Carbon-Based Radar Absorbing Materials toward Stealth Technologies

Multifunctional bacterial cellulose‑derived carbon hybrid aerogel for ultrabroad microwave absorption and thermal insulation

Carbon aerogel has gained intense attention as one of the most promising microwave absorption materials. It can overcome severe electromagnetic pollution, thanks to its 3D macroscopic structure and superb conductive loss capacity. However, there is still a big challenge to endow multifunctionality to carbon aerogel while maintaining its good electromagnetic wave absorption (EWA) so as to adapt wide practical application. Herein, a novel carbon-based aerogel consisting of Cu and TiO2 nanoparticles dispersed on carbon nanofiber framework was derived from carbonized bacterial cellulose (CBC) decorated with its mother bacteria via freeze-drying, in situ growth and carbonization strategies. The synthesized carbon-based CBC/Cu/TiO2 aerogel achieved an excellent EWA performance with a broad effective absorption bandwidth (EAB) of 8.32 GHz. It is attributed to the synergistic loss mechanism from multiple scattering, conductive network loss, interfacial polarization loss and dipolar polarization relaxation. Meanwhile, the obtained aerogel also shows an excellent thermal insulation with a 3-mm-thick sample generating a temperature gradient of over 42 °C at 85 °C and a maximum radar cross-section (RCS) reduction of 23.88 dB m2 owing to the cellular structure and synergistic effects of multi-components. Therefore, this study proposes a feasible design approach for creating lightweight, effective, and multifunctional CBC-based EWA materials, which offer a new platform to develop ultrabroad electromagnetic wave absorber under the guidance of RCS simulation.

Lessons from Nature: Advances and Perspectives in Bionic Microwave Absorption Materials

Inspired by the remarkable electromagnetic response capabilities of the complex morphologies and subtle microstructures evolved by natural organisms, this paper delves into the research advancements and future application potential of bionic microwave-absorbing materials (BMAMs). It outlines the significance of achieving high-performance microwave-absorbing materials through ingenious microstructural design and judicious composition selection, while emphasizing the innovative strategies offered by bionic manufacturing. Furthermore, this work meticulously analyzes how inspiration can be drawn from the intricate structures of marine organisms, plants, animals, and non-metallic minerals in nature to devise and develop BMAMs with superior electromagnetic wave absorption properties. Additionally, the paper provides an in-depth exploration of the theoretical underpinnings of BMAMs, particularly the latest breakthroughs in broadband absorption. By incorporating advanced methodologies such as simulation modeling and bionic gradient design, we unravel the scientific principles governing the microwave absorption mechanisms of BMAMs, thereby furnishing a solid theoretical foundation for understanding and optimizing their performance. Ultimately, this review aims to offer valuable insights and inspiration to researchers in related fields, fostering the collective advancement of research on BMAMs.

Thermally tailoring dielectric genes of graphene hybrids for tuning electromagnetic properties

The functions of graphene have garnered significant attention in recent research. A profound understanding of the principles of temperature-dependent electromagnetic responses is crucial for guiding the design of advanced functional materials and devices. From this perspective, the thermally tailored mechanisms of polarization genes and conduction genes are emphasized. The synergistic effect between thermally tailored polarization relaxation and charge transport behaviors is revealed. More importantly, microwave absorption, electromagnetic shielding, and temperature sensing at elevated temperatures are discussed by customizing the conduction and polarization genes. The tunable variable-temperature electromagnetic performance enables the possibilities of diversified electromagnetic energy conversion. Three electromagnetic energy conversion devices for consuming waste electromagnetic energy are predicted, which can support the next generation of energy management and smart devices and promote efficient utilization of resources and sustainable development.

