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The reactivity and reaction pathway of Fenton reactions driven by substituted 1,2- dihydroxybenzenes Pablo Raúl Salgado, Victoria Melin, Yasna Duran, Hector D. Mansilla, and David Contreras Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b05388 • Publication Date (Web): 08 Mar 2017 Downloaded from http://pubs.acs.org on March 10, 2017
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1
The reactivity and reaction pathway of Fenton
2
reactions driven by substituted 1,2-
3
dihydroxybenzenes
4
Pablo Salgadoa,b, Victoria Melina,b, Yasna Durána,b, Héctor Mansillab, David
5
Contreras*a,b.
6
a
7
160-C, Concepción 4070386, Chile.
8
b
9
Casilla 160-C, Concepción 4070386, Chile.
Centro de Biotecnología, Universidad de Concepción. Barrio Universitario s/n. Casilla
Facultad de Ciencias Químicas, Universidad de Concepción. Barrio Universitario s/n.
10 11
ABSTRACT
12
Fenton systems are interesting alternative to advanced oxidation processes (AOPs) applied
13
in soil or water remediation. 1,2-Dihydroxybenzenes (1,2-DHBs) are able to amplify the
14
reactivity of Fenton systems and have been extensively studied in biological systems and
15
for AOP applications. To develop efficient AOPs based on Fenton systems driven by 1,2-
16
DHBs, the change in reactivity mediated by different 1,2-DHBs must be understood. For
17
this, a systematic study of the reactivity of Fenton-like systems driven by 1,2-DHBs with
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different substituents at position 4 was performed. The substituent effect was analyzed
19
using the Hammett constant (σ), which has positive values for electron-withdrawing groups
20
(EWGs) and negative values for electron-donating groups (EDGs). The reactivity of each
21
system was determined from the degradation of a recalcitrant azo dye and hydroxyl radical
22
(HO•) production. The relationship between these reactivities and the ability of each 1,2-
23
DHB to reduce Fe(III) was determined. From these results, we propose two pathways for
24
HO• production. The pathway for Fenton-like systems driven by 1,2-DHBs with EDGs
25
depends only on the Fe(III) reduction mediated by 1,2-DHB. In Fenton-like reactions
26
driven by 1,2-DHBs with EWGs, the Fe(III) reduction is not primarily responsible for
27
increasing the HO• production by this system in the early stages.
28
INTRODUCTION
29
Advanced oxidation processes (AOPs) encompass several methods for the chemical or
30
photochemical oxidation of molecules.1,
2
31
constitute a promising technology for wastewater treatment.3, 4 Although different reaction
32
systems exist for these processes, all are based on the production of reactive oxygen species
33
(ROS), mainly hydroxyl radical (HO•).5, 6 This radical is extremely unstable and reactive
34
(E°(HO•/H2O)= 2.8 V/SHE7) and is consequently able to react quickly with different
35
organic compounds, leading to mineralization of the substrate.8, 9
AOPs performed at near ambient temperatures
36
The production of HO• from the reduction of hydrogen peroxide (H2O2) catalyzed by
37
Fe(II) is known as the Fenton reaction (1).10 The reaction between the Fe(III) produced in
38
(1) and H2O2 is known as the Fenton-like reaction (2) and involves the formation of
39
hydroperoxyl radical (HO2•).11 The Fenton-like reaction represents the limiting step in this
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redox system because it is three orders of magnitude slower than the Fenton reaction. Both
41
Fenton and Fenton-like reactions participate, at the same time, in a redox system.
42
Fe(II) + H2O2 → Fe(III) + HO• + HO- k= 76 molL-1s-1(ref.12)
(1)
43
Fe(III) + H2O2 → Fe(II) + HOO• + H+ k= 0.01molL-1s-1(ref. 13)
(2)
44
Fenton and Fenton-like systems are popular AOPs due to their oxidation power, low
45
toxicity, moderate cost and simple operation.9,
14
46
dependent on the reaction conditions. For example, the pH in the system can change the
47
reaction rate by changing the iron speciation.15, 16 The Fenton reaction is limited at acidic
48
pH to avoid the oxidation of Fe(II) to Fe(OH)3 or Fe2O3.17
However, these systems are highly
49
Several ligands can enhance the production of reactive species by Fenton and Fenton-like
50
systems, of which 1,2-dihydroxybenzenes (1,2-DHBs) have been studied in different
51
systems such as metabolic pathways in biological systems18-22 and AOPs for water and
52
wastewater treatment.23-26 1,2-DHBs form complexes with Fe(III) with a prooxidant or
53
antioxidant activity that is related to the coordination number, which is pH dependent.27
54
These complexes keep the iron in solution, but only monocomplexes [Fe(1,2-DHB)]+ can
55
reduce Fe(III), increasing the reactivity of Fenton systems at acidic pH up to pH 5.520 In
56
this monocomplex a tautomeric valence equilibrium is achieved,28 after that Fe(II) is
57
released (Scheme 1).Thus, 1,2-DHBs increase Fe(III) reduction, which is the limiting step
58
in the Fenton redox system (2).29
59 60
Scheme 1. Mechanism of Fe(III) reduction by 1,2-DHB.
