Electronic Modulation Strategy for Mass-Producible Ultrastrong Multifunctional Biomass-Based Fiber Aerogel Devices: Interfacial Bridging

Multifunctional carbon aerogels loaded with pea-pod-like carbon nanotubes for outstanding electromagnetic wave absorption performance

Although ordered porous carbon materials (PCMs) have shown promising potential in the field of electromagnetic wave absorption (EWA), creating multifunctional PCMs with outstanding microwave absorption performance remains a significant challenge. Herein, ordered porous carbon aerogels loaded with pea-pod-like nitrogen-doped carbon nanotubes (CNTs) were fabricated via orientation freeze-drying followed by high-temperature pyrolysis. The optimized aerogel exhibits extraordinary EWA performance with a broad effective absorption bandwidth of 7.68 GHz and exceptionally strong absorption of -91.58 dB at a low filling ratio of only 3 wt%, which is the largest absorption strength among all known aerogels to date. The exceptional EWA performance is attributed to the synergistic effect of abundant loss mechanisms resulting from a unique pod-like structure in ordered porous carbon aerogel, where nitrogen-doped CNTs encapsulate magnetic alloy nanoparticles. Optimized aerogel exhibits superior compressive elasticity, thermal insulation, and light weight, laying the groundwork for designing practical next-generation EWA materials.

Multi-interfacial bridging engineering of flexible MXene film for efficient electromagnetic shielding and energy conversion

Accompanied by the progressive development of electronic equipment, excellent electromagnetic interference (EMI) shielding materials display a satisfying prospect in protecting electronic devices against electromagnetic pollution/radiation, while integrating energy conversion. Heretofore, it remains a conundrum to availably construct thin films with multi-interfacial bridging engineering as multifunctional shielding devices. To effectively achieve electromagnetic wave attenuation and integrate energy conversion, a co-mixed vacuum-assisted filtration strategy is designed to synthesize Au@MXene/cellulose nanocrystal/dodecylbenzenesulfonic acid-doped polyaniline (AMCP) films. Profited from the interfacial engineering, the total EMI shielding effectiveness (SE) can be increased by 27 % with the highest value of 67.9 dB. MXene with localized surface plasmon resonance characteristics gives the composite films good energy conversion performance, that is, the composite film can be rapidly heated up to 100 °C under the irradiation of an infrared lamp, and its surface temperature remains stable after continuous irradiation. Additionally, the infrared emissivity is as low as 0.173 within the 8-14 μm, which is necessary to adapt various application scenarios. Therefore, it is reliable that the AMCP films constructed by multicomponent offer a facile strategy for MXene-based EMI shielding devices with integration characteristics.

MXene-Enabled Pneumatic Multiscale Shape Morphing for Adaptive, Programmable and Multimodal Radar-infrared Compatible Camouflage

Achieving radar-infrared compatible camouflage with dynamic adaptability has been a long-sought goal, but faces significant challenges owing to the limited dispersion relations of conventional material systems operating in different wavelength ranges. Here, this work proposes the concept of pneumatic multiscale shape morphing and design a periodically arranged pneumatic unit consisting of MXene-based morphable conductors and intake platforms. During gas actuation, the morphable conductor transforms centimeter-scale 2D flat sheets into 3D balloon shapes to enhance microwave absorption behavior, and also reconfigures micrometer-scale MXene wrinkles into smooth planes in combination with cavity-induced low heat transfer to minimize infrared (IR) signatures. Through theory-guided reverse engineering, the final pneumatic matrix shows remarkable frequency tunability (2.64-18.0 GHz), moderate IR emissivity regulation (0.14 at 7-16.5 µm), rapid responsiveness (≈30 ms), wide-angle operation (>45°), and excellent environmental tolerance. Additionally, the multiplexed pneumatic matrix enables over 14 programmable coding sequences that independently alter thermal radiation without compromising radar stealth, and allows multimodal camouflage switching between three distinct compatible states. The approach may facilitate the evolution of camouflage techniques and electromagnetic functional materials toward multispectral, adaptability and intelligence.

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.

