Ultrabroad Band Microwave Absorption of Carbonized Waxberry with Hierarchical Structure

Developing microwave absorption materials with broadband and lightweight characters is of great significance. However, it is still a great challenge for carbonized biomass without loading magnetic particles to cover the broad microwave frequency. Herein, it is proposed to carbonize freeze‐dried waxberry to make full use of its natural hierarchical gradient structure to target the ultrabroad band microwave absorption. The carbonized freeze‐dried waxberry shows radial‐gradient and hierarchical structure. The different components of hierarchical waxberry demonstrate gradient dielectric properties: the outer component shows anisotropic dielectric constants with smaller value, while the inner core shows higher dielectric constants. This gradient dielectric property is beneficial to the impedance matching and strong polarization. As a result, the bandwidth of carbonized waxberry exhibits an ultrabroad band microwave absorption, ranging from 1 to 40 GHz with the reflection loss value below ?8 dB. Meanwhile, the bandwidth can cover from 8 to 40 GHz when the reflection loss is below ?15 dB. The ultrabroad microwave absorption is attributed to the hierarchical radial‐gradient structure of carbonized waxberry, which provides good impedance matching with air media. This achievement paves the way for the exploitation of natural hierarchical biomass as a superlight and broadband high‐performance microwave absorption material.     

Investigation of adjacent spacing dependent microwave absorption properties of lamellar structural Ti3C2Tx MXenes

Ti₃C₂Tx MXenes and their composites play a vital role in the research on microwave absorbing materials. Herein, the different interlamellar spaces of Ti₃C₂Tx MXene materials were prepared by an etching process. The dependence of the microwave absorbing properties of the Ti₃C₂Tx MXene nanosheets on different interlamellar spaces was studied. The complex permittivity, dielectric loss, impedance matching characteristic and the minimum reflection loss (RL) value with the variation in interlamellar space were systematically investigated. Results showed that 40% ratio paraffin-bonded composites (S3) have a strong electromagnetic wave absorption performance and large effective absorbing bandwidth. The maximum RL reaches −36.3 dB at 4.67 GHz with the thickness of 4.5 mm, ascribed to its a high dielectric loss and good impedance matching characteristics. The RL value of Ti₃C₂Tx MXenes is strongly dependent on the inter-lamellar space. The enhanced microwave absorption originates from the unique 2-D structure, good impedance matching characteristics, and enhanced space-charge polarization effects. This work provides a new avenue for exploring high-performance microwave absorbers based on MXene materials.     

MWCNTs as Conductive Network for Monodispersed Fe3O4 Nanoparticles to Enhance the Wave Absorption Performances

Magnetic oxides are widely used as electromagnetic (EM) wave absorbers. To promote the absorption efficiency, tremendous efforts have been contributed to adjusting the composite, structure, and size of magnetic loss materials. Employing carbon materials (CNTs, CF, graphene, PANI) is an efficient way to improve the dielectric loss of the matrix. Anchoring the tiny‐monodispersed Fe₃O₄ nanoparticles (NPs) onto the lightweight multi ? walled carbon nanotubes (MWCNTs) leads to improve dielectric loss and impedance matching characteristic. Magnetic Fe₃O₄ NPs along the one‐dimensional nanotubes direction play a good synergetic role with MWCNTs due to the interfacial strong chemical and structure bonding. The as‐synthesized Fe₃O₄/MWCNTs nanocomposites exhibit efficient EM wave absorption characteristics (R_L av?10 dB) with a maximum reflection loss of ?63.64 dB at 12.08 GHz and a diminutive thickness of only 1.6 mm. The magnetic Fe₃O₄ NPs show strong chemical and structure bonding with the one‐dimensional MWCNTs. This work may show a way to broaden the application of such kinds of lightweight high‐performance absorbing materials frameworks.

