还原性气体的气相敏感性

SensorsandActuatorsA199 (2013) 236–240

ContentslistsavailableatSciVerseScienceDirect

SensorsandActuatorsA:Physical

journalhomepage:www.elsevier.com/locate/sn

a

FabricationofNi1−xZnxFe2O4(x=0,0.5and1)nanoparticlesgassensorforsomereducinggases

DeepshikhaRathorea,b,RajnishKurchaniab,∗,R.K.Pandeya,c

a

DepartmentofPhysics,BarkatullahUniversity,Bhopal462026(M.P.),India

DepartmentofPhysics,MaulanaAzadNationalInstituteofTechnology(MANIT),Bhopal462051(M.P.),Indiac

NIITUniversity,Neemrana301705(Raj.),India

b

article

info

abstract

Articlehistory:

Received6March2013

Receivedinrevisedform15May2013Accepted3June2013

Available online 11 June 2013

Keywords:GassensorSensitivity

IntermediatetemperatureLiquefiedpetroleumgasEthanolAmmonia

FabricationofNi1−xZnxFe2O4(x=0,0.5and1)nanoparticlesgassensorforLPG,ethanol,ammoniaandchlorinegasismaingoalofthiswork.Theresponseofthesegaseswasstudiedintheformofsensitivity(%)asafunctionofcomposition,temperatureandflowrate(ppm).Sensitivity(%)wasfoundtobemaximumatintermediatetemperatureanditwasfoundthattherearetwovaluesofintermediatetemperatureforcompositionsx=0.5and1.Itwasalsoobservedthatflowrateincreasesupto200ppm,sensitivity(%)ishighestandfurtherincreaseinflowrate,sensitivity(%)becomessaturateforeachcompositionandatbothintermediatetemperature.FromtheresultsitwasconcludedthatNi1−xZnxFe2O4nanoparticlesofcompositionx=0,0.5and1areverygoodsensorforethanol,ammoniaandchlorinegasrespectively.

2013 Elsevier B.V. All rights reserved.

1.Introduction

Today,thehumanlifeandalllivingorganismsarebeingaffectedbyincreaseintheuseoflargenumberofvehiclesandavari-etyofmachines[1].Thevastgrowingindustriesareresponsibleforcreatingpollutionintheatmosphere.Theairpollutionisalsofoundtobeveryhazardousinfluencingtherespiratorysystemdirectly[2].SomereducingandtoxicgaseslikeLPG,H2S,CO,hydro-carbons,CO2,H2andCl2arealsoreportedtoberesponsibleforcausingallergicandrespiratorydiseasessuchasasthma,aller-gicbronchialasthma,andrhinitis[3].Softferritessuchasnickel,zincandcombinationofnickel–zincferritehavebeenintroducedinmanypotentialapplicationsduetoinverse,normalandmixedspinelstructureoftheseferritesrespectively[4].Recently,gassensingapplicationsofsoftferriteshavebeenidentifiedfordetec-tingsomereducinggases[5],whichareusedfrequentlyathomes,car,laboratories,industriesandservicestations[6].

Theelectricalresistivityofferritescanbechangedbyadsorp-tionofgases.Thispropertyisbeingusedinsensorfordetectionofinflammableandtoxicgases[7].Thecapabilityofgassensingpropertiesdependsuponthesurfaceareaofthesensingmateri-als,operatingtemperatureandconcentrationofgas[8].Ithasbeen

∗Correspondingauthor.Tel.:+[1**********]5;fax:+[1**********]2.

E-mailaddresses:[email protected](D.Rathore),[email protected](R.Kurchania),[email protected](R.K.Pandey).

observedthatlargersurfacearea[9]givesthehighestsensitivitytowardthegasesandnanoparticlespossesshighersurfacetovol-umeratio.Theinteractionbetweenthesensingmaterialandtestgasoccursonthesurfaceofthematerialandthereforetheamountofatomsresidingingrainboundariesandtheinterfacesiscriticalforcontrollingthepropertiesofthegassensor[10].

