SONOCATALYTIC DEGRADATION OF METHYL ORANGE DYE IN AQUEOUS EFFLUENTS

S.A. Md Ali1, A.Z. Abdullah2 1.Faculty of Chemical Engineering, Universiti Teknologi Mara(UiTM),Permatang Pauh, 13500 Pulau

Pinang,Malaysia. E-mail:sitiaminah.mdali@ppinang.uitm.edu.my 2.School of Chemical Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Malaysia. E-

mail:chzuhairi@eng.usm.my Sonocatalytic degradation of dye effluent by utilizing titanium dioxide (TiO2) as sonocatalyst is

the subject of this research. Methyl orange was used as a sample of dye effluent. Commercial TiO2 was successfully prepared. A Comparative study has been done between commercial and modified TiO2 catalysts. The characteristic of both catalysts were determined by XRD, SEM and BET. The results showed the modified TiO2 were better than the commercial TiO2. XRD pattern showed the presence of TiO2 element in both catalysts. From SEM images, the morphology of commercial TiO2 showed large aggregation of smaller particles than modified TiO2 catalyst. BET surface analysis also indicated that higher surface area, total pore volume and average pore diameter for modified TiO2. In this research, commercial TiO2 and modified TiO2 were used for the degradation of methyl orange by using ultrasonic probe. The effect of various experimental parameters including catalyst loading (250 – 1250 mg/L) and initial concentration (5 – 30 mg/L) were evaluated. The optimized parameters that have been obtained were; catalyst loading of 1000 mg/L and initial concentration of methyl orange 10 mg/L in irradiation time for 1hour. The modified TiO2 showed higher activity as compared to commerciall TiO2 by degrading 82% of methyl orange.

Keywords: Comparative study; Methyl Orange; ModifiedCatalyst; Sonocatalytic degradation; Titanium Dioxide (TiO2);

1. Introduction Textile industries are among the most polluting industries in terms of the volume and the complexity of

treatment of its effluents discharge. It has been reported that wastewaters generated by textile industries are known to contain large amounts of toxic aromatic compounds, especially azo dyes [1].

It is well known that some azo dyes and their degradation products, such as aromatic amines, are highly carcinogenic. It is estimated that 10–15 % of the overall production of dyes is released into the environment, mainly via wastewater. It has been reported that the discharge of very small amounts of dyes (less than 1 ppm for some dyes) is aesthetically displeasing, impedes light penetration, affects gas solubility damaging the quality of the receiving streams and may be toxic to treatment processes, food chain organisms and aquatic life. The removable of the non-biodegradable organic chemicals is a crucial ecological problem because effluent from the textiles industry can contain a variety of polluting substance including non-biodegradable organic and inorganic material. Since the conventional method is inadequate, there is a need for efficient tertiary treatment process. As the characteristics of dye wastewater are very variable, many different types of physical, chemical and biological treatments have been employed for its treatment. Although numerous physical/chemical schemes, including coagulation, flocculation, adsorption and membrane filtration have been used to decolorize textile effluents, these techniques suffer disadvantages of sludge generation, adsorbent regeneration and membrane fouling [2].

Therefore, alternative option such as sonocatalytic technology should be emphasized in the effort to reduce the negative environmental impact for such dye effluent from textile industries. In this study, the

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2011 International Conference on Environment and Industrial Innovation IPCBEE vol.12 (2011) © (2011) IACSIT Press, Singapore

Abstract.

ultrasonic irradiation was used to degrade the methyl orange in aqueous solution in order to compare the sonocatalytic activity of commercial and modified TiO2 powders. In many semiconductor material, TiO2 powder is considered to be a very efficient catalyst[3]. From literature, heterogeneous TiO2 catalyst was capable of promoting the sonocatalytic degradation of dye respectively. Oxidation processes with TiO2 could be workable for degradation of dye pollutant[4].

2. EXPERIMENTAL

2.1. Materials Methyl orange and TiO2 powder obtained from R&M marketing, Essex, UK were chosen as a model of

compound for investigating sonocatalytic ability. The sodium hydroxide (NaOH) and Hydrochloric acid (HCl) from Merck were used in this work. Deionized water obtained using ELGA system was used in the whole experimental work.

