Novel one-step synthesis of silica nanoparticles from sugarbeet bagasse by laser ablation and their effects on the growth of freshwater algae culture

ContentslistsavailableatScienceDirect

Particuology

j ou rn a l h o m ep a g e :w w w . e l s e v i e r . c o m / l o c a t e / p a r t i c

Novel

one-step

synthesis

of

silica

nanoparticles

from

sugarbeet

bagasse

by

laser

ablation

and

their

effects

on

the

growth

of

freshwater

algae

culture

Nalan

Oya

San

_,

_Canan

_Kurs¸

_ungöz

_,

_Yasin

_Tümtas¸

_,

_Öncay

_Yas¸

_a

_,

_Bülend

_Ortac¸

_,

Turgay

Tekinay

a_{PolatlıScienceandLiteratureFaculty,BiologyDepartment,GaziUniversity,Ankara06900,Turkey} b_{LifeSciencesApplicationandResearchCenter,GaziUniversity,Ankara06830,Turkey}

c_{UNAMInstituteofMaterialsScienceandNanotechnology,BilkentUniversity,Ankara06800,Turkey}

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received21September2013

Receivedinrevisedform6November2013 Accepted25November2013 Keywords: Laserablation One-stepsynthesis Raman Silicananoparticle Microalgae

a

b

s

t

r

a

c

t

Scientificresearchinvolvingnanotechnologyhasgrownexponentiallyandhasledtothedevelopment ofengineerednanoparticles(NPs).SilicaNPshavebeenusedinnumerousscientificandtechnological applicationsoverthepastdecade,necessitatingthedevelopmentofefficientmethodsfortheirsynthesis. Recentstudieshaveexploredthepotentialoflaserablationasaconvenientwaytopreparemetaland oxideNPs.Duetoitshighsilicacontent,lowcost,andwidespreadavailability,sugarbeetbagasseishighly suitableasarawmaterialforproducingsilicaNPsvialaserablation.Inthisstudy,twodifferentNP pro-ductionmethodswereinvestigated:laserablationandNaOHtreatment.Wedevelopedanovel,one-step methodtoproducesilicaNPsfromsugarbeetbagasseusinglaserablation,andwecharacterizedthesilica NPsusingenvironmentalscanningelectronmicroscopy(ESEM),energydispersivespectrometry(EDS), dynamiclightscattering(DLS),transmissionelectronmicroscopy(TEM),attenuatedtotal reflectance-Fouriertransforminfraredspectroscopy(ATR–FTIR),X-rayphotoelectronspectroscopy(XPS)andRaman spectroscopy.EDSanalysisandXPSconfirmedthepresenceofsilicaNPs.TheNPsproducedbylaser ablationweresmaller(38–190nm)thanthoseproducedbyNaOHtreatment(531–825nm).Finally,we demonstratedpositiveeffectsofsilicaNPsproducedfromlaserablationonthegrowthofmicroalgae,and thus,ournovelmethodmaybebeneficialasanenvironmentallyfriendlyproceduretoproduceNPs.

©2014PublishedbyElsevierB.V.onbehalfofChineseSocietyofParticuologyandInstituteofProcess Engineering,ChineseAcademyofSciences.

1. Introduction

Silica is beneficial to many plants (Ding, Ma, Shui, Wan, &

Li,2005).Itiswellknownthatcertainplants,includinggrasses

(Poaceae),rice(Oryzasativa),sugarbeet(Betavulgaris),and

horse-tail(Equisetum),containhighlevelsofbiogenicsilica(Sun&Gong,

2001).Inparticular,sugarbeetisanattractivesourceofbiogenic

sil-icabecausethesilicacontentofthisplantismainlyconcentrated

inbagasse.Sugarbeetbagasseisproduced inlargequantitiesas

anagro-industrialbyproductandisoftenusedasboilerfuelfor

generatingsteamduringtheprocessingofsugar.

∗ Correspondingauthor.Tel.:+903122903526;fax:+903122664365. ∗∗ Correspondingauthorat:PolatlıScienceandLiteratureFaculty,Biology Depart-ment,GaziUniversity,Ankara06900,Turkey.Tel.:+903124846270;

fax:+903124846271.

E-mailaddresses:ortac@unam.bilkent.edu.tr(B.Ortac¸),ttekinay@gazi.edu.tr

(T.Tekinay).

