Study the Photodegradation of Aniline Blue dye in aqueous Phase ...

Asian Transactions on Basic and Applied Sciences (ATBAS ISSN: 2221-4291) Volume 03 Issue 02Study the Photodegradation of Aniline Blue dyein aqueous Phase by using DifferentPhotocatalystsHanaa Kadtem Egzar, Muthana Saleh Mashkour and Amer Muosa JudaChemistry Department, College of Science,Kufa University, Najaf, Iraq.Abstract-- This study involves the photocatalytic degradation ofAniline blue(AB) dye, employing heterogeneous photocatalyticprocess. Photocatalytic activity of different semiconductors suchas zinc oxide (ZnO) ,zinc sulfide (ZnS) and Tin dioxide (SnO 2 )has been investigated. An attempt has been made to study theeffect of process parameters through amount of catalyst,concentration of dye, pH of dye solution and temperature onphotocatalytic degradation of AB solution. The experiments werecarried out by varying pH (2-12), amount of catalyst (0.05–1.5 g),initial concentration of dye (25–100ppm ) and temperaturerange(293-323)K. The optimum catalyst dose was found to be( 0.1,0.5 g and 1) g\L by using ZnO ,ZnS and SnO 2 , respectively. Inthe case of ZnO and SnO 2 , maximum rate of photoreaction ofAB solution was observed in acidic medium at pH 4, whereas thedegradation of AB reached maximum at pH 5 when using ZnScatalyst . The performance of photocatalytic system employingZnO/UV light was observed to be better than ZnS /UV andSnO 2 /UV system. The complete degradation of AB was observedafter 12 min with ZnO, whereas with ZnS, only 75% dyedegraded and 24.5% with SnO 2 in 12 min. Photocatalyticdegradation was found to increase with increasing temperature.Arrhenius plot shows that the activation energy is equal to 20.94kJ mol −1 with ZnO, 17.97 kJ mol −1 with ZnS and 14.1 mol −1 withSnO 2 catalyst.Index Term-- Decolorization; Triphenylmethane;Aniline blue ; Photocatalysis1. INTRODUCTIONThe treatments of industrial wastewater for aqueous wasteeffluents include different techniques such as biologicaltreatment, reverse osmosis and activated carbon adsorption. (1)These techniques often utilize potentially hazardous orpolluting materials and even most of them are nonbiodegradable.(2) Therefore, the development of an effectivetreatment technique that can convert pollutants into non-toxicor less harmful materials is highly required.Advanced oxidation processes are of ample interestcurrently for the effective oxidation of a wide variety oforganics and dyes (3) . Advanced Oxidation Processes (AOP)are an attractive alternative for the treatment of contaminatedground, surface, and waste waters containing hardlybiodegradableanthropogenic substances as well as for thepurification and disinfection of drinking waters (4) .Photocatalysis is a phenomenon that occurs when a reactionchain is taking place in the presence of light and solid catalystin the solution (5) .Photocatalyst is also called photochemical catalyst and thefunction is similar to the chlorophyll in the photosynthesis. Ina photocatalytic system, photo-induced moleculartransformation or reaction takes place at the surface of catalystFig.(1). The initial step of photocatalysis is the adsorption ofphotons by a molecule to produce highly reactiveelectronically excited states. The photon needs to have energyof (hυ) equal to or more than the band gap energy of thesemiconductor. The energy absorbed will cause an electron tobe excited from the valence band to the conduction band,leaving a positive hole in the valence band. This movement ofelectrons forms (e-/h+) or negatively chargedelectron/positively charged hole pairs . The positively chargedholes in valence band are powerful oxidants, whereas thenegatively charged electrons in conduction band are goodreductants (5) .Fig. 1. Mechanism of radical formation reactions during photocatalyticprocess as a results of photocatalyst excitation with light (6)Following are the reactions involving in photocatalysis:-Concerning photocatalysis with photocatalyst, electrons inconduction band (ecb-) and holes in the valence band (hvb+) areproduced when the catalyst is irradiated with light energyhigher than its band gap energy Ebg(hν>Ebg).TiO2+ hν (UV< 400nm) → TiO2(ecb-+ hvb+) (1)hvb++ H2 O → h + + HO (2)hvb++ HO-→ HOOrganic molecule +hvb+→ oxidation products (4)ecb-+ O2 → O2-(3)(5)May 2013 ATBAS-80314020©Asian Transactions 23

