Removal of acid brown 348 dye from aqueous solution by ultrasound irradiated exfoliated graphite

Transcription

1 Indian Journal of Chemical Technology Vol. 15, September 2008, pp Removal of acid brown 348 dye from aqueous solution by ultrasound irradiated exfoliated graphite Ya-Li Song a,b, Ji-Tai Li a,* & Hua Chen a a College of Chemistry and Environmental Science, Hebei University, Key Laboratory of Analytical Science and Technology of Hebei Province, Baoding , P R China b College of Vocational and Technological Sanitation, Hebei University, Baoding , P R China lijitai@hbu.edu.cn Received 15 January 2008; revised 28 July 2008 Acid brown 348 dye was removed from aqueous solution using ultrasound-assisted adsorption on exfoliated graphite. The effects of relevant parameters, namely, contact time, sorbent dosage, temperature, initial dye concentration and ph have been investigated. The results show that ultrasound irradiation significantly improves removal of acid brown 348 from aqueous solutions in presence of exfoliated graphite. The ultrasound/exfoliated graphite process yielded 90% removal rate within 120 min using 2.0 g L 1 exfoliated graphite at ph 1 and 40 C. Keywords: Ultrasound, Acid brown 348, Exfoliated graphite, Decolourization Synthetic dyes are extensively used in textile industry, leather tanning industry, paper production, food industry, pharmaceutical industry, etc 1. It is estimated that over 10,000 tons dyes are produced per year, and it is assumed that a loss of 1-2% in production and of 1-10% in use are a fair estimate. Due to the largescale production and extensive application, synthetic dyes cause considerable environment pollution and pose serious health-risks 2. A number of traditional methods have been developed for the removal of synthetic dyes from wastewaters to reduce their impact on the environment. The methods involve adsorption on inorganic matrices 3,4 or organic matrices 5-7, decolourization by photocatalysis 8,9, degradation by electrochemical 10, and/or oxidation processes 11, microbiological 12 or enzymatic decomposition 13, etc. However, in spite of their potential utility, some of the conventional treatment methodologies have proved to be markedly ineffective for treatment of wastewater containing synthetic textile dyes because of the chemical stability of such pollutants. The ultrasonic irradiation of liquids can produce a plethora of high energy chemical reactions. This occurs because ultrasound causes several physical phenomena in liquids that create the conditions necessary to drive chemical reactions. In recent years, ultrasound in combination with other methods has been used for the removal of dyes and other pollutants, such as, ultrasound combined oxidation processes 14,15, electrooxidation/ultrasound 16, ultrasound/ UV irradiation 17. Exfoliated graphite is an excellent inorganic material extensively used in chemical, mechanical, and atomic energy fields because of its excellent properties. Due to its large pores structure, exfoliated graphite has been tried as an absorbent with a high sorption capacity especially for macromolecular organic materials, such as heavy oils and biomedical molecules. Recently, the removal of disperse blue 2BLN from aqueous solution by combination of ultrasound and exfoliated graphite 18 has been reported. In the present paper the decolourization of aqueous acid brown 348 solution using sonication in the presence of exfoliated graphite has been attempted. Experimental Procedure Materials Acid brown 348 dye was purchased from Hebei Dingzhou Arpino LCD Material Co., Ltd. and used without further purification. The chemical structure of acid brown 348 is shown in scheme 1. An aqueous solution of acid brown 348 was prepared by dissolving calculated amount of acid brown 348 in distilled water. Exfoliated graphite was prepared according to the reported method 18. The exfoliated volume was about 300 ml g 1 (20-40 mesh). Analytical grade activated carbon having particle size

