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Supporting Information
Kinetics of the reaction between hydrogen peroxide and aqueous iodine:
Implications for technical and natural aquatic systems
Jaedon Shin1,2, Yunho Lee2, Urs von Gunten1,3,4*
1School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique
Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland
2School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and
Technology (GIST), Gwangju 61005, Republic of Korea
3Eawag, Swiss Federal Institute of Aquatic Science and Technology, Ueberlandstrasse 133, CH-
8600 Duebendorf, Switzerland
4Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, 8092 Zurich, Switzerland
*Corresponding author: Urs von Gunten. Telephone: 41-58-765-5270. Fax: 41-58-765-5802. Email:
Submitted to Water Research
This SI includes 3 Text, 4 Tables, and 18 figures as supplementary materials and data.
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SI-Text-1. Standards and reagents
The following chemicals used were of the highest purity available from Sigma or Merck: 2,2 -
azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) (11557, Sigma),
potassium iodide (1.05044, Merck), hydrogen peroxide solution (31642, Sigma), sodium
hypochlorite solution (425044, Sigma), and silver nitrate (1.01512, Merck). The following chemicals
were commercially available and used as pH buffers, acids, bases, and solvents: acetic acid (1.00063,
Merck), sodium dihydrogen phosphate (71496, Sigma), disodium hydrogen phosphate (S9763,
Sigma), sodium tetraborate (221732, Sigma), sulfuric acid (1.12080, Merck), sodium hydroxide
(1.06498, Merck), and tripotassium phosphate (P5629, Sigma).
SI-Text-2. Conditions for the kinetic simulations
In this study, the role of H2O2 in water treatment systems (i.e., UV/H2O2, O3/H2O2, PAA, and
Fe(VI)) and sea water was evaluated by kinetic simulations using Kintecus (Ianni, 2017). All the
reactions and rate constants used during the simulations are summarized in Tables S3 and S4.
SI-Text-3. Kinetic simulations to evaluate the effect of the HOI and H2O2 steady-state
concentrations on the O3 deposition on the seawater surface
The influence of the HOI concentration on the O3 deposition to the sea surface in presence of Br-
and H2O2 was assessed. Steady-state concentrations of each compound were assumed as follows:
[O3]ss = 1 nM, [H2O2]ss = 100 nM, [Br-]ss = 500 µM, and various concentrations of [HOI]ss = 25, 50,
100, 200, and 500 nM. HOI showed the same influence as H2O2 in terms of the O3 consumption.
Figure S17b (SI) shows that the resulting steady-state concentration of I- ([I-]ss) and the total O3
consumptions over 1 year depend on the [HOI]ss. According to the kinetic modeling results, the [I-]ss
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increased linearly with increasing HOI concentrations (25 – 500 nM). As a consequence, the total
yearly O3 consumption increased proportionally (6.6 – 83.2 mM per year).
In a second modeling approach, the HOI steady-state concentration was fixed at 100 nM and the
H2O2 concentration was varied from 0 – 500 nM (Figure S18, SI). The results of this approach are
discussed in the main manuscript.
