In Situ Loading of Ni3ZnC0.7 Nanoparticles with Carbon Nanotubes to 3D Melamine Sponge Derived Hollow Carbon Skeleton toward Superior Microwave Absorption and Thermal Resistance

The simple and low-cost construction of a 3D network structure is an ideal way to prepare high-performance electromagnetic wave (EMW) absorption materials. Herein, a series of carbon skeleton/carbon nanotubes/Ni3ZnC0.7 composites (CS/CNTs/Ni3ZnC0.7) are successfully prepared by in situ growth of Ni3ZnC0.7 and CNTs on 3D melamine sponge carbon. With the increase of precursor, Ni3ZnC0.7 nanoparticles nucleate and catalyze the generation of CNTs on the surface of the carbon skeleton. The minimum reflection loss (RL) value of the S60min composite (loading time of 60 min) reaches -86.6 dB at 1.6 mm and effective absorption bandwidth (EAB, RL≤-10 dB) is up to 9.3 GHz (8.7-18 GHz). The 3D network sponge carbon with layered micro/nanostructure and hollow skeleton promotes multiple reflection and absorption mechanisms of incident EMW. The N-doping and defects can be equivalent to an electric dipole, providing dipole polarization to increase dielectric relaxation. The uniform Ni3ZnC0.7 nanoparticles and CNTs play a key role in dissipating electromagnetic energy, blocking heat transfer, and enhancing the mechanical properties of the skeleton. Fortunately, the composite displays a quite low thermal conductivity of 0.09075 W m·K-1 and good flexibility, which can provide insulation and quickly recover to its original state after being stressed.

Freeze-Cast Ni-MOF Nanobelts/Chitosan-Derived Magnetic Carbon Aerogels for Broadband Electromagnetic Wave Absorption

The exceptional benefits of carbon aerogels, including their low density and tunable electrical characteristics, infuse new life into the realm of creating ultralight electromagnetic wave absorbers. The clever conceptualization and straightforward production of carbon-based aerogels, which marry aligned microporous architecture with nanoscale heterointerfaces and atomic-scale defects, are vital for effective multiscale microwave response. We present an uncomplicated synthesis method for crafting aligned porous Ni@C nanobelts anchored on N, S-doped carbon aerogels (Ni@C/NSCAs), featuring multiscale structural intricacies─achieved through the pyrolysis of freeze-cast Ni-MOF nanobelts and chitosan aerogel composites. The well-ordered porous configuration, combined with multiple heterointerfaces adopting a "nanoparticles-nanobelts-nanosheets" contact schema, along with a wealth of defects, adeptly modulates conductive, polarization, and magnetic losses to realize an equilibrium in impedance matching. This magnetically doped carbon aerogel showcases an impressive effective absorption bandwidth of 8.96 GHz and a minimum reflection loss of -68.82 dB, while maintaining an exceptionally low filler content of 1.75 wt %. Additionally, the applied coating exhibits an astonishing radar cross-section reduction of 51.7 dB m2, signifying its superior radar wave scattering capabilities. These results offer key insights into the attainment of broad-spectrum microwave absorption features by enhancing the multiscale structure of current aerogels.

Metal Valence State Modulation Strategy to Design Core@shell Hollow Carbon Microspheres@MoSe2/MoOx Multicomponent Composites for Anti-Corrosion and Microwave Absorption

The exploitation of multicomponent composites (MCCs) has become the main pathway for obtaining advanced microwave absorption materials (MAMs). Herein, a metal valence state modulation strategy is proposed to tune the electromagnetic (EM) parameters and improve microwave absorption performances. Core@shell hollow carbon microspheres@MoSe2 and hollow carbon microspheres@MoSe2/MoOx MCCs with various mixed-valence states content are well-designed and produced by a simple hydrothermal reaction or/and heat treatment process. The results reveal that the thermal treatment of hollow carbon microspheres@MoSe2 in Ar and Ar/H2 leads to the in situ formation of MoOx and multivalence state, respectively, and the enhanced content of Mo4+ in the designed MCCs greatly boosts their impedance matching characteristics, polarization, and conduction loss capacities, which lead to their evidently improved EM wave absorption properties. Amongst, the as-prepared hollow carbon microspheres@MoSe2/MoOx MCCs achieve an effective absorption bandwidth of 5.80 GHz under a matching thickness of 1.97 mm and minimum reflection loss of -21.49 dB. Therefore, this work offers a simple and universal method to fabricate core@shell hollow carbon microspheres@MoSe2/MoOx MCCs, and a novel and feasible metal valence state modulation strategy is proposed to develop high-efficiency MAMs.

Wrinkle Structure Regulating Electromagnetic Parameters in Constructed Core-shell ZnFe2O4@PPy Microspheres as Absorption Materials

Structure engineering of magnetic-dielectric multi-components is emerging as an effective approach for presuming high-performance electromagnetic (EM) absorption, but still faces bottlenecks due to the ambiguous regulation mechanism of surface morphology. Here, a novel wrinkled surface structure is tailored on the ZnFe2O4 microsphere via a spray-pyrolysis induced Kirkendall diffusion effect, the conductivity of the sample is affected, and a better impedance matching is adjusted by modulating the concentration of metal nitrate precursors. Driven by a vapor phase polymerization, conductive polypyrrole (PPy) shell are in situ decorated on the ZnFe2O4 microsphere surfaces, ingeniously constructing a core-shell ZnFe2O4@PPy composites. Moreover, a systematic investigation reveals that this unique wrinkled surface structure is highly dependent on the metal salt concentration. Optimized wrinkle ZnFe2O4@PPy composite exhibits a minimum reflection loss (RLmin) reached -41.0 dB and the effective absorption bandwidth (EAB) can cover as wide as 4.1 GHz. The enhanced interfacial polarization originated from high-density ZnFe2O4-PPy heterostructure, and the conduction loss of PPy contributes to the boosted dielectric loss capability. This study gives a significant guidance for preparing high-performance EM composites by tailoring the surface wrinkle structure.

Study on Properties of Glass-Fiber-Fabric-Reinforced Microwave-Absorbing Composites

In this paper, the glass-fiber-fabric-reinforced resin-based absorbing composites were prepared, and their microwave-absorbing properties were studied via simulation and experiment. The simulation results show that the absorption bandwidth of the absorbing material can cover the X\C\S band, respectively, at different thicknesses. The minimum reflection loss (RL) of the composite with a thickness of 2.2 mm is -27.4 dB at 5.95 GHz. However, the experiment results are quite different from those of the simulation. The metallographic results indicate that it is the change of the mass fraction of the absorbents in the composites after curing that causes the difference. According to the metallographic results, three shape approximation methods were proposed to calculate the real mass ratio of the absorbents in the composites, namely, parallelogram approximation, bows approximation, and elliptical approximation. Meanwhile, the structural parameter Kf was introduced to optimize the calculation results. The electromagnetic parameters of the material based on the calculation results were measured, and the results show that the simulation results obtained via bow approximation have a better coincidence to the experiment results, and the mass ratio of the absorbent raises by around 9.95%, which lays a foundation for the subsequent design of microwave-absorbing composites.

Microwave-Absorbing Foams with Adjustable Absorption Frequency and Structural Coloration

Microwave-absorbing materials with regulatable absorption frequency and optical camouflage hold great significance in intelligent electronic devices and advanced stealth technology. Herein, we present an innovative microwave-absorbing foam that can dynamically tune microwave absorption frequencies via a simple mechanical compression while in parallel enabling optical camouflage over broad spectral ranges by adjusting the structural colors. The vivid colors spanning different color categories generated from thin-film interference can be precisely regulated by adjusting the thickness of the conformal TiO2 coatings on Ni/melamine foam. Enhanced interfacial and defect-induced polarizations resulting from the introduction of TiO2 coating synergistically contribute to the dielectric attenuation performance. Consequently, such a foam exhibits exceptional microwave absorption capabilities, and the absorption frequency can be dynamically tuned from the S band to the Ku band by manipulating its compression ratio. Additionally, simulation calculations validate the adjustable electromagnetic wave loss behavior, offering valuable insights for the development of next-generation intelligent electromagnetic devices across diverse fields.

