High-Temperature Stable and Metal-Free Electromagnetic Wave-Absorbing SiBCN Ceramics Derived from Carbon-Rich Hyperbranched Polyborosilazanes

Research Progress on High-Temperature-Resistant Electromagnetic Wave Absorbers Based on Ceramic Materials: A Review

Ceramic materials have the merits of an adjustable dielectric constant, high strength, high temperature resistance, and oxidation resistance, and are thus being used as the protection matrix for carbon series, metal oxides, and other wave-absorbing materials at high temperatures. Here, progress on high-temperature-resistant wave-absorbing ceramic materials is introduced through the aspects of their composition and structure. In addition, metamaterials used for such purposes, which are mainly produced through 3D printing, are also highlighted. The pros and cons of high-temperature-resistant electromagnetic wave absorbers based on ceramic materials are systematically analyzed, and possible development directions are proposed. This work may assist in the design and manufacture of a new generation of radars, ships, and aircraft.

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.

Integration of Multiple Heterointerfaces in a Hierarchical 0D@2D@1D Structure for Lightweight, Flexible, and Hydrophobic Multifunctional Electromagnetic Protective Fabrics

The development of wearable multifunctional electromagnetic protective fabrics with multifunctional, low cost, and high efficiency remains a challenge. Here, inspired by the unique flower branch shape of "Thunberg's meadowsweet" in nature, a nanofibrous composite membrane with hierarchical structure was constructed. Integrating sophisticated 0D@2D@1D hierarchical structures with multiple heterointerfaces can fully unleash the multifunctional application potential of composite membrane. The targeted induction method was used to precisely regulate the formation site and morphology of the metal-organic framework precursor, and intelligently integrate multiple heterostructures to enhance dielectric polarization, which improves the impedance matching and loss mechanisms of the electromagnetic wave absorbing materials. Due to the synergistic enhancement of electrospinning-derived carbon nanofiber "stems", MOF-derived carbon nanosheet "petals" and transition metal selenide nano-particle "stamens", the CoxSey/NiSe@CNSs@CNFs (CNCC) composite membrane obtains a minimum reflection loss value (RLmin) of -68.40 dB at 2.6 mm and a maximum effective absorption bandwidth (EAB) of 8.88 GHz at a thin thickness of 2.0 mm with a filling amount of only 5 wt%. In addition, the multi-component and hierarchical heterostructure endow the fibrous membrane with excellent flexibility, water resistance, thermal management, and other multifunctional properties. This work provides unique perspectives for the precise design and rational application of multifunctional fabrics.

High-temperature resistant electromagnetic protection bilayer structure based on the low-reflection metasurface and wave-absorbing material

In this paper, we propose a high-temperature resistant bilayer structure for electromagnetic protection with low reflection, consisting of a metasurface and an absorbing layer. The bottom metasurface decreases the reflected energy by using a phase cancellation mechanism to make electromagnetic wave scattering in the 8-12 GHz range. While the upper absorbing layer assimilates the incident electromagnetic energy through electrical losses and simultaneously regulates the reflection amplitude and phase of the metasurface to enhance scattering and expand its operating bandwidth. Research shows that the bilayer structure achieves a low reflection of -10 dB in the range of 6.7-11.4 GHz due to the combined effect of the above two physical mechanisms. In addition, long-term high-temperature and thermal cycling tests verified the stability of the structure in the temperature range of 25-300°C. This strategy provides the feasibility of electromagnetic protection in high-temperature conditions.

Digital Light Processing 3D-Printed Ceramic Metamaterials for Electromagnetic Wave Absorption

Combining 3D printing with precursor-derived ceramic for fabricating electromagnetic (EM) wave-absorbing metamaterials has attracted great attention. This study presents a novel ultraviolet-curable polysiloxane precursor for digital light processing (DLP) 3D printing to fabricate ceramic parts with complex geometry, no cracks and linear shrinkage. Guiding with the principles of impedance matching, attenuation, and effective-medium theory, we design a cross-helix-array metamaterial model based on the complex permittivity constant of precursor-derived ceramics. The corresponding ceramic metamaterials can be successfully prepared by DLP printing and subsequent pyrolysis process, achieving a low reflection coefficient and a wide effective absorption bandwidth in the X-band even under high temperature. This is a general method that can be extended to other bands, which can be realized by merely adjusting the unit structure of metamaterials. This strategy provides a novel and effective avenue to achieve "target-design-fabricating" ceramic metamaterials, and it exposes the downstream applications of highly efficient and broad EM wave-absorbing materials and structures with great potential applications.

