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Graduate School of Sciences

Electroanalytical Research Laboratory atChemistry Department

Institut Francilien des Sciences Appliques

Laboratoire Gomatriaux etEnvironnement

DOCTORAL THESIS

To obtain the degree of Doctorof the "University of Paris-Est"- France and "Anadolu University"- Turkey

Speciality: Environmental Science and Techniques

Ali OZCAN

March 19th, 2010

DEGRADATION OF HAZARDOUS ORGANIC COMPOUNDS BY

USING ELECTRO-FENTON TECHNOLOGY

DEGRADATION DES POLLUANTS ORGANIQUES PAR LATECHNOLOGIE ELECTRO-FENTON

Supervisors: Prof. Mehmet A. OTURAN (Universit Paris-Est)

Prof. Ycel SAHIN (Anadolu University)

Jury:

Reviewers: Prof. Figen KADIRGAN Istanbul Technical University

Prof. Otavio GIL Universit de Caen Basse Normandie

Examinators: Prof Kadir PEKMEZ Hacettepe University

Dr. Nihal OTURAN Universit Paris-Est

tel00742451,version1

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Acknowledgement

This thesis has been carried out at the Electroanalytical Research Laboratory of

Chemistry Department and Laboratoire Gomatriaux et Environnement in the frame of

convention for the joint supervision of thesis between Anadolu University and University of

Paris-Est.

First of all, I wish to express my heartfelt thanks to the laboratory directors, Prof. Dr.

Mehmet A. OTURAN and Prof. Dr. Ycel AHN for giving me the chance to conduct the

experiments.

I would like to acknowledge my sincere gratitude to my supervisors, Prof. Dr. Mehmet

A. OTURAN and Prof. Dr Ycel AHN for their endless support, innovative guidance and

continuous encouragement throughout this work.

I want to express my gratitude to reviewers of this thesis, Prof. Dr. Figen KADIRGAN

(Istanbul Technical university) and Prof. Dr. Otavio GIL (Universit de Caen Basse

Normandie) for accepting to read and evaluate my work and for providing valuable

suggestions and comments.

I wish to thank my dissertation committee, Prof. Dr. Mehmet A. OTURAN, Prof. Dr.

Ycel AHN, Prof. Dr. Figen KADIRGAN, Prof. Dr. Otavio GIL, Prof. Dr. Kadir

PEKMEZ (Hacettepe university-Ankara) and Dr. Nihal OTURAN for their valuablecomments and suggestions on this work.

I gratefully acknowledge financial support of Anadolu University Research Found

(Project No: 061022).

A very special thanks to Prof. Dr. Mehmet A. OTURAN, Dr. Nihal OTURAN and

their family for their hosptality during my studies in France.

I would like to thank to Prof. Dr A. Sava KOPARAL (Anadolu University-Eskisehir)

for his support, suggestions and comments.I thank to Anadolu University Plant, Drug and Scientific Researches Center and Erol

ENER for performing the LC-MS analysis.

I also would like to thank to my colleaques of the Chemistry Department, especially to

Levent ZCAN for their assistance, their support and friendship.

I express my gratitude to The Scientific and Technical Research Council of Turkey

(TUBITAK) Scientific Human Resources Development (BAYG) for the fellowship.


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Finally, I would like to dedicate the thesis to my wife Aya Atlr ZCAN and my son

Hasan Berk ZCAN and all my family for their guidance, support, love and enthusiasm.

Without these things this thesis could not have been possible.


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ABSTRACT

In this thesis, a detailed investigation has been carried out on the use of electro-Fenton

technique for the oxidation of the some persistent organic pollutants for the sake of waterremediation. This technique produces OH radicals electrocatalytically and uses them to

oxidize the organic pollutants.

The overall study can be divided into three parts. In the first part, the removal of

selected synthetic dyes and pesticides from water was investigated by using carbon felt (CF)

cathode. The oxidation kinetics of the synthetic dyes (Acid Orange 7 and Basic Blue 3) and

pesticides (picloram, propham, azinphos-methyl and clopyralid) were determined.

Mineralization kinetics of the related organic pollutants in aqueous medium was followed by

total organic carbon and chemical oxygen demand analysis. The overall mineralization was

obtained in all cases. Identification and quantification of the oxidation by-products of the

given synthetic dyes and pesticides were performed by high performance liquid

chromatography, gas chromatography-mass spectrometry, liquid chromatography-mass

spectrometry and ion chromatography. These systematic analysis showed that the initial

organic pollutants were converted into three intermediate forms; organic intermediates, short-

chain aliphatic carboxylic acids and inorganic ions. Based on the intermediates identified, a

plausible mineralization pathway was proposed for each dye and pesticide.

In the second part of the study, the H2O2 production ability of carbon sponge (CS) as a

novel cathode material for the electro-Fenton technique was investigated for the first time in

the literature. The obtained results indicated that CS has a H2O2 production ability three times

higher than the classical cathode CF.

In the third and last part, the efficiency of boron doped diamond (BDD) as an anode in

the electro-Fenton technique was investigated. Firstly, the oxidation and mineralization ability

of BDD was tested for herbicide propham in anodic oxidation conditions. Then, the

combination of CS and BDD electrode in the electro-Fenton technique was examined. The

obtained results indicated that this combination allowed the most efficient results throughout

the thesis. Moreover, the use of BDD anode in the electro-Fenton technique had considerable

effect on the oxidation and mineralization of organics and especially carboxylic acids such as

oxalic and oxamic acids which were highly resistant to mineralization in the case of Pt anode.


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RESUME

Une tude dtaille a t effectue sur l'utilisation de la technique lectro-Fenton pour

l'oxydation de quelques polluants organiques persistants (POP) dans le but du traitement des

eaux uses. Cette technique gnre, in situ et de manire lectrocatalytique, les radicauxhydroxyles (OH) afin de les utiliser pour oxyder la polluants organiques.

Le travail de thse est constitu en trois parts. Dans la premire partie, l'limination de

l'eau des colorants synthtiques et pesticides choisis comme polluants modles a t effectue

en utilisant une cathode en feutre de carbone. Les cintiques d'oxydation des colorants

synthtiques (Acide Orange 7 et Bleu Basique 3) et des pesticides (picloram, prophame,

azinphos-mthyl et clopyralid) ont t dtermines. La cintique de minralisation des

solutions aqueuses des polluants organiques en question a t suivie par des analyses decarbone organique totale (COT) et demande chimique en oxygne (DCO). Une minralisation

quasi-totale a t obtenue dans tous les cas. L'identification et la quantification des sous-

produits d'oxydation des colorants synthtiques et pesticides ont t effectues par les

techniques d'analyse suivantes: Chromatographie liquide haute performance (CLHP),

chromatographie en phasegazeuse-spectromtrie de masse (GC/MS), chromatographie liquide

haute performances-pctromtrie de masse (HPLC/MS) et chromatographie ionique. Ces

analyses systmatique ont mis en vidence que les polluants organiques initiaux ont sont

convertis en trois formes d'intermdiaires ractionnels; intermdiaires organiques, acides

carboxyliques courte chane et ions inorganiques. Bas sur l'identification ces des

intermdiaires ractionnels, une schma de minralisation plausible a t propos pour chaque

colorant et pesticide tudi.

