Kinetics of EDTA degradation induced by dioxygen activation in the Fe(0)/air/water (ZEA) system Frank Cheng*Tina Noradoun University of Idaho Chemistry Department Moscow, ID

3/15/05 Cheng & Noradoun, University of Idaho 2 The search for a “green” oxidant Problems with chlorine based bleaching methods. Oxygen is the ultimate green oxidant. Oxygen is kinetically stable

3/15/05 Cheng & Noradoun, University of Idaho 3 Molecular Oxygen O 2 is kinetically stable Oxygen’s two unpaired electrons make it difficult to accept a bonding pair Partially reduced oxygen

3/15/05 Cheng & Noradoun, University of Idaho 4 Reactive Oxygen Forms HO-OH b.o. = 1  50 kcal/mol GG O=O b.o. = 2  120 kcal/mol +4e - +4H + 2H 2 O O-O b.o. = 1.5  80 kcal/mol +e - +2e - +2H +

3/15/05 Cheng & Noradoun, University of Idaho 5 The Fenton Reaction H 2 O 2 + e -  HO + HO - Fe(II)  Fe(III) + e - Fe(II) + H 2 O 2  Fe(III) + HO + HO - H.J.H. Fenton. J. Chem. Soc. 1894, 65, 889. F. Haber and J.J. Weiss. Proc. Roy. Soc. London, Ser. A. 1934, 147, 332.

3/15/05 Cheng & Noradoun, University of Idaho 6 Oxygen Activation Biological  cytochrome P450 enzymes, monooxygenase

3/15/05 Cheng & Noradoun, University of Idaho 7 Molecular Oxygen as an Oxidant Diagram showing reaction oxygen intermediates between O 2 and H 2 O. H + left out for simplicity  Most attractive oxidant for green oxidations is O 2 from air.

3/15/05 Cheng & Noradoun, University of Idaho 8 Fe°, EDTA, Air (ZEA) system IF Cheng, et al, Ind. & Eng. Chem. Res. 2003, 42(21), Fe 0 II EDTA Fe III EDTA e - + H 2 O 2 + OH - + Fe II EDTA Fe III EDTA O 2 O H + O 2.- Fe 2+ + EDTA HO· Fe(0), EDTA, & air The only nonbiological system know to date that can activate O 2 under RTP and produce a facile oxidizing species capable of extensively degrading xenobiotics Organophosphorous agents Halocarbons Organics

3/15/05 Cheng & Noradoun, University of Idaho 9 Outline Introduction  Environmental Impact of EDTA  The RTP Dioxygen Activation General Reaction Scheme  Zero-valent iron/EDTA/air(ZEA) system Degradation Kinetics and Reaction Products  EDTA  Chlorinated phenols  Organophosphorus and UXO compounds Mechanisms  Rate-limiting Step Conclusions

3/15/05 Cheng & Noradoun, University of Idaho 10 EDTA Finds widespread use in food, cosmetic and pharmaceutical preparations Newer uses – manufacture of textiles and in paper-pulp bleaching  Swedish pulping industry where the use of EDTA has increased from 2,000 metric tons to about 8,000 metric tons per year from 1990 to Ekland, B; Bruno, E; Lithner, G.; Hans, B.; “Use of Etheylenediaminetetraacetic acid in Pulp Mills and Effects on Metal Mobility and Primary Products”; Environ. Toxicol. Chem.; 2002; 21(5),

3/15/05 Cheng & Noradoun, University of Idaho 11 EDTA Control of metal ion activities, Fe, Mn, Zn, Cu, Mg, Ca -Corrosion -Catalysis -“Green” bleaching - H 2 O 2  Sillanpaa, M; Pirkanniemi, K.; Sorokin, A.; “Degradative hydrogen peroxide oxidation of chelates catalysed by metallophthalocyanines”; The Science of the Total Environment; 2003; 307,