2 444 INDIAN J. CHEM. TECHNOL., SEPTEMBER 2008 Removal of acid brown 348 from industrial wastewaters The effluents from dye-synthesizing factory (Hebei Dingzhou Arpino LCD Material Co., Ltd.), which contained known amounts of acid brown 348, was treated with exfoliated graphite irradiated with 25 khz ultrasound and results were recorded. Results and Discussion Scheme 1 Chemical structure of acid brown mesh was purchased from the Chemical Experimental Factory of Tianjin University, China. Other reagents were of analytical grade. Apparatus and analysis Sonication was performed on a BUG ultrasonic cleaner (Shanghai Branson, with a frequency of 25 khz, and a nominal power of 250 W). The total acoustic power injected into the sample solution was found to be 0.63 W by calorimetry 19. A TU-1901 double beam UV-Vis spectrophotometer (Beijing Purkinje General Instrument Co., Ltd.) was used to determine the dye concentrations. The colour removal ratio was calculated as follows: Colour removal ratio = (1 C t /C 0 ) 100%, where C 0 is the initial dye concentration, C t is the dye concentration after time t of ultrasound or combined ultrasound/exfoliated graphite treatment. Method A 100 ml flask was charged with aqueous acid brown 348 solution (50 ml) and the sorbent, either exfoliated graphite or activated carbon. The ph of the solution was adjusted by adding HCl or NaOH. The mixture was irradiated in the ultrasonic cleaning bath at a set temperature for a controlled period. In order to compare the decolourization efficiency with and without ultrasonic, a thermostat stirring was employed to agitate the acid brown 348 solution containing exfoliated graphite or activated carbon. At selected intervals, samples were withdrawn, filtered and analyzed. The dye concentration was measured using the UV-Vis spectrophotometer with a 1 cm path length. The measurements were made at 522 nm, the maximum absorbance of acid brown 348 solution. The calibration curve was linear in the range studied. Effect of ultrasound coupled with exfoliated graphite or activated carbon The UV-Vis spectra of the original acid brown 348 solution and after treatment were recorded in the wavelength range from 200 to 800 nm. As shown in Fig. 1, for exfoliated graphite, the maximal absorbency at 522 nm decreased by 74% with ultrasound irradiation, while only 34% decolourization was observed with stirring. When activated carbon was used as the sorbent, the colour removal ratio was 21% by ultrasound and 18% by stirring, respectively. It is clear that ultrasound irradiation can improve the removal ratio, and the combination of ultrasound irradiation and exfoliated graphite was the most efficient system. The pore structure of sorbents also plays a significant role. The exfoliated graphite has patterns of large crevice-like pore, but activated carbon shows patterns of small pores on the surface of particles. Exfoliated graphite with a majority of macro pore can adsorb large Fig.1 UV-Visible spectra of acid brown 348 solutions. (a) original, (b) only ultrasound, (c) only activated carbon (stirring without ultrasound), (d) ultrasound+activated carbon, (e) only exfoliated graphite (stirring without ultrasound), (f) ultrasound+exfoliated graphite, (g) ultrasound+exfoliated graphite, ph=1. Other conditions: ph=6 except (g); Contact time: 120 min; Temperature: 40±2 o C; Sorbent dosage: 2.0 g L 1 ; Acid brown 348: 50 mg L 1.