Asian Transactions on Basic and Applied Sciences (ATBAS ISSN: 2221-4291) Volume 03 Issue 02O2-+ h+→ HO2Organic molecule +ecb-reduction products (7)HO , HO2 + organic compounds → degradation products (8)Semiconductor compounds have drawn much attention duringthe last few years because of their novel optical and transportproperties which have great potential for many optoelectronicapplications. (7)Among the listed semiconductors, TiO 2 has proven to be themost suitable for widespread environmental applications. ZnOalso seems to be a suitable photocatalyst but it dissolves inacidic solutions it is a semiconductor material for variousphotonic and electrical applications. ZnO shows a unique setof physical and chemical properties, such as a wide band gap(3.2 eV), large exaction binding energy (60 meV) at roomtemperature, radiation hardness (8) .Tin dioxide (SnO 2 ) is a n-type semiconductor with a largeband gap (Eg = 3.9 eV ) which shows promise for a number ofapplications including transparent conductors.Zinc sulfide (ZnS) is a wide band gap and direct transitionsemiconductor (9) . Zinc sulfide is an important semiconductormaterial with a wide direct band gap Eg = 3.68 eV (10) .Dyes are typically organic compounds that absorblight in specific areas of the visible spectrum. Aniline Bluedye it is water soluble dye (11) , it is used for dying wool andcotton directly and widely used in dye industries therefore itspresence in the industrial discharge water also contributes toenvironmental pollution (12) . Due to its stability , it has longresidence time in water. (13) Molecular structure of AnilineBlue has been illustrated in Fig. 2. Aniline Blue, also calledacid blue 22, china blue, soluble blue 3M, and Marine blue. Itis very soluble in water,(6)insulated in a wooden box to prevent the escape of harmfulradiation and minimized temperature fluctuations caused bydraughts.Zinc oxide with 99% purity were supplied by Fluka-Garantie, Zinc sulfide with 99.3% purity supplied byM.B.LTD Dagenham and Tin dioxide SnO 2 with 99% puritywas supplied by Fluka-Garantie . Aniline blue dye (analyticalgrade) was purchased from (RDS-Hannover) and used withoutfurther purification. Solutions were prepared using doubledistilled water. In all experiments, the required amount of thecatalyst was suspended in 200 cm 3 of aqueous solutions ofAB, using a magnetic stirrer. At predetermined times; 5 cm 3 ofreaction mixture was collected and centrifuged (3000 rpm, 15minutes) in centrifuge. The supernatant was carefully removedby a syringe with a long pliable needle and centrifuged againat same speed and for the same period of time. This secondcentrifugation was found necessary to remove fine particles ofcatalysts. After the second centrifugation the absorbance at(309, 586) nm of the supernatants was determined usingultraviolet-visible spectrophotometer, type UV-1650pc.P.D.E. of AB was followed spectrophotometrically by acomparison of the absorbance, at specified interval times, witha calibration curve accomplished by measuring theabsorbance, at(λ max 586) nm, with different concentrations ofthe dye solution.