3/15/05 Cheng & Noradoun, University of Idaho 12 Concerns about EDTA  Many industrial chelating agents are not degradable by methods currently found in wastewater treatment facilities  Not readily biodegradable  Considerable quantities of EDTA pass through wastewater treatment facilities in the form of Fe III EDTA, as high as 18µM. Sillanpaa, Mika; Orma, Marjatt; Ramo, Jaakko; Oikair; “The importance of ligand speciation in environmental research: a case study”; The Science of the Total Environment; 2001; 267, Sillanpaa, M; Pirkanniemi, K.; “Recent Developments in Chelate Degradation”; Environmental Technology, 2001, 22, 791. Kari, F. G.; Giger W; Modeling the Photochemical Degradation of Ethylenediaminetetraacetate in the River Glatt; Environmental Science and Technology; 1995, 29, Nirel, P. et. al.; Method for EDTA Speciation Deteremination: Application to Sewage Treatment Plant Effluents; Wat. Res; 1998; 32, Kari, F. G. and Giger W.; Speciation and fate of EDTA in municipal wasterwater treatment. Wat. Res., 1996, 30,

3/15/05 Cheng & Noradoun, University of Idaho 13 Concerns about EDTA Questions regarding the ability to mobilize metals in the environment.  Currently not being monitored or treated at waste water treatment facilities  Concern for heavy metal mobility and longer bioavailability of metals to aquatic plants and animals  Stable in aquatic environment EDTA is anthropogenic and long-lived.

3/15/05 Cheng & Noradoun, University of Idaho 14 Goals The destruction or neutralization of EDTA (xenobiotics) Search for in situ conditions that will aid in the reduction in the release of EDTA in emerging green chemistries. Inexpensive & Safe Processes. Room Temperature and Pressure Conditions (RTP) Common Reagents – Long Term Storage No Specialized Catalysts System that may be incorporated into existing water treatment systems

3/15/05 Cheng & Noradoun, University of Idaho 15 Overall Goals of Our Green Oxidation Program  The destruction or neutralization of xenobiotics, including nerve agents and chlorinated pesticides using green oxidation chemistry.  Focus on non-biological oxygen activation to eliminate the need for tricky enzyme based systems

3/15/05 Cheng & Noradoun, University of Idaho 16 Oxygen activation system The ZEA system uses only zero-valent iron, EDTA and air The only nonbiological system know to date that can activate O 2 under RTP and produce a facile oxidizing species capable of extensively degrading xenobiotics Industrial and Engineering Chemistry Research 2003, 42,

3/15/05 Cheng & Noradoun, University of Idaho 17 Experimental Setup Bioanalytical Systems – RPM controlled stir plate stir bar 2.5 g Fe° 125 ml round bottom flask 1 mM EDTA (Total Vol. 50mL) 2.5g Fe° mesh Aldrich Open to the Atmosphere Aliquots were taken directly from reaction vessel, diluted, filtered and injected into HPLC

3/15/05 Cheng & Noradoun, University of Idaho 18 Evidence for Production of Reactive Oxygen Species ROS  O 2 -, H 2 O 2, HO., Fe IV =O, etc. Two Analyses were performed  Thiobarbituric acid-reactive substances (TBARS) assay  Addition of known radical scavenger, 1-butanol

3/15/05 Cheng & Noradoun, University of Idaho 19 Thiobarbituric acid reactive substances assay (TBARS) Nonselective detection of reactive oxygen species oxidizing species. HO·, Fe IV =O Malonaldehyde bis(dimethyl acetal) TBA Deoxyribose 534 nm Junqueira VB; Mol Aspects Med Feb-Apr;25(1-2):5-16. Hader D; Photochem Photobiol Sci Oct;1(10):

3/15/05 Cheng & Noradoun, University of Idaho 20 TBARS results 30 minutes of reaction time with 0.10 g mesh Fe(0), under aerobic conditions. Absorbance Units at 534 nm Control 1 – 0 mM deoxyribose, 2.39 mM EDTA 0.0 Control 2 – 3.18 mM deoxyribose, 0 mM EDTA, - also N 2 flow, -No Fe(0) mM deoxyribose, 2.39 mM EDTA0.846 Ind. & Eng. Chem. Res. 2003, 42(21),