2.2. Apparatus The ultrasonic apparatus (Branson, USA) was used to irradiate the methyl orange solution operating at

ultrasonic frequency of 20 kHz and output power of 70 w. UV-vis spectrometer (Shimadzu UV-1601, Shimadzu Scientific Instruments, USA) was used to inspect degradation percentage of methyl orange. The pH meter used for measurements was a Mettler Toledo 320, from Germany.

2.3. Preparation of modified TiO2 The modified TiO2 catalysts were obtained by pressing 2.0 g of commercial TiO2 catalyst using manual

hydraulic press at 2280 psi to form pellets. The diameter and thickness of the pellet were set to 20 mm and 2 mm respectively. The pellet than was crushed and sieved to particle sizes of between 250 µm and 350 µm.

2.4. Characterization of the TiO2 The X-ray diffraction (XRD) analysis was made using Philips PW 1729 X-ray generator, Philips PW

1820 diffractometer and Philip 1710 diffraction controller. The specific surface area, total pore volume and average pore diameter of powders sample were measured by N2 adsorption-desorption method using a Micromeritics ASAP-2000 instrument (Norcross, GA) A scanning electron microscope (SEM) (Model: Leo Supra 50VP Field Emission, Germany) was used to examine the surface morphology of the granular and structured catalysts.

2.5. Experimental procedure One thousand (1000) mg of methyl orange powder was added to 1L of deionised water in a volumetric

flask. The stock solution was stirred to dissolve make a good dispersion of methyl orange in the deionised water. The prepared methyl orange solution (200mL) and TiO2 were put in the beaker. After that the beaker was placed inside an ultrasonic apparatus and irradiated for 1 hour. All experiments were conducted at ambient temperature. The Uv-vis spectra of the methyl orange solution during degradation was determined in the wavelength of 500 nm.

3. RESULT AND DISCUSSIONS

3.1. SEM, XRD, and BET surface area of the TiO2 powder Figure 1(a) and 1(b) represent the particle morphology of the commercial and modified TiO2 catalysts by

using SEM at 20,000 X magnification. Both commercial TiO2 and modified TiO2 shown that the surfaces were well formed particles of spherical shape. However, modified TiO2 could be totally different from commercial TiO2 on physical property. It can be seen that the morphology of modified TiO2 shown large aggregates of smaller particles and more agglomerates than commercial TiO2 catalyst.

It is noted that the modified TiO2 catalyst exhibited better uniformity in size and shape than in the commercial TiO2 catalyst.The size of commercial TiO2 and modified TiO2 are 150-280 nm and 90-160 nm, respectively, showing that the modified TiO2 catalyst could inhibit the increasing of grain size. The observed data of grain sizes for commercial and modified TiO2 was tabulated in the Table 1.

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This fact has been reported that an addition of more TiO2 or smaller-size TiO2 into the solution offers more reaction sites for producing the ·OH that accelerated the degradation rate of sonocatalytic process [5].

In order to confirm the appearance of TiO2, the XRD pattern of the commercial TiO2 powder and modified TiO2 were determined and the result is shown in Figure 2a) and 2b). Figure 3 shows a comparison of XRD pattern between commercial and modified TiO2. Also it is noted that the XRD peaks of commercial TiO2 and modified TiO2 have the same positions by the height, demonstrating that anatase and rutile could not be detected. Moreover, it could be seen that the modified TiO2 has lower intensity than commercial TiO2 at 9159 and 11741 respectively. It could be seen that at 2θ=25.3º modified TiO2 has wider peak than commercial TiO2. This implies that modified TiO2 has smaller grain size and spherical shape, and therefore in the crystallites size. Large crystallites give rise to sharp peaks, while the peaks width increases as crystallite size decreases.

The crystallite size calculation can be made by using Scherrer formula [6]:

Crystallite size= ( )

( cos )K λ

β θ×

×

where K = constant (0.9) λ = X-Ray wavelength (1.5406 Ǻ )

β = full width at half maximum (FWHM) measured in radians. θ = the angle of peak position

In order to calculate the crystallite size, the full width at half maximum (FWHM) for commercial and

modified TiO2 can be obtained from Figure 4 and 5 respectively. Hence, calculated crystallite size for modified TiO2 and commercial TiO2 was 50 nm and 53 nm, respectively. The modification process of TiO2

was attributed to a change in crystallite size after treatment. The mechanical impact produced by mortar have induced breakage on the particles, therefore the size of modified TiO2 was reduced. This was very encouraging as small grain led to small crystallites.

