Scholarly article on topic 'A Photo-Fentontreatment of a Mixture of Three Cationic Dyes'

A Photo-Fentontreatment of a Mixture of Three Cationic Dyes Academic research paper on "Chemical sciences"

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Procedia Engineering
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{Photocatalysis / "Solar radiation" / "Hydrogen peroxide" / "Iron salts" / Photo-Fenton}

Abstract of research paper on Chemical sciences, author of scientific article — Souâd Bouafia-Chergui, Nihal Oturan, Hussein Khalaf, Mehmet A. Oturan

Abstract Application of photo-Fenton process, UV/Fe3+/H2O2, to treatment for a mixture of three cationic dyes was investigated. The effect of the oxidative agent's initial concentration was investigated as well as the effect of the initial concentration of Fe+3 and H2O2 on the dyes degradation was studied. The best results were obtained using 0.6mM of Fe3+ and 12mM hydrogen peroxide. Under these experimental conditions, 90% of TOC and 100% of color removal were achieved.

Academic research paper on topic "A Photo-Fentontreatment of a Mixture of Three Cationic Dyes"

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Procedía Engineering 33 (2012) 181 - 187

Procedía Engineering


A Photo-Fentontreatment of a Mixture of Three Cationic Dyes

Souâd Bouafia-Chergui*a'b'c, Nihal Oturana, Hussein Khalaf and Mehmet A. Oturana

a Université Paris-Est, Laboratoire Géomatériaux et Géologie de l'Ingénieur, 5 bd Descartes, 77454 Marne la Vallée cedex 2, France. b Centre de développement des énergies renouvelables, BP. 62 Route de l'Observatoire Bouzaréah - Alger, Algérie, c Université de Saad Dahlab, Laboratoire de génie chimique, BP 270, 09000 Blida, Algérie.


Application of photo-Fenton process, UV/Fe /H2O2, to treatment for a mixture of three cationic dyes was investigated. The effect of the oxidative agent's initial concentration was investigated as well as the effect of the initial concentration of Fe+3 and H2O2 on the dyes degradation was studied. The best results were obtained using 0.6 mM of Fe3+ and 12 mM hydrogen peroxide. Under these experimental conditions, 90% of TOC and 100% of color removal were achieved.

© 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ISWEE' 11

keywords: Photocatalysis; Solar radiation; Hydrogen peroxide; Iron salts; Photo-Fenton

1. Introduction

In recent years, there is a great interest for so-called advanced oxidation processes (AOPs) which constitute an attractive alternative to treating wastewater containing toxic and persistent pollutants. They are based on the in situ generation of a powerful non specific oxidizing agent, the hydroxyl radical (OH^) which is able to oxidize a broad range of organic pollutants quickly and non-selectively [1]. There are several methods for generating OH\[2] such as Fenton's reagent,[3, 4] H2O2 photolysis,[5] Fe(III) photolysis,[6-8] anodic oxidation,[9,10] electro-Fenton,[11-14] and heterogeneous photocatalysis.[15,16]. Among them, the photo-Fenton process, combining the Fenton's reagent, a mixture of H2O2 and a ferrous salt, with UV irradiations is able to extensively degrading organic contaminants in a variety of wastewater, streams and soils.

* Corresponding author. Tel.: 213 21 90 15 03; fax: 213 21 90 15 60. E-mail address:

1877-7058 © 2012 Published by Elsevier Ltd. doi:10.1016/j.proeng.2012.01.1192

In the photo-Fenton process, the Fenton's reagent produces *OH radicals by the addition of H2O2 to a Fe2+salts. (Eq. (1)). Hydroxyl radicals can also produce by addition of H2O2 to a Fe3+salt (Fenton like process)(Eq. (2)) in excess of H2O2.The reactions involved are briefly described as follow:

Fe2+ + H2O2^Fe(OH)2+ + 'OH (1)

Fe3++H2O2 Fe - OOH2+ + H + (2)

Fe-OOH2+^ Fe2+ + HO2* (3)

When the solution is irradiated by UV or visible light, supplementary hydroxyl radicals are produced Eq. (4)) by photoreduction of Fe3+ions generated by Fenton's reaction (Eq. (1)):

Fe(OH)2+ hv ) Fe2+ + OH (4)

Another importance of reaction (3) is to catalyze the Fenton's reaction (Eq. (3)) producing continuously ferrous iron needed by this reaction. Thus the organic pollutant degradation rate is strongly accelerated by irradiation with UV-vis light in photo-Fenton. Under these conditions, the photolysis of Fe3+complexes promotes Fe2+regeneration and ironmaybeconsidered a truecatalyst.

In this study, photo- Fenton "like" (UV/Fe3+/H2O2) processes was applied to removea synthetic dyes mixture from water in order to eliminate their strong colour and their ecotoxicological consequences on aquatic environment.

