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

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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
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