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Fenton-like Oxidation of Reactive Black 5 Solutions Using Acid-activated Kuala Kangsar Clay

H. Hassan, Zuraida Wan,

Faculty of Chemical Engineering, Universiti Teknologi Mara (UiTM) Permatang Pauh, Pulau Pinang, Malaysia hamizura179@ppinang.uitm.edu.my

Abstract- Decolorization of azo dye Reactive Black 5(RB5) in an aqueous solution was investigated by using Fe-activated Kuala Kangsar clay (Fe-AKKC) as heterogeneous catalyst. The best reacting conditions were found to be 1.0 wt.% of iron ions loading on Kuala Kangsar clay (KKC) when the dosage of the catalyst is 2.5 g/L with initial pH of 4.0, [H2O2]0 of 8 mM, [RB5]o of 50 mgL-1at temperature 30 °C. Under these conditions, 99% decolorization efficiency of RB5 was achieved within 180 min reaction time. The results indicated that Fe-AKKC has proven to be a superior heterogeneous catalyst for decolorization of RB5 in an aqueous solution. Keywords: Fe-AKKC, Reactive Black 5, heterogeneous catalyst, decolorization

I. INTRODUCTION Textile industry is the third largest foreign exchange earner after the electronic and palm oil industries in Malaysia, contributing total earning of RM18.0 million (US$ 5.4 million) from manufactured exports in 2007. According to Firmino et al. [1] the textile industry represents 1.7% of world exportation in 2007 which corresponds to the amount of US$ 238.1 billion. There are about 1500 textile factories in Malaysia mostly operate as backyard or cottage industries producing the local “batik”. Textile processing consumes large amounts of water which in turn discharge large volumes of effluent. Color has been included in the water quality standards for the discharge of industrial effluents in Malaysia. Under the Environment Quality (Industrial Effluents) Regulations, 2009, the limits of colour for discharge of effluents according to standards A and B are 100 and 200 Platinum-Cobalt (PtCo) units, respectively [2]. Reactive dyes which are the dominant type of dyes are widely used in textile industries. These are designed to produce long lasting color and have simple dyeing procedure [3]. Colored effluents can cause problems in several ways; dyes can have acute and/or chronic effects on exposed organisms in many rivers and water-ways [4]. This kind of effluent is also resistant to biological degradation. Therefore removal of such colored agents from aqueous effluents is a significant environmental issue. Fenton technology is widely studied and reported as an attractive alternative for the treatment of industrial wastewater containing non-biodegradable organic pollutants [5, 6]. The process however have some significant drawbacks mainly on high operating cost for wastewater treatment due to high iron loss to the environment, sludge formation and high consumption of H2O2 [7]. This poses a major barrier to the applications of this treatment in less wealthy countries. On the

other hand, heterogeneous solid catalysts can mediate Fenton-like reactions over a wide range of pH. This is because the Fe(III) species in such catalysts is immobilized within the structure and in the pore/interlayer space of the catalyst. As a result, the catalyst can maintain its ability to generate hydroxyl radical from H2O2, and iron hydroxide precipitation is prevented. Besides showing limited leaching of iron ions, the catalysts can easily be recovered after the reaction, and remain active during the successive operations [8]. Clay minerals posses structural and surface charge characteristics that are conducive to be use as supports of catalytically active (Fe, Cu) phases, or as solid heterogeneous catalysts for the Fenton-like reaction. The use of clay as support for the dye removal was first studied most extensively by Feng’s group. Briefly, the surface of the clays can be designed or modified to give higher activity, selectivity and longer catalyst lifetime [9]. Clays can be pretreated with acid to activate the clay structure and composition to their desired properties for specific reaction. Acid treatment opens up the edges of the platelets resulting in expansion of the surface area and increase in the pore diameter [10]. In addition, acid treatment also replaces exchangeable cations with H+ ions with the simultaneous loss of some Al3+ and other cations from both tetrahedral and octahedral layers leaving the SiO4 group intact [11]. This process could improve the catalytic activity of the catalyst by immobilizing more iron on the support [12]. Yip et al. [13] have successfully developed Cu/acid activated bentonite clay as catalyst for the heterogeneous photo-Fenton for degradation of an azo organic dye, Acid Black 1 (AB1). They found that the acid activation process of clay could significantly reduce the leaching problem by almost 72% and improve the catalytic activity of the catalyst. These improvements came from the active site and the addition of sulfonate functional group on the clay surface. In this study, the Fe-activated Kuala Kangsar clay (Fe-AKKC) was developed as a new heteregenous catalyst for decolorization of an azo dye. The effects of different loading of iron ions on Kuala Kangsar clay (KKC), catalyst dosage, initial concentration of dye and H2O2, and initial pH and temperature range were assessed. Reactive Black 5 (RB5) was employed as a model pollutant of an azo dye, which has been used extensively in dyeing industry.