Controllable graphitization degree of carbon foam bulk toward electromagnetic wave attenuation loss behavior

The graphitization degree is of great importance for determining the electromagnetic (EM) wave attenuation loss behavior. The conductive loss is considered to be the mechanism resulting from tailoring the graphitization degree. There is a lack of in-depth research on the dipole polarization caused by defects and functional groups and the interface polarization caused by graphite/amorphous carbon. Herein, lightweight carbon foam (CF) bulk derived from mesophase pitch was prepared to clarify the effect of the graphitization degree systematically. The results demonstrate that with an increase graphitization degree, the interfacial polarization improves and dipole polarization decreases. The synergistic effect of conduction loss and dipole and interfacial polarization dominates the impedance matching and further changes the EM loss behavior of CFs. Particularly, the minimum reflection loss is - 16.69 dB and effective absorption bandwidth is 3.63 GHz, the EM interference shielding effectiveness attains 35.13 dB and the compressive strength is up to 11.73 MPa when the optimal graphitization degree is achieved. Therefore, this work elucidates the effect of the interface polarization of graphite/amorphous carbon, thus providing a valuable insight into the design of advanced carbon-based materials for EM wave absorption and shielding.

Enhanced Electromagnetic Wave Absorption for Y2O3-Doped SiBCN Ceramics

Polymer-derived SiBCN ceramics (PDCs-SiBCN) are promising ultrahigh-temperature ceramics owing to their excellent high-temperature oxidation resistance and electromagnetic wave (EMW)-absorbing capability. In this paper, the microstructure evolutions, the dielectric properties, and EMW absorption properties of Y₂O₃-doped SiBCN ceramics were investigated. The results reveal that Y₂O₃ acting as a catalyst promotes the formation of SiC, BN(C), and graphite crystalline phases in the SiBCN ceramics, and these crystalline phases are constructed as conduction phases and polarization phases to enhance the EMW-adsorbing properties. The minimum reflection loss (RL_min) reaches -42.22 dB at 15.28 GHz, and the effective absorption bandwidth is 4.72 GHz (13.28-18.00 GHz). In addition, there is only 0.56 wt % mass loss for the Y₂O₃-doped SiBCN ceramics when they are heated from ambient temperature to 1500 °C in air, indicating that the Y₂O₃-doped SiBCN ceramics obtain excellent oxidation resistance at high temperature. We believe that rare metal oxidation is beneficial for the growth of crystalline phases in the PDCs, resulting in high EMW-absorbing properties and oxidation resistance. Thus, the research extends a novel method and design strategy for microstructure regulation and property enhancement of PDCs.

Maximum Achievable N Content in Atom-by-Atom Growth of Amorphous Si-B-C-N Materials

Amorphous Si-B-C-N alloys can combine exceptional oxidation resistance up to 1500 °C with high-temperature stability of superior functional properties. Because some of these characteristics require as high N content as possible, the maximum achievable N content in amorphous Si-B-C-N is examined by combining extensive ab initio molecular dynamics simulations with experimental data. The N content is limited by the formation of unbonded N2 molecules, which depends on the composition (most intensive in C rich materials, medium in B rich materials, least intensive in Si-rich materials) and on the density (increasing N2 formation with decreasing packing factor when the latter is below 0.28, at a higher slope of this increase at lower B content). The maximum content of N bonded in amorphous Si-B-C-N networks of lowest-energy densities is in the range from 34% to 57% (materials which can be grown without unbonded N2) or at most from 42% to 57% (at a cost of affecting materials characteristics by unbonded N2). The results are important for understanding the experimentally reported nitrogen contents, design of stable amorphous nitrides with optimized properties and pathways for their preparation, and identification of what is or is not possible to achieve in this field.

