Different Synthesis Routes of Graphene-Based Metal Nanocomposites

Joydip Sengupta

ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Graphene and Its Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Synthesis of Graphene-Metal/Metal Oxide Nanocomposites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Solution Mixing Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Sol-Gel Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Hydrothermal/Solvothermal Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Self-Assembly Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Microwave Irradiation Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Ball Milling Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Electrochemical Deposition Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Other Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Summary and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Cross-References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

AbstractNanocomposite material proves to be the best candidate to match today’s tech-nological need as fascinating properties can be achieved by combining two ormore nanomaterials. Among various nanomaterials, graphene is able to stand out

J. Sengupta (*)Department of Electronic Science, Jogesh Chandra Chaudhuri College, Kolkata, Indiae-mail: joydipdhruba@gmail.com

© Springer Nature Switzerland AG 2019C. M. Hussain, S. Thomas (eds.), Handbook of Polymer and Ceramic Nanotechnology,https://doi.org/10.1007/978-3-030-10614-0_30-1

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far ahead of all others because of its novel structure and exclusive characteristics.In particular, graphene-metal nanocomposites have attracted enormous interestfor their prospective use in various fields, including electronics and electrical andenergy-related areas. However, for the utmost use of potential of graphene, it hasto be homogenously embedded into metal matrices. Thus, appropriate synthesisroute is decisive to obtain graphene-metal nanocomposites with desired proper-ties. This chapter will summarize the different synthesis routes of high-qualitygraphene-metal nanocomposites along with their current developments.

KeywordsGraphene · Nanocomposite · Solution mixing · Sol-gel · Hydrothermal ·Solvothermal · Self-assembly · Microwave irradiation · Ball milling ·Electrochemical deposition

Introduction

Development of new material is the fundamental culture of human race sinceits birth. Thus in order to accomplish unique properties, two or more materials canbe combined resulting in a new material called composite material. Compositematerials are solids that are comprised of two or more different elements or phases,on a scale larger than the size of an atom. Since the birth of civilization, the synthesisof composite material started its journey with the invention of mudbricks andconcrete. In general, composites are comprised of two types of materials, one isthe called matrix or binder which encloses and binds together fragments or fibers ofthe other material, termed as reinforcement. If one of the constituent materials of thecomposite is of nanometer dimension, then the composite is called nanocomposite,and in most of the cases, the nanomaterial is used as a reinforcement material. Sincethe advent of nanomaterial, several of them were used to synthesize nanocomposite,as nanomaterial possesses remarkable improvement in their properties compared totheir bulk counterpart (Roduner 2006). The inclusion of nanomaterial as the rein-forcement in the parent matrix also significantly enhances the properties of theresulting nanocomposite (Kumar and Krishnamoorti 2010). Among the differentnanomaterials, graphene has emerged as one of the most prospective nanomaterialsdue to the unique combination of its exotic properties (Novoselov et al. 2012). Basedon the binder material, graphene nanocomposite can be categorized as graphene-metal/metal oxide nanocomposite, graphene - ceramic nanocomposite, graphene -semiconductor nanocomposite, and graphene - polymer nanocomposite. Amongvarious nanocomposites, graphene-metal/metal oxide composites have attractedconsiderable attention because of their potential applications in energy (Su et al.2012) and health-related (Ali et al. 2017) areas. However the quality of graphene andits homogeneous dispersion in the nanocomposite is the key to success.

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Graphene and Its Synthesis

Graphene is an atomically thin 2D allotrope of carbon, made of a single sheet of sp2

hybridized carbon atoms, and has exotic properties with a planar density of 0.77 mg/m2. Graphene possesses strongest crystal structure, outstanding mechanical proper-ties, extremely high thermal conductivity, electron mobility, and electrical conduc-tivity (Fig. 1).

