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Functionalized Graphene Reinforced Hybrid Nanocomposites and Their Applications
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FUNCTIONALIZED GRAPHENE REINFORCED HYBRID NANOCOMPOSITES AND THEIR APPLICATIONS
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N. Saba, Mohammad Jawaid Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, Selangor, Malaysia
1. INTRODUCTION Graphene is a multifunctional 2-D atomic crystal and an allotrope of carbon with several unique properties, including high electrical conductivity, thermal conductivity of 5000 W m1 K1, high electron mobility in room temperature (250,000 cm2 V1 s1), high aspect ratio, large surface area (2630 m2 g1), and high modulus of elasticity (w1 TPa) [1,2]. The single-layer, bilayer, and multilayer graphene, graphene oxide (GO), reduced GO (rGO), and chemically modified graphene are widely known as graphene nanofibers (GFNs) [1]. It has been reviewed that graphene can be processed as nanoribbons, platelets, foams, and even as quantum dots for immense use in semiconductor, energy storage devices, hydrogels, and biological applications. Graphene also been used as a reinforcing agent in variety of thermoset and thermoplastics polymer composites to improve their physical, mechanical strength, fracture toughness, electrical and thermal properties due to its homogeneous dispersion [3]. Various approaches for fabricating graphene/polymer nanocomposites have been reported, including blending polymers with graphite particles and the intercalation of polymers within graphite interlayers through in situ polymerization and solution blending as well as melt compounding [4,5]. However, significant challenges remain to be overcome in the development of promising graphene-based polymer composites in consumer products due to the irreversible aggregation or even restacking of graphene to graphite [6]. Thus, the homogeneous dispersion of graphene sheets in polymer is still a matter of concern or interest in polymer science. Furthermore, researchers reported that the modification of graphene or introduction of a functional group can successfully overcome this problem [7]. Functionalization can be carried out through covalent and noncovalent techniques (hydrogen bonding, electrostatic forces, pep stacking, and hydrophobic interactions) [6]. Research studies also revealed that chemical functionalization is one of the most effective methods for modifying the surface of graphite or 3-D graphene [4]. Developed functionalized hybrid polymer nanocomposites show wide engineering industrial applications ranging from cosmetics and aerospace to energy storage, transistors, fuel cells, batteries, and supercapacitors [3]. Functionalized Graphene Nanocomposites and Their Derivatives. https://doi.org/10.1016/B978-0-12-814548-7.00010-6 Copyright © 2019 Elsevier Inc. All rights reserved.
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2. GRAPHENE AND ITS SYNTHESIS Good-quality micron-size graphene was first discovered in 2004 by Andre Geim and Konstantin Novoselov by peeling graphite with adhesive tape [8] as an amazingly thin transparent film composed of carbon with exciting and outstanding electric, mechanical, and thermal properties, displayed in Fig. 10.1. Graphene is a monolayer of carbon atoms packed into honeycomb lattice [9]. Graphene carbon atoms are arranged as hexagons in flat layers, where each carbon atom is covalently joined to the other three carbon atoms in flat, hexagonal layers [1,10]. Each sheet of graphene is only one atom thick, and each graphene sheet is considered a single molecule. Graphene currently grabs enormous attention and research motives among other nanomaterials as physically, it is superstrong, stiffer, lighter, has a larger surface-to-volume ratio and is a good conductor of electricity/heat [11]. Graphene can be made from natural graphite or from synthetic graphite and is regarded as a basic 2-D building block of all the carbon nanostructures of other dimensionalities. It forms 0-D fullerene or buckyballs by wrapping, 1-D cylindrical carbon nanotubes (CNTs) by rolling with respect to its axis, and a planar 3-D stacked structure of graphite [12,13]. A possible dimensional structure from 2-D graphene is illustrated in Fig. 10.2. Several techniques and methods have been established to produce graphene sheets, such as mechanical cleaving (epitaxial growth), electrochemical exfoliation, chemical exfoliation, liquidphase exfoliation of graphene nanosheets (GNS), thermal chemical vapor deposition (CVD) of monolayer and multilayer GNS, chemical synthesis or organic synthesis of graphene nanoribbons, electrochemical reduction of exfoliated graphite oxide precursor at cathodic potentials [10], solvothermal reduction, photocatalyst reduction [14], Hummers’ method [15], and chemical reduction of exfoliated graphite oxide and rGO in the presence of different reducing agents, including hydrazine, hydrazine hydride, sodium borohydride, hydroquinone, and ascorbic acid [11,16,17]. Among the many reducing agents, hydrazine hydride is referred to as the best reducing agent to produce very thin graphene sheets [16]. Some other techniques are also reported in literature to produce few-layer graphene, such as unzipping of CNTs, electron beam irradiation of poly(methyl methacrylate) nanofibers, arc discharge of graphite, conversion of nanodiamond, solid carbon heating, silicon carbide heating, thermal fusion of polycyclic aromatic hydrocarbons (PAHs), and
FIGURE 10.1 Graphene or single-layer graphite structure [1].
2. GRAPHENE AND ITS SYNTHESIS
(A)
(B)
(C)
(D)
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FIGURE 10.2 (A) Two-dimensional graphene building material, (B) stacked 3-D graphite, (C) rolled 1-D nanotubes, and (D) wrapped 0-D buckyballs [13].
FIGURE 10.3 Several synthetic approaches for graphene [13].
microwave synthesis [12,18,19]. Although chemical vapor deposition and mechanical exfoliation using atomic force microscopy (AFM) cantilevers are regarded as some of the most promising techniques to produce monolayers of graphene sheets on a large scale [20]. Fig. 10.3 summarizes some of the significant synthetic approaches for graphene [13]. Researchers stated that properties of graphene, such as lateral size (from several nanometers to centimeters), stacked layers, morphology, structure, surface chemistry, solubility, electrical and thermal conductivities, defects, and impurity contents strongly rely on the applied synthetic method [1,21]. Furthermore, synthesized graphene is characterized by several instrumental techniques to define its properties, such as crystallinity and molecular and functional structure. Currently, several instruments available for characterization include X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), ultravioletevisible (UVevis) spectroscopy, scanning electron microscopy (SEM), highresolution transmission electron microscopy, dark-field transmission electron microscopy, and X-ray photoelectron spectroscopy (XPS) [15].
