Research ArticleStudy of Reduced Graphene Oxide Preparation byHummersrsquo Method and Related Characterization
Ning Cao and Yuan Zhang
College of Mechanical and Electrical Engineering China University of Petroleum Qingdao 266580 China
Correspondence should be addressed to Ning Cao caoning1982gmailcom
Received 13 August 2014 Accepted 25 September 2014
Academic Editor Liang-Wen Ji
Copyright copy 2015 N Cao and Y ZhangThis is an open access article distributed under theCreative CommonsAttribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
As a novel two-dimensional carbon material graphene has fine potential applications in the fields of electron transfer agent andsupercapacitor material for its excellent electronic and optical property However the challenge is to synthesize graphene in a bulkquantity In this paper graphite oxide was prepared from natural flake graphite by Hummersrsquo method through liquid oxidizationand the reduced graphene oxide was obtained by chemical reduction of graphene oxide using NH
3sdotH2O aqueous solution and
hydrazine hydrate The raw material graphite graphite oxide and reduced graphene oxide were characterized by X-ray diffraction(XRD) attenuated total reflectance-infrared spectroscopy (ATR-IR) and field emission scanning electron microscope (SEM) Theresults indicated that the distance spacing of graphite oxide was longer than that of graphite and the crystal structure of graphitewas changed The flake graphite was oxidized to graphite oxide and lots of oxygen-containing groups were found in the graphiteoxide In the morphologies of samples fold structure was found on both the surface and the edge of reduced graphene oxide
1 Introduction
Graphene is a novel 2-dimensional material which was firstseparated from graphite by mechanical stripping method in2004 [1] As an allotrope of element carbon it is a planar sheetof carbon atoms arranged into hexagon [2] The ldquothinnestrdquoknown material graphene can be used for biosensors [3]transparent electrodes [4] hydrogen storage composites [5]and high energy supercapacitors [6] for its high optical andelectron transparency and excellent mechanical properties[7]
There are many ways to synthesize graphene [1 8 9]such as exfoliation and cleavage chemical vapor deposition(CVD) thermal decomposition and electrochemical reduc-tion Among these preparation methods solution-basedreduction of graphite oxide (GO) is attractive for its easyoperation in recent years It includes three typical steps inthis method They are graphite oxidation GO aqueous dis-persion and GO reductionThemethods invented by BrodieStaudenmaier and Hummers are widely used for graphiteoxidation [10] And Hummersrsquo method is popular for thefollowing reasons First KClO3 was replaced by KMnO4 asthe oxidation agent In this condition the byproducts of toxic
gas were eliminated and the securities of experiments wereimproved Moreover the oxidation time was shortened andlast it was easy to exfoliate the resulted product in waterIn this paper Hummersrsquo method was employed to prepareGO and reduced GO (rGO) was obtained with the aid ofNH3sdotH2O aqueous and hydrazine hydrate
2 Experimental
21 Raw Materials Flake graphite powder 98wt H2SO4
KMnO4 NaNO
3 deionized water NH
3sdotH2O aqueous dilute
HCl aqueous 30 H2O2aqueous and 80 hydrazine
hydrate aqueous
22 Graphene Preparation221 GO Preparation Themixture of flake graphiteNaNO
3
was prepared in weight ratio of 2 1 The mixture was addedinto a beaker with a certain amount of 98wt H
2SO4at
15∘C and a suspension was obtained Then KMnO4powder
which acted as an oxidation agent was gradually added intothe suspension with continuous stirring The weight of theKMnO
4powder is 3 times as much as the one of the mixture
Hindawi Publishing CorporationJournal of NanomaterialsVolume 2015 Article ID 168125 5 pageshttpdxdoiorg1011552015168125
2 Journal of Nanomaterials
Figure 1 Pattern of resulting suspension
There were 3 steps for the following process First of allit is the low temperature reaction The temperature of themixture was controlled below 20∘C for 2 hours at the sametime the suspension should be stirred continuously Thesecond step is themid temperature reactionThe temperatureof the mixture was maintained at 35∘C for 30 minutesafter KMnO
4was totally dissolved Finally it is the high
temperature reaction A certain amount of deionized waterwas added into the mixture slowly therefore a large amountof heat was released when concentrated H
2SO4was diluted
15 minutes later certain amounts of hot water and 30H2O2aqueouswere added into themixture respectively with
continuously stirring As Figure 1 shows the bright yellowresulted suspension was filtered by the qualitative filter paperwhen it was still hot and the solid mixture was washed withdilute HCl aqueous and distilled water and dried in vacuumoven at 70∘C for 24 h
222 rGO Preparation 400mgGOwas dispersed in 400mLwater by means of 30 minutesrsquo ultrasonic treatment As aresult a homogeneous brown GO aqueous suspension wasobtained The pH of the suspension was adjusted to 10 bydropping NH
3sdotH2O A mount of hydrazine hydrate was
added into suspension and heated at 80∘C for 24 hours andthe weight ratio of hydrazine hydrate and GO was controlledat 10 7 A kind of black flocculent substance was graduallyprecipitated out of the solutionThe product was obtained byfiltered with the qualitative filter paper Finally the resultingblack productwaswashedwithmethanol andwater and driedat 80∘C for 24 h
