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________________________________________ Author for correspondence E-mail: rakshit_ametayahoo.in Int. J. Chem. Sci.: 144 2016 3237-3248 ISSN 0972-768X www.sadgurupublications.com EFFECT OF DOPING MANGANESE ON PHOTOCATALYTIC PERFORMANCE OF TITANIA IN DEGRADATION OF ROSE BENGAL RINKU BAIRAGI MEENAKSHI SINGH SOLANKI and RAKSHIT AMETA Department of Chemistry PAHER University UDAIPUR – 313003 Raj. INDIA ABSTRACT In the present work nanoparticles of pure TiO 2 and manganese doped TiO 2 were prepared by sol-gel method. As-prepared photocatalyst performance was evaluated by degradation of rose Bengal in synthetic waste water system under visible light. The degradation of dye was studied spectrophotometrically. Optimum conditions were achieved for degradation of dye by varying different rate affecting parameters like pH concentration of dye amount of photocatalyst and light intensity and these were found to be 7.0 0.90 × 10 −5 M 0.12 g and 60.0 mWcm -2 respectively. The physicochemical properties of samples were characterized by XRD and SEM. The observations revealed that Mn doped TiO 2 showed better photocatalytic performance than pure TiO 2 . Key words: Mn doped TiO 2 Photocatalytic degradation Rose Bengal Zeolite. INTRODUCTION Many of the industries discharge their effluents in nearby water resources without treatment which creates water pollution. Although dyeing and textile industries are important in our society but these are also a major source of water pollution. Although there are some methods available for removal of pollutants from water such as chemical oxidation adsorption coagulation and biological process but these are not sufficient to remove pollutants from waste water and also have their own demerits. Photocatalysis has emerged as a promising technology for waste water treatment in last few decades which provides an eco-friendly solution for this problem. Tayade et al. 1 used nanocrystalline anatase and rutile TiO 2 for photocatalytic degradation of dyes and organic contaminants in waste water whereas Ameta et al. 2 used antimony trisulphide photocatalyst for degradation of naphthol green B. Sima and Hasal 3 reported degradation of different textile dyes by using TiO 2

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R. Bairagi et al.: Effect of Manganese Doped Titania on…. 3238 under ultraviolet light. Ameen et al. 4 prepared novel graphene/polyaniline nanocomposites and studied its photocatalytic activity toward the degradation of rose Bengal. Rauf et al. 5 reported photolytic decolorization of rose Bengal by UV/H 2 O 2 and data optimization using response surface method while Li et al. 6 carried out photoelectrocatalytic oxidation of rose Bengal in aqueous solution using a Ti/TiO 2 mesh electrode. Kaur and Singhal 7 studied effect of operational parameters for degradation of rose Bengal using ZnO while Liu et al. 8 investigated degradation of rose Bengal by photocatalytic and photoelectrocatalytic reaction. Sharma et al. 9 studied photocatalytic degradation of rose Bengal using semiconducting zinc sulphide as the photocatalyst. Jain et al. 10 prepared N S-codoped titania and used it for degradation of amaranth while Tachikawa et al. 11 used nitrogen-doped TiO 2 powders for visible light-induced degradation of ethylene glycol. Sahoo et al. 12 carried out photocatalytic degradation of methyl red dye in aqueous solutions under UV irradiation using Ag + doped TiO 2 while Wang et al. 13 reported wavelength-sensitive photocatalytic degradation of methyl orange in aqueous suspension over ironIII-doped TiO 2 nanopowders under UV and visible light irradiation. Zhao et al. 14 studied efficient degradation of toxic organic pollutants with Ni 2 O 3 /TiO 2-x B x under visible irradiation. Ameta et al. 1516 investigated visible light induced photocatalytic degradation of toluidine blue-O and erythrosine using molybdenum doped titania and manganese doped titania supported on zeolite respectively. In the present work effect of manganese doping on titania has been investigated where rose Bengal dye has been selected as a model system. EXPERIMENTAL Materials and method Rose Bengal is a bright bluish pink compound which is soluble in water. Its maximum absorbance λ max is at 540 nm in an aqueous solution. Its chemical structure in shown in Fig. 1. Fig. 1: Chemical structure of rose Bengal

