Graphene Functionalization Strategies

Reduced graphene oxide (RGO), atomically thin two-dimensional carbon nanosheets, owns outstanding chemical, electrical, material, optical, and physical properties due to its large surface area, high electron mobility, thermal conductivity, and stability. These unique properties have made reduced graphene oxide an ideal platform for constructing a series of RGO-based functional nanomaterials. Specifically, RGO and RGO derivatives have been utilized as templates for the synthesis of various noble-metal/metal oxide nanocomposites. These hybrid nanocomposites materials are promising alternatives to reduce the drawback of using only transition metal nanoparticles in various applications, such as electrochemical energy storage and conversion technology of supercapacitors and fuel cells. The goal of this chapter is to discuss the state-of-the-art of reduced graphene oxide-based metal and metal oxide nanocomposites with a detailed account of their synthesis and properties. Especially, much attention has been paid to their synthesis and a wide range of applications in various fields, such as electrochemical and electrical fields. This chapter is presented first time with an introduction, followed by synthetic methods of RGO and RGO-based nanocomposites. Then, the application of this novel RGO/metal-metal oxide nanocomposites in fuel cells and supercapacitors are summarized and discussed. Finally, the future research trends and challenges of design and synthesis of RGO/metal-metal oxide nanocomposites are presented.

Graphene (GR) and its derivatives are highly interesting carbon nanoforms which possess layered morphology and unique structural/chemical/physical features. These extraordinary properties make GR materials highly applicable for multiple scientific applications, however, zero band gap, hydrophobic nature are among few limitations which make its functionalization a mandatory step to expand its practical applications. To achieve the best out of GR materials, different covalent and noncovalent functionalization schemes have been proposed governed by disruption of sp² lattice in case of covalent scheme and retention of its structural integrity in case of noncovalent functionalization. The chapter addresses a brief discussion on different GR functionalization schemes. Moreover, it focuses on noncovalently functionalized GR nanohybrids with metal based nanoparticles (MNPs) as electrochemical sensors taking some relevant examples. Synergistic effects of GR materials and MNPs enhance the electro-activity of nanohybrids for electrochemical detection of different targets.

For the last two decades, application of ultrasound in materials synthesis has been a very promising topic especially for the fabrication or modification of various nanomaterials. Simplicity, high efficacy, short reaction tenure along with power saving features are responsible for the popularization of sonochemistry. The physical phenomenon essential for sonochemical process is largely accepted owing to acoustic cavitation, involving formation, growth, and implosive collapse of the micro-bubbles inside liquid. The resulting hot spots/microjets generate very high temperatures ~5000 K and high pressure ~150 MPa due to collapsing bubbles within a nanosecond, with high cooling rates exceeding 10¹¹ Ks⁻¹ at the local reaction centre, providing necessary activation for faster kinetics. These extreme reaction conditions are not typically attainable through conventional synthesis techniques, generating smarter systems with unique properties. Subsequently, ultrasound techniques have been massively employed in graphene preparation along with its dispersion in various solvents which otherwise requires several days with poor yield using conventional techniques. Graphene has been the material of the millennium owing to its unique large surface area, high charge transport features and mechanical properties and widely employed in nearly every aspects of modern technology. Ultrasonic irradiation offers tuning of graphene layer thickness also. Even oxidation to graphene oxide and subsequent reduction to reduced-graphene oxide at faster kinetics are possible without the use of any external redox agents. Besides, thin-layered functionalized graphenes has been achieved by sonochemistry. Ultrasonic treatment provides scope for direct exfoliation of graphite to graphene layers in presence of suitable intercalating/stabilizing agents with substantial dispersion stability. In addition, various geometries such as scrolled graphene, ribbon or foam graphenes can be purposefully designed. Even smooth and rough edged graphenes have displayed unique implications in energy storage, catalysis, biomedical and other technological fields. Ultrasonic-assisted synthesis of various graphene based composites lead to more homogeneous with diversified nanostructures formation like core-shell, nano-discs, nano-platelets, etc. along with specific deposition at the graphene edges have become feasible. This chapter provides comprehensive fundamental concepts of sonochemistry with first hand outline on the sonochemical/ultrasound assisted synthesis of graphene and its various derivatives. Moreover, the ultrasound assisted-dispersion, exfoliation of graphenes and formation of various graphene-based nanocomposites has been emphasized. Important tuneable sonochemical parameters including ultrasound frequency, input power, sonication time, type of sonication probes, etc. have been highlighted to provide an overview of the topic.

