Fabrication Of Aerogels Research Articles

Vitamin C-Assisted Fabrication of Aerogels from Industrial Graphene Oxide for Gaseous Hexamethyldisiloxane Adsorption

Volatile methyl siloxanes (VMSs) as a trace impurity in biogas decreases its energy utilization, and thus need to be removed. In this paper, a one-step hydrothermal reduction was performed to produce three-dimensional reduced graphene oxide aerogels (rGOAs) using industrial-grade graphene oxide (IGGO) as raw material and vitamin C (VC) as a reductant to facilitate the fabrication of rGOAs. The synthesis of rGOAs was a simple, green, and energy-efficient process. The developed rGOAs were characterized using the Brunauer–Emmett–Teller method, Raman spectrometry, scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction measurements and contact angle. The results obtained showed that rGOA-1 with a VC/IGGO ratio of 1/1 (m/m) exhibited a hierarchical porous structure and super-hydrophobicity, yielding a high specific surface area (137.9 m2 g−1) and superior water contact angle (143.8°). The breakthrough adsorption capacity of rGOA-1 for hexamethyldisiloxane (L2, a VMS model) was 11 times higher than that of IGGO. Low inlet concentration and bed temperature were considered beneficial for the L2 adsorption. Interestingly, rGOA-1 was less sensitive to water, and it was readily regenerated for reuse by annealing at 80 °C. The rGOAs have been demonstrated to have great potential for the removal of siloxanes from biogas.

Fabrication and modification of cellulose aerogels from Vietnamese water hyacinth for oil adsorption application

Fabrication and modification of cellulose aerogels from Vietnamese water hyacinth for oil adsorption application

Fabrication of aerogels from cellulose nanofibril grafted with β-cyclodextrin for capture of water pollutants

Fabrication of aerogels from cellulose nanofibril grafted with β-cyclodextrin for capture of water pollutants

Fabrication of chitin nanofiber-PDMS composite aerogels from Pickering emulsion templates with potential application in hydrophobic organic contaminant removal

Natural polymers have aroused increasing attention in water treatment but their application in removing hydrophobic organic contaminants (HOCs) was limited due to their hydrophilicity. Herein, hydrophobic aerogels were successfully fabricated from Pickering emulsions stabilized by chitin nanofibers (ChNF) with polydimethylsiloxane (PDMS) as dispersed phase and glutaraldehyde as a crosslinking agent, and their performance in HOCs removal were evaluated. The Pickering emulsions with PDMS ratios of 2.5–20% v/v showed high stability, demonstrating great potential as aerogel templates. The solidified PDMS droplets were evenly distributed within the matrix, contributing to homogeneous and permanent hydrophobicity. The composite aerogels with water contact angles of over 130° could selectively remove non-aqueous phase HOCs from water. The CCl4 adsorption capacity was 521–2820 wt%, depending on PDMS contents. Meanwhile, the mechanical resilience of the composite aerogels was significantly improved, facilitating the adsorbent regeneration by simple mechanical squeezing. The adsorption capacity remained above 85% for 24 cycles. Moreover, the aerogels could also remove dissolved HOCs from water with a maximum adsorption capacity of 1.34 mg/g for 10 mg/L TCE. This work reveals the potential of Pickering emulsions in the fabrication of composite hydrophobic materials from natural biopolymers with promising application in HOCs related water treatment.

High energy density and extremely stable supercapacitors based on carbon aerogels with 100% capacitance retention up to 65,000 cycles

In terms of ideal future energy storage systems, besides the always-pursued energy/power characteristics, long-term stability is crucial for their practical application. Here, we report a facile and sustainable strategy for the scalable fabrication of carbon aerogels with three-dimensional interconnected nanofiber networks and rationally designed hierarchical porous structures, which are based on the carbonization of bacterial cellulose assisted by the soft template of Zn-1,3,5-benzenetricarboxylic acid. As binder-free electrodes, they deliver a fundamentally enhanced specific capacitance of 352 F ⋅ g-1 at 1 A ⋅ g-1 in a wide potential window (1.2 V, 6 M KOH) in comparison with those of bacterial cellulose-derived carbons (178 F ⋅ g-1) and most activated carbons (usually lower than 250 F ⋅ g-1). The as-assembled supercapacitors exhibit an ultrahigh capacitance of 297 F ⋅ g-1 at 1 A ⋅ g-1, remarkable energy density (14.83 Wh ⋅ kg-1 at 0.60 kW ⋅ kg-1), and extremely high stability, with 100% capacitance retention for up to 65,000 cycles at 6 A ⋅ g-1, representing their superior energy storage performance when compared with that of state-of-the-art supercapacitors of commercial activated carbons and biomass-derived analogs.