     

Heterostructure design of Fe3N alloy/porous carbon nanosheet composites for efficient microwave attenuation

The self-dissipation and attenuation capacity of materials play an important role in realizing efficient electromagnetic absorption,in this case,the roles of macroscopic composition and micro-structure should be emphasized simultaneously in the reasonable design of microwave absorbent.Given that,Fe₃N alloy embedded in two-dimensional porous carbon composites were fabricated via facile sol-gel and sacrificial template methods.Satisfactorily,the magnetic/dielectric materials combination and porous structure introduction are conductive to the optimization of impedance matching property,as result of the enhancement of microwave absorption capacity.In addition,sufficient magnetic loss capacity,strong conductivity as well as polarization attenuation bring about the outstanding microwave absorbing performance with an effective absorption bandwidth of 6.76 GHz and a minimum reflection loss value of-65.6 d B.It is believed that this work not only lay a foundation to achieve microwave response materials in a wide frequency range,but also emphasize the significant role of the component selection and structural design.     

Facile synthesis of N-doped Co/graphite C composites with melamine as carbon and nitrogen source with enhanced microwave absorption performance

Magnetic metals are vital microwave absorbing materials, while they face the problems of a large density and relatively narrow absorption band in practical microwave absorption applications. The combination of magnetic metals with carbon materials can effectively ameliorate the electromagnetic (EM) parameters to resolve these the problems to a certain extent. In this study, we successfully fabricated the N-doped Co/graphite C (Co/NC) composites via directly calcining a dry mixture of Co powders and melamine in an Ar atmosphere. This method is simple and low cost. The effects of the variation in the phase composition and morphology on EM parameters and the microwave absorbing property were investigated. The graphite C content in Co/NC was relatively larger than Co content. Thus, the contribution of the dielectric loss to EM energy dissipation was more than that of the magnetic loss. Compared to pure Co, the Co/NC composites exhibit superior EM wave absorbency and are easier to realize strong absorption and lightweight. A minimum reflection loss of???41.45 dB was obtained at 3.84 GHz. The effective absorbing bandwidth (EABW, RL?≤????10 dB) reached 14.80 GHz (3.20?18.00 GHz) at a coating thickness d of 1.54?5.00 mm. The maximum EABW was as large as 5.50 GHz at only 1.54 mm thick. The main reasons for the enhanced EM wave absorption performance of Co/NC were the well impedance matching and strong attenuation capability (interfacial and dipolar polarization, conduction loss, magnetic loss, and microwave multiple scattering and reflections on rough surfaces). Our study can provide a simple guideline for preparing other light carbon-based magnetic metal composites.

Graphical abstract

The Co/NC composites with melamine as C and N source more favor for realization of strong absorption and lightweight compared to Co.

     

Controllable Architecture of ZnO/FeNi Composites Derived from Trimetallic ZnFeNi Layered Double Hydroxides for High-Performance Electromagnetic Wave Absorbers

The optimization design of micro-structure and composition is an important strategy to obtain high-performance metal-based electromagnetic (EM) wave absorption materials. In this work, ZnO/FeNi composites derived from ZnFeNi layered double hydroxides are prepared by a one-step hydrothermal method and subsequent pyrolysis process, and can be employed as an effective alternative for high-performance EM wave absorber. A series of ZnO/FeNi composites with different structures are obtained by varying the molar ratios of Zn²⁺/Fe³⁺/Ni²⁺, and the ZnO/FeNi composites with a Zn²⁺/Fe³⁺/Ni²⁺ molar ratio of 6:1:3 show a hierarchical flower-like structure. Owing to the strong synergistic loss mechanism of dielectric-magnetic components and favorable structural features, this hierarchical flower-like ZnO/FeNi sample supplies the optimal EM wave absorption performance with the highest reflection loss of −52.08 dB and the widest effective absorption bandwidth of 6.56 GHz. The EM simulation further demonstrates that impedance matching plays a determining role in EM wave absorption performance. This work provides a new way for the fabrication of a high-performance metal-based EM wave absorber.     