3/15/05 Cheng & Noradoun, University of Idaho 21 Suppression of EDTA degradation with the addition of Radical Scavenger ( ■ ) k obs = M -1 hr -1 ( ▲ )k obs = M -1 hr -1 with 5mM 1-butanol (2.5 g ZVI g, 1.00mM EDTA, open to air) Mantzavinos D; Water Res Jul;38(13): J Hazard Mater Apr 30;108(1-2): butanol is a OH radical scavenger

3/15/05 Cheng & Noradoun, University of Idaho 22 Summary of ZEA system and O 2 Both TBARS and butanol tests indicate that ZEA system is able to produce facile oxidant from air at RTP Form of abiotic O 2 activation at RTP Identity of oxidant isn’t clear  HO·  Fe IV =O

3/15/05 Cheng & Noradoun, University of Idaho 23 Degradation of EDTA by ZEA reaction 1 mM EDTA (50mL, aqueous) 2.5g Fe° + air

3/15/05 Cheng & Noradoun, University of Idaho 24 Products of ZEA System None of the products of EDTA are significant metal chelation agents. All are more easily biodegraded. The ZEA system has proven successful at the degradation of other organic xenobiotics. Halocarbons Organophosphorus Organics

3/15/05 Cheng & Noradoun, University of Idaho 25 Carbon Balance - Total Organic Carbon*, ESI-MS**, HPLC # Trapping of the volatile gases using Tenax® showed no volatile organic carbon of molecular weight C4 and above released from the system during the course of the reaction

3/15/05 Cheng & Noradoun, University of Idaho 26 Degradation products for -EDTA -Malathion -4-chlorophenol -pentachlorophenol -phenol iminodiacetic acid (degrades after 12 hrs) succinic acid bicarbonate propionic acidOxalic acid Kinetically stable organic products from ZEA degradation.

3/15/05 Cheng & Noradoun, University of Idaho 27 Summary of EDTA degradation EDTA is degraded by the ZEA system to LWM acids and inorganic carbons All products are more biodegradable than EDTA RTP O 2 activation Next: Kinetic studies

3/15/05 Cheng & Noradoun, University of Idaho 28 Overall Scheme (simplified) Metal dissolution: Fe(0)  Fe e - (1) Complex formation Fe 2+ + EDTA  Fe II EDTA(2) Homogeneous O 2 activation: 2Fe II EDTA + O 2 + 2H +  2Fe III EDTA + H 2 O 2 (3) Fenton Reaction Fe II EDTA + H 2 O 2  Fe III EDTA + OH + OH- (4) EDTA degradation: OH + FeEDTA  Fe 2+/3+ + EDTA*(5)  EDTA* = damaged EDTA Redox Cycling: Fe III EDTA + e -  Fe II EDTA(6)

3/15/05 Cheng & Noradoun, University of Idaho 29 Kinetic Parameters Examined Effects of  EDTA concentration  Possible Scale-up  Fe° mass (surface area)  Omitted  Rate of mixing  Omitted  Temperature  Rate-limiting Step

3/15/05 Cheng & Noradoun, University of Idaho 30 Kinetics of EDTA degradation [EDTA] initial = 1 mM k obs = 1.22 /M hr 1mM EDTA, 2.5 g Fe° and air (▲), control in the absence of iron (■) Pseudo-first order plot showing linearity for EDTA degradation from 10min-2.5hrs.

3/15/05 Cheng & Noradoun, University of Idaho 31 EDTA degradation rate is effected by initial EDTA concentration 2.5 g Fe°, open to atmosphere, 450 rpm, total rxn volume 50mL Narrow optimal range for EDTA concentration. Important point: adding more EDTA will not speed up reaction.

3/15/05 Cheng & Noradoun, University of Idaho 32 How does [EDTA] i effect the ZEA reaction rate? Corrosion Rate Rate of Fe III EDTA reduction by Fe(0). Rate of Fenton Reaction O 2 activation

3/15/05 Cheng & Noradoun, University of Idaho 33 Corrosion studies Electrochemical Studies - Tafel Analysis i 0 is the exchange current which is the rate of the corrosion.

