Scholarly article on topic 'Degradation of Sunset Yellow FCF using copper loaded bentonite and H2O2 as photo-Fenton like reagent'

Degradation of Sunset Yellow FCF using copper loaded bentonite and H2O2 as photo-Fenton like reagent Academic research paper on "Chemical sciences"

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{"Sunset Yellow FCF" / Degradation / Photo-Fenton / Bentonite}

Abstract of research paper on Chemical sciences, author of scientific article — Kiran Chanderia, Sudhish Kumar, Jyoti Sharma, Rakshit Ameta, Pinki B. Punjabi

Abstract In the present work, photo-Fenton degradation of Sunset Yellow FCF under visible light was carried out by using copper loaded bentonite and hydrogen peroxide. The photocatalyst was prepared by loading copper ions on bentonite by wet impregnation method. The rate of photocatalytic degradation of dye was measured spectrophotometrically by measuring absorbance of the reaction mixture at regular time intervals. The effect of various parameters such as pH, concentration of dye, amount of photocatalyst, amount of H2O2 and light intensity on the reaction rate has also been studied. Characterization of photocatalyst has been done by IR spectroscopy, scanning electron microscopy and X-ray diffraction. The Chemical Oxygen Demand (COD) of the reaction mixture has been determined before and after treatment. A tentative mechanism involving OH radical as an oxidant for degradation of dye has also been proposed. Involvement of OH radicals as an active oxidizing agent has been confirmed by using isopropanol and butylated hydroxy toluene (BHT) as radical scavengers. It has been observed that the rate of reaction is drastically reduced in the presence of these scavengers. The rate of reaction is much retarded by using BHT as compared with isopropanol.

Academic research paper on topic "Degradation of Sunset Yellow FCF using copper loaded bentonite and H2O2 as photo-Fenton like reagent"

King Saud University Arabian Journal of Chemistry

www.ksu.edu.sa www.sciencedirect.com

ORIGINAL ARTICLE

Degradation of Sunset Yellow FCF using copper loaded bentonite and H2O2 as photo-Fenton like reagent

Kiran Chanderia a, Sudhish Kumar b, Jyoti Sharma a, Rakshit Ameta a, Pinki B. Punjabi a *

a Photochemistry Laboratory, Department of Chemistry, University College of Science, M.L. Sukhadia University, Udaipur-313002, Rajasthan, India

b Department of Physics, M.L. Sukhadia University, Udaipur-313002, Rajasthan, India

Received 20 December 2011; accepted 23 July 2012

KEYWORDS

Sunset Yellow FCF; Degradation; Photo-Fenton; Bentonite

Abstract In the present work, photo-Fenton degradation of Sunset Yellow FCF under visible light was carried out by using copper loaded bentonite and hydrogen peroxide. The photocatalyst was prepared by loading copper ions on bentonite by wet impregnation method. The rate of photo-catalytic degradation of dye was measured spectrophotometrically by measuring absorbance of the reaction mixture at regular time intervals. The effect of various parameters such as pH, concentration of dye, amount of photocatalyst, amount of H2O2 and light intensity on the reaction rate has also been studied. Characterization of photocatalyst has been done by IR spectroscopy, scanning electron microscopy and X-ray diffraction. The Chemical Oxygen Demand (COD) of the reaction mixture has been determined before and after treatment. A tentative mechanism involving .OH radical as an oxidant for degradation of dye has also been proposed. Involvement of .OH radicals as an active oxidizing agent has been confirmed by using isopropanol and butylated hydroxy toluene (BHT) as radical scavengers. It has been observed that the rate of reaction is drastically reduced in the presence of these scavengers. The rate of reaction is much retarded by using BHT as compared with isopropanol.

© 2012 King Saud University. Production and hosting by Elsevier B.V. All rights reserved.

1. Introduction

Water is the basic need of every living organism. But a continuous increase in multifarious activities by human beings like

* Corresponding author. Tel.: +91 09460970590. E-mail addresses: kiranchanderia21@gmail.com (K. Chanderia), pb_punjabi@yahoo.com (P.B. Punjabi). Peer review under responsibility of King Saud University.

industrialization, urbanization etc. has led to pollution of our water resources. Numerous industries like textile, paper, pulp, dyeing and printing industries are throwing their effluents into water bodies causing water pollution (Mckay and Allen, 1980; Mckay et al., 1981). Effluents of textile industries contain dyes which make the water coloured and toxic and thus making it unfit for any use.

