Degradation characteristic of monoazo, diazo and anthraquinone dye by UV / H 2 O 2processChe Zulzikrami Azner Abidin, Muhammad Ridwan Fahmi, Md Ali Umi Fazara, and Siti Nurfatin Nadhirah Citation: AIP Conference Proceedings 1621, 271 (2014); doi: 10.1063/1.4898478 View online: http://dx.doi.org/10.1063/1.4898478 View Table of Contents: http://scitation.aip.org/content/aip/proceeding/aipcp/1621?ver=pdfcov Published by the AIP Publishing Articles you may be interested in The Electrolytic Effect on the Catalytic Degradation of Dye and Nitrate Ion by New Ceramic Beads of NaturalMinerals and TiO2 AIP Conf. Proc. 909, 166 (2007); 10.1063/1.2739846 Theoretical investigation of substituted anthraquinone dyes J. Chem. Phys. 121, 1736 (2004); 10.1063/1.1764497 Relaxation process for secondorder nonlinear optical properties of poled diazodyesubstituted polymers J. Appl. Phys. 79, 4358 (1996); 10.1063/1.361745 Secondorder nonlinearity of a novel diazodyeattached polymer J. Appl. Phys. 68, 6024 (1990); 10.1063/1.346935 Physical processes in degradation of amorphous Si:H Appl. Phys. Lett. 48, 846 (1986); 10.1063/1.96687

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Degradation Characteristic of Monoazo, Diazo and Anthraquinone Dye by UV/H2O2 Process

Che Zulzikrami Azner Abidin1,a), Muhammad Ridwan Fahmi1,b), Md Ali Umi Fazara1,c) and Siti Nurfatin Nadhirah1,d)

1School of Environmental Engineering, University Malaysia Perlis (UniMAP), Kompleks Pusat Pengajian Jejawi 3,

02600 Arau, Perlis, Malaysia

a)zulzikrami@unimap.edu.my b)Corresponding author: drfahmi@unimap.edu.my

c)umifazara@unimap.edu.my d)fatinnadhirah89@gmail.com

Abstract. In this study, the degradation characteristic of monoazo, diazo and anthraquinone dye by UV/H2O2 process was evaluated based on the trend of color, chemical oxygen demand (COD) and total organic carbon (TOC) removal. Three types of dyes consist of monoazo, diazo and anthraquinone dyes were used to compare the degradation mechanism of the dyes. The UV/H2O2 experiments were conducted in a laboratory scale cylindrical glass reactor operated in semi-batch mode. The UV/Vis characterization of monoazo, diazo and anthraquinone dye indicated that the rapid degradation of the dyes by UV/H2O2 process is meaningful with respect to decolourization, as a result of the azo bonds and substitute antraquinone chromophore degradation. However, this process is not efficient for aromatic amines removal. The monoazo MO was difficult to be decolorized than diazo RR120 dye, which imply that number of sulphonic groups in the dye molecules determines the reactivity with hydroxyl radical. The increased in COD removal is the evidence for oxidation and decreased in carbon content of dye molecules. TOC removal analysis shows that low TOC removal of monoazo MO and diazo RR120, as compared to anthraquinone RB19 may indicate an accumulation of by-products that are resistant to the H2O2 photolysis.

INTRODUCTION

It is well known that effluents from textile and dyestuff industries that draw off during the textile dyeing and finishing operations generate a severe pollution problem to the environment (1). These effluents generally contain different types of synthetic dyes with high level of COD, total suspended solid and strong color, which are mostly toxic, mutagenic, carcinogenic and persistent in the environment (2,3). Recently, more than one million tons of synthetic dyes are produced throughout the year and approximately 10% of the synthetic dyes are released as textile and dyestuff industrial effluent (4,5). Azo dye, which is widely used as additives in industry, constitutes the largest and the most important family of organic dyes. (6). The residual azo dye from dyeing and finishing operation that flows to the water body would threaten the safety of the aquatic environment and has an adverse health effect to human.