Three-dimensional network structure Co/CNT derived from bimetal MOFs toward efficient electromagnetic wave absorber

The development of radar stealth technology and the innovation of modern communication technology have put forward new requirements for microwave absorbing materials. Herein, the novel cobalt/carbon nanotube (Co/CNT) material with a three-dimensional (3D) network structure was prepared through the pyrolysis of nanosized bimetallic CoZn-ZIF precursor. The material exhibits excellent performance under the synergistic effect of multiple loss mechanisms. The minimum reflection loss (RL_min) value reaches −43 dB with 3.3 mm at a filled ratio of 20 wt%. In addition, its effective absorption bandwidth (EAB) can reach 4.2 GHz with a thickness of 3 mm. Furthermore, based on the systematic analysis of the absorption mechanism, an MA fabric with EAB covering the entire X band was successfully constructed with polyimide (PI) fabric as the substrate. The interconnected graphite network provides strong conduction loss and polarization loss, and the existence of Co nanoparticles not only provides magnetic loss but also effectively adjusts impedance matching performance. Overall, this research provides a new perspective for the design and application of high-performance microwave absorbing materials.     

Enhanced microwave absorption properties of polymer-derived SiC/SiCN composite ceramics modified by TiC

Porous SiCN(Ti) composite ceramics with good microwave absorbing performance were fabricated by pyrolysis of solid polysilazane modified by tetrabutyl titanate. The introduction of Ti not only acted as active filler to react with free carbon in the matrix to form TiC, but also played the role as catalyst to promote the formation of SiC nanowires. Finally, SiCN(Ti) composite ceramics formed a microstructure containing multi-nanophases and multi-nano heterogeneous interfaces when annealing temperature reached 1500 °C. The complex microstructure annealed at 1500 °C made composite ceramics have good matching impedance, as well as greatly increase the interfacial polarization loss and dipole polarization loss. As a result, the TiC/SiC/SiCN composite ceramics showed the excellent performance of electromagnetic wave absorption in X band. The minimum reflection loss (RL) of samples was ??17.1 dB at the thickness of 1.9 mm, and the maximum effective absorption bandwidth (EAB) of composite ceramics was 3.2 GHz when the thickness of sample was 2.1 mm, which exhibited a promising prospect as a structural and microwave absorbing integration material.

     

Induced Crystallization-Controllable Nanoarchitectonics of 3D-Ordered Hierarchical Macroporous Co@N-Doped Carbon Frameworks for Enhanced Microwave Absorption

The construction of ordered hierarchical porous structures in metal–organic frameworks (MOFs) and their derivatives is highly promising to meet the low-density and high-performance demands of microwave absorption materials. However, traditional methods based on sacrificial templates or corrosive agents inevitably suffer from the collapse of the microporous framework and the accumulation of nanoparticles during the carbonization transformation, resulting in the deteriorating impedance match, which greatly limits the incident and attenuation of microwaves. Herein, an induced crystallization and controllable nanoarchitectonics strategy is employed to replace traditional growing-etching methods and successfully synthesize carbonized 3D-ordered macroporous Co@N-doped carbon (3DOM Co@NDC) based on the 3D-ordered template. The obtained 3D-ordered macroporous structure ensures the stable growth of hybrid carbon frameworks and Co C nanoparticles without collapse, preserves abundant interfaces for both the incident and attenuation performance, so as to significantly improve the impedance matching and absorption properties compared to conventional MOFs derivatives. The minimum reflection loss of 3DOM Co@NDC is −57.36 dB at the thickness of 1.9 mm, and the effective bandwidth is 7.36 GHz at 1.6 mm. Moreover, the innovative strategy to prepare 3D-ordered hierarchical macroporous structures opens up a new avenue for advanced MOFs-derived absorbers with excellent performance.     

NiO/Ni Heterojunction on N-Doped Hollow Carbon Sphere with Balanced Dielectric Loss for Efficient Microwave Absorption

Hollow carbon spheres are potential candidates for lightweight microwave absorbers. However, the skin effect of pure carbon-based materials frequently induces a terrible impedance mismatching issue. Herein, small-sized NiO/Ni particles with heterojunctions on the N-doped hollow carbon spheres (NHCS@NiO/Ni) are constructed using SiO₂ as a sacrificing template. The fabricated NHCS@NiO/Ni displayed excellent microwave absorbability with a minimum reflection loss of −44.04 dB with the matching thickness of 2 mm and a wider efficient absorption bandwidth of 4.38 GHz with the thickness of 1.7 mm, superior to most previously reported hollow absorbers. Experimental results demonstrated that the excellent microwave absorption property of the NHCS@NiO/Ni are attributed to balanced dielectric loss and optimized impedance matching characteristic due to the presence of NiO/Ni heterojunctions. Theoretical calculations suggested that the redistribution of charge at the interfaces and formation of dipoles induced by N dopants and defects are responsible for the enhanced conduction and polarization losses of NHCS@NiO/Ni. The simulations for the surface current and power loss densities reveal that the NHCS@NiO/Ni has‑ applicable attenuation ability toward microwave under the practical application scenario. This work paves an efficient way for the reasonable design of small-sized particles with well-defined heterojunctions on hollow nanostructures for high-efficiency microwave absorption.     