23 Characterization of Materials Crystal features of flakegraphite GO and rGO were obtained by XRD [10] (AXScooperation Germany) with a scan speed of 4∘min from 5to 60∘ of 2120579 angles The layer spacing (119889 spacing) could becalculated with the aid of Bragg equation and the change ofdiffraction peak could also be observed The micromorphol-ogy of rGO was observed by SEM (JSM-6700F Japan) withthe acceleration voltage from 05 to 30KV Spectra of driedGO and rGO were obtained by Tensor 27 FTIR-ATR (Bruker
cooperation Germany) with the resolution of 4 cmminus1 from3700 to 500 cmminus1 of spectral region and functional groups ofGO and rGO can be observed
3 Result and Discussion
31 X-Ray Diffraction As shown in Figure 2(a) Flakegraphite exhibits a basal diffraction peak (002) at 2120579 = 265∘(119889 spacing = 033630 nm) which is very sharp There is alsoa very weak diffraction peak (004) at 2120579 = 548∘ (119889 spacing= 016738 nm) The diffraction peak (004) is the seconddiffraction [11] of the diffraction peak (002) according to layerspatial arrangement rules of microcrystals thus diffractionpeak (004) intensity is much weaker than that of diffractionpeak (002) The diffraction peak at about 2120579 = 98∘ is verytypical for GO no apparent diffraction peak could be foundfor rGO in its XRD pattern This result is similar to thatof Tapas Kuila [2] who had already described the structureof GO and rGO by XRD Figures 2(b) and 2(c) show theenlarged XRD patterns of GO and rGO Diffraction peakbecomes broader in the enlarged pattern of GO at 2120579 = 98∘ (119889spacing = 088160) and the significant increase in 119889 spacingis believed due to the following reason oxygen functionalgroups intercalate in the interlayer of graphiteThere is a veryweak diffraction peak at 2120579 = 423∘ which is believed due tothe incomplete oxidation As is shown in Figure 2(c) a veryweak and broad diffraction peak can be observed in the XRDpattern of rGO at 2120579 = 25ndash30∘ the diffraction peak of rGOis so weak that it cannot be visible when drawn together inthe XRD pattern with graphite and GO (Figure 2(a)) Thereis also a weak diffraction peak at 2120579 = 423∘
32 FTIR-ATR FTIR-ATR spectra of GO and rGOare shownin Figures 3 and 4 Some carbon-oxygen functional groupsof GO are observed in Figure 3 such as OndashH C=O CndashOHand CndashO Characteristic peak (sim3464 cmminus1) [12] is believedto be attributed to OndashH stretching of hydroxyl and carboxylgroups and characteristic peaks of C=O (sim1639 cmminus1) CndashOH (sim1288 cmminus1) and CndashO (sim1003 cmminus1) are also believed tobe attributed to carboxylic acid and carbonyl groups [13] Andthe characteristic peak at 1493 cmminus1 is corresponding to theC=C skeletal vibration of unoxidized graphitic domainTheseoxygen functional groups indicate that the flake graphitepowder has been oxidized to GO As shown in Figure 4no obvious peak could be observed which means that fullreduction of GO was made While carbon-oxygen functionalgroups all existed their characteristic peaks are just veryweak
33 Scanning ElectronMicroscope Figure 5 shows SEMmor-phologies of rGO which was dried at 80∘C for 1 day As isshown in Figure 5 2-dimensional material can be observedFold structure can be found on both the surface and the edgeof rGO powder They are the typical morphologies of few-layer rGo [14] The thickness of rGO may be 10 nm and it isobviously that rGO layers have fairly large dimension (muchlarger than 100 nm) and rGO retacked together The reasonof the reagglomerate may be the long-time high temperature
Journal of Nanomaterials 3
5 10 15 20 25 30 35 40 45 50 55 60
Inte
nsity
GraphiteGOrGO
(002)
(004)
2120579 (deg)
(a)
5 10 15 20 25 30 35 40 45 50 55 60
Inte
nsity
GO
2120579 (deg)
(b)
5 10 15 20 25 30 35 40 45 50 55 60
Inte
nsity
rGO
2120579 (deg)
(c)
Figure 2 X-ray diffraction patterns (a) graphite GO and rGO (b) enlarged view of GO (c) enlarged view of rGO
3500 3000 2500 2000 1500 1000 500
GO
OH (coupling)C=O
C=CCndashO
CndashOH
Wave number (cmminus1)
Figure 3 FTIR-ATR spectra of GO
4 Journal of Nanomaterials
3500 3000 2500 2000 1500 1000 500
OH (coupling)
rGO
C=O
CndashO
CndashOH
Wave number (cmminus1)
Figure 4 FTIR-ATR spectra of rGO
Fold structure of the surface
100nm
(a)
Fold structure of the edge
100nm
(b)
Figure 5 SEM morphology of rGO
treatment The morphology of graphite (fold structure) canalso be found in Figure 5
Reaction mechanism of solution-based reduction ofgraphite oxidewill be discussed to beginwith themechanismof Hummers though KMnO
4is used as a kind of oxidizing
agent Dreyer et al [15] believed that the active species wasMn2O7 The following equation gives the reaction between
KMnO4and H
2SO4
KMnO4+ 3H2SO4997888rarr K+ +MnO+
3+H3O+ + 3HSOminus
4
MnO+3+MnOminus
4997888rarr Mn
2O7
(1)
In low temperature reaction the edge of graphite was oxi-dized and intercalated with the aid of oxidizing agent minusOHwas formed during this process Inmid temperature reactionwith the increasing of temperature the oxidation abilityimproves furthermore More oxygen functional groups areformed in this process and the oxidizing agent penetratesinto the internal of graphite layer therefore this processresults in the increasing of 119889 spacing In the high temperaturereaction concentrated H
2SO4releases large amount of heat
during the process of watering Force between layers is