%Decolorization = 100 × (C 0 − C)/C 0where C 0 = initial concentration of dye solution, C =concentration of dye solution after photoirradiation. In order todetermine the effect of catalyst loading, the experiments wereperformed by varying catalyst concentration from 0.05 to 1.5 gfor dye solutions of 100ppm at natural pH (5.57). Similarexperiments were carried out by varying the pH of the solution(pH 2–12) and concentration of dye(25,50,100 )ppm. thereaction temperatures amounted to 293,303,313 and 323K.Fig. 2. structure of Aniline Blue dye (14) .Aniline Blue dye is a acidic dye belongs to triphenylmethane class of dye (15) Triphenylmethane dyes are those dyesin which a central carbon atom is bonded to two benzene ringsand one p-quinoid group (chromophore) (16) . The auxochromesare - NH 2 , NR 2 and –OH (17) . Triphenylmethane dyes are usedextensively in the textile industries for dyeing of nylon,polyacrylon nitrile, modified nylon, wool, silk and cotton.3. RESULTS AND DISCUSSION3.1. UV–vis spectra of dyeResults of the present study clearly show that thephotocatalytic treatment of aqueous solution of aniline blueunder UV light, leads to decolorization and degradation ofdye. Figs.3 to 5 shows the typical time dependent UV-Visspectrum of AB solution during photoirradiation with ZnO,ZnS andSnO 2 respectively. The rate of degradation wasrecorded with respect to the change in the intensity ofabsorption peak in ultraviolet region and visible region. Theprominent peaks were observed at λ max (309,586) nm whichdecreased gradually and finally disappeared indicating (18) thatthe dye had been degraded.2. EXPERIMENTALA homemade photoreactor equipped with a Philips 250W,medium pressure mercury lamp as a source for UV radiation,was used to determine P.D.E. The reactor was consisted ofgraduated 1000 cm 3 Pyrex glass beaker and a magnetic stirringsetup. The lamp was positioned perpendicularly above thebeaker. The distance between the lamp and the graduatedPyrex glass was 15 cm. The whole photocatalytic reactor wasMay 2013 ATBAS-80314020©Asian Transactions 24

P.D.EAsian Transactions on Basic and Applied Sciences (ATBAS ISSN: 2221-4291) Volume 03 Issue 021009080706050403020100Fig. 3. Time dependent UV-Vis absorption spectra for degradation of anilineblue dye(100ppm) ,(0.1g) ZnO catalyst, time(min).Fig. 4. Time dependent UV-Vis absorption spectra for degradation of anilineblue dye(100ppm),(0.5g) ZnS catalyst, time(min).Fig. 5. Time dependent UV-Vis absorption spectra for degradation of anilineblue dye (100ppm),(1.0g) SnO 2catalyst,time(hours) .3.2 Degradation of AB solution Under DifferentExperimental ConditionsDegradation of AB solution was investigated under sevendifferent experimental conditions through UV alone, UV +ZnS, UV + ZnO,UV+ SnO 2 , Dark + ZnS , Dark + ZnO andDark + SnO 2 . Fig.1 depicts the photocatalytic degradation ofAB solution under these experimental conditions. Initiallyblank experiments were performed under UV irradiationwithout addition of any catalyst (UV alone) and only 10%degradation was observed after 60min.Fig. 6. Photocatalytic degradation of AB dye (dye initial concentration—100ppm, (0.1g)ZnO,(0.5g)ZnS ,(1g) SnO 2 after 12min.Thereafter the adsorption of the dye was observed withboth catalysts, i.e., Dark + ZnS, Dark+ SnO 2 and Dark + ZnO.Only 14.3%, 32% and 7.7respectively adsorption of the dyewas seen in the same time with both catalysts under darkconditions. Then photocatalytic experiments were carried outusing all catalysts at fixed dye concentration (100ppm) andcatalyst amount of 0.1g of ZnO ,0.5g of ZnS and1g of SnO 2 .When experiments were performed under UV irradiation withZnO as photocatalyst (UV + ZnO), the complete degradationof dye was achieved after 12 min, whereas with ZnS as aphotocatalyst (UV + ZnS), only 75% decolorization of ABsolution was observed and only 24.3% byusingSnO 2 in thesame duration. It indicates that ZnO exhibits higherphotocatalytic activity than other semiconductors for thedecolorization of AB dye.3.3Degradation of Dye by ZnO, SnO 2 and ZnS asPhotocatalystsThe experiments