1. Destruction of Organic Pollutants Through Zero-Valent Metals Via Reductive and Oxidative Pathways
Department of Chemistry, University of Idaho
Moscow, ID , Tel (208)
Frank Cheng, Assistant Professor of Chemistry
Graduate Students Mark Engelmann Edmund Wong
Tina Noradoun Jose’ Morales
Undergraduates Ryan Hutcheson Kevin Breen
Tim Cantrell John Doyle Layne Pitcher
Matt McLaughlin Ryan Neale Erik Parker
Kristy Henscheid TeriAnn Miles
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2. Redox Processes in Environmental, Analytical, & Biological Chemistries
-I] Destruction of Organic Pollutants by Reductive and Oxidative Pathways
-RTP Reductive Dechlorination of Halocarbons
-RTP Hydrogenation of Aromatics
-Hydrocarbon Skeleton GC/HPLC
-RTP O2 oxidation of Organic Pollutants
-II] Understanding Redox Pathways in the Mechanisms of Dietary Antioxidants
-Flavonoids
-Salicylate
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3. I] Redox Pathways for Pollutant Destruction
The Search for Alternatives for the Bulk Destruction of Organic Pollutants
PCB, DDT, Pentachlorophenol, phenol
Field-based Destruction of Pollutant Through O2 Activation; RTP Mineralization.
Organophosphorous Nerve Agents
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4. PCB History & Background
209 possible congeners
Dielectric fluid, oil-based solvents
Valued for chemical stability and fire resistance
Used as insulating fluids and coolants in electrical equipment and machinery from
150 million pounds of PCBs are dispersed throughout the environment, an additional 290 million pounds are located in landfills and storage in the USA
Toxic Substances Control Act 1978
Analtyical Chemistry of PCBs, 2nd Ed. M.E. Erikson, CRC Press 1997
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5. Present Method of PCB Destruction
Incineration
Problems with Incineration
Dioxin Emission; T > C
Costs
NIMBY
DDT - Pentachloropehnol
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6. Ideal Characteristics for Pollutant Destruction Method
Minimal Costs & Environmental Impact
Abundant Reagents
Spent Reagents & Products Must Have Minimal Environmental Consequences if Released
Mild Reaction Conditions, i.e. aqueous, room temperature and pressure, (RTP)
Field Portability
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7. Outline of Redox Pathways
Reductive:
M(0) + H+ + R-Cl  R-H + M2+ + Cl-
M(0) + 2H+ + -R=R-  -RH-RH- + M2+
Oxidative:
Fe(0) + O2 + 2 H+  Fe2+ + H2O2
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8. Reductive Pathways Strategy: R-Cl + 2H+ + e- ® R-H + Cl-
Possible Reducing Agents:
Electrochemical
Zero-Valent Metals: Fe(0) and Mg(0)
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9. Reductive Dechlorination by Zero-Valent Metals
M(0)  Mn+ + ne- Eanode
R-Cl + H+ + e-  R-H + Cl- Ecathode
Fe(0) + R-Cl + H+  Fe2+ + R-H + Cl- Ecell
Both Fe(0) and Mg(0) are inexpensive
Both Fe2+ and Mg2+ are environmentally benign
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10. Thermodynamics of CCl4 Dechlorination
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11. Kinetics of R-Cl Reduction by Unmodified Zero-Valent Metals
Formation of kinetically stable intermediates
Matheson, LJ; Tratnyek, P.G. Environ. Sci. Technol, 1994, 28,
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12. PCBs are Kinetically Stable in the Presence of Fe(0) or Mg(0)
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13. Catalyzed Reductions of Halocarbons by Pd modified Bimetallic Systems
2M + PdCl62-  2M2+ + 6Cl- + Pd(s)
% Pd (w/w)
Results in complete dechlorination of TCE
Muftikian, Fernando, Korte, Water Research. 1995, 29, 2434.
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14. The role of Pd in hydrodehalogenation of chloro-organics by Pd/Fe
Cheng, Fernando, Korte, Environ Sci &Technol, 1997, 31(4)
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15. Halocarbon Reduction by Pd/Fe
Muftikian, Fernando, Korte, Water Research. 1995, 29, 2434
*Cheng et al, unpublished results
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16. Reductive Dechlorination by Pd/Mg
Zero-valent Metals as Reducing Agents
Fe(s) ® Fe2+ + 2e- E0red = volts
Mg(s) ® Mg2+ + 2e- E0red = volts
Na(s) ® Na+ + e- E0red = volts
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17. Reactivities of Metal Candidates
Mn+ + n OH-  M(OH)n(s)
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18. DDT Dechlorination Reactions
Needle for venting
of H2 gas
Palladization and dechlorination begin spontaneously after addition of H2O.