destroyed and finally the GO could be fully exfoliated tosingle layers Secondly the fully exfoliatedGOwill be reducedto rGO with the help of NH
3sdotH2O aqueous and hydrazine
hydrateThe mechanism of solution-based reduction of GO
is quite different with that of the traditional CVD onesThe formation of graphene on bulk metal through CVDincludes three steps [1 16 17] First a hydrocarbon couldbe dissociated through dehydrogenation second the carbonspecies diffuse and dissolve into the bulk metal at thegrowth temperature the reason why transition metals couldserve as an electron acceptor is because of the empty d-shell third carbon species precipitate out of the bulk metalonto the metal surface upon the rapid quenching start thesegregation process and build up honeycomb lattice becausethe solubility decreases during the cooling process
4 Conclusion
GO was prepared by Hummersrsquo method and rGO wasprepared with the aid of NH
3sdotH2O aqueous and hydrazine
hydrate successfullyThe characterization results indicate that
Journal of Nanomaterials 5
the layer spacing of graphite oxide was longer than thatof graphite The crystal structure of graphite was changedGraphite was oxidized to GO and lots of oxygen-containinggroups were found in the GO The typical fold morphologieswere found on both the surface and the edge of rGO
Compared with the traditional CVD method Hummersrsquomethod can synthesize GO in large scale then rGO can beprepared with the help of reduced agent and this processcosts a little Meanwhile the prepared GO is dispersed easilyin solution In this case the modification of the GO is easyand it is suitable for GO application in composites and energystorage devices
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publishing of this paper
Acknowledgments
The authors acknowledge funding from the National NaturalScience Foundation of China (no 51302320) and the Fun-damental Research Funds for the Central Universities (no14CX05094A)
References
[1] V Singh D Joung L Zhai S Das S I Khondaker and S SealldquoGraphene based materials past present and futurerdquo Progressin Materials Science vol 56 no 8 pp 1178ndash1271 2011
[2] M I Katsnelson ldquoGraphene carbon in two dimensionsrdquoMaterials Today vol 10 no 1-2 pp 20ndash27 2007
[3] T Kuila S Bose P Khanra A K Mishra N H Kim andJ H Lee ldquoRecent advances in graphene-based biosensorsrdquoBiosensors and Bioelectronics vol 26 no 12 pp 4637ndash46482011
[4] G Eda G Fanchini and M Chhowalla ldquoLarge-area ultrathinfilms of reduced graphene oxide as a transparent and flexibleelectronic materialrdquo Nature Nanotechnology vol 3 no 5 pp270ndash274 2008
[5] T Kuilla S Bhadra D Yao N H Kim S Bose and J HLee ldquoRecent advances in graphene based polymer compositesrdquoProgress in Polymer Science vol 35 no 11 pp 1350ndash1375 2010
[6] B G Choi M YangW H Hong J W Choi and Y S Huh ldquo3Dmacroporous graphene frameworks for supercapacitors withhigh energy and power densitiesrdquo ACS Nano vol 6 no 5 pp4020ndash4028 2012
[7] Y Zhu S Murali W Cai et al ldquoGraphene and graphene oxidesynthesis properties and applicationsrdquo Advanced Materialsvol 22 no 35 pp 3906ndash3924 2010
[8] T Kuila S Bose A K Mishra P Khanra N H Kim andJ H Lee ldquoChemical functionalization of graphene and itsapplicationsrdquo Progress in Materials Science vol 57 no 7 pp1061ndash1105 2012
[9] S Y Toh K S Loh S K Kamarudin and W R WanDaud ldquoGraphene production via electrochemical reductionof graphene oxide synthesis and characterisationrdquo ChemicalEngineering Journal vol 251 pp 422ndash434 2014
[10] C Bao L Song W Xing et al ldquoPreparation of graphene bypressurized oxidation and multiplex reduction and its polymer
nanocomposites by masterbatch-based melt blendingrdquo Journalof Materials Chemistry vol 22 no 13 pp 6088ndash6096 2012
[11] A Bagri C Mattevi M Acik Y J Chabal M Chhowallaand V B Shenoy ldquoStructural evolution during the reduction ofchemically derived graphene oxiderdquo Nature Chemistry vol 2no 7 pp 581ndash587 2010
[12] Y Jin S Sun and X Qi National Defense Industry Press 2008(Chinese)
[13] Q Deng L Liu and H Deng Spectrum Analysis TutorialScience Press 2007 (Chinese)
[14] FHong L Zhou andYHuang ldquoSynthesis and characterizationof graphene by improved hummers methodrdquo Chemical ampBiomolecular Engineering vol 29 pp 31ndash33 2012 (Chinese)
[15] D R Dreyer S Park C W Bielawski and R S Ruoff ldquoThechemistry of graphene oxiderdquoChemical Society Reviews vol 39no 1 pp 228ndash240 2010
[16] Y Kai F Lei L P Hai and F L Zhong ldquoDesigned CVD growthof graphene via process engineeringrdquo Accounts of ChemicalResearch vol 46 pp 2263ndash2274 2013
[17] C-M Seah S-P Chai and A R Mohamed ldquoMechanisms ofgraphene growth by chemical vapour deposition on transitionmetalsrdquo Carbon vol 70 pp 1ndash21 2014
There were 3 steps for the following process First of allit is the low temperature reaction The temperature of themixture was controlled below 20∘C for 2 hours at the sametime the suspension should be stirred continuously Thesecond step is themid temperature reactionThe temperatureof the mixture was maintained at 35∘C for 30 minutesafter KMnO
4was totally dissolved Finally it is the high
temperature reaction A certain amount of deionized waterwas added into the mixture slowly therefore a large amountof heat was released when concentrated H
2SO4was diluted
