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

A greener approach for synthesizing metal-decorated carbogels from alginate for emerging technologies

In the present work, a series of metal nanoparticle-decorated carbogels (M-DCs) was synthesized starting from beads of parent metal-crosslinked alginate aerogels (M-CAs). M-CAs contained Ca(ii), Ni(ii), Cu(ii), Pd(ii) and Pt(iv) ions and were converted to M-DCs by pyrolysis under a N2 atmosphere up to pyrolysis temperatures of TP = 600 °C. The textural properties of M-CAs are found to depend on the crosslinking ion, yielding fibrous pore networks with a high specific mesoporous volume and specific surface area SV (SV ∼ 480-687 m2 g-1) for M-CAs crosslinked with hard cations, Ca(ii), Ni(ii) and Cu(ii), and comparably loose networks with increased macroporosity and lower specific surface (SV ∼ 240-270 m2 g-1) for Pd(ii) and Pt(iv) crosslinked aerogels. The pyrolysis of M-CAs resulted in two simultaneously occurring processes: changes in the solid backbone and the growth of metal/metal oxide nanoparticles (NPs). The thermogravimetric analysis (TGA) showed a significant influence of the crosslinking cation on the decomposition mechanism and associated change in textural properties. Scanning electron microscopy-backscattered electron imaging (SEM-BSE) and X-ray diffraction revealed that metal ions (molecularly dispersed in the parent aerogels) formed nanoparticles composed of elementary metals and metal oxides in varying ratios over the course of pyrolytic treatment. Increasing the TP led to generally larger nanoparticles. The pyrolysis of the nickel-crosslinked aerogel (Ni-CA) preserved, to a large extent, the mesoporous structure and resulted in the evolution of fine (∼14 nm) homogeneously dispersed Ni/NiO nanoparticles. Overall, this work presents a green approach for synthesizing metal-nanoparticle containing carbon materials, useful in emerging technologies related to heterogeneous catalysis and electrocatalysis, among others.

Preparation and Properties of Starch-Cellulose Composite Aerogel

In this study, we conducted research on the preparation of aerogels using cellulose and starch as the primary materials, with the addition of N,N'-methylenebisacrylamide (MBA) as a cross-linking agent. The chemical, morphological and textural characteristics of the aerogels were found to be influenced by the proportions of cellulose, starch, and cross-linking agent that were utilized. An increase in the proportion of cellulose led to stronger adsorption forces within the aerogel structure. The aerogel showed a fine mesh internal structure, but the pores gradually increased with the further increase in cellulose. Notably, when the mass fractions of starch and cellulose were 5 wt% and 1 wt% respectively, the aerogels exhibited the smallest pore size and largest porosity. With an increase in the crosslinking agent, the internal structure of the aerogel first became dense and then loose, and the best internal structure was displayed at the addition of 3 wt%. Through texture analysis and the swelling test, the impact of the proportion of cellulose and MBA on the aerogel structure was significant. Dye adsorption experiments indicated that MBA affected the water absorption and expansion characteristics of the aerogel by improving the pore structure. Lastly, in tests involving the loading of vitamin E, the aerogels exhibited a higher capacity for incorporating vitamin E compared to native starch.

Modification of natural zeolite clinoptilolite and ITS application in the adsorption of herbicides

The clinoptilolite natural zeolites (NZs) posses low herbicide adsorption capacity demanding acid-, alkali-, or salt chemical modifications that enhance its adsorption. However, this may affect the material structure and charge distribution. Alternatively, zeolites may be synthesized at a high cost and time-consuming process. Consequently, new methods, such as the hydrothermal method, for NZ modification needs to be studied. In this sense, a novel surface-modified zeolite (SMZ), using hexadecyltrimethylammonium bromide (CTAB), in acid media was produced by the hydrothermal method and applied for the adsorption of Atrazine (ATZ), Diuron (DIU) and 2,4-D. Commercial NZ and SMZ were characterized by SEM, XRD, TGA, FT-IR, AA spectroscopy, pHPZC, Zeta potential and N2-physisorption. The SMZ chosen for the adsorption experiments was the one with the highest modification yield and adsorption capacity obtained from a complete design of experiments (CTAB=0.74 ; D=12 Mesh; HCl=0.1 M; t=6 h and T=205 ºC). The adsorption experiments revealed that the SMZ adsorption capacity for the herbicide 2,4-D (qmax=9.02 mg/g) was greater than that obtained for ATZ (qmax=2.11 mg/g) and DIU (qmax=1.85 mg/g), which was explained by the presence of the hydroxyl group and by geometric characteristics of the 2,4-D. Adsorption models' fitting showed that the adsorption of 2,4-D onto SMZ were best described by pseudo-second order kinetic (k2=0.005-0.006 g/mg.min; qe,exp=7.122-8.614 mg/g) and Langmuir isothermal model (KL=0.283-0.499 L/mg; qm=7.167-7.995 mg/g). These results indicate that the hydrothermal method is a viable alternative to enable the use of NZs for the adsorption of emerging contaminants from wastewater.

