Always look on the "light" side of life: sustainable carbon aerogels

Ultralight Biomass-Derived Carbonaceous Nanofibrous Aerogels with Superelasticity and High Pressure-Sensitivity

Superelastic and pressure-sensitive carbonaceous nanofibrous aerogels with a honeycomb-like structure are fabricated through the combination of sustainable konjac glucomannan biomass and flexible SiO₂ nanofibers. The aerogels can detect dynamic pressure with a wide pressure range and high sensitivity, which enables real pressure signals, such as human blood pulses, to be monitored in real time and in situ.

Colloidal and micro-carbon spheres derived from low-temperature polymerization reactions

Carbon spheres (CSs) have recently attracted major interest due to their new applications, mainly in energy storage and conversion but also in hard-templating, sorption/catalysis processes, and drug delivery systems. This is attributable to their physico-chemical properties, including their tunable morphology (solid, hollow and core-shell), size, surface area/porosity, good electrical conductivity, low external surface-to-volume ratio, high packing density, enhanced mass transport, robust mechanical stability, low cytotoxicity, and excellent biocompatibility. They can be obtained from a wide variety of carbon precursors and methods. This review covers their production by carbonization of polymer spheres from low-temperature polymerization reactions, considered here as below 250°C. This is a very important method because it allows the synthesis of CSs with different morphologies and doped with other elements or chemical compounds. The preparation of polymer spheres by this technique is well documented in the literature, and the objective of this review is to summarize and give an overview of the most significant publications, proposing a novel classification based on the formation mechanism of the polymer spheres. This classification includes the following polymerization processes: emulsion polymerization and its derivatives, seeded emulsion and inverse emulsion polymerization; precipitation polymerization and its derivative, dispersion polymerization; hard-templating; spray-drying; and hydrothermal or solvothermal treatment of carbohydrates and biomass in general. This review also reports on the morphology and surface characteristics of the CSs obtained by different synthetic approaches. The final section of the review describes the current applications of these CSs, notably in energy storage (supercapacitors and rechargeable batteries) and energy conversion (fuel cells and dye-sensitized solar cells). Besides the numerous applications listed above, they are utilized as sacrificial hard templates to prepare single- and multi-shell hollow spheres of metal oxides and other inorganic compounds and filters, as well as in adsorption and catalysis processes, drug delivery systems, and other minority applications (e.g., lubricants, black pigment in e-papers, and microwave absorber).

A Facile and Low-Cost Route to Heteroatom Doped Porous Carbon Derived from Broussonetia Papyrifera Bark with Excellent Supercapacitance and CO2 Capture Performance

In this work, we present a facile and low-cost approach to synthesize heteroatom doped porous carbon via hydrothermal treatment of stem bark of broussonetia papyrifera (BP) as the biomass precursor in diluted sulfuric acid, and following thermal activation by KOH at 800 °C. The morphology, structure and textural property of the prepared porous carbon (PC) are investigated by scanning electron microscopy, transmission electron microscopy, N₂ sorption isotherms, and X-ray photoelectron spectroscopy. The porous carbon possesses a high BET surface area of 1759 m² g⁻¹ and an average pore size of 3.11 nm as well as hetero-oxygen (9.09%) and nitrogen (1.7%) doping. Such porous carbon shows outstanding capacitive performances of 416 F g⁻¹ and 300 F g⁻¹ in three and two-electrode systems, respectively. As a solid-state adsorbent, the obtained porous carbon has an excellent CO₂ adsorption capacity at ambient pressures of up to 6.71 and 4.45 mmol g⁻¹ at 0 and 25 °C, respectively. The results present one novel precursor-synthesis route for facile large-scale production of high performance porous carbon for a variety of great applications including energy storage and CO₂ capture.

Eutectic Syntheses of Graphitic Carbon with High Pyrazinic Nitrogen Content

Mixtures of phenols/ketones and urea show eutectic behavior upon gentle heating. These mixtures possess liquid-crystalline-like phases that can be processed. The architecture of phenol/ketone acts as structure-donating motif, while urea serves as melting-point reduction agent. Condensation at elevated temperatures results in nitrogen-containing carbons with remarkably high nitrogen content of mainly pyrazinic nature.

An Interesting Class of Porous Polymer--Revisiting the Structure of Mesoporous α-D-Polysaccharide Gels

The processes involved in the transformation of non-porous, native polysaccharides to their highly porous equivalents introduce significant molecular complexity and are not yet fully understood. In this paper, we propose that distinct changes in polysaccharide local short-range ordering promotes and directs the formation of meso- and micro-pores, which are investigated here using N2 sorption, FTIR, and solid-state (13)C NMR. It is found that an increase in the overall double helical amylose content, and their local association structures, are responsible for formation of the porous polysaccharide gel phase. An exciting consequence of this local ordering change is elegantly revealed using a (19)F NMR experiment, which identifies the stereochemistry-dependent diffusion of a fluorinated chiral probe molecule (1-phenyl-2,2,2-trifluoroethanol) from the meso- to the micro-pore region. This finding opens opportunities in the area of polysaccharide-based chiral stationary phases and asymmetric catalyst preparation.

