Pelagia Research Library

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Menka Surana, b Rajeev Mehta and c B.V. Kabra** #,b Department of Chemistry, Institute of Technology & Management, Bhilwara (Raj.) a Department of Chemistry, Mewar University, Chittorgarh (Raj.

1 Available online at Der Chemica Sinica, 2011, 2(5): ISSN: CODEN (USA) CSHIA5 Heterogeneous photocatalytic treatment of textile dye effluent containing Azo Dye: Direct Crysophenine G Preeti Mehta #, a Menka Surana, b Rajeev Mehta and c B.V. Kabra** #,b Department of Chemistry, Institute of Technology & Management, Bhilwara (Raj.) a Department of Chemistry, Mewar University, Chittorgarh (Raj.) c Department of Chemistry, M. L. V. Govt. College, Bhilwara (Raj.) ABSTRACT Photocatalytic bleaching of hydrolyzed textile azo dye Direct Crysophenine G using titanium dioxide (TiO 2 ) was analyzed in our study. The effect of various operating parameters like ph, concentration of the dye, amount of photocatalyst and nature of photocatalyst on the efficiency of the reaction has been studied. The progress of reaction was observed spectrophotometrically.the. Kinetic analysis of photocatalytic bleaching reveals that the degradation follows approximately pseudo first order kinetics according to the Longmuir- Hinshelwood model. The optimum conditions for the photocatalytic bleaching had been established. The effect of addition of transition metal ions (Fe 2+, Cu 2+, Mn 2+, Zn 2+, Ag + ) on photo bleaching efficiency of TiO 2 have been investigated. It was observed that trace quantities of all the added metal ions increases the reaction rate to some extent. The increase in the photocatalytic activity may be due to introduction of new trapping sites by incorporation of transition metal ions on semiconductor surface. A tentative mechanism has been proposed. Key words: Direct Crysophenine G, photocatalytic bleaching, semiconductor TiO 2, transition metal ions. INTRODUCTION A large number of organic substances are nowadays introduced into the water system from various sources such as industrial effluents, agricultural runoff and chemical spills. Their toxicity, stability to natural decomposition and persistence in the environment has been the cause of much concern to societies and regulation authorities around the world. 37

2 The textile dyes and dye intermediates with high aromaticity and low biodegradability have emerged as major environmental pollutants [1-2]. Azo dyes, being the largest group of synthetic dyes, constitute up to 70% of all commercial dyes produced [3]. Highly substituted aromatic rings joined by one or more azo groups (-N=N-), characterize their chemical structures [4]. Being released in to the environment, these dyes not only impart colour to water sources but also damage leaving organism by stopping the reoxygenation capacity of water, blocking sunlight and therefore disturbing the natural activity of aquatic life [5]. These dyes do not decompose rapidly through natural processes and are resistant to aerobic degradation. The azo linkage is reduced to aromatic amines under anaerobic conditions that can be toxic and potentially carcinogenic and allergenic [6-7]. Hence decolorization of the dye- bearing effluent is of great interest. Various physical, chemical and biological pretreatment and post treatment techniques have been developed over last two decades to remove color from dye contaminated wastewater [8-10]. However application of these methods is somewhat restricted due to some limitations such as operational costs, formation of hazardous byproducts intensive energy requirement, limited adaptability to a wide range of effluent [11-12]. The utilization of Advance oxidation processes for the treatment of dyes are based generation of hydroxyl radicals ( OH) that oxidize organic pollutant [13-14]. Among the AOPs heterogeneous photocatalytic oxidation using TiO 2 as photocatalyst has been extensively studied. TiO 2 is very effective, relatively inexpensive, easily available and chemically stable photocatalyst. The appropriate illumination of these particles produces excited-state high energetic electron and hole pairs (e - /h + ). These pairs are able to initiate a wide range of chemical reactions that may lead to complete mineralization of organic and inorganic pollutants [15-17]. The aim of this work to asses the photocatalytic treatment of azo dye Direct Chrysophenine G [MF: C 30 H 26 N 4 Na 2 O 8 S 2, MW: ] selected due to its toxicity, carcinogenic in nature as well as its presence in wastewater of several industries such as textile dying, printing, tannery etc. Two main aspects are studied: The first one was the optimization of the operational conditions for the removal of dye by means of spectrophotometeric method to measure optical density. All the possible significant factors are investigated such as dye concentration, ph, amount of catalyst, nature of catalyst. The second aspect is the influence of dissolve transition metal ions on photocatalytic properties of TiO 2. In photocatalysis addition of metal ions to a semiconductor can change the photocatalytic process by changing the semiconductor surface properties. It creates new trapping sites on semiconductor surface to inhibit electron hole recombination during illumination, thereby enhance the rate of photocatalytic reaction [18-19]. On irradiation, electron migrates on metal where it becomes trapped and electron hole recombination is suppressed. The hole is then free to diffuse on the semiconductor surface where oxidation of organic species can occur. MATERIALS AND METHODS Materials For the present studies the commercially available azo dye Direct Chrysophenine G having 95% dye content and the photocatalyst titanium dioxide (Merck, 99% purity) were used. For 38

