Carbon-based Aerogels Research Articles

Adsorptive removal and recovery of organic pollutants from wastewater using waste paper-derived carbon-based aerogel

In this study, carbon-based aerogels derived from waste paper (CWP) were explored as an efficent adsorbent to remove organic pollutants including phenol (Ph) and 2-chlorophenol (2CP) from wastewater. CWP exhibited a highly porous structure and large specific surface area of 892 m2 g−1, which facilitated the adsorption of Ph and 2CP in wastewater. The adsorption behavior of Ph and 2CP on CWP could be well described by the pseudo-second-order kinetics and Langmuir isotherm models. Based on the Langmuir isotherm, the maximum adsorption capacities of CWP for Ph and 2CP were 238 and 278 mg g−1, respectively, and these values were much higher than those of other adsorbents. The removal of the organic pollutants mainly occurred through electrostatic attraction, pore-filling, hydrogen bonding, and π-π interactions. The CWP can be directly applied for the removal of Ph and 2CP at low concentration (<200 mg L−1) in the wastewater, while they can be used with additional pre-treatment for wastewater containing high concentration of organic pollutants. The adsorptive recovery of organic compounds and potential reuse of treated wastewater were also discussed. This work provides an efficient approach to produce effective adsorbent for the removal and recovery of chemicals from wastewater.

Highly Compressible, Thermally Conductive, yet Electrically Insulating Fluorinated Graphene Aerogel.

Carbon-based aerogels have drawn substantial attention for a wide scope of applications. However, the high intrinsic electrical conductivity limits their potential thermal management application in electronic packaging materials. Herein, a highly compressible, thermally conductive, yet electrically insulating fluorinated graphene aerogel (FGA) is developed through a hydrofluoric acid-assisted hydrothermal process. The macroscopic-assembled FGA constituting of tailored interconnected graphene networks with tunable fluorine coverage shows excellent elasticity and fatigue resistance for compression, despite a low density of 10.6 mg cm-3. Moreover, the aerogel is proved to be highly insulating, with the observed lowest electrical conductivity reaching 4 × 10-7 S cm-1. Meanwhile, the aerogel exhibits prominent heat dissipation performance in a typical cooling procedure, which can be used to fabricate thermoconductive polymer composites for electronic packaging.

Three-Dimensional Graphene Hybrid SiO2 Hierarchical Dual-Network Aerogel with Low Thermal Conductivity and High Elasticity

We describe lightweight three-dimensional (3D) graphene hybrid SiO2 aerogels (GSAs) with hierarchically robust interconnected networks fabricated via an in situ deposition procedure after a hydrothermal assembling strategy with graphene oxide sheets. The nano-/micron-thick SiO2 coating conformably grew over porous graphene templates with two constituents (e.g., graphene and SiO2) and formed chemically bonded interfaces. In addition, it significantly refined the primary graphene pores by hundreds of microns into smaller porous patterns. Studies of its mechanical properties verified that the graphene interframework made the ceramic composites elastic, while SiO2 deposition enhanced the strength required it to resist deformation. The higher SiO2 contents resulted in lower elasticity but larger strength because of the apparent nanosize effect of SiO2 ceramic thickness; GSAs with a density of 82.3–250.3 mg/cm3 (corresponding to SiO2 sol with concentration ranging from 5 to 20 wt %) could reach a good balance of strength and elasticity. Benefiting from hierarchical micronetworks consisting of semiclosed or closed pores, GSAs offer excellent thermal-insulation performance, with thermal conductivity as low as 0.026 W/(m·K). GSAs offer improved fire-resistant capacity rather than that of pure carbon-based aerogels via the synergic protection of SiO2 ceramic accretion. This highlights the promising applications of GSAs as lightweight thermal-shielding candidates for industrial equipment, civil architectures, and defense transportation vehicles.

Ultralight, flexible carbon hybrid aerogels from bacterial cellulose for strong microwave absorption

Carbon-based aerogels have demonstrated to have a great promise as advanced microwave absorption materials due to their ultralow volumetric density, unique pore structure, and high electrical conductivity. However, the comparatively complex fabrication process, weak machinability and difficulty in regulation of electromagnetic properties still hinder their large-scale application. Here, we reported a facile and scalable fabrication of novel carbon hybrid aerogels with adjustable electromagnetic properties from naturally abundant bacterial cellulose. Composed of robust network of ultrahigh-aspect-ratio metal/carbon nanofibers, the carbon hybrid aerogels exhibited combined characteristics of highly porous structure, ultralow density, physical flexibility and electromagnetic properties. As fillers of microwave absorption materials, the fabricated hybrid aerogels delivered strong microwave-absorbing ability with the minimum reflection loss of −70.1 dB even at the filler loading as low as 0.8 wt%, superior to previously reported carbon-based aerogels. Especially, the naturally unique surface chemistry and physical properties of bacterial cellulose provided the possibility of manipulating the microstructure and morphology of carbon hybrid aerogels in easy ways as demonstrated in this work, which can be utilized to optimize microwave absorption property and absorption band. Thus, biocarbon materials exhibit promising potential for meeting the increasing demand for scalable, high-efficiency and requirement-guided microwave absorption materials.