Zhangetal.[11]reportedthatapplicationoftheZnFe2O4tubesasgassensormaterialsdisplayedlow-energyconsumptionandhighsensitivitytoorganicssuchasethanolandacetone,duetotheuniqueinterconnectedchannelstructureandsmallcrystalsizeofthetubes,showingtheirpotentialapplicationinsensorareas.Arshaketal.[12]investigatedtheuseofironandzincoxidethickfilmmaterials,screen-printedontoglasssubstrateswithsilverelectrodes.Thesensorwasinterfacedwiththreeresistorstoformabridgecircuit.Thiswasthenusedtodetectmethanol,ethanolandpropanolvaporswithinaconcentrationrangeof0–3000ppm.Thesensitivityofthesensorisdefinedasthechangeinbridgeoutputvoltage(mV)withrespecttochangeingasconcentra-tion(ppm).Satyanarayanaetal.[13]synthesizednanocrystallineNi1−xCoxMnxFe2−xO4bythehydrazinemethodandstudiedthegassensingbehaviortoreducinggaseslikeliquefiedpetroleumgas(LPG),ethanol,COandCH4.TheyproposedinteractionofLPGwithferritethroughFT-IRstudiesandreportedthechangeinconductivitybasedontheworkfunctionofthesemiconductingoxide.

ThemainobjectiveofthisworkwastodeveloptheeffectofsizeandtemperatureonthegassensingbehaviorofNi1−xZnxFe2O4

0924-4247/$–seefrontmatter 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.sna.2013.06.002

D.Rathoreetal./SensorsandActuatorsA199 (2013) 236–240

237

Fig.1.Fabricationofnanoferritegassensingdevice.

(x=0,0.5and1)nanoparticlebasedgassensorsandtoexaminetheirapplicationinthedetectionofethanol,ammonia,LPG(lique-fiedpetroleumgas)andchlorinegases.Synthesisofnanoparticlesandfabricationofgassensingdevice,theirsensingpropertieshavebeenanalyzedanddiscussedsystematically.Detailsaboutthesyn-thesistechnique,structural,magneticanddielectricpropertiesofNi1−xZnxFe2O4(x=0,0.5and1)nanoparticleshavebeenreportedelsewherebyauthors[4].

2.Experimental

FinepowderofNi1−xZnxFe2O4(x=0,0.5and1.0)nanoparticlesweresynthesizedbychemicalco-precipitationmethod.Theaque-oussolutionsofNiCl2·6H2O(Merck,99.9%pure)andZnCl2·6H2O(Merck,99.9%pure)1:0,1:1and0:1wt%ratioswerefirstmixedwithasolutionof2%FeCl3·6H2O(SDFineIndia,99.9%pure).Thesolutionsoobtainedwasthenpouredinto16%NaOH(Merck,99.9%pure)solutionkeptat30◦C.Afterstirringfortwohourswithacon-stantspeed,precipitationofdarkbrowncoloredpowderoccurred.Theprecipitatewaswashedwithdistilledwateranddriedatroomtemperature.

TofabricatethedeviceusingNi1−xZnxFe2O4(x=0,0.5and1)nanoparticlesgassensor,theultrafinepowderofthesenanofer-riteswerepressedusinguniaxialpressintopelletsofsize10mmdiameterand0.1mmthickness.Thegoldfingerselectrodeswerevacuumevaporatedonthepellet.TheschematicofthegassensingdevicehasbeenillustratedinFig.1.Inthisgeometry,thegoldfin-gerselectrodescovermaximumsurfaceareaofnanoferritepellet,inordertoobtainthebestresponseofdetectinggases.

ExperimentalarrangementformeasuringtheresponseofthenanoferritegassensordevicehasbeenshowninFig.2.Inthisarrangement,thenanoferritegassensingdevicewaskeptinsideaU-shapedtubeinwhichaconstantflowrateofagastobesensedwasensured.Ahalogenlampwasplacedbehindthegassensorandradiationheatingwasusedtoincreasethetemperatureofthedevice.Thetemperaturewascontrolledbyregulatingthe

current

Fig.2.Experimentalarrangementfornanoferritegassensor.

throughthefilamentofthehalogenlamp.Athermocouplecon-nectedtoatemperatureindicatorwasusedtosensetemperatureofsurfaceofthedevice.AprecisionLCRmeterwasusedtomeasuretheresistance.

Theresponseofgasonthesurfaceofthenanoferritesensorintheform

ofsensitivity(%)isgivenbytherelation(1)[14],

S(%)=

R

R

a−Rg

g

×100=

g

×100

(1)

whereRaandRgaretheresistanceintheairandgasatmosphererespectivelyand Risthechangeinresistance.

3.Resultsanddiscussion

ThegassensingapplicationoftheNi1−xZnxFe2O4(x=0,0.5and1)nanoparticleswasestablishedforanyoneofthegasesviz.LPG,ethanol,ammoniaandchlorine.ThesensorresponseexpressedasS%usingequationonewasdeterminedatacontrolledflowrateforallsensorcompositionsinthetemperaturerangefrom30◦Cto350◦C.

