driving force in the Fenton reaction for the complete degradation and mineralization
of organic pollutants, even in the presence of LMWOAs.
Orange II, the 4-(2-hydroxy-1-naphthylazo)benzenesulfonic acid Na salt was
taken as a model for the oxidation of organic compounds in photo-assisted Fenton
process in the presence of Cl
À in solution [32]. The HO
• radicals seem to originate
due to the photolysis of Fe(OH)
2+ complexes in solution, whereas the Cl 2
-• radical
was a product of the photolysis of the FeCl 2
+ complexes. The rate constants for the
reaction of HO
• and Cl 2
-• radicals with Orange II were determined by laser kinetic
spectroscopy. A significant decrease in the decoloration rate was observed for
Orange II upon addition of Cl
À (10 mM), but further addition of Cl
À only marginally
affected the latter reaction rate. Chlorinated hydrocarbons were observed as the
products of Orange II oxidation in photo-assisted and dark Fenton processes in the
presence of Cl
À anions. Light irradiation decreased the amount of chlorinated
organic products in solution as compared to dark Fenton processes. The results
obtained are in agreement with the radical reaction theory for the particular case of
the Fenton reaction. Kinetic modeling of the Orange II decoloration was carried out
taking into consideration the rate constants found for the reactions with HO
• and Cl 2
-•
,
respectively.
1.0
a
a
b
b
c
c
d
d
e
e
0.8
0.6
0.4
0.2
MG C
t /C
o
MG C
t /C
o
0.0
1.0
0.8
0.6
0.4
0.2
0.0
0
50
100
150
200
250
300
Reaction time/min
A
B
Fig. 11.6 Fenton
degradation of MG in the
presence of (A) malonic acid
and (B) EDTA: (a) in the
dark, (b) under visible
irradiation, (c) in the
presence of hydroquinone in
the dark, (d) in the presence
of hydroquinone under
visible irradiation, (e) under
UV irradiation. Initial
concentrations for (A):
1 Â 10
À5 M Fe
3+ ; 1 Â 10
À2
M H 2 O 2 ; 5 Â 10
À5 M
malonic acid; 2 Â 10
À5 M
hydroquinone; 2 Â 10
À5 M
MG. Initial concentrations
for (B): 2 Â 10
À4 M Fe
3+ ;
2 Â 10
À3 M H 2 O 2 ; 2 Â 10
À5
M hydroquinone; 2 Â 10
À5
M MG; 5 Â 10
À4 M EDTA.
Reprinted with the
permission from ref.
[31]. Copyright 2011
American Chemical Society
272
11 Photo-Fenton Reaction
of organic pollutants, even in the presence of LMWOAs.
Orange II, the 4-(2-hydroxy-1-naphthylazo)benzenesulfonic acid Na salt was
taken as a model for the oxidation of organic compounds in photo-assisted Fenton
process in the presence of Cl
À in solution [32]. The HO
• radicals seem to originate
due to the photolysis of Fe(OH)
2+ complexes in solution, whereas the Cl 2
-• radical
was a product of the photolysis of the FeCl 2
+ complexes. The rate constants for the
reaction of HO
• and Cl 2
-• radicals with Orange II were determined by laser kinetic
spectroscopy. A significant decrease in the decoloration rate was observed for
Orange II upon addition of Cl
À (10 mM), but further addition of Cl
À only marginally
affected the latter reaction rate. Chlorinated hydrocarbons were observed as the
products of Orange II oxidation in photo-assisted and dark Fenton processes in the
presence of Cl
À anions. Light irradiation decreased the amount of chlorinated
organic products in solution as compared to dark Fenton processes. The results
obtained are in agreement with the radical reaction theory for the particular case of
the Fenton reaction. Kinetic modeling of the Orange II decoloration was carried out
taking into consideration the rate constants found for the reactions with HO
• and Cl 2
-•
,
respectively.
1.0
a
a
b
b
c
c
d
d
e
e
0.8
0.6
0.4
0.2
MG C
t /C
o
MG C
t /C
o
0.0
1.0
0.8
0.6
0.4
0.2
0.0
0
50
100
150
200
250
300
Reaction time/min
A
B
Fig. 11.6 Fenton
degradation of MG in the
presence of (A) malonic acid
and (B) EDTA: (a) in the
dark, (b) under visible
irradiation, (c) in the
presence of hydroquinone in
the dark, (d) in the presence
of hydroquinone under
visible irradiation, (e) under
UV irradiation. Initial
concentrations for (A):
1 Â 10
À5 M Fe
3+ ; 1 Â 10
À2
M H 2 O 2 ; 5 Â 10
À5 M
malonic acid; 2 Â 10
À5 M
hydroquinone; 2 Â 10
À5 M
MG. Initial concentrations
for (B): 2 Â 10
À4 M Fe
3+ ;
2 Â 10
À3 M H 2 O 2 ; 2 Â 10
À5
M hydroquinone; 2 Â 10
À5
M MG; 5 Â 10
À4 M EDTA.
Reprinted with the
permission from ref.
[31]. Copyright 2011
American Chemical Society
272
11 Photo-Fenton Reaction