Table Of ContentCarbon Microfibers with Hierarchical
Porous Structure from Electrospun
SUBJECTAREAS: Fiber-Like Natural Biopolymer
SYNTHESISAND
PROCESSING
POROUSMATERIALS YeruLiang,DingcaiWu&RuowenFu
SUSTAINABILITY
BIOINSPIREDMATERIALS MaterialsScienceInstitute,PCFMLabandDSAPMLab,SchoolofChemistryandChemicalEngineering,SunYat-senUniversity,
Guangzhou510275,P.R.China.
Received
30October2012 Electrospinningoffersapowerfulrouteforbuildingone-dimensional(1D)micro/nanostructures,buta
commonrequirementfortoxicorcorrosiveorganicsolventsduringthepreparationofprecursorsolution
Accepted haslimitedtheirlargescalesynthesisandbroadapplications.Herewereportafacileandlow-costwayto
19December2012 prepare1Dporouscarbonmicrofibersbyusinganelectrospunfiber-likenaturalproduct,i.e.,silkcocoon,as
precursor.Wesurprisinglyfoundthatbyutilizingasimplecarbonizationtreatment,thecocoonmicrofiber
Published canbedirectlytransformedinto1Dcarbonmicrofiberofca.6 mmdiameterwithauniquethree-dimensional
24January2013 porousnetworkstructurecomposedofinterconnectedcarbonnanoparticlesof10,40nmdiameter.We
furthershowedthattheas-preparedcarbonproductpresentssuperiorelectrochemicalperformanceas
binder-freeelectrodesofsupercapacitorsandgoodadsorptionpropertytowardorganicvapor.
Correspondenceand
requestsformaterials Micro/nanomaterialshaveattractedgreatinterestduetopotentialapplicationsinadsorption,separation,
shouldbeaddressedto catalysis, energy, sensors, nanoelectronic devices, biotechnology and other areas1–8. Therefore, it is
D.W.(wudc@mail. importanttodevelopreliablemethodsforfabricationofmicro/nanomaterials,withdesignedarchitec-
sysu.edu.cn) tureaswellascustomizedframeworkstructure.Developmentofone-dimensional(1D)micro/nanomaterialshas
beenoneofthemostactiveareasinthemicro/nanomaterialsscienceowingtotheiruniquestructurecharacter-
isticsincludinghighlength/diameterratio,largeporevolumeandhighsurfacearea9–17.Amongsuch1Dmicro/
nanomaterials,porouscarbonwith1Dmicro/nanostructurehasattractedsignificantattention,notonlyforits
fundamentalscientificinterest,butalsoformanymodern-daytechnologicalapplications9,18–23.Thiswasmoti-
vatedbyitsuniquephysicochemicalproperties,i.e.,goodelectricalconductivity,highsurfacearea,andexcellent
chemicalstability.Alargenumberofadvancedtechniqueshavebeendevelopedtofabricate1Dporouscarbona-
ceousnanostructurewithwell-controlledmorphologyandchemicalcomposition.Generally,1Dmicro/nano-
materialscanbepreparedbymanymethodsincludingnanocasting,self-assembly,solvothermalsynthesisand
chemical vapor deposition12,15,19,24–26. However, each of these methods has limitations, such as rigid reaction
conditions,highcost,andcomplicatedmultiplesyntheticsteps.
Recently,electrospinning hasbeendemonstrated to beapowerfultechnique tofabricate 1Dmicro/nanos-
tructure.Thismethodfacilitatescontrolovercomposition andtopologyofproducts,enablingenhancedper-
formanceinnumerousapplications18,27–29.Despiterapidadvancesofelectrospinningmethodologiesandtheir
synthesisadvantages(easiness,versatility,rapidity,etc.),currentelectrospinningproceduresofteninvolvetoxic
orcorrosiveorganicsolventsduringthepreparationofsolutionofstartingmaterials,whichisnotinaccordance
withtheurgentrequirementsofenergy-savingandenvironmentalprotection.Hence,establishinganefficient
andfacilesynthesisprotocolusingtheprecursorsobtaineddirectlyfromnatureforpreparationof1Dnanopor-
ouscarbonswithwell-tailoredarchitectureswouldbeofgreatbenefittotheirlargescaleproductionandbroad
applications.