In-situ growth of carbon nanotubes for the modification of wood-derived biomass porous carbon to achieve efficient Low/Mid-Frequency electromagnetic wave absorption

Ideal wave-absorbing materials are required to possess the characteristics such as being "broad, lightweight, thin, and strong." Biomass-derived materials for absorbing electromagnetic waves (EMWs) are widely explored due to their low cost, lightweight, environmentally friendly, high specific surface area, and porous structure. In this study, wood was used as the raw material, and N-doped carbon nanotubes were grown in situ in porous carbon derived from wood, loaded with magnetic metal Co nanoparticles through chemical vapor deposition. The Fir@Co@CNT composite material exhibited a three-dimensional conductive electromagnetic network structure and excellent impedance matching, thereby demonstrating excellent wave absorption performance. By controlling the introduction of carbon nanotubes, the roles of polarization loss and conduction loss in the Fir@Co@CNT composite material were precisely regulated. The Fir@Co@CNT 1:5 composite material achieved a minimum reflection loss (RLmin) of -43.03 dB in the low-frequency region and a maximum effective absorption bandwidth (EABmax) of 4.3 GHz (1.5 mm). Meanwhile, the Fir@Co@CNT 1:10 composite material achieved a RLmin of -52 dB with a thickness of only 2.3 mm, along with an EABmax of 4.2 GHz (1.6 mm). Both materials collectively cover the entire C-band, X-band, and Ku-band in terms of EAB. This work introduces a method for regulating polarization loss and conduction loss, showcasing the potential of biomass carbon materials as low-frequency EMW absorption materials for the first time. It also provides a new direction for the development and application of environmentally friendly, lightweight, high-performance wave-absorbing materials.

Multifunctional microwave absorption materials: construction strategies and functional applications

The widespread adoption of wireless communication technology, especially with the introduction of artificial intelligence and the Internet of Things, has greatly improved our quality of life. However, this progress has led to increased electromagnetic (EM) interference and pollution issues. The development of advanced microwave absorbing materials (MAMs) is one of the most feasible solutions to solve these problems, and has therefore received widespread attention. However, MAMs still face many limitations in practical applications and are not yet widely used. This paper presents a comprehensive review of the current status and future prospects of MAMs, and identifies the various challenges from practical application scenarios. Furthermore, strategies and principles for the construction of multifunctional MAMs are discussed in order to address the possible problems that are faced. This article also presents the potential applications of MAMs in other fields including environmental science, energy conversion, and medicine. Finally, an analysis of the potential outcomes and future challenges of multifunctional MAMs are presented.

A Developed Approach for Synthesizing Novel Fe3O4/FeO/BaCl2 Composites with Broadband and High-Efficiency Microwave Absorption Performance

Designing high-performance microwave absorbing materials that are thin and exhibit strong absorption capabilities across a wide frequency range is critical for mitigating electromagnetic pollution through a simple, highly adaptable, and cost-effective approach. However, achieving these three targets remains a significant challenge. In this research a simple approach suitable for large-scale production of microwave absorbing materials, namely, Fe3O4/FeO/BaCl2 composites, is proposed, which includes the processes of chemical coprecipitation and calcination. The above approach can adjust the mass ratio of Fe3O4/FeO while prompt the formation of BaCl2 with mesoporous structure on the surface of Fe3O4/FeO, meeting the need for desirable microwave absorbing performance. Subsequently, the impacts of varying mass ratios of the Fe3O4/FeO/BaCl2 composites on microstructures, magnetic properties, and microwave absorption properties were examined. Based on this investigation, a mass ratio close to 3.5:5.5:1 was determined to be optimal. At this ratio, the Fe3O4/FeO/BaCl2 composites realize an effective absorption bandwidth of 6.70 GHz at only 1.16 mm thickness, covering the whole Ku-band, and the maximum reflection loss can be close to -46.8 dB at 1.4 mm. The robust microwave absorption performance of Fe3O4/FeO/BaCl2 composites can be attributed to heterostructured multi-interface structural design, the comprehensive effects of multiple reflections and dielectric/magnetic losses induced by BaCl2 with mesoporous structure as well as the aggregated Fe3O4/FeO particles. This work may offer insights into designing and preparing effective microwave absorption materials.

