材料专业文献翻译Word文档格式.docx

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10-6formaldehydeattheoptimizedoperatingtemperatureof410°

Candagoodlevelofselectivityoverotherpossibleinterferencegasessuchasethanol,toluene,acetone,methanol,andammonia.ThegassensingmechanismofIn2O3/CdOsensorhasbeendiscussedindetail.

1Introduction

Formaldehyde（HCHO）isacolorlessandstrong-smellinggascomingfrombuildingmaterials,interiordecorationmaterials,woodfurniture,carpetandsoon.

HCHOisoneofthemostdangerousindoorpollutantsamongvolatileorganiccompounds（VOCs）,andisfoundtobeassociatedwithasthma,nasopharyngeal

cancer,andmultiplesubjectivehealthcomplaints.Inparticular,HCHOisconsideredasamajorcauseofsickbuildingsyndrome（SBS）.WorldHealthOrganization（WHO）establishedastandardof0.08×

10-6（volumefraction）averagedover30minforlong-termexposureinformaldehydevapor.ManymethodstodetectVOCshavebeeninvestigated.Amongthem,semiconductorgassensorsarewidelyusedsincetheyarecheapandeasytobeavailable.Thesensingmaterials,includingSnO2,10-12ZnO,13NiO,14andIn2O3,15,16havebeenexploredforformaldehydedetection.

Inrecentyears,nanostructuresemiconductormaterialshavebeenextensivelystudiedduetotheirexceptionalpropertiesandpotentialapplicationsinvariousfields.Amongthem,indiumoxide（energygap3.67eV,Bohrradius2.14nm）materialhasbeenwidelystudiedbecauseofitsuniqueoptoelectronicproperties,suchashighelectricalconductivityandhighUVtransparency.Ithasbeenwidelyusedintheoptoelectronicdevicessuchassolarcells,windowheaters,andliquidcrystaldisplays。

Ithasbeenalsoexploredforsensingmaterialsfordetecting

O3，HCHO,trimethylamine（TMA）,NO2CO,andNH3。

Variousvapor-phaseorphysicaltemplatemethodsweredevelopedtoprepareIn2O3nanocrystals.Forexample,In2O3nanowiresweresynthesizedbyusingthevapor-liquid-solidtechnique。

TheIn2O3nanowirearraysornanorodswereinducedbytemplate-assistedgrowth,andtheIn2O3nanobeltswereobtainedthroughthermalevaporation。

Besidesthesephysicalmethods,therearealsowet-chemistrymethodstopreparespecificIn2O3nanostructures.Forinstance,In2O3withstructuresofnanorodbundles,spherelikeagglomerates,lotus-root-like,andnanotubesweresuccessfullysynthesizedbyhydrothermalroute。

Quasi-monodisperseIn2O3nanocrystalswereobtainedthroughanorganicsolutionsyntheticroute。

Inthiswork,theflower-likehierachicalnanostructureIn2O3composedofthetinysphericalnanocrystallineswasfabricatedbyusingthehydrothermalmethod.Then,theas-synthesizedIn2O3powdersweremixedwithCdOinamolarratioof1:

1toformagassensingmaterial.TheformaldehydesensingpropertiesoftheIn2O3/CdO-basedsensorswerecarriedout.

2Experimental

2.1Preparationandcharacterizationofmaterials

InCl3·

4H2O（99.5%）wasobtainedfromSinopharmChemicalReagentCo.,Ltd.,China.Ethylenediaminetetraaceticacid（99.5%,EDTA,C10H16N2O8）andCS（NH2）2（99.0%）wereobtainedfromTianjinKermelChemicalReagentCo.,Ltd.,

China.CdO（99.5%）powderwasanalyticalgradewith30nmparticlesize,andpurchasedfromHaitaiNanometerMaterialsCo.,China.Allofthereagentsusedintheexperimentswereanalyticalgradeandutilizedwithoutfurtherpurification.

Flower-likeIn2O3wassynthesizedbyahydrothermalmethod.Inatypicalprocedure,1mmolInCl3·

4H2Oand2mmolCS（NH2）2weredissolvedin30mLEDTA.Afewdropsofammoniaweredrippedintothesolution,andthesolutionwasundertheconditionsofultrasonicdispersingandconstantstirringalternatelyfor20min.Then,themixturewastransferredintoa50mLTeflon-linedstainlesssteelautoclave.Theautoclavewassealedandmaintainedinanelectricovenat180°

Cfor18h.Afterthat,theautoclavewascooledtoroomtemperaturenaturally.Thepinkprecipitatewascollectedandwashedwithethanolanddeionizedwateralternatelyforseveraltimes.Thenitwasdriedinelectricovenat80°

Candtheprecursorwasgenerated.FlowerlikeIn2O3wasobtainedbyroastingtheprecursorat600°

Cinmufflefor1h.

X-raydiffraction（XRD）patternsofthepowderswereexaminedin2θregionof20°

-80°

withCuKα（0.154nm）radiationonRigaku,ModelD/MAX2400,Japan.Scanningelectronmicroscopy（SEM）imageswereexaminedonaFEIQUANTA200F（UnitedStates）microscopeequippedwithenergydispersiveX-ray（EDX）spectroscopy.Transmissionelectronmicroscopy（TEM）imagewascarriedouttoobtaindirectinformationaboutthesizeandstructurebyTecnaiG220S-Twintransmissionelectronmicroscope.

