DTIC ADA550298: Photothermal Deoxygenation of Graphene Oxide for Distributed Ignition and Patterning Applications (Postprint)

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13-04-2009 Journal Article
4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER

Photothermal Deoxygenation of Graphene Oxide to Graphitic Carbon for Distributed 5b. GRANT NUMBER

Ignition and Patterning Applications (Postprint)
5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S) 5d. PROJECT NUMBER
Scott Gilje & Jabarri Farrar (Northrop Grumman); Sergey Dubin & Richard B. Kaner
(UCLA); Alireza Badakshan (Sverdrup); S.A. Danczyk (AFRL/RZSA)
5f. WORK UNIT NUMBER
43470876
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
REPORT NUMBER
Air Force Research Laboratory (AFMC)
AFRL/RZSA AFRL-RZ-ED-JA-2009-152
10 E. Saturn Blvd.
Edwards AFB CA 93524-7680
9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S
ACRONYM(S)

Air Force Research Laboratory (AFMC)
AFRL/RZS 11. SPONSOR/MONITOR’S
5 Pollux Drive NUMBER(S)
Edwards AFB CA 93524-7048 AFRL-RZ-ED-JA-2009-152
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13. SUPPLEMENTARY NOTES
Published in Advanced Materials, 2010, 22, 419-423. © 2010 WILEY-VCH Verlag GmbH & Co., KGaA, Weinheim
14. ABSTRACT
In recent years, several researchers have reported on an enhanced photothermal effect exhibited when nanoscale materials such as
carbon nanotubes, polyaniline nanofibers or Si nanowires were irradiated using a photographic flash. [1-3]. In these studies, the
high surface to volume ratio of the nanomaterials being flashed, coupled with the inability of the small structures to efficiently
dissipate the absorbed energy, led to a rapid increase in temperature and subsequent ignition/welding of the materials. Although
heating materials through the use of light energy is not a new phenomenon, achieving such a rapid and dramatic temperature
change using only millisecond pulses of light demonstrates a tangible and technologically significant capability, unique to
nanoscale materials. [4] We have been able to achieve an enhanced photothermally activated reaction by exposing nanostructured
graphene oxide (GO) porous networks, to a photographic flash. The exposure results in a pronounced photoacoustic effect along
with a rapid temperature increase, which initiates a secondary deoxygenation reaction to yield graphitic carbon and CO . A photo-
2
initiated reaction could be used to achieve multiple ignition nucleation sites simultaneously. This type of “distributed ignition” has
applications in liquid fuel rocket engines and in high efficiency homogenous charge compression ignition (HCCI) engines,
where ignition control is of paramount importance.
15. SUBJECT TERMS

16. SECURITY CLASSIFICATION OF: 17. LIMITATION 18. NUMBER 19a. NAME OF RESPONSIBLE
OF ABSTRACT OF PAGES PERSON
Dr. S.A. Danczyk
a. REPORT b. ABSTRACT c. THIS PAGE 19b. TELEPHONE NUMBER
SAR 6 (include area code)
Unclassified Unclassified Unclassified N/A
Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. 239.18
www.advmat.de
Photothermal Deoxygenation of Graphene Oxide for C
O
M
Patterning and Distributed Ignition Applications
M
U
N
By Scott Gilje,* Sergey Dubin, Alireza Badakhshan, Jabari Farrar,
I
C
Stephen. A. Danczyk, and Richard B. Kaner A
T
I
O
N
A xenon discharge tube, such as is used to produce a deoxygenation of GO to create functionalized graphene sheets
photographic flash, has been reported to cause the ignition of upon rapidheating to11008Cunder aninert atmosphere.[27,28]
carbonnanotubes,siliconnanowires,andweldingofnanofibers Theseorganicsolventdispersiblesheetshaveenabledthedirect
oftheconductingpolymerpolyaniline.[1–3]Inthesereactions,the creation of polymer composites, without the need for surfac-
high surface-to-volume ratio of the nanomaterials being tants.[29]ThermaldeoxygenationofGOtoformgraphiticcarbon
irradiated, coupled with the inability of the small structures to datesbacktothe1960swhenBoehmandScholzfirstreportedon
efficientlydissipatetheabsorbedenergy,leadstoarapidincrease the ignition and deflagration of graphite oxides prepared by
in temperature and subsequent ignition or welding of the different methods.[30] Upon rapid heating to temperatures of
materials. Although heating materials through the use of light (cid:1)2008C,GOdecomposestothemostthermodynamicallystable