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To develop an efficient AOP based on Fenton systems driven by 1,2-DHBs that can be
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applied in water or soil remediation, the reactivity change mediated by different 1,2-DHBs
63
must be understood. Therefore, a systematic study of the reactivity of Fenton-like systems
64
driven by 1,2-DHBs with different substituents at position 4 was performed. The
65
substituent effect was analyzed using the Hammett constant (σ), which takes on positive
66
values for electron-withdrawing groups (EWGs) and negative values for electron-donating
67
groups (EDGs). The reactivity of each system was determined through the degradation of a
68
recalcitrant azo dye (methyl orange, MO) and HO• production. The relationship between
69
these reactivities and the ability of each 1,2-DHB to reduce Fe(III) was evaluated.
70
MATERIALS AND METHODS
71
Reagents. Ferric nitrate nonahydrate (Fe(NO3)3•9H2O), MO, potassium fluoride (KF), 3-
72
(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-p,p′-disulfonic
acid
(ferrozine),
4-
73
morpholineethanesulfonic acid (MES), potassium nitrate (KNO3), 5,5-dimethyl-1-pyrroline
74
N-oxide (DMPO), 1,2-benzendiol (catechol), 4-tertbutylcatechol, 4-ethylcatechol, 4-
75
methylcatechol, 3,4-dihidroxibenzylamine, noradrenaline, caffeic acid, dopamine, 4-
76
chlorocatechol, adrenaline and 3,4-dihydroxybenzonitrile were purchased from Sigma-
77
Aldrich. Nitric acid (HNO3), 30 % H2O2, hydrocaffeic acid, 3,4-dihydroxybenzaldehyde,
78
3,4-dihydroxybenzoic acid and 4-nitrocatechol were purchased from Merck.
79
All reagents were used without additional purification.
80
General Procedure. All reagent solutions were prepared in the dark under an argon
81
atmosphere. The ionic strengths of all solutions were adjusted to 0.10 mol·L−1 with KNO3.
82
All experiments were performed at 20 ± 0.1 °C in triplicate (n = 3). The pH of each
83
solution was adjusted to 3.4 with HNO3 prior to the experiments using a Thermo Scientific
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Orion 3-Star pH meter. This pH value was selected because is the optimal pH value
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observed for Fenton systems driven by 1,2-DHB.2, 30
86 87
All the experiments were performed at pseudo first order conditions (1,2-DHB/Fe(III) molar ratio 1:20).
88
A UV–Vis diode array spectrophotometer (Agilent 8453) coupled to a stopped-flow
89
system (applied photophysics RX2000) was used for spectrophotometric measurements.
90
The spectra (190-1100 nm) were recorded every 0.1 s for 20 s.
91
Oxidation of MO. The degradation of MO (λmax= 499 nm, Figure S1 in Supplementary
92
Information, SI) at pH 3.4 in the Fenton-like system driven by different 1,2-DHBs was
93
followed spectrophotometrically. The final concentrations in the systems were 1.0x10-
94
6
95
initiated by adding Fe(III). The kinetics data were analyzed with UV-Vis ChemStation
96
software. The pseudo-first order constant (kobs) was determined 20 s after initiating the
97
reaction (Figure S2 in SI).