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II. EXPERIMENTAL

A. Materials KKC was obtained from the place called Sayong, one of the areas in Perak, Malaysia. The commercial azo dye RB5 and hydrogen peroxide (30% w/w) was purchased from Sigma-Aldrich (M) Sdn Bhd, Malaysia. The structural diagram of RB5 is shown in Fig. 1. HCI used for acid activation of clay was obtained from Merck, Malaysia. All chemicals were of analytical grade and were used without any further purification.

Fig.1. Structural diagram of RB5

B. Preparation of acid activated KKC The acid activated KKC was prepared by standard procedure [14]. 30 g of original KKC were refluxed with 300 ml of 1.0 M HCI for 1 hour. The solid obtained after this treatment was washed several times until no chloride anions could be detected and dried in the oven at 80 °C for 12 h.

C. Preparation of Fe-AKKC The Fe-AKKC was prepared by the impregnation method [15]. In this process, Fe SO4.7H2O (Merck) was dissolved in a beaker containing distilled water. Then, KKC was added to this aqueous solution and was stirred by a glass rod uniformly in the water bath until all water was evaporated. The resulted products were finally dried at 85°C for 12 h and then calcined at 500 °C for 4 h in a muffle furnace.

D. Catalyst Characterization Scanning electron microscope (SEM) was used to study the surface morphology of the KKC and Fe-AKKC. The analysis was carried out using a scanning electron microscope (Model SEM-JEOL-JSM6301) with an Oxford INCA/ENERGY-350 microanalysis system. The amounts of iron in the original clay and in the catalyst were determined using Energy Dispersive X-Ray (EDX) (Oxford INCA 400, Germany) linked to SEM. Specific Brunauer-Emmett-Teller (BET) surface areas were determined by adsorption of nitrogen at 77 K, by using a Micromeritics, ASAP 2020 surface area and porosity analyzer. Fourier transform infrared (FTIR) spectroscopy was conducted to study the surface chemistry of KKC and Fe-AKKC by identifying the functional group presented on the samples. The spectra were measured from 4000 to 400 cm-1 by using Model Perkin Elmer FTIR-2000, US with He-Ne laser

source in KBr pellet (1 mg sample with 300 mg KBr) and 15 scan per minute to improve the signal-to noise ratio.

E. Catalytic Activity Experimental runs were carried out in a 250 mL-stoppered glasses (Erlenmeyer flask) filled with 200 mL diluted solutions (50–100 mg/L). The pH was adjusted to the desired value by using 1.0 M H2SO4 or 1.0 M NaOH which was followed by the addition of catalyst. The reactions were commenced by adding predetermined amounts of H2O2 solution to the flask. The flasks were then placed in a thermostated water bath shaker and agitation was provided at 130 rpm. The samples were taken out from the flasks periodically and were filtered by using BOECO filter (SFCA-membrane, 0.45 um) for the separation of catalysts from the aqueous solution. The concentrations of dyes were measured using a double beam UV/Vis spectrophotometer (Shimadzu, model UV 1601, Japan) at 532 nm wavelength. At each stage, the samples withdrawn were returned into the conical flask to prevent any loss of contents. The decolorization efficiency of RB5 was defined as follows:

Decolorization efficiency (%) = %1000

���

����

� −C

CC to (1)

where Co (mg/L) is the initial concentration of RB5 and Ct (mg/L) is the concentration of RB5 at reaction time, t (min).

III. RESULTS AND DISCUSSIONS

A. Catalyst Characterization Fig. 1(a) and (b) shows the SEM images of KKC and impregnated KKC. The natural KKC has a very fine, irregular, curved flakes and mats of coalesced flakes. In general, the flakes seem to be anhedral, but it was difficult to determine their exact texture because of particle coalescence [12]. However, the impregnated KKC, show a clear decrease in the particle size caused by an impregnation process. This sample predominantly consists of small aggregates of particles and exhibits a distinct porous structure.

(a)

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(b)

Fig.1. SEM images of (a) KKC (b) 1.0 wt. % Fe–AKKC (magnification: 3 kx).