The effect of synthesis conditions and process parameters on aerogel properties

Aerogels are remarkable nanoporous materials with unique properties such as low density, high porosity, high specific surface area, and interconnected pore networks. In addition, their ability to be synthesized from various precursors such as inorganics, organics, or hybrid, and the tunability of their properties make them very attractive for many applications such as adsorption, thermal insulation, catalysts, tissue engineering, and drug delivery. The physical and chemical properties and pore structure of aerogels are crucial in determining their application areas. Moreover, it is possible to tailor the aerogel properties to meet the specific requirements of each application. This review presents a comprehensive review of synthesis conditions and process parameters in tailoring aerogel properties. The effective parameters from the dissolution of the precursor step to the supercritical drying step, including the carbonization process for carbon aerogels, are investigated from the studies reported in the literature.

Development of starch-based amorphous CoOx self-supporting carbon aerogel electrocatalyst for hydrogen evolution

Hydrogen energy is turning into a major research topic in this complex and changing world. In recent years, more and more research has been done on transition metal oxides and biomass composites. In this study, potato starch and amorphous cobalt oxide were assembled into carbon aerogel by sol-gel method and high-temperature annealing (CoOx/PSCA). The connected porous structure of the carbon aerogel is conducive to HER mass transfer, and its structure can avoid the agglomeration of transition metals. It also has great mechanical properties and can be directly used as a self-supporting catalyst for electrolysis with 1 M KOH for hydrogen evolution, which showed excellent HER activity and yielded the effective current density of 10 mA cm^-2 at 100 mV overpotential. Electrocatalytic experiments further showed that the better performance of CoOx/PSCA for HER can be attributed to the high electrical conductivity of carbon and the synergistic effect of unsaturated catalytic sites on the amorphous CoOx cluster. The catalyst comes from a wide range of sources, is easy to produce, and has good long-term stability, so it can be used in large-scale production. This paper provides a simple and easy method to make biomass-based transition metal oxide composites for electrolyzing water to produce hydrogen.

Development of highly reusable, mechanically stablecorn starch-based aerogel using glycerol for potential application in the storage of fresh spinach leaves

Impact of glycerol on the physico-functional, morphological, mechanical, and rehydration properties ofcorn starch-based aerogel has been investigated. The aerogel was prepared from hydrogel (sol-gel method) using solvent exchange and supercritical CO₂ drying. Glycerol-infused aerogel had a more connected, denser structure (0.38-0.45 g/cm³), enhanced hygroscopic behavior, and was reusable up to eight times in terms of its capacity to absorb water after being drawn from the soaked sample. However, the inclusion of glycerol reduced the aerogel's porosity (75.89-69.91 %) and water absorption rate (WAR; 118.53-84.64 %) but enhanced its percentage shrinkage (75.03-77.99 %) and compressive strength (26.01-295.06 N). The most effective models for describing the rehydration behavior of aerogel were determined to be the Page, Weibull, and Modified Peleg models. Glycerol addition improved the internal strength of the aerogel so could be recycled without significant change in the physical characteristics of the aerogel. By effectively eliminating the condensed moisture that was developed inside the packing owing to the transpiration of fresh spinach leaves, the aerogel extended the storage life of the leaves by up to eight days. The glycerol-based aerogel has the potential to be employed as a carrier matrix for various chemicals and a moisture scavenger.