energy is not a new phenomenon, achieving such a rapid and oxideofcarbon,CO .AlongwiththeexothermicreleaseofCO ,
2 2
dramatic temperature change using only millisecond pulses of H O,and COalsoform asminor products.[31]
2
light demonstrates a tangible and technologically significant Carbonnanotubeshavebeenconsideredasadditivestorocket
capability thatisunique tonanoscale materials.[4] fuels to attain distributed fuel ignition because of the dramatic
Graphene oxide (GO) is a deeply colored, water dispersible, temperatureincrease(inexcessof15008C)thatcanbeachieved
oxidized form of graphene obtained through the treatment of usingmillisecondpulsesoflight.Ifdifferentpartsofthefuelcan
graphitepowderwithpowerfuloxidizingagents.[5]AlthoughGO beignitedsimultaneously,bettercontrolandstabilityalongwith
hasbeenknownforover150years,onlyrecentlyhavescientists lowered weight should be achievable.[32–34] Attempts aimed at
hadaccesstothetoolsnecessarytoproperlyanalyzeitsatomically usingCNTsforignitionapplications,however,havefailed,since
thinsheetstructure.Thishasrekindledinterestingraphiteoxide theCNTcombustionrequiresoutsideoxygen.Infact,theCNTs
and has led to a number of recent discoveries, including: the themselves – like C and carbon soot – play little role in the
60
stacking of GO platelets to form paper-like materials of high ignitionprocess,insteaditistheironnanoparticlecatalystusedto
modulusandstrength.[6,7]ManystudieshavesuggestedthatGO grow them, along with oxygen, that supports combustion.[35–37]
can be reduced to graphene-like carbon sheets by applying Even with sufficient catalyst, uniformly dispersing CNTs into
chemical reducing agents or by using thermal treatments.[8–10] liquidfuelsremainsproblematic.Herewereportthediscoveryof
ThishasledtospeculationthatGOcouldfinduseasaprecursor the photothermally initiated deflagration of GO that can take
in a bulk route to dispersible graphene sheets.[11–13] Already, placeeveninanoxygendeficientenvironment.SinceGOreadily
several groups have succeeded in creating conducting polymer disperses in alcohols and other polar organic solvents, pre-
composites,transparentconductingfilms,andsimpleelectronic liminary results indicate that with some chemical modification
devicesbasedonreducedGO.[14–26]Inadditiontothechemical GO could be dispersed in fuels as well. This along with the
reduction of GO, Aksay, et al. have reported the thermal currentinterestinGOasananoscaleplateletmaterialgaveusthe
impetustoinvestigatethisphotothermallydrivenprocessfurther.
A random porous network of GO platelets is created by
[*] Dr.S.Gilje,Dr.J.Farrar freeze-dryingGOdispersions.Theporousstructureresultsfrom
NorthropGrummanAerospaceResearchLabs theextractionofwaterwithoutcausingcollapseofthesolidmatrix
NorthropGrummanCorporation of GO platelets due to capillary action, as would happen with
RedondoBeach,California,90278(USA)
conventional evaporation. Creating dry, low-density networks of
E-mail:[email protected]
nanoscaleGOplateletsservestwopurposes:first,thesurfaceto
S.Dubin,Prof.R.B.Kaner
volume ratio of the platelets is increased providing maximum
DepartmentofChemistryandBiochemistryandCalifornia
NanoSystemsInstitute,UniversityofCaliforniaLosAngeles surfaceareaforenergyabsorption;second,thermallyconductive
LosAngeles,California,90095(USA) pathways through which absorbed energy can diffuse are
Dr.A.Badakhshan reduced. The GO dispersions were comprised of platelets
JacobsTechnology/RossGroupAirForce ranginginsizefrom100nm–5mmindiameterwiththemajority
ResearchLabEdwardsAFB,CA93524(USA)
of platelets around 500nm in diameter as analyzed by atomic
Dr.S.A.Danczyk forcemicroscopy.TheGOfoamnetworksenablegreaterenergy
AeroPhysicsBranch,CombustionDevicesGroup
absorption and confinement leading to dramatic temperature
AirForceResearchLaboratory;EdwardsAFB,California(USA)
increases on exposure to a camera flash. Using freeze-drying,
DOI: 10.1002/adma.200901902 porousGOfoamscanbemadetodensitiesdownto5mgcm(cid:2)3
Adv.Mater.2010,22,419–423 (cid:1)2010WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim 419
www.advmat.de
N graphitic platelets can be observed. Using
O the scale bar as a gauge, the thickness of the
I thinnestexpandedsheetscanbeseentorange
T
A from10to20nm.
