Mesoporous α-Fe2O3 Nanostructures for Highly Sensitive Gas S

J.Phys.Chem.C2010,114,18753–1876118753

SynthesisofMesoporousr-Fe2O3NanostructuresforHighlySensitiveGasSensorsandHighCapacityAnodeMaterialsinLithiumIonBatteries

BingSun, JosipHorvat, HyunSooKim,§Woo-SeongKim,#JunghoAhn,¶andGuoxiuWang*,

SchoolofChemistryandForensicScience,UniVersityofTechnologySydney,Broadway,Sydney,NSW2007,Australia,InstituteforSuperconductingandElectronicMaterials,UniVersityofWollongong,Wollongong,NSW2522,Australia,BatteryResearchCenter,KoreaElectrotechnologyResearchInstitute,Changwon641-120,Korea,DaejungEnergyMaterialsCo.,Ltd,Namdong-gu,Incheon405-820,Korea,andDepartmentofMaterialsEngineering,AndongNationalUniVersity,Gyungbuk760-749,Korea

ReceiVed:March13,2010;ReVisedManuscriptReceiVed:September28,2010

MesoporousR-Fe2O3materialswerepreparedinlargequantitybythesofttemplatesynthesismethodusingthetriblockcopolymersurfactantF127asthetemplate.Nitrogenadsorption-desorptionisothermalmea-surementsandtransmissionelectronmicroscopeobservationrevealedthattheas-preparedmesoporousR-Fe2O3nanostructureshavelargemesoporesinawidesizerangeof5-30nm.IthasbeenfoundthattheMorintransitiondependsonthermalhistoryofmesoporousR-Fe2O3,whichisdrivenbysurfaceanisotropy.SuperparamagneticbehaviorofmesoporousR-Fe2O3isalsoassociatedwithsurfacespinswithblockingtemperaturearound50K.Whenappliedasgassensors,mesoporousR-Fe2O3nanostructuresexhibitedhighgassensitivitytowardaceticacidandethanolgas.Asanodesinlithiumioncells,mesoporousR-Fe2O3materialsshowahighspeci ccapacityof1360mAh/gwithexcellentcyclingstabilityandhighratecapacity.

1.Introduction

Asann-typesemiconductor,hematite(R-Fe2O3)hasattractedagreatdealofattentionfromresearchersindifferent eldsbecauseofitsnontoxicity,lowcost,highstabilityunderambientconditions,andmultiplefunctions.Ithasbeenintensivelyinvestigatedforapplicationsinlithiumbatteries,1,2sensors,3catalysts,4pigments,5andmagneticdevices.6TheperformanceofR-Fe2O3stronglydependsontheparticlesize,morphology,andstructure.Foruseasanodematerialinthelithiumionbattery,thereversibilityoflithiumintercalationinR-Fe2O3dependsstronglyonthestructureandparticlesize.NanosizeR-Fe2O3exhibitsbetterperformancethanmicroscalesamplesasthesmallerparticlesizecangreatlyreducethediffusionlengthofthelithiumions.7,8Fromtheinvestigationsongas-sensingperformance,thesensitivitiesofR-Fe2O3nanospheresaremuchhigherthanthoseofmicrocrystallineR-Fe2O3powders.Theinterconnectedporesinthenanospheresareofbene tforthediffusionofgasandhavebeenprovedtooffermoreactivesitesforgaschemisorption.9Thereisgrowinginterestsinthepreparationofnanomaterialswithspeciallydesignedstructures.NanostructuredR-Fe2O3withone-dimensionalnanowire/nano-tubestructures,10,11two-dimensional ake/ lmstructures,12,13andthree-dimensionalhollow/porousstructures6,14havealreadybeensynthesizedbyavarietyofmethods,suchasthesol-gelmethod,15,16electrostaticspraydeposition,17hydrothermaltreatment,18,19andtemplatemethod.20,21

SincethediscoveryofMCM-41mesoporoussilicain1992,mesoporousmaterialshavebeendevelopedintoanimportant

*Towhomcorrespondenceshouldbeaddressed.E-mail:Guoxiu.Wang@uts.edu.au.Fax:+61-2-95141460.

UniversityofTechnologySydney.

UniversityofWollongong.§

KoreaElectrotechnologyResearchInstitute.#

DaejungEnergyMaterialsCo.,Ltd.¶

AndongNationalUniversity.

classofmaterialsandoccupyaveryimportantpositioninmaterialsscience.22Themesoporestructurecandramaticallyincreasethesurfacearea/volumeratio,whichmakesthemesoporousmaterialsveryusefulinthesurface-relatedapplica-tions.Thereisintenseinterestinpreparingmesoporoustransi-tion-metaloxidesbecauseoftheiruniquecatalytic,magnetic,adsorptive,andelectrochemicalpropertiesinapplicationsascatalysts,23magneticmaterials,24absorbents,25andenergycon-vertionandstoragematerials.26Severalmesoporoustransition-metaloxideshavealreadybeensynthesized,suchasCo3O4,27Mn2O3,24Fe2O3,28TiO2,29andV2O5;30however,itisstillmuchmoredif culttosynthesizemesoporoustransition-metaloxidesthanmesoporoussilica.Thematerialswiththree-dimensionalmesoporousarchitecturesarenormallyobtainedthroughtemplate-directedmethods,whichcanbesimplyclassi edintothehardtemplatemethodandthesofttemplatemethod.Thehardtemplates(usuallymesoporoussilicaorcarbon)normallypossesswell-con nedchannelsandpores,whichstronglyin uencethestructureoftheresultingsolidproduct.Softtemplatesareusuallysurfactants,long-chainpolymers,andviruses,whichfunctionasstructure-directingagentsthatassistintheassemblyofreactingspecies.20Yangetal. rstreportedthesynthesisofaseriesofmetaloxidesbyemployingnonionicpolymersurfactantsastemplates,whichcouldbeeasilyremovedbysolventextractionorthermaltreatment.31,32Thehardtemplatemethodsusuallyinvolveamultistepsynthesisprocess.Meso-poroussilicaorcarbonmustbeprepared rst.Then,theinorganicprecursorsarecombinedwiththetemplatesbyimpregnationorincorporation.The nalproductcanbeobtainedbytemplateremovalafterthesolidspecieshasformedthroughreaction,nucleation,andgrowth.20However,forthesofttemplatemethods,thetemplatescanformbyself-assemblyinliquidsolutionandcanbeeasilyremovedbysolventorcalcination.Therefore,thesofttemplatemethodisgenerallyeasiertobescaledupforlarge-scaleproductionthanthehard

10.1021/jp102286e 2010AmericanChemicalSociety

PublishedonWeb10/15/2010