S-NiSe/HG Nanocomposites with Balanced Dielectric Loss Encapsulated in Room-Temperature Self-Healing Polyurethane for Microwave Absorption and Corrosion Protection

Exploring anticorrosion electromagnetic wave (EMW) absorbing materials in harsh conditions remains a challenge. Herein, S-NiSe/HG nanocomposites encapsulated in room-temperature self-healing polyurethane (S-NiSe/HG/SPU) were exploited as superior anticorrosion EMW absorbing materials. A dual-defect engineering collaborative Schottky interface construction endows S-NiSe/HG with a high vacancy concentration, abundant defects, and moderate conductivity. These structural merits synergistically balance dielectric loss by enhancing dipole-interface polarization loss and optimizing conduction loss. As a result, S-NiSe/HG demonstrates the optimal EMW absorption performance with a minimum reflection loss (RLmin) of -54.8 dB and an adequate absorption bandwidth (EAB) of 7.1 GHz. Besides, S-NiSe/HG/SPU combines the maze effect of S-NiSe/HG with the active repair capability of SPU, thereby providing long-term corrosion resistance for the Mg alloy. Even under corrosion for 10 days, S-NiSe/HG/SPU affords a low corrosion current density (1.3 × 10-5 A) and high charge transfer resistance (3796 Ω cm2). Overall, this work provides valuable insights for in-depth exploration of dielectric loss and development of multifunctional EMW-absorbing materials.

Lightweight, Flexible, and Thermal Insulating Carbon/SiO2 @CNTs Composite Aerogel for High-Efficiency Microwave Absorption

A complex electromagnetic environment is a formidable challenge in national defense areas. Microwave-absorbing materials are considered as a strategy to tackle this challenge. In this work, lightweight, flexible, and thermal insulating Carbon/SiO2 @CNTs (CSC) aerogel is successfully prepared coupled with outstanding microwave absorbing performance, through freeze-drying and high-temperature annealing techniques. The CSC aerogel shows a strong reflection loss (-55.16 dB) as well as wide effective absorbing bandwidth (8.5 GHz) in 2-18 GHz. It also retains good microwave absorption properties under tension and compression. Radar cross-sectional (RCS) simulation result demonstrates the CSC processing a strong reduction ability of RCS compared with a metal plate. Further exploration shows amazing flexibility and good thermal insulation properties of CSC. The successful preparation of this composite aerogel provides a broad prospect for the design of microwave-absorbing materials.

Linkage Effect Induced by Hierarchical Architecture in Magnetic MXene-based Microwave Absorber

Hierarchical architecture engineering is desirable in integrating the physical-chemical behaviors and macroscopic properties of materials, which present great potential for developing multifunctional microwave absorption materials. However, the intrinsic mechanisms and correlation conditions among cellular units have not been revealed, which are insufficient to maximize the fusion of superior microwave absorption (MA) and derived multifunctionality. Herein, based on three models (disordered structure, porous structure, lamellar structure) of structural units, a range of MXene-aerogels with variable constructions are fabricated by a top-down ice template method. The aerogel with lamellar structure with a density of only 0.015 g cm-3 exhibits the best MA performance (minimum reflection loss: -53.87 dB, effective absorption bandwidth:6.84 GHz) at a 6 wt.% filling ratio, which is preferred over alternative aerogels with variable configurations. This work elucidates the relationship between the hierarchical architecture and the superior MA performance. Further, the MXene/CoNi Composite aerogel with lamellar structure exhibits >90% compression stretch after 1000 cycles, excellent compressive properties, and elasticity, as well as high hydrophobicity and thermal insulation properties, broadening the versatility of MXene-based aerogel applications. In short, through precise microstructure design, this work provides a conceptually novel strategy to realize the integration of electromagnetic stealth, thermal insulation, and load-bearing capability simultaneously.

Effect of Crystal Transformation on the Intrinsic Defects and the Microwave Absorption Performance of Mo2 TiC2 Tx /RGO Microspheres

The nitrides and carbides of transition metals are highly favored due to their excellent physical and chemical properties, among which MXene is a hot research topic for microwave absorption. Herein, the controlled preparation of 3D Mo2 TiC2 Tx -based microspheres toward microwave absorption is reported for the first time. With the merits of the performances of both reduced graphite oxide (RGO) and MXene sufficiently considered, the influence of carbonization temperature on the internal crystal structure and the effective microwave-material interaction surface of the prepared Mo2 TiC2 Tx /RGO is systematically investigated. The structure-activity relationships relating the apparent morphology and crystal structure to the microwave absorption performance are deeply explored, and the wave absorption mechanism is put forward as well. The results show that the Mo2 TiC2 Tx /RGO-700 product obtained after heating treatment at 700 °C exhibits excellent microwave absorption performance, with the RLmin being up to -55.1 dB@2.1 mm@13.8 GHz, and the corresponding effective absorption bandwidth covering 5.7 GHz. The outstanding microwave absorption characteristics are attributed to the appropriate impedance matching, high specific surface area, rich intrinsic defects, desirable conductivity, and strong multipolarization capabilities. This work enriches the types of MXene-based composite absorbers and provides a new strategy for controlled preparation of high-performance 3D composite absorbers.

3D Lightweight Interconnected Melamine Foam Modified with Hollow CoFe2O4/MXene toward Efficient Microwave Absorption

Considering the increasing severity of electromagnetic wave pollution, the development of high-performance low-filler-content microwave absorbers possessing wide frequency bands and strong absorption for practical applications is a demanding research hotspot. In this study, from the perspectives of the electromagnetic component coordination and structural design, a three-dimensional (3D) interconnected CoFe2O4/MXene-melamine foam (MF) was constructed via simple impregnation and a single freeze-drying step. By changing the absorber (CoFe2O4/MXene) concentration, the pore opening and electromagnetic properties of the 3D foams can be effectively adjusted. When the absorber concentration is sufficiently high to clog the internal pores, the microwave absorption is hindered. When the filler (CoFe2O4/MXene-MF) content is just ∼5.8 wt % (at a density of ∼33.3 mg cm-3), a minimum reflection loss (RLmin) of -72.1 dB is achieved at a matching thickness of 3.32 mm, and an effective absorption bandwidth (4.54 GHz) covering the whole X band is achieved at a thickness of 3 mm. CoFe2O4/MXene-MF, which possesses a 3D porous electromagnetic network structure, optimizes impedance matching and enhances multiple polarization relaxations and reflections/scattering, resulting in superior absorption capabilities. In particular, the continuous network structure ensures the uniform distribution of electromagnetic fields in the microstructure, achieving high absorption at low filler contents. This work provides a reference for subsequent 3D absorber concentration studies and a novel engineering strategy for preparing a low-filler-content, lightweight, and efficient electromagnetic wave absorber, which could be applied in the fields of radar security and information communications.

Regulation Dipole Moments of N-Doped Graphene Coordinated with FePc Toward Highly Efficient Microwave Absorption Performance in C Band

The development of composites with highly efficient microwave absorption (MA) performance deeply depends on polarization loss, which can be induced by charge redistribution. Considering the fact that polarization centers can be easily obtained in graphene, herein, iron phthalocyanine (FePc) is used as polarization site to coordinate with nitrogen-doped graphene (FePc/N-rGO) to optimize MA performance comprehensively. The factors influencing MA properties focus on the interaction between FePc and N-rGO, and the change of dipole moments. The density functional theory (DFT) results demonstrated that FePc has strong interaction with N defect sites in graphene. The charge loss for FePc and charge accumulation for N-rGO occurred, leading to great increase of dipole moment, and the increased dipole moment can be acted as a descriptor to evaluate the enhanced polarization loss. Due to high charge redistribution capacity of N defect sites and FePc polarization centers, the FePc/N-rGO showed excellent MA properties in C band, and the minimum reflection loss value can reach -49.3 dB at 5.4 GHz with thickness of 3.8 mm. In addition, the fabric loaded with FePc/N-rGO showed good heat dissipation property. This work opens the door to the development of MA performance bound to polarization site with dipole moment.