C X-ray powder diffraction of a compressed
I
N pellet of the reduced graphite oxide shows a
U broad, low-intensity peak centered at
M 2u¼26.48 indicating that after deflagration
M the product is, in fact, graphitic in nature.[30]
Thebroadnessofthediffractionpeakismost
O
likelyduetoboththesmallcrystallinedomain
C
sizes of the graphitic planes and the turbos-
tratic nature of the expanded sheets. The
deoxygenated carbon material that remains
after photothermally induced deoxygenation
wasanalyzedforitscarbonandoxygencontent
usingX-rayphotoelectronspectroscopy(XPS)
(see Supporting Information). The carbon
content increases from 68.7% in the GO
starting material, to 92.1%, while the oxygen
content decreases from 29.3 to 7.7%. The
remaining oxygen is most likely contained in
residualfunctionalities((cid:2)COOH,(cid:2)OH,etc.)
Figure1. a) An image of a GO foam sample before exposure to a photographic flash. b) A due to incomplete deoxygenation. Resistivity
scanningelectronmicrograph(SEM)showstheporousnatureoftheGOfoam.c)Afterflashing,
measurements taken on the deoxygenated
theGOfoamignitesreleasingCO andHOandleavingbehindanexfoliated,deoxygenated
2 2 carbon resulted in a resistivity decrease from
graphiticcarbon.d)AnSEMimageofthematerialshowsexfoliatedlayers.(inset)Underhigh
magnification,thelayersmeasure10–20nminthickness. 9.98(cid:3)104V(cid:4)cmbeforeflashingto2.23V(cid:4)cm
afterphotoinduceddeoxygenation.Thechange
inresistivityofoverfourordersofmagnitude
beforethestructurecollapsesunderitsownweight.Mostofthe isconsistentwithotherformsofreducedGOobtainedbythermal
GO foams used in this study had a density of 15mgcm(cid:2)3. means.[27,28]
Figure 1a is a photograph of a light-brown GO foam sample DuetotheexpandednatureoftheflashedGOfoams,theywere
prepared by freeze drying a 15mgml(cid:2)1 dispersion to achieve a analyzedforsurfaceareabymeasuringN gasuptakeusingthe
2
densityof15mgcm(cid:2)3.Figure1bshowsanSEMmicrographof Brunaur-Emmett-Teller(BET)analysismethod.Beforeflashing,a
thesamesamplemagnified1000(cid:3).IntheSEMimage,theGO GO foam with a density 15mg cm(cid:2)3 was measured to have a
platelets appear as crumpled sheets ranging in diameter from surface area of 6m2 g(cid:2)1. After flashing, the measured surface
500nm to 20mm, that assemble to form a porous three- areayieldedarangefrom400to980m2g(cid:2)1.Webelievethelarge
dimensionalnetwork.ThemechanicalintegrityoftheGOfoams range in values can be attributed to difficulties in determining
increase with increasing density. Foams with a density of thesampleweightandadsorbedwatercontent.Exposureofthe
<5mgcm(cid:2)3 typically collapsed easily and were difficult to flashed, deoxygenated carbon to hydrogen was performed,
handle. Foams with a density ranging from 10 to 20mgcm(cid:2)3 resulting in anuptakeof 0.5wt%at 77K.
were robust but required careful handling, while denser foams In additiontoGO foammaterials,it ispossible tomakeGO
were quite sturdy much like a commercial silica aerogel. After filmswhichcanbephotothermallypatterned.Toaccomplishthis,
flashing,thefoamslosetheirstructuralrobustness,fallapart,and thin GO films (<1mm in thickness) were created by filtering a
areeasily blownaround bygusts ofair. dilute GO dispersion through a 0.2mm Nylon Millipore filter.