3 SONG et al.: REMOVAL OF ACID BROWN 348 DYE 445 molecules like acid brown 348 more readily. The equilibrium adsorption capacity of exfoliated graphite and activated carbon have been found as 5.3 mg L 1 and 18.8 mg L 1, respectively. The maximum capacity are 37.2 mg L 1 and 67.8 mg L 1 respectively. The sonication can cause exfoliated graphite particles to rupture, with a consequent decrease in particle size and increase in surface area available for adsorption 20. In addition, cavitation during ultrasonic irradiation can enhance dye transfer to the surface of exfoliated graphite and facilitate the contact of sorbates to sorbent sites. The synergistic effect of exfoliated graphite and ultrasound may have led to the improved performance during the adsorptive process. Effect of contact time and ultrasound The removal of acid brown 348 at different contact times was investigated up to 120 min. Figure 2 shows the different removal efficiency of this pollutant after different contact times. Sonication of acid brown 348 solutions produced a small effect over 120 min. The colour removal ratio in the presence of exfoliated graphite increased gradually and reached to 36% at 120 min. However, in the presence of exfoliated graphite and ultrasound, the removal ratio was 59% for an initial dye concentration of 100 mg L 1. While using ultrasound alone, the removal ratio was only 2%. These results also indicate that the removal efficiency of acid brown 348 increases significantly when the combination of exfoliated graphite and ultrasound are used than that using exfoliated graphite or ultrasound irradiation individually. Effect of exfoliated graphite dosage The effect of exfoliated graphite dosage on the ultrasonic decolourization of acid brown 348 was investigated in the range of g L 1. As shown in Fig. 3, the ultrasonic decolourization efficiency increased with the exfoliated graphite dosage, until the dosage reached 2.0 g L 1. For this reason, exfoliated graphite dosage used in further experiments was 2.0 g L 1. The enhancement of sorption with higher amount of sorbent can be attributed to the increased surface area of sorbent and availability of more sorption sites. The addition of exfoliated graphite exceeding 2.0 g L 1 suppressed the adsorption, possibly due to the shielding and scattering of ultrasound radiation by the particles 21. Effect of ph The effect of the initial ph values on the ultrasonic decolourization of acid brown 348 in the presence of exfoliated graphite was studied in the ph range from 1.0 to As shown in Fig. 1 (curve g) and Fig. 4, the ultrasonic decolourization of acid brown 348 in the presence of exfoliated graphite was influenced by the initial ph of the solution. The lower was the solution ph, the higher was the decolourization efficiency. It indicates that low ph value favours the decolourization of the dye. In the previous report 18, a similar trend was observed for the effect of ph on removal of organic dyes when ultrasound coupled with another technique was used. Probably, the change in the solution ph value results in the change Fig. 2 Effect of contact time on the colour removal of acid brown 348. ( ) ultrasound +exfoliated graphite, ( ) only exfoliated graphite (stirred without ultrasound), ( ) only ultrasound. Acid brown 348: 100 mg L 1 ; Temperature: 50 o C; Dosage of exfoliated graphite: 1.2 g L 1 ; ph=1. Fig. 3 Effect of exfoliated graphite dosage on the colour removal of acid brown 348. Acid brown 348: 100 mg L 1 ; ph=1; Temperature: 30 C; Dosage of exfoliated graphite: ( ) 0.4, ( ) 0.8, () 1.2, ( ) 1.6, ( ) 2.0, () 2.4, and () 2.8 g L 1.

