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Decoloration of Reactive Black 5 in Aqueous Solution by Electro-Fenton Reaction

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DECOLORATION OF REACTIVE BLACK 5 IN AQUEOUS SOLUTION BY

ELECTRO-FENTON REACTION

Chyow-San Chiou,1,* Ching-Yuan Chang,2 Je-Lueng Shie,1 Cheng-Chung Liu1 and Yuan-Shan Li1

1Department of Environmental Engineering

National I-Lan University I-Lan 260, Taiwan

2Graduate Institute of Environmental Engineering

National Taiwan University Taipei 106, Taiwan

Key Words : Electrochemical, electro-Fenton, decoloration ABSTRACT

In a three-electrode electrochemical reactor, oxygen and Fe3+ were reduced into H2O2 and Fe2+

by appropriate working electrode voltage in aqueous solution, initiating and facilitating Fenton reaction to proceed a combined reaction named as electro-Fenton reaction. Reactive black 5 (RB5) dye was chosen as the target compound to evaluate the efficiency of electro-Fenton reaction in this

study. The results revealed that an optimal decoloration efficiency of RB5 (ηRB5) was achieved at the

working electrode voltage of -550 mV/(Ag/AgCl), and the ionic strengths of KNO3 and Fe3+of the

solution of 0.1 M and 20 mg L-1, respectively. Furthermore, when Fe3+ in the reaction solution was

substituted by Cu2+, about the same η

RB5 can also be achieved. A first-order kinetic model was

adopted to describe the decoloration of RB5 by the electro-Fenton process, yielding the reaction rate constant expressed as k = 165.5(CFe3+,0)

0.55, where the units of k, initial concentration of Fe3+ (C Fe3+,0),

and 165.5 are min-1, mg L-1, and min-1(mg L-1)-0.55, respectively.

*Corresponding author

Email: cschiou@niu.edu.tw

INTRODUCTION

Azo dyes are the most widely used commercial reactive dyes in the dyeing processes with the

world-wide production of more than 7 × 105 tons per year [1].

Approximately 10-15 wt% of the dye is lost during the dyeing process which contributes to the organic con-centration of the effluent [1]. It has been shown that neither simple chemical nor biological treatment can achieve the desirable decoloration and depletion of dye organic matter [2,3]. The value of ratio of

BOD5/COD normally indicates the extent of the

bio-logical degradability of the organics, and that of dyes is usually less than 0.1 [4]. Therefore, the destruction of biologically recalcitrant organics in the textile wastewater has to be accomplished by those methods which enhance the biological degradability of the or-ganics, such as advanced oxidation processes (AOPs) [5,6].

The application of the Fenton process to decom-pose organic pollutants has attracted extensive atten-tion because of its satisfactory performance [7-9]. The

Fenton reaction involves the reaction of H2O2 with

iron salt, which generates strong oxidizing radical

( OH⋅ ) to decompose the organics. The main reaction

is as follows [10,11]: − + + + + + OH OH Fe O H Fe2 2 2 3 (1)

Fenton reaction using Fe2+ can achieve good

treatment efficiency, but the precipitate of ferric hy-droxide that requires additional separation and dis-posal limits its application.

The electrochemical technologies have attracted a great attention because of their versatilities and envi-ronmental compatibilities. Organic pollutants can be destructed by the electrochemical reactions which possess abilities of oxidation and reduction. However, when working electrode is directly used to oxidize or reduce the organic pollutants (direct mode), the reac-tion efficiency is inhibited because of the low contact surface area between the electrode and target pollut-ants [12]. In order to overcome this drawback, organic pollutants can be decomposed by an indirect electroly-sis, which generates reactive chemical reactant

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(indi-rect mode). Panizza et al. [13] added chloride ions into the solution, of which the purpose was to electrolyze

chloride ions to produce ClO- ions to further oxidize

the organic compounds in the solution enhancing the treatment efficiency of an electrochemical system.

