Review Article Synthesis and Applications of

Review ArticleSynthesis and Applications of Semiconducting Graphene

Shahrima Maharubin1 Xin Zhang2 Fuliang Zhu3 Hong-Chao Zhang1

Gengxin Zhang4 and Yue Zhang5

1Department of Industrial Engineering Texas Tech University Lubbock TX 79415 USA2Fundamental and Computational Sciences Directorate Pacific Northwest National Laboratory Richland WA 99352 USA3School of Materials Science and Engineering Lanzhou University of Technology Qilihe Lanzhou 730050 China4Corporation Quality Network Intel Corporation Chandler AZ 85226 USA5Department of Mechanical and Industrial Engineering Texas AampM University-Kingsville Kingsville TX 78363 USA

Correspondence should be addressed to Gengxin Zhang gengxinzhangintelcom and Yue Zhang yuezhangtamukedu

Received 15 August 2016 Revised 1 October 2016 Accepted 3 October 2016

Academic Editor Stefano Bellucci

Copyright copy 2016 Shahrima Maharubin et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Semimetal-to-semiconductor transition in graphene can bestow graphenewith numerous novel and enhanced structural electricaloptical and physicochemical characteristicsThe scope of graphene and its prospective for an array of implications could be signif-icantly outspread by this transition In consideration of the recent advancements of semiconducting graphene this article widelyreviews the properties production and developing operations of this emergent material The comparisons among the benefitsand difficulties of current methods are made intending to offer evidences to develop novel and scalable synthesis approachesThe emphasis is on the properties and applications resulting from various conversion methods (doping controlled reduction andfunctionalization) expecting to get improved knowledge on semiconducting graphene materials Intending to motivate furtherefficient implications the mechanisms leading to their beneficial usages for energy conversion and storage are also emphasized

1 Introduction

Graphene has upraised far-reaching attention in very broadscientific society for its surprising electrical mechanicaloptical and thermal properties [1] It is an allotrope of carbonhaving a single layer of sp2-bonded carbon atoms denselypacked into a two-dimensional honeycomb lattice [2 3] EachC-atom in the structure has s and three p orbitals Two of porbitals (px and py) and s orbital in the structure hybridizeto form a strong covalent sp2 C-C bond The remainingpz orbital overlaps the neighboring C-atom pz orbital toform a filled 120587 orbital (valence) and the empty 120587lowast orbital(conduction) [1] Due to the structural formation grapheneoffers an excellent thermal conductivity exhibits high chargemobility and possesses high theoretical specific surface area[2 4] Among all these properties themost interesting aspectof graphene is assumed to be its unique electronic propertiesGraphenersquos electron mobility is considerably greater thansilicone (sim1400 cm2 Vminus1 sminus1) which is a widely used semi-conductor [1] Therefore for the applications in postsilicon

electronics graphene has been considered as a candidatematerial

Although graphene possesses several exceptional char-acteristics however due to the absence of a substantialbandgap its use as an electronic material for semiconductingapplications is one of the greatest challenges Graphene isbasically a semimetal or a zero bandgap semiconductor [5 6]This semimetal characteristic of graphene does not affect itsuse in numerous applications but it considerably restrictsits use in all other semiconducting applications where anappropriate bandgap is requisite An identical atmosphere ofthe two C-atoms in the graphene unit cell is the major reasonfor this zero bandgap present in graphene [7] Consequentlybreaking the adjacent in-plane lattice symmetry is the majorway to open up a bandgap in graphene This could be doneby different structural and chemical alterations For instanceif an atom substitutes the carbon atom in the structure thesymmetry in the lattice could be broken This may result inthe creation of a gap between 120587 and 120587lowast bandsThis symmetry

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2016 Article ID 6375962 19 pageshttpdxdoiorg10115520166375962

2 Journal of Nanomaterials

n-doped

p-dopedPristine

120587

120587lowast

120587

120587lowast

120587

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EF

(a) (b) (c)

Figure 1 Schematic band structures of (a) n-type graphenewith bandgap (b) pure graphene and (c) p-type graphenewith bandgap (reprintedfrom [10] copyright 2016 PCCP Owner Societies)

could also be broken through other means [7] For theuse of graphene in electronic devices opening a well-tunedconsiderable bandgap in graphene is the major challenge

Figure 1 is the representation of the graphene band struc-tures presented where there is a linear energy momentumdispersion relation near the Dirac point [8 9] The coneshaped valence band and conduction bands meet across 119870point The Fermi level (119864F) lies at the crossover point in theband structure of pure graphene with zero bandgap 119864F liesin valence and conduction band in the band structures of 119901-type graphene and 119899-type graphene respectively including abandgap [10]

The surface properties of graphene are possible to beadjusted via structural alteration including chemical dop-ing chemical functionalization and controlled reductionwhich proposes remarkable prospects for the developmentof graphene-based semiconducting materials with uniqueelectronic characteristics These materials show advantagesfor numerous prospective applications including energyconversion energy storage catalysis sensing field effecttransistor and many more because of their high powerdensity and long lifecycle [11ndash14]

There are many methods that incorporate semiconduct-ing properties into graphene which include the preparationof graphenenanoparticle hybrids patterning graphene inthe form of a graphene nanoribbon nanomesh or quantumdot These methods have shown substantial developing andemerging interest from both theoretical and experimentalviewpoints and have been reviewed in several literatures [215ndash18] This review focuses on converting metallic grapheneinto semiconducting graphene by chemical alteration ofgraphene through doping controlled reduction and func-tionalization Although these newly developedmethods haverisen to rigorous attention in research these methods arenot classified or summarized in a single document Hence amethodical synopsis on these significantmethods for produc-ing semiconducting graphene and its exceptional character-istics and functions compared to graphene is greatly requiredThis review provides an overall context and structure on thelatest advancements in the area of semiconducting graphenematerials

The conversion processes discussed in this reviewcould be categorized into three major sections (1) doping

of graphene through surface transfer and substitutionalapproach (2) controlled reduction of graphene oxide (GO)and (3) functionalization of graphene via chemical methodsDoping of graphene with alien atoms instigates the electronicand structural distortions inside the carbon sheet leading tochanges in the graphene bandgap properties Partial reduc-tion of GO controls the level of oxygen-containing functionalgroup into the graphene structure During functionalizationdifferent functionalities are grafted onto graphene by covalentor noncovalent approaches All these methods are actuallyutilized for the bandgap opening in graphene and Fermilevel tuning of grapheneThe semiconducting graphene findsapplications in many scientific fields ranging from fuelcell solar cell and thermoelectric devices to supercapacitorand lithium-ion batteries These applications are carefullyreviewed in the manuscript

2 Fabrication Methods

21 Doping of Graphene A number of methods have beenproposed in the literature [19ndash21] tomodify the graphene andits electronic structure for the introduction of a substantialbandgap in it Among all the approaches one utmost reason-able approach is doping which helps in tuning the bandgapin graphene The concentration and nature of the chargecarriers can be regulated by doping For the band engineeringof graphene two major kinds of doping styles have beenappliedmdashsurface transfer doping and substitutional dopingSurface transfer doping involves the adsorption of an atominto the graphene lattice structure This incorporation ofatom could shift the voltage point of graphene at Diracpoint from zero gate voltage to +ve or minusve gate voltage asan outcome of p- or n-type graphene Substitutional dopinginvolves the replacement of carbon atoms inside the graphenelattice The incursion of atoms into the natural graphene willunavoidably instigate the electronic and structural distortionsinside the carbon sheet leading to changes in the graphenebandgap properties In this section an overview of recentexperimental and theoretical investigations on the doping ofgraphene is given and the possible reason for the semicon-ducting behavior of doped graphene is explained

Journal of Nanomaterials 3

O

O O

O

C

O

O O

O

C

O

O O

O

CAu3+

Au3+

Au3+

Au3+

Au0

Au0

Au0

eminus

eminus

eminus

eminus

Figure 2 Surface transfer doping of graphene (reprinted from [24] copyright 2009 Elsevier)

211 Surface Transfer Doping Surface transfer doping ofgraphene could be attained through the interchange of elec-trons between graphene and the surface absorbed-dopantspresent in grapheneTherefore this type of dopingmight alsobe termed as adsorbate-induced doping This type of dopingdoes not interrupt the graphene structure and it generally canbe reversible [22 23]

For surface transfer doping of graphene a considerablehole-doping in the graphene (with conical band structure)might be attained through the adsorption of atoms (mostlymetal atoms) having high affinity for electrons These atomsincluding gold (Au) bismuth (Bi) and antimony (Sb) couldbe adsorbed on the surface of graphene and may modifythe electronic properties in graphene [24] Benayad et alexamined the result of Au-ion treatment on the WF andthe change in electronic structure of rGOs The relativepercentage of carbon gradually decreased and the relativepercentage of Au0 increased markedly with increased dopingconcentration This might be due to a charge-transfer fromsp2 electrons to Au-ion solution The carbon oxide specieswith functional groups C=O and O-C=O also contribute todonating electrons to the Au-ions and the Au-ions are spon-taneously transformed into Au0 by a charge-transfer from thereduced GO to the Au-ions [24] (Figure 2) Usually the Diracpoint (minimum conductivity point) of original graphene isat the zero gate voltageThis voltage point moves in graphenein the direction of positive gate voltage due to p-type dopingor a negative gate voltage due to n-type dopingThe adsorbedBi and Sb atoms on the surface withdraw electrons fromgraphene then the Dirac point moves in the direction of theFermi level but does not overlap with it However Au has thehigher electron affinity and it moves the Dirac point to thevacant states prompting the p-type doping in graphene

It was found in the literature that the charge-transferis motivated by the difference in work function (WF) andthe chemical interactions among the metal component andgraphene [25] If the work function of metal is largercompared to the work function of graphene graphene isexpected to be doped with holes In contrast if the workfunction of graphene is larger compared to the work functionof metal graphene is expected to be doped with electronsAlkaline metals have strong ionic bonding characteristics sothey are able to donate electrons This assists the discharge oftheir lone-paired electrons in the graphene conduction bandand rises the intensely charge carrier amount in graphene

[26] Alkaline metals become excellent applicants for n-typedopants because of the development of this firm ionic bondand substantial charge transportation [27]

212 Substitutional Doping Substitutional doping of graphe-ne is attained by the substitution or replacement of carbonatoms in the graphene lattice by a foreign atom Substitutionaldoping has got specific consideration because of its capabilityof charge infusion in the graphene electronic structure Thistype of doping involves the replacement of carbon atom withanother atom near the locations of single or multiple open-ings Generally heteroatoms (nitrogen boron phosphoroussulfur etc) and metal atoms (gold platinum etc) are usedfor this doping These gap defects in lattice are formed bydirecting a beam of electron using scanning transmissionelectron microscopy (STEM) or by bombardment of ions[28]