Inthepresentwork,wereportafacileandcost-effectivewaytoprepare1Dporouscarbonmicrofibersbyusing
an electrospun fiber-like natural product, i.e., silk cocoon, as precursor. This biopolymer is obtained by a
silkwormthroughaninartificialelectrospinning-like process,inwhichthesilkwormspinssilkmicrofibersto
form a cocoon around itself. We surprisingly found that by utilizing a simple carbonization treatment, the
electrospunfiber-likenaturalcocoonmicrofiberscanbedirectlytransformedinto1Dcarbonmicrofiberswith
anaveragediameterof6 mm(Figure1).The1Dcarbonmicrofibersconsistofnumerouscarbonnanoparticle
unitsof10,40 nminsize,whichareinterconnectedwitheachothertoformauniquethree-dimensional(3D)
porous network structure. These carbon nanoparticle units are microporous, and their compact and loose
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Figure1|Schematicillustrationoftheapproachtofabricatehierarchicalporouscarbonmicrofibersfromsilkcocoon.
aggregationleadstomesoporesandmacropores,respectively.Inthe Furthermore, interlacement of these 1D carbon microfibers them-
past,fabricationofporousnetworkstructuresusuallyneededfussy selves in the carbonized cocoon forms a great number of micron-
andmultiplesyntheticstepsincludingreaction-inducedphasesepa- scaledlargemacropores(Figure2A).
rationandsupercriticaldrying14.Therefore,directcarbonizationof N adsorptionmethodisusedtofurtherquantitativelyelucidate
2
such a natural biopolymer material without any additional harsh the hierarchical porous structure of the as-obtained HPCMF. As
proceduresmakesthepresentapproachmoreattractiveinconstruc- shown in N adsorption-desorption isotherm of Figure 3, the
2
tion of micro/nanostructures. Furthermore, interlacement of these HPCMF has a high adsorption uptake at low relative pressure (P/
1Dcarbonmicrofibersthemselvesinthecarbonizedcocoonleadsto P ),indicativeoftheexistenceofplentifulmicropores.Inaddition,
0
formationoflargemacropores. theadsorptionamountincreasesgraduallyandstilldoesnotreacha
Duetogoodporeinterconnectivity,highsurfacearea,largepore plateau neartheP/P of1.0, demonstrating thepresence ofmeso-
0
volumeaswellas highnitrogen content, theas-prepared 1Dhier- poresandmacropores,whichisingoodagreementwiththeobser-
archical porous carbon microfibers (HPCMF) show superior vationfromSEMandTEMimages.Theporesizedistribution(PSD)
electrochemicalperformanceasbinder-freeelectrodesofsupercapa- curveobtainedusingdensityfunctionaltheory(DFT)isdisplayedin
citorsandgoodadsorptionpropertytowardorganicvapor.Wehope Figure3.Threeregionscanbeconfirmed:(1)micropores(,2 nm)
thatourpresentmethodwillopenupnewavenuestoadvancedand with a PSD peak at 1.3 nm; (2) mesopores (2,50 nm) with a
sustainablematerials,consideringthattheemploymentoflow-cost
andenvironmentfriendlysilkcocoonascarbonsourceavoidsmany
chemicalreactionsandphysicalprocessesinnormalproceduresfor
fabricationof1Dporouscarbonfibers.
