A green chemistry approach for degradation of dye Azur-A in the presence of photocatalyst BaCrO 4

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1 ISSN Brijesh Pare et al Int. J. Chem. Vol 3 (4) (2014) : pp A green chemistry approach for degradation of dye Azur-A in the presence of photocatalyst Brijesh Pare 1, Deependra Singh 1, Vijendra Singh Solanki 2, Premlata Gupta 2, Sreekanth Jonnalagadda 3 1 Department of Chemistry, Laboratory of Photocatalysis, Madhav Science P G College, Ujjain , India 2 Department of Chemistry, ISLE, IPS Academy, Indore , India 3 School of Chemistry, University of KwaZulu-Natal, West Ville Campus, Chilten Hills, Private Bag 54001, Durban-4000, South Africa brijeshpare2009@hotmail.com vijendrasingh0018@gmail.com Abstract In the complex environment today, technology has been increasingly sought by government agencies and commercial industries to manage environmental challenges and problems. One of such techniques which could bring effective potential benefits to environmental management is photocatalysis. Photocatalysis speeds up photoreaction in the presence of a catalyst. The efficiency of photocatalysis to degrade Azur - A was investigated in the presence of hydrogen peroxide and persulfate ions as oxidants-sacrificial electron acceptors under visible light. The degradation rates were found to be strongly influenced by the addition of oxidants. Higher degradation rates were observed in the presence of oxidants in the following order: H 2 > 2-. Ôhe effect of solution ph in the range of 5 12 was investigated and the photodegradation rate was found to increase with increasing ph. We have also studied the effect of various parameters like NaCl and Na 2 CO 3, concentration, catalyst screening and dye concentration on the rate of degradation of dye Azur A. UV-Visible spectrum, measuring the initial and final values of COD and C indicated the complete mineralization of dye in visible light. showed excellent result for degradation of Azur-A. 99% degradation was obtained in presence of in 90 min. Keywords: Photocatalysis, Azur - A, semiconductor, mineralization, visible light, scavengers, oxidants, electron acceptors. Introduction Organic dyes used in textile, paper and food industries are important sources of environmental contamination due to their non-biodegradability and high toxicity to aquatic creatures and carcinogenic effects on humans and plants. Hence, it is crucial to remove these dyes from colored effluents. Conventional chemical and physical diecoloration processes cannot be effectively utilized to treat these dyes. Therefore, interest in developing processes which can destroy these dyes effectively has been a hotspot recently 1. Heterogeneous photocatalysis appears to be a new emerging advanced oxidation process (AOP), with more than 2000 recent publications on the subject. Heterogeneous photocatalysis is simultaneously efficient in fine chemicals and in emerging AOP 2. They are based on the generation of highly reactive and oxidizing hydroxyl radicals. O 3 /UV, H 2 / UV, Fe 2 O 3 /UV and Ti /air/uv are the main types of AOPs that have been suggested. These processes do not Vol. 3 (4) October - December

