Graphene-based Aerogels Research Articles

A Review of Nitrogen-Doped Graphene Aerogel in Electromagnetic Wave Absorption.

Graphene aerogels (GAs) possess a remarkable capability to absorb electromagnetic waves (EMWs) due to their favorable dielectric characteristics and unique porous structure. Nevertheless, the introduction of nitrogen atoms into graphene aerogels can result in improved impedance matching. In recent years, nitrogen-doped graphene aerogels (NGAs) have emerged as promising materials, particularly when combined with magnetic metals, magnetic oxides, carbon nanotubes, and polymers, forming innovative composite systems with excellent multi-functional and broadband absorption properties. This paper provides a comprehensive summary of the synthesis methods and the EMW absorption mechanism of NGAs, along with an overview of the absorption properties of nitrogen-doped graphene-based aerogels. Furthermore, this study sheds light on the potential challenges that NGAs may encounter. By highlighting the substantial contribution of NGAs in the field of EMW absorption, this study aims to facilitate the innovative development of NGAs toward achieving broadband absorption, lightweight characteristics, and multifunctionality.

Quantitative morphometry of topological graphene-based aerogels and carbon foams by x-ray micro-computed tomography

In this work, we report quantitative morphometry of freeze-dried graphene-based aerogels (i.e., graphene aerogel-GA, nitrogenated GA-NGA, graphene-carbon nanotube hybrid-Gr-MWCNTs, carbon foam-CF, and CF-GA hybrid-CF-GA) and monoliths, prepared by hydrothermal and organic sol-gel methods, respectively. X-ray micro-computed tomography (XMCT) in combination with scanning and transmission electron microscopy allowed visualization of internal microstructures in three-dimensional space. Quantitative morphometry analysis through the reconstructed volume renderings from two-dimensional sliced images revealed hierarchical structures possessing interlaced thin sheets, honeycomb organization, and topological interconnected pore background domains. The influence of small-diameter functionalized multi-walled carbon nanotubes (MWCNTs) inclusions to graphene-like sheets and integration with CF is assessed through quantitative morphometry analysis in terms of volume-weighted pore size, wall thickness, and porosity levels. Hybrid composite porous solids elucidated cross-linking reinforced by a homogeneous distribution of CNTs into complex sheets of GA and CF matrices. A consistent trend impacting porosity and interconnectedness was found following NGA ≥ GA > CF > Gr-MWCNT2:1 > CF-GA > Gr-MWCNT3:1 > Gr-MWCNT5:1, from XMCT image processing and analyses in corroboration with physical properties and reliability. The experimental results provide insights and guide the design of characteristic porous carbonaceous and graphene-based functional nanomaterials for energy sciences, environmental engineering, and fundamental reactive transport of fluids.

Nanolayered Ceramic-Confined Graphene Aerogel with Conformal Heterointerfaces for Low-Frequency Microwave Absorption.

Graphene-based aerogels have garnered considerable attention for their lightweight and efficient microwave absorption (MA) properties; however, optimizing the relationship between impedance matching and attenuation capability at low frequencies remains a challenge. In this study, a three-dimensional (3D) silicon carbonitride (SiCN) nanoceramic-coated graphene aerogel with conformal heterogeneous interfaces is constructed by precursor infiltration and pyrolysis to optimize MA performance at low frequencies. Thanks to the enhanced impedance matching and significant interfacial polarization of the two-dimensional sandwiched SiCN/graphene/SiCN cell walls and multiple scattering occurring within the 3D porous skeleton, the aerogel achieves a minimum reflection loss of -57.9 dB at an ultralow frequency of 4.92 GHz (C-band) and a broad bandwidth of 5.0 GHz at an ultralow thickness of 1.7 mm. The strategy developed here provides a method for enhancing dielectric polarization loss in graphene aerogels by the joint optimization of interfacial polarization and impedance matching, inspiring the design of high-performance graphene-based materials for low-frequency MA.