In recent years, there hasbeen an increasing trend toward

themoreefficientuseofagro-industrialby-productsfor animal

nutrition,fuel,andfermentativeproducts.Severalprocessesand

productsusingsugarbeetbagasseastherawmaterialhavebeen

reported,particularlyinpulpandpaperproduction;itisalsoused

asafeedstockinfermentationprocesses(Alves,Felipe,Silva,Silva,

&Prata,1998;Pandey,Soccol,Nigam,&Soccol,2000).However,

sugarbeetbagassecanalsobeprocessedtoproducehigh-purity

sil-ica,exceeding99%purityandprimarilybearingK2O,andMgOas

impurities(Affandi,Setyawan,Winardi,Purwanto,&Balgis,2009).

Assuch,bagasseisaneconomicallyviablerawmaterialforsilica

nanoparticle(NP)production.

Nanoparticlesarefrequentlyusedinseveral

nanotechnologi-calapplications.Inparticular,silicaNPsarewidelyusedindrugs,

cosmetics,printertoners,varnishes,andfoodpreservatives(Baek

&An,2011;Bagwe,Hilliard,&Tan,2006;Huaetal.,2009; Lin, Huang,Zhou,&Ma,2006).Inaddition,theuseofsilicaNPshas

recently beenextended tothe biomedicaland biotechnological

1674-2001/$–seefrontmatter©2014PublishedbyElsevierB.V.onbehalfofChineseSocietyofParticuologyandInstituteofProcessEngineering,ChineseAcademyofSciences.

silicaNPsynthesismaybeunsustainableandcostprohibitiveinthe

nearfuture.Therefore,itishighlydesirabletoidentifyalternative

approachestoreduceproductioncosts.

MostNPsynthesistechniques,suchasphysicalvapor

deposi-tion(Yousefi&Muhamad,2010),precipitation(Yang&Hu,2010),

solvothermal/hydrothermalmethods(Wang,Shi,Qi,&Liu,2010),

andsol–gelmethods(e.g.,sol–gelcombustion),areexpensiveand

complex and offer only limited control over particle size and

sizeuniformity.Inrecentyears,pulsed-laserablationofsolidsin

solutionhasattractedinterestduetoitsversatilityandlowcost

(Alkis,Oruc¸,Ortac¸,Kos¸ger,&Okyay,2012;Amendola&Meneghett, 2009;Wu,Dickinson,&Lele,2012).Sajti,Sattari, Chichkov,and Barcikowski(2010)demonstratedrecentlythebulksynthesis of

NPsbylaserablation,yieldingceramicNPsonascaleofseveral

grams.Theirstudyindicatesthepotentialfeasibilityoflaser

abla-tionforlarge-scalesynthesisapplications.

Based on the available literature (Affandi et al., 2009), we

hypothesizedthatsugarbeetbagasse,whichisinherentlyrichin

silica,canbeusedtosynthesizesilicaNPs.Inthisstudy,wedescribe

forthefirsttimetheuseoflaserablationforthesynthesisof

sil-ica NPsfrom agro-industrialbyproducts.It is alsoimportantto

investigatetheeffects ofnanomaterialexposureontheaquatic

environment.Greenalgaeareknowntobesensitivetomany

chem-icals.Theyhavebeenconsideredindicatorsofthebioactivityof

industrial wastes,and theyvaryin theirresponsestoa variety

oftoxicants.Theirecologicalpositionatthebaseofmostaquatic

foodwebsandtheiressentialrolesinnutrientcyclingandoxygen

productionarecriticaltomanyecosystems.Therefore,we

exam-inedhowsilicaNPsimpactthegrowthofafreshwatergreenalgae

speciesthatisamongthemostwidespreadofallalgae:Chlorella

vulgaris.Ourresultsmayaidthedevelopmentofenvironmentally

friendlyandeconomicallyattractivealternativestocurrentNP

pro-ductionmethods.

2. Materialsandmethods

2.1. Nanoparticleproduction

Sugarbeetbagasse wasobtainedfromtheAnkaraSugar

Fac-tory,Etimesgut,Ankara,Turkey.Twoseparatetreatments were

adopted toextractsilica fromthebagasse samples. Inthe first

approach,bagasseashwasobtainedbycalciningsugarbeetbagasse

at500◦Cfor12h.Onegramofbagasseashwasthentreatedwith

concentratedHCl:HNO3=1:3(v/v)at35◦Cfor2handoven-dried

at 60◦C. Then, 50mL of water was added to the residue, and

thesolutionwasalkalized toa pHof13–14withconcentrated

NaOH.Followingovernightincubation,thealkalinesolutionwas

sampleswerefilteredwitha0.22␮mfiltertoremovethefibers

fromtheNPsolution.

