1
Application of O2 Activation toward Organic Pollutant Degradation
Derek F. Laine and I. Frank ChengUniversity of IdahoChemistry DepartmentMoscow, ID [email protected]@uidaho.edu208-885-6387
The ZEA Organic Pollutant Degradation System
2
ZEA Pollutant Degradation System
Zero valent iron (ZVI) EDTA
(Ethylenediaminetetraacetic acid)
Air
Stir Plate
Stir bar and ZVI particles
Open round bottom flask
Aqueous Solution of 4-chlorophenol
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The Search For Alternatives to the Bulk Destruction of Organic Pollutants
High temperature use of O2 Incineration
Expensive Dioxins Public reluctance
Low temperature use of O2 ZEA system
Operates at room temperature and pressure Inexpensive Common reagents Long term storage No specialized catalysts Simple Reactor Design Easily transportable Versatile (can be applied to water treatment)
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Destruction of 4-Chlorophenol
y = 1.23E-03e-1.16E+00x
R2 = 9.66E-01
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
0 0.5 1 1.5 2 2.5 3 3.5 4
Time (hours)
Con
cent
ratio
n (M
olar
ity)
Reaction Curve
Expon. (Reaction Curve)
Noradoun, Christina, et al. Ind. Eng. Chem. Res. 2003, 42, 5024-5030.
Products include low molecular weight acids and CO2.
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Pollutants destroyed by the ZEA System Halocarbons
4-chlorophenol Pentachlorophenol
Organophosphorus Compounds (nerve agents) Malathion (vx surrogate) Malaoxon
Organics EDTA Phenol
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Hypothesis-Oxygen Activation
Oxygen has a triplet ground state, while organic compounds have a singlet ground state.
How to overcome this kinetic barrier. Add energy in the form of heat. Addition of electrons (activation)
The ZEA system works by Reducing O2 to form reactive oxygen species
O2.-, H2O2, HO.
http://www.meta-synthesis.com/webbook/39_diatomics/diatomics.html
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Hypothesis-Site for O2 Activation (I) Heterogeneous
activation at the ZVI surface.
(II) Homogeneous activation by FeIIEDTA.
I Fe(0)
O2FeIIIEDTA + HO∙ + HO-
H+ H2O2
Fe2+ + EDTA → FeIIEDTA
II Fe(0)Fe2+ + EDTA FeIIEDTA
FeIIIEDTA O2
H+
H2O2
FeIIIEDTAHO∙ + HO-
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Electrochemical Homogeneous Degradation System - Cell Design
Three electrode system:
1. Working electrode• (RVC)
2. Auxiliary electrode• Graphite rod• A salt bridge keeps
the auxiliary electrode separated from the bulk solution.
3. Reference electrode• Ag/AgCl
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Electrochemical Pollutant Degradation System
• FeIIEDTA can reduce oxygen to form the superoxide ion (O2·- ), as well as other reactive oxygen species.
• Degradation of EDTA is measured in this system
• HPLC is used to measure the degradation of EDTA.
FeIIIEDTA
FeIIEDTA
2O2
2O2°- + 2H+ → H2O2 + O2
FeIIIEDTA + OH- + OH▪
+
FeIIEDTA
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Experimental Conditions
• FeIII(NO3)3 and Na2H2EDTA were added in a 1:1 ratio to make 80 ml of a 0.5 mM FeIIIEDTA solution.
• -120 mV potential is applied to the working electrode.
• A high stir rate and large surface area working electrode is used to facilitate fast and efficient electrolysis.
• KCl is used as the supporting electrolyte.
• Oxygen is bubbled through the system.
FeIIIEDTA
FeIIEDTA
2O2
2O2°- + 2H+ → H2O2 + O2
FeIIIEDTA + OH- + OH▪
+
FeIIEDTA
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HPLC Results
FeEDTA degradationAbsorption detection at 258 nm
-5
0
5
10
15
20
0 1 2 3 4
minutes
mV
t=0 hr
t=1.0 hr
t=2 hr
t=3 hr
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Results
FeIIIEDTA degradation
0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6 8
time (hr)
[Fe
ED
TA
] m
M
W/O2 (-120mV)
W/N2 (-120mV)
W/O2 (+120mV)
FeIIIEDTA
FeIIEDTA
2O2
2O2°- + 2H+ → H2O2 + O2
FeIIIEDTA + OH- + OH▪
+
FeIIEDTA
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Comparison of FeII/IIIEDTA degradation and pH
0
0.1
0.2
0.3
0.4
0.5
0.6
0 1 2 3 4 5 6 7
hours
[FeE
DTA
] mM
012345678910
pH
FeEDTA
pH
FeIIIEDTA
FeIIEDTA
2O2
2O2°- + 2H+ → H2O2 + O2
FeIIIEDTA + OH- + OH▪
+
FeIIEDTA
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Detection of Intermediate Oxidizing Agents (H2O2 and HO·)
Graf, Ernst; Penniston, John T. Method for Determination of Hydrogen Peroxide, with its Application illustrated by Glucose Assay. Clin. Chem. 1980, 26/5, 658-660.