Uponexposuretoaphotographicflash,theGOfoamemitsa Figure 2a shows optical microscope images of a copper
poppingsoundmostlikelyattributabletoaphotoacousticeffect transmission electron microscope (TEM) grid placed on top of
similar to the flashing of CNTs.[38] A color change from light aGOfilmwhilestillattachedtotheNylonfilter.UsingtheTEM
browntodarkblackcanbeseenimmediatelyafterexposuretothe gridasamask,theGOfilmwasexposedtoaflashatcloserange
flashindicatingconversiontodeoxygenatedgraphiticcarbon.A inducing deoxygenation to graphitic carbon. Figure 2b is an
photographoftheflashedGOfoamisshowninFigure1c.The opticalmicroscopeimageoftheGOfilmafterflashing.Lookingat
lightbrownspotsaroundtheperipheryofthesamplecorrespond the image, defined regions of black (exposed) and brown
totheunreactedregionsattheedgesofthesampleasaresultof (masked) can clearly be seen mimicking the TEM grid mask.
cooling and expansion of the foam as the reaction front SEMimagesofthemaskedfilm(Fig.2c)showhowtheexposed
propagates. Figure 1d, shows an expanded structure much like regions on the GO film expand outward upon ignition by the
that of exfoliated graphite and comparable to recent reports on flash.ThereleaseofCO andH Oduringdeflagrationislikelythe
2 2
thermallyreducedGO.[27,28]TheinsetpictureofFigure1dshows causeof theplatelets pushing out fromthe surfaceof thefilm.
the flashed GO foam at 100000(cid:3) magnification. At this Another promising application for photothermally initiated
magnification, the expanded nature of the flash deoxygenated reactionsisasanignitionpromoterforfuels.BydispersingGO
420 (cid:1)2010WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim Adv.Mater.2010,22,419–423
www.advmat.de
In preliminary experiments, we have been C
abletosuccessfullyigniteethanolfuelsusing O
GO as a photothermal initiator. Figure 3a M
showsaphotoofaGOfoamsampleplacedon M
a paper soaked with ethanol. Upon flashing U
(Fig.3b),theethanolvaporreadilycombustsas N
a result of the GO ignition. After the ethanol I
C
fuelisconsumed,wecanseethedeoxygenated A
carbonproductglowingbrightredasaresult T
I
ofthecombustionreactionandthevolumeof O
the sample increases due to exfoliation N
(Fig. 3c). Pyrometer readings of this ignition
processindicatethatbyflashingGOachieves
temperatures of 400–5008Cwithin a few ms.
In our experiments, we were able todisperse
GO platelets into ethanol and methanol with
mild sonication. The GO platelets did not
disperse well in more aliphatic fuels such as
Figure2. a) An opticalmicroscopyimage shows a GO film with a Cu transmission electron kerosene. We speculate that dispersibility of
microscopy(TEM)gridontopbeforeflashing.b)AfterflashingandremovingtheTEMmask,the GOinorganicscouldbefacilitatedwiththeuse
patternoftheTEMgridhasbeentransferredtotheGOfilmasseenintheopticalmicroscope ofsurfactantswithoutlossofthephotothermal
images.c)ThedeoxygenationandsubsequentreleaseofCO2andH2Oblowtheplateletsof function of GO platelets as an ignition
deoxygenatedcarbonoutfromthesurfaceasdepictedinseriesofSEMimagesatprogressively
promoter.
highermagnifications.