2.2. Nanoparticlecharacterization

Themorphologyandelementalcompositionofrawbagassewas

measuredbyanenvironmentalscanningelectronmicroscopewith

EDS(ESEM,Quanta200FEG,FEIInstruments,USA).Theparticlesize

anddistributionofparticlesdispersedindistilledwaterwere

mea-suredusingdynamiclightscattering(DLS)(MalvernInstruments

Ltd.,Malvern,UK).ThestabilityofthesilicaNPswasmeasuredfrom

thezetapotentialofthesolution(NanoZS,MalvernInstruments

Ltd.,Malvern,UK).ThemorphologyofsilicaNPswasalsoanalyzed

usingaFEITecnaiG2F30transmissionelectronmicroscope(TEM)

connectedtoahighresolutionimagingsystem.NPsampleswere

preparedbydryingatotalof2␮Lofthelaserablatedmixtureon

carboncoatedcoppergridsatroomtemperature.

Fourier transform infrared spectroscopy (ATR/FTIR) analysis

wasperformed using a Nicolet 6700(Thermo Fisher Scientific,

USA)ATR–FTIRspectrometer.Spectrawereobtainedwithinthe

4000–500cm−1rangewitharesolutionof4cm−1(Bruker,Vertex

70withHyperionScanningMicroscope,Germany).Thesamples

(100␮L)wereplacedintheattenuatedtotalreflectance(ATR,ZnSe)

analyzerandanalyzed.

X-rayphotoelectronspectroscopy(XPS)(K␣-Monochromated

highperformance)(Thermo,USA)measurementswereperformed

inanultra-highvacuum(UHV)withaconventionalX-raysource

(Mg-K␣).

Ramanspectrawereacquiredatroomtemperaturebyusinga

WitecAlpha300S+RamanModule(Witec,Germany).Asolid-state

532nmwavelengthlaserwasusedforexcitation.Raman

measure-mentsofsinglespectraweretakenat50×magnificationandwith

2.03sintegrationtimes.

2.3. EffectsofsilicananoparticlesonC.vulgarisgrowth

ThealgaC.vulgariswasobtainedfromaculturecollectionat

GaziUniversityLifeSciencesApplicationandResearchCenterand

sub-culturedinthelaboratory.C.vulgariswascultivatedin

steril-izedTapmedium(Tris–acetate–phosphate)underanillumination

intensity of 4000lux. The temperature in the air-conditioned

growthchamberwasmaintainedat25◦C.WeexposedsilicaNPs

producedfromtwodifferenttreatmentstoalgalcultures.Thealgal

densityofthreereplicateswasthencalculatedbymeasuringthe

opticaldensity (OD) at a wavelengthof 750nmwith a UV–vis

spectrophotometer(Shimadzu,UV-1201V,Japan).Medium

Fig.1.Flowdiagramoftheprocedureusedtoproducesilicananoparticlesfromsugarbeetbagasse.

Fig.2.(a)ESEMimagesand(b)EDSspectrumofrawsugarbeetbagasse.

cultures werevisuallyinspectedforcontaminationusinga light

microscope.

3. Resultsanddiscussion

Inthepresentstudy,thesilicaNPswerepreparedusingtwo

differentmethods:(1)calcinationofsugarbeetbagasseand

sub-sequenttreatmentofsugarbeetbagasse ashwithNaOHand (2)

synthesisofsugarbeetbagasseusinglaserablation(Fig.1).

Fig.2(a)and(b)shows theESEM imagesandEDS spectrum,

respectively, ofrawbagasse. TheESEMmicrographofraw

sug-arbeet bagasse (Fig. 2(a)) clearly revealsits fibrous texture. In

Fig.3.TheparticlenumberdistributionsofsilicaNPsobtainedby(a)NaOH treat-mentand(b)laserablation.

Fig.4. (a)TEMimageofsilicaNPs,inset:sizedistribution,(b)XPSanalysisrecordedfromsilicaNPs,(c)amorphousstructureofsilicaNPs,and(d)nanocrystal(NC)structure ofsilicaNPs.

addition,EDS analysis showedthat rawsugarbeet bagasse was

primarilycomposedofmetaloxides,suchasMg,K,andSi(Fig.2(b)).

Fig.3showstheintensityandparticlenumberdistributionsof

silicaNPsofvarioussizesafter(a)NaOHtreatmentand(b)laser

ablation.Fig.3(a)demonstratesthatthesilicaparticlesproduced

bycalcinationandNaOHtreatmentweresubstantiallylargerthan

thoseformedvialaserablation,withasizerangeof531–825nm.

