Super-elasticity of three-dimensionally cross-linked graphene materials all the way to deep cryogenic temperatures

Enhancing Interface Connectivity for Multifunctional Magnetic Carbon Aerogels: An In Situ Growth Strategy of Metal-Organic Frameworks on Cellulose Nanofibrils

Improving interface connectivity of magnetic nanoparticles in carbon aerogels is crucial, yet challenging for assembling lightweight, elastic, high-performance, and multifunctional carbon architectures. Here, an in situ growth strategy to achieve high dispersion of metal-organic frameworks (MOFs)-anchored cellulose nanofibrils to enhance the interface connection quality is proposed. Followed by a facile freeze-casting and carbonization treatment, sustainable biomimetic porous carbon aerogels with highly dispersed and closely connected MOF-derived magnetic nano-capsules are fabricated. Thanks to the tight interface bonding of nano-capsule microstructure, these aerogels showcase remarkable mechanical robustness and flexibility, tunable electrical conductivity and magnetization intensity, and excellent electromagnetic wave absorption performance. Achieving a reflection loss of -70.8 dB and a broadened effective absorption bandwidth of 6.0 GHz at a filling fraction of merely 2.2 wt.%, leading to a specific reflection loss of -1450 dB mm-1, surpassing all carbon-based aerogel absorbers so far reported. Meanwhile, the aerogel manifests high magnetic sensing sensibility and excellent thermal insulation. This work provides an extendable in situ growth strategy for synthesizing MOF-modified cellulose nanofibril structures, thereby promoting the development of high-value-added multifunctional magnetic carbon aerogels for applications in electromagnetic compatibility and protection, thermal management, diversified sensing, Internet of Things devices, and aerospace.

Size Effect of Graphene Oxide on Graphene-Aerogel-Supported Au Catalysts for Electrochemical CO2 Reduction

The lateral size of graphene nanosheets plays a critical role in the properties and microstructure of 3D graphene as well as their application as supports of electrocatalysts for CO2 reduction reactions (CRRs). Here, graphene oxide (GO) nanosheets with different lateral sizes (1.5, 5, and 14 µm) were utilized as building blocks for 3D graphene aerogel (GA) to research the size effects of GO on the CRR performances of 3D Au/GA catalysts. It was found that GO-L (14 µm) led to the formation of GA with large pores and a low surface area and that GO-S (1.5 µm) induced the formation of GA with a thicker wall and isolated pores, which were not conducive to the mass transfer of CO2 or its interaction with catalysts. Au/GA constructed with a suitable-sized GO (5 µm) exhibited a hierarchical porous network and the highest surface area and conductivity. As a result, Au/GA-M exhibited the highest Faradaic efficiency (FE) of CO (FECO = 81%) and CO/H2 ratio at -0.82 V (vs. a Reversible Hydrogen Electrode (RHE)). This study indicates that for 3D GA-supported catalysts, there is a balance between the improvement of conductivity, the adsorption capacity of CO2, and the inhibition of the hydrogen evolution reaction (HER) during the CRR, which is related to the lateral size of GO.

Superelastic chitin nanofibril/chitosan aerogel for effective circulating and continuous oil-water separation

Elastic and hydrophobic aerogels have received a lot of attention in dealing with the increasing oil pollution due to their recyclable properties. Herein, we present an ultralight and superelastic aerogel with highly oriented polygon structure based on chitin nanofibril (ChNF) and chitosan (CS) by directional freezing. The chemical cross-linking enables good mechanical strength at low aerogel density. After 500 compression-release cycles, the aerogel can retain the deformation recovery rate of 88 % in air, demonstrating the excellent resilience. The bio-based aerogel has high absorption capacity (52-114 g/g) for various oils and organic solvents, and it is able to achieve the absorption retention of 90 % even after 20 absorption-extrusion cycles. Moreover, owing to the good elasticity, the pore size of the aerogel can be adjusted by compression to selectively separate water-in-oil emulsions of different particle sizes with separation efficiencies higher than 99.5 %. The bio-based aerogel with good cycle performance has broad application prospects in the field of oil-water separation.