The unpaired electrons of a pristine graphene are power-fully attached and passivated in the delocalized 120587 structure ofgraphene making it chemically not reactive which obstructsits reactivity and absorption capability [21] The insertionof heteroatoms can give graphene extremely rich activesites The electroneutrality in graphene could be broken byaddition of heteroatom that has a dissimilar electronegativitycompared to the carbon atom This might create instablecharged zones in it [29] which could function as activesites These sites could also be existent as structural defectsthat may rise from the strain in the lattice imparted fromthe atomic size differences with the dopants [30] Generallythe roots of these sites enrich the chemical properties ingraphene for better interaction and simultaneously introducea bandgap that introduce semiconducting properties intographene it can thus be utilized in so many applicationsSubstitutional doping of graphene with heteroatoms has beenachieved by several approaches including direct synthesissolid-phase synthesis and liquid-phase synthesis Among allthese approaches the most widely used ones are discussed inthis section

The direct synthesis method includes CVD and segre-gation-growth approach The chemical vapor deposition isa suitable way for doping different heteroatoms while thegraphene films are produced by catalytic growth mechanismThis method involves particularly direct incorporation ofheteroatoms into the graphitic carbon lattices [31] In thisprocess a metal catalyst is used as the substrate A gaseous


H2 CH4

H3N-BH3

Ar

Hot platecontainer

Furnace

Cu foil on quartz plate Scrollpump

(a)

N-doped graphene-porous sheet(NG-silica)

(4-1) removal of silica

N-doped graphene(NG)

OH4eO2 + H2O

C Graphitic NPlyrolic N Pyridinic N

(3-1

)an

neal

ing

anne

alin

gin

NH

3

(1) adsorption of CTAB

(2) hydrolysis of TEOSGraphene oxide

(GO)Graphene oxide-porous sheet(GO-silica)

(3-2

)

inH

2S


S-doped graphene-porous sheet(SG-silica)

S-doped graphene(SG)

CS-O

Thiophene S

(b)

Figure 3 Preparation methods of heteroatom-doped graphene (a) CVD doping experimental setup (reprinted from [31] copyright 2013American Chemical Society) (b) N- or S-doping on porous silica confined GO sheets by thermal annealing (reprinted from [50] copyright2012 John Wiley and Sons)

source of carbon is then mixed with another solid liquid orgas containing heteroatom at high temperature in the furnacetogether (Figure 3(a)) On the surface of the catalyst theseprecursors tend to dissociate and then try to recombine byprecipitation into the heteroatom-graphene [32ndash35] CVDmethod has been extensively employed for the formationof nitrogen-doped graphene Most literature studies predict

this type of substitutional doping of nitrogen may transformgraphene into an n-type semiconductor complemented bysignificant modification of electronic transport and chargemobility [36ndash38] Doping of nitrogen in graphene resultsin a transition from metal to semiconductor which has abandgap varying till 5 eV thus increasing probable applica-tions of graphene in mostly electronic and optoelectronic


side [39] The CVD approach enables the growth and dopingsimultaneously and thus allows controllable doping This isa complex process which needs high operating temperatureWaste gases and hazardous materials are sometimes alsoproduced in this process This method involves high costand usually yield is low [35 40ndash45] The segregation-growthapproach is one more significant approach to synthesizedoped graphene through direct synthesisThismethod allowsthe selective doping of graphene through the incorporationof heteroatoms into specific areas of the graphene surface[46] In a recent study Zhang et al produced nitrogen-dopedgraphene through this segregation-growth method [47] Intheir study they squeezed C-containing Ni layers and the N-containing B layers through thermal annealing This processformed uniform N-doped graphene which exhibited a sub-stantial bandgap of 016 eV This method provides the optionof controlling the concentration and position of dopantsTheresultant doped graphene has application in FET [47]

The solid-phase synthesis involves reactions at high tem-perature including thermal annealing and arc-dischargemethod [48] The thermal annealing of GO or reducedGO is effective in attaining doping with heteroatom whensuitable precursors are present Thermal annealing is themethod of producing heteroatom-doped graphene usinghigh temperature For instance nitrogen-doped graphene hasbeen obtained by Wu et al by annealing reduced GO in NH3and argon atmosphere at 600∘C [49] Porous silica was usedby Yang et al to confine GO sheets for N- or S-doping foravoiding aggregation and ensuring free gas transport duringthe annealing process S-doping was found to be less effectivecompared to N-doping and it forms thiophene-like structureat the defect sites (Figure 3(b)) [50] Thermal annealingmethod gives wide choices of dopant precursors (gasesliquids or solids) It provides controllable doping Althoughhigh temperature is required in this process it is still helpfulto recover sp2 carbon network [51ndash59] The arc-dischargeapproach is one more significant approach to synthesizedoped graphene [60] This method produces heteroatomreactive radicals for the doping Arc-discharge method mayobtain doped graphene by evaporating the carbon sourceat high temperature Nitrogen-doped graphene is widelyproduced by the arc-dischargemethod Rao et al successfullysynthesized nitrogen-doped graphene by application of thistechnique in the presence of NH3 or vapor of pyridine [6162] Li et al have produced multilayered nitrogen-dopedgraphene sheets by this method where NH3 used as buffergas acts as N precursor [63] Arc-discharge approach has alsobeen applied to prepare boron-doped graphene For examplePanchakarla et al have prepared bilayer graphene with borondoping by arc-discharge method in the presence of H2 andB2H6 where a boron-filled graphite electrode was used [62]Thismethod givesmass production However it requires highvoltage or current The main limitation is low doping levelThismethod is generally applied formultilayer graphene [62ndash64]

The liquid-phase synthesis involves hydrothermal andsolvothermal treatment [48] The solvothermal synthesiswas first applied for the production of gram-scale graphene[65] Currently the gram-scale production of nitrogen-doped

graphene is attained through using the method at nearly300∘C Nitrogen-doped graphene with varying content ofnitrogen was achieved by mixing lithium nitride with tetra-chloromethane or cyanuric chloride with lithium nitride andtetrachloromethane [66] Another solvothermal synthesisof nitrogen-doped graphene was developed by Deng et alunder mild condition reaction of the tetrachloromethaneand lithium nitride [66] Sulfur doped graphene can also beprepared by solvothermal method Liu et al achieved sulfurdoped graphene with pure thiophene S-bonding by a rapidmicrowave-assisted solvothermal method using grapheneoxide and benzyl disulfide This experiment attained a sulfurdoping level nearly at 23 percentage in 6 minutes Dopedgraphene prepared by this method develops superior electro-chemical properties [67]

22 Controlled Reduction of Graphene Oxide Controlledreduction of graphene oxide (GO) is a possible way toattain substantial bandgap opening in the graphene structureamong several other approaches [68] This offers tunableoptoelectrical properties into the structure of grapheneModified graphene with this tuned bandgap properties couldbe employed in many fields including electronic and opticaldevices [69] sensors [70] catalysts [71] and supercapacitors[72]

Graphene oxides are generally electrically insulatingbecause of the existence of substantial sp3 hybridized carbonatoms bonded with oxygen The alteration of sp2 and sp3carbon segments present in graphene oxide are beneficialfor the manipulation of its bandgap therefore controllingthe transformation of graphene oxide from an insulator toa semiconductor [73] Reduction of graphene oxide cre-ates numerous defects in the lattice of graphene whichfurther may affect the resultant transportation propertiesThe energy gap in GO might be tuned through regulatingthe reduction extent The bandgap engineering probabilitywithin the GO is of attention due to its application inseveral sectors including electronic and photonic devicesGO can go through controlled reduction for obtaining thesemiconducting properties in its structure [74 75] Variousreduction methods have been proposed for this purposeThechemical and thermal reduction routes are mostly impliedones among all reduction approaches

221 Chemical Reduction Chemical reduction is advisedas very simple and reasonable solution-processing approachthat is able to be performed at low temperature and mayimply wide-ranging reductants [70 76] Controlled chemicalreduction of GO leads to substantial bandgap opening in thestructure GO experiences the transition from insulator tosemiconductor and then to semimetal with large-scale reduc-tion The variation in the transportation gap moves frominsulating to semiconducting range and advances to zerowith extensive reduction [73]Therefore proper control in thereduction process is important for tuning the semiconductingproperties in GO

A recent study demonstrated the evidence of controlledremoval of chemical functional groups from the surface ofGOby the chemical reduction ofGO [77]This study has used


(a)

Calculated optical gap

Tertiary alcoholremoval occurs

at 108 hours

Reduction ofReduction of

epoxide moietyphenol and carbonylafter first 16 hours

0

10

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e of h

ydra

zine

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rs)

15 20 25 30 35 40 4510

Optical gap (eV)

(b)

Figure 4 Controlled chemical reduction of GO (a) Structural model of GO with the carbonyl (green) phenols (orange) tertiary alcohols(gray) and epoxide (red) functional groups (reprinted from [78] copyright 2009 Nature Publishing Group) (b) Change in optical bandgapon disclosure to hydrazine vapors (reprinted from [77] copyright 2012 American Chemical Society)

hydrazine vapors as a reducing agent for stepwise removingthe functionalities (Figure 4(a)) in GO at room temperature

The data from this study showed that carbonyl groups arethe most reactive to hydrazine vapors and they were the firstthat were reduced at eight hours Next reduced groups werethe phenolic group that were reduced after sixteen hoursThen the epoxy groups are reduced at 215 hoursThe tertiaryalcohols take the longest to be reduced and are reduced after108 hours of exposure The optical-gap variation during thereduction process with hydrazine vapor is summarized inFigure 4(b) The initial insulating properties of GO (sim35 eVat 0 hours) are indicated in the figure In the first 4 hours anoteworthy reduction has been observed in the optical energygap (sim30 eV at 4 hours)

The optical energy gap value close to semiconductorcharacteristics (sim16 eV at 30 hours) resulted from the con-sequential elimination of the phenolic and epoxy groupsTheradical decrease in bandgap decelerates after this point nearlyafter forty-five hours This provides a qualitative knowledgeabout the challenges related to the elimination of the tertiaryalcohol After completely removing the functional groups thebandgap decreases to nearly 1 eV at 108 hours [77]

This study provides the information of the bandgapcontrol at different stages of reduction which creates thepotentials for alternating chemical configuration of grapheneand GO and regulating their electric and optical propertiesaimed at their use in a wide range of applications [79 80]

222 Thermal Reduction Thermal reduction is usuallyattained by heating GO in the presence of inert atmosphereat high temperature [81ndash83] Appropriate control in thereduction process is important for tuning the semiconductingproperties in GO as extensive reduction may result in zerobandgap in the structure

The gradual transition of GO from electric insulatorto semiconductor and further to semimetal like graphene

with thermal reduction was reported in a study by Junget al The results suggested a close correlation among theelectrical properties and the chemical structure of GO [84]Another study by Eda et al extended the works of Jung etal which provided a whole scenario of transportation in GOat different extents of reduction In particular they reportedthe dependence of the transportation properties in GO ontemperature as a function of the reduction treatments At lowtemperature a transportation gap was observed for moder-ately reduced GOThe energy gap was found to be dependenton the degree of the reduction process The transport gapseems to be ranging from 10 to 50meV and advances towardszero with large-scale reduction treatment Proper regulationin the thermal reduction process is able to generate bandgapin GO and induce semiconducting properties in it [73]

