Electrochemical Advanced Oxidation of 4, 4′-Sulfonyldiphenol on BDD and Pt Anodes in Aqueous Medium

Electrochemical Advanced Oxidation of 4, 4′-Sulfonyldiphenol on BDD and Pt Anodes in Aqueous Medium

Naimi Imen1*, Louhaichi Mohamed Radhouan2, Ben Rayana Mohamed Chiheb2 and Bellekhal Nizar1.

1Unité de recherche de Catalyse dElectrochimie de Nanomatériaux et leurs Applications et de Didactique CENAD, Institut National des Sciences Appliquées et de Technologie (INSAT), B.P.N°676, 1080 Tunis Cedex, Tunisie.

2. Laboratoire National de Contrôle des Médicaments, 11 bis Rue Jebel Lakhdar Bab Saadoun, 1006 Tunis, Tunisie.

Abstract In this paper, degradation of Bisphenol S (BPS), an environmental endocrine disruptor, in an aqueous medium by the electrochemical advanced oxidation process Electro-Fenton is studied using carbon felt as cathode and two different types of anode materials: Platinum (Pt) and boron doped diamond (BDD). The effect of some operating conditions, such as the current density, nature of the supporting electrolyte and catalyst, has been evaluated. The comparative study of BPS removal during the electro-Fenton treatment using Pt or BDD anodes showed that optimal conditions led to total degradation of the pollutant for both anodes but the removal rate with the BDD anode is higher than the Pt anode due to the higher oxidizing power of the BDD anode. Kinetic data showed a pseudo first- order reaction between hydroxyl radical and BPS with an absolute rate constant of 2.22×109 M1 s1 for Pt anode and 4.31×109 M1 s1 for BDD anode. The performance of the process has been followed in terms of BPS conversion to by-products and carboxylic acids using GC-MS and HPLC, respectively.

KeywordsBisphenol S; Electro-Fenton process; hydroxyl radicals; BDD anode; Degradation.

1. INTRODUCTION

   Bisphenol analogues are widely used in industrial and consumer products. Among these compounds is bisphenol A (BPA), produced in quantities of over eight billion pounds each year worldwide, and frequently used in the production of polycarbonate plastics and resin lining of food and beverage cans [1]. BPA has been identified as a weak estrogenic chemical, which modifies natural endocrine functions by binding to the estrogen receptor which consequently causes adverse effects on the human health and wildlife like breast cancer, endometriosis and infertility [2].

   Concerns about the health risks of BPA are increasing, and restrictions/regulations have been put forward to limit its

   substitute have increased recently [1, 3], leading to its detection as a contaminant in the aquatic environment.

   Furthermore, many studies [2, 5-7], have shown that BPS possesses acute toxicity, genotoxicity, and estrogenic activity of a comparable potency to BPA. Beyond health impacts, BPS may also pose risks to the environment. It is not amenable to biodegradation and might be persistent and become an ecological burden. Thus, alternative degradation methods are needed for the removal of BPS in the environment [8].

   Advanced Oxidation processes (AOPs) seem to be a useful method to remove or pre-oxidize remaining organic micropollutants from the effluents of waste water treatment plants [9]. These processes involve chemical, photochemical or electrochemical techniques to bring about chemical degradation of organic pollutants. The principal active species in such systems is the hydroxyl radical (OH), a highly oxidizing agent of organic contaminants [10-16]. These radicals react with organic pollutants and thus lead to their degradation by three modes of action: hydrogen atom abstraction, electrophilic addition to systems or electron transfer (redox) reactions [17]. During degradation, oxidation intermediates are formed and in their turn are oxidized until complete mineralization to carbon dioxide, inorganic ions and water.

   Since it is an economically and environmentally friendly process, Electro-Fenton (EF) is a commonly used Electrochemical Advanced Oxidation process, widely used to remove the toxicity of persistent, non biodegradable and refractory organic pollutants from water such as dyes [14, 17, 18], pharmaceutical and personal care products [9, 10, 12, 15],

   pesticides [11, 19, 20] and other persistent organic pollutants

   [16].