Results
SEMimageinFigureS1Ademonstratesthatthesilkcocooniscom-
posed of interlaced 1D silk microfibers with about 15 mm in dia-
meter. The silk microfibers are essentially nonporous, judging
fromtheirsmoothframeworksurface(FiguresS1BandS1C)aswell
asverylowBrunauer–Emmett–Teller(BET)surfaceareaof7 m2/g
(TableS1).Afteracarbonizationtreatmentat900uC,theas-prepared
carbon microfibers in the carbonized cocoon preserve the well-
definedfibrousmorphology(Figure2A).Thediameterofthesecar-
bonmicrofibersismeasuredtobeabout6 mm,whichissmallerthan
that of silk microfibers, indicating that the fibrous frameworks
undergo an obvious shrinkage during carbonization because of
burn-off of non-carbon elements and carbon-containing com-
pounds. Surprisingly, it is obviously found from magnified SEM
imageofFigure2Bthatthefibrousframeworksareuniformlyfrac-
tured on the nanometer scale to form numerous interconnected
carbonnanoparticlesof10,40 nmdiameterduringthehightem-
peraturepyrolysistreatment,althoughretainingthefibrousmorpho-
logy (Figures 2A and 2C). As a result, the carbon microfibers
obtainedherehaveauniquehierarchicalporousnetworkstructure:
carbonnanoparticleunitscontainnumerousmicropores(seeTEM
imageinFigure2D),andtheircompactandlooseaggregationleads Figure2|(A,B)SEMand(C,D)TEMimagesofHPCMF. (B)and(D)
to mesopores and macropores, respectively (Figure 2B). correspondtotheareaindicatedbyarectanglein(A)and(C),respectively.
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Figure3|N adsorption-desorptionisothermofHPCMF. TheinsetshowsitsDFTporesizedistribution.
2
maximum PSD peak at 9 nm; and (3) macropores (50,400 nm) deconvoluted into four functional components30, i.e., pyridinic N
withamaximumPSDpeakat68 nm.Itshouldbenotedthatlarge (N-6),quaternaryN(N-Q),pyrrolicN(N-5),andpyridine-N-oxide
macropores,i.e.,thespacesbetweeninterlaced1Dcarbonfibersand (N-X), whose percentage is 23.9 at.%, 24.6 at.%, 47.7 at.% and
between very loosely aggregated carbon nanoparticles may be too 3.8 at.%,respectively(TableS2).
largeandtooopentoleadtocapillarycondensationandthustobe Besidestheaboveuniquehierarchicalstructure,anotherimport-
reflected in pore size distribution. As shown in Table S1, a BET antcharacteristicofHPCMFisitsstable,regulableandversatilebulk
calculation gives the BET surface area for the HPCMF equal to form.Figures5Aand5Bdisplay thephotographsofasilkcocoon
796 m2/g; and the t-plot method gives the surface areas of micro- before and after carbonization. It can be found that the elliptical
pores and external large-sized pores equal to 569 and 227 m2/g, shape of cocoon is well retained after pyrolysis, although its color
respectively. Moreover, the total pore volume is calculated to be turnsfromwhitetoblackbecauseofcarbonization.Thecarbonized
0.43 cm3/gaccordingtotheamountadsorbedatarelativepressure cocoon is easily tailored into various forms, e.g., rectangle felt
P/P of0.99. (FigureS4).
0
TheHPCMFfromsilkcocoonisfoundtohavenitrogen-contain- Inthisstudy,totestitsfeasibilityforpracticalapplication,thesilk
ing functional groups by means of thecombustion analysis, X-ray cocoon-basedHPCMFintheformofrectanglefeltisdirectlyusedas
photoelectronspectroscopy(XPS)andelectronenergylossspectro- a binder-free electrode for supercapacitor without any fussy elec-
scopy(EELS).Thenitrogencontent,asmeasuredbythecombustion trodepreparationprocesseswhicharenecessaryfornormalproduc-
analysis,isabout6.5 wt.%(TableS1),and4.5 at.%,accordingtoXPS tionofcarbonelectrodes.Thesupercapacitordeviceisassembledby
(Table S2). The nitrogen element is distributed homogeneously attachingtwopiecesofHPCMFfeltsthatareimmersedinasmallseal
withinthecarbonframeworkofHPCMF,accordingtoEELSmap- bag containing 6 mol/L KOH aqueous electrolytes, as shown in
ping images of carbon and nitrogen elements (Figure 4). The Figure5C.ItisshownthattheHPCMFhasgoodcapacitiveperform-
nitrogen-containingfunctionalgroupsaredeterminedbythedecon- ance(Figures5DandS5).Forexample,atthesweeprateof2 mV/s,
volution of high resolution N 1s XPS spectrum (Figure S2). As HPCMF possesses a mass specific capacitance as high as 215 F/g,
schematically illustrated in Figure S3, the N 1s spectrum can be whichtranslatesintoacapacitancepersurfaceareaupto27 mF/cm2,
Figure4|EELSmappingimagesofHPCMF:(A)bright-fieldimage,(B)carbonand(C)nitrogen.