Insights on Some Polysaccharide Gel Type Materials and Their Structural Peculiarities

Global resources have to be used in responsible ways to ensure the world's future need for advanced materials. Ecologically friendly functional materials based on biopolymers can be successfully obtained from renewable resources, and the most prominent example is cellulose, the well-known most abundant polysaccharide which is usually isolated from highly available biomass (wood and wooden waste, annual plants, cotton, etc.). Many other polysaccharides originating from various natural resources (plants, insects, algae, bacteria) proved to be valuable and versatile starting biopolymers for a wide array of materials with tunable properties, able to respond to different societal demands. Polysaccharides properties vary depending on various factors (origin, harvesting, storage and transportation, strategy of further modification), but they can be processed into materials with high added value, as in the case of gels. Modern approaches have been employed to prepare (e.g., the use of ionic liquids as "green solvents") and characterize (NMR and FTIR spectroscopy, X ray diffraction spectrometry, DSC, electronic and atomic force microscopy, optical rotation, circular dichroism, rheological investigations, computer modelling and optimization) polysaccharide gels. In the present paper, some of the most widely used polysaccharide gels will be briefly reviewed with emphasis on their structural peculiarities under various conditions.

Fabrication of Carbon Aerogels Derived from Metal-Organic Frameworks/Carbon Nanotubes/Cotton Composites as an Efficient Sorbent for Sustainable Oil–Water Separation

Due to the continuous occurrence of water pollution problems, practical separation methods for oil–water mixtures have attracted more and more attention. To date, different kinds of materials have been developed with good hydrophobic properties and strong separation ability. Carbon aerogels, as a promising ideal adsorbent for dealing with oil-spill accidents, have received extensive attention. In this work, zeolitic imidazolate frameworks (ZIFs), nanoparticles, and carbon nanotubes (CNTs) in the three-dimensional (3D) interconnected network structure of cotton balls (CBs) were successfully prepared by a simple and scalable process. The as-prepared carbonized CBs with carbonized ZIF-8 and CNTs (CZIF-8/CNTs/CCBs) were characterized. The oil–water separation performance of the composite was also measured. The results show that the ZIF-8 clusters intercalated with abundant CNTs are fully loaded into the porous structure of the CBs after the in situ synthesis process. Additionally, ZIF-8/CNTs/CBs was carbonized in nitrogen, leading to the formation of CZIF-8/CNTs/CCBs. The prepared material possesses excellent hydrophobicity with a water contact angle of 152.7°, showing good absorption capacities Q1 in the range of 48 to 84 times its original weight for oil and organic liquids. In addition, CZIF-8/CNTs/CCBs exhibits good recyclability in the absorption–distillation test. In summary, this study proposes a novel and simple method for the preparation of a superhydrophobic material that could have wide application in the separation of oil–water mixtures.

Ultrahigh-strength carbon aerogels for high temperature thermal insulation

Carbon aerogels with nanoporous structure are attractive for thermal insulation under extreme conditions, but their practical applications are usually plagued by the inherent brittleness and easy-oxidation characteristic at high temperature. Herein, silica-modified carbon aerogels (SCAs) with extraordinarily high strength are prepared via a facile sol-gel polymerization of phenolic resin and siloxane, followed by ambient pressure drying and carbonization. The resulting SCAs possess medium-high density of ∼0.5 g·cm^-3 and mesoporous structure with the mean pore size of 33 nm. During carbonization process, the siloxane could be gradually transformed into the amorphous SiO₂ particles and crystalline SiC particles, which are coated on the surface of carbon nanoparticle and consequently improve the oxidation-resistance of carbon aerogels. Due to the density-porosity trade-off, the SCAs have high compressive strength of 10.0 MPa and satisfied thermal conductivities of 0.118 W·m^-1·K^-1 at 25 °C and 0.263 W·m^-1·K^-1 at 1000 °C. Furthermore, needled carbon fiber-reinforced SCAs (CF-SCAs) with ultrahigh compressive strength of 210.5 MPa are prepared, which exhibit good thermal conductivities of 0.207 W·m^-1·K^-1 at 25 °C and 0.407 W·m^-1·K^-1 at 1000 °C. The ultrahigh mechanical strength, good oxidation-resistance, good thermal insulation as well as the facile preparation make the SACs great promising in high-temperature insulations especially under harsh conditions.