The greener mechanistic cavitation method has been applied for synthesis of graphene oxide (GrO) based functionalized materials. The GrO functionalization with various amine substituted heterocyclic moieties (ASHM) have an emerging technology towards biomedical processing of graphene. Hence, an ultrasound energy has been applied for GrO functionalization with 2-Amino-1,3,4-thidiazole (ATDZ) to synthesize Covalent functionalized product f-(ATDZ)GrO. Structural investigations have confirmed the covalent functionalization (CF) of GrO to synthesize f-(ATDZ)GrO. The structure of f-(ATDZ)GrO has confirmed with Fourier-transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV), RAMAN, X-ray diffraction (XRD), thermogravimetric analysis (TGA)/differential thermal analysis (DTA)/Differential thermal Gravimetry (DTG), Dynamic Light Scattering (DLS), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), atomic force microscopy (AFM), scanning electron microscopy (SEM). The structural insights provide a mechanistic understanding of functional expression, through the contribution of atomic domains (CAD). TGA of f-(ATDZ)GrO validates total percentage weight loss of 95.5% at 198.17 °C. Thermal stability of f-(ATDZ)GrO as temperature aspects also certified an exothermic curve obtained with DTA. The calculated PL band gap of 3.87 eV in noncompatible f-(ATDZ)GrO is indicating towards biosensing applications. In extension of functionalization series of GrO with heterocyclic derivative, the cytotoxicity of f-(ATDZ)GrO has evaluated with Sulforhodamine B (SRB) assay to living cells, HaCaT and Vero cell lines. The average estimated cell viabilities have observed ~91.575% with HaCaT cell lines over a wide concentration range of 10–80 μg mL⁻¹. The high cytocompatibility of f-(ATDZ)GrO has further extent with Vero cell lines of ~36.825% biocompatibility. However, the morphological effect on HaCaT cell line and some extinct significant with Vero have evidently confirmed that higher cytocompatibility of f-(ATDZ)GrO can be explore for the cytocompatibility as Nanotoxicity aspects. Therefore, f-(ATDZ)GrO appeared as an advanced material which can be further used for development of various biomedical applications.

Nanofiber composites materials produced by electrospinning may have a very high specific surface area owing to their small diameters, and nanofiber mats can be highly porous with excellent pore interconnection. However, applications using nanofiber composites also require specific properties such as good electrical conductivity, are flame retardant, anti-static and anti-radiative as well. Over the past few decades, the carbon nanomaterial, graphene has been researched widely owing to its intrinsic properties such as large surface area, excellent thermal, electrical, and optical properties in addition to superior chemical and mechanical characteristics needed in specific applications. The chemical functionalization of graphene nanosheet improved its dispersibility in common organic solvents, which is important when developing novel graphene-based nanocomposites. Moreover, graphene may also be functionalized in order to modify its intrinsic characteristics, for example, its electronic properties can be modified to control the conductivity and band gap in nano-electronic devices. Functionalized graphene-based polymer nanofiber composites exhibit a variety of improved, or even new properties such as adsorption performance, anti-bacterial, hydrophobicity and conductivity valued across a wide range of applications in sensors, biosensors, transparent conductive films, high-frequency circuits, toxic material removal, capacitors, spintronic devices, fuel cells, touch screens, flexible electronics and batteries. This book chapter summarizes the recent progress in functionalized graphene-based polymer nanofibers composites, with an emphasis on their applications.

This chapter focuses on the functionalization of graphene, mainly in graphene oxide (GO) and reduced graphene oxide (rGO). In this sense the main syntheses for obtaining GO and rGO, as well as their characterizations and applications, were described. To evaluate the electrochemical, spectrophotometric and morphological properties of functionalized graphene, the GO obtained commercially and the rGO synthesized by the chemical method using sodium borohydride were characterized by scanning electron microscopy, Raman, UV-vis, cyclic voltammetry and electrochemical impedance spectroscopy. Through these characterizations it is possible to comprehend the differences between GO and rGO. After that, the importance of the graphene functionalized in the development of electrochemical biosensors and sensors are presented.

Graphene is a very advantageous material with its excellent electronic properties as well as its physical properties. The use of graphene and its derivatives in addition to polymers is very suitable for applications such as flexible devices, functional nanocomposites, and sensors. Graphene with a 2D network has been an important material due to its excellent physicochemical values (excellent conductivity, functionalization, mass production ease, high surface area, and high mechanical strength). In this study, graphene oxide based glassy carbon electrode (GO/GCE) was used for the simultaneous detection of dopamine (DA) and uric acid (UA) in the presence of chemically synthesized the graphene oxide (GO). To define the uric acid (UA) and dopamine (DA) levels simultaneously and separately, measurements were obtained by cyclic voltammetry (CV). Accordingly, it has been found that dopamine and uric acid can be measured simultaneously with these sensors in biological samples and are hoped to be used in future applications.