Peelable Microwave Absorption Coating with Reusable and Anticorrosion Merits

The peelable microwave absorption (MA) coating with reversible adhesion for stable presence on substrates and easy release without any residuals is highly desired in temporary electromagnetic protection, which can quickly enter and disengage the electromagnetic protection state according to the real-time changeable harsh surroundings. On the contrary, with the incorporation of abundant absorbent to achieve excellent MA ability, the tunable adhesion and sufficient cohesion are extremely challenging to fulfill the above requirement. The reported peelable coatings still have problems in controlling adhesion/cohesion strength and coating release, facing substantial residuals after peeling even using complex chemical modification or abundant additives. Herein, a peelable MA coating based on the block characteristics of polar and nonpolar segments of poly(styrene-(ethylene-co-butylene)-styrene) (SEBS) is successfully developed. The polyaniline-decorated carbon nanotube as a microwave absorber plays a positive influence on the adhesion/cohesion of the coating due to bonding interaction. The competitive effective absorption bandwidth (EAB) of 8.8 GHz and controllable yet reversible adhesion release on various substrates and complex surfaces have been achieved. The reusability endows peelable MA coating with 93% retention of EAB even after ten coating-peeling cycles. The coating with excellent chemical and adhesion stability can effectively protect substrates from salt/acid/alkali corrosion, showing over 98% retention of EAB even after 8 h of accelerated corrosion. Our peelable MA coating via a general yet reliable approach provides a prospect for temporary electromagnetic protection.

Hierarchical-Bioinspired MOFs Enhanced Electromagnetic Wave Absorption

Proteins exhibit complex and diverse multi-dimensional structures, along with a wide range of functional groups capable of binding metal ions. By harnessing the unique characteristics of proteins, it is possible to enhance the synthesis of metal-organic frameworks (MOFs) and modify their morphology. Here, the utilization of biomineralized bovine serum albumin (BSA) protein as a template for synthesizing Mil-100 with superior microwave absorption (MA) properties is investigated. The multi-dimensional structure and abundant functional groups of biomineralized BSA protein make it an ideal candidate for guiding the synthesis of Mil-100 with intricate network structures. The BSA@Mil-100 synthesized using this method exhibits exceptional uniformity and monodispersity of nanocrystals. The findings suggest that the BSA protein template significantly influences the regulation of nanocrystal and microstructure formation of Mil-100, resulting in a highly uniform and monodisperse structure. Notably, the synthesized 2-BSA@Mil-100 demonstrates a high reflection loss value of -58 dB at 8.85 GHz, along with a maximum effective absorption bandwidth value of 6.79 GHz, spanning from 6.01 to 12.8 GHz. Overall, this study highlights the potential of utilizing BSA protein as a template for MOF synthesis, offering an effective strategy for the design and development of high-performance MA materials.

Entropy-Driven Morphology Regulation of MAX Phase Solid Solutions with Enhanced Microwave Absorption and Thermal Insulation Performance

Morphology regulation and composition design have proved to be effective strategies for the fabrication of desirable microwave absorbers. However, it is still challenging to precisely control the microstructure and components of MAX phases. Herein, an entropy-driven approach, a transition from irregular grains (low entropy) to sheet structure (high entropy), is proposed to modulate the morphology of MAX phases. The theoretical calculation indicates that the morphology evolution can be ascribed to the enlarged energy difference between (11_00) and (0001) facets. The enriched structural defects and optimized morphologies yield significant dipolar polarization, interfacial polarization, multiple reflections, and scattering, which all enhance the electromagnetic wave absorption performance of (V0.25 Ti0.25 Cr0.25 Mo0.25 )2 GaC. Specifically, its minimum reflection loss can reach up to -47.12 dB at 12.13 GHz, and the optimal effective absorption bandwidth is 4.56 GHz (2.03 mm). Meanwhile, (V0.25 Ti0.25 Cr0.25 Mo0.25 )2 GaC shows also pronounced thermal insulation properties affording it good reliability in the harsh working environment. This work offers a novel approach to designing and regulating the morphology of the high entropy MAX phase, and also presents an opportunity to elucidate the relationship between entropy and electromagnetic wave absorption performance.

Magnetic Bimetallic Heterointerface Nanomissiles with Enhanced Microwave Absorption for Microwave Thermal/Dynamics Therapy of Breast Cancer

Microwave thermotherapy (MWT) has shown great potential in cancer treatment due to its deep tissue penetration and minimally invasive nature. However, the poor microwave absorption (MA) properties of the microwave thermal sensitizer in the medical frequency band significantly limit the thermal effect of MWT and then weaken the therapeutic efficacy. In this paper, a Ni-based multilayer heterointerface nanomissile of MOFs-Ni-Ru@COFs (MNRC) with improved MA performance in the desired frequency band via introducing magnetic loss and dielectric loss is developed for MWT-based treatment. The loading of the Ni nanoparticle in MNRC mediates the magnetic loss, introducing the MA in the medical frequency band. The heterointerface formed in the MNRC by nanoengineering induces significant interfacial polarization, increasing the dielectric loss and then enhancing the generated MA performance. Moreover, MNRC with the strong MA performance in the desired frequency range not only enhances the MW thermal effect of MWT but also facilitates the electron and energy transfer, generating reactive oxygen species (ROS) at tumor sites to mediate microwave dynamic therapy (MDT). The strategy of strengthening the MA performance of the sensitizer in the medical frequency band to improve MWT-MDT provides a direction for expanding the clinical application of MWT in tumor treatment.

A Comprehensive Review of Electromagnetic Interference Shielding Composite Materials

The interaction between matter and microwaves assumes critical significance due to the ubiquity of wireless communication technology. The selective shielding of microwaves represents the only way to achieve the control on crucial technological sectors. The implementation of microwave shielding ensures the proper functioning of electronic devices. By preventing electromagnetic pollution, shielding safeguards the integrity and optimal performances of devices, contributing to the reliability and efficiency of technological systems in various sectors and allowing the further step forwards in a safe and secure society. Nevertheless, the microwave shielding research is vast and can be quite hard to approach due to the large number and variety of studies regarding both theory and experiments. In this review, we focused our attention on the comprehensive discussion of the current state of the art of materials used for the production of electromagnetic interference shielding composites, with the aim of providing a solid reference point to explore this research field.

Controllable Synthesis of Highly Symmetrical Streamlined Structure for Wideband Microwave Absorption

Highly symmetrical and streamlined nanostructures possessing unique electron scattering, electron-phonon coupling, and electron confinement characteristics have attracted a lot of attention. However, the controllable synthesis of such a nanostructure with regulated shapes and sizes remains a huge challenge. In this work, a peanut-like MnO@C structure, assembled by two core-shell nanosphere is developed via a facile hydrogen ion concentration regulation strategy. Off-axis electron holography technique, charge reconstruction, and COMSOL Multiphysics simulation jointly reveal the unique electronic distribution and confirm its higher dielectric sensitive ability, which can be used as microwave absorption to deal with currently electromagnetic pollution. The results reveal that the peanut-like core-shell MnO@C exhibits great wideband properties with effective absorption bandwidth of 6.6 GHz, covering 10.8-17.2 GHz band. Inspired by this structure-induced sensitively dielectric behavior, promoting the development of symmetrical and streamlined nanostructure would be attractive for many other promising applications in the future, such as piezoelectric material and supercapacitor and electromagnetic shielding.

Confined In-Situ Encapsulation of Co/C Composites with Increased Heterogeneous Interface Polarization for Enhanced Electromagnetic Performance

It is an urgent problem to realize reliable microwave absorption materials (MAMs) with low density. To address this issue, a series of controlled experiments w ere carried out, which indicated that the tubular structure enables excellent microwave absorption properties with a lower powder filling rate. This performance is attributable to the combined dielectric and magnetic loss mechanisms provided by Co/C and the interface polarization facilitated by multiple heterogeneous interfaces. Particularly, Co@C nanotubes, benefiting from the enhanced heterointerface polarization due to their abundant specific surface area and the reduced electron migration barrier induced by their 1D stacked structure, effectively achieved a dual enhancement of dielectric loss and polarization loss at lower powder filling ratios. Furthermore, the magnetic coupling effect of magnetic nanoparticle arrays in tubular structures is demonstrated by micromagnetic simulation, which have been few reported elsewhere. These propertied enable Co@C nanotubes to achieve minimum reflection loss and maximum effective absorption broadband values of 61.0 dB and 5.5 GHz, respectively, with a powder filling ratio of 20 wt% and a thickness of 1.94 mm. This study reveals the significance of designing 1D structures in reducing powder filling ratio and matching thickness, providing valuable insights for developing MAMs with different microstructures.

