Preface

We currently live in the era of the Anthropocene – the time period where the actions and consequences of human society and practices are the predominant geological, environmental and climate driving forces. As a consequence, the terms “sustainable” and “sustainability” are increasingly becoming common terms in the chemical industry and sociopolitical discussions as we look to a future beyond unsustainable fossil-based resources. These terms, at least in the public domain, are typically associated with the agricultural industry but also with ever-increasing exposure in the context of energy, fuel and consumer product provision. This latter point relates to societies dependence on fossil-fuel-derived products (e.g. gasoline, plastics, etc.) and their ever-dwindling reserves. Therefore, human society is looking to the development of innovative and “green” technologies to address the challenge of providing for an ever-increasing population. This must be approached without reducing the capability of future generations to live in the manner in which the western world is accustomed and allow the developing world to achieve the same standards. Underpinning a “sustainable” society will the development of innovative materials ideally based on abundant precursors/elements, synthesised in a “green” manner, providing the necessary application behaviour suitable to provide sustainable energy, chemicals and products for society.

Perhaps one of, if not the most, important elements of the sustainable challenge, is carbon. In the context of our existing and hopefully a future sustainable society, carbon will be present in many forms. For example, CO₂ is the major product of the combustion of carbon-based fossil fuels that is driving the greenhouse effect and associated changes in the global climate. In a closed cycle, CO₂ could be taken up by photosynthetic organisms (e.g. green plants) and converted to solid sinks of carbon (e.g. biomass) ultimately transforming back into the fossil deposits that underpin our current society. However, the latter process unfortunately occurs on a time scale that is not relevant to human society, with consumption occurring at a rate resulting in the near exploitation of reserves by the end of the current century. Therefore, new cyclical, carbon-neutral energy and chemical provision schemes are needed to allow the establishment of a sustainable society. As will be briefly introduced in this book, alternative schemes such as the Biorefinery and Methanol Economy have been proposed and aspects of each scheme are gradually entering the energy, fuel and chemical market place. Notably, both these alternative future economies rely on CO₂ and its natural derivatives (e.g. biomass). Furthermore, as for existing industrial practices, these new economies will require the development of increasingly efficient, active materials to perform the conversion, catalysis and separation processes needed to synthesize and produce the myriad of (e.g. carbon-based) products that modern society demands.

The establishment of a sustainable society represents one of the greatest challenges facing human kind and will require the transition from an essentially resource consumptive economy to a new sustainable, carbon-neutral (and even carbon-negative) approach based on renewable resources to deliver the material, chemical and energy demands of a modern sustainable society. To establish sustainable chemical, energy and fuel provision, the development and ultimately implementation of innovative sustainable chemical practices is required. With regard to current energy and chemical provision, fossil-based industries (e.g. petrorefineries, coal-fired power stations, etc.) still dominate, although their viability will dwindle over the coming century. To counteract this reduction, future energy/chemical supply from renewable energies (e.g. solar, water, wind, etc.) will dramatically increase over the same time frame. This in itself creates challenges regarding cost-efficient energy storage and transportation. In this regard, there are several options by which to generate and store renewable energy provided by the sun, wind, water, geothermal or biomass sources. These solutions will all be reliant on porous materials technologies to allow for their efficient implementation and conversion and storage of photonic, thermal or kinetic energy into suitable chemical energy-vector molecules. The materials developed to address this task should be low cost, scalable, industrially and economically attractive, based on renewable and highly abundant resources, whilst of course achieving application performances that exceed the performance of existing technologies.

In this regard, new porous materials (e.g. catalysts, separation media, etc.) with improved properties relative to the current state of the art are required, synthesised with as minimal a carbon footprint as possible. If these synthetic approaches can be based on sustainable resources (e.g. biomass), abundant elements (e.g. C, N, P, etc.) and sustainable synthetic techniques, this has the potential to aid the overall “C” balance in the material or chemical synthesis pathway. This book aims to demonstrate how this might be possible via a number of emerging approaches, predominantly focusing on carbon-based materials. Furthermore, from a materials-chemistry perspective, sustainable biomass precursors appear to be excellence platform compounds from which to synthesise a variety of carbon-based materials, particularly when one considers the range of naturally occurring nanostructures and also the range of opportunities that molecules including the saccharides, polysaccharides, nucleotides, and proteins offer, (e.g. in terms of functionality, self-assembly properties, etc.). It is in this context that this book draws its inspiration.

