InternationalJournalofNanoelectronicsandMaterialsVolume11,No.2,Apr2018[179‐194]

SynthesisandCharacterizationofZincOxideNanoparticlesusing

GreenandChemicalSynthesisTechniquesforphenoldecontamination

H.ShokryHassan1*,M.F.Elkady2,3**,E.M. El‐Sayed3A.M.Hamed4,A.M.Hussein4andIslamM.

Mahmoud4

1ElectronicMaterialsResearchesDepartment,AdvancedTechnologyandNewMaterialsResearchInstitute,CityofScientificResearchandTechnologicalApplications,NewBorgEl‐Arab,21934,Alexandria,Egypt.

2ChemicalandPetrochemicalEngineeringDepartment,Egypt‐JapanUniversityofScienceandTechnology,NewBorgEl‐Arab,Alexandria,Egypt.

3FabricationTechnologyResearchesDepartment,AdvancedTechnologyandNewMaterialsResearchInstitute,CityofScientificResearchandTechnologicalApplications,NewBorgEl‐Arab,21934,Alexandria,

Egypt.4ChemistryDepartment,FacultyofScienceAl‐AzharUniversity,Al‐AzharuniStreet,71524Assiut,Egypt.

Received27September2017;Revised24October2017;Accepted6December2017

ABSTRACTZincoxidenanoparticles(ZnO‐NPs)weresuccessfullysynthesizedusingbothbiologicalandchemical techniques. This study is mainly focused on the green synthesis (biological)methodofZnO‐NPsusingdifferentplantleafextractsfromleavesofguava,olive,fig,andlemon. The plant leaf extracts (polyphenols) act as reductants and zinc nitratehexahydrate(Zn(NO3)2.6H2O)actsasaprecursor.ChemicalsynthesismethodofZnO‐NPswascarriedoutusingpreparedsodiumhydroxideandzincnitrate.TheproducedZnO‐NPswere characterizedusingX‐ raydiffraction (XRD), scanning electronmicroscope (SEM),transmission electron microscopy (TEM), fourier transform infrared (FTIR), Thermalgravimetricanalysis(TGA),andparticlesizeanalysis(PSA).Theaveragecrystallitesizeofgreen‐synthesized zinc oxide nanopowders range from 7.1 to 28 nm,while the averagecrystallite size of chemical‐synthesized zinc oxide powders range from 19.6 to 148 nmaccordingtotheXRDcalculationsandTEMobservations.BothZnOnanopowdersshowedhigh thermal stability up to 600 oC. The green‐synthetized ZnO‐NPswere evaluated forphenoldecontamination inpollutedwastewater.Themaximumrecordedphenolremovalwas 99.7% within 250 minutes using 0.1g ZnO‐NPs, making ZnO‐NPs a promisingadsorbentmaterialforphenoldecontaminationinpollutedwastewater.Keywords: Zinc Oxide Nanoparticles (ZnO‐NPs), Green Synthesis, Biological andChemicalSynthesis,PlantLeafExtract,PhenolRemoval.

1. INTRODUCTION

The growth and development of mankind have always been closely associated with theprogress of materials technology. In the last decades, the field of nanotechnology andassociated researches were continuously in rapid growth due to the experience andcapitalization of accumulated knowledge [1]. A large variety of nanomaterials has attractedmore consideration because of their desirable properties and the possibility to be used ininnovativetechnologyapplications[2,3].Ananoparticlecanbedefinedasasmallobjectthat*CorrespondingAuthor:marwa.f.elkady@gmail.com