Polymer-Derived Lightweight SiBCN Ceramic Nanofibers with High Microwave Absorption Performance

Lightweight SiBCN ceramic nanofibers were prepared by a combination of electrostatic spinning and high-temperature annealing techniques, showing tunable electromagnetic wave absorption. By controlling the annealing temperature, the nanoscale architectures and atomic bonding structures of as-prepared nanofibers could be well regulated. The resulting SiBCN nanofibers ∼300 nm in diameter, which were composed of an amorphous matrix, β-SiC, and free carbon nanocrystals, were defect-free after annealing at 1600 °C. SiBCN nanofibers annealed at 1600 °C exhibited good microwave absorption, obtaining a minimum reflection coefficient of -56.9 dB at 10.56 GHz, a sample thickness of 2.6 mm with a maximum effective absorption bandwidth of 3.45 GHz, and a maximum dielectric constant of 0.44. Owing to the optimized A + B + C microstructure, SiBCN ceramic nanofibers with satisfying microwave absorption properties endowed the nanofibers with the potential to be used as lightweight, ultrastrong radar wave absorbers applied in military and the commercial market.

Superparamagnetic Silicon Carbonitride Ceramic Fibers Through In Situ Generation of Iron Silicide Nanoparticles During Pyrolysis of an Iron-Modified Polysilazane

Ceramic fibers are high-tech structural key components of ceramic matrix composites (CMCs), which are a very promising class of materials for applications in next-generation turbines, especially nonoxide ceramic fibers, usually produced by the polymer-derived ceramics (PDC) route, which possess the enhanced mechanical and thermostructural properties necessary to withstand the harsh conditions (temperature and atmosphere) imposed on CMCs. However, recycling composite materials, such as fiber-reinforced polymers and CMCs, is still a big challenge. Here, we present for the first time the processing of superparamagnetic iron-containing ceramic fibers, which, due to their magnetic properties, can be separated from the matrix material of a composite. The synthesis strategy of the novel functional ceramic fibers is based on a tailored reaction of polyorganosilazane with an iron complex, resulting in a suitable, meltable polymer. After melt-spinning and curing, subsequent pyrolysis leads to superparamagnetic ceramic fibers with a saturation magnetization of 1.54 emu g^-1 because of in situ-formed iron silicide nanoparticles of an average size of 7.5 nm, homogeneously dispersed in an amorphous SiCNO matrix. Moreover, the ceramic fibers exhibit a tensile strength of 1.24 GPa and appropriate oxidation resistance. The developed versatile reaction strategy allows also for the incorporation of other elements to implement further functionalities for processing of multifunctional composites.

Strong and thermostable hydrothermal carbon coated 3D needled carbon fiber reinforced silicon-boron carbonitride composites with broadband and tunable high-performance microwave absorption

Excellent electromagnetic wave (EMW) absorbing materials with high-temperature stable and superior mechanical properties are among the most promising candidates for practical application. Here, novel hydrothermal carbon coated three-dimensional (3D) needled carbon fiber reinforced silicon-boron carbonitride (HC-CF/SiBCN) composites with a hierarchical A (CF)/B (HC)/C (SiBCN) structure were constructed and prepared for the first time by combining hydrothermal transformation and precursor infiltration and pyrolysis (PIP) process. The thickness of the HC coating controlled by the glucose concentration played a crucial role in tailoring the EMW capacity of the composite. The incorporation of SiBCN could not only effectively improve the oxidation resistance but also actively enhance the mechanical properties of the HC coated CF structure. Compared to the weak high-temperature oxidation resistance and mechanical properties of pristine 3D needled CF felt, the composites after the introduction of HC and SiBCN were thermostable in air atmosphere beyond 1000 °C to about above 70% weight retention, and the maximum flexural and compression strength of the composites could reach to 23.51 ± 1.37 and 12.22 ± 1.12 MPa, respectively. A substantial enhancement of EMW absorption ability was achieved through incorporation of HC and SiBCN, which could be attributed to the matched characteristic impedance and enhanced loss ability, whose optimization EMW absorption performance was the minimum reflection loss (RL_min) of -52.08 dB and effective absorption bandwidth (EAB) of 7.64 GHz for the composite obtained by two PIP cycles with 24 wt% glucose solution, demonstrating that the HC-CF/SiBCN composites with high-temperature stable, excellent mechanical and superior EMW absorption properties could be considered as a promising candidate for the applications in harsh environments.