The chemical composition of the original KKC and 1.0 wt.% Fe-AKKC were listed in Table 1. The EDX analyses indicated the presence of iron, silica, alumina and oxide as major constituents with the different percentages in the catalyst. The results also revealed that iron concentration of the Fe-AKKC catalyst is 6.53 wt.% while it is 5.71 wt.% in the original clay. Chang et al. [16] stated that all of the iron species in the clays have been found to be catalytically active towards the activation of H2O2 to degrade organic dyes under visible irradiation, but the degradation kinetic and reaction pathway vary with the state and environment of the iron species. In heterogeneous catalyst, the iron species were bound to the surface of the catalyst and the formation of hydroxyl radical is due to Fe2+ catalyzed decomposition of H2O2 on the surface of the support. Table 1: Chemical composition of KKC and 1.0 wt. % Fe–AKKC determined

by EDX.

The FTIR spectra of the KKC and Fe-AKKC are shown in Fig. 2. As can be seen, the KKC sample shows a band at 3620.93 cm-1 attributed to stretching vibrations of the OH group associated with cations. The bands at 3446.12 cm-1 and 1637.36 cm-1 show the stretching and deformation vibrations, respectively, for –OH groups interlayer water molecules present in the clay. The bands at 1115.42 cm-1, 1007.95 cm-1, 754.92 cm-1, 788.26 cm-1, 536.09 cm-1 and 470.82 cm-1 are attributed to the stretching and bending vibrations of SiO4

2- tetrahedral [17]. The bands corresponding to Al-Al-OH bending vibrations is observed at 912.29 cm-1 [18]. The Si-O bands are strongly evident in the silicate structure and can be readily recognized in the infrared spectrum by the strong absorption bands in the 1100-1000 cm-1 region, while the bands at 536.09 cm-1 and 470.82 cm-1 are due to Al-O-Si and Si-O-Si bending vibrations, respectively. Comparing the spectrum of natural KKC and Fe-AKKC, two peaks of KKC sample were shifted or disappeared which are 646.78 cm-1 and 754.92 cm1 corresponding to coupled Al-O and Si-O out of the plane vibrations and bending vibrations

of SiO42- tetrahedra. The bands at 1007.95 cm-1 and 1115.42

cm-1 of KKC are shifted and formed a broad band at 1039 of Fe-KKC sample, which indicate the degree of disorder of the Fe-KKC. The dissolution of octahedral sheets caused by acid treatment can be followed by an intensity decreased of the band corresponding to –OH bending vibrations at 912.29 cm-1 (AlAlOH) shows the substitution of octahedral by iron ions [12]. The IR spectra of the KKC the intensities of the corresponding bands at 536. 09 cm-1 (Si-O-Al), 470.82 (Si-O-Si), 1007.95 cm-1 and 3620 cm-1 (Si-O) were slighty reduced. Therefore, acid treatment and impregnation process leads not only decreased the intensity some of the bands but also leads to structural modifications of KKC.

Fig.2. FTIR spectra of (a) KKC and (b) 1.0 wt.% Fe-AKKC

B. Effect of Iron Ions Loading on KKC The effect of iron ions loading on KKC was investigated by

varying the iron ions concentration from 0.20 wt.% to 1.0wt.% the results are shown in Fig. 3. By increasing iron ions loading on the KKC, the decolorization rate increased efficiently and 99% decolorization was achieved for 1.0 wt.% within 180 min. Hence, 1.0 wt.% of iron ions loading was found to be optimum for maximum efficiency. The fact that higher decolorization efficiency achieved at high iron ions concentration was mainly attribute to the higher production of •OH with the increase of iron ions concentration.

C. Effect of Catalyst Dosage The influence of catalyst dosage on decolorization efficiency against time is illustrated in Fig. 4. In heterogeneous Fenton type processes the reaction between ferrous ion or ferric ion with hydrogen peroxide take place at the solid surface of catalysts which depends on the specific area of the catalyst [19]. As expected, when the amount of catalyst employed increased up to 2.5 g L-1, the decolorization rate of RB4 increased efficiently in which 99% decolorization was achieved within 180 min. The more catalyst dosage, the more active iron sites on the catalyst surface for accelerating the decomposition of H2O2 (heterogeneous catalysis), and more iron ions leaching in the solution, leading to an increase in the number of OH radicals (homogeneous catalysis). In the

Element Concentration (wt %)