Multi-Scale Design of Ultra-Broadband Microwave Metamaterial Absorber Based on Hollow Carbon/MXene/Mo2C Microtube

Developing various nanocomposite microwave absorbers is a crucial means to address the issue of electromagnetic pollution, but remains a challenge in satisfying broadband absorption at low thickness with dielectric loss materials. Herein, an ultra-broadband microwave metamaterial absorber (MMA) based on hollow carbon/MXene/Mo₂C (HCMM) is fabricated by a multi-scale design strategy. The microscopic 1D hierarchical microtube structure of HCMM contributes to break through the limit of thickness, exhibiting a strong reflection loss of -66.30 dB (99.99997 wave absorption) at the thinnest matching thickness of 1.0 mm. Meanwhile, the strongest reflection loss of -87.28 dB is reached at 1.4 mm, superior to most MXene-based and Mo₂C-based microwave absorbers. Then, the macroscopic 3D structural metasurface based on the HCMM is simulated, optimized, and finally manufactured. The as-prepared flexible HCMM-based MMA realizes an ultra-broadband effective absorption in the range of 3.7-40.0 GHz at a thickness of 5.0 mm, revealing its potential for practical application in the electromagnetic compatibility field.     

Microwave absorption characteristics of CH<Subscript>3</Subscript>NH<Subscript>3</Subscript>PbI<Subscript>3</Subscript> perovskite/carbon nanotube composites

The CH₃NH₃PbI₃ (MAPbI₃) and CH₃NH₃PbI₃/carbon nanotube (MC) composite have been successfully synthesized by a facile in situ solution method, which are investigated as the microwave absorption materials. For the MAPbI₃ particles, the minimum reflection loss is only ?4.9 dB around 16.4 GHz due to the poor relative complex permittivity. Then, the relative complex permittivity of MC composites could be adjusted by changing the mass fraction of CNTs in composite, which is a vital role for the dielectric loss. The reflection loss of MC-5 composite (MAPbI₃/CNT, 5:1 wt%) can be improved to ?35.7 dB with thickness of 1.3 mm at 13.1 GHz. When the thickness is <3.0 mm, the microwave absorption bandwidth of MC-5 is 11.8 GHz (5.0–16.8 GHz) under the reflection loss lower than ?20 dB. The quarter-wavelength (λ/4) matching model is used to discuss the microwave absorption mechanism of MC composites. These results indicate that MC-5 composite could be used as the microwave absorption materials with strong reflection loss, lightweight and broad bandwidth.     

Carbon nanotubes/Ni and chain-like carbon nanospheres/Ni nanocomposites: selective production and their microwave absorption performances

It was well recognized that constructing the dielectric/magnetic nanocomposites was considered as an effective way to develop excellent microwave absorption materials (MAMs). Herein, we proposed a simple water-assisted chemical vapour deposition process to selectively produce carbon nanotubes (CNTs)/Ni and chain-like carbon nanospheres (CCNSs)/Ni nanocomposites in high yield by controlling the decomposition temperature. The ultrahigh yield of CCNSs could be achieved when C₂H₂ was catalytically decomposed at 515 °C, which was up to ca. 211.0. The results suggested that electromagnetic and microwave absorption properties of as-prepared samples were highly dependent on their microstructures and composition parameters, which could be regulated by the introduction of water vapour and decomposition temperature. It was worth mentioning that the obtained CCNSs/Ni nanocomposites could simultaneously present an optimal reflection loss of ? 28.32 dB with a matching thickness of 1.68 mm, and an effective frequency bandwidth of 4.60 GHz with the matching thickness of 1.71 mm. Our results provided an effective and facile strategy to produce CCNSs/Ni in high yield, which provided a new idea for the designing and synthesis of lightweight and excellent MAMs.