15 minutes later certain amounts of hot water and 30H2O2aqueouswere added into themixture respectively with
continuously stirring As Figure 1 shows the bright yellowresulted suspension was filtered by the qualitative filter paperwhen it was still hot and the solid mixture was washed withdilute HCl aqueous and distilled water and dried in vacuumoven at 70∘C for 24 h
222 rGO Preparation 400mgGOwas dispersed in 400mLwater by means of 30 minutesrsquo ultrasonic treatment As aresult a homogeneous brown GO aqueous suspension wasobtained The pH of the suspension was adjusted to 10 bydropping NH
3sdotH2O A mount of hydrazine hydrate was
added into suspension and heated at 80∘C for 24 hours andthe weight ratio of hydrazine hydrate and GO was controlledat 10 7 A kind of black flocculent substance was graduallyprecipitated out of the solutionThe product was obtained byfiltered with the qualitative filter paper Finally the resultingblack productwaswashedwithmethanol andwater and driedat 80∘C for 24 h
23 Characterization of Materials Crystal features of flakegraphite GO and rGO were obtained by XRD [10] (AXScooperation Germany) with a scan speed of 4∘min from 5to 60∘ of 2120579 angles The layer spacing (119889 spacing) could becalculated with the aid of Bragg equation and the change ofdiffraction peak could also be observed The micromorphol-ogy of rGO was observed by SEM (JSM-6700F Japan) withthe acceleration voltage from 05 to 30KV Spectra of driedGO and rGO were obtained by Tensor 27 FTIR-ATR (Bruker
cooperation Germany) with the resolution of 4 cmminus1 from3700 to 500 cmminus1 of spectral region and functional groups ofGO and rGO can be observed
3 Result and Discussion
31 X-Ray Diffraction As shown in Figure 2(a) Flakegraphite exhibits a basal diffraction peak (002) at 2120579 = 265∘(119889 spacing = 033630 nm) which is very sharp There is alsoa very weak diffraction peak (004) at 2120579 = 548∘ (119889 spacing= 016738 nm) The diffraction peak (004) is the seconddiffraction [11] of the diffraction peak (002) according to layerspatial arrangement rules of microcrystals thus diffractionpeak (004) intensity is much weaker than that of diffractionpeak (002) The diffraction peak at about 2120579 = 98∘ is verytypical for GO no apparent diffraction peak could be foundfor rGO in its XRD pattern This result is similar to thatof Tapas Kuila [2] who had already described the structureof GO and rGO by XRD Figures 2(b) and 2(c) show theenlarged XRD patterns of GO and rGO Diffraction peakbecomes broader in the enlarged pattern of GO at 2120579 = 98∘ (119889spacing = 088160) and the significant increase in 119889 spacingis believed due to the following reason oxygen functionalgroups intercalate in the interlayer of graphiteThere is a veryweak diffraction peak at 2120579 = 423∘ which is believed due tothe incomplete oxidation As is shown in Figure 2(c) a veryweak and broad diffraction peak can be observed in the XRDpattern of rGO at 2120579 = 25ndash30∘ the diffraction peak of rGOis so weak that it cannot be visible when drawn together inthe XRD pattern with graphite and GO (Figure 2(a)) Thereis also a weak diffraction peak at 2120579 = 423∘
32 FTIR-ATR FTIR-ATR spectra of GO and rGOare shownin Figures 3 and 4 Some carbon-oxygen functional groupsof GO are observed in Figure 3 such as OndashH C=O CndashOHand CndashO Characteristic peak (sim3464 cmminus1) [12] is believedto be attributed to OndashH stretching of hydroxyl and carboxylgroups and characteristic peaks of C=O (sim1639 cmminus1) CndashOH (sim1288 cmminus1) and CndashO (sim1003 cmminus1) are also believed tobe attributed to carboxylic acid and carbonyl groups [13] Andthe characteristic peak at 1493 cmminus1 is corresponding to theC=C skeletal vibration of unoxidized graphitic domainTheseoxygen functional groups indicate that the flake graphitepowder has been oxidized to GO As shown in Figure 4no obvious peak could be observed which means that fullreduction of GO was made While carbon-oxygen functionalgroups all existed their characteristic peaks are just veryweak
33 Scanning ElectronMicroscope Figure 5 shows SEMmor-phologies of rGO which was dried at 80∘C for 1 day As isshown in Figure 5 2-dimensional material can be observedFold structure can be found on both the surface and the edgeof rGO powder They are the typical morphologies of few-layer rGo [14] The thickness of rGO may be 10 nm and it isobviously that rGO layers have fairly large dimension (muchlarger than 100 nm) and rGO retacked together The reasonof the reagglomerate may be the long-time high temperature
Journal of Nanomaterials 3
5 10 15 20 25 30 35 40 45 50 55 60
Inte
nsity
GraphiteGOrGO
(002)
(004)
2120579 (deg)
(a)
5 10 15 20 25 30 35 40 45 50 55 60
Inte
nsity
GO
2120579 (deg)
(b)
5 10 15 20 25 30 35 40 45 50 55 60
Inte
nsity
rGO
2120579 (deg)
(c)
Figure 2 X-ray diffraction patterns (a) graphite GO and rGO (b) enlarged view of GO (c) enlarged view of rGO
3500 3000 2500 2000 1500 1000 500
GO
OH (coupling)C=O
C=CCndashO
CndashOH
Wave number (cmminus1)
Figure 3 FTIR-ATR spectra of GO
4 Journal of Nanomaterials
3500 3000 2500 2000 1500 1000 500
OH (coupling)
rGO
C=O
CndashO
CndashOH
Wave number (cmminus1)
Figure 4 FTIR-ATR spectra of rGO
Fold structure of the surface
100nm
(a)
Fold structure of the edge
100nm
(b)
Figure 5 SEM morphology of rGO
treatment The morphology of graphite (fold structure) canalso be found in Figure 5