Highly Compressible, Light-Weight and robust Nitrogen-Doped graphene composite aerogel for sensitive pressure sensors

The demand for compressible multifunctional carbon aerogels with reliable mechanical properties and high response sensitivity has increased in the competitive smart electronics era. This study presents a novel nitrogen-doped graphene composite aerogel that exhibits exceptional robustness, elasticity, and lightweight characteristics. The synthesis involves combining dispersions of Graphene Oxide (GO), Dopamine (DA), and Polyaniline (PANI), followed by chemical reduction, crosslinking at 90 °C, freeze-drying, and thermal annealing. The incorporation of flexible DA with the graphene sheet enhances the composite gel’s toughness, while the π-π stacking interaction between PANI and the graphene sheet strengthens the aerogel framework. The resulting composite aerogel, named GDPA demonstrates outstanding strength, toughness, and compressibility due to the combined effects of DA and PANI. Furthermore, GDPA is assembled into a pressure sensor that exhibits excellent compressive cycle stability. The sensor achieves a low detection limit of 0 Pa and a wide detection range of 0 to 25.48 kPa, surpassing the performance of most previously reported graphene-based aerogels. The remarkable properties of GDPA suggest its immense potential for application in healthcare detection, wearable electronics, and intelligent packaging.

Synthesis of nitrogen-doped graphene-based binary composite aerogels for ultralightweight and broadband electromagnetic absorption

The development of ultralightweight and broadband electromagnetic wave (EMW) absorbing materials remains a big challenge. In this work, porous magnesium ferrite microspheres decorated nitrogen-doped reduced graphene oxide (NRGO/MgFe2O4) composite aerogels were prepared by a two-step route of solvothermal synthesis and hydrothermal self-assembly. Results of microscopic morphology characterization showed that NRGO/MgFe2O4 composite aerogels had a unique hierarchical porous structure. Moreover, the influence of additive amounts of graphene oxide on the electromagnetic parameters and EMW absorption properties of NRGO/MgFe2O4 composite aerogels was explored. Remarkably, the attained binary composite aerogel with the content of NRGO of 70.21 wt% exhibited the best EMW absorption performance. The minimum reflection loss reached up to −55.7 dB, and the corresponding effective absorption bandwidth was as large as 5.36 GHz at a thin matching thickness of 1.98 mm. Furthermore, when the matching thickness was slightly increased to 2.29 mm, the widest effective absorption bandwidth was enlarged to 7.1 GHz, covering the entire Ku-band. The magnetodielectric synergy and unique hierarchical porous structure in NRGO/MgFe2O4 composite aerogels not only improved the impedance matching, but also greatly enhanced the EMW absorption capacity. It was believed that the results of this work could be helpful for the preparation of graphene-based magnetic composites as broadband and efficient EMW absorbers.

Towards Understanding Aerogels’ Efficiency for Oil Removal—A Principal Component Analysis Approach

In this study, our aim was to estimate the adsorption potential of three families of aerogels: nanocellulose (NC), chitosan (CS), and graphene (G) oxide-based aerogels. The emphasized efficiency to seek here concerns oil and organic contaminant removal. In order to achieve this goal, principal component analysis (PCA) was used as a data mining tool. PCA showed hidden patterns that were not possible to seek by the bi-dimensional conventional perspective. In fact, higher total variance was scored in this study compared with previous findings (an increase of nearly 15%). Different approaches and data pre-treatments have provided different findings for PCA. When the whole dataset was taken into consideration, PCA was able to reveal the discrepancy between nanocellulose-based aerogel from one part and chitosan-based and graphene-based aerogels from another part. In order to overcome the bias yielded by the outliers and to probably increase the degree of representativeness, a separation of individuals was adopted. This approach allowed an increase in the total variance of the PCA approach from 64.02% (for the whole dataset) to 69.42% (outliers excluded dataset) and 79.82% (outliers only dataset). This reveals the effectiveness of the followed approach and the high bias yielded from the outliers.