Bimetallic MOF-derived hollow ZnNiC nano-boxes for efficient microwave absorption

In this work, we report the facile synthesis of a hollow ZnNiC nano-box using a hollow ZnNi-MOF as the sacrificial template through a one-step pyrolysis process. Remarkably, the as-prepared hollow ZnNiC/paraffin composite exhibited a minimum reflection loss (RLmin) of -66.1 dB at 15.3 GHz and effective absorption bandwidth of 4.4 GHz with a thickness of 1.6 mm.

Strong and Thermostable Boron-Containing Phenolic Resin-Derived Carbon Modified Three-Dimensional Needled Carbon Fiber Reinforced Silicon Oxycarbide Composites with Tunable High-Performance Microwave Absorption Properties

This paper focuses on the preparation of boron-containing phenolic resin (BPR)-derived carbon modified three-dimensional (3D) needled carbon fiber reinforced silicon oxycarbide (SiOC) composites through a simple precursor infiltration and pyrolysis process (PIP), and the influence of PIP cycle numbers on the microstructure, mechanical, high-temperature oxidation resistance. The electromagnetic wave (EMW) absorption properties of the composites were investigated for the first time. The pyrolysis temperature played an important role in the structural evolution of the SiOC precursor, as temperatures above 1400 °C would cause phase separation of the SiOC and the formation of silicon carbide (SiC), silica (SiO2), and carbon. The density and compressive strength of the composites increased as the PIP cycle number increased: the value for the sample with 3 PIP cycles was 0.77 g/cm3, 7.18 ± 1.92 MPa in XY direction and 9.01 ± 1.25 MPa in Z direction, respectively. This composite presented excellent high-temperature oxidation resistance and thermal stability properties with weight retention above 95% up to 1000 °C both under air and Ar atmosphere. The minimal reflection loss (RLmin) value and the widest effective absorption bandwidth (EAB) value of as-prepared composites was −24.31 dB and 4.9 GHz under the optimization condition for the sample with 3 PIP cycles. The above results indicate that our BPR-derived carbon modified 3D needled carbon fiber reinforced SiOC composites could be considered as a promising material for practical applications.

Wide-Band Tunable Microwave-Absorbing Ceramic Composites Made of Polymer-Derived SiOC Ceramic and in Situ Partially Surface-Oxidized Ultra-High-Temperature Ceramics

Microwave-absorbing materials in a high-temperature harsh environment are highly desired for electronics and aerospace applications. This study reports a novel high-temperature microwave-absorbing ceramic composites made of polymer-derived SiOC ceramic and in situ partially surface-oxidized ultra-high-temperature ceramic (UHTC) ZrB₂ nanoparticles. The fabricated composites with a normalized weight fraction of ZrB₂ nanoparticles at 40% has a significantly wide microwave absorption bandwidth of 13.5 GHz (26.5-40 GHz) covering the entire K_a-band. This is attributed to the extensive nanointerfaces introduced in the composites, attenuation induced by the interference of electromagnetic wave, attenuation from the formed current loops, and the electronic conduction loss provided by the partially surface-oxidized ZrB₂ nanoparticles. The minimum reflection coefficient (RC) was -29.30 dB at 29.47 GHz for a thickness of 1.26 mm for the composites with a normalized weight fraction of ZrB₂ nanoparticles at 32.5%. The direct current (dc) conductivity of the nanocomposites showed a clear percolation phenomenon as the normalized weight fraction of ZrB₂ nanoparticles increases to 30.49%. The results provide new insights in designing microwave-absorbing materials with a wide absorption frequency range and strong absorption loss for high-temperature harsh environment applications.