Reaction mechanism of solution-based reduction ofgraphite oxidewill be discussed to beginwith themechanismof Hummers though KMnO
4is used as a kind of oxidizing
agent Dreyer et al [15] believed that the active species wasMn2O7 The following equation gives the reaction between
KMnO4and H
2SO4
KMnO4+ 3H2SO4997888rarr K+ +MnO+
3+H3O+ + 3HSOminus
4
MnO+3+MnOminus
4997888rarr Mn
2O7
(1)
In low temperature reaction the edge of graphite was oxi-dized and intercalated with the aid of oxidizing agent minusOHwas formed during this process Inmid temperature reactionwith the increasing of temperature the oxidation abilityimproves furthermore More oxygen functional groups areformed in this process and the oxidizing agent penetratesinto the internal of graphite layer therefore this processresults in the increasing of 119889 spacing In the high temperaturereaction concentrated H
2SO4releases large amount of heat
during the process of watering Force between layers is
destroyed and finally the GO could be fully exfoliated tosingle layers Secondly the fully exfoliatedGOwill be reducedto rGO with the help of NH
3sdotH2O aqueous and hydrazine
hydrateThe mechanism of solution-based reduction of GO
is quite different with that of the traditional CVD onesThe formation of graphene on bulk metal through CVDincludes three steps [1 16 17] First a hydrocarbon couldbe dissociated through dehydrogenation second the carbonspecies diffuse and dissolve into the bulk metal at thegrowth temperature the reason why transition metals couldserve as an electron acceptor is because of the empty d-shell third carbon species precipitate out of the bulk metalonto the metal surface upon the rapid quenching start thesegregation process and build up honeycomb lattice becausethe solubility decreases during the cooling process
4 Conclusion
GO was prepared by Hummersrsquo method and rGO wasprepared with the aid of NH
3sdotH2O aqueous and hydrazine
hydrate successfullyThe characterization results indicate that
Journal of Nanomaterials 5
the layer spacing of graphite oxide was longer than thatof graphite The crystal structure of graphite was changedGraphite was oxidized to GO and lots of oxygen-containinggroups were found in the GO The typical fold morphologieswere found on both the surface and the edge of rGO
Compared with the traditional CVD method Hummersrsquomethod can synthesize GO in large scale then rGO can beprepared with the help of reduced agent and this processcosts a little Meanwhile the prepared GO is dispersed easilyin solution In this case the modification of the GO is easyand it is suitable for GO application in composites and energystorage devices
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publishing of this paper
Acknowledgments
The authors acknowledge funding from the National NaturalScience Foundation of China (no 51302320) and the Fun-damental Research Funds for the Central Universities (no14CX05094A)
References
[1] V Singh D Joung L Zhai S Das S I Khondaker and S SealldquoGraphene based materials past present and futurerdquo Progressin Materials Science vol 56 no 8 pp 1178ndash1271 2011
[2] M I Katsnelson ldquoGraphene carbon in two dimensionsrdquoMaterials Today vol 10 no 1-2 pp 20ndash27 2007
[3] T Kuila S Bose P Khanra A K Mishra N H Kim andJ H Lee ldquoRecent advances in graphene-based biosensorsrdquoBiosensors and Bioelectronics vol 26 no 12 pp 4637ndash46482011
[4] G Eda G Fanchini and M Chhowalla ldquoLarge-area ultrathinfilms of reduced graphene oxide as a transparent and flexibleelectronic materialrdquo Nature Nanotechnology vol 3 no 5 pp270ndash274 2008
[5] T Kuilla S Bhadra D Yao N H Kim S Bose and J HLee ldquoRecent advances in graphene based polymer compositesrdquoProgress in Polymer Science vol 35 no 11 pp 1350ndash1375 2010
[6] B G Choi M YangW H Hong J W Choi and Y S Huh ldquo3Dmacroporous graphene frameworks for supercapacitors withhigh energy and power densitiesrdquo ACS Nano vol 6 no 5 pp4020ndash4028 2012
[7] Y Zhu S Murali W Cai et al ldquoGraphene and graphene oxidesynthesis properties and applicationsrdquo Advanced Materialsvol 22 no 35 pp 3906ndash3924 2010
[8] T Kuila S Bose A K Mishra P Khanra N H Kim andJ H Lee ldquoChemical functionalization of graphene and itsapplicationsrdquo Progress in Materials Science vol 57 no 7 pp1061ndash1105 2012
[9] S Y Toh K S Loh S K Kamarudin and W R WanDaud ldquoGraphene production via electrochemical reductionof graphene oxide synthesis and characterisationrdquo ChemicalEngineering Journal vol 251 pp 422ndash434 2014
[10] C Bao L Song W Xing et al ldquoPreparation of graphene bypressurized oxidation and multiplex reduction and its polymer
nanocomposites by masterbatch-based melt blendingrdquo Journalof Materials Chemistry vol 22 no 13 pp 6088ndash6096 2012
[11] A Bagri C Mattevi M Acik Y J Chabal M Chhowallaand V B Shenoy ldquoStructural evolution during the reduction ofchemically derived graphene oxiderdquo Nature Chemistry vol 2no 7 pp 581ndash587 2010
[12] Y Jin S Sun and X Qi National Defense Industry Press 2008(Chinese)
[13] Q Deng L Liu and H Deng Spectrum Analysis TutorialScience Press 2007 (Chinese)
[14] FHong L Zhou andYHuang ldquoSynthesis and characterizationof graphene by improved hummers methodrdquo Chemical ampBiomolecular Engineering vol 29 pp 31ndash33 2012 (Chinese)
[15] D R Dreyer S Park C W Bielawski and R S Ruoff ldquoThechemistry of graphene oxiderdquoChemical Society Reviews vol 39no 1 pp 228ndash240 2010
