SynthesisofCadmiumSulfideNanoparticlesAdaptedbyKayleenMooreandThomasC.Keane,Ph.D

April20,2008

I.AbstractThisexperimentisanintroductorystudyofCadmiumsulfidenanoparticles.The

Cadmiumsulfidenanoparticlesareinversephasemicelles.2Micellesareanaggregateofsurfactantmoleculesdispersedinaliquidcolloid1,andareusedinawidevarietyofdifferentbiochemicalandindustrialapplications.Specifically,thislabstudiestheshiftintheabsorptionspectrumfromthebulksampleofCdStothemicelleCdSabsorptionspectrum.Thisshiftinabsorptioncan aidincalculatingthemicelleradius.Theexperimentallyobtainedaverageshiftis71nm.Usingthisaveragethemicelleradiuswasfoundtobe2.15nm.

II.LearningObjectives1) InterpretUVVisabsorptionspectra2) ApplytheconceptofpolaritytoMicelleformation

III.IntroductionAmicelleisanaggregateofsurfactantmoleculesdispersedinaliquidcolloid.

Surfactantmoleculesareorganiccompoundsthatareamphiphilic.Amphiphilicmeansthattheyhavebothapolar(hydrophilic)endandanonpolar(hydrophobic)end.Throughthisunderstandingamicellecanbedefinedasananoparticleofanorganizedorganicmoleculeinaparticularsolvent.

Inthesynthesisofcadmium sulfide(CdS)nanoparticleswewillbeusinghexadecyltrimethylammoniumbromideasthesurfactantmolecule.Thismoleculedoesnotdissolvewellinaqueousororganicsolvents,butitisessentialinmakingthemicelle.Thehexadecyltrimethylammoniumbromidestructureisshownbelow:

Therearedifferenttypesofmicellephases.Thetwophasesthatwillbefocusedonarethenormalandinversecylindricalphases.Thenormalphasemicelleisproducedwhenitisinapolarsolutionandthepolarendofthesurfactantisattractedtothepolarsolvent.Thehydrophobicnonpolarhydrocarbonsformthecoreofthemicelle,andthepolarendofthesurfactantformstheouterlayerofthemicelle.Thisisalsoknownastheoilinwatermicelle.Theinversecylindricalphaseisformedinjusttheoppositeenvironment.Thesolventisnonpolar.Inthiswaythehydrocarbonsmaketheouterlayerandthepolarendmakesthecoreofthemicelle.Thisisknownasthewaterinoilmicelle.

Hydrophilic

Hydrophobic Hydrophobic

Hydrophilic

OrganicSolventAqueousSolvent

Inordertoformthecadmiumsulfidemicelles,hexadecyltrimethylammoniumbromidewillbemixedwithpentanolinahexanesolution.Pentanolisacosurfactantthathastwomainfunctions.Thefirstfunctionofpentanolisthatinrelativeamountsitcontrolsthesizeof themicelles.PentanolisalsousedasacappingagenttostabilizetheCdSparticles.

Cd+micellesaremadeandmixedwithSmicelleswhichproduceCdSparticles.CdSisfoundinthecoreofthemicelle.Theaqueoussolutionservesasananoreactorandtheparticlescannotgrowbiggerthanthemicelle.Thisphenomenonhasaneffectonthequantumsizeofthemicelle.SincethereisadifferenceinsizefromthebulkCdSandthemicelletheabsorptionspectrumcanbetakenforeachandthancompared.Therewillbeashiftofwavelengthbasedonsize.ThischangeinwavelengthcanbecalculatedandusedtofindtheradiusoftheCdSmicelle.Anexampleoftheshiftphenomenonandequationisshownbelow.

bulk=512nmEg=hc/

Thexinterceptofthelinearportionoftheabsorbanceasafunctionofwavelengthgraphisameasureof Eg.

ExampleCalculation

r=2.34nm

IV.Materials*0.012MCdCl2(0.110gin50mLdistilledwater)*0.012MNa2S(0.144gin50mLdistilledwater)0.20ghexadecyltrimethylammoniumbromide4mLHeptane1mLPentanolMortarandpestle2testtubes

e=1.60x1019C0=8.85x10

12

C2/N/m2

=5.7h=6.63x1034Jsc=2.998x108m/sme*=1.73x10

31kgmh*=7.29x10

31kg

nano=495nmEgnano=hc/Egnano=(6.63E34)(3.0E8)/495E9m

Egnano=4.018E19J

bulk=550nmEgbulk=hc/Egbulk=(6.63E34)(3.0E8)/550E9m

Egbulk=3.616E19J

2smallmagneticstirbarsMagneticStirrerPlasticCuvettsVolumetircpipets,11mL,25mL

*premade

V.Procedure

1) TurnontheUVVis,andconnectittothecomputer.Itwilltakealittletime.Goontotheothersteps.

2) Obtainedabout5mleachoftheCdCl2solutionandtheNa2Ssolutioninseparate,smallvials.

3) TestthereagentsCdCl2andNa2Sbyaddingadropofeachtogether.IfayellowcolorappearsthisshowsthattheNa2Ssolutionisgood.Ifthemixturestaysclear,remaketheNa2Ssolution.

4) ReturningbacktotheUVVis,itshouldbeconnected.Takeabaseline.5) Placeequalamountsof CdCl2andNa2Sintoacuvet,mixgentlywithpipet(do

notmakebubbles).Immediatelyobtain avisibleabsorptionspectrum,usinganemptycuvetastheblank.Visuallynote thechangeincolorbeforeandafteraddingtheNa2S totheCdCl2.