Progress in microwave absorbing materials: A critical review

Microwave-absorbing materials play a significant role in various applications that involve the attenuation of electromagnetic radiation. This critical review article provides an overview of the progress made in the development and understanding of microwave-absorbing materials. The interaction between electromagnetic radiation and absorbing materials is explained, with a focus on phenomena such as multiple reflections, scattering, and polarizations. Additionally, types of losses that affect the performance of microwave absorbers are also discussed, including dielectric loss, conduction loss, relaxation loss, magnetic loss, and morphological loss. Each of these losses has different implications for the effectiveness of microwave absorbers. Further, a detailed review is presented on various types of microwave absorbing materials, including carbonaceous materials, conducting polymers, magnetic materials, metals and their composites, 2D materials (such as MXenes and 2D-transition metal dichalcogenides), biomass-derived materials, carbides, sulphides, phosphides, high entropy (HE) materials and metamaterials. The characteristics, advantages, and limitations of each material are examined. Overall, this review article highlights the progress achieved in the field of microwave-absorbing materials. It underlines the importance of optimizing different types of losses to enhance the performance of microwave absorbers. The review also recognizes the potential of emerging materials, such as 2D materials and high entropy materials, in further advancing microwave-absorbing properties.

Achieving Ultra-Broad Microwave Absorption Bandwidth Around Millimeter-Wave Atmospheric Window Through an Intentional Manipulation on Multi-Magnetic Resonance Behavior

The utilization of electromagnetic waves is rapidly advancing into the millimeter-wave frequency range, posing increasingly severe challenges in terms of electromagnetic pollution prevention and radar stealth. However, existing millimeter-wave absorbers are still inadequate in addressing these issues due to their monotonous magnetic resonance pattern. In this work, rare-earth La3+ and non-magnetic Zr4+ ions are simultaneously incorporated into M-type barium ferrite (BaM) to intentionally manipulate the multi-magnetic resonance behavior. By leveraging the contrary impact of La3+ and Zr4+ ions on magnetocrystalline anisotropy field, the restrictive relationship between intensity and frequency of the multi-magnetic resonance is successfully eliminated. The magnetic resonance peak-differentiating and imitating results confirm that significant multi-magnetic resonance phenomenon emerges around 35 GHz due to the reinforced exchange coupling effect between Fe3+ and Fe2+ ions. Additionally, Mössbauer spectra analysis, first-principle calculations, and least square fitting collectively identify that additional La3+ doping leads to a profound rearrangement of Zr4+ occupation and thus makes the portion of polarization/conduction loss increase gradually. As a consequence, the La3+-Zr4+ co-doped BaM achieves an ultra-broad bandwidth of 12.5 + GHz covering from 27.5 to 40 + GHz, which holds remarkable potential for millimeter-wave absorbers around the atmospheric window of 35 GHz.

Toward Enhancing Performance of Electromagnetic Wave Absorption for Conductive Metal-Organic Frameworks: Nanostructure Engineering or Crystal Morphology Controlling

Conductive metal-organic frameworks (cMOFs), which have high porosity and intrinsic electron conductivity, are regarded as ideal candidates for electromagnetic wave (EMW) absorption materials. Controlling the nanostructure of absorbers may be one of the effective strategies to improve the electromagnetic wave (EMW) absorption performance. Herein, a series of conductive Cu-HHTP MOFs (HHTP = 2,3,6,7,10,11-hexahydroxytriphenyl hydrates) with different nanostructures or crystal morphologies were successfully synthesized by using different structural inducers to regulate the changes in the morphology, thereby improving the EMW absorption performance. Specifically, when ammonia was used as an inducer, the obtained A-Cu-HHTP with a nanosheet structure exhibited excellent EMW absorption performance. The minimum reflection loss (RLmin) can reach -51.08 dB at 7.25 GHz with a thickness of 4.4 mm, and the maximum effective absorption bandwidth (EAB) can cover 5.73 GHz at 2.5 mm. The influence of the nanostructures of the cMOFs on the dielectric and EMW absorption performance was clarified. The nanosheet structure of A-Cu-HHTP increases its specific surface area, which expands multiple scattering and reflection paths of incident EMW; Meanwhile, the unique structure facilitates the formation of more heterogeneous interfaces, optimizing impedance matching. The significant improvement in EMW performance is mainly attributed to multiple reflections and scattering as well as impedance matching. This work not only provides a simple and effective strategy for improving electromagnetic wave absorption performance but also offers guidelines for preparing morphology functional cMOF materials.