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acts as a whole unit in terms of its transport and properties. The engineering and sciencetechnologyofnano‐systemsareconsidered themostdemandingandrapid‐growingareasofnanotechnology. Physical and chemical processes are convenient for nanoparticle synthesis,buttheuseoftoxiccompoundsrestrictstheirapplication[4].Zinc oxide has been an essential material for industries for centuries and is presently thesubjectofasignificantnewinterest.ZnO isawhitepowderthat is insoluble inwater that isalreadywidelyusedinoursocietyasanadditiveinnumerousmaterialsandproducts.Indeedit is a key element in many industrial manufacturing processes but most zinc oxides areprepared synthetically [5]. It is well known that the sizes, phases, andmorphologies of thenanomaterials have a large impact on their properties and technological applications.Therefore,many researchershave focusedon the controlof themorphological structuresofnanomaterialsintheirresearches[6].Biosynthesis of nanoparticles has gained significant importance in recent years and hasbecome one of themost preferred syntheses [7‐9]. In the biosynthesismethod of ZnONPs,plant leaf extract is used for a controlled synthesis of zinc oxide nanoparticles, using theaqueousextractofdifferentplantleavesasreductanttodevelopanenvironmentallyfriendlyprocessthroughbiomimeticapproachesratherthanthetraditionalmethodsthatusevariousroutesforthesynthesisofZnONPs.These techniques in general can be divided into three: chemical, physical, and biologicalmethod.Chemicalsynthesiscanbefurtherdividedintoliquidandgasphasesynthesis.Liquidphase synthesis includes the following 10 methods; precipitation, coprecipitation [10],colloidal,sol‐gelprocessing[11],water–oilmicroemulsions[12],hydrothermalsynthesis[13],solvothermal,sonochemical[14],polyol[15],andvaporphasemethod[16].Fabricationssuchas pyrolysis, inert gas condensation methods, and laser ablation are classified as physicalmethods[17].However,thesementionedtechniquesareextremelyexpensiveandhavemanydisadvantages due to the difficulty of scaling‐up the process of synthesis, separation, andpurification of nanoparticles from surfactants, co‐surfactants, organic solvents, and toxicmaterials, which involve use of toxic, hazardous chemicals like borohydride, hydrazinehydrate,citrate,andhydrazinehydrochlorideasreductants.Phenolsareconsideredoneofthetop45mostimportantriskysubstancesthatarerequiredtobe treated before its release into the environment, as referred from the Agency for ToxicSubstances&DiseaseRegistry,USAclassification.Indeed,evenatalowconcentration,phenolshave decimating effects on life forms such as sour mouth, diarrhea, impaired vision, andexcretionofdarkurine[18].Recently, the growth of awareness towards green chemistry and other biological processeshave led to the improvement of rapid, cost‐effective, and eco‐friendly biosynthesis of zincoxideNano powder using the plant leaf extract approach for the synthesis of nanoparticles[19]. This study compares the physico‐chemical properties of ZnO nano powder materialsproducedfromchemicalandbiologicalroutes.2. MATERIALANDMETHODS

2.1 Materials

Pure,highgradeZn(NO3)2.6H2OandNaOHweresuppliedbySigma‐Aldrichchemicals.Freshplant leaves of guava, olive, fig, and lemon were collected early in the morning during themonthofMay2016fromSohag–Egypt.

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2.2.ExtractionoftheAntioxidants(PolyPhenols)fromPlantLeavesPlantleafextractswerecollectedfromfreshplantleavesofolive,guava,fig,andlemon.Theseleaveswerecollected,washedwithwateranddistilledwaterfordustremoval,andthendriedovernightinanovenat70°C.Then,thedryleavesweregrindedintofinepowder.Theextractthatwouldbeusedforthereductionofzincions(Zn2+)to(ZnO)nanoparticleswaspreparedbyplacing12.5gofdriedleavesina250mlbeakerfilledwith200mlofwater.Themixturewasthenboiledfor2hoursat60‐80˚Cusingastirrerheateruntilthecoloroftheaqueoussolutionchangedfromwaterytolightyellow.Theextractwascooledtoroomtemperatureandfilteredusing filter paper. The extracted filtratewas stored in a refrigerator and used as a reducingagent[20].2.3.SynthesisofZnONanoparticlesZnONPswereprepared in twoways; chemically and throughgreen synthesisusing sodiumhydroxideandtheplantleafextractscollectedfromfreshanddryplantleavesofolive,guava,fig,andlemon.2.3.1.BiosynthesisofZnOnanoparticlesInthismethod,liquidextractofantioxidants(polyphenols)fromtheplantleaveswasusedforzincsaltreduction.70mlofZn(NO3)2.6H2Owithaconcentrationof0.2Mwasreducedby30mlof(olive,guava,fig,lemon)leavesextracts(storedinrefrigerator).Theseextractswereaddedunder constant stirring, dropwise, and thenboiled to60˚Cusing a stirrer‐heater for1hour.The produced powdermaterials were dried at 100°C overnight. During the drying process,completeconversionofzinchydroxideintozincoxidetookplaceuntiltheoxideturnedintoadark yellow‐colored paste. This paste was collected in a ceramic crucible and calcinated at500˚C for 2 hours. A sunny yellow powderwas produced after the calcination process. Thematerialwasgrindedaftercalcinationtoproducefinepowder.TheschematicdiagramoftheZnObiosynthesismethodisshowninFigure1[20,21].