Dans la deuxime partie de l'tude, la capacit de production de peroxyde d'hydrogne

(H2O2) de la cathode en ponge de carbone comme matriau original de cathode pour la

technique lectro-Fenton a t tudie pour la premire fois. Les rsultats obtenus ont indiqu

que le l'ponge de carbone possde une capacit de la production d'H2O2 trois fois plus

leve par rapport la cathode classique (feutre de carbone).

La troisime et dernire partie de cette thse a t consacre l'tude de l'efficacit et

l'utilisation en lectro-Fenton d'une anode de nouvelle gnration, le diamant dop au bore

(BDD pour "Boron Doped Diamond"). Tout d'abord, l'efficacit d'oxydation et la capacit de

minralisation de l'anode BDD ont t examines sur l'herbicide propham dans les conditions

d'oxydation anodique. Ensuite, la combinaison de cathode en feutre de carbone et l'anode

BDD dans la technique lectro-Fenton a t examine. Les rsultats obtenus ont montr que


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cette combinaison conduit aux rsultats significativement meilleurs que le systme classique

feutre de carbone - Pt. L'utilisation de l'anode BDD dans l'lectro-Fenton amliore

considrablement la cintique d'oxydation et l'efficacit de minralisation des polluants

organiques et en particulier des acides carboxyliques tels que les acides oxalique et oxamique

qui rsistent la minralisation dans le cas de l'anode Pt.


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SUMMARY

1. INTRODUCTION 1

1.1. Principles of electrochemical advanced oxidation processes. 11.2. Criteria for selection of organic pollutants. 3

1.3. Objectives of study.5

2. EXPERIMENTAL SECTION 6

2.1. Electrochemical system.. 6

2.2. Analytical Measurements...6

3. RESULTS AND DISCUSSION 8

3.1. Removal of selected hazardous organic pollutants

by electro-Fenton technology using carbon felt (CF) cathode...8

3.1.1. Synthetic dyes..... 8

3.1.1.1. Acid orange 7.. 9

Paper 1.. 11

3.1.1.2. Basic Blue 3. 20Paper 2. 22

3.1.2. Pesticides32

3.1.2.1. Picloram... 33

Paper 3. 36

3.1.2.2. Propham... 47

Paper 4. 50

3.1.2.3. Clopyralid 59

Paper 5. 62

3.1.2.4. Azinphos-Methyl. 72

Paper 6. 74

3.2. Investigation of the H2O2 production ability of carbon sponge (CS)

as a novel cathode material for electro-Fenton process.......... 79

Paper 7. 82

3.3. Investigation of the efficiency of boron doped diamond (BDD)

anode in the electro-Fenton process... 91


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Paper 8. 95

Paper 9. 106

REFERENCES 114

CURRICULUM VITEA 120


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1. INTRODUCTION

1.1. Principles of Electrochemical Advanced Oxidation Processes

Water is of fundamental importance for life on the Earth. The whole mechanism

of metabolism, the synthesis and structure of colloidal cellular constituents, the

solution and transport of nutrients inside the cells and interactions with the

environment are closely related to the specific characteristics of water. On the other

hand, the part of the freshwater (grounwater, lakes and rivers, polar ice and glaciers in

height) that can be used by the human beings is only 2.66% of the global water

resource. Furthermore, these freswater resources, in particular surface water is

exposed to the pollution coming from various human activity. Therefore, in order to

protect natural water resources it is necessary to treat efficiently wastewater effluents

before their injection in the natural water system.

Common physico-chemical wastewater treatment methods such as activated

carbon adsorption and membrane filtration transform the pollutants from one phase to

another, so they separate but not eliminate the water pollutants. Ozone and

hypochlorite oxidations are efficient methods for water disinfection but remaininefficient in case of effluents of hard COD (effluents from industrial or agricultural

activities). On the other hand, they are not desirable because of the high cost of

equipment, operating costs and the secondary pollution arising from the residual

chlorine (Malik and Saha, 2003).

Recent progress in the treatment of persistent organic pollutants (POPs) in water

and/or wastewater has led to the development of advanced oxidation processes

(AOPs). These processes involve chemical, photochemical or electrochemicaltechniques to bring about chemical degradation of organic pollutants. The most

commonly used oxidation processes use H2O2, O3 or O2 as the bulk oxidant to form

principal active specie in such systems, i.e., the hydroxyl radical, OH, a highly

oxidizing agent of organic contaminants (Lin and Lo, 1997; Huston and Pignatello,

1999; Oturan, 2000; Dutta et al., 2001; Malik and Saha, 2003; Swaminathan et al.,

2003; Pignatello et al., 2006. Brillas et al., 2009). These radicals react with organic

pollutants and thus lead to their degradation by hydrogen abstraction reaction


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(dehydrogenation), by redox reaction or by electrophilic addition to systems

(hydroxylation) (Oturan, 2000).

The most commonly used AOPs for the removal of persistent organic pollutants

from water are based on the Fentons reaction. However, this reaction has somelimitations in application such as the use of large quantities of chemical reagents,

large production rates of ferric hydroxide sludge and slow catalysis of the ferrous ions

generation (Boye et al., 2002; Brillas et al., 2004). Electrochemical AOPs overcome

these drawbacks and offer many advantages such as low operational cost and high

mineralization degree of pollutants compared to other known chemical and

photochemical ones. In this sense, anodic oxidation and electro-Fenton processes are

very commonly used electrochemical AOPs.In anodic oxidation, pollutants are mineralized by direct electron transfer

reactions or action of radical species (i.e. hydroxyl radicals) formed on the electrode

surface. In this manner, a wide variety of electrode materials have been investigated

recently, but the boron doped diamond (BDD) has attracted great attention because of

its high O2 evolution overvoltage, high stability and efficiency (Chen and Chen, 2006;

Guinea et al., 2008). This electrode allows to produce large quantities of hydroxyl

radicals from water or hydroxide oxidation decomposition on the electrode surface

(Eqs. 1.1 and 1.2) (Comminellis, 1994; Marselli et al., 2003; Michaud et al., 2003;

Canizares et al., 2004; Panizza and Cerisola, 2005). The formation of H2O2 is also

possible depending on the cathode materials used during the anodic oxidation process.

The oxidation of formed H2O2 to HO2 (Eq. 1.3) or to O2 (Eq. 1.4) takes place at

anode surface (Boye et al., 2002). The formed reactive species may react with the

organics but their oxidation ability are poor compared to adsorbed OH radicals.