Combing an electrochemical reaction with a Fenton reaction in one integrated process, which is so called an electro-Fenton reaction [14], gives an elec-trode potential capable of continuously reducing the

dissolved oxygen (DO) and Fe3+ of the solution to

form H2O2 [15]and Fe2+, respectively. Therefore, the

Fenton reaction of this indirect mode proceeds with continuous re-installation without the external

addi-tion of Fe2+ and H2O2. Recently, numerous studies

have investigated the application of electro-Fenton action to decompose the aromatic compounds and re-fractory pollutants with satisfactory efficiencies [16,17].

The aim of this study was to investigate the de-coloration of Reactive black 5 (RB5) by means of the electro-Fenton reaction system. Major factors

affect-ing the values of ηRB5 were examined. These included

the working electrode potential (EWE), the ionic

strength (I), the CFe3+,0 , and the value of pH. Because

other metal, e.g., Cu+, can also initiate the Fenton

re-action [18], the effect of Cu2+ on η

RB5 was also

evalu-ated in this study. Further, a first-order kinetic expres-sion was derived based on the observed experimental results.

MATERIALS AND METHODS

RB5, supplied by Aldrich (USA), was used as the target substance in this study. Its molecule

struc-ture is shown in Fig. 1. Fe(NO3)3, Cu(NO3)2, and

KNO3 were purchased from Sigma (St. Louis, MO,

USA). All the other chemicals used in this study are reagent grade obtained from several suppliers. De-ionized water from a Milli-Q system (Millipore, Bed-ford, MA, USA) was used to prepare all buffers and sample solutions.

Figure 2 shows the schematic diagram of the re-action system. A potentiostate-galvanostate electro-chemical apparatus (Radiometer’s multipurpose model PGP 201) was used for electrolyses. Electroly-ses were carried out in a three-electrode

electrochemi-cal cell, of which the volume is 200 cm3 with a

mag-netic stirrer. Furthermore, DO was supplied by purg-ing oxygen. The value of pH of the solution was

con-trolled by the addition of 0.05 N HNO3/NaOH and

maintained at a constant value during the entire reac-

Fig. 1. The molecular structure of RB5 with molecular formula of C26H21N5O19S6Na4. RE Potentiostat WE CE Pt Thermostat Sampling Ag/AgCl O2 Stirrer RE WE CE Potentiostat

Fig. 2. The experimental apparatus sketch. RE, WE, CE: reference (Ag/AgCl), working (Pt), and counter (Pt) electrodes.

tion period. The material of working (WE) as well as counter (CE) electrode was platinum. CE was placed

in the anodic compartment containing saturated KNO3

solution. A porous glass was used to separate the an-odic compartment and the bulk solution of WE. The reference electrode (RE) was Ag/AgCl electrode (sil-ver/silver chloride electrode, SSCE). The standard re-duction potential of SSCE with saturated KCl is 197 mV/NHE [19], with NHE denoting normal hydrogen electrode.

The concentration of RB5 was determined by the UV-Vis spectrophotometer (Perkin Elmer, Lambda 25). The intensity measured at the maximum visible

absorbance wavelength (i.e., Aλmax with wavelength of

595 nm) of RB5 by the UV/Vis spectrophotometer was used to calculate the decoloration efficiency. The relative standard deviation of analyses of RB5 sam-ples via UV/Vis with triple measurements was below 5%. The concentration of DO was determined by an oxygen electrode (Model 97, Orion Research Inc.)

RESULTS AND DISCUSSION 1. Optimal EWE

DO and Fe3+ in the solution can be reduced to

H2O2 and Fe2+ by electrochemical reaction,

respec-tively. The standard reduction potentials to reduce DO

and Fe3+ versus SSCE are 573 and 498 mV,

respec-tively, as shown in Eqs. 2 and 3.

