Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456                                                                    ...
Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456        Photo catalysis is a phenomenon, in which an electron-hole p...
Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456shown in Table 1. A plot of 1+log O.D. (optical density) against tim...
Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456The effect of variation of light intensity on the photo catalytic de...
Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456It is evident from the data in the tables that the rate of photo cat...
Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-4562H2O2*                            2H2O + O2SC                       ...
Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456                                               Fig.1(b)International...
Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456ZnO could be used powerfully in photo catalytic degradation of texti...
Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-45612. U.S. Environmental Protection Agency, “Handbook of Advanced Phot...
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Photo catalytic degradation of m dinitrobenzene using semiconductor zn o and h2o2

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Photo catalytic degradation of m dinitrobenzene using semiconductor zn o and h2o2

  1. 1. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456 ISSN:2249-5347 IJSID International Journal of Science Innovations and Discoveries An International peer Review Journal for Science Research Article Available online through www.ijsidonline.info PHOTO CATALYTIC DEGRADATION OF M-DINITROBENZENE USING SEMICONDUCTOR ZnO AND H 2O2 Rekha Rani Agarwal and Sangita Gupta* Global College of Technology, Sitapura, Jaipur, India ABSTRACTReceived: 15-07-2012 Photo catalytic degradation of chemical pollutant in water was investigated for various parameters such as pH (5-10), irradiation time (0.0-180min.), light intensityAccepted: 08-10-2012 (40.0-90.0mW/cm2), concentration of substrate (0.10mM-2.50mM), concentration of catalyst (0.06-0.22grams) and concentration of H2O2(0.05-0.35mL/h) etc. The m-*Corresponding Author Dinitrobenzene acts as a substrate, ZnO acts as a photo catalyst and H 2O2 used as an accelerator. The photo catalytic degradation of 10mM m-Dinitrobenzene is optimum at pH 8.5, light intensity 70 mW/cm2, with concentration of ZnO is 0.14grams and conc. of H2O2 is 0.30mL/h respectively. Keywords : Photo catalytic degradation, Zinc Oxide, m-Dinitrobenzene.Address: INTRODUCTIONName:Sangita GuptaPlace:Global College of Technology,Jaipur, India.E-mail:sangita.uor@gmail.com INTRODUCTION International Journal of Science Innovations and Discoveries, Volume 2, Issue 5, September-October 2012 448
  2. 2. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456 Photo catalysis is a phenomenon, in which an electron-hole pair is generated on exposing a semiconducting material. INTRODUCTIONThis electron can be used for reducing a substrate, whereas the hole may be utilized for oxidation. Thus the chemical reactionsthat occur in the presence of a semiconductor and light are collectively termed as photo catalytic reaction. Semiconductor canbe used as a photo catalyst and degrade organic pollutants in water to less harmful in organic material [1]. m-Dinitrobenzeneis an important compound used as an intermediate or precursor in the manufacture of organic dyes, pesticides ,antisepticagents, medicine and the synthesis of pharmaceuticals. Nitro aromatic compounds (NAC) are widely used in chemicalindustries (synthesis of dyes, pesticides, explosives, etc.) and have been associated with groundwater contamination [2]. Thelarge-scale manufacture and use of NAC has led to significant contamination of soils and groundwater. Biological treatment ofaqueous solutions