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Figure1.BiosynthesisofZnOnanoparticlesschematicdiagram.

2.3.2.ChemicalSynthesisofZincOxideNanoparticlesThefacilesol‐geltechniquewasusedforzincsaltreduction.ThesolutionofZn(NO3)2.6H2Oataconcentration of 0.2 M was reduced using a 9.8ml of 2 M sodium hydroxide. The reducingagentwasaddeddropwiseunderconstantstirringuntil thesolution’spHreach12.AfterthecompleteadditionofNaOH,thereactioncontinuedfor2 hour.Thesolutionwaskeptovernightand the produced solid materials were separated using centrifugal force. The separatedpowder materials were washed using distilled water. Finally, the materials were dried at100°C.Duringthedryingprocess,theconversionofzinchydroxideintoZnOtookplace[22].2.4.CharacterizationofthePreparedZincOxideNanoparticlesX‐ray diffraction patterns of the nanopowders were obtained using a (Schimadzu 7000)diffractometer,operatingwithCuKαradiation(λ=0.15406nm).Thepatternsweregeneratedat 30kV and 30mAwith a scan rate of 2◦ min−1 for 2θ values between 20 and 80 degrees.Scanningelectronmicroscope (SEM) analyses (JEOL JSM6360LA, Japan)wereperformed todetermine the shapeandmorphologyofZnOnanoparticles.Themorphologyandsizeof thepreparedZnOmaterialsweredetectedusingTEM(JEOLJEM1230,Japan).FTIRspectrumsofthe prepared ZnO materials were established using (Shimadzu FTIR‐8400 S, Japan) at awavelengthrangeof400–4000cm−1.ThethermalstabilityofthepreparedZnOwasevaluated

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through thermo gravimetric analysis (TGA) using a Thermo Gravimetric Analyzer(ShimadzuTGA–50H, Japan). The particle size of the ZnOmaterial and its distributionweredeterminedusingaparticlesizeanalyzer(PSA)(LA‐960combines).2.5.AssessmentoftheGreenSynthetizedZnO‐NpsforPhenolSorptionTheaffinityofgreen‐synthetizedZnO‐NPstowardphenolsorptionwasverifiedusingsyntheticpollutedwater in a batchmanner.Thephenol sorptionprofilesof 0.1gof green‐synthetizedZnO‐NPsweredeterminedagainstcontacttime(0‐250min).ThepercentageoftheremovalofphenolusingtestedZnO‐NPswasestimatedfromequation(1)

%Removal=((Co−C)/Co)∗100 (1)whereCo is the initialphenol concentration in the solution (mg/l), andC is the finalphenolconcentrationaftertreatmentprocess(mg/l).3. RESULTSANDDISCUSSION

The end product of the successfully synthesized zinc oxide nanoparticles using the green‐synthesismethodislightyellow‐coloredpowderprecipitate,whiletheproductofthechemicalsynthesismethodiswhiteprecipitate.Bio‐reduction of the zinc ions (Zn2+) to ZnO during exposure to the plant leaf extractswasfollowed by a color change from pale yellow to yellowish brown after the drying process.Fromthechemicalsynthesismethod,zincsaltwasreactedwithsodiumhydroxidetoproducezinc hydroxide and sodium nitrate. This hydroxide decomposes upon heating to zinc oxide.Both green and chemical preparation techniques of ZnO nanomaterials depend on aspontaneousreductionofzincsaltshownasEq.(2)and(3).