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SI-Tables
Table S1. Measured first-order rate constants (kobs), and derived second-order rate constants (kapp)
(based on excess H2O2 concentrations) as a function of the pH and the total concentration of HOI and
H2O2
pH [HOI]tot, µM
[H2O2]tot, µM Buffer kobs, s-1 kapp, M-1s-1
4.0 1 200 5mM phosphate+ 6 mM acetate
(6.80.2) × 10-3 (3.40.1) × 101
4.1 1 200 5mM phosphate+ 6 mM acetate
7.4 × 10-3 3.7 × 101
5.0 1 100 5mM phosphate + 3 mM acetate
7.6 × 10-3 7.6 × 101
5.0 2 100 3 mM acetate 9.1 × 10-3 9.1 × 101
6.0 1 20 5 mM phosphate (1.90.1) × 10-2 (9.40.6) × 102
6.2 2 20 5 mM phosphate 2.6 × 10-2 1.3 × 103
7.14 3 4′000 10 mM phosphate 3.6 × 10 8.9 × 103
7.14 3 8′000 10 mM phosphate 7.5 × 10 9.4 × 103
7.14 3 16′000 10 mM phosphate 1.8 × 102 1.1 × 104
8 3 100 10 mM phosphate 5.9 5.9 × 104
8 3 200 10 mM phosphate 1.3 × 101 6.3 × 104
8 3 400 10 mM phosphate 2.6 × 101 6.6 × 104
8 3 800 10 mM phosphate 5.0 × 101 6.3 × 104
9 3 12 5 mM phosphate+ 5 mM borate
4.3 3.6 × 105
9 3 20 5 mM phosphate+ 5 mM borate
7.3 3.6 × 105
9 3 40 5 mM phosphate+ 5 mM borate
1.5 × 101 3.8 × 105
9 3 80 5 mM phosphate+ 5 mM borate
3.0 × 101 3.8 × 105
9.24 3 12 10 mM borate 6.9 5.7 × 105
10.28 3 12 5 mM phosphate+ 0.1 mM NaOH
6.5 × 101 5.4 × 106
11.1 3 12 5 mM phosphate+ 1 mM NaOH
2.0 × 102 1.7 × 107
11.84 3 12 5 mM phosphate+ 10 mM NaOH
5.2 × 102 4.3 × 107
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Table S2. Apparent second order rate constants for the reactions of HOI with H2O2 in the presence of
different buffer types and concentrations. Experimental conditions: [HOI]0 = 3.0 μM (2.5 μM at pH
4.7) , [H2O2]0 = 200 μM at pH 4.7 (ABTS method), 4 mM at pH 7.3, and 40 μM at pH 9.0,
T=223℃.
pH Buffer kapp, M-1s-1
4.7 1 mM acetate + 2 mM phosphate 5.2 × 101
4.7 2.5 mM acetate + 2 mM phosphate 6.9 × 101
4.7 10 mM acetate + 2 mM phosphate 1.0 × 102
4.7 25 mM acetate + 2 mM phosphate 1.4 × 102
7.3 1.25 mM phosphate 7.6×103
7.3 5 mM phosphate 1.2×104
7.3 12.5 mM phosphate 2.3×104
7.3 25 mM phosphate 3.3×104
9.0 No phosphate, 5 mM borate 3.6×105
9.0 2 mM phosphate, 5 mM borate 3.7×105
9.0 10 mM phosphate, 5 mM borate 4.2×105
9.0 50 mM phosphate, 5 mM borate 5.6×105
9.0 0.5 mM borate 2.5×105
9.0 1.25 mM borate 2.6×105
9.0 5 mM borate 3.2×105
9.0 12.5 mM borate 4.2×105
9.0 25 mM borate 5.4×105
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Table S3. Major reactions for the kinetic simulations for the reactions of HOI with H2O2 in the presence of phenol
No. Reactionsa kspecies-specific, kapp (pH 7.0) kapp (pH 9.0) Reference
1 HOI + HO2- I- + O2 + H2O 3.1×108 M-1 s-1 4.9×103 M-1 s-1 4.8×105 M-1 s-1 This study
2 HOI + PhOH I-PhOH 1.0×102 M-1 s-1 1.0×102 M-1 s-1 8.5×10 M-1 s-1 (Bichsel and von Gunten, 2000a)