KKC 1.0 wt. % Fe–AKKC Fe 5.71 6.53 Si 28.15 25.57 Al 25.06 24.34 O 41.08 43.56

400 320 200 100

3733.61

3672.9

3650.1

3621.0

3445.66

2360.21636.6

1039.0

914.8

776.4

727.5

694.9

538.8467.3

3694.6

3650.5

3620.9

3568.13446.1

2375.1

2346.3

1637.3

1115.4 1007.9

912.2

788.2

754.9

695.5646.7

536.0

470.8T

rans

mitt

ance

(%)

40

(a) KKC

(b) 1.0 wt.% Fe-KKC

Wave number cm-1

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present study, the best catalyst concentration for the decolorization of RB5 was experimentally determined to be 2.5 g/L.

0

20

40

60

80

100

0 30 60 90 120 150 180Time (min)

Dec

olou

rization Efficien

cy (%

)

0.20 wt.%Fe-AKKC

0.40 wt.%Fe-AKKC

0.60 wt.%Fe-AKKC

0.80 wt.%Fe-AKKC

1.0 wt.%Fe-AKKC

Fig.3. Effect of iron ions loading on KKC on the decolorization of RB5. Reactions conditions: [RB5]o = 50 mg L-1, [H2O2]o = 4 mM, pH = 2.5, catalyst

= 2.5 g L-1, temperature = 30 °C and 130 rpm.

0

20

40

60

80

100

0 30 60 90 120 150 180

Time (min)

Dec

olor

ization effic

ienc

y (%

)

0.5 g/LFe-AKKC

1 g/L Fe-AKKC

1.5 g/LFe-AKKC

2.0 g/LFe-AKKC

2.5 g/LFe-AKKC

Fig.4. Effect of catalyst dosage on the decolorization of RB5. Reactions

conditions: [RB5]o = 50 mg L-1, [H2O2]o = 4 mM, pH = 2.5, 1.0 wt.% of Fe–AKKC, temperature = 30 °C and 130 rpm.

D. Effect of pH The effect of initial pH solutions on the decolorization of RB5 was studied in the pH range of 2.0-5.0 and the result is shown in Fig. 5. The pH of the solution controls the production of hydroxyl free radical and thus the oxidation efficiency. The best solution pH for decolorization of RB5 was achieved at pH 3 with 99% decolorization efficiency within 180 min reaction time. This is consistent with the proved opinion that the optimum pH of Fenton oxidation mostly falls in the pH range of 2.5-3.5 [20]. It is noteworthy that 99% decolorization of RB5 was still obtained after 120 min reaction even the initial pH value was as high as 4. This is an important advantage because it allows using less acid to acidify the medium and reduce the cost for the sludge treatment. Chen et al. [21] also reported that more than 90% decolorization of RED RBN was achieved at pH 5.5 to 10 by newly isolated bacterial strains. Melero et al. [22] in their study of catalytic wet peroxidation of phenolic aqueos solution stated that the control of pH is a good method for preventing the leaching of iron species that decrease the activity of the catalyst.

0

20

40

60

80

100

0 30 60 90 120 150 180

Time (min)

Dec

olor

izat

ion

effic

ienc

y (%

) pH 2.0

pH 2.5

pH 3.0

pH 4.0

pH 5.0

Fig.5. Effect of pH on the decolorization of RB5. Reactions conditions:

[RB5]o = 50 mg L-1, [H2O2]o = 4 mM, 1.0 wt. % of Fe–AKKC, catalyst = 2.5 g L-1, temperature = 30 °C and 130 rpm.

E. Effect of Initial Concentration of H2O2 Fig. 6 shows the effect of initial H2O2 concentrations on the decolorization of RB5 against time. The results obtained show: 8.0 mM was the optimum value for the H2O2 concentration when the initial concentration of RB5 was 50 mg L-1 and the initial pH 4. The reaction went more slowly when the reaction was lower (4.0 mM) or higher (20 mM). At low concentration, H2O2 cannot generate enough •OH and the oxidation rate is logically slow. The increase of the oxidant concentration from 4.0 to 8.0 mM led to an increase in the reaction rate, as expected, because more radicals will be formed. Nevertheless, for a very high H2O2 concentration (20 mM), the performance decreased. At higher H2O2 cocentrations, the scavenging of •OH radicals will occur, which can be expressed by the following reaction:

•• +→+ 2222 HOOHHOOH (2) Although the other radicals (HO2

•) are produced, their oxidation potential is much smaller than of the HO• species [23].

