All-Ceramic SiC Aerogel for Wide Temperature Range Electromagnetic Wave Attenuation

Self-Standing MOF-Derived Co@SiCnw Nanocomposite Aerogel with a Hierarchical Microstructure for Highly Effective and Wideband Electromagnetic Attenuation

To meet the requirements of lightweight and wideband attenuation for advanced electromagnetic (EM) absorption materials, the combination of both MOF composition and hierarchical structural design was applied as the strategy to prepare the MOF-derived Co@SiC nanowire (Co@SiCnw) nanocomposite aerogel. The hierarchical and laminated structures with multiple Co@SiCnw layers were constructed via a mixed growth-assisted freeze-drying and calcination process. The ultralightweight Co@SiCnw presents a low density of 0.11 g/cm3. With abundant second-phase polarization interfaces and enlarged EM wave attenuation channels to enhance dielectric and conductive loss, the optimized Co@SiCnw offers a minimal reflection loss (RLmin) of -61.4 dB at 10.0 GHz (2.64 mm) and an effective absorption bandwidth (EAB) as wide as 7.44 GHz with a sample thickness of only 2.16 mm. Furthermore, multifunctionalities, including low density, thermal insulation, and self-standing, were demonstrated for Co@SiCnw, making it a high-performance and practical microwave absorption material.

Biomimetic Leaf-Vein Aerogel for Electromagnetic Wave Absorption and Thermal Superinsulation

Electromagnetic protection in extreme environments requires materials with excellent thermal insulation capability and mechanical property to withstand severe temperature fluctuations and complex external stresses. Achieving strong electromagnetic wave absorption (EMA) while sustaining these exceptional properties remains a significant challenge. Herein, a facile approach is demonstrated to fabricate a biomimetic leaf-vein MXene/CNTs/PI (MCP) aerogel with parallel venations through bidirectional freeze-casting method. Due to its multi-arch lamellar structure and parallel venations within the aerogel layers, the ultralight MCP aerogel (16.9 mg·cm-3) achieves a minimum reflection loss (RLmin) of -75.8 dB and a maximum effective absorption bandwidth (EABmax) of 7.14 GHz with an absorber content of only 2.4 wt%, which also exhibits superelasticity and structural stability over a wide temperature range from -196 to 400 °C. Moreover, this unique structure facilitates rapid heat dissipation within the layers, while significantly impeding heat transfer between adjacent layers, achieving an ultralow thermal conductivity of 15.3 mW·m-1·K-1 for thermal superinsulation. The combination of excellent EMA performance, robust structural stability, and thermal superinsulation provides a potential design scheme under extreme conditions, especially in aerospace applications.

Customizable Resilient Multifunctional Graphene Aerogels via Blend-spinning assisted Freeze Casting

Graphene aerogels have gained considerable attention due to their unique physical properties, but their poor mechanical properties and lack of functionality have hindered their advanced applications. In this study, we propose a blend-spinning-assisted freeze-casting (BSFC) strategy to incorporate particle-modified carbon fibers into graphene aerogels for mechanical strengthening and functional enhancement. This method offers a great deal of freedom in the creation of customizable multimaterial, multiscale structural graphene aerogels. For example, we fabricated silicon carbide particle modified carbon fiber reinforced graphene (SiC/CF-GA) aerogels. The resulting aerogels display excellent properties such as being ultralightweight and highly resilient and having fatigue compression resistance (1000 cycles at 50% strain). Meanwhile, enhanced resilience inspired the effective strain-sensing capabilities of SiC/CF-GA aerogels with a sensitivity of 13.8 kPa-1. The adjustable dielectric properties due to SiC particle incorporation endow the SiC/CF-GA aerogel with a broad-band (8.0 GHz) effective electromagnetic wave attenuation performance. Besides, different particles could be incorporated into graphene aerogels via the BSFC strategy, allowing for customizable designs. Moreover, multifunctionalities were demonstrated by the modified aerogels, including noise absorption, thermal insulation, fire resistance, and waterproofing, further diversifying their practicality. Hence, the BSFC strategy provides a customized solution for fabricating modified graphene aerogels for advanced functional applications.