Advanced Applications of Polymer Hydrogels in Electronics and Signal Processing

The current state of affairs in the field of using polymer hydrogels for the creation of innovative systems for signal and image processing, of which computing is a special case, is analyzed. Both of these specific examples of systems capable of forming an alternative to the existing semiconductor-based computing technology, but assuming preservation of the used algorithmic basis, and non-trivial signal converters, the nature of which requires transition to fundamentally different algorithms of data processing, are considered. It is shown that the variability of currently developed information processing systems based on the use of polymers, including polymer hydrogels, leads to the need to search for complementary algorithms. Moreover, the well-known thesis that modern polymer science allows for the realization of functional materials with predetermined properties, at the present stage, receives a new sounding: it is acceptable to raise the question of creating systems built on a quasi-biological basis and realizing predetermined algorithms of information or image processing. Specific examples that meet this thesis are considered, in particular, promising information protection systems for UAV groups, as well as systems based on the coupling of neural networks with holograms that solve various applied problems. These and other case studies demonstrate the importance of interdisciplinary cooperation for solving problems arising from the need for further modernization of signal processing systems.

Electrochemical Switching of Electromagnetism by Hierarchical Disorder Tailored Atomic Scale Polarization

High-frequency electronic response governs a broad spectrum of electromagnetic applications from radiation protection, and signal compatibility, to energy recovery. Despite various efforts to manage electric conductivity, dynamic control over dielectric polarization for real-time electromagnetic modulation remains a notable challenge. Herein, an electrochemical lithiation-driven hierarchical disordering strategy is demonstrated for actively modulating electromagnetic properties. The controllable formation and diffusion of coherent interfaces and cation vacancies tailor the coupling of atomic electric field and thus the locally polarized domains, which leads to the reversible electromagnetic transparency/absorption switching with a tunable range of -0.8--20.4 dB for the reflection loss and a broad operation bandwidth of 4.6 GHz. Compared to traditional methods of heteroatomic doping, hydrogenation, mechanical deformation, and phase transition, the electrochemical strategy shows a larger regulation scope of dielectric permittivity with the maximum increase ratios of 260% and 1950% for real and imaginary parts, respectively. This enables the construction of various device architectures including the adaptive window and pixelated metasurface. The results offer opportunities to achieve intelligent electromagnetic devices and pave an avenue to rejuvenate various electromagnetic functions of semiconductive oxides.

Multifunctional Metamaterial with Reconfigurable Electromagnetic Scattering Properties for Advanced Stealth and Adaptive Applications

The rapid development of radar detection systems has led to an increased sensitivity to the electromagnetic (EM) scattering properties of detected targets. Flexible and adaptable EM scattering properties significantly enhance the survivability of battlefield weapons. This paper presents the design of a novel multifunctional metamaterial with reconfigurable EM scattering properties based on a bistable curved beam. In addition to the cushioning and energy absorption properties of curved beams, the metamaterial achieves more than 90% EM absorption in the frequency range of 2.17-17.31 GHz, with a relative thickness of only 0.09λL. The bistable nature of the metamaterial allows it to switch between different states. Moreover, combined with the digital coding, this metamaterial can continuously adjust the absorbing bandwidth and further enhance the EM absorption rate within a specific frequency band range. If applied to satellite configurations, the developed metamaterial significantly reduces the radar cross section and offers potential applications in reconfiguring EM scattering properties, when applied to satellite configurations. By actively controller and reconstructing the EM scattering properties at certain frequency points, the metamaterial can achieve camouflage, providing innovative solutions for future stealth technology, electronic countermeasures, and deception jamming in radar detection.

Multi-scale design of MWCNT/glass fiber/balsa wood composite multilayer stealth structure with wide broadband absorption and excellent mechanical properties

In unmanned aircraft applications, electromagnetic wave (EMW) absorbers suffer from defects in narrow absorption bands and poor mechanical properties. To solve the problems, a lightweight multilayer stealth structure with wide broadband absorption performance and excellent mechanical properties was designed and prepared by adjusting microscopically the number of multi-walled carbon nanotubes (MWCNT) and modulating macroscopically the thickness-matching relationship of the structure to promote the absorption of EMW synergistically. Under the MWCNT of 30 wt% and the depletion layer with the thickness of 0.2 mm, the effective absorption bandwidth (EAB) covers the entire Ku-band while maintaining a minimum reflection loss (RL) of -15 dB. Besides, the radar cross-sectional area attenuation is as high as 23.1 dBm2, as well as the mechanical properties of the radar absorbing structures (RAS) were improved significantly due to the reducing structural density from balsa wood and the enhancement effect of glass fiber mats (GFM). The study constructed balsa-based RAS with excellent EMW absorbing and mechanical properties from both micro-nano scale and macro-structure, providing a research route for designing high-performance and lightweight stealth structures.