3/15/05 Cheng & Noradoun, University of Idaho 34 Tafel Corrosion Analysis Corrosion normally occurs at a rate determined by an equilibrium between opposing electrochemical reactions. Anodic reaction: metal oxidized, releasing electrons into the metal. Fe°  Fe e - Cathodic reaction: solution species (often O 2 or H + ) reduced, removing electrons from the metal. 2H + + 2e -  H 2

3/15/05 Cheng & Noradoun, University of Idaho 35 Corrosion Cell Working Electrode: Fe° (99%), 3/8" diameter by 1/2" length (surface area 5.22 x m 2 ) Counter Electrode: high density graphite rod Reference: Standard Calomel Electrode (SCE), glass luggin capillary 1 liter glass cell Polished working electrode with 600 grit sandpaper between sample runs Used 50mM KNO 3 as electrolyte in all samples

3/15/05 Cheng & Noradoun, University of Idaho 36 Corrosion Rate N 2 purge Air purge Addition of EDTA does enhance dissolution rates to ~5mM Overall corrosion rates for in the presence of N 2 are higher than air Passivation layer forming on the Fe° surface in the presence of O 2 in air Important point is the dissolution is not hindered by excess EDTA

3/15/05 Cheng & Noradoun, University of Idaho 37 Comparison of Corrosion to ZEA rates Red: ZEA reaction Blue: Corrosion studies EDTA probably stabilizes Fe 2+ Inversely correlated! Slower rxn kinetics with higher [EDTA] is not attributable to effects on corrosion.

3/15/05 Cheng & Noradoun, University of Idaho 38 Other Possibilities for effects of [EDTA] on ZEA reaction rates Kinetic barriers  Electrochemical  Fe III EDTA + e - = Fe II EDTA  Fenton Rxn  Fe II EDTA + H 2 O 2  Fe III EDTA +HO - + HO·  Oxygen Reduction/Activation  Fe II EDTA + O 2  Fe III EDTA + O 2.-  Other routes

3/15/05 Cheng & Noradoun, University of Idaho 39 Excess EDTA does not affect the rate of Fe III EDTA reduction Cyclic voltammograms of 0.1 mM Fe IIIEDTA  0.1 M HEPES pH 7.4  10 mV/s  carbon disk electrode A) 0.1 mM B) 10 mM EDTA 10 V/s

3/15/05 Cheng & Noradoun, University of Idaho 40 Other Possibilities

3/15/05 Cheng & Noradoun, University of Idaho 41 Excess EDTA inhibits the Fenton Rxn. Cyclic voltammograms of 0.1 mM FeII with 10 mM H 2 O mV/s [Fe II ]:[EDTA] (A) 1:1 (B) 1:10

3/15/05 Cheng & Noradoun, University of Idaho 42 [FeIII]:[EDTA] Fenton Rxn trends  EDTA may act as an anti- or pro-oxidant.  Highly dependent on [EDTA] i

3/15/05 Cheng & Noradoun, University of Idaho 43 Other Possibilities

3/15/05 Cheng & Noradoun, University of Idaho 44 Temperature Experiments An Arrhenius plot - activation energy May allow us to determine rate-limiting step  Metal Dissolution  Complex Formation  Homogeneous O 2 Activation  Fenton Rxn  EDTA oxidation  Heterogeneous Redox Cycling

3/15/05 Cheng & Noradoun, University of Idaho 45 Arrhenius plot - dependence of observed rate constants on temperature 2.5g Fe°, 1mM EDTA, 50ml total volume, reactions conducted using a temperature bath and a water-jacketed cell k = A exp (-Ea/RT)

3/15/05 Cheng & Noradoun, University of Idaho 46 Summary of Arrhenius Studies This study:E a = 25.5 kJ/mol Under vigorous stirring; Mass transport limited region This activation energy includes all steps. How may this determine which of the 6 processed is rate-limiting? Comparison with literature regarding: O 2 reduction by Fe II EDTA