3 HOI + PhO- I-PhOH 2.0×106 M-1 s-1 2.5×103 M-1 s-1 2.2×105 M-1 s-1 (Bichsel and von Gunten, 2000a)
Acid-base equilibrium Ka, M pKa
HOI OI- + H+ 4.0×10-11 10.4 (Bichsel and von Gunten, 2000b)
H2O2 HO2- + H+ 2.5×10-12 11.6 (Staehelin and Hoigné, 1982)
PhOH PhO- + H+ 1.0×10-10 9.99 (Lide 2006)aThe reactions are expressed considering the major species of HOI and H2O2 controlling the overall rate of each reaction in the pH range of 7.0 – 9.0
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Table S4. Major reactions for the kinetic simulations in water treatment and natural systems
No. Reactionsa kspecies-specific, kapp (pH 7.0) kapp (pH 8.0) Reference
1 HOI + HO2- I- + O2 + H2O + P1 3.1×108 M-1 s-1 4.9×103 M-1 s-1 4.9×104 M-1 s-1 This study
2 HOBr + HO2- Br- + O2 + H2O + P2 7.6×108 M-1 s-1 1.9×104 M-1 s-1 1.6×105 M-1 s-1 (von Gunten and Oliveras, 1997)
3 O3 + I- OI- + O2 + P3 2.0×109 M-1 s-1 2.0×109 M-1 s-1 2.0×109 M-1 s-1 (Bichsel and von Gunten, 1999)
4 O3 + HOI IO2- + O2 + H+ + P4 3.6×104 M-1 s-1 3.6×104 M-1 s-1 3.6×104 M-1 s-1 (Bichsel and von Gunten, 1999)
5 O3 + OI- IO2- + O2 + P5 1.6×106 M-1 s-1 6.4×102 M-1 s-1 6.3×103 M-1 s-1 (Bichsel and von Gunten, 1999)
6 O3 + IO2- IO3
- + O2 + P6 1.6×108 M-1 s-1 1.6×108 M-1 s-1 1.6×108 M-1 s-1 (Bichsel and von Gunten, 1999)
7 O3 + Br- OBr- + O2 + P7 1.6×102 M-1 s-1 1.6×102 M-1 s-1 1.6×102 M-1 s-1 (Haag and Hoigné, 1983)
8 PAAH + I- HOI 4.2×102 M-1 s-1 4.0×102 M-1 s-1 2.6×102 M-1 s-1 (Awad et al., 2003)
9 PAAH + Br- HOBr 2.4×10-1 M-1 s-1 2.3×10-1 M-1 s-1 1.5×10-1 M-1 s-1 (Shah et al., 2015)
10 I- + HFeVIO4- HOI + Fe(III) 4.5×104 M-1 s-1 2.8×104 M-1 s-1 6.2×103 M-1 s-1 (Shin et al., 2018)
11 HOI/OI- + HFeVIO4- IO2
- + Fe(III) 2.5×105 M-1 s-1 1.5×105 M-1 s-1 3.4×104 M-1 s-1 (Shin et al., 2018)
12 IO2- + HFeVIO4
- IO3- + Fe(III) 7.5×106 M-1 s-1 4.6×106 M-1 s-1 1.0×106 M-1 s-1 (Shin et al., 2018)
13 2Fe(IV) 2Fe(III) + 1/3H2O2 + 1/3O2b 1.0×106 M-1 s-1 1.0×106 M-1 s-1 (Shin et al., 2018)
Acid-base equilibrium Ka, M pKa
HOI OI- + H+ 4.0×10-11 10.4 (Bichsel and von Gunten, 2000)
H2O2 HO2- + H+ 2.5×10-12 11.6 (Staehelin and Hoigné, 1982)
HFeVIO4- FeVIO4
2- + H+ 6.3×10-8 7.2 (Sharma et al., 2001)
PAAH PAA- + H+ 6.3×10-9 8.2 (Koubek et al., 1963)
HOBr OBr- + H+ 1.6×10-9 8.8 (Haag and Hoigné, 1983)aThe reactions are expressed considering the major species of HOI, H2O2, Fe(VI), peracetic acid, and HOBr controlling the overall rate of each reaction in the neutral pH ranges, bThe reaction is balanced only for electron equivalents
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SI-Figures
Figure S1. UV spectrum and molar absorption coefficient (ɛ) of I- (50 µM) in the pH range of 5.0 –
7.0 in the presence of phosphate (5 mM). pH was adjusted by adding NaOH.