Strong and Robust Core-Shell Ceramic Fibers Composed of Highly Compacted Nanoparticles for Multifunctional Electronic Skin

Functional fibers composed of textiles are considered a promising platform for constructing electronic skin (e-skin). However, developing robust electronic fibers with integrated multiple functions remains a formidable task especially when a complex service environment is concerned. In this work, a continuous and controllable strategy is demonstrated to prepare e-skin-oriented ceramic fibers via coaxial wet spinning followed by cold isostatic pressing. The resulting core-shell structured fiber with tightly compacted Al-doped ZnO nanoparticles in the core and highly ordered aramid nanofibers in the shell exhibit excellent tensile strength (316 MPa) with ultra-high elongation (33%). Benefiting from the susceptible contacts between conducting ceramic nanoparticles, the ceramic fiber shows both ultrahigh sensitivity (gauge factor = 2141) as a strain sensor and a broad working range up to 70 °C as a temperature sensor. Furthermore, the tunable core-shell structure of the fiber enables the optimization of impedance matching and attenuation of electromagnetic waves for the corresponding textile, resulting in a minimum reflection loss of -39.1 dB and an effective absorption bandwidth covering the whole X-band. Therefore, the versatile core-shell ceramic fiber-derived textile can serve as a stealth e-skin for monitoring the motion and temperature of robots under harsh conditions.

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.

Unveiling the scope and perspectives of MOF-derived materials for cutting-edge applications

Although synthesis and design of MOFs are crucial factors to the successful implementation of targeted applications, there is still lack of knowledge among researchers about the synthesis of MOFs and their derived composites for practical applications. For example, many researchers manipulate study results, and it has become quite difficult to quit this habit specifically among the young researchers Undoubtedly, MOFs have become an excellent class of compounds but there are many challenges associated with their improvement to attain diverse applications. It has been noted that MOF-derived materials have gained considerable interest owing to their unique chemical properties. These compounds have exhibited excellent potential in various sectors such as energy, catalysis, sensing and environmental applications. It is worth mentioning that most of the researchers rely on commercially available MOFs for use as precursor supports, but it is an unethical and wrong practice because it prevents the exploration of the hidden diversity of similar materials. The reported studies have significant gaps and flaws, they do not have enough details about the exact parameters used for the synthesis of MOFs and their derived materials. For example, many young researchers claim that MOF-based materials cannot be synthesized as per the reported instructions for large-scale implementation. In this regard, current article provides a comprehensive review of the most recent advancements in the design of MOF-derived materials. The methodologies and applications have been evaluated together with their advantages and drawbacks. Additionally, this review suggests important precautions and solutions to overcome the drawbacks associated with their preparation. Applications of MOF-derived materials in the fields of energy, catalysis, sensing and environment have been discussed. No doubt, these materials have become excellent class but there are still many challenges ahead to specify it for the targeted applications.

In Situ Exsolution-Prepared Solid-Solution-Type Sulfides with Intracrystal Polarization for Efficient and Selective Absorption of Low-Frequency Electromagnetic Wave

The excellent dielectric properties and tunable structural design of metal sulfides have attracted considerable interest in realizing electromagnetic wave (EMW) absorption. However, compared with traditional monometallic and bimetallic sulfides that are extensively studied, the unique physical characteristics of solid-solution-type sulfides in response to EMW have not been revealed yet. Herein, a unique method for preparing high-purity solid-solution-type sulfides is proposed based on solid-phase in situ exsolution of different metal ions from hybrid precursors. Utilizing CoAl-LDH/MIL-88A composite as a precursor, Fe0.8Co0.2S single-phase nanoparticles are uniformly in situ formed on an amorphous substrate (denoted as CoAl), forming CoAl/Fe0.8Co0.2S heterostructure. Combing with density functional theory (DFT) calculations and wave absorption simulations, it is revealed that Fe0.8Co0.2S solid solution has stronger intracrystal polarization and electronic conductivity than traditional monometallic and bimetallic sulfides, which lead to higher dielectric properties in EM field. Therefore, CoAl/Fe0.8Co0.2S heterostructure exhibits significantly enhanced EMW absorption ability in the low-frequency region (2-6 GHz) and can achieve frequency screening by selectively absorbing EMW of specific frequency. This work not only provides a unique method for preparing high-purity solid-solution-type sulfides but also fundamentally reveals the physical essence of their excellent EMW absorption performance.