2.1. Chemicals

Three dyes, Basic Blue 41, Basic Yellow 28 and Basic red 46were provided by company Fuital (Textile Processing Industry of Bab-Ezzouar, Algiers Algeria) and were used without anypurification. Their chemical structures and other characteristicsare listed in Table 1. Iron (III) sulphatepentahydrateFe2(SO4)3,5H2O and hydrogen peroxide (30% wt) of analytical grade were purchased from Merck. The pH of solution was adjusted to desired value using 1.0 M H2SO4 solutions.

Table l.Characteristics of dyes under study.

^max M

nm g.mol-1

Chemical structure

Sandocryl Red B-RLN 200%

Red 46 cationic

Sandocrylbrillant Basic blue Blue 41

B-RLE 300%


Sandocryl Gold Basic yellow Yellow

B-GRL 300% 28


2.2. Photoreactor and experimental procedures

All experiments were carried out in a batch Photoreactor (Fig.1), a cylindrical 1.3 L borosilicate double walled reaction vessel with water circulation through the walls to maintain constant temperature. A peristaltic pump was used to re-circulate the solution with a rate of 9.5 L min-1.A quartz tube was placed vertically in the middle of the photoreactor with low pressure mercury vapour lamp (HeraeusNoblelight-NNI 40/20).

The pH value influences the generation of •OH0 and thus the process efficiency, it was shown that the photo-Fenton system has a maximum catalytic activity at pH=3. In each experiment, the pH value of the solution was set to 3 by adding required amounts of H2SO4 solution. A given weight of iron salt was added and mixed very well with the prepared dye solution before the addition of a given volume of H2O2. The time at which the ultraviolet lamp was turned on was considered time zero. The temperature of the solution was kept constant at 20°C throughout all experiments. Samples were taken at predetermined time intervals to measure absorbance and TOC. The samples were analyzed immediately to avoid further reaction. Most of the experiments were performed in triplicate and the average value was giving.

Fig. l.Experimental set-up for photo-Fenton experiments.

2.3. Analytical method

The pH of the solutions was measured by using Eutech instruments digital pH meter. Sample solutions were withdrawn at certain time intervals for mineralization analysis. The total organic carbon (TOC) of initial BB41 dye solutions and its evolution during photo-Fenton treatment was performed in order to determine the mineralization efficiency of the process. TOC values were determined by catalytic oxidation using a Shimadzu VCSH TOC analyzer. All samples were filtered (0.22 ^m) and acidified with 1% HCl to pH 2. The injection volumes were 50 ^L. Calibrations were performed by using the potassium hydrogen phthalate solutions as standard.

3. Results

Most work on the photodegradation of dyes generally relates solutions containing a single dye molecule. However, industrial effluents are complex matrices containing many chemical contaminants, including several dyes. This section aims to verify the effectiveness of advanced oxidation processes studied in the treatment of wastewater containing a mixture of dyes. Basic Blue 41 (BB41), Basic Red 46 (BR46) and Basic Yellow 28 (BY28), cationic dyes are used as model molecules in this work.

3.1. Degradation rate

Under the same operating conditions defined in a recent publication [17] for the degradation of an aqueous solution of BB41 (Co = 0.05 mM, [H2O2] / [Fe+3] = 10)[17], we studied the degradation of two cationic dyes: BY28 and BR46. Comparative degradation kinetics is given in Fig.2.The kinetic curves of degradation in photo-Fenton treatment of BB41, BY28 and BR46 show that the concentration of dye decreases exponentially involving a kinetic of pseudo-first order. Moreover, the three dyes (BB41, BY28 and BR46) have similar kinetic behavior. In the same operating conditions, the degradation of BB41, BY28 and BR46 is completed after 5, 6 and 8 min of treatment, respectively.

[BB41 ] [BY28] [BR46]

[BB41 ] • [BY28] * [BR46]

Irradiation time (min)

irradiation time (min)

Fig. 2. First order reaction plot for initial oxidation of dyes (a) and kinetic analysis (b). [dye]0 = 0.05mM, R = [H2O2]/[Fe3+] = 10 ; [Fe3+] =0.2

The decolorization of dyes by photo-Fenton process was observed to be a function of time. The experimental data on initial oxidation were fitted into the following integrated equation from pseudo-first order kinetics: Ln(At/A0) =kt; where A0 and At are absorbance of the dyes at time 0 and at time t. k is the first order rate constant in min-1 and t is the time in min.

When [lnAt/A0] was plotted against time (Fig. 2 b) a linear relationship was obtained indicating that the oxidation of dyes by •OH follow a pseudo-first order kinetics. The rate of oxidation of the dyes were in the order BB41>BR46>BY28.Under our operating conditions (C =0.05mM, [Fe3+] =0.2mM and [H2O2] =2mM), the TOC abatement of the solution during treatment of the three dyes (BB41, BR46 and BY28) and their mixture was performed with a concentration of 0.05mMeachdye. The results are shown in Figure 3.