Freestanding Nitrogen-Doped Carbons with Hierarchical Porosity for Environmental Applications: A Green Templating Route with Bio-Based Precursors

Powdery hierarchical porous carbons serve as cost-effective, functional materials in various fields, namely energy storage, heterogeneous catalysis, electrochemistry, and water/wastewater treatment. Such powdered activated carbons (PAC) limit new module designs and require further preparation steps, for example, adding polymeric binders, to be shaped into a standalone geometry. Polymeric binders, however, can block PACs' catalytic and active sites and, more importantly, pose the risk of secondary pollution for environmental purposes, especially in the context of clean water supply. This study introduces a novel synthesis method for fabricating freestanding nitrogen-doped carbons with hierarchical porosity using chitosan and sucrose as green precursors. Chitosan supplies nitrogen and acts as a backbone, giving a freestanding geometry to the final product, and sucrose is a carbon-rich precursor. The proposed method employs ice- and hard-templating for macropores and mesopores and combines carbonization and activation steps with no required activating agent. Final freestanding carbons function as adsorbents for removing persistent pollutants, as binder-free electrodes with high specific surface area and capacitive current, and as tubular gas diffusion electrodes for oxygen reduction reactions. These freestanding carbons enable new module designs and can be scaled-up by numbering-up, serving as bio-based functional materials for a wide range of applications involving porous heteroatom-doped carbons.

Aerogels as promising materials for antibacterial applications: a mini-review

The increasing cases of bacterial infections originating from resistant bacteria are a serious problem globally and many approaches have been developed for different purposes to treat bacterial infections. Aerogels are a novel class of smart porous materials composed of three-dimensional networks. Recently, aerogels with the advantages of ultra-low density, high porosity, tunable particle and pore sizes, and biocompatibility have been regarded as promising carriers for the design of delivery systems. Recently, aerogels have also been provided with antibacterial activity through loading of antibacterial agents, incorporation of metal/metal oxides and via surface functionalization and coating with various functional groups. In this mini-review, the synthesis of aerogels from both conventional and low-cost precursors is reported and examples of aerogels displaying antibacterial properties are summarized. As a result, it is clear that the encouraging antibacterial performance of aerogels promotes their use in many antibacterial applications, especially in the food industry, pharmaceutics and medicine.

Ultralight-Weight Graphene Aerogels with Extremely High Electrical Conductivity

The integration of 2D graphene sheets into a porous and macroscopic structure is extremely attractive for application in several electrochemical fields. In this regard, for the first time, the synthesis of 3D graphene aerogels is reported by using a rapid, easy, cost-effective, and scalable at industrial level methodology. These aerogels integrate the intrinsic properties of graphene with a high pore volume. To achieve this ultraporous graphene network, resorcinol/formaldehyde polymer with controllable porosity is employed as a binder and a cross-linker material, and a graphene oxide solution provides the graphene building blocks. Two series of materials with and without catalyst for resorcinol/formaldehyde reaction and with different synthesis conditions and graphene contents are studied. The resulting graphene aerogels present low density, large macroporosity, and electrical conductivity values as high as 852 S m^-1 , with 97.58% of porosity, which is the highest value of electrical conductivity reported so far in the literature for ultralight-weight graphene aerogels.

Recent advances in lignin-based porous materials for pollutants removal from wastewater

Water pollution is one of the most serious threats facing mankind today and has obtained widespread attention. Significant advances have been made in the past decades to apply porous materials in wastewater treatment, due to their large specific surface areas (S_BET) for interaction with the aimed ions or molecules. However, the majority of porous materials are prepared from fossil-based resources and still possess some drawbacks, such as high cost and non-degradability, which inevitably cause secondary pollution to the environment from their production to disposal. Lignin is the most abundant and the only scalable renewable aromatic resource on earth. Due to its unique physicochemical properties including high carbon content, plentiful functional groups and environmental friendliness, the lignin-based porous materials (LPMs) have shown promising prospects in efficient removal of soluble pollutants from wastewater. In this review, we firstly described the structural and chemical basis of LPMs, following presented the recent progress in the decontamination of heavy metal ions, organic dyes, antibiotics, anions and radionuclides from aqueous systems. Additionally, the outlook was provided to promote more practical implementation of LPMs in the near future.

Sucrose-derived N-doped carbon xerogels as efficient peroxydisulfate activators for non-radical degradation of organic pollutants

Metal-free activation of peroxydisulfate (PDS) for degrading organic pollutants in water has received increasing attention because it can prevent secondary pollution. However, most of the catalysts that are efficient are derived from non-renewable fossil resources, are very expensive and have complex preparation processes. Also, the emerging non-radical mechanism is still unclear. Herein, 3D sucrose-derived N-doped carbon xerogels (NCXs) were synthesized by a simple and sustainable hydrothermal process and then employed as novel metal-free PDS activators to degrade organic pollutants. The structure, composition and performance of NCXs were regulated by changing the carbonization temperature. The sample carbonized at 900 °C (NCX900) exhibited the best catalytic performance, completely removing bisphenol A in 60 min. Quenching experiments and linear sweep voltammograms demonstrated that PDS was activated mainly through an electron-transfer non-radical mechanism. It was found that graphitic N played a critical role in activating PDS. With this non-radical mechanism, the NCX900/PDS system could adapt well to the wide pH range (3-11) and high Cl^- concentration; it selectively oxidized organic pollutants with low ionization potentials. This work provides a sustainable approach to the low-cost and efficient metal-free catalysts for wastewater treatment.