Designing Symmetric Gradient Honeycomb Structures with Carbon-Coated Iron-Based Composites for High-Efficiency Microwave Absorption

The impedance matching of absorbers is a vital factor affecting their microwave absorption (MA) properties. In this work, we controllably synthesized Material of Institute Lavoisier 88C (MIL-88C) with varying aspect ratios (AR) as a precursor by regulating oil bath conditions, followed by one-step thermal decomposition to obtain carbon-coated iron-based composites. Modifying the precursor MIL-88C (Fe) preparation conditions, such as the molar ratio between metal ions and organic ligands (M/O), oil bath temperature, and oil bath time, influenced the phases, graphitization degree, and AR of the derivatives, enabling low filler loading, achieving well-matched impedance, and ensuring outstanding MA properties. The MOF-derivatives 2 (MD2)/polyvinylidene Difluoride (PVDF), MD3/PVDF, and MD4/PVDF absorbers all exhibited excellent MA properties with optimal filler loadings below 20 wt% and as low as 5 wt%. The MD2/PVDF (5 wt%) achieved a maximum effective absorption bandwidth (EAB) of 5.52 GHz (1.90 mm). The MD3/PVDF (10 wt%) possessed a minimum reflection loss (RLmin) value of - 67.4 at 12.56 GHz (2.13 mm). A symmetric gradient honeycomb structure (SGHS) was constructed utilizing the high-frequency structure simulator (HFSS) to further extend the EAB, achieving an EAB of 14.6 GHz and a RLmin of - 59.0 dB. This research offers a viable inspiration to creating structures or materials with high-efficiency MA properties.

Mixed-Dimensional Assembly Strategy to Construct Reduced Graphene Oxide/Carbon Foams Heterostructures for Microwave Absorption, Anti-Corrosion and Thermal Insulation

Considering the serious electromagnetic wave (EMW) pollution problems and complex application condition, there is a pressing need to amalgamate multiple functionalities within a single substance. However, the effective integration of diverse functions into designed EMW absorption materials still faces the huge challenges. Herein, reduced graphene oxide/carbon foams (RGO/CFs) with two-dimensional/three-dimensional (2D/3D) van der Waals (vdWs) heterostructures were meticulously engineered and synthesized utilizing an efficient methodology involving freeze-drying, immersing absorption, secondary freeze-drying, followed by carbonization treatment. Thanks to their excellent linkage effect of amplified dielectric loss and optimized impedance matching, the designed 2D/3D RGO/CFs vdWs heterostructures demonstrated commendable EMW absorption performances, achieving a broad absorption bandwidth of 6.2 GHz and a reflection loss of - 50.58 dB with the low matching thicknesses. Furthermore, the obtained 2D/3D RGO/CFs vdWs heterostructures also displayed the significant radar stealth properties, good corrosion resistance performances as well as outstanding thermal insulation capabilities, displaying the great potential in complex and variable environments. Accordingly, this work not only demonstrated a straightforward method for fabricating 2D/3D vdWs heterostructures, but also outlined a powerful mixed-dimensional assembly strategy for engineering multifunctional foams for electromagnetic protection, aerospace and other complex conditions.