mmol·L−1 1,2-DHB and 20x10-6 mol·L−1 Fe(NO3)3, MO and H2O2. The reaction was
98
Hydroxyl Radical Production. HO• was detected by a DMPO spin-trapping method
99
using EPR spectroscopy.31 The final concentrations in the systems were 50x10-6 mol·L−1
100
1,2-DHB, 20x10-3 mol·L−1 DMPO and 1.0x10-3 mol·L−1 H2O2 and Fe(NO3)3. The reactions
101
were initiated by adding Fe(III). Samples were subsequently transferred via syringe to an
102
AquaX capillary in a Bruker EMX micro instrument. The EPR spectra of the DMPO-OH
103
adduct was recorded every 15 s on the X band (~9GHz). The amount of DMPO-OH adduct
104
produced was considered proportional to the height of the second peak in the adduct spectra
105
(Figure S3 in SI). All decay plots were normalized and adjusted to pseudo-first-order
106
kinetics (3) according to Contreras et al.,32 and a pseudo-first-order constant (kp) and the
107
initial signal (I0) was determined for each system.
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= − +
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(3)
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Reduction of Fe(III). Reduced Fe(III) was quantified in a spectrometric method by
110
measuring the levels of Fe(II) formed at different reaction times as a colored complex with
111
ferrozine (λmax=562 nm).33 The reduction of Fe(III) by each 1,2-DHB was determined at pH
112
3.4. The final concentrations in the systems were 4.0x10-4 mol·L−1 Fe(NO3)3 and 2.0x10-5
113
mol·L−1 1,2-DHB. The kinetics was assessed in a stopped-flow apparatus. The kinetics data
114
were processing with UV-Vis ChemStation software. The pseudo-first order constant (kred)
115
was determined.
116
Determination of the Redox Potential of 1,2-DHB. The redox potential of each 1,2-
117
DHB was determined by cyclic voltammetry using a method modified from Contreras et
118
al.34 The final concentration was 5.0x10-3 mol·L−1 1,2-DHB, which was prepared in an
119
aqueous solution at pH 3.0. The ionic strength was adjusted to 1.0 mol·L−1 KNO3.
120
Electrochemical measurements were performed on a computer controlled by a CHI1207A
121
potentiostat (CH Instruments, TX, USA) using a 20 mL glass chamber with a three-
122
electrode system. The working electrode was carbon graphite (3 mm in diameter), an
123
Ag/AgCl electrode was used as the reference electrode, and a platinum wire was used as the
124
auxiliary electrode. The instrumental parameters were as follows: Einitial = -0.4 V, Emax = 0.8
125
V, Emin = -0.4 V and scan rate = 0.2 V/s.
126 127 128
From the anodic (Epa) and cathodic (Epc) potential, the standard potential (E°) was estimated in equation (4).
° = −
(4)
129 130 131
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RESULTS AND DISCUSSION
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Oxidation of MO. The oxidation of MO was performed for 20 s under pseudo-first-order
134
conditions. The fifteen 1,2-DHBs shown in Table 1 were utilized. Their structures are
135
shown in SI (Figure S4).
136
Table 1. 1,2-DHBs utilized in this study and their Hammett parameters. Hammett Parameters 1
1,2-DHBs
σm
σp
Σσ = (σm + σp)
4-Tert-Butylcatechol
-0.10
-0.20
-0.30
2
4-Ethylcatechol
-0.07
-0.17
-0.24
3
4-Methylcatechol
-0.07
-0.15
-0.22
4
3,4-Dihydroxybenzilamine
-0.03
-0.11
-0.14
5
Hydrocaffeic acid
-0.03
-0.07
-0.10
6
Catechol
0.00
0.00
0.00
7
Norepinephrine
0.11
0.09
0.20
8
Caffeic acid
0.14
0.09
0.23
9
Dopamine
0.23
0.17
0.40
10
4-Chlorocatechol
0.37
0.23
0.60
11
Epinephrine
0.36
0.30
0.66
12
3,4-Dihydroxybenzaldehyde
0.35
0.42
0.77
13
3,4-Dihydroxybenzoic acid
0.37
0.45
0.82
14
3,4-Dihydroxybenzonitrile
0.56
0.66
1.22
15
4-Nitrocatechol
0.71
0.78
1.49
137 138
The pseudo-first-order rate constant (kobs) was determined for each assayed system (Table
139
S1 in SI). The oxidation ability of each Fenton-like system driven by a 1,2-DHB was
140
significantly different. The Hammett equation (5) was used to determine whether the
141
substituent on 1,2-DHB had a direct influence on the observed changes in reactivity of the
142
system, where kobs is the rate constant for X substituent and k°obs is the rate when X=H
143
(catechol). The reaction constant (ρ) is a measure of the sensitivity of the reaction to
144
electronic effects and is independent of the substituent.35 The Hammett parameters (σ) for
145
meta (σm) and para (σp) substituents are defined from this equation. If the substituent is an
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EWG on the aromatic ring, σ is greater than 0. If the substituent is an EDG, σ is lower than
147
0. The absolute values of σ indicate the relative capacity of the substituent to withdraw or
148
donate electron density to the aromatic ring.