The graphene can be synthesized via top-down processes like micromechanicalexfoliation, electrochemical exfoliation, thermal exfoliation, reduction of grapheneoxide, arc discharge, unzipping carbon nanotubes, and sonication. The othergraphene growth methods that come under the category of bottom-up process arepyrolysis, chemical vapor deposition, and epitaxial growth on silicon carbide. Thereare good-quality review papers (Cheun Lee et al. 2017; Bhuyan et al. 2016) on thedifferent synthesis processes of graphene, and in particular the pros and consof different synthesis routes are reported by Raccichini et al. (2015) (Fig. 2).

Fig. 1 Graphene is a 2D material that acts as a building block for carbonaceous materials of allother dimensions (Reproduced with permission from Geim and Novoselov 2007)

Different Synthesis Routes of Graphene-Based Metal Nanocomposites 3

Synthesis of Graphene-Metal/Metal Oxide Nanocomposites

There are various routes to synthesize graphene-metal/metal oxide nanocompositesas shown in the illustration below (Fig. 3).

Fabrication processes

Solution mixing

Sol-gel

Hydrothermal/solvothermal

Self-assembly

Microwave irradiation

Ball milling

Electrochemical deposition

Others

Liquid-phaseexfoliation

Top-down

Bottom-up

Graphene

Si

SiC

Chemical vapourdeposition

GraphiteOxidationexfoliation

GO

Reduction

rGO

Micromechanicalcleavage

Fig. 2 Schematic representation of the graphene synthesis methods (Reproduced with permissionfrom Wang et al. 2017a)

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Solution Mixing Method

Solution mixing method is widely used to synthesize graphene-metal/metaloxide nanocomposite as it can be performed at low temperature, promote fasterde-aggregation and dispersion of reinforcement material, and produce compositeswith uniform reinforcement dispersion. Tang et al. (2014) used in situ chemicalreduction method to prepare graphene nanosheets (GNS) decorated with Ni nano-particles, and afterward GNS-Ni hybrids were wet-mixed with electrolytic Cupowder to produce GNS-Ni/Cu nanocomposite. The mechanical properties of theresulting nanocomposite revealed high Young’s modulus of 132 GPa and yieldstrength of 268 MPa. Li et al. (2014) used natural graphite powder to preparegraphene oxide (GO) via Hummer’s method (Hummers et al. 1958) and synthesizedNi nanoparticles decorated graphene platelets (GPL) using chemical reduction ofNi ions on the surface of the GO. Afterward Cu powder was solution mixed withNi nanoparticles decorated GPL to synthesize Ni-GPL-Cu nanocomposite withultimate tensile strength of 250 MPa. Wang et al. (2017b) used reduced grapheneoxide (rGO) and Cu(OH)2 composite sheets to fabricate micro-layered structure ofrGO-Cu powder and sintered it with spark plasma. The tensile strength of resultingnanocomposite was 608 MPa which is more than three times higher than that of theCu matrix. Zeng et al. (2018) added Al powder in the aqueous GO suspension whichwas followed by ultrasonic treatment, stirring, and drying to obtain graphene-Al

Fig. 3 Schematic illustration of binding mechanisms of the nanoparticles onto rGO sheets(Reproduced with permission from Khan et al. 2015)

Different Synthesis Routes of Graphene-Based Metal Nanocomposites 5

nanocomposites with ultimate tensile strength of 255 MPa. Other than improvementin mechanical properties graphene-metal/metal oxide nanocomposites are also usedto address different environmental and energy-related issues. Paek et al. (2009) usedethylene glycol to disperse chemically reduced GNS and later on reassembled it inthe presence of SnO2 nanoparticles to synthesize graphene-SnO2 nanocompositewith superior cyclic performances. Williams (2008) proposed an efficient way tofabricate graphene-TiO2 nanocomposites via UV-assisted photocatalytic reductionof GO in solution phase. Bell et al. (2011) used a solution phase photocatalyticreduction method to integrate GO into TiO2 film to manufacture photovoltaic cellsthat exhibited a tenfold increase in the photo-generated current that of TiO2 only.Akhavan and Ghaderi (2009) used the similar methodology for the formation of GO-TiO2 thin film and studied the antibacterial activity of the thin films against theEscherichia coli bacteria.