Various conventional treatment methods are used for removing colour from water. Riera-Torres et al. reported a combination of coagulation-flocculation and nanofiltration techniques for removal of dye from water (Riera-Torres et al., 2010). Namasivayam and Kavitha investigated the removal of congo red from water by adsorption on activated

1878-5352 © 2012 King Saud University. Production and hosting by Elsevier B.V. All rights reserved. http://dx.doi.Org/10.1016/j.arabjc.2012.07.023

carbon (Namasivayam and Kavitha, 2002). The conventional processes generate large amount of sludge. This is the major drawback of these processes. To overcome the drawbacks of conventional methods, Advanced Oxidation Processes (AOP) have been used in past recent years. AOP are based on the generation of highly reactive radicals especially hydroxyl (.OH) radicals which possess high reactivity and low selectivity. Common AOP involve photocatalytic processes, Fenton processes, photo-Fenton processes, ozonation etc.

Photocatalytic degradation of azo dyes using TiO2 in aqueous solution was studied by Konstantinou and Albanis (2004). Tayade et al. reported photocatalytic degradation of dyes and organic contaminants in water using nanocrystalline anatase and rutile TiO2 (Tayade et al., 2007). The TiO2/UV photocat-alytic degradation of indigo and indigo carmine has been studied by Vautier et al. (2001). Photocatalytic mineralization of methylene blue using TiO2 coated polystyrene beads has been studied by Fabiyi and Skelton (2000). Dhananjeyan et al. observed the effect of dopants and calcination temperature on the photocatalytic reaction of TiO2 with certain pyrimidine bases (Dhananjeyan et al., 2000). Effect of surface modification of TiO2 with ascorbic acid on photocatalytic decolorization of an azo dye has been studied by Ou et al. (2005).

The homogeneous Fenton reaction has been used in industrial wastewater purification by Centi et al. (2000). Haseneder et al. compared degradation of polyethylene glycol by Fenton reaction with other advanced oxidation processes. They found that the rate of degradation was significantly higher for the homogeneous Fenton system (Haseneder et al., 2007). Bossmann et al. investigated degradation of polyvinyl alcohol by homogeneous and heterogeneous photocatalysis and Fenton reaction (Bossmann et al., 2001). Degradation of 20 different dyes in aqueous solutions by the Fenton process was reported by Xu et al. (2004). Lim et al. studied the highly active heterogeneous Fenton catalyst using iron oxide nanoparticles immobilized in alumina coated mesoporous silica (Lim et al., 2006).

EI-Morsi et al. observed degradation of 1, 2, 9, 10-tetra-chlorodecane in an aqueous solution using hydrogen peroxide, iron and UV light (El-Morsi et al., 2002). The homogeneous photo-Fenton degradation of reactive blue-4 dye using a photo-Fenton process under artificial and solar irradiation was investigated by Carneiro et al. (2007). Fenton and photo-Fenton degradation of 2-chlorophenol was studied by Perez-Moya et al. (2007). Degradation of the emerging contaminant ibuprofen in water by photo-Fenton was studied by Mendez-Arriaga et al. (2010). Huang et al. reported the removal of citrate and hypophosphite binary components using Fenton, photo-Fenton and electro-Fenton processes (Huang et al., 2009). Macias-Sanchez reported the degradation of a model mixture composed of acid yellow 36 and methyl orange azo dyes (Macias-Sanchez et al., 2011).

Photocatalytic degradation of Sunset Yellow FCF and phenol red using transition metal complexes and hydrogen peroxide has been reported by Punjabi et al. (Lodha etal., 2008a,b). Punjabi et al. also reported the degradation of bismark brown R dye using copper loaded neutral alumina as heterogeneous photo-Fenton reagent (Sharma et al., 2010).

Looking at the importance of photo-Fenton processes, a visible light sensitive photo-Fenton like reagent has been prepared by loading copper ions in bentonite clay. It has been used for the degradation of Sunset Yellow FCF dye.

2. Materials and methods

2.1. Preparation of photocatalysts

The photocatalyst was prepared by loading copper ions on bentonite clay by wet impregnation method.

Firstly, Na2CO3, as a powder, was added slowly into the solution of Cu(NO3)2 under magnetic stirring, until the ratio of [Na + ]/[Cu2 + ] becomes 1:1. Then this solution was kept in an oven at 60 0C for one day. This solution was then added to the clay suspension under stirring. The final [Cu2 + ]/[clay] ratio was equal to 0.5 mol/kg of dry clay. The catalyst was then filtered, washed with deionized water several times. Finally, it was dried at 105 0C overnight.