   O

   HO S OH

   application in some consumer products [1] and several

   manufacturers are gradually replacing BPA with a number of alternatives, such as 4,4-sulfonyldiphenol known as bisphenol S (BPS) (Fig. 1). BPS is a Bisphenol analogue, used as an anticorrosive agent in epoxy glues and as a reagent in polymer reactions [3, 4]. The production and consumption of the

   O

   Fig. 1. The molecular structure of Bisphenol S (BPS)

   In Electro-Fenton process, the source of hydroxyl radical (OH) is the Fenton reaction (1) in which Fenton reagent is produced electrochemically and regenerated in situ.

   H2O2 + Fe2+ Fe3+ + OH + OH (1)

   O2 or air gas is injected into either the reaction medium or directly at the cathode to generate H2O2 via reaction (2).

   O2 + 2H+ + 2e H2 O2 (2)

   Fe3+ + e Fe2+ (3)

   H2O2 is produced continuously at the carbonaceous cathodes as carbon felt that can provide high yield. Small quantities of Fe2+ are usually added to form Fe3+ (3) to enhance the zing power of electro-generated H2O2.

   Using an undivided electrolytic cell for the EF process, the organic compounds can be also destroyed by heterogeneous hydroxyl radicals (M(OH)) produced at the anode surface (M) from water oxidation following the (4) thus accelerating the mineralization rate of the pollutants [21].

   M + H2O M OH + H+ + e (4)

   In the present work, we have undertaken a study on BPS degradation by the Electro-Fenton process in aqueous medium. The experiments are carried out in an undivided cell using Pt or BDD as anodes and commercial graphite felt as cathode. Initially, we investigated the effects of some operating parameters on the removal rate such as current density, catalyst dose and nature of supporting electrolyte. The decay kinetics of BPS was investigated and the absolute rate constant of the reaction between OH and BPS was determined by using competition kinetics method. Aromatic intermediates were identified by gas chromatography-mass spectrometry (GC MS). Carboxylic acids were also identified and quantified by HPLC.

2. MATERIALS AND METHODS

   1. Chemicals

      4,4-dihydroxydiphenyl sulfone (BPS, purity 98%) was purchased from SigmaAldrich. Table 1 summarizes the major physicochemical properties of BPS.

      Parameter	Range
      Molecular formula	C12H10O4S
      Molecular weight (g/mol)	250.27
      Solubility (g/L)	1.1
      max (nm)	258
      Density (g/cm3)	1.37
      Melting point (°C)	240 248

      TABLE 1. Physicochemical properties of Bisphenol S

      Iron heptahydrated sulfate (Fe2(SO4)3·7H2O ) used as a ferrous ion source, was supplied by Prolabo. Anhydrous Sodium Sulfate (Na2SO4) used as an inert supporting electrolyte, was purchased from Acros organics. Tetramethylammonium hydroxide (TMAH in water), a derivatisation product, was acquired from Sigma Aldrich. Acetonitrile (HPLC grade) was obtained from Sigma-Aldrich, sulfuric acid (H2SO4) from Merck. All the other chemicals were analytically graded from Prolabo and Sigma-Aldrich.

   2. Electrochemical system

      Experiments, at room temperature, were performed with an open, undivided an cylindrical cell containing a 250mL solution. The carbon felt piece (Carbone Lorraine RVG 4000 Mersen, Paris La Défense, France) was used as a cathode. It was placed on the inner wall of the cell covering the totality of the internal perimeter. The anode is a platinum electrode (Radiometer) or a BDD thin film, having the same surface (5 cm²), placed on the centre of the cell. The initial pH of the solutions, measured with a Mettler Toledo EL20 pH-meter, was adjusted to 3 by Sulphuric Acid. Prior to the electrolysis, a moderate compressed air is bubbled for 10 min through the cell to saturate the solution, which was agitated continuously by a magnetic stirrer. Fe2(SO4)3·7H2O is introduced to the cell just before the beginning of the electrolysis. Electrolyses were carried out under current controlled conditions. The current was kept at the desired level with an Amel 2053 potentiostat- galvanostat and samples were withdrawn at regular electrolysis times. The ionic strength was maintained constant by additions of 50 mM Na2SO4.

