kinetics of edta degradation induced by dioxygen activation in the fe(0)/air/water (zea) system...

Kinetics of EDTA degradation induced by dioxygen activation in the Fe(0)/air/water (ZEA) systemFrank Cheng* Tina Noradoun

University of IdahoChemistry DepartmentMoscow, ID [email protected]

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

Molecular Oxygen O2 is kinetically stable

Oxygen’s two unpaired electrons make it difficult to accept a bonding pair

Partially reduced oxygen


4

Reactive Oxygen Forms

HO-OH b.o. = 1 50 kcal/mol

G

•O=O• b.o. = 2 120 kcal/mol

+4e-

+4H+

2H2O

•O-O• b.o. = 1.5 80 kcal/mol

+e-

+2e-

+2H+


5

The Fenton Reaction

H2O2 + e- HO• + HO- Fe(II) Fe(III) + e-

Fe(II) + H2O2 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.


6

Oxygen Activation Biological

cytochrome P450 enzymes, monooxygenase


7

Molecular Oxygen as an Oxidant

Diagram showing reaction oxygen intermediates between O2 and H2O. H+ left out for simplicity

Most attractive oxidant for green oxidations is O2 from air.

OHH2O2

O2 OH2

OHH2O2

O2

•-

O2

•-

hydroxyl radical

hydrogen peroxide

superoxide radical

+ e-+ e- + e-

+ e-

- e-

- e-- e-

- e-


8

Fe°, EDTA, Air (ZEA) system

IF Cheng, et al, Ind. & Eng. Chem. Res. 2003, 42(21), 5024-5030.

Fe0

FeIIEDTA

FeIIIEDTA

e-

+ H2O2 + OH- +FeIIEDTA FeIIIEDTA

O2

O2

.-+ +2H

+O2

.-

Fe2++ EDTA

HO·Fe(0), EDTA, & air

The only nonbiological system know to date that can activate O2 under RTP and produce a facile oxidizing species capable of extensively degrading xenobiotics

Organophosphorous agentsHalocarbonsOrganics


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


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 2000.

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), 1040-1051.

NN

CH2COOH

CH2COOH

HOOCH2C

HOOCH2C


11

EDTA Control of metal ion activities, Fe, Mn, Zn, Cu,

Mg, Ca

-Corrosion

-Catalysis

-“Green” bleaching - H2O2

Sillanpaa, M; Pirkanniemi, K.; Sorokin, A.; “Degradative hydrogen peroxide oxidation of chelates catalysed by metallophthalocyanines”; The Science of the Total Environment; 2003; 307, 11-18.


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 FeIIIEDTA, 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, 23-31.

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, 2814.

Nirel, P. et. al.; Method for EDTA Speciation Deteremination: Application to Sewage Treatment Plant Effluents; Wat. Res; 1998; 32, 3615.

Kari, F. G. and Giger W.; Speciation and fate of EDTA in municipal wasterwater treatment. Wat. Res., 1996, 30, 122-134.


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.


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


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


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 O2 under RTP and produce a facile oxidizing species capable of extensively degrading xenobiotics

Industrial and Engineering Chemistry Research 2003, 42, 5024-5030


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° 30-40 mesh Aldrich

Open to the Atmosphere

Aliquots were taken directly from reaction vessel, diluted, filtered and injected into HPLC


18

Evidence for Production of Reactive Oxygen Species

ROS O2

-•, H2O2, HO., FeIV=O, etc.

Two Analyses were performed Thiobarbituric acid-reactive

substances (TBARS) assay Addition of known radical

scavenger, 1-butanol

O2

F e 0O2

.- O2.-+ + 2H+

e-

+ H2O2 + OH-+ OHFeIIEDTA FeIIIEDTA

Fe2++ EDTA

II: Homogeneous O2 Activation

F e 0

O2

O2.- O2

.-+ + 2H+


FeIIEDTA

FeIIIEDTA

e-

Fe2++ EDTA

I: Heterogeneous O2 Activation


19

Thiobarbituric acid reactive substances assay (TBARS)

Nonselective detection of reactive oxygen species oxidizing species.

HO·, FeIV=O

Malonaldehyde bis(dimethyl acetal)

TBA

Deoxyribose

534 nm

Junqueira VB; Mol Aspects Med. 2004 Feb-Apr;25(1-2):5-16. Hader D; Photochem Photobiol Sci. 2002 Oct;1(10):729-36.