A facile strategy to construct flexible and conductive silk fibroin aerogel for pressure sensors using bifunctional PEG

Silk fibroin (SF) has excellent biocompatibility and can be regenerated to obtain diverse materials. However, high brittleness and poor elasticity limit its applications in flexible devices, mainly due to high amounts of β-sheet structures in SF. Herein, a flexible SF aerogel is prepared by coupling polyethylene glycol (PEG) containing double-carboxyl end group with fibroin chains. This is followed by ammonium persulfate (APS)-initiated deposition of polypyrrole (PPy) units onto the scaffold. The bifunctional PEG not only improves the elasticity of SF aerogel, but it also promotes the accumulation of pyrrole cations on the fibroin surface and guides the formation of PPy. Meanwhile, PPy distributed in the SF matrix forms an electrically conductive pathway with an encouraging static conductivity, which is responsive to environmental humidity and external pressure. The sensitivity of the prepared SF-based conductive aerogel as a pressure sensor is much better than those reported in literature. Meanwhile, the stress and resistance show good synchronization during cyclic compressions. The present work provides a promising alternative for the fabrication of fibroin-based flexible and conductive aerogels as highly sensitive pressure sensors.

Polydopamine-mediated synthesis of Si@carbon@graphene aerogels for enhanced lithium storage with long cycle life

The application of Si as the anode materials for lithium-ion batteries (LIBs) is still severely hindered by the rapid capacity decay due to the structural damage caused by large volume change (> 300%) during cycling. Herein, a three-dimensional (3D) aerogel anode of Si@carbon@graphene (SCG) is rationally constructed via a polydopamine-assisted strategy. Polydopamine is coated on Si nanoparticles to serve as an interface linker to initiate the assembly of Si and graphene oxide, which plays a crucial role in the successful fabrication of SCG aerogels. After annealing the polydopamine is converted into N-doped carbon (N-carbon) coatings to protect Si materials. The dual protection from N-carbon and graphene aerogels synergistically improves the structural stability and electronic conductivity of Si, thereby leading to the significantly improved lithium storage properties. Electrochemical tests show that the SCG with optimized graphene content delivers a high capacity (712 mAh/g at 100 mA/g) and robust cycling stability (402 mAh/g at 1 A/g after 1500 cycles). Furthermore, the full cell using SCG aerogels as anode exhibits a reversible capacity of 187.6 mAh/g after 80 cycles at 0.1 A/g. This work provides a plausible strategy for developing Si anode in LIBs.

Facile Fabrication of Superhydrophobic Cross-Linked Nanocellulose Aerogels for Oil-Water Separation.

A facile and environmental-friendly approach was developed for the preparation of the cross-linked nanocellulose aerogel through the freeze-drying process and subsequent esterification. The as-prepared aerogel had a three-dimensional cellular microstructure with ultra-low density of 6.05 mg·cm−3 and high porosity (99.61%). After modifying by chemical vapor deposition (CVD) with hexadecyltrimethoxysilane (HTMS), the nanocellulose aerogel displayed stable super-hydrophobicity and super-oleophilicity with water contact angle of 151°, and had excellent adsorption performance for various oil and organic solvents with the adsorption capacity of 77~226 g/g. Even after 30 cycles, the adsorption capacity of the nanocellulose aerogel for chloroform was as high as 170 g/g, indicating its outstanding reusability. Therefore, the superhydrophobic cross-linked nanocellulose aerogel is a promising oil adsorbent for wastewater treatment.

