论文英文模板范文

论文英文模板范文论文英文模板范文 Effect of different surfactantson the morphologies of CoSb3nanocrystals synthesized with solvothermal methods DingxuHu1 Fang Wu1 Rutao Li1 Xing Hu1 Zhengzhou University Zhengzhou450052 Abstract Thermoelectric CoSb3nanocrystals withvarious morphologies such asquasi ellipsoid plate shaped flower like cube andspheripol clusters were obtainedthrough asurfactant directed growthprocess withsolvothermal methods Effect of different surfactants such asSodium dodecyl benzene sulfonate SDBS polyvinyl pyrrolidone PVP Ethylene Diamine Tetraacetic Acid EDTA or Cetyltrimethyl Ammonium Bromide CTAB as wellas differentprecursors Co NO3 2 6H2O andK SbO C4H4O6 1 2H2O on themorphologies of CoSb3nanocrystals wereinvestigated The shapes and sizesof the obtained powders were observedby scanning electron microscopy SEM and thephase of the powders were characterizedby X ray diffraction XRD The resultsrevealed thatsurfactants hadsignificantly effecton themorphologies of theobtainedproducts A possiblemechanism wasproposed to aount for the formation of CoSb3nanocrystals obtainedwith PVPsurfactant Keywords skutterudite CoSb3 nanocrystals solv othermal surfactant1Introduction Theproblem of the energycrisis andenvironment isof considerablerelevance toenergy generation and conversion Novel thermoelectric TE materials havepromising applicationin powergenerator andcooling deviceas theycan directlyconvert thermalenergy intoelectrical energythrough theSeebeck effect 1 Compared withconventional coolingand energy generation systems thermoelectric deviceshave many advantages such assmall lightweight quiet and nomajor pollution Unfortunately TE materialshave notbeen verywidely useddue tolow efficiency The thermoelectricefficiency isproportional to the valueof thenon dimensional figure of merit ZT S2 T where Sis Seebeckcoefficient T the average absolutetemperature of the hotand coldsides the electricalconductivity and the totalthermal conductivitywhich is the sumof thecontributions fromboth the crystal lattice l and thecharge carrier e From this it isobvious thata largeS and as wellas asmall are desirable 2 3 4 The bestTE materialis supposedto possessthermal properties similar to that of amorphous solidswith lowthermal conductivitiesbut alsohave electricalpropertiessimilartothatofasingle crystalwith ahigh electricalpower factorS2 4 Among agreat manyof TE materials researched skutterudite poundshave beenregarded as a kindof promisingTEmaterialsbecause the crystalline systemspossess glass like thermalproperties which isapproximate to the criteriaof theabove concept The binary skutterudites can be representedby ageneral formula MX3 M Co Rh Ir X P As Sb as shown in Figure1 and theyhave ab structure with spacegroup Im3with eightMX3formula unitsin theprimitive celland theirunit cellhas32atoms 5 10 the typicalcharacteristic of this structureistheexistence oftwo interstitialvoids in the crystallattice Of differenttypes of the binaryskutterudite pounds CoSb3has beenbeing thefocal pointof moderndiscussion andresearch dueto itsexcellent electricalconductivity andlarge Seebeckcoefficient However the thermal conductivity of CoSb3is toohigh tomake itto bean efficientthermoelectric material In orderto lowerits thermalconductivity two effectiveapproaches have been supposed The firstapproach is to fillthe voidsof thestructurewithforeign atomssuch asrare earth metals 8 9 11 or alkalineearth metals 12 13 acting asphonon rattlers The rattling of thefilled atomscan effectivelyscatter phonons with theresult that the latticethermalconductivityof the skutterudite poundswas significantlyreduced Another approachisto form nanostructuredskutterudite whichcan providehigh concentrationof grainboundaries ina bulk resulting inlower thermalconductivity and a largerfigureofmeritZT 2 6 14 Nanostructured skutteruditeare generallysynthetized by the solvothermalmethod There aremanyadvantagesof thismethod such aslow reaction temperature low cost large scale production and the size and the shape of theproducts canbe controlledwith different surfactants 5 The