20

TBARS results

30 minutes of reaction time with 0.10 g 40-70 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 N2 flow, -No Fe(0)

0.149

3.18 mM deoxyribose, 2.39 mM EDTA 0.846

Ind. & Eng. Chem. Res. 2003, 42(21), 5024-5030.


21

Suppression of EDTA degradation with

the addition of Radical Scavenger

(■) kobs = -1.11 M-

1hr-1

(▲)kobs = -0.08 M-

1hr-1 with 5mM 1-butanol

(2.5 g ZVI g, 1.00mM EDTA, open to air)

Mantzavinos D; Water Res. 2004 Jul;38(13):3110-8. J Hazard Mater. 2004 Apr 30;108(1-2):95-102.

-10

-9.5

-9

-8.5

-8

-7.5

-7

-6.5

0 1 2 3 4 5 6

Time (hrs)

ln [

Fe

III E

DT

A]

Control (no Fe)

EDTA, Air

5 mM 1-butanol

Linear ( EDTA,Air)Linear (5 mM 1-butanol)

1-butanol is a •OH radical scavenger


22

Summary of ZEA system and O2 Both TBARS and butanol tests indicate that

ZEA system is able to produce facile oxidant from air at RTP

Form of abiotic O2 activation at RTP Identity of oxidant isn’t clear

HO· FeIV=O


23

Degradation of EDTA by ZEA reaction

1 mM EDTA (50mL, aqueous)2.5g Fe° + air

NN

COOH

COOH

HOOC

HOOC

NHCOOH

COOH

COOH

COOHHOOC

CO2/HCO3-


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


25

Carbon Balance - Total Organic Carbon*, ESI-

MS**, HPLC# Table 1 : Carbon Balance 1mM EDTA, 2.5g ZVI, air, reaction volume 50mL, 6hrs

% C

CO2 35% (± 5)*

Iminodiacetic Acid 28% (± 3)**

Oxalic acid 17% (± 2)**

Propionic Acid 14 % (± 2)**

EDTA 2% (± 2)#

Total 96%

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


26

Degradation products for -EDTA-Malathion-4-chlorophenol-pentachlorophenol-phenol

iminodiacetic acid (degrades after

12 hrs)

succinic acid bicarbonate

propionic acid Oxalic acid

Kinetically stable organic products from ZEA degradation.


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 O2 activation

Next: Kinetic studies


28

Overall Scheme (simplified) Metal dissolution: Fe(0) Fe2+ + 2e- (1)

Complex formation Fe2+ + EDTA FeIIEDTA (2)

Homogeneous O2 activation: 2FeIIEDTA + O2 + 2H+ 2FeIIIEDTA + H2O2 (3)

Fenton Reaction FeIIEDTA + H2O2 FeIIIEDTA + OH• + OH- (4)

EDTA degradation: OH• + FeEDTA Fe2+/3+ + EDTA* (5)

EDTA* = damaged EDTA

Redox Cycling: FeIIIEDTA + e- FeIIEDTA (6)


29

Kinetic Parameters ExaminedEffects of

EDTA concentration Possible Scale-up

Fe° mass (surface area) Omitted

Rate of mixing Omitted

Temperature Rate-limiting Step


30

Kinetics of EDTA degradation [EDTA]initial = 1 mM

R2 = 0.9998

-10

-9.5

-9

-8.5

-8

-7.5

-7

-6.5

0 0.5 1 1.5 2 2.5 3Time (hrs)

ln [

FeII

I ED

TA

]

kobs = 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.

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0 1 2 3 4 5 6 7

Time (hr)

[Fe

III E

DT

A]

Air

control (No Fe)


31

EDTA degradation rate is effected by initial EDTA concentration

[EDTA] (M)

0 2x10-3 4x10-3 6x10-3 8x10-3 10x10-3

k ob

s(M

-1h

-1)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

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.


32

How does [EDTA]i effect the ZEA reaction rate?

F e 0F e 0

Fe-oxide

+ H2O2 + OH- + OHFeIIEDTA FeIIIEDTA

EDTA2-

Interaction of EDTA and Fe-Oxide layer

FeIIEDTA

FeIIIEDTA

Fe2++ EDTA

Corrosion Rate

Rate of FeIIIEDTA reduction by Fe(0).

Rate of Fenton Reaction

O2 activation


33

Corrosion studies

Electrochemical Studies - Tafel Analysis

i0 is the exchange current which is the rate of the corrosion.