H2OOHads+H

+ +e (1.1)

OH OHads +e (pH10) (1.2)

H2O2 HO2 + H+ + e- (1.3)

HO2 O2 + H

+ + e- (1.4)

In the electro-Fenton process, pollutants are destroyed by the action of Fentons

reagent in the bulk together with anodic oxidation at the anode surface in the case of

the use of a high O2 evolution overvoltage anode such as BDD. Fentons reagent is

formed in the electrolysis medium by the simultaneous electrochemical reduction of

O2 to H2O2 (Eq. 1.5) and Fe (III) to Fe (II) ions (Eq. 1.6) on the cathode surface.


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(Gzmen et al., 2003; Guivarch et al., 2003). The reaction between these two species

in the homogeneous medium allows the formation ofOH radicals (Eq. 1.7) (Oturan,

2000; Oturan et al., 2001; Brillas et al., 2005). The Eqs. 1.3 and 1.4 can also take

place during the electro-Fenton process. Moreover, the oxidation of regenerated Fe2+to Fe3+ may occur at the same time (Eq. 1.8) on the anode surface. On the other hand,

the existence of these reactions (Eqs. 1.3, 1.4 and 1.8) are negligible compared to

reaction (1.7) which occurs in the bulk because of the limited surface area of anode.

Finally, iron species (Fe3+/Fe2+) can react with the formed reactive species from

anodic and cathodic reactions (Eq. 1.9-1.11) (Sirs et al., 2007). The overall effect of

these reactions influences the mineralization process of organics in the electro-Fenton

treatment.O2 + 2H

+ + 2e- H2O2 (1.5)

Fe(OH)2+ + e- Fe2+ + OH- (1.6)

Fe2+ + H2O2 + H+ Fe3+ + H2O +

OH (1.7)

Fe2+ Fe3+ + e- (1.8)

Fe3+ + H2O2 Fe2+ + H+ + HO2

(1.9)

Fe3+ + HO2 Fe2+ + H+ + O2 (1.10)

Fe2+

+ HO2

Fe3+

+ HO2-

(1.11)The hydroxyl radicals (OH) formed by the electrochemical (Eq. 1.1) or bulk (Eq. 1.7)

are very powerful oxidizing agents. They react unselectively with organics giving

dehydrogenated and/or hydroxylated reaction intermediates before their total

conversion into CO2, water and inorganic ions, whenOH are produced in continue.

Because OH production does not involve the use of harmful chemical reagents which

can be hazardous for the environment, electrochemical processes can be seen as

environmentally friendly techniques. In conclusion, these processes seem to be verypromising for the purification of water polluted by persistent and/or toxic organic

pollutants.

1.2. Criteria for selection of organic pollutants

In this study, organic pollutants were chosen from synthetic dyes and pesticides

which are the most prominent pollutants of water.


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Synthetic dyes are extensively used in textile, leather, paper, pharmaceutical and

food industries. They thus constitute the major components of wastewaters released

from these industries. The dyes are generally designed to resist biodegradation, so

they cause severe ecological and environmental problems (Allen et al., 1995). Thisenvironmental problem is highlighted by the estimation of a charge up to 50 000 tons

of dye wastes discharged annually from dyeing installations worldwide (Brown,

1987). In addition, some dyes or their metabolites are either toxic or mutagenic and

carcinogenic (Heiss et al., 1992; Chen et al., 2003). Thus, the treatment of the

effluents containing such compounds is important for the protection of natural waters

and environment.

Synthetic dyes divided into two categories as acidic and basic dyes according totheir acidic characters. We have chosen two synthetic dyes, Acid Orange 7 and Basic

Blue 3, which represent these two subgroups.

Natural or synthetic pesticides are used to kill various kinds of animal and plant

pests. Pesticides cover a wide range of products including weedkillers, insecticides,

fungicides, wood preservatives and rodenticides. Of the pesticides that are used far

less than 1% actually reaches a target organism; the rest ends up contaminating the air,

soil, water, plants and animals.

Pesticides have been used extensively to increase the agricultural productivity as

well as their household usage. Food and Agriculture Organization reported that more

than 1.2 million metric tons of pesticides were sold to the agricultural sectors during

the middle of the last decade (Shulze et al., 2002). These substances are in fact very

effective against the harmful microorganisms, weed and insects in order to increase

agricultural yields; however, because of their hazardous nature, the waste and rinsate

from spray and storage equipment have been considered as one of the major threats to

the environment. Thus, treatment of effluents containing pesticides is of

environmental importance. In this study, we investigated the ability of the electro-

Fenton process to eliminate three herbicides which belong to different chemical

family: Picloram (systemic herbicide), propham (carbamate herbicide) and

chlopyralid (systemic herbicide) and a organophosphorus non systemic insecticide:

Azinphos-methyl.

According to our knowlodge, the electro-Fenton removal of the selected organic

pollutants were not reported before.


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1.3. Objectives of Study

This study is aiming to achieve the following objectives:

a) To investigate various operational parameters affecting oxidation and

mineralization kinetics of the selected synthetic dyes and pesticides in the

electro-Fenton technique using carbon felt cathode.

b) To determine and quantify the oxidation intermediates such as aromatic

indermediates, short-chain aliphatic carboxylic acids and inorganic ions as

end-products formed during the electro-Fenton treatment.

c) To study the mineralization reaction pathways of the related pollutants.

d) To investigate the effectivenes of a novel cathode material, carbon sponge,

in the electrogeneration of hydrogen peroxide in acidic solutions.

e) To investigate the effectivenes of boron doped diamond (BDD) electrode as

anode in the electro-Fenton process.


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2. EXPERIMENTAL SECTION

2.1. Electrochemical System

Experiments were performed at room temperature in an undivided cylindrical

glass cell equipped with two electrodes. Carbon felt, carbon sponce and Pt gauze were

used as cathode. The anode was Pt gauze and boron doped diamond (BDD). Prior to

the electrolysis, compressed air was bubbled through the aqueous solution, which was

agitated continuously by a magnetic stirrer. In the case of electro-Fenton experiments,

a catalytic quantity of iron(III) sulphate pentahydrate was introduced into the

electrolysis solution and the pH of the solution was setted at 3 by addition of aqueous

H2SO4 (1 M). The current and the amount of charge passed through the solution was

measured and displayed continuously throughout electrolyses by aDC power supply.

The ionic strength was maintained constant by the addition of 0.05 M Na2SO4.

2.2. Analytical Measurements

The evaluation of the concentrations of the selected organic pollutants were

monitored by high performance liquid chromatography (HPLC) using an Agilent

1100 system equipped with a diode array detector and an autosampler. A reversed

phase Inertsil ODS-3 (5 m ID, 4.6 mm x 250 mm) column was used in the analyses.

The column was thermostated at 40 C. 20 L samples were injected. A suitable

eluent mixture was used during the analysis. Carboxylic acids were identified and

quantified by a Supelcogel H column ( = 7.8300 mm) which was thermostated at

40 C with a mobile phase of 4 mM H2SO4. The detection was performed at 210 nm.

The formed aromatic reaction intermediates during the electrolysis of the

selected hazardous organic compound were determined by HPLC, gas

chromatography coupled with mass spectroscopy (GC-MS) or liquid chromatography

coupled with mass spectroscopy (LC-MS).