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Figure5|Photographsofasilkcocoonbefore(A)andafter(B)carbonization,(C)theas-fabricatedbinder-freeHPCMFbasedsupercapacitor,
and(D)specificcapacitancesatvarioussweepratesforbinder-freeHPCMFbasedelectrodes.
a value higher than those of most porous carbons31. With further diameterandahighsurfaceareaofca.800 m2/g.Itisworthmen-
increasing the sweep rate to 50 mV/s, a high mass specific capa- tioningthattheemploymentofnaturalsilkcocoonascarbonsource
citance (154 F/g)isstillobserved, indicativeofexcellentratecap- helps to avoid many chemical reactions and physical processes in
abilityinHPCMFelectrodes.Thegoodcapacitiveperformanceof normal synthetic procedures of 1D porous carbon fibers, such as
HPCMFmayarisefromitsuniquehierarchicalporestructurethat preparationofcarbonsourcesandtemplates,utilizationofabundant
is beneficial to ionic transportation and storage. The interpene- hazardousorganicsolutionduringelectrospinning process,and/or
tratedfibernetworktexturecombinedwiththehierarchicalnano- subsequenttemplateremoval.Furthermore,thecombinationof1D
porous structure in the carbon fiber framework ensures quick fibrousmorphology,hierarchicalporousnetworkstructureandgood
penetration of electrolytes, thus reducing the resistance for the poreinterconnectivityfacilitateseasyaccessofreactionspeciestothe
ions32–34. Moreover, it is believed that the plentiful nitrogen func- innersurfaceofcarbonfiber,andthesesmall-sizednanoporeseffec-
tional groups in the carbon framework can not only improve the tively increase the surface area available for active site dispersion,
wettability of the as-prepared material in the electrolyte but also whichisveryhelpfulinmanyapplications.
provide great pseudocapacitance35,36. Ontheotherhand,thisnaturalbiopolymersilkcocooniscom-
AnotherpotentialuseoftheHPCMFisexploredforadsorption posedoffibroin(72,81%),sericin(19,28%)andverylittleother
towardorganicvapor.Asshowninadsorptionisothermofmethanol materialssuchasfats,wax,sandpigmentsplusminerals.Asshownin
vaporforHPCMFinFigureS6,HPCMFexhibitsanuptakeinthe Table S1, silk cocoon contains considerable nitrogen atoms
rangeoflowrelativepressures,becauseofthepresenceofnumerous (16.2 wt.%), becauseitschemicalstructureismainlycharacterized
micropores. With increasing the relative pressure, the adsorption bythepresenceof18typesofaminoacidssuchasglycine,alanine
capacity continuously increases because of condensation of meth- andserine.Therefore,itisnotsurprisingthattheHPCMFmaterials
anol in mesopores and macropores. Therefore, HPCMF gives the containacertainamountofnitrogen-containingfunctionalgroups.
adsorptioncapacityofmethanolashighas243 mg/g. It is expected that the introduction of these nitrogen-containing
functional groups can not only boost the material performance,
Discussion e.g., in the case of energy storage or catalysis, but also completely
Wehavesuccessfullyfabricatedaclassofnovel1DHPCMFusinga changetheelectronicpropertiesthatareattractiveforawidevariety
simpleone-stepcarbonizationofelectrospunfiber-likenaturalbio- ofapplications37.
polymer, i.e., silk cocoon. As one of the most abundant types of Inaddition,thetailorablebulkformofHPCMFisalsoavaluable
naturalbiomass,silkcocooncanbeproducedviaaninartificialelec- characteristic,whichisderivedfromgoodshapestabilityofsilkcocoon
trospinning-like process. After carbonization, the silk microfibers duringcarbonization.Thisfeatureprovidesanopportunitytocontrol
can be directly transformed into 1D carbon microfibers of ca. thebulkformtocatertotheneedofanytargetedapplication.