149
=
(5)
150
Considering that 1,2-DHBs have two hydroxyl groups and one substituent, the effect of
151
this substituent was evaluated by Σσ, which includes the effect in the meta (σm) and para
152
(σp) position.
153
Figure 1 shows the dependence of log (kobs/k°obs) on the Hammett constant (∑σ), and a
154
nonlinear Hammett relationship with a concave upward deviation was observed. According
155
to the literature,36, 37 this type of deviation indicates that the mechanism of the oxidation of
156
MO in a Fenton-like system changes depending on whether the substituent on 1,2-DHB is
157
an EWG or EDG. A possible explanation for the rate processes is a dual reaction
158
mechanism, with the overall rate constant kobs being given by the sum of two rate constants
159
kl and k2.After adjusting these results to equation (6), described by Exner,37 these kinetics
160
constants are 0.1440 and 0.9998, respectively.
161
= log 10#$ % + & 10#' % (ref. 37) (6)
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0.35
log(kobs/k°obs)
0.30 0.25 0.20
14
1 2 3 10
0.15
4
11
0.10 0.05
15
7
5
8
13 12
9
Equation data
Experimental data 6 0.00 -0.40 -0.20 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60
Σσ 162 163
Figure 1.Hammett plot for MO oxidation (kobs) in Fenton-like systems driven by different
164
1,2-DHBs.
165
Two values for ρ were determined from the plot in Figure 1. For the Fenton-like systems
166
driven by 1,2-DHBs with EWGs, ρ=0.2145, and for the Fenton-like systems driven by 1,2-
167
DHBs with EDGs, ρ=-2.8076.
168
The magnitude of ρ indicates that the mechanism of the oxidation of MO in Fenton-like
169
systems driven by 1,2-DHBs with EDGs is most affected by the change in the substituent
170
and that the limiting step is probably highly dependent on the ability of the hydroxyl groups
171
to donate electron density. Conversely, the mechanism of the oxidation of MO in Fenton-
172
like systems driven by 1,2-DHBs with EWGs is relatively less influenced by the
173
substituent. The positive value for ρ in these systems indicates that the limiting step in the
174
mechanism includes an increase in the electron density of the transition state or
175
intermediate.38
176
Hydroxyl Radical Production. Several reports have emphasized the importance of HO•
177
in the oxidizing ability of Fenton systems. For the Fenton-like system driven by 1,2-DHBs,
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HO• production was determined from EPR measurements. The decay kinetics of each
179
studied system was fit to a pseudo-first-order equation, obtaining values for the pseudo-
180
first-order constant (kp) and initial signal (I0) of the DMPO-OH adduct (Table S2 in SI).
181
The studied systems showed different abilities to produce HO• (Figure 2).
A
0.0000
B
-0.0005
1.20 1.10
-0.0010
1.00 0.90
-0.0020 -0.0025 -0.0030
Io
kp (s-1)
-0.0015
0.80 0.70
-0.0035
0.60
-0.0040
0.50
-0.0045
0.40
182 183
Figure2. Hydroxyl radical production by Fenton-like systems driven by different 1,2-
184
DHBs. A) Pseudo-first-order constant (kp) and B) initial signal (I0) determined from decay
185
kinetics.
186
The kinetics parameter I0 is related to the Hammett constant in a similar manner to that
187
observed for MO oxidation (Figure 3, A). According Contreras et al.,32 this parameter is
188
proportional to the initial amount of HO•. In this way, I0 linearly increases in systems
189
driven by 1,2-DHBs with EWGs and linearly decreases in systems driven by 1,2-DHBs
190
with EDGs, observing a minimum in I0 when the Fenton-like system is driven by catechol.
191
A linear relationship was observed between I0 and kobs from MO oxidation (Figure 3, B;
192
r=0.9842). Therefore, although the mechanism of the Fenton reaction differs based on the
193
1,2-DHBsubstituent, the HO• is the main oxidizing species responsible for MO oxidation.