Over the past decade, extraordinary efforts
havebeenundertakentobothimprovethefuel
efficiency of traditional gasoline engines and
plateletsinaliquidfuel,itcouldbepossibletoinitiateignitionof searchforclean,renewablealternativefuelstogasoline.Oneidea
the fuel using a flash of light as opposed to a traditional spark thathassurfacedfromthisthrustisthenotionofahomogeneous
plug. Illumination of a fuel/oxidizer mixture would enhance charge compression ignition (HCCI) engine that combines the
combustionbyallowingignitiontooccuratnumerouslocations high efficiency of a diesel engine with the low emissions of a
simultaneously.Oneofthemajordrawbacksofcurrentelectrical sparkignitionengine.InatypicalHCCIengine,fuelandairare
sparkignitionisthatitisasingle-pointignitionsource.Ideally, mixedhomogeneouslylikeasparkignitionengine,butignition
multipleignitionnucleationsiteswillallowformorecontrollable, occursbymeansofauto-ignitionunderhighcompressionsimilar
and therefore more efficient and reliable ignition and combus- to a diesel engine.[40] The high compression ratio of HCCI
tion.Thisisofcriticalimportanceforapplicationssuchasliquid engines provides an efficiency increase of up to 15% over
fueledrockets,wherecurrentignitionmethodsareknowntobe traditional spark ignition engines.[41,42] Currently, one of the
plagued by several problems. Issues such as combustion majorchallengesfacingHCCIengineshasbeencontrollingthe
instability and start-up transients not only can cause severe unpredictable compression-induced ignition process. By using
damage,butalsodegradationinengineefficiencyandanincrease anignitionpromotersuchasGO,itcouldbepossibletoachieve
in emissions of pollutants. It is thought that nearly 30% of distributed ignition in HCCI engines, thus providing accurate
thecombustioninstabilitiesinrocketengines,leadingtoengine ignitiontiming,resultinginthehomogeneousdetonationoffuel
damageandpossiblelossofcargoandhumanlife,canbetraced andair.
back to the nature of the propellant’s initial energy release Highlyabsorbingnanoparticulatematerialsareabletoachieve
process,as describedbyHarrjeandReardon.[39] adramatictemperatureincreaseuponexposuretoshortpulsesof
The short-comings of the existing systems combined with moderateintensitylight.Thesetemperatureincreasesoccurasa
intuitive engineering advantages of low-
energy, lightweight distributed ignition, has
motivatedpreviousattemptstousesinglewall
carbon nanotubes (SWNTs) as photoignition
enabling additives to fuels.[32–34] In these
experiments, the SWNTs were found to only
igniteinthepresenceofambientoxygenand
didnotdispersewellinthetestfuels.Flashing
ofSWNTsisalsoheavilydependentontheFe
catalystconcentration.Incontrast,GOcarries
Figure3. AseriesofphotographsshowingaGOfoamsamplebefore,duringandafterflash
itsownoxygensupplyandishighlydispersible
ignitionwiththetimeintervallabeledinmilliseconds(ms).ByplacingaGOfoamsampleontoa
infuelssuchasalcohol;therefore,GOmaybe
papersoakedwithethanolandflashing,theGOfoamiscapableofignitingtheethanolvaporas
a promising additive as an ignition promoter depictedin the centerphotograph. Afterignition,the deoxygenated GO samplecanbe seen
forfuels. glowingredfromtheenergyreleasedduringthereaction.
Adv.Mater.2010,22,419–423 (cid:1)2010WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim 421
www.advmat.de
N consequenceofthehighsurfacetovolumeratioandlownumber A liquid nitrogen bath (77K) was used for N2 and H2 isotherm
O ofthermallyconductingpathwaysbywhichtodissipateabsorbed measurements. The N2, H2, and He gases used were UHP grade. For
measurementoftheapparentsurfaceareas(SLang),theLangmuirmethod
I light energy. One of the distinguishing characteristics that sets
T wasappliedusingtheadsorptionbranchesoftheN isothermsassuminga
A photothermal ignition of GO apart from the flashing of other N cross-sectionalareaof16.2A˚2/molecule.Them2icroporevolumes(Vp)
C nanomaterials, is that instead of merely igniting or melting a we2re determined using the Dubinin-Raduskavich (DR) transformed N
I 2
N material, an exothermic decomposition reaction occurs. The isothermsacrossthelinearregionofthelowpressuredata.