2 generate any sludge or solid material of hazardous character. Various combinations of these processes are employed for the complete mineralization of the organic dyes 3. The use of heterogeneous photocatalytic treatment is more attractive for the degradation of organic dyes as compared to physical process as it can facilitate the complete mineralization of organic dyes to carbon dioxide, water and mineral acids. Moreover, photocatalysis does not require expensive oxidant and can be carried out using visible light 4. Various types of semiconductors e.g. Ti, ZnO, Fe 2 O 3 and CdS can act as photocatalysts and they have been applied to a variety of problems of environmental interest with respect to water purification. The photocatalytic degradation of various classes of dyes using TiO2 has been studied extensively and it is the most promising catalyst due to its high efficiency, stability and low cost 5. Nevertheless, one disadvantage of the use of TiO2 for industrial applications is the necessity of filtration after the photo degradation. ZnO has been reported to be photoactive for degradation of various classes of dyes in spite of some photocorrosion effects in the liquid solid phase. Fe 2 O3 has also been investigated in the photodegradation of organic compounds under UV radiation, inspite of its oxidative dehydrogenation of n- butane to butenes but its use in photocatalysis has not been reported 6, 7. This work is mainly aimed at the degradation of Azur A used widely in the UV-Visible region, using well defined AOP system. Parameters COD and C and UV - Visible spectral studies are used to measure the extent of mineralization along with spectrophotometric studies. Process conditions are optimized by varying initial dye concentration, solution ph and catalyst amount. Materials and Methods Materials and reagents Dye Azur A was purchased from Sigma-Aldrich. Commercial photocatalyst was obtained from Qualigen fine chemicals (99 % pure with surface area of 10 m 2 /g). Hydrogen peroxide (30% w/w), HCl (37%), NaOH (99%), Na 2 CO 3 (99%) and NaCl (99%) were products of Merck (Germany). K 2 was purchased by Sigma Aldrich. The required solutions were prepared by dissolving appropriate amount of the dye in double distilled water before each experiment. Photocatalytic tests All experiments were carried out in a batch photoreactor with a radiation source of a halogen lamp of 500 W, manufactured by Philips, Holland, fixed at 40 cm from the upper water level in the reactor. The pyrex glass vessel equipped with magnetic stirrer was surrounded by thermostatic water circulation arrangement to keep temperature in the range of 30±0.3 0 C. In each experiment desired volume of the dye solution of known concentration was used and in 10 min time intervals, 2 ml of sample was withdrawn and analysed by a UV-vis spectrophotometer (Systronics - 166) and then returned back to the reactor. The intensity of visible light on the surface of the solution was measured by a digital lux-meter (Lutron LX-101). Initial ph was monitored using HCl and NaOH and measured by a ph meter. The experiments were performed at room temperature, with a constant lamp power of 500 W ( Philips), The spectra were taken with UV vis spectrophotometer (Systronics - 166). The decolorization efficiency (%) has been calculated as: Decolorization Efficiency (%) = {(C 0 C t ) / C 0 } 100 where Co is the initial concentration of dye and C t is the concentration of dye after photoirradiation 8. Azur- A Azur- A is a phenothiazine class of dye in which an atom of sulphur replaces oxygen in the heterocyclic ring. This dye has phenazonium nucleus as chromophore with amino groups para to the group ring nitrogen as auxochromes (Fig. 1). It is used in various paper and textile industries in large quantities for coloring paper, tannin mordant cotton and silk. 352 International Journal of Chemistry

3 CH 3 Structure of Azur -A A green chemistry approach for degradation of dye Azur-A in the presence of photocatalyst H 3 C N N S + NH 2 surface of. However, on irradiating the dye with in aqueous slurry, about 95 % of the dye got decolorized within 90 min. Results and Discussion Preliminary experiments The degradation of Azur A in water can be modeled following pseudo-first-order kinetics at 600 nm. The results for a typical run are given in Fig. 2. The absorbance of Azur- A dye decreased with an increase in irradiation time. The plot of log (absorbance) versus time followed pseudo first order kinetics with correlation co-efficient of 0.98, rate constant of s -1 and half life time of s. In the presence of using visible light a much faster degradation of Azur A occurred as compared to reactions using radiation only (Fig. 3). No degradation was observed in the presence of only visible light, however, in the presence of without irradiation, a slight decrease in absorbance was observed which may be due the adsorption of the dye on to the Fig. 2: Pseudo first order kinetics: [Azur- A] = mol dm -3, ph = 10.0, = 200 mg/100 ml, Light intensity = lux, Temperature = 30 ± C. Fig. 3. Decolorisation of Azure A: [Azur- A] = mol dm -3, ph = 10.0, Light intensity = lux, Temperature = 30± C. Catalyst screening Use of excess catalyst is a waste and also hinders the rate of degradation of organic compounds therefore, the choice of catalyst amount is important 9. The effect of catalyst loading on Azur- A is given in Fig. 4. The rate of degradation of the Azur- A dye increased form s -1 to s -1 with increase in amount of from 50 mg/100 ml to 200 mg/100 ml. Further increase in amount of from 200 mg/100 ml to 300 mg/ 100 ml resulted in decrease in rate constant of photo catalytic reaction from s -1 to s -1. Rate constant has been found to be maximal at 200 mg/ 100 ml of amount. This observation indicated that beyond the optimum catalyst concentration, other factors affect the degradation of dyes. It is clear that the rate of degradation did not increase linearly with the increase in the amount of the catalyst in the reactor, and that a limiting rate was achieved when high amounts of were used. This could be explained by the fact that when a low amount of was used, the rate of reaction on the surface area was limited and the reaction rate was proportional to the amount of particles. The attainment of limiting value and further Vol. 3 (4) October - December