purposeofthisarticle isto synthetizelow dimensional structured CoSb3nanocrystals withvarious morphologiesvia solvothermalsynthesis method The effectofdifferentadditives such asCTAB EDTA SDBS andPVP on theparticle size dispersion and surface morphology isdiscussed in particularly the effectof addition of PVP on thesurfacemorphologyand thepossible growthmechanism arediscussed indetail These resultswill beexpected toput forwardthe greatinfluence of the optimizationof ZT void spaceMXFig 1 The crystalstructure ofbinaryskutteruditeMX3 M Co Rh Ir X P As Sb 2Experimental2 1Synthesis ofnanosized CoSb3Analytically pureCo NO3 2 6H2O andK SbO C4H4O6 1 2H2O ina molarratio of1 3were usedas the precursors withoutfurther purification The precursorswere placedin FDK 1Cr18Ni9Ti magicrotation autoclave which was then filledwith deionized water upto40 of itsvolum 1000ml 2 0g sodium dodecyl benzene sulfonate SDBS or polyvinyl pyrrolidone PVP or Ethylene Diamine Tetraacetic Acid EDTA or Cetyltrimethyl Ammonium Bromide CTAB was addedas surfactants 15 0g NaOHwas usedas thePH value controller andasufficient amountof NaBH4as areducing agentwas graduallyadded into the autoclaveunder vigorously stirring withglass stirring rod forabout2min and the colourof thesolution turnedgray blackwithin onlya fewminutes Then the autoclavewas sealedand thenheated to290 C undervigorouslystirringwith magicstirringrodat therotate rateof about150r min holding atthis temperaturefor4days When the reaction finished the autoclavewas cooleddown toroom temperaturenaturally whereby grayblack powderswould precipitateform thesolution The resultingproduct wassucked througha strawto drawup from the insidebody of the autoclave and thenfiltered out washed severaltimes withdeionizedwater absolute ethylalcohol 99 7 and acetoneand finallyvacuum driedat100 C for6h The CoSb3samples producedwith SDBS PVP EDTA and CTABare termedas CoSb3 SDBS CoSb3 PVP CoSb3 EDTA andCoSb3 CTAB respectively 2 2Characterization ofSamples Thephase structure of thepowderswereinvestigated byX ray diffractometer XRD using anX Pert Prodiffractometer withCu Ka radiation 0 15406nm in the range of2 10 85 The crystalparameters werecalculated througha least square methodfrom XRDdate The shapeand sizeof thepowderswereanalyzed usinga field emission scanningelectron microscopy FESEM onaJSM 6700F microscope JEM JEOL Tokyo Japan 3Results anddiscussion3 1X ray DiffractionFigure2shows theXRD patternsof the CoSb3powers synthesizedbythesolvothermalmethodwith surfaceactive agents Almost allthe reflectionsof the patterns canbe wellindexed to the binaryskutterudite type CoSb3with cubicphase PDF No 01 047 1769 the latticeconstant ofa 9 04nm and spacegroup Im3 204 There areno remarkablediffraction peaks of other phases from thepatterns which demonstratethat therelatively pure CoSb3has beenobtained underthereactionconditions forall samples The possiblereaction processforthe formation of CoSb3in the sodium hydroxide solution isproposed andcanbeexpressed asthe followingionic equationsand chemicalequations 1 15 4Co2 BH4 8OH 4Co BO2 6H2O 1 2SbO BH4 2OH Sb BO2 H2O 2 Co Sb CoSb 3 CoSb2 Sb CoSb3 4 20304050607080543633136622532600530431422332420330123013 220211200Intensity a u 2Theta degree a b c d CoSb2Fig 2 XRD patternsof CoSb3samples solvothermallysynthesized at290 C for4days a synthesized with CTAB b synthesized with SDBS c synthesized with PVP d synthesized with EDTAThe reductionofCoand Sbatoms shouldbe carriedout veryquickly viathe reactions 1 and 2 asaresult of the strongreducing effectof NaBH4 The standardelectric potentialin aqueoussolution forSbO Sb andCo2 Co are0 212V and 0 28V respectively For thisreason the reductionof Sb ions in the sodiumhydroxide solutionis supposedto bemuch easierthan thatofCoions resulting in the mostSbionsfirstly reducedtoformparticles 10 Compared toother reportedwork aboutthe CoSb3powers preparedin hydrothermalsynthesis 1 5 16 17 18 theprecursors the solvent reactiontemperatureand timewere differentin thisD Program Files 有道 Dict resultui queryresult html experiment Some weakpeaksofotherphasesappear