Sol-Gel Method

The sol-gel route (Hench and West 1990) provides simple, inexpensive preparationof a homogeneous composite material with excellent compositional control and isthus used in many applications. Zhang et al. (2010a) used tetra butyl titanate and GOas the starting materials for the sol-gel synthesis of graphene-TiO2 nanocompositesand found that the photocatalytic activity of the composite was affected by bothgraphene content and the calcinations atmosphere. Li et al. (2013) used sol-gelmethod to ultra-disperse TiO2 nanoparticles on graphene with extreme control sothat the grown material can achieve twice the specific capacity as that of mechan-ically mixed composites. Innocenzi et al. (2014) made optically transparentgraphene-SiO2 nanocomposite via sol-gel process using 1-vinyl-2-pyrrolidone andSiCl4 to avoid aggregation of graphene sheet. The grown nanocomposites can bepotentially used in optical limiters. Hintze et al. (2016) fabricated controlled carbonphase-based rGO-SiO2 nanocomposite using sol-gel technique with appreciableelectrical conductivity. Mohammad-Rezaei and Razmi (2016) used sol-gel processto fabricate graphene-SiO2 nanocomposite with remarkable specific capacitance of428 Fg�1 at current density of 1 Ag�1 and good cycling stability. Graphene-TiCnanocomposites were synthesized byWang et al. (2016) for shock/impact absorptionvia sol-gel process using furfuryl alcohol (FA) as a carbon source. A nanocompositeof functional GNS and cobalt sulfide with high reversible capacity of 466 mAhg�1

and good rate capability was prepared by Chen et al. (2017). Damavandi et al. (2017)used graphene and carbon nanotube (CNT) as the reinforcement material in Al2O3

matrix, and the resulted sol-gel-derived nanocomposite exhibited fracture toughnessand flexural strength of 6.2 MPam1/2 and 420 MPa, respectively. Graphene-BiFO3

composite was prepared by Nayak et al. (2018) via sol-gel process for electrochem-ical supercapacitor application as it revealed maximum specific capacitance of17 mF/cm2 and 95% retention of capacitance after 2000 cycles. Giampiccolo et al.(2019) synthesized graphene-TiO2 nanocomposite via sol-gel route for the sensingof harmful gas NO2 with the detection limit of about 50 ppb to provide a saferenvironment.

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Hydrothermal/Solvothermal Method

