1 Application of O 2 Activation toward Organic Pollutant Degradation Derek F. Laine and I. Frank Cheng University of Idaho Chemistry Department Moscow, ID 83843-2343 [email protected][email protected]208-885-6387 The ZEA Organic Pollutant Degradation System
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1 Application of O 2 Activation toward Organic Pollutant Degradation Derek F. Laine and I. Frank Cheng University of Idaho Chemistry Department Moscow,
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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
3
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)
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-
8
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.