   3. Analytical methods

   The evolution of BPS concentration was detected using Thermo Separation Products (TSP) High Performance Liquid Chromatography (HPLC) using Spectra system (P1000), equipped with an isocratic pump and UV/Visible detector model Spectra series UV100, fitted with reversed phase C-18 analytical column (Agilent, 5 m; 4.6 mm × 250 mm). The detection of BPS was carried out at 258 nm. The mobile phase was a mixture of water-acetonitrile (70:30, V/V). It was eluted at a flow rate of 1 mL.min1. The injection volume was 20 L. Generated aliphatic carboxylic acids were also identified and quantified by the same HPLC at room temperature. The detection was performed at 210 nm with a mobile phase of 4 mM H2SO4 at a flow rate of 1 mL.min-1.

   Intermediates of Electro-Fenton treatment of BPS were directly deduced from mass spectra obtained from GC-MS applications. Sample preparation for GC-MS analysis consisted of dissolving 4 mL of the BPS solution treated in 2 mL of methanol. Prior to the measurement, 10 L of (0.25 M) TMAH (10% water) was added to 100 L of the BPS derivatives. The mixture was allowed to stand for 1 h prior to analysis. The analyses were performed with a 6890 Agilent gas chromatograph. The flow rate was 1.9 mL/min. The temperature of the oven program of the gas chromatograph started at 100 °C with increments of 15 °C/min immediately up to 320 °C. This temperature was kept for 5 min. For mass spectral detection, a MS 5973 was used. The Selective Ion Mode (SIM) of the mass spectrometer was applied for the quantification of BPS [22].

3. RESULTS AND DISCUSSION

   1. Effect of experimental parameters on the BDD degradation

      1. Effect of the current density on the BPS degradation

         Applied current density is the ratio between the applied current and the surface of the working electrode. It is considered as a key variable parameter for Electrochemical advanced oxidation processes. In order to investigate the effect of this parameter on the degradation of BPS by Electro-Fenton process, several experiments were performed on 10 mg.L-1 BPS solution of pH 3 at different current density values, in range of 20 to 80 mA/cm², in the presence of 0.2 mM of

         Fe2+ as a catalyst and 50 mM Na2SO4 as an inert support electrolyte.

         Fig. 2 shows that the concentration of BPS decreased exponentially. A very quick drop of BPS concentration for different values of j over than 20 mA/cm² can also be seen. For the EF-Pt treatment (Fig.2 (a)), the BPS was completely removed at 30, 35 and 40 min for 60, 80 and 40 mA/cm², respectively. For the EF-BDD treatment (Fig. 2 (b)) and the same values of j, molecules were eliminated at shorter time of 15, 20 and 25 min. Thus, the BPS degradation kinetic was enhanced by increasing the applied current density. This effect could be explained by increasing the formation rate of the

         Fenton reagent H2O2 and Fe2+, leading to the generation of a higher amount of OH from Fenton's reaction (1).

         The BPS degradation kinetic was also enhanced by using a BDD anode. This phenomenon can be explained by the very high O2 evolution overpotential of BDD electrode (1.27 V) vs. Pt one (0.27 V) since the oxidative action of M(OH) is rather ineffective for classical electrodes such as Pt but much more efficient for a high O2 overpotential anode such as BDD [23,24]. Besides having a larger amount of BDD(OH) generated on the electrodes surface, another advantage of this electrode is that the OH are physisorbed and thus are labile and more reactive in contrast to Pt one where they are chemisorbed [25] thus relatively strongly attached to the surface and less reactive [26].

         It should be noted that for the EF-Pt treatment, the decay of the kinetic curves being closed between 60 and 80 mA/cm², and further increase in applied current density do not contribute in any enhancement in degradation rates of BPS. The efficiency of Electro-Fenton is less at higher current density. This is due to the competitive electrode reactions in the electrolytic cell. The discharge of oxygen at the anode (5) and the evolution of hydrogen at the cathode (6) occur at a higher current. These reactions inhibit main reactions such as (7) and

         (3) [27], which lead to a decrease in the efficiency of the Electro-Fenton [28].