Chemical and physical methods, such as coagulation, adsorption, reverse osmosis and ultra-filtration were effective to be applied for the treatment of wastewater containing azo dyes (7,8). However, these treatment methods transfer most of the azo dye in industrial effluent to the solid phase that requires post-treatment of solid wastes, which is an expensive operation (1,9). Biological treatment offers an economical and environmentally friendlier

3rd International Conference on Fundamental and Applied Sciences (ICFAS 2014)AIP Conf. Proc. 1621, 271-277 (2014); doi: 10.1063/1.4898478

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alternative when compared to chemical and physical treatment (10-12). Mabrouk and Yusef (13) reported that aerobic treatment is the favorable biodegradation method for azo dye removal. Unfortunately, most of azo dyes are considered to be resistant to aerobic biodegradation (14). On the other hand, anaerobic treatment would be decomposing azo compounds lead to the formation of aromatic amines, which have higher toxicity and carcinogenity, but easily biodegraded by aerobic treatment (15,16). Therefore, anaerobic treatment on azo dyes will be effective if sequentially combined with aerobic treatment (17).

Nowadays, advanced oxidation processes (AOP’s) involving O3, O3/H2O2, O3/UV, UV/H2O2, O3/UV/H2O2 and Fe2+/H2O2 have been considered as an emerging technology for degradation of azo dyes in textile and dyestuffs industrial effluent (18,19). AOP’s produces hydroxyl radicals, which effectively decolorized and reduce the refractory pollutants in the wastewater (20). However, AOP alone requires higher chemical input that eventually induced higher costs of wastewater treatment operation (1). It is expected that the combination of AOP and biological treatment would be more efficient in order to remove residual color, COD and BOD of wastewater containing dye. In this combination, AOP is considered as a pre-treatment to improve the biodegradability of dyes whereas biological treatment removes the biodegradable fraction produced in AOP.

Recently, UV/H2O2 or other AOPs have been intensively studied to evaluate the effectiveness of this treatment for decolourization, COD and TOC removal in wastewater containing dyes. It is expected that the combination of biodegradation with AOP will effectively reduce COD, TOC, total dissolved solids and total suspended solids in dyes and tannin (21,22). It is expected that oxalate, formate and benzene sulfonate are the main products of AOPs that can be easily biodegraded by microorganisms (23). Therefore, AOP such as UV/H2O2 alone may efficiently remove color of dyes without significant effect on COD and TOC removal (24).

In this study, UV/H2O2 process was carried out in a laboratory scale reactor to clarify the degradation characteristic of dyes in term of color, COD and TOC removal. For this purpose, three types of dyes consist of monoazo, diazo and anthraquinone dyes were used to compare the degradation mechanism of the dyes. In addition, chemical functional groups were analyzed to characterize the intermediate products of UV/H2O2 process.

MATERIALS AND METHODS

Synthetic Dye Preparation

Three types of dye, namely Methyl Orange (MO), Reactive Red 120 (RR120) and Reactive Blue 19 (RB19) were used to represent monoazo, diazo and anthraquinone dye. Stock solutions of 10,000 mg.L-1 were used for preparation of dye solutions of desired concentrations by dilution. The pH of aqueous solutions was adjusted using 1N NaOH to raise the pH or 1N HCl to lower the pH upon decolourization. All solutions were prepared by using distilled water.

Experimental Set-up

The UV/H2O2 experiments were conducted in a cylindrical glass reactor (380 mm x 90 mm ID), with a volume of 1.6 L. The experimental set-up mainly consists of glass reactor, UV lamp, circulating water bath, UV lamp, and light source. The artificial irradiation was performed by using a 14 Watt preheated UV lamp model GPH 295T5L/4P (Atlantic Ultraviolet Corporation, USA). The lamp was 295 mm length, and provided an approximate total UV output of 3.7 Watt (254 nm). It was inserted into the hollow quartz sleeve (350 mm x 22 mm ID) located at the center of the reactor.

The quartz sleeve was used because it is transparent to the 254 nm light. In addition, the reactor was surrounded by a water jacket that prevents the lamp from overheating and allowed the control of reactor temperature, by means of continuous water recirculation. The lamp was turned on 30 min prior to perform the experiments. Dye solutions were then added into the reactor, and then being stirred by using a magnetic stirrer. The stirring speed was held constant for all runs. Ultimately, the reactor was protected from external light with aluminum foil cover. The addition of H2O2 to the reactor was performed by injecting appropriate volume of solution. Furthermore, the reaction mixture of dye solutions and predetermined amount of H2O2 was then continuously stirred with magnetic bar. Samples were taken at intervals and analyses as soon as possible.

To perform the experiments, the selected dyes, namely MO, RR120 and RB19 were mixed with H2O2 (0, 0.33, 0.67, 1.00, 1.33 and 1.67 mL H2O2.L-1 dye) at the beginning of the treatment period. Then, preheated UV lamp was immediately inserted into the quartz sleeve, which accounted the start of the reactions. The experiments were

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conducted at room temperature with different contact time of 0, 20, 40, 60, 80, 100 and 120 min. Finally, the samples were withdrawn at definite intervals for analyses. The pH was adjusted approximately 7.0 for all the experiments. The samples were taken at different intervals, depending on the treatment for and ultraviolet-visible (UV-Vis), COD and total organic carbon (TOC) analysis.

