Graphene-based Carbocatalysts: Synthesis, Properties and Applications

Carbocatalysis has emerged as a promising field of catalysis. The exceptional surface morphology, pore distribution, thermal conductivity, chemical inertness, electrical property and renewability of carbon materials have rendered them suitable for various catalytic processes namely, photocatalysis, electrocatalysis, biocatalysis and chemical catalysis. Therefore, the introductory chapter on carbocatalysis describes the useful properties of carbonaceous materials which govern their catalytic behaviour. Moreover, synthetic approaches for the fabrication of diverse carbon polymorphs such as active carbon, graphite, fullerene, glassy carbon, carbon black, carbon nanotubes, carbon nanofibres, nanodiamonds, carbon nano-onions, and graphene have also been briefly discussed in this chapter. The scope of carbocatalysts over broad areas has also been elucidated by quoting instances. 

 Graphene is an allotrope of carbon that is made up of very strongly bonded carbon atoms. The structure of graphene is a hexagonal lattice. Graphene shows sp2 hybridization and an extremely thin atomic thickness of approximately 0.345Nm. This chapter deals with graphene structure, including hybridization, critical parameters of the unit cell, the formation of σ and π bonds, electronic band structure, edge orientations, and the number and stacking order of graphene layers. The remarkable characteristics of graphene occur because of the extended chain of π conjugation that results in high charge mobility, high conductivity & high Young's modulus value. Due to these attractive properties, graphene has gained much attention. Graphene, with the unique combination of bonded carbon atom structures with its myriad and complex physical properties is balanced to have a big impact on the future of material sciences, electronics, and nanotechnology. Graphene is converted to Graphene nanoparticles, Graphene oxide nanoparticles; Polymer-based graphene composite materials and Graphene nanoribbons, etc by chemical methods. Some of the application areas are batteries and ultracapacitors for energy storage and fuel cell and solar cell for energy generation and some of the possible future directions of research have been discussed. 

Over the past few decades, graphene and its derivatives have carved a niche for themselves in material science. These carbon nanomaterials exhibit a broad range of applications owing to their enchanting features like high specific surface area, chemical inertness, astonishing electrical and thermal properties, elevated intrinsic mobility, inimitable optical properties, and huge mechanical strength. Considering the ubiquitous applications of graphene in different industries, diverse top-down and bottom-up methods have been developed. This chapter outlines the various methods used for the synthesis of graphene and graphene-based derivatives, such as exfoliation, unrolling or unzipping of carbon nanotubes, electric arc discharge method, laser ablation technique, oxidative exfoliation-reduction of graphene oxide, chemical vapour deposition, epitaxial growth, template synthesis, pyrolysis, substrate-free synthesis, total organic synthesis, and biological methods, highlighting the advantages of these methods. Upcoming challenges concerning the commercial synthesis of graphene have also been addressed in the concluding part. 

Graphene bearing 2D (dimensional) layer of carbon atoms bonded in sp2 hybridized state are only 1 atomic-scale thick. However, the graphene can be extended along the horizontal dimension. The alternate double bonds leading to perfect conjugation with sp2 hybridization are exhibited in the hexagonal structure (honeycomb) of graphene. Theoretically and experimentally, the thicknesses of graphene have been determined and are in the nano-meter range. The extraordinary mechanical and electrical properties exhibited by such a 2D material have inspired scientists for device fabrication methodologies that can shift the synthesis from lab scale to large scale. It is considered the strongest material on earth, almost 100 times stronger (i.e., strength) than the best steel. Since graphene is only 1 atomic-scale thick and transparent, the characterization of graphene is complex but essential. The thickness down to one atomic layer in graphene can be identified by the light interference causing color contrast. Thus, optical microscopy-based methods enable the identification of graphene or its derivatives; on the other hand, Raman spectroscopy, which is sensitive to molecular bonding and geometric structure, is commonly employed for the quality determination of graphene-based materials. In this chapter, various characterization techniques are discussed, enabling the characterization of graphene and graphene-based materials (GBMs). 