of NAC is a complicated problem. NAC are not well biodegraded [3]. Their biological treatment is limited bytheir toxicity at high concentrations to microorganisms and sometimes produces recalcitrant or toxic by-products [4]. Somechemical oxidation methods have been recommended as a pre-treatment step for the purification of NAC-containingwastewater. Photocatalytic oxidation with Ti[O.sub.2] [5, 6]; various advanced oxidation processes (AOPs) including ozone, UVradiation, and hydrogen peroxide [7, 8]; elemental iron ([Fe.sup.0])/ultrasound [9]; etc.. The photo catalytic degradation ofvarious types of pollutants using solar radiation was studied at pilot scale. This technology has been developed and it iscurrently being evaluated for application at pilot plant and semi-industrial scales of testing (Zhang et al., 1994)[10]. The use ofphotochemical technologies has been shown to be a promising alternative for the detoxification of industrial effluents [11-13],especially from the environmental point of view [14]. The possibility of combining heterogeneous catalysis with solartechnology to achieve complete mineralization of toxic organic pollutants has received much attention in recent years [15].The sun can be used as an economic and ecological source of light, which will save the installation and energy consumptionexpenses of an artificial light source [16]. Hussein et al.[17] reported that TiO 2 and ZnO have good photo catalytic propertiesnominated both catalyst to be promising substrate for photo-degradation of water pollutant and show the appropriate activityin the range of solar radiation. Semiconductors (ZnO, TiO 2) and mediated photo catalysis are fast emerging technology for thetreatments of organic contaminants in wastewater[18-22]. Solutions were prepared in absolute alcohol and double distilled water. Reagent such as p- nitro aniline, H2O2 and ZnO EXPERIMENTALwere used. Measurements of pH, irradiation time, light intensity and optical density were carried out using digital pH meter(Systronics Model 335), 200W tungsten lamp (Philips), Solarimeter (Surya Mapi Model CEL201) and spectrophotometer(Systronics Model 106). The solution of 10mM m-Dinitrobenzene was prepared by dissolving in absolute alcohol and doubledistilled water. H2O2 was added in this solution and it was divided into four parts. First part was kept in dark, second part wasexposed to light, third part added with ZnO and it was kept in dark and last fourth part containing above solution and ZnO,was exposed to light. After keeping these solutions for three hours, the amount of unreacted M m-Dinitrobenzene wasmeasured in each solution. There was no change in the optical density of first three solutions; however in the fourth solutionthe concentration of unreacted M m-Dinitrobenzene decreases with exposure of light, it means optical density changes. Fromthis observation one can conclude that this reaction requires presence of light as well as ZnO and this reactions follows photocatalytic route. The solution of 10mM m-Dinitrobenzene with pH = 8.5 was prepared taking, and added the quantity of ZnO =0.14gram and H2O2 = 0.30mL/h. It was then exposed to 200W tungsten lamp. The optical density of this solution was observedat regular time intervals. It was observed that the amount of p- nitro aniline decreases with increasing time of exposure as International Journal of Science Innovations and Discoveries, Volume 2, Issue 5, September-October 2012 449