+ − + + 2 3 Fe e Fe E0 = 573 mV/SSCE (2) 2 2 2 2H 2e H O O + ++ − → E0 = 498 mV/SSCE (3)

From Eqs. 2 and 3, the quantities of H2O2 and

Fe2+ depend on the applied EWE, as well as the

elec-tron-Fenton reaction efficiency. Hence, the optimal

EWE can be found by noting the relationship between

ηRB5 and EWE. The result of CRB5/CRB5,0 vs. EWE for

RB5 is shown in Fig. 3, where CRB5,0 and CRB5 are the

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EWE, mV/SSCE -800 -700 -600 -500 -400 -300 CRB5 /C RB 5 ,0 0.42 0.44 0.46 0.48 0.50 0.52 0.54 0.56 0.58 0.60 0.62

Fig. 3. Variation of CRB5/CRB5,0 of RB5 with EWE.

Experimental conditions: CRB5,0 = 20 mg L-1, I of KNO3 = 0.1 M, CFe3+,0= 20 mg L-1, initial pH = 3, reaction time = 25 min, T = 298 K. CRB5, CFe3+,0:

concentrations of RB5, Fe3+. T = reaction

temperature. 0: initial condition. EWE: working

electrode voltage. I: ionic strength.

As EWE > -500 mV, CRB5/CRB5,0 increased or ηRB5 ( =

1 - CRB5/CRB5,0) decreased quickly with increasing

voltage, interpreting that the potential was not

suffi-cient to reduce Fe3+ and DO resulting in decreasing

the production of Fe2+ and H2O2. When EWE < -600

mV, ηRB5 also dropped as EWE decreased. It may be

due to the reason that the excessively strong reduction

potential caused the transformation of H+ and H2O2

into H2 [19] and H2O by the reactions of Eqs. 4 and 5,

respectively, as follows. 2H+ + 2e- → H2 E0 = -197 mV/SSCE (4) O H e H O H2 2 +2 ++2 − →2 2 E0 = 1566 mV/SSCE (5)

The competitive reactions lessened the net

production quantities of H2O2 and Fe2+. As a result,

the suitable ηRB5 was obtained at EWE of -600 to -500

mV. The value of EWE was fixed at -550 mV for

fur-ther experiments. 2. pH Effect

The value of pH of the solution is an important parameter affecting the Fenton reaction efficiency.

The values of solubility product constants Ksp of

Fe(OH)2(s) and Fe(OH)3(s) are 5×10−15 M3 and

M

38

10

6× − 4, respectively. The small values of K

sp

in-dicate that OH- can easily combine with Fe2+ and Fe3+.

Hence, at a high pH value of the solution, Fe2+ forms

metal hydroxide complex and loses its capacity to catalyze H2O2, which is not favorable for a traditional

Fenton reaction. Therefore, the electro-Fenton

Time (min) 0 5 10 15 20 25 CRB5 /C RB5, 0 0.4 0.5 0.6 0.7 0.8 0.9 1.0 pH = 4.0 pH = 3.5 pH = 3.2 pH = 3.0 pH = 2.8 pH = 2.5

Fig. 4. Time variation of CRBR/CRB5,O of RB5 at various initial pH values. Experimental conditions: EWE = -550 mV/SSCE, CRB5,0 = 20 mg L-1, I of KNO3 =

0.1 M, CFe3+,0= 20 mg L-1, T = 298 K. Other

notations are the same as specified in Fig. 3. reaction may also be inhibited at high solution pH

values. The time variation of CRB5/CRB5,0 at various

pH values is shown in Fig. 4. The results indicated

that ηRB5 decreased as value of pH increased with ηRB5

< 0.1% at pH > 4. On the other hand, the reduction re-action of Eq. 4 is favorable for working electrode at highH concentration (low pH), resulting in the de-+

crease of ηRB5 as pH < 3. As a result, the optimal pH

value of ηRB5 was at pH = 3. The value of pH of

solu-tion was kept at 3 for the following experiments. 3. Effect of I

Supporting electrolyte plays an important role of current conduction in the electrochemical reaction. Its ability of conduction is reflected by the I. Therefore, unless the solution possesses sufficient I to overcome the resistance of the electrochemical cell, redox reac-tions can not occur in the system. In addition, the effi-ciency of electro-Fenton reaction is also affected by the amount of ions in the solution. Figure 5 illustrates the time variation of CRB5/CRB5,0 at various initial I of