Super-compressible and mechanically stable reduced graphene oxide aerogel for wearable functional devices

ABSTRACT The graphene-based aerogels with good electrical conductivity and compressibility have been reported. However, it is challenging to fabricate the graphene aerogel to have excellent mechanical stability for its application in wearable devices. Thus, inspired by macroscale arch-shaped elastic structures and the importance of crosslinking in microstructural stability, we synthesized the mechanically stable reduced graphene oxide aerogels with small elastic modulus by optimizing the reducing agent to make the aligned wrinkled microstructure in which physical crosslinking is dominant. We used L-ascorbic acid, urea, and hydrazine hydrate as reducing agents to synthesize the graphene aerogels rGO-LAA, rGO-Urea, and rGO-HH, respectively. Hydrazine hydrate was found to be best in enhancing the physical and ionic interaction among graphene nanoflakes to achieve a wavy structure with excellent fatigue resistance. Notably, the optimized rGO-HH aerogel maintained structural stability even after 1000 cycles of compression of 50% strain and decompression, showing 98.7% stress retention and 98.1% height retention. We also studied the piezoresistive properties of the rGO-HH aerogel and showed that the rGO-HH-based pressure sensor exhibited excellent sensitivity (~5.7 kPa−1) with good repeatability. Hence, a super-compressible and mechanically stable piezoresistive material for wearable functional devices was demonstrated by controlling the microstructure and surface chemistry of the reduced graphene oxide aerogel.

Construction of nitrogen-doped graphene-based ternary magnetic composite aerogel towards excellent electromagnetic absorption in the Ku-band

The development of advanced electromagnetic wave (EMW) absorbing materials with broad bandwidth, strong absorption, low filler loading ratio and small thickness remains a great challenge. In this work, nitrogen-doped reduced graphene oxide/multi-walled carbon nanotubes/hollow nickel ferrite (NRGO/MWCNTs/hollow NiFe2O4) ternary magnetic composite aerogel with the ultralow bulk density was synthesized via the two-step route of solvothermal synthesis and hydrothermal self-assembly. Results of microscopic morphology characterization showed that as-synthesized binary and ternary magnetic composite aerogels exhibited the special three-dimensional hierarchical porous network structure. Moreover, the EMW absorption performance of ternary composite aerogel was obviously enhanced in comparison with NRGO/MWCNTs and NRGO/hollow NiFe2O4 binary composite aerogels. Remarkably, the attained NRGO/MWCNTs/hollow NiFe2O4 ternary composite aerogel showed the maximum absorption bandwidth of 6.7 GHz (11.3–18.0 GHz) and robust absorbing intensity of − 42.8 dB at a thin matching thickness of 2.0 mm and a low loading ratio of 12.5 wt%. It was worth noting that when the matching thickness was slightly increased to 2.1 mm, the optimal minimum reflection loss could reach − 69.0 dB. The special hierarchical porous network structure and magnetodielectric synergy in the ternary composite aerogel optimized the impedance matching, and notably enhanced the EMW absorbing capacity. Therefore, this work could contribute to the construction of graphene-based hybrid nanocomposites as advanced EMW absorbers.

Exploring interfacial engineering in 3D porous, lightweight ZnFe2O4/rGO aerogel for electromagnetic wave absorption

Exploring interfacial engineering in metal oxide/reduced graphene oxide composite becomes a hotspot in the field of electromagnetic wave (EMW) absorption. In this work, three-dimensional (3D) porous ZnFe2O4/reduced graphene oxide (ZFO/rGO) composite aerogel was synthesized in situ by a hydrothermal reduction method combined with freeze-drying technique. The results reveal that dispersed ZFO nanoparticles (NPs) are bonded to defect-rich 3D conductive rGO skeleton in a bridging mode with Fe-O-C, resulting in enhanced conduction loss. Consequently, the defect-rich ZFO/rGO composite aerogel exhibits an outstanding EMW absorbing properties: a minimum reflection loss (RLmin) value of − 29.12 dB and an effective absorption bandwidth (EAB with RL less than −10 dB) of 3.57 GHz at an ultra-thin matching thickness of 1.51 mm. This work provides a new strategy for constructing defect-rich graphene-based composite aerogel as an efficient EMW absorbing materials.