Multifunctional Hierarchical Metamaterial for Thermal Insulation and Electromagnetic Interference Shielding at Elevated Temperatures

The custom design of lightweight cellular materials is widely concerned due to effectively improved mechanical properties and functional applications. However, the strength attenuation and brittleness behavior hinder honeycomb structure design for the ceramic monolith. Herein, the ceramic matrix composite metamaterial (CCM) with a negative Poisson's ratio and high specific strength, exhibiting superelasticity, stability, and high compressive strength, is customized by combining centripetal freeze-casting and hierarchical structures. CCM maintains a negative Poisson's ratio response under compression with the lowest value reaching -0.16, and the relationship between CCM's specific modulus and density is E ∼ ρ^1.3, which indicates the mechanical metamaterial characteristic of high specific strength. In addition to the extraordinary mechanical performance endowed by hierarchical structures, the CCM exhibits excellent thermal insulation and electromagnetic interference shielding properties, in which the thermal conductivity is 30.62 mW·m^-1·K^-1 and the electromagnetic interference (EMI) shielding efficiency (SE) reaches 40 dB at room temperature. The specific EMI shielding efficiency divided by thickness (SSE/t) of CCM can reach 9416 dB·cm²·g^-1 at 700 °C due to its stability at elevated temperatures, which is 100 times higher than that of traditional ceramic matrix composites. Moreover, the designed hierarchical structure and metamaterial properties provide a potential scheme to implement cellular materials with collaborative optimization in structure and function.

Low temperature-resistant superhydrophobic and elastic cellulose aerogels derived from seaweed solid waste as efficient oil traps for oil/water separation

Aerogel has excellent application potential in adsorption, heat preservation, and other areas due to its typical advantages of low density and high porosity. However, there are several issues with the use of aerogel in oil/water separation, including weak mechanical qualities and challenges in eliminating organic contaminants at low temperature. Inspired by cellulose Iα, which has excellent performance at low temperature, this study used cellulose Iα nanofibers extracted from seaweed solid waste as the skeleton, through covalent cross-linked with ethylene imine polymer (PEI) and hydrophobic modification of 1, 4-phenyl diisocyanate (MDI), supplemented by freeze-drying technology to form three-dimensional sheet, and successfully obtained cellulose aerogels derived from seaweed solid waste (SWCA). The compression test shows that the maximum compressive stress of SWCA is 61 kPa, and the initial performance still maintains 82% after 40 cryogenic compression cycles. In addition, the contact angles of water and oil on the surface of the SWCA were 153° and 0°, respectively, and the stable hydrophobic time in simulated seawater is more than 3 h. By combining the elasticity and superhydrophobicity/superoleophilicity, the SWCA with an oil absorption capacity of up to 11-30 times its mass, might be utilized repeatedly for the separation of an oil/water mixture.

Highly cross-linked carbon tube aerogels with enhanced elasticity and fatigue resistance

Carbon aerogels are elastic, mechanically robust and fatigue resistant and are known for their promising applications in the fields of soft robotics, pressure sensors etc. However, these aerogels are generally fragile and/or easily deformable, which limits their applications. Here, we report a synthesis strategy for fabricating highly compressible and fatigue-resistant aerogels by assembling interconnected carbon tubes. The carbon tube aerogels demonstrate near-zero Poisson's ratio, exhibit a maximum strength over 20 MPa and a completely recoverable strain up to 99%. They show high fatigue resistance (less than 1.5% permanent degradation after 1000 cycles at 99% strain) and are thermally stable up to 2500 °C in an Ar atmosphere. Additionally, they possess tunable conductivity and electromagnetic shielding. The combined mechanical and multi-functional properties offer an attractive material for the use in harsh environments.

Ultra-stretchable graphene aerogels at ultralow temperatures

Graphene aerogels (GAs) possess workable deformation and sensing properties at extreme temperatures. However, their poor tensile properties have restricted their applications in stretchable electronic devices, smart soft robots, and aerospace. Herein, an ultra-stretchable and elastic graphene aerogel with record elongation from -95% to 400% was achieved by constructing a highly crimped and crosslinked graphene network using a microbubble-filled GA precursor by a simple compress-annealing process. This conductive aerogel with near zero Poisson's ratio showed rubber-like but temperature-invariant elasticity from 196.5 °C to 300 °C, and special strain insensitivity from 50% to 400% tensile strain and high sensitivity below 50% tensile strain. Therefore, it can be used as a highly stretchable but strain-insensitive conductor under extreme environments, in which these polymer-based stretchable conductive materials are not workable. Moreover, this work provides new thoughts on constructing inorganic ultra-stretchable materials.

A High-Temperature Accelerometer with Excellent Performance Based on the Improved Graphene Aerogel

A high-temperature accelerometer plays an important role for ensuring normal operation of equipment in aerospace, such as monitoring and identifying abnormal vibrations of aircraft engines. Phase transitions of piezoelectric crystals, mechanical failure and current leakage of piezoresistive/capacitive materials are the prominent inherent limitations of present high-temperature accelerometers working continuously above 973 K. With the rapid development of aerospace, it is a great challenge to develop a new type of vibration sensor to meet the crucial demands at high temperature. Here we report a high-temperature accelerometer working with a contact resistance mechanism. Based on the improved graphene aerogel (GA) prepared by a modulated treatment process, the accelerometer can operate continuously and stably at 1073 K and intermittently at 1273 K. The developed sensor is lightweight (sensitive element <5 mg) and has high sensitivity (an order of magnitude higher than MEMS accelerometers) and wide frequency response range (up to 5 kHz at 1073 K) with marked stability, repeatability and low nonlinearity error (<1%). These merits are attributed to the excellent and stable mechanical properties of the improved GA in the range of 299-1073 K. The accelerometer could be a promising candidate for high-temperature vibration sensing in space stations, planetary rovers and others.