The 3D Printing of Novel Honeycomb-Hollow Pyramid Sandwich Structures for Microwave and Mechanical Energy Absorption

Honeycomb sandwich (HS) structures are important lightweight and load-bearing materials used in the aerospace industry. In this study, novel honeycomb-hollow pyramid sandwich (HPS) structures were manufactured with the help of fused deposition modeling techniques using PLA and PLA/CNT filaments. The microwave and mechanical energy absorption properties of the HPS structures with different geometry parameters were studied. Compared with the HS structure, the HPS structure enhanced both microwave absorption and mechanical properties. The HPS structures possessed both broadband and wide-angle microwave absorption characteristics. Their reflection loss at 8-18 GHz for incident angles of up to 45° was less than -10 dB. As the thickness of the hollow pyramid increased from 1.00 mm to 5.00 mm, the compressive strength of the HPS structure increased from 4.8 MPa to 12.5 MPa, while mechanical energy absorption per volume increased from 2639 KJ/m3 to 5598 KJ/m3. The microwave absorption and compressive behaviors of the HPS structures were studied.

State-of-the-Art Review on Amorphous Carbon Nanotubes: Synthesis, Structure, and Application

Carbon nanotubes (CNTs) have rapidly received increasing attention and great interest as potential materials for energy storage and catalyst fields, which is due to their unique physicochemical and electrical properties. With continuous improvements in fabrication routes, CNTs have been modified with various types of materials, opening up new perspectives for research and state-of-the-art technologies. Amorphous CNTs (aCNTs) are carbon nanostructures that are distinctively different from their well-ordered counterparts, such as single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs, respectively), while the atoms in aCNTs are grouped in a disordered, crystalline/non-crystalline manner. Owing to their unique structure and properties, aCNTs are attractive for energy storage, catalysis, and aerospace applications. In this review, we provide an overview of the synthetic routes of aCNTs, which include chemical vapor deposition, catalytic pyrolysis, and arc discharge. Detailed morphologies of aCNTs and the systematic elucidation of tunable properties are also summarized. Finally, we discuss the future perspectives as well as associated challenges of aCNTs. With this review, we aim to encourage further research for the widespread use of aCNTs in industry.

Exploring the role of oxygen vacancies on the magnetic and electromagneticabsorption properties of La3+-modified M-Type hexaferrite with Al3+doping

The demand for effective microwave-absorbing materials has recently surged due to rapid advancements in electromagnetic devices. Recently, engineering oxygen vacancies has also become one of the effective ways to develop efficient microwave- absorbing materials. So, understanding the electromagnetic absorption mechanism of these materials has become crucial for better engineering of such materials. This article investigates the magnetic properties along with the electromagnetic absorption mechanism of M-type hexaferrite, with optimal incorporation of rare-earth element La3+and dopping of transition metal Al3+. The presence of La3+ions at an optimal level promotes the reduction of Fe3+to Fe2+cations create oxygen vacancies to offset the electrical charge imbalance. This phenomenon impacts both the magnetic and electromagnetic characteristics of the materials. The presence of Fe2+cations enhanced the spin-orbital interaction, resulting in the strong magnetic anisotropy field along the c-axis. The lowest reflection loss (RL) of -36.37 dB at 14.19 GHz, is observed with a bandwidth of 3.61 GHz below -10 dB for x = 0.6. These microwave absorption properties can be attributed to the mutual compensation between dielectric and magnetic losses, which arise from phenomena like dielectric relaxation, magnetic resonance, and conduction loss due to electron hopping between Fe3+and Fe2+, with proper incorporation of the attenuating constant and excellent impedance matching, along with microstructure of the materials. Furthermore, the material's exceptional absorption properties are also influenced by the rapid movement of oxygen vacancies from its interior to its surface when exposed to high frequencies, thereby impacting its conductivity. Therefore, it is believed that the regulation of oxygen vacancies can serve as a versatile strategy for developing materials with efficient microwave-absorbing capabilities.

Engineering Phase to Reinforce Dielectric Polarization in Nickel Sulfide Heterostructure for Electromagnetic Wave Absorption

Engineering phase transition in micro-nanomaterials to optimize the dielectric properties and further enhance the electromagnetic microwave absorption (EMA) performance is highly desirable. However, the severe synthesis conditions restrict the design of EMA materials featuring controllable phases, which hinders the tunability of effective absorption bandwidth (EAB) and leads to an unclear loss mechanism. Herein, a seed phase decomposition-controlled strategy is proposed to induct nickel sulfide (NiSx ) absorbers with controllable phases and hollow sphere nature. Transmission electron microscopy holography and theoretical calculations evidence that the reconstruction of atoms in phase transition induces numerous heterogeneous interfaces and lattice defects/sulfur vacancies to cause varied work functions and local electronic redistribution, which contributes to reinforced dielectric polarization. As a result, the optimized NiS2 /NiS heterostructure enables enhanced EM attenuation capability with a wide EAB of 5.04 GHz at only 1.6 mm, compared to that of NiS2 and NiS. Moreover, the correlation between EAB and NiS phase content is demonstrated as the "volcano" feature. This study on the concept of phase transition of micro-nanomaterials can offer a novel approach to constructing highly efficient absorbers for EMA and other functionalities.

Porous Carbonaceous Aerogels Composed of Multiscale Carbon-Based Units for High-Performance Microwave Absorption

Structural engineering is definitely a promising and effective approach to develop excellent microwave absorbing materials with quantities of advantages. Especially, when carbon materials act as the constituents, the fabricated absorbers are available to gain more prominent absorption performance. However, extra high conductivities and the widespread aggregations and stacking of low-dimensional carbon materials always detrimentally affect the impedance matching and weaken the attenuation capacity, inevitably confining their further absorption applications. Herein, by introducing the amorphous chiral carbon nanocoils to overcome the challenges and achieve the strategies of structure optimization and multicomponent recombination, the reduced graphene oxide/carbon nanocoil/carbon nanotube aerogels were successfully synthesized by a successive hydrothermal method and freeze-drying strategy. The as-obtained aerogels possess a porous architecture that contribute to the extraordinary impedance matching and multiple reflections, which integrate the multifarious dielectric loss mechanisms of diverse carbon materials simultaneously. Benefiting from the tricomponent synergistic effect, the ultralight aerogels reach an outstanding microwave absorption property with an extremely low filler content of only 6 wt %. This work provides a helpful approach to design hierarchical absorbers consisted by multidimensional carbon materials for fantastic microwave absorption.

Controlled Synthesis of MOF-Derived Nano-Microstructure toward Lightweight and Wideband Microwave Absorption

Correlating metal-organic framework (MOF) synthesis processes and microwave absorption (MA) enhancement mechanisms is a pioneer project. Nevertheless, the correlation process still relies mainly on empirical doctrine, which hardly corresponds to the specific mechanism of the effect on the dielectric properties. Hereby, after the strategy of modulation of protonation engineering and solvothermal temperature in the synthesis route, the obtained sheet-like self-assembled nanoflowers were constructed. Porous structures with multiple heterointerfaces, abundant defects, and vacancies are obtained by controlled design of the synthesis procedure. The rearrangement of charges and enhanced polarization can be promoted. The designed electromagnetic properties and special nano-microstructures of functional materials have significant impact on their electromagnetic wave energy conversion effects. As a consequence, the MA performance of the samples has been enhanced toward broadband absorption (6.07 GHz), low thickness (2.0 mm), low filling (20%), and efficient loss (-25 dB), as well as being suitable for practical environmental applications. This work establishes the connection between the MOF-derived materials synthesis process and the MA enhancement mechanism, which provides insight into various microscopic microwave loss mechanisms.

