaminant, catalytic loading, light wavelength, intensity,
etc. play an important role in the degradation of the pollutants on the surface of
Scheme 1.1 Active oxygen species produced as a result of the irradiation of TiO 2 . (Reprinted with
permission from Ref. [3]. Copyright 1995 American Chemical Society)
1.4 Influence of Different Parameters on the Degradation of Pollutants
5