A Review of Graphene-Based Materials/Polymer Composite Aerogels

The fabrication of composite materials is an effective way to improve the performance of a single material and expand its application range. In recent years, graphene-based materials/polymer composite aerogels have become a hot research field for preparing high-performance composites due to their special synergistic effects in mechanical and functional properties. In this paper, the preparation methods, structures, interactions, properties, and applications of graphene-based materials/polymer composite aerogels are discussed, and their development trend is projected. This paper aims to arouse extensive research interests in multidisciplinary fields and provide guidance for the rational design of advanced aerogel materials, which could then encourage efforts to use these new kinds of advanced materials in basic research and commercial applications.

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.

Structural Design and Fabrication of Multifunctional Nanocarbon Materials for Extreme Environmental Applications

Extreme environments represent numerous harsh environmental conditions, such as temperature, pressure, corrosion, and radiation. The tolerance of applications in extreme environments exemplifies significant challenges to both materials and their structures. Given the superior mechanical strength, electrical conductivity, thermal stability, and chemical stability of nanocarbon materials, such as carbon nanotubes (CNTs) and graphene, they are widely investigated as base materials for extreme environmental applications and have shown numerous breakthroughs in the fields of wide-temperature structural-material construction, low-temperature energy storage, underwater sensing, and electronics operated at high temperatures. Here, the critical aspects of structural design and fabrication of nanocarbon materials for extreme environments are reviewed, including a description of the underlying mechanism supporting the performance of nanocarbon materials against extreme environments, the principles of structural design of nanocarbon materials for the optimization of extreme environmental performances, and the fabrication processes developed for the realization of specific extreme environmental applications. Finally, perspectives on how CNTs and graphene can further contribute to the development of extreme environmental applications are presented.

Tailoring centripetal metamaterial with superelasticity and negative Poisson's ratio for organic solvents adsorption

Graphene metamaterials with a radial-like structure and negative Poisson's ratio (NPR) were assembled using a unique centripetal freezing technique. Driven by the centripetal temperature gradient, ice crystals were grown toward the center of an aqueous graphene dispersion and form a radially arranged skeleton. A reentrant structure was formed at the diagonal of the monolith as the ice crystals sublimate. The obtained centripetal graphene metamaterial (CGM) was endowed with NPR response. CGM maintained NPR under 50% compression, which reached a minimum (-0.18) at 10% strain. After 50 compressive cycles at 50% strain, CGM retained approximately 96% of the original compressive strength. The radial channels endowed CGM with fast absorption kinetics, and the NPR response effectively accommodated the damage caused by volume shrinkage during repeated adsorption-regeneration cycles. This strategy is an effective method for achieving NPR response and improving the mechanical properties of porous materials.

Superelastic graphene aerogel-based metamaterials

Ultralight, ultrastrong, and supertough graphene aerogel metamaterials combining with multi-functionalities are promising for future military and domestic applications. However, the unsatisfactory mechanical performances and lack of the multiscale structural regulation still impede the development of graphene aerogels. Herein, we demonstrate a laser-engraving strategy toward graphene meta-aerogels (GmAs) with unusual characters. As the prerequisite, the nanofiber-reinforced networks convert the graphene walls’ deformation from the microscopic buckling to the bulk deformation during the compression process, ensuring the highly elastic, robust, and stiff nature. Accordingly, laser-engraving enables arbitrary regulation on the macro-configurations of GmAs with rich geometries and appealing characteristics such as large stretchability of 5400% reversible elongation, ultralight specific weight as small as 0.1 mg cm⁻³, and ultrawide Poisson’s ratio range from −0.95 to 1.64. Additionally, incorporating specific components into the pre-designed meta-structures could further achieve diversified functionalities.

Graphene aerogels are highly porous and have very low density; despite this they also exhibit high mechanical strength. Here the authors present a laser-engraving strategy for producing graphene meta-aerogels with different configurations and properties.