Cyclodextrin (CD) is the general name for a series of cyclic oligosaccharides produced via glucotransferase by Bacillus. The inner cavity of cyclodextrin is hydrophobic, while the outer cavity is hydrophilic, which enables interactions with many organic or inorganic molecules through van der Waals forces and hydrophobic interactions. In this chapter, we summarized the incorporation of graphene with CD through different strategies and the resulting applications. Surface functionalization processes, including covalent interactions and noncovalent interactions, were discussed in detail. Then, the applications of surface-CD-functionalized graphene in drug delivery, chiral recognition, electrochemical sensing, and pollutant removal were summarized.

Graphene derivatives have occurred as central materials in the development of anticancer drug delivery systems. Graphene, graphene oxide and graphene quantum dots have been used for the effective delivery of different anticancer drugs. Graphene oxide (GO) nanomaterials have drew wide attention due to their surface properties. The oxygen-containing functional groups on the surface provide it modification by functionalization with molecules with focus to enlarge the range of biological applications with the impact on reduce toxicity effect. In this chapter, the properties of GO as a nanocarrier to load drug molecules and improve the solubility of carrier-drug systems effectively when functionalized with various hydrophilic molecules or polymers, implying potential applications in clinical treatments is performed in the frame of density functional theory (DFT) and molecular dynamics (MD) calculations.

Graphene, which was discovered in the last ten years, has attracted considerable attention in the field of material science and has been one of the most important materials. Graphene has a two-dimensional structure, and this structure gives the structural, electronic, and optical properties characteristic of the graphene. Thanks to these characteristics, many graphene-based materials have been synthesized for use in many potential applications, such as electronics, energy storage, catalysis, gas absorption, separation, and detection. The function, surface area and porosity, adjustable for energy-based materials and stable graphene are of great importance to these applications. The most important feature that makes the graphene a very useful nanoparticle is its electronic feature. Also, graphene is used as an electrode in solar cells with unprecedented transparency and conductivity. Moreover, a certain amount of graphene can store energy. In this chapter, we outline the structure, properties of graphene, and developments in energy storage systems, and graphene-based hydrogen storage systems.

The unique characteristics of functionalized graphene make it a multifaceted molecule having crucial therapeutic as well as medical significance. Different aspects of functionalized graphene are being discussed here. Functionalization of graphene could even scale up its importance. Functionalization can be done by different methods namely covalent functionalization, covalent functionalization with reaction intermediates, functionalization with nanoparticles, multi-functionalization, substitutional doping. These functionalization strategies mainly aim at reducing the in vivo and in vitro toxicity and agglomeration, moreover the main goal of functionalization is to disperse or solubilize it in different solvents. An Improvised drug and gene targeting nanocarrier system with unique properties have become possible with this graphene functionalization. The anticancer and antibacterial effect and several other applications of functionalized graphene are also being discussed.

Nowadays, microwave heating to graphene derivatives for carbon based materials processing (reduction, exfoliation and modifications) is new approach because strong interaction with microwave radiation, fast and localized heating can be achieved in a very short time. For graphene derivatives, microwave heating method is facile, simple, fast, controllable and energy-saving and provides an effective way to control nanoparticle size distribution on the surfaces. By tuning the microwave irradiation power, time and temperature different graphene based morphologies has been studied. For clear understanding, this chapter has been written basically into two parts. In first part, the literature published on interaction of microwave with grapheme derivatives and their transformations into reduced graphene oxide have been surveyed. The oxygen containing functional groups in different forms on surfaces of graphene derivatives strongly interact with microwave incident photons and easily detached from its surfaces. By microwave heating, graphite oxide/graphene oxide are easily reduced to very less oxygen containing graphene and also exfoliate into high surface containing porous graphene. In second part, graphene derivatives have been modified with different kind of metal/metal oxide for various kinds of applications. It is focused on the latest developments and the current status of graphene-metal oxide research using microwave processing. The high power microwave irradiation on graphene derivatives with metal oxide offers homogenous reaction environment and leads to controlled shape, size distribution of nanoparticles without any agglomeration. Detailed overview has been discussed on the possibilities and achievements of graphene derivatives–metal oxide research using microwave-based heating approaches. Microwave-assisted hydrothermal/solvothermal methods have also been described to synthesize metal oxides loaded graphene derivatives.