  3. 3. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456shown in Table 1. A plot of 1+log O.D. (optical density) against time was linear as shown in Fig. 1. The rate constant wascalculated with this expression: k = 2.303 × slope .The above same procedure was repeated at different pH (5.0-10.0) and rate constant was calculated. The effect of pH isEffect of pHdepicted in Table 1(a) and graphically represented in Fig. 1(a)The effect of concentration of m-Dinitrobenzene on the rate of its photo catalytic degradation was studied by variation inEffect of concentration of m-Dinitrobenzeneconcentrations of m-Dinitrobenzene, keeping all other factors constant. The results obtained are summarized in Table 1(b)and Fig. 1(b) . TABLE-1 0 0.6253 Time (min.) 1+log (O.D.) 15 0.6052 30 0.5934 45 0.5803 60 0.5683 75 0.5564 90 0.5477 105 0.5286 120 0.5204 135 0.5114 150 0.4941 165 0.4805 180 0.4704 TABLE-1(a) 5 1.9 pH K × 105 (sec -1) 5.5 2.13 6 2.38 6.5 2.59 7 2.77 7.5 2.98 8 3.16 8.5 3.26 9 3.1 9.5 2.98 10 2.83The effect of variation in the amount of photo catalyst on the rate of photo catalytic degradation of m-Dinitrobenzene wasEffect of concentration of photo catalystperformed. The results give in Table 1(c) and Fig. 1(c)The effect of addition of amount of H2O2 on the rate of the photo catalytic degradation of m-Dinitrobenzene was alsoEffect of concentration of hydrogen peroxideinvestigated. The results give in Table 1(d) & Fig.1(d). International Journal of Science Innovations and Discoveries, Volume 2, Issue 5, September-October 2012 450
  4. 4. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456The effect of variation of light intensity on the photo catalytic degradation of m-Dinitrobenzene was also investigated and theEffect of light intensityobservations are summarized in Table 1 (e) and Fig1 (e). TABLE-1(b) 0.1 1.41 [ m-Dinitrobenzene] ×10-2M k × 105(sec -1) 0.2 1.67 0.3 1.72 0.4 1.83 0.5 1.97 0.6 2.25 0.7 2.71 0.8 3.26 0.9 2.93 1 2.55 1.1 2.44 TABLE-1(c) 0.06 2.16 Amount of photo catalyst(g) k × 105 (sec-1) 0.08 2.27 0.1 2.36 0.12 2.8 0.14 3.26 0.16 3.24 0.18 3.25 0.20 3.22 0.22 3.24 TABLE-1(d) 0.05 2.45 H2O2(mLh-1) k × 105 (sec -1) 0.1 2.6 0.15 2.74 0.2 2.96 0.25 3.11 0.3 3.26 0.35 3.27 Light Intensity (mW cm-2) TABLE-1(e) 40 1.67 k × 105 (sec -1) 50 2.08 60 2.51 70 3.26 80 3.86 90 4.4The results of experimental observations have been reported in above Tables 1 (a-e) and Fig. 1(a-e). The effect of various RESULTS AND DISCUSSIONparameters on the rate of photo catalytic degradation of m-Dinitrobenzene is being presented as follows: International Journal of Science Innovations and Discoveries, Volume 2, Issue 5, September-October 2012 451
  5. 5. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456It is evident from the data in the tables that the rate of photo catalytic degradation of m-Dinitrobenzene increases withEffect of pHincrease in pH up to 8.5 and further increase in pH decreases the rate of reaction. It was observed that the m-Dinitrobenzenedegrade photo catalytically in the presence of H2O2 at pH 8.5. The neutral compound m-Dinitrobenzene degrades in slightlybasic medium. Perret and holleck [23] observed that ArNO 2 show bathochromic effect with increasing pH. The effect of pH issimilar to that observed earlier in the case of trinitrotoluene[24-26] on increasing the pH further a decrease in the rate ofdegradation was observed. The bathochromic shift and hypochromic effect will make the solution dark yellow in color and itsλmax is also shifted to the red shift, so that it will not permit the desired light intensity to reach the surface of ZnO.It was observed that the rate of photocatalytical degradation increases on increasing the concentration of m-DinitrobenzeneEffect of concentration of p- nitro anilinereaches an optimum for (m-Dinitrobenzene) =10 mM and further increase in concentration, decreases the rate of reaction. Itmay be concluded that the concentration of m-Dinitrobenzene was increased, more molecules were available for excitationand then the energy transfer but if the concentration of m-Dinitrobenzene was increased above a particular limit, thiscompound will start acting like a filter for incident light.It was observed that the rate of photo catalytically degradation was increased on increasing concentration of photo catalystEffect of concentration