Ni-Carbon Microtube/Polytetrafluoroethylene as Flexible Electrothermal Microwave Absorbers

Flexible microwave absorbers with Joule heating performance are urgently desired to meet the demands of extreme service environments. Herein, a type of flexible composite film is constructed by homogeneously dispersing a hierarchical Ni-carbon microtube (Ni/CMT) into a processable polytetrafluoroethylene (PTFE) matrix. The Ni/CMT are interconnected into a 3D conductive network, in which the huge interior cavity of the carbon microtube (CMT) improves impedance matching and provides additional hyper channels for electromagnetic (EM) waves dissipation, and the hierarchical magnetic Ni nanoparticles enhance the synergistic interactions between confined heterogeneous interfaces. Such an ingenious structure endows the composites with excellent electrothermal performance and improves their serviceability for application under extreme environments. Moreover, under a low fill loading of 3 wt.%, the Ni/CMT/PTFE (NCP) can achieve excellent low-frequency microwave absorption (MA) property with a minimum reflection loss of -59.12 dB at 5.92 GHz, which covers almost the entire C-band. Relying on their brilliant MA property, an EM sensor is designed and achieved by the resonance coupling of the patterned NCP. This work opens up a new way for the design of next-generation microwave absorbers that meet the requirements of EM packaging, proofing water and removing ice, fire safety, and health monitoring.

Metal-Organic Framework-Manipulated Dielectric Genes Inside Silicon Carbonitride toward Tunable Electromagnetic Wave Absorption

Heterointerface engineering for different identifiable length scales has emerged as a key research area for obtaining materials capable of high-performance electromagnetic wave absorption; however, achieving controllable architectural and compositional complexity in nanomaterials with environmental and thermal stabilities remains challenging. Herein, metal-containing silicon carbonitride (SiCN/M) nanocomposite ceramics with multiphase heterointerfaces were in situ synthesized via coordination crosslinking, catalytic graphitization, and phase separation processes using trace amounts of metal-organic frameworks (MOFs). The results reveal that the regulation of dielectric genes by MOFs can yield considerable lattice strain and abundant lattice defects, contributing to strong interfacial and dipole polarizations. The as-prepared SiCN/M ceramics demonstrate excellent microwave absorption performance: the minimum reflection loss (RLmin ) is -72.6 dB at a thickness of only 1.5 mm and -54.1 dB at an ultralow frequency of 3.56 GHz for the SiCN/Fe ceramics and the RLmin is -55.1 dB with a broad bandwidth of 3.4 GHz at an ultralow thickness of 1.2 mm for the SiCN/CoFe ceramic. The results are expected to provide guidance for the design of future dielectric microwave absorption materials based on heterointerface engineering while offering a paradigm for developing MOF-modified SiCN nanocomposite ceramics with desirable properties.

A "Win-Win" Strategy to Modify Co/C Foam with Carbon Microspheres for Enhanced Dielectric Loss and Microwave Absorption Characteristics

3D carbon foams have demonstrated their superiority in the field of microwave absorption recently, but the preparation processes of traditional graphene foams are complicated, while some novel carbon foams usually suffer from inadequate dielectric property. Herein, a simple "win-win" strategy is demonstrated to synchronously realize the construction of 3D Co/C foam and its surface decoration with carbon microspheres. Therein, the host Co/C foams and guest carbon microspheres interact with each other, resulting in the improvement of the dispersity of carbon microspheres and Co nanoparticles. The bilaterally synergistic effect can effectively enhance the interfacial polarization and conductive loss of these obtained samples. Electromagnetic analysis reveals that the optimized sample with moderate carbon microsphere content (about 33.5 wt%) displays a widened maximum effective absorption bandwidth of 5.2 GHz and a consolidated reflection loss intensity of -67.6 dB. Besides, the microwave absorption enhancement mechanisms are investigated and discussed in detail. It is believed that this work provides valuable ideas for the development of 3D-foam-based microwave absorbing materials for practical applications.

Commonly Neglected Ester Groups Enhanced Microwave Absorption

Oxygen-containing functional groups have high potential to excite polarization loss. The nature and mechanism of the polarization loss brought on by oxygen-containing functional groups, however, remain unclear. In this study, metal-organic framework precursors are in situ pyrolyzed to produce ultrathin carbon nanosheets (UCS) that are abundant in oxygen functional groups. By altering the pyrolysis temperature, the type and concentration of functional groups are altered to produce good microwave absorption capabilities. It is demonstrated that the main processes of electromagnetic loss are polarization caused by "field effects and induced effects" brought on by strongly polar ester functional groups. Moreover, links between various oxygen functional groups and structural flaws are established, and their respective contributions to polarization are sharply separated. The sample with the highest ester group content ultimately achieves an effective absorption bandwidth of 6.47 GHz at a pyrolysis temperature of 800°C. This research fills a theoretical hole in the frequently overlooked polarization mechanism in the microwave band by defining the key polarization parameters in chaotic multiple dipole systems and, in particular, redefining the significance of ester groups.

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.

3D Honeycomb Fe/MXene Derived from Prussian Blue Microcubes with a Tunable Structure for Efficient Low-Frequency and Flexible Electromagnetic Absorbers

The unique layered structure and high conductivity of MXene materials make them highly promising for microwave absorption. However, the finite loss mechanism and severe agglomeration present challenging obstacles for ideal microwave absorbers, which could be effectively improved by constructing a three-dimensional (3D) porous structure. This study reports a 3D honeycomb MXene using a straightforward template method. The 3D MXene framework offers ample cavities to anchor the Prussian blue microcubes and their derivatives including Fe microboxes and Fe clusters by a simple annealing process. Based on the superiority of the 3D honeycomb architecture and magnetic-dielectric synergistic effects, the Fe/MXene absorbers demonstrate outstanding microwave absorption capabilities with the optimum reflection loss value of -40.3 dB at 2.00 mm in the low-frequency range from 4.2 to 5.6 GHz. The absorber also manifests superior radar wave attenuation by finite element analysis and exhibits great potential to be a flexible and thermal insulation material in a wide range of temperatures. This work proposes a useful reference for the design of 3D MXene-based porous architectures, and the synergistic magnetic-dielectric strategy further expands the potential of MXene-based absorbers, enabling them to be used as flexible and highly efficient microwave absorbers.

Dual Resonance Behavior and Enhanced Microwave Absorption Performance of Fe3O4@C@MoS2 Composites with Shape Magnetic Anisotropy

Ternary hierarchical Fe3O4@C@MoS2 composites and binary hierarchical Fe3O4@C composites were successfully fabricated by a modified mixed solvothermal method, a self-oxidation polymerization method, and a hydrothermal process. Their magnetic properties and microwave absorption performance were investigated. Dual resonance behavior was observed in the Fe3O4@C@MoS2 composites. One of the resonances was attributed to natural resonance with a resonance frequency of 2.58 GHz, which was much higher than that for Fe3O4 bulk (1.5 GHz). The other originated from the superparamagnetic/ferromagnetic relaxation with a resonance frequency of 12.45 GHz. The minimum reflection loss (RLmin) reached -64.30 dB with a matched thickness of 2.24 mm at 11.64 GHz, and the maximum effective absorption bandwidth (EABmax) covered 6.39 GHz with a matched thickness of 1.89 mm. In addition, the maximum Radar cross section (RCS) reduction value reached 31.90 dB m2 at a scattering angle of 0°. Electron holography analysis confirmed a dense magnetic absorption network in the Fe3O4@C@MoS2 composites. The boost in microwave absorption performance was caused by the synergistic effects of magnetic and dielectric properties owing to the ternary hierarchical structure, shape magnetic anisotropy, and incorporation of 1T/2H MoS2. Besides, the binary hierarchical Fe3O4@C composites also exhibited good absorbing performance caused by natural resonance, with an RLmin of -52.90 dB at 5.80 mm, an EABmax of 5.98 GHz at 3.38 mm, and a relatively high RCS reduction value of 13.04 dB m2 at θ = 20°. This work paves the way for designing multicomponent hierarchical absorbers with broadband and intensive microwave absorption.

