Destruction of Organic Pollutants Through Zero-Valent Metals Via Reductive and Oxidative Pathways Department of Chemistry, University of Idaho Moscow, ID 83844-2343, Tel (208) 885-6387 ifcheng@uidaho.edu 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 9/18/2018

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 9/18/2018

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 9/18/2018

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 1929-1977 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 http://www.epa.gov/history/topics/pcbs/01.htm, Analtyical Chemistry of PCBs, 2nd Ed. M.E. Erikson, CRC Press 1997 9/18/2018

Present Method of PCB Destruction Incineration Problems with Incineration Dioxin Emission; T > 1300 0C Costs NIMBY DDT - Pentachloropehnol 9/18/2018

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 9/18/2018

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 9/18/2018

Reductive Pathways Strategy: R-Cl + 2H+ + e- ® R-H + Cl- Possible Reducing Agents: Electrochemical Zero-Valent Metals: Fe(0) and Mg(0) 9/18/2018

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 9/18/2018

Thermodynamics of CCl4 Dechlorination 9/18/2018

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, 2045-2053 9/18/2018

PCBs are Kinetically Stable in the Presence of Fe(0) or Mg(0) 9/18/2018

Catalyzed Reductions of Halocarbons by Pd modified Bimetallic Systems 2M + PdCl62-  2M2+ + 6Cl- + Pd(s) 0.05-0.25 % Pd (w/w) Results in complete dechlorination of TCE Muftikian, Fernando, Korte, Water Research. 1995, 29, 2434. 9/18/2018

The role of Pd in hydrodehalogenation of chloro-organics by Pd/Fe Cheng, Fernando, Korte, Environ Sci &Technol, 1997, 31(4) 1074-1078. 9/18/2018

Halocarbon Reduction by Pd/Fe Muftikian, Fernando, Korte, Water Research. 1995, 29, 2434 *Cheng et al, unpublished results 1998-1999 9/18/2018

Reductive Dechlorination by Pd/Mg Zero-valent Metals as Reducing Agents Fe(s) ® Fe2+ + 2e- E0red = -0.44 volts Mg(s) ® Mg2+ + 2e- E0red = -2.36 volts Na(s) ® Na+ + e- E0red = -2.71 volts 9/18/2018

Reactivities of Metal Candidates Mn+ + n OH-  M(OH)n(s) 9/18/2018

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) 9/18/2018

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), 97-108 Cheng et al Chemosphere 2001, 43, 195-199 Cheng et al, LC-GC, 1999, 18, 154-160. Cheng et al, Microchemical Journal 1999, 60, 290-295 9/18/2018

Summary of Dechlorination by Pd/Mg First demonstration of the complete dechlorination of: PCP DDT PCB Reaction conditions: STP 9/18/2018

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 9/18/2018

RTP Hydrogenation of Phenol 5 mL aqueous 5 mM Phenol, 10 minutes Palladized 1.00 g Mg particles 0.079 m2 Palladized 0.66 g Fe particles 0.079 m2 3. 1.00 g Mg 20 mesh - 0.5 g 1/8” Pd/alumina Cheng et al; Industrial and Engineering Chemistry Research, 2002 41, 3071-3074 9/18/2018

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 9/18/2018

RTP Hydrogenation Product Yields 9/18/2018

Summary of Reaction Routes Rapid;  40% C balance Pd/Mg Pd/Fe N.R. Pd/alumina Mg  100% C balance 9/18/2018

Proposed Pathways Pd/Mg Pd/alumina Mg 100% Low MW volatiles? 9/18/2018

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. 9/18/2018

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 9/18/2018

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 9/18/2018

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 9/18/2018

HPLC of Arochlor 1221 Top: Arochlor 1221 treated with Pd/Mg Bottom: Arochlor 1221 9/18/2018

Biphenyl Calibration Curve Estimated LOD – 80 ppb Cheng et al, Microchemical Journal 1999, 60, 290-295 9/18/2018

Biphenyl Yields From 1221 & 1260 9/18/2018

Modified Procedure 4.0 Fe(0) 40-70 mesh Arochlor 1260 0.05% Pd, 2 hours Arochlor 1260 10 ml 10-4000 ppb 60/40 Acetone/H2O Lower MW Chloro-biphenyl 0.25 Mg(0) 20 mesh 0.4% Pd, 30 minutes 100% 9/18/2018

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 9/18/2018

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 9/18/2018

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 9/18/2018

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) 9/18/2018

Partially Reduced Oxygen E0reduction O2 + e- = O2.- -0.45 volts O2 + 2H+ + 2e- = H2O2 +0.30 volts O2 + 4H+ + 4e- = H2O +1.23 volts 9/18/2018

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 9/18/2018

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 9/18/2018

“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 9/18/2018

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 9/18/2018

Pollutant Destruction H2O2 O2 + 2H+ + EDTA Iron particles 0.1-1 mm Fe2+ FeIIEDTA FeIIIEDTA + HO- + HO. Aqueous pollutant CO2 + H2O 9/18/2018

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 9/18/2018

Summary of degradation of the chlorophenols in this study . All runs included 0.5 g of 40-70 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 9/18/2018

Kinetic Studies Pseudo first-order rate constant = -1.11 /hr. 0.5-g 40-70 mesh Fe(0) 0.72 mM EDTA 0.54 mM 4-chlorophenol Aerobic conditions 9/18/2018

Destruction of other pollutants 100% removal (GC-FID)  10% VX surrogate - malathion 9/18/2018

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 9/18/2018

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 9/18/2018

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 9/18/2018

Acknowledgements 9/18/2018

Acknowledgements Thank you for Attention University of Idaho Research Foundation Mark Engelmann – Ph.D. candidate – Dechlorination Jose’ Morales – M.S. 2001 – Hydrogenation Tina Noradoun – Ph.D. candidate – Aero-Fenton 9/18/2018