U benefitofsuchaprocessisthattheenergyrequiredforignitionis
M notprovidedsolelybythesourceoftheflashasitwouldbewith
M other nanomaterials. This enables the use of lower power light Acknowledgements
sourcesand/orlargerparticlesinordertoachieveignition,since
O
C the combustion of the particles themselves adds energy to the The authors thank Hsiao Hu Peng for use of his lab facilities and
system. In the future, GO or other oxygen bearing, self- freeze-dryingsystem;ChristinaBaker,VincentTung,JonathanWassei,and
decomposing particles may make it possible to tune the HenryTranfortheirhelpincarryingoutmeasurementsandintellectual
photoignition behavior of a fuel to provide more controllable contributions;YanXuforhelpmakingopticalmeasurements;Dr.Hiroyasu
Furukawaforcarryingouthydrogenabsorptionmeasurements;andGrant
distributed ignition. In patterning applications, the solubility
UmedaforhishelpwiththeBETmeasurements.Fundingforthisresearch
differencesbetweenGOanddeoxygenatedgraphiticcarboncould
has been provided by The Northrop Grumman Corporation, Aerospace
beusedtoquicklyseparateexposedandmaskedregionsofathin SystemsDivision,AerospaceResearchLabs(ARL)internalresearchand
GOfilm.Usinganorganicsolvent,thebroken-upflashedareasof development(IRAD)fundwithmatchingsupportfromtheUniversityof
aGOfilmcouldbewashedawayleavingthemaskedGOportions California Discovery Program (RBK), the Focused Center Research
intact. Subsequent thermal or chemical reduction of the ProgramFunctionalEngineeredNanoArchitectonics(FCRP/FENA)Center
(RBK),andtheAirForceResearchLabs(AFRL)NanoEnergeticsStrategic
patterned GO films to conducting, reduced GO would make it
TechnologyTeams(STT).SupportingInformationisavailableonlinefrom
possible tocreatehighly conducting patterns.[43]
WileyInterScienceorfromtheauthor.
Received:June5,2009
Publishedonline:October26,2009
Experimental
Synthesis: GrapheneoxidewassynthesizedusingamodifiedHummer’s
method as reported previously in ref. [14]. Dispersions of GO were
freeze-dried using an FTS systems Dura-Stop mP Freeze-drying system. [1] P.M.Ajayan,G.Ramanath,M.Terrones,T.W.Ebbesen,Science2002,297,
Dispersion concentrations of 30, 15, 7.5, and 3.25mg ml(cid:2)1 were
192.
freeze-dried resulting in porous GO materials with densities of 30, 15,
[2] J.Huang,R.B.Kaner,Nat.Nanotechnol.2004,3,783.
7.5, and 3.25mg cm(cid:2)3, respectively. Figure S1 is an SEM image of the
[3] N.Wang,B.D.Yao,Y.F.Chan,X.Y.Zhang,NanoLett.2003,3,475.
lowestdensity3.25mgcm(cid:2)3sampleshowingthenetworkofthinplatelets.
[4] J.Ying,NanostructuredMaterials,AcademicPress,NewYork2001.
FilmsamplesofGOwereobtainedbyfiltrationofaGOdispersionthrough
[5] B.Brodie,Ann.Chim.Phys.1855,45,351.
a 0.22mm Anapore filter for free-standing films, and a 0.2mm Nylon
[6] D. Dikin, S. Stankovich, E. J. Zimney, R. D. Piner, H. B. Dommett,
Milliporefilterforthinfilmsthatremainedboundtothefiltermembranefor
G.Evmenenko,S.T.Nguyen,R.S.Ruoff,Nature2007,448,457.
stability.
Characterization: X-ray diffraction (XRD) was carried out using a [7] S.Park,K.S.Lee,G.Bozoklu,W.Cai,S.Nguyen,R.S.Ruoff,ACSNano
PANalyticalXPertProdiffractometerwithCuKaradiation(l¼1.5418A˚). 2008,2,572.