A novel aerogel with forced thermoelastic deformation

In order to overcome the brittleness of traditional aerogels, we report the copolymer of polysiloxane as a precursor for the fabrication of high-performance aerogels. The copolymer of poly (methyl methacrylate-co-vinylmethyldimethoxysilane) was synthesized by radical copolymerization, using methyl methacrylate (MMA) and vinylmethyldimethoxysilane (VMDMS), and multifunctional silane compounds including the VMDMS, vinyltrimethoxysilane (VTMS) and tetraethyl orthosilicate (TEOS) were used to promote the formation of the cross-linked network. Our reported aerogels have excellent mechanical properties and stability. Moreover, the recovery of these aerogels can be improved by more than 14% after heat treatment, which can recover over 80% of the original height. The morphologies and microstructures of these co-polymer aerogels were characterized by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), Brunauer-Emmett-Teller (BET) and pore size distribution. The structural and chemical compositions were analyzed by 1H NMR spectra and Fourier transform infrared spectra (FTIR). The thermal analysis was evaluated by differential scanning calorimetric (DSC) and thermogravimetric analysis (TG), and the thermal insulation properties and the mechanical properties were determined by a thermal conductivity analyzer and uniaxial compression testing, respectively. The specific compressive strength of our reported aerogels is in the range of 6.99–27.70 MPa, the multi-point specific surface area is in the range of 752–1271 m2g-1, and thermal insulation performance is 0.030–0.061 W m−1 K−1. Finally, we suggest that radical copolymerization can also be employed for other co-polymer aerogels, including the monomers of CC double bonds.

Green fabrication of flexible aerogels from polypropylene fibers for heat insulation and oil/water separation

For the first time, hydrophobic polymer-based aerogels have been developed from polypropylene fibers for heat insulation and oil spill treatments. By physically cross-linking polypropylene fibers with non-toxic polyvinyl alcohol and carboxymethyl cellulose, followed by eco-friendly freeze–drying method, the fabricated aerogels exhibit an extremely low density of 0.024–0.054 g/cm3 and a high porosity of 94.71–97.82%. The developed polypropylene aerogels express excellent flexibility and good heat insulation with remarkably low compressive modulus and thermal conductivity of 27.54–58.58 kPa and 0.036–0.039 W/m.K, respectively. Experimental results have demonstrated that methyltrimethoxysilane-coated PP aerogels have great water repellency with a water contact angle of 123.5–133.8°. Therefore, they show a good maximum absorption capacity of 12.9–27.3 g/g for fuel oil, 10.2–24.5 g/g for 5w30 motor oil, and 10.2–23.5 g/g for diesel oil; these good characteristics are attributed to their porous hollow structure. Moreover, the oil absorption of polypropylene aerogels in this work is 5 times better than that of the previous one and equivalent to that of commercial absorbents and other polymer aerogels from plastics.

Marine biomass-derived composite aerogels for efficient and durable solar-driven interfacial evaporation and desalination

• Construction of an interfacial steam generator by using nanocellulose extracted from marine biomass. • Rational fabrication of nanocellulose-based aerogels as structural elements. • Realization of a 3D monolithic interfacial steam generator for efficient and durable solar evaporation. Solar-driven interfacial evaporation is an emerging and sustainable technology with growing potential for applications in water distillation and desalination. Despite the ongoing progress in clean water production, the high cost, delicate structures, leaching and disposal of synthetic materials remain the major roadblocks toward large-scale and real-world applications. Herein, nanocellulose (NC) is successfully extracted from abundant, inexhaustible and biodegradable biomass Ulva (Enteromorpha) prolifera that collected from the coast of Qingdao, China. Incorporation of polyvinyl alcohol (PVA) into the NC scaffolds and subsequent cross-linking endow the composite aerogels with efficient water diffusion, enhanced mechanical strength and good deformation resistance. The cross-linked composite aerogels can serve as main structural elements and integrate a monolithic, self-floating and durable steam generator. Under one sun, the good water evaporation rate of 1.4 kg m −2 h −1 is among the best-performing interfacial steam generators constructed by using cellulose-based materials as structural components. This study demonstrates a new concept of using marine (blue) biomass-derived NC as crude material and building block to construct high-performance and durable interfacial steam generators, synergistically considering clean water production and sustainability of marine ecosystems.

Facet-Dependent Long-Term Stability of Gold Aerogels toward Ethylene Glycol Oxidation Reaction.