KNO3. The ionic strength I is defined as

, where C

=1/2 2 i iZ C

I i is the molar concentration

of the ith ion and Zi is its charge. The results showed

that if I was less than 0.075 M, ηRB5 rapidly decreased

with decreasing I. The deficiency of the supporting electrolyte caused the increase of the resistance of chemical reaction cell, subsequently hindering the electrochemical reaction. On the other hand, as I ≥

0.075 M, values of ηRB5 for various I values were

about the same. As a result, at I = 0.1 M, the I was sufficient to achieve a successful electrochemical re-action. Therefore, the following experiments were performed with I = 0.1 M.

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Time (min) 0 2 4 6 8 10 12 14 16 18 20 22 CRB 5 /C RB 5 ,0 0.4 0.5 0.6 0.7 0.8 0.9 1.0 2.5 x 10-2 M 5.0 x 10-2 M 7.5 x 10-2 M 10.0 x 10-2 M 12.5 x 10-2 M 15.0 x 10-2 M

Fig. 5. Time variation of CRB5/CRB5,0 of RB5 at various

ionic strengths of KNO3 (I). Experimental

conditions: EWE = -550 mV/SSCE, CRB5,0 = 20

mg L-1, C

Fe3+,0= 20 mg L-1, initial pH = 3, T = 298 K. Other notations are the same as specified in Fig. 3.

4. Concentration Effect of Fe3+

Comparing the reduction potentials of Fe3+ and

O2 as shown in Eqs. 2 and 3, we note that it is easier

to reduce Fe3+ to Fe2+ than O2 to H2O2. The effect of CFe3+,0 on the time variation of CRB5/CRB5,0 is shown in

Fig. 6. As the reaction was carried out without addi-tion of Fe3+ (with CFe3+,0 = 0), ηRB5 at 25 min was

around 0.16, indicating low decoloration efficiency obtained by means of the direct electrode reaction. As

CFe3+,0 increased up to 20 mg L

-1, the produced Fe2+

can consequently react with H2O2 to form hydroxyl

radical to decompose RB5, resulting in an increase of ηRB5 with the increase of CFe3+,0. However, as CFe3+,0

was greater than 20 mg L-1, ηRB5 tended to decrease,

indicating that a significant competition arose between

the reduction reactions of Fe3+/Fe2+ of Eq. 2 with

ex-cessive Fe3+ and of DO/H

2O2 of Eq. 3 causing the less

production of H2O2. This thus decreased the formation

of hydroxyl radicals, resulting in the decrease of ηRB5.

As a result, the optimal range of CFe3+,0 in this

investi-gation was 15-20 mg L-1 for the electro-Fenton

reac-tion with RB5.

5. Kinetics of Decoloration of RB5

The reaction kinetic expression of the decolora-tion of RB5 by electro-Fenton process is as follows.

m

kC dt dC =

(6) where C, m, t, and k represent the concentration of

RB5, order of the reaction, time, and reaction rate constant, respectively. For a first-order reaction (m = 1), Eq. 6 can be integrated and expressed as Eq. 7.

