Carbon quantum dots applications

362|Chm.Soc.R.,2015,44,362381Thisjournalis©ThRoyalSocityofChmistry2015Citthis:Chm.Soc.R.,2015,44,362CarbonquantumdotsandthirapplicationsShiYingLim,WiShnandZhiqiangGaoFluorscntcarbonnanoparticlsorcarbonquantumdots(CQDs)aranwclassofcarbonnanomatrialsthathamrgdrcntlyandhagarnrdmuchintrstaspotntialcomptitorstoconntionalsmiconductorquantumdots.Inadditiontothircomparablopticalproprtis,CQDshathdsirdadantagsoflowtoxicity,nironmntalfrindlinsslowcostandsimplsynthticrouts.Moror,surfacpassiationandfunctionalizationofCQDsallowforthcontrolofthirphysicochmicalproprtis.Sincthirdiscory,CQDshafoundmanyapplicationsinthfildsofchmicalsnsing,biosnsing,bioimaging,nanomdicin,photocatalysisandlctrocatalysis.ThisarticlriwsthprogrssinthrsarchanddlopmntofCQDswithanmphasisonthirsynthsis,functionalizationandtchnicalapplicationsalongwithsomdiscussiononchallngsandprspctisinthisxcitingandpromisingfild.1.IntroductionThuniquproprtisofcarbonicnanomatrialssuchasnanodiamonds,fullrns,carbonnanotubs,graphnshtsandfluorscntcarbonnanoparticlsorcarbonquantumdots(CQDs)hainspirdxtnsistudisonthmdutothirgratpotntialforawidarityoftchnicalapplications.AmongthlctronicandphysicochmicalcharactristicsofCQDs,thiropticalproprtisandthirfluorscncmissionsinparticularhaattractdincrasingintrstinrcntyars.Formanyyars,smiconductorquantumdotshabnxtnsilyinstigatdforthirstrongandtunablfluorscncmissionproprtis,whichnablthirapplicationsinbiosnsingandbioimaging.Howr,smiconductorquantumdotsposssscrtainlimitationssuchashightoxicitydutothusofhaymtalsinthirproduction.1–3Itisknownthathaymtalsarhighlytoxicnatrlatilylowlls,whichmayproprohibititoanyclinicalstudis.4,5ThispromptdthcrationofCQDstorplacsmiconductorquantumdotsdutothirlowtoxicity,biocompatibility,lowcostandchmicalinrtnssinadditiontohaingsimilarfluorscncproprtis.ThaccidntaldiscoryofCQDsduringthsparationandpurificationofsinglwalldcarbonnanotubs(SWCNTs)byXutal.in2004triggrdsubsquntstudistoxploitthfluorscncproprtisofCQDsandcratanwclassofiablfluorscntnanomatrials.6Fluorscntcarbonnanoparticlsrcidthirnam‘‘carbonquantumdots’’in2006fromSuntal.7whoproposdasynthticrouttoproducCQDswithmuchnhancdfluorscncmissionsiasurfacpassiation.CQDsarsynthsisdbytworouts,namlythtopdownrout7–9andthbottomuprout.3,10–12CQDsartypicallyquasisphricalDpartmntofChmistry,NationalUnirsityofSingapor,Singapor117543.Email:chmgaoz@nus.du.sg;Fax:+6567791691;Tl:+6565163887ShiYingLimMsShiYingLimwasborninSingapor.ShrcidhrBScinChmistryfromthNationalUnirsityofSingaporin2014andiscurrntlyagraduatstudntinthDpartmntofChmistryatthsaminstitution.Hrrsarchfocussoncamrabasdfluorscnccorrlationspctroscopy.WiShnMsWiShnrcidhrBScinChmistryfromZhjiangUnirsityin2011.ShiscurrntlyagraduatstudntinthDpartmntofChmistryNationalUnirsityofSingapor.Hrrsarchintrstsincludbiosnsorsandopticalassaysfornuclicacidsandprotins.Rcid