Versatile fabrication of anisotropic and superhydrophobic aerogels for highly selective oil absorption

Aerogels have shown great potential as oil absorbents, but they typically suffer from poor hydrophobicity and inferior mechanical property. Herein, anisotropic, superhydrophobic and superoleophilic fluorinated aerogels were prepared by directionally freeze-casting aqueous suspensions of graphene oxide and agarose in the presence of fluorine containing organosilane sol. The hydrogen bonding interactions between graphene oxide and agarose, and the directionally aligned porous structure gave the fluorinated aerogel prominent compression and recoverability properties. Due to its superoleophilicity, the fluorinated aerogel could collect a wide range of organic solvents and oils with excellent absorption capacities, which exceeded those of all cellulose-based aerogels and most carbon-based aerogels. The fluorinated aerogel also proved to be highly efficient in removing oil spills from water surface with outstanding selectivity due to its superhydrophobic and superoleophilic characteristics. Moreover, the high compression flexibility of the fluorinated aerogel facilitated fast and efficient recovery of the absorbed oil by simple mechanical squeezing, and ensured stable performance over repeated use. The present study provided a versatile method for design and fabrication of anisotropic, superhydrophobic and superoleophilic aerogels for environmental remediation and other potential applications.

Superelastic Hard Carbon Nanofiber Aerogels.

Superelastic carbon aerogels have been widely explored by graphitic carbons and soft carbons. These soft aerogels usually have delicate microstructures with good fatigue resistance but ultralow strength. Hard carbon aerogels show great advantages in mechanical strength and structural stability due to the sp3 -C-induced turbostratic "house-of-cards" structure. However, it is still a challenge to fabricate superelastic hard carbon-based aerogels. Through rational nanofibrous structural design, the traditional rigid phenolic resin can be converted into superelastic hard carbon aerogels. The hard carbon nanofibers and abundant welded junctions endow the hard carbon aerogels with robust and stable mechanical performance, including superelasticity, high strength, extremely fast recovery speed (860 mm s-1 ), low energy-loss coefficient (<0.16), long cycle lifespan, and heat/cold-endurance. These emerging hard carbon nanofiber aerogels hold a great promise in the application of piezoresistive stress sensors with high stability and wide detection range (50 kPa), as well as stretchable or bendable conductors.

PC-12 cells adhesion and differentiation on carbon aerogel scaffolds

Abstract

Green‐Synthesized Nitrogen‐Doped Carbon‐Based Aerogels as Environmentally Friendly Catalysts for Oxygen Reduction in Microbial Fuel Cells

AbstractA green approach to the synthesis of nitrogen‐doped, carbon‐based aerogels with good conductivity and catalytic properties is presented. With the aim to design an easily sustainable process, the starting precursors are selected from abundant waste‐related organic materials. The naturally derived polysaccharide agar acts as the carbon source in a water solution and an amino acid, glycine or lysine, is used as the nitrogen source. Using this synthesis approach, nitrogen defects are created in a 3D porous aerogel. They are shown to act as active catalytic sites for the reaction of oxygen reduction to water as demonstrated by electrochemical measurements. The best performing materials are tested as cathodes in microbial fuel cells for 50 days, in conditions close to those the device would face in a real environment. The glycine‐derived carbon aerogels with the higher content of pyridinic nitrogen exhibit the best performance, as confirmed by several morphological characterizations.

Controlled synthesis of flexible graphene aerogels macroscopic monolith as versatile agents for wastewater treatment

Emerging applications for environmental purification require agents that not only possess high decontamination efficiency, but also are capable of withstanding mechanical deformation without secondary pollution and degradation of performance. To this end, we have controlled synthesis of mechanically flexible graphene aerogel (GA) by vacuum freeze-drying of their hydrogel precursors obtained from heating the aqueous mixtures of graphene oxide (GO) and Vitamin C (VC) without stirring. Through the adaptable process conditions, such as the particle size of carbon, GO concentration, dosage of reducing agent and solution pH, the highly porous, ultralight and mechanically flexible GA are synthesized. Owing to the porous, robust and stable structure, the resulting GA show very promising performance in water purification including enrichment of organic liquid solvents (alcohols, oil and alkanes), removal of hexavalent chromium Cr(VI) and purified industrial wastewater, as well as flexible conductors. The successful creation of the GA may provide new insights into the design of carbon-based aerogels for various applications, as the GA can be prepared via a very simple procedure and available in macroscopic diverse morphologies with tunable porosity.