In Situ Atomic Reconstruction Engineering Modulating Graphene-Like MXene-Based Multifunctional Electromagnetic Devices Covering Multi-Spectrum

With the diversified development of big data, detection and precision guidance technologies, electromagnetic (EM) functional materials and devices serving multiple spectrums have become a hot topic. Exploring the multispectral response of materials is a challenging and meaningful scientific question. In this study, MXene/TiO2 hybrids with tunable conduction loss and polarization relaxation are fabricated by in situ atomic reconstruction engineering. More importantly, MXene/TiO2 hybrids exhibit adjustable spectral responses in the GHz, infrared and visible spectrums, and several EM devices are constructed based on this. An antenna array provides excellent EM energy harvesting in multiple microwave bands, with |S11| up to - 63.2 dB, and can be tuned by the degree of bending. An ultra-wideband bandpass filter realizes a passband of about 5.4 GHz and effectively suppresses the transmission of EM signals in the stopband. An infrared stealth device has an emissivity of less than 0.2 in the infrared spectrum at wavelengths of 6-14 µm. This work can provide new inspiration for the design and development of multifunctional, multi-spectrum EM devices.

Enhanced Microwave Deicing Capacity of Cement Pavement with Carbon Fiber Screens

The combination of an absorbing structure and a road is a promising strategy for road deicing using microwaves. In this study, cement mortar (CM) specimens containing a carbon fiber screen (CFS) were prepared to concentrate electromagnetic losses on a road surface. The effect of the size and depth of the CFS on the surface heating efficiency of the microwave was studied and optimized, and a microwave deicing experiment was conducted. The results indicated that the destructive interference produced by the CFS led to the effective surface heating of the CM/CFS specimens. The optimal surface heating rate was 0.83 °C/s when the spacing, depth, and width of the CFS were 5.22, 13.31, and 2.80 mm, respectively. The deicing time was shortened by 21.68% from 83 to 65 s, and the heating rate increased by 17.14% from 0.70 to 0.82 °C/s for the specimen with CFS-1, which was 15 mm depth. Our results demonstrate that CM/CFS composite structures can be effectively applied to increase the capacity and accelerate the development of the microwave deicing of roads.

A novel portable anechoic chamber using ultra-thin 2D microwave absorber for industrial 5.0

In this paper, the authors, for the first time, have shown the use of 2D conformal microwave absorbing material (MAM) in the design and fabrication of a portable Anechoic chamber (AC). The MAM is fabricated on the transparent and conductive metal oxide layer named indium-tin-oxide (ITO) with Polyethylene terephthalate as the substrate and the ground plane for zero transmission having overall thickness of 0.012 λ where λ is calculated at 0.7 GHz. The MAM is characterized for 0.7 to 18 GHz for both TE- and TM-polarisation and oblique incidence. High sheet resistance, dipole-like resonance structure patterned on the ITO, and the air-spacing between the layers is optimized to achieve broadband absorption. The MAM is used to line the six sides of the rectangular anechoic chamber having inner dimensions of: (L × W × H: 850 × 650 × 720 mm3). The return loss (RL), gain, and radiation pattern of three antenna working at 1.56, 2.43, and 4.93 GHz are analyzed inside the AC. The measurement results for all frequencies very well match with the simulation studies, thus validating and opening the door for the future use of ultra-thin and planar MAM in the AC.

Regulation of high value-added carbon nanomaterials by DC arc plasma using graphite anodes from spent lithium-ion batteries

With the extensive use of lithium-ion batteries (LIBs), neglecting to recycle graphite anodes from LIBs leads to environmental pollution and the waste of graphite resources. Thus, developing an efficient and environment-protecting approach to reusing spent graphite anodes is necessary. Here, high value-added graphene sheets (GS), carbon nanohorns (CNHs), fluorine-doped CNHs (F-CNHs), and amorphous carbon nanoballs (ACNs) were prepared from spent graphite anodes of LIBs via DC arc plasma. In order to control the conversion of spent graphite anodes into various carbon nanomaterials, the growth mechanism of carbon nanomaterials is investigated by quenching rate. Benefiting from the extremely high quenching rates (>1.8 × 106 K/s) produced by DC arc plasma, the particle size of the prepared ACNs and CNHs is small and evenly distributed. The CNHs show a "dahlia-like" structure, and the number of graphene layers is only 3-8. Furthermore, the structural transformation mechanism of carbon nanomaterials is researched by deposition temperature. The ACNs, few-layer GS, and CNHs produced by the high quenching rates are unstable and prone to structural transformation. When these carbon nanomaterials are deposited on the cathode surface and cathode holder, the ACNs, "dahlia-like" CNHs, and GS undergo processes of fusing and overlaying at high temperatures, respectively, resulting in the agglomeration and increased particle size of ACNs and "seed-like" CNHs. Meanwhile, the GS is bent and converted into carbon nanocages (CBCs). Overall, the carbon nanomaterials prepared using spent anodes from LIBs by arc plasma are a facile, environment-friendly, and economical strategy to achieve high value-added utilization of the graphite.

