Optimization of methyl orange removal from aqueous ...

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2,Jiaolong FU1'. 2,JiaoyaⅡ. TANG1'. 2,. Cuiying HU1'. 2 l school of Chemisty and Bioengineehng,suzhou1Jnivcrsity of science and Technology,suzhou215011 ...
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Optimization of methylorangeremovalfrom aqueoussolution by responsesurfacemethodologyusingspent tea leavesas adsorbent Liangzhi LI(DΞ

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Abstract The effectivedisposalof redundantteawasteis crucial to environmentalprotection and comprehensive utilization of trashresources.In this work, the removalof methyl orange(MO) from aqueoussolutionusingspenttea leaves as the sorbent was investigated in a batch experiment.First, the effectsof various parameterssuch as temperature,adsorptiontime, doseof spenttea leaves, and initial concentation of MO were investigated.Then, the responsesurfacemethodology(RSM), basedon BoxBehnken design, was employed to obtain the optimum adsorptionconditions. The optimal conditions could be obtainedat an initial concentrationof MO of 9.75mg.L-', temperature of 35.3oC,contacttime of 63.8min, and an adsorbentdosage3.90g.L-1.Underthe optimizedconditions, the maximalremovalof MO was 58.27o.The results indicatethat spenttea leavescould be usedas an effective and economicaladsorbentin the removal of MO from aqueoussolution.

consideredfor the removal of MO from wastewater[131.Of all the methods,adsorptionis the most costeffective method.The useof variousadsorbents forremoving MO is gaining increasingattention.For example,Asuha et al. reportedthat the mesoporous1-Fe2O3could be usedas an adsorbentfor the water treatment.and most of MO could be removedwithin a shortperiodof time [4]. As a novel adsorbent.u'hen polyaniline was coated onto wood sawdust(PaniSD). PanilSDcan be usedto removeMO from aqueoussolutions[5]. Very recently,the removalof MO from aqueoussolution using penta-bismuthheptaoxide nitratewas srudied.and the adsorptioncapacitywas foundto be 18.9mg.g ' [6]. Althoughtheseadsorbents are efficient in wastewatertreatment,the preparationof the adsorbingmaterialis complicated. On the other hand, from a practical and economical view, the adsorbentsthemselves,haveto be availableand no-poisonous.Therefore,in recentyearsmorestudieshave begunto explore agriculturalwastesas adsorbingagents. Keywords spenttea leaves,adsorption,responsesurface Studies have reported that various agricultural waste methodology,methyl orange(MO) materialssuchas peanuthull [7], bagasse[8], garlic peel [9], cottonplant waste[0] and chemicallymodified straw As teais beingconsumedin a Il] havebeeninvestigated. 1, lntroduction largeamountsin many Asian counffies,moreandmoretea waste is being produced. Therefore, some researchers Methyl orange(MO) is an azo dye, widely usedin textile, investigatedthe dye removalwith tea waste.A very good foodstuff, dying and printing, and leather industries. exampleis the removal of methyleneblue (MB) by tea However,the releaseof MO and the productsrelatedto waste. The results obtainedfrom Hameed'sstudy show the environmenthave causedseriouspollution problems. that the spenttea leavescould be usedfor the removalof A number of methods,such as adsorption,flocculation, MB from aqueoussolution[2]. They alsousedspenttea oxidation, and photocatalytic degradation, have been leavesas an adsorbentand found the adsorptionof MB from aqueoussolution fitting better with the Langmuir isothermmodel.Adsorptioncapacities were 156mg.g-t at ReceivedFebruary25,2013; acceptedAugust 25, 2013 50"C [3]. In 2011, Nasuha and Hameed further E-mail: liliangzhi0I @ I 63.com investigatedthe removal of MB from aqueoussolution

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Liangzhi LI et al. Optimization of methyl orange removal

,:sing NaOH-modifiedrejected tea, and the results ndicatedthattheequilibriumdataalsofollowedLangmuir sotherm with a monolayer adsorptioncapacity of l+2.1lmg.g ' [4]. In fact, MO is also a typicalazo jy e; however,to the bestof our knowledge,teawastehas rever beenutilized for the removalof MO from waste,\'ater. In this study, the spent tea leaves were investigated :reliminary for removalof MO from aqueoussolutions. Severalcritical factorsaffectingthe removalprocesshave .eendiscussed. Finally,the response surfacemethodology rnd its Box-Behnkenexperimental design,which includes :our factors:temperature,initial methyl orangeconcentra:ion,contacttime,andadsorbent wereemployedto dosage, .otimizethe adsomtionconditions.

