1 Application of O 2 Activation toward Organic Pollutant Degradation Derek F. Laine and I. Frank Cheng University of Idaho Chemistry Department Moscow, ID 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 O 2  Incineration Expensive Dioxins Public reluctance Low temperature use of O 2  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)

4 Destruction of 4-Chlorophenol Noradoun, Christina, et al. Ind. Eng. Chem. Res. 2003, 42, Products include low molecular weight acids and CO 2.

5 Pollutants destroyed by the ZEA System Halocarbons 4-chlorophenol Pentachlorophenol Organophosphorus Compounds (nerve agents) Malathion (vx surrogate) Malaoxon Organics EDTA Phenol

6 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 O 2 to form reactive oxygen species O 2.-, H 2 O 2, HO.

7 Hypothesis-Site for O 2 Activation (I) Heterogeneous activation at the ZVI surface. (II) Homogeneous activation by Fe II EDTA. I Fe(0) O2O2 Fe III EDTA + HO∙ + HO - H + H2O2H2O2 Fe 2+ + EDTA → Fe II EDTA II Fe(0) Fe 2+ + EDTAFe II EDTA Fe III EDTAO2O2 H+H+ H2O2H2O2 HO∙ + 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

9 Electrochemical Pollutant Degradation System Fe II EDTA can reduce oxygen to form the superoxide ion (O 2 · - ), as well as other reactive oxygen species. Degradation of EDTA is measured in this system HPLC is used to measure the degradation of EDTA. Fe III EDTA Fe II EDTA 2O 2 2O 2 °- + 2H + → H 2 O 2 + O 2 Fe III EDTA + OH - + OH▪ + Fe II EDTA

10 Experimental Conditions Fe III (NO 3 ) 3 and Na 2 H 2 EDTA were added in a 1:1 ratio to make 80 ml of a 0.5 mM Fe III EDTA solution 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. Fe III EDTA Fe II EDTA 2O 2 2O 2 °- + 2H + → H 2 O 2 + O 2 Fe III EDTA + OH - + OH▪ + Fe II EDTA

11 HPLC Results

12 Results Fe III EDTA Fe II EDTA 2O 2 2O 2 °- + 2H + → H 2 O 2 + O 2 Fe III EDTA + OH - + OH▪ + Fe II EDTA

13 Comparison of Fe II/III EDTA degradation and pH Fe III EDTA Fe II EDTA 2O 2 2O 2 °- + 2H + → H 2 O 2 + O 2 Fe III EDTA + OH - + OH▪ + Fe II EDTA

14 Detection of Intermediate Oxidizing Agents (H 2 O 2 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, Fe III EDTA Fe II EDTA 2O 2 2O 2 °- + 2H + → H 2 O 2 + O 2 Fe III EDTA + OH - + OH · + Fe II EDTA Electrochemical system ZEA system

15 Formation of H 2 O 2 Starch reagents concentrated starch 40 mM HCl 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 H 2 O 2 ) will oxidize the iodide to iodine. Iodine combines with iodide to form triiodide which will then complex with starch to form a blue color. H 2 O 2 (aq) + 3I - (aq) + 2 H + (aq) → I 3 - (aq) + 2 H 2 O(aq) E. Graf, J.T. Penniston, Clin. Chem. 26/5 (1980)

16 Formation of H 2 O 2 Fe III EDTA Fe II EDTA 2O 2 2O 2 °- + 2H + → H 2 O 2 + O 2 Fe III EDTA + OH - + OH · + Fe II EDTA

17 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, Yamazaki, Isao; Piette, Lawrence H. J. Am. Chem. Soc. 1991, 113, Fe III EDTA Fe II EDTA 2O 2 2O 2 °- + 2H + → H 2 O 2 + O 2 Fe III EDTA + OH - + OH · + Fe II EDTA ·

18 Formation of HO· Before electrolysis, the same signal is obtained from a simple solution of Fe III EDTA, KCl, and O 2 Fe III EDTA Fe II EDTA 2O 2 2O 2 °- + 2H + → H 2 O 2 + O 2 Fe III EDTA + OH - + OH · + Fe II EDTA

19 Formation of HO· The two processes can be distinguished by adding methanol as a scavenger. ·

20 Formation of HO· · · ·

21 A B Formation of HO· A) B) · 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 = 10 9 M -1 S -1 Reaction dominates before electrolysis Yamazaki, Isao; Piette, Lawrence H. J. Biol. Chem. 1990, 265,

22 Formation of HO·

23 Formation of HO· Fe III EDTA Fe II EDTA 2O 2 2O 2 °- + 2H + → H 2 O 2 + O 2 Fe III EDTA + OH - + OH · + Fe II EDTA

24 Cyclic voltammetry can be used to show the catalytic mechanism. Fe III EDTA + e- → Fe II EDTA Fe II EDTA + O 2 → Fe III EDTA + O 2 ·- Fe III EDTA Fe II EDTA 2O 2 2O 2 °- + 2H + → H 2 O 2 + O 2 Fe III EDTA + OH - + OH · + Fe II EDTA

25 Cyclic Voltammetry Fe III EDTA + O 2 O 2 only Fe III EDTA only Niether Fe III EDTA or O 2 5 mV/s

26 pH Dependency Zang, V; van Eldik, R. Inorg. Chem. 1990, 29,

27 Free Fe(II) Fe II EDTA(H) Fe II EDTA Fe II EDTA(H 2 ) Fe II EDTA(OH)

28 Geometrical Considerations [Fe II (EDTA)(H 2 O)] 2- + H + = [Fe II (EDTAH)(H 2 O)] 1- Mizuta, T.; Wang, J.; Miyoshi, K. Bull. Chem. Soc. Jpn. 1993, 66, Mizuta, T.; Wang, J.; Miyoshi, K. Inorg. Chimica Acta. 1993, 230, SpeciesBite angle on water coordinate Bond distance from Fe II to OH 2 Fe II EDTA164.0°2.19 Å Fe II EDTAH172.1°2.21 Å

29 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 Fe II EDTA followed by the Fenton reaction. The ZEA system produces H 2 O 2 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.

30 Acknowledgments Dr. I. Frank Cheng Simon McAllister University of Idaho Dept. of Chemistry ACS Funding  NSF award number BES  NIH Grant No. 1 R15 GM