Dielectric behavior of Fe3N@C composites with green synthesis and their remarkable electromagnetic wave absorption performance

Self-Templating Engineering of Hollow N-Doped Carbon Microspheres Anchored with Ternary FeCoNi Alloys for Low-Frequency Microwave Absorption

Rational design and precision fabrication of magnetic-dielectric composites have significant application potential for microwave absorption in the low-frequency range of 2-8 GHz. However, the composition and structure engineering of these composites in regulating their magnetic-dielectric balance to achieve high-performance low-frequency microwave absorption remains challenging. Herein, a self-templating engineering strategy is proposed to fabricate hollow N-doped carbon microspheres anchored with ternary FeCoNi alloys. The high-temperature pyrolysis of FeCoNi alloy precursors creates core-shell FeCoNi alloy-graphitic carbon nano-units that are confined in carbon shells. Moreover, the anchored FeCoNi alloys play a critical role in maintaining hollow structural stability. In conjunction with the additional contribution of multiple heterogeneous interfaces, graphitization, and N doping to the regulation of electromagnetic parameters, hollow FeCoNi@NCMs exhibit a minimum reflection loss (RLmin) of -53.5 dB and an effective absorption bandwidth (EAB) of 2.48 GHz in the low-frequency range of 2-8 GHz. Furthermore, a filler loading of 20 wt% can also be used to achieve a broader EAB of 5.34 GHz with a matching thickness of 1.7 mm. In brief, this work opens up new avenues for the self-templating engineering of magnetic-dielectric composites for low-frequency microwave absorption.

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

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

Fabrication of 1D Ni nanochains@Zn2+ doping polypyrrole/reduced graphene oxide composites for high-performance electromagnetic wave absorption

Nowadays, electromagnetic radiation significantly impacts the normal operation of electronic devices and poses risks to human health. To effectively address this problem, the development of composites that exhibit exceptional electrochemical wave absorption through the combination of different components holds great promise. In this study, we have successfully prepared 1D Ni nanochains@Zn2+ doping polypyrrole/reduced graphene oxide (Ni NCs@Z-P/RGO, denoted as R-x) composites using a combination of hydrothermal, solvothermal, in situ polymerization, and physical blending methods. Notably, the R-2 composite demonstrates a remarkable minimum reflection loss (RLmin) of -63.58 dB at 14.3 GHz, with a thickness of 1.61 mm. Furthermore, the R-2 composite exhibits an impressive effective absorption bandwidth (EAB) of 5.08 GHz (11.92 GHz-17 GHz) at a thickness of 1.67 mm. These outstanding performances can be attributed to the synergistic effect of the different components and a well-thought-out structural design. Moreover, to showcase the practical applicability of the material, we have conducted additional investigations on the reduction of the radar cross-sectional area (RCS). The results strongly demonstrate that the prepared composite material, when used as a coating, effectively reduces the RCS value by up to 26.6 dB m2 for R-2 at θ = 0°. The experimental methods and simulations presented in this study hold significant potential for application in wave absorption research and practical implementations. Additionally, the prepared Ni NCs@Z-P/RGO composites demonstrate feasibility as wave-absorbing materials for future utilization.

Multiphase Molybdenum Carbide Doped Carbon Hollow Sphere Engineering: The Superiority of Unique Double-Shell Structure in Microwave Absorption

In order to achieve excellent electromagnetic wave (EMW) absorption properties, the microstructure design and component control of the absorber are critical. In this study, three different structures made of Mo₂ C/C hollow spheres are prepared and their microwave absorption behavior is investigated. The Mo₂ C/C double-shell hollow spheres consisting of an outer thin shell and an inner rough thick shell with multiple EMW loss mechanisms exhibit good microwave absorption properties. In order to further improve the microwave absorption properties, MoC_1-x /C double-shell hollow spheres with different crystalline phases of molybdenum carbide are prepared to further optimize the EMW loss capability of the materials. Finally, MoC_1-x /C double-shell hollow spheres with α-phase molybdenum carbide have the best microwave absorption properties. When the filling is 20 wt.%, the minimum reflection loss at 1.8 mm is -50.55 dB and the effective absorption bandwidth at 2 mm is 5.36 GHz, which is expected to be a microwave absorber with the characteristics of "thin, light, wide, and strong".

Construction of heterointerfaces and honeycomb-like structure for ultrabroad microwave absorption

Heterointerface design is an effective strategy to improve the effective absorption bandwidth in electromagnetic wave EMW absorbing materials. In this paper, honeycomb-like Fe-doped tremella carbide composites (FCT) with a large number of heterogeneous interfaces were obtained by in-situ construction of multiphase composite particles (Fe₃C, Fe₃O₄, and a-Fe) during the carbonization process. The effects of Fe doping on the phase, structure, morphology, and absorption properties of FCT were investigated. The results show that the porous structure and the heterogeneous interface can significantly improve the electromagnetic wave absorption performance of FCT. Iron doping introduces a heterogeneous multiphase structure into FCT, which increases the interfacial loss and magnetic loss of the material, thereby improving the overall impedance matching of the material. FCT-4 composite exhibited excellent microwave attenuation capability with a reflection loss of -34.6 dB. Simultaneously, the widest effective absorption bandwidth is up to 8.84 GHz (9.16-18 GHz) with a matching thickness of 2.8 mm, which covers almost the entire X (8-12 GHz) and Ku (12-18 GHz) bands. Thus, this paper provides an effective strategy for the preparation of excellent electromagnetic wave absorbing materials by in situ construction of heterointerfaces.

Molybdenum Blue Preassembly Strategy to Design Bimetallic Fe0.54Mo0.73/Mo2C@C for Tunable and Low-Frequency Electromagnetic Wave Absorption