FeIIIEDTA
FeIIEDTA
2O2
2O2°- + 2H+ → H2O2 + O2
FeIIIEDTA + OH- + OH·
+
FeIIEDTA
Electrochemical system ZEA system
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Formation of H2O2
Starch reagents concentrated starch 40 mM HCl 0.077 mM ammonium molybdate 80 mM KI.
Add an aliquot of reaction mixture to starch reagents and analyze with UV-VIS after a 20 minute color formation period.
Any suitable oxidizing agent (such as H2O2) will oxidize the iodide to iodine.
Iodine combines with iodide to form triiodide which will then complex with starch to form a blue color.
H2O2(aq) + 3I-(aq) + 2 H+(aq) → I3-(aq) + 2 H2O(aq)
E. Graf, J.T. Penniston, Clin. Chem. 26/5 (1980) 658-660.
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Formation of H2O2
H2O2 formation
-0.05
0
0.05
0.1
0.15
0.2
0 2 4 6 8
Time (Hrs)
[H2O
2] m
M
O2 bubbled, -120mV, 0.5 mMFeEDTAO2 bubbled, -120mV, no FeEDTA
N2 bubbled, -120mV, 0.5 mMFeEDTAO2 bubbled,+500mV, 0.5 mMFeEDTA
FeIIIEDTA
FeIIEDTA
2O2
2O2°- + 2H+ → H2O2 + O2
FeIIIEDTA + OH- + OH·
+
FeIIEDTA
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Formation of HO·
•Accomplished using the spin trapping abilities of 5,5-dimethylpyrroline-N-oxide (DMPO) and electron spin resonance spectroscopy (ESR).
•The DMPO-HO· adduct has a well characterized 1:2:2:1 quartet.
Das, Kumuda C.; Misra, Hara P. Mol. Cell. Biol. 2004, 262, 127-133.
Yamazaki, Isao; Piette, Lawrence H. J. Am. Chem. Soc. 1991, 113, 7588-7593.
FeIIIEDTA
FeIIEDTA
2O2
2O2°- + 2H+ → H2O2 + O2
FeIIIEDTA + OH- + OH·
+
FeIIEDTA
N+
O
H
H O
N
O
H
OH+ ·
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Formation of HO·
-80000
-60000
-40000
-20000
0
20000
40000
60000
80000
3480 3490 3500 3510 3520 3530 3540 3550
G
Inte
ns
ity
•Before electrolysis, the same signal is obtained from a simple solution of FeIIIEDTA, KCl, and O2
-80000
-60000
-40000
-20000
0
20000
40000
60000
80000
3480 3490 3500 3510 3520 3530 3540 3550
G
Inte
ns
ity
FeIIIEDTA
FeIIEDTA
2O2
2O2°- + 2H+ → H2O2 + O2
FeIIIEDTA + OH- + OH·
+
FeIIEDTA
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Formation of HO·
-80000
-60000
-40000
-20000
0
20000
40000
60000
80000
3480 3490 3500 3510 3520 3530 3540 3550
G
Inte
ns
ity
N+
O
H
Fe(III)
OH
HN
O
H
OH
EDTA
Fe(II)
EDTA+ -80000
-60000
-40000
-20000
0
20000
40000
60000
80000
3480 3490 3500 3510 3520 3530 3540 3550
G
Inte
ns
ity
•The two processes can be distinguished by adding methanol as a scavenger.