3.1.SensingpropertiesofNi1−xZnxFe2O4(x=0)

Toobtainthegassensingproperties,theoperatingtemperatureisoneofthesignificantparametersthatmaintaintheactivationprocessessuchasthespeedofchemicalreactiononthesurfaceoftheparticleandspeedofthediffusionofthegasmoleculetothesurface[14].Thetemperatureatwhichbothprocessesbecomeequalisknownasintermediatetemperature.

Sensitivity(%)ofNi1−xZnxFe2O4(x=0)hasbeentestedforethanol,ammonia,LPGandchlorineattemperaturerangefrom30◦Cto350◦Cat200ppmflowrate,whichisillustratedinFig.3(a).ItcanbeseenfromFig.3(a)thatsensitivity(%)increasesastemper-atureincreasesandreachesatamaximumvalue.Thetemperatureatwhichsensitivityachieveshighestvalueisknownasinter-mediatetemperature.Furtherincreaseintemperatureresultsadecreaseinsensitivity(%)andreachesaminimumvalue.IncaseofNi1−xZnxFe2O4(x=0)gassensortheintermediatetemperaturewasfoundat215◦Cforallthegases.Comparisonofsensitivity(%)atdifferenttemperatureforethanol,ammonia,LPGandchlorinegasisshowninFig.3(b).Thesensingresponseoftestedgasesfallsintheorderof,ethanol>ammonia>LPG>chlorineattemperaturerangefrom30◦Cto350◦CintheNi1−xZnxFe2O4(x=0)nanoparticlesasshowninFig.3(a)and(b).

238D.Rathoreetal./SensorsandActuatorsA199 (2013) 236–240

Fig.3.(a)Sensitivity(%)asafunctionoftemperatureat200ppm(b)sensitivityatinitial,intermediateandfinaltemperature(c)sensitivity(%)asafunctionofflowrate(ppm)ofNi1−xZnxFe2O4(x=0)nanoparticlesforethanol,ammonia,LPGandchlorinegas.

Sensitivity(%)asafunctionofflowrateofNi1−xZnxFe2O4(x=0)fordifferentgasesatintermediatetemperatureisshowninFig.3(c).ItcanbeobservedfromFig.3(c)thatsensitivity(%)increaseslin-earlyasflowrateincreasesuptoabout140,160,140and140ppmforethanol,ammonia,LPGandchlorinegasrespectively.Furtherincreaseinflowrateupto200ppm,sensitivity(%)increasesandshowsdeviationfromlinearity.ItwasalsoobservedfromFig.3(c)thatathigherflowrates,Ni1−xZnxFe2O4(x=0)sensorshowssatu-rationeffectforallthegases.

3.2.SensingpropertiesofNi1−xZnxFe2O4(x=0.5)

SubstitutionofZn2+ionsintheNiFe2O4nanoparticlesalsogivesgoodsensingresponseforreducinggases.Temperaturedepend-entsensitivity(%)forethanol,LPG,ammoniaandchlorinegasofNi1−xZnxFe2O4(x=0.5)nanoparticlesisillustratedinFig.4(a).Fig.4(a)demonstratesthattherearetwointermediatetemper-aturesatwhichsensitivity(%)achieveshighestvalue.IncaseofNi1−xZnxFe2O4(x=0)nanoparticles,thereisonlyonevalueofintermediatetemperature,on50%substitutionofZn+2ionsintheNiFe2O4nanoparticles,sensitivity(%)gainsmaximumvalueattwointermediatetemperaturesduetothemixedeffectofNiFe2O4andZnFe2O4nanoparticles.ItcanbeseenfromFig.4(a)thatsensitiv-ity(%)followstheorderofammonia>LPG>chlorine>ethanolatfirstintermediatetemperature,whichare100◦C,100◦C,100◦Cand105◦Cforammonia,ethanol,LPGandchlorinegasrespec-tively.Atsecondintermediatetemperature,sensitivity(%)comesin

theorderofammonia>ethanol>LPG>chlorineandforthesegasesintermediatetemperaturesare305◦C,305◦C,300◦Cand300◦Crespectively.Thisslightchangeintheresponseofgaseswithinter-mediatetemperatureisbelievedtobeduetothedopingeffectofZn+2intheNiFe2O4nanoparticles.

Thevariationinsensitivity(%)withflowratefordifferentgasesat(b)firstintermediatetemperatureand(c)secondintermedi-atetemperatureofNi1−xZnxFe2O4(x=0.5)wasshowninFig.4.ItwasobservedfromFig.4(b)thatsensitivity(%)increaselinearlyonincreaseinflowrateupto200ppmandonfurtherincreasingtheflowrateitbecomessaturatedforallgases.FromFig.4(c)itwasobservedthatsensitivity(%)increaseslinearlyasflowrateincreasesupto160,140,140and180ppmforammonia,ethanol,LPGandchlorinegasrespectively.Furtherincreaseinflowratesensitivity(%)isdeviatedfromlinearityandbecomessaturateforallthegases.