4thAugust2014DOI:10.1039c4cs00269www.rsc.orgcsrChmSocRREVIEWARTICLEPublishdon15Octobr2014.Downloaddon1002201702:32:43.ViwArticlOnlinViwJournal|ViwIssuThisjournalis©ThRoyalSocityofChmistry2015Chm.Soc.R.,2015,44,362381|363nanoparticlscomprisingamorphoustonanocrystallincorswithprdominantlygraphiticorturbostraticcarbon(sp2carbon)orgraphnandgraphnoxidshtsfusdbydiamondliksp3hybridisdcarboninsrtions(Fig.1).13–16OxidisdCQDscontainconsidrablamountsofcarboxylmoitisatthirsurfac.Dpndingonthsynthticrout,thoxygncontntinthoxidisdCQDsrangsfrom5to50%(wight).14AsshowninFig.1,thrarmanycarboxylmoitisonthCQDsurfac,whichimpartxcllntwatrsolubilityandsuitablchmicallyractigroupsforfurthrfunctionalizationandsurfacpassiationwithariousorganic,polymric,inorganicorbiologicalmatrialstoCQDs.Uponsurfacpassiation,thfluorscncproprtisofCQDsarnhancd.Surfacfunctionalizationalsomodifisthirphysicalproprtis,likthirsolubilityinaquousandnonaquoussolnts.Asagroupofnwlymrgdfluorscntnanomatrials,CQDshashowntrmndouspotntialasrsatilnanomatrialsforawidrangofapplications,includingchmicalsnsing,biosnsing,bioimaging,drugdliry,photodynamicthrapy,photocatalysisandlctrocatalysis.Compardtoconntionalsmiconductorquantumdots,thuniquattributsofCQDs,forxamplthirbnignchmicalcomposition,tunablfluorscncmissions,facilfunctionalizationandxcllntphysicochmicalandphotochmicalstability(nonphotoblachingornonphotoblinking),rndrthmryattractifortchnicalapplications.Togthrwithothradantagssuchaslowcostandasofsynthsis,17CQDsarinafaourablpositionforachiingunprcdntdprformanc.Onthothrhand,complxprocdursforthirsparation,purificationandfunctionalization,thirgnrallylowquantumyilds,andambiguityinthirgomtry,compositionandstructurarsomofthissusthatndtobtackldbforthycantrulyoutprformthirsmiconductorquantumdotcountrpartsinaraslikbioimaging,biosnsingandnanomdicin.ThisarticlriwsthprogrssinthrsarchanddlopmntofCQDsandthirtchnicalapplications.WfirstxaminthfluorscncproprtisofCQDsandthirtunablmissions.Thn,wdiscusstharioussynthticapproachsforthirproductionandpossiblsurfacpassiationandfunctionalizationroutstoimpartdsirdproprtistoCQDs.Finally,wdiscussingratdtailthapplicationsofCQDsinchmicalsnsing,biosnsing,bioimaging,nanomdicin,photocatalysisandlctrocatalysis,spciallythadantagsthycouldbringtothsfilds.IniwofsralxcllntriwarticlsfocusingondiffrntaspctsofCQDs,suchasthirsynthsisandphysicochmicalproprtis,14,18surfacfunctionalization,19bioimagingandbiosnsing19,20andphotocatalysisandoptolctronics,18itishopdthatthisarticlwillproidacomprhnsioriwofthcurrntstatusofCQDrsarchandopnnwprspctistowardthrsarchanddlopmntofCQDswithmuchimprodphysicochmicalproprtis.2.FluorscncproprtisofCQDsCQDsaranwclassofnanomatrialsthathaattractdsignificantattntioninthpastdcad.TwoclasssoffluorscncmissionmchanismshabnproposdforCQDsnthoughthxactoriginsofthirfluorscncmissionsrmaindbatablandmorrsarchisnddinordrtopaintaclarrpicturofthmchanismsofthirfluorscncmissions.Thfirstclassoffluorscncmissionmchanismisthatofbandgaptransitionscausdbyconjugatdpdomains,whilthscondclassinolsmorintricatoriginsassociatdwithsurfacdfctsinCQDs.2.1FluorscncmissionsfrombandgaptransitionsofconjugatdpdomainsForthfirstclassoffluorscncmchanism,bandgaptransitionsarisfromconjugatdpdomains.Thspdomainsarisolatdbycratingsp2hybridisdislandsrichinplctronsthroughthrductionofgraphnoxidsobtaindbyusingHummrsmthodofoxidisingandxfoliatinggraphitflaks.21Thyarcratdinawaythatthrarnopconnctionsbtwnthsp2islands,bcausanypconnctionsbtwnthsp2islandswouldladtointrislandqunchingofdsirdfluorscncmissions.22,23Inthistypofbandgaptransitions,singllayrgraphnshtshatobusdtoprntintrlayrqunching.24Thsingllayrgraphnshtsarusdasprcursorsforlctronicallyslicingintoisolatdpconjugatddomains,whichrsmbllargaromaticmolculswithxtnddpconjugationFig.1ChmicalstructurofCQDs.(Rproducdwithprmissionfromrf.13.)ZhiqiangGaoDrZhiqiangGaoisanassociatprofssoratthDpartmntofChmistryNationalUnirsityofSingapor.HrcidhisBScandPhDinChmistryfromWuhanUnirsity.ThfollowingyarshworkdasapostdoctoralfllowatÅboAkadmiUnirsityandThWizmannInstitutofScinc.AftrspndingthryarsinthUnitdStatsandightyarsatthInstitutofBionginringandNanotchnology,hjoindNUSinApril2011.Rsarchinhislaboratorycurrntlyincludslctrochmistry,analyticalchmistryandmatrialsscinc.RiwArticlChmSocRPublishdon15Octobr2014.Downloaddon1002201702:32:43.ViwArticlOnlin364|Chm.Soc.R.,2015,44,362381Thisjournalis©ThRoyalSocityofChmistry2015ofspcificlctronicnrgybandgapforopticalabsorptionandfluorscncmissions.25Suchlctronictransitionsdisplaystrongabsorptioninthultraiolt(UV)rgion,butwakornofluorscncmissions(Fig.2A).Thstrongabsorptionisliklydutolightabsorptionbyalargamountofhighdnsityplctronsinthsp2hybridisdislands,whichformxcitonicstatswhilthwakmissionsarpossiblyarsultofqunchingiaradiationlssrlaxationstothgroundstatduringxcitonmigrationtonrgytraps.132.2FluorscncmissionsofsurfacdfctdridoriginsThscondclassofthfluorscncmchanismarissfromsurfacrlatddfctisits–gnrallyanysitsthathanonprfctsp2domainswillrsultinsurfacnrgytraps.Bothsp2andsp3hybridisdcarbonsandothrfunctionalisdsurfacdfcts,26,27suchascarbonylrlatdlocalisdlctronicstats,24,28prsntinCQDscontributtothirmulticolourmissionsthatarconcntratdinthbluandgrnrgionsofthisibllightspctrum.Thssurfacdfctsbhalikaromaticmolculsthatarindiiduallyincorporatdintosolidhosts,xhibitingmulticolourmissionsdutothxistncofmultiplsurfacdfctswithdiffrntxcitationandmissionproprtis.13,25RobrtsonandO’Rillysuggstdthatthopticalproprtisofcarbonnanomatrialswhichcontainbothsp2andsp3bondsardtrmindbythpstatsofthsp2sits.29Thus,thbrightsurfacdfctdridfluorscncofCQDsisdutothrcombinationoflctron–holpairsinthstronglylocalisdpandplctronicllsofthsp2sits.Thssitslibtwnthbandgapofthsandsstatsofthsp3matrix,30,31ladingtostrongisiblmissions.Suchlctronictransitionsxhibitwakabsorptioninthnarultraioltisibl(UVis)rgionbutstrongmissionsinthisiblrgionasshowninFig.2B.Inaddition,uponsurfacpassiationorfunctionalization,thsurfacdfctsbcommorstabltofacilitatmorffctiradiatircombinationofsurfacconfindlctronsandhols,thusachiingbrightrfluorscncmissions.252.3TunablfluorscncmissionsofCQDsOnuniquproprtyofCQDsisthirtunablfluorscncmissions.Gnrally,CQDsposssstunablmissionsnwithoutanysurfacpassiation,butthyusuallyharylowquantumyildsdutounstablsurfacdfctsladingtorducdradiatircombination.Uponsurfacpassiationwithorganicorpolymricmatrials,suchaspoly(propionylthylnimincothylnimin)(PPEIEI)attachdtothCQDsurfac,surfacdfctsarstabilisdandstrongfluorscncmissionsbothinsolutionliksuspnsionandinsolidstatwrdtctd.ThmissionsofsuchpassiatdCQDscordabroadrangofthisiblrgionandxtnddintothnarinfrard(NIR)rgionasshowninFig.3.7ItshouldbnotdthatthsurfacpassiationagntsusdwrnotmissiinthisiblandNIRrgions,thusanyfluorscncmissionsobsrdmusthaoriginatdfromthsurfacpassiatdCQDs.ThtunablmissionproprtyofCQDsisclarlydmonstratdinFig.3.FromthfluorscncspctraofPPEIEIpassiatdCQDs,itisidntthatthmissionsarbroadandxcitationwalngthdpndnt.7,26ThtunablmissionsofthsurfacpassiatdCQDscouldbarsultofaridfluorscnccharactristicsofparticlsofdiffrntsizsofthCQDsandthdistributionofdiffrntmissisitsonthsurfacofthCQDs.Howr,thxactmchanismaccountingforthxcitationwalngthdpndntmissionFig.2(A)CQDswithstrongabsorptioninthUVrgionandwakmissionsand(B)CQDswithwakabsorptioninthnarUVisrgionbutstrongmulticolourmissionsinthisiblrgion.(Rproducdwithprmissionfromrf.13.)Fig.3(A)AquoussolutionsofPEG1500NpassiatdCQDs(a)xcitdat400nmand(b)xcitdatthindicatdwalngths;(B)absorptionandmissionspctraofPPEIEIpassiatdCQDsinwatrwithincrasinglxfrom400nmonthlftwith20nmincrmnts.Inst:missionintnsitisnormalizdtoquantumyilds.(Rproducdwithprmissionfromrf.7.)ChmSocRRiwArticlPublishdon15Octobr2014.Downloaddon1002201702:32:43.ViwArticlOnlinThisjournalis©ThRoyalSocityofChmistry2015Chm.Soc.R.,2015,44,362381|365rmainstobstablishdandthrquirmntforsurfacpassiationinordrtoproducfluorscncmissionsispoorlyundrstood.Exprimntalobsrationsarnothlpfulsinccontrorsialrsultsaroftnobsrd.Moror,thopticalproprtisofCQDsarcloslyassociatdwiththsynthticroutsusdinthirprparation.Forxampl,SunandcoworkrsattributdthfluorscncmissionstothradiatircombinationofxcitonsofsurfacnrgytrapsofCQDs.Uponsurfacpassiation,thsnrgytrapsarstabilisdandthrforbcommissi–aphnomnonthathasbnobsrdinsmiconductorquantumdots.32ThypostulatdthatthrmustbaquantumconfinmntffctofmissinrgytrapsonthsurfacofthCQDs.Nonthlss,suchtunablfluorscncmissionproprtyofCQDsproidsanadddadantaginthslctionofdiffrntmissionwalngthswithdiffrntxcitationwalngthsthatcanbapplidtoopticallabllingandfluorscncimaging.Inadditiontothxcitationwalngthdpndntmission,sralrportshaindicatdthatthfluorscncmissionsofCQDsarpHdpndnt.10,33,34LiuandcollagusnoticdthatthfluorscncintnsityofthirCQDsdcrasswhnthpHofthsolutionisshiftdfromthoptimalaluof7.0rgardlssofwhthrpHisincrasdordcrasd.10Inanothrrport,itwasobsrdthatthfluorscncintnsityofCQDsonlyshowsaslightdcrasofB3%whnthpHofthsolutionischangdfrom5to9.33Jiatal.rportdthatCQDsprpardfromdircthatingofascorbicacidsolutionshowapracticallylinardpndnconthpHofthsolutioninthrangof4.0to8.0.Thfluorscncintnsitydcrasdbyasmuchas90%frompH4.0to8.0.VaryingthpHofthsolutionfrom4.0to8.0,corrspondingtothdprotonationofthcarboxylgroupsonthsurfacofthCQDs,mightcauslctrostaticdopingchargingtothCQDsandshiftthFrmill.35Assnabo,thsignificantlylargariationoffluorscncintnsitywiththpHofthsolutionandthsynthticroutsusdinthprparationofthCQDsaddsadditionalcomplxityinfindingoutawidlyaccptdfluorscncmissionmchanism.2.4UpconrsionfluorscncInadditiontoconntionaldownconrsionfluorscncmissions,rportshaalsoshownthatcrtainCQDshaupconrsionfluorscncmissionproprtis.1,26,34,36–39Upconrsionfluorscncmissionisanopticalphnomnonwhrinthfluorscncmissionwalngthisshortrthanthusdxcitationwalngth,whichisparticularlyattractiforiniobioimagingsincbioimagingatlongrwalngthsspciallyinthNIRrgionisusuallyprfrrdowingtothimprodphotontissupntrationandrducdbackgroundautofluorscnc.Cao’stamfirstobsrdthatthirCQDsmitisibllightwhnxcitdbya800nmfmtoscondpulsdlasr,1thrbysuggstingthatsuchCQDspossssupconrsionproprtis.Latr,sralothrgroupsalsoobsrdupconrsionfluorscncmissionsfromCQDsprpardbydrasticallydiffrntsynthticrouts.26,34,36–39Forinstanc,Jiatal.dmonstratdthatCQDsprpardbydirctlyhatingascorbicacidsolutionat901Cxhibitxcllntupconrsionfluorscncmissionproprtisinadditiontothirnormaldownconrsionfluorscncmission.34UponxcitationinthNIRrgionof800–1000nm,grnlightwithapakwalngthof540nmwasmittdfromthirCQDs.Thupconrsionflorscncmissionsliklyoriginatdfromamultiphotonxcitationprocss–anssntialfaturofupconrsionfluorscncmission.Thisis,howr,notwithoutdisput.IniwofthpracticallyconstantnrgydiffrncofB1.1Vbtwnthxcitationlightandmissionlight,ShnandcollagusargudthatthmultiphotonxcitationisinadquattoaccountforthupconrsionfluorscncmissionproprtisofCQDs.26Thypostulatdthatthupconrsionfluorscncmissionoriginatsfromthrlaxationoflctronsfromahighrnrgystatofthporbital(LUMO)tothsorbitalsincsomlctronswouldinitablytransittothLUMOwhnalargnumbroflownrgyphotonsxcitthlctronsinthporbital.Ofcours,thlctronsinthsorbitalcanalsobxcitd,butthyonlymitconntionaldownconrsionlight.Onthothrhand,Wntal.blidthatsomofthapparntupconrsionfluorscncmissionsarartfactsoriginatingfromthconntionaldownconrsionmissionswhichhabnxcitdbythlakingcomponntfromthsconddiffractioninthmonochromatorofthspctrofluoromtr.40Bysimplyinsrtingalongpassfiltrintothxcitationpathwaythlakingcomponntcanbrmod.Thus,gratcarmustbtaknwhnintrprtingthfluorscncmissionsofCQDsandfurthrclarificationisncssarytoxplainupconrsionCQDs.