Preparation and characterization of hexagonal SrMnO3 nanofibers by electrospinning

Zhu Hua, Zhong Xin

(School of Chemistry and Chemical Engineering, Sichuan University of Arts and Science, Dazhou 635000)

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Preparation and characterization of hexagonal SrMnO3nanofibers by electrospinning

Zhu Hua, Zhong Xin

(School of Chemistry and Chemical Engineering, Sichuan University of Arts and Science, Dazhou 635000)

SrMnO3/polyvinylpyrrolidone(PVP)compositenanofibershavebeenpreparedsuccessfullybyelectrospinningprocessfromstrontium(Ⅱ)nitrateandmanganese(Ⅱ)acetatetetrahydrate.ThehexagonalSrMnO3nanofiberswasobtainedaftercalcinationat800 ℃for3h.TheeffectofPVPconcentrationonthefiberstructurewasinvestigated.Thestructureandpropertiesofnanofiberswerecharacterized.TheresultsshowedthatSrMnO3/PVPcompositenanofibersbecameuniformandthebeadedstructuredisappearedwhenthemassfractionofPVPreached8%;PVPcompletelydecomposedandallthefeedstockstransformedintoSrMnO3duringthecalcinationat700 ℃,thusagoodpurityhexagonalSrMnO3fiberof150-200nminthediameterwereobtained.

strontiummanganate;polyvinylpyrrolidone;electrospinning;calcination;nanofibers

Electrospinningtechniquehasbeenactivelyexploitedasasimpleandversatilemethodforgeneratingcontinuousnanofiberswhichhashighporousstructure,lowdensityandhighspecificsurfacearea[1-3].DuetothespecialskeletalstructurewhichwasconsistedofathreedimensionalnetworkofMnO6octahedra,strontiummanganate(SrMnO3)hassomepropertiessuchaselectronicproperties,thermochromism,thermalconductivity,magneticproperty,etc[4].Recently,themixtureofinorganicandorganicsaltsdissolvinginpolyvinylpyrrolidone(PVP)asstartingmaterials,inorganic-polymericfibershavepreparedbyelectrospinning.Theinorganic-polymericfiberswouldtransformintonanofibersbysubsequentcalcinationsathightemperature.Asfarasweknow,thepreparationofSrMnO3nanofibershasneverbeenreported.HerewereportthepreparedofSrMnO3nanofibersviaelectrospinningcombinedwithsol-gelprocess,andthepropertieswerecharacterizedforitsfutureapplications.

1　Experimental

Strontium(Ⅱ)nitrateandmanganese(Ⅱ)acetatetetrahydratewereusedastherawmaterialsforthepreparationofSrMnO3nanofibers.PVPwiththerelativemolecularmassof1.3×106wasusedasaviscosity-controllingagent.Asolutionwaspreparedbydissolving4mmolstrontium(Ⅱ)nitrateand4mmolmanganese(Ⅱ)acetatetetrahydratein3mLdemonizedwater,whichwasaddedwithacertainamountofPVPdissolvingin11mLethanolaqueous,stirringfor12hatroomtemperature.Thenthehomogeneoushybridsolwasobtained.Theaboveprecursorsolwasloadedina20mLplasticsyringeof25gaugeswithstainlesssteelneedle.Thedistancebetweenthespinneretandcollectorwasfixedas10cmandthehigh-voltagesupplywasmaintainedat15kV.Thespinningratewascontrolledat1.5mL/h.SrMnO3/PVPcompositenanofiberswascollectedonthecollector.Thesefiberswerecalcinatedatarateof2 ℃/minandremainedinairatmospherefor3hat800 ℃.ThushexagonalSrMnO3nanofiberswereobtained.

TheX-raydiffraction(XRD)patternsweremeasuredonaRigakuGeigerfluxinstrument.ThesizeandmorphologyofSrMnO3fiberswereobservedwithJEOLJSM-6390scanningelectronmicroscope(SEM).EnergydispersiveX-ray(EDX)spectrographwasrecordedonINCA200EDSattachedwithSEMtostudythephasepurityofSrMnO3nanofibersthroughtheelementalanalysis.Thermogravimetric(TG)analysiswascarriedoutonaTAQ50thermogravimetricanalyzerinnitrogenatmosphere,andthetemperature-risingratewas10 ℃/min.Fouriertransformationinfrared(FTIR)spectroscopywasrecordedonaPerkinElmerspectrum100.

2　Results and discussion

2.1SEMandEDXanalysis

Fig.1showsthattheconcentrationofPVPhasasignificanteffectontheformation,uniformityandhomogeneityofnanofibers.Thesizeandmorphologyhasmarkeddifferenceunderdifferentconcentrations.Non-uniformfiberswithbeadedstructureareformedwhenthemassfractionofPVPwasbelow6%.WiththeincreaseofPVPconcentration,thesurfacetensionandviscosityarecorrespondinglyincreased,theresistanceairflowtensileforceandstaticelectricityarealsoincreasedintheelectrospinningprocess,andthestructureoftheobtainedfibersbecomeuniform.ThebeadedstructuredisappearsandthefibersbecomeuniformatthePVPmassfractionof8%.Therandomlyorientedhybridfiberswithsmoothsurfaceandaveragediameterof300-400nmcanbeobservedasthemassfractionofPVPwas10%.TheobtainedfiberismoreuniformthanthatoflowPVPconcentration.Theresultsarewellconsistentwiththepublishedliterature[5].