Thermal reduction of GO-based composites is a popularmethod to fabricate 3D graphene networks [85]Thismethodneeds the construction of a GO-based composite and thenreduction of the GO for the production of the 3D graphenenetworks A challenge in making 3D networks via thermalreduction frequently results in collapse of the pore structurewithout a support which must be subsequently removedHowever it is hard to remove the supportmaterial completelyand the residual would influence the thermal and electricalproperties of reduced graphene oxide Zhang et al recentlyimplied a method using NC as support materials (Figure 5)NC is an energetic material fill and GO forms a compositematerial with NC with easy dispersion NC is easily decom-posed during the thermal degradation of the composite andthus provides an efficient technique for reducing GOwithoutany support [85]

23 Functionalization of Graphene The functionalization ofgraphene via chemical methods suggests an alternatemethodto govern its electronic characteristics In the process offunctionalization of graphene sp2 network is converted into


Go-NC composites 3D graphene networks

Heating

Figure 5 Synthesis of 3D graphene network by thermal reduction (reprinted from [85] copyright 2014 American Chemical Society)

sp3 structure with the transformation of metal characteristicsin graphene towards insulating The metallic properties ofgraphene are able to be altered to semiconducting by appositesurface functionalization [86 87] Furthermore the largesurface exposure can be attained via attachment with otherfunctional groups on graphene or graphene derivatives [88]By functionalization graphene surfaces or edges become richin functional groups which helps the tuning in molecularlevel [89] Graphene could be functionalized by covalentnoncovalent and also some further approaches that comeacross the precise necessities of diverse types of applicationsFunctional group is able to widen the characteristics ofgraphene by the development of graphene donor-acceptorcomplex which gives tunability in electrical conductivity andphotovoltaic and optical characteristics [90] Functionaliza-tion of the sheet of pure graphene is very challenging andsometimes almost impossible because of the poor solubilityThe GO sheet having reactive groups (carboxylic acid as wellas hydroxyl and epoxy groups on its edge and basal planeresp) is one of the utmost common starting materials forgraphene functionalization

231 Covalent Functionalization Covalent interaction in-volves covalent bond formation either at the basal planes orat the edges of graphene Graphene derivatives that are cova-lently attached are formed through attachment of moleculargroups or atoms to sp2 carbons This conversion upholdsthe graphene two-dimensional lattice However there aresignificant alterations to the characteristics of graphenebecause of the loss of the 120587-electron cloud existing in thestructure of graphene (above and below) Functionalizationof graphene can be achieved through the reaction withunsaturated 120587-bonds present in graphene the oxygen atomson GO and organic functional moieties [91 92] Thesereactions transform sp2 carbon atoms to sp3 hybridizationgenerating nonconducting and semiconducting areas in thelayers of graphene [93] Literature shows that most of thestudy focuses on the covalent-linkage among the oxygenmoieties in GO as well as other functional groups [90 94 95]

Covalent functionalization of graphene with organiccompounds has been used to utilize semiconducting appli-cation of graphene In a recent study Yu et al have explored

a new class of charge transport materials in PSCs [96] Theyhave chemically grafted CH2OH-terminated region regularpoly(3-hexylthiophene) (P3HT) onto carboxylic groups ofGO via esterification reaction (Figure 6(a)) A bilayer pho-tovoltaic device established on this functionalized compoundshowed two hundred percent increment in the power conver-sion efficiency compared to the P3HTC60 counterpart

The significant improvement in the performance of thisdevice is attributed to the strong electronic interactionand good matching in the bandgap among the P3HT andgraphene to increase charge transportation The energy leveldiagram is shown in Figure 6(b) for the G-P3HTC60 deviceThis experiment demonstrates that derivatives of graphenecould be utilized as effective hole transporting materialin the active layer of PSCs [96] Recently Zhang et alhave also exploited the functionalization of graphite oxidewith fullerene via the covalent fisher esterification reactionThis covalent bonding 2D graphene with 0D fullerene isanticipated to bring together some novel characteristics intothe structure of graphene and display enormous prospectivein solar cells hydrogen storage and sensors applications [97]

232 Noncovalent Functionalization For the modificationof graphene sheets noncovalent functionalization reactionsare also frequently utilized With respect to the covalentmodification these noncovalent approaches do not interruptthe novel sp2 structure of graphene which furthermostretains the high electrical conductivity The noncovalentinteractions between graphene and other functional groupsgenerally involve 120587-120587 stacking [98 99] hydrogen bonding[100ndash102] van der Waals interaction [101 103] and elec-trostatic forces [85 100 104] Among these methods 120587-120587stacking and electrostatic interaction are most commonlyused for the semiconducting applications [105 106] RecentlyZhang et al have noncovalently functionalized graphenewith semiconducting fullerene via 120587-120587 interaction and inte-grated this compound into the epoxy composites [107] andconjugated polymer [108] to enhance the thermoelectricperformance of the polymer materials Zhang et al have alsosuccessfully demonstrated the successful enhancement ofthe thermoelectric properties of rGO119909F-C60119910 nanohybridsprepared by a noncovalent lithiationmethod [109] (Figure 7)


O

OS

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2CH

CH2OH

CH2OH

CH2OH

CH2OH

C6H13C6H13

C6H13C6H13

C6H13

C6H13

n

n

n

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nn

CH2

CH2

H2C

(1) SOCl2 65∘C 24hrs

(2) trimethylamine THF 36hrs

Graphene oxide P3HT with -CH2OH group P3HT grafted graphene

+

(a)0

ITO PEDOTPSS G-P3HT C60 Al

h

h

minus470 eVminus500 eV

minus539 eV

minus356 eV

minus440 eV minus430 eV

minus610 eV

e

minus7

minus6

minus5

minus4

minus3

(b)

Figure 6 (a) A representation of the synthesis process for chemical grafting on graphene with CH2OH-terminated P3HT chains (reprintedfrom [96] copyright 2010 American Chemical Society) (b) Energy level diagram of a photovoltaic device (reprinted from [96] copyright2010 American Chemical Society)

F-C60 rGO rGOF-C60

EF

LUMO

HOMO

+ =

HOMOmdash73 eV

LUMOmdash44 eV

Figure 7 Band structure modulation of rGO through F-C60 (reprinted from [109] copyright 2015 Elsevier)

This interactionwith semiconducting nanoparticles increasesthe bandgap of graphene to 29 eV and demonstrates p-typecharacteristics

Noncovalent functionalization can be implied to graphe-ne by using different types of organicmodifiers Table 1 showsdifferent noncovalent modification of GO using differentmodifying agents with the changes in electrical conductivity

3 Application of Semiconducting Graphene

31 Fuel Cell Fuel cells directly convert chemical energyinto electrical energy to provide a green solution to theenvironment This process involves high energy conversionby oxidizing at the anode (H2 gas) and reducing at cathode(O2 gas) [118]The electrical power is provided by the electron


Table 1 Electrical Conductivity of noncovalent functionalized GOwith different modifying agents

Modifying agent Conductivity (Smminus1) ReferenceSPANI 30 [110]PMMA 247 times 10minus5 [111]PVA 9 times 10minus3 [112]PE 10 [113]PET 211 [114]PBA 200 [115]Amine terminated polymer 1500 [116]PIL 3600 [117]

current that comes from the anode while proton reducesoxygen and generates water at the cathode [118] The oxygenreduction reaction (ORR) is a slow reaction (rate-limitingstep) on the cathode that can be fast in the presence of aconsiderable quantity of catalyst Pt is themostly used catalystfor this process however its high price is a limitation tocommercialize the application of the fuel cells

In recent research proposals carbon based materialsare being considered to replace platinum based electrodesin the fuel cells as reasonable catalysts with exceptionalperformanceThis accompanies the progress of carbon basedelectrocatalysts for ORR [119 120] Literature study revealedthat pristine graphene is not effective in facilitating electrontransfer and thus catalytic activities towards ORR are absentin it [121] Structural modification in graphene (such asdoping functionalization) could cause electron modulationto convert it into efficient electrocatalyst for oxygen reductionreaction (ORR) through achieving required electronic struc-tures for catalytic activity [32]

Doping of graphene with heteroatoms may increase thecatalytic activity of graphene in oxygen reduction reactionprocessThe doping-induced ORR improvement mechanismis still not entirely figured out Multiple steps and numerousintermediates are assumed to be involved with the ORRmethod depending on the surface chemistry of the catalystConsidering a general 4-electron pathway first the oxygenis absorbed on the catalyst surface and then reduced intohydroxyl group The oxygen adsorption and cleavage inoxygen-oxygen bond are promoted by heteroatom dopants(including N- B- S- P- and Se-doped graphene) due tothe charge-polarization of the bond between heteroatomand carbon [122 123] andor increase in spin density [124125] Heteroatom doping in graphene could also increasethe selectivity stability and electrochemical window alongwith the improved catalytic activity for ORR Consequentlygraphene materials doped with heteroatoms have possibilityof being applied in fuel cells to replace the currently usedPt catalysts For instance codoping of graphene with N andS exhibits exceptional activity towards the oxygen reductionreaction compared to regular platinum based catalysts Thisheteroatom-doped material could be a promising cathodicORR electrocatalyst for fuel cells due to its simple produc-tion method reasonable price and high performance [126](Figure 8(a))

The electrocatalytic activities of graphene in oxygenreduction reaction have also been observed through nonco-valent functionalization along with doping which involvesintermolecular charge-transfer in the process and causes littleor no change to the graphene structure For instance avery simple method to chemically functionalize heteroatom-doped graphene sheetswith small organic-molecules for theirimplication as electrocatalysts for the ORR was presented byUlsan National Institute of Science and Technology (UNIST)research team (Figure 8(b))They confirmed that by the vari-ation in the amount and arrangements of the N-dopant theelectrochemical performance can be enhanced Furthermorethis method was extended to the doping graphene with otherheteroatoms such as- B- and S-doped graphene Greaterstability was seen from the N-doped graphene nanosheets incontrast with regular PtC catalysts

To understand the complete mechanism of this catalyticactivity and the enhanced lifetime of the fuel cells additionalstudy is needed Further research in this developing arenamay be proved to be advantageous for fuel cell technologywith metal-free graphene-based ORR catalysts

32 Solar Cell Doped and functionalized graphene withsemiconducting properties has remarkable implication insolar cell [127] Atomic doping may bestow graphene with n-type or p-type semiconducting performance Consequentlythese resultant doped compounds could be implied for p-njunction solar cells Doping enhances the catalytic activity aswell as work function in graphene [128ndash130] In a recent studya boron-doped graphene has been used as a p-type electrodein solar cells through interfacing boron-doped graphene withn-type Si (Figure 9(a)) [128] Immense development in thesolar cell performance has been experienced due to theimproved electrical conductivity in the cell

Functionalized graphene-based materials are also usedfor application in solar cells For instance polymer solar cells(PSCs) apply a hole-extraction layer among the electrodeand the active layer to facilitate the charge collection byelectrode [131] The major role of these layers is to minimizethe energy barrier for the extraction of charge carrier Thesegraphene layers develop very selective interaction for theholes and block the electrons near the electrode Thereforethe graphene layers modify the morphology of the activelayer Functionalization of grapheneGO in a controlledway has been observed to be advantageous for the chargeextraction and active layers in polymeric solar cells [96 132]For instance in a recent study chemically grafted poly(3-hexylthiophene) (P3HT) onto GO has been observed to give200 rise of the power conversion efficiency (PCE) comparedto the counterpart P3HTC60 [96] This improvement inthe performance of the device is attributed to the firmelectronic interaction and great coordination in bandgapamong the graphene and P3HT to increase charge transport[96] Another study using a covalently attached C60 ontographene in the active layers of a P3HT-based polymersolar cell as electron acceptor resulted in 25-fold rise in thePCE [96 133] (Figures 9(b) and 9(c)) Consequently C60-grafted graphene has been acted as an excellent electronaccepting or transporting materials in polymer solar cells