Hierarchical and Orderly Surface Conductive Networks in Yolk-Shell Fe3 O4 @C@Co/N-Doped C Microspheres for Enhanced Microwave Absorption

Constructing the adjustable surface conductive networks is an innovation that can achieve a balance between enhanced attenuation and impedance mismatch according to the microwave absorption mechanism. However, the traditional design strategies remain significant challenges in terms of rational selection and controlled growth of conductive components. Herein, a hierarchical construction strategy and quantitative construction technique are employed to introduce conductive metal-organic frameworks (MOFs) derivatives in the classic yolk-shell structure composed of electromagnetic components and the cavity for remarkable optimized performance. Specifically, the surface conductive networks obtained by carbonized ZIF-67 quantitative construction, together with the Fe3 O4 magnetic core and dielectric carbon layer linked by the cavity, achieve the cooperative enhancement of impedance matching optimization and synergistic attenuation in the Fe3 O4 @C@Co/N-Doped C (FCCNC) absorber. This interesting design is further verified by experimental results and simulation calculations. The products FCCNC-2 yield a distinguished minimum reflection loss of -66.39 dB and an exceptional effective absorption bandwidth of 6.49 GHz, indicating that moderate conduction excited via hierarchical and quantitative design can maximize the absorption capability. Furthermore, the proposed versatile methodology of surface assembly paves a new avenue to maximize beneficial conduction effect and manipulate microwave attenuation in MOFs derivatives.

Fabrication and Investigation of the Microwave Absorption of Nonwovens Modified by Carbon Nanotubes and Graphene Flakes

This study aims to investigate the influences of carbon nanotubes (CNTs) and graphene flakes (GFs) on the microwave absorption performance of nonwovens. Nonwovens were modified with CNTs and GFs through an impregnation method, creating a series of absorption samples with different carbon nanomaterial contents. Then the absorption performance of the samples was tested on both sides in the X-band (8.2~12.4 GHz) and the Ku-band (12~18 GHz) using the arch method. The experimental results showed that the absorption performance of GF-impregnated nonwovens was superior to that of CNT-impregnated nonwovens, and the overall absorption performance in the Ku-band was better than in the X-band. At a CNT content of 5 wt.%, the reflection loss of the impregnated nonwovens on the backside reached a minimum of -14.06 dB and remained below -10 dB in the 17.42~17.88 GHz frequency range. The sample fabricated with 4 wt.% GFs in the impregnation solution exhibited the best absorption performance, with minimum reflection losses of -15.33 dB and -33.18 GHz in the X-band and Ku-band, respectively. When the GFs were at 3 wt.%, the absorption bandwidth below -10 dB reached 4.16 GHz. In contrast to CNT-impregnated nonwovens, the frontside of GF-impregnated nonwovens demonstrated better absorption performance in the Ku-band. The results of this work provide experimental data support for the fabrication and application of microwave absorption materials.

Hierarchical and Porous Structures of Carbon Nanotubes-Anchored MOF Derivatives Bridged by Carbon Nanocoils as Lightweight and Broadband Microwave Absorbers

High-performance microwave absorption (MA) materials have attracted more and more attention because they can effectively prevent microwave radiation and interference from electronic devices. Herein, a new type of MA composite is constructed by introducing carbon nanotubes (CNTs)-anchored metal-organic framework derivatives (MOFDs) into a conductive carbon nanocoil (CNC) network, denoted as CNC/CNT-MOFD. The CNC/MOFD shows a wide effective absorption band of 6.7 GHz under a filling ratio of only 9% in wax-matrix. This is attributed to the hierarchical and porous structures of MOFD bridged by the uniformly dispersed conductive CNC network and the cross-polarization induced by the 3D spiral CNCs. Besides, the as-grown 1D CNTs improve space utilization, porosity, and polarization loss of the composites, resulting in the increase of imaginary permittivity, which further realizes impedance matching and energy attenuation. The Ni nanoparticles in layers of MOFD and at the tips of CNTs generate magnetic loss, promoting the low-frequency absorption ability. Resultantly, RCS values of the optimized composite in all tested theta (θ) ranges are less than -25 dB m2 at 9.5 GHz, effectively reducing the probability of the target detected by the radar.

A One-Step Self-Flowering Method toward Programmable Ultrathin Porous Carbon-Based Materials for Microwave Absorption and Hydrogen Evolution

Ultrathin 2D porous carbon-based materials offer numerous fascinating electrical, catalytic, and mechanical properties, which hold great promise in various applications. However, it remains a formidable challenge to fabricate these materials with tunable morphology and composition by a simple synthesis strategy. Here, a facile one-step self-flowering method without purification and harsh conditions is reported for large-scale fabrication of high-quality ultrathin (≈1.5 nm) N-doped porous carbon nanosheets (NPC) and their composites. It is demonstrated that the layered tannic/oxamide (TA/oxamide) hybrid is spontaneously blown, exfoliated, bloomed, in situ pore-formed, and aromatized during pyrolysis to form flower-like aggregated NPC. This universal one-step self-flowering system is compatible with various precursors to construct multiscale NPC-based composites (Ru@NPC, ZnO@NPC, MoS2 @NPC, Co@NPC, rGO@NPC, etc.). Notably, the programmable architecture enables NPC-based materials with excellent multifunctional performances, such as microwave absorption and hydrogen evolution. This work provides a facile, universal, scalable, and eco-friendly avenue to fabricate functional ultrathin porous carbon-based materials with programmability.

Nanolayered Ceramic-Confined Graphene Aerogel with Conformal Heterointerfaces for Low-Frequency Microwave Absorption

Graphene-based aerogels have garnered considerable attention for their lightweight and efficient microwave absorption (MA) properties; however, optimizing the relationship between impedance matching and attenuation capability at low frequencies remains a challenge. In this study, a three-dimensional (3D) silicon carbonitride (SiCN) nanoceramic-coated graphene aerogel with conformal heterogeneous interfaces is constructed by precursor infiltration and pyrolysis to optimize MA performance at low frequencies. Thanks to the enhanced impedance matching and significant interfacial polarization of the two-dimensional sandwiched SiCN/graphene/SiCN cell walls and multiple scattering occurring within the 3D porous skeleton, the aerogel achieves a minimum reflection loss of -57.9 dB at an ultralow frequency of 4.92 GHz (C-band) and a broad bandwidth of 5.0 GHz at an ultralow thickness of 1.7 mm. The strategy developed here provides a method for enhancing dielectric polarization loss in graphene aerogels by the joint optimization of interfacial polarization and impedance matching, inspiring the design of high-performance graphene-based materials for low-frequency MA.

NiCo2 O4 /Hollow Mesoporous Carbon Nanosphere Hybrids Enabling Super-Hydrophobicity, Thermal Insulation, and Highly Efficient Microwave Absorption

The combination of 2D magnetic nanosheets and mesoporous carbon with unique interfaces shows considerable prospects for microwave absorption (MA). However, traditional assembly procedures make it impossible to accurately manage the assembly of magnetic nanosheets in carbon matrices. Herein, a reverse strategy for preparing complex magnetic nanosheet cores inside carbon-based yolk-shell structures is developed. This innovative approach focuses on controlling the initial crystallite formation sites in a hydrothermal reaction as well as the inflow and in situ growth behavior of 2D NiCo-layered double hydroxide precursors based on the capillary force induced by hollow mesoporous carbon nanospheres. Accordingly, the as-prepared YS-CNC-2 absorber exhibits remarkable MA performances, with an optimal reflection loss as low as -60.30 dB at 2.5 mm and an effective absorption bandwidth of 5.20 GHz at 2.0 mm. The loss of electromagnetic waves (EMW) depends on natural resonance loss, dipole polarization relaxation, and multiple scattering behavior. On top of that, the functionalized super-hydrophobic MA coating is produced in spraying and curing processes utilizing YS-CNC-2 nanoparticles and fumed silica additives in the polydimethylsiloxane matrix. The excellent thermal insulation, self-cleaning capability, and durability in diverse solutions of the coating promise potential applications for military equipment in moist situations.