AsFig.2ashown,thefibrousstructureisretainedonthewholeexceptthatasmallamountoffibersarebrokenafterannealingat800 ℃.Andtheaveragediameterisreducedto150-200nmduetotheevaporationanddecompositionofPVPandvolatilecomponents.ThefiberssurfacebecomesroughbecauseofthedecompositionofPVPandtheformationofcrystallites.SrMnO3nucleialsogrowtoformlargernanoparticles.AsFig.2bshown,allpeaksarecorrespondingtoSr,MnandO,exceptAupeak(Auissprayedontothenanofibersbeforescanninginordertogethighqualitymorphologyimages).TheresultshowsthattheSrMnO3nanofibersholdgoodpurityafterremovalofPVP.

Fig.2　SEM images and EDX pattern of SrMnO3 nanofibers

2.2XRDanalysis

AsindicatedinFig.3,strongpeaksareobservedat2θof32.84°associatedwith(110)planes.Othermaindiffractionpeaksat2θof27.22°, 35.19°, 43.19°, 48.90°, 58.62°, 60.17°and68.87°areassignedtothediffractionof(102), (103), (202), (203), (300), (213)and(220)crystalfacets,respectively.AlldiffractionpeaksshowgoodconsistencywithJCPDSCardNo.24—1213ofperovskitephaseofSrMnO3[6].Asinglehexagonalperovskitesystemwasdetermined.NotypicalpeakofpolymerisobservedinFig.3,indicatingthatPVPwasdecomposedandremovedafterannealingat800 ℃.

Fig.3　XRD patterns of SrMnO3 nanofibers

2.3Thermogravimetricanalysis

AsshowninFig.4,theweightlossprocesshas3stages.Theweightlossis11.4 %atthefirststagebelow120 ℃,whichwascausedbythelossofsurfaceadsorbatesandresidualmoisture[7];theweightlossof35.5%over250-400 ℃isduetothedecompositionoforganiccontents(PVP)[5];similarly,theweightlossof33.7%over400-700 ℃isduetothedecompositionoftheorganometallicprecursor(manganeseacetate)andstrontiumnitrate;theweightlossiscompletedbelow700 ℃andthetotalweightlossisabout80.4%;noweightlossisobservedabove700 ℃andtheTGcurvebecomeshorizontal.TheTGcurveindicatesthatSrMnO3fibersamplescanbefabricatedatatemperatureof700 ℃andabove.

Fig.4　TG curve of SrMnO3/PVP composite nanofiber

2.4FTIRspectrometry

AsFig.5shown,forPVP,thebroadbandaround3 200-3 600cm-1correspondstoO—Hstretchingvibration;thetripletpeakspresentat2 954cm-1correspondingtotheasymmetricandsymmetricC—Hstretchingvibrationsofmethylgroups(fromacetate)[8];andtheotherthreedominantpeaksatabout1 654, 1 442and1 292cm-1correspondtothestretchingvibrationofCO,C—HandC—Nbonds,respectively[9].ForSrMnO3/PVPcompositenanofiber,theCOstretchingvibrationcharacteristicpeakred-shiftsto1 652cm-1,theC—Hstretchingvibrationpeaksblue-shiftsto2 956and1 444cm-1,respectively;andthestretchingofC—Nat1 292cm-1isweakened.ForSrMnO3nanofiber,allthePVPpeaksvanish,indicatingthatthePVPwasfulldecomposed,threenewpeaksappearat765, 663, 542cm-1,whichareascribedtothestretchingvibrationofmetal-oxide(M—O)bondsinSrMnO3,matchingwellwiththepublishedliterature[6].TheFTIRresultsareingoodagreementwiththeSEM,XRDandTGresults.

Fig.5　FTIR spectra of PVP and SrMnO3/PVP composite nanofiber and SrMnO3 nanofiber1—PVP；2—SrMnO3/PVP composite nanofiber；3—SrMnO3 nanofiber

3　Conclusions

a.SrMnO3/PVPcompositenanofiberswithadiameterof300-400nmweresuccessfullyfabricatedbyelectrospinningtechniqueandpurehexagonalSrMnO3fiberswithadiameterof150-200nmwerepreparedbytheheattreatmentofSrMnO3/PVPcompositenanofibersat800 ℃ .

b.PVPconcentrationplaysanimportantroleintheformation,uniformityandhomogeneityofnanofibers.ThefiberbecameuniformwhenthePVPmassfractionreached8%.

c.PVPwasdecomposedandremovedfromSrMnO3/PVPcompositefiberaftertheheattreatmentat700 ℃ .

References

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靜電紡絲技術合成SrMnO3納米纖維及結構表征朱華，鐘欣(四川文理學院化學化工學院,四川 達州 635000)摘要:以四水乙酸錳和硝酸鍶為原料，通過靜電紡絲法制備了錳酸鍶(SrMnO3)/聚乙烯吡咯烷酮(PVP)復合納米纖維，在800 ℃下處理3h，得到六方晶形結構的SrMnO3納米纖維，考察了PVP濃度對纖維結構的影響，并對纖維的結構與性能進行了表征。結果表明：PVP質量分數為8%時，SrMnO3/PVP復合纖維表面光滑，均勻性好；熱處理溫度達700 ℃時，SrMnO3/PVP復合纖維中PVP完全分解，原料全部轉化為SrMnO3，所得SrMnO3納米纖維直徑為150～200nm的六方晶形結構，且具有良好的純度。關鍵詞：錳酸鍶聚乙烯吡咯烷酮靜電紡絲法燒結納米纖維

date:10- 06- 2016;reviseddate: 25- 06- 2016.

AppliedBasicResearchProgramsofScienceandTechnologyDepartmentofSichuan(2015JY0254).

TQ343.2Documentcode:AArticleID: 1001- 0041(2016)04- 0058- 03

Biography:HuaZhu(1981-),male,lecturer,beengagedinthestudyoffinechemicals.E-mail：Zhuhua2006@163.com.