Carbon and its driven materials have been a foundation of living and nonliving systems for centuries due to their amazing experimental expressions in light, temperature, pressure, and pH. Being light-weighted and electronically active with equal energy partitioning in its four orbitals (2s12px12py12pz1), the C atoms have been at the core of natural sciences, providing valuable resources like high-grade wood, cotton, and many others. Thus, carbon-driven materials like diamond, graphite, and graphene ink have been attracting the attention of scientists, researchers, and industries. The chapter reviews recent chemical methodologies for the synthesis and structural investigation of graphene and its derivatives by various analytical techniques that provide information about basic knowledge to understand the role of graphene and graphene-based composites in various qualitative and quantitative applications. Here, several methods have been enlisted for the surface alteration of graphene oxide by a synthetic approach, such as ultrasound, a microwave-assisted synthesis that avoids the use of hazardous chemicals. Also, conventional methods have been discussed, including various types of reactions, such as nucleophilic, electrophilic, condensation, and cycloaddition. This review article highlights the key points to understanding the 2D carbon material for researchers and users to learn about the chemical modification of graphene at the initial stage. This write-up also discusses a brief explanation of various carbon nanomaterials that concern graphene and its oxide forms. We have explained the synthetic value of 2D carbon materials so that it covers a lot of the needs of researchers for synthetic aspects in graphene and allied fields of interest. Currently, such unique experiments are noted as milestones in the field of material synthesis for various applications. So, a review of chemically altered graphene materials reinforced with structural multi-functionalities is highly informative as a ready reckoner for needed information and understanding.

In recent years, the progress of doped carbon catalysts (such as graphene-based nanocomposites), has attracted the tremendous attention of the scientific community because of their broad area of applications involving unique mechanical, electrical and industrial chemical production processes. The catalytic nature of metaldoped graphene-based nanocomposites has significantly improved, and provides alternatives to traditional transition metal-based catalysts. In addition, the progress of simple and easy synthetic approaches for graphene-based nanocomposites provides a wide range of opportunities for the synthesis of graphene-based nanocomposites via incorporating various metal or polymer-based nanomaterials for diverse applications. In this context, the recent development in the synthesis of graphene-based nanocomposites, their properties and applications are summarized in this chapter. The future insights and challenges towards the design and utilization of graphene-based nanocomposites with decent stability and enhanced catalytic performance are also outlined in this chapter.

The catalytic potential of graphene oxide (GO) and graphite oxide has been well explored in recent years. The reactivity of metal-supported graphite oxide as a solid-phase heterogeneous catalyst has started to be an exceptionally powerful tool for the construction of C-C bonds in synthetic organic chemistry. Among them, palladium has been widely used in different catalysts for a variety of cross-coupling reactions such as Mizoroki-Heck, Suzuki-Miyaura, Kumada, Stille, Negishi, Hiyama, and Buchwald-Hartwig, etc., because of its high catalytic activity and the rapid installation of a complex molecular structure with selectivity in comparison to other transition metal catalysts. A description of recent advances in graphene-supported palladium nanocatalysts for cross-coupling reactions is presented in this chapter. Catalyst synthesis and mechanistic aspects are also given, followed by comparisons with traditional methods.

The research on the development of high-performance metal-free carbocatalysis is one of the emerging areas in chemical sciences. The possible active sites of the surfaces of graphene, oxygenated, and reduced graphene oxide materials are responsible for diversified synthetic transformations, including redox reactions. At present, the advanced research is focused on scalable, sustainable, biocompatible, green, and cost-effective graphene-based carbocatalysts as wonderful alternatives over the noble metallic catalytic materials which are being employed despite their scarcity, high cost, and relative toxicity. The present chapter describes the utility of graphene-based carbocatalysts in multicomponent reactions. 

Graphene has several features, such as charge mobility, high conductivity, and a large specific surface area with a two-dimensional structure. It also has exceptional electrical, mechanical, and thermal properties. Graphene has exceptional mechanical, physical, and chemical properties, which are responsible for the development of efficient graphene-based catalysts for selective organic synthesis. This chapter recapitulates the various applications of graphene-based catalysts in oxidation and reduction reactions. It gives a complete overview of graphene, reduced graphene oxide, functionalized graphene oxide, N-doped graphene oxide, and their catalytic applications in various oxidation and reduction reactions. The previous studies reveal that metal-free GO has many catalytic applications. Owing to its high surface area, graphene oxide has a high adsorption tendency for hydrocarbons, gases, and ions.When reacting with oxygenating functionalities, GO provides several paths for introducing and modifying various functional groups. The large potential is employed for the use of metal-free carbon catalysts to resolve the industrial problems arising from traditional catalysts. Since graphene/GO catalysts are synthesized from environmental-friendly material, their applications in green synthesis should be discovered vigorously. The graphene-based catalysts have several applications. They allow only selective, mild, and highly effective transformations and undergo the synthesis and synthesis in an easy, recyclable, regenerable, and environmentally friendly manner.

Enzymes have catalytic properties and can be used for different purposes as biocatalysts in some industrial processes. However, their applications are limited due to some drawbacks, such as lack of long-term stability and recovery under conditions of any particular process. Enzymes can improve their catalytic activity, stability, reusability, and half life, if these are immobilized on some support. Graphene and graphene based nanomaterials are good supports for enzymes as they are also non-toxic materials in nature. Such materials can also find applications in the fields of medical diagnostics, biofuel cells, biosensors, etc. These particular aspects have been discussed in this chapter.