O2 + H2O OHminus

4eminus

S O

C

N

(a)

O

NH

NH

N

NH

NN

Anode reaction Cathode reaction

H2 O2

Fuel cellMetal-air battery

Heteroatom-doped graphene nanosheet

O

O

O

O O

O

O

O

O

O

O

OHOH

OH

OH

OH

OH

Ominus

Ominus

Ominus

Ominus

H

H

NH3+

NH3+

NH3+

NH3+

HN

+H3N

+H3N

Chemically functionalized graphene oxide nanosheet

2H2 997888rarr 4H++ 4e

minus 2O2 + 4eminus+ 4H

+997888rarr 2H2O

(b)

Figure 8 (a) Electrocatalytic activity in fuel cell with heteroatom-doped graphene (reprinted from [126] copyright 2016 John Wiley andSons) (b) Application of semiconducting graphene in fuel cell (credit UNIST)

and many other optoelectronic devices These efforts pointout that functionalized semiconducting graphene is able tobe operated in the active layer of PSCs as effective holetransportation materials

33 Thermoelectric Devices Thermoelectric devices directlyconvert the temperature gradient into electric potential dif-ference These devices are mainly used for heating or coolingpurposes They have vast applications in many industries


Cu

Boronethanol

CVD

Etching Transfer

BG

BG

n-Si

1000∘C

(a)

S

S

h

C6H13

C6H13

n

n

e

ee

e

(b)

(c)Figure 9 (a) Schematic representation of the preparation of boron-doped graphene and solar cell assembly (reprinted from [128] copyright2012 John Wiley and Sons) (b) C60-grafted graphene for electron transport in a P3HT-based PSC (C60-G) (reprinted from [134] copyright2010 American Chemical Society) (c) Diagram of a polymeric solar cell including the C60-GP3HT composite as the active layer (reprintedfrom [96] copyright 2010 American Chemical Society)

including automotive and power generation [135] The ther-moelectric effect is seen in many thermoelectric materials(TE) [136] Among them organic TE have received consid-erable attention as a result of their abundance environmentfriendliness and characteristic of being easily processablebut the prospective of these materials is considerably limiteddue to the insufficient thermoelectric properties In a recentstudy Zhang et al have enhanced the thermoelectric perfor-mance by integrating noncovalently functionalized graphenewith fullerene by 120587-120587 stacking into a conjugated polymerPEDOTPSS (Figure 10) Proper controlling of the fullerene-graphene ratio in this nanohybrid can result in a synergisticeffect which may enhance the overall thermoelectric proper-ties [108]

34 Supercapacitors Energy storage has also dominant im-portance in addition to the energy conversion devices(including fuel cells solar cells) mentioned before Super-capacitors and batteries have drawn significant attention asenergy storage devices due to their long lifecycle and highpower density Supercapacitors are the lower energy storage

devices which possess greater energy delivery capability [137138] These devices require high power delivery capabilityhigh energy storage capacity and long cycle of life for theirapplications in large scale Recently graphene has been usedin supercapacitors because of its greater electric double-layer capacitance (EDLC) [139ndash141] Although the applica-bility of graphene-based materials in supercapacitors hasencountered some significant challenges pristine grapheneis chemically inert and does not offer any electrochemicalcapacitance (pseudocapacitance) Therefore functionalizedor doped graphene materials are proved to be favorable forthe application in supercapacitors due to their greater EDLCand presence of pseudocapacitance [142]

Some substantial quantity of deviations in the struc-ture of graphene could be introduced by doping for theuse of graphene in supercapacitors Literature reveals thatheteroatom-doped graphene (B- N- and P-doped graphene)offers increased stability improved conductivity and betterchemical reactivity compared to pristine graphene Thesematerials are more advantageous to be used in supercapaci-tors as they enhance electrochemical activity lower charge-transfer resistance and improve conductivity compared to


PEDOTPSSPEDOTPSS

rGO-PEDOTPSS

Graphene

Graphene

Thin PEDOTPSS layer

Thin PEDOTPSS layer

C60rGO-PEDOTPSS

C60 nanoparticles

Figure 10 Graphic representation of transportation of the carrier in an orderly polymer film reduced GO polymer and a polymer compositefilled with C60rGO nanohybrids (reprinted from [108] copyright 2013 Nature Publishing Group)

(a) (b)

Figure 11 (a) Schematic representation of an assembled structure of a supercapacitor with the SEM image in the top-view (reprinted from[147] copyright 2011 American Chemical Society) (b) Illustration of a supercapacitor model which consists of GO electrodes (ten percentoxidation) with pure EMI+BF4minus (reprinted from [149] copyright 2013 American Chemical Society)

pure graphene [143ndash146] Study demonstrates that super-capacitor based on graphene doped with nitrogen showedfourfold greater capacitance compared to its counterpartbased on pure graphene [147] (Figure 11(a)) These materialsmay expedite electron transfer lower the charge-transferresistance of the electrode and thus improve the capacitance[147 148]

Influence of codoping of graphene with two or moreatoms is also observed in different studies For exampleanother experiment showed that an electrode based on B

and N codoped graphene resulted in capacitance way highercompared to counterpart electrodes of pristine grapheneor only boron-doped graphene or only nitrogen-dopedgraphene This might be due the synergetic effects amongthe two codopants When these electrodes are implied insupercapacitors they seemed to attain increased energy andpower density [143]

Controlled oxidized graphene is also used in semicon-ducting applications Recently Deyoung et al revealed thedependency of capacitance on the oxidation extent [149]


Functionalized graphene cathode(delithiated state)

Current collector (Al)

Separator

Reduced graphene oxide anode(lithiated state)

Current collector (Cu)

Reaction in cathode

Reaction in anodeLiC3 larrrarr 3C + Li+ + eminus

-C=O + Li+ + eminus larrrarr -C-O-LiC

OLi

CLi

Figure 12 Application of functionalized graphene in Li-ion battery (reprint permission from [158] copyright 2014 Nature publishingGroup)

(Figure 11(b)) since oxidation modifies the ion accessibil-ity towards electrode surface This method demonstratesexcessive potential to catalyze electrode optimizations eventhough there are restrictions in the parameters measured forthe calculations

35 Lithium-Ion Batteries Lithium-ion batteries are regard-ed as energy storage devices with high energy storage capacityand poor energy delivery capability [138] In a lithium-ionbattery during charging ions move to the anode fromcathode and go in the reverse direction during dischargingPure graphene materials possess low binding energy towardslithium-ion and high energy barrier for the penetration ofions through the graphene sheet Therefore they are notappropriate for lithium-ion storage [150ndash152] Modifiedgraphene and carbon materials are often used in lithium-ionbatteries [153] The presence of defects in graphene materialallows lithium-ion penetration and prevents clustering oflithium as firm contact exists among the lithium and defectsites [151] However the number of defect sites should becontrolled to avoid some difficulties [154]

Heteroatom doping has been proved to maintain optimalbalance between storage of lithium and diffusion for elec-trodes [155]Theoretical and experimental study showed thatlithium atom is a potent electron donorTherefore the storagecapacity is increased in case of doping of graphene with anelectron-deficient atom (such as boron) [156] This restrictslithium diffusion (delithiation) though increasing bindingenergy among lithium and boron-doped graphene So overallthese materials enhance the battery capacity [156] Nitrogen-doped graphene shows reduced storage capacity but moreefficient delithiation which may be due to the decreasedbinding energy and the electrostatic repulsion betweenlithium and nitrogen Therefore these materials increase

the chargedischarge rate performance [150 156 157] Func-tionalized graphene and chemically modified graphene elec-trodes are also used in Li-ion batteries for better performanceThese modified graphene electrodes provide better paths forelectrons and ions conduction in batteries therefore intro-ducing greater capacity as well as improved rate capability

Lithium-ions and electrons are reserved at comparativelyhigher potential in the functional groups on the surfaceof graphene in the functionalized graphene cathode whilein the reduced GO anode Lithium-ions and electrons arereserved at comparatively lower potential on the graphenesurface An all-graphene-battery was prepared by Kim et althrough joining a reduced GO anode with a functionalizedgraphene cathode in lithiated state (Figure 12) This batteryshowed improved electrochemical properties The specificcapacity was almost 170mAhgminus1 depending on the cathodemass which matched approximately hundred percent imple-mentation of this cathode [158]

4 Conclusion and Perspective

As discussed in this review the high surface area exceptionalmechanical characteristics and reasonable price of graphenematerials make them promising material for application inseveral energy storage and conversion devices Althoughthe use of pristine graphene in these electronic applicationexperiences so many challenges due to the high conductivityand zero bandgap properties of graphene different methodshave been developed to overcome these limitations andintroduce a tunable bandgap in graphene to convert it intosemiconducting material Primarily three major approachessuch as doping controlled reduction and functionalizationof graphene are discussed in this article The enormousprospects of these semiconducting graphene materials for


energy conversion and storage applications have also beenexplored in this paper Appropriate surface modificationthrough doping reduction or functionalization may implytheir use in fuel cell solar cell thermoelectric devicessupercapacitors and batteries

Despite the tremendous progress made in the field ofsemiconducting graphenematerials still many difficulties areassociated with their synthesis procedure In case of surfacetransfer doping of graphene the materials do not possesslong-term stability This is due to the fact that the adsorbedspecies may desorb from graphene surface and react withreactive molecules The substitutional doped graphene (withmetal or heteroatoms) may have more stability in this caseas the atoms are attached to the carbon linkage of grapheneAlthough the substitutional doped graphene still experiencessome critical challenges in the large-scale production dopingcontrollability and mechanisms The large-scale productionhas been impeded by the requirement of harsh condition andhigh temperature A green synthesis method and controlledsynthesis of doped graphene are highly desirable Due to theconstant progression of novel materials and innovative appli-cations the mechanisms for reactions are still complicated inmany electrochemical systems Additional investigations inthis interesting field of doped graphene materials will makecontribution to the green energy systems The controlledreduction provides a way for mass production of semicon-ducting graphene The major challenge of this method isassociated with the effective removal of oxygen-containinggroups and proper control over reduction process which ishighly significant to appropriately tune the electrical conduc-tivity into the graphene structure Moreover as this processintroduces many defects to graphene further improvementsare desired to produce semiconducting graphene of high-quality The application of semiconducting graphene mate-rials into energy storage devices also experiences somemajor challengesThough doped or functionalized graphenematerials are proved to be favorable for the application insupercapacitors due to the presence of pseudocapacitanceand greater EDLC however the mechanical stability ofthese compounds is not so high The use of semiconductinggraphene materials in lithium-ion batteries is also discussedin this manuscript although a material with high specificsurface area as graphene may cause some major difficultiesincluding high irreversible capacity and SEI formation in thebattery electrodes In spite of the difficulties semiconductinggraphene has been considered as an attractive candidate forenergy applications Our expectation is that this review willinspire more exciting applications of this growing family ofsemiconducting graphene materials