maybe attributed to thedegree ofreaction orionic bindingselectivity in thesodiumhydroxidesolution As forthecrystalfaces 220 in Fig 1 a and1 d the peaksare muchmore enhancedprobably duetotherelatively fastgrowth inthecrystalorientation with the help of additionof CTABor EDTA Some informationon particleshapes andsizes canbe obtained fromthefollowing SEManalysis performedon theas obtained powders 3 2SEM observationFig 3shows the SEM image of theCoSb3nanoparticles preparedwith additivesas structure forming agentsand grainsize controller Fig 3a 3eand3f showstheSEM imageof the samplesynthesized withSDBS EDTA andCTAB respectively Compared totheCoSb3sample withoutany surfactants 5 these productssynthesized withdifferentsurfactantsshow areduced particlesize inthe rangeof10nm The quasi ellipsoid particleswere formedsynthesized inthe presence of thesurfactant SDBSas shownin Fig 3a The SEM image in Fig 3e showsthe morphology of theCoSb3 EDTA samplesynthesizedwithEDTA The powdersreveal theparticles similartoacube with thesizeof about40 60nm Sample obtainedwith CTAB Fig 3f forms thegranule appearedastheshapeofa ball withthesize intherangeof20 50nm Fig 3b presentsa typicalSEMimageof CoSb3 PVP consisting oftwo differentmorphologies withflower like morphologyand plate shaped particles The resultshavebeenconfirmed inFig 3c andd representing two different placesofthesame CoSb3 PVP sample One ofthem hasa micron scale flower like morphology with athickness ofabout10 20nm Fig 3c andtheother revealthe crystalsgrow inlamellar shape Fig 3d The resultsare likelyattributedtothe PVP molecules which areeasily dissolvedinthesolution andpossess strongbinding ability The molecularstructureofPVP isas showninFig 4 As canbe seenfromthechart the Nand Oatoms existinginthePVP moleculeswill bineon theirsurface 19 Some CoSb3nuclei formatthesecond stageand thengrow along thea b plane The growthof thesecrystal nucleusesalong thea b planeis fasterthan thatalongthec axis andends upwith nanoflakemorphology These nanoflakesget closerto eachother underthe movementofthePVP moleculesintheform ofangle deformation and thenthe flower like clusterswere obtained Fig 5 While theother partof CoSb3nuclei formedin thisorder first formingcrystalline grain then graingrowth andfinally withthe helpofPVPmolecules aggregation intheformofthelamellar structureto reducesurface energy Fig 6 Fig 3SEMimageoftheCoSb3powders preparedwith additives a CoSb3 SDBS synthesizedwithSDBS b c anddCoSb3 PVP synthesizedwithPVP eCoSb3 EDTA synthesizedwithEDTA fCoSb3 CTAB synthesizedwithCTAB All theresults aboveobtainedfromfield emissionscanningelectronmicroscope indicatethat differentmorphologiesof CoSb3are relatedtothetype ofsurfactants Through theabove experimentalresults we knowthat thesurfactant iscrucial forthe formationofdifferentshapesandsizes It isworth notingthat withthehelpofthePVP surfactant hydrothermaltreatment twodifferentmorphologies wereobtained asshowninFig 3b 3c and3d which aredifferent fromthe workof LathaKumari 5 The differencesare attributedtothedifferent reactionconditions suchas temperature time reactant PH valueand solvent Although themechanism isnot clearbetween theCoSb3raw materialandthesurfactant under hydrothermal conditions we presumeit maybe attributedtothetemplate functionofthesurfactant Fig 4The structureofthepolyvinyl pyrrolidone PVP Fig 5The simpleschematic illustrationsoftheformation mechanism of flower like morphologyFig 6The simpleschematic illustrationsoftheformation mechanismof plate shaped morphology4 Conclusions Inconclusion the skutteruditeCoSb3nanoparticles havebeen synthesizedonalarge scaleunderhydrothermalconditions withadditives The surfactantsnot onlyprovide amicroenvironment forthe growthofCoSb3nanoparticles butalso playa templaterole fordirecting theformationofvarious morphologies Spheripol cube quasi ellipsoid plate shaped particlesand flower like clusters The growthmechanismofCoSb3inthepresenceofPVP insolution hasbeen discussedin moredetail It wasfound fromour experimentsthat theadditionofsurfactants havesignificant effectsonthemor