6) Setuptwocleantesttubesover twoseparate magneticstirrers.7) Place0.20gofhexadecyltrimethylammoniumbromidetotesttube one.Adda

smallstirbartoeachtesttube.8) Add4.0mLofHeptaneand1.0mLof1Pentanolintotesttubeone.Note:

Rememberthattheamountofpentanolisthecappingagentandchangesthesizeofthemicelle.Makesurethat thepentanoldoesntgetstuckonthesideofthetesttube.Stirtogiveasuspension.

9) Withvolumetricpipettransferalittleover2.5mLofthesuspensionintothesecondtesttube.

10) Totesttubeone,add0.1mL(3drops)of0.012Mof CdCl2.Addthesolutiondropwiseuntilthesuspensioninthetesttubeclears,dontaddmorethan3drops.

11) Add0.1mL(3drops)of0.012MNa2S totesttube2.Addthesolutiondropwiseuntilthesuspensioninthetesttubeclears.IFTHESOLUTIONCLEARSBEFOREADDINGALLTHREEDROPSDONTADDMORE.

12) Placethesolutionfromtesttubetwointotesttubeone.Solutioncouldeitherhavealightyellowhueorbeclear.

13) Recordthevisibleabsorptionspectrumin eitheraglassorplasticcuvet.

VI.Questions

1) Whatisamicelle?Stateitinyourownwords.Drawadiagramandlabelitsparts.

2) Whatisthedifferencebetweenanormalandreversephasemicelle?WhatmicellephasedoestheCadmiumSulfidenanoparticleforminto?

3) Whatpartdoespentanolplayinformingthemicelle?

4) Whattwochangesoccurbetweenin theabsorptionspectraof theCdSsolutionandtheCdSmicelles?Talkaboutthedifferenceinabsorbanceandshiftinwavelength.

5) Whentheformationofthemicellehasoccurred, whereisthelocationoftheCdSsalt? Whatistheothersaltbyproductthatisformed?

6) Iftherewasashiftintheabsorptionspectrafrom575cm1to480cm1,wouldthemicellebesmallerorbiggerthantheoriginalsample?

7) Whataretwopracticalusesformicelles?

8) Whatwastheradiusofyourmicelle

VII. References

ImagesofNormalandInversePhaseMicelles.(2007).RetrievedApril19,2008.Website:http://en.wikipedia.org/wiki/Micelle

Linsensky,GeorgeandHansen,Paul.(2005).SynthesisofCadmiumSulfideNanoparticle.RetrievedonMarch24,2008.Website:http://mrsec.wisc.edu/Edetc/nanolab/CdS/text.htm

PremadeMaterials

0.012MNa2Ssolution1. Weighout0.144gofthepowderNa2S,placeinamortorandgrindintoafind

powder.2. PlacethepowderedNa2Sina50mLgraduatedflaskandfillitwiththedeionized

watertothemark.

0.012MCdCl2solution

1. Weighout0.110gofCdCl2 intoa50mlgraduatedflask,andfilltheflaskuptotheline.Swirlmixtureuntilallthedissolves.

VIII. Answers

1) Amicelleisclustersof organizedsurfactant, organiccompoundsthathaveapolarandnonpolarhead,thatform inaheterogeneousmixture.Maindefinition:Amicelleisanaggregate ofsurfactantmoleculesdispersedinaliquidcolloid.

2) A)Normalphase:Thepolarregionisincontactwiththesolvent.(Polarhead,Polarsolvent)B)Reversephase:Thenonpolarchainregionisincontactwiththesolvent.(Nonpolarchain,Nonpolarsolvent)CdSmicellesarereversephase.

3) Thepentanolcontrolsthesizeofthemicelle,italsoactsasacappingagenttostabilizetheCdSparticles.

4) Absorbance:InthesolutiontheCdSisdiluteinthemicellesolution.Shift:Thesizeoftheparticlesdeterminestheshiftinwavelength.

5) A)CdSislocatedinthecoreofthemicelle.B)NaCl.6) Smaller7) AnswerDependant8) Basedoffofdata.

IX.ConclusionsandPlacement

Thislabisveryinteresting,butnotforgeneralchemistrystudents.Thereissomedifficultyincreatingthemicellesandthecalculationmightbealittledifficulttounderstand.Thesuspensionsinthetesttubeswillnotalwaysclear,butwillstillformmicellesthathavetheappropriateabsorptionshift.Thislabmightbegoodforanalyticalchemistrybecauseitisdealingwithabsorption,concentrationandpH,butdoesntfocusontitration.Thiswillgivethestudentsabreakfromtitration,butleadstothesametypesofconcepts.Furthercalculationscanbedoneontheconcentrationofmicellesbasedoffofabsorption(BeersLaw).Applicationsofmicellescanalsobediscussed(forexampleinbiochemistryandindustry)duringanalyticalchemistrytomakethetopicinterdisciplinary.Theabsorptionspectraareinthelaboratorynotebook.

Chemicals

CdO

OleicAcid

Selenium

Trioctylphosphine

TechnicalGradeOctadecene(ODE)

SupplyListfor10Students

100Smalltesttubes

10Testtuberacks

10tubesforice(bigenoughtofitthetesttuberackinto)

Ice

10Heatingmantles

10Variacs

10Thermometerscapableofmeasuring225oC

10Roundbottomflasks(each)

10ml 25ml

10Syringes(capableofdelivering0.4ml)andmediumsizeneedle(10cmlong).

10GlassPipettes

10Volumetricpipettes(each)

1ml graduated1mltodeliver0.6ml 10ml 5ml