     

Facile synthesis and excellent electromagnetic wave absorption properties of flower-like porous RGO/PANI/Cu<Subscript>2</Subscript>O nanocomposites

Novel porous ternary nanocomposite systems containing reduced graphene oxide (RGO)/polyaniline (PANI)/cuprous oxide (Cu₂O) were prepared via one-step in situ redox method. The RGO/PANI/Cu₂O nanocomposites present a flower-like structure with an average size of 2.0 μm in diameter. The morphologies and properties of the products can be controlled by adjusting the molar ratios of aniline to Cu²⁺. When the molar ratio of aniline to Cu²⁺ is 1:1, the product exhibits excellent microwave absorption property in the frequency range of 2–18 GHz. It can be seen that the maximum reflection loss (RL) of the ternary composite is up to ?52.8 dB at 2.7 GHz with a thickness of only 2 mm, and the absorption bandwidth corresponding to ?10 dB (90% of EM wave absorption) is 13.2 GHz. The microwave absorption property of ternary RGO/PANI/Cu₂O composite is significantly improved due to its special flower-like porous structure, dielectric loss property and well impedance matching characteristics, which is 8.12 times than that of pure RGO and 5.28 times than that of pure PANI. Therefore, our study paves a new way to prepare the promising lightweight and high-performance composite materials combined with the characteristics of three components for electromagnetic absorption.     

Enhanced microwave absorption performance of graphene/doped Li ferrite nanocomposites

In the present study, Microwave absorbing Li-Sr, Li-Co ferrite nanoparticles and RGO/Li-Sr, RGO/Li-Co ferrite nanocomposites containing Li ferrite and reduced graphene oxide (RGO) were synthesized to further improve the microwave absorption performance of Li ferrite nanoparticles (LiFe₅O₈). The Li-Sr and Li-Co nanoparticles were synthesized by thermal treatment method, the RGO/Li-Sr and RGO/Li-Co nanocomposites were obtained by a polymerization method and were characterized by different techniques. The electromagnetic wave absorption properties of the samples were evaluated by vector network analyzer (VNA) in the frequency range of 2–18 GHz. The magnetic and dielectric loss, impedance matching, and electromagnetic wave absorption of the samples are significantly improved through the addition of RGO. Experimental results revealed that the RGO/Li-Co nanocomposite considerably increased microwave absorption. The minimum reflection loss (RL) of RGO/Li-Co also was found to reach −46.80 dB at the thickness of 3 mm and the effective absorption bandwidth (≤-10 dB) amounted to 6.80 GHz (from 10.52 to 17.32 GHz), which was much higher in comparison with pure Li and Li-Co ferrites nanoparticles. Due to the synergistic effect between magnetic loss and dielectric loss and the good impedance matching, the RGO/Li-Co nanocomposite may be regarded as a new candidate for microwave absorbing materials characterized with a broad effective absorption bandwidth at thin thicknesses.     

Effect of carbonization temperature on microwave absorbing properties of polyacrylonitrile-based carbon fibers

The pre-oxidized fibers were carbonized at the temperature ranging from 400 to 1300 °C for 1 h. The microwave absorption properties of carbon fibers (CFs) were examined in the frequency range of 2–18 GHz. It is found that the reflection loss characteristics are highly sensitive to the carbonization temperature. At a thickness of 2 mm, the CFs obtained at 710 °C exhibit the best microwave absorbing ability with a maximum reflection loss of ?22.9 dB at 15 GHz, and a bandwidth exceeding ?10 dB in the range 12.4–18 GHz. Results indicate that dielectric loss in cooperation with better matched characteristic impedance results in the excellent microwave absorption of CFs. Low temperature makes ?′ and ?″ too small to consume the energy of microwave, while over high temperature makes ?′ and ?″ too large to transmit the microwave into the CFs.     