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Figure S2. Stopped-flow experiments: Formation of I- from the reaction of HOI with H2O2 at pH 7.1,
8.0, and 9.0 monitored at 226 nm. The symbols represent the experimental data and the blue lines
represent the fitting by the software Kinetic Studio 2.x.
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Figure S3. Stopped-flow experiments: Linear plot of the logarithmic relative concentration of
{([HOI]0-[I-])/[HOI]0} as a function of the reaction time during the reaction of 3 M of HOI with
excess H2O2 (see graph) at pH 9 (data are from Figure 1 in the main text).
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Figure S4. Plot of the pseudo first order rate constants (kobs) for varying H2O2 concentrations during
the reaction of HOI with H2O2 at (a) pH 8.0 and (b) pH 9.0. The inset shows the log(kobs) versus
log([H2O2]0) plot as a confirmation of a reaction order of ‘1’.
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Figure S5. Stopped-flow experiments: Logarithmic relative residual concentrations of {([HOI]0-
[I-])/[HOI]0} as a function of time during the reaction of 3 M of HOI with excess H2O2 (1, 2, and 4
mM) in the absence of Ag+ at pH 6.
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Figure S6. Speciation of I2/HOI/OI- as a function of the pH and I- concentration in the presence of (a)
0.1 µM of I- (12.7 µg /L) and (b) 2 µM of I- (254 µg /L) in the pH range of 3 – 13.
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Figure S7. Linear plots of the logarithmic relative residual concentration of HOI as a function of time
during reaction of 1 or 2 M of HOI with excess of H2O2 (200, 100, 20 µM for pH 4, 5, and 6,
respectively) in the presence of 100 µM Ag+ for pHs (a) 4.0 (5 mM phosphate (PBS) + 6 mM acetate
(ACE) buffer), (b) 4.0 (5 mM PBS + 6 mM ACE), (c) 5.0 (5 mM PBS + 3 mM ACE), (d) 5.0 (3 mM
ACE), (e) pH 6.0 (5 mM PBS), and (f) pH 6.0 (5 mM PBS) (data are from Figure 1 in the main text).
The slopes of the linear plots are proportional to the pseudo-first order rate constants (kobs) and the
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apparent second-order rate constants can be determined by dividing kobs by the corresponding initial
H2O2 concentrations (i.e., 20, 100, or 200 M).
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Figure S8. Stopped-flow experiments: Formation of I- from the reaction of HOI (3 µM) with H2O2
(40 µM at pH 9.0 and 4 mM at pH 7.3) monitored at 226 nm: (a) pH 7.3 and (b) 9.0 in the presence
of different concentrations of phosphate. The symbols represent the experimental data and the blue
lines represent the fitting by the software Kinetic Studio 2.x,TgK Scientific
Figure S9. Stopped-flow experiments: Formation of I- from the reaction of HOI (3 µM) with H2O2
(40 µM) at pH 9.0 in the presence of different concentrations of borate (0.5, 5, and 25 mM)
monitored at 226 nm. The symbols represent the experimental data and the blue line represents the
fitting by the software Kinetic Studio 2.x, TgK Scientific.
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Figure S10. Batch experiment with the ABTS method: Linear plots of the logarithm of the relative
residual concentrations of HOI as a function of time during the reaction of 2.5 M of HOI with 100
M of H2O2 at pH 4.7 in the presence of varying concentrations of acetate (ACE) and 100 µM of
Ag+.
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Figure S11. Effect of buffer concentration on the apparent second order rate constants (kapp) for the
reaction of HOI with H2O2: (a) phosphate at pH 7.3, (b) phosphate at pH 9.0 (in the presence of 5
mM borate), (c) borate at pH 9.0, and (d) acetate at pH 4.7. The kapp values are from Table S2 and
Figures S8 – S10.