The natural products of CO₂ capture and recycling, namely biomass, as this book will highlight, can be transformed into useful, applicable, carbon-based porous materials. It is also important to highlight the significance of porous materials in both current energy and chemical provisions (e.g. the petrorefinery) and the aforementioned alternative future provisions schemes. In the context of sustainable precursors and specifically biomass-derived compounds, their direct conversion into carbon-based materials typically requires high temperatures and/or activation agents, resulting in the production of either nonporous or predominantly microporous, hydrophobic materials. As an example, such materials may not be suitable for the aqueous phase catalysis required in the Biorefinery, although they may find application in gas-separations challenges of the Methanol Economy. Therefore, there is a need to develop new synthetic practices with regard porous carbon materials that enable control over physicochemistry (e.g. surface functionality, conductivity, hydrophobicity, etc.) in tandem with material texture and porosity (e.g. micro- vs. mesoporosity, hierarchical structuring, particle morphology, etc.). The following chapters will introduce to the reader solutions to this problem based on the use of sustainable precursors and technologies, allowing the preparation of a range of materials with properties that have the potential to fill the “gap” between classical inorganic and organic materials (e.g. mesoporous silica vs. microporous carbon).

The book introduces approaches to this end using sustainable, predominantly biomass-derived precursors, with a particular focus on the two leading synthetic approaches; namely Starbon^® technology and hydrothermal carbonisation (HTC). The book features contributions from a global collective of up and coming young scientists revealing the wide range of materials and applications that are possible using the aforementioned synthetic platforms and derivations therefrom. The book starts with an introduction from the Editor, providing a context for the following chapters with regards to the demands of future energy and chemical provision schemes, whilst highlighting the material demands of these cyclical economies. Part 1 provides contributions on the topic of Starbon^® technology, developed and elaborated predominantly at the Green Chemistry Centre of Excellence, University of York, (York, UK), demonstrating the exciting porous properties of these polysaccharide-derived materials, with promising application in aqueous-phase heterogeneous catalysis (e.g. esterification of succinic acid) and separations science (e.g. separation of polar sugar analytes). Part 2 covers the topic of hydrothermal carbonisation as a platform for the conversion of biomass to porous carbonaceous materials, a topic initially reinvigorated by researchers from the Max Planck Institute for Colloids and Interfaces, (Golm, Germany), which has now proliferated, as reflected by the authors assembled, to the different corners of the scientific globe. Hydrothermal carbon materials are discussed in the context of porosity development (e.g. templating, gelation, etc.) and functionality control (e.g. heteroatom doping), with the resulting materials discussed in the context of applications in heterogeneous catalysis, electrochemistry (e.g. battery electrodes, metal-free oxygen-reduction reaction, etc.) and gas sorption (e.g. CO₂ capture). Part 3 introduces and discusses the challenges and analytical techniques associated with the development and characterisation of the innovative porous carbon materials discussed in Parts 1 and 2 (e.g. gas sorption, microscopy, etc.). Finally, the book concludes in Part 4, with a brief review of more recent, emerging platforms for the synthesis of porous carbons from sustainable precursors that are still in their infancy (at the time of writing). Part 4 also provides an overview of the commercial efforts underway to bring porous carbon materials sustainably from the laboratory curiosity to industrial-scale products (e.g. Starbon^® Technologies).

This book is aimed at a broad readership, encompassing advanced undergraduates, graduates, researchers and industrialists alike whose interests lie in the topics of renewable energy, nanomaterials, sustainability, green chemistry, and functional/porous materials. The book brings together, for the first time in one volume, the different approaches to porous carbons synthesised from sustainable precursors and hopefully as such provides the reader with an indepth account of the benefits and applications of converting biomass and biomass-derived precursors into functional, porous carbon-based nanomaterials for a variety of increasingly topical applications.

The Editor would like to express his gratitude to all the contributing authors who have given their time and effort to writing their respective chapters. The Editor would also like to thank the publication team of the Royal Society of Chemistry for all their help in assistance in bringing this book to print – it is very much appreciated.

Robin J. White

Freiburg, Germany