N+
O
H
H O
N
O
H
OH+ ·
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Formation of HO··CH3OH H O CH2OH+ ·
N+
O
H
CH2OHN
O
H
CH2OH+ ·-80000
-60000
-40000
-20000
0
20000
40000
60000
80000
3480 3490 3500 3510 3520 3530 3540 3550
G
Inte
ns
ity
T=3 hr, 20% Methanol
T=3 hr, no Methanol
N+
O
H
Fe(III)
EDTA
CH3OHN
O
H
OMe Fe(II)
EDTA+
-80000
-60000
-40000
-20000
0
20000
40000
60000
80000
3480 3490 3500 3510 3520 3530 3540 3550
G
Inte
ns
ity
T=3 hr, no Methanol
T=0 hr, 20% Methanol
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0
20000
40000
60000
80000
100000
120000
140000
0 100 200 300 400 500 600
Seconds
Inte
nsi
ty
A
B
Formation of HO·
A)
B) N+
O
H
Fe(III)
OH
HN
O
H
OH
EDTA
Fe(II)
EDTA+
N+
O
H
H O
N
O
H
OH+ ·
-80000
-60000
-40000
-20000
0
20000
40000
60000
80000
3480 3490 3500 3510 3520 3530 3540 3550
G
Inte
ns
ity
Growth of the quartet when adding the reaction mixture to DMPO after electrolysis.
Growth of the quartet when adding the reaction mixutre to DMPO before electrolysis
Reaction dominates after electrolysis. K = 109 M-1 S-1
Reaction dominates before electrolysis
Yamazaki, Isao; Piette, Lawrence H. J. Biol. Chem. 1990, 265, 13589-13594
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Formation of HO·Intensity of 1:2:2:1 quartet after 3 hrs of
electrolysis and variable amounts of CH3OH scavenger
0
10000
20000
30000
40000
50000
-5 5 15 25 35 45
[Methanol] % v/v
Inte
ns
ity
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Formation of HO·H2O2 Formation
0
0.05
0.1
0.15
0.2
0 1 2 3 4 5 6 7
Time (hr.)
[H2O
2] m
M
Intensity vs electrolysis time
0
10000
20000
30000
40000
50000
60000
0 1 2 3 4 5 6 7
Time (hr)
Inten
sity
FeIIIEDTA
FeIIEDTA
2O2
2O2°- + 2H+ → H2O2 + O2
FeIIIEDTA + OH- + OH·
+
FeIIEDTA
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Cyclic voltammetry can be used to show the catalytic mechanism.
FeIIIEDTA + e- → FeIIEDTA
FeIIEDTA + O2 → FeIIIEDTA + O2·-
FeIIIEDTA
FeIIEDTA
2O2
2O2°- + 2H+ → H2O2 + O2
FeIIIEDTA + OH- + OH·
+
FeIIEDTA
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Cyclic Voltammetry
Oxygen Activation pH=3.0
-0.20
0.20.40.60.8
11.21.41.61.8
-0.5-0.3-0.10.10.3
V
uA
FeIIIEDTA + O2
O2 only
FeIIIEDTA only
Niether FeIIIEDTA or O2
5 mV/s
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pH Dependency
Current vs pH
0.0000
0.2000
0.4000
0.6000
0.8000
1.0000
1.2000
0 2 4 6 8 10 12
pHCu
rrent
(uA)
Zang, V; van Eldik, R. Inorg. Chem. 1990, 29, 1705-1711.
Oxygen Activation pH=3.0
-0.20
0.20.40.60.8
11.21.41.61.8
-0.5-0.3-0.10.10.3
V
uA
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0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 2 4 6 8 10 12pH
Cu
rren
t (u
A)
0.00.10.20.30.40.50.60.70.80.91.01.1
0 2 4 6 8 10 12
pH
Mo
le F
ract
ion
Free Fe(II)
FeIIEDTA(H)
FeIIEDTA
FeIIEDTA(H2)
FeIIEDTA(OH)
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Geometrical Considerations
[FeII(EDTA)(H2O)]2- + H+ = [FeII(EDTAH)(H2O)]1-
Mizuta, T.; Wang, J.; Miyoshi, K. Bull. Chem. Soc. Jpn. 1993, 66, 2547-2551.Mizuta, T.; Wang, J.; Miyoshi, K. Inorg. Chimica Acta. 1993, 230, 119-125.
Species Bite angle on water coordinate
Bond distance from FeII to OH2
FeIIEDTA 164.0° 2.19 Å
FeIIEDTAH 172.1° 2.21 Å
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Summary and Conclusion The ZEA system can destroy organic pollutants non-
selectively. How does the ZEA system destroy pollutants?
The ZEA system has a homogeneous reaction mechanism with activation of oxygen by FeIIEDTA followed by the Fenton reaction.
The ZEA system produces H2O2 as an intermediate. The ZEA system produces HO· which can non-selectively destroy organic
pollutants.
How can the ZEA system be made to work better? Bubble air or oxygen through the system. Optimize for pH = 3 conditions.
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Acknowledgments
Dr. I. Frank Cheng Simon McAllister University of Idaho Dept. of Chemistry ACS Funding
NSF award number BES-0328827NIH Grant No. 1 R15 GM062777-01