The inorganic end-products formed during the mineralization of selected

hazardous organic compound were measured by ion chromatography. A cationic


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exchanger column was used to determine cationic species and an anionic exchanger

column was used to determine anionic species.

The total organic carbon (TOC) of the initial and treated samples was

determined by a Shimadzu TOC-V analyzer. A platinium catalyst was used in thecombustion reaction. The carrier gas was oxygen with a flow rate of 150 ml min1. A

non-dispersive infra-red detector, NDIR, was used in the TOC system. Calibration of

the analyzer was attained with potassium hydrogen phthalate (99.5%, Merck) and

sodium hydrogen carbonate (99.7%, Riedel-de Han) standards for total carbon (TC)

and inorganic carbon (IC), respectively. The difference between TC and IC values

gives TOC value of the sample.

The chemical oxygen demand (COD) analysis and hydrogen peroxidedetermination were performed according to certified analytical methods.

The mineralization current efficiency (MCE) values were determined by using the

following expression (Eq. 2.1) (Brillas et al., 2004; Sires et al., 2006; Diagne et al.,

2007):

100)TOC(

)TOC(MCE

theor

exp

= (2.1)

where (TOC)exp is the experimental TOC at a given time and (TOC)theor is thetheoretical TOC value considering the applied electrical charge (=current x time)

consumed for the complete mineralization of organic pollutant under study according

to its electrochemical oxidation reaction.tel00742451,version1

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3. RESULTS AND DISCUSSION

The obtained results throughout this thesis work are divided into three main

sections; (i) Removal of selected hazardous organic pollutants by electro-Fenton

technology using carbon felt (CF) cathode, (ii) H2O2 production ability of carbon

sponge (CS) as a novel cathode material for electro-Fenton process, and (iii) Use and

efficiency study of boron doped diamond (BDD) anode in the electro-Fenton process.

3.1. Removal of selected hazardous organic pollutants by electro-

Fenton technology using carbon felt (CF) cathode

3.1.1. Synthetic dyes

Synthetic dyes are extensively used in textile, leather, paper, pharmaceutical and

food industries. They thus constitute the major components of wastewaters released

from these industries. The dyes are generally designed to resist biodegradation, so

they cause severe ecological and environmental problems (Allen et al., 1995). This

environmental problem is highlighted by the estimation of a charge up to 50 000 tons

of dye wastes discharged annually from dyeing installations worldwide (Brown,

1987). In addition, some dyes or their metabolites are either toxic or mutagenic and

carcinogenic (Heiss et al., 1992; Chen et al., 2003). Thus, the treatment of the

effluents containing such compounds is important for the protection of natural waters

and environment.

Common physico-chemical treatment methods for the decolourization of dye

wastewaters such as activated carbon adsorption and extraction are able to separate

these pollutants to form a concentrated waste to be treated subsequently, and so they

are inefficient to eliminate the pollutants. Ozone and hypochlorite oxidations are

efficient decolorizing methods, but they are not desirable because of the high cost of

equipment, operating costs and the secondary pollution arising from the residual

chlorine (Malik and Saha, 2003) or because of remained oxidation reaction

intermediates. Other conventional processes based on biological treatment (aerobic

anaerobic) are relatively ineffective in effluent decolourisation, because high


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molecular weight compounds are not easily degraded by bacteria, and thus coloured

compounds pass through the treatment system largely undegraded (Banat et al.,

1996).

3.1.1.1. Acid orange 7

The azo dye Acid Orange 7 (AO7), also called Orange II (Fig. 3.1) is a widely

used synthetic dye. It does not decompose biologically, and resists to photochemical

degradation and chemical oxidation. It is generally used as a model substrat for the

azo dyes. Therefore, its removal has been studied by several research groups; Bandara

et al. (1996) used photo-Fenton reactions in the presence ofnatural sunlight, Kiwi etal. (2001) reported a catalytic photo-assisted system, Fe3+/nafion/glass fibers,

Daneshvar et al. (2003) employed electrocoagulation, Ray et al. (2004) performed

photocatalytic oxidation in the presence of TiO2, Ramirez et al. (2005) investigated

optimum conditions for Fenton's oxidation and Inoue et al. (2006) used ultrasound

waves. In addition, Daneshvar et al. (2008) were studied the electrochemical

degradation of AO7 in potentiostatic conditions and obtained a mineralization ratio of

75%.

N

OH

N SO3Na

Figure 3.1. The molecular structure of Acid Orange 7

In this part of the study, we report a detailed discussion on the oxidative

degradation of AO7 in acidic aqueous solution by the electro-Fenton process. Theexperiments were carried out under constant current electrolysis conditions in

undivided electrochemical cell by using a carbon-felt cathode and a Pt anode. The

kinetics of AO7 degradation by OH during electro-Fenton process has been

examined. The absolute rate constant of the reaction between AO7 and OH was

determined as (1.20 0.17) x 1010 M-1 s-1 by the competition kinetic methodusing

benzoic acid as a reference competitor (Gzmen et et al., 2003). The effect of the

applied current and catalyst concentration on the degradation of AO7 was studied.


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The optimal current value and Fe2+ concentration for the degradation of AO7 were

found as 300 mA and 0.1 mM, respectively. AO7 degradation rate was found to

decrease by increase in Fe3+ concentration beyond 0.1 mM. Mineralization of AO7

aqueous solutions was followed by total organic carbon (TOC) measurements and themineralization degree was found to be 92% after 8 h of treatment.

The reaction between organics and hydroxyl radicals has led to the formation of

aromatic intermediates, short-chain aliphatic carboylic acids and inorganic ions.

Several aromatic intermediates such as 1,2-naphthaquinone, 1,2-naphthalenediol, 4-

aminobenzenesulfonic acid, 4-aminophenol, 4-hydroxybenzenesulfonic acid, 2-

formyl-benzoic acid, 2-hydroxy-1,4-naphthalenedione, 2,3-dihydroxy-1,4-

naphthalenedione, salicylic acid, 1,4-benzoquinone, hydroquinone and 1,2,4-benzentriol were identified by high performance liquid chromatography (HPLC) and

gas chromatography-mass spectrometry (GC-MS) analysis. Maleic, acetic, malonic,

glyoxylic, formic and oxalic acids were identified as short-chain aliphatic carboxylic

acids by ion exclusion chromatography. The sulphate, nitrate and ammonium was

determined as final by-products by ion exchange chromatography. Based on TOC

evolution and identification of aromatic intermediates, short-chain carboxylic acids

and inorganic ions released during treatment, a plausible mineralization pathway was

proposed.

The thorough results of this section are included in the following paper (Paper 1).

Ali zcan, Mehmet A. Oturan, Nihal Oturan, Ycel ahin, (2009). Removal of

Acid Orange 7 from water by electrochemically generated Fentons reagent.