Incontrast,silicaNPsformedvialaserablationwereintherange

of38–190nm,withanaveragesizeof∼74nm(Fig.3(b)).

AdetailedTEManalysiswasperformedtoidentifythestructural

propertiesofthecolloidalnanoparticlesolution(CNS).Fig.4shows

thattheCNSwassuccessfullyproducedbypulsedlaserablation

methodindeionizedwater.TheCNSconsistsofspheroid-shaped

anduniformlydispersednanoparticles,withoutanyaggregation.

Inaddition,zetapotentialmeasurementswerecarriedout,andthe

zetapotentialwas−21.0mV,indicatingthatthesilicaNPswere

sta-ble.ThedataindicatetheCNSindeionizedwaterwasstableand

welldispersedafterthelaserablationprocess.Toobtainaccurate

particlesizeinformation,wemeasuredthesizesof150particles

observedintheTEMimages.AsapparentfromtheinsetofFig.4(a),

nanoparticlesrangedinsizebetween40and160nm,withan

aver-ageparticlesizeof100nm.Toverifythechemicalcomposition

oftheCNS, XPSanalysiswasperformed.Thepeak at102.43eV

correspondstotheSi2pspectra,indicatingtheexistenceofSi O

bondsofSiO2nanoparticles(Yang,Kuperman,Coombs,

Mamiche-Afara,&Ozin,1996).ThesedatashowthatthecolloidalNPsolution

consistsofSiO2 NPs(Fig.4(b)).Inaddition,Fig.4(a)showsthat

theone-stepproductionmethodyieldedNPswithamorphousand

crystalstructure.Fig.4(c)showsanisolatedamorphousNP,and

Fig.4(d) shows an isolated nanocrystal(NC). The lattice-fringe

structureapparentintheHR-TEMimageofthesingleisolatedNC

evidencesthegenerationofnanoparticlesintheformofa

crys-tallinestructurebylaserablationtechnique.

ProductionofSiNPshaspreviouslybeenreportedfrom

silica-containingagro-industrialwaste,suchasricehuskashandcoffee

(Estevez,Vargas,Casta ˜no,&Rodriguez,2009;Li&Wang,2008).

Inthesestudies,Si NPswereobtainedbyashingfollowed bya

chemicaltreatmentof6horlonger.Ourresultsdemonstratethat

laserablationcanbeusedasaone-step,uncomplicatedmethod

toproducesilicaNPsthataresignificantlysmallerthanthose

pro-ducedbychemicalmethods,suchascalcinationfollowedbyNaOH

treatment.

InfraredspectraofthesilicaNPssynthesizedusingtwodifferent

methodswererecordedbyFTIRspectroscopyandarepresentedin

Fig.5.AsseeninFig.5,silicapeaksareclearlyvisible.The

Fig.5. FTIRspectraofNPsobtainedfromlaserablationofbagasseandNaOH-treated bagasseash.

region.Thebandsat1200–1000cm−1and807areduetothe

asym-metricandsymmetricstretchingmodesofSi O Si(Beganskien ˙e,

Sirutkaitis,Kurtinaitien ˙e,Juˇsk ˙enas,&Kareiva,2004).Thebandat

955cm−1wasascribedtotheSiO Hasymmetrybendingvibration.

Thebroad peak atapproximately3200–3600cm−1 corresponds

to the stretching vibrations of hydroxyl groups, whereas the

band at 1630–1640cm−1 is due to the deformation of water

moleculesabsorbedthroughthesilicaparticlesurface(Martinez,

Ruiz,Vorobiev,Perez-Robles,&Gonzalez-Hernandez,1998).The

peaks centered at approximately 1100cm−1 show an obvious

broadeningandashoulderinthe1160–1290cm−1range.This

pat-terncanbeattributedtotheasymmetricstretchingvibrationsof

thetetrahedralSiO4coordinationunits(Pol,Gedanken,&

Calderon-Moreno,2003;Wangetal.,2011).Similaritiesbetweenthespectra

ofthetwosilicasamplesindicatethatthepretreatmentdoesnot

affectthechemicalstructure ofthesynthesizedsilica,although

NaOHtreatmentproducedmoreresiduesthanthelaserablation

method.

Throughitssensitivitytovibrationalproperties,Raman

scatter-ingoffersavaluabletoolforunderstandingstructuralaspectsof

materials(Dreschera&Kneipp,2012;Woods&Bain,2012).Inthis

work,theWitecAlpha300S+RamanModulewith532nm

excita-tionwasusedtocharacterizethebondpropertiesofsilicaNPs.The

resultsofRamanscatteringinthespectralrangeof300–3600cm−1

areshowninFig.6.Severaldifferencesareapparentamongthe

Ramanspectraofthethreesamples.ThenoiselevelintheNaOH

treatmentspectraismuchhigherthanthatofthelaserablation

treatment,althoughbothspectrawererecordedunderthesame

conditions.The probablesourceofthis highnoise is thelarger

amountofporewaterincorporatedinNPsduetoNaOHtreatment.