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Int. J. Chem. Sci.: 144 2016 3239 Doubly distilled water was used for preparation of all solutions. A 200 W tungsten lamp was used for irradiation of the dye solution in the visible range. The progress of the reaction was monitored using a UV-visible spectrophotometer Systronics 106. A digital pH meter Systronic 335 was used to measure pH of the solutions and pH was adjusted by using previously standardized H 2 SO 4 and NaOH solutions. Rose Bengal MnSO 4 NaOH H 2 SO 4 were purchased from Himedia and titanium tetraisopropoxide from Spectrochem and used as received. Preparation of Mn doped TiO 2 /zeolite Mn doped TiO 2 was prepared by sol-gel method. Ethanol and nitric oxide were mixed first and then it was added dropwise in titanium tetraisopropoxide solution with continuous stirring. Thereafter manganese sulphate was added to the solution as a dopant. The obtained solution was stirred continuous for 10-12 hours at 4°C. After stirring it was kept in ice bath for three days. This solution was then evaporated at 35°C where its gel was formed. This gel was dried in oven for 5-6 hours and further calcined in furnace at 450°C for 20-30 min. At last Mn doped TiO 2 was mixed with zeolite slurry in 1:2 ratio to prepare the final product. Photocatalytic degradation The photocatalytic activity of catalyst was measured by degradation of rose Bengal. A standard solution of the dye 1.0 x 10 -3 M was prepared. This stock solution was diluted as required. pH of the solution was measured by digital pH meter. The prepared photocatalyst was used as a semiconductor in the present work. The reaction mixture was exposed 200 W tungsten lamp. The intensity of light was varied by changing the distance between the light source and reaction mixture. The absorbance of solution was measured at different time intervals at 540 mm. Effect of various parameters like pH concentration of dye amount of semiconductor and light intensity was observed. As time of irradiation was increased absorbance of solution decreases which indicates that dye is degrading. A plot between time interval and 1 + log A was found linear which means that the reaction followed pseudo-first order. The rate constant was measured by the expression k 2.303 × slope …1

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R. Bairagi et al.: Effect of Manganese Doped Titania on…. 3240 RESULTS AND DISCUSSION Characterization of pure TiO 2 and Mn-doped TiO 2 The average particle size and morphology of as-prepared pure and Mn-doped TiO 2 semiconductors were characterized by X-ray diffraction XRD and Scanning electron microscopy SEM techniques. X-ray diffraction XRD XRD studies of the sample were conducted using PANalytical Singapore make XPERT-PRO model with Cu K α radiation λ 1.54060 A ° 2 θ 10 to 80 ° with generator setting 40 mA 45 kV. Diffraction pattern was taken over the 2 θ range 10º-100º. Figure 2 and 3 shows the XRD pattern of pure TiO 2 and Mn-doped TiO 2 . Fig. 2: XRD of pure TiO 2 X-ray diffraction was used to calculate the average particle size of the sample. The particle size of the synthesized pure TiO 2 and Mn-doped TiO 2 was calculated using Sherrer formula: D K λ / β cos θ …2 Where K is a constant which depends on the shape of the crystal and its value is 0.9 assuming spherical shape λ is the wavelength nm D is the crystallite size nm β is full width of half maxima FWHM-in radian and θ is Bragg’s diffraction angle degree.