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A
1.30
B
1.20
Io
0.50 0.40 0.30 -0.50
194
kobs (x10-3 s-1)
3
0.90
0.60
15
14
1
1.00
0.70
14
8.00
1.10
0.80
9.00
15
11
2 4
7 5
-0.25
0.00
13
8
6
12
10
0.50
0.75
1.00
1.25
1.50
1.75
1
2 10
6.00
13 11
8
5
3 12
4 9
5.00
7 6
4.00
9
0.25
7.00
3.00 0.30
0.40
0.50
0.60
Σσ
0.70
0.80
0.90
1.00
1.10
1.20
1.30
Io
195
Figure 3. Relationship between the A) initial signal of HO• production (I0) and Hammett
196
constant and the B) pseudo-first-order rate constant for MO oxidation (kobs) and I0.
197
Fe(III) Reduction. To understand the deviations in the obtained Hammett equation, the
198
ability of each 1,2-DHB to reduce Fe(III) was studied. Fe(II) production from Fe(III)
199
reduction mediated by 1,2-DHB has been considered essential to the increased oxidizing
200
ability of Fenton-like systems driven by 1,2-DHBs. The reduction rate constants (kred) were
201
obtained from the kinetics profiles of Fe(III) reduction (Table S2 in SI). A quasi-linear
202
relation was obtained between log(kred/k°red), where kred is the rate constant of Fe(III)
203
reduction mediated by different 1,2-DHBs and k°red is the rate constant of Fe(III) reduction
204
mediated by catechol (unsubstituted), and the Σσ values of the substituents on1,2-DHB
205
(Figure 4, A). This trend suggests an increase in Fe(III) reduction by 1,2-DHBs with EDGs
206
and a decrease with 1,2-DHBs with EWGs. The ρ constant for this reduction reaction is -
207
0.6701 (r=0.9839), which indicates a loss of electron density in the aromatic ring during the
208
limiting step of the reaction, according to Exner.37 The redox potential of 1,2-DHB (Table
209
S3 in SI) was significantly dependent on the type of substituent on 1,2-DHB (Figure 4, B).
210
1,2-DHB is easier to oxidize when the substituent has a more negative σ value. Overall,
211
these results suggest that an EDG on 1,2-DHB increases the electron density over the
212
hydroxyl group of the catechol portion, promoting internal electron transfer in the complex
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[Fe(1,2-DHB)]+, which results in the reduction of iron in the coordination sphere. This
214
result agrees with other reports,39, 40 wherein E° is strongly related to the ability of another
215
DHB molecule to reduce Fe(III).
0.20 0.00
log(kred/kored)
B
0.40 1
4 23
5
-0.20
7
8
6
0.70 0.65 15
0.60 9
E° (volt)
A
10 11
-0.40
13 12
-0.60
12
0.55
13
0.50 0.45
6 2
0.40
-0.80 14
-1.00 -0.4 -0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
3 1
0.35 15
-1.20
14
1.4
1.6
0.30 -0.4
-0.2
0.1
0.4
0.6
0.9
1.1
1.4
1.6
Σσ
Σσ
216 217
Figure 4. A) Hammett plot of Fe(III) reduction (kred) by different 1,2-DHBs. B)
218
Relationship between the Hammett constants of different 1,2-DHBs with the standard redox
219
potential (E°).
220
Proposed pathways for HO• production. According to our results, more than one
221
pathway can produce HO• in Fenton-like systems driven by 1,2-DHBs. Although several
222
publications indicate the reduction of Fe(III) as the main mechanism by which 1,2-DHBs
223
promote the Fenton reaction, it is remarkable that the relationship obtained between ∑σ and
224
MO oxidation is different than the relationship between ∑σ and the reduction of Fe(III)
225
(kred). While the first relationship follows a concave upward deviation (Figure 1, B), the
226
second has a linear relationship with a negative slope (Figure 4, A). Despite this
227
disagreement, the MO degradation is closely related to the amount of HO• produced in each
228
system. Both results indicate that only Fenton-like systems driven by 1,2-DHBs with EDGs
229
depend on the ability of 1,2-DHB to reduce Fe(III) and produce HO•. In addition, a
230
significant difference was observed between the stability of the monocomplex when the
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231
substituent was EDG or EWG (Figure S5 in SI). After 1 min, the spectrophotometric signal
232
of the monocomplex formed from 1,2-DHBs with EDGs decreased by 70.2 % (Figure 5,
233
A), where as the monocomplex formed from1,2-DHBs with EWGs did not significantly
234
change (Figure 5, B). This higher stability of the monocomplex with EWGs will allow the
235
reaction of the monocomplex with H2O2 and the subsequent production of HO•. A
B
0.35
0.30
0.30
0.25 0.20 0.15
0.25 0.20 0.15
0.10
0.10
0.05
0.05
0.00
0.00 320
236
0.40
0.35
Absorbance
Absorbance
0.40
420
520
620
720
820
920
1020
1120
320
420
520
Wavelength (nm)
620
720
820
920
1020
1120
Wavelength (nm)
237
Figure 5. Absorption spectra for solutions with Fe(III) (1x10-4 mol·L−1) and 1,2-DHB
238
(1x10-2 mol·L−1) at the initial time (t=0 s, continuous lines) and after 60 s (dotted lines): A)
239
4-tert-butylcatechol (σ = -0.30) and B) 3,4-dihydroxybenzonitrile (σ = 1.49).