Journal of Hazardous Materials, 163(2-3), 1213-1220.

The following presentations in a congress are related to this work:

Ali zcan, Ycel ahin, Nihal Oturan, Mehmet A. Oturan, Removal of Acid

Orange 7 from water by electrochemically generated Fentons reagent, Journees

dElectrochimie 2007, Lyon, France, 2-6 July 2007 (Poster presentation).


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Paper 1

Ali zcan, Mehmet A. Oturan, Nihal Oturan, Ycel ahin (2009).

Removal of Acid Orange 7 from water by electrochemically generated Fentons

reagent.



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3.1.1.2. Basic Blue 3

Basic Blue 3 (BB3) is a cationic dye (Fig. 3.2). Cationic dyes, commonly known

as basic dyes, are widely used in acrylic, nylon, silk, and wool dyeing. Due to theircomplex chemical structure, they are recalcitrant to treatment by chemical, physical

and biological methods. Furthermore, any degradation by physical, chemical or

biological treatments may produce toxic and carcinogenic products (McKay et al.,

1985; Gregory et al., 1991).

O

N

N N

Cl-

Figure 3.2. Chemical structure of BB3 ((7-Diethylamino-phenoxazin-3-ylidene)-diethyl-

ammonium chloride).

The removal of BB3 from water was already investigated by different process.

Akbari et al. (2002) used a polyamide-based nanofiltration membrane for the removal

of BB3 from textile dye effluent. Moreover, Daneshvar et al. (2006) used

electrocoagulation for decoloration of BB3 containing solutions. Adsorption process

for the removal of BB3 from water was also performed by using peat ( Allen et al.,

2004) and rice straw (Abdel-Aal et al., 2006).

In this part of the study, we focused our effort on the identification of the

oxidation reaction intermediates and the elucidation of the degradation pathway

during electro-Fenton treatment of synthetic BB3 aqueous solutions.

The decay of BB3 and the evolution of its oxidation products during electrolysis

were monitored by high performance liquid chromatography (HPLC). The absoluterate constant of the BB3 hydroxylation reaction has been determined as (2.61 0.06)

x 109 M-1 s-1 by using the competition kinetic method. The effect of the applied

current on the BB3 removal rate was examined. The optimal current value for the

mineralization of BB3 aqueous solution was found as 300 mA. It was also observed

that the catalyst (Fe3+) concentration values more than 0.2 mM have a negative effect

on the mineralization rate of BB3. The mineralization of BB3 aqueous solution was


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followed by total organic carbon (TOC) measurements. The mineralization ratio was

found upper to 98%.

Decolorization of a solution can be observed when the chromophore responsible

of the color is chemically destroyed but this does not constitute an indication ofelimination of the organic compounds from the treated solution. In addition, the

oxidation treatment can lead to a more toxic solution when the formed chemical

intermediates are more toxic than the parent dye molecule. Thus, information relative

to chemical compounds produced during the decolorization process constitues an

important issue. In order to determine aromatic degradation products of BB3, several

experiments were performed by using chromatographic and mass analysis. Generation

of short chain carboxylic acids is expected from the oxidative breaking of the arylmoiety of aromatic products. The qualification and quantification of short chain

carboxylic acids was performed by ion-exclusion chromatography. The obtained

results indicate the formation of several carboxylic acids. We could only determine

oxalic and oxamic acids which are the dominant ones. The ion chromatography

analysis allowed qualitative and quantitative monitoring of inorganic ions resulting

from the mineralization of BB3. The formed inorganic ions were determined as

ammonium, nitrate, diethylammonium and methylammonium by retention time

comparison and standard addition method. Based on the identified intermediates, a

general mineralization mechanism was proposed.


Ali zcan, Ycel ahin, A. Sava Koparal, Mehmet A. Oturan (2009).

Electro-Fenton removal of the cationic dye Basic Blue 3 by using carbon felt

cathode.

Journal of Environmental Engineering and Management, 19(5), 267-275.


Ali zcan, Ycel ahin, A. Sava Koparal, Mehmet A. Oturan

Removal of Basic Blue 3 from Water by Electrochemically Generated

Fentons Reagent

The 6th Spring Meeting of the International Society of Electrochemistry, Foz do

Iguau, Brasil, 16-19 March 2008. (Poster presentation).


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Paper 2

Ali zcan, Ycel ahin, A. Sava Koparal, Mehmet A. Oturan, 2009.

Electro-Fenton removal of the cationic dye Basic Blue 3 by using carbon

felt cathode.

Journal of Environmental Engineering and Management, 19(5), 267-275.


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3.1.2. Pesticides

Pesticides are natural or synthetic substances used to kill various kinds of animal

and plant pests. Pesticides cover a wide range of products including weedkillers,

insecticides, fungicides, wood preservatives and rodenticides. Of the pesticides that

are used far less than 1% actually reaches a target organism; the rest ends up

contaminating the air, soil, water, plants and animals. As a result, pesticides constitues

a potential threat to human health because of their solubility in lipid and accumulation

in our fatty tissues in a process called bioconcentration. Biomagnification is what

happens when organisms eating contaminated organisms concentrate the pesticides

and then in turn are eaten by other organisms. As a result those on the top of the foodchain (all meat-eating humans) are most at risk because the concentration is magnified

at each step of the food chain. Furthermore because pesticides are designed to kill

organisms due to their neurological or reproductive toxicity they also have many

similar deleterious effects in humans, and many show adverse effects on the immune

system at very low doses. Pesticides have many ecological effects of concern as well.

Ecological effects are often considered to be an early warning indicator of potential

human health impacts. In the environment pesticides can kill organisms, causecancers, tumors and lesions in fish and wildlife, suppress the immune system, cause

reproductive failure, damages on DNA, disrupt the endocrine (hormonal) system, and

cause physiological birth defects (teratogenic effects) (Sazova, 2004).

These substances have been used extensively to increase the agricultural

productivity as well as their household usage. Food and Agriculture Organization

reported that more than 1.2 million metric tons of pesticides were sold to the

agricultural sectors during the middle of the last decade (Shulze et al., 2002). These

substances are in fact very effective against the harmful microorganisms, weed and

insects in order to increase agricultural yields; however, because of their hazardous

nature, the waste and rinsate from spray and storage equipment have been considered

as one of the major threats to the environment. Thus, treatment of effluents containing

pesticides is of environmental importance. In this study we investigated the ability of

the electro-Fenton process to eliminate three herbicides belonging to different

chemical family: Picloram (systemic herbicide), propham (carbamate herbicide),


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chlopyralid (systemic herbicide) and a organophosphorus non systemic insecticide:

Azinphos-methyl.

