Application of O2 Activation toward Organic Pollutant Degradation

1
Application of O2 Activation toward Organic
Pollutant Degradation
The ZEA Organic Pollutant Degradation System

• Derek F. Laine and I. Frank Cheng
• University of Idaho
• Chemistry Department
• Moscow, ID 83843-2343
• lain3267_at_uidaho.edu
• ifcheng_at_uidaho.edu
• 208-885-6387

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ZEA Pollutant Degradation System

• Zero valent iron (ZVI)
• EDTA (Ethylenediaminetetraacetic acid)
• Air

Open round bottom flask
Aqueous Solution of 4-chlorophenol
Stir bar and ZVI particles
Stir Plate
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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

• Products include low molecular weight acids and
  CO2.

Noradoun, Christina, et al. Ind. Eng. Chem. Res.
2003, 42, 5024-5030.
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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.

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Electrochemical Homogeneous Degradation System -
Cell Design

• Three electrode system
• Working electrode
• (RVC)
• Auxiliary electrode
• Graphite rod
• A salt bridge keeps the auxiliary electrode
  separated from the bulk solution.
• 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.

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Experimental Conditions

• FeIII(NO3)3 and Na2H2EDTA were added in a 11
  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.

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HPLC Results
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Results
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Comparison of FeII/IIIEDTA degradation and pH
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Detection of Intermediate Oxidizing Agents (H2O2
and HO)
Electrochemical system
ZEA system
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.
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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
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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
  1221 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.
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Formation of HO

• Before electrolysis, the same signal is obtained
  from a simple solution of FeIIIEDTA, KCl, and O2

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Formation of HO

• The two processes can be distinguished by adding
  methanol as a scavenger.

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Formation of HO
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Formation of HO
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
A)
Reaction dominates after electrolysis. K 109
M-1 S-1
B)
Reaction dominates before electrolysis
Yamazaki, Isao Piette, Lawrence H. J. Biol.
Chem. 1990, 265, 13589-13594
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Formation of HO
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Formation of HO
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Cyclic voltammetry can be used to show the
catalytic mechanism.

• FeIIIEDTA e- ? FeIIEDTA
• FeIIEDTA O2 ? FeIIIEDTA O2-

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Cyclic Voltammetry
5 mV/s
FeIIIEDTA O2
O2 only
FeIIIEDTA only
Niether FeIIIEDTA or O2
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pH Dependency
Zang, V van Eldik, R. Inorg. Chem. 1990, 29,
1705-1711.
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Geometrical Considerations
FeII(EDTA)(H2O)2- H FeII(EDTAH)(H2O)1-

Species Bite angle on water coordinate Bond distance from FeII to OH2
FeIIEDTA 164.0 2.19 Å
FeIIEDTAH 172.1 2.21 Å
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.
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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-0328827
• NIH Grant No. 1 R15 GM062777-01