Zn(NO3)2+2NaOH→Zn(OH)2+2NaNO3(2)Zn(OH)2→ZnO+H2O(3)

During the decomposition of Zn(OH)2 into ZnO nanoparticles, the yield obtained was 1.6 gwhichmeans about 60% of the precursor usedwas converted into pure ZnO nanoparticlesusing the green synthesis method. However, this production yield of ZnO nanoparticlesincreasedto87%whenthechemicalpreparationtechniquewasused.

3.1XRDAnalysisXRDwasused to characterize thedifferentmethodsused toprepare theZnOnanopowders.Figure2 shows theXRDpattern for theZnOnanopowder synthesizedbybothchemical andgreentechniquesusingextractsfromfreshanddryplantleavesofolive,guava,fig,andlemon.X‐raydiffractionoftheZincoxideNPssynthesizedusingthechemicalmethodwithzincnitrateandsodiumhydroxideasmaterials isstudiesbasedonFigure2(A). It is indicatedfromthisfigure that distinctive peaks appear at (100), (002), (101), (102), (110), (103), (200), (112)and(201).TheresultsconfirmthatthepreparedZnOnanoparticlesareofwurtzitehexagonalstructureandshowahighdegreeofcrystallinity.TheX‐RaydiffractionpatternofthesamplesynthesizedfromaqueousplantleafextractusingthegreensynthesismethodisillustratedinFigure2(B1,B2,C1,C2,C3,C4).Itindicatesthatthedistinctive peaks that appear at (100), (002), (101), (102), (110), (103), (200), (112), and(201)are ingoodagreementwithwurtziteZnO(JCPDSCARDNO:36‐1451)[23].TheX‐raypattern clearly demonstrates that all diffraction peaks of the prepared ZnO NPs have high

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purity and degree of crystallinity structure. The X‐ray diffraction peaks clearly demonstratethatfreshanddryplantleafextractsresultingreen‐synthesizedZnONPswithsamediffractionpeakswithoutanychanges.Thesharpandnarrowdiffractionpeaksindicatethattheproductiswellcrystallineinnature.Themeancrystallinesize(D)oftheparticleswasdeterminedfromtheXRDlinebroadeningmeasurementusingScherrerequationequation4.

D=0.89λ/(βCosθ)(4)WhereDisthemeansizeofcrystallites(nm),KistheScherrerconstantcrystalliteshapefactorwithagoodapproximatedvalueof0.9,λisthe0.1541nmwavelengthofthex‐raysource(CuKα)used inXRD,B is the fullwidthathalf themaximumof thediffractionpeak (FWHM) inradians of the X‐ray diffraction peak, andθ is the Bragg (diffraction) angle. The XRD peaksfrom the green synthesis method are not as sharp as those from the chemical synthesismethod.Thisshowsaslightdecreaseincrystallinity,whichsuggeststheformationofparticlesof smaller size. The calculated average crystalline size of zinc oxide nanoparticles preparedusing the chemical synthesismethod is19.6nm, and is reduced to8.5,9.49,7.10,10.34,9.3,and13.76nmwhenthechemicalsynthesiswasreplacedbythegreensynthesisusingextractsfromdifferentfreshanddryplantleafextractsofoliveandguava,anddryplantleafextractsoffigandlemonrespectively.Itcanbeclearlyseenthatthebroadeningofpeaksfromthegreensynthesismethodusingextractsofoliveandguavaanddryplantleafextractoffigandlemonisgreatercompared to those fromthechemical synthesismethod, indicating that thegreen‐synthesizedparticleshavesmallerparticlesizes[24,25].