BeforetakingX-rayscanstheGOwasdriedfor48hundervacuumatroom [8] S.Stankovich,D.A.Dikin,R.D.Piner,K.A.Kohlhaas,A.Kleinhammes,
temperature followedby 24h under vacuum over PO which acts as a Y.Jia,Y.Wu,S.T.Nguyen,R.S.Ruoff,Carbon2007,45,1558.
2 5
drying agent. Powder X-ray diffraction can be used to verify that the [9] S. Stankovich, R. D. Piner, X. Chen, N. Wu, S. T. Nguyen, R. S. Ruoff,
oxidationreactionhasreachedcompletionsincetheintroductionofoxygen J.Mater.Chem.2006,16,155.
moietiesexpandstheinterplanargalleriesingraphitefrom3.34to(cid:1)6.9A˚. [10] U.Hofmann,A.Frenzel,KolloidZ1934,68,149.
Our graphite oxide exhibits a characteristic peak at 12.75 degrees 2u [11] V.C.Tung,M.J.Allen,Y.Yang,R.B.Kaner,Nat.Nano.2008,4,25.
corresponding to the 002 interplanar spacing of 6.94A˚, while the most [12] D.Li,M.B.Muller,S.Gilje,R.B.Kaner,G.G.Wallace,Nat.Nano.2007,3,
intensepeakfromthestartinggraphiteat26.4degrees2u,corresponding 101.
toa d-spacingof3.34A˚,is completelyabsent. Thed-spacingofslightly [13] S.Park,J.An,R.D.Piner,I.Jung,D.Yang,A.Velamakanni,S.T.Nguyen,
>6.9A˚forthesynthesizedGOindicatesthatdespitedryingundervacuum R.S.Ruoff,Chem.Mater.2008,20,6592.
for24h,somewaterhasbeenabsorbedbytheGO.
[14] S.Gilje,S.Han,M.S.Wang,K.L.Wang,R.B.Kaner,NanoLett.2007,7,
The GO and reduced GO samples were inserted into the analysis
3394.
chamberofaThermoVGESCALAB250,X-rayphotoelectronspectrometer.
[15] C. Gomez-Navarro, R. T. Weitz, A. M. Bittner, M. Scolari, A. Mews,
Spectrawereobtainedbyirradiatingthesamplewitha320mmdiameter
M.Burghrd,K.Kern,NanoLett.2007,7,3499.
spotofmonochromatedaluminumKaX-raysat1486.6electronVolts(eV)
[16] S.Stankovich,D.A.Dikin,G.H.B.Dommett,K.M.Kohlhaas,E.J.Zimney,
under ultrahigh vacuum conditions. The analysis consisted of acquiring
E. A. Stach, R. D. Piner, S. T. Nguyen, R. S. Ruoff, Nature 2006, 442,
10–20scansandsignalaveraging.Thesurveyscanswereacquiredwitha
282.
passenergyof80eV,andthehighresolutionscanswereacquiredwitha
pass energy of 20eV. Low pressure gas adsorption isotherms were [17] S. Watcharotone, D. A. Dikin, S. Stankovich, R. Piner, I. Jung,
measured volumetrically on an Autosorb-1 analyzer (Quantachrome G. H. B. Dommett, G. Evmenenko, S. E. Wu, S. F. Chen, C. P. Liu,
Instruments). Conductivity data were obtained using a Jandel RM3-AR S.T.Nguyen,R.S.Ruoff,NanoLett.2007,7,1888.
resistivitytesterusinganappliedcurrentof4.532mAincombinationwitha [18] H.Chen,M.B.Muller,K.J.Gilmore,G.G.Wallace,D.Li,Adv.Mater.2008,
four-point probe head. Optical microscope images were taken using a 20,3557.
ZeissAxioTech100reflectedlightmicroscopewithZeissAxioCamMRc [19] R. Arsat, M. Breedon, M. Shafiei, P. G. Spizziri, S. Gilje, R. B. Kaner,
camera. K.Kalantar-zadeh,W.Wlodarski,Chem.Phys.Lett.2008,467,344.
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