were carried out to study the degradationof AB solution employing ZnO, ZnS , SnO 2 as catalysts underUV light. Various parameters which affect the degradationefficiency such as catalyst loading (0.05–1.5 g), pH (2-8),initial concentration of dye (25–100 ppm), and temperature(293-323)K of degradation were assessed under UV light.3.3.1Effect of Catalyst weightFigures 7 show the effect of ZnO, ZnS and SnO 2 catalystamount on the degradation of AB solution at natural pH. It canbe seen that initial slopes of the curves increase greatly byincreasing catalyst weight from 0.05 to 0.1 g for ZnO , 0.5gfor ZnS, and1g for SnO 2 thereafter the rate of degradationremains constant or decreases. Further increase in the dose ofcatalyst had no effect on degradation of dye. Thephotocatalytic destruction of other organic pollutants has alsoexhibited the same dependency on catalyst dose . This can beexplained on the basis that optimum catalyst loading is foundto be dependent on initial solute concentration because withthe increase in catalyst dosage, total active surface areaincreases, hence availability of more active sites on catalystsurface (18) . At the same time, due to an increase in turbidity ofthe suspension with high dose of photocatalyst, there will bedecrease in penetration of UV light and hence photoactivatedvolume of suspension decreases (19) . Thus it can be concludedMay 2013 ATBAS-80314020©Asian Transactions 25

P.D.EP.D.EAsian Transactions on Basic and Applied Sciences (ATBAS ISSN: 2221-4291) Volume 03 Issue 02that higher dose of catalyst may not be useful both in view ofaggregation as well as reduced irradiation field due to lightscattering (20) .1009080706050403020100ZnOZnS0.05 0.1 0.25 0.5 0.75 1 1.25 1.5weight(Fig. 7. Effect of ZnO ,ZnS and SnO 2 dose on degradation efficient of AB dye(at natural pH(5.57), and initial concentration of dye 100ppm),after (12min)3.3.2Effect of pHWastewater containing dyes is discharged at different pH;therefore it is important to study the role of pH on degradationof dye. In order to study the effect of pH on the degradationefficiency, experiments were carried out at various pH values,ranging from 2 to 12 for constant dye concentration (100ppm)and catalyst weight (0.1,0.5 and 1 g, respectively, for ZnO,ZnS and SnO 2 ). Figures 4 show the photodegradationefficiency of AB solution as a function of pH. It has beenobserved that by using ZnO and SnO 2 , the degradationefficiency increases with increase in pH exhibiting maximumrate of degradation at pH 4. In the case of ZnS, the maximumdegradation was observed at pH 5. Similar behavior has alsobeen reported for the photocatalytic efficiency of ZnS fordecolorization of acid dyes. The interpretation of pH effectson the efficiency of the photocatalytic degradation process is avery difficult task, because of its multiple roles. First, it isrelated to the acid base property of the metal oxide surface andcan be explained on the basis of zero point charge (21) . Theadsorption of water molecules at sacrificial metal sites isfollowed by the dissociation of OH − charge groups, leading tocoverage with chemically equivalent metal hydroxyl groups(M-OH) (22) . Due to amphoteric behavior of most metalhydroxides, the following two equilibrium reactions areconsidered (Eqs. 9 and 10).M-OH + H + + M-OH 2(9)M-OH M-O - +H + (10)1008060402002 3 4 5 6 7 8pHFig. 