The prepared photocatalyst has been used for the degradation of Sunset Yellow FCF dye. For this purpose a stock solution of Sunset Yellow FCF (10~3 M, Aldrich) was prepared. Degradation of dye was observed by taking 40.0 mL mixture of 1.5 x 10~5M dye solution, 0.20 mL H2O2 (CBH, 30% vol.) and 0.025 g Cu-loaded bentonite. The reaction mixture was irradiated with a 200 W tungsten lamp (Philips). The intensity of light at various distances from the lamp was measured using a Solarimeter (SM CEL 201). A water filter has been used to cut off thermal radiations. A digital pH meter (Model 232) was used to measure the pH of the reaction mixture. pH of the solution was adjusted by the addition of previously standardized 0.1 N sulphuric acid and 0.1 N sodium hydroxide solution. The progress of the degradation was monitored by measuring the absorbance of the reaction mixture at regular time intervals using UV visible spectrophotometer (Systronics Model 106) (Fig. 1).

2.2. Characterization of photocatalyst

2.2.1. Scanning electron microscopy

Scanning electron microscopy (Model-Leo 430 Cambridge) has been used to observe the morphological changes caused by loading of copper ions on the surface of bentonite. It has been observed that loading of copper ions leads to the formation of smaller particles of the catalyst. This factor has led to the increased surface area of catalyst and increased rate of degradation. The SEM photographs of loaded and unloaded ben-tonite are shown in Figs. 2 and 3, respectively.

The particle size of Cu-loaded bentonite and naive benton-ite was measured with the help of SEM and it was observed that the average particle size is 5.0 im and 35.0 im, respectively.

2.2.2. X-ray diffraction (XRD) studies

XRD patterns of the samples were recorded on a powder X-ray diffractometer using Cu Ka radiation. Diffraction patterns were recorded in the 29 range from 100 to 900 with a step size of 0.020.

Figure 1 Sunset Yellow FCF.

Figure 2 Copper loaded bentonite.

agreement with reported values a = 5.170 A, b = 8.940 A, c = 9.950 A and unit cell volume = 454.085 A3.

Relative changes in the peak positions and peak intensities in the Cu loaded samples clearly indicate that Cu atoms are well incorporated in the clay matrix. The obtained values of the cell parameters for Cu loaded bentonite are a = 5.1732 A, b = 8.9410 A and c = 9.9346 A and unit cell volume = 453.952 A3.

Thus Cu loading in bentonite leads to a small decrease in the unit cell volume.

2.2.3. Atomic absorption spectroscopy (AAS) Stability of the catalyst was checked by Atomic Absorption Spectroscopy (Model ECTL 4129A). Even after 1 month leaching of copper ions from the catalyst was found to be nil. Thus the catalyst was found to possess good stability for its use as a photo-Fenton like reagent under visible range.

3. Results and discussion

I ' % é* *

к vr _ r m * «

* a t * .: •» '

1 ^ ф \

HHT-20.00 KU WD- 33 lin Hag- 1 .01 К X

Шип I-1 Photo No.=975 Detector^ SEI

Figure 3 Bentonite.

Figs. 4 and 5 illustrate the indexed XRD patterns of the pure bentonite and copper loaded bentonite. All the Bragg reflections can be indexed in a rhombohedral structure. The obtained values of the cell parameters for the pure bentonite: a = 5.1774 A, b = 8.9428 A, c = 9.9439 A are in very good

An aliquot of 3.0 mL was taken out from the reaction mixture at definite time intervals and the absorbance was measured at 480 nm. It was observed that the optical density of the solution decreases with increasing time intervals, which indicates that the concentration of Sunset Yellow FCF decreases with increasing time of exposure. A plot of 2+ log A against time was linear and follows pseudo-first order kinetics. The rate constant was measured with the expression

k — 2.303 x slope

The photodegradation efficiency of the catalyst was calculated from the following expression:

CODbefore

where, g = Photodegradation efficiency (%); CODbefore = -COD of dye solution before illumination; CODafter = COD of dye solution after illumination.

Figure 4 X-ray diffraction pattern of bentonite.

Table 1 Typical run.