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Int. J. Chem. Sci.: 144 2016 3241 Fig. 3: XRD of Mn-doped TiO 2 Crystallite size was found to be 27.8 nm and 181.02 nm respectively. The intensity of XRD peaks of the semiconductors reflected that the as-prepared synthesized nanoparticles of TiO 2 were crystalline in nature. As the peaks in the XRD of pure TiO 2 and Mn-doped TiO 2 were observed at 25.30 o and 25.20 o respectively which confirms the formation of anatase form of titania. It was also observed that the peak remain almost unshifted in the doped sample indicating that doping of manganese did not perturbed TiO 2 lattices. Scanning Electron Microscopy SEM The morphology of pure and Mn doped titania was studied by scanning electron microscopy. SEM images of pure TiO 2 and Mn-doped TiO 2 are given in Figs. 4 and 5. Fig. 4: SEM of pure TiO 2 Fig. 5: SEM of Mn-doped TiO 2

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R. Bairagi et al.: Effect of Manganese Doped Titania on…. 3242 SEM images indicate that particles are unevenly distributed in size. Zhang et al. 17 observed that the particle size of TiO 2 was reduced due to copper doping but no such results was observed in the Mn-doped TiO 2 . This may be explained on the basis that manganese does not like to dwell in grain boundary regions or on the surface of TiO 2 particle to inhibit its growth. Doping of manganese is clearly visible in SEM image Fig. 5 in form of blisters on the surface of TiO 2 particles. Typical run The results for typical run are given in Table 1 and represented in Fig. 6. Typical run of pure TiO 2 and Mn doped TiO 2 showed that reaction rate of doped TiO 2 was more than of pure TiO 2 . Table 1: A typical run pH 7.0 Pure TiO 2 /Mn doped–TiO 2 0.12 g Rose Bengal 9.00 × 10 -6 M Light intensity 60.0 mWcm –2 Time min. Pure TiO 2 Mn doped–TiO 2 Absorbance A 1 + log A Absorbance A 1 + log A 0 0.718 0.8561 0.718 0.8561 20 0.700 0.8450 0.683 0.8344 40 0.684 0.8351 0.624 0.7952 60 0.661 0.8202 0.582 0.7649 80 0.638 0.8048 0.545 0.7364 100 0.624 0.7952 0.507 0.7050 120 0.602 0.7796 0.473 0.6749 140 0.582 0.7649 0.442 0.6454 160 0.569 0.7551 0.412 0.6149 180 0.549 0.7396 0.376 0.5752 Rate constant for Pure TiO 2 k 2.44 × 10 -5 sec -1 Rate constant for Mn–TiO 2 k 5.75 × 10 -5 sec -1

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Int. J. Chem. Sci.: 144 2016 3243 Fig. 6: Typical runs Effect of pH The pH of the solution is likely to affect the degradation of rose Bengal. The effect of pH on the rate of degradation of the dye was investigated in the pH range 5.0-10.0. The results are reported in Table 2. Table 2: Effect of pH Rose Bengal 9.00 × 10 -6 M Light intensity 60.0 mWcm –2 Mn doped–TiO 2 0.12 g pH k × 10 5 sec -1 5.0 4.84 5.5 5.19 6.0 5.49 6.5 5.51 7.0 5.75 7.5 5.02 8.0 4.69 8.5 4.25 9.0 3.95 9.5 3.75 10.0 3.42

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R. Bairagi et al.: Effect of Manganese Doped Titania on…. 3244 It has been observed that the rate of photocatalytic degradation was increased with increase in pH from 5.0 to 7.0 further increase in pH leads to a decrease in the rate of reaction. The increase in the rate of photocatalytic degradation with increase in pH may be due to formation of more • OH radicals which are generated from the interaction of OH ⎯ and hole h + of the photocatalyst. These • OH radicals are responsible for the oxidative degradation of dye. On further increasing pH OH − ions increase and these will be adsorbed on the surface of the semiconductor making it negatively charged so that the approach of anionic rose Bengal to the semiconductor surface will be retarded due to repulsion between two negatively charged species. This will result into decrease in the rate of degradation. Effect of rose Bengal concentration The effect of dye concentration was studied by taking different concentrations of rose Bengal. The results are tabulated in Table 3. Table 3: Effect of rose Bengal concentration pH 7.0 Light intensity 60.0 mWcm –2 Mn doped–TiO 2 0.12 g Rose Bengal × 10 5 M k × 10 5 sec -1 0.60 2.70 0.70 3.84 0.80 5.12 0.90 5.75 1.00 3.23 1.10 2.58 1.20 1.70 1.30 1.68 It has been observed that the rate of photocatalytic degradation increases with increase in concentration of dye up to 9.00 × 10 -6 M. This may be attributed to the fact that as the concentration of dye was increased more dye molecules were available for excitation followed by inter system crossing and hence there was an increase in the rate. The rate of photocatalytic degradation was observed to decrease with further increase in the concentration of dye. Here the dye starts acting as a filter for the incident light and it does