Engineering 2D MXene and LDH into 3D Hollow Framework for Boosting Photothermal Energy Storage and Microwave Absorption

2D MXene is highly preferred for photothermal energy conversion and microwave absorption. However, the aggregation issue, insufficient dielectric loss capacity, and lack of magnetic loss capacity for MXene severely hinder its practical applications. Herein, the authors propose multi-dimensional nanostructure engineering to electrostatically assemble 2D MXene and layered double hydroxides (LDH) derived from ZIF-67 polyhedron into a 3D hollow framework (LDH@MXene), and subsequently calcined to construct a Co nanoparticle-modified 3D hollow C-LDH@MXene framework to encapsulate a paraffin wax (PW) phase change material (PCM). The 3D hollow C-LDH@MXene framework not only prevents 2D MXene from aggregation but also contributes a high thermal energy storage density (131.04 J g-1 ). Benefiting from a 3D conductive network facilitating the rapid transport of photons and phonons from the interface to the interior and the synergistic localized surface plasmon resonance (LSPR) effect of MXene and Co magnetic nanoparticles, the C-LDH@MXene-PW composite PCM yielded a high photothermal storage efficiency of 96.52%. Besides, C-LDH@MXene-PW composite PCMs also exhibited efficient microwave absorption with a minimum reflection loss of -20.87 dB at 13.30 GHz with a matching thickness of only 2 mm. This distinctive design provides constructive references for the development of integrated composite materials for energy storage and microwave absorption.

The Ordered Mesoporous Barium Ferrite Compounded with Nitrogen-Doped Reduced Graphene Oxide for Microwave Absorption Materials

Nanocomposites with hierarchical pore structure hold great potentials for applications in the field of microwave-absorbing materials because of their lightweight and high-efficiency absorption properties. Herein, M-type barium ferrite (BaM) with ordered mesoporous structure (M-BaM) is prepared via a sol-gel process enhanced by mixed anionic and cationic surfactants. The surface area of M-BaM is enhanced almost ten times compared with BaM together with 40% reflection loss enhancing. Then M-BaM compounded with nitrogen-doped reduced graphene oxide (MBG) is synthesized via hydrothermal reaction in which the reduction and nitrogen doping of graphene oxide (GO) in situ occur simultaneously. Interestingly, the mesoporous structure is able to provide opportunity for reductant to enter the bulk M-BaM reducing its Fe3+ to Fe2+ and further forms Fe3 O4 . It requires an optimal balance among the remained mesopores in MBG, formed Fe3 O4 , and CN in nitrogen-doped graphene (N-RGO) for optimizing impedance matching and greatly increasing multiple reflections/interfacial polarization. MBG-2 (GO:M-BaM = 1:10) achieves the minimum reflection loss of -62.6 dB with an effective bandwidth of 4.2 GHz at an ultra-thin thickness of 1.4 mm. In addition, the marriage of mesoporous structure of M-BaM and light mass of graphene reduces the density of MBG.

Gradient Hierarchical Hollow Heterostructures of Ti3C2Tx@rGO@MoS2 for Efficient Microwave Absorption

Heterostructure engineering has emerged as a promising approach for creating high-performance microwave absorption materials in various applications such as advanced communications, portable devices, and military fields. However, achieving strong electromagnetic wave attenuation, good impedance matching, and low density in a single heterostructure remains a significant challenge. Herein, a unique structural design strategy that employs a hollow structure coupled with gradient hierarchical heterostructures to achieve high-performance microwave absorption is proposed. MoS₂ nanosheets are uniformly grown onto the double-layered Ti₃C₂T_x MXene@rGO hollow microspheres through self-assembly and sacrificial template techniques. Notably, the gradient hierarchical heterostructures, comprising a MoS₂ impedance matching layer, a reduced graphene oxide (rGO) lossy layer, and a Ti₃C₂T_x MXene reflective layer, have demonstrated significant improvements in impedance matching and attenuation capabilities. Additionally, the incorporation of a hollow structure can further improve microwave absorption while reducing the overall composite density. The distinctive gradient hollow heterostructures enable Ti₃C₂T_x@rGO@MoS₂ hollow microspheres with exceptional microwave absorption properties. The reflection loss value reaches as strong as -54.2 dB at a thin thickness of 1.8 mm, and the effective absorption bandwidth covers the whole Ku-band, up to 6.04 GHz. This work provides an exquisite perspective on heterostructure engineering design for developing next-generation microwave absorbers.

Long-Range Uniform SiCxOy Beaded Carbon Fibers for Efficient Microwave Absorption

SiC_xO_y beaded carbon fibers were successfully fabricated for the first time using a facile and stable electrospinning and temperature process. The resulting fibers showcase a unique micro-nanocomposite structure, in which β-SiC beads with a silica-enriched surface are strung together with defect carbon fibers, as confirmed by XRD, XPS, and HRTEM investigation. The SiC_xO_y beaded carbon fibers display efficient microwave absorption performance, with a minimum reflection loss of -58.53 dB and an effective absorption bandwidth of 5.92 GHz. A modified Drude-Lorentz model was developed for SiC_xO_y beaded carbon fibers to reveal the double-peaked feature of the permittivity of these fibers, which is in good agreement with experimental measurements. Moreover, simulations were performed to extract polarized electric fields and microwave energy volume losses within a typical distribution of SiC_xO_y beaded carbon fibers. It is concluded that the dipole relaxation and hopping migration of localized electrons give a superior contribution to the overall decay of the microwave energy. This study indicates that SiC_xO_y beaded carbon fibers with a unique micro-nanocomposite structure hold great promise for microwave absorption applications. Additionally, this fabrication strategy offers a unique approach to producing micro-nanocomposite structures and highlights their potential applications.

Performance Optimization Engineering of Multicomponent Absorbing Materials Based on Machine Learning

Multicomponent materials are microwave-absorbing (MA) materials composed of a variety of absorbents that are capable of reaching the property inaccessible for a single component. Discovering mostly valuable properties, however, often relies on semi-experience, as conventional multicomponent MA materials' design rules alone often fail in high-dimensional design spaces. Therefore, we propose performance optimization engineering to accelerate the design of multicomponent MA materials with desired performance in a practically infinite design space based on very sparse data. Our approach works as a closed-loop, integrating machine learning with the expanded Maxwell-Garnett model, electromagnetic calculations, and experimental feedback; aiming at different desired performances, Ni surface@carbon fiber (NiF) materials and NiF-based multicomponent (NMC) materials with target MA performance were screened and identified out of nearly infinite possible designs. The designed NiF and NMC fulfilled the requirements for the X- and Ku-bands at thicknesses of only 2.0 and 1.78 mm, respectively. In addition, the targets regarding S, C, and all bands (2.0-18.0 GHz) were also achieved as expected. This performance optimization engineering opens up a unique and effective way to design microwave-absorbing materials for practical application.

Core-Shell Structured Silica-Coated Iron Nanowires Composites for Enhanced Electromagnetic Wave Absorption Properties

In this study, we successfully prepared core-shell heterostructured nanocomposites (Fe NWs@SiO₂), with ferromagnetic nanowires (Fe NWs) as the core and silica (SiO₂) as the shell. The composites exhibited enhanced electromagnetic wave absorption and oxidation resistance and were synthesized using a simple liquid-phase hydrolysis reaction. We tested and analyzed the microwave absorption properties of Fe NWs@SiO₂ composites with varied filling rates (mass fractions of 10 wt%, 30 wt%, and 50 wt% after mixing with paraffin). The results showed that the sample filled with 50 wt% had the best comprehensive performance. At the matching thickness of 7.25 mm, the minimum reflection loss (RL_min) could reach -54.88 dB at 13.52 GHz and the effective absorption bandwidth (EAB, RL < -10 dB) could reach 2.88 GHz in the range of 8.96-17.12 GHz. Enhanced microwave absorption performance of the core-shell structured Fe NWs@SiO₂ composites could be attributed to the magnetic loss of the composite, the core-shell heterogeneous interface polarization effect, and the small-scale effect induced by the one-dimensional structure. Theoretically, this research provided Fe NWs@SiO₂ composites with highly absorbent and antioxidant core-shell structures for future practical applications.