RT

F

RT

Fiitotal

)1(expexp0


34

Tafel Corrosion AnalysisCorrosion normally occurs at a

rate determined by an equilibrium between opposing electrochemical reactions.

Anodic reaction: metal oxidized, releasing electrons into the metal.

Fe° Fe2+ + 2e-

Cathodic reaction: solution species (often O2 or H+) reduced, removing electrons from the metal.

2H+ + 2e- H2


35

Corrosion Cell•Working Electrode: Fe° (99%), 3/8" diameter by 1/2" length (surface area 5.22 x 10-4 m2)

•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 KNO3 as electrolyte in all samples


36

Corrosion Rate

[EDTA] (mM)

0 2 4 6 8 10 12 14 16

Cor

rosi

on R

ate

(mm

/yr)

0

2

4

6

8

10

12

14

N2 purge

Air purge

• Addition of EDTA does enhance dissolution rates to ~5mM

• Overall corrosion rates for in the presence of N2 are higher than air

• Passivation layer forming on the Fe° surface in the presence of O2 in air

• Important point is the dissolution is not hindered by excess EDTA


37

Comparison of Corrosion to ZEA rates

[EDTA] (mM)

0 2 4 6 8 10 12 14 16

Co

rro

sio

n R

ate

(m

m/y

r)

0

1

2

3

4

5

k obs

(M-1

h-1)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

• Red: ZEA reaction

• Blue: Corrosion studies

• EDTA probably stabilizes Fe2+

• Inversely correlated!

• Slower rxn kinetics with higher [EDTA] is not attributable to effects on corrosion.


38

Other Possibilities for effects of [EDTA] on ZEA reaction rates Kinetic barriers

Electrochemical FeIIIEDTA + e- = FeIIEDTA

Fenton Rxn FeIIEDTA + H2O2 FeIIIEDTA +HO- + HO·

Oxygen Reduction/Activation FeIIEDTA + O2 FeIIIEDTA + O2

.-

Other routes


39

Excess EDTA does not affect the rate of FeIIIEDTA reduction

Cyclic voltammograms of 0.1 mM FeIIIEDTA

0.1 M HEPES pH 7.4 10 mV/s carbon disk electrode

A) 0.1 mM B) 10 mM EDTA

10 V/s


40

Other Possibilities

Kinetic barriers ElectrochemicalElectrochemical

FeFeIIIIIIEDTA + eEDTA + e-- = Fe = FeIIIIEDTAEDTA

Fenton Rxn FeIIEDTA + H2O2 FeIIIEDTA +HO- + HO·

Oxygen Reduction FeIIEDTA + O2 FeIIIEDTA + O2

.-

Other routes


41

Excess EDTA inhibits the Fenton Rxn. Cyclic

voltammograms of 0.1 mM FeII with 10 mM H2O2. 10 mV/s

[FeII]:[EDTA] (A) 1:1 (B) 1:10


42

[FeIII]:[EDTA] Fenton Rxn trends

EDTA may act as an anti- or pro-oxidant.

Highly dependent on [EDTA]i


43

Other Possibilities

Kinetic barriers ElectrochemicalElectrochemical

FeFeIIIIIIEDTA + eEDTA + e-- = Fe = FeIIIIEDTAEDTA

Fenton RxnFenton Rxn

FeFeIIIIEDTA + HEDTA + H22OO22 Fe FeIIIIIIEDTA +HOEDTA +HO-- + + HOHO·

Oxygen Reduction (future work) FeIIEDTA + O2 FeIIIEDTA + O2

.-

Other routes


44

Temperature Experiments

An Arrhenius plot - activation energy

May allow us to determine rate-limiting step Metal Dissolution Complex Formation Homogeneous O2 Activation Fenton Rxn EDTA oxidation Heterogeneous Redox Cycling


45

Arrhenius plot - dependence of observed rate constants on temperature

1/T (1/K)

0.0031 0.0032 0.0033 0.0034 0.0035 0.0036 0.0037

k ob

s (

1/h

)

-1.6

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

Activation Energy25.5 kJ/mole

2.5g Fe°, 1mM EDTA, 50ml total volume, reactions conducted using a temperature bath and a water-jacketed cell

k = A exp(-Ea/RT)


46

Summary of Arrhenius Studies• This study: Ea = 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:• O2 reduction by FeIIEDTA


47





EDTA degradation: OH• + FeEDTA Fe2+/3+ + EDTA* (5)

EDTA* = damaged EDTA



48

Comparison to kinetics of homogeneous O2 reduction by FeIIEDTA in literatureR. Van Eldik; Inorg. Chem.; 1990, 29, 1705-1711.