Effects of pore size and surface charge on Na ion storage in carbon nanopores

Na ion batteries (NIBs) are considered as a promising low cost and sustainable energy storage technology.

Hydrothermal formation of graphene aerogel for oil sorption: the role of reducing agent, reaction time and temperature

Different reducing agents including vitamin C, ammonia and ethanediamine can significantly affect the density, strength, morphology and adsorption performance of graphene aerogels.

Incorporation of graphene into silica-based aerogels and application for water remediation

Graphene/silica nanocomposites in the form of highly porous aerogels are obtained for the first time by integrating a novel approach for the production of low defectivity graphene with a two-step route for the synthesis of a silica-based monolith.

Versatile Cellulose-Based Carbon Aerogel for the Removal of Both Cationic and Anionic Metal Contaminants from Water

Hydrothermal carbonization of cellulose in the presence of the globular protein ovalbumin leads to the formation of nitrogen-doped carbon aerogel with a fibrillar continuous carbon network. The protein plays here a double role: (i) a natural source of nitrogen functionalities (2.1 wt %) and (ii) structural directing agent (S(BET) = 38 m(2)/g). The applicability in wastewater treatment, namely, for heavy metal removal, was examined through adsorption of Cr(VI) and Pb(II) ion solely and in a mixed bicomponent aqueous solutions. This cellulose-based carbogel shows an enhanced ability to remove both Cr(VI) (∼68 mg/g) and Pb(II) (∼240 mg/g) from the targeted solutions in comparison to other carbon materials reported in the literature. The presence of competing ions showed little effect on the adsorption efficiency toward Cr(VI) and Pb(II).

Polymer/Carbon-Based Hybrid Aerogels: Preparation, Properties and Applications

Aerogels are synthetic porous materials derived from sol-gel materials in which the liquid component has been replaced with gas to leave intact solid nanostructures without pore collapse. Recently, aerogels based on natural or synthetic polymers, called polymer or organic aerogels, have been widely explored due to their porous structures and unique properties, such as high specific surface area, low density, low thermal conductivity and dielectric constant. This paper gives a comprehensive review about the most recent progresses in preparation, structures and properties of polymer and their derived carbon-based aerogels, as well as their potential applications in various fields including energy storage, adsorption, thermal insulation and flame retardancy. To facilitate further research and development, the technical challenges are discussed, and several future research directions are also suggested in this review.

Carbon-Based Sorbents with Three-Dimensional Architectures for Water Remediation

Over the past decade, carbon-based 3D architectures have received increasing attention in science and technology due to their fascinating properties, such as a large surface area, macroscopic bulky shape, and interconnected porous structures, enabling them to be one of the most promising materials for water remediation. This review summarizes the recent development in design, preparation, and applications of carbon-based 3D architectures derived from carbon nanotubes, graphene, biomass, or synthetic polymers for water treatment. After a brief introduction of these materials and their synthetic strategies, their applications in water treatment, such as the removal of oils/organics, ions, and dyes, are summarized. Finally, future perspective directions for this promising field are also discussed.

Towards a feasible and scalable production of bio-xerogels

HYPOTHESIS

The synthesis process of carbon xerogels is limited, mainly due to two drawbacks that prevent their introduction onto the market: (i) the long time required for producing the material and (ii) the reagents used for the synthesis, which are costly and harmful to the environment. Microwave radiation is expected to produce a reduction in time of more than 90%, while the use of tannin instead of resorcinol will probably result in a cost-effective carbonaceous material.

EXPERIMENTS

Resorcinol-tannin-formaldehyde xerogels containing different amounts of tannin, either with or without a surfactant (sodium dodecyl sulphate), were synthesized by means of two different heating methods: conventional and microwave heating. The effects of the surfactant, the heating method and the addition of tannin upon the porous structure and the chemical composition of the final materials were evaluated.

FINDINGS

It was found that the addition of surfactant is essential for obtaining highly porous xerogels when using tannins. The heating method also plays an important role, as conventionally synthesized samples display a greater volume of large pores. However, tannins are less sensitive to microwave radiation and their use results in tannin-formaldehyde xerogels that have a porous structure and chemical composition similar to those of resorcinol-formaldehyde xerogels.

A sustainable freeze-drying route to porous polysaccharides with tailored hierarchical meso- and macroporosity

Bio-derived polysaccharide aerogels are of interest for a broad range of applications. To date, these aerogels have been obtained through the time- and solvent-intensive procedure of hydrogel fomation, solvent exchange, and scCO2 drying, which offers little control over meso/macropore distribution. A simpler and more versatile route is developed, using freeze drying to produce highly mesoporous polysaccharide aerogels with various degrees of macroporosity. The hierarchical pore distribution is controlled by addition of different quantities of t-butanol (TBA) to hydrogels before drying. Through a systematic study an interesting relationship between the mesoporosity and t-butanol/water phase diagram is found, linking mesoporosity maxima with eutectic points for all polysaccharides studied (pectin, starch, and alginic acid). Moreover, direct gelation of polysaccharides in aqueous TBA offers additional time savings and the potential for solvent reuse. This finding is a doorway to more accessible polysaccharide aerogels for research and industrial scale production, due to the widespread accessibility of the freeze drying technology and the simplicity of the method.