Time (min.) Absorbance (A) 2+ log A

0 0.310 1.491

10 0.250 1.397

20 0.224 1.350

30 0.205 1.311

40 0.187 1.271

50 0.171 1.232

60 0.161 1.206

70 0.144 1.158

80 0.130 1.113

90 0.119 1.075

100 0.108 1.033

110 0.097 0.986

120 0.084 0.924

к = 1.55 x 10-4 sec-1.

pH = 8.5, [Sunset Yellow FCF] = 1.55 x 10-4 M, amount of

photocatalyst = 0.025 g, H2O2 = 0.20 mL, light

intensity = 70 mW cm-2.

1.6 1.5 1.4 1.3 1.2 1.1 1

0.9 0.8 0.7 0.6 0.5

0 10 20 30 40 50 60 70 80 90 100 110 120

Time (min.)

Figure 6 Typical run-degradation of Sunset Yellow FCF: pH 8.5, [Sunset Yellow FCF] = 1.50 x 10-5 M, amount of photocatalyst = 0.025 g, H2O2 = 0.20 mL, light intensity = 70 mW cm-2.

3.1. Typical run

The typical run for the degradation of dye under optimum conditions is reported in Table 1 and Fig. 6

3.2. Effect ofpH - Effect ofpH on rate of reaction is graphically presented in Fig. 7

The effect of pH on the rate of degradation has been investigated in pH range 6.5-9.5. It has been observed that with an increase in pH, the rate of reaction increases and after attaining the maximum value at pH 8.5, the rate decreases with further increase in pH. The optimum value was obtained for pH 8.5. The rate of reaction increases on increasing the pH of the medium as the number of ~OH ions increases. As a con-

sequence, the .OH radical also increases resulting in a higher rate of degradation of dye. But on increasing the pH above 8.5, the number of ~OH ions will increase to a greater extent and these will start repelling the anionic dye so that the rate of degradation of Sunset Yellow FCF starts decreasing on increasing the pH of medium further (pH > 8.5).

3.3. Effect of concentration of dye - Effect of concentration of dye on the rate of reaction is graphically shown in Fig. 8

The effect of variation of concentration on the rate of degradation has been observed in the range from 0.25 x 10-5 M to 2.0 x 10~5 M. It has been observed that the rate of degradation increases with increasing concentration of dye up to 1.5 x 10 M. Further increase in concentration beyond 1.5 x 10~5 M decreases the rate of degradation. This may be explained on the basis that initially, on increasing the concentration of

Figure 7 Effect of pH: [Sunset Yellow FCF] = 1.50 x 10-5 M, amount of photocatalyst = 0.025 g, H2O2 = 0.20 mL, light intensity = 70 mW cm-2.

X ■M

0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 Amount (g)

Figure 9 Effect of amount of photocatalyst: pH 8.5, [Sunset Yellow FCF] = 1.50 x 10"5M, H2O2 = 0.20 mL, light intensity = 70 mW cm"2.

0 -1-1-1-1-1-1-1-1-

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25

[Sunset Yellow FCF] x 105M

Figure 8 Effect of concentration of dye: pH 8.5, amount of photocatalyst = 0.025 g, H2O2 = 0.20 mL, light intensity = 70 mW cm"2.

dye, the reaction rate increases as more molecules of dyes are available for degradation. But further increase in concentration beyond 1.5 x 10"5M causes retardation of reaction because the number of collisions between dye molecules increases whereas, collisions between dye and .OH radicals decrease. As a consequence, the rate of reaction is retarded.

3.4. Effect of amount of photocatalyst - The effect of variation in amount of catalyst is shown in Fig. 9

The effect of variation of amount of catalyst on the rate of dye degradation has been observed in the range from 0 .015 gm to 0.045 gm.

As clear from the above data with an increase in the amount of catalyst to a certain level (0.025 g), the rate of degradation increases, which may be regarded as a saturation point. Beyond this point, the rate of reaction decreases with increase in the amount of catalyst. This may be explained by the fact that with an increase in the amount of catalyst, the surface area of catalyst will increase. Hence, the rise in the rate of reaction has been observed. But after a certain limiting amount of catalyst, if the amount of catalyst was further increased, it would also increase the number of copper ions and then there is a possibility of short circuiting of cuprous and cupric ions. As a result, a less number of hydroxyl radicals are formed and reaction rate is retarded.

t 1-20 01

— 1.00 %

£ 0.80 0.60 0.40 0.20

0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 H202 (mL)

Figure 10 Effect of amount of H2O2: pH 8.5, [Sunset Yellow FCF] = 1.50 x 10"5M, amount of photocatalyst = 0.025 g, light intensity = 70 mW cm"2.