Time (min) 0 5 10 15 20 25 CRB 5 /C RB5,0 0.4 0.6 0.8 1.0 0 mg L-1 5 mg L-1 10 mg L-1 15 mg L-1 20 mg L-1 25 mg L-1 30 mg L-1

Fig. 6. Time variation of CRB5/CRB5,0 of RB5 at various

initial concentrations of Fe3+. Experimental

conditions: EWE = -550 mV/SSCE, CRB5,0 = 20

mg L-1, I of KNO

3 = 0.1 M, initial pH = 3, T =

298 K. Other notations are the same as specified in Fig. 3. kt C C = ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ 0 ln (7)

where C0 is the initial concentration of RB5 (mg L-1).

The experimental data of Fig. 6 with CFe3+,0 ranging

from 5 to 20 mg L-1 were followed by the first-order

reaction kinetics. The results indicated that the values

of R2 of regression analysis were all larger than 0.93.

Furthermore, the values of k obtained from the slope of the linear regression curve were varied with CFe3+,0.

Therefore, the relationship of k and CFe3+,0 can be

fur-ther examined and was assumed to be in the form of Eq. 8 as follows. n Fe C k k = 0( 3+,0) (8)

In Eq. 8, n is the order of reaction with respect to

CFe3+,0 (CFe3+,0: already defined). The value of n of 0.55

can be calculated from the slope of linear regression curve by plotting ln k against CFe3+,0. The value of

k

0

can also be obtained by plotting k versus (CFe3+,0) 0.55,

giving k0 of 165.5 min-1 (mg L-1)-0.55 at T = 298 K. Therefore, Eq. 6 can be expressed as k = 165.5 (CFe3+,0)0.55 , which is applicable for the conditions with

CFe3+,0 in the ranges of 5-20 mg L

-1, E

WE = -550

mV/SSCE, initial I = 0.1 MKNO3, pH = 3, and T =

298 K.

6. Electro-Fenton Reaction with Cu2+

H2O2 reacts with transitional metal ions of

low-valent except iron ions, generating strong oxidizing

radical ( OH⋅ ). The reaction is commonly called as

Fenton-like reaction [18]. Fe3+ or other

transition-metal ions can be continually reduced to lower oxida-tion state throughout the electrochemical treatment.

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Time (min) 0 5 10 15 20 CRB5 /C RB5,0 0.4 0.5 0.6 0.7 0.8 0.9 1.0 a: CFe3+,0 = 0, [Cu2+] = 0 b: CFe3+,0 = 0, [Cu2+] = 20 mg L-1 c: CFe3+,0 = 20 mg L-1, [Cu2+] = 0

Fig. 7. Time variation of CRB5/CRB5,0 of RB5 at various conditions. Expérimental conditions: a ( △ ):

CFe3+,0= 0, [Cu2+]0 = 0; b (□): [Cu2+]0 = 20 mg L-1,

CFe3+,0= 0; c (○): CFe3+,0= 20 mg L-1, [Cu2+]0 = 0. [ ]: concentration. Other experimental conditions are as specified in Fig. 6.

The reduced metal ions thus generated can act as cata-lysts in the electro-Fenton system. The standard

re-duction potential to reduce Cu2+ versus SSCE is 39

mV as shown in Eq. 9 [19]. + − +

+

Cu

e

Cu

2 E0 = 39 mV/SSCE (9)

In this work, ηRB5 of the system employing Cu2+

instead of Fe3+ during electro-Fenton type treatment

was obtained as shown in Fig. 7. The case a [[Cu2+]0 =

0 and CFe3+,0 = 0] exhibited a low ηRB5 (0.16 at 25 min),

where the symbol [ ] denotes the concentration. The results signified that ηRB5 contributed by the direct

re-action of working electrode was inefficient. The cases b ([Cu2+]0 = 20 mg L-1, CFe3+,0= 0 ) and c ([Cu

2+] 0 = 0, CFe3+,0= 20 mg L-1 ) were used to investigate the

reac-tion kinetics as described in Eq. 7. The values of k of

lines b and c were 29.1 and 28.3 min-1, respectively.

Further, the k value for case b with CCu2+,0 = 20 mg L-1

was close to that of case c with CFe3+,0 = 20 mg L

-1.