4 decrease in the reaction rate with increase in the amount of catalyst might be due to (i) aggregation of particles at high concentrations causing decrease in the number of surface active sites and (ii) increase in opacity and light scattering of particles at high concentration leading to decrease in the passage of irradiation through the sample 10. Fig. 4: Effect of catalyst screening: [Azur- A] = mol dm -3, ph = 10.0, = 200 mg /100 ml, Light intensity = lux, Temperature = 30± C. Effect of oxidants To keep the efficiency of the added H 2 at the maximum, it was necessary to choose the optimum concentration of H 2 according to the type and concentration of the pollutants. The effect of addition of aqueous solution of H 2 in the range of mol dm -3 to the range of mol dm -3 on the photocatalytic oxidation has been investigated. The results are shown in Fig. 5. The addition of H 2 and K 2 in the range of mol dm mol dm -3 increased the rate from s -1 to s -1 and s -1 to s -1 respectively. Further increase in the H 2 concentration limited the removal rate. Hence, mol dm -3 H 2 concentration appeared to be optimal for the degradation. An increase in H 2 level enhanced the degradation rate up to the optimal load beyond which inhibition occurred 11. The enhancement of decolourisation and degradation by addition of H 2 might be due to the increase in the hydroxyl radical concentration in the following ways: (i) Oxygen is the primary acceptor of the conduction band electron with formation of superoxide radical anion (ii) H 2 can compensate for the lack of and play a role as an external electron scavenger. (iii) H 2 can trap the photogenerated conduction band electron, thus inhibiting the electron hole recombination and producing hydroxyl radicals 12, e Reaction with superoxide radical anion : H 2 + HO + HO e - CB + H 2 HO + OH - 3 Trapping of photogenerated electrons: H 2 + 2e - 2OH - 4 Self-decomposition by photolysis: H 2 + hv 2HO 5 H 2 + h + + 2H + 6 Excess H 2 acts as hydroxyl radical or hole scavenger to form the perhydroxyl radical (HO 2 ), which is a much weaker oxidant than hydroxyl radicals 14. H 2 + HO H 2 O + H 7 H + HO H 2 O + 8 Similarly, the enhancement can be attributed to the ability of persulfate to act as an electron acceptor preventing the charge recombination but also to the production of very strong oxidants HO and sulphate radicals. Due to its high potential (2.6 ev) sulphate radicals are powerful oxidants which are able to participate in the dye Azur A degradation. Although the concentration of SO 4 2" increases with oxidant loading, above the optimum value the generated ions can be adsorbed onto particles leading to the modification of their surfaces and subsequently decrease its catalytic activity 15. Effect of initial concentration of dye Effect of initial concentration of dye on the degradation rate was studied at different concentrations of Azur- A 354 International Journal of Chemistry

5 A green chemistry approach for degradation of dye Azur-A in the presence of photocatalyst 2- + e - CB 2 SO SO 4 9 SO e - 2- (CB) SO 4 10 SO H 2 O SO 4 +. OH + H + 11 SO Azur - A SO 4 + dye intermediates 12 SO dye intermediates mineralization 13 SO 4 + h + SO SO OH SO OH - 15 varying from mol dm -3 to mol dm -3. The rate constant (k) for the degradation of Azur - A first increased from s -1 to s -1 with the increase in substrate concentration and reached the highest efficiency at the concentration of mol dm -3. The results are shown in Fig. 6. The presumed reason is that when the initial concentration of dye is increased, more and more dye molecules are adsorbed on the surface of. The degradation rate at this concentration was more than double the value at mol dm -3 concentration. Figure 6 shows that further increase in the concentration, produced no significant improvement in the degradation rate. This fact contributes to inhibition of the reaction of dye molecules with holes or hydroxyl radicals, due to the lack of any direct contact between them. Increased dye concentration also promotes the dye molecules to absorb light and hence the protons cannot reach the photocatalyst surface causing decrease in the photodegradation efficiency 16. Fig. 5 : Effect of oxidant: [Azur- A] = mol dm -3, ph = 10.0, = 200 mg /100 ml Light intensity = lux, Temperature = 30± C. Vol. 3 (4) October - December

Fig. 6: Effect of dye concentration: = 200 mg/100 ml, ph = 10.0, Temperature = 30± 0.3 0 C, Light intensity = 27 10 3 lux.