3/15/05 Cheng & Noradoun, University of Idaho 47 Overall Scheme (simplified) Metal dissolution: Fe(0)  Fe e - (1) Complex formation Fe 2+ + EDTA  Fe II EDTA(2) Homogeneous O 2 activation: 2Fe II EDTA + O 2 + 2H +  2Fe III EDTA + H 2 O 2 (3) Fenton Reaction Fe II EDTA + H 2 O 2  Fe III EDTA + OH + OH- (4) EDTA degradation: OH + FeEDTA  Fe 2+/3+ + EDTA*(5)  EDTA* = damaged EDTA Redox Cycling: Fe III EDTA + e -  Fe II EDTA(6)

3/15/05 Cheng & Noradoun, University of Idaho 48 Comparison to kinetics of homogeneous O 2 reduction by Fe II EDTA in literature R. Van Eldik; Inorg. Chem.; 1990, 29, [Fe II EDTA] = 0.02M pH=5 Fe II EDTA + O 2  Fe II EDTAO 2 k 1 = 10 7 /Ms Fe II EDTAO 2  Fe III EDTA + O 2 - k 2 = 10 2 /Ms Fe II EDTAO 2 + H +  Fe III EDTA + HO 2 k 3 = /Ms  Rate limiting step is the activation of oxygen at the iron coordination site  Activation energy, 33.9 kJ/mol*

3/15/05 Cheng & Noradoun, University of Idaho 49 Summary of Van Eldik Study Van Eldik, R. Inorg. Chem, 1997, 36, Fe II EDTAH(H 2 O) + O 2  Fe II EDTAH(O 2 ) + H 2 O Fe II EDTAH(O 2 )  Fe III EDTAH(O 2 - ) Fe III EDTAH(O 2 - ) + Fe II EDTAH(H 2 O)  Fe III EDTAH(O 2 2- )Fe III EDTAH + H 2 O Fe III EDTAH(O 2 2- )Fe III EDTAH + H 2 O + 2H +  2Fe III EDTAH(H 2 O) + H 2 O 2 2Fe II EDTAH(H 2 O) + H 2 O 2  2Fe III EDTAH(H 2 O) + H 2 O *Proposes H 2 O 2 as intermediate *Saw no evidence of H 2 O 2 or Fenton Rxn

3/15/05 Cheng & Noradoun, University of Idaho 50 Comparison to kinetics of homogeneous O 2 reduction by Fe II EDTA in literature Beenackers, A.; Ing. Eng. Chem. Res. 1992, 32, 2580 [Fe II EDTA]=0.10 MpH=7.5  2Fe II EDTA + O 2 + H +  2Fe III EDTA + H 2 O 2 (overall)  Activation energy, 27.2 kJ/mol

3/15/05 Cheng & Noradoun, University of Idaho 51 Overall Scheme (simplified) Metal dissolution: Fe(0)  Fe e - (1) Complex formation Fe 2+ + EDTA  Fe II EDTA(2) Homogeneous O 2 activation: 2Fe II EDTA + O 2 + 2H +  2Fe III EDTA + H 2 O 2 (3) Fenton Reaction Fe II EDTA + H 2 O 2  Fe III EDTA + OH + OH- (4) EDTA degradation: OH + FeEDTA  Fe 2+/3+ + EDTA*(5)  EDTA* = damaged EDTA Redox Cycling: Fe III EDTA + e -  Fe II EDTA(6) This study25.5 kJ/mol Beenackers27.2 kJ/mol Van Eldik33.9 kJ/mol Step 3 is Rate-Limiting

3/15/05 Cheng & Noradoun, University of Idaho 52 Conclusions This system is a viable option for the destruction of a variety of pollutants and has a strong possibility for scale up. The only system known to date that can obtain non-biological Oxygen Activation at room temperature and pressure to produce reactive oxygen species that are capable of fully degrading pollutants to LMW carboxylates and inorganic forms Due to the duality of EDTA acting as both a pro-oxidant and antioxidant, controlling the [EDTA] is imperative to the success of the process. Rate-limiting steps is (are) oxygen activation Fe II EDTA may provide insights into biological oxygen activation This study may provide insights as to how EDTA release can be controlled  Future studies – how many oxidative hits & redox cycles required to degrade EDTA to inorganic forms Search for more suitable reducing agents