Farrow-derived layered porous carbon aerogel for AP catalytic thermal decomposition

We extract natural fibers from waste palm bamboo leaves to prepare a composite carbon aerogel. This is a new type of environmentally friendly catalyst that shows excellent catalytic performance for the thermal decomposition of ammonium perchlorate.

Mesoporous Carbons from Polysaccharides and Their Use in Li-O2 Batteries

Previous studies have demonstrated that the mesoporosity of carbon material obtained by the Starbon^® process from starch-formed by amylose and amylopectin can be tuned by controlling this ratio (the higher the amylose, the higher the mesoporosity). This study shows that starch type can also be an important parameter to control this mesoporosity. Carbons with controlled mesoporosity (V_meso from 0.1–0.7 cm³/g) have been produced by the pre-mixing of different starches using an ionic liquid (IL) followed by a modified Starbon^® process. The results show that the use of starch from corn and maize (commercially available Hylon VII with maize, respectively) is the better combination to increase the mesopore volume. Moreover, “low-cost” mesoporous carbons have been obtained by the direct carbonization of the pre-treated starch mixtures with the IL. In all cases, the IL can be recovered and reused, as demonstrated by its recycling up to three times. Furthermore, and as a comparison, chitosan has been also used as a precursor to obtain N-doped mesoporous carbons (5.5 wt% N) with moderate mesoporosity (V_meso = 0.43 cm³/g). The different mesoporous carbons have been tested as cathode components in Li-O₂ batteries and it is shown that a higher carbon mesoporosity, produced from starch precursor, or the N-doping, produced from chitosan precursor, increase the final battery cell performance (specific capacity and cycling).

Advances in Manufacturing Composite Carbon Nanofiber-Based Aerogels

This article provides an overview on manufacturing composite carbon nanofiber-based aerogels through freeze casting technology. As known, freeze casting is a relatively new manufacturing technique for generating highly porous structures. During the process, deep cooling is used first to rapidly solidify a well-dispersed slurry. Then, vacuum drying is conducted to sublimate the solvent. This allows the creation of highly porous materials. Although the freeze casting technique was initially developed for porous ceramics processing, it has found various applications, especially for making aerogels. Aerogels are highly porous materials with extremely high volume of free spaces, which contributes to the characteristics of high porosity, ultralight, large specific surface area, huge interface area, and in addition, super low thermal conductivity. Recently, carbon nanofiber aerogels have been studied to achieve exceptional properties of high stiffness, flame-retardant and thermal-insulating. The freeze casting technology has been reported for preparing carbon nanofiber composite aerogels for energy storage, energy conversion, water purification, catalysis, fire prevention etc. This review deals with freeze casting carbon nanofiber composite materials consisting of functional nanoparticles with exceptional properties. The content of this review article is organized as follows. The first part will introduce the general freeze casting manufacturing technology of aerogels with the emphasis on how to use the technology to make nanoparticle-containing composite carbon nanofiber aerogels. Then, modeling and characterization of the freeze cast particle-containing carbon nanofibers will be presented with an emphasis on modeling the thermal conductivity and electrical conductivity of the carbon nanofiber network aerogels. After that, the applications of the carbon nanofiber aerogels will be described. Examples of energy converters, supercapacitors, secondary battery electrodes, dye absorbents, sensors, and catalysts made from composite carbon nanofiber aerogels will be shown. Finally, the perspectives to future work will be presented.