Sustainable-Macromolecule-Assisted Preparation of Cross-linked, Ultralight, Flexible Graphene Aerogel Sensors toward Low-Frequency Strain/Pressure to High-Frequency Vibration Sensing

Ultralight and highly flexible aerogel sensors, composed of reduced graphene oxide cross-linked by sustainable-macromolecule-derived carbon, are prepared via facile freeze-drying and thermal annealing. The synergistic combination of cross-linked graphene nanosheets and micrometer-sized honeycomb pores gives rise to the exceptional properties of the aerogels, including superior compressibility and resilience, good mechanical strength and durability, satisfactory fire-resistance, and outstanding electromechanical sensing performances. The corresponding aerogel sensors, operated at an ultralow voltage of 0.2 V, can efficiently respond to a wide range of strains (0.1-80%) and pressures (13-2750 Pa) even at temperatures beyond 300 °C. Moreover, the ultrahigh-pressure sensitivity of 10 kPa^-1 and excellent sensing stability and durability are accomplished. Strikingly, the aerogel sensors can also sense the vibration signals with ultrahigh frequencies of up to 4000 Hz for >1 000 000 cycles, significantly outperforming those of other sensors. These enable successful demonstration of the exceptional performance of the cross-linked graphene-based biomimetic aerogels for sensitive monitoring of mechanical signals, e.g., acting as wearable devices for monitoring human motions, and for nondestructive monitoring of cracks on engineering structures, showing the great potential of the aerogel sensors as next-generation electronics.

Organic Single-Crystal Actuators and Waveguides that Operate at Low Temperatures

Applications in extreme conditions, such as those encountered in space exploration, require lightweight materials that can retain their elasticity in extremely cold environments. However, cryogenic treatment of most soft polymeric and elastomeric materials results in complete loss of their ability for elastic flow, whereby such materials that are normally ductile become stiff, brittle, and prone to cracking. Here, a facile method for preparation of hybrid organic crystalline materials that are not only cryogenically robust but are also capable of large, recoverable, and reversible deformation at low temperatures is reported. To that end, flexible organic crystals are first mechanically reinforced by a polymer coating and combined with a thermally responsive polymer. The resulting hybrid materials respond linearly and reversibly to temperatures from -15 to -120 °C without fatigue in air as well as in cold vacuum. The approach proposed here not only circumvents one of the main drawbacks that are inherent to the amorphous nature and has thus far limited the applications of polymeric materials at low temperatures, but it also provides a cost-effective access to a myriad of lightweight sensing, electronic, optical or actuating devices that can operate in low-temperature environmental settings.

Twin-Structured Graphene Metamaterials with Anomalous Mechanical Properties

Typically, solid materials exhibit transverse contraction in response to stretching in the orthogonal direction and transverse expansion under compression conditions. However, when flexible graphene nanosheets are assembled into a 3D porous architecture, the orientation-arrangement-delivered directional deformation of micro-nanosheets may induce anomalous mechanical properties. In this study, a 3D hierarchical graphene metamaterial (GTM) with twin-structured morphologies is assembled by manipulating the temperature gradient for ice growth during in situ freeze-casting procedures. GTM demonstrates anomalous anisotropic compression performance with programable Poisson's ratios (PRs) and improved mechanical properties (e.g., elasticity, strength, modulus, and fatigue resistance) along different directions. Owing to the designed three-phase deformation of 2D graphene sheets as basic microelements, the twin-structure GTM delivers distinctive characteristics of compressive curves with an apparent stress plateau, and follows a strengthening tendency. This multiscale deformation behavior facilitates the enhancement of energy loss coefficient. In addition, a finite element theory based numerical model is established to optimize the structural design, and validate the multiscale tunable PR mechanism and oriented structural evolution. The mechanical and thermal applications of GTM indicate that the rational manipulation-driven design of meta-structures paves the way for exploring graphene-based multifunctional materials with anomalous properties.

Zero Poisson's ratio in single-layer arsenic

Zero (or near-zero) Poisson's ratio (ZPR) materials have important applications in the field of precision instruments because one of their faces is stable and will not be affected by strain. However, ZPR materials are extremely rare. Here, we report a novel ZPR material, two-dimensional P2/m arsenene, by first principles calculations. Its Poisson's ratio is -0.00021 (strain along zigzag direction), which is smaller than all the known near-zero Poisson's ratio crystal materials, and even 10 times smaller than Me-graphene (0.002). This feature makes it have huge potential applications in the field of precision instruments such as aviation, medicine, and flexible electronic devices. Besides, the band-gap range of P2/m arsenene is 1.420-2.154 eV (the corresponding wavelength is 873-575 nm) under strain from -5% to 5% along the zigzag direction, which is suitable for infrared and visible optoelectronic devices.

Fabrication of graphene-based porous materials: traditional and emerging approaches

The anisotropic nature of ‘graphenic’ nanosheets enables them to form stable three-dimensional porous materials. The use of these porous structures has been explored in several applications including electronics and batteries, environmental remediation, energy storage, sensors, catalysis, tissue engineering, and many more. As method of fabrication greatly influences the final pore architecture, and chemical and mechanical characteristics and performance of these porous materials, it is essential to identify and address the correlation between property and function. In this review, we report detailed analyses of the different methods of fabricating porous graphene-based structures – with a focus on graphene oxide as the base material – and relate these with the resultant morphologies, mechanical responses, and common applications of use. We discuss the feasibility of the synthesis approaches and relate the GO concentrations used in each methodology against their corresponding pore sizes to identify the areas not explored to date.