8. Effect of pH on degradation rate of AB dye (ZnO dose—0.1 g, ZnSdose—0.5 g and 1.0gSnO 2 ,dye initial concentration100ppm ).The zero point charge (zpc) for ZnO is 9 and 6.7for ZnS,surface is positively charged below this point and above thispH, surface is negatively charged by adsorbedOH − ions (23) .photocatalytic activity of anionic dyes (mainlysulfonated dyes) such as AB dye reaches a maximum value inlower zero point charge. At pH > zpc, the surface is positivelycharged and the dye is anion (24) . The experimental resultsrevealed that higher degradation of AB solution was found tobe in acidic conditions. This may be attributed to theelectrostatic interactions between the positive catalyst surfaceand dye anions leading to strong adsorption of the latter on themetal oxide support (25) .3.3.3Effect of Concentration of DyeAfter optimizing the pH conditions and catalyst dose (pH4 and catalyst dose 0.1 g for ZnO, pH 5 and catalyst dose 0.5 gfor ZnS, pH 4 and catalyst dose 1 g for SnO 2 ), thephotocatalytic degradation of dye was carried out by varyingthe initial concentrations of the dye (25,50, 100) ppm in orderto assess the appropriate amount of catalyst dose. As theconcentration of the dye was increased, the rate ofphotoreaction decreased indicating for either to increase thecatalyst dose or time span for the complete removal. Figure 5depict the time-dependent graphs of degradation of ABsolution at different concentrations of dye . The possibleexplanation for this behavior is that as the initial concentrationof the dye increases, the path length of the photons enteringthe solution decreases and in low concentration the reverseeffect is observed, thereby increasing the number of photonabsorption by the catalyst in lower concentration (26,27) .ZnOMay 2013 ATBAS-80314020©Asian Transactions 26

P.D.EAsian Transactions on Basic and Applied Sciences (ATBAS ISSN: 2221-4291) Volume 03 Issue 02100ZnO(0.338232)min -1 , (0.165280)min -1 and (0.017087)min -1 for ZnO, ZnS, and SnO 2 respectively.8060ZnS1412ZnOZnSSnO24020025 50 100Con.(ppFig. 9. Effect of initial concentration of AB dye on photodegradationefficiency when using (ZnO dose0.1g, pH 4, ZnS dose0.5g and1.0g SnO 2, pH5.57 )3.3.4Effect of temperature:The photocatalytic degradation was studied at varioustemperatures in the range (293–323)K and rate constant, k,was determined from the first-order plots. An increase intemperature helps the reaction to compete more efficientlywith e–/H+ recombination (28) . The energy of activation, Ea,was calculated from the Arrhenius plot of ln k vs. 1/T (figure10). Arrhenius plot shows that the activation energy forphotocatalytic degradation of AB solution is equal to 20±1 kJmol-1 ,17±1 and14±1 by using ZnO ,ZnS and SnO 2respectively. The experimental activation energy wasassociated with the energy required to promote photoelectronfrom trapping centers into tin dioxide conduction band. thepresent value probably arises from the surface area and thepurity of catalysts (29) .02.9-0.53 3.1 3.2 3.3 3.4 3.5-1-1.5-2-2.5-3-3.5-4-4.5Fig. 10. Arrhenius plot for photocatalytic degradation of AB on ZnO , ZnSand SnO 2 catalysts.3.3.5Kinetic StudyFigure 11 show the kinetics of disappearance of AB foran initial concentration of 100ppm under optimizedconditions. The results show that the photocatalyticdegradation of dye in aqueous ZnO , ZnS and SnO 2 can bedescribed by the first-order kinetic according to theLangmuir–Hinshelwood model (30-32) , ln (C/C 0 ) =- kt, where C 0is the initial concentration and C is the concentration at anytime, t. The semi-logarithmic plots of the concentration datagave a straight line. The rate constants were calculated to beZnOlnCC 010864200 5 10 15 20 25 30Fig. 11. Kinetics analysis for AB dye (dye initial concentration100ppm), (0.1gZnO), (0.5g ZnS) , and 1.0gSnO 2.4. CONCLUSIONExperimental results indicated that the degradation of dyeis facilitated in the presence of catalyst. Comparison ofphotocatalytic activity of different semiconductors has clearlyindicated that the ZnO is better photocatalyst for degradationof AB solution. Besides higher efficiency, the other advantageof ZnO is its low cost. The initial rate of photodegradationincreased with increase in catalyst dose up to an optimumloading. Further increase in catalyst dose showed no effect. Asthe initial