The Renewable and Sustainable Conversion of Chitin into a Chiral Nitrogen-Doped Carbon-Sheath Nanofiber for Enantioselective Adsorption

Well-known hard-template methods for nitrogen (N)-doped chiral carbon nanomaterials require complicated construction and removal of the template, high-temperature pyrolysis, harsh chemical treatments, and additional N-doping processes. If naturally occurring chiral nematic chitin nanostructures [(C₈ H₁₃ NO₅ )_n ] in exoskeletons were wholly transformed into an N-doped carbon, this would be an efficient and sustainable method to obtain a useful chiral nanomaterial. Here, a simple, sacrificial-template-free, and environmentally mild method was developed to produce an N-doped chiral nematic carbon-sheath nanofibril hydrogel with a surface area >300 m²  g^-1 and enantioselective properties from renewable chitin biomass. Calcium-saturated methanol physically exfoliated bulk chitin and produced a chiral nematic nanofibril hydrogel. Hydrothermal treatment of the chiral chitin hydrogel at 190 °C produced an N-doped chiral carbon-sheath nanofibril hydrogel without N-doping. This material preferentially adsorbed d-lactic acid over l-lactic acid and produced 16.3 % enantiomeric excess of l-lactic acid from a racemic mixture.

Sustainable Graphene Aerogel as an Ecofriendly Cell Growth Promoter and Highly Efficient Adsorbent for Histamine from Red Wine

The utilization of a sustainable and lightweight graphene aerogel (GA), synthesized from crude biomass, as a cell growth promoter and an adsorbent for the efficient removal of histamine (HIS), a food toxicant, from the real food matrix has been explored. Due to the self-supported three-dimensional nanoporous honeycomb-like structure of the graphene framework and the high surface area, the synthesized GA achieved an 80.69 ± 0.89% removal of HIS from red wine (spiked with HIS) after just 60 min under both acidic (3.0) and neutral (7.4) pH conditions. Furthermore, simple cleaning with 50% ethanol and deionized water, without any change in weight, allowed them to be reused more than 10 times with a still significant HIS removal ability (more than 71.6 ± 2.57%). In vitro cell culture experiments demonstrated that the synthesized GA had nontoxic effects on the cell viability (up to 80.35%) even at higher concentrations (10 mg mL^-1), as determined via the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and lactate dehydrogenase assays using human lung bronchial epithelial cells. Interestingly, GA promotes the wound-healing ability on the scratched epithelial cell surfaces via enhancing the cell migrations as also validated by the western blot analysis via expression levels of epithelial β-catenin and E-cadherin proteins. The distinct structural advantage along with the nontoxicity of the green synthesized GA will not only facilitate the economic feasibility of the synthesized GA for its practical real-life applications in liquid toxin and pollutant removal from the food and environment but also broaden its applicability as a promising biomaterial of choice for biomedical applications.

Polysaccharide-derived mesoporous materials (Starbon®) for sustainable separation of complex mixtures

The recovery and separation of high value and low volume extractives are a considerable challenge for the commercial realisation of zero-waste biorefineries. Using solid-phase extractions (SPE) based on sustainable sorbents is a promising method to enable efficient, green and selective separation of these complex extractive mixtures. Mesoporous carbonaceous solids derived from renewable polysaccharides are ideal stationary phases due to their tuneable functionality and surface structure. In this study, the structure-separation relationships of thirteen polysaccharide-derived mesoporous materials and two modified types as sorbents for ten naturally-occurring bioactive phenolic compounds were investigated. For the first time, a comprehensive statistical analysis of the key molecular and surface properties influencing the recovery of these species was carried out. The obtained results show the possibility of developing tailored materials for purification, separation or extraction, depending on the molecular composition of the analyte. The wide versatility and application span of these polysaccharide-derived mesoporous materials offer new sustainable and inexpensive alternatives to traditional silica-based stationary phases.

New and Advanced Porous Carbon Materials in Fine Chemical Synthesis. Emerging Precursors of Porous Carbons

The efficiency of porous carbons in fine chemical synthesis, among other application fields, has been demonstrated since both the porous structure and chemical surface provide the appropriated chemical environment favoring a great variety of relevant chemical transformations. In recent years, metal organic frameworks (MOFs) and covalent organic frameworks (COFs) have emerged as interesting opportunities in the preparation of porous carbons with improved physico-chemical properties. Direct calcination of MOFs or COFs, in the presence or not of others carbon or heteroatom sources, could be considered an easy and practical approach for the synthesis of highly dispersed heteroatom-doped porous carbons but also new porous carbons in which single atoms of metallic species are present, showing a great development of the porosity; both characteristics of supreme importance for catalytic applications. The goal of this review is to provide an overview of the traditional methodologies for the synthesis of new porous carbon structures together with emerging ones that use MOFs or COFs as carbon precursors. As mentioned below, the catalytic application in fine chemical synthesis of these kinds of materials is at present barely explored, but probably will expand in the near future.