Analytical Methods

The decolourization of dyes was measured by Hitachi UV-Vis U-2810 spectrophotometer at 535 nm, while the pH was measured by Hanna Instruments HI 223 pH meter. The decolourization efficiency was determined by the difference between concentration before and after the treatment. COD test of the sample was determined based on the procedure derived in HACH Unit APHA method. The interference of H2O2 on COD value was corrected according to empirical equation derived by Kang et al (25). TOC was analyzed using commercially available test kits (HACH Direct Method, 10173) with the concentration range of 15-150 mg.L-1.

RESULT AND DISCUSSION

UV-Vis Absorption Spectra

The UV-Vis spectra of different dyes as a function of contact times in H2O2 photolysis are illustrated in Figure 1. As observed, the intensity of the maximum absorption peak for MO, RR120 and RB19 appeared at a wavelength 465, 535 and 595 nm in the visible region and decreased with the exposure time to UV irradiation. The wavelength of the maximum absorption peak tended to shift with time to lower values in the visible band. The monoazo MO absorbance bands at 240 nm attributed to the benzene ring in the UV region, where azo group at 465 nm in the visible band account for its color. While, the absorption spectrum of the diazo RR120 is characterized by 3 main bands, 535 in the visible range that responsible for the red color, and the spectrum at 240 and 290 nm in the UV region that characterized the benzene and naphthalene rings structure, respectively. Furthermore, the major characteristic absorption bands, 240 nm in the UV region characterized the benzene ring structure, and 595 nm in visible region corresponds to the blue color of the substitute anthraquinone RB19 chromophore.

The decrease of the maximum absorption peak indicates a rapid degradation of the dyes. The decrease is also meaningful with respect to the azo bonds and also substitute anthraquinone chromophore in the visible band that account for its color, as the most active site for oxidative attack. Although the cleavage of the azo bond and substitute antraquinone chromophore removes the visible color, it remains the problem of the aromatic amines. In general, the subsequent H2O2 photolysis treatment causes continuous decreases of the UV region intensities, and abrupt disappearance of the visible region spectra that accounts for color.

The absorption intensity in the visible region decreased rapidly in comparison to aromatic rings in the UV region, as reaction time proceeded. For examples, during 60 min reaction time, the absorbance reductions are 2.4 and 31.5% for the benzene and azo group of MO, respectively. In addition, the absorbance reductions are 61.0, 85.7 and 100% for benzene, naphthalene, and azo groups, respectively for diazo RR120. Furthermore, anthraquinone RB19 produced results which similar to MO and RR120. The absorbance reductions are 35.3, 26.8 and 42.9% for benzene, anthraquinone structure and substitute anthquinone chromophore, respectively with similar reaction time. Therefore, it is possible that the hydroxyl radicals were generated by the H2O2 molecules photolysis and, consequently, these radicals oxidized the dye molecules leading to intermediate compounds and, finally, to the decolourization. The results are consistent with reactions by hydroxyl radicals that initially attacked the azo and substitute anthraquinone chromophore, consequently caused decolourization.

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(a)

(b)

(c)

FIGURE 1. UV-Vis spectra of (a) MO, (b) RR120 and (c) RB19 after UV/H2O2 treatment at different contact time

Color Removal

The effectiveness of decolourization of synthesized MO, RR120 and RB19 wastewater was evaluated by UV/H2O2 are shown in Figure 2, which presents the color removal over contact time with initial H2O2 dosage of 0.67 mL.L-1. From the figure, it is obvious that extent of decolourization increased with reaction time, as H2O2 is applied simultaneously with UV irradiation. Nevertheless, the decolourization efficiency was nearly negligible despite the presence of H2O2 without UV irradiation. It showed that H2O2 alone was not sufficient for decolourization. However, it is apparent that color for RR120 was completely removed during 60 min irradiation time. Contrarily, the color for MO and RB19 were still present under identical operating conditions with barely 50 and 37.9 % removal, respectively. Furthermore, it reached maximum removal of 83.5 and 65.3% at the end of irradiation time. The results indicated the different decolourization pattern of dyes according to its chemical structure or chromophore. Therefore, the order of dye decolourization is RR120, MO and RB19.