Continuous SiCN Fibers with Interfacial SiC xN y Phase as Structural Materials for Electromagnetic Absorbing Applications

SiCN ceramics are one of the most important electromagnetic wave (EMW) absorbing materials for application in harsh environments, but research studies on optimizing phase distribution in SiCN ceramics for excellent EMW absorbing properties are still lacking. Herein, continuous SiCN fibers with an interfacial SiC _xN _y phase were prepared through nanochannel diffusion-controlled nitridation of polycarbosilane fibers with an NH₃ gas flow. The existence of the interfacial SiC _xN _y phase distributed between the carbon-rich SiC phase and Si₃N₄ phase can improve the impedance matching and efficiently promote the production of macroscopic dipole moments in the heterointerfaces of SiC _xN _y-SiC and SiC _xN _y-Si₃N₄ for an enhanced multifarious polarization relaxation loss. The EMW absorption properties can be further improved by optimizing the microstructure with a continuous carbon-rich SiC phase for possessing an excellent conductive loss by converting the EMW energy into current flow. Finally, under the synergy of the interfacial SiC _xN _y phase and the continuous carbon-rich SiC phase, SiCN fibers can present excellent EMW absorption properties with extremely strong absorption ability (reflection loss of -63.7 dB), ultrathin thickness (1.78 mm), and wide effective absorption bandwidth (4.20 GHz). These obtained SiCN fibers also possess excellent mechanical properties with the tensile strength higher than 2.0 GPa and excellent high-temperature stability up to 1500 °C. This work provides a strategic method for optimizing the microstructure of SiCN ceramics for admirable EMW absorption properties, and the obtained SiCN fibers can be used as reinforcements of ceramic matrix composites for stealth applications under harsh environments.

Ultralight Cellular Foam from Cellulose Nanofiber/Carbon Nanotube Self-Assemblies for Ultrabroad-Band Microwave Absorption

Microwave absorption materials (MAMs) with lightweight density and ultrabroad-band microwave absorption performance are urgently needed in advanced MAMs, which are still a big challenge and have been rarely achieved. Here, a new wide bandwidth absorption model was designed, which fuses the electromagnetic resonance loss ability of a periodic porous structure in the low-frequency range and the dielectric loss ability of dielectric materials in the high-frequency range. Based on this model, a lightweight porous cellulose nanofiber (CNF)/carbon nanotube (CNT) foam consisting of a cellular vertical porous architecture with the macropore diameters between 30 and 90 μm and a nanoporous architecture at a scale of 1.7-50 nm was obtained by an ice-template method using CNTs and CNFs as "building blocks". Benefiting from the unique architecture, the effective absorption bandwidth reaches 29.7 GHz, and its specific microwave absorption performance exceeds 80,000 dB·cm^-2·g^-1, which far surpasses those of the MAMs previously reported, including all CNT-based composites. Moreover, the CNF/CNT foam possesses ultralow density (9.2 mg/cm³) and strong fatigue resistance, all coming from the well-interconnected porous structure and the strong hydrogen bonds among CNF-CNF and CNF-CNT molecular chains.

Nitrogen-Rich Porous Organic Polyamines for Stabilization of Highly Dispersed Metal Nanoparticles and Catalytic Application

Nitrogen-rich triazine-based porous organic polyamines (POPa) synthesized via a one-step polycondensation of melamine and 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde is employed to synthesize Au and Pd nanoparticles well-dispersed on POPa. The as-prepared POPa-supported Au NPs and Pd NPs (AuNPs@POPa, PdNPs@POPa) with a narrow size distribution show remarkable catalytic activity for the reduction of nitrobenzene compounds and organic dyes and the Suzuki-Miyaura coupling reaction, respectively. Benefitting from POPa the AuNPs@POPa and PdNPs@POPa catalysts can be readily recovered and reused almost without loss of activity. The nitrogen-rich porous organic polyamines provide great opportunities to prepare functional metal nanocatalysts with potential in the heterogeneous catalysis field.

Poly(dimethylsilylene)diacetylene-Guided ZIF-Based Heterostructures for Full Ku-Band Electromagnetic Wave Absorption

Zeolitic imidazolate frameworks (ZIFs), a group of metal-organic frameworks (MOFs), hold promise as building blocks in electromagnetic (EM) wave absorbing/shielding materials and devices. In this contribution, we proposed a facile strategy to synthesize three-dimensional ZIF-67-based hierarchical heterostructures through coordinated reaction of a preceramic component, poly(dimethylsilylene)diacetylene (PDSDA) with ZIF-67, followed by carbonizing the PDSDA-wrapped ZIF at high temperature. The introduction of PDSDA leads to controllable generation of a surface network containing branched carbon nanotubes and regional distributed graphitic carbons, in addition to the nanostructures with a well-defined size and porous surface made by cobalt nanoparticles. The surface structures can be tailored through variations in pyrolysis temperatures, therefore enabling a simple and robust route to facilitate a suitable structural surface. The heterostructure of the ZIF nanocomplex allows the existence of dielectric loss and magnetic loss, therefore yielding a significant improvement on EM wave absorption with a minimum reflection coefficient (RC_min) of -50.9 dB at 17.0 GHz at a thickness of 1.9 mm and an effective absorption bandwidth (EAB) covering the full Ku-band (12.0-18.0 GHz).