3.5. Effect of amount of H2O2 - Effect of variation of amount of hydrogen peroxide is presented in Fig. 10

The effect of variation of amount of H2O2 on the dye degradation has been investigated in the range from 0.10 mL to 0.35 mL.

It has been observed that on increasing the amount of H2O2 from 0.10 mL to 0.20 mL, the .OH radical concentration increases and hence the rate of degradation of dye also increases. At high H2O2 concentration i.e., beyond 0.20 mL scavenging of hydroxyl radical also takes place by increasing the amount of H2O2 generating perhydroxyl radicals (Eq. (2)). Perhydroxyl radical is less strong oxidant as compared to hydroxyl radical. Therefore the rate of degradation of dye decreases when the amount of H2O2 is increased beyond 0.20 mL.

H2O2 + OH ! H2O + HO2 (2)

3.6. Effect of light intensity - Effect of light intensity on the rate of degradation is shown in Fig. 11

The data indicate that as we increase light intensity, the rate of reaction increases and a maximum rate has been found at 70.0 mW cm"2. It may be explained on the basis that as light

f> 1.2

X JC 1.1

10 20 30 40 50 60 Light intensity (mW cm 2)

Figure 11 Effect of light intensity: pH 8.5, [Sunset Yellow FCF] = 1.50 x 10~5M, amount of photocatalyst = 0.025 g, H2O2 = 0.20 mL.

intensity was increased, the number of photons striking per unit area also increases, resulting in a higher rate of degradation. Further an increase in the light intensity beyond 70.0 mW cm~2 results in a decrease in the rate of reaction. It may be probably due to thermal side reactions.

3.7. Mechanism

3.8. Chemical oxygen demand

Chemical oxygen demand of dye solutions before and after illumination has been determined by redox method. COD of dye solution before and after exposure was found to be 70.36 mg/L and 26.40 mg/L, respectively. The photodegradation efficiency after 2 h of illumination has been found to be 62.47%.

4. Conclusion

Cu-loaded bentonite catalyst has been prepared, by wet impregnation method, using bentonite and copper nitrate. The amount of photocatalyst required (typically around 0.025 g in 40 mL) is much below than that usually used earlier. The effect of amount of photocatalyst, amount of hydrogen peroxide, concentration of dye, pH of the reaction mixture and light intensity was studied in the present work. The results show an appreciable degradation of Sunset Yellow FCF dye. At optimal conditions, the rate of degradation of Sunset Yellow FCF was obtained as k = 1.55 x 10-4sec~\ During heterogeneous photo-Fenton like process, .OH radicals react with dye and degrade them into smaller products like H2O, CO2~, SO3~, NO3~ ions etc.

On the basis of the experimental observations and corroborating the existing literature, a tentative mechanism has been proposed for the degradation of Sunset Yellow FCF by heterogeneous photo-Fenton like reagent. Initially, cupric ions from photocatalyst react with water in the presence of light and get reduced to cuprous state along with the formation of hydroxyl radicals. The cuprous ions so formed react with hydrogen peroxide without the requirement of photons generating cupric ions and .OH radicals. The cupric state is again converted into cuprous state with the aid of photons in aqueous medium:

Cu2+ + H2O ! Cu+ + OH + H+ (3)

Cu+ + H2O2 ! Cu2+ + OH + OH (4)

The .OH radical is non selective and is a strong oxidizing agent with high oxidation potential, which is relatively high as compared to common oxidizing agents like H2O2, O3, O2 etc. These .OH radicals react with dye and degrade it into smaller gaseous products like CO3, NO^, SO^3, SO43 ions etc. These products have been identified by usual chemical

tests:

'[Dye]!'[Dye]* (5)

'[Dye]* ü3[Dye]* (6)

3[Dye]* + 'OH ! Smaller products (7)

The involvement of .OH radicals in the reaction has been confirmed by carrying out the reaction in the presence of .OH radical scavenger, e.g., 2-propanol and butylated hydroxy toluene (BHT). In the presence of 2-propanol and BHT, the reaction rate has been found to be drastically reduced.

Acknowledgements

The authors (PBP and KC) are highly thankful to Prof. Suresh C. Ameta for his valuable critical suggestions during the progress of work. The authors also pay thanks to Head, Department of Chemistry & Geology, M.L.S. University, Udaipur and Dr. Mukul Gupta UGC-DAE Consortium, Indore for providing laboratory, SEM and XRD facilities, respectively.

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