Wearable Aerogels for Personal Thermal Management and Smart Devices

Extreme climates have become frequent nowadays, causing increased heat stress in human daily life. Personal thermal management (PTM), a technology that controls the human body's microenvironment, has become a promising strategy to address heat stress. While effective in ordinary environments, traditional high-performance fibers, such as ultrafine, porous, highly thermally conductive, and phase change materials, fall short when dealing with harsh conditions or large temperature fluctuations. Aerogels, a third-generation superinsulation material, have garnered extensive attention among researchers for their thermal management applications in building energy conservation, transportation, and aerospace, attributed to their extremely low densities and thermal conductivity. While aerogels have historically faced challenges related to weak mechanical strength and limited secondary processing capacity, recent advancements have witnessed notable progress in the development of wearable aerogels for PTM. This progress underscores their potential applications within extremely harsh environments, serving as self-powered smart devices and sensors. This Review offers a timely overview of wearable aerogels and their PTM applications with a particular focus on their wearability and suitability. Finally, the discussion classifies five types of PTM applications based on aerogel function: thermal insulation, heating, cooling, adaptive regulation (involving thermal insulation, heating, and cooling), and utilization of aerogels as wearable smart devices.

A 1064 nm laser adaptive limiter with visible light transparency based on one dimensional photonic crystals of LiNbO3 defects

Herein, we present the investigation of the visible light transparency and optical limiting characteristics of one dimensional photonic crystals with LiNbO3 defects fabricated by the sputtering technique. Transmission spectroscopy measurements reveal a broad photonic band gap with a 1064 nm defect mode and high transmittance within the visible range. The optical energy limiting performance in the photonic crystal can be attributed to the strong confinement of the optical field surrounding the LiNbO3 defect layer. The low energy 1064 nm laser demonstrates a transmittance of 82.15%. Notably, the optical limiting threshold is lower at 62.03 mJ cm-2 in comparison with conventional optical limiting materials. Additionally, the optical limiter achieves a transmittance of 68.57% within the visible light band.

Pneumatic Structural Deformation to Enhance Resonance Behavior for Broadband and Adaptive Radar Stealth

Ideal radar absorbing materials (RAMs) require instantaneous, programmable, and spontaneous adaptability to cope with a complex electromagnetic (EM) environment across the full working frequency. Despite various material systems and adaptive mechanisms having been demonstrated, it remains a formidable challenge to integrate these benefits simultaneously. Here, we present a pneumatic matrix that couples morphable MXene/elastomer conductors with dielectric spacers, which leverages controllable airflow to reconfigure the spatial structure between a flat sheet and a hemispherical crown while maintaining resistance stability via wrinkle folding and unfolding. The interdimensional reconfigurations drastically induce multiple resonance behavior, enabling the matrix remarkable frequency tunability (144.5%), ultrawide bandwidth (15 GHz), weak angular dependence (45° incidence), ultrafast responsiveness (∼30 ms), and excellent reproducibility (1000 cycles). With multichannel fluidic and conceptual automated control systems, the final pneumatic device demonstrates a multiplexed, programmable, and autonomous transformable mode that builds a promising platform for smart radar cloaking.

Construction of Hierarchical Yolk-Shell Co/N-Dope C@void@C@MoS2 Composites with Multiple Heterogeneous Interfaces toward Broadband Electromagnetic Wave Absorption

The synthesis of materials with a multicomponent hierarchical structure is an essential strategy for achieving high-performance electromagnetic wave (EMW) absorption. However, conventional design strategies face challenges in terms of the rational construction of specific architecture. In this study, we employ a combined space-restricted and hierarchical construction strategy to surface-plant MoS2 nanosheets on yolk-shell structural carbon-modified Co-based composites, leading to the development of high-performance Co/NC@void@C@MoS2 absorbers with advanced architecture. The surface-planted MoS2 nanosheets, the Co/NC magnetic yolk, and the dielectric carbon shell work together to enhance the impedance matching characteristics and synergistic loss capabilities in the composites. Experimental results indicate that Co/NC@void@C-700@MoS2 exhibited the best absorption performance with an effective absorption bandwidth of 7.54 GHz (at 2.05 mm) and a minimum reflection loss of -60.88 dB (at 1.85 mm). Furthermore, radar cross-section simulation results demonstrate that Co/NC@void@C-700@MoS2 effectively suppresses the scattering and transmission of EMWs on perfect electric conductor substrates, implying its superior practical application value. This study provides inspiration and experimental basis for designing and optimizing EMW absorption materials with hierarchical yolk-shell architecture.