Anion Exchange of Metal Particles on Carbon-Based Skeletons for Promoting Dielectric Equilibrium and High-Efficiency Electromagnetic Wave Absorption

The combination of carbon materials and magnetic elements is considered as an effective strategy to obtain high-performance electromagnetic wave (EMW) absorption materials. However, using nanoscale regulation to the optimization of composite material dielectric properties and enhanced magnetic loss properties is facing significant challenges. Here, the dielectric constant and magnetic loss capability of the carbon skeleton loaded with Cr compound particles are further tuned to enhance the EMW absorption performance. After 700 °C thermal resuscitation of the Cr3-polyvinyl pyrrolidone composite material, the chromium compound is represented as a needle-shaped structure of nanoparticles, which is fixed on the carbon skeleton derived from the polymer. The size-optimized CrN@PC composites are obtained after the substitution of more electronegative nitrogen elements using an anion-exchange strategy. The minimum reflection loss value of the composite is −105.9 dB at a CrN particle size of 5 nm, and the effective absorption bandwidth is 7.68 GHz (complete Ku-band coverage) at 3.0 mm. This work overcomes the limitations of impedance matching imbalance and magnetic loss deficiency in carbon-based materials through size tuning, and opens a new way to obtain carbon-based composites with ultra-high attenuation capability.     

Fabrication of Graphdiyne/Graphene Composite Microsphere with Wrinkled Surface via Ultrasonic Spray Compounding and its Microwave Absorption Properties

Advanced carbon materials are constantly being used in the field of microwave absorption. Herein, in order to enrich the variety and expand the application fields of graphdiyne (GDY), the wrinkled graphene (RGO) nanosheet coated and embedded with GDY porous microspheres (RGO/GDY) are prepared by GDY synthesis, ultrasonic spray, and pyrolysis. The study finds that RGO and GDY have effective synergistic effects. The suitable pores and composition, conductive network formed by overlapping 0D and 2D materials, special surface and internal morphology design, and high-temperature activation process make RGO/GDY exhibit excellent impedance matching and attenuation capabilities. Under the best amount of GDY (20 mg), the particle sizes of the microspheres (≈6 µm), and filler content (27.5%), the minimum reflection loss (RL_min) is −58 dB@8.3 GHz, and the corresponding matching thickness is 2.7 mm. The effective absorption bandwidth is 4.3 GHz as the thickness is 1.9 mm. By adjusting the thickness, the absorber can completely absorb microwaves of all the C, X, and Ku bands. The microwave absorbing mechanisms are elucidated. GDY materials are first applied to the field of microwave absorption, enhancing the absorption performance of RGO/GDY. It provides a new way to manufacture electromagnetic wave absorbers with satisfactory performance.     

Ordered mesoporous inter-filled SiC/SiO<Subscript>2</Subscript> composites with high-performance microwave absorption by adding ethylenediamine

In this study, ordered mesoporous inter-filled silicon carbide/silica composites containing ethylenediamine (EDA-SiC/SiO₂) were fabricated by nanocasting and cold-pressing. The as-prepared composites exhibited enhanced microwave absorption. By multi-technique approach utilization, it was demonstrated that EDA acted as a carbon source during pyrolysis progress. The EDA-SiC/SiO₂ fabricated at 1300 °C exhibited a minimum reflection loss (RL) of ?53.0 dB at 10.1 GHz, and effective absorption bandwidth (RL < ?10 dB) covered the entire X-band. It was also illustrated that the enhanced dielectric loss originated from the high electrical conductivity induced by the ordered inter-filled network and crystalline carbon. Furthermore, the optimal absorbing thickness was also determined by the impedance match and quarter-wavelength law.     

石墨烯基吸波材料的研究进展

诸如铁氧体、磁性金属粒子及其合金等传统吸波材料,密度大、环境稳定性差、对电磁波的吸收弱以及吸收频带窄的缺陷限制了其在吸波领域的应用,而石墨烯因其较高的机械强度、较小的密度以及优异的介电性能受到了吸波材料领域众多学者的关注;但由于石墨烯的阻抗匹配性能较差,损耗机制比较单一,导致其吸波性能较差,因此,研究人员通常将石墨烯与其他介电损耗型或者磁损耗型材料复合来增强其吸波性能,此外对吸波剂的结构进行合理的设计也是增强其吸波性能的有效途径。结合国内外的发展状况,对石墨烯基吸波材料的制备以及性能研究做了综述性介绍,并展望了未来石墨烯基吸波材料的发展方向。