3.3.SensingpropertiesofNi1−xZnxFe2O4(x=1)

Thenoticeablebehaviorofsensitivity(%)ofNi1−xZnxFe2O4(x=1)nanoparticleswithtemperaturerangefrom30◦Cto350◦Cforethanol,ammoniaandLPGat200ppmisdepictedinFig.5(a).FromFig.5(a),itisclearthattherearetwointermediatetempera-turesandbothintermediatetemperaturesaredifferentforallthegases.FurtherfromFig.5(a),itwasobservedthatsensitivity(%)isintheorderofammonia>ethanol>LPGforfirstintermediatetemperatureandforsecondintermediatetemperaturethisorderchangestoethanol>ammonia>LPG.Thissignificantbehaviorof

Fig.4.(a)Sensitivity(%)asafunctionoftemperatureat200ppm(b)sensitivity(%)asafunctionofflowrateforethanol,LPG,chlorineandammoniagasofNi1−xZnxFe2O4(x=0.5)nanoparticles.

D.Rathoreetal./SensorsandActuatorsA199 (2013) 236–240

239

Fig.5.Influenceoftemperatureonsensitivity(%)(a)forethanol,ammoniaandLPG,(b)forchlorinegas.Sensitivity(%)asafunctionofflowrateat(c)firstintermediatetemperatureand(d)secondintermediatetemperatureofNi1−xZnxFe2O4(x=1)nanoparticles.

Ni1−xZnxFe2O4(x=1)nanoparticlesgassensorforallgasesisingoodagreementwithBangaleetal.[2].ThesensitivityatloweroperatingtemperatureofNi1−xZnxFe2O4(x=1)gassensorisproba-blyduetoitslargerspecificsurfaceareaandhighersurfaceactivity,whichresultsinstrongerinteractionbetweenthetestedgasesandthesensingmaterialsurface.

Sensitivity(%)asafunctionoftemperatureforchlorinegasofNi1−xZnxFe2O4(x=1)nanoparticlesisdepictedinFig.5(b).FromFig.5(a)and(b),itwasobservedthatsensitivity(%)ismuchhigheratalltemperatureforchlorinegasthanothergases.Atsecondintermediatetemperaturethisvaluereaches85.8%forchlorinegas.Therefore,itcanbeconcludedthat,chlorinegasismorereactiveonthesurfaceoftheNi1−xZnxFe2O4(x=1)nanoparticles[11].

Sensitivity(%)asafunctionofflowrateofNi1−xZnxFe2O4(x=1)fordifferentgasesat(c)firstintermediatetemperatureand(d)sec-ondintermediatetemperatureisshowninFig.5.ItwasobservedfromFig.5(c)thatsensitivity(%)increaseslinearlyupto200ppmflowrateincaseofchlorineandammoniagas.Furtherincreaseintheflowrate,sensitivity(%)becomessaturateforbothgases.ItwasalsoobservedfromFig.5(c)thatsensitivity(%)increasesalmostlinearlyasflowrateincreasesincaseofLPGandethanolgas.FromFig.5(d),itcanbeobservedthatsensitivity(%)increasesasflowrateincreaseslinearlyupto160and140ppmforchlorineandethanolrespectively.Furtherincreaseinflowrateupto200ppm,sensitiv-ity(%)increasesveryfastandshowsadeviationfromlinearityandbecomessaturatedathigherflowratesforboththegases.IncaseofammoniaandLPG,itwasalsoobservedfromFig.5(d)thatthesensitivity(%)increaseslinearlyasflowrateincreases.

Theobservationoftwointermediatetemperaturesforthesesensorscanbeexplainedonthebasisoftheadsorptionbehavioranditsdependenceonthestructureofthenanoparticles.Thegas-sensingmechanisminbasedonthechangesintheadsorbanceofatmosphericoxygenanditsdesorptioninpresenceofthegasbeingsensed.

adsorptionsite,andoperatingtemperatureofthesensor.ZnFe2O4possessesnormalspinelstructure[AtetraB2octaO4][4],inwhichZnionsoccupyA-tetrahedralsiteandFeionsoccupyB-octahedralsite.ApossibleexplanationfortheoccurrenceoftwosensitivitypeaksmaybeaccountedforbyinvokingtwopossibleadsorptionpathwaysfortheAandBsites.Therefore,twointermediatetem-peratureswillbeobtainedinZnFe2O4nanoparticlesbasedsensors.OnthecontrarysinceNiFe2O4possessesinversespinelstructure[Btetra(AB)octaO4]inwhichFeionsoccupybothsites(A-tetrahedralandB-octahedral)andNiionoccupyonlyB-octahedralsites.Suchasiteoccupancyintheinversespinelstructuremayleadtoonlyoneadsorptionpathway.ItisnoteworthythatNi50Zn50Fe2O4alsoshowstwointermediatetemperaturesduetomixed(normalandinverse)spinelstructure[4].