Graphene-based aerogel microspheres with annual ring-like structures for broadband electromagnetic attenuation

Graphene aerogels have attracted extensive attention in electromagnetic protection due to lightweight and efficient microwave absorbing properties, but until now the design of its shape and structure is still a research hotspot. Herein, reduced graphene aerogel microspheres (CSA-RGO AMs) with annual ring structure with regular interlayer spacing are synthesized by wet spinning-chemical reduction-lyophilization. Due to the special chiral helical structure and electromagnetic cross-polarization, the impedance matching and attenuation ability of microspheres to electromagnetic waves are enhanced. The CSA-RGO AMs at a low load of 4 wt% can achieve the minimum reflection loss (RLmin) of − 63 dB with a thickness of 3.6 mm, and the effective absorption bandwidth (EAB) reaches 7.04 GHz. On this basis, we further obtain polyaniline@reduced graphene oxide microspheres (PANi@RGO AMs) with the same chiral helical structure through in-situ doping polymerization of polyaniline. Heterogeneous interfaces bring the interface polarization and enhance the reflection and scattering of electromagnetic waves. And the corresponding RLmin can reach − 48 dB when the thickness is only 2.8 mm, and the EAB remains 6.88 GHz. Therefore, the new strategy for constructing chiral structures proposed in this study provides a new idea for realizing high-performance electromagnetic wave absorption of graphene-based aerogel absorbers.

Construction of multi-dimensional NiCo/C/CNT/rGO aerogel by MOF derivative for efficient microwave absorption

The development of high-performance microwave absorption materials is currently imperative in order to solve the problem of electromagnetic pollution. Herein, we successfully obtained a multi-dimensional graphene-based aerogel (NiCo/C/CNT/rGO aerogel) decorated with one-dimensional carbon nanotubes (CNTs) and metal-organic framework (MOF) derivatives. The introduction of rGO aerogel significantly modifies the phase composition (NiCo/C/CNT and rGO) and hierarchical structure (1D CNT, 3D NiCo/C/CNT and rGO aerogel) of the composite, resulting in a multi-dimensional gradient, defects, heterogeneous interfaces, and superior microwave absorption properties. The optimum electromagnetic wave absorption performance of −58.8 dB is achieved at a filler loading of 20 wt%, with a thickness of 1.8 mm and an effective absorption bandwidth of 7.6 GHz, covering the entire Ku-band. The excellent electromagnetic wave absorption performance can be attributed to the synergistic effect of impedance matching, electromagnetic attenuation capability, unique multi-dimensional porous structure, abundant defects and interfaces. In summary, the present work provides a novel approach for the synthesis of multi-dimensional lightweight magnetic/dielectric microwave absorbers.

A Graphene-Based Aerogel Was Prepared as Solid Adsorbent for the Enrichment of Platinum (IV) at Trace Concentration

A three-dimensional graphene-based composite was prepared by a simple one-step in-site reduced-oxide method under atmospheric pressure. The obtained hydrogel was modified with 4-amino-benzenesulfonic acid and connected with ethylenediamine, and freeze-dried into an aerogel, which was characterized. Then the surface interaction with platinum (Pt, IV) was explored. The obtained aerogel showed good adsorption for Pt (IV) at acid conditions, giving a rising to the adsorption rate > 98% while pH ≥ 6. Using hexadecyl trimethyl ammonium bromide of 2% (m/V) as an eluent to desorb the Pt (IV) from the surface of the aerogel, a desorption rate of 81.1% was obtained in this process. Urea, buffer aquation and other surfactants were used in the desorption experiment to understand the adsorption mechanism between the aerogel and Pt (IV). In this work, hydrogen bond, van der Waals force and electronic interaction force mainly drove the adsorption process. For obtaining more purified Pt (IV), we used 0.5% CTAB to desorb Pd (II). A new three-dimensional graphene-based composite was prepared and the surface interaction between Pt (IV) and composite was experimented for understanding the adsorption mechanism and exploring its potential application in sample preparation in low concentration.