Crucial Factors for the Application of Functional Nanoporous Carbon-Based Materials in Energy and Environmental Applications

This special issue of C—Journal of Carbon Research is dedicated to “Functional Nanoporous Carbon-Based Materials”. It contains contributions reporting on the synthesis of nanoporous carbons for the adsorption of proteins, their applications in electrochemical energy storage/conversion, and on the characterization/modification of their surface chemistry. Nanoporous carbon-based materials are widely researched, but at the same time, the field is still full of unutilized potential. The atomic construction of the carbon framework, pore sizes, pore geometries, presence of heteroatoms, particle size and shape, and many other “internal screws” are available; in the end, the high potential of carbon-based materials will only be fully explored if the interplay of these crucial factors is precisely controlled. This article is a summary of what we consider important for future targeted improvement of porous carbon nanomaterials for energy and environmental applications.

Emerging Carbon-Nanofiber Aerogels: Chemosynthesis versus Biosynthesis

Carbon aerogels that are typically prepared using sol-gel chemistry have unique three dimensional networks of interconnected nanometer-sized particles and thus exhibit many fascinating physical properties and great application potentials in widespread fields. To boost the practical applications, it is necessary to develop efficient and low-cost methods to produce high-performance carbon aerogels on a large-scale, preferably in a sustainable way. In 2012, two new classes of aerogels consisting of carbon-nanofiber (CNF) networks were prepared from biomass-derived precursors by chemosynthesis (i.e. template-directed hydrothermal carbonization of carbohydrate) and biosynthesis (i.e. use of bacterial cellulose as precursor), respectively. This Review gives a critical overview of this emerging and rapidly developing field, focusing on the synthetic strategies of the carbon-nanofiber aerogels and their outstanding physical properties. We also discuss the multifunctional application potentials of the two sorts of carbon aerogels and their nanocomposites, and highlight the challenges and future opportunities in this field.

Cellulose Aerogels: Synthesis, Applications, and Prospects

Due to its excellent performance, aerogel is considered to be an especially promising new material. Cellulose is a renewable and biodegradable natural polymer. Aerogel prepared using cellulose has the renewability, biocompatibility, and biodegradability of cellulose, while also having other advantages, such as low density, high porosity, and a large specific surface area. Thus, it can be applied for many purposes in the areas of adsorption and oil/water separation, thermal insulation, and biomedical applications, as well as many other fields. There are three types of cellulose aerogels: natural cellulose aerogels (nanocellulose aerogels and bacterial cellulose aerogels), regenerated cellulose aerogels, and aerogels made from cellulose derivatives. In this paper, more than 200 articles were reviewed to summarize the properties of these three types of cellulose aerogels, as well as the technologies used in their preparation, such as the sol⁻gel process and gel drying. In addition, the applications of different types of cellulose aerogels were also introduced.

Advanced Materials through Assembly of Nanocelluloses

There is an emerging quest for lightweight materials with excellent mechanical properties and economic production, while still being sustainable and functionalizable. They could form the basis of the future bioeconomy for energy and material efficiency. Cellulose has long been recognized as an abundant polymer. Modified celluloses were, in fact, among the first polymers used in technical applications; however, they were later replaced by petroleum-based synthetic polymers. Currently, there is a resurgence of interest to utilize renewable resources, where cellulose is foreseen to make again a major impact, this time in the development of advanced materials. This is because of its availability and properties, as well as economic and sustainable production. Among cellulose-based structures, cellulose nanofibrils and nanocrystals display nanoscale lateral dimensions and lengths ranging from nanometers to micrometers. Their excellent mechanical properties are, in part, due to their crystalline assembly via hydrogen bonds. Owing to their abundant surface hydroxyl groups, they can be easily modified with nanoparticles, (bio)polymers, inorganics, or nanocarbons to form functional fibers, films, bulk matter, and porous aerogels and foams. Here, some of the recent progress in the development of advanced materials within this rapidly growing field is reviewed.