         2H2 O 2H+ + O2 + 4 e (5)

         2H+ + 2e H2 (6)

         1

         0,9

         0,8

         0,7

         0,6

         C/C0

         0,5

         0,4

         0,3

         0,2

         0,1

         0

         1

         0,9

         0,8

         0,7

         C/C0

         0,6

         0,5

         0,4

         0,3

         0,2

         0,1

         (a)

         0

         10

         20

         30 40

         Time (min)

         5

         4

         3

         2

         1

         0

         Ln(C0/C)

         0 10 20 30 Time (min) 40 50 60

         6

         5

         4

         3

         2

         1

         0

         Ln(C0/C)

         (b)

         0

         10

         30 40

         Time (min)

         a

         H2O OH + H+ + e (7)

         50

         BPS oxidation can be described by a pseudo-first order reaction kinetic, because the concentration of BPS decreased exponentially (Fig. 2). In addition, the inset of the (Fig. 2) highlights the linear correlations obtained for different values of the current density (R² > 0.98) of the kinetic analysis. Apparent rate constants for oxidative degradation of BPS, obtained from the slope of the curve of Ln (C0/C) = f (t) (Fig. 2), are reported in Table 2. According to the apparent rate constants values given in Table 2, the current density value of 80 mA/cm² is the optimal value to degrade BPS by EF-BDD treatment in 15 min with kapp of 0.316 min-1.

         50

         20

         J (mA/cm²)	Pt		BDD
         	Kapp (min-1)	R²	Kapp (min-1)	R²
         20	0.025	0.99	0.025	0.98
         40	0.111	0.98	0.171	0.99
         60	0.124	0.99	0.228	0.98
         80	0.122	0.99	0.316	0.99

         TABLE 2. Apparent rate constants of BPS oxidation by Electro-Fenton process (Experimental conditions of Fig. 2)

         0

         0 10 20 30 Time (min)

         40 50 60

         Fig. 2. Degradation Kinetics of BPS by Electro-Fenton process at several current density values using (a) Pt anode and (b) BDD anode.

         Current density (mA/cm²): () 20; () 40; () 60, (x) 80. [BPS]0 = 0.04 mM, pH = 3, [Fe3+] = 0.2 mM, [Na2SO4] = 50 mM

      2. Effect of Fe3+ concentration

         The effect of Fe3+ concentration as catalyst on the Electro- Fenton degradation of BPS, using a BDD or Pt anode, was studied in the presence of different initial Fe3+ concentrations at a constant Bisphenol S oncentration of 10 mg. L-1 applying a constant current of 200 mA. Fig. 3 shows that the degradation of BPS is significantly affected by the concentration of Fe3+ for both of the anodes. The degradation rate increased with decreasing Fe3+ concentration from 1 to 0.1 mM, and Electro- Fenton process seems to be more efficient with a low concentration of 0.1 mM of Fe3+.

         For the EF-Pt treatment, complete degradation can be seen only for the initial Fe3+ concentration less than 0.2 mM. Degradation needs more time for a complete removal of the molecule for the initial concentration of the catalyst up to

         0.5 mM, , and the degradation efficiency of BPS reached only a maximum value of 52 % and 90 % for 1 and 0.5 mM respectively for 40 minutes of electrolysis.

         For EF-BDD treatment, a fast and complete degradation of BPS can be seen varying initial Fe3+ concentrations from 0.1 to

         0.5 mM within 25 to 40 min. However, for 1 mM initial concentration of catalyst, after 40 minutes, the degradation efficiency of BPS enhanced using BDD anode and reached 76 %.

         1

         (a)

         Thus, the removal efficiency declined with the higher Fe3+ concentration for both of the anodes. This negative effect of the higher catalyst concentration on degradation kinetics can be related to the increase of the rate of parasitic reaction (8) which is strongly accelerated when much larger amounts of Fe2+ are formed from reaction 3 as more Fe3+ is added to the starting solution [21].

