Properties Of Graphene Aerogels Research Articles

Comparative study on the H2S gas-sensing properties of graphene aerogels synthesized through hydrothermal and chemical reduction

BackgroundIn this study, graphene aerogels (GAs) were successfully prepared through hydrothermal reduction (GA-HR) and chemical reduction (GA-CR) to determine the effect of two reduction approaches on the properties of GAs in gas-sensing applications. MethodsThe GA thin films were used for the detection of H2S, and the gas-sensing performances were investigated at room temperature. Significant findingsThe H2S gas sensitivity of GA-HR and GA-CR were 0.255 and 0.3984 ppm−1 H2S gas, respectively. GA-CR had a more compact surface morphology and slightly lower reduction degree than GA-HR. The high electrical conductivity of GA-CR, which resulted from its strong sp2 character as indicated by its ID/IG ratio (intensity ratio of D an G band in Raman spectrum), was an essential factor for its high sensitivity to H2S gas. Moreover, simulation based on density functional theory was employed to investigate the various adsorption sites for H2S gas molecules on the GAs. The theoretical calculations based on adsorption energy, charge transfer, and density of states were consistent with the experimental results indicating that the GAs had strong H2S gas-sensing characteristics.

A Review of the Mechanical Properties of Graphene Aerogel Materials: Experimental Measurements and Computer Simulations

Graphene aerogels (GAs) combine the unique properties of two-dimensional graphene with the structural characteristics of microscale porous materials, exhibiting ultralight, ultra-strength, and ultra-tough properties. GAs are a type of promising carbon-based metamaterials suitable for harsh environments in aerospace, military, and energy-related fields. However, there are still some challenges in the application of graphene aerogel (GA) materials, which requires an in-depth understanding of the mechanical properties of GAs and the associated enhancement mechanisms. This review first presents experimental research works related to the mechanical properties of GAs in recent years and identifies the key parameters that dominate the mechanical properties of GAs in different situations. Then, simulation works on the mechanical properties of GAs are reviewed, the deformation mechanisms are discussed, and the advantages and limitations are summarized. Finally, an outlook on the potential directions and main challenges is provided for future studies in the mechanical properties of GA materials.

The influence of the drying method on the microstructure and the compression behavior of graphene aerogel

Supercritical CO2 drying and freeze-drying are two standard drying methods for fabricating aerogels. We conducted a comprehensive experimental study for clarifying the influence of the drying method on the properties of graphene aerogel, and further discussed its deformation mechanism via characterization and simulation results. The results showed that the specific modulus of two drying methods prepared graphene aerogels is similar. The supercritical CO2 dried sample had a higher compression strength due to the plastic collapse of the mesopore walls. In the freeze-drying process without thermal baffle, the reformed honeycomb geometric microstructure can be divided into three regions according to the growth of ice crystals: vertical, transition, and gradient regions. Therefore, the freeze-dried graphene aerogels exhibited a nonlinear superelastic behavior due to the random out-of-plane buckling of the thicker pore walls. In addition, two cellular structures were developed by mimicing the microstructure of two kinds of graphene aerogels for numerical analysis. Simulation results highlighted the decisive role of geometric nonlinearity in the deformation mechanism.

Uncertainty quantification and prediction for mechanical properties of graphene aerogels via Gaussian process metamodels

Graphene aerogels (GAs), a special class of 3D graphene assemblies, are well known for their exceptional combination of high strength, lightweightness, and high porosity. However, due to microstructural randomness, the mechanical properties of GAs are also highly stochastic, an issue that has been observed but insufficiently addressed. In this work, we develop Gaussian process metamodels to not only predict important mechanical properties of GAs but also quantify their uncertainties. Using the molecular dynamics simulation technique, GAs are assembled from randomly distributed graphene flakes and spherical inclusions, and are subsequently subject to a quasi-static uniaxial tensile load to deduce mechanical properties. Results show that given the same density, mechanical properties such as the Young’s modulus and the ultimate tensile strength can vary substantially. Treating density, Young’s modulus, and ultimate tensile strength as functions of the inclusion size, and using the simulated GA results as training data, we build Gaussian process metamodels that can efficiently predict the properties of unseen GAs. In addition, statistically valid confidence intervals centered around the predictions are established. This metamodel approach is particularly beneficial when the data acquisition requires expensive experiments or computation, which is the case for GA simulations. The present research quantifies the uncertain mechanical properties of GAs, which may shed light on the statistical analysis of novel nanomaterials of a broad variety.