3.1.2.1. Picloram

Picloram (4-amino-3,5,6-trichloro-2-pyridincarboxylic acid) is a herbicide used

for broadleaf weed control in pasture and rangeland, wheat, barley, oats, and for

woody plant species (Fig. 3.3) (Ahrens, 1994). Picloram is moderately to highly

persistent in the soil environment, with reported field half-lives from 20 to 300 days

and an estimated average of 90 days (Wauchope et al., 1992). Photodegradation is

significant only on the soil surface and volatilization is practically nil. Degradation bymicroorganisms is mainly aerobic. Increasing of soil organic matter enhances the

sorption of picloram and the soil residence time (Ahrens, 1994). Picloram is poorly

bounded to soils, although its adsorption became better by soils with higher

proportions of organic matter (Ahrens, 1994). It is soluble in water, and therefore may

be mobile (Kidd and James, 1991). These properties, combined with its persistence,

mean it may constitute a risk of groundwater contamination.

N

ClCl

Cl

2

O

OH

Figure 3.3. Chemical structure of picloram

The degradation and removal of picloram from water was investigated by

several authors in the literature. Ghauch (2001) used zero-valent iron for the

degradation of picloram. He observed that picloram is converted to 4-amino-2-

pridylcarbinol molecule in one hour reaction but it is not degraded completely to non-

hazardous species. Rahman and Munuer (2005) used heteregenous photocatalysis in

the presence of different kinds of titanium oxide catalysts. Adsorption process by

using the calcinated hydrotalcite (Pavlocia, 2005) and calcinated Mg-Al-CO3-LDH

(Cardoso and Valim, 2006) as sorbents for the removal of picloram from water was


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also performed. According to literature there was no study on the degradation and

mineralization of picloram by using electro-Fenton process.

In this part of the study, we investigated the removal of picloram from its

aqueous solution by electro-Fenton technique using carbon felt cathode. Firstly, thedegradation kinetics of picloram was investigated. Kinetic results evidence a pseudo-

first-order reaction, with an oxidation reaction rate constant of picloram by hydroxyl

radicals of (2.73 0.08) x 109 M-1 s-1. The effect of applied current and catalyst

concentration on the degradation and mineralization of picloram was also

investigated. The optimum applied current and catalyst concentration values for the

degradation of picloram was determined as 300 mA and 0.2 mM Fe3+, respectively.

Mineralization of picloram aqueous solutions was followed by the total organiccarbon (TOC) analysis. At the end of 8 h ofelectrolysis, 95% of the initial TOC was

removed.

The HPLC analysis of electro-Fenton treated aqueous solution of picloram (I)

showed the formation of several intermediate products. In order to determine these

products several analysis were performed by using some chromatographic techniques.

LC-MS analysis showed that picloram degradation has led to the formation of several

products but a dominant aromatic intermediate; 4-amino dichloro hydroxy picolinic

acid. 2,3,5-Trichloro-pyridin-4-ylamine, 3,5,6-Trichloro-pyridine-2-carboxylic acid, 4

amino-5,6-dichloro-3-hydroxy-pyridine-2-carboxylic acid and 5,6-Dichloro-3-

hydroxy-pyridine-2-carboxylic acid were identified by GC-MS analysis. The oxalic,

oxamic, glyoxylic, glycolic, and formic acids were detected by ion-exclusion

chromatography as short-chain carboxylic acids. The formation of chloride, nitrate

and ammonium was observed during the electro-Fenton treatment of picloram. The

identified by-products allowed to propose a mineralization pathway for the picloram

mineralization.


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Ali zcan, Ycel ahin, A. Sava Koparal, Mehmet A. Oturan (2008)

Degradation of picloram by the electro-Fenton process.



1. Ali zcan, Mehmet A. Oturan, Ycel ahin, A. Sava Koparal

Degradation of picloram by the electro-Fenton process

Journees dElectrochimie 2007, Lyon, France, 2-6 July 2007 (Poster

presentation).

2. Ali zcan, Ycel ahin, Mehmet A. Oturan

Identification Of Oxidation By-Products Of Picloram

6th Aegean Analytical Chemistry Days, Denizli, Turkey, 9-12 October 2008

(Poster presentation).


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Paper 3


Degradation of picloram by the electro-Fenton process,

Journal of Hazardous Materials, 153(1-2), 718-727


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3.1.2.2. Propham

Propham is a carbamate herbicide used for the control of weeds in alfalfa,

clover, flax, lettuces, afflow, spinach, sugar beets and pees. It prevents cell divisionand acts on meristematic tissues. Moreover, it could be degraded into aniline

metabolites which are more dangerous substances than the parent molecule (Orejuela

and Silva, 2004). The presence of this herbicide in surface water was reported by

Meister (2000). On the other hand, the maximum allowed amount of this substance in

water intented to human consumption is 0.1 g L-1 in water intended for human

consumption according to the EU Directive 98/83(EC, 1999). Therefore, the removal

of this substance from aqueous solutions has great importance.

N

H

O

O

Figure 3.3. Chemical structure of propham

In this part of the study, the removal of a carbamate herbicide, propham, from

aqueous solution has been carried out by the electro-Fenton technique. The

degradation kinetics of propham evidenced a pseudo-first-order degradation. The

absolute (or second-order) reaction rate constant of the reaction between propham and

hydroxyl radicals was determined as (2.20.10) x 109 M-1 s-1. The mineralization of

propham was followed by the total organic carbon (TOC) removal. The optimal Fe3+

concentration was found as 0.5 mM at 300 mA. 94% of initial TOC of 0.25 mM

propham aqueous solution was removed in 8 h.

HPLC, GC-MS and LC-MS analysis were used to determine the aromatic by-

products of propham oxidation and the results are given in Table 1. The HPLC

chromatograms showed that the degradation of propham has led to formation of

several intermediates. Two of them exhibits dominant peaks but they have not been

identified by HPLC. A single electrolysis was performed for 15 min and the formed

aromatic intermediates were extracted with dichloromethane, and then the obtained

extract was analyzed by GC-MS. Two dominant peaks in the GC chromatogram were

identified as o- and p-hydroxypropham based on their molecular ion and mass

fragmentation. Moreover, we prepared the trimethylsilyl (TMS) derivatives of the


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intermediates and identified a new product which was different from those obtained

by using HPLC and GC-MS analysis. In the LC-MS analysis, two dominant peaks in

the LC chromatogram were identified as p- and o-hydroxypropham according to

(M+1)+

values and mass fragmantations.The oxidative breaking of the aryl moiety of aromatic products forms the short

chain carboxylic acids during the electro-Fenton process. These substances were

identified and quantified by ion-exclusion chromatography with two well-defined

peaks related to oxalic (tr: 7.04 min) and oxamic (tr: 10.60 min) acids as ultimate

carboxylic acids. Oxamic acid can be produced from the degradation of nitrogen

containing by-products of propham. In the first 80 min of the electrolysis, the

formation of maleic, glyoxylic, lactic, formic, acetic and fumaric acids were alsoobserved.

The nitrogen atom found in the propham structure was converted to nitrate and

ammonium ions which were identified by ion chromatography analysis. The

formation rate of ammonium ions in the first 30 min of the electrolysis was very fast.