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Figure S12. Effect of the buffer concentration on the apparent second order rate constants (kapp) for
the reaction of HOI with H2O2: acetate (0 – 10 mM) at pH 4.7 (Δ), phosphate (0 – 10 mM) at pH 7.3
(Δ), and borate (0 – 10 mM) at pH 9.0 (Δ). kapp values are from Figures 1 and S11 and Tables S1 and
S2. kapp at zero buffer concentration (pHs 4.7, 7.3, and 9.0) and at 10 mM phosphate (pH 7.3) were
estimated by Figure S11.
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Figure S13. Arrhenius plot for the reaction of HOI with H2O2 in the temperature range of 10.0 – 23.2
℃ (10, 15.3, 15.8, 16.6, 18.9, 20.1, 20.7, 21.1, 21.3, 21.8, 21.9, 23.2 ℃) at pH 9.0 (5 mM phosphate
+ 5 mM borate buffer).
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Figure S14. Kinetic modeling of an iodide-containing water during the O3/H2O2 process: Calculated
relative contributions of the three reaction pathways, i.e., catalytic oxidation of I -, reaction with H2O2
(OH radical formation), and oxidation of HOI to IO3- to the consumption of O3 during treatment of 1
μM I- with 1.0 mg/L O3 (20.8 μM) in the presence of various concentrations (0 –10 mg/L) of H2O2 (0
– 294 μM). The model calculations are based on reactions 1, 3, 4, 5, and 6 in Table S4.
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Figure S15. Kinetic modeling of the oxidation of an iodide-containing ocean-type water by peracetic
acid in presence of H2O2. Evolution of HOI, HOBr, H2O2, and PAA during treatment of 0.5 µM of I-
and 460 µM of Br- by 2.15 mM PAA in the presence of 0.65 mM H2O2 at pH 8.0. The model
calculations are based on reactions 1, 2, 8, and 9 in Table S4.
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Figure S16. Kinetic modeling of a treatment of an iodide-containing water by ferrate(VI) in presence
of H2O2: Evolution of HOI, IO3-, H2O2, and Fe(VI) during treatment of 1 µM I- by 17.9 µM Fe(VI) (1
mgFe/L) in the presence of 5.4 µM H2O2 (0.18 mg/L) at (a) pH 7.0, (b) pH 8.0, and (c) pH 9.0. The
model calculations are based on reactions 1, 10, 11, 12, and 13 in Table S4.
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Figure S17. Role of the HOI concentration on the ozone deposition: Kinetic modeling of the O3
consumption in a sea water in the presence of HOI, Br-, O3, and H2O2. (a) Calculated relative
contributions to the O3 consumption, by the following reactions: Oxidation of I-, oxidation of Br-, and
oxidation of HOI to IO3- (Table S4). (b) The total O3 consumption over one year and the resulting
steady-state concentrations of I-. Assumed concentrations for each compound: [O3]ss = 1 nM, [H2O2]ss
= 100 nM, [Br-]ss = 500 µM, and various concentrations of [HOI]ss = 25, 50, 100, 250, 500 nM. The
model calculations are based on reactions 1 – 7 in Table S4.
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Figure S18. Role of the hydrogen peroxide concentration on the ozone deposition: Kinetic modeling
of the O3 consumption in a sea water in the presence of HOI, Br -, O3, and H2O2. (a) Calculated
relative contributions to the O3 consumption, by the following reactions: Oxidation of I-, oxidation of
Br-, and oxidation of HOI to IO3- (Table S4). (b) The total O3 consumption over one year and the
resulting steady-state concentrations of I-. Assumed concentrations for each compound: [O3]ss = 1
nM, [HOI]ss = 100 nM, [Br-]ss = 500 µM, and various concentrations of [H2O2]ss = 0, 10, 25, 100, 250,
500 nM. The model calculations are based on reactions 1 – 7 in Table S4.
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