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3. GRAPHENE PROPERTIES AND APPLICATIONS Graphene is basically one of the most abundant, thinnest minerals and is the world’s strongest single atomic layer of graphite; besides that, it is highly flexible and one of the most promising nanomaterials having one-atom carbon sheets that are highly conductive, even more than copper [18,22]. It is found to be the most chemically reactive form of carbon. Graphene has the same structure of carbon atoms linked in hexagonal shapes to form CNTs, but graphene is flat rather than cylindrical. Defect-free, monolayer graphene is considered to be the strongest material ever known, as it possesses exceptional mechanical strength and modulus and fracture toughness [20]. The reason for the exceptional mechanical properties of graphene lies in the stability of the sp2 bonds that form the hexagonal lattice and oppose a variety of in-plane deformations, or simply the strength of covalent bonds between carbon atoms are extremely strong; hence graphene has a very high tensile strength [3,20], as shown in Fig. 10.4. An overview of mechanical properties of graphene and its derivatives is presented in Table 10.1. The table clearly reveals that an increased number of GNS layers leads to a reduction in properties [16]. Graphene has zero rest mass of charge carriers in the crystal, and electrons travel with the speed of light through the crystal. Researchers revealed that this type of electron transport is even not found in any semiconductor, thus resulting in graphene as the most conductive nonsuperconducting material at room temperature, having resistivity of 106 cm1 [8]. Moreover, graphene is harder than diamond and 100e300 times stronger than steel; it can be stretched up to 20% of its original length [15], it absorbs 2.3% of light that passes through it due to its unique electronic properties, and it is the most permeable and transparent material ever discovered. Reported physical, mechanical, and electrical properties of graphene are tabulated in Table 10.2. Table 10.2 signifies the characteristics extraordinary combination of physical, mechanical, chemical, electrical, and thermal properties of graphene offered toward several potential industrial-oriented
FIGURE 10.4 Graphene monolayer. Modified from Soldano C, Mahmood A, Dujardin E. Production, properties and potential of graphene. Carbon 2010;48:2127e50.
3. GRAPHENE PROPERTIES AND APPLICATIONS
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Table 10.1 Mechanical Properties of Graphene and Its Derivatives [16] Material Graphene (monolayer) Reduced graphene oxide (rGO) Graphene nanosheets (GNS; bilayer/trilayer/multilayers)
Young’s Modulus (MPa)
Tensile Strength (MPa)
Fracture Toughness (MPa)
106 2.5 105 1.04 106e0.98 106
1.3 105 0.9 103 1.26 105e1.01 105
4e5 2.8e3 4.7e3.8
Table 10.2 Overview of Physical, Mechanical, and Electrical Properties of Graphene Mechanical and Electrical Properties
Approximated Values
Electrical conductivity Thermal conductivity Charge carrier mobility at electron density w2 1011 cm2 Melting point Current density Bandgap Energy gap Transparency Tensile strength Young’s modulus Fracture toughness Shear modulus Poisson’s ratio Specific surface area Covalent bonding energy Sigma bonds with a bond length
w108 S m1 w5000 W m1 K1 w15,000e200,000 cm2 V1 s1 4510K w1.6 109 A cm2 Zero 0.26 Ev w97.4% w1100 GPa w106 MPa 4e5 MPa w0.213e0.233 w1.285e1.441 w2630 m2 g1 w5.9 Ev ˚ w1.42 A
Nag A, Mitra A, Mukhopadhyay SC. Graphene and its sensor-based applications: a review. Sensor Actuator Phys 2017; Dasari BL, Nouri JM, Brabazon D, Naher S. Graphene and derivativesesynthesis techniques, properties and their energy applications. Energy 2017;140:766e78; Lee SK, Kim H, Shim BS. Graphene: an emerging material for biological tissue engineering. Carbon Lett 2013; 14:63e75.
applications. These include its wider application in electrochemical sensors, strain sensors, firefighting, smoke suppression agents for polymer (polystyrene) composites [24], and structural engineering applications such as airplane appliances [15]. Some of the promising applications of graphene in the scientific community are shown in Fig. 10.5. Graphene’s exceptional and remarkable electrical conductivity and high surface area also makes it a promising material for energy conversion and storage applications such as batteries, nanoelectronics, electrical sensors including temperature sensing and photodetectors [15], electromechanical resonators,
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FIGURE 10.5 Versatile applications of graphene [1].
supercapacitors, fuel cells, transparent conducting electrodes, optoelectronic devices, energy storage devices, and transistors [18]. Graphene’s electron mobility is faster than any known material and is currently replacing transistors built on silicon wafers, as the field-effect transistors on graphene are much faster. Besides this, it is regarded as the most potential material for applications such as single-molecule gas sensing or detection, biomedical devices, tissue regeneration, carriers for drug or gene delivery, detection materials for bioimaging and biosensors, neural interfaces, ultrasensitive sensors, actuators [15], environmental such as heavy metal or transition metals detection, electrochemical sensing, and polymer composites, owing to its honeycomb structure having closely packed sp2-bonded carbon atoms [16,23]. Research findings analyzed that energy-related applications and electronic applications occupy the highest percentages, whereas its involvement in polymer composites still not satisfactory [16]. Graphene also presents unsuspected applications in making durable footwear, impact and pressure sensors, electromagnetic barriers, photonic, heat dissipation systems, inks, hydrogen storage, and roller screens. Graphene stands out as potential nanofiller in polymeric melts due to its outstanding mechanical, dielectric, barrier, thermal and dynamic properties [25], besides this graphene shows certain shortcomings that limit its practical applications, most remarkably as a reinforcement material in polymer composites, which require more insight, investigation and study. Limitations include incompatibility with the polymer matrix, orientation, zero bandgap, agglomeration/restacking of graphene layers leading to nonhomogeneous distribution within the matrix, and the hindrances in physical handling of graphene sheets due to its poor solubility in most solvents or polymer matrix [11]. Interestingly, graphene has a potential to replace the conventional reinforcements for the metal matrix composites.