4 446 INDIAN J. CHEM. TECHNOL., SEPTEMBER 2008 Fig. 4 Effect of initial ph values on the colour removal of acid brown 348. Acid brown 348: 80 mg L 1 ; Dosage of exfoliated graphite: 2.0 g L 1 ; Temperature: () 40; and ( ) 30 o C. of hydrophobic characteristic of the dye, which affects the ultrasonic decolourization efficiency. Hydrogen ion concentration primarily affects the surface properties of the adsorbents. This can be explained on the basis of the formation of positively charged surface on exfoliated graphite. Lower ph values reduce the negative charge on the surface of the exfoliated graphite, and increase the positive charge, thus enhance the adsorption of the negatively charged adsorbate molecules 22. Effect of initial concentration The effect of initial concentration of acid brown 348 on the removal ratio is shown in Fig. 5. It is evident from the figure that different initial acid brown 348 concentrations gave different removal ratios. The removal ratio decreased with increasing initial concentration in the presence of exfoliated graphite and ultrasound. For an exfoliated graphite dose of 2.0 g L 1, the removal mass of 1 L acid brown 348 aqueous solution was 132 mg for an initial dye concentration of 200 mg L 1, while it was 36 mg for an initial concentration of 40 mg L 1. The adsorption sites probably get saturated at higher dye concentrations. Effect of temperature The effect of temperature on the removal ratio of acid brown 348 was investigated at 30, 40 and 50 o C. From the figure it is evident that the best removal of acid brown 348 was achieved at 40 o C (Fig. 6). The temperature can affect the adsorption process, both the kinetics and the thermodynamics. Increasing the temperature is known to increase the rate of diffusion Fig. 5 Effect of initial concentration on the colour removal of acid brown 348. Acid brown 348: ( ) 40, ( ) 80, 100, () 150, ( ) 200 mg L 1 ; Dosage of exfolited graphite: 2.0 g L 1 : Tempreature: 40 o C; ph=1. Fig. 6 Effect of temperature on the colour removal of acid brown 348. Acid brown 348: 80 mg L 1 ; ph=1; Dosage of exfoliated graphite: 2.0 g L 1 ; Temperature: ( ) 30, ( ) 40, and ( ) 50 o C. of the adsorbate molecules across the external boundary layer and in the internal pores of the adsorbent particle, owing to the decrease in the viscosity of the solution. Thus, a change in temperature will change the equilibrium capacity of the adsorbent for a particular adsorbate 23 ; shifts the equilibrium towards the endothermic direction. In addition, increasing the ambient temperature raises the vapour pressure of the medium, which leads to easier cavitation and increases the intensity of cavitation, which will enhance the sonochemical effects. At higher temperature a large numbers of cavitation bubbles are generated concurrently. These act as a barrier to sound transmission and dampen the effective ultrasonic energy from the source which

5 SONG et al.: REMOVAL OF ACID BROWN 348 DYE 447 enters the liquid medium 24, and bring about a decrease in sonochemical effects. Thus, reaction temperature has a great influence on the removal of dye under ultrasound irradiation. Adsorption isotherm models For adsorption isotherms, dye solutions of different concentrations ( mg L 1 ) were irradiated under ultrasound with 2.0 g-1 amount of exfoliated graphite at ph 1.0 at 40 C till the equilibrium was reached. Langmuir [Eq.(2)], Freundlich [Eq.(3)] isotherm models 25,26 were selected to describe the adsorption: C e = q e 1 q 0b C + q e 0 (2) Fig. 7 Langmuir plots for adsorption of acid brown 348 on exfoliated graphite. logq e = logk f + n 1 logce (3) where q e (mg g 1 ) is the adsorption capacity, C e (mg L 1 ) is the equilibrium concentration of solute, q 0 (mg g 1 ) is the maximum capacity of adsorbate to form a complete monolayer on the surface, b (L mg 1 ) is the Langmuir constant related to the heat of adsorption. When C e /q e is plotted against C e and the data are regressed linearly, q 0 and b constants can be calculated from the slope and the intercept. The constant K f [mg 1 (1/n) L 1/n g 1 ] is related to the adsorption capacity and 1/n is another constant related to the surface heterogeneity. When C e /qe is plotted against C e and the data are treated by linear regression analysis, Langmuir plots are obtained (Fig. 7), and according to the experimental data, the Langmuir plot is fit for the experimental data corresponding to the