[16] Y Kai F Lei L P Hai and F L Zhong ldquoDesigned CVD growthof graphene via process engineeringrdquo Accounts of ChemicalResearch vol 46 pp 2263ndash2274 2013
[17] C-M Seah S-P Chai and A R Mohamed ldquoMechanisms ofgraphene growth by chemical vapour deposition on transitionmetalsrdquo Carbon vol 70 pp 1ndash21 2014
Figure 2 X-ray diffraction patterns (a) graphite GO and rGO (b) enlarged view of GO (c) enlarged view of rGO
3500 3000 2500 2000 1500 1000 500
GO
OH (coupling)C=O
C=CCndashO
CndashOH
Wave number (cmminus1)
Figure 3 FTIR-ATR spectra of GO
4 Journal of Nanomaterials
3500 3000 2500 2000 1500 1000 500
OH (coupling)
rGO
C=O
CndashO
CndashOH
Wave number (cmminus1)
Figure 4 FTIR-ATR spectra of rGO
Fold structure of the surface
100nm
(a)
Fold structure of the edge
100nm
(b)
Figure 5 SEM morphology of rGO
treatment The morphology of graphite (fold structure) canalso be found in Figure 5
Reaction mechanism of solution-based reduction ofgraphite oxidewill be discussed to beginwith themechanismof Hummers though KMnO
4is used as a kind of oxidizing
agent Dreyer et al [15] believed that the active species wasMn2O7 The following equation gives the reaction between
KMnO4and H
2SO4
KMnO4+ 3H2SO4997888rarr K+ +MnO+
3+H3O+ + 3HSOminus
4
MnO+3+MnOminus
4997888rarr Mn
2O7
(1)
In low temperature reaction the edge of graphite was oxi-dized and intercalated with the aid of oxidizing agent minusOHwas formed during this process Inmid temperature reactionwith the increasing of temperature the oxidation abilityimproves furthermore More oxygen functional groups areformed in this process and the oxidizing agent penetratesinto the internal of graphite layer therefore this processresults in the increasing of 119889 spacing In the high temperaturereaction concentrated H
2SO4releases large amount of heat
during the process of watering Force between layers is
destroyed and finally the GO could be fully exfoliated tosingle layers Secondly the fully exfoliatedGOwill be reducedto rGO with the help of NH
3sdotH2O aqueous and hydrazine
hydrateThe mechanism of solution-based reduction of GO
is quite different with that of the traditional CVD onesThe formation of graphene on bulk metal through CVDincludes three steps [1 16 17] First a hydrocarbon couldbe dissociated through dehydrogenation second the carbonspecies diffuse and dissolve into the bulk metal at thegrowth temperature the reason why transition metals couldserve as an electron acceptor is because of the empty d-shell third carbon species precipitate out of the bulk metalonto the metal surface upon the rapid quenching start thesegregation process and build up honeycomb lattice becausethe solubility decreases during the cooling process
4 Conclusion
GO was prepared by Hummersrsquo method and rGO wasprepared with the aid of NH
3sdotH2O aqueous and hydrazine
hydrate successfullyThe characterization results indicate that
Journal of Nanomaterials 5
the layer spacing of graphite oxide was longer than thatof graphite The crystal structure of graphite was changedGraphite was oxidized to GO and lots of oxygen-containinggroups were found in the GO The typical fold morphologieswere found on both the surface and the edge of rGO
Compared with the traditional CVD method Hummersrsquomethod can synthesize GO in large scale then rGO can beprepared with the help of reduced agent and this processcosts a little Meanwhile the prepared GO is dispersed easilyin solution In this case the modification of the GO is easyand it is suitable for GO application in composites and energystorage devices
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publishing of this paper
Acknowledgments
The authors acknowledge funding from the National NaturalScience Foundation of China (no 51302320) and the Fun-damental Research Funds for the Central Universities (no14CX05094A)
References
[1] V Singh D Joung L Zhai S Das S I Khondaker and S SealldquoGraphene based materials past present and futurerdquo Progressin Materials Science vol 56 no 8 pp 1178ndash1271 2011
[2] M I Katsnelson ldquoGraphene carbon in two dimensionsrdquoMaterials Today vol 10 no 1-2 pp 20ndash27 2007
[3] T Kuila S Bose P Khanra A K Mishra N H Kim andJ H Lee ldquoRecent advances in graphene-based biosensorsrdquoBiosensors and Bioelectronics vol 26 no 12 pp 4637ndash46482011
[4] G Eda G Fanchini and M Chhowalla ldquoLarge-area ultrathinfilms of reduced graphene oxide as a transparent and flexibleelectronic materialrdquo Nature Nanotechnology vol 3 no 5 pp270ndash274 2008
[5] T Kuilla S Bhadra D Yao N H Kim S Bose and J HLee ldquoRecent advances in graphene based polymer compositesrdquoProgress in Polymer Science vol 35 no 11 pp 1350ndash1375 2010
[6] B G Choi M YangW H Hong J W Choi and Y S Huh ldquo3Dmacroporous graphene frameworks for supercapacitors withhigh energy and power densitiesrdquo ACS Nano vol 6 no 5 pp4020ndash4028 2012
[7] Y Zhu S Murali W Cai et al ldquoGraphene and graphene oxidesynthesis properties and applicationsrdquo Advanced Materialsvol 22 no 35 pp 3906ndash3924 2010
[8] T Kuila S Bose A K Mishra P Khanra N H Kim andJ H Lee ldquoChemical functionalization of graphene and itsapplicationsrdquo Progress in Materials Science vol 57 no 7 pp1061ndash1105 2012
[9] S Y Toh K S Loh S K Kamarudin and W R WanDaud ldquoGraphene production via electrochemical reductionof graphene oxide synthesis and characterisationrdquo ChemicalEngineering Journal vol 251 pp 422ndash434 2014