Table 2 shows the basic physicochemical and textural properties of commercial TiO2 and modified TiO2. The BET surface area (SBET) of commercial TiO2 is 13 m2/g with the total pore volume of 0.032 cm3/g and average pore diameter of 8.7 nm. The modification process of the TiO2 catalyst lead to an increase of the surface area, pore volume and average pore diameter to 14, 0.079 and 15.6, respectively. The BET area of the modified TiO2 is higher than commercial TiO2.

The modified TiO2 catalysts were prepared by crushing followed by grinding and sieving that could reduce the size of TiO2. This led to higher thermal stability, hinder the increase of the crystallite size, and increase its surface area [7]. Increasing surface area of TiO2 particles would provide more active sites to produce radicals[8]. Furthermore, the increased in BET surface area was a result of enhancement of pore volume or powder porosity.

Fig.1. SEM images of TiO2 powders: (a) Commercial TiO2 powder and (b) Modified TiO2 powder

Table 1Grain sizes of commercial and modified TiO2

Type of sample Grain size(nm) Range(nm)

Commercial TiO2

195.4, 189.8, 195.4, 234.5, 173.1, 156.3, 178.6, 184.2, 273.5, 256.8.

150-280

(b)

298

Modified TiO2 94.9, 139.6, 106.1, 128.4, 156.3, 94.9,

134.0, 117.2, 106.1, 134.0.

90-160

Fig. 2 XRD patterns for ((a) commercial TiO2 and (b) modified TiO2

Fig.3. Comparison of XRD pattern for commercial TiO2 and modified

Fig.4 Determining FWHM for commercial TiO2

Lin

(Cou

nts)

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1000

2000

3000

4000

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8000

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12000

2-Theta - Scale10 20 30 40 50 60 70 80 9

2th=25.254 °, int=11616 Counts, d=3.52376

(a)Li

n (C

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1000

2000

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2-Theta - Scale10 20 30 40 50 60 70 80 9

2th=25.252 °, int=9106 Counts, d=3.52397

(b)

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2-Theta - Scale22.8 23 24 25 26 27 28

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Fig.5 Determining FWHM for modified TiO2

Table 2 Textural properties of commercial TiO2 and modified TiO2 powders.

3.2. Effect of Catalyst Loading For the sonocatalytic degradation in the presence of heterogeneous catalysts, the amount of catalysts is an

important parameter. In this study, the catalyst loading was set in the range from 250 to 1250 mg/L. This range of catalyst loading was chosen based on similar work [9]. Figure 6 showed that all the degradation percentage values are increased with respect to TiO2 amount. With the modified TiO2 catalyst, the degradation percentage shows increasing up to 80 % and reached a steady value at 1000 mg/L. This can be explained by mutual screens among the TiO2 particles keep methyl orange decomposed, which resulted in the decreasing of sonocatalytic activity of TiO2 powder to a certain extent [10].

Fig.6 Effect of catalyst loading on degradation efficiency

As observed in this study, modified TiO2 demonstrated the higher degradation percent of methyl orange compared to commercial TiO2. Taking into account of the surface analysis result, the modified catalyst TiO2 samples having a larger surface area could allow a larger amount of surface adsorbed species. Apart from that, this high degradation percentage could be due to the presence of higher amount of hydroxyl radicals within the solution. Increasing surface area of TiO2 particles was reported to provide more active sites for producing radicals [8].

Effect of Initial Concentration The commercial catalyst and modified TiO2 catalysts were tested with initial methyl orange of 5, 10, 15,

20, 25 mg/L, respectively in the period of one hour. This range of methyl orange concentration was chosen based on similar work done by using the same sonocatalytic method [11]. Methyl orange concentration as the

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Samples BET surface

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Total pore

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cm3/g)

Average pore

diameter (dp, nm)

Commercial TiO2

13 0.032 8.7

Modified TiO2

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