A B1

B2 C1

C2 C3

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Figure2.XRDspectrumsofsynthesizedpurenanozincoxideusingbothchemicalandgreensynthesismethods:(A)chemical,(B1)olivefresh,(B2)guavafresh,(C1)olivedry,(C2)guavadry,(C3)figdryand

(C4)lemondry.

3.2SEMAnalysis Thescanningelectronmicroscope(SEM)analysiswasperformedtodeterminetheshapeandmorphology of pure ZnO nanoparticles under various magnifications and the results aredepictedinFigure3.TheSEMresultsofthestudiedZnOnanoparticlessynthesizedusingbothchemical and green synthesismethod using the extracts from fresh and dry plant leaves ofolive,guava,fig,andlemonrevealtheformationofstableZnOnanoparticles.TheSEMimagesshow spherical, spongy, and irregular shapes of ZnO nanoparticles in addition to individualzincparticlesaswellasanumberofagglomerates.TheSEMimage(Figure3)showsthattheparticle size of green‐synthesized zinc oxide nanoparticles (Figure 4 from B1‐C4) iscomparatively smaller than the chemical‐synthesized nanoparticles (Figure. 3 A) and theparticlesizeoffreshgreen‐synthesized,sphericalshapedzincoxidenanoparticles(Figure3B1,B2) iscomparativelysmaller than thedrygreen‐synthesized irregularandspongyzincoxidenanoparticles(Figure3C1,C2,C3,C4).TheseresultsareingoodagreementwiththeXRDresults[21].

B1 A

C4

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Figure3.SEMAnalysisofsynthesizedpurenanozincoxidebybothchemicalandgreensynthesis

methods:(A)chemical,(B1)olivefresh,(B2)guavafresh,(C1)olivedry,(C2)guavadry,(C3)figdryand(C4)lemondry.

3.3TransmissionElectronMicroscopy(TEM)Figure 4shows the TEM images of the ZnO nanoparticles synthesized with a zincnitrateprecursorthroughbothchemical(A)andgreensynthesis,usingdifferentfreshanddryplant leaf extracts of olive, guava, fig, and lemon (B1.1,B1.2), B2, C1, C2, C3 and C4). It can be

C4

C2 C3

B2 C1

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observedthattheparticlessynthesizedusingbothmethodshavealmost‐sphericalshapeswithsmall agglomeration, except when fresh olive plant leave extracts were used for the greensynthesis method where the resulting particles have nano rod shapes with an average sizebetween 12‐48nm, as shown in Figure 4 (B1.1). The average particle size of ZnO from thechemicalsynthesismethodwasfoundtobefrom44to145nm.Whensodiumhydroxidewasreplaced by fresh and dry plant leaf extracts of olive, guava, fig, and lemon and the sameprocedurewas conducted, the average size of the particles reduces to 7.32 to 28nm. Theseresultsare ingoodagreementwith theXRDresults.Awell‐dispersedrod‐likestructurewithanaveragediameterof8.9‐21nmproducedusingfresholiveplantleafextractwasobserved,whichisalsoinrelative agreementwiththeXRDresults.ItisclearfromtheTEMstudythattheaveragediameters of theZnONPs are almost the sameeven if the extractswereused fromdifferentFreshanddryplantleavesofolive,guava,fig,andlemon[26].

A B1.1

B1.2

C1 C2

B2

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Figure4.TEMimagesoftheZnOnanoparticlessynthesizedusingbothchemicalandgreensynthesismethods:(A)chemical,(B1.1,B1.2)olivefresh,(B2)guavafresh,(C1)olivedry,(C2)guavadry,(C3)figdry

and(C4)lemondry.