Due to their anisotropic nature, graphene nanosheets can be used to form 3-dimensional porous materials using template-free and template-directed methodologies. These fabrication strategies are found to influence the properties of the final structure.

Mechanically Tunable Spongy Graphene/Cellulose Nanocrystals Hybrid Aerogel by Atmospheric Drying and Its Adsorption Applications

For expanding applications of spongy graphene aerogels (GAs) cost-effectively, we report a marriage of the two-step hydrothermal reduction and atmospheric drying method to fabricate a spongy CNC-graphene aerogel (CNG) with oil/water selectivity and tunable mechanical strength by a low-cost and straightforward approach. The reduced graphene oxide (rGO) with CNC by the ice-templated method can give rise to forming the hierarchical structure of hybrid GAs within the PUS network. Meanwhile, the fractured structure of PUS with a pre-compressive step arouses more versatility and durability, involving its selective and high-volume absorbability (up to 143%). The enhanced elastic modulus and more significant swelling effect than pure sponge materials give it a high potential for durable wastewater treatment.

A Highly Compressible and Stretchable Carbon Spring for Smart Vibration and Magnetism Sensors

Porous carbon materials demonstrate extensive applications for their attractive characteristics. Mechanical flexibility is an essential property guaranteeing their durability. After decades of research efforts, compressive brittleness of porous carbon materials is well resolved. However, reversible stretchability remains challenging to achieve due to the intrinsically weak connections and fragile joints of the porous carbon networks. Herein, it is presented that a porous all-carbon material achieving both elastic compressibility and stretchability at large strain from -80% to 80% can be obtained when a unique long-range lamellar multi-arch microstructure is introduced. Impressively, the porous all-carbon material can maintain reliable structural robustness and durability under loading condition of cyclic compressing-stretching process, similar to a real metallic spring. The unique performance renders it as a promising platform for making smart vibration and magnetism sensors, even capable of operating at extreme temperatures. Furthermore, this study provides valuable insights for creating highly stretchable and compressible porous materials from other neat inorganic components for diverse applications in future.

Biological Characterization of Polymeric Matrix and Graphene Oxide Biocomposites Filaments for Biomedical Implant Applications: A Preliminary Report

Carbon nanostructures application, such as graphene (Gr) and graphene oxide (GO), provides suitable efforts for new material acquirement in biomedical areas. By aiming to combine the unique physicochemical properties of GO to Poly L-lactic acid (PLLA), PLLA-GO filaments were produced and characterized by X-ray diffraction (XRD). The in vivo biocompatibility of these nanocomposites was performed by subcutaneous and intramuscular implantation in adult Wistar rats. Evaluation of the implantation inflammatory response (21 days) and mesenchymal stem cells (MSCs) with PLLA-GO took place in culture for 7 days. Through XRD, new crystallographic planes were formed by mixing GO with PLLA (PLLA-GO). Using macroscopic analysis, GO implanted in the subcutaneous region showed particles' organization, forming a structure similar to a ribbon, without tissue invasion. Histologically, no tissue architecture changes were observed, and PLLA-GO cell adhesion was demonstrated by scanning electron microscopy (SEM). Finally, PLLA-GO nanocomposites showed promising results due to the in vivo biocompatibility test, which demonstrated effective integration and absence of inflammation after 21 days of implantation. These results indicate the future use of PLLA-GO nanocomposites as a new effort for tissue engineering (TE) application, although further analysis is required to evaluate their proliferative capacity and viability.

Super-elasticity at 4 K of covalently crosslinked polyimide aerogels with negative Poisson's ratio

The deep cryogenic temperatures encountered in aerospace present significant challenges for the performance of elastic materials in spacecraft and related apparatus. Reported elastic carbon or ceramic aerogels overcome the low-temperature brittleness in conventional elastic polymers. However, complicated fabrication process and high costs greatly limited their applications. In this work, super-elasticity at a deep cryogenic temperature of covalently crosslinked polyimide (PI) aerogels is achieved based on scalable and low-cost directional dimethyl sulfoxide crystals assisted freeze gelation and freeze-drying strategy. The covalently crosslinked chemical structure, cellular architecture, negative Poisson's ratio (-0.2), low volume shrinkage (3.1%), and ultralow density (6.1 mg/cm³) endow the PI aerogels with an elastic compressive strain up to 99% even in liquid helium (4 K), almost zero loss of resilience after dramatic thermal shocks (∆T = 569 K), and fatigue resistance over 5000 times compressive cycles. This work provides a new pathway for constructing polymer-based materials with super-elasticity at deep cryogenic temperature, demonstrating much promise for extensive applications in ongoing and near-future aerospace exploration.

