2D Materials: Chemistry and Applications (Part 2)

Graphene-based supercapacitors (SC) are rising as the most efficient and smart energy storage systems. Nonpareil physiochemical properties of graphene offer immense potential for their use in developing next-generation energy storage and portable devices. Since the rise of graphene, this material has been seen as the best alternative to activated carbon in SC applications. Being a 2D material, its high surface area enables it to store electrostatic charge even after high cycling. Since the first graphene-based SC was fabricated in 2008, this material has been explored beyond the boundaries of pristine graphene. The recent invention paved the way for ultrafast charging devices with excellent efficiency. However, the widespread use of these devices in daily life seems far-fetched, but recent results in graphene-based architectures are fetching these possibilities to life. In the last decade, various revamped and manipulated graphene derivatives have also been investigated and found to have great potential in SC applications. These derivatives have shown tremendous specific capacitance with enhanced cyclability. Graphene derivatives can even exhibit capacitance retention of almost 100% after 20,000 cycles. This book chapter discusses the current state of affairs in various graphene-based SC devices, such as crumpled graphene, graphene-metal oxide composites, graphene-based aerogels, graphene nanoparticle systems, graphene-based fibers, graphene/carbon-based hybrid composites for their potential application in the fabrication of efficient energy devices. This comprehensive study aims to analyze current trends and the opportunities and challenges offered by graphene and its derivatives in the development of nextgeneration SCs.

Recently, graphene sheets have attracted a huge awareness for their special optical, mechanical, magnetic, electronic, and thermal characteristics. This has been possible due to the thin yet robust two-dimensional structural arrangement. The special properties may further be enhanced by smart chemical modifications on the twodimensional structure. Meanwhile, nanoparticles also have come up as an emerging platform for their size, shape, surface area, optoelectronic properties and flexibility in functionalization. To utilize the advantages of both worlds, the scientific community has combined graphene with metallic nanoparticles. This event has brought about extreme enhancements in the above properties. Both inorganic and organic nanoparticles have been attached to the graphene surface. However, the attachment of metallic nanoparticles has increased their applications in developing sensors and catalysts. In this literature review, we want to concentrate on synthesizing and functionalizing graphene with different metallic nanoparticles. At the same time, we would discuss their applications in various fields.

 Graphene family nanomaterials (GFNs) appeared to be extensively exploited in numerous diverse fields predominantly in the biomedical sector, owing to distinctive physical, chemical as well as biological/biocompatible characteristics. With the expanding uses, individuals are now exposed to GFNs more often and through a variety of different routes. Upon exposure, these materials exhibit varying amounts of toxicity in biological systems used for toxicological examinations. Administration by various routes leads to penetration by breaching physical barriers and eventually gets disseminated in various tissues or may accumulate in the cells, and subsequently may get eliminated from the body. The present chapter provides information about the toxic effect of the GFNs in several organs encompassing studies in various animals and cell lines. Different factors including lateral size, functionality, concentration as well as protein corona formation, etc. influencing the toxicity status of the GFNs have been elaborated. Furthermore, some representative toxicity mechanisms include mitochondrial as well as DNA impairment, and oxidative damage to name a few. At last, we have provided toxicity remediation approaches for GFNs.

The sustainable development goals have provided a boost and economic appeal to recycling and reusing waste. Waste materials like plastic, industrial, and biomass can be exploited as a foundation to produce valuable products, including wonder materials like graphene. It is utilized in almost every field of life, from environmental sustainability to smart clothing. Waste material contains a variety of organic polymers which can be converted into graphene and its derivatives. It uses various methods like metal catalysis, laser ablation techniques, flash Joule heating, and pyrolysis. These methods may produce 3D, 2D, 1D, and 0D graphene. The obtained products have exclusive properties like thermal, optoelectronic, and electrical properties. The potential for removing and converting waste into the revolutionary material of the century opens possibilities for a sustainable and progressive yet less hazardous world for our future generations. Some approaches promise the fabrication of graphene and its spin-offs from biowaste like sugarcane bagasse, dog feces, and grass. Similarly, liquid phase exfoliation of graphene provides less hazardous and sustainable graphene production from materials without using toxic materials or burdening the earth with waste products. The carbon-negative approach proves an environmentally friendly alternative to prevalent waste-burning practices to dispose of such waste. The obtained graphene and related products have distinctive properties and tremendous applications at a fraction of the cost. The potential for removing and converting waste into the revolutionary material of the century opens possibilities for a sustainable and progressive yet less hazardous world for our future generations. This chapter reviews the efficient methods for synthesizing graphene from waste products and its various applications.