6 mm diameter with a unique hierarchical porous structure com- Duetotheseexcellentphysicalandchemicaladvantagesdiscussed
posed of interconnected carbon nanoparticles of 10,40 nm above, the HPCMF materials have been proven to present great
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potentialforuseasbinder-freeelectrodesforsupercapacitordevices 19.Li,W.etal.ASelf-TemplateStrategyfortheSynthesisofMesoporousCarbon
(e.g.,acapacitanceashighas215 F/g)andasanadsorbenttoward NanofibersasAdvancedSupercapacitorElectrodes.Adv.EnergyMater.1,
382–386(2011).
organic vapors like methanol (e.g., an adsorption capacity up to
20.Hunt,M.A.,Saito,T.,Brown,R.H.,Kumbhar,A.S.&Naskar,A.K.Patterned
243 mg/g).Wehopethatourfindingwillprovideanewbenchmark functionalcarbonfibersfrompolyethylene.Adv.Mater.24,2386–2389(2012).
for fabricating sustainable materials with advanced micro/nanos- 21.Su,D.S.etal.Hierarchicallystructuredcarbon:Synthesisofcarbonnanofibers
tructure, given that the huge amount of silk cocoon is produced nestedinsideorimmobilizedontomodifiedactivatedcarbon.Angew.Chem.Int.
Ed.44,5488–5492(2005).
anditsrelatedcarbonmaterialcanbepreparedfacilelyatlowcost.
22.Yang,Q.H.,Xu,W.H.,Tomita,A.&Kyotani,T.Thetemplatesynthesisofdouble
coaxialcarbonnanotubeswithnitrogen-dopedandboron-dopedmultiwalls.
J.Am.Chem.Soc.127,8956–8957(2005).
Methods
23.Lv,R.T.etal.Open-Ended,N-DopedCarbonNanotube-GrapheneHybrid
Bombyxmorisilkcocoonwasdirectlyusedasthestartingmaterialwithoutanypre- NanostructuresasHigh-PerformanceCatalystSupport.Adv.Funct.Mater.21,
treatment.Thesilkcocoonwassubjectedtocarbonizationbyheatingat900uCfor3h 999–1006(2011).
underN2flow.Theheatingratewas2uC/min. 24.Su,D.S.etal.Mount-Etna-Lava-SupportedNanocarbonsforOxidative
ThemicrostructureofthesampleswasinvestigatedbyaJSM-6330Fscanning DehydrogenationReactions.Adv.Mater.20,3597–3600(2008).
electronmicroscope(SEM)andJEM-2010HRtransmissionelectronmicroscope 25.Chen,J.T.,Chen,W.L.&Fan,P.W.HierarchicalStructuresbyWettingPorous
(TEM).EELSmappingimageswereobtainedbyaFEIF30TEM.Elementalanalysis TemplateswithElectrospunPolymerFibers.ACSMacroLett.1,41–46(2011).
wasperformedonanElementarAnalysensystemeGmbHVarioELanalyzer.XPS 26.Wang,X.&Li,Y.Selected-ControlHydrothermalSynthesisofa-andb-MnO2
measurementwasaccomplishedusinganESCALAB250instrument.N2adsorption SingleCrystalNanowires.J.Am.Chem.Soc.124,2880–2881(2002).
measurementwascarriedoutusingaMicromeriticsASAP2010analyzerat77K.The 27.Cavaliere,S.,Subianto,S.,Savych,I.,Jones,D.J.&Roziere,J.Electrospinning:
BETsurfacearea(SBET)wasanalyzedbyBrunauer–Emmett–Teller(BET)theory. designedarchitecturesforenergyconversionandstoragedevices.EnergyEnviron.
Thetotalporevolume(Vt)wasestimatedfromtheamountadsorbedatarelative Sci.4,4761–4785(2011).
pressureP/P0of0.99.Theexternalsurfacearea(Sext)andmicroporesurfacearea 28.Chen,Y.M.,Lu,Z.G.,Zhou,L.M.,Mai,Y.W.&Huang,H.T.Triple-coaxial
(Smic)wasdeterminedbyt-plottheory.Theporesizedistributionwasanalyzedby electrospunamorphouscarbonnanotubeswithhollowgraphiticcarbon
originaldensityfunctionaltheory(DFT)combinedwithnon-negativeregularization nanospheresforhigh-performanceLiionbatteries.EnergyEnviron.Sci.5,
andmediumsmoothing. 7898–7902(2012).