concentration of dyes was increased, the rate ofdegradation decreased in each semiconductor, Experimentalresults indicated that the decolorization of dyes is facilitated inthe presence of catalyst and were favorable in acidic region,and the rate of decolorization and degradation of aniline bluesolution increases with the increase of the temperature. Thephotocatalytic degradation followed pseudo-first orderkinetics.REFERENCE[1] A. S.Erses, , T. T. Onay; 2008.Bioresource Technology;(99):5418,5426[2] J. Lee, E. Kulla , 2008.Physics of Fluids; (20): 9[3] B .Boye, M .M .Dieng and E .Brillas , 2002. Env. Sci. & Technol.(36):3030[4] E.Pelizzetti, and M.Schiavello, Eds. 1991.PhotochemicalConversion andStorage of Solar Energy. thesis, Kluwer AcademicPublishers: Dordrecht.[5] D. Oussi, A. Mokrini, and S. Esplugas, 1997. J. Photochem.Photobiol. A: Chem.; (1):77[6] Karpova, T. and y. Lappeenranta teknillinen, 2007. AqueousPhotocatalytic Oxidation of Steroid Estrogens. thesis,Lappeenranta University of Technology.[7] M. Barbeni, , E. Pramauro, E. Pelizzetti, E. Borgarello, N.Serpone; 1985. Chemosphere; ( 14):195,208.[8] D.C. Look, C.Coskun, B.Claflin and G.C. Farlow . 2003. PhysicaB: Condensed Matter.(340):32-38.[9] L. I. Berger, B. P. Pamplin, 1993.Properties of semiconductors, inR. C. Weast (ed.) Handbook of Chemistry and Physics, 73rd edn.,CRC Press, Boca Raton, FL, p. 12-78 to 12- 85.[10] K. Sooklal, B.S. Cullumn, S.M. Angel, C.J. Murphy, 1996.J. Phys.Chem.(100):45-51,[11] E.L.Grabowska and Gryglewicz. 2007.Dyes Pigm.;(74):34‐40[12] G.R. Eykholt and D.T. Davenport. 1998.Environ. Sci. Technol.,(32):1482-1487,May 2013 ATBAS-80314020©Asian Transactions 27

Asian Transactions on Basic and Applied Sciences (ATBAS ISSN: 2221-4291) Volume 03 Issue 02[13] B. Pare, A. Soni and V.W. Bhagwat . 2008.Rasayan J. Chem .(1):413-420[14] N. Daneshvar, D. Salari, and A.R. Khataee, J. 2003.Photochem.Photobiol. A.(157):111[15] J. Fabian, H. Hartmann . 1980.Springer Verlag, Berlin, (12):137.[16] L. M. Canle, A. J. Sataballa, et al. .2005.Journal of photochemistryand photobiology A: Chemistry , (175):192-200,[17] I. Sires, E. Guivarch, N. Oturan, and M.A. Oturan. 2008.Chemosphere,(72): 592.[18] S.K. Kansal , M. Singh, and D. Sudc.2006. Studies onphotodegradation of two commercial dyes in aqueous phase usingdifferent photocatalysts. Panjab University, Chandigarh, India.[19] S. Lathasree, R. Nageswara, B. Sivasankar, V. Sadasivam, K.Rengaraj.2004.J. Mole. Catal. A: Chem. (223) : 101[20] Nevim San, Arzu Hatipo glu, Gulin Koçturk, ZekiyeÇinar.2001.Journal of Photochemistry and Photobiology A:Chemistry (139) : 225–232[21] C.Lizama, J.Freer, J.Baeza, H.D.Mansilla.2002. Catal.Today.,(76):235.[22] A. Akyol, H.C. Yatmaz, M. Bayramoglu.2004. Appl. Catal. B:Environ.,(54):19.[23] S.Sakthivel, B.Neppolian, M.V.Shankar , B.Arabindoo,M.Palanichamy, and V.Murugesan.2003. Sol. Energy Mater. Sol.Cells. ,(77):65.[24] W. Stumm, J.J.Morgan .1981. Specific Adsorption of Cation onHydrous ɤ-Al 2O 3, Aquatic Chemistry. New York: Wiley.[25] M.A.El Hajj Hassan, L.M.A.Fayoumi, and M.M.El Jamal.2011.journal of the university of chemical technology and melallurgy;(46)4:395-400.[26] R.J. Davis, J.L.Gainer, G.O.Neal, I.W.Wu.1994. Water Environ.Res. ,(66): 50.[27] H. Al-Ekabi, P. De Mayo. 1986. J. Phys. Chem (90) :4075.[28] Mills A and Hunte S L 1977 J. Photochem. & Photobiol. A:Chem.(108): 1[29] F.Hussein, M. Obies, & D. Bahnemann.2011.PhotocatalyticDegradation of Bismarck Brown R Using Commercial ZnO andTiO 2, to be published later.[30] Pare B, Jonnalagadda S B, Tomar H., Singh P and Bhagwat V W.2008.Desalination (232):1-3[31] Sharma S D, Saini K K, Kant C, Sharma C P and Jain S C. 2008.Applied Catalysis B: Environmental, (84):1- 2.[32] Chiou C, HWu CY and Juang, R S. 2008. Sep Purif Technol., 62:3.May 2013 ATBAS-80314020©Asian Transactions 28