4. FUNCTIONALIZED GRAPHENE Graphene is regarded as a promising reinforcing material for variety of polymer matrices. However, the tendency to irreversible agglomerate or restack to form graphene sheets via pep stacking, strong van der-Waals interactions among its sheets, and the weak compatibility with most polymer matrices restricts its potentiality as effective reinforcing agent. The effective way to overcome or address these
5. HYBRID NANOCOMPOSITES
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challenges includes surface modification of graphene by adding a functional group called functionalization. Functionalization increases the graphene compatibility with specific polymers, thus improving its reinforcing effect [26]. Researchers revealed two types of graphene functionalization as chemical and nonchemical functionalization methods [27]. Chemical functionalization is a chemical (or electrochemical) process that proceeds at an atomic/molecular level and is realized through the formation of new covalent bonds between the atoms native to rGO/GO and the introduced functional groups contrast to physical interaction. Physical or nonchemical functionalization is primarily based on p-interaction between guest molecules and rGO/GO. Chemical functionalization is proposed by incorporating different atoms/organic groups into graphene, including heterogeneous atoms doping, diazonium coupling, amidation, esterization, substitution, silanization, and cycloaddition [27]. Various kinds of functional groups have been chemically anchored on graphene and are found to be more effective, offering extensive applications in polymer science and technology. Doping of nitrogen, boron, phosphorous, fluorine, sulfur, and chloride atoms into graphene is highly desirable, as these doping agents effectively convert graphene from gapless structure to semiconductor and also provide an effective step to modulate the surface chemistry and the optoelectrical properties of graphene [28]. Functionalized doped graphene possesses enhanced dispersity within solvents/polymers along with intriguing electrical, water retention, membranes proton conductivity [29], thermal stability, mechanical strength and high processability properties. Besides this, it also offered a innovative way for fabricating 3-D materials and nanocomposite materials having unique and superior properties [11,27]. Researchers also reviewed that functionalization also modifies intrinsic features, including electronic properties, to enable the control of conductivity and bandgap for state-of-the-art nanoelectronic devices [7,30].
5. HYBRID NANOCOMPOSITES Nanocomposites, which exhibit superior mechanical and physical properties compared to their respective matrix materials, are among the most technologically promising materials to meet the worldwide demand for high-performance applications in many fields [31,32]. A hybrid material is defined as advanced engineering material composed of an intimate mixture of inorganic components, organic components, or both types of components. Currently, enormous attention has been observed toward the development of nanostructured hybrid materials as prominent advanced materials owing to their unique characteristics featuring superior dielectric, mechanical, physical properties, lightweight, ultrahigh tunable modulus of resilience, and versatile nanoscale with great potential for diverse applications. Hybrid nanocomposites show high-tech applications that require ultrahigh mechanical resilience, efficient energy harvesting, strength, environmental pollutants sensors, energy storage, capacitors, and conservation [33]. Intensive study on high-performing hybrid polymer nanocomposites for application in the sectors of automotive, aerospace, and construction industries has been reported merely by incorporating highly conductive nanofillers such as CNTs and graphene and nonconductive ones like layered silicates/ferroelectric ceramics and layered double hydroxide in the polymeric matrix [34]. However, aggregation of these fillers represents a major barrier in their development [32,35,36]. Other researchers also indicated that the effectiveness of reinforced nanofiller in the polymer matrix greatly depends on perfect dispersion and intimate filler/matrix interactions [37,38].
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6. FUNCTIONALIZED GRAPHENEeREINFORCED HYBRID POLYMER NANOCOMPOSITES Graphene-reinforced hybrid polymer nanocomposite materials are of great interest for their structural fabrications from past decades. Immense interest in reinforcing graphene materials arose due to graphene’s promising, unique, excellent mechanical, thermal, electrical, optoelectronic, and physicochemical properties along with intrinsic flexibility and nanophysical existence [13] in all fields of technologies [13,39]. Currently, many successful efforts have been made for fabricating functionalized grapheneereinforced polymer composites by incorporating functionalized graphene at low filler loading (1%e5% by weight) [31], with a perfect dispersion within a polymer matrix owing to graphene’s high-end properties. Varied chemical and physical synthesis techniques are known for homogenous distribution and dispersion of functionalized graphene in a variety of thermoset and thermoplastic polymers, including solution blending, melt blending, shear mixing, solution casting, combination of melt blending/solution casting/in situ polymerization, three roll mill, in situ polymerization, ball milling/hot pressing, laminates, sequential transfer, vacuum filtration, water-assisted extrusion, latex cocoagulation, latex mixing, latex compounding, wet spinning, melt compounding, mechanical stirring, ultrasonication, hydrothermal/solvothermal, gas-phase deposition, solegel processing, template method, mechanical mixing, ultrasonication along with high-pressure homogenization, stirring along with ultrasonication, centrifugal mixing and vacuum impregnation [13,15,40,41]. Recent developments, fabrication, and applications of functionalized grapheneereinforced hybrid polymer nanocomposite materials with other nanofiller or natural/synthetic fibers are summarized in Table 10.3. Several characterization techniques are currently known to analyze and investigate the developed functionalized grapheneehybrid polymer nanocomposites like other polymer nanocomposites. Most commonly used characterization techniques include SEM, TEM, FTIR, energy-dispersive X-ray spectroscopy AFM, UVevis absorption spectroscopy, Raman spectroscopy, Zeta potential analysis, X-ray fluorescence, XPS, BrunauereEmmetteTeller and XRD [41,53,54].