0

20

40

60

80

100

0 30 60 90 120 150 180

Time (min)

Dec

olor

izat

ion

effic

ienc

y (%

) 4 mM H2O2

8 mM H2O2

12 mM H2O2

16 mM H2O2

20 mM H2O2

H2O2

H2O2

H2O2

H2O2

H2O2

Fig.6. Effect of initial concentration of H2O2 on the decolorization of RB5.

Reactions conditions: [RB5]o = 50 mg L-1, 1.0 wt.% of Fe–AKKC, catalyst = 2.5 g L-1, pH = 3.0, temperature = 30 °C and 130 rpm

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F. Effect of Initial Concentration of RB5 The influence of various initial RB5 concentration on the decolorization process were investigated between 25 and 100 mg/L RB5 solutions when other parameters were maintained constant. The results are illustrated in Fig. 7. At initial stages of the process, the decolorization rate decreased with an increase in the initial concentration of RB5 due to the interface reaction processes. In heterogeneous Fenton process, the reaction occurs at the surface of Fe-AKKC between OH radicals generated at the active sites and RB5 molecules adsorbed on the surface. Thus, when the RB5 concentration is too high, the number of active sites available is decreased by the RB5 molecules due to their competitive adsorption on the catalytic surface. In addition, the intermediates product of RB5 oxidation might also compete for the limited adsorption sites with RB5 molecules, which blocked their interactions with Fe(II)/Fe(III) active sites [20]. Zhang et al. [19] also reported the same trend on the effect of initial dye concentration on the decolorization of Acid Orange 7 using goethite as catalyst. They found that at different initial dye concentration the color was nearly removed completely despite of the parallel consumption of hydroxyl radical. This behavior indicated that hydroxyl radicals generated from goethite-catalyzed hydrogen peroxide decomposition was sufficient enough to oxidize Acid Orange 7 completely after 30 min reaction.

G. Effect of Temperature Temperature is critical to the reaction rate, the product yield and distribution [24]. The result is illustrated in Fig. 8. It can be seen that the temperature exerts a strong effect on the decolorization efficiency of RB5 and the decolorization was accelerated by a rise in the temperature (30, 40 and 50 °C). This is because higher temperature increased the reaction rate between hydrogen peroxide and the catalyst, thus increasing the rate of generation of oxidizing species such as �OH radical or high-valence iron species [25]. In addition, higher temperature can provide more energy for the reactant molecules to overcome the activation energy barrier [26].

0

20

40

60

80

100

0 30 60 90 120 150 180

Time (min)

Dec

olor

ization effic

ienc

y (%

)

25 mg/L

50 mg/L

75 mg/L

100 mg/L

Fig.7. Effect of initial concentration of RB5 on the decolorization of RB5.

Reactions conditions: [H2O2]o = 8 mM, 1.0 wt.% of Fe–AKKC, catalyst = 2,5 g L-1, pH = 4.0, temperature = 30 °C and 130 rpm.

0

20

40

60

80

100

0 30 60 90 120 150 180

Time (min)

Dec

olor

ization Ef

ficienc

y (%

) 30 C

40 C

50 C

Fig.8. Effect of temperature on the decolorization of RB5. Reactions conditions: [RB5]o = 50, [H2O2]o = 8 mM, 1.0 wt.% of Fe–AKKC, catalyst =

2,5 g L-1, pH = 3.0 and 130 rpm

IV. CONCLUSIONS Fenton-like oxidation of Reactive Black 5 solutions using acid-activated Kuala Kangsar Clay has been proven as effective heterogeneous catalyzed process. The initial dye concentration, the increase in catalyst loading, and hydrogen peroxide concentration favor the decolorization efficiency. The best operation parameters for the Fenton oxidation of RB5 were 1.0 wt.% of iron ions loading, 2.50 g L-1 of catalyst dosage, and 8 mM of H2O2 for 50 mg/L initial dye concentration at an initial pH 4 with 30 °C temperature. Under these conditions, 99% decolorization efficiency of RB5 in an aqueous solution was achieved after 180 min reaction time. Fe-BC represents an attractive heterogeneous catalyst in the application of industrial treatment plant since they are low-cost, natural and environmentally friendly

V. ACKNOWLEDGEMENT The authors acknowledge the research grant provided by Universiti Teknologi Mara, under excellent fund grant (Project No 600-RMI/ST/DANA5/3/Dst 121/2011) that has resulted in this article.

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