Alpha Al2O3 Nanosheet-Based Biphasic Aerogels with High-Temperature Resistance up to 1600 °C

Alumina aerogels are desirable for lightweight and highly efficient thermal insulation. However, they are typically constrained by brittleness and structural collapse at high temperatures. The manufacture of alumina aerogels with ultralow thermal conductivity and excellent thermal stability at high temperatures beyond 1300 °C is still challenging. Herein, alumina aerogels with superior ultrahigh-temperature-resistant and thermal insulation were successfully prepared by assembling the α-Al₂O₃ nanosheets with silica sols as the high-temperature binders. Benefiting from the generation of the mullite-covered alumina biphasic structure, the α-Al₂O₃ nanosheet-based aerogels (ANSAs) exhibit excellent thermal and chemical stabilities even after calcination at as high as 1600 °C. The ANSAs had a low thermal conductivity (0.029 W·m^-1·K^-1 at room temperature), structural stability with a measured compressive strength of 0.6 MPa, and good thermal shock resistance. Furthermore, the 2D α-alumina@mullite core-shell sheets were also prepared as assembly units to construct aerogels (AMSAs). This core-shell structure can improve temperature resistance through inter-lattice suppression under continuous energy input at high temperatures. The AMSAs have a linear shrinkage of only 2.7% after calcination at 1600 °C for 30 min, further improving the temperature resistance, making them an ideal super-insulating material for applications at extremely high temperatures.

Phase-Transformation Nanoparticles Synchronously Boosting Mechanical and Electromagnetic Performance of SiBCN Ceramics

Precursor-derived silicoboron carbonitride ceramic (PDC-SiBCN) has attracted significant attention as an advanced electromagnetic (EM) wave-absorbing material. However, the inherent porous and brittle characteristics limit its application as a structural load component in an EM interference environment. In this study, phase-transformation HfO₂ nanoparticles were incorporated into PDC-SiBCN to reduce volume shrinkage, improve bonding interactions, and control structural defects, simultaneously boosting the plastic deformation and EM performance of brittle ceramics. The obtained HfO₂/SiBCN ceramic showed enhanced flexural strength of up to 430.1% compared with that of the pure SiBCN ceramic. Furthermore, the HfO₂/SiBCN ceramic also demonstrated excellent high-temperature EM absorption. The minimum reflection coefficient (RC_min) could reach -45.26 dB, and the effective absorption bandwidth (EAB) covered 2.80 GHz of the X band at 2.28 mm thickness at room temperature. Furthermore, the RC_min can still reach -44.83 dB, and the EAB can cover 2.4 GHz at 1.58 mm even at 1073 K. This work shows that phase-transformation nanoparticles could simultaneously improve the deformation ability and EM wave absorption properties of SiBCN ceramics. The results could guide the design and preparation of PDCs with strong carrying capacity and excellent EM absorption, even in harsh environments.

Carbon Material-Based Aerogels for Gas Adsorption: Fabrication, Structure Design, Functional Tailoring, and Applications

Carbon material-based aerogels (CMBAs) have three-dimensional porous structure, high specific surface area, low density, high thermal stability, good electric conductivity, and abundant surface-active sites, and, therefore, have shown great application potential in energy storage, environmental remediation, electrochemical catalysis, biomedicine, analytical science, electronic devices, and others. In this work, we present recent progress on the fabrication, structural design, functional tailoring, and gas adsorption applications of CMBAs, which are prepared by precursor materials, such as polymer-derived carbon, carbon nanotubes, carbon nanofibers, graphene, graphene-like carbides, fullerenes, and carbon dots. To achieve this aim, first we introduce the fabrication methods of various aerogels, and, then, discuss the strategies for regulating the structures of CMBAs by adjusting the porosity and periodicity. In addition, the hybridization of CMBAs with other nanomaterials for enhanced properties and functions is demonstrated and discussed through presenting the synthesis processes of various CMBAs. After that, the adsorption performances and mechanisms of functional CMBAs towards CO₂, CO, H₂S, H₂, and organic gases are analyzed in detail. Finally, we provide our own viewpoints on the possible development directions and prospects of this promising research topic. We believe this work is valuable for readers to understand the synthesis methods and functional tailoring of CMBAs, and, meanwhile, to promote the applications of CMBAs in environmental analysis and safety monitoring of harmful gases.