After 15 minutes, the products are extracted into 1 mL of hexane and analyzed by GC.
Teflon septa
1.0 mL hexane
(extraction only)
1.0 mL water
1.0 mL MeOH
100 mg DDT
0.5g 20 mesh Mg, 5.0 mg
K2PdCl6 (0.3% wt/wt)
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19. Pd/Mg is more Effective Than Pd/Fe
Complete dechlorination occurs within a few minutes
Cheng et al Microchemical Journal, accepted April 2002.
Cheng et al, Journal of Hazardous Materials, B90 (2002),
Cheng et al Chemosphere 2001, 43,
Cheng et al, LC-GC, 1999, 18,
Cheng et al, Microchemical Journal 1999, 60,
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20. Summary of Dechlorination by Pd/Mg
First demonstration of the complete dechlorination of:
PCP
DDT
PCB
Reaction conditions:
STP
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21. Hydrogenation of Phenol
Common component of industrial waste streams.
As high as 1% m/m
Expensive treatment processes, i.e. high T and/or P processes, adsorption
Cyclohexanol/-one less problematic
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22. RTP Hydrogenation of Phenol
5 mL aqueous 5 mM Phenol, 10 minutes
Palladized 1.00 g Mg particles m2
Palladized 0.66 g Fe particles m2
g Mg 20 mesh g 1/8” Pd/alumina
Cheng et al; Industrial and Engineering Chemistry Research, ,
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23. Phenol Decay Rates () 1/8”Pd/alumina with 20 mesh Mg
() Mg/Pd(2.6 ppt)
()1/8”Pd/alumina with 20 mesh Mg 2% (v/v) glacial HAc
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24. RTP Hydrogenation Product Yields
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25. Summary of Reaction Routes
Rapid;  40% C balance
Pd/Mg
Pd/Fe
N.R.
Pd/alumina Mg
 100% C balance
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26. Proposed Pathways
Pd/Mg
Pd/alumina Mg
100%
Low MW volatiles?
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27. Disappearance of phenol (), appearance of cyclohexanone/cyclohexanol (), and carbon balance () after reaction with 1/8”Pd/alumina with 20 mesh Mg as a function of reaction time.
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28. Analytical Chemistry of Halocarbon mixtures
Polychlorinated biphenyl, 209 possible conformation isomers (congeners)
-problematic for GC-ECD
-aging effects
-environmental matrix
more………..
Complete dechlorination of PCB yields one product  Biphenyl
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29. Typical GC-FID of a PCB Mixture
80 ppm of Arochlor 1260
Alltech AT-5 column; Splitless injection; initial temperature,
125 oC; initial time, 5 min.; rate, 10 oC/min; final temperature,
275 oC; final time, 5 min
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30. Treatment Procedure for Analytical Methods
Halocarbon mixture – 3 mL of 100 ppb to 10 ppm in
50/50 isopropyl alcohol/water
Initial dechlorination agent – 0.7 g 20 mesh Mg +
0.4 mg K2PdCl6
Reaction Time – 10 minutes
HPLC – C18 reversed phase 65/35 (v/v) acetonitrile/water
200 nm absorbance detection
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31. HPLC of Arochlor 1221 Top: Arochlor 1221 treated with Pd/Mg
Bottom: Arochlor 1221
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32. Biphenyl Calibration Curve
Estimated LOD – 80 ppb
Cheng et al, Microchemical Journal 1999, 60,
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33. Biphenyl Yields From 1221 & 1260
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34. Modified Procedure 4.0 Fe(0) 40-70 mesh Arochlor 1260
0.05% Pd, 2 hours
Arochlor 1260
10 ml ppb
60/40 Acetone/H2O
Lower MW
Chloro-biphenyl
0.25 Mg(0) 20 mesh
0.4% Pd, 30 minutes
100%
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35. Factors Controlling BP Yield
Reaction time with 0.25 g Pd (0.4%)/Mg
Acetone/Water (v/v)
> 50% Acetone 100% yield
< 50% yield decreases
60/40 optimal for extraction into hexane
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36. GC-FID chromatograms 19.4 ppm PCB (Aroclor 1248) 19.6 ppm DDT
Internal Standard
5 minutes 10 20
biphenyl
diphenylethane
After 2-step treatment
tetraphenylbutane
diphenylmethane
phenylcyclohexane
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37. Detection Limits 100 ppb for DDT & 40 ppb for PCB
EPA Methods 508A, 8081A, & 8082
- 0.6 ppb for DDT & 0.14 ppb for PCB
Advantages over EPA methods
- Simplified procedure
- Better Precision
- Faster work up time
- Ability to resolve halocarbon interferences
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38. Oxidative Pathways -Active Oxygen
-Oxidations by O2 from air
-CxHyClz + O2 = CO2 + H2O + HCl (unbalanced) G<0
-Room temperature oxidations by air are kinetically slow
-enzymatic or enzyme-mimics
-Partially reduced O2 (active oxygen)
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39. Partially Reduced Oxygen
E0reduction
O2 + e- = O2.-
-0.45 volts
O2 + 2H+ + 2e- = H2O2
+0.30 volts
O2 + 4H+ + 4e- = H2O
+1.23 volts
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40. Fenton Reaction -Reduction of HO-OH H2O2 + FeII = FeIII + HO- + HO.