According to the standard reduction potential, the

re-duction of Cu2+ to Cu+ is more difficult than that of

Fe3+ to Fe2+. However, the reaction rate of Cu+ with

H2O2 to produce hydroxyl radical is higher than that

of Fe3+ with H2O2 [18]. These two reasons cause

op-posite effects, resulting in similar values of ηRB5 via

Cu2+ and Fe3+ in the electrochemical system. This

re-sult revealed that, in the aqueous electrochemical sys-tem, Cu2+ can act as a catalyst in the presence of H2O2,

expanding the application of copper ion. CONCLUSIONS

The electro-Fenton reaction can be used to de-compose RB5. From the obtained results, the follow-ing conclusions were drawn.

1. The ηRB5 with electro-Fenton reaction was optimal

under the conditions: EWE = -550 mV, initial I =

0.1 M KNO3, pH = 3, and CFe3+,0 = 20 mg L-1.

2. The values of ηRB5 with Cu2+ were about the same

as those with Fe3+ in this electrochemical system.

3. The observed experimental data showed a reasonably good agreement with the first-order kinetic model with respect to the concentration of RB5 in terms of UV/Vis absorbance intensity. The reaction rate constant k can be expressed as the following equation: k=165.5(CFe3+,0)0.55 , where the

units of k, CFe3+,0, and 165.5 are min-1, mg L-1, and

min-1(mg L-1)-0.55, respectively. The obtained k is

applicable for the conditions: CFe3+,0= 5-20 mg L -1, EWE = -550 mV/SSCE, I = 0.1 MKNO3, pH = 3, and T = 298 K. NOMENCLATURE 0 3 , Fe

C + initial loading concentration of Fe3+ in

aqueous solution, mg L-1

CRB5 present concentration of RB5 in aqueous

solution, mg L-1

CRB5,0 initial concentration of RB5 in aqueous

solution, mg L-1

E0 standard reduction potential, mV

EWE working electrode potential, mV

I ionic strength in aqueous solution in terms

of KNO3, M

k reaction rate constant, min-1

m order of reaction with respect to CRB5, -

n order of reaction with respect to CFe3+,0

R2 correlation coefficient

t reaction time, min

Greek symbols

ηRB5 decoloration efficiency of RB5,

1- (CRB5/CRB5,0)

Acronyms

AOPs advanced oxidation processes

BOD5 five days’ biological oxygen demand

CE counter electrode

COD chemical oxygen demand

DO dissolved oxygen

NHE normal hydrogen electrode

RB5 reactive black 5 dye

RE reference electrode

SSCE saturated Ag/AgCl electrode

WE working electrode

REFERENCES

1. Spadaro, J.T., L. Isabelle and V. Renganathan, Hydroxyl radical mediated degradation of azo dyes:

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evidence for benzene generation. Environ. Sci. Technol., 28(7), 1389-1393 (1994).

2. Koch, M., A. Yediler, D. Lienert, G. Insel and A. Kettrup, Ozonation of hydrolyzed azo dye reactive yellow 84 (CI). Chemosphere, 46(1), 109-113 (2002).

3. Krull, R., M. Hemmi, P. Otto and D.C. Hempel, Combined biological and chemical treatment of highly concentrated residual dyehouse liquors. Water Sci. Technol., 38(4-5), 339-346 (1998). 4. Liakou, S., S. Pavlou and G.. Lyberatos, Ozonation

of azo dyes. Water Sci. Technol., 35(4), 279-286 (1997).

5. Alaton, I.A. and I.A. Balcioglu, Photochemical and heterogeneous photocatalytic degradation of waste vinylsulphone dyes: a case study with hydrolysed reactive black 5. J. Photoch. Photobio. A, 141(2-3), 247-254 (2001).

6. Solpan, D. and O. Guven, Decoloration and degradation of some textile dyes by gamma irradiation. Radiat. Phys. Chem., 65(4-5), 549-558 (2002).