         Fe2+ + OH Fe3+ + OH (8)

      3. Effect of supporting electrolyte type

         The type of the supporting electrolyte is also an important parameter in the Electro-Fenton process. Indeed, the addition of an electrolyte in a solution can influence the treatment since it modifies the conductivity of the solution, facilitates the passage of the electrical current, and reduces the energy cost of the process. The effect of supporting electrolytes such as NaCl, Na2SO4 and NaNO3 on BPS oxidation at BDD and Pt studied at a BPS concentration of 0.04 mM and applied current density of 40 mA.cm2 and the results are shown in Fig. 4. It can be seen, from the kinetic curves of BPS degradation obtained with Pt and BDD anode, complete degradation of the organic matter was achieved in the presence of NaCl and Na2SO4 as a supporting electrolyte. However, the presence of NaNO3 did not accelerate the removal of BPS and the performance of both anodes in this case was weak. This behavior can be explained by the fact that NO3- is a strong oxidant (0.8 V/ESH) at pH 3, so it competes with the chemisorbed O2 for the adsorbed

         0,9

         0,8

         0,7

         0,6

         0,5

         0,4

         0,3

         0,2

         0,1

         0

         atomic H; suppressing H2O2 production and BPS degradation

         [29].

         15 20

         time (min)

         C/C0

         Using a Pt anode (Fig 4 (a)), in the presence of Na2SO4 as a supporting electrolyte, the BPS removal occurred slowly, reaching 100 % degradation after 40 minutes of electrolysis. BPS degradation is dramatically enhanced in the presence of NaCl, and achieved after 28 minutes. This behavior can be explained by the fact that Na2SO4 is a stable electrolyte, while chloride ions can be oxidized at the anode surface to active chlorine according to the following equation [21]:

         0

         5

         10

         25

         30

         35

         40

         2Cl Cl2 + 2e (9)

         0,9

         0,8

         0,7

         0,6

         0,5

         0,4

         0,3

         0,2

         0,1

         0

         (b)

         1

         The electrogenerated active chlorine can act as an oxidation mediator in the bulk of the solution and a parallel degradation reaction in the solution takes place, accelerating the reaction rate.

         C/C0

         Using a BDD anode, (Fig. 4 (b)), the removal of BPS decreased when NaCl was used as a supporting electrolyte

         instead of Na2SO4. It can be explained by the fact that during electrolysis with the BDD anode, which has a high O

         2

         evolution overpotential, persulfates ions are known to be very powerful oxidants (E° = 2.01 V), and sulfate radicals are generated in situ according to the following equations:

         0

         5

         10 15 20 25 30 35 40

         Time (min)

         2SO2 S O2 + 2e (10)

         Fig. 3. Influence of Fe3+ concentration on the degradation Kinetics of BPS by Electro-Fenton process using (a) Pt anode and (b) BDD anode.

         3+

         4 2 8

         OH + SO2 SO + OH (11)

         [Fe

         ] (mM) : () 1; () 0.5; () 0.2, (x) 0.1. [BPS]0 = 0.04mM, pH = 3, 4 4

         [Na2SO4] = 50mM, I = 200mA.

         SO + SO S O2 (12)

         4 4 2 8

         (a)

         1

         1

         0,9

         0,8

         0,7

         0,6

         0,5

         0,4

         0,3

         0,2

         0,1

         0

         0,9

         Ln(C0/C)

         0,8

         0,7

         C/C0

         C/C0

         0,6

         0,5

         0,4

         0,3

         0,2

         0,1

         25 30 35 40

         15 20

         Time (min)

         5 10

         0

         0

         6

         5

         4

         3

         2

         1

         0

         y = 0,3162x

         R² = 0,9913

         y = 0,1355x R² = 0,9906

         0

         30

         Time (min)

         40 50

         10 20

         0 5 10 15 20 25 30 35

         Time (min)

         (b)

         1

         Fig. 5. Normalized concentration decay of BPS with electrolysis time during Electro-Fenton treatment using (x) Pt anode and () BDD anode.

         0,9

         0,8

         0,7

         0,6

         0,5

         0,4

         0,3

         0,2

         0,1

         0

         Inset: corresponding kinetic analysis.