Hydrothermal and solvothermal syntheses are the methods of producing compositesgenerally in an autoclave under high temperatures and pressures (Feng and Li 2017).Aqueous solution is used in hydrothermal method, while in solvothermal methodnonaqueous solution is used. GO-TiO2 nanocomposite was synthesized via two-stephydrothermal method by Liang et al. (2010) which showed superior photocatalyticactivity to other forms of TiO2. Yang et al. (2011) deposited Ag nanoparticle ongraphene using solvothermal method to fabricate graphene-Ag nanocomposites withexcellent electroconductibility using ethylene glycol or deionized water/hydrazine.The hydrazine proved to be better reducing agent and thus had more control over thesize and morphology of Ag nanoparticle. Lin-jun et al. (2012) did similar experi-ment, and the resulted graphene-Ag nanocomposites showed electroconductibilityof 2.94 scm�1. A novel hydrothermal route was devised by Lee et al. (2012) tosynthesize graphene-wrapped TiO2 nanoparticle for enhancing the photocatalyticactivity of TiO2 under visible light. For precise detection of nonenzymatic glucose,Song et al. (2013) synthesized GO-CuO nanocomposite using hydrothermal methodand also varied the different parameters such as hydrothermal temperature, amount,and structure of CuO in order to optimize the process, and the grown materialshowed the possibility to be used for highly enhanced nonenzymatic glucosedetection. Graphene-CeO2 nanocomposite with high catalytic activity was preparedby Srivastava et al. (2013) using hydrothermal method. Zhang et al. (2014) synthe-sized rGO-Fe3O4 nanocomposite using one-pot hydrothermal route which depictedhigh capacity of 884 mAhg1 after 100 cycles indicating its potential application asanode material of LIBs. Graphene-Mn3O4 nanocomposite was synthesized by Liu etal. (2014) via solvothermal process in ethanol solution. The grown material isa promising candidate for supercapacitor as with the mass percent of Mn2+:GO(10:90), it exhibited high specific capacitance (�245 F/g) at 5 mV/s. Ma et al. (2014)developed a unique solvothermal synthesis route to prepare self-assembled three-dimensional graphene-CoO nanocomposite with enhanced electrochemical perfor-mance for use in lithium ion battery (LIB). Graphene-MnFe2O4 nanocomposite wasprepared by Chella et al. (2015) using solvothermal method and investigated itsadsorbent and antimicrobial properties. The examination revealed that preparednanocomposite had good adsorption efficiency regarding the removal of toxicheavy metal ions (Pb and Cd) and can also act as an efficient antimicrobial agent.Zhang et al. (2015) synthesized graphene-CuFe2O4 nanocomposite employingsolvothermal process and studied the electrochemical properties, and the materialexhibited electrochemical capacitance of 576.6 F�g�1 at current density 1 A�g�1 withhigh-rate performance and cycling stability. Graphene-NiO nanocomposite wasprepared by Narasimharao et al. (2016) via hydrothermal synthesis which wasof high potential for application in supercapacitor as electrode. Venkateshalu etal. (2017) synthesized rGO-CoS2 nanocomposite via hydrothermal process forapplication in supercapacitor, and the grown material showed a specific capacitanceof 28 F/g at a current density of 0.5 A/g. N-doped graphene-Fe2O3 composites weresynthesized via hydrothermal process by Pu et al. (2018) using melamine as the

Different Synthesis Routes of Graphene-Based Metal Nanocomposites 7

nitrogen source. The resultant material showed a remarkable specific capacitancevalues at low and high current densities 698 (1 A/g) and 354 (20 A/g) F/g, respect-ively, and established its candidature as material for supercapacitor. Sagadevan et al.(2018) prepared graphene-SnO2 nanocomposite using hydrothermal approach withhigh photocatalytic activity, and the synthesized product can be potentially used forindustrial waste water management. GO-MnO2 nanocomposite was synthesized byLiang et al. (2018) via one-step hydrothermal process, which can be used as anadsorbent for the removal of heavy metal ions (Pb2+, Cu2+, Cd2+, and Zn2+) fromaqueous solution.

Self-Assembly Method

Self-assembly (Genix 2018) is a process in which a system’s constituent reorganizesinto some specific order or structure or pattern as a result of precise local interactionsamong the constituents themselves. Wang et al. (2009) used anionic sulfate surfac-tants to stabilize graphene in aqueous medium and finally to felicitate self-assembledgrowth of graphene-TiO2 nanocomposite which can be potentially used in LIB for itshigh specific capacity. Liu et al. (2010) devise an approach to self-assemble TiO2