7. APPLICATIONS OF FUNCTIONALIZED GRAPHENE HYBRID NANOCOMPOSITES Functional grapheneereinforced polymer nanocomposites have attracted wide promising industrial interest due to their light weight, high strength, chemical resistance, and long durability [49]. Brittle and electrically insulating functional grapheneereinforced alumina matrix nanocomposites show extensive applications in electronics, defense, aerospace, and transportation. They are also found to be wear resistant and structural materials for extreme environments, such as high temperature/pressure, nuclear radiation, and chemicals [31]. Functional grapheneehybrid polymer nanocomposites open a broad window into applications as such as nanoelectronics in sensors, biosensors, dopamine sensing, catalysis, energy storage, and conversion devices [55]. Graphene functionalized by CdS nanohybrids offered great potential electrochemical applications in various fields, such as electrochemical sensing, catalytic reaction, and in supercapacitors [56]. GOeamideefunctionalized metaleorganic framework nanocomposites fabricated through ultrasound irradiation show applications for photocatalysis, solar cells, and also for
Table 10.3 Reported Research on Functionalized Graphene Hybrid Polymer Nanocomposites Reinforcements
Polymer Matrix
Fabrication Techniques
Applications
References
Functionalized-rice husk/graphene oxide (GO) Functionalized graphene decorated with cupric oxide (CuO) nanoparticles
Polyamide 6
Solution casting
Wastewater purification
[42]
Poly(diallyldimethylammonium chloride) (PDDA)
e
[43]
Magnetic functional GO
Polyaniline
Solution electropolymerization
Functionalized GO (FGO) with 3-glycidoxypropyltrimethoxysilane (GPTMS) Gold nanoparticle FGO
Polysiloxane
Solegel and epoxy/amino curing reactions
Nonenzymatic glucose sensor; quantification of glucose concentration in serum samples Nanocomposite materials for electrochemical redox capacitors; supercapacitor Antiscratch coatings
L-cysteine
Ultrasonication
Functionalized GO nanosheets (GONs)
Polyaniline
In situ electropolymerization
Supramolecular polymerfunctionalized graphene (SPFG) Water-soluble Prussian blue nanoparticles (PB NPs) supported on nitrogen-doped graphene nanoparticles Hexamethylenediamine (HMDE) FGO Cellulose nanocrystals (CNCs) and GONs FGO and multiwalled carbon nanotubes (MWCNTs) NanoeSiOeFGO GONs/carboxyl-functionalized MWCNTs
Poly(L-lactic acid) (PLLA)
Solvent blending
Prussian blue
[44]
[45]
[46]
Centrifugation
Biosensor for the detection of nitrite with low detection limit in the pickled radish Capacitive pseudocapacitors and electrochemical redox capacitors Electronic and biomedical applications Hybrid battery supercapacitor.
Epoxy Polyvinyl alcohol (PVA)
Ultrasonication Solvent casting
e Food packaging
[26] [48]
Polyimide
In situ polymerization
[49]
Polypropylene Polyimide
Melt blending In situ polymerization
1-D ZnO nanorod and 2-D reduced GO (rGO) b-cyclodextrin functionalized rGO (b-rGO)
e
Hydrothermal process
Glucose-functionalized rGO Organo-soluble dodecylamine amine (DDA)emodified GO
PVA Polyurethane
High mechanical performance materials e Potential application in ocean fields; tribological applications under both dry sliding and seawater lubrication conditions Highly efficient catalysts and effective water remediation Electrochemical sensors and glucose sensor with remarkable sensitivity up to 327.79 mA mM1 cm2 e e
Electrodeposition in situ growth Ultrasonication Solvent casting
[29] [47] [28]
[4] [50]
[51] [41]
[6] [52]
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the adsorption of methylene blue from aqueous solution [57]. Ultrasound assisted copper-catalyzed nanoparticleefunctionalized GOehybrid nanocomposites displayed a blue fluorescent and are extensively used as drug delivery system for the detection of tumor and breast cancer in mice [54]. Schiff bases composed of azo pyridinium salt and chromene segments functionalized GO by noncovalent interactions exhibit good antibacterial activity against the two tested bacterial species: Escherichia coli and Staphylococcus aureus [58]. In another study, calcium lignosulfonate was functionalized in graphene to form porous graphene nanocomposites, showing great feasibility for the determination of environmental metallic pollutants and as electrochemical sensors for heavy metal ions [53]. Functionalized magnetic GOereinforced cationic PDDA sponge nanocomposites also possess great potential as a promising magnetic flocculant applied to efficient harvesting of oleaginous microalgae [59]. Researchers also claimed that functionalized sulfonated GOereinforced polyvinylidene fluoride promotes membrane permeability and antifouling performance and are in ultrafiltration membranes applications [60].
8. CONCLUSION Graphene has acquired great scientific and technological interest in recent years. Graphene is one of the allotropes and represents the basic structure cell of all the other carbon-based materials such 3-D graphite, 1-D CNTs, and 0-D fullerenes. It has a 2-D honeycomb lattice structure with a carbonecarbon (CeC) bond length of 0.142 nm. A variety of techniques, including top-down or bottom-up routes, are known to synthesize graphene both in the laboratory and industrial scale. Graphene is regarded as an emerging and most promising nanomaterial for diverse advanced applications due to its extraordinary and superior properties. Potential applications include cosmetics, biomedical, biosensor, thermal management devices, transparent conductive electrodes, energy storage, spintronic devices, frequency circuits, elimination of toxic material, drug delivery, and aerospace. Besides its extreme applications, it possesses some practical drawbacks, including agglomeration, nonhomogeneous distribution, zero bandgap, and poor interfacial interactions with the polymer matrix due to its high specific surface area and van der Waals interactions, which limit its usage as reinforcement filler in polymer composite industries. However, functionalization of graphene effectively leads to overcoming this problem by expanding the reactive sites and bandgap of the graphene. Chemical functionalization is found to be more effective and simplest route in comparison to physical to prevent agglomeration/restacking of GNS in the polymer matrices. The chemical species grafted on the sheets inhibit the restacking process either through electrostatic repulsion and steric hindrance mechanisms. Extensive research and development has been imposed on graphene-reinforced polymer composites in the last two decades due to its excellent mechanical, thermal, electrical, and physicochemical properties along with thin physical existence. Reinforcements of graphene enhanced the mechanical, electrical and thermal properties of variety of polymers including thermosets, thermoplastics and biopolymers for diverse technical applications.
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ACKNOWLEDGMENTS All authors acknowledge Universiti Putra Malaysia (UPM) for providing access throughout to complete this review article.