         25 30 35 40

         15 20

         Time (min)

         5 10

         0

         C/C0

         In order to evaluate the reaction rate constant of the BPS degradation by hydroxyl radicals, the competition kinetics method was used choosing benzoic acid (BA) as a standard competitor. The literature value of the absolute rate constant of BA with the hydroxyl radical is 4.3 × 109 M1 s1. Electrolyses of a mixture of BPS and BA at equimolar concentrations were carried out with the two anodes. The degradation of BPS was studied under optimal conditions determined above for each anode (Fig. 5). The absolute rate constant for BPS can be deduced as follows:

         Fig. 4. Influence of electrolyte support on the degradation Kinetics of BPS by Electro-Fenton process using (a) Pt anode and (b) BDD anode.

         Electrolyte support: () NaCl; () Na2SO4; () NaNO3. [BPS]0 = 0.04 mM, pH = 3, [electrolyte support] = 50 mM, I = 200 mA

         kBPS

         = kapp BPS k

         kapp BA BA

         (15)

         The oxidants are either consumed for the degradation of the BPS molecule or coupled with a water molecule to form peroxomonosulfuric acid (H2SO5) which in turn can produce H2O2 [30, 31].

         Using the pseudo-first order model, the constant apparent

         rates of BA and BPS were calculated by linear regression (inset of Fig. 5). For the Pt and BDD anode, the BPS kapp values of

         0.135 and 0.316 min-1 were obtained respectively and the Benzoic acid Kapp values (data not shown) were 0.261 and

         0.315 min-1. The value of the constant absolute rate of BPS hydroxylation was 4.31×109 M1 s1 for the BDD anode and

         H SO + H O H O + H SO

         (13)

         was 2.22 ×109 M1 s1 for the Pt anode.

         2 5 2 2 2 2 4

   2. Determination of the apparent and absolute rate constants

      Since hydroxyl radicals are non-selective, have high reactivity towards organic compounds, posses a very short life span of a few nanoseconds, and do not accumulate in the solution, the quasi-stationary state can be applied to their concentration, and the oxidation reaction of organic compounds by OH can be considered as a pseudo first-order reaction. Therefore, the following equation can be written:

   3. Identification of by-products during the oxidative degradation of BPS

   During the Electro-Fenton treatment, the oxidation reactions produced intermediates, identified in two stages: identification of aromatics and carboxylic acids. The first one included identification of primary aromatic intermediatesformed during the oxidation of BPS by GC-MS analysis. The GC-MS spectrums showed the formation only of two intermediates species: Butanol (tR=8.4 min) and (4-hydroxyphenyl)(5-

   d[BPS ] = k

   dt

   BPS

   OH BPS = k

   app

   [BPS] (14)

   Oxocyclohex-1,3-diene) sulfonylphenol which was the most abundant intermediate detected at tR=10.3 min. This finding

   Where kBPS is the absolute rate constant and kapp the apparent rate constant.

   evidences that other potential aromatic intermediates are always oxidized at the same rate as formed, without being accumulated in the solution, and they rapidly undergo oxidative ring opening reactions [32].

   .

   TABLE 3. The detected carboxylic acids during the degradation of BPS by Electro-Fenton process using Pt anode.

   Carboxylic acid	Chemical structure
   Oxalic acid	HO O O OH
   Acetic acid	O H3C OH
   Maleic acid	OHHO O O
   Formic acid	O H OH
   Succinic acid	O HO OH O

   In the second stage, aromatic intermediates were oxidized in their turn to the formation of short-chain carboxylic acids before complete mineralization. In order to identify and follow the evolution of the carboxylic acids generated during BPS removal by the Electro-Fenton process, a 0.04 mM BPS aqueous solution was treated. The carboxylic acids detected are presented in table 4. Oxalic, Acetic and maleic acids were identified at significant concentration and their evolutions are presented in Fig. 6, while succinic and formic acids were detected at a low concentration.

   Concentration (mM)

   As can be seen in Fig. 6, Oxalic, Acetic and Maleic acids are generated as soon as the electrolysis is started, reaching their maximum concentrations after 3 to 4 h of treatment

   0,03

   0,025

   0,02

   0,015

   0,01

   0,005

   0

   0

   1

   2

   3

   Time (h)

   4

   5

   6

   Fig.6. Evolution of carboxylic acids during the Electro-Fenton treatment of BPS aqueous solution

   [BPS]0 = 0.04 mM, pH = 3, I = 300 mA, [Fe3+] = 0.1 mM, V = 205 mL.