of photo catalystand it was constant with further increase the concentration of photo catalyst. When the amount of semiconductor wasincreased, the exposed surface area also increases but after the certain amount (0.14g) of ZnO was increased then there wereno increases in the surface area of the photo catalyst because these saturation points will also increases the thickness of thelayer at the bottom of the vessel.It was observed that as the rate of addition and consequently amount of H 2O2 was increased; the rate of reaction was increasedEffect of concentration of hydrogen peroxideand it attained an optimum value at 0.30mLh-1. Virtually no further or negligible increase in the rate of reaction was observedon increasing the rate of addition further. The increase in reaction rate at higher H 2O2 concentration can consequently beattributed to an acceleration of the dark reaction by a higher concentration of oxygen formed (27). However, the saturationlike behavior was observed due to the excess of H2O2.It has been observed that on increasing the light intensity, the rate of reaction was increased. A linear behavior between lightEffect of Light Intensityintensity and rate of reaction was observed. It can be attributed to the fact that any increase in the light intensity will increasethe number of photons striking per unit area of the semiconductor, which in turn will increase the number of electrons holepairs. This increase is clearly reflected in term of increased rate of the reaction. Further increase in the intensity of light mayincrease the temperature of the reaction mixture. Thus thermal may occur in place of photo catalytic reaction and thereforehigher intensities of light avoidable.On the basis of above observations a mechanism has been proposed for the photo catalytic degradation of ArNO 2 in general inMECHANISMpresence of semiconductor ZnO and H2O2ArNO2 ⇋ ArNO2*ArNO2*+H2O2 ArNO2 +H2O2* International Journal of Science Innovations and Discoveries, Volume 2, Issue 5, September-October 2012 452
  6. 6. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-4562H2O2* 2H2O + O2SC e-(CB) + h+(VB)ArNO2*+e ArNO2-.H2O2+ e- HO. + OH-ArNO2-. + O2 ArNO2 + O2-.ArNO2*+ h+ ArNO2 +.ArNO2+. ArNO2.+ H+ArNO2. Decomposition productsAromatic nitro compounds (ArNO2) absorbs incident radiation and it is excited to ArNO 2*, which may transfer its energy toH2O2 and gives the excited state of H2O2*. It may degrade into water and oxygen; the zinc oxide will also absorb suitableradiations generating electron hole pair. The electron from the CB may be accepted by exited nitro aromatics to form anionradicals. However a conductive pathway is reported to in effective for photo degradation of nitro aromatics [28]. This anionradical will transfer its electron to the O2 generating oxygen radical anion. The (ArNO2) may also transfer its electron to holeand thus, forming the corresponding cationic radical. It may release a proton and a radical give the decomposition product. Fig.1 Fig. 1(a) International Journal of Science Innovations and Discoveries, Volume 2, Issue 5, September-October 2012 453
  7. 7. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456 Fig.1(b)International Journal of Science Innovations and Discoveries, Volume 2, Issue 5, September-October 2012 454
  8. 8. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-456ZnO could be used powerfully in photo catalytic degradation of textile industrial waste water. The catalyst system is active CONCLUSIONunder the solar radiation which results the photo degradation of nitro aromatic compound in dyes in waste waterAuthors wish to thanks the Head, Dept. of Chemistry, Mohan Lal Sukhadiya University, Udaipur and GCT, Sitapura Jaipur for ACKNOWLEDGEMENTproviding the necessary facilities.1. Fang Bai Li, Xian Zhang Li and Kok Wai Cheah, Environmental Chemistry, 2005, 2 (2), 130 . REFERENCES2. Guittonneau, S., De