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FIGURE 2. Color removal after UV/H2O2 treatment for MO, RR120 and RB19 at different contact time

In the process, UV irradiates the H2O2 to generate the strong reactive and non-selective oxidants, the hydroxyl

radicals. Since the hydroxyl radicals are very strong oxidants, it can react with the dye molecules promptly to produce oxidation products which can cause the decolourization of the original dye solutions (26). The results indicated that monoazo MO was difficult to be decolorized than diazo RR120 dye. Hence, a higher number of sulphonic groups in the RR120 structure, the lower the decolourization time. It seems possible that these results in better interaction between the dye molecules with the hydroxyl radicals (27). In contrast, it is possible that azo bonds are more easily attacked by hydroxyl radicals than anthraquinone RB19 dye with resonance structure.

COD Removal

Figure 3 compares the removal efficiencies of COD between MO, RR120 and RB19. The initial COD concentration for MO, RR120 and RB19 were 91.5, 26.4 and 97.9 mg.L-1, respectively. From the data, it is obvious that significant increase in COD removal efficiency as the reaction time proceeded. The increased in COD removal is the evidence for oxidation and decreased in carbon content, hence indicated the extent of sample mineralization. The UV irradiation penetrates the wastewater as soon as exciting the H2O2 molecules to produce the hydroxyl radicals that react with the dye molecules. A COD removal of about 48.7 and 36.2% was observed for MO and RRB19, and 100% for RR120 under identical operational condition of 120 min. In general, the COD removal efficiency was following the trend of color removal, but it was not sufficient for complete oxidation of organic substances Thus, the order of COD removal was RR120, MO and RB19. The results may be explained by the fact that RR120 has the highest number of sulphonic group, which responsible for its high water solubility. Therefore, the increased in solubility resulted better interaction between the dyes molecules with hydroxyl radicals (27).

FIGURE 3. Percentage of COD removal after UV/H2O2 treatment for MO, RR120 and RB19 at different contact time

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TOC Removal

The variation of TOC removal efficiency and concentration with time by the H2O2 photolysis are shown in Figure 4. The results indicated an increase in TOC removal efficiency with reaction time. The initial concentration for MO, RR120 and RB19 are 57.0, 24.0, 48.0 mg.L-1, respectively. The removal reached 26.3, 50.0 and 58.3% for MO, RR120 and RB19 respectively during 120 min of UV/H2O2 under identical operating conditions. It is apparent that low TOC removal was recorded for monoazo MO and diazo RR120, as compared to anthraquinone RB19. Thus, it may indicate accumulation of by-products that are resistant to the H2O2 photolysis. These findings suggest that incomplete oxidation organic compounds under current experimental conditions. Thus, new organic substances were formed, which were no longer colored but need additional reaction time for degradation (28).

FIGURE 4. TOC removal after UV/H2O2 treatment for MO, RR120 and RB19 at different contact time

SUMMARY AND CONCLUSIONS

The objective of this study is to clarify the degradation characteristic of dyes in term of color, COD and TOC removal by UV/H2O2 process. TOC is related to carbon content of the sample, while COD to the extent of oxidation process. The specific conclusions derived from this study are as follows:

1. The UV/Vis characterization of monoazo, diazo and anthraquinone dye indicated that the rapid degradation of the dyes by UV/H2O2 process is meaningful with respect to decolourization, as a result of the azo bonds and substitute antraquinone chromophore degradation. However, this process is not efficient for aromatic amines removal. It is expected that the hydroxyl radicals were generated by the H2O2 molecules photolysis and these radicals primarily attacked the azo and substitute anthraquinone chromophore leading to formation of intermediate compounds.

2. The monoazo MO was difficult to be decolorized than diazo RR120 dye, which imply that number of sulphonic groups in the dye molecules determines the reactivity with hydroxyl radical. In addition, azo bonds are more easily attacked by hydroxyl radicals than anthraquinone RB19 dye with resonance structure.

3. In UV/H2O2 process, the increased in COD removal is the evidence for oxidation and decreased in carbon content, hence indicated the extent of sample mineralization.

4. TOC removal analysis shows that low TOC removal of monoazo MO and diazo RR120, as compared to anthraquinone RB19 may indicate accumulation of by-products that are resistant to the H2O2 photolysis, which is suggests incomplete oxidation of the dyes.

ACKNOWLEDGEMENT

This work was financially supported by the Malaysian Ministry of Higher Education through Fundamental Research Grant Scheme (FRGS 9003-00379).

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