Other Approaches and the Commercialisation of Sustainable Carbonaceous Material Technology

To conclude the book, this chapter aims to provide the reader with an overview of a number of developing approaches to the production of porous carbons from sustainable precursors. Discussion will focus predominantly on the production of carbon-based materials from bacterial cellulose, lignins, tannins and finally to examine the possibility of employing ionic liquids. The relative merits of the approaches discussed will also be highlighted. The use of the resulting carbons synthesised based on these approaches in applications including energy storage, energy generation and purification/remediation will also be briefly discussed. Finally, the chapter will conclude with an overview of the latest developments regarding the commercialisation of the approaches to the synthesis of porous carbons from sustainable precursors discussed in this book will also be provided.

From Polysaccharides to Starbons®

Many commercially employed carbon materials are typically hydrophobic, chemically inert and microporous. Therefore, with an eye to the future, there is a need to develop new, carbon-based porous materials, the properties of which can be easily tuned to address the catalytic and separation challenges of future energy and chemical provision schemes (e.g. the Methanol Economy or Biorefinery schemes). In this regard, the synthesis of such materials must be conducted in as sustainable a manner as possible, ideally providing a flexible platform upon which to tailor properties such as functionality, porosity at different length scales (e.g. micro-, meso-, and macroporosity), hydrophilic character and macrophology (e.g. monoliths, particulates, etc.) amongst others. This chapter therefore aims to introduce one top-down synthetic approach to this end, the Starbon® materials concept. An accompanying material development history will be provided followed by a review of the variety of interesting functionally rich, highly mesoporous, high surface area (e.g. > 0.5 cm3 g–1; > 200 m2 g–1) carbonaceous materials that are accessible via the development of porous polysaccharide-derived materials and their subsequent carbonaceous derivatives. The chapter intends to provide the reader with an overview of the exciting opportunities that are open to the carbon materials chemist based on the discussed synthetic approach.

The Search for Functional Porous Carbons from Sustainable Precursors

The design and development of carbon-based porous materials perhaps represents one of the most adaptable areas of materials science research. These materials are ubiquitous with the current energy and chemical production infrastructure and as will be highlighted in this book will be absolutely critical in technology development associated with green, sustainable energy/chemical provision (e.g. electricity generation and storage; the Methanol Economy, Biorefinery, etc.) and environmental science (e.g. purification/remediation, gas sorption, etc.). However, alongside these environmental and sustainable provision schemes, there will also be a concurrent need to produce and develop more sustainable porous carbon materials (e.g. microporous, mesoporous, carbon aerogels, etc.). This is particularly relevant when considering the whole life cycle of a product (i.e. from precursor “cradle” to “green” manufacturing and the product end-of-life “grave”). In this regard, carbon materials scientists can take their inspiration from nature and look to the products of natural photosynthetic carbon cycles (e.g. glucose, polysaccharides, lignocellulosics, etc.) as potential precursors in the synthesis of applicable porous carbon materials. If such synthetic strategies are coupled with simpler, lower-energy synthetic processes, then materials production (e.g. the separation media) can in turn contribute to the reduction in greenhouse-gas emissions or the use of toxic elements. These are crucial parameters to be considered in sustainable materials manufacturing. Furthermore, these materials must present useful, beneficial (and preferably tuneable) physicochemical and porous properties, which are least comparable and ideally better than carbon materials (e.g. carbon aerogels, activated carbons, etc.) synthesised via more energy-intensive and less-sustainable pathways. This introductory chapter introduces these concepts and provides the basis for the following book which will provide an introduction and discussion of the possible synthetic pathways to the production of applicable porous carbon materials from sustainable precursors and practices. Furthermore, throughout this book, the application of these exciting sustainable carbon-based materials in the increasingly important field of sustainable chemical and energy provision will be introduced and discussed.

Sustainable carbon materials

Carbon-based structures are the most versatile materials used in the modern nanotechnology. Therefore there is a need to develop increasingly more sustainable variants of carbon materials.

Biosourced graphitic nanoparticle loaded hyperbranched polyurethane composites – application as multifunctional high-performance coatings

Dynamic mechanical thermal analysis of GP-PU depicting a drastic increase in E′ and T_g with minuscule incorporation of GP-COOH.

N-doped porous carbon material made from fish-bones and its highly electrocatalytic performance in the oxygen reduction reaction

N-doped porous carbon material derived of fish bones showed excellent catalytic activity towards oxygen reduction reaction in alkaline medium, as well as long-term stability.

Recent advances in carbon nanospheres: synthetic routes and applications

Various strategies to carbon nanospheres together with a brief introduction of applications are presented in this feature article.

Physicochemical and micromechanical investigation of a nanocopper impregnated fibre reinforced nanocomposite

This paper outlines the synthesis of a novel sustainable nanocomposite and the investigation of its physicochemical and mechanical properties using micromechanical models.