3/15/05 Cheng & Noradoun, University of Idaho 53 Acknowledgments Thank You! Christina Noradoun Funding NSF BES UI Foundation Seed Grant  NIH  EPRI Dr. Malcolm and Mrs. Renfrew  Renfrew Scholarships

3/15/05 Cheng & Noradoun, University of Idaho 54 The ZEA system is durable ZVI maintains EDTA degradation without significant loss in the observed rate over a time period of several hours All systems mixed at 450 rpm, open to atmosphere, unbuffered using 2.5g ZVI.

3/15/05 Cheng & Noradoun, University of Idaho 55 Comparison Studies Auto-oxidation of Fe II to Fe III by O 2 in aqueous solutions  Significantly enhanced by EDTA  Fe II :EDTA ratios were important 1:1 ratios were reported as optimal 1:20 ratios showed a significant decrease in the autoxidation process R. Van Eldik; Inorg. Chem.; 1990, 29, (* 0.02M [Fe(EDTA)])

3/15/05 Cheng & Noradoun, University of Idaho 56 Role of Fe° mass/surface area in observed rate constant 0.10g g Fe°, 1.00mM EDTA, open to atmosphere, 450 rpm, total rxn volume 50mL BET surface area analysis m 2 /g : Porous Material Inc., Ithaca, NY surface area, k obs (0.29 m 2, /Mh) Increased levels of Fe°, enhance the rate of degradation by maintaining a balance between the Fe 2+ and [EDTA] (0.028 m 2, /Mh)

3/15/05 Cheng & Noradoun, University of Idaho 57 Maintaining proper Fe°to EDTA ratios Interactions between EDTA and Fe 2+ are important factor controlling the degradation rates Due to the duality of EDTA acting as both a pro-oxidant and antioxidant, controlling the [EDTA] is imperative to the success of the process. Rate-limiting step 1. Surface chemistry : Reduction of Fe II/III at the iron surface inhibited by excess EDTA 2. Solution chemistry: High Fe II/III :EDTA ratios inhibiting Fenton reactivity.

3/15/05 Cheng & Noradoun, University of Idaho 58 General Model Mass Transport-limited Kinetics 1) mass transport of Fe III EDTA to the Fe° surface 2) Fe III EDTA + e-  Fe II EDTA 3) mass transport of Fe II EDTA to the bulk soln. “A common criterion for detecting mass transport-limited kinetics is variation in reaction rate with intensity of mixing. Rates that are controlled by chemical reaction step should not be affected, where as aggressive mixing usually accelerates diffusion- controlled rates by reducing the thickness of the diffusion layer.” Leah Matheson and Paul Tratnyek; ES&T. 1994,

3/15/05 Cheng & Noradoun, University of Idaho 59 Effect of mixing rate on observed degradation rate constant for EDTA 2.5 g Fe° g, 1.00mM EDTA, open to air, total rxn volume 50mL Good indication that rate-limiting step of EDTA degradation involves mass transport and not chemical reactions occurring in the bulk solution

3/15/05 Cheng & Noradoun, University of Idaho 60 If reaction is mass transport controlled rate limiting step likely:  Fe II/III EDTA reduction at iron surface Can not rule out the heterogeneous O 2 activation Mass transport of oxygen from the bulk solution to the reacting iron surface is enhanced by the fluid flow. Typical bulk oxygen concentrations at room temperature in aqueous solutions are 0.25mM (8ppm).