nanorods on GO sheets, and the resulted nanocomposite showed enhanced photo-catalytic activity under UV irradiation. Yang et al. (2010) devised a novel strategyfor the formation of graphene-metal oxide nanoparticle (SiO2 and Co3O4) core-shellhybrids by electrostatic forces leading to notable lithium-storage performance,inclusive of high reversible capacity and exceptional cycle performance. Wang etal. (2010) demonstrated a ternary self-assembly route employing graphene as basicbuilding block to synthesize ordered graphene-metal oxide nanocomposite. One ofsuch kind of material, graphene-SnO2 nanocomposite exhibited near theoreticalspecific energy density for lithium ion insertion/extraction without significant deg-radation of charge/discharge. Li et al. (2011) reported a facile one-pot, template-freeself-assembly production route to synthesize graphene-TiO2 nanocomposite. Thenanocomposite depicted considerable enhancement in lithium-specific capacity, highphotocatalytic activity in removing organic pollutant, and finally hydrogen evolutionby splitting the water. Du et al. (2011) fabricated hierarchically ordered macro-mesoporous graphene-TiO2 nanocomposite via self-assembly which showed thecharacteristic of rapid adsorption and photodegradation of organic dyes for potentialapplication in wastewater treatment. Electrostatically derived self-assembled growthof titanate and rGO was carried out by Kim et al. (2012) which revealed an enhancedperformance in the photodegradation of organic molecules. Guoxin and Xu (2014)prepared rGO-Fe2O3 nanocomposites via self-assembly method in aqueous phasethrough electrostatic attraction. Lin et al. (2015) synthesized graphene-Co nano-composite via carbonization of a self-assembly, which comprises of a Co-basedmetal organic framework, ZIF-67, and GO. The grown material can serve as theeffective catalyst to activate peroxymonosulfate in the advanced oxidation process.Xu et al. (2018) prepared self-assembled Ag nanowires-graphene nanocompositesfor use in electrically conductive adhesives to improve its electrical conductivity and

8 J. Sengupta

mechanical properties. Zhang et al. (2018a) prepared rGO-encapsulated Cu nano-particles employing electrostatic self-assembly procedure which revealed excep-tional electrocatalytic activity toward glucose oxidation along with a widedetection range, low detection limit, and high sensitivity.

Microwave Irradiation Method

Microwave radiation (Langa et al. 1997) generates rapid intense heating in theinterior of the sample and consequently reduces reaction time to provide cleanerreactions environment while saving energy. Zhang et al. (2010b) prepared graphene-magnetite nanocomposites employing microwave radiation which depictedhigh reversible as well as rate capacities (350 mAhg�1) and enhanced cyclingperformances (650 mAhg�1) thus suitable to be used as anode material of LIBs.Graphene-MnO2 nanocomposite was synthesized using microwave irradiation byYan et al. (2010a) which showed enhanced high-rate electrochemical performancewith specific capacitance as high as 310 Fg�1. The same group (Yan et al. 2010b)also prepared graphene-Co3O4 nanocomposite having long cycle life via microwaveirradiation; however the obtained maximum specific capacitance was 243.2 Fg�1.Graphene-metal (Ag, Au, Pt, and Pd) nanocomposites were synthesized bySubrahmanyam et al. (2010) under microwave irradiation which displayed signifi-cant electronic interaction between the constituents resulted from the ionizationenergy and electron affinity of the metal particles. Marquardt et al. (2011) usedstable Ru or Rh metal nanoparticles to produce graphene-metal nanocomposite viamicrowave irradiation which were capable to act as catalyst in hydrogenationreactions resulting in complete conversion of cyclohexene or benzene to cyclohex-ane under organic solvent-free conditions. A simple two-step microwave-assistedsynthesis of GO-Fe2O3 nanocomposite was carried out by Zhu et al. (2011a) whichdisplayed discharge and charge capacities of 1693 and 1227 mAh/g, respectively,with enhanced cycling performance and rate capability indicating its potential useas electrode materials for LIBs. Hsu and Chen (2014) synthesized rGO-Ag nano-composite via microwave irradiation for use as surface-enhanced Raman scattering(SERS) substrate with high homogeneity and sensitivity. Three-dimensionalexpanded graphene-metal oxide (Fe2O3 and MnO2) nanocomposite was preparedvia solid-state microwave irradiation by Yang et al. (2015) and built asymmetricsupercapacitor using Fe2O3-graphene and MnO2-graphene as electrodes. Theresulted supercapacitor displayed large potential window of 1.8 V which can com-bine high energy and power densities along with a good cycling life. Darvishi et al.(2017) prepared graphene-CuO nanocomposite and studied the photocatalytic per-formance of the material which indicated that increase in graphene amount increasesthe average rate constant. Nanocomposite of rGO-titanium oxide was prepared byAtes et al. (2017) using microwave irradiation. Supercapacitors made using theresulted nanocomposite displayed large specific capacitance with a high energyand power density which made it a suitable material for supercapacitor application.Nagaraju et al. (2018) synthesized graphene-WO3 nanocomposite using in situ