6 Fig. 6: Effect of dye concentration: = 200 mg/100 ml, ph = 10.0, Temperature = 30± C, Light intensity = lux. Role of ph The interpretation of ph effect on photocatalytic degradation process was a very difficult task since it has multiple roles. Because of the amphoteric behavior of most semiconductor oxides, an important parameter govering the rate of reaction taking place on semiconductor particle surface was the ph of the dispersions, since it influenced the surface charge properties of the photocatalyst 17. Therefore the role of initial ph on the degradation efficiency of Azur- A was investigated in the ph range 5 to 12. The results indicate that the initial photodegradation rates is highest in alkaline solution and lowest in acidic solution, (Fig. 7). Added OH - ions favour the photodegradation as they can react with holes and produce HO ions 18. O H + H 17 H + H H 2 + HO + OH (h + VB) + OH - + HO 16 In acidic solution photocatalytic degradation is probably due to the formation of HO ions but to lesser extent. Fig. 7: Effect of ph: [Azur- A] = mol dm -3, = 200 mg/100 ml, Light intensity = lux, Temperature = 30± C. 356 International Journal of Chemistry

7 A green chemistry approach for degradation of dye Azur-A in the presence of photocatalyst Effect of NaCl and Na 2 CO 3 Sodium chloride and Sodium carbonate are commonly used in textile industries. Therefore textile wastewaters contain a considerable amount of carbonate and chloride ions. The effect of addition NaCl and Na 2 CO 3 on the photocatalytic degradation of Azur - A is shown in Fig. 8. The degradation percentage of the dye gradually decreased from s -1 to s -1 with increasing carbonate ion concentration. Similarly, the results of the studies carried out with the addition of NaCl revealed that the degradation percentage of the dye decreased from s -1 to s -1 with increase in the amount of chloride ions. The inhibition of the degradation efficiency in the presence of ions is often explained by the scavenging of HO radicals by ions 19, CO 3 + HO OH CO 3 (20) HCO HO H 2 O + CO 3 - (21) Cl - + h + VB Cl. (22) Cl - + HO Cl. + OH - (23) Effect of temperature The photocatalytic systems have been studied due to their ability to photosensitize the complete mineralization of a wide range of dyes at ambient temperatures and pressures, without the production of harmful byproducts 21. Because of photonic activation, photocatalytic systems do not play a significant role in photochemical processes, and hence do not require heat and operate at room temperatures. The decrease in temperature favors adsorption, which is a spontaneous exothermic phenomenon. As a consequence, the optimum temperature is generally between 20 and 80 C 22, 23. The influence of temperature has been studied in the range 30 0 C to 55 0 C. Fig. 9 shows that the rate constant increased from s -1 to 3.12 to 10-4 s -1 with increase in temperature from 30 0 C to 40 0 C. This is because of more radiation falling on catalyst surface per unit time and hence generation of increasing number of electron-hole pairs and consequently production of more hydroxyl radicals for decolorization process. High temperatures may have a negative impact on the concentration of dissolved oxygen in the solution and consequently, the recombination of holes and electrons increases at the surface of photocatalyst 24. Fig. 8: Effect of salt: [Azur- A] = mol dm -3, ph = 10.0, = 200 mg/100 ml, Light intensity = lux, Temperature = 30± C. Fig. 9 : Effect of temperature: [Azur -A] = mol dm -3, ph = 10, = 200 mg/ 100mL Light intensity = lux. Photocatalytic Mineralization of Azur- A The Chemical Oxygen Demand (COD), C and a typical time-dependent UV Vis spectrum of samples have been used as criteria to study Azur- A decomposition and mineralization. As Fig. 10 shows, after 8 hours of irradiation, COD values decreased from 360 mg/l to 4.5 mg/l, while there was an increase in C values and inorganic ions. Fig. 11 shows a typical time-dependent Vol. 3 (4) October - December