Highly compressible composite aerogels constructed by coaxial electrospun fibres and graphene for water sterilization

The electrospun fibres/graphene composite aerogels were assembled with the addition of amino trimethylene phosphonic acid (ATMP). Coaxial electrospinning was employed to attach nanosized-zinc pyrithione, a broad-spectrum biocide, on polyacrylonitrile (PAN) fibre surfaces. Reaction between ATMP and graphene oxide promoted the crosslinking structure of graphene-based aerogels, while producing antibacterial quaternary ammonium and attaching phosphonic acid groups to chelate the metal ions. The addition of the electrospun fibres in the composite aerogels improved the compressive stress at 50% strain by 540% upon the heat treatment at 200 °C, while the sterilization ratio of E. coli reached 100%. The heat treatment was critical for the mechanical properties of the composite aerogels because the linear chains of PAN were turned into rigid ladder polymer upon cyclization, while covalent interaction was introduced between residual carboxyl groups on graphene layers and CN groups of cyclized PAN. The electrospun fibres/graphene composite aerogels can be effectively applied to remove pathogenic bacteria, organic dyes and heavy metal ions in polluted water.

3D printing of architectured graphene-based aerogels by cross-linking GO inks with adjustable viscoelasticity for energy storage devices

3D printing of architectured graphene-based aerogels by cross-linking GO inks with adjustable viscoelasticity for energy storage devices

Front Cover: Antifungal Graphene‐based Absorbers as Advanced Materials for Preventive Conservation of Cultural Objects (ChemNanoMat 12/2022)

Graphene-based aerogels with an ionic liquid (IL) additive have been found to show remarkable anti-fungal activity, preventing the aerogel contamination with Aspergillus niger. When exposed to a volatile organic compound (VOC) saturated microenvironment, this aerogel was highly suitable for the absorption of acetaldehyde, formic acid, acetic acid, and formaldehyde. These combined anti-fungal and VOC absorption properties are prerequisites for bringing preventive conservation to a higher level. More information can be found in the Research Article by Costas Galiotis, Gabriella Di Carlo, Henri Stefan Schrekker et al. Statue in image from Freepik.com.

Influence of the reducing agent on the physicochemical and electrocatalytic properties of graphene-based aerogels

In-depth research was carried out with different characterization techniques (Scanning Electron Microscope (SEM), Fourier-Transform InfraRed spectroscopy (FTIR), X-ray Diffraction (XRD), picnometry, N2 adsorption/desorption) on the influence various nitrogenous and non-nitrogenous reducing agents have on the properties of graphene-based aerogels. The reducing agent used were ethylene glycol, hydrazine monohydrate, 2-chloroethylamine hydrochloride and ethylenediamine. These aerogels were synthesized by hydrothermal reduction of graphene oxide (GO) and later underwent freeze-drying. Thus, the relationship between the underlying reduction conditions with each reducing agent and certain properties such as textural and crystallographic ones and these, in turn, with electrochemical performance were elucidated.Electrocatalytic performance of the resulting graphene-based aerogels was strongly influenced by porosity, density, crystallinity and the presence of nitrogenous and oxygenated functional groups. To maximize electrocatalytic performance in the hydrogen evolution reaction (HER), a nitrogen-doped graphene aerogel with a low level of remaining oxygen functional groups, high surface mesopore area and porosity and exceptionally low density was needed. The presence of N species was found to have a positive effect on HER performance. Furthermore, adding N through hydrazine assisted hydrothermal synthesis seemed to be preferable for HER.

Multifunctional Thermal, Acoustic, and Piezoresistive Properties of In Situ-Modified Composite Aerogels with Graphene Oxide as the Main Phase.

Automotive and aerospace industries require advanced materials capable of multifunctional abilities while guaranteeing limited weight and volume and simple processing. Cellular materials such as graphene-based aerogels represent a promising solution. In this study, chemical modification approaches of graphene oxide and polyvinyl alcohol (GOP) aerogels are presented. The combination of a plasticizing agent, glycerol, and a cross-linking agent, glutaraldehyde, is exploited to obtain a mechanically balanced and robust cellular structure. Modified GOP aerogels show high elastic resilience (energy loss coefficient of 29% and compressive strength of 5 kPa at 30% strain, after the 10th compression cycle), low thermal conductivity (0.0424 W mK–1), and high sound absorption (average coefficient of 0.72 between 500 and 1500 Hz) while maintaining a low density of 6.51 kg m–3 with a maximum thickness of 25 mm. Moreover, chemically reduced GOP (rGOP) aerogels are also synthesized. They are characterized by the additional feature of piezoresistive behavior, with only a marginal impact on the other properties. These results show that modified GOP and rGOP aerogels are promising candidates for the fabrication of multifunctional structures to be applied in advanced engineering applications.