   () Oxalic acid, () Acetic Acid and () Maleic acid.

   Thereafter, acetic and maleic acids disappeared within 6 hours. Although, oxalic acid decreased weakly with the electrolysis time and remained present even at the end of the treatment. This is due to the presence of stable Ferric-oxalate complexes formed in the bulk, which are persistent and slowly destroyed by hydroxyl radicals [33- 35].

4. CONCLUSION

The Electro-Fenton process is a very efficient method for the effective removal of BPS from an aqueous medium. Based on the above experiments, it was evident that the efficiency of the Electro-Fenton process depends mainly on the anode material used in the electrolysis. In fact, in optimum experimental conditions, a complete degradation was realized on the BDD anode in a short time due to the high oxidation power of the hydroxyl radicals that were electrogenerated and weakly adsorbed at its surface. However, the degradation processes became much slower using the Pt.

The oxidation of BPS by hydroxyl radicals was found to obey pseudo-first-order kinetics, and the absolute rate constant using the BDD and the Pt anode was determined by the competition kinetic method and found to be 4.31×109 M1 s1 and 2.22 ×109 M1 s1 respectively.

The identification, using HPLC and GC-MS, of aromatic oxidation products and short-chain carboxylic acids during the treatment, confirmed the effectiveness of Electro-Fenton process to remove BPS from water.

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11. A. Kesraoui Abdessalem, N. Bellakhal, N. Oturan, M. Dachraoui, M. A. Oturan, Treatment of a mixture of three pesticides by photo- and electro-Fenton processes. Desalination, vol. 250, pp. 450-455, January 2010.

12. D. Mansour, F. Fourcade, N. Bellakhal, M. Dachraoui, D. Hauchard, A. Amrane, Biodegradability Improvement of Sulfamethazine Solutions by Means of an Electro Fenton Process, Water, Air, Soil Pollut., vol. 223, pp. 2023- 2034, June 2012.

13. D. Mansour, F. Fourcade, S. Huguet, I. Soutrel, N. Bellakhal, M. Dachraoui, D. Hauchard, A. Amrane, Improvement of the activated sludge treatment by its combination with electro Fenton for the mineralization of sulfamethazine, International Biodeterioration & Biodegradation, vol. 88, pp. 29-36, March 2014.

14. A. Mhemdi, M. A. Oturan, N. Oturan, R. Abdelhédi, S. Ammara,

    Electrochemical advanced oxidation of 2-chlorobenzoic acid using BDD or Pt anode and carbon felt cathode, Journal of Electroanal. Chem., vol. 709, pp. 111-117, November 2013.

15. I. Naimi, N. Bellakhal, Removal of 17 -estradiol by Electro-Fenton process, Materials Sciences and Applications, vol. 3, pp. 880-886, December 2012.

16. S. Trabelsi, N. Oturan, N. Bellakhal, M. A. Oturan, Electrochemical oxidation of phthalic anhydride in aqueous medium by Electro-Fenton process, J. Environ. Eng. Manage., vol. 19, pp. 291-297, September 2009.

17. A. Özcan, M. A. Oturan, N. Oturan, Y. Sahin, Removal of Acid Orange

    7 from water by electrochemically generated Fentons reagent, J. Hazard. Mater., vol. 163, pp. 1213-1220, April 2009.

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18. S. Hammami, N. Bellakhal, N. Oturan, M. A. Oturan, M. Dachraoui,

    Degradation of Acid Orange 7 by electrochemically generated OH radicals in acidic aqueous medium using a boron-doped diamond or platinum anode: A mechanistic study. Chemosphere, vol. 73, pp. 678- 684, October 2008.

19. M. A. Oturan, M. C. Edelahi, N. Oturan, K. El Kacemi, J. J. Aaron,

    Kinetics of oxidative degradation/mineralization pathways of the phenylurea herbicides diuron, monuron and fenuron in water during application of the electro-Fenton process. Appl. Catal. B: Environ., vol. 97, pp. 82-89, June 2010.

20. M. A. Oturan, N. Oturan, M. C. Edelahi, F. I. Podvorica, K. El Kacemi,

    Oxidative degradation of herbicide diuron in aqueous medium by Fenton's reaction based advanced oxidation processes, Chem. Eng. J., vol. 171, pp. 127-135, June 2011.