3.SynthsisofCQDs3.1TopdownsynthticroutSynthticapproachsforCQDsargnrallyclassifidintotwocatgoris–‘‘topdown’’and‘‘bottomup’’.Thformrinolsbrakingdownlargrcarbonstructurs,suchasnanodiamonds,41graphit,7carbonnanotubs,42carbonsoot,10actiatdcarbon43andgraphitoxid44bymthodslikarcdischarg,lasrablationandlctrochmicaloxidation.Xutal.discordthfirstxamploffluorscntCQDswhnthywrpurifyingSWCNTsfromarcdischargdsoot.6Tharcdischargdsootwasoxidisdwithnitricacid,xtractdusingsodiumhydroxidsolutionandthblacksuspnsionfromthxtractwasthnsubjctdtogllctrophorsistoobtainCQDs.Subsquntly,SunandcollaguspionrdthsynthsisofCQDsbylasrablationofacarbonmatrialusingargonasacarrirgasinthprsncofwatrapour.7NanosizdcarbonparticlsinaggrgatsofdiffrntsizswrformdbutthsCQDsganoobiousfluorscncmissions.Thrfor,thsamplwasginanacidoxidatitratmntfollowdbysurfacpassiationinordrtoobsrbrightfluorscnc.Zhou’sgroupfirstdscribdanlctrochmicalmthodtoprparCQDs.42Itinoldgrowingmultiwalldcarbonnanotubsonacarbonpapr,whichwasthninsrtdintoanlctrochmicalcllthatcontainddgassdactonitrilwith0.1Mttrabutylammoniumprchloratasthsupportinglctrolyt.TosignificantlycutdownthcostofthstartingmatrialsandincrasthscalofCQDproduction,RiwArticlChmSocRPublishdon15Octobr2014.Downloaddon1002201702:32:43.ViwArticlOnlin366|Chm.Soc.R.,2015,44,362381Thisjournalis©ThRoyalSocityofChmistry2015aonstplctrochmicalapproachutilisinglowcostandradilyaailablgraphitasacarbonsourcwasrcntlyproposdbyMingtal.45ThprpardCQDswrprdominantlymultilayrgraphnoxidxhibitingbothdownandupconrsionfluorscncmissions.3.2BottomupsynthticroutOnthothrhand,th‘‘bottomup’’approachssynthsisCQDsfrommolcularprcursorssuchascitrat,46carbohydrats47,48andpolymr–silicananocomposits3throughcombustionthrmaltratmnts,andsupportdsynthticandmicrowasynthticrouts.Forinstanc,Liu’stamrportdasynthticmthodbasdonthusofmodifidsilicasphrsascarrirsandrsolsascarbonprcursors(Fig.4).3Bourlinostal.dscribdanasy,onstpthrmaldcompositionmthodofobtainingfluorscntCQDsfromammoniumcitrat.46ZhuandcoworkrsshowdthatCQDsarradilyformdbyhatingasolutionofpoly(thylnglycol)(PEG)andsaccharidina500Wmicrowaonfor2to10min.49CostisonofthimportantdtrminantsofCQDsbcomingiablcomptitorstosmiconductorquantumdots.Howr,thabodscribdapproachsrquirithrcostlyprcursors,complxinstrumntalstupsorposttratmntstosynthsisfluorscntCQDs.Rcntly,grnsynthticapproachswrintroducd.Withthsgrnrouts,CQDswrproducdinonstpwithoutthndforxpnsimatrialsandlaboratxprimntalstups.Li’stamwasonofthfirstgroupstointroducthconcptofprparingfluorscntCQDsusingasimplandgrnrout.50Thirapproachonlyinoldasingllctrochmicaltratmntstpofthanolwithsodiumhydroxid.Thisapproachislsscostlyandasirtomanag,andthCQDsproducdwrfoundtopossssdsirablfluorscncproprtisalongwithhighwatrsolubility,stabilityandsnsitiitytopH.Thraftr,thusofothrinxpnsiandbiocompatiblstartingmatrials,likthanol,50citrat,51glucosamin,52ascorbicacid,53,54saccharids,49,55,56candlsoot,57watrmlonpls,58pomlopls,59orangjuic,60strawbrryjuic,61sugarcanjuic,62chicknggs,63chitosan,64,65organogl66andglatin,67wrdlopd.Manyofths‘‘grn’’CQDsdisplaydxcllntprformancincllimagingandchmicalsnsingapplications.Tabl1summarissthrprsntatixamplsofthgrnsynthticroutsdlopdforthprparationofCQDs.Inadditiontoacidoxidatitratmntandsurfacpassiation,othrmthodshabnxplordinabidtoincrasquantumyildandobtainCQDswithbttrfluorscncproprtis.OnapproachistodopnwlyproducdandsurfacpassiatdCQDswithinorganiccompoundssuchasZnSandZnO.74AnaquoussuspnsionofCQDsandZn(CH3COO)2washydrolysdwithNaOHorprcipitatdwithNa2StoobtainZnOandZnSdopdCQDs,rspctily.InthcasofdopingwithZnO,anadditionalthrmalannalingstpwasrquirdtotransformZn(OH)2toZnO.ThrspctiquantumyildsofthZnSandZnOdopdCQDsinaquoussolutionswrabo50%andaround45%withthformrbingryclostothquantumyildofcommrciallyaailablsmiconductorCdSZnSquantumdots.55Itwasspculatdbythauthorsthatdopingmightharinforcdthsurfacpassiationffctornsrdasanadditionalformofsurfacpassiationmodtogthrwiththxistingorganicpassiatingagnts.ThsdopdCQDswrshowntohastrongmultiphotonfluorscncproprtis,55giingthmgratpotntialinthfildofonandtwophotonxcitationimagingapplications.3.3SurfacpassiationandfunctionalizationSurfacsofCQDsposssshighsnsitiitytocontaminantsinthirnironmnt,suchthatthirproprtisarasilyaffctdbytinyllsofcontaminants.Inordrtoalliatthisproblm,surfacpassiationofCQDsisprformdtorducthdtrimntalffctofsurfaccontaminationtothiropticalproprtis.75SurfacpassiationisusuallyattaindbythformationofaFig.4SupportdsynthsisofCQDsusingmodifidsilicasphrsascarrirsandrsolsascarbonprcursors.(Rproducdwithprmissionfromrf.3.)ChmSocRRiwArticlPublishdon15Octobr2014.Downloaddon1002201702:32:43.ViwArticlOnlinThisjournalis©ThRoyalSocityofChmistry2015Chm.Soc.R.,2015,44,362381|367thininsulatinglayr,usuallybythattachmntofpolymricmatrials,suchasoligomricPEG,PEG1500N,onanacidtratdCQDsurfac.7ItwasshownthatffctisurfacpassiationisanssntialstpinordrtoproducCQDswithhighfluorscncintnsitis.Furthrmor,Dongandcoworkrsrportdthatlctrochmiluminscncactiitisarpartlyrsponsitosurfacpassiation,whrthsurfacpassiatdCQDsxhibitdwaklctrochmiluminscncactiitisbutstrongfluorscnc.43Incontrast,CQDswhossurfacsarunpassiatdor‘‘nakd’’mightmitcolourfulfluorscnc,butthirquantumyildsargnrallylow,9,10,42,57,76xcptforarcntrportbyShn’sgroup.77AftrrductitratmntwithNaBH4,thydmonstratdthathydrothrmallytratdCQDshaquantumyildsashighas40.5%.58Ths‘‘bar’’CQDsmightsrasgoodaltrnatistoacidtratdCQDssincthirsurfacsarprontooxidatirosionduringchmicaloxidationusingstrongacids.Howr,thismthodofsynthsisingbarCQDswithhighquantumyildsdosnotsmtobhighlyfficintandrproducibl.Thrfor,manystillrlidonthacidtratmntandsurfacpassiationtonhancthquantumyildofCQDs.Wangtal.prpardCQDswithquantumyildsashighas60%,78whichputsthmonparwiththbstcommrcialCdSZnSsmicon