After that time, ammonium formation rate gradually decreased and reached a steady

state value. This behaviour can be explained via the slow degradation rate of oxamic

acid because it forms stable iron complexes and shows resistance to the

mineralization.

The identified by-products allowed proposing a pathway for the propham

mineralization.


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Ali zcan, Ycel ahin, Mehmet A. Oturan (2008)

Removal of propham from water by using electro-Fenton technology: Kinetics

and mechanismChemosphere, 73(5), 737-744.



Mineralization of Propham in Aqueous Medium by using an

Electrochemical Advanced Oxidation Process

The 58th Annual Meeting of the International Society ofElectrochemistry, Banff, Canada, 9-14 September 2007 (Oral

presentation).


Determination Of Degradation Intermediates Of Propham With

Chromatographic And Mass Spectrometric Analysis

6th Aegean Analytical Chemistry Days, Denizli, Turkey, 9-12 October 2008.

(Poster presentation)


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Paper 4


Removal of Propham from Water by Using Electro-Fenton Technology; Kinetics

and Mechanism

Chemosphere,, 73(5), 737-744


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3.1.2.3. Clopyralid

Clopyralid (CLPYD, 3,6-dichloro-2-pyridinecarboxylic acid) is a systemic

herbicide registered by US environmental protection agency (US EPA, 1998) forcontrol of weeds and woody plants on rangeland and permanent grass pastures, non-

cropland areas and rights-of-way. It affects plant cell respiration and growth. This

herbicide is generally active in the soil and may be persistent in soils under anaerobic

conditions and with low microorganism content. The half-life in soil can range from

15 to more than 280 days. Degradation products have not been identified in the soil up

to now (Corredor et al., 2006). Due to its high solubility in water, this herbicide is not

adsorbed onto soil particles. It may leach into ground-water by surface water infiltration and constitute a potential threat to the human health and environment.

Therefore, the removal of this herbicide from water resources is very important.

N

Cl

Cl

O

OH

Figure 3.4. Chemical structure of clopyralid

The removal of CLPYD from aqueous solutions was performed by the electro-

Fenton process using carbon felt cathode. The decay kinetics well fitted to pseudo-

first order reaction and absolute rate constant of the oxidation reaction of CLPYD was

determined as (4.4 0.2) x 108 M-1 s-1. Mineralization ability of the system was

followed by the chemical oxygen demand (COD) analysis. The total mineralization

was achieved at almost 120 and 240 min electrolysis for 1.5 and 3.0 mM CLPYD

solutions, respectively. The obtained results indicate that the electro-Fenton process is

very effective for the removal of this pollutant from water.

HPLC analysis of electro-Fenton treated solutions of CLPYD showed the

formation of several by-products but three of them were dominant. The CLPYD peak

was rapidly decreased and the peaks corresponding to the by-products were appeared

and increased in the first 5 min. After that time, they gradually decreased and

completely disappeared in 20 min. This situation indicates that the formed by-


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products were unstable at the given oxidizing conditions. Therefore, they did not

accumulate during the electrolysis. Moreover, the gas chromatography-mass

spectrometry (GC-MS) analysis of the samples gave no meaningful results.

Formic, oxalic, maleic, fumaric, oxamic and glyoxylic acids were determinedas short-chain carboxylic acids. While the formation rates of oxalic, maleic and

oxamic acids are very high in the first 90 min, after that time, their accumulation rates

gradually decreased.

The ion chromatography analysis indicated the formation of ammonium, nitrate

and chloride ions. The formation rate of chloride ions was very high in the first 30

min of electrolysis. The released quantity of chloride ions was almost reached to its

maximal value at 60 min. After that time, its concentration is nearly the same. Thestoichiometric ratio of initial chlorine was achieved at the end of the electrolysis.

Nitrogen atom found in the CLPYD structure was rapidly converted to ammonium

ions in the first 30 min of the electrolysis. After that time, ammonium formation rate

gradually decreased and reached a steady state value. This behaviour can be explained

via the slow degradation rate of oxamic acid because it forms stable iron complexes

and shows resistance to the mineralization. The formation of nitrate ions can be

attributed to the oxidation of ammonium ions on the Pt anode. The obtained

concentrations of NO3- and NH4

+ ions showed that 98% of the initial nitrogen was

converted to the NH4+ ions during the electro-Fenton process. We quantified almost

99% of initial nitrogen as NH4+ and NO3

- ions after 6 h electrolysis.

Based on these intermediates, a general oxidation mechanism was proposed in

acid medium.


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Ali zcan, Nihal Oturan, Ycel ahin,Mehmet A. Oturan (2010)

Electro-Fenton treatment of aqueous Clopyralid solutions

International Journal of Environmental Analytical Chemistry(in press).


Ali zcan, Nihal Oturan, Ycel ahin, Mehmet A. Oturan

Electro-Fenton treatment of aqueous Clopyralid solutions

,5th European Conference on Pesticides and Related Organic Micropollutants

in the Environment and11th Symposium on Chemistry and Fate of Modern

Pesticides, October 22-25, 2008, Marseille, France. (Poster presentation)


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Paper 5

Ali zcan, Nihal Oturan, Ycel ahin,Mehmet A. Oturan (2010)Electro-Fenton Treatment of Aqueous Clopyralid Solutions

International Journal of Environmental Analytical Chemistry, in press.


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3.1.2.4. Azinphos-Methyl

Azinphos-methyl (AZPM) is an organophosphorus non-systemic pesticide

widely used to control a variety of insects in food and non-food crops, ornamentalsand forest trees (Fig. 3.5). It is mainly applied as a foliar spray during the growing

season. It has been reported that AZPM had the seventh highest use of all pesticides in

the United States in 1997 (US EPA, 1998). Although its high toxicity and widespread

usage, a limited number of studies was reported in literature for the removal of AZPM

from water resources. To the best of our knowledge, the degradation of AZPM by the

electro-Fenton process was not reported previously in the literature.

This part of the study deals with the degradation of AZPM and its commercialformulation, (GMWP25), by the electro-Fenton process using carbon felt cathode.

The degradation kinetics and mineralization efficiency was deeply investigated. The

identification and evolution of the degradation intermediates was also performed by

HPLC, GC-MS and IC analysis. Based on identified intermediates, a general reaction

sequence was proposed for the degradation of AZPM in acidic media by

electrochemically generated hydroxyl radicals.

OCH3

P

OCH3S

S

N

N

N

O

Figure 3.5. Chemical structure of azinphos-methyl


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The study related to the work on AZPM resulted to the following publication in 5th

European Conference on Pesticides and Related Organic Micropollutants in the

Environment which is published in the congress proceedings.


Mineralization of a commercial formulation of Azinphos-methyl, Gusathion M WP

25, in aqueous medium by indirect electrochemical advanced oxidation method,

Proceedings of 5th European Conference on Pesticides and Related Organic

Micropollutants in the Environment and 11th Symposium on Chemistry and Fate

of Modern Pesticides, October 22-25, 2008, Marseille, France.