There is a great deal of interest in other 2D compounds due to the development and practicality of graphene in many fields. Due to its similar properties to graphene, the boron nitride (BN) nanosheet has become one of the most thoroughly studied and investigated nanomaterials in this area. The next wave of electrical and optoelectronic products can incorporate 2D-hBN and other 2D materials like graphene. In this chapter, our main aim is to summarize the 2D h-BN nanosheets and their synthesis process via two different mechanisms, i.e., exfoliation techniques and the Chemical Vapour Deposition (CVD) process. The chapter also provides insights into the 2D h-BN's energy-associated properties and their applications in fabricating various energy storage devices, including batteries, supercapacitors, and solar and fuel cells.

Recently, 2D Boron Nitride (BN) and its derivatives have emerged as materials of great interest due to their intriguing structure, similar to graphene, and possessing remarkable physical, chemical, and optoelectronic properties. BN has shown great applications in various fields, including electronics, energy storage and conversion, advanced composites, lubricants, and many more. Moreover, the hybrid materials of 2D BN with graphene and other nanomaterials have evolved as excellent dielectric substrates widely used in electronic devices. However, the extensive application of this material is severely restricted for various reasons. The book chapter elaborates different 2D BN nanostructures with a focused view on their striking applications. The mechanistic aspects of surface revamping through covalent functionalization have been discussed for the readers' comprehensive overview and a concise discussion on the challenges associated with this. The book chapter reviews the application of BN in electronics, biomedical applications, and smart composites in depth. This book chapter will provide a comprehensive outlook to the readers in understanding the recent and significant epistemological evidence.

The discovery of graphene stimulated the intense search for possibilities of other 2D analogs of it. These investigations resulted in many wonder materials, especially from elements of the 14th group of the periodic table. One of the most celebrated 2D structures of the 14th group after graphene is a germanium-based 2D structure known as germanene. Like graphene, germanene is also a single-atom-thick 2D structure. There are several similarities in the structures and properties of graphene and germanene; however, they are distinct in several other properties due to the difference in atomic size, effective nuclear charge, and band structures. One of the most defining phenomena in the structures of graphene and germanene is the buckled structure of the germanene derivative. The buckled structure allows unique orbital mixing and changes the hybridization mode among combining germanium atoms. On the one hand, carbon atoms in graphene exhibit a planer geometry with mesmerizing consistency of the sp2 -hybridized orbitals. On the other hand, germanium atoms tend to exhibit mixed sp2 and sp3 hybridizations. Germanene has gained more popularity due to ease in manipulating its band structure with possibilities to revamp the existing electronics. In addition, mixed hybridization offers the remarkable potential to use this material in various energy and catalytic applications. This chapter deals with various aspects of its chemistry and properties ranging from different methods of synthesis of germanene and its functionalized derivatives, band gap manipulation in these structures, and catalytic applications.

Due to its distinct physicochemical properties, silicene, a silicon allotrope with a 2-D honeycomb assembly, has attracted considerable interest from the entire research community. The mixed sp2 /sp3 hybridization of silicon atoms increases surface chemical activity and enables a range of mechanical and electronic characteristics. A new topology of silicon-based nanoparticles known as 2D silicene has recently been developed. It has a distinctive planar structure with a considerable surface, unusual physiochemical characteristics, and favorable biological effects. In theoretical observation, it exhibits remarkable characteristics and has many advantages over graphene as a 2D material, which makes it a more exciting component and a matter of deep study. So, the present chapter provides a complete overview of this 2D material covering its wide applications in different sectors. The chapter mainly provides insights into the synthesis approach and its characteristics, including its mechanical, electrical, and spintronic attributes. Then, to shed light on the various phases of silicene seen on the metal surfaces on its electrical structures, we describe the experimental characterization of silicene. The chapter also covers the most current uses of silicene outlined in the context of nanoelectronics. 

In recent years, there has been a notable surge of interest in Stanene, MXene, and Transition Metal Chalcogenides. The chapter offers a comprehensive exploration of these cutting-edge 2D materials and their multifaceted applications. Stanene, with its remarkable quantum effects and physicochemical properties, holds promise for the future of nanoelectronics and optoelectronics. Similarly, MXene and Transition Metal Chalcogenides exhibit exceptional characteristics that make them indispensable in various fields, from theranostics to sensor nano-systems and spintronics. Practical applications often hinge on the successful manipulation of molecules through quantum dynamics, but limited synthesis methods for 2D materials pose challenges in this regard. The chapter delves into the structures, synthesis techniques, and applications associated with these materials, providing a comprehensive overview of their potential and current advancements. While a substantial portion of research on these materials has remained theoretical, the chapter underscores the pressing need for increased experimental endeavours. It serves as an invaluable resource for researchers, scientists, and professionals interested in harnessing the unique properties of Stanene, MXene, and Transition Metal Chalcogenides across a spectrum of innovative applications.