Hydroplastic Micromolding of 2D Sheets

Processing 2D sheets into desired structures with high precision is of great importance for fabrication and application of their assemblies. Solution processing of 2D sheets from dilute dispersions is a commonly used method but offers limited control over feature size precision owing to the extreme volume shrinkage. Plastic processing from the solid state is therefore a preferable approach to achieve high precision. However, plastic processing is intrinsically hampered by strong interlayer interactions of the 2D sheet solids. Here, a hydroplastic molding method to shape layered solids of 2D sheets with micrometer-scale precision under ambient conditions is reported. The dried 2D layered solids are plasticized by intercalated solvents, affording plastic near-solid compounds that enable local plastic deformation. Such an intercalated solvent-induced hydroplasticity is found in a broad family of 2D materials, for example graphene, MoS₂ , and MXene. The hydroplastic molding enables fabrication of complex spatial structures (knurling, origami) and microimprinted tubular structures down to diameters of 390 nm with good fidelity. The method enhances the structural accuracy and enriches the structural diversity of 2D macroassemblies, thus providing a feasible strategy to tune their electrical, optical, and other functional properties.

High-Performance Multifunctional Carbon-Silicon Carbide Composites with Strengthened Reduced Graphene Oxide

Materials with low density, exceptional thermal and corrosion resistance, and ultrahigh mechanical and electromagnetic interference (EMI) shielding performance are urgently demanded for aerospace and military industries. Efficient design of materials' components and microstructures is crucial yet remains highly challenging for achieving the above requirements. Herein, a strengthened reduced graphene oxide (SrGO)-reinforced multi-interfacial carbon-silicon carbide (C-SiC)_n matrix (SrGO/(C-SiC)_n) composite is reported, which is fabricated by depositing a carbon-strengthening layer into rGO foam followed by alternate filling of pyrocarbon (PyC) and silicon carbide (SiC) via a precursor infiltration pyrolysis (PIP) method. By increasing the number of alternate PIP sequences (n = 1, 3 and 12), the mechanical, electrical, and EMI shielding properties of SrGO/(C-SiC)_n composites are significantly increased. The optimal composite exhibits excellent conductivity of 8.52 S·cm^-1 and powerful average EMI shielding effectiveness (SE) of 70.2 dB over a broad bandwidth of 32 GHz, covering the entire X-, Ku-, K-, and Ka-bands. The excellent EMI SE benefits from the massive conduction loss in highly conductive SrGO skeletons and polarization relaxation of rich heterogeneous PyC/SiC interfaces. Our composite features low density down to 1.60 g·cm^-3 and displays robust compressive properties (up to 163.8 MPa in strength), owing to the uniformly distributed heterogeneous interfaces capable of consuming great fracture energy upon loadings. Moreover, ultrahigh thermostructural stability (up to 2100 °C in Ar) and super corrosion resistance (no strength degradation after long-term acid and alkali immersion) are also discovered. These excellent comprehensive properties, along with ease of low-cost and scalable production, could potentially promote the practical applications of the SrGO/(C-SiC)_n composite in the near future.

One pot facile transformation of CO2 to an unusual 3-D nano-scaffold morphology of carbon

An electrosynthesis is presented to transform CO₂ into an unusual nano and micron dimensioned morphology of carbon, termed Carbon Nano-Scaffold (CNS) with wide a range of high surface area graphene potential usages including batteries, supercapacitors, compression devices, electromagnetic wave shielding and sensors. Current CNS value is over $323 per milligram. The morphology consists of a series of asymmetric 20 to 100 nm thick flat multilayer graphene platelets 2 to 20 µm long orthogonally oriented in a 3D neoplasticism-like geometry, and appears distinct from the honeycomb, foam, or balsa wood cell structures previously attributed to carbon scaffolds. The CNS synthesis splits CO₂ by electrolysis in molten carbonate and has a carbon negative footprint. It is observed that transition metal nucleated, high yield growth of carbon nanotubes (CNTs) is inhibited in electrolytes containing over 50 wt% of sodium or 30 wt% of potassium carbonate, or at electrolysis temperatures less than 700 °C. Here, it is found that a lower temperature of synthesis, lower concentrations of lithium carbonate, and higher current density promotes CNS growth while suppressing CNT growth. Electrolyte conditions of 50 wt% sodium carbonate relative to lithium carbonate at an electrolysis temperature of 670 °C produced over 80% of the CNS desired product at 85% faradaic efficiency with a Muntz brass cathode and an Inconel anode.