Different Synthesis Routes of Graphene-Based Metal Nanocomposites 9

microwave irradiation, and the nanocomposite displayed specific capacitanceof 761 Fg�1 at the current density of 1 Ag�1 with excellent cyclic stability whichindicates the potential use in supercapacitor.

Ball Milling Method

In ball milling (Delogu et al. 2017) or mechanical alloying process, a powdermixture is placed in a closed vessel and thereafter undergoes high-energy collisionfrom the balls. In this high-energy process, graphite can be ruptured to producegraphene sheets which can be further mixed with other materials to producenanocomposite. He et al. (2009) prepared graphene-Al2O3 composite powders byball milling method for different milling times. They concluded that addition ofgraphene hinders the grain growth of Al2O3 resulting in production of finer particles.Composites of GPL and powdered Al were prepared by Bartolucci et al. (2011)using ball milling and compared with pure Al and multi-walled carbon nanotubecomposites. The comparative study reflected that strength and hardness weredecreased for graphene-Al composite as a result of aluminum carbide formation.Bastwros et al. (2014) prepared a 1.0 wt% graphene-reinforced aluminum (Al6061)composite via ball milling and reported that flexural strength was enhanced by 47%compared with the reference Al6061 processed at the same condition. GNP/Alcomposites were produced employing mechanical alloying by Pérez-Bustamante etal. (2015) and studied their mechanical behavior which exhibited that hardnessincreases with milling time. Dutkiewicz et al. (2015) used GPL and mixed it withCu nanoparticles via milling process, and the resulted nanocomposite revealednearly 50% increase in hardness and about 30% decrease in electrical resistivitycompared to the composite with coarse GPL. Tribological and mechanical propertiesof multilayer graphene reinforced Ni3Al matrix composites prepared by Zhai et al.(2015) via ball milling. It was found that the elastic modulus and hardness of themetal nanocomposite were improved with increasing multilayer graphene content upto 1.0 wt% while decreased afterward. Moreover addition of multilayer graphenedecreases the friction coefficient and improves the wear resistance of the nano-composite. Yue et al. (2016) prepared GNS-Cu nanocomposite via ball millingmethod and studied the effect of variation of GNS content on elongation to fractureand ultimate tensile strength. The measurement revealed that GNS content in thecomposite must be 0.5 wt% to achieve the best results. Du et al. (2017) fabricatedgraphene-Mg nanocomposite using ball milling of a pure Mg powder, and GNS.Si@SiOx/graphene nanocomposites were prepared by Tie et al. (2018) using ballmilling technique which depicted high reversible capacity, enhanced cycling stabil-ity, and good rate capability to be used as high-performance anode materials forLIBs. Zhang et al. (2018b) prepared GNS-Al nanocomposite using ball millingwhich revealed increase in hardness by 115.1% due to the refined microstructureand Orowan strengthening.