Folded graphene/copper oxide hybrid aerogels: folding, self-reinforcement, and electrochemical performance

In our previous work, the Origami and enhancement theory was introduced into the construction of graphene aerogels to achieve the self-enhancement effect of graphene aerogels through the folding process of graphene lamellae. Based on the above work, after the graphene lamination was folded by Cu ion, it was further converted to cupric oxide by in situ mode, thus participating in the enhancement of the electrochemical behavior of graphene aerogels, and the "folding—enhanced—electrochemical" multiple effects were obtained. The innovation of this article was to use copper ions to achieve the folding of graphene sheet, and convert copper ions into copper oxides to improve the electrochemical properties of graphene aerogels, thereby achieving self-enhancement and electrochemical applications of graphene aerogels.The molecular structure and elemental composition of fGA/CuO were studied by FTIR and XPS. The surface microstructure of fGA/CuO was studied by SEM and bet. The results showed that fGA/CuO was successfully prepared with small and round micropores on the surface.The mechanical and electrochemical properties of fGA/CuO were studied by mechanical properties test, CV, GCD, and EIS tests. The results show that fGA/CuO has good mechanical and electrochemical properties.

Intrinsically microstructured graphene aerogel exhibiting excellent mechanical performance and super-high adsorption capacity

Highly porous graphene aerogels (GAs) demonstrate extensive applications in damping blocks, thermal insulation, sensors, catalyst carriers and energy storage because of their ultralow density, superelasticity and functional versatility. These properties have been regulated by topological structural design and composite of materials, but the effect of the structural unit on the properties of GA has not been reported. Herein, highly porous GAs with excellent mechanical performances and improved adsorption capacities have been prepared by a freezing-drying process. Ultra-flyweight (ρ < 1 mg cm−3), superelastic (low energy loss factor) and high-strength (i.e., high Young’ modulus) aerogels can be obtained by integrating different wall thicknesses and pore sizes. And it has been found that the grain refinement of ice crystals has a positive impact on the strength and modulus of as-prepared GAs during freezing-drying, which is similar to typical Hall-Petch strengthening in fine crystal metal materials. The as-prepared GA with the thinnest wall thickness exhibits the highest adsorption properties with respect to the oil solvents, and the adsorption capacity is 1272 times of its own weight. This study enriches our understanding of the structure and performance of GAs and indicates a practical methodology to ensure precise structural control of high-performance GAs for various applications.

Precise control of versatile microstructure and properties of graphene aerogel via freezing manipulation.

A deep understanding of the shaping technique is urgently required to precisely tailor the pore structure of a graphene aerogel (GA) in order to fit versatile application backgrounds. In the present study, the microstructure and properties of GA were regulated by freeze-casting using an ice crystal template frozen from -10 °C to -196 °C. The phase field simulation method was applied to probe the microstructural evolution of the graphene-H2O system during freezing. Both the experimental and simulation results suggested that the undercooling degree was fundamental to the nucleation and growth of ice crystals and dominated the derived morphology of GA. The pore size of GA was largely regulated from 240 to 6 μm via decreasing the freezing temperature from -10 °C to -196 °C but with a constant density of 8.3 mg cm-3. Rapid freeze casting endowed GA with a refined pore structure and therefore better thermal, electrical, and compressive properties, whereas the GA frozen slowly had superior absorption properties owing to the continuous and tube-like graphene lamellae. The GA frozen at -196 °C exhibited the highest Young's modulus of 327 kPa with similar densities to those reported in the literature. These findings demonstrate the diverse potential applications of GA with regulated pore morphologies and also contribute to cryogenic-induced phase separation methods.

Grass-modified graphene aerogel for effective oil-water separation

Grass-modified graphene aerogel (GGA) was successfully fabricated via simple, low-cost and environment-friendly hydrothermal treatment. The samples exhibited porous structure, low density of 6.99mg/cm3, good thermostability, excellent hydrophobicity with water contact angle of 146°. The properties of graphene aerogel have been significantly improved by introducing grass powder, leading to highly efficient selective adsorption. The adsorption capacity of GGA ranged from 68.40 to 145.84g/g for various liquid solvents, which is superior to that of unmodified graphene aerogel (GA). Moreover, GGA can be regenerated by repeated heat treatment and its adsorption capacity maintaining at above 90% of initial value after regeneration. GGA can realize oil-water separation of mixed solution by different manipulation methods. On one hand, GGA removed little oils in water through adsorption. On the other hand, GGA can act as filter media dealing with oil-water mixtures and collecting oils continuously by gravity or peristaltic pump. Good selectivity, high adsorption capacities and satisfactory recoverability make it possible to become a potential candidate in the field of oil-water separation and spill oil cleanup to realize environmental remediation. In the meantime, the incorporation of grass improves the performances of graphene aerogel in hydrophobicity, mechanical property and oil adsorption efficiency, providing a new path for high-value utilization of biomass waste.