2

Materialsand methods

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Materials

using a UV-Vis spectrophotometer(UV-2401PC, Shimadzt Co., Japan) at a wavelength of 465 nm. To minimize the measurementerror, the UV absorption intensity of each samplewas measuredin triplicate, and the average value was then used to calculate the equilibrium concentrationbasedon the standardcalibraof 0.99. tion curvewithin R2(coefficientof determination) 2.4 Batchadsorption studies The effects of different controlling parametersincluding temperature,contacttime, initial methyl orangeconcentration, andadsorbent dosageofspenttealeaveswerestudied using batch adsorptionexperiments.The sorptionexperimentswere performedin shakeflasksof capacity250 rn[with a workingvolumeof 100mL at a rotatespeedof 100 rpm. The sampleswere takenfrom the flasksat fixed time intervals and analyzed for MO concentrations.Every samplewas measuredtriplicate and averaged.Finally, the percentageMO removal(I) was calculatedas follows:

(l) r :Ci ^cr x roovo, \lethyl orange (C14Hr4N3NaO3S) was purchasedfrom ci Sigma-Aldrich(St. Louis, MO, USA). All otherreagents ,rsedfor experimentalstudieswere of analltical grade. where C; andCyarethe initial and final MO concentration Stocksolutionwaspreparedby dissolving1.0g of methyl (mg.L-'), respectively. )range(MO) in 1 L deionizedwater. The experimental .olution was then diluted with deionizedwater to obtain 2.5 Box-Behnken experimental design iesiredconcentrations. The responsesurfacemethodology(RSM) is a collection :.1 Preparation of Adsorbent of statisticaland mathematicaltechniquesuseful for improving and optimizing processes.In this study, the fhe greentea wastewas obtainedfrom the Don Shantea percent MO removal was statistically modeled and :lantationlocatedin Suzhou,China.Spenttealeaveswere designedby RSM, and the four factorsat 3-levels(-1, :r'peatedlyboiled and washed with distilled water to 0, + 1) Box-Behnkendesignsas shownin Table I were :r'rrov€solubleand color components RSM optimization until the waterwas usedfor the optimizationexperiments. -'.rmpletely the solidresidue experimentswere repeatedthreetimes and eachtime with colorless. After preheatments, .c'parated from the aqueousphasewas collectedand dried arunof 27 sets,namelythata totalof 27 experiments were ,.i emightat 60'C for 48 h. Thereafter, the spenttealeaves necessaryto estimate the model coefficients of the ''iere crushedusing a ball mill and the resultingpowder polynomial equation.The experimentalBox-Behnken '.iassievedthi'ough100meshstainlesssteelsieve. design,analysisof variance(ANOVA) and 3D response surface were calculatedby using the software-Design 1.3 Analysis Expert 7.1.2-(Stat-Ease, Inc., Minneapolis,USA). The resultsof theconsequent RSM optimizationaredepictedin The residualMO concentration in solutionwas measured Table2. Iable I

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To investigatethe effect of temperatureon the removal of MO from aqueoussolution, the dosageof spenttea leaves andthe initial MO concentation were controlledat2 g.t\ and 6mg.I;1, respectively.The adsorptionstudieswere ca:ried out at four different temperatures,25"C, 35"C, 45"C and 55oC,and the adsorptivetime was 90 min. The results of experimentswere presentedin Fig. 1. First, the removal of MO was found to boost with the temperature temperamrc/℃ increasefrom 25oCto 35oC. Subsequently,the removal of Fig. 1 Effect of temperatureon MO removal. MO concenhation MO decreasedfrom 47.4Voto 45.l%pas the temperature = Ond.L l; spenttea leaves= 2 g.tr; and time = 90 min was increasedfrom 35oCto 55oC.The maximum removal of MO was observedat 35oCand the minimum removal of MO at 55oC.The enhancementof the adsorptioncapacity or decreasein the thickness of the adsorption boundary by temperaturemay be attributedto increasein the number layer surrounding the biosorbent with temperature [15]. of active sitesavailablefor biosorption due to bond nrpture Moreover, becausethe adsorption reaction was generally

Liangzhi LI et al. Optimization of methyl orange removal

499

t..rthermic. the _sreater removalof MO at lower tempera.i:'S\\'3Sobtainedin the study.This is in accordance with '-' resultsdiscussedin the perviousreportsabout the :ption of by usedotherbiosorbents116,17l.