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[53] Yu L, Zhang Q, Yang B, Xu Q, Xu Q, Hu X. Electrochemical sensor construction based on Nafion/calcium lignosulphonate functionalized porous graphene nanocomposite and its application for simultaneous detection of trace Pb2þ and Cd2þ. Sensor Actuator B Chem 2018;259:540e51. [54] Hashemi H, Namazi H. Sonochemically synthesized blue fluorescent functionalized graphene oxide as a drug delivery system. Ultrason Sonochem 2018;42:124e33. [55] Ruiyi L, Sili Q, Zhangyi L, Ling L, Zaijun L. Histidine-functionalized graphene quantum dot-graphene micro-aerogel based voltammetric sensing of dopamine. Sensor Actuator B Chem 2017;250:372e82. [56] Wang L, Qi W, Su R, He Z. Noncovalent functionalization of graphene by CdS nanohybrids for electrochemical applications. Thin Solid Films 2014;568:58e62. [57] Tanhaei M, Mahjoub AR, Safarifard V. Sonochemical synthesis of amide-functionalized metal-organic framework/graphene oxide nanocomposite for the adsorption of methylene blue from aqueous solution. Ultrason Sonochem 2018;41:189e95. [58] Omidi S, Kakanejadifard A, Azarbani F. Noncovalent functionalization of graphene oxide and reduced graphene oxide with Schiff bases as antibacterial agents. J Mol Liq 2017;242:812e21. [59] Liu P-R, Zhang H-L, Wang T, Yang W-L, Hong Y, Hou Y-L. Functional graphene-based magnetic nanocomposites as magnetic flocculant for efficient harvesting of oleaginous microalgae. Algal Res 2016;19: 86e95. [60] Ayyaru S, Ahn Y-H. Application of sulfonic acid group functionalized graphene oxide to improve hydrophilicity, permeability, and antifouling of PVDF nanocomposite ultrafiltration membranes. J Membr Sci 2017;525:210e9.
FUNCTIONALIZED GRAPHENE REINFORCED HYBRID NANOCOMPOSITES AND THEIR APPLICATIONS
10
N. Saba, Mohammad Jawaid Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, Selangor, Malaysia
1. INTRODUCTION Graphene is a multifunctional 2-D atomic crystal and an allotrope of carbon with several unique properties, including high electrical conductivity, thermal conductivity of 5000 W m1 K1, high electron mobility in room temperature (250,000 cm2 V1 s1), high aspect ratio, large surface area (2630 m2 g1), and high modulus of elasticity (w1 TPa) [1,2]. The single-layer, bilayer, and multilayer graphene, graphene oxide (GO), reduced GO (rGO), and chemically modified graphene are widely known as graphene nanofibers (GFNs) [1]. It has been reviewed that graphene can be processed as nanoribbons, platelets, foams, and even as quantum dots for immense use in semiconductor, energy storage devices, hydrogels, and biological applications. Graphene also been used as a reinforcing agent in variety of thermoset and thermoplastics polymer composites to improve their physical, mechanical strength, fracture toughness, electrical and thermal properties due to its homogeneous dispersion [3]. Various approaches for fabricating graphene/polymer nanocomposites have been reported, including blending polymers with graphite particles and the intercalation of polymers within graphite interlayers through in situ polymerization and solution blending as well as melt compounding [4,5]. However, significant challenges remain to be overcome in the development of promising graphene-based polymer composites in consumer products due to the irreversible aggregation or even restacking of graphene to graphite [6]. Thus, the homogeneous dispersion of graphene sheets in polymer is still a matter of concern or interest in polymer science. Furthermore, researchers reported that the modification of graphene or introduction of a functional group can successfully overcome this problem [7]. Functionalization can be carried out through covalent and noncovalent techniques (hydrogen bonding, electrostatic forces, pep stacking, and hydrophobic interactions) [6]. Research studies also revealed that chemical functionalization is one of the most effective methods for modifying the surface of graphite or 3-D graphene [4]. Developed functionalized hybrid polymer nanocomposites show wide engineering industrial applications ranging from cosmetics and aerospace to energy storage, transistors, fuel cells, batteries, and supercapacitors [3]. Functionalized Graphene Nanocomposites and Their Derivatives. https://doi.org/10.1016/B978-0-12-814548-7.00010-6 Copyright © 2019 Elsevier Inc. All rights reserved.
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2. GRAPHENE AND ITS SYNTHESIS Good-quality micron-size graphene was first discovered in 2004 by Andre Geim and Konstantin Novoselov by peeling graphite with adhesive tape [8] as an amazingly thin transparent film composed of carbon with exciting and outstanding electric, mechanical, and thermal properties, displayed in Fig. 10.1. Graphene is a monolayer of carbon atoms packed into honeycomb lattice [9]. Graphene carbon atoms are arranged as hexagons in flat layers, where each carbon atom is covalently joined to the other three carbon atoms in flat, hexagonal layers [1,10]. Each sheet of graphene is only one atom thick, and each graphene sheet is considered a single molecule. Graphene currently grabs enormous attention and research motives among other nanomaterials as physically, it is superstrong, stiffer, lighter, has a larger surface-to-volume ratio and is a good conductor of electricity/heat [11]. Graphene can be made from natural graphite or from synthetic graphite and is regarded as a basic 2-D building block of all the carbon nanostructures of other dimensionalities. It forms 0-D fullerene or buckyballs by wrapping, 1-D cylindrical carbon nanotubes (CNTs) by rolling with respect to its axis, and a planar 3-D stacked structure of graphite [12,13]. A possible dimensional structure from 2-D graphene is illustrated in Fig. 10.2. Several techniques and methods have been established to produce graphene sheets, such as mechanical cleaving (epitaxial growth), electrochemical exfoliation, chemical exfoliation, liquidphase exfoliation of graphene nanosheets (GNS), thermal chemical vapor deposition (CVD) of monolayer and multilayer GNS, chemical synthesis or organic synthesis of graphene nanoribbons, electrochemical reduction of exfoliated graphite oxide precursor at cathodic potentials [10], solvothermal reduction, photocatalyst reduction [14], Hummers’ method [15], and chemical reduction of exfoliated graphite oxide and rGO in the presence of different reducing agents, including hydrazine, hydrazine hydride, sodium borohydride, hydroquinone, and ascorbic acid [11,16,17]. Among the many reducing agents, hydrazine hydride is referred to as the best reducing agent to produce very thin graphene sheets [16]. Some other techniques are also reported in literature to produce few-layer graphene, such as unzipping of CNTs, electron beam irradiation of poly(methyl methacrylate) nanofibers, arc discharge of graphite, conversion of nanodiamond, solid carbon heating, silicon carbide heating, thermal fusion of polycyclic aromatic hydrocarbons (PAHs), and
FIGURE 10.1 Graphene or single-layer graphite structure [1].
2. GRAPHENE AND ITS SYNTHESIS
(A)
(B)
(C)
(D)
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FIGURE 10.2 (A) Two-dimensional graphene building material, (B) stacked 3-D graphite, (C) rolled 1-D nanotubes, and (D) wrapped 0-D buckyballs [13].