Thebinder-freeelectrodesweredirectlyobtainedfromthecarbonizedsilkcocoon 29.Tsaroom,A.,Matyjaszewski,K.&Silverstein,M.S.Spontaneouscore-sheath
whichwascutintotheformofrectanglefeltbeforecarbonization.Thesimple formationinelectrospunnanofibers.Polymer52,2869–2876(2011).
supercapacitordevicewasfabricatedbyattachingtwopiecesofHPCMFfeltelec- 30.Hulicova-Jurcakova,D.,Seredych,M.,Lu,G.Q.&Bandosz,T.J.CombinedEffect
trodeswiththesamemassthatwereimmersedinasmallsealbagcontaining6mol/L ofNitrogen-andOxygen-ContainingFunctionalGroupsofMicroporous
KOHaqueoussolution.Apieceofpolypropylene-basednon-wovenfabricasa ActivatedCarbononitsElectrochemicalPerformanceinSupercapacitors.Adv.
separatorwasplacedbetweentheHPCMFfeltelectrodesandtwonickelfoamswere Funct.Mater.19,438–447(2009).
insertedontotheedgeoftheelectrodesinordertoconnecttheelectrochemicaltest 31.Huang,C.H.etal.Three-dimensionalhierarchicallyorderedporouscarbonswith
instruments.TheelectrochemicalmeasurementswerecarriedoutusinganIM6e partiallygraphiticnanostructuresforelectrochemicalcapacitiveenergystorage.
electrochemicalworkstation.Thespecificcapacitance(Cm)wascalculatedaccording Chemsuschem5,563–571(2012).
totheequationCm~v2:mI ,whereI,vandmrepresentthecurrentatthemiddle 32.Epel-rKfoardmy,anMc.eFa.n,dStfrloexnigb,leVg.,raDpuhbeinne,-Sb.a&sedKealneecrt,roRc.hBe.mLiacsaelrcascpraicbiitnogrso.fSchiiegnhc-e335,
voltageofthepotentialwindow,thesweeprateandthemassofsingleHPCMFfelt 1326–1330(2012).
electrode,respectively.Theadsorptionmeasurementtowardmethanolvaporwas 33.Liang,Y.,Wu,D.&Fu,R.Preparationandelectrochemicalperformanceofnovel
carriedoutat25uCbyusinganIG-3intelligentgravimetricanalyzer(Hiden orderedmesoporouscarbonwithaninterconnectedchannelstructure.Langmuir
Isochema,Ltd.,Warrington,UK). 25,7783–7785(2009).
34.Wang,D.W.,Li,F.,Liu,M.,Lu,G.Q.&Cheng,H.M.3Daperiodichierarchical
porousgraphiticcarbonmaterialforhigh-rateelectrochemicalcapacitiveenergy
1. Seo,M.&Hillmyer,M.A.ReticulatedNanoporousPolymersbyControlled storage.Angew.Chem.Int.Ed.47,373–376(2008).
Polymerization-InducedMicrophaseSeparation.Science336,1422–1425(2012). 35.Yang,X.,Wu,D.,Chen,X.&Fu,R.Nitrogen-EnrichedNanocarbonswitha3-D
2. Joo,S.H.etal.Orderednanoporousarraysofcarbonsupportinghighdispersions ContinuousMesoporeStructurefromPolyacrylonitrileforSupercapacitor
ofplatinumnanoparticles.Nature412,169–172(2001). Application.J.Phys.Chem.C114,8581–8586(2010).
3. Liu,C.,Li,F.,Ma,L.P.&Cheng,H.M.AdvancedMaterialsforEnergyStorage. 36.Simon,P.&Gogotsi,Y.Materialsforelectrochemicalcapacitors.Nat.Mater.7,
Adv.Mater.22,E28–E62(2010). 845–854(2008).