Competing Interests

The authors declare that they have no competing interests

References

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[2] M J Allen V C Tung and R B Kaner ldquoHoneycomb carbona review of graphenerdquo Chemical Reviews vol 110 no 1 pp 132ndash145 2010

[3] R K Joshi M Yoshimura and A Kumar ldquoGraphenerdquo Journalof Nanomaterials vol 2010 Article ID 915937 1 page 2010

[4] A K Geim and K S Novoselov ldquoThe rise of graphenerdquo NatureMaterials vol 6 no 3 pp 183ndash191 2007

[5] K S Novoselov A K Geim S V Morozov et al ldquoTwo-dimensional gas of massless Dirac fermions in graphenerdquoNature vol 438 no 7065 pp 197ndash200 2005

[6] I Meric M Y Han A F Young B Ozyilmaz P Kim andK L Shepard ldquoCurrent saturation in zero-bandgap top-gatedgraphene field-effect transistorsrdquoNature Nanotechnology vol 3no 11 pp 654ndash659 2008

[7] P Avouris ldquoGraphene electronic and photonic properties anddevicesrdquo Nano Letters vol 10 no 11 pp 4285ndash4294 2010

[8] A H Castro Neto F Guinea N M R Peres K S Novoselovand A K Geim ldquoThe electronic properties of graphenerdquoReviews of Modern Physics vol 81 no 1 pp 109ndash162 2009

[9] K S Novoselov S V Morozov T M G Mohinddin et alldquoElectronic properties of graphenerdquo Physica Status Solidi (B)vol 244 no 11 pp 4106ndash4111 2007

[10] M Pykal P Jurecka F Karlicky and M Otyepka ldquoModellingof graphene functionalizationrdquo Physical Chemistry ChemicalPhysics vol 18 no 9 pp 6351ndash6372 2016

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[12] S Stankovich D A Dikin G H B Dommett et al ldquoGraphene-based composite materialsrdquo Nature vol 442 no 7100 pp 282ndash286 2006

[13] H Sadeghi D T H Lai J-M Redoute and A ZayeghldquoClassic and quantumcapacitances in bernal bilayer and trilayergraphene field effect transistorrdquo Journal of Nanomaterials vol2013 Article ID 127690 7 pages 2013

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[30] Z Jin H Nie Z Yang et al ldquoMetal-free selenium doped carbonnanotubegraphene networks as a synergistically improvedcathode catalyst for oxygen reduction reactionrdquo Nanoscale vol4 no 20 pp 6455ndash6460 2012

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[42] T Wu H Shen L Sun B Cheng B Liu and J Shen ldquoNitrogenand boron doped monolayer graphene by chemical vapordeposition using polystyrene urea and boric acidrdquoNew Journalof Chemistry vol 36 no 6 pp 1385ndash1391 2012

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[46] H Wang T Maiyalagan and X Wang ldquoReview on recentprogress in nitrogen-doped graphene synthesis characteriza-tion and its potential applicationsrdquo ACS Catalysis vol 2 no 5pp 781ndash794 2012

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[49] Z-S Wu W Ren L Xu F Li and H-M Cheng ldquoDopedgraphene sheets as anode materials with superhigh rate andlarge capacity for lithium ion batteriesrdquo ACS Nano vol 5 no7 pp 5463ndash5471 2011

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[51] A Abdelhafiz A Vitale C Joiner E Vogel and F M AlamgirldquoLayer-by-layer evolution of structure strain and activity forthe oxygen evolution reaction in graphene-templated Pt mono-layersrdquo ACS Applied Materials amp Interfaces vol 7 no 11 pp6180ndash6188 2015

[52] E J Biddinger D V Deak and U S Ozkan ldquoNitrogen-containing carbon nanostructures as oxygen-reduction cata-lystsrdquo Topics in Catalysis vol 52 no 11 pp 1566ndash1574 2009

[53] S Chen and S-Z Qiao ldquoHierarchically porous nitrogen-dopedgraphene-NiCo2O4 Hybrid Paper as an advanced electrocat-alytic water-splitting materialrdquo ACS Nano vol 7 no 11 pp10190ndash10196 2013

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active tetraruthenium homogeneous catalyst for water oxida-tionrdquoAngewandte ChemiemdashInternational Edition vol 47 no 21pp 3896ndash3899 2008

[55] J W Hong S W Kang B-S Choi D Kim S B Lee and SW Han ldquoControlled synthesis of Pd-Pt alloy hollow nanostruc-tures with enhanced catalytic activities for oxygen reductionrdquoACS Nano vol 6 no 3 pp 2410ndash2419 2012

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[57] H Jin J Wang D Su Z Wei Z Pang and Y Wang ldquoInsitu cobalt-cobalt oxideN-doped carbon hybrids as superiorbifunctional electrocatalysts for hydrogen and oxygen evolu-tionrdquo Journal of the American Chemical Society vol 137 no 7pp 2688ndash2694 2015

[58] G Singh D S Sutar V D Botcha et al ldquoStudy of simultaneousreduction and nitrogen doping of graphene oxide LangmuirndashBlodgett monolayer sheets by ammonia plasma treatmentrdquoNanotechnology vol 24 no 35 Article ID 355704 2013

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[64] B Shen J Chen X Yan and Q Xue ldquoSynthesis of fluorine-doped multi-layered graphene sheets by arc-dischargerdquo RSCAdvances vol 2 no 17 pp 6761ndash6764 2012

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[68] F Schwierz ldquoGraphene transistorsrdquoNatureNanotechnology vol5 no 7 pp 487ndash496 2010

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[80] X An T Simmons R Shah et al ldquoStable aqueous dispersions ofnoncovalently functionalized graphene from graphite and theirmultifunctional high-performance applicationsrdquo Nano Lettersvol 10 no 11 pp 4295ndash4301 2010

[81] K N Kudin B Ozbas H C Schniepp R K PrudrsquoHomme IA Aksay and R Car ldquoRaman spectra of graphite oxide andfunctionalized graphene sheetsrdquo Nano Letters vol 8 no 1 pp36ndash41 2008

[82] Y ZhuM D StollerW Cai et al ldquoExfoliation of graphite oxidein propylene carbonate and thermal reduction of the resultinggraphene oxide plateletsrdquoACSNano vol 4 no 2 pp 1227ndash12332010

[83] W Xueshen L Jinjin Z Qing Z Yuan and Z MengkeldquoThermal annealing of exfoliated graphenerdquo Journal of Nano-materials vol 2013 Article ID 101765 6 pages 2013

[84] I Jung D A Dikin R D Piner and R S Ruoff ldquoTunableelectrical conductivity of individual graphene oxide sheetsreduced at lsquoLowrsquo temperaturesrdquo Nano Letters vol 8 no 12 pp4283ndash4287 2008

[85] X Zhang K S Ziemer K Zhang et al ldquoLarge-area prepara-tion of high-quality and uniform three-dimensional graphenenetworks through thermal degradation of graphene oxide-nitrocellulose compositesrdquo ACS Applied Materials and Inter-faces vol 7 no 2 pp 1057ndash1064 2015

[86] Z Sun S-I Kohama Z Zhang J R Lomeda and J M TourldquoSoluble graphene through edge-selective functionalizationrdquoNano Research vol 3 no 2 pp 117ndash125 2010


[87] X Peng Y Li G Zhang F Zhang and X Fan ldquoFunction-alization of graphene with nitrile groups by cycloaddition oftetracyanoethylene oxiderdquo Journal of Nanomaterials vol 2013Article ID 841789 5 pages 2013

[88] N J Kybert G H HanM B Lerner E N Dattoli A Esfandiarand A T Charlie Johnson ldquoScalable arrays of chemical vaporsensors based on DNA-decorated graphenerdquo Nano Researchvol 7 no 1 pp 95ndash103 2014

[89] M Mathesh J Liu N D Nam et al ldquoFacile synthesis ofgraphene oxide hybrids bridged by copper ions for increasedconductivityrdquo Journal of Materials Chemistry C vol 1 no 18pp 3084ndash3090 2013

[90] Z-B Liu Y-F Xu X-Y Zhang X-L Zhang Y-S Chen andJ-G Tian ldquoPorphyrin and fullerene covalently functionalizedgraphene hybrid materials with large nonlinear optical proper-tiesrdquo Journal of Physical Chemistry B vol 113 no 29 pp 9681ndash9686 2009

[91] V Georgakilas M Otyepka A B Bourlinos et al ldquoFunction-alization of graphene covalent and non-covalent approachesderivatives and applicationsrdquo Chemical Reviews vol 112 no 11pp 6156ndash6214 2012

[92] L Aijiang ldquoPiezoelectric phenomenon of fullerene-graphenebonded structurerdquo Journal of Nanomaterials vol 2014 ArticleID 943013 4 pages 2014

[93] E Bekyarova M E Itkis P Ramesh et al ldquoChemical modifica-tion of epitaxial graphene spontaneous grafting of aryl groupsrdquoJournal of the American Chemical Society vol 131 no 4 pp1336ndash1337 2009

[94] C Shan H Yang D Han Q Zhang A Ivaska and L NiuldquoWater-soluble graphene covalently functionalized by biocom-patible poly-L-lysinerdquo Langmuir vol 25 no 20 pp 12030ndash12033 2009

[95] M Fang K Wang H Lu Y Yang and S Nutt ldquoCovalent poly-mer functionalization of graphene nanosheets and mechanicalproperties of compositesrdquo Journal of Materials Chemistry vol19 no 38 pp 7098ndash7105 2009

[96] D Yu Y Yang M Durstock J-B Baek and L Dai ldquoSolu-ble P3HT-grafted graphene for efficient bilayer-heterojunctionphotovoltaic devicesrdquo ACS Nano vol 4 no 10 pp 5633ndash56402010

[97] Y Zhang L Ren S Wang A Marathe J Chaudhuri andG Li ldquoFunctionalization of graphene sheets through fullereneattachmentrdquo Journal of Materials Chemistry vol 21 no 14 pp5386ndash5391 2011

[98] A A Castellanos-Gomez andB J vanWees ldquoBand gap openingof graphene by noncovalent 120587-120587 interaction with porphyrinsrdquoGraphene vol 2 no 4 2013

[99] W Lv M Guo M-H Liang et al ldquoGraphene-DNA hybridsSelf-assembly and electrochemical detection performancerdquoJournal of Materials Chemistry vol 20 no 32 pp 6668ndash66732010

[100] A J Patil J L Vickery T B Scott and S Mann ldquoAqueousstabilization and self-assembly of graphene sheets into layeredbio-nanocomposites using DNArdquo Advanced Materials vol 21no 31 pp 3159ndash3164 2009

[101] X Yang X Zhang Z Liu Y Ma Y Huang and Y ChenldquoHigh-efficiency loading and controlled release of doxorubicinhydrochloride on graphene oxiderdquo The Journal of PhysicalChemistry C vol 112 no 45 pp 17554ndash17558 2008

[102] X Zhang W M Hikal Y Zhang et al ldquoDirect laser initia-tion and improved thermal stability of nitrocellulosegraphene

oxide nanocompositesrdquo Applied Physics Letters vol 102 no 142013

[103] S-Z Zu and B-HHan ldquoAqueous dispersion of graphene sheetsstabilized by pluronic copolymers formation of supramolecularhydrogelrdquo The Journal of Physical Chemistry C vol 113 no 31pp 13651ndash13657 2009