Wefoundanotablepeakat522cm−1 inbothtreatments,which

isclosetothevalueobservedforbulksilicon(Inada,Nakagawana,

Umezu,&Sugimura,2002).

Fig.7 shows theoptical density (OD)of C. vulgarisexposed

to silica NPs produced by laser ablation and NaOH treatment.

Understandingtheeffectsofnanomaterialexposureontheaquatic

environmentisextremelyimportant.Becauseoftheirwidespread

use,NPswilllikelymoveintoaquatic,terrestrial,andatmospheric

environments. Therefore, concerns have been raised about the

potentialenvironmentalrisksposedbyNPs.Greenalgaeareknown

tobesensitivetomanychemicals,andtheyareconsidered

indica-torsofthebioactivityofindustrialwastes.Theirecologicalposition

atthebaseofmostaquaticfoodwebsandtheiressentialrolesin

Fig.6. RamanscatteringspectraofNPsresultingfromlaserablationofbagasseand NaOHtreatedbagasseash.

nutrientcyclingandoxygenproductionarecriticaltomany

ecosys-tems.However,fewstudieshaveinvestigatedNPtoxicitytoalgae.

Zhu,Zhu,Tian,Lang,andLi(2008)studiedthetoxicityofZnO,

CuO,andTiO2NPstothegreenalgaeScenedesmusobliquus.They

foundthatZnONPswerethemosttoxic,followedbyCuONPsand

TiO2NPs.Inthepresentstudy,SiNPsdidnotinhibitalgalgrowth

butinsteadincreasedthegrowthrate.

Weietal.(2010)showedthatSiO2NPsof10–20nmindiameter

weretoxictoS.obliquus.Theyfoundthatthesmallertheparticle,

thegreateritstoxicity.ThetoxicityofSiNPsismostlikelydueto

theirsorptiontothealgalcellsurface.Inthepresentstudy,the

sizeofNPsproducedbylaserablationwas38–190nm.Therefore,

wespeculatethatthelaser-ablatedSiNPscannotsorbtothecell

surface.Inaddition,themorphologyofthealgalcellsdidnotchange

whenobservedunderanopticalmicroscope.

Majornutrients,includingcarbon,nitrogen,phosphorus,and

silica, aredefined assuchbecausetheyare essentialfor life in

Fig.7.EffectsofsilicaNPsproducedfromlaserablationandNaOHtreatmenton growthofChlorellavulgaris.

bagasse notonlytakes fulladvantageofthehighsilicacontent

ofsugarbeetbagassebutalsominimizestheenvironmentalissues

associatedwithcurrentapplicationsanddisposalmethodsof

sug-arbeetbagasse.Assuch,themethodpresentedhereinmayaidthe

developmentofneweconomicalapproaches involvingthe

syn-thesisofvaluablenanomaterialsfromagro-industrialresiduesas

alternativestotheenergy-intensiveandpotentiallyhazardous

pro-cessescurrentlyadoptedbyindustry.

Here,wereportthesuccessfulpreparationofenvironmentally

friendlysilicaNPsusinglaserablation,asconfirmedbySEM,TEM,

andDLS.OurresultsshowthattheNPsobtainedbylaserablation

aresignificantlysmaller(38–190nm)thanthosepreparedusing

chemicaltreatment.

Last,thisstudydemonstratestheeffectofsilicaNPsproduced

usingtwodifferentnanoparticlemethodsonalgalgrowth.From

ourresults,weconcludethatsilicaNPsproducedfromchemical

treatmenthaveanegativeeffectonaquaticalgae,asmanifestedby

thedecreasedgrowthofalgalcells.However,silicaNPsproduced

bylaserablationincreasedthegrowthofC.vulgaris.Ourresults

suggestthatsilicaNPsproducedbylaserablationmayposenoharm

totheaquaticenvironment.

Acknowledgments

TheauthorsthankZeynepErgülÜlgerforprocuringthe

sugar-beetbagassesamples,ÖmerFarukSarıo˘gluforhelpinanalyzing

theATR/FTIRdata,AlperDevrimÖzkanforobtainingtheRaman

spectraandAhmetEminTopalforperformingtheXPSanalysis.

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