Assembly of Ultralight Dual Network Graphene Aerogel with Applications for Selective Oil Absorption

High-performance graphene aerogels with well-developed internal structures are generally obtained by means of introducing additive materials such as carbon nanotubes, cellulose, and lignin into the aerogel network, which not only enhances the cost but also complicates the preparation process. Therefore, tailoring the internal structure of pristine graphene aerogel in a feasible way to achieve high performance is of great significance to the practical applications. Herein, a novel cysteamine/l-ascorbic acid graphene aerogel (CLGA) was fabricated by a simple one-step hydrothermal method followed by freeze-drying. Through the creative combination of the reducing agent l-ascorbic acid and cross-linking agent cysteamine, a dual-network structure was constructed by both layered physical stacking and vertical chemical cross-linking. The addition of cysteamine not only enhanced the reduction degree but also assisted the formation of more vertical connections between graphene nanosheets, resulting in more abundant pores with smaller sizes compared with graphene aerogels prepared by the traditional hydrothermal reduction method. CLGA possessed an ultra-low density of 4.2 mg/cm³ and a high specific surface area of 397.9 m²/g. As expected, this dual-network structure effectively improved the absorption capacity toward a variety of oil and organic solvents, with an outstanding oil absorption capacity up to 310 g/g. Furthermore, CLGA possessed good mechanical properties and oil/water selectivity. The absorbed oil could be recovered by both continuous absorption-removal process and mechanical squeezing, making the as-prepared aerogel superior absorbent material for a variety of applications, such as selective oil absorption and water treatment.

Self-Waveguide Single-Benzene Organic Crystal with Ultralow-Temperature Elasticity as a Potential Flexible Material

With the increasing popularity and burgeoning progress of space technology, the development of ultralow-temperature flexible functional materials is a great challenge. Herein, we report a highly emissive organic crystal combining ultralow-temperature elasticity and self-waveguide properties (when a crystal is excited, it emits light from itself, which travels through the crystal to the other end) based on a simple single-benzene emitter. This crystal displayed excellent elastic bending ability in liquid nitrogen (LN). Preliminary experiments on optical waveguiding in the bent crystal demonstrated that the light generated by the crystal itself could be confined and propagated within the crystal body between 170 and -196 °C. These results not only suggest a guideline for designing functional organic crystals with ultralow-temperature elasticity but also expand the application region of flexible materials to extreme environments, such as space technology.

Highly compressible and anisotropic lamellar ceramic sponges with superior thermal insulation and acoustic absorption performances

Advanced ceramic sponge materials with temperature-invariant high compressibility are urgently needed as thermal insulators, energy absorbers, catalyst carriers, and high temperature air filters. However, the application of ceramic sponge materials is severely limited due to their complex preparation process. Here, we present a facile method for large-scale fabrication of highly compressible, temperature resistant SiO₂-Al₂O₃ composite ceramic sponges by blow spinning and subsequent calcination. We successfully produce anisotropic lamellar ceramic sponges with numerous stacked microfiber layers and density as low as 10 mg cm^-3. The anisotropic lamellar ceramic sponges exhibit high compression fatigue resistance, strain-independent zero Poisson's ratio, robust fire resistance, temperature-invariant compression resilience from -196 to 1000 °C, and excellent thermal insulation with a thermal conductivity as low as 0.034 W m^-1 K^-1. In addition, the lamellar structure also endows the ceramic sponges with excellent sound absorption properties, representing a promising alternative to existing thermal insulation and acoustic absorption materials.

Retarding Ostwald Ripening to Directly Cast 3D Porous Graphene Oxide Bulks at Open Ambient Conditions

Graphene aerogels (GAs) with attractive properties have shown tremendous potentials in energy- and environment-related applications. Unfortunately, current assembly methods for GAs such as sol-gel and freeze-casting processes must be conducted in enclosed spaces with unconventional conditions, thus being literally inoperative for in situ and continuous productions. Herein, a direct slurry-casting method at open ambient conditions is established to arbitrarily prepare three-dimensional (3D) porous graphene oxide (GO) bulks without macroscopic dimension limits on a wide range of solid surfaces by retarding Ostwald ripening of 3D liquid GO foams when being dried in air. A subsequent fast thermal reduction (FTR) of GO foams leads to the formation of graphene aerogels (denoted as FTR-GAs) with hierarchical closed-cellular graphene structures. The FTR-GAs show outstanding high-temperature thermal insulation (70% decrease for 400 °C), as well as superelasticity (>1000 compression-recovery cycles at 50% strain), ultralow density (10-28 mg cm^-3), large specific surface area (BET, 206.8 m² g^-1), and high conductivity (ca. 100 S m^-1). This work provides a viable method to achieve in situ preparations of high-performance GAs as multifunctional structural materials in aircrafts, high-speed trains, or even buildings for the targets of energy efficiency, comfort, and safety.