Fabrication of super-elastic graphene aerogels by ambient pressure drying and application to adsorption of oils

Three-dimensional graphene-based aerogels have promising applications in oil adsorption and environmental restoration. However, current research of graphene-based aerogels is often hindered by high preparation cost, poor mechanical properties and low recycling efficiency. Here, super-elastic graphene aerogel (SGA) was prepared through one-step freezing and twice hydrothermal reduction followed by drying under ambient pressure. The simple atmospheric drying provides a possibility for large-scale preparation of high performance graphene-based aerogels. The prepared SGA not only has the ability of highly repeatable compression rebound, but also exhibits excellent oil adsorption performance. And the overall performance of SGA is better than most of graphene-based aerogels prepared by freeze drying. After the SGA was cyclically compressed with 70% strain for 300 times, it can return to the original shape and height substantially. SGA retained about 90% of the initial adsorption capacity after 50 cycles of adsorption and compression regeneration for cyclohexane.

Controlling surface porosity of graphene-based printed aerogels

The surface porosity of graphene-based aerogels strongly influences their performance in applications involving mass transfer. However, the factors determining the surface porosities are not well-understood, hindering their application-specific optimisation. Here, through experiments and hydrodynamic simulations, we show that the high shear stress during the graphene-based aerogel fabrication process via 3D printing leads to a non-porous surface. Conversely, crosslinking of the sheets hinders flake alignment caused by shearing, resulting in a porous surface. Our findings enable fine control of surface porosity of printed graphene-oxide aerogels (GOA) through regulation of the crosslinking agents and shear stress. Using this strategy, we demonstrate the performance advantages of GOA with porous surface over their non-porous counterpart in dye adsorption, underscoring the importance of surface porosity in certain application scenarios.

Robust and Multifunctional 3D Graphene-Based Aerogels Reinforced by Hydroxyapatite Nanowires for Highly Efficient Organic Solvent Adsorption and Fluoride Removal.

In view of the serious perniciousness and complex diversity of actual wastewater systems, exploiting a robust and multifunctional adsorbent material featuring high sorption efficiency, broad-spectrum applicability, and excellent recyclability in treating multifarious pollutants in water (such as oils and fluoride ions) is highly required; however, it is still a daunting goal to pursue to date. In this work, novel mechanically robust and exceptional graphene oxide/hydroxyapatite nanowire (GO/HAPNW) aerogels (RGHAs/polydopamine (PDA)@RGHAs) with adjustable surface wettability were developed through a facile sol-gel self-assembly technology and subsequently optional bioinspired hydrophilic modification. Thanks to the reinforcing effect of HAPNWs with higher aspect ratio, a remarkably improved mechanical robustness (including superior compressibility and superelasticity) was acquired for the resulting aerogels. Based on the cooperative effect of the favorable selective wetting properties (i.e., hydrophobic/oleophilic for RGHAs) and the excellent mechanic stability, the aerogels displayed an outstanding sorption performance for diverse oils/organic solvents accompanied with a prominent recyclability. Specifically, a fairly high adsorption capacity of as high as 191 times of its own mass (for pump oil) was achieved based on a fast adsorption kinetic process. More importantly, superamphiphilic three-dimensional (3D) PDA@RGHAs revealed an extraordinary removal capability for water-soluble fluoride ions, exhibiting a superior equilibrium adsorption capacity (qe, 9.93 mg/g), which is distinctly superior to those of low-dimensional fluorine adsorbent materials recently reported. Accordingly, the as-prepared 3D aerogels combining both superior oil/organic solvent adsorption and excellent defluorination capability reveal a competitive application prospect toward effective intricate oily wastewater purification.