[104] Y Liang D Wu X Feng and K Mullen ldquoDispersion ofgraphene sheets in organic solvent supported by ionic interac-tionsrdquo Advanced Materials vol 21 no 17 pp 1679ndash1683 2009

[105] J Yang M Heo H J Lee S-M Park J Y Kim and H SShin ldquoReduced graphene oxide (rGO)-wrapped fullerene (C60)wiresrdquo ACS Nano vol 5 no 10 pp 8365ndash8371 2011

[106] S Yang X Feng S Ivanovici and K Mullen ldquoFabricationof graphene-encapsulated oxide nanoparticles towards high-performance anode materials for lithium storagerdquo AngewandteChemiemdashInternational Edition vol 122 no 45 pp 8586ndash85892010

[107] K Zhang Y Zhang and S Wang ldquoEffectively decouplingelectrical and thermal conductivity of polymer compositesrdquoCarbon vol 65 pp 105ndash111 2013

[108] K Zhang Y Zhang and S Wang ldquoEnhancing thermoelectricproperties of organic composites through hierarchical nanos-tructuresrdquo Scientific Reports vol 3 article 3448 2013

[109] K Zhang S Wang X Zhang Y Zhang Y Cui and J QiuldquoThermoelectric performance of p-type nanohybrids filledpolymer compositesrdquo Nano Energy vol 13 pp 327ndash335 2015

[110] H Bai Y Xu L Zhao C Li and G Shi ldquoNon-covalentfunctionalization of graphene sheets by sulfonated polyanilinerdquoChemical Communications no 13 pp 1667ndash1669 2009

[111] Y-K Yang C-E He R-G Peng et al ldquoNon-covalentlymodified graphene sheets by imidazolium ionic liquids formultifunctional polymer nanocompositesrdquo Journal of MaterialsChemistry vol 22 no 12 pp 5666ndash5675 2012

[112] R K Layek S Samanta and A K Nandi ldquoThe physical prop-erties of sulfonated graphenepoly(vinyl alcohol) compositesrdquoCarbon vol 50 no 3 pp 815ndash827 2012

[113] H Pang T Chen G Zhang B Zeng and Z-M Li ldquoAnelectrically conducting polymergraphene composite with avery low percolation thresholdrdquo Materials Letters vol 64 no20 pp 2226ndash2229 2010

[114] H-B Zhang W-G Zheng Q Yan et al ldquoElectrically con-ductive polyethylene terephthalategraphene nanocompositesprepared bymelt compoundingrdquoPolymer vol 51 no 5 pp 1191ndash1196 2010

[115] Y Xu H Bai G Lu C Li and G Shi ldquoFlexible graphene filmsvia the filtration of water-soluble noncovalent functionalizedgraphene sheetsrdquo Journal of the American Chemical Society vol130 no 18 pp 5856ndash5857 2008

[116] E-Y Choi T H Han J Hong et al ldquoNoncovalent functional-ization of graphene with end-functional polymersrdquo Journal ofMaterials Chemistry vol 20 no 10 pp 1907ndash1912 2010

[117] T Kim H Lee J Kim and K S Suh ldquoSynthesis of phasetransferable graphene sheets using ionic liquid polymersrdquo ACSNano vol 4 no 3 pp 1612ndash1618 2010

[118] R OrsquoHayre S Cha W Colella and F Prinz Fuel Cell Funda-mentals John Wiley amp Sons New Jersey NJ USA 2006

[119] D Yu E Nagelli F Du and L Dai ldquoMetal-free carbonnanomaterials becomemore active thanmetal catalysts and lastlongerrdquo The Journal of Physical Chemistry Letters vol 1 no 14pp 2165ndash2173 2010


[120] X Ji X Zhang and X Zhang ldquoThree-dimensional graphene-based nanomaterials as electrocatalysts for oxygen reductionreactionrdquo Journal of Nanomaterials vol 2015 Article ID 3571969 pages 2015

[121] D A C Brownson L J Munro D K Kampouris and C EBanks ldquoElectrochemistry of graphene not such a beneficialelectrode materialrdquo RSC Advances vol 1 no 6 pp 978ndash9882011

[122] Y Zheng Y Jiao L Ge M Jaroniec and S Z Qiao ldquoTwo-step boron and nitrogen doping in graphene for enhancedsynergistic catalysisrdquo Angewandte Chemie vol 52 no 11 pp3110ndash3116 2013

[123] Z-H Sheng H-L Gao W-J Bao F-B Wang and X-HXia ldquoSynthesis of boron doped graphene for oxygen reductionreaction in fuel cellsrdquo Journal ofMaterials Chemistry vol 22 no2 pp 390ndash395 2012

[124] X Kong Q Chen and Z Sun ldquoEnhanced oxygen reduc-tion reactions in fuel cells on H-decorated and B-substitutedgraphenerdquo ChemPhysChem vol 14 no 3 pp 514ndash519 2013

[125] L Zhang andZ Xia ldquoMechanisms of oxygen reduction reactionon nitrogen-doped graphene for fuel cellsrdquo The Journal ofPhysical Chemistry C vol 115 no 22 pp 11170ndash11176 2011

[126] F Pan Y Duan X Zhang and J Zhang ldquoA facile synthesis ofnitrogensulfur cominusdoped graphene for the oxygen reductionreactionrdquo ChemCatChem vol 8 no 1 pp 163ndash170 2016

[127] A Manzano-Ramırez E J Lopez-Naranjo W Soboyejo YMeas-Vong and B Vilquin ldquoA review on the efficiency ofgraphene-based BHJ organic solar cellsrdquo Journal of Nanomate-rials vol 2015 Article ID 406597 15 pages 2015

[128] X Li L Fan Z Li et al ldquoBoron doping of graphene forgraphene-silicon p-n junction solar cellsrdquo Advanced EnergyMaterials vol 2 no 4 pp 425ndash429 2012

[129] Y Xue J Liu H Chen et al ldquoNitrogen-doped graphenefoams as metal-free counter electrodes in high-performancedye-sensitized solar cellsrdquo Angewandte ChemiemdashInternationalEdition vol 51 no 48 pp 12124ndash12127 2012

[130] S Das P Sudhagar V Verma et al ldquoAmplifying charge-transfercharacteristics of graphene for triiodide reduction in dye-sensitized solar cellsrdquo Advanced Functional Materials vol 21no 19 pp 3729ndash3736 2011

[131] R Steim F R Kogler and C J Brabec ldquoInterface materials fororganic solar cellsrdquo Journal of Materials Chemistry vol 20 no13 pp 2499ndash2512 2010

[132] Q Liu Z Liu X Zhang et al ldquoPolymer photovoltaic cellsbased on solytion-processable graphene and P3HTrdquo AdvancedFunctional Materials vol 19 no 6 pp 894ndash904 2009

[133] D S Yu K ParkMDurstock and LMDai ldquoFullerene-graftedgraphene for efficient bulk heterojunction polymer photovoltaicdevicesrdquo Journal of Physical Chemistry Letters vol 2 no 10 pp1113ndash1118 2011

[134] D Yu K Park M Durstock and L Dai ldquoFullerene-graftedgraphene for efficient bulk heterojunction polymer photovoltaicdevicesrdquoThe Journal of Physical Chemistry Letters vol 2 no 10pp 1113ndash1118 2011

[135] S Hu Exploring SiSiGe quantum-well thin-film thermoelectricdevices using TCAD simulation [PhD thesis] 2012

[136] T Feng and X Ruan ldquoPrediction of spectral phonon meanfree path and thermal conductivity with applications to ther-moelectrics and thermal management a reviewrdquo Journal ofNanomaterials vol 2014 Article ID 206370 25 pages 2014

[137] L L Zhang and X S Zhao ldquoCarbon-based materials assupercapacitor electrodesrdquo Chemical Society Reviews vol 38no 9 pp 2520ndash2531 2009

[138] R J Brodd K R Bullock R A Leising R L Middaugh J RMiller and E Takeuchi ldquoBatteries 1977 to 2002rdquo Journal of theElectrochemical Society vol 151 no 3 pp K1ndashK11 2004

[139] Y Xue H Chen D Yu et al ldquoOxidizing metal ions withgraphene oxide the in situ formation ofmagnetic nanoparticleson self-reduced graphene sheets for multifunctional applica-tionsrdquo Chemical Communications vol 47 no 42 pp 11689ndash11691 2011

[140] Z Yang J ZhangMCWKintner-Meyer et al ldquoElectrochemi-cal energy storage for green gridrdquoChemical Reviews vol 111 no5 pp 3577ndash3613 2011

[141] N Cao and Y Zhang ldquoStudy of reduced graphene oxidepreparation by hummersrsquo method and related characterizationrdquoJournal of Nanomaterials vol 2015 Article ID 168125 5 pages2015

[142] T Kwon H Nishihara H Itoi Q-H Yang and T KyotanildquoEnhancement mechanism of electrochemical capacitancein nitrogen-boron-doped carbons with uniform straightnanochannelsrdquo Langmuir vol 25 no 19 pp 11961ndash11968 2009

[143] Z-S Wu A Winter L Chen et al ldquoThree-dimensional nitro-gen and boron co-doped graphene for high-performance all-solid-state supercapacitorsrdquo Advanced Materials vol 24 no 37pp 5130ndash5135 2012

[144] B Xu S Yue Z Sui et al ldquoWhat is the choice for supercapac-itors graphene or graphene oxiderdquo Energy amp EnvironmentalScience vol 4 no 8 pp 2826ndash2830 2011

[145] P Karthika N Rajalakshmi and K S DhathathreyanldquoPhosphorus-doped exfoliated graphene for supercapacitorelectrodesrdquo Journal of Nanoscience and Nanotechnology vol 13no 3 pp 1746ndash1751 2013

[146] W Fan Y-Y Xia W W Tjiu P K Pallathadka C He and TLiu ldquoNitrogen-doped graphene hollow nanospheres as novelelectrode materials for supercapacitor applicationsrdquo Journal ofPower Sources vol 243 pp 973ndash981 2013

[147] H M Jeong J W Lee W H Shin et al ldquoNitrogen-dopedgraphene for high-performance ultracapacitors and the impor-tance of nitrogen-doped sites at basal planesrdquoNano Letters vol11 no 6 pp 2472ndash2477 2011

[148] V H Pham T V Cuong S H Hur et al ldquoChemical func-tionalization of graphene sheets by solvothermal reductionof a graphene oxide suspension in N-methyl-2-pyrrolidonerdquoJournal of Materials Chemistry vol 21 no 10 pp 3371ndash33772011

[149] A D Deyoung S-W Park N R Dhumal Y Shim Y Jungand H J Kim ldquoGraphene oxide supercapacitors A ComputerSimulation Studyrdquo Journal of Physical Chemistry C vol 118 no32 pp 18472ndash18480 2014

[150] Y Liu V I Artyukhov M Liu A R Harutyunyan and B IYakobson ldquoFeasibility of lithium storage on graphene and itsderivativesrdquo Journal of Physical Chemistry Letters vol 4 no 10pp 1737ndash1742 2013