Highly compressible ultra-light anisotropic cellulose/graphene aerogel fabricated by bidirectional freeze drying for selective oil absorption

Low density aerogels are promising materials for oil absorption, but they typically suffer from low compressibility and elasticity. Herein, three-dimensional (3D) highly compressible, elastic, anisotropic, cellulose/graphene aerogels (CGAs) were prepared by bidirectional freeze drying. After the grafting of long carbon chains through chemical vapor deposition, the modified cellulose/graphene aerogels (MCGA) gained superhydrophobicity. The synergistic effects of flexible cellulose, stiff graphene, and the special bidirectionally aligned porous structure gave MCGA outstanding compression and recoverability properties. MCGA was able to recover 99.8% and 96.3% when compressed to 60% and 90% strain, respectively. Due to its ultra lightweight (bulk density of 5.9 mg/cm3) and high surface area (47.3 m2/g), MCGA possesses a remarkable absorption capacity of 80–197 times its weight, which surpasses all hydrophobic cellulose aerogels and most carbon-based aerogels. Furthermore, the high elasticity of MCGA facilitates fast and efficient recovery of the absorbed oil by simple mechanical squeezing, and ensures excellent performance stability over repeated use. The high compressibility and high oil recovery ability though mechanical squeezing has never been achieved by other aerogels. Hence, MCGA can serve as a promising super absorbent material for selective oil absorption and recovery.

Superhydrophobic Graphene/Cellulose/Silica Aerogel with Hierarchical Structure as Superabsorbers for High Efficiency Selective Oil Absorption and Recovery

Carbon-based aerogels have been recognized as a promising 3D superabsorbent material for oil absorption due to their high absorption capacity. However, their selective absorption efficiency is limited because of their relatively low hydrophobicity. Here, we report the fabrication of a fluorinated hybrid aerogel (FHA) consisting of graphene oxide (GO), cellulose nanofibrils (CNFs), and silica nanoparticles by one-pot hydrothermal synthesis and subsequent freeze-drying and chemical vapor deposition modification. The CNFs in FHA prevented volume shrinkage, greatly reduced the bulk density, and increased the surface area, while the GO retained its mechanical strength and the free-standing characteristic of FHA. Silica particles and CNFs created hierarchical structures on pore walls, and the grafted fluorochains reduced the surface energy. The synergistic effect of the hierarchical structure and low surface energy contributed to the excellent superhydrophobicity (water contact angle of 157°) and water repellen...

Ultralight Multifunctional Carbon-Based Aerogels by Combining Graphene Oxide and Bacterial Cellulose.

Nanostructured carbon aerogels with outstanding physicochemical properties have exhibited great application potentials in widespread fields and therefore attracted extensive attentions recently. It is still a challenge so far to develop flexible and economical routes to fabricate high-performance nanocarbon aerogels, preferably based on renewable resources. Here, ultralight and multifunctional reduced graphene oxide/carbon nanofiber (RGO/CNF) aerogels are fabricated from graphene oxide and low-cost, industrially produced bacterial cellulose by a three-step process of freeze-casting, freeze-drying, and pyrolysis. The prepared RGO/CNF aerogel possesses a very low apparent density in the range of 0.7-10.2 mg cm-3 and a high porosity up to 99%, as well as a mechanically robust and electrically conductive 3D network structure, which makes it to be an excellent candidate as absorber for oil clean-up and an ideal platform for constructing flexible and stretchable conductors.

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.

Always Look on the “Light” Side of Life: Sustainable Carbon Aerogels

The production of carbon aerogels based on the conversion of inexpensive and abundant precursors using environmentally friendly processes is a highly attractive subject in materials chemistry today. This article reviews the latest developments regarding the rapidly developing field of carbonaceous aerogels prepared from biomass and biomass-derived precursors, highlighting exciting and innovative approaches to green, sustainable nanomaterial synthesis. A review of the state-of-the-art technologies will be provided with a specific focus on two complimentary synthetic approaches developed upon the principles of green chemistry. These carbonaceous aerogel synthesis strategies, namely the Starbon and carbogel approaches, can be regarded as "top-down" and "bottom-up" strategies, respectively. The structural properties can be easily tailored by controlling synthetic parameters such as the precursor selection and concentration, the drying technique employed and post-synthesis temperature annealing. In addition to these parameters, the behavior of these sustainable carbon aerogel platforms in a variety of environmental and energy-related applications will also be discussed, including water remediation and fuel cell chemistry (i.e., the oxygen reduction reaction). This Review reveals the fascinating variety of highly porous, versatile, nanostructured, and functional carbon-based aerogels accessible through the highlighted sustainable synthetic platforms.

Original design of nitrogen-doped carbon aerogels from sustainable precursors: application as metal-free oxygen reduction catalysts

A new sustainable approach based on the hydrothermal carbonization of biomass-derivatives is reported for the synthesis of nitrogen-doped carbon-based aerogels. The catalyst-free hydrothermal treatment of both carbohydrate-based derivatives, i.e. glucose, D-glucosamine and/or N-acetyl-D-glucosamine, and phenolic compounds, i.e. phloroglucinol and/or cyanuric acid, led to highly porous monolithic gels. After pyrolysis under an inert atmosphere, conductive N-doped carbon aerogels were obtained, displaying nitrogen-doping levels of 3–5 wt% and BET surface areas of up to 450 m2 g−1. These original materials showed the first promising results as electrocatalysts for the oxygen reduction reaction and are expected to be used in a wide variety of fields, including for advanced energy conversion and storage devices.