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increasein the driving force of the chemical potential gradientwith increasinginitial MO concentrations. At low concentrationsof MO, increasingthe MO concentration from 2 to 8 mg.L-' resultedin a ratherlargeincreasein the percentage MO removal,i.e.,from I2.27oto 52.l%a.These I Effectof biosorbent dosase observationswere similar to those of MB removal by phoenix tree leavesand can be explainedin a similar .::' r'ariationin the MO removal at different qualitiesof fashion. That is to say, the uptake of dye is highly ,' teawaste(2.0-10.0g'L ') wasinvestigated at an initial dependent on initial dye concentrations [21]. On the other :rcentration of MO at 6mg'L I. After 90min of hand,when the concentrationsof the MO were more than l..rrptionat 35oC,the MO concentration in the solution 8 mg.L r, thepercentMO removalwaschangedlittle.This .:. rTreosuf€d. Figure 2 showedthe effect of biosorbent phenomenoncould be due to the fact that the adsorption .r- on the removalof MO from aqueoussolutions.When reactionreachedequilibrium. J concentrations from 2 to 4 g.L't, of teawasteincreased - removalof MO increasedfrom 47.4%to 49.5Vo. This -:!'asein thebiosorptioncapacitywasdueto an increase .orbentsurfaceandadsorptionsites[18].Thereafter, the . ':roral of MO changedfrom 49.5% to 49.17awhen the .,,.iry of tea waste was increasedfrom 0.4 to 0.6g. .':rr'ly.the removalhad changedlittle with the adsorbent -.'. indicating that the adsorptionreaction reached : -irce. In addition, the removal of MO at higher . r r r b € tdt to s e ss. u c ha s 0 . 8 g . L I a n d l . 0 g ' L r , w e r e '; 17.770and47.37o.Theseresultscould be explained 24681012 1) ,: theadsorbentaggregationor saturation.Similarresults initialconcentration of MO in solution/(me.L -:!' also found in the processof metal complex dye -:tion onto pine sawdust Fig. 3 Effect of initial concenhationof MO on MO removal. [19]. Moreover,a similar Spent tea dosage: 4 g.L-' . temperature:35oC, and time: -::nghas also beenreportedfor MB adsorptionon tea 90 min .:.. f201. >ハ cFΦ ι ⌒∪ ˇ'〓 ハ

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i::tct of initial MO concentrationand contacttime :- :lti\r' studies were conducted in different initial ,-'rtrations of MO with 4.0mg'L t of tea waste at \ftc'r 90min of adsorption at 100r.min-r, the --':rlrationsof the MO solutions were determined.As :-'.'.iits in Fig. 3 show, the increasing initial MO - J:::r.ltion led to an increase in the amount of MO - :^,'J br spenttea leaves,which can be attributedto an

investigatedover the range of 20-l20min with a MO concentration 6 mg.L-t and0.2g spenttea leavesin 100 mL MO solution.After dynamicadsorptionat 100rpm and 35"C, the relevant variations about removal of MO are seen in Fig. 4. The efficiency of the removal increased rapidly duringthe initial stagesofthe sorptionprocess,and then slowly increaseduntil adsorptionequilibrium.When the contacttime increasedfrom 20 Io 60 min, the removal efficiencyincreasedfrom32.5Voto 47.97o.Figure4 clearly indicatedthat the maximalremovalof MO was obtainedat 60 min of adsorptionand thereafterremainedconstantat 47.857o.This trendwas in agreement with thosereported previously[2]. In addition,due to the dynamicequilibrium of the adsorption,the removalof MO at 120min was slightlyhigherthanthe valuesat 80 and l00min. 3.4 RSM optimization of MO removal The resultsof the RSM optimizationare depictedin Table 2. Moreover, statisticalanalysis about the model of removalof MO by teawastecanbe seenin Tables3 and4. As the resultsin Table 3 shows,the model F-value of 186.14impliedthe modelwas significant.Therewasonly a 0.017ochancethat the F-valuewas out of designdue to noise.Moreover,thevaluesof "Prob> F" lessthan0.0500

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