3/15/05 Cheng & Noradoun, University of Idaho 61 HPLC conditions for Fe III EDTA detection EDTA non-extractable using organic solvent must use direct aqueous injection EDTA alone not absorb, however Fe III EDTA complex does at 258nm Mobile phase: 0.02M formate buffer, pH 3.3 Containing: TBA-Br (0.001M) and acetonitrile (8%) Flow rate: 1ml/min Temp: ambient temp UV = 258 nm Sample volume 20µL Column RP-C18 Nowack et. al.; Anal. Chem. 1996, 68, 561 TBA-Br +

3/15/05 Cheng & Noradoun, University of Idaho 62 TNT surrogate, nitrobenzene (985 ppm) was decomposed in 24 hours. VX surrogate, malathion (49 ppm) was consumed in 4 hours, to give diethyl succinate. Malathion was the only pollutant to give a by- product detectable by GC-FID. Organophosphorous Nerve Agents and Nitrated Explosive Surrogates

3/15/05 Cheng & Noradoun, University of Idaho 63 Malathion Degradation PO SO 4 2- malathion DES malaoxon max: 4-6 hrs Max: 7 hrs SO 4 2- :0.0593mM (14% yield) (24hrs) PO 4 2- : mM (19 % yield) (24hrs)

3/15/05 Cheng & Noradoun, University of Idaho 64 Kinetics of Malathion Degradation GC/FID chromatograph: each data point indicates an individual reaction vial extracted using 50/50 hexane/ethyl acetate, error bars indicate the standard deviation between three measurements of each sample vial. Malathion Diethyl Succinate (DES)

3/15/05 Cheng & Noradoun, University of Idaho 65 Reaction Conditions 0.44mM Malathion 0.44mM EDTA 0.5g Fe O Air Time: 0 hrs Time: 12 hrs EDTA Malathion (m/z 329) Iminodiacetic Acid HCO 3 - oxalate propionic acid Malaoxon (m/z 315) ESI-MS

3/15/05 Cheng & Noradoun, University of Idaho 66 ESI-MS background No Fe°, N 2 1mM FeSO 4 1mM EDTA 4hrs Fe°, Air 1mM EDTA 4hrs

3/15/05 Cheng & Noradoun, University of Idaho g Fe; mesh 0.44mM Xenobiotic 10.0 mL water Air flow 2.0 mL 50/50 hexane/ethyl acetate (extraction only) Stir bar 0.44mM EDTA General reaction conditions for Xenobiotic degradation  Beaker Rxn 25°C, pH Ind. & Eng. Chem. Res. 2003, 42(21),

3/15/05 Cheng & Noradoun, University of Idaho g Fe; mesh 0.44mM Xenobiotic 10.0 mL water Air flow 2.0 mL 50/50 hexane/ethyl acetate (extraction only) Stir bar 0.44mM EDTA General reaction conditions for Xenobiotic degradation  One reaction vessel was generated for each data point.  Degradation curves represent 8-15 individual reaction vials each extracted and analyzed using GC-FID or HPLC. 25°C, pH Ind. & Eng. Chem. Res. 2003, 42(21),

3/15/05 Cheng & Noradoun, University of Idaho 69 Stumm, W; “Chemistry of the Solid-Water Interface”; John Wiley & Sons, Inc. NY, © 1992, p204 EDTA and other dicarboxylic acids enhance dissolution by shifting electron density towards the metal ion and simultaneously enhancing surface protonation therefore weakening the Fe- oxygen lattice bonds.

3/15/05 Cheng & Noradoun, University of Idaho 70 Calcium Addition The addition of 10mM Ca 2+ did not effect degradation rate. 10mM EDTA, 2.5g Fe ° k obs = M -1 h -1 (with Ca 2+ ) 2.5 g Fe°,open to air, total rxn volume 50mL k obs = M -1 h -1 k obs = M -1 h -1 1mM EDTA, 2.5g Fe ° k obs = M -1 h -1

3/15/05 Cheng & Noradoun, University of Idaho 71 Calcium Addition cont. Ca 2+ addition had no overall effect on the rate of degradation The added Ca 2+ also did not help sequester excess EDTA in solution Therefore there was no improvement of Fenton Reactivity with the Ca 2+ addition Alternative way of examining the problem was to hold EDTA concentration constant and vary amount of Fe° present