240
In summary, the monocomplex stability change depending of the substituent on the 1,2-
241
DHB. This change in the reactivity affect the ability of the system to reduce Fe(III) but not
242
their ability to increase the HO• production.
243
If the tautomeric valence equilibrium is consider the substituent in the 1,2-DHB could be
244
displacing this equilibrium Fe(III)-catecholate/Fe(II)-semiquinone. In this way the EDG,
245
displaced the equilibrium from Fe(III)-catecholate to Fe(II)-semiquinone (Scheme 2, A).
246
Whereby the EDG on the 1,2-DHB, promote the internal electron transference with the
247
consequent release of Fe(II). Otherwise, the systems of 1,2-DHB with EWG shows a low
248
amount of free Fe(II) since the iron should remains inside of the monocomplex. This is
249
because the tautomeric valence equilibrium is displaced from Fe(II)-semiquinone to Fe(III)-
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catecholate (Scheme 2, B). Thus it can be concluded that the main iron species available to
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react with H2O2 are different in the studied Fenton systems, depending on the kind of 1,2-
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DHB. In Fenton systems driven by 1,2-DHB with EDGs, the H2O2 reacts with free Fe(II)
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by a conventional Fenton reaction (Scheme 2, A). Otherwise, in Fenton systems driven by
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1,2-DHB with EWG the H2O2 react mainly with the iron inside the monocomplex which
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has higher stability because the EWG on the 1,2-DHB.
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The formation of Fe(III) peroxocomplexes have been described in literature.16,
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Scheme 2, B is postulated a possible pathway to produce HO• from iron-peroxocomplexes.
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When the monocomplex of Fe(III) is formed with a 1,2-DHB with EWG the H2O2 reacts
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mainly with Fe(III)-catecholate monocomplex, but also with a few portion of Fe(II)-
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semiquinone monocomplex (Scheme 2, B). The reactivity of the peroxocomplexes of Fe(II)
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is expected to be higher than peroxocomplexes with Fe(III) whereby the H2O2 react faster
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with Fe(II) producing HO• and Fe(III). In this way the Fe(II)-semiquinone is consumed and
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the tautomeric valence equilibrium is displaced. If this pathway is considered, the electron
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is transferred from the 1,2-DHB to H2O2 through the iron.
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Scheme 2. Proposed pathways for Fenton-like systems driven by 1,2-DHB with A)
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electron-donating group (EDG) and B) with electron-withdrawing group (EWG).
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ASSOCIATED CONTENT
269
Supporting Information
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The structure and absorption spectrum of MO, structures and E° of 1,2-DHBs employed in
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this study, absorption spectra of complexes formed at pH 3.4 after 1 minute of mixing
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Fe(III) with 1,2-DHB and kinetic data obtained from MO oxidation and HO• production.
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AUTHOR INFORMATION
274
Corresponding Author
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David Contreras, phone: +56412204601, email address:
[email protected]*
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Notes: The authors declare no competing financial interest.
277 278
ACKNOWLEDGMENT
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The
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(grant 1160100), FONDEQUIP (grant EQM140075), FONDAP Solar Energy Research
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Center, SERC-Chile (grant 15110019), CONICYT (Ph.D. grant 21120966), REDOC-
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UDEC and UDT-CCTE fellowship (grant PFT-072).
financial
support
for
this
work
was
provided
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FONDECYT
Environmental Science & Technology
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