3 photocatalytic degradation 0.001M (0.680g/L) stock solution of dye was prepared in double distilled water. Aqueous solutions of desired concentrations were prepared from the stock solution. The desired ph of the solution was adjusted by the addition of previously standardized sulphuric acid and sodium hydroxide solutions. All laboratory reagents were of analytical grade. Fig. 1. Structure of Direct Chrysophenine G Procedure and Analysis To carry out the photochemical reaction 100 ml of dye solution of desired concentration (2.5x 10-5 M) was taken in 250 ml round bottom flask and appropriate amount of solid TiO 2 catalyst (0.30 g) was added to it. The mixture was then irradiated under light [2x200 W Tungsten lamps] to provide energy to excite TiO 2 loading. To ensure thorough mixing of TiO 2 catalyst, oxygen was continuously bubbled with the help of aerator. A water filter was used to cut off thermal radiation. The ph was measured with ph meter (Systronics, 106). The progress of the reaction was observed at definite time intervals by measuring absorbance using spectrophotometer (Schimadzu, UV pharmaspec) at 402 nm. The rate of decrease of color with time was continuously monitored. After complete mineralization, the presence of inorganic ions such as sulphate and nitrate and evolution of CO 2 were tested by standard procedure. RESULTS AND DISCUSSION Control experiments (in absence of photocatalyst, oxygen and light) confirm the necessity of photocatalyst, oxygen and light to follow the photocatalytic path for the photobleaching of dye log Abs Fig Time(min) A plot showing a typical run of photochemical degradation of Direct Chrysophenine G observed under the optimum conditions. 39

4 The photocatalytic bleaching of Direct Chrysophenine G was studied at 402 nm. The optimum conditions for the removal of dye is [Dye] = M, ph = 9.0, TiO 2 = 0.30g. The result of photocatalytic bleaching of Direct Chrysophenine G is graphically presented in Fig.2. It was observed that absorbance (Abs) decreases with increase in time of irradiation indicating that the dye is degraded on irradiation. The plot of 1+log Abs was found to be straight line suggesting that bleaching of dye by TiO 2 follows a pseudo first order rate law. The rate constant of this photobleaching process was determined using the expression: Rate (K) = Slope = 5.86 x 10-5 sec -1 The effect of variation in reaction parameters has been studied like ph, concentration of the dye, amount of catalyst, nature of photocatalyst and presence of transition metal ions. Effect of variation in ph The ph of the reaction medium has a significant effect on the surface properties of TiO 2 catalyst. The effect of ph on photocatalytic bleaching of Direct Chrysophenine G with TiO 2 was investigated in the ph range of 6.0 to 10.0 under visible light source, reported in Fig -3. It was found that the rate of photocatalytic bleaching increases with an increase in ph up to 9.0. Thereafter there is an adverse effect on the rate of reaction on increasing ph further. This observation can be explained on the basis that as the ph of solution increases, more OH - ions are available. These OH - ions will generate more OH radicals by combining with the hole of the semiconductor. The hydroxyl radical is an extremely strong, non selective oxidant [E 0 = +3.06], which leads to the partial or complete mineralization of several organic chemicals. After a certain ph value, more OH - ions will make the surface of semiconductor negatively charged and is retarded the approach of dye molecules toward the semiconductor surface due to repulsive force between semiconductor surface and anionic dye molecule. This will result into a decrease in rate of photocatalytic bleaching of dye Kx10 5 [sec -1 ] ph Fig.3: Effect of ph on the photocatalytic bleaching of Direct Chrysophenine G by TiO 2, [Direct Chrysophenine G = 2.5x10-5 M, TiO 2 = 0.30 g] 40