7. Rivas, F.J., F.T. Beltran, J. Frades and P. Buxeda, Oxidation of p-hydroxybenzoic acid by Fenton’s reagent. Water Res., 35(2), 387-396 (2001). 8. Walling, C., Fenton’s reagent revisited. Accounts

Chem. Res., 8(4), 125-131 (1975).

9. Wang, Q. and A.T. Lemley, Kinetic model and optimization of 2,4-D degradation by anodic Fenton treatment. Environ. Sci. Technol., 35(22), 4509-4514 (2001).

10. Chen, R.Z. and J.J. Pignatello, Role of quinone intermediates as electron shuttles in Fenton and photoassisted oxidation of aromatic compounds. Environ. Sci. Technol., 31(8), 2399-2406 (1997). 11. Turan-Ertas, T. and M.D. Gurol, Oxidation of

diethylene glycol with ozone and modified Fenton process. Chemosphere, 47(3), 293-301 (2002).

12. Juttner, K., U. Galla and H. Schmieder,

Electrochemical approaches to environmental problems in the process industry. Electrochim.

Acta, 45(15-16), 2575-2594 (2000).

13. Panizza, M., C. Bocca and G. Cerisola,

Electrochemical treatment of wastewater containing polyaromatic organic pollutants. Water Res., 34(9), 2601-2605 (2000).

14. Tzedakis, T., A. Savall and M.J. Clifton, The electrochemical regeneration of Fenton’s reagent in the hydroxylation of aromatic substrates: batch and continuous processes. J. Appl. Electrochem., 19(6), 911-921 (1989).

15. Qiang, Z.M., J.H. Chang and C.P. Huang,

Electrochemical generation of hydrogen peroxide from dissolved oxygen in acidic solutions. Water Res., 36(1), 85-94 (2002).

16. Oturan, M.A, An ecologically effective water

treatment technique using electrochemically generated hydroxyl radicals for in situ destruction of organic pollutants: application to herbicide 2,4-D. J. Appl. Electrochem., 30(4), 475-482 (2000). 17. Oturan, M.A., N. Oturan, C. Lahitte and S. Trevin,

Production of hydroxyl radicals by electrochemically assisted Fenton’s reagent – Application to the mineralization of an organic micropollutant, pentachlorophenol. J. Electroanal. Chem., 507(1-2), 96-102 (2001).

18. Masarwa, M., H. Cohen, D. Meyerstein, D.L. Hickman, A. Bakac and J.H. Espenson, Reactions of low-valent transition – metal complexes with hydrogen peroxide – Are they Fenton-like or not? 1. The Case of Cu+aq and Cr2+aq. J. Am. Chem. Soc.,

110(13), 4293-4297 (1988).

19. Bard, A.J. and L.R. Faulkner, Electrochemical Methods, Fundamentals and Applications. John Wiley, New York (1980).

Discussions of this paper may appear in the discus-sion section of a future issue. All discusdiscus-sions should be submitted to the Editor-in-Chief within six months of publication.

Manuscript Received: December 15, 2005 Revision Received: March 22, 2006 and Accepted: March 28, 2006

數據

Fig. 1. The molecular structure of RB5 with molecular  formula of C 26 H 21 N 5 O 19 S 6 Na 4
Fig. 3.  Variation  of  C RB5 /C RB5,0  of RB5 with E WE .  Experimental conditions: C RB5,0  = 20 mg L -1 , I of  KNO 3  = 0.1 M, C Fe 3+ ,0 = 20 mg L -1 , initial pH = 3,  reaction time = 25 min, T = 298 K
Fig. 6.  Time variation of C RB5 /C RB5,0  of RB5 at various  initial concentrations of Fe 3+
Fig. 7.  Time variation of C RB5 /C RB5,0  of RB5 at various  conditions. Expérimental conditions: a ( △ ):

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