[FeIIEDTA] = 0.02M pH=5

FeIIEDTA + O2 FeIIEDTAO2 k1 = 107/MsFeIIEDTAO2 FeIIIEDTA + O2

- k2 = 102/MsFeIIEDTAO2 + H+ FeIIIEDTA + HO2 k3 = 1010/Ms

Rate limiting step is the activation of oxygen at the iron coordination site

Activation energy, 33.9 kJ/mol*


49

Summary of Van Eldik Study

Van Eldik, R. Inorg. Chem, 1997, 36, 4115-4120

FeIIEDTAH(H2O) + O2 FeIIEDTAH(O2) + H2O

FeIIEDTAH(O2) FeIIIEDTAH(O2-)

FeIIIEDTAH(O2-) + FeIIEDTAH(H2O) FeIIIEDTAH(O2

2-)FeIIIEDTAH + H2O

FeIIIEDTAH(O22-)FeIIIEDTAH + H2O + 2H+ 2FeIIIEDTAH(H2O) + H2O2

2FeIIEDTAH(H2O) + H2O2 2FeIIIEDTAH(H2O) + H2O

*Proposes H2O2 as intermediate*Saw no evidence of H2O2 or Fenton Rxn


50

Comparison to kinetics of homogeneous O2 reduction by FeIIEDTA in literatureBeenackers, A.; Ing. Eng. Chem. Res. 1992, 32, 2580

[FeIIEDTA]=0.10 M pH=7.5

2FeIIEDTA + O2 + H+ 2FeIIIEDTA + H2O2 (overall) Activation energy, 27.2 kJ/mol


51





EDTA degradation:

OH• + FeEDTA Fe2+/3+ + EDTA* (5) EDTA* = damaged EDTA


This study 25.5 kJ/mol

Beenackers 27.2 kJ/mol

Van Eldik 33.9 kJ/mol

•Step 3 is Rate-Limiting


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

FeIIEDTA 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


53

Acknowledgments

Thank You!

Christina Noradoun

Funding NSF BES-0328827 UI Foundation Seed Grant

NIH EPRI

Dr. Malcolm and Mrs. Renfrew Renfrew Scholarships


54

The ZEA system is durable

Time (hrs)0 2 4 6 8 10 12 14

[Fe

IIIE

DT

A]

(M)

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

0.0012

1mM EDTA Aliquot Added

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.


55

Comparison Studies

Auto-oxidation of FeII to FeIII by O2 in aqueous solutions Significantly enhanced by EDTA FeII: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, 1705-1711. (* 0.02M [Fe(EDTA)])


56

ZVI mass (g/L)

0 10 20 30 40 50

k ob

s(M

-1h

-1)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Role of Fe° mass/surface area in observed rate constant

0.10g - 2.5 g Fe°, 1.00mM EDTA, open to atmosphere, 450 rpm, total rxn volume 50mL

BET surface area analysis 0.1106 m2/g : Porous Material Inc., Ithaca, NY

surface area, kobs

(0.29 m2, -1.11 /Mh)

Increased levels of Fe°, enhance the rate of degradation by maintaining a balance between the Fe2+ and [EDTA]

(0.028 m2, -0.014 /Mh)


57

Maintaining proper Fe°to EDTA ratios Interactions between EDTA and Fe2+ 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 FeII/III at the iron

surface inhibited by excess EDTA 2. Solution chemistry: High FeII/III:EDTA ratios inhibiting

Fenton reactivity.


58

General Model Mass Transport-limited Kinetics

1) mass transport of FeIIIEDTA to the Fe° surface 2) FeIIIEDTA + e- FeIIEDTA 3) mass transport of FeIIEDTA 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, 28 2045-2053.


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

-11

-10.5

-10

-9.5

-9

-8.5

-8

-7.5

-7

-6.5

0 1 2 3 4 5 6

Time (hrs)

ln [

Fe

IIIE

DT

A]

50 rpm200 rpm350 rpm450 rpmLinear (50 rpm)Linear (200 rpm)Linear (350 rpm)Linear (450 rpm)

0

0.2

0.4

0.6

0.8

1

1.2

0 100 200 300 400 500 600

rpmk o

bs

(M-1

h-1

)

Good indication that rate-limiting step of EDTA degradation involves mass transport and not chemical reactions occurring in the bulk solution


60

If reaction is mass transport controlled rate limiting step likely: FeII/IIIEDTA reduction at iron

surface Can not rule out the

heterogeneous O2 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).