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Int. J. Chem. Sci.: 144 2016 3245 not allow the desired light intensity to penetrate into solution and reach the semiconducting particles and thus decreasing the rate of the photocatalytic bleaching of dye. Effect of semiconductor The effect of amount of Mn-doped TiO 2 was observed by taking different amounts of semiconductor. The results are reported in Table 4. Table 4: Effect of amount of Mn-doped TiO 2 semiconductor pH 7.0 Light intensity 60.0 mWcm –2 Rose Bengal 9.00 × 10 -6 M Mn-doped TiO 2 g k × 10 5 sec -1 0.02 3.62 0.04 3.71 0.06 3.82 0.08 4.22 0.10 4.94 0.12 5.75 0.14 4.54 0.16 4.23 Amount of semiconductor was varied in range from 0.02-0.16 g. It was observed that rate of reaction increases on increasing semiconductor amount upto 0.12 g because its exposed surface area also increases. Thereafter rate showed a declining behaviour because now only thickness of semiconductor layer will increase and not the exposed surface area. Effect of light intensity To investigate the effect of light intensity on the photocatalytic degradation of rose Bengal the distance between the light source and the exposed surface area was varied. The results are summarized in Table 5. It was observed that degradation of dye was enhanced on increasing the intensity of light because number of photon striking per unit area in per unit time increases. After achieving optimum conditions rate of degradation decreases because of some side thermal reactions.

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R. Bairagi et al.: Effect of Manganese Doped Titania on…. 3246 Table 5: Effect of light intensity pH 7.0 Mn doped TiO 2 0.12 g Rose Bengal 9.00 × 10 -6 M Intensity of light mWcm –2 k × 10 5 sec -1 20.0 2.49 30.0 3.14 40.0 3.48 50.0 5.66 60.0 5.75 70.0 5.48 Mechanism On the basis of the observations a tentative mechanism for photocatalytic degradation of rose Bengal dye is proposed as – Dye Dye 1 1 h ν 0 1 ⎯→ ⎯ ...3 1 3 ISC 1 1 Dye Dye ⎯→ ⎯ ...4 VB h CB e SC h ν + − + ⎯→ ⎯ ...5 OH OH h – • + ⎯→ ⎯ + .... 6 Dye Leuco OH Dye 1 3 ⎯→ ⎯ + • ...7 Products Dye Leuco ⎯→ ⎯ ...8 Rose Bengal dye absorbs radiations of suitable wavelength and gives rise to its first excited singlet state. Then it undergoes intersystem crossing ISC to give its triplet state. On the other hand the semiconducting Mn doped TiO 2 SC also utilizes the radiant energy to excite its electron from valence band to the conduction band thus leaving behind a hole. This hole abstracts an electron from – OH ions to generate • OH radicals. These radicals will oxidize the dye to its leuco form which may ultimately degrade to products. The

