Graphene-based Carbocatalysts: Synthesis, Properties and Applications (Volume 2)

Graphene is a single layer of graphite with a unique two-dimensional structure with high conductivity, superior electron mobility, absorptivity, and specific surface area. The extraordinary mechanical, thermal, and electrical properties of graphene are due to long-range π conjugation. Due to these properties, graphene can be used in nanosystems and nano- devices. The photocatalytic efficiency of composites (semiconductor-based metal oxides and graphene-based photocatalysts) can be improved under visible light. Graphene behaves as an electron acceptor in these types of composite photocatalysts. Different types of graphene-based composites (graphene (G)-semiconductor, graphene oxide (GO)-semiconductor, and reduced graphene oxide (RGO)-semiconductor, where the semiconductor is TiO2, ZnO, CdS, Zn2SnO4, etc.) can be prepared through simple mixing and/or sonication, sol-gel process, liquid-phase, hydrothermal, and solvothermal methods. This chapter includes the most recent advances in different applications of graphene-based semiconductor photocatalysts for degrading various contaminants (treatment of waste water) and producing hydrogen (fuel of future) by photosplitting water, and photo-catalytically reducing carbon dioxide to energy-rich synthetic fuels (combating against global warming and energy crisis), etc.

Recently, graphene-based materials have attracted significant attention from scientific and industrial communities due to their potential applications in various electrochemical energy conversion technologies. Since pure graphene is electrochemically inert despite its outstanding versatile properties, different strategies are employed to modify the graphene to enhance its electrochemical activity. In this chapter, first, we discuss the basics of electrocatalysis and then the recent advances in electrocatalysis by graphene-based materials. Electrocatalytic activities of non-metal doped graphene, graphene-based 2D heterostructures, and graphene-plasmonic nanostructures have drawn particular attention. The challenges and future prospects of graphene-based electrocatalysts are also highlighted.

Solar hydrogen production from water splitting can solve two big issues i.e. energy and environmental pollution. Since the discovery of graphene, its importance has been proven in many fields including light-driven hydrogen generation from water. This chapter offers a contemporary overview of the progress of graphene-based materials including graphene oxide, reduced graphene oxide and graphene oxide quantum dots for hydrogen evolution from photocatalytic water splitting. This chapter begins with a concise introduction to the current status of hydrogen energy generation from water. The chemical and physical characteristics of this extraordinary plasmonic metamaterial were also elaborated. Afterwards, the synthesis methods, various models, and associated properties of the tailored graphene oxides, reduced graphene oxide and graphene oxide quantum dots in the forms of pristine, binary and ternary compounds are discussed for their application in hydrogen production. In these modified compounds, the graphene acts as a surfactant, a charge-carrier recombination suppressor, an electron-sink and transporter, a co-catalyst, a photocatalyst, and a photosensitizer which, are elaborated . Finally, the chapter ends with a concluding remark on the challenges and future perspectives in this promising field.

Energy is an incising subject matter and has had both positive and negative impacts on our society. Admittance to profuse, inexpensive, unharmed, hygienic energy is advantageous for human beings. However, the process of changing one form of energy into another, hauling and plentiful use can have negative impacts on health, the environment, and cost-cutting measures of our society. These days and at this age, the production of energy and stockpiles is one of the two main burning issues. Regrettably, conventional energy producers are not competent enough to respond to ecological transformations, whereas accustomed energy storage devices are deficient in special functionalities apart from supplying electricity. Graphene, composed of a single-layered graphite with a two-dimensional sp2-hybridized carbon network, has recently gained tremendous research interest due to its peculiar physical and chemical properties. Gratifying from unrivalled physicochemical properties, graphene-based materials facilitate dealing with the aforesaid smoldering issues and, in recent times, have been widely studied in various energy conversion and storage applications such as supercapacitors, fuel cells, batteries, and photovoltaic devices or solar cells. In this book chapter, we summarise the recent progress reported in the synthesis and fabrication of graphene-based smart energy materials with their applications in various energy storage systems. In addition to this, the panorama and future challenges in both scalable manufacturing and more energy storage-related applications are covered in this chapter as well.

Graphene-based electrodes are potential candidates and significantly participate in electrochemical reactions, providing high reactivity and selectivity. Their reaction assists in transferring electrons between the electrode and reactants and facilitates an intermediate chemical transformation described by an overall half-cell reaction. Graphene-based materials with metal/metal oxides and sulphides have been extensively applied for the fabrication of highly sensitive electrochemical sensors. They have excellent physical, chemical, electrical, and surface properties and are extensively used in the development of sensors. Graphene-based nanomaterials have also been successfully utilised for clinical diagnosis, disease treatment, and many biocompatible sensors. This chapter mainly focuses on the sensing mechanism of graphene-based electrochemical sensors via different approaches of potentiometry, amperometry/voltammetry, and conductometry. The electronic properties of graphenebased nanomaterials have been briefly discussed and are responsible for their outstanding sensing ability. We have also explored different forms of graphene and its derivatives with their properties and applicability in fabricating electrochemical sensors to better influence graphene for superior functioning. There is also a discussion about the general reactions (reduction/oxidation) involved within analytes and graphene materials in fabricating electrochemical sensors. Finally, a conclusion was drawn on the basis of the usage of graphene-based materials in electrochemical sensors for future electrocatalytic applications in various fields of biomedical diagnosis, environmental monitoring, food sensors, and hazardous fumes.

The global surge in the demand for sustainable protocols and catalytic processes has led to an enormous rise in the research in the field of carbocatalysis. Graphene and its derivatives have surfaced as a novel category of green heterogeneous catalysts. This chapter summarizes the current trends in the synthesis, properties and applications of graphene-based carbocatalyst. The future challenges in the area of graphene-based catalysts have also been addressed.