[10] C Bao L Song W Xing et al ldquoPreparation of graphene bypressurized oxidation and multiplex reduction and its polymer
nanocomposites by masterbatch-based melt blendingrdquo Journalof Materials Chemistry vol 22 no 13 pp 6088ndash6096 2012
[11] A Bagri C Mattevi M Acik Y J Chabal M Chhowallaand V B Shenoy ldquoStructural evolution during the reduction ofchemically derived graphene oxiderdquo Nature Chemistry vol 2no 7 pp 581ndash587 2010
[12] Y Jin S Sun and X Qi National Defense Industry Press 2008(Chinese)
[13] Q Deng L Liu and H Deng Spectrum Analysis TutorialScience Press 2007 (Chinese)
[14] FHong L Zhou andYHuang ldquoSynthesis and characterizationof graphene by improved hummers methodrdquo Chemical ampBiomolecular Engineering vol 29 pp 31ndash33 2012 (Chinese)
[15] D R Dreyer S Park C W Bielawski and R S Ruoff ldquoThechemistry of graphene oxiderdquoChemical Society Reviews vol 39no 1 pp 228ndash240 2010
[16] Y Kai F Lei L P Hai and F L Zhong ldquoDesigned CVD growthof graphene via process engineeringrdquo Accounts of ChemicalResearch vol 46 pp 2263ndash2274 2013
[17] C-M Seah S-P Chai and A R Mohamed ldquoMechanisms ofgraphene growth by chemical vapour deposition on transitionmetalsrdquo Carbon vol 70 pp 1ndash21 2014
treatment The morphology of graphite (fold structure) canalso be found in Figure 5
Reaction mechanism of solution-based reduction ofgraphite oxidewill be discussed to beginwith themechanismof Hummers though KMnO
4is used as a kind of oxidizing
agent Dreyer et al [15] believed that the active species wasMn2O7 The following equation gives the reaction between
KMnO4and H
2SO4
KMnO4+ 3H2SO4997888rarr K+ +MnO+
3+H3O+ + 3HSOminus
4
MnO+3+MnOminus
4997888rarr Mn
2O7
(1)
In low temperature reaction the edge of graphite was oxi-dized and intercalated with the aid of oxidizing agent minusOHwas formed during this process Inmid temperature reactionwith the increasing of temperature the oxidation abilityimproves furthermore More oxygen functional groups areformed in this process and the oxidizing agent penetratesinto the internal of graphite layer therefore this processresults in the increasing of 119889 spacing In the high temperaturereaction concentrated H
2SO4releases large amount of heat
during the process of watering Force between layers is
destroyed and finally the GO could be fully exfoliated tosingle layers Secondly the fully exfoliatedGOwill be reducedto rGO with the help of NH
3sdotH2O aqueous and hydrazine
hydrateThe mechanism of solution-based reduction of GO
is quite different with that of the traditional CVD onesThe formation of graphene on bulk metal through CVDincludes three steps [1 16 17] First a hydrocarbon couldbe dissociated through dehydrogenation second the carbonspecies diffuse and dissolve into the bulk metal at thegrowth temperature the reason why transition metals couldserve as an electron acceptor is because of the empty d-shell third carbon species precipitate out of the bulk metalonto the metal surface upon the rapid quenching start thesegregation process and build up honeycomb lattice becausethe solubility decreases during the cooling process
4 Conclusion
GO was prepared by Hummersrsquo method and rGO wasprepared with the aid of NH
3sdotH2O aqueous and hydrazine
hydrate successfullyThe characterization results indicate that
Journal of Nanomaterials 5
the layer spacing of graphite oxide was longer than thatof graphite The crystal structure of graphite was changedGraphite was oxidized to GO and lots of oxygen-containinggroups were found in the GO The typical fold morphologieswere found on both the surface and the edge of rGO
Compared with the traditional CVD method Hummersrsquomethod can synthesize GO in large scale then rGO can beprepared with the help of reduced agent and this processcosts a little Meanwhile the prepared GO is dispersed easilyin solution In this case the modification of the GO is easyand it is suitable for GO application in composites and energystorage devices
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publishing of this paper
Acknowledgments
The authors acknowledge funding from the National NaturalScience Foundation of China (no 51302320) and the Fun-damental Research Funds for the Central Universities (no14CX05094A)
References
[1] V Singh D Joung L Zhai S Das S I Khondaker and S SealldquoGraphene based materials past present and futurerdquo Progressin Materials Science vol 56 no 8 pp 1178ndash1271 2011
[2] M I Katsnelson ldquoGraphene carbon in two dimensionsrdquoMaterials Today vol 10 no 1-2 pp 20ndash27 2007
[3] T Kuila S Bose P Khanra A K Mishra N H Kim andJ H Lee ldquoRecent advances in graphene-based biosensorsrdquoBiosensors and Bioelectronics vol 26 no 12 pp 4637ndash46482011
[4] G Eda G Fanchini and M Chhowalla ldquoLarge-area ultrathinfilms of reduced graphene oxide as a transparent and flexibleelectronic materialrdquo Nature Nanotechnology vol 3 no 5 pp270ndash274 2008
[5] T Kuilla S Bhadra D Yao N H Kim S Bose and J HLee ldquoRecent advances in graphene based polymer compositesrdquoProgress in Polymer Science vol 35 no 11 pp 1350ndash1375 2010
[6] B G Choi M YangW H Hong J W Choi and Y S Huh ldquo3Dmacroporous graphene frameworks for supercapacitors withhigh energy and power densitiesrdquo ACS Nano vol 6 no 5 pp4020ndash4028 2012
[7] Y Zhu S Murali W Cai et al ldquoGraphene and graphene oxidesynthesis properties and applicationsrdquo Advanced Materialsvol 22 no 35 pp 3906ndash3924 2010