In this work, a series of AuPNR6-50 aerogels with different percentages of {110} facets (from ∼12 to 36%) were controllably prepared and then used to investigate their performance (specific activity and long-term stability) toward ethylene glycol oxidation reaction (EGOR), in which PNR represents the particle number ratio of 6 nm Au NPs to 50 nm Au NPs. It is found that their specific activity and long-term stability highly depend on the sum of the percentage of the {100} and {111} facets and the percentage of {110} facets, respectively. In addition, Au246-50 aerogels with the highest percentage of {110} facets can possess excellent long-term stability (retaining about 95% of the initial current) but still have excellent specific activity (about 90.42 mA cm-2). Thus, the specific activity and long-time stability of AuPNR6-50 aerogels toward EGOR can be well balanced by controlling the proper percentage of {110} facets on their surfaces. Therefore, the successful fabrication of AuPNR6-50 aerogels with greatly improved long-term stability and excellent specific activity not only provides a novel method for the design of electrocatalysts but also would boost the commercial development of direct ethylene glycol fuel cells.

Polyimide aerogel with controlled porosity: Solvent-induced synergistic pore development during solvent exchange process

Despite intensive studies on polymer aerogels, the fabrication of polyimide aerogels mostly relies on supercritical drying; however, the development of suitable ambient or vacuum drying methods and a shortened solvent exchange process are important for industrial applications. This study highlights the effect of the solvent type used for the solvent exchange process on the porosity and pore structure of vacuum-dried polyimide aerogels. By combining two different solvents, we could achieve a much higher aerogel porosity than when using either solvent independently. This synergistic effect cannot be simply explained by the surface tension of the exchange solvent but is shown to be related to the solvent–polymer affinity, solvent-induced structural change during the solvent exchange process, and shrinkage behavior during the solvent exchange and drying processes. The pore structure and porosity are shown to be easily controllable by simply adjusting the solvent ratios. Moreover, the solvent exchange time is much shorter (~10 h) than that in previous reports on polyimide aerogels, which is highly beneficial for industrial application. The mechanical properties were highly dependent on the porosity and pore structure, and the relative permittivity could be adjusted in a wide range according to the controlled porosity. Together with high thermomechanical stability, various electronic applications are expected. Moreover, the idea proposed in this study is expected to serve as a useful guideline for the fabrication of various other polymer aerogels with efficient processability.

Arbitrary-shaped reduced graphene oxide aerogels via an unsaturated water vapor reduction

It still remains a challenge to explore facile, economic, and environmental friendly process for the fabrication of graphene aerogels with low density and high purity to meet the various applications. Herein, arbitrary-shaped reduced graphene oxide (rGO) aerogels are prepared by freeze-drying process and followed unsaturated water vapor reduction method staring from GO aqueous suspensions for the first time. Water vapor hydrothermal treatment can decompose all oxygen-containing functional groups in GO and repair GO surface defects effectivly. At higher temperatures (≥175 °C), the carbon in GO may react with water vapor via water-gas shift reaction to form CO, which could also be used as the reductant for the reduction of GO aerogels. The water volume as well as the temperature are key parameters for realizing high reduction degree as well as good shape control of rGO aerogels. Arbitrary shaped rGO aerogels could be prepared by using various molds for freezing GO suspensions. rGO aerogels exhibit a high oil/water separation performance, which could absorb various oils up to 40-55 times of its initial weight with high recyclability. Moreover, the rGO aerogels exhibit typical pressure sensing behavior and excellent energy storage capacitance, which hold great potential applications in flexible pressure sensors and supercapacitors.

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.

Multifunctional Inorganic Nanomaterial Aerogel Assembled into fSWNT Hydrogel Platform for Ultraselective NO2 Sensing.

Facile fabrication of multifunctional porous inorganic aerogels remains an outstanding challenge despite the considerable demand for extensive applications. Here, we present the production of a multifunctional porous inorganic nanomaterial aerogel by controllable surface chemistry of a functionalized SWNT (fSWNT) hydrogel platform for the first time. The versatile functional inorganic nanoparticles can be incorporated uniformly on the porous 3D fSWNT hydrogel platform through a facile dip coating method at ambient conditions. The morphology of the multifunctional inorganic aerogel is manipulated by designing the fSWNT hydrogel platform for different requirements of applications. In particular, Pt-SnO2@fSWNT aerogels exhibit high porosity and uniformly distributed ultrafine Pt and SnO2 on the fSWNT platform with controllable particle size (1.5-3.5 nm), which result in significantly high surface area (393 m2 g-1). The ultrafine Pt-SnO2@fSWNT aerogels exhibit highly sensitive (14.77% at 5 ppm) and selective NO2 sensing performance even at room temperature due to the increased active surface area and controllable porous structure of the ultrafine aerogel, which can provide fast transport and penetration of a target gas into the sensing layers. The newly designed multifunctional inorganic aerogel with ultrahigh surface area and high open porosity is a prospective materials platform of high performance gas sensors, which could be also broadly expanded to widespread applications including catalysis and energy storages.