Laat, J., Duguet, J. P., Bonnel, C. & Dore, M. Oxidation of parachloronitrobenzene in dilute aqueous solution by [O.sub.3] + UV and [H.sub.2][O.sub.2] + UV: a comparative study. Ozone: Sci. & Engng., 1990, 12, 73-94.3. Rodgers, J. D. & Bunce, N. J. Electrochemical treatment of 2,4,6-trinitrotoluene and related compounds. Environ. Sci. Technol., 2001, 35, 406-410.4. Kuo, C. H., Zappi, M. E. & Chen, S. M. Peroxone oxidation of toluene and 2,4,6-trinitrotoluene. Ozone: Sci. & Engng., 2000, 22, 519-534.5. Piccinini, P., Minero, C., Vincenti, M. & Pelizzetti, E. Photocatalytic mineralization of nitrogen-containing benzene derivates. Catal. Today, 1997, 39, 187-195.6. Makarova, O. V., Rajh, T., Thurnauer, C., Martin, A., Kemme, P. A. & Cropek, D. Surface modification of TiO2 nanoparticles for photochemical reduction of nitrobenzene. Environ. Sci. Technol., 2000, 34, 4797-4803.7. Beltran, F. J., Rivas, J., Alvarez, P. M., Alonso, M. A. & Acedo, B. A kinetic model for advanced oxidation processes of aromatic hydrocarbons in water: application to phenanthrene and nitrobenzene. Ind. Eng. Chem. Res., 1999, 38, 4189-4199.8. Bin, A. K., Machniewski, P., Sakowicz, R., Ostrowska, J. & Zielinski, J. Degradation of nitro aromatics (MNT, DNT, and TNT) by AOPs. Ozone: Sci. & Engng., 2001, 23, 343-349.9. Hung, H. M., Ling, F. H. & Hoffmann, M. R. Kinetics and mechanism of the enhanced reductive degradation of nitrobenzene by elemental iron in the presence of ultrasound. Environ. Sci. Technol., 2000, 34, 1758-17610. Zhang, Y., Crittenden, J.C., Hand, D.W. and Perram, D.L., 1994, Fixedbed photocatalysis for solar decontamination of water, Environ Sci. Technol, 28: 435–442.11. O. Legrini, E. Oliveros, and A. M. Braun, 1993,“Photochemical Processes for Water Treatment”, Chem. Rev., 93, p. 671. International Journal of Science Innovations and Discoveries, Volume 2, Issue 5, September-October 2012 455
  9. 9. Rekha Rani Agarwal et al., IJSID, 2012, 2 (5), 448-45612. U.S. Environmental Protection Agency, “Handbook of Advanced Photochemical Oxidation Processes”, 1998, EPA/625/R- 98/004.13. S. Parsons (ed.) ,2004, Advanced Oxidation Processes for Water and Wastewater Treatment. London: IWA Publishing.14. I. Munoz, J. Rieradevall, F. Torrades, J. Peral, and X. Domenech, , “Environmental Assessment of Different Solar Driven Advanced Oxidation Processes”, Sol. Energy, 79, 369.15. M. Lindner, D. W. Bahnemann, B. Hirthe, and W. D. Griebler, 1997,J. Sol. Ener. Eng., 119, p. 120.16. R. Goslich, R. Dillert, and D. Bahnemann,1997, “Solar Water Treatment: Principles and Reactors”, Water Sci. Technol.,35.17. Ahmed N. Alkhateeb, Falah H. Hussein, Kahtan A. Asker,2005, Asian J. Chemistry,17(2),1155.18. Li, S., Z. Ma, J. Zang, Y. Wu and Y. Gong;2008, Catalysis Today, 139, 109-112 .19. Hosseini, S.N., S. M. Borghei, M. Vossoughi and N. Tanghavinia;2007, Applied Catalysis B. Environmental, 74, 53-62.20. Yashodharan, S. and S. Devipriya; 2005, Solar Energy Matter. Solar Cells, 86, 309-348.21. Celik, G.Y., B. Aslim and Y. Beyatti; 2008, J. Environ.Biology, 29, 867-870.22. Madhu, G. M., M. A. Lourdu Antony Raj, K. Vasantha K. Pai; 2009, J Environ. Biology, 30, 259-264.23. G. Perret and L. Holleck;1956, Ber. Bunsenges Phys. Chem., 60,463.24. C. C. Andrews; 1980, Weapons Quality Engg. Center, Naval Weapons Support Center, Crane, IN.,84,684.25. L. A.Kaplan, N. E. Burlinson and M.E. Sitzmann;1975, Explosives Chemistry Branch, Naval Surface Weapon Center, White Oak, Silver Spring,M.D.75.26. W. R. Mabey, D.Tse, A. Baraza and T.Mill;1983, Chemosphere,12,3.27. R. Hass, I.Hchreiber and G.Stork;1990, Unweltchem.Okotox,2,139.28. H.G.O. Becker (ed.),1991, Einfuhrung; Einfuhrung in die Photochemie, Deutsche, Verlag deg Wissenschaften,Berlin,3rd edit International Journal of Science Innovations and Discoveries, Volume 2, Issue 5, September-October 2012 456

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