Graphene is a two-dimensional allotrope of the carbon element, which is one of the most powerful materials of the 21st century. In order to facilitate the processing of the graphene, solvent-supported methods such as rotation coating, layer by layer assembly, and filtration are used. Single layer graphene prevents agglomeration of the material while reducing reactions occur. According to the studies in the literature, the chemical functionalization of graphene is performed by covalent and non-covalent modification techniques on substrate like copper. Besides, graphene can be used in many material production areas, such as polymer nanocomposites, drug delivery system, supercapacitor devices, solar cells, biosensors, and memory devices.

Penta-Graphene (PG), proposed in 2014 on the basis of theoretical simulations, is a two dimensional (2D) metastable carbon allotrope composed of carbon pentagons. PG is proposed to be synthesized by exfoliation from T12-carbon by hydrogen intercalation. Theoretical calculations confirm that PG is appreciably stable and can sustain the temperature as high as 1000 K. Unlike graphene which needs to be functionalized for opening a band gap, PG is itself a quasi-direct band gap semiconductor having a band gap of ~3.25 eV. PG offers an unusual negative Poisson’s ratio and very high mechanical strength exceeding than that of graphene. According to prediction, successful synthesis of penta-graphene may bring forth considerable makeover in future nano-electronics arena. However, synthesis of PG is still a challenge. It is not only difficult to isolate PG from the plethora of alternative isomers; it may rapidly restructure itself towards graphene in the presence of even a trace amount of specific catalytic impurities. Though unstable in its pure form, theoretical simulation shows suitable chemical functionalization stabilizes the penta-graphene structure by partially releasing the strain, which paves the path towards successful synthesis of penta-graphene considering its functionalized state as the precursor. In this book chapter, the strikingly interesting features/properties, procedure for predicting the characteristics through theoretical simulations, synthesis process, potential applications and critical bottlenecks of functionalized penta-graphene have been comprehensively discussed with special emphasis on its future prospects for next generation electronic device applications. Mainly three types of chemical functionalizations have been considered employing (i) hydrogen, (ii) fluorine and (iii) oxygen. Improvement of stability of functionalized PG, in terms of energy, lattice dynamics, mechanical and thermal in comparison to that of pristine PG have been discussed. Underlying mechanism for the corresponding dramatic improvement in electronic, mechanical and thermal properties of PG for the above mentioned functionalization(s) have also been discussed. Hydrogenation and fluorination of PG changes the Poisson’s ratio from negative to positive and turns the PG from a semiconductor to an insulator. Thermal conductivity of PG enhances dramatically on full hydrogenation. The three types of functionalizations mentioned above, improve mechanical strength of PG by enhancing the value of failure stress and failure strain. Chemical functionalizations widen the application potentiality of PG. Improvement in thermal conductivity of PG by partial functionalization facilitates its application in thermoelectric devices. Band gap tailoring by judicious chemical functionalization lays the foundation stone for future application of PG in the field of optoelectronic and photovoltaic devices. Hydrogen adsorption remarkably enhances the magnetic moment of PG which is useful for potential application in magnetic storage technology and next generation spintronic nano-devices. However, the practical implementation (synthesis and subsequent technology development to couple it successfully with device fabrication) is still in nascent stage and the future research endeavor of the researchers is inclined towards mitigating that bottleneck.

3D graphene based nanomaterials have been extensively used in various fields due to their excellent and tunable physio-chemical properties such as electrical conductivity, higher surface area, strength etc. Extensive research has been achieved for the built of 3 Dimensional graphene and its nanocomposites with excellent properties for multidisciplinary applications. The applications of these nanomaterials have been increased dramatically in the energy field for the recent years and it has become a rapidly developing area. This chapter focuses on the latest developments of these novel 3D graphene-based nanomaterial and their multifunctional applications in field of energy i.e. fuel cells and lithium-ion batteries.

Direct ethanol fuel cells (DEFCs) use ethanol as a fuel to obtain energy in a low temperature. This makes them one of the most important among fuel cells. However, in order to increase the efficiency of these fuel cells, highly effective catalysts should be developed. These catalysts may be of a wide variety of nanoparticles like platinum-based nanoparticles as a most efficient fuel cell catalyst. Generally, the nanoparticles related to the catalyst are obtained using functionalized carbon derivatives. The catalyst obtained in this study shows a higher electrocatalyst activity than the Pt and demonstrates excellent electrocatalytic performance for ethanol oxidation reaction. In this chapter, the reduced graphene oxide was used as a support and a composite material was obtained by synthesizing platinum–ruthenium nanoparticles (PtRu@rGO) with the help of chemical reduction method. The resultant PtRu@rGO nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The electrochemical activity of the catalyst was determined using chronoamperometry (CA) and cyclic voltammetry (CV) techniques for ethanol oxidation reaction. The results showed that the prepared nanocomposite has a high catalytic activity for alcohol oxidation reaction.