Nanochannel Diffusion-Controlled Nitridation of Polycarbosilanes for Diversified SiCN Fibers with Interfacial Gradient-SiC xN y Phase and Enhanced High-Temperature Stability

Diversified SiCN fibers with gradient-SiC _xN _y phase in the interfacial regions between the major phases of carbon-rich SiC phase and Si₃N₄ phase were prepared via nanochannel diffusion-controlled nitridation of polycarbosilane fibers under different NH₃ flow rates. The obtained fibers with excellent mechanical properties showed a different nanostructure and improved high-temperature behavior compared with polysilazane- and polysilylcarbodiimide-derived SiCN ceramics. The enhanced high-temperature properties could be contributed to the inhibition of carbothermal reduction of the Si₃N₄ phase by the gradient-SiC _xN _y phase in the interfacial region between the Si₃N₄ phase and carbon-rich SiC phase. Meanwhile, a suitable amount of interfacial SiC _xN _y phase as well as the fine distributed microstructure can be helpful to inhibit the high-temperature crystallization of both the SiC phase and Si₃N₄ phase. Additionally, a nanostructural model has been proposed to understand the effect of interfacial gradient-SiC _xN _y phase and compositional-dependent high-temperature behavior of obtained SiCN fibers. Our findings provide a novel strategy to prepare SiCN-based ceramic materials with excellent high-temperature stabilities, which we expect to possess great potential in structural and (multi)functional applications at high temperatures and under harsh environments.

Nontronite and intercalated nontronite as effective and cheap absorbers of electromagnetic radiation

The paper presents the thermal, structural and dielectric properties of natural nontronite and nontronite intercalated with DMSO, ethylene glycol and formamide. These materials were tested for the electromagnetic wave absorption ability. It was shown that nontronite and its intercalates were better absorbers than the materials previously obtained from kaolinite and halloysite.

Biomass-Derived Porous Carbon-Based Nanostructures for Microwave Absorption

Currently, electromagnetic (EM) pollution poses severe complication toward the operation of electronic devices and biological systems. To this end, it is pertinent to develop novel microwave absorbers through compositional and structural design. Porous carbon (PC) materials demonstrate great potential in EM wave absorption due to their ultralow density, large surface area, and excellent dielectric loss ability. However, the large-scale production of PC materials through low-cost and simple synthetic route is a challenge. Deriving PC materials through biomass sources is a sustainable, ubiquitous, and low-cost method, which comes with many desired features, such as hierarchical texture, periodic pattern, and some unique nanoarchitecture. Using the bio-inspired microstructure to manufacture PC materials in mild condition is desirable. In this review, we summarize the EM wave absorption application of biomass-derived PC materials from optimizing structure and designing composition. The corresponding synthetic mechanisms and development prospects are discussed as well. The perspective in this field is given at the end of the article.

Lightweight Ti2CT x MXene/Poly(vinyl alcohol) Composite Foams for Electromagnetic Wave Shielding with Absorption-Dominated Feature

Lightweight absorption-dominated electromagnetic interference (EMI) shielding materials are more attractive than conventional reflection-dominated counterparts because they minimize the twice pollution of the reflected electromagnetic (EM) wave. Here, porous Ti₂CT _x MXene/poly(vinyl alcohol) composite foams constructed by few-layered Ti₂CT _x (f-Ti₂CT _x) MXene and poly(vinyl alcohol) (PVA) are fabricated via a facile freeze-drying method. As superior EMI shielding materials, their calculated specific shielding effectiveness reaches up to 5136 dB cm² g^-1 with an ultralow filler content of only 0.15 vol % and reflection effectiveness (SE_R) of less than 2 dB, representing the excellent absorption-dominated shielding performance. Contrast experiment reveals that the good impedance matching derived from the multiple porous structures, internal reflection, and polarization effect (dipole and interfacial polarization) plays a synergistic role in the improved absorption efficiency and superior EMI shielding performance. Consequently, this work provides a promising MXene-based EMI shielding candidate with lightweight and high strength features.