[151] D Das S Kim K-R Lee andA K Singh ldquoLi diffusion throughdoped and defected graphenerdquo Physical Chemistry ChemicalPhysics vol 15 no 36 pp 15128ndash15134 2013

[152] F Liu CW Lee and J S Im ldquoGraphene-based carbonmaterialsfor electrochemical energy storagerdquo Journal of Nanomaterialsvol 2013 Article ID 642915 11 pages 2013


[153] Y Nomura I V Anoshkin C Okuda et al ldquoCarbon nanotubenanofibers and graphite hybrids for li-ion battery applicationrdquoJournal of Nanomaterials vol 2014 Article ID 586241 7 pages2014

[154] F Yao F Gunes HQ Ta et al ldquoDiffusionmechanismof lithiumion through basal plane of layered graphenerdquo Journal of theAmerican Chemical Society vol 134 no 20 pp 8646ndash86542012

[155] C Ma X Shao and D Cao ldquoNitrogen-doped graphenenanosheets as anodematerials for lithium ion batteries A First-Principles Studyrdquo Journal of Materials Chemistry vol 22 no 18pp 8911ndash8915 2012

[156] D H Wu Y F Li and Z Zhou ldquoFirst-principles studies ondoped graphene as anode materials in lithium-ion batteriesrdquoTheoretical Chemistry Accounts vol 130 no 2-3 pp 209ndash2132011

[157] Y-X Yu ldquoCan all nitrogen-doped defects improve the perfor-mance of graphene anode materials for lithium-ion batteriesrdquoPhysical Chemistry Chemical Physics vol 15 no 39 pp 16819ndash16827 2013

[158] H Kim K-Y Park J Hong and K Kang ldquoAll-graphene-battery bridging the gap between supercapacitors and lithiumion batteriesrdquo Scientific Reports vol 4 article 5278 2014

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


n-doped

p-dopedPristine

120587

120587lowast

120587

120587lowast

120587

120587lowast

EF

(a) (b) (c)

Figure 1 Schematic band structures of (a) n-type graphenewith bandgap (b) pure graphene and (c) p-type graphenewith bandgap (reprintedfrom [10] copyright 2016 PCCP Owner Societies)

could also be broken through other means [7] For theuse of graphene in electronic devices opening a well-tunedconsiderable bandgap in graphene is the major challenge

Figure 1 is the representation of the graphene band struc-tures presented where there is a linear energy momentumdispersion relation near the Dirac point [8 9] The coneshaped valence band and conduction bands meet across 119870point The Fermi level (119864F) lies at the crossover point in theband structure of pure graphene with zero bandgap 119864F liesin valence and conduction band in the band structures of 119901-type graphene and 119899-type graphene respectively including abandgap [10]

The surface properties of graphene are possible to beadjusted via structural alteration including chemical dop-ing chemical functionalization and controlled reductionwhich proposes remarkable prospects for the developmentof graphene-based semiconducting materials with uniqueelectronic characteristics These materials show advantagesfor numerous prospective applications including energyconversion energy storage catalysis sensing field effecttransistor and many more because of their high powerdensity and long lifecycle [11ndash14]

There are many methods that incorporate semiconduct-ing properties into graphene which include the preparationof graphenenanoparticle hybrids patterning graphene inthe form of a graphene nanoribbon nanomesh or quantumdot These methods have shown substantial developing andemerging interest from both theoretical and experimentalviewpoints and have been reviewed in several literatures [215ndash18] This review focuses on converting metallic grapheneinto semiconducting graphene by chemical alteration ofgraphene through doping controlled reduction and func-tionalization Although these newly developedmethods haverisen to rigorous attention in research these methods arenot classified or summarized in a single document Hence amethodical synopsis on these significantmethods for produc-ing semiconducting graphene and its exceptional character-istics and functions compared to graphene is greatly requiredThis review provides an overall context and structure on thelatest advancements in the area of semiconducting graphenematerials

The conversion processes discussed in this reviewcould be categorized into three major sections (1) doping

of graphene through surface transfer and substitutionalapproach (2) controlled reduction of graphene oxide (GO)and (3) functionalization of graphene via chemical methodsDoping of graphene with alien atoms instigates the electronicand structural distortions inside the carbon sheet leading tochanges in the graphene bandgap properties Partial reduc-tion of GO controls the level of oxygen-containing functionalgroup into the graphene structure During functionalizationdifferent functionalities are grafted onto graphene by covalentor noncovalent approaches All these methods are actuallyutilized for the bandgap opening in graphene and Fermilevel tuning of grapheneThe semiconducting graphene findsapplications in many scientific fields ranging from fuelcell solar cell and thermoelectric devices to supercapacitorand lithium-ion batteries These applications are carefullyreviewed in the manuscript

2 Fabrication Methods

21 Doping of Graphene A number of methods have beenproposed in the literature [19ndash21] tomodify the graphene andits electronic structure for the introduction of a substantialbandgap in it Among all the approaches one utmost reason-able approach is doping which helps in tuning the bandgapin graphene The concentration and nature of the chargecarriers can be regulated by doping For the band engineeringof graphene two major kinds of doping styles have beenappliedmdashsurface transfer doping and substitutional dopingSurface transfer doping involves the adsorption of an atominto the graphene lattice structure This incorporation ofatom could shift the voltage point of graphene at Diracpoint from zero gate voltage to +ve or minusve gate voltage asan outcome of p- or n-type graphene Substitutional dopinginvolves the replacement of carbon atoms inside the graphenelattice The incursion of atoms into the natural graphene willunavoidably instigate the electronic and structural distortionsinside the carbon sheet leading to changes in the graphenebandgap properties In this section an overview of recentexperimental and theoretical investigations on the doping ofgraphene is given and the possible reason for the semicon-ducting behavior of doped graphene is explained


O

O O

O

C

O

O O

O

C

O

O O

O

CAu3+

Au3+

Au3+

Au3+

Au0

Au0

Au0

eminus

eminus

eminus

eminus










H2 CH4

H3N-BH3

Ar

Hot platecontainer

Furnace


(a)




OH4eO2 + H2O


(3-1

)an

neal

ing

anne

alin

gin

NH

3




(3-2

)

inH

2S




CS-O

Thiophene S

(b)














(a)



at 108 hours



0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

Tim

e of h

ydra

zine

expo

sure

(hou

rs)

15 20 25 30 35 40 4510

Optical gap (eV)

(b)













Heating









O

OS

C

C

C

C

O

S

SS

S

S

O

O

O

O

O

O

O

O

OO

O

O

S

COOH

COOH

COOH

HOOC

HO

HO

HO

HOH2C

HOH2C

HOH2C

2CH

2CH

CH2OH

CH2OH

CH2OH

CH2OH

C6H13C6H13

C6H13C6H13

C6H13

C6H13

n

n

n

n

nn

CH2

CH2

H2C




+

(a)0


h

h


minus539 eV

minus356 eV


minus610 eV

e

minus7

minus6

minus5

minus4

minus3

(b)


F-C60 rGO rGOF-C60

EF

LUMO

HOMO

+ =

HOMOmdash73 eV

LUMOmdash44 eV

















O2 + H2O OHminus

4eminus

S O

C

N

(a)

O

NH

NH

N

NH

NN


H2 O2



O

O

O

O O

O

O

O

O

O

O

OHOH

OH

OH

OH

OH

Ominus

Ominus

Ominus

Ominus

H

H

NH3+

NH3+

NH3+

NH3+

HN

+H3N

+H3N


2H2 997888rarr 4H++ 4e


+997888rarr 2H2O

(b)





Cu

Boronethanol

CVD

Etching Transfer

BG

BG

n-Si

1000∘C

(a)

S

S

h

C6H13

C6H13

n

n

e

ee

e

(b)







PEDOTPSSPEDOTPSS

rGO-PEDOTPSS

Graphene

Graphene

Thin PEDOTPSS layer

Thin PEDOTPSS layer

C60rGO-PEDOTPSS

C60 nanoparticles


(a) (b)









Separator



Reaction in cathode



OLi

CLi












Competing Interests


References













































































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




O

O O

O

C

O

O O

O

C

O

O O

O

CAu3+

Au3+

Au3+

Au3+

Au0

Au0

Au0

eminus

eminus

eminus

eminus










H2 CH4

H3N-BH3

Ar

Hot platecontainer

Furnace


(a)




OH4eO2 + H2O


(3-1

)an

neal

ing

anne

alin

gin

NH

3




(3-2

)

inH

2S




CS-O

Thiophene S

(b)














(a)



at 108 hours



0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

Tim

e of h

ydra

zine

expo

sure

(hou

rs)

15 20 25 30 35 40 4510

Optical gap (eV)

(b)













Heating









O

OS

C

C

C

C

O

S

SS

S

S

O

O

O

O

O

O

O

O

OO

O

O

S

COOH

COOH

COOH

HOOC

HO

HO

HO

HOH2C

HOH2C

HOH2C

2CH

2CH

CH2OH

CH2OH

CH2OH

CH2OH

C6H13C6H13

C6H13C6H13

C6H13

C6H13

n

n

n

n

nn

CH2

CH2

H2C




+

(a)0


h

h


minus539 eV

minus356 eV


minus610 eV

e

minus7

minus6

minus5

minus4

minus3

(b)


F-C60 rGO rGOF-C60

EF

LUMO

HOMO

+ =

HOMOmdash73 eV

LUMOmdash44 eV

















O2 + H2O OHminus

4eminus

S O

C

N

(a)

O

NH

NH

N

NH

NN


H2 O2



O

O

O

O O

O

O

O

O

O

O

OHOH

OH

OH

OH

OH

Ominus

Ominus

Ominus

Ominus

H

H

NH3+

NH3+

NH3+

NH3+

HN

+H3N

+H3N


2H2 997888rarr 4H++ 4e


+997888rarr 2H2O

(b)





Cu

Boronethanol

CVD

Etching Transfer

BG

BG

n-Si

1000∘C

(a)

S

S

h

C6H13

C6H13

n

n

e

ee

e

(b)







PEDOTPSSPEDOTPSS

rGO-PEDOTPSS

Graphene

Graphene

Thin PEDOTPSS layer

Thin PEDOTPSS layer

C60rGO-PEDOTPSS

C60 nanoparticles


(a) (b)









Separator



Reaction in cathode



OLi

CLi












Competing Interests


References













































































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




H2 CH4

H3N-BH3

Ar

Hot platecontainer

Furnace


(a)




OH4eO2 + H2O


(3-1

)an

neal

ing

anne

alin

gin

NH

3




(3-2

)

inH

2S




CS-O

Thiophene S

(b)














(a)



at 108 hours



0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

Tim

e of h

ydra

zine

expo

sure

(hou

rs)

15 20 25 30 35 40 4510

Optical gap (eV)

(b)













Heating









O

OS

C

C

C

C

O

S

SS

S

S

O

O

O

O

O

O

O

O

OO

O

O

S

COOH

COOH

COOH

HOOC

HO

HO

HO

HOH2C

HOH2C

HOH2C

2CH

2CH

CH2OH

CH2OH

CH2OH

CH2OH

C6H13C6H13

C6H13C6H13

C6H13

C6H13

n

n

n

n

nn

CH2

CH2

H2C




+

(a)0


h

h


minus539 eV

minus356 eV


minus610 eV

e

minus7

minus6

minus5

minus4

minus3

(b)