A General and Programmable Synthesis of Graphene-Based Composite Aerogels by a Melamine-Sponge-Templated Hydrothermal Process

Three-dimensional (3D) graphene networks are performance boosters for functional nanostructures in energy-related fields. Although tremendous intriguing nanostructures-decorated 3D graphene network...

Facile synthesis of flexible and hydrophobic polymethylsilsesquioxane based silica aerogel via the co-precursor method and ambient pressure drying technique

The fragility, hydrophilicity and high cost fabrication of aerogels have limited their applications in industrial and civilian fields. Herein, we have described a method for preparing a novel flexible and hydrophobic silica aerogel by using the co-precursors method via ambient pressure drying technique. The optimal MTMS volume percentage is determined at 60%. The resulting aerogel obtains agglomerated particles with diameters at ~20–30 nm and mesopores at several tens of nanometers. The Si-C-H bond ratio maintains at 13. 36% after heat treatment at 300 °C, which results in the high water contact angle of 153.9°. Moreover, the 300 °C heat treated aerogel has a much more homogeneous microstructure with its BET specific surface area as large as 895.5 m2/g. The oxidation peak of -CH3 groups is observed at 492 °C. The aerogel exhibits an excellent flexibility under 50 compression cycles, as well as a superior thermal insulation property.

Solid waste and graphite derived solar steam generator for highly-efficient and cost-effective water purification

Utilizing the clean and renewable solar energy to generate steam for wastewater purification or seawater desalination is a promising solution to the worldwide scarcity of fresh water. Herein, we report a highly-efficient, eco-friendly and cost-effective solar steam generator based on ball-milling graphite and cellulose fiber from waste paper. Ball-milling graphite/cellulose fiber composite aerogels are facilely developed via a freeze casting-drying method, endowing a featured vertically aligned porous structure. The fabrication of composite aerogels and the construction of evaporation systems take full advantages of recycled materials, contributing to the low cost and solid waste reclamation. High porosity, strong solar absorption, hydrophilicity and low thermal conductivity of the composite aerogels collectively contribute to a splendid solar evaporation rate of water as high as 1.61 kg m−2 h−1, with photothermal efficiency of ~90% under one sun illumination (1 kW m−2). Quantitative studies reveal the effects of ball-milling graphite/cellulose fiber ratio, ball-milling graphite concentration and thickness of composite aerogels on the solar evaporation rates, suggesting the optimal design of composite aerogels. Furthermore, the cycling stability and the capability for seawater desalination as well as polluted water purification manifest the potential of the composite aerogels to purify diverse water. Outdoor tests show 8–13 L of fresh water could be produced daily by 1 m2 of composite aerogel.

Fabrication and properties of anisotropic polyimide aerogels with aligned tube‐like pore structure

ABSTRACTPolyimide (PI) aerogels with highly aligned tube‐like pores were fabricated by unidirectional ice crystal‐induced self‐assembly method. During this process, the mold bottom contacted with the freezing medium, the aqueous solution of poly(amic acid) (PAA) ammonium salt in the mold was unidirectionally frozen, the ice crystals grew from the bottom to top of PAA ammonium salt (PAS) solution along the freezing direction, which endowed PI aerogels with aligned tube‐like pores after sublimation of ice crystals and thermal imidization of PAS. The obtained aerogels had low densities (0.077–0.222 g cm−3) and high porosities (83.8–94.2%) and exhibited anisotropic morphology and properties. Their compression strength in vertical direction (parallel to freezing direction) was higher than that in horizontal direction (perpendicular to freezing direction). Their heat transport in horizontal direction was much slower than that in vertical direction; the aerogels had better thermal insulating property in horizontal direction. This facile approach contributed to prepare new type of PI aerogel materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48769.