PPyNT/NR/NBR Composites with Excellent Microwave Absorbing Performance in X-Band

To meet the comprehensive demand for flexible microwave absorbing (MA) materials, a novel MA rubber containing homemade Polypyrrole nanotube (PPyNT) is produced based on the natural rubber (NR) and acrylonitrile-butadiene rubber (NBR) blends. To achieve the optimal MA performance in the X band, the PPyNT content and NR/NBR blend ratio are adjusted in detail. The 6 phr PPyNT filled NR/NBR (90/10) composite has the superior MA performance with the minimum reflection loss value of -56.67 dB and the corresponding effective bandwidth of 3.7 GHz at a thickness of 2.9 mm, which has the merits in virtue of achieving strong absorption and wide effective absorption band with low filler content and thickness compared to most reported microwave absorbing rubber materials over the same frequency. This work provides new insight into the development of flexible microwave-absorbing materials.

Flexible and Ultrathin Graphene/Aramid Nanofiber Carbonizing Films with Nacre-like Structures for Heat-Conducting Electromagnetic Wave Shielding/Absorption

Electromagnetic interference (EMI) shielding and electromagnetic wave absorption (EWA) materials with good thermal management and flexibility properties are urgently needed to meet the more complex modern service environment, especially in the field of smart wearable electronics. How to balance the relation of electromagnetic performance, thermal management, flexibility, and thickness in material design is a crucial challenge. Herein, graphene nanosheets/aramid nanofiber (C-GNS/ANF) carbonizing films with nacre-like structures were fabricated via the blade-coating/carbonization procedure. The ingenious configuration from highly ordered alignment GNS interactively connected by a carbonized ANF network can effectively improve the thermal/electrical conductivity of a C-GNS/ANF film. Specifically, the ultrathin C-GNS/ANF film with a thickness of 17 μm shows excellent in-plane thermal conductivity (TC) of 79.26 W m^-1 K^-1 and superior EMI shielding up to 56.30 dB. Moreover, the obtained C-GNS/ANF film can be used as a lightweight microwave absorber, achieving excellent microwave absorption performance with a minimum reflection loss of -56.07 dB at a thickness of 1.5 mm and a maximum effective absorption bandwidth of 5.28 GHz at an addition of only 5 wt %. Furthermore, the C-GNS/ANF films demonstrate good flexibility, outstanding thermal stability, and flame retardant properties. Overall, this work indicates a prospective direction for the development of the next generation of electromagnetic wave absorption/shielding materials with high-performance heat conduction.

Regulation of Impedance Matching and Dielectric Loss Properties of N-Doped Carbon Hollow Nanospheres Modified With Atomically Dispersed Cobalt Sites for Microwave Energy Attenuation

The rational design of lightweight, broad-band, and high-performance microwave absorbers is urgently required for addressing electromagnetic pollution issue. Metal single atoms (M-SAs) absorbers receive considerable interest in the field of microwave absorption due to the unique electronic structures of M-SAs. However, the simultaneous engineering of the morphology and electronic structure of M-SAs based absorbers remains challenging. Herein, a template-assisted method is utilized to fabricate isolated Co-SAs on N-doped hollow carbon spheres (NHCS@Co-SAs) for high-performance microwave absorption. The combination of atomically dispersed Co sites and hollow supports endows NHCS@Co-SAs with excellent microwave absorption properties. Typically, at an ultralow filler content of 8 wt%, the minimum reflection loss and effective absorption bandwidth of the NHCS@Co-SAs are up to -44.96 dB and 5.25 GHz, respectively, while the absorbing thickness is only 2 mm. Theoretical calculations and experimental results indicate that the impedance matching characteristic and dielectric loss of the NHCSs can be tuned via the introduction of M-SAs, which are responsible for the excellent microwave absorption properties of NHCS@Co-SAs. This work provides an atomic-level insight into the relationship between the electronic states of absorbers and their microwave absorption properties for developing advanced microwave absorbers.

Multifunctional Organic-Inorganic Hybrid Perovskite Microcrystalline Engineering and Electromagnetic Response Switching Multi-Band Devices

High-efficiency electromagnetic (EM) functional materials are the core building block of high-performance EM absorbers and devices, and they are indispensable in various fields ranging from industrial manufacture to daily life, or even from national defense security to space exploration. Searching for high-efficiency EM functional materials and realizing high-performance EM devices remain great challenges. Herein, a simple solution-process is developed to rapidly grow gram-scale organic-inorganic (MAPbX₃ , X = Cl, Br, I) perovskite microcrystals. They exhibit excellent EM response in multi bands covering microwaves, visible light, and X-rays. Among them, outstanding microwave absorption performance with multiple absorption bands can be achieved, and their intrinsic EM properties can be tuned by adjusting polar group. An ultra-wideband bandpass filter with high suppression level of -71.8 dB in the stopband in the GHz band, self-powered photodetectors with tunable broadband or narrowband photoresponse in the visible-light band, and a self-powered X-ray detector with high sensitivity of 3560 µC Gy_air ^-1  cm^-2  in the X-ray band are designed and realized by precisely regulating the physical features of perovskite and designing a novel planar device structure. These findings open a door toward developing high-efficiency EM functional materials for realizing high-performance EM absorbers and devices.

Multifunctional Nanocrystalline-Assembled Porous Hierarchical Material and Device for Integrating Microwave Absorption, Electromagnetic Interference Shielding, and Energy Storage

Multifunctional applications including efficient microwave absorption and electromagnetic interference (EMI) shielding as well as excellent Li-ion storage are rarely achieved in a single material. Herein, a multifunctional nanocrystalline-assembled porous hierarchical NiO@NiFe₂ O₄ /reduced graphene oxide (rGO) heterostructure integrating microwave absorption, EMI shielding, and Li-ion storage functions is fabricated and tailored to develop high-performance energy conversion and storage devices. Owing to its structural and compositional advantages, the optimized NiO@NiFe₂ O₄ /15rGO achieves a minimum reflection loss of -55 dB with a matching thickness of 2.3 mm, and the effective absorption bandwidth is up to 6.4 GHz. The EMI shielding effectiveness reaches 8.69 dB. NiO@NiFe₂ O₄ /15rGO exhibits a high initial discharge specific capacity of 1813.92 mAh g^-1 , which reaches 1218.6 mAh g^-1 after 289 cycles and remains at 784.32 mAh g^-1 after 500 cycles at 0.1 A g^-1 . In addition, NiO@NiFe₂ O₄ /15rGO demonstrates a long cycling stability at high current densities. This study provides an insight into the design of advanced multifunctional materials and devices and provides an innovative method of solving current environmental and energy problems.

An Ion-Engineering Strategy to Design Hollow FeCo/CoFe2 O4 Microspheres for High-Performance Microwave Absorption

Although assembled hollow architectures have received considerable attention as lightweight functional materials, their uncontrollable self-aggregation and tedious synthetic methods hinder precise construction and modulation. Therefore, this study proposes a bi-ion synergistic regulation strategy to design assembled hollow-shaped cobalt spinel oxide microspheres. Dominated by the coordination-etching effects of F^- and the hydrolysis-complex contributions of NH₄ ⁺ , the unique construction is formed attributed to the dynamic cycles between metal complexes and precipitates. Meanwhile, their basic structures are perfectly retained after reduction treatment, enabling FeCo/CoFe₂ O₄ bimagnetic system to be obtained. Subsequently, in-depth analyses are conducted. Investigations reveal that multiscale magnetic coupling networks and enriched air-material heterointerfaces contribute to the remarkable magnetic-dielectric behavior, supported by the advanced off-axis electron holography technique. Consequently, the obtained FeCo/CoFe₂ O₄ composites exhibit excellent microwave absorption performances with minimal reflection losses (RL_min ) as high as -51.6 dB, an effective absorption bandwidth (EAB) of 4.7 GHz, and a matched thickness of 1.4 mm. Thus, this work provides an informative guide for rationally assembling building blocks into hollow architectures as advanced microwave absorbers through bi-ion and even multi-ion synergistic engineering mechanisms.