2.2Fabricationandmeasurementofgassensors

TheIn2O3andCdOpowdersweremixedinamolarradioof1:

1andgroundwithdeionizedwatertoformapaste.Thepastewaspaintedonacleanceramictube（Φ2mm×

4mm）onwhichapairofAuelectrodeswerepreviouslyprinted,andthensinteredat600°

Cfor2h.ANi-Crheatingwirewith30Ωasaheaterwasinsertedthroughthetubetoprovideheatingforgassensor.Theelectrodeandheaterwireswereweldedonabasetoformgassensor.Thefabricatedgassensorswereagedwithaheatingtemperatureof300°

Cfor240hinair.

ThegassensingpropertiesofIn2O3/CdOcompositegassensorsweretestedinasealedchamber.Thetestingtemperatureandhumiditywere~20°

Cand~20%RH（relativehumidity）,respectively.Aheatingvoltagewhichwasprovidedbyad.c.powersupply（GPS-3303C,GuweiElectronic,Taiwan）wassuppliedtothewireofsensorforprovidingaoperatingtemperature,andacircuitvoltagewassuppliedacrossthesensorandtheloadresistorconnectedtothesensorinseries.Theoutputvoltageacrosstheloadresisterwasrecordedbyadataacquisitioncardwhichwasconnectedtoacomputertorecordthereal-timedata.Thewholesystemwascontrolledbyacomputerautomatically.

3Resultsanddiscussion

3.1CharacterizationsofIn2O3andIn2O3/CdOcomposite

TheXRDpatternoftheIn2O3isshowninFig.1.AllpeakscanbeindexedtopurecubicphaseofIn2O3（JCPDSNo.65-3170）,indicatingthatapurephaseofIn2O3wasobtainedbycalciningtheprecursor.ThecrystallinesizeoftheIn2O3wascalculatedbyusingDebyeScherrorformula,D=0.89λ/βcosθ,whereDistheaveragegrainsize,λistheX-raywavelength（0.154nm）,βisfull-widthathalf-maximum,andθisdiffractionangle.ThecalculatedaveragecrystallinesizeoftheIn2O3isabout22nm.

Fig.2showstheSEMimagesoftheIn2O3material.Itcanbeseenthattheas-preparedIn2O3nanoparticleswerecongregatedtogetherandformedflower-likemicrostructurewithadiameterofseveraltotenmicrometers.Fig.2（b）showsthattherearemanywrinklesandholesonthe“flower”.

Fig.3showstheTEMimageoftheas-synthesizedIn2O3.TheIn2O3nanoparticlesareuniformandtheshapesofthecrystallitesaresphericalandellipse.ThegrainsizeoftheIn2O3isaround20nmconsistentwiththecalculatedresult.FromFigs.2and3,itcanbeseenthattheas-preparedflower-likeIn2O3particleswereformedwiththetinycrystallitesindicatingahierarchicalnanostructureinnature.

Theformationoftheflower-likehierarchicalstructureIn2O3byusingthehydrothermalmethodcouldbedescribedasfollows.ThechemicalreactionoccurredintheInCl3mixtureduringthepreparationprocess:

In3++EDTA=In（EDTA）

（1）

Then,thefollowingreactionswerepresented:

NH3·

H2O=NH4++OH-

（2）

CS（NH2）2+2OH-=S2-+CO2+2NH3（3）

2In（EDTA）+3S2-=In2S3+2（EDTA）3-（4）

2In2S3+9O2=2In2O3+6SO2（5）

EDTAisastrongcomplexagentandeasilyreactswithmetalions.EDTAchemicalreaction

（1）wasthecomplexreactionandresultantwasIn（EDTA）.Thentheammoniaionizedtoprovideanalkalinecondition（reaction

（2））.CS（NH2）2caneasilyhydrolyzeinthealkalineconditionandthereaction（3）occurredtogenerateS2-ions.AreplacementreactionoccurredbetweenIn（EDTA）andS2-inreaction（4）,consequentlyformingtheprecursor.Theultrasonicdispersingandstirringprocessmadenano-clustersbeuniform.TheprecursorIn2S3dispersedataformofnano-clusters.Ontheotherhand,EDTAhadstrongadsorbabilityanditwaseasytoconglomerate.WhenTeflon-linedstainlesssteelautoclaveprovidedahightemperatureandhighpressuresituation,someprecursorparticlesconglomeratedtogetherandformedsomesphericalandellipsestructurerowmaterialswithdifferentmagnitudesinthisexperiment.Eventually,therowmaterialswerecalcinedandtheinnerorganicmattersbecamevaporsofCO2,SO2,andH2O,andtheIn2O3wasobtained（reaction（5））.Thevaporswentintosurroundingairthroughsomeporecanalsintherowmaterial,whilewrinklesappearedonthesurfaceandformedflower-likeIn2O3material.

ThecompositeofIn2O3/CdOnanoparticles（amixtureofIn2O3andCdO）wasexaminedbyXRDasshowninFig.4.Allpeakscan