8 UV Vis spectrum of Azur- A dye during photo irradiation with. The rate of decolorization of dye was recorded with respect to the change in the intensity of absorption peak in visible region. The prominent peak at ë max, i.e., 600 nm got decreased gradually and finally disappeared indicating that the dye got decolorized. Similarly the peak in the UV region at 300 nm got decreased with the passage of time, thereby confirming the complete mineralization of the dye Azur- A. Fig. 10: Measurement of COD and C : [Azur- A] = mol dm -3, = 200 mg/100 ml ph = 10.0, Temperature = 30± C. Conclusions The photocatalytic degradation of the dye Azur - A by visible light irradiation and photocatalyst was employed which is a green chemistry reaction. The apparent firstorder rate constants (k ap ) were evaluated which confirms pseudo first-order kinetics. The findings also indicate that the presence of oxidants could has an important impact on the photocatalytic degradation efficiency of the parent compound as well as on the transformation rate of the organic intermediates. The degradation rates were found to be strongly influenced by the concentration levels of the oxidants. The initial concentration of oxidants showed an obviously positive effect on the degradation process appreciably enhancing degradation efficiency of Azur - A. However, it was observed that above a certain level of oxidant concentration, the reaction rate becomes constant or even decreases due to their ability to act as scavenger of valence band holes and HO radicals. The effects of initial ph value and initial concentration of dye and salts on degradation kinetics were also investigated. The results indicated that the adsorption of Azur - A on surface determined their photocatalytic degradation rates and surface reaction on played a significant role in the degradation of Azur - A. Further, studies indicated that OH are responsible for the major degradation of Azur A. Acknowledgement The authors would like to thank the Principal of Government Madhav Science College, Ujjain, India for providing experimental facilities. References 1. Zhong J. B., 2013, Iranian Journal of Chemistry and Chemical Engineering, 32, 57. Fig. 11: UV-Vis spectrum at 0 to 90 min.:[azur- A] = mol dm -3, ph = 10.0 = 200 mg/ 100 ml, Light intensity = lux, Temperature = 30± C. 2. Herrmann J. M., Duchamp C., Karkmaz M., Hoai B. T., Lachheb H., Puzenat E.and Guillard C., 2007, Journal of Hazardous Materials, 146, Andreozzi R., Caprio V., Insola A. and Marotta R., 1999, Catalysis Today, 53, International Journal of Chemistry

9 A green chemistry approach for degradation of dye Azur-A in the presence of photocatalyst 4. Gopalappa H., Yogendra K., Mahadevan K. M. and Madhusudhana N., 2014, Chemical Science Transactions, 3, Marc G., Augugliaro V., Lopez- Munoz M. J., Martin C., Palmisano L., Rives V., Schiavello M., Tilley R. J. D. and Venezia A. M., 2001, Journal of Physical Chemistry B., 105, Villasenor J., Reyes P. and Pecchi G., 1998, Journal of Chemical Technology and Biotechnology, 72, Pal B. and Sharon M , Journal of Chemical Technology and Biotechnology, 73, Morteza M., Masoud N. and Shiva J., 2012, Environment Protection Engineering, 38, Wang W. and Yang S., 2010, Journal Water Resource Protection, 2, Kavitha S. K. and Palanisamy P. N., 2010, World Academy of Science, 3, Malato S., Blanco J., Richter C., Braun B. and Maldonado M., 1998, Applied Catalysis B:, Environment, 17, Galvez J. B. and Rodriguez S. M., 2010, Journal Solar Detoxification, United Nations Educational, Scientific and Cultural Organization, Electronic Copy, Dong D., Peijun Li., Li X., Zhao Q., Zhang Y., Jia C. and Li P., 2010, Journal of Hazardous Materials, 174, Konstantinou I. and Albanis T., 2004, Applied Catalysis. B: Environment, 49, Antonopoulou M. and Konstantinou I. K., 2014, Global NEST Journal, 16, Nikazar M., Gholivand K. and Mahanpoor K., 2008, Desalination, 219, Koneco S., Rahmana M. A., Suzuki T., Katsumata H., and Ohta K. 2004, Journal of Photochemistry and Photobiology A, 163, Chen Y., Sun Z., Yang Y. and Ke Q., 2001, Journal of Photochemistry and Photobiology A,Chemistry, 142, Bahnemann D. W., Cunningham J. and Fox M. A., Pelizzetti E., Pichat P., In Zeep R.G., Helz G.R., Crosby D.G., 1994, Aquatic Surface Photochemistry, Guillard C., Lachheb H., Houas A., Ksibi M. and Elaloui E., 2003, Journal of Photochemistry and Photobiology A:, 158, Kansal S. K., Singh M., and Sud D., 2007, Indian Institute Chemical Engineering, 49, Turchi C. S., Mehos M. S. and Link H. F., 1992, NREL Technical Paper, 22, Ichimura T., Matsushita Y., Sakeda K. and Suzuki T., 2009, Microchemical Engineering in Practice, edited by T. R. Dietrich Wiley-Blackwell, John Wiley and Sons, Inc., New Jersey, p WolfruM E. I. and Turchi S., 1992, Journal of Catalysis, 136, 626. MS Received July 4, 2014, Accepted July 30, 2014 Vol. 3 (4) October - December

Chapter - III THEORETICAL CONCEPTS. AOPs are promising methods for the remediation of wastewaters containing

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