[8] T Kuila S Bose A K Mishra P Khanra N H Kim andJ H Lee ldquoChemical functionalization of graphene and itsapplicationsrdquo Progress in Materials Science vol 57 no 7 pp1061ndash1105 2012
[9] S Y Toh K S Loh S K Kamarudin and W R WanDaud ldquoGraphene production via electrochemical reductionof graphene oxide synthesis and characterisationrdquo ChemicalEngineering Journal vol 251 pp 422ndash434 2014
[10] C Bao L Song W Xing et al ldquoPreparation of graphene bypressurized oxidation and multiplex reduction and its polymer
nanocomposites by masterbatch-based melt blendingrdquo Journalof Materials Chemistry vol 22 no 13 pp 6088ndash6096 2012
[11] A Bagri C Mattevi M Acik Y J Chabal M Chhowallaand V B Shenoy ldquoStructural evolution during the reduction ofchemically derived graphene oxiderdquo Nature Chemistry vol 2no 7 pp 581ndash587 2010
[12] Y Jin S Sun and X Qi National Defense Industry Press 2008(Chinese)
[13] Q Deng L Liu and H Deng Spectrum Analysis TutorialScience Press 2007 (Chinese)
[14] FHong L Zhou andYHuang ldquoSynthesis and characterizationof graphene by improved hummers methodrdquo Chemical ampBiomolecular Engineering vol 29 pp 31ndash33 2012 (Chinese)
[15] D R Dreyer S Park C W Bielawski and R S Ruoff ldquoThechemistry of graphene oxiderdquoChemical Society Reviews vol 39no 1 pp 228ndash240 2010
[16] Y Kai F Lei L P Hai and F L Zhong ldquoDesigned CVD growthof graphene via process engineeringrdquo Accounts of ChemicalResearch vol 46 pp 2263ndash2274 2013
[17] C-M Seah S-P Chai and A R Mohamed ldquoMechanisms ofgraphene growth by chemical vapour deposition on transitionmetalsrdquo Carbon vol 70 pp 1ndash21 2014
the layer spacing of graphite oxide was longer than thatof graphite The crystal structure of graphite was changedGraphite was oxidized to GO and lots of oxygen-containinggroups were found in the GO The typical fold morphologieswere found on both the surface and the edge of rGO
Compared with the traditional CVD method Hummersrsquomethod can synthesize GO in large scale then rGO can beprepared with the help of reduced agent and this processcosts a little Meanwhile the prepared GO is dispersed easilyin solution In this case the modification of the GO is easyand it is suitable for GO application in composites and energystorage devices
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publishing of this paper
Acknowledgments
The authors acknowledge funding from the National NaturalScience Foundation of China (no 51302320) and the Fun-damental Research Funds for the Central Universities (no14CX05094A)
References
[1] V Singh D Joung L Zhai S Das S I Khondaker and S SealldquoGraphene based materials past present and futurerdquo Progressin Materials Science vol 56 no 8 pp 1178ndash1271 2011
[2] M I Katsnelson ldquoGraphene carbon in two dimensionsrdquoMaterials Today vol 10 no 1-2 pp 20ndash27 2007
[3] T Kuila S Bose P Khanra A K Mishra N H Kim andJ H Lee ldquoRecent advances in graphene-based biosensorsrdquoBiosensors and Bioelectronics vol 26 no 12 pp 4637ndash46482011
[4] G Eda G Fanchini and M Chhowalla ldquoLarge-area ultrathinfilms of reduced graphene oxide as a transparent and flexibleelectronic materialrdquo Nature Nanotechnology vol 3 no 5 pp270ndash274 2008
[5] T Kuilla S Bhadra D Yao N H Kim S Bose and J HLee ldquoRecent advances in graphene based polymer compositesrdquoProgress in Polymer Science vol 35 no 11 pp 1350ndash1375 2010
[6] B G Choi M YangW H Hong J W Choi and Y S Huh ldquo3Dmacroporous graphene frameworks for supercapacitors withhigh energy and power densitiesrdquo ACS Nano vol 6 no 5 pp4020ndash4028 2012
[7] Y Zhu S Murali W Cai et al ldquoGraphene and graphene oxidesynthesis properties and applicationsrdquo Advanced Materialsvol 22 no 35 pp 3906ndash3924 2010
[8] T Kuila S Bose A K Mishra P Khanra N H Kim andJ H Lee ldquoChemical functionalization of graphene and itsapplicationsrdquo Progress in Materials Science vol 57 no 7 pp1061ndash1105 2012
[9] S Y Toh K S Loh S K Kamarudin and W R WanDaud ldquoGraphene production via electrochemical reductionof graphene oxide synthesis and characterisationrdquo ChemicalEngineering Journal vol 251 pp 422ndash434 2014
[10] C Bao L Song W Xing et al ldquoPreparation of graphene bypressurized oxidation and multiplex reduction and its polymer
nanocomposites by masterbatch-based melt blendingrdquo Journalof Materials Chemistry vol 22 no 13 pp 6088ndash6096 2012
[11] A Bagri C Mattevi M Acik Y J Chabal M Chhowallaand V B Shenoy ldquoStructural evolution during the reduction ofchemically derived graphene oxiderdquo Nature Chemistry vol 2no 7 pp 581ndash587 2010
[12] Y Jin S Sun and X Qi National Defense Industry Press 2008(Chinese)
[13] Q Deng L Liu and H Deng Spectrum Analysis TutorialScience Press 2007 (Chinese)
[14] FHong L Zhou andYHuang ldquoSynthesis and characterizationof graphene by improved hummers methodrdquo Chemical ampBiomolecular Engineering vol 29 pp 31ndash33 2012 (Chinese)
[15] D R Dreyer S Park C W Bielawski and R S Ruoff ldquoThechemistry of graphene oxiderdquoChemical Society Reviews vol 39no 1 pp 228ndash240 2010
[16] Y Kai F Lei L P Hai and F L Zhong ldquoDesigned CVD growthof graphene via process engineeringrdquo Accounts of ChemicalResearch vol 46 pp 2263ndash2274 2013
[17] C-M Seah S-P Chai and A R Mohamed ldquoMechanisms ofgraphene growth by chemical vapour deposition on transitionmetalsrdquo Carbon vol 70 pp 1ndash21 2014