10 J. Sengupta

Electrochemical Deposition Method

Electrochemical (Abdel-Karim 2016) deposition is synthesis method where afilm of solid metal is deposited from a solution of ions onto an electricallyconducting surface. This inexpensive and scalable method offers several advantageslike high purity of deposited materials and rigid control of the composition. Yin et al.(2010) deposited monocrystalline ZnO nanorods having high donor concentrationon highly conductive rGO films, and the resultant nanocomposite was incorporatedin an inorganic-organic hybrid solar cell to increase its efficiency. Graphene-MnO2 nanowall hybrids were synthesized by Zhu et al. (2011b) via a one-stepelectrochemical approach, and the synthesized materials exhibited potential forapplications in electrochemical biosensors and supercapacitors. Gao et al. (2011)devised a simple single-step ultrasonication-assisted electrochemical route for thesynthesis of graphene-PtNi nanocomposites which showed excellent electrochemi-cal performance in detecting nonenzymatic amperometric glucose in human urinesamples. Jagannadham studied the thermal (Jagannadham 2012a) and electrical(Jagannadham 2012b) conductivity of the graphene-Cu nanocomposite films syn-thesized by electrochemical deposition, and the results indicated that the resultantmaterial is suitable for electrofriction applications. Graphene-Ni nanocompositeswere synthesized employing electrodeposition in a nickel sulfamate solution withGO sheets by Kuang et al. (2013). Measurements on the nanocomposite showedincreased thermal conductivity and significantly improved hardness. Xie et al.(2014) synthesized rGO-Cu nanocomposite films with one-step electrochemicalreduction deposition method which exhibited high electroactivity and thus can beused in electrical contact materials. Ren et al. (2015) successfully synthesizedgraphene-Ni nanocomposite via electrochemical deposition, and further examinationrevealed that elastic modulus of 240 GPa with a hardness of 4.6 GPa can be obtainedwith an addition of graphene as low as 0.05 g L�1. GO-TiO2 nanotube compositewas synthesized via one-step anodization by Ali et al. (2017), and the nano-composite revealed a high photocatalytic activity for organics degradation undervisible light.

Other Methods

Other than the common methods described before, some other methods or mixedmethods are also used for the synthesis of graphene-metal/metal oxide nano-composite. Sun et al. (2010) employed heterogeneous coagulation method for thesynthesis of graphene-TiO2 nanocomposites, and upon incorporation it enhanced thepower conversion efficiency of dye-sensitized solar cells. Biju (2018) used bothhydrothermal and solution mixing method for the preparation of α-Fe2O3-graphenenanocomposite.

Different Synthesis Routes of Graphene-Based Metal Nanocomposites 11

Summary and Outlook

Graphene-based metal nanocomposites demonstrated peerless potential whichis reflected in their exponential increase in usage in various technological fields.As the requirements of high-performance graphene-metal/metal oxide nano-composite increase with time, so much more research work has to be carried out inthis field. There are already seven major synthesis routes, namely, solution mixing,sol-gel, hydrothermal/solvothermal, self-assembly, microwave irradiation, ball mill-ing, and electrochemical deposition for the production of graphene-metal/metaloxide nanocomposite. The measurement of the resultant material depicted a greatenhancement in mechanical, thermal, and electrical properties. However, there arefew key challenges still remain related to synthesis methods, where scalable, eco-nomical, sustainable high-quality graphene growth and reproducible homogeneousdispersion of graphene in metal matrix are most significant. The scalable economical(Zou et al. 2018) sustainable (Wang et al. 2017c) high-quality graphene growth isa matter of continuous challenge, and researchers are seamlessly striving to addressthese issues. Functionalization of graphene (Gong et al. 2016) is proposed as aremedy to address the issues as it can modify the graphene-metal interface in orderto achieve homogeneous dispersion of graphene. Low bulk density of the grapheneis another barrier to achieve homogeneous dispersion. All these studies indicatethat the possibility of fabricating advanced graphene-based metal nanocompositesis strongly dependent on the graphene-metal interface engineering (Zhang etal. 2018c).

Cross-References

▶Applications of Graphene-Based Nanomaterials▶Graphene Nanocomposite▶Novel Graphene Based Nanocomposite

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