4.Conclusions

O2(gas)⇒O2ad

Ni1−xZnxFe2O4gassensoratcompositionx=0,0.5and1havebeenemployedforLPG,ethanol,ammoniaandchlorinegas.Atx=0,sensitivity(%)ofNiFe2O4gassensorwasfoundinthefollowingorderethanol>ammonia>LPG>chlorineatalltemperature.Sensi-tivity(%)forthesegasesare77.5%,74.9%,51%and26%respectively.Forcompositionx=0.5,on50%substitutionofZn+2ionsintheNiFe2O4nanoparticles,sensitivity(%)reachesmaximumvalueattwointermediatetemperaturesduetothemixedeffectofNiFe2O4andZnFe2O4nanoparticles.Sensitivity(%)followsanorderammo-nia>LPG>chlorine>ethanolatfirstintermediatetemperatureandammonia>ethanol>LPG>chlorineatsecondintermediatetem-perature.Inbothcasesammoniagaswasfoundtobemostsensitive.

Forcompositionx=1,sensitivity(%)ofZnFe2O4isintheorderofchlorine>ammonia>ethanol>LPGforfirstintermediatetempera-tureandforsecondintermediatetemperaturethisorderchangestochlorine>ethanol>ammonia>LPG.

FromabovementionedresultsitcanbeconcludedthatNi1−xZnxFe2O4withcompositionx=0,0.5and1areverygoodsen-sorforethanol,ammoniaandchlorinegasesrespectively.

O2ad⇒O−ad

Acknowledgement

AuthorswouldliketothankDr.DhirendraK.GuptaforExperi-mentalarrangementforgassensingproperties.

O−ad⇒2O−ad

2O

−

ad

⇒2O

2−

ad

Theinletgashelpsindesorptionoftheoxygenbyreleasingtheelectronandthuschangingthecarrierconductanceofthesensor.Theamountofthesurfaceadsorbedoxygenandhencetheinletgaswilldependontheparticlesize,specificarea,natureofthe

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Biographies

DeepshikhaRathorereceivedherM.Sc.inPhysicsfromDr.HariSinghGourUni-versity,Sagarin2006andM.Tech.inMaterialsSciencefromBarkatullahUniversity,Bhopalin2008.ShehassubmittedherPh.D.thesisinOctober2012.AtpresentsheisAssistantProfessorinDepartmentofPhysics,MaulanaAzadNationalInstituteofTechnology(MANIT),Bhopal.Hercurrentresearchinterestinvolvessemiconduc-torgassensor,PropertiesofMagneticNanoparticles,SpintronicandSemiconductorDevices.

RajnishKurchaniareceivedhisM.Sc.inPhysicsfromBarkatullahUniversity,Bhopalin1991.HereceivedhisPh.D.inMaterialsSciencefromUniversityofLeeds,Leeds(UK)in1998.PresentlyheisAssociateProfessorinDepartmentofPhysicsatMANIT,Bhopal,India.HeisrecipientofUKIERI-ThematicPartnership,RoyalAcademyofEngineering:ResearchExchangeAwardwiththeUniversityofBath,UKandalsoarecipientoftheOverseasResearchStudentAwardfromtheCommitteeofVice-ChancellorsandPrincipalsoftheUniversitiesoftheUK.HeisalifememberoftheMRSI,ISTEandmemberoftheIOM3.HisresearchinterestincludesFunctionalMaterials,ThinFilms,SolarPhotovoltaics.

R.K.PandeyreceivedPh.D.inPhysicsfromRavishankarUniversity,Raipur.HewasappointedasProfessorofPhysicsin1994andthenDirectorofUniversityInstituteofTechnology,BarkatullahUniversity,Bhopal,India.HewastheViceChancellorofITMUniversity,Gwalior,Indiain2011–2012.Presentlyheisservingaspresi-dentofNIITUniversity,Neemrana,Rajasthan,India.Hehaspublishedonereview,over80originalresearchpapersininternationaljournalofrepute,co-authoredabookforMarcelDekker,USA.HisresearchinterestsareinthefieldofNanoscienceandtechnology,SemiconductorDevices,SolarCells,Thin/ThickfilmTechnologyandMaterialsScience.