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Paper 6


Mineralization of a commercial formulation of Azinphos-methyl, Gusathion M

WP 25, in aqueous medium by indirect electrochemical advanced oxidation

method.

Proceedings of 5th European Conference on Pesticides and Related Organic

Micropollutants in the Environment and 11th Symposium on Chemistry and

Fate of Modern Pesticides, October 22-25, 2008, Marseille, France.


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3.2. Investigation of the H2O2 production ability of carbon sponge

(CS) as a novel cathode material for electro-Fenton process

Considerable efforts have been made by many researchers to find appropriate

treatment systems in order to remove pollutants and impurities from wastewaters

emanated from the textile industries. Among the treatment Technologies developed,

the advanced oxidation processes (AOPs) are considered as the most attractive

methods for the treatment of water and wastewater containing toxic, persistent and

non-biodegradable pollutants. AOPs are based on the generation of very reactive non-

selective transient oxidizing species such as hydroxyl radicals (OH), which were

identified as the dominant oxidizing species. In this context, the electro-Fenton

process constitute an emergent and promising wastewater treatmrnt method.

Oxidation power of the electro-Fenton system was mainly related to H2O2

production ability of cathode material used in the electrolysis. Therefore, the cathode

materials which have high H2O2 production ability are very important for the effective

destruction of pollutants since the formation rate of hydroxyl radicals through

Fentons reaction is conditioned by H2O2 formation rate on the cathode employed. In

this manner, several electrode materials such as mercury pool (Oturan and Pinson,1995), graphite (Do and Chen, 1994), reticulated vitreous carbon (Alvarez-Gallegos

and Pletcher, 1999), carbon felt (Oturan, 2000; Oturan et al., 2000 and 2001), O2-fed

carbon polytetrafluoroethylene (Brillas et al., 1996; Boye et al., 2003; Sirs et al.,

2007), and activated carbon fiber (Wang et al., 2005) were investigated as the cathode

material in the electro-Fenton process. Consequently, we have investigated carbon

sponge (CS) as a novel cathode material for the first time in the literature. The

efficiency of the CS electrode was comparatively discussed with carbon felt (CF)electrode for degradation of the synthetic dye, Basic Blue 3 (BB3).

Fig. 3.6 shows the H2O2 concentration produced on the CS and CF electrodes as

a function of time. As can be seen, the electrogeneration of H2O2 on both electrodes

showed similar behaviours. In the first fifty minutes of electrolysis, there was a fast

electrogeneration of H2O2 but after that time the H2O2 accumulation rate was

decreased and reached to a steady state value when its generation rate at the cathode

(Eq. 2) and its decomposition rate at the anode become equal. The concentration of

H2O2 reached via CS and CF electrodes was 8.05 and 2.70 mM, respectively, at the


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end of the 180 min. electrolysis. The results obtained with the CS was nearly three

times higher than that of CF. According to these results, it can be concluded that CS

was a favorable cathode material for the electrogeneration of H2O2.

The effect of some operational parameters such as applied current value, type ofsupporting electrolyte, O2 flow rate, pH and temperature on the generation of H2O2 by

CS was investigated. The optimal current value for the H2O2 production was 100 mA

(5.6 mA cm-2). The temperature and O2 flow rate have also a significant effect on the

amount of electrogenerated H2O2, whereas supporting electrolyte and pH of the

solution have a slight affect. The degradation and mineralization of the BB3 were

followed by using HPLC and TOC analysis, respectively. The degradation and

mineralization of BB3 using CS cathode was found faster than that of CF cathode. Atthe end of eight hour electrolysis under the same conditions, 91.6% and 50.8% of the

initial TOC of the BB3 aqueous solution was removed by using CS and CF cathodes,

respectively. The mineralization current efficiency (MCE) of CS electrode was four

times higher than that of CF electrode. The results showed that the CS electrode

provides an alternative cathode material for future designing of water treatment

system in the electro-Fenton process.

0

3

6

9

0 50 100 150 200

Time / min

[H2O2]/mM

Figure 3.6. The amount of electrogenerated H2O2 on the CS () and CF () surfaceas a function of time at room temperature. [Na2SO4] : 0.05 M, I : 100 mA, pH : 3, V :0.125 L, O2 flow rate : 100 mL min

-1.


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Carbon sponge as a new cathode material for the electro-Fenton process.Comparison with carbon felt cathode and application to degradation of

synthetic dye basic blue 3 in aqueous medium.

Journal of Electroanalytical Chemistry, 616 (1-2), 71-78.

The following presentation in a congress is also related to this work:

Ali zcan, Ycel ahin, Nihal Oturan, Mehmet A. Oturan

H2O2 production ability of carbon sponge(CS) as a novel cathode material for

the electro-Fenton process.

Electrochimie et ses Applications Industrielles et Environnementales RNE

05 (Cinquime Rencontre Nationale d'Electrochimie), Agadir (Marocco), 27-29

March, 2008. (Poster presentation).


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Paper 7


Carbon sponge as a new cathode material for the electro-Fenton process.

Comparison with carbon felt cathode and application to degradation of

synthetic dye basic blue 3 in aqueous medium

Journal of Electroanalytical Chemistry, 616 (1-2), 71-78.


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interesting to note that while the initial degradation rate of propham was almost the

same for all applied current values, the TOC removal values greatly increased at

higher applied current values. This situation can be explained in the following way.

The aromatic reaction intermediates formed by the oxidation of propham are morereactive towards hydroxyl radicals than propham. By increasing applied current

values, the formation rate of OH also increased and these radicals were consumed

simultaneously by the aromatic and aliphatic by-products. As a result the degradation

rate of propham did not change significantly. On the other hand, the TOC removal

values remained almost constant at 300 and 500 mA. The results show that the

optimal current value was about 300 mA for mineralization of propham.

The effect of temperature on the anodic oxidation behavior of propham wasinvestigated at different temperature values between 15 and 35 C at 100 mA constant

current. The degradation of propham showed similiar trend for all temperature values.

By increasing the temperature from 15 C to 35 C, a significant increase was

obtained in the degradation rate of propham.

The pH of electrolyses medium is the other important parameter for the

electrochemical oxidation procedures. The results indicated that the efficiency of the

process was increased in acidic media.

In order to verify the influence of the supporting electrolyte on the degradation

kinetics and mineralization efficiency of propham aqueous solutions, the experiments

were performed in acidic medium (pH 3) containing different supporting electrolytes

as 0.05 M Na2SO4, 0.1 M NaNO3, LiClO4 and NaCl. The degradation rate of propham

was slightly increased when the Na2SO4 was used as supporting electrolyte instead of

NaNO3. The complete degradation of propham almost took place in a 180 min

electrolyses period in the presence of Na2SO4, NaNO3 and LiClO4. However, it

finished in 15 min in the case of NaCl. The TOC removal values of propham

mineralization were increased in the following order: NaCl < NaNO3 < LiClO4

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These Ozcan 19 Mars 2010