3.4FTIRSpectroscopy

Figure5 (A,B1) is recorded in thewavelength rangeof400cm‐1 to4000cm‐1 and shows theFTIRspectraofZnOnanoparticlessynthesizedbychemical(Figure5(A))andgreen(Figure5(B1)) methods using plant leaf extracts. Generally, ZnO nanoparticles have characteristicabsorptionbands in regionbelow1000cm‐1due to inter‐atomicvibrations.Thebroadpeakresulted from the chemical synthesismethod isobservedat3439.19and1103.32cm‐1whilefrom the green synthesismethod the broad peak is observed at 3398.89 and 1035.81 cm‐1,which correspond to O‐H stretching band ormay be due towater adsorption on themetalsurface.Thepeaksat1639.55,1635.69cm‐1,1456.30cm‐1andallbandsat449.43‐557.45cm‐1are attributed to ZnO nanoparticles that correspond to Zn‐O’s stretching and deformationvibrationrespectively.Thebroadpeakat1456.30cm‐1isduetotheeffectofpolyphenolsandnaturalpigmentsfromtheplantleafextracts.Thebroadpeakat3398.69and3439.19cm‐1areduetometal‐oxygen(metaloxides)frequenciesobservedfortherespectiveZnOnanoparticles[7].

B1

A

C3 C4

Figure5.FTIRspectroscopyofchemical(A)andgreen(B1)synthesismethods.

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3.5ThermalPropertiesofthePreparedMaterials(TGA)Figure 6 (A, B1, and B3) showed the thermal decomposition behavior of the chemical andgreen‐synthesizedZnOnanoparticlesoverthestudiedtemperaturerangeof0to600°CinN2atmosphere. With regard to chemical‐synthesized zinc oxide nanoparticles, the firstdegradationstepthatstartedat25°Candendedaround256°Cisattributedtotheevaporationofsurfaceadsorbedwater.Thesecondandthirdthermaldegradationstepthatstartat256°Cand ended around 599°C may be caused by the decomposition of the condensationdehydrationofthehydroxyls.Theaveragesampleweightlossforthistemperaturerangeforchemical‐synthesized ZnO nanoparticles does not exceed 9.1% of the material weight, asshowninFigure6(A).Thefirstdegradationstepofgreen‐synthesizedZnOnanoparticles‐‐thatcalcinatedinanairheatedfurnaceat500°Cfor2hrbeforethermaldecompositionandstartedat19°Candendedaround200°Cisattributedtotheremovalofsurfacewasteadsorbedontozincoxide.Thesecondthermaldegradationthatstartedat200°Candendedaround598°Cisattributedtotheevaporationofsurfaceadsorbedwateranddehydrationofthehydroxyls.Theaverage sample weight loss for this temperature range for green‐synthesized ZnOnanoparticlesdoesnotexceed2.2%of thematerialweight.This result clearly indicates thattheobtainedpowderhasextremepurityasshowninFigure6(B1).Ontheotherhand,thefirstdegradationstepofgreen‐synthesizedZnOnanoparticlespastethatarenon‐calcinatedbeforethermal decomposition and started at 38°C and ended around 93°C is attributed to theremovalofsurfacewasteadsorbedontozincoxide.Thedegradationthatstartedat93°Candendedaround177°Cisattributedtotheevaporationofsurfaceadsorbedwater,andthenfrom177°C to 282°C, the degradationmay be caused by the decomposition of the condensationdehydration of the hydroxyls. The last thermal degradation step that started at 282°C andendedaround491°Cmight indicate theexistenceoforganicmaterial, in smallamounts.Theaverage sample weight loss for this temperature range for green‐synthesized ZnOnanoparticlesthatdoesnotexceed51.6%ofthematerialweightmaybefromthepolyphenolsornaturalpigments that resulted from theplant leaf extract degradation shown inFigure 6(B3)[27,28].

A

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3.6ParticleSizeAnalysis(PSA)A laser diffraction method withmultiple scattering was used to determine the particle sizedistribution of the powder. The particle size distribution curve for ZnO nanoparticlessynthesizedusingbothchemicalandgreensynthesismethods isshowninFigures7(A)and(B1)respectively.ThefirstpeaksinFigures(7‐A)and(8‐B1)thatappeararound40and10nmrepresent chemical synthesized nanoparticleswith a diameter of 9.2nmmethod and green‐synthesizednanoparticleswithadiameterof8.2nmrespectively.Thepresenceofthesecondpeaks indicatethattheaveragediameter is526.6nmforthechemicalsynthesismethodand197.6nm for the green synthesis method. The results correspond with the crystallite sizecalculatedfromtheSEMandXRDpatternsandit isalsoclear thattheaveragediameterandparticle sizeof theZnOnanoparticlesaresmaller for thegreensynthesismethod, comparedwiththechemicalsynthesismethod.