F-C60 rGO rGOF-C60

EF

LUMO

HOMO

+ =

HOMOmdash73 eV

LUMOmdash44 eV

















O2 + H2O OHminus

4eminus

S O

C

N

(a)

O

NH

NH

N

NH

NN


H2 O2



O

O

O

O O

O

O

O

O

O

O

OHOH

OH

OH

OH

OH

Ominus

Ominus

Ominus

Ominus

H

H

NH3+

NH3+

NH3+

NH3+

HN

+H3N

+H3N


2H2 997888rarr 4H++ 4e


+997888rarr 2H2O

(b)





Cu

Boronethanol

CVD

Etching Transfer

BG

BG

n-Si

1000∘C

(a)

S

S

h

C6H13

C6H13

n

n

e

ee

e

(b)







PEDOTPSSPEDOTPSS

rGO-PEDOTPSS

Graphene

Graphene

Thin PEDOTPSS layer

Thin PEDOTPSS layer

C60rGO-PEDOTPSS

C60 nanoparticles


(a) (b)









Separator



Reaction in cathode



OLi

CLi












Competing Interests


References













































































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials













(a)



at 108 hours



0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

Tim

e of h

ydra

zine

expo

sure

(hou

rs)

15 20 25 30 35 40 4510

Optical gap (eV)

(b)













Heating









O

OS

C

C

C

C

O

S

SS

S

S

O

O

O

O

O

O

O

O

OO

O

O

S

COOH

COOH

COOH

HOOC

HO

HO

HO

HOH2C

HOH2C

HOH2C

2CH

2CH

CH2OH

CH2OH

CH2OH

CH2OH

C6H13C6H13

C6H13C6H13

C6H13

C6H13

n

n

n

n

nn

CH2

CH2

H2C




+

(a)0


h

h


minus539 eV

minus356 eV


minus610 eV

e

minus7

minus6

minus5

minus4

minus3

(b)


F-C60 rGO rGOF-C60

EF

LUMO

HOMO

+ =

HOMOmdash73 eV

LUMOmdash44 eV

















O2 + H2O OHminus

4eminus

S O

C

N

(a)

O

NH

NH

N

NH

NN


H2 O2



O

O

O

O O

O

O

O

O

O

O

OHOH

OH

OH

OH

OH

Ominus

Ominus

Ominus

Ominus

H

H

NH3+

NH3+

NH3+

NH3+

HN

+H3N

+H3N


2H2 997888rarr 4H++ 4e


+997888rarr 2H2O

(b)





Cu

Boronethanol

CVD

Etching Transfer

BG

BG

n-Si

1000∘C

(a)

S

S

h

C6H13

C6H13

n

n

e

ee

e

(b)







PEDOTPSSPEDOTPSS

rGO-PEDOTPSS

Graphene

Graphene

Thin PEDOTPSS layer

Thin PEDOTPSS layer

C60rGO-PEDOTPSS

C60 nanoparticles


(a) (b)









Separator



Reaction in cathode



OLi

CLi












Competing Interests


References













































































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a)



at 108 hours



0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

Tim

e of h

ydra

zine

expo

sure

(hou

rs)

15 20 25 30 35 40 4510

Optical gap (eV)

(b)













Heating









O

OS

C

C

C

C

O

S

SS

S

S

O

O

O

O

O

O

O

O

OO

O

O

S

COOH

COOH

COOH

HOOC

HO

HO

HO

HOH2C

HOH2C

HOH2C

2CH

2CH

CH2OH

CH2OH

CH2OH

CH2OH

C6H13C6H13

C6H13C6H13

C6H13

C6H13

n

n

n

n

nn

CH2

CH2

H2C




+

(a)0


h

h


minus539 eV

minus356 eV


minus610 eV

e

minus7

minus6

minus5

minus4

minus3

(b)


F-C60 rGO rGOF-C60

EF

LUMO

HOMO

+ =

HOMOmdash73 eV

LUMOmdash44 eV

















O2 + H2O OHminus

4eminus

S O

C

N

(a)

O

NH

NH

N

NH

NN


H2 O2



O

O

O

O O

O

O

O

O

O

O

OHOH

OH

OH

OH

OH

Ominus

Ominus

Ominus

Ominus

H

H

NH3+

NH3+

NH3+

NH3+

HN

+H3N

+H3N


2H2 997888rarr 4H++ 4e


+997888rarr 2H2O

(b)





Cu

Boronethanol

CVD

Etching Transfer

BG

BG

n-Si

1000∘C

(a)

S

S

h

C6H13

C6H13

n

n

e

ee

e

(b)







PEDOTPSSPEDOTPSS

rGO-PEDOTPSS

Graphene

Graphene

Thin PEDOTPSS layer

Thin PEDOTPSS layer

C60rGO-PEDOTPSS

C60 nanoparticles


(a) (b)









Separator



Reaction in cathode



OLi

CLi












Competing Interests


References













































































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





Heating









O

OS

C

C

C

C

O

S

SS

S

S

O

O

O

O

O

O

O

O

OO

O

O

S

COOH

COOH

COOH

HOOC

HO

HO

HO

HOH2C

HOH2C

HOH2C

2CH

2CH

CH2OH

CH2OH

CH2OH

CH2OH

C6H13C6H13

C6H13C6H13

C6H13

C6H13

n

n

n

n

nn

CH2

CH2

H2C




+

(a)0


h

h


minus539 eV

minus356 eV


minus610 eV

e

minus7

minus6

minus5

minus4

minus3

(b)


F-C60 rGO rGOF-C60

EF

LUMO

HOMO

+ =

HOMOmdash73 eV

LUMOmdash44 eV

















O2 + H2O OHminus

4eminus

S O

C

N

(a)

O

NH

NH

N

NH

NN


H2 O2



O

O

O

O O

O

O

O

O

O

O

OHOH

OH

OH

OH

OH

Ominus

Ominus

Ominus

Ominus

H

H

NH3+

NH3+

NH3+

NH3+

HN

+H3N

+H3N


2H2 997888rarr 4H++ 4e


+997888rarr 2H2O

(b)





Cu

Boronethanol

CVD

Etching Transfer

BG

BG

n-Si

1000∘C

(a)

S

S

h

C6H13

C6H13

n

n

e

ee

e

(b)







PEDOTPSSPEDOTPSS

rGO-PEDOTPSS

Graphene

Graphene

Thin PEDOTPSS layer

Thin PEDOTPSS layer

C60rGO-PEDOTPSS

C60 nanoparticles


(a) (b)









Separator



Reaction in cathode



OLi

CLi












Competing Interests


References













































































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




O

OS

C

C

C

C

O

S

SS

S

S

O

O

O

O

O

O

O

O

OO

O

O

S

COOH

COOH

COOH

HOOC

HO

HO

HO

HOH2C

HOH2C

HOH2C

2CH

2CH

CH2OH

CH2OH

CH2OH

CH2OH

C6H13C6H13

C6H13C6H13

C6H13

C6H13

n

n

n

n

nn

CH2

CH2

H2C




+

(a)0


h

h


minus539 eV

minus356 eV


minus610 eV

e

minus7

minus6

minus5

minus4

minus3

(b)


F-C60 rGO rGOF-C60

EF

LUMO

HOMO

+ =

HOMOmdash73 eV

LUMOmdash44 eV

















O2 + H2O OHminus

4eminus

S O

C

N

(a)

O

NH

NH

N

NH

NN


H2 O2



O

O

O

O O

O

O

O

O

O

O

OHOH

OH

OH

OH

OH

Ominus

Ominus

Ominus

Ominus

H

H

NH3+

NH3+

NH3+

NH3+

HN

+H3N

+H3N


2H2 997888rarr 4H++ 4e


+997888rarr 2H2O

(b)





Cu

Boronethanol

CVD

Etching Transfer

BG

BG

n-Si

1000∘C

(a)

S

S

h

C6H13

C6H13

n

n

e

ee

e

(b)







PEDOTPSSPEDOTPSS

rGO-PEDOTPSS

Graphene

Graphene

Thin PEDOTPSS layer

Thin PEDOTPSS layer

C60rGO-PEDOTPSS

C60 nanoparticles


(a) (b)









Separator



Reaction in cathode



OLi

CLi












Competing Interests


References













































































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials














O2 + H2O OHminus

4eminus

S O

C

N

(a)

O

NH

NH

N

NH

NN


H2 O2



O

O

O

O O

O

O

O

O

O

O

OHOH

OH

OH

OH

OH

Ominus

Ominus

Ominus

Ominus

H

H

NH3+

NH3+

NH3+

NH3+

HN

+H3N

+H3N


2H2 997888rarr 4H++ 4e


+997888rarr 2H2O

(b)





Cu

Boronethanol

CVD

Etching Transfer

BG

BG

n-Si

1000∘C

(a)

S

S

h

C6H13

C6H13

n

n

e

ee

e

(b)







PEDOTPSSPEDOTPSS

rGO-PEDOTPSS

Graphene

Graphene

Thin PEDOTPSS layer

Thin PEDOTPSS layer

C60rGO-PEDOTPSS

C60 nanoparticles


(a) (b)









Separator



Reaction in cathode



OLi

CLi












Competing Interests


References













































































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




O2 + H2O OHminus

4eminus

S O

C

N

(a)

O

NH

NH

N

NH

NN


H2 O2



O

O

O

O O

O

O

O

O

O

O

OHOH

OH

OH

OH

OH

Ominus

Ominus

Ominus

Ominus

H

H

NH3+

NH3+

NH3+

NH3+

HN

+H3N

+H3N


2H2 997888rarr 4H++ 4e


+997888rarr 2H2O

(b)





Cu

Boronethanol

CVD

Etching Transfer

BG

BG

n-Si

1000∘C

(a)

S

S

h

C6H13

C6H13

n

n

e

ee

e

(b)







PEDOTPSSPEDOTPSS

rGO-PEDOTPSS

Graphene

Graphene

Thin PEDOTPSS layer

Thin PEDOTPSS layer

C60rGO-PEDOTPSS

C60 nanoparticles


(a) (b)









Separator



Reaction in cathode



OLi

CLi












Competing Interests


References













































































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Cu

Boronethanol

CVD

Etching Transfer

BG

BG

n-Si

1000∘C

(a)

S

S

h

C6H13

C6H13

n

n

e

ee

e

(b)







PEDOTPSSPEDOTPSS

rGO-PEDOTPSS

Graphene

Graphene

Thin PEDOTPSS layer

Thin PEDOTPSS layer

C60rGO-PEDOTPSS

C60 nanoparticles


(a) (b)









Separator



Reaction in cathode



OLi

CLi












Competing Interests


References













































































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




PEDOTPSSPEDOTPSS

rGO-PEDOTPSS

Graphene

Graphene

Thin PEDOTPSS layer

Thin PEDOTPSS layer

C60rGO-PEDOTPSS

C60 nanoparticles


(a) (b)









Separator



Reaction in cathode



OLi

CLi












Competing Interests


References













































































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






Separator



Reaction in cathode



OLi

CLi












Competing Interests


References













































































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






Competing Interests


References













































































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



























































































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials
























































































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






















































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials

















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Documents

Review Article Synthesis and Applications of