FIGURE 10.3 Several synthetic approaches for graphene [13].
microwave synthesis [12,18,19]. Although chemical vapor deposition and mechanical exfoliation using atomic force microscopy (AFM) cantilevers are regarded as some of the most promising techniques to produce monolayers of graphene sheets on a large scale [20]. Fig. 10.3 summarizes some of the significant synthetic approaches for graphene [13]. Researchers stated that properties of graphene, such as lateral size (from several nanometers to centimeters), stacked layers, morphology, structure, surface chemistry, solubility, electrical and thermal conductivities, defects, and impurity contents strongly rely on the applied synthetic method [1,21]. Furthermore, synthesized graphene is characterized by several instrumental techniques to define its properties, such as crystallinity and molecular and functional structure. Currently, several instruments available for characterization include X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), ultravioletevisible (UVevis) spectroscopy, scanning electron microscopy (SEM), highresolution transmission electron microscopy, dark-field transmission electron microscopy, and X-ray photoelectron spectroscopy (XPS) [15].
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3. GRAPHENE PROPERTIES AND APPLICATIONS Graphene is basically one of the most abundant, thinnest minerals and is the world’s strongest single atomic layer of graphite; besides that, it is highly flexible and one of the most promising nanomaterials having one-atom carbon sheets that are highly conductive, even more than copper [18,22]. It is found to be the most chemically reactive form of carbon. Graphene has the same structure of carbon atoms linked in hexagonal shapes to form CNTs, but graphene is flat rather than cylindrical. Defect-free, monolayer graphene is considered to be the strongest material ever known, as it possesses exceptional mechanical strength and modulus and fracture toughness [20]. The reason for the exceptional mechanical properties of graphene lies in the stability of the sp2 bonds that form the hexagonal lattice and oppose a variety of in-plane deformations, or simply the strength of covalent bonds between carbon atoms are extremely strong; hence graphene has a very high tensile strength [3,20], as shown in Fig. 10.4. An overview of mechanical properties of graphene and its derivatives is presented in Table 10.1. The table clearly reveals that an increased number of GNS layers leads to a reduction in properties [16]. Graphene has zero rest mass of charge carriers in the crystal, and electrons travel with the speed of light through the crystal. Researchers revealed that this type of electron transport is even not found in any semiconductor, thus resulting in graphene as the most conductive nonsuperconducting material at room temperature, having resistivity of 106 cm1 [8]. Moreover, graphene is harder than diamond and 100e300 times stronger than steel; it can be stretched up to 20% of its original length [15], it absorbs 2.3% of light that passes through it due to its unique electronic properties, and it is the most permeable and transparent material ever discovered. Reported physical, mechanical, and electrical properties of graphene are tabulated in Table 10.2. Table 10.2 signifies the characteristics extraordinary combination of physical, mechanical, chemical, electrical, and thermal properties of graphene offered toward several potential industrial-oriented
FIGURE 10.4 Graphene monolayer. Modified from Soldano C, Mahmood A, Dujardin E. Production, properties and potential of graphene. Carbon 2010;48:2127e50.
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Table 10.1 Mechanical Properties of Graphene and Its Derivatives [16] Material Graphene (monolayer) Reduced graphene oxide (rGO) Graphene nanosheets (GNS; bilayer/trilayer/multilayers)
Young’s Modulus (MPa)
Tensile Strength (MPa)
Fracture Toughness (MPa)
106 2.5 105 1.04 106e0.98 106
1.3 105 0.9 103 1.26 105e1.01 105
4e5 2.8e3 4.7e3.8
Table 10.2 Overview of Physical, Mechanical, and Electrical Properties of Graphene Mechanical and Electrical Properties
Approximated Values
Electrical conductivity Thermal conductivity Charge carrier mobility at electron density w2 1011 cm2 Melting point Current density Bandgap Energy gap Transparency Tensile strength Young’s modulus Fracture toughness Shear modulus Poisson’s ratio Specific surface area Covalent bonding energy Sigma bonds with a bond length
w108 S m1 w5000 W m1 K1 w15,000e200,000 cm2 V1 s1 4510K w1.6 109 A cm2 Zero 0.26 Ev w97.4% w1100 GPa w106 MPa 4e5 MPa w0.213e0.233 w1.285e1.441 w2630 m2 g1 w5.9 Ev ˚ w1.42 A
Nag A, Mitra A, Mukhopadhyay SC. Graphene and its sensor-based applications: a review. Sensor Actuator Phys 2017; Dasari BL, Nouri JM, Brabazon D, Naher S. Graphene and derivativesesynthesis techniques, properties and their energy applications. Energy 2017;140:766e78; Lee SK, Kim H, Shim BS. Graphene: an emerging material for biological tissue engineering. Carbon Lett 2013; 14:63e75.
applications. These include its wider application in electrochemical sensors, strain sensors, firefighting, smoke suppression agents for polymer (polystyrene) composites [24], and structural engineering applications such as airplane appliances [15]. Some of the promising applications of graphene in the scientific community are shown in Fig. 10.5. Graphene’s exceptional and remarkable electrical conductivity and high surface area also makes it a promising material for energy conversion and storage applications such as batteries, nanoelectronics, electrical sensors including temperature sensing and photodetectors [15], electromechanical resonators,
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FIGURE 10.5 Versatile applications of graphene [1].
supercapacitors, fuel cells, transparent conducting electrodes, optoelectronic devices, energy storage devices, and transistors [18]. Graphene’s electron mobility is faster than any known material and is currently replacing transistors built on silicon wafers, as the field-effect transistors on graphene are much faster. Besides this, it is regarded as the most potential material for applications such as single-molecule gas sensing or detection, biomedical devices, tissue regeneration, carriers for drug or gene delivery, detection materials for bioimaging and biosensors, neural interfaces, ultrasensitive sensors, actuators [15], environmental such as heavy metal or transition metals detection, electrochemical sensing, and polymer composites, owing to its honeycomb structure having closely packed sp2-bonded carbon atoms [16,23]. Research findings analyzed that energy-related applications and electronic applications occupy the highest percentages, whereas its involvement in polymer composites still not satisfactory [16]. Graphene also presents unsuspected applications in making durable footwear, impact and pressure sensors, electromagnetic barriers, photonic, heat dissipation systems, inks, hydrogen storage, and roller screens. Graphene stands out as potential nanofiller in polymeric melts due to its outstanding mechanical, dielectric, barrier, thermal and dynamic properties [25], besides this graphene shows certain shortcomings that limit its practical applications, most remarkably as a reinforcement material in polymer composites, which require more insight, investigation and study. Limitations include incompatibility with the polymer matrix, orientation, zero bandgap, agglomeration/restacking of graphene layers leading to nonhomogeneous distribution within the matrix, and the hindrances in physical handling of graphene sheets due to its poor solubility in most solvents or polymer matrix [11]. Interestingly, graphene has a potential to replace the conventional reinforcements for the metal matrix composites.