Reduced Graphene Oxide/Silicon Nitride Composite for Cooperative Electromagnetic Absorption in Wide Temperature Spectrum with Excellent Thermal Stability

The fabrication of a sandwich-like composite that consists of reduced graphene oxide (RGO) and Si₃N₄ ceramic (RGO/Si₃N₄) was achieved through the combination of modified freeze-drying approach and chemical vapor infiltration process. Due to a hierarchical structure and a high ratio of I_D/ I_G (1.27), the RGO/Si₃N₄ exhibits an unprecedented high polarization relaxation loss (PRL), which accounts for 32% of the whole dielectric loss. The outstanding PRL endows the RGO/Si₃N₄ composites with unique temperature-independent dielectric properties and electromagnetic (EM) wave absorption performance. Even at a low absorbent content of only 0.16 wt %, the effective absorption bandwidth of RGO/Si₃N₄ composites can cover the whole X-band (8.2-12.4 GHz) at broad sample thicknesses ranging from 4.3 to 4.6 mm and temperatures ranging from 323 to 873 K. The mechanism for the enhancement of PRL and conductive loss was explicitly investigated. The outstanding absorption performance toward EM waves indicated that the resultant porous RGO/Si₃N₄ composite can be a promising candidate for the applications under elevated temperature.

Performance enhanced electromagnetic wave absorber from controllable modification of natural plant fiber

Short, surface rough carbon rods, which were derived from natural sisal fiber and went through two different modifications, with excellent electromagnetic wave absorption performance, were studied in this work for the first time. The structure–property relationship was clearly established here. It was shown that these green, cheap and easily obtained carbon rods with mass preparation possibility presented eye-catching absorbing behaviors towards electromagnetic wave. Based on the natural structure of sisal fiber, the minimum reflection loss of KOH activated product reached −51.1 dB and the maximum effective absorbing bandwidth achieved 7.88 GHz. The magnetically modified sample presented −48.6 dB of minimum reflection loss and 4.32 GHz of optimal absorbing bandwidth. Its pioneering application in this field not only opens a new road for this traditional textile sisal fiber but also would possibly make a referable contribution to the design and synthesis of superior carbonaceous electromagnetic wave absorption materials based on bioresource.

Novel carbon rods derived from plant fiber with excellent electromagnetic wave absorption performance have been facilely accomplished via two different modifications.

Graphene Shield by SiBCN Ceramic: A Promising High-Temperature Electromagnetic Wave-Absorbing Material with Oxidation Resistance

As cutting-edge emerging electromagnetic (EM) wave-absorbing materials, the Achilles' heel of graphenes is vulnerable to oxidation under high temperature and oxygen atmosphere, particularly at temperatures more than 600 °C. Herein, a graphene@Fe₃O₄/siliconboron carbonitride (SiBCN) nanocomplex with a hierarchical A/B/C structure, in which SiBCN serves as a "shield" to protect graphene@Fe₃O₄ from undergoing high-temperature oxidation, was designed and tuned by polymer-derived ceramic route. The nanocomplexes are stable even at 1100-1400 °C in either argon or air atmosphere. Their minimum reflection coefficient (RC_min) and effective absorption bandwidth (EAB) are -43.78 dB and 3.4 GHz at ambient temperature, respectively. After oxidation at 600 °C, they exhibit much better EM wave absorption, where the RC_min decreases to -66.21 dB and EAB increases to 3.69 GHz in X-band. At a high temperature of 600 °C, they also possess excellent and promising EW wave absorption, for which EAB is 3.93 GHz, covering 93.6% range of X-band. In comparison to previous works on graphenes, either the EAB or the RC_min of these nanocomplexes is excellent at high-temperature oxidation. This novel nanomaterial technology may shed light on the downstream applications of graphenes in EM-wave-absorbing devices and smart structures worked in harsh environments.