Unveiling the sp2 ─sp3 C─C Polar Bond Induced Electromagnetic Responding Behaviors by a 2D N-doped Carbon Nanosheet Absorber

The infertile electromagnetic (EM) attenuating behavior of carbon material makes the improvement of its performance remain a significant challenge. Herein, a facile and low-cost strategy radically distinct from the prevalent approaches by constructing polar covalent bonds between sp2 -hybridized and sp3 -hybridized carbon atoms to introduce strong dipolar polarization is proposed. Through customizing and selectively engineering the N moieties conjugated with carbon rings, the microstructure of the as-synthesized 2D nanosheet is gradually converted with the partial transition from sp3 carbons to sp2 carbons, where the electric dipoles between them are also tuned. Supported by the DFT calculations, a progressively enhanced sp2 ─sp3 C─C dipolar polarization is caused by this controllable structure evolution, which is demonstrated to contribute dominantly to the total dielectric loss. By virtue of this unduplicated loss behavior, a remarkable effective absorption bandwidth (EAB) beyond -10 dB of 8.28 GHz (2.33 mm) and an ultrawide EAB beyond -5 dB of 13.72 GHz (4.93 mm) are delivered, which upgrade the EM performance of carbon material to a higher level. This study not only demonstrates the huge perspective of sp2 ─sp3 -hybridized carbon in EM elimination but also gives pioneering insights into the carbon-carbon polarization mechanism for guiding the development of advanced EM absorption materials.

3D Printed Bioinspired Flexible Absorber: Toward High-Performance Electromagnetic Absorption at 75-110 GHz

Although various bioinspired devices designed to increase absorption and minimize reflection have been developed, there is no research focusing on wideband electromagnetic (EM) absorbers at 75-110 GHz, which is not conducive to the advancement of millimeter wave technology. Herein, inspired by the ultrablack butterfly scale nanostructure, an innovative flexible multistage honeycomb structure absorber (FMHSA) of carbonyl iron (CIP)/multiwalled carbon nanotubes (MWCNTs)/flexible photopolymer resin (FPR) composite is successfully prepared by digital light processing (DLP) 3D printing. FMHSA exhibits excellent EM wave absorption performance with full band absorption at 75-110 GHz under different bending states. At the bending angle of 150°, The effective absorption bandwidth of FMHSA is 35 GHz, covering the whole W-band, and its minimum reflection loss (RL) value is -37.04 dB. Moreover, integrated functionalities are revealed in the FMHSA, including superior flexibility, recoverability, and lightweight feature. Such findings may prove to be useful for the design of flexible absorbers with potential EM absorption and improved wearability.

Construction of MoS2-ReS2 Hybrid on Ti3C2Tx MXene for Enhanced Microwave Absorption

Utilizing interface engineering to construct abundant heterogeneous interfaces is an important means to improve the absorbing performance of microwave absorbers. Here, we have prepared the MXene/MoS2-ReS2 (MMR) composite with rich heterogeneous interfaces composed of two-dimensional Ti3C2Tx MXene and two-dimensional transition metal disulfides through a facile hydrothermal process. The surface of MXene is completely covered by nanosheets of MoS2 and ReS2, forming a hybrid structure. MRR exhibits excellent absorption performance, with its strongest reflection loss reaching -51.15 dB at 2.0 mm when the filling ratio is only 10 wt%. Meanwhile, the effective absorption bandwidth covers the range of 5.5-18 GHz. Compared to MXene/MoS2 composites, MRR with a MoS2-ReS2 heterogeneous interface exhibits stronger polarization loss ability and superior absorption efficiency at the same thickness. This study provides a reference for the design of transition metal disulfides-based absorbing materials.