Nanocellulose: a promising nanomaterial for advanced electrochemical energy storage

Nanocellulose has emerged as a sustainable and promising nanomaterial owing to its unique structures, superb properties, and natural abundance. Here, we present a comprehensive review of the current research activities that center on the development of nanocellulose for advanced electrochemical energy storage. We begin with a brief introduction of the structural features of cellulose nanofibers within the cell walls of cellulose resources. We then focus on a variety of processes that have been explored to fabricate nanocellulose with various structures and surface chemical properties. Next, we highlight a number of energy storage systems that utilize nanocellulose-derived materials, including supercapacitors, lithium-ion batteries, lithium-sulfur batteries, and sodium-ion batteries. In this section, the main focus is on the integration of nanocellulose with other active materials, developing films/aerogel as flexible substrates, and the pyrolyzation of nanocellulose to carbon materials and their functionalization by activation, heteroatom-doping, and hybridization with other active materials. Finally, we present our perspectives on several issues that need further exploration in this active research field in the future.

Self-Sacrificial Salt Templating: Simple Auxiliary Control over the Nanoporous Structure of Porous Carbon Monoliths Prepared through the Solvothermal Route

The conventional sol-gel method for preparing porous carbons is tedious and high-cost to prepare porous carbons and the control over the nanoporous architecture by solvents and carbonization is restricted. A simple and novel self-sacrificial salt templating method was first presented to adjust the microporous structure of porous carbon monoliths synthesized via the solvothermal method. Apart from good monolithic appearance, the solvothermal route allowed for ambient drying because it made sure that the polymerization reaction was completed quickly and thoroughly. The intact and crack-free porous carbon monoliths were investigated by scanning electron microscopy (SEM), thermogravimetric differential scanning calorimetry (TG-DSC), Fourier transform infrared (FT-IR), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and nitrogen sorption measurements. It was proven that the self-sacrificial salts NH₄SCN had been removed during pyrolyzing and so, porous carbon monoliths could be directly obtained after carbonization without the need of washing removal of salts. Most importantly, the microporous specific surface area of the resultant porous carbon monoliths was dramatically increased up to 770 m²/g and the Brunauer–Emmett–Teller (BET) specific surface area was up to 1131 m²/g. That was because the salts NH₄SCN as self-sacrificial templating helped to form more around 0.6 nm, 0.72 nm and 1.1 nm micropores. The self-sacrificial salt templating is also a suitable and feasible method for controlling the nanoporous structure of other porous materials.

Wheat flour-derived N-doped mesoporous carbon extrudate as superior metal-free catalysts for acetylene hydrochlorination

The As metal free catalysts, the wheat flour/gluten derived granular N-doped mesoporous carbons featured superior catalytic performance for acetylene hydrochlorination.

Reductive mineralization of cellulose with vanadium, iron and tungsten chlorides and access to MxOy metal oxides and MxOy/C metal oxide/carbon composites

M_xO_y and M_xO_y/C composites (M=V, Fe and W) were obtained by mineralization of cellulose with several metal chlorides. Cellulose was used both as a templating agent and as an oxygen and a carbon source. Soluble chloride molecules (VOCl₃ and WCl₆) and a poorly soluble ionic chloride compound (FeCl₃) were chosen as metal oxide precursors. In a first time, primary metal oxide/cellulose composites were obtained via a thermal treatment by reacting urea impregnated filter paper with the corresponding metal chlorides in an autoclave at 150°C after 3days. After either pyrolysis or calcination steps of these intermediate materials, interesting metal oxides with various morphologies were obtained (V₂O_5, V₂O₃, Fe₃O₄, WO_3, H_0.23WO₃), composites (V₂O₃/C) as well as carbides (hexagonal W₂C and WC, Fe₃C) This result highlight the reductive role that can play cellulose during the pyrolysis step that allows to tune the composition of M_xO_y/C composites. The materials were characterized by FTIR, Raman, TGA, XRD and SEM. This study highlights that cellulose can be used for a convenient preparation of a variety of highly demanded M_xO_y and M_xO_y/C composites with original shapes and morphologies.

Carbon-Based Functional Materials Derived from Waste for Water Remediation and Energy Storage

Carbon-based functional materials hold the key for solving global challenges in the areas of water scarcity and the energy crisis. Although carbon nanotubes (CNTs) and graphene have shown promising results in various fields of application, their high preparation cost and low production yield still dramatically hinder their wide practical applications. Therefore, there is an urgent call for preparing carbon-based functional materials from low-cost, abundant, and sustainable sources. Recent innovative strategies have been developed to convert various waste materials into valuable carbon-based functional materials. These waste-derived carbon-based functional materials have shown great potential in many applications, especially as sorbents for water remediation and electrodes for energy storage. Here, the research progress in the preparation of waste-derived carbon-based functional materials is summarized, along with their applications in water remediation and energy storage; challenges and future research directions in this emerging research field are also discussed.