5 Effect of amount of catalyst [TiO 2 ] The amount of catalyst is one of the main parameters for the degradation studies from economical point of view. In order to avoid the use of excess catalyst it is necessary to find the optimum loading for efficient removal of dye. Keeping all the factors identical, different amounts of Titanium dioxide were used in degradation of Direct Chrysophenine G. The results are graphically represented in fig It was observed that the rate of dye decolourization increases with increasing catalyst level up to 0.30 g and beyond this, the rate of reaction becomes almost constant (Fig.4). This may be due to the fact that, initially the increase in the amount of catalyst increases the number of TiO 2 active sites on the surface that in turn increases the number of OH and O 2 radicals. As a result the rate of degradation is increased. Above a certain level (saturation point) the number of substrate molecules is not sufficient to fill the active sites of TiO 2 and increase in turbidity of solution reduces the light transmission through the solution. Hence, further addition of catalyst does not lead to the enhancement of the degradation rate and it remains constant. Kx10 5 [sec -1 ] Amount of semiconductor[tio 2 ]g Fig.4: Effect of catalyst concentration [TiO 2 ] on the photocatalytic bleaching of Direct Chrysophenine G, [Direct Chrysophenine G = 2.5x 10-5, ph= 9.0] Effect of initial concentration of Dye [Direct Chrysophenine G] The effect of substrate concentration on the degradation of Direct Chrysophenine G was studied at different concentrations varying from M to M at fixed concentration of TiO 2 =0.30 g, ph=9.0the highest efficiency was observed at lower concentration, which decreases with the increase in substrate concentration from M to M (Fig-5). This may be due to the fact that with the increase in initial concentration of the dye, while the irradiation period and catalyst dose are kept constant, more dye molecules are adsorbed onto the surface of TiO 2. Thus, an increase in the number of substrate ions accommodating in interlayer spacing inhibits the action of the catalyst, which thereby decreases the number of reactive OH and O 2 free radicals attacking the dye molecules and photodegradation efficiency. 41

6 8 7 Kx10 5 [sec -1 ] [Dye] x10 5 M Fig.5: Effect of initial concentration of Direct Chrysophenine G photocatalytic bleaching of Direct Chrysophenine G by TiO 2, [TiO 2 = 0.30 g, ph= 9.0] Effect of nature of semiconductor photocatalyst Keeping all the factors identical the effect of the nature of the photocatalyst on photocatalytic bleaching of Direct Chrysophenine G was studied by using different photocatalyst such as TiO 2, ZnO, SnO 2, and Fe 2 O 3. It was observed that under visible light irradiation, the rate of photobleaching of Direct Chrysophenine G decreases with the increase in the band gap of semiconductor (Fig.6). The rate of photobleaching of Direct Chrysophenine G is found to be decreasing in the following order; Fe 2 O 3 > TiO 2 > ZnO > SnO 2 Fe 2 O 3 having 2.2 ev band gap energy, is more efficient photocatalyst in visible region as compare to ZnO and SnO 2 having large band gap energy. It can be explained on the basis that the semiconductor oxides having λmax > 400 nm absorb more efficiently in visible region. 1+log Abs Time (min) Fig.6: Effect of nature of semiconductor photocatalyst on photocatalytic bleaching of Direct Chrysophenine G for 180 min. 42