4. FUNCTIONALIZED GRAPHENE Graphene is regarded as a promising reinforcing material for variety of polymer matrices. However, the tendency to irreversible agglomerate or restack to form graphene sheets via pep stacking, strong van der-Waals interactions among its sheets, and the weak compatibility with most polymer matrices restricts its potentiality as effective reinforcing agent. The effective way to overcome or address these
5. HYBRID NANOCOMPOSITES
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challenges includes surface modification of graphene by adding a functional group called functionalization. Functionalization increases the graphene compatibility with specific polymers, thus improving its reinforcing effect [26]. Researchers revealed two types of graphene functionalization as chemical and nonchemical functionalization methods [27]. Chemical functionalization is a chemical (or electrochemical) process that proceeds at an atomic/molecular level and is realized through the formation of new covalent bonds between the atoms native to rGO/GO and the introduced functional groups contrast to physical interaction. Physical or nonchemical functionalization is primarily based on p-interaction between guest molecules and rGO/GO. Chemical functionalization is proposed by incorporating different atoms/organic groups into graphene, including heterogeneous atoms doping, diazonium coupling, amidation, esterization, substitution, silanization, and cycloaddition [27]. Various kinds of functional groups have been chemically anchored on graphene and are found to be more effective, offering extensive applications in polymer science and technology. Doping of nitrogen, boron, phosphorous, fluorine, sulfur, and chloride atoms into graphene is highly desirable, as these doping agents effectively convert graphene from gapless structure to semiconductor and also provide an effective step to modulate the surface chemistry and the optoelectrical properties of graphene [28]. Functionalized doped graphene possesses enhanced dispersity within solvents/polymers along with intriguing electrical, water retention, membranes proton conductivity [29], thermal stability, mechanical strength and high processability properties. Besides this, it also offered a innovative way for fabricating 3-D materials and nanocomposite materials having unique and superior properties [11,27]. Researchers also reviewed that functionalization also modifies intrinsic features, including electronic properties, to enable the control of conductivity and bandgap for state-of-the-art nanoelectronic devices [7,30].
5. HYBRID NANOCOMPOSITES Nanocomposites, which exhibit superior mechanical and physical properties compared to their respective matrix materials, are among the most technologically promising materials to meet the worldwide demand for high-performance applications in many fields [31,32]. A hybrid material is defined as advanced engineering material composed of an intimate mixture of inorganic components, organic components, or both types of components. Currently, enormous attention has been observed toward the development of nanostructured hybrid materials as prominent advanced materials owing to their unique characteristics featuring superior dielectric, mechanical, physical properties, lightweight, ultrahigh tunable modulus of resilience, and versatile nanoscale with great potential for diverse applications. Hybrid nanocomposites show high-tech applications that require ultrahigh mechanical resilience, efficient energy harvesting, strength, environmental pollutants sensors, energy storage, capacitors, and conservation [33]. Intensive study on high-performing hybrid polymer nanocomposites for application in the sectors of automotive, aerospace, and construction industries has been reported merely by incorporating highly conductive nanofillers such as CNTs and graphene and nonconductive ones like layered silicates/ferroelectric ceramics and layered double hydroxide in the polymeric matrix [34]. However, aggregation of these fillers represents a major barrier in their development [32,35,36]. Other researchers also indicated that the effectiveness of reinforced nanofiller in the polymer matrix greatly depends on perfect dispersion and intimate filler/matrix interactions [37,38].
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6. FUNCTIONALIZED GRAPHENEeREINFORCED HYBRID POLYMER NANOCOMPOSITES Graphene-reinforced hybrid polymer nanocomposite materials are of great interest for their structural fabrications from past decades. Immense interest in reinforcing graphene materials arose due to graphene’s promising, unique, excellent mechanical, thermal, electrical, optoelectronic, and physicochemical properties along with intrinsic flexibility and nanophysical existence [13] in all fields of technologies [13,39]. Currently, many successful efforts have been made for fabricating functionalized grapheneereinforced polymer composites by incorporating functionalized graphene at low filler loading (1%e5% by weight) [31], with a perfect dispersion within a polymer matrix owing to graphene’s high-end properties. Varied chemical and physical synthesis techniques are known for homogenous distribution and dispersion of functionalized graphene in a variety of thermoset and thermoplastic polymers, including solution blending, melt blending, shear mixing, solution casting, combination of melt blending/solution casting/in situ polymerization, three roll mill, in situ polymerization, ball milling/hot pressing, laminates, sequential transfer, vacuum filtration, water-assisted extrusion, latex cocoagulation, latex mixing, latex compounding, wet spinning, melt compounding, mechanical stirring, ultrasonication, hydrothermal/solvothermal, gas-phase deposition, solegel processing, template method, mechanical mixing, ultrasonication along with high-pressure homogenization, stirring along with ultrasonication, centrifugal mixing and vacuum impregnation [13,15,40,41]. Recent developments, fabrication, and applications of functionalized grapheneereinforced hybrid polymer nanocomposite materials with other nanofiller or natural/synthetic fibers are summarized in Table 10.3. Several characterization techniques are currently known to analyze and investigate the developed functionalized grapheneehybrid polymer nanocomposites like other polymer nanocomposites. Most commonly used characterization techniques include SEM, TEM, FTIR, energy-dispersive X-ray spectroscopy AFM, UVevis absorption spectroscopy, Raman spectroscopy, Zeta potential analysis, X-ray fluorescence, XPS, BrunauereEmmetteTeller and XRD [41,53,54].