Highly Conductive and Fracture-Resistant Epoxy Composite Based on Non-oxidized Graphene Flake Aerogel

Graphene aerogel (GA) has shown great promise as reinforcement of polymeric composites with exceptional electrical and mechanical characteristics. Although there has been significant progress in controlling the structure of GAs, no studies have appeared on the enhanced properties of GAs by employing high-quality precursor graphene flakes (GFs). However, the assembly of high-quality GFs is particularly challenging due to their highly hydrophobic and agglomerative nature in aqueous media, and of the few methods available to synthesize high-quality GFs, most produce flakes with very small lateral sizes. Herein, we report the fabrication of highly crystalline GAs using large nonoxidized graphene flakes (NOGFs) prepared by a novel graphite intercalation compound-based method. Bidirectional freeze casting is utilized for aligning NOGFs in two orthogonal directions, vertically and laterally, where the NOGF walls individually function as effective conductive pathways. The as-prepared nonoxidized graphene aerogel (NOGA) exhibits a defect concentration as low as 1.4% of impurity oxygen with an excellent electrical conductivity of 202.9 S/m at a low density of 5.7 mg/cm3. The corresponding NOGA-epoxy composite shows a remarkable electrical conductivity of 122.6 S/m and a fracture toughness of 1.74 MPa·m1/2 at a low filler content of 0.45 vol %.

Nanographene Aerogels: Size Effect of the Precursor Graphene Oxide on Gelation Process and Electrochemical Properties

AbstractImproving the electrochemical properties of graphene aerogels (GAs) without doping or making composites is an attractive synthetic strategy. In this work we report some effects of graphene sheet dimensions on the properties of GAs. Nanographene aerogels (nG‐AGs) were synthesized using nanographene oxide (nGO) powder with a mean platelet diameter of 90 nm. In‐situ Fourier tranformation infrared (FTIR) spectroscopy during gelation revealed a longer fast‐gelation regime for nG‐AGs than for standard graphene aerogels (stdG‐AGs). The surface‐area‐normalized capacitance of nG‐AGs calculated from cyclic voltammetry is 16% higher than that of stdG‐AGs, and the onset of hydrogen evolution is observed at a lower over‐potential. These observations can be attributed to an increased density of edge sites and defects in nanographene sheets. Our results indicate that the diameter of the precursor graphene sheets can be used as a parameter to optimize the electrochemical properties of GAs depending on the application.

A Facile Approach to Tune the Electrical and Thermal Properties of Graphene Aerogels by Including Bulk MoS₂.

Graphene aerogels (GAs) have attracted extensive interest in diverse fields, owing to their ultrahigh surface area, low density and decent electrical conductivity. However, the undesirable thermal conductivity of GAs may limit their applications in energy storage devices. Here, we report a facile hydrothermal method to modulate both the electrical and thermal properties of GAs by including bulk molybdenum disulfide (MoS2). It was found that MoS2 can help to reduce the size of graphene sheets and improve their dispersion, leading to the uniform porous micro-structure of GAs. The electrical measurement showed that the electrical conductivity of GAs could be decreased by 87% by adding 0.132 Vol % of MoS2. On the contrary, the thermal conductivity of GAs could be increased by ~51% by including 0.2 vol % of MoS2. The quantitative investigation demonstrated that the effective medium theories (EMTs) could be applied to predict the thermal conductivity of composite GAs. Our findings indicated that the electrical and thermal properties of GAs can be tuned for the applications in various fields.

Synthesis and Electro-Magneto-Mechanical Properties of Graphene Aerogels Functionalized with Co-Fe-P Amorphous Alloys.

Graphene aerogels (GAs) are functionalized with Fe-Co-P alloy using an electro-deposition method. The Fe-Co-P alloy coated on the graphene nanosheets is found to possess an amorphous structure and a nanoporous architecture of GAs. The electro-mechanical properties of GAs are significantly affected by the Fe-Co-P nanoparticles embedded inside GAs. The electro-mechanical responses of GA/Fe-Co-P nanoporous hybrid structures are sensitive to an applied magnetic field, demonstrating that they are promising for electro-magneto-mechanical applications. The light-weight, high-strength and nanoporous GAs functionalized with Fe-Co-P amorphous alloys are desirable sensors, actuators, and nano-electro-mechanical systems that could be controlled or manipulated by mechanical, electric and magnetic fields.

Effects of heat treatment on the thermal properties of highly nanoporous graphene aerogels using the infrared microscopy technique

Graphene aerogels (GAs), fabricated from graphene oxide (GO) suspensions using a mild chemical reduction method, are promising for many applications. Here we report the thermal conductivities of GAs having various graphene volume fractions from 0.67% to 2.5%, with and without annealing treatment, measured using a comparative infrared microscopy technique. The thermal conductivities of the GAs are measured to be 0.12–0.36W/(mK). This is the first systematical study of the thermal properties of GAs and the results elucidate the factors limiting their thermal conductivities. The developed thermal measurement technique can be applied to other porous material systems.

Morphology effects on electrical and thermal properties of binderless graphene aerogels

Three-dimensional self-assembled graphene aerogels (GAs) are successfully developed by a simple chemical reduction with l-ascorbic acid at low temperature. And for the first time, the relationship among morphologies, electrical and thermal properties of GAs is studied comprehensively by controlling reaction conditions. The electrical conductivities of the GAs are also improved by four times after an annealing at 400°C for 5h under Ar environment. The results are very useful to optimize the best morphology, electrical and thermal properties of GAs for the best performance of GA-based electrodes of energy storage devices such as supercapacitors and batteries.