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Int. J. Chem. Sci.: 144 2016 3247 participation of • OH radicals as an active oxidizing species was confirmed by using hydroxyl radical scavengers 2-propanol where the rate of degradation was drastically reduced. CONCLUSION The results of the present investigation revealed that the doping of titania with manganese enhances its photocatalytic activity which was confirmed from the higher values of rate constants observed for photocatalytic degradation of rose Bengal in presence of Mn- doped TiO 2 in compare to pure titania. REFERENCES 1. R. J. Tayade P. K. Surolia R. G. Kulkarni and R. V. Jasra Photocatalytic Degradation of Dyes and Organic Contaminants in Water using Nanocrystalline Anatase and Rutile TiO 2 Sci. Technol. Adv. Mater 8 455-462 2007. 2. R. Ameta P. B. Punjabi and S. C. Ameta Photodegradation of Naphthol Green B in the Presence of Semiconducting Antimony Trisulphide J. Serb. Chem. Soc. 76 1049- 1055 2008. 3. J. Sima and P. Hasal Photocatalytic Degradation of Textile Dyes in aTiO 2 /UV System Chem. Engg. Trans. 32 79-84 2013. 4. S. Ameen H. K. Seo M. S. Akhtar and H. S. Shin Novel Graphene/Polyaniline Nanocomposites and its Photocatalytic Activity Toward the Degradation of Rose Bengal Dye Chem. Engg. J. 210 220-228 2012. 5. M. A. Rauf N. Marzouki and B. K. Korbahti Photolytic Decolorization of Rose Bengal by UV/H 2 O 2 and Data Optimization using Response Surface Method J. Hazard. Mater. 159 602-609 2008. 6. X. Z. Li H. L. Liu P. T. Yue and Y. P. Sun Photoelectrocatalytic Oxidation of Rose Bengal in Aqueous Solution using a Ti/TiO 2 Mesh Electrode Environ. Sci. Technol. 34 401-4406 2000. 7. J. Kaur and S. Singhal Heterogeneous Photocatalytic Degradation of Rose Bengal: Effect of Operational Parameters Physica B: Cond. Matter 450 49-53 2014. 8. H. L. Liu D. Zhou X. Z. Li and P. T. Yue Photoelectrocatalytic Degradation of Rose Bengal J. Environ. Sci. China 15 595-599 2003. 9. S. Sharma R. Ameta R. K. Malkani and S. C. Ameta Photocatalytic Degradation of Rose Bengal using Semiconducting Zinc Sulphide as the Photocatalyst J. Serb. Chem. Soc. 78 897-905 2013.

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R. Bairagi et al.: Effect of Manganese Doped Titania on…. 3248 10. A. K. Jain S. Sharma and R. Ameta Enhanced Photocatalytic Activity of NS- Codoped Titania for Degradation of Amaranth Merit Res. J. Enviorn. Sci. Toxicol. 3 25-30 2015. 11. T. Tachikawa Y. Takai S. Tojo M. Fujitsuka H. Irie K. Hashimoto and T. Majima Visible Light-Induced Degradation of Ethylene Glycol on Nitrogen-Doped TiO 2 Powders J. Phys. Chem. B 110 13158-13165 2006. 12. C. Sahoo A. K. Gupta and A. Pal Photocatalytic Degradation of Methyl Red Dye in Aqueous Solutions under UV Irradiation using Ag + Doped TiO 2 Desalination 18 91- 100 2005. 13. X. H. Wang J. G. Li H. Kamiyama Y. Moriyoshi and T. Ishigaki Wavelength- Sensitive Photocatalytic Degradation of Methyl Orange in Aqueous Suspension over IronIII-Doped TiO 2 Nanopowders Under UV and Visible Light Irradiation J. Phys. Chem. B 110 6804-6809 2006. 14. W. Zhao W. Ma C. Chen J. Zhao and Z. Shuai Efficient Degradation of Toxic Organic Pollutants with Ni 2 O 3 /TiO 2-x B x Under Visible Irradiation J. Am. Chem. Soc. 126 4782-4783 2004. 15. R. Ameta S. Sharma S. Sharma and Y. Gorana Visible Light Induced Photocatalytic Degradation of Toluidine Blue-O by using Molybdenum Doped Titanium Dioxide Europ. J. Adv. Engg. Technol. 2 95-99 2015. 16. R. Bairagi and R. Ameta Photocatalytic Degradation of Erythrosine by using Manganese Doped TiO 2 Supported on Zeolite Int. J. Chem. Sci. 143 1768-1776 2016. 17. W. J. Zhang Y. Li S. L. Zhu F. H. Wang Copper Doing in Titanium Oxide Catalyst Film Prepared by DC Reactive Magnetron Sputtering Catal. Today 93 589-594 2004. Accepted : 28.09.2016