7. APPLICATIONS OF FUNCTIONALIZED GRAPHENE HYBRID NANOCOMPOSITES Functional grapheneereinforced polymer nanocomposites have attracted wide promising industrial interest due to their light weight, high strength, chemical resistance, and long durability [49]. Brittle and electrically insulating functional grapheneereinforced alumina matrix nanocomposites show extensive applications in electronics, defense, aerospace, and transportation. They are also found to be wear resistant and structural materials for extreme environments, such as high temperature/pressure, nuclear radiation, and chemicals [31]. Functional grapheneehybrid polymer nanocomposites open a broad window into applications as such as nanoelectronics in sensors, biosensors, dopamine sensing, catalysis, energy storage, and conversion devices [55]. Graphene functionalized by CdS nanohybrids offered great potential electrochemical applications in various fields, such as electrochemical sensing, catalytic reaction, and in supercapacitors [56]. GOeamideefunctionalized metaleorganic framework nanocomposites fabricated through ultrasound irradiation show applications for photocatalysis, solar cells, and also for
Table 10.3 Reported Research on Functionalized Graphene Hybrid Polymer Nanocomposites Reinforcements
Polymer Matrix
Fabrication Techniques
Applications
References
Functionalized-rice husk/graphene oxide (GO) Functionalized graphene decorated with cupric oxide (CuO) nanoparticles
Polyamide 6
Solution casting
Wastewater purification
[42]
Poly(diallyldimethylammonium chloride) (PDDA)
e
[43]
Magnetic functional GO
Polyaniline
Solution electropolymerization
Functionalized GO (FGO) with 3-glycidoxypropyltrimethoxysilane (GPTMS) Gold nanoparticle FGO
Polysiloxane
Solegel and epoxy/amino curing reactions
Nonenzymatic glucose sensor; quantification of glucose concentration in serum samples Nanocomposite materials for electrochemical redox capacitors; supercapacitor Antiscratch coatings
L-cysteine
Ultrasonication
Functionalized GO nanosheets (GONs)
Polyaniline
In situ electropolymerization
Supramolecular polymerfunctionalized graphene (SPFG) Water-soluble Prussian blue nanoparticles (PB NPs) supported on nitrogen-doped graphene nanoparticles Hexamethylenediamine (HMDE) FGO Cellulose nanocrystals (CNCs) and GONs FGO and multiwalled carbon nanotubes (MWCNTs) NanoeSiOeFGO GONs/carboxyl-functionalized MWCNTs
Poly(L-lactic acid) (PLLA)
Solvent blending
Prussian blue
[44]
[45]
[46]
Centrifugation
Biosensor for the detection of nitrite with low detection limit in the pickled radish Capacitive pseudocapacitors and electrochemical redox capacitors Electronic and biomedical applications Hybrid battery supercapacitor.
Epoxy Polyvinyl alcohol (PVA)
Ultrasonication Solvent casting
e Food packaging
[26] [48]
Polyimide
In situ polymerization
[49]
Polypropylene Polyimide
Melt blending In situ polymerization
1-D ZnO nanorod and 2-D reduced GO (rGO) b-cyclodextrin functionalized rGO (b-rGO)
e
Hydrothermal process
Glucose-functionalized rGO Organo-soluble dodecylamine amine (DDA)emodified GO
PVA Polyurethane
High mechanical performance materials e Potential application in ocean fields; tribological applications under both dry sliding and seawater lubrication conditions Highly efficient catalysts and effective water remediation Electrochemical sensors and glucose sensor with remarkable sensitivity up to 327.79 mA mM1 cm2 e e
Electrodeposition in situ growth Ultrasonication Solvent casting
[29] [47] [28]
[4] [50]
[51] [41]
[6] [52]
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the adsorption of methylene blue from aqueous solution [57]. Ultrasound assisted copper-catalyzed nanoparticleefunctionalized GOehybrid nanocomposites displayed a blue fluorescent and are extensively used as drug delivery system for the detection of tumor and breast cancer in mice [54]. Schiff bases composed of azo pyridinium salt and chromene segments functionalized GO by noncovalent interactions exhibit good antibacterial activity against the two tested bacterial species: Escherichia coli and Staphylococcus aureus [58]. In another study, calcium lignosulfonate was functionalized in graphene to form porous graphene nanocomposites, showing great feasibility for the determination of environmental metallic pollutants and as electrochemical sensors for heavy metal ions [53]. Functionalized magnetic GOereinforced cationic PDDA sponge nanocomposites also possess great potential as a promising magnetic flocculant applied to efficient harvesting of oleaginous microalgae [59]. Researchers also claimed that functionalized sulfonated GOereinforced polyvinylidene fluoride promotes membrane permeability and antifouling performance and are in ultrafiltration membranes applications [60].
8. CONCLUSION Graphene has acquired great scientific and technological interest in recent years. Graphene is one of the allotropes and represents the basic structure cell of all the other carbon-based materials such 3-D graphite, 1-D CNTs, and 0-D fullerenes. It has a 2-D honeycomb lattice structure with a carbonecarbon (CeC) bond length of 0.142 nm. A variety of techniques, including top-down or bottom-up routes, are known to synthesize graphene both in the laboratory and industrial scale. Graphene is regarded as an emerging and most promising nanomaterial for diverse advanced applications due to its extraordinary and superior properties. Potential applications include cosmetics, biomedical, biosensor, thermal management devices, transparent conductive electrodes, energy storage, spintronic devices, frequency circuits, elimination of toxic material, drug delivery, and aerospace. Besides its extreme applications, it possesses some practical drawbacks, including agglomeration, nonhomogeneous distribution, zero bandgap, and poor interfacial interactions with the polymer matrix due to its high specific surface area and van der Waals interactions, which limit its usage as reinforcement filler in polymer composite industries. However, functionalization of graphene effectively leads to overcoming this problem by expanding the reactive sites and bandgap of the graphene. Chemical functionalization is found to be more effective and simplest route in comparison to physical to prevent agglomeration/restacking of GNS in the polymer matrices. The chemical species grafted on the sheets inhibit the restacking process either through electrostatic repulsion and steric hindrance mechanisms. Extensive research and development has been imposed on graphene-reinforced polymer composites in the last two decades due to its excellent mechanical, thermal, electrical, and physicochemical properties along with thin physical existence. Reinforcements of graphene enhanced the mechanical, electrical and thermal properties of variety of polymers including thermosets, thermoplastics and biopolymers for diverse technical applications.
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ACKNOWLEDGMENTS All authors acknowledge Universiti Putra Malaysia (UPM) for providing access throughout to complete this review article.
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