7 Effect of transition metal ions on photocatalytic bleaching of Direct Chrysophenine G by TiO 2 The effect of addition of transition metal ions (M n+ = Fe 2+, Cu 2+, Mn 2+, Zn 2+ ) photodegradation efficiency of TiO 2 has been investigated, and results are reported in fig. (7) log Abs Time (min) Fig. 6.7: Effect of transition metal ions (M n+ ) on photocatalytic bleaching of Direct Chrysophenine G by TiO 2, [Direct Chrysophenine G = 2.5x10-5 M,TiO 2 = 0.30 g, M n+ = 1x10-5 M, ph= 9.0] The result shows that the trace quantities of all the added metal ions enhance the rate of photocatalytic bleaching of Direct Chrysophenine G to some extent. Mechanism Photocatalysis over a semiconductor oxide such as TiO 2 is initiated by the absorption of photons with energy equal to, or greater than the band gap energy of the semiconductor (3.2 ev), producing electron hole (e - /h + ) pairs. TiO 2 + hν TiO 2 * + h + (vb) + e - (cb) Where cb is conduction band and vb is valence band. The photo produced holes and electrons may migrate to the particle surface, where the hole can react with surface bound hydroxyl group (OH - ) and adsorbed water molecules to form hydroxyl radicals ( OH). h + + OH - h + + H 2 O OH OH + H + The presence of oxygen prevents recombination by trapping electrons through the formation of superoxide ions, maintaining electrical neutrality within TiO 2 particles [20]. The final product of the reduction is hydroxyl radicals ( OH) and hydroperoxy radicals (HO 2 ). e - + O 2 (ads.) O 2 (ads.) O 2 + H + HO 2 2 O H + 2 OH + O 2 43

8 HO 2, OH and O 2 are strong oxidizing species and they react with dye molecules to oxidize them. In the second pathway where a dye absorbs radiation of suitable wavelength and excited to its first singlet state followed by intersystem crossing to triplet state. 1 Dye 0 hν 1 Dye 1 1 Dye 1 (singlet excited state) 3 Dye 1 (triplet excited state) The excited dye may be oxidize to product by highly reactive hydroxyl radical ( OH).The participation of OH radical as an active oxidizing species was confirmed using its scavenger, i.e. 2-propanol, where the rate of bleaching was drastically reduced. Initially the OH radicals attack on the azo linkage of the dye molecule and abstract a hydrogen atom or add itself to double bond. After continuous irradiation, the complete mineralization of dye occurred via into end products. The end products are simple molecules or ions and less harmful to environment. Direct Chrysophenine G + OH / HO 2 /O 2 intermediates End Products [C 30 H 26 N 4 Na 2 O 8 S 2 ] [CO 2 + H +, NO - 3, SO 2-4 ] The end products were detected and their presence in the reaction mixture was ascertained either by chemical test or by ion selective electrode method. Nitrate ions were detected and confirmed by using nitrate ion selective electrode which is having a solid-state PVC polymer membrane. Sulphate ions were detected and confirmed by gravimetric analysis in which excess of barium chloride solution was used and sulphate ions are precipitated as BaSO 4. CO 2 was confirmed by introducing the gas to freshly prepared limewater. The lime water turns milky which indicates its presence. The effect of addition of transition metal ions (M n+ = Fe 2+, Cu 2+, Mn 2+, Zn 2+ ) on photodegradation efficiency of TiO 2 has been investigated. The result shows that the trace quantities of all the added metal ions enhance the rate of photocatalytic bleaching of Chrysophenine G. The increase in the photocatalytic activity may be due to introduction of new trapping sites by incorporation of transition metal ions. As the surface of catalyst particles is negatively charged in alkaline medium and hence, it permits more metal ions to get adsorbed on the TiO 2 particles surface. As consequence, the surface of semiconductor will become positively charged. As Direct Chrysophenine G is an anionic dye, so it will face more electrostatic attraction with metal ions (M n+ ) adsorbed on the semiconductor surface. The electron from TiO 2 conduction band is transferred to metal ion to convert it into its lower oxidation state, in turn transfer this electron to oxygen molecule. Thus prevent electron-hole recombination. At the same time, the positively charged vacancies(h + ) remaining in the valence band of TiO 2 can extract electron from hydroxyl ions in the solution to produce the hydroxyl radicals(( OH). These hydroxyl radicals oxidize the dye molecule into colorless products. Metal ion modification TiO 2 + hν TiO 2 * (h + vb + e - cb) 44