HO. + e- = HO- Eo = 1.8 volts
-HO. reacts with organics with diffusion limited kinetics
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41. RTP Production of Active Oxygen
O2 reducing agents
-Zero-valent iron, Fe(0)
Inexpensive
Spent agent, Fe2+/Fe3+ environmentally benign.
Chelated forms, capable Fenton reaction agents
Fe(0) + O2 + 2H+  Fe2+ + H2O2
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42. “Aero”-Fenton Reaction
-Fe2+ chelation agent - EDTA
FeIIETDA + HOOH  FeIIIEDTA + HO- + HO.
Inexpensive
Efficient Binding Agent for Fe2+/3+
FeIIEDTA highly effective Fenton Reaction reagent
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43. Proposed Overall Scheme
Fe(0) + O2(aq) + 2H+(aq)  Fe2+(aq) + HOOH(aq)
Fe2+(aq) + EDTA  FeIIEDTA
FeIIEDTA + HOOH  FeIIIEDTA + HO- + HO·
Regeneration:
2FeIIIEDTA + Fe(0)  Fe2+(aq) + 2FeIIEDTA
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44. Pollutant Destruction
H2O2
O2 + 2H+ +
EDTA
Iron
particles
0.1-1 mm
Fe2+
FeIIEDTA
FeIIIEDTA + HO- + HO.
Aqueous
pollutant
CO2 + H2O
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45. Aero-Fenton Reaction 0.5 g of 40-70 mesh Fe(0) 10 mL of solution
0.32 mM EDTA
140 ppm 4-chlorophenol
4 hour reaction time
GC and LC-MS
RTP
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46. Summary of degradation of the chlorophenols in this study
. All runs included 0.5 g of mesh Fe(0) in 10 mL of solution.
I) 0.32 mM EDTA
Aerobic
II) 0.0 mM EDTA
III) 0.32 mM EDTA
Anaerobic (N2 purge)
IV) dark conditions 0.32 mM EDTA aerobic
140 ppm 4-chlorophenol
Complete degradation after 4 h. (GC-FID)
No reaction after 4 h.
Complete degradation after 4 h.
162 ppm
pentachlorophenol suspension
Complete degradation after 70 h. (GC-FID)
No reaction after 70 h.
N/A
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47. Kinetic Studies Pseudo first-order rate constant = -1.11 /hr.
0.5-g mesh Fe(0)
0.72 mM EDTA
0.54 mM 4-chlorophenol
Aerobic conditions
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48. Destruction of other pollutants
100% removal (GC-FID)
 10%
VX surrogate - malathion
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49. Technical Summary Ability to degrade organic pollutants
Under room temperature, atmospheric pressure conditions
Inexpensive Reagents – Iron particles, water, air & EDTA
Unspecialized reactors
Process is easily transportable, iron particles & EDTA
Strong possibility of scale-up
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50. Scientific Summary
First example of abiotic RTP activation of O2 able to oxidize destructively organics
Control experiments indicate process is dependent on Fe(0), EDTA, air, and water
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51. Future Investigations
Mechanisms – Understanding the process
Kinetics – Speeding up the process
Search for an oxidatively stable iron chelate
Survey of Pollutants – oxidizable and nonoxidizable functional groups
Application & Scale-up
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52. Acknowledgements
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53. Acknowledgements Thank you for Attention
University of Idaho Research Foundation
Mark Engelmann – Ph.D. candidate – Dechlorination
Jose’ Morales – M.S – Hydrogenation
Tina Noradoun – Ph.D. candidate – Aero-Fenton
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