In vitro and in vivo Biological Responses to Graphene and Graphene Oxide: A Murine Calvarial Animal Study

BACKGROUND

Graphene and its derivatives have recently gained popularity in the biomedical field. Previous studies have confirmed that both the mechanical strength and wear resistance of graphene-containing polyethylene have been greatly improved. Therefore, it is being considered as an alternative for artificial joint replacement liners. Based on the literature, the wear debris generated from the traditional polymers used for orthopedic liners could lead to particle-induced osteolysis and, consequently, failure of joint replacement. However, the biological response of this novel graphene-based polymer is still unclear. Therefore, the current study aimed to investigate the in vitro and in vivo biological effects of graphene and graphene oxide (GO) particles on bone.

MATERIALS AND METHODS

The biological responses of graphene and GO particles were tested via in vitro and murine calvarial in vivo models. In the in vitro model, murine macrophage cells were mixed with particles and hydrogel and printed into two differently designed scaffolds; the induced proinflammatory cytokines were then tested. In the murine in vivo model, the particle size distribution was measured via SEM, and these particles were then administrated in the calvarial area, referring to our established model. A micro-CT and histological analysis were performed to examine the biological effects of the particles on bone health. The data were analyzed via the one-way analysis of variance to determine the differences between the groups.

RESULTS

Both graphene and GO induced significantly higher TNF-α and IL-6 secretion compared with the control in the three-dimensional in vitro model. In the murine calvarial in vivo test, the graphene and GO particles increased the bone mass compared with the sham groups in the micro-CT analysis. Bone formation was also observed in the histological analysis.

CONCLUSION

In these in vivo and in vitro studies, the graphene and GO wear debris did not seem to induce harmful biological response effect to bone. Bone formation around the skull was observed in the calvarial model instead. Graphene-containing biomaterials could be a suitable new material for application in orthopedic prostheses due to their benefit of eliminating the risk of particle-induce osteolysis.

Scalable Fabrication of Resilient SiC Nanowires Aerogels with Exceptional High-Temperature Stability

Resilient ceramic aerogels exhibit great potential for applications in harsh environments owing to their unique combination of ultrahigh porosity, lightweight, reversible compressibility, and good thermal and chemical stabilities. However, their applications are severely restricted by the limited size and low yield due to their complicated and time-consuming synthetic procedures. Herein, we developed an efficient method for large-scale production of resilient SiC nanowire aerogels (SiC NWAGs) with tunable densities and desired shapes. The as-synthesized SiC NWAGs displayed excellent high-temperature stability (the maximum working temperature in Ar and air can reach to 1400 and 1000 °C, respectively), outstanding flame-erosion resistance and low thermal conductivity (25 mW m^-1 K^-1). The easy fabrication of such ceramic aerogel on a large scale will pave the way for the widespread applications of ceramic aerogels.

An Organic Crystal with High Elasticity at an Ultra-Low Temperature (77 K) and Shapeability at High Temperatures

Organic single crystals with elastic bending capability and potential applications in flexible devices and sensors have been elucidated. Exploring the temperature compatibility of elasticity is essential for defining application boundaries of elastic materials. However, related studies have rarely been reported for elastic organic crystals. Now, an organic crystal displays elasticity even in liquid nitrogen (77 K). The elasticity can be maintained below ca. 150 °C. At higher temperatures, the heat setting property enables us to make various shapes of crystalline fibers based on this single kind of crystal. Through detailed crystallographic analyses and contrast experiments, the mechanisms behind the unusual low-temperature elasticity and high-temperature heat setting are disclosed.

Hierarchical Cellular Structured Ceramic Nanofibrous Aerogels with Temperature-Invariant Superelasticity for Thermal Insulation

Silica aerogels are attractive for thermal insulation due to their low thermal conductivity and good heat resistance performance. However, the fabrication of silica aerogels with temperature-invariant superelasticity and ultralow thermal conductivity has remained extremely challenging. Herein, we designed and synthesized a hierarchical cellular structured silica nanofibrous aerogel by using electrospun SiO₂ nanofibers (SNFs) and SiO₂ nanoparticle aerogels (SNAs) as the matrix and SiO₂ sol as the high-temperature nanoglue. This pathway leads to the intrinsically random deposited SNFs assembling into a fibrous cellular structure, and the SNAs are evenly distributed on the fibrous cell wall. The unique hierarchical cellular structure of the ceramic nanofibrous aerogels endows it with integrated performances of the ultralow density of ∼0.2 mg cm^-3, negative Poisson's ratio, ultralow thermal conductivity (23.27 mW m^-1 K^-1), temperature-invariant superelasticity from -196 to 1100 °C, and editable shapes on a large scale. These favorable multifeatures present the aerogels ideal for thermal insulation in industrial, aerospace, and even extreme environmental conditions.