9 M n+ + TiO 2 * (e - cb) M ( n-1) + (electron trapping) M (n-1) + + O 2 M n+ + O 2 TiO 2 * (h + vb) + OH - TiO 2 + OH 3 Dye 1 + OH Degradation of the dye The concentration of transition metal ions is very small and large concentrations are adverse. The whole process can be summarized as: Fig.8: TiO 2 -semiconductor photocatalytic processes. CONCLUSION The TiO 2 mediated heterogeneous photocatalytic treatment of textile dye effluent containing azo dye Direct Chrysophenine G was evaluated. The degradation followed pseudo first order kinetics. The efficiency of decolorization is influenced by the initial dye concentration, photocatalyst amount, ph, nature of photocatalyst. Simultaneously, the addition of trace quantities of metal ions enhances the rate of photocatalytic bleaching to some extent. The finding of the above work may open new era in research that the transition metal ions may modify the surface properties of photocatalyst. The simplicity of the procedure may be a significant advantage to degrade some dye waste water that is difficult to deal with using biological and conventional methods. It can be termed as e-chemistry because it is easy, effective, economical and ecofriendly and it is believed to be step forward Green Chemistry. 45

10 Acknowledgement The authors are thankful to Dr.V.K.Vaidya ( Prof. ITM college,bhilwara), Dr. R.L. Pitliya (Principal, S.D.College, Bhilwara) and all the faculty members of Department of Chemistry, M.L.V. Govt. College, Bhilwara, for continuous encouragement in accomplishing this work. REFERENCES [1] I. Arslan, I.A Balcioglu, D.W. Bahnemann, Appl. Catal. B: Environ., 2000, 26. [2] T. Sauer, G.C. Neto, H.J. Jose, R.F.P.M Moreira, J. Photochem. Photobiol. A: Chem., 2002, 149. [3] H. Kasic, A.L. Bozic, N. Koprivanace, Dyes and pigments, 2006, 1. [4] R. S. Jain, S. Sikarwar, Inter. J. Phy. Sci., 2005, 3(12), 299. [5] N.M. Hilal, Der Chemica Sinica, 2011, 2(4), 262. [6] S. Sandhya, S. Padmavathy, K. Swaminathan, Y.V. Subrahmanyam, S. N. Kaul, Process Biochemistry, 2005, 40, 885. [7] R.S. Shelke, J.V. Bharad, B.R. Madje, M.B. Ubale, Der Chemica Sinica, 2011, 2(4), 6. [8] S.M. Husseiny.: J. Applied Sci. Res., 2008, 4(6). [9] R. Jain, S. Sikarwar, Int. J. Environ. And Pollut., 2006, 27(1/2/3), 158. [10] G.M. Waller, L. Hansen, J.A. Hanna, S.J. Allen, Wat. Res., 2003, 37, [11] Y. Fu, T. Virraghvan, A Rev. Bioresour. Technol., 2001, 79, 251. [12] T.V.N. Padmesh, K. Vijayraghvan, G. Sekaran, M. Velan, J. Hazard. Mater., 2005, 125, 121. [13] M. Muruganandham, M. Swaminathan, Dyes & Pigments, 2007, 72, 137. [14] M. Surana, P. Mehta, K. Pamecha, B.V. Kabra, Der Chemica Sinica, 2011, 2(2), 177. [15] L Zou; B Zhu, J. Photochem. Photobiol. A: Chem., 2008,196 (1), 24l. [16] L. Lhomme, S. Brosillon, D Wolbert, Chemosphere, 2008, 70(3), 381. [17] W. Baran, A. Makowaski, W. Wardas, Dyes & pigments, 2008, 76, 226. [18] M. Zhou, J. Yu, B. Cheng, J. Hazard. Maert., 2006, 137(3)1838. [19] C. Sahoo; A.K. Gupta, A. Pal. Dyes & Pigments, 2005, 66(3) 189. [20] D. Chatterjee, Bull. Cata. Soc. Ind., 2004, 3,

Pelagia Research Library

Pelagia Research Library Available online at www.pelagiaresearchlibrary.com Der Chemica Sinica, 2011, 2 (2): 177-186 ISSN: 0976-8505 CDEN (USA) CSHIA5 Treatment of water contaminated with Reactive Red 198 (RR198) by Photo-Fenton