21. S. Loaiza-Ambuludi, M. Panizza, N. Oturan, A. Özcan, M. A. Oturan,

    Electro-Fenton degradation of anti-inflammatory drug ibuprofen in hydroorganic medium, J. Electroanal. Chem., vol. 702, pp. 31-36, August 2013.

22. V. Becerra, J. Odermatt, Interferences in the direct quantification of bisphenol S in paper by means of thermochemolysis, J. Chromatogr. A, vol. 1275, pp. 70-77. February 2013.

23. C. A. Martínez-Huitle, E. Brillas, Decontamination of wastewaters containing synthetic organic dyes by electrochemical methods. A general review, Appl. Catal. B: Environ., vol. 87, pp. 105-145, April 2009.

24. M. Panizza, G. Cerisola, Application of diamond electrodes to electrochemical processes, Electrochim. Acta, vol. 51, pp. 191-199, October 2005.

25. E. Brillas, I. Sires, M. A. Oturan, Electro-Fenton process and related electrochemical technologies based on Fentons reaction chemistry, Chem. Rev., vol. 109, pp. 6570-6631, October 2009.

26. N. Oturan, M. Hamza, S. Ammar, R. Abdelhédi, M. A. Oturan,

    Oxidation/mineralization of 2-Nitrophenol in aqueous medium by electrochemical advanced oxidation processes using Pt/carbon-felt and BDD/carbon-felt cells. J. Electroanal. Chem., vol. 661, pp. 66-71, October 2011.

27. H. Zhang, C. Fei, D. Zhang, F. Tang, Degradation of 4-nitrophenol in aqueous medium by electro-Fenton method. Journal of Hazard. Mater., vol. 145, pp. 227-232, June 2007.

28. P. V. Nidheesh, R. Gandhimathi, Trends in electro-Fenton process for water and wastewater treatment: An overview. Desalination, vol. 299, pp. 1-15, August 2012.

29. X. Xu, P. Liao, S. Yuan, M. Tong, M. Luo, W. Xie, Cu-catalytic generation of reactive oxidizing species from H2 and O2 produced by water electrolysis for electro-Fenton degradation of organic contaminants, Chem. Eng. J., vol. 233, pp. 117-123, November 2013.

30. M. Murugananthan, S. S. Latha, G. Bhaskar Raju, S. Yoshihara,

    Anodic oxidation of ketoprofenAn anti-inflammatory drug using boron doped diamond and platinum electrodes, J. Hazard. Mater., vol. 180, pp. 753-758, August 2010.

31. K. Serrano, P. A. Michaud, C. Comninellis, A. Savall, Electrochemical preparation of peroxodisulfuric acid using boron doped diamond thin film electrodes, Electrochimica Acta, vol. 48, pp. 431-436, December 2002.

32. S. Loaiza-Ambuludi, M. Panizza, N. Oturan, A. Özcan, M. A. Oturan,

    Kinetic behavior of anti-inflammatory drug ibuprofen in aqueous medium during its degradation by electrochemical advanced oxidation, Environ. Sci. Pollut. Res., vol. 20, pp. 2381-2389, April 2013.

33. B. Boye, M. M. Dieng, E. Brillas, Anodic oxidation, electro-Fenton and photoelectron-Fenton treatments of 2,4,5-trichlorophenoxyacetic acid, Journal of Electroanal. Chem.,vol. 557, pp. 35-146, 2003.

34. E. Brillas, B. Boye, I. Sirès, J. A. Garrido, R. M. Rodriguez, C. Arias, P.

    L. Cabot, C. Comninellis , Electrochemical destruction of chlorophenoxy herbicides by anodic oxidation and electro-Fenton using a boron-doped diamond electrode, Electrochim. Acta, vol. 49, pp. 4487-4496, October 2004.

35. M. A. Oturan, M. Pimentel, N. Oturan, I. Sirés, Reaction sequence for the mineralization of the short-chain carboxylic acids usually formed upon cleavage of aromatics during electrochemical Fenton treatment, Electrochim. Acta, vol. 54, pp. 173-182, December 2008.