II: Homogeneous O2 Activation

F e 0

O2.- O2

.-+ + 2H+


FeIIEDTA

FeIIIEDTA

e-

Fe2++ EDTA

O2

F e 0O2

.- O2.-+ + 2H+

e-


Fe2++ EDTA

I: Heterogeneous O2 Activation

O2


61

HPLC conditions for FeIIIEDTA detection

EDTA non-extractable using organic solvent must use direct aqueous injection

EDTA alone not absorb, however FeIIIEDTA 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

+


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.

N+

O-O

nitrobenzene

S

OCH3

O

O

CH3

O

S

P

O

OCH3

CH3

malathion

SO

P N

CH3CH3

CH3

CH3

O

CH3

CH3

VX

CH3

N+

O

O-

N+

O

-O

N+

O-O

TNT

Organophosphorous Nerve Agents and Nitrated Explosive Surrogates


63

Malathion DegradationO

CH3 O

O CH3

O

PO43-

+ SO42-

S

OCH3

O

O

CH3

O

S

P

O

OCH3

CH3

malathionDES

malaoxon

O

CH3

O

O

CH3

O

S

P

O

O

CH3

O

CH3

max: 4-6 hrs

Max: 7 hrs

SO42- :0.0593mM (14% yield) (24hrs)

PO42- : 0.0825 mM (19 % yield) (24hrs)


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.

MalathionDiethyl Succinate (DES)


65

Reaction Conditions

0.44mM Malathion

0.44mM EDTA

0.5g FeO Air

25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400m/z0

100

%

140.9

124.9

60.9

60.0

96.978.9

156.9

291.1

163.9

203.0187.0273.1

315.1

292.1329.1 335.1

25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400m/z0

100

%

x2

61.0

59.0

140.9

73.9

88.0 131.9

88.9

125.9 154.0157.0

Time: 0 hrs

Time: 12 hrs

EDTA

Malathion (m/z 329)

Iminodiacetic Acid

HCO3-

oxalate

propionic acid

Malaoxon (m/z 315)

ESI-MS


66

ESI-MS0,C:\MASSLYNX\noradoun.PRO\Data\,FEEDTA1,RAW,1,1,1,0

20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440m/z0

100

%

0

100

%

0

100

%

x6

62.043626496

61.026985472 96.9

10873856

x6 96.9618070016

61.060764160

60.019196928

62.015208448

344.1140525568

98.934430976

300.119373056132.0

7510272273.0

6948864

255.04822528

342.18591360

345.120764672

x661.0

98426880

60.013406208

73.065916928

132.043970560

88.041005056

96.920006912

154.011402240 344.1

6284032273.0

3862016

background

No Fe°, N2

1mM FeSO4

1mM EDTA

4hrs

Fe°, Air1mM EDTA4hrs


67

0.5g Fe; 40-70 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 5.5-6.5

Ind. & Eng. Chem. Res. 2003, 42(21), 5024-5030


68

0.5g Fe; 40-70 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 5.5-6.5

Ind. & Eng. Chem. Res. 2003, 42(21), 5024-5030


69Stumm, 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.


70

Time (hrs)

0 1 2 3 4 5 6 7

ln [

Fe

III E

DT

A]

-11

-10

-9

-8

-7

-6

-5

-4

Addition of 10mM Ca2+

Calcium Addition The addition of 10mM Ca2+ did not effect degradation rate.

10mM EDTA, 2.5g Fe °

kobs = 0.042 M-1h-1 (with Ca2+)

2.5 g Fe°,open to air, total rxn volume 50mL

kobs = -0.044 M-1 h-1kobs = -0.042 M-1 h-1

1mM EDTA, 2.5g Fe °

kobs = -1.11 M-1h-1


71

Calcium Addition cont.

Ca2+ addition had no overall effect on the rate of degradation The added Ca2+ also did not help sequester excess EDTA in

solution

Therefore there was no improvement of Fenton Reactivity with the Ca2+ addition

Alternative way of examining the problem was to hold EDTA concentration constant and vary amount of Fe° present

kinetics of edta degradation induced by dioxygen activation in the fe(0)/air/water (zea) system...

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