Preface

With escalating world population, unsustainable consumption of fossil fuels, increased energy demand, global climate change and rapid environmental degradation, energy and environmental issues are receiving considerable attention worldwide in the context of sustainable development. In order to address these interconnected challenges, the development of clean energy technologies and environmental remediation techniques has intensified in recent years. By virtue of its enormous specific surface area, outstanding electrochemical stability and superior mechanical properties, two-dimensional (2D) graphene holds significant promise for a range of energy and environmental applications. However, just as any other carbon allotrope, graphene as a bulk material tends to form irretrievable agglomerates due to strong van der Waals interactions between the individual graphene sheets. This agglomeration leads to incompetent utilization of isolated graphene layers for practical applications. In order to overcome this restacking issue, the integration of 2D graphene nanosheets into three-dimensional (3D) macrostructures, and ultimately into a functional system, has emerged as an innovative approach in recent years.

The unification of graphene macromolecules into 3D macrostructures not only prevents their restacking, but also largely translates the intriguing characteristics of individual graphene sheets into the resulting monoliths, thereby improving their application potential. The 3D graphene-based macrostructures (3D GBMs), such as sponges, foams, hydrogels, and aerogels manifest extraordinary nanoscale effects due to their superlative properties, novel functionalities, structural integrity and interconnected porosity. Furthermore, owing to their intense porosity, these 3D GBMs can serve as ideal scaffolds for functionalization with heteroatoms, functional polymers, inorganic nanostructures, as well as a whole range of topologically different carbon architectures. The change in the geometrical configuration of 3D GBMs in turn leads to the conceptualization of original material systems with unique properties and novel functionalities. As a consequence, 3D GBMs are being extensively synthesized and rigorously explored for a wide range of potential applications in clean energy technologies (such as batteries, supercapacitors, fuel cells, solar cells, water splitting devices and hydrogen storage) and environmental remediation methods (wastewater treatment, water purification, air pollution control and artificial photosynthesis).

In fact, in the last seven years, over 1000 research articles have been published with a particular focus on fabricating high performance 3D GBMs for energy production and storage as well as environmental remediation applications. As such, a comprehensive and up-to-date synthesis of the current knowledge pertaining to 3D GBMs explored for sustainable energy and environmental applications is highly desirable. The consolidation of fundamental knowledge and practical applications of 3D GBMs would promote further advances in this rapidly evolving cross-disciplinary research field of current global interest. With this goal in mind, we invited well-known experts in the area of 3D GBMs from nine nations across the globe to share their key research outcomes in this book.

We believe that this book will be useful to emerging researchers and senior scientists who are interested in gaining deep insights into various aspects of 3D GBMs from multidisciplinary perspectives and in applying these materials to tackle global energy and environmental challenges in a sustainable manner. Specifically, this book will make a strong appeal to chemists, chemical engineers, material scientists and engineers, environmental scientists and engineers, and energy specialists.

The book is organized into 16 chapters. The first two chapters deal with the fundamental properties and architectures of 3D GBMs and their practical significance. Specifically, Chapter 1 explores the various types of graphene-based aerogels reported-to-date, and explains how their architecture influences their ultimate performance. Chapter 2 provides a fundamental understanding of the structure–property relationship of 3D GBMs to precisely tune their physicochemical properties and expand their application potential. The next 14 chapters are put together in two sections. Section 1 focuses on sustainable energy applications (Chapters 3 to 10) while section 2 deals with environmental remediation applications (Chapters 11 to 16).

In particular, Chapter 3 summarizes the recent advances in the design and fabrication of 3D GBMs-based high performance foldable and stretchable electrodes for applications in lithium ion batteries. Chapter 4 provides an overview of the significant progress achieved on 3D graphene-based anodes and cathodes for application in sodium ion batteries. Chapter 5 presents the latest developmental status in 3D GBMs-based supercapacitors with unprecedented performance. Chapter 6 brings together the recent progress in the development of 3D GBM-supported transition-metal oxide nanocatalysts and heteroatom doped 3D graphene electrocatalysts for potential application in fuel cells. Chapter 7 collates the applications of 3D graphene-based scaffolds with high conductivity and biocompatibility in microbial fuel cells (MFCs). In addition, it discusses the key scientific and technological challenges in using them to improve the performance of MFCs. Chapter 8 describes the synthesis of 3D GBMs through bottom-up strategies and their potential in improving the overall performance of dye sensitized solar cells. Chapter 9 presents a systematic, updated summary of the current status on the application of 3D GBMs in hydrogen production and storage. Chapter 10 provides a broad overview of the latest development in 3D GBMs-mediated solar steam generation for potential applications in sterilization of waste and seawater desalination.

Chapter 11 collates the current state-of-the-art on the development and application of ultralight and mechanically resilient 3D GBMs for the selective absorption of a broad variety of oils and organic solvents, with an emphasis on underlying mechanisms. Chapter 12 critically reviews the recent advances in the development of novel graphene and graphene oxide-based 3D macrostructures for fast and efficient removal of a variety of pollutants from water and air, with a special focus on interaction mechanisms with contaminant molecules. Chapter 13 summarizes the recent advances in the rational design of 3D GBM-based photocatalysts and highlights their applications in photocatalytic environmental remediation, with an emphasis on the corresponding reaction mechanisms and pollutant transformation pathways. Chapter 14 introduces the basic principles of sensor design and explores the application of flexible 3D GBM-based sensors for the on-site detection of various classes of chemical pollutants and biological contaminants in various environmental matrices. Chapter 15 summarizes the most recent advances in 3D GBM-mediated CO₂ adsorption, and describes the numerous surface modification schemes that are actively pursued to enrich the CO₂ adsorption capacity of 3D GBMs. Finally, Chapter 16 provides a systematic overview of the recent progress in the development and application of 3D GBM-based photocatalysts for CO₂ reduction to solar fuels.

We are indeed grateful to all Lead as well as Contributing Authors for sharing their valuable expertise in various aspects of 3D GBMs, without which this book would not have been possible. We also thank the RSC editorial team, especially Dr Helen Armes and Mr Lewis Pearce, for their constructive feedback, logistical support and constant encouragement.