4. Brezesinski,T.,Wang,J.,Tolbert,S.H.&Dunn,B.Orderedmesoporousalpha- 37.Mane,G.P.etal.PreparationofHighlyOrderedNitrogen-Containing
MoO3withiso-orientednanocrystallinewallsforthin-filmpseudocapacitors. MesoporousCarbonfromaGelatinBiomoleculeanditsExcellentSensingof
Nat.Mater.9,146–151(2010). AceticAcid.Adv.Funct.Mater.22,3596–3604(2012).
5. Tang,C.etal.Nanoporouscarbonfilmsfrom"hairy"polyacrylonitrile-grafted
colloidalsilicananoparticles.Adv.Mater.20,1516–1522(2008).
6. Choi,M.&Ryoo,R.Orderednanoporouspolymer-carboncomposites.Nat.
Mater.2,473–476(2003). Acknowledgements
7. Zhu,Y.etal.Carbon-basedsupercapacitorsproducedbyactivationofgraphene. ThisresearchwassupportedbytheprojectofNNSFC(51173213,51172290,51232005,
Science332,1537–1541(2011). 50802116),ProgramforNewCenturyExcellentTalentsinUniversity,ProgramforPearl
8. Nagai,A.etal.Poresurfaceengineeringincovalentorganicframeworks.Nat. RiverNewStarofScienceandTechnologyinGuangzhou,theFundamentalResearchFunds
Commun.2,536–544(2011). fortheCentralUniversities(09lgpy18),andtheProjectofDemonstrationBaseof
9. Zhang,J.etal.Surface-modifiedcarbonnanotubescatalyzeoxidative DepartmentofEducationofGuangdongProvince(cgzhzd0901).Mr.ChaolunLiang
dehydrogenationofn-butane.Science322,73–77(2008). (InstrumentalAnalysis&ResearchCenter,SunYat-senUniversity)isacknowledgedfor
10.Lu,X.F.,Wang,C.&Wei,Y.One-DimensionalCompositeNanomaterials: helpwithEELSmeasurements.
SynthesisbyElectrospinningandTheirApplications.Small5,2349–2370(2009).
11.Bourret,G.R.&Lennox,R.B.1DCu(OH)(2)NanomaterialSynthesisTemplated
Authorcontributions
inWaterMicrodroplets.J.Am.Chem.Soc.132,6657–6659(2010).
D.W.conceivedtheproject.Y.L.conductedtheexperiments.Alltheauthorsdiscussedthe
12.Hartgerink,J.D.,Beniash,E.&Stupp,S.I.Self-assemblyandmineralizationof
results.Y.L.andD.W.wrotethemanuscript.
peptide-amphiphilenanofibers.Science294,1684–1688(2001).
13.Su,D.S.&Schlogl,R.NanostructuredCarbonandCarbonNanocompositesfor
ElectrochemicalEnergyStorageApplications.Chemsuschem3,136–168(2010). Additionalinformation
14.Wu,D.etal.DesignandPreparationofPorousPolymers.Chem.Rev.112, Supplementaryinformationaccompaniesthispaperathttp://www.nature.com/
3959–4015(2012). scientificreports
15.Dong,Z.X.,Kennedy,S.J.&Wu,Y.Q.Electrospinningmaterialsforenergy-
Competingfinancialinterests:Theauthorsdeclarenocompetingfinancialinterests.
relatedapplicationsanddevices.J.PowerSources196,4886–4904(2011).
16.Wu,D.etal.PreparationofPolymericNanoscaleNetworksfromCylindrical License:ThisworkislicensedunderaCreativeCommons
MolecularBottlebrushes.ACSNano6,6208–6214(2012). Attribution-NonCommercial-NoDerivs3.0UnportedLicense.Toviewacopyofthis
17.Su,D.S.TheUseofNaturalMaterialsinNanocarbonSynthesis.Chemsuschem2, license,visithttp://creativecommons.org/licenses/by-nc-nd/3.0/
1009–1020(2009). Howtocitethisarticle:Liang,Y.,Wu,D.&Fu,R.CarbonMicrofiberswithHierarchical
18.Inagaki,M.,Yang,Y.&Kang,F.Carbonnanofiberspreparedviaelectrospinning. PorousStructurefromElectrospunFiber-LikeNaturalBiopolymer.Sci.Rep.3,1119;
Adv.Mater.24,2547–2566(2012). DOI:10.1038/srep01119(2013).
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