B1

B3

Figure6.Thermogravimetricanalysis(TGA) forZnOnanoparticles:(A)chemical,(B1)greensynthesismethodscalcinatedZnOnanoparticlesat500˚Cfor2hrand(B3)greensynthesis

methodswithoutcalcinationofZnOpaste.

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Figure7.ParticleSizeAnalysis(PSA)forZnOnanoparticles(A)chemicaland(B1)greensynthesismethods.

3.7AssessmentoftheGreenSynthetizedZno‐NpsForPhenolSorptionThekineticadsorptionprofileofphenolontoZnO‐NPs indicated inFigure8wasdeterminedthroughthevariationofcontacttimefrom0minto250minattheoptimumconcentrationofphenol(5ppm)withadoseofadsorbent(0.1gm),atpH8,atatemperatureof25°C,andwithagitationspeedof300rpm.ItisevidentthatphenoladsorptionontoZnO‐NPsincreaseswithincreasingcontacttime.ThisresultindicatesthatthelargesurfaceareaofthepreparedZnO‐NPsdecreasestheresistanceagainstphenoldiffusion,thusimprovingitsmobilityduringtheadsorption processwith time [29].Moreover, Figure 5 indicates that the contact timehas apositiveimpactonthephenoladsorptionontoZnO‐NPs.Itispredictedfromthisbehaviorthattheadsorptionprocessismainlydiffusion‐controlled.Inconclusion,theadsorptionaffinityofphenolontoZnO‐NPsincreaseswithincreasingcontacttimeuntilequilibriumstateisreached[30].

0 50 100 150 200 250

20

40

60

80

100

% R

emoval

Time (min)

effect of contact time

Figure8.EffectofcontacttimeonphenolremovalontogreensynthetizedZnO‐NPs.

A

B1

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4. CONCLUSIONS

Inthepresentstudy,itisfoundthatbiosynthesisasagreentechnologycanbeagoodmethodforthesynthesisofzincoxidenanoparticles,whencomparedwithchemicalsynthesismethod.Thebio‐reductionofaqueouszincionsusingplantextractsofguava,olive,fig,andlemonplantleavestoproduceZnOnanoparticleshasbeendemonstrated.Thegreenchemistrytechniquecharacterizedbyvariousadvantagessuchassimpletobescaledup,economicallyviable,easilyavailable, familiar and eco‐friendly. TheobtainedZnOwas characterized throughXRD, SEM,TEM,FT‐IR,TGA,andPSAanalysis. Itcanbeobservedthat theZnOnanoparticles frombothchemical and green synthesis methods have an almost‐spherical shape with smallagglomerationexceptwhen the greensynthesismethod isusedwith theoliveextract,wheretheparticleshaveanaverageparticlesizeof8‐28nm,whichcorrespondswiththecrystallitesize calculated from the SEM and XRD patterns. The thermal analysis results of the ZnOnanoparticlesproducedfromchemicalandgreensynthesisindicatethattheypossessthermalstability up to a temperature of 600°C. The green‐synthetized ZnO‐NPs were evaluated forphenol decontamination frompollutedwastewater. It shows amaximumphenol removal of99.7%within150minutesusing0.1gZnO‐NPsthus,makingZnO‐NPsaspromisingadsorbentmaterialforphenoldecontaminationfrompollutedwastewater.REFERENCES[1] M.F.Elkady,H.ShokryHassan.Curr.Nanosci.11(2015)805.[2] E.T. Salem, R. A. Ismail, M.A. Fakhry, Y. Yusof, Int. J. Nanoelectronics and Materials9

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