• Mixture [BB41 ]+[BR46]+[BY28]

* [BR46] ■ [BB41 ] * [BY28]

Irradiation time (min)

Fig.3. Evolution of TOC as a function of irradiation time during treatment with photo-Fenton process of the three dyes and theirmixture.[Dye] =

0.05 mM, [Fe3+] = 0.2 mM and [H2O2] = 2 mM.

These curves show that the variation of removal TOC, both for the three dyes treated separately as well as their mixture, follows an exponential decay over time, which suggests a first order kinetics. The mineralization rate is around 93% for the BB41, 85% for BR46 and95% for BY28 for a treatment time of 5 hours. Furthermore, the mineralization rate of a solution formed by a mixture of three dyes was 77% (initial concentration of dyes3 times greater than individual dyes solutions) after 5h of treatment. And as can be seen in FigureVI-3, the mixture requires a longer processing time to achieve a mineralization rate of 91% (8 of irradiation).

3.2. Effect of initial(Fe3+) concentration

The concentration of iron ion as catalyst is one of the main parameters that influence the degradation kinetics in photo-Fenton process. The effect of [Fe3+] was investigated for the followingFe3+concentrations: 0.2, 0.4, 0.6 and 1 mM at 2 mMH2O2 initial concentration and obtained results are depicted in Figure 4.As it can be seen, the initial concentration of Fe3+ influences significantly the TOC removal, the best concentration value being 0.6mM.The TOC removal ratio increases until 0.6 mM whereas it decreases for value of 1.0 mM.

The TOC removal ratio is about 84% after 5 hours of irradiation with 0.6 mM Fe3+against 77% with 0.2 mM. However, further increase of Fe3+ concentration on 0.6 mM, decreases the mineralization efficiency, this may be due to the increase of a brown turbidity that hinders the absorption of light required for the photo-Fenton process and to scavenging effects of hydroxyl radicals by Fe3+ and Fe2+as follows [18] since these parasitic reactions become competitive at higher Fe2+ or Fe3+ concentrations.

Fe2+ + •OH ^ Fe3+ + OH- (4)

Fe3+ + ^HO2 ^ Fe2+ + O2 + H+

[Fe3+]= • 0,2 mM * 0,4 mM A 0,6 mM ♦ 1 mM

Irradiation time (min)

Fig. 4.Effect of the initial concentration of Fe3+on the TOC removal in the photo-Fenton process. [BB41]0=0.05 mM, [BR46]0=0.05 mM,

[BY28]o=0.05 mM, [H2O2]0=2 mM, pH=3, V=1.4 L.

3.3. Effect of initial H2O2 concentration

Photo-Fenton reactions at two different molar concentration of H2O2were carried out to investigate the influence of hydrogen peroxide. Figure 5 presents the TOC removal as function of reaction time during photo-Fenton reaction according to the following conditions: ([BB41]o=[BR46]o=[BY28]o= 0.05 mM and pH 3 and fixed initial Fe3+ concentration 0.6 M.

This figure shows that the initial concentration of hydrogen peroxide and the ratio R are critical variables in the photo-Fenton process. Indeed, increasing the initial concentration of hydrogen peroxide from 6 (R = 10) to 12 mM (R = 20) at a constant concentration of Fe3+ (0.6 mM) results in increased efficiency of the process. After 5 h of irradiation, the TOC abatement rate increases from 84 to 90% for R = 10 and R = 20 respectively. These results are in good agreement with the literature [19, 20] where it was shown that increasing the concentration of hydrogen peroxide improves the efficiency of photo-Fenton process.

■ R= 10 * R = 20

Irradiation time (min)

Fig. 5.Effect of the initial concentration of H2O2on the mineralization efficiency of photo-Fenton process. [BB41]0=0.05 mM, [BR46]0=0.05 mM,

[BY28]0=0.05 mM, [Fe3+]0=0.6 mM, pH=3, V=1.4 L.

4. Conclusion

The degradation of a mixture of three cationic dyes by photo-Fenton process was reported in this study. The degradation rate and mineralization efficiency of the process were influenced by the initial concentration of hydrogen peroxide and iron salt and their ration R = [H2O2]/[Fe3+]. The degradation follows a first-order kinetic law.The TOC removals weredetermined using 0.6 mM of Fe3+ and 12 mM of H2O2 in 5 hour of irradiationThe optimal [H2O2]/[Fe3+] ratio was found to be 20 at pH = 3 Under this conditions, the TOC removal valuesof 93, 85 and 95 %were foundforBB41BR46andBY28 respectively. A quasi complete mineralization efficiency of 91% was achieved at 8 h of treatment for the mixture of three dyes with an initial concentration of 0.15 mM.

5. References

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