correlation coefficient Values of q 0 and b are and Freundlich plots are shown in Fig. 8, the correlation coefficient , the values of K f and 1/n are and Removal of acid brown 348 from industrial wastewaters The results in Table 1 show that the removal ratio was 23.3% when wastewater containing 400 mg L 1 acid brown 348 was equilibrated with 2.0 g L 1 exfoliated graphite, at ph 1 and 40 C, for 120 min; when the concentration of acid brown 348 in industrial wastewater was 40 mg L 1, the removal ratio reached 54.3% under the same conditions. The improved removal ratio, 85.0% for acid brown 348 was observed when 10.0 g L 1 exfoliated graphite was used. Compared with the results of dye removal from Fig. 8 Freundlich plots for adsorption of acid brown 348 on exfoliated graphite. Table 1 The removal of acid brown 348 from industrial wastewater The concentration of acid brown 348 in industrial wastewater, A, 400 mg L 1, B, 40 mg L 1 ; ph=1, Bath temp. 40 o C. Sl. Dose of exfoliated Mass removed (mg L 1 ) No. graphite (g L 1 ) A B aqueous solutions, the removal ratio is lower. The lower values for the removal ratio as compared to the removal from aqueous solutions of the dye may be due to the fact that the compounds, NaCl and organic substances for producing dye, are also adsorbed on

6 448 INDIAN J. CHEM. TECHNOL., SEPTEMBER 2008 the exfoliated graphite as well. The preliminary results indicate that the approach could be applied to treat the industrial wastewater containing acid brown 348 if appropriate conditions are selected. Conclusion This study provides a simply yet effective method for the removal of acid brown 348 from aqueous solutions by combining ultrasound irradiation and exfoliated graphite adsorption. By using 25 khz ultrasound irradiation, the removal ratio for a 120 min contact time was improved from 36 to 90%, using 2.0 g L 1 exfoliated graphite dose, at ph 1 and 40 C solution temperature. Because the adsorption on exfoliated graphite and ultrasound are not chemically specific, this method may be amenable to many other industrially important dyes. The simplicity of the method may be a significant advantage for adsorption in the treatment of dye wastewaters that are difficult to deal with using chemical and biological methods. Acknowledgements Authors thank the Natural Science Foundation of Hebei Province ( ), China, for financial support References 1 Sayan E, Chem Eng J, 119 (2006) Forgacs E, Cserháti T & Oros G, Environ Int, 30 (2004) Tsai W T, Hsu H C, Su T Y, Lin K Y, Lin C M & Dai T H, J Hazard Mater, 147 (2007) Wang Y, Zhou H, Yu F, Shi B & Tang H, Colloids Surf A, 299 (2007) Banat F, Al-Asheh S, Al-Ahmad R & Bni-Khalid F, Bioresour Technol, 98 (2007) Sulak M T, Demirbas E & Kobya M, Bioresour Technol, 98 (2007) Batzias F A & Sidiras D K, J Hazard Mater, 141 (2007) Chen C C, J Mol Catal A Chem, 264 (2007) Chen C C, Lu C S, Chung Y C & Jan J L, J Hazard Mater, 141 (2007) Rajkumar D, Song B J & Kim J G, Dyes Pigm, 72 (2007) Zhang F, Yediler A & Liang X, Chemosphere, 67 (2007) Zhao X, Lu Y, Phillips D R, Hwang H M & Hardin I R, J Chromatogr A, 1159 (2007) Cheng X, Jia R, Li P, Tu S, Zhu Q, Tang W & Li X, Enzyme Microb Technol, 41 (2007) Okitsu K, Iwasaki K, Yobiko Y, Bandow H, Nishimura R & Maeda Y, Ultrason Sonochem, 12 (2005) Vončina D B & Majcen-Le-Marechal A, Dyes Pigm, 59 (2003) De Lima Leite R H, Cognet P, Wilhelm A M & Delmas H, Chem Eng Sci, 57 (2002) Ma C Y, Xu J Y & Liu X J, Ultrasonics, 44 (2006) Li J T, Li M, Li J H & Sun H W, Ultrason Sonochem, 14 (2007) Kimura T, Sakamoto T, Leveque J M, Sohmiya H, Fujita M, Ikeda S & Ando T, Ultrason Sonochem, 3 (1996) Wang Y H, Zhua J L, Zhao C G & Zhang J C, Desalination, 186 (2005) Entezari M H & Sharif Al-Hoseini Z, Ultrason Sonochem, 14 (2007) Iida Y, Kozuka T, Tuziuti T & Yasui K, Ultrasonics, 42 (2004) Iqbal M J & Ashiq M N, J Hazard Mater B, 139 (2007) Mason T J, Practical Sonochemistry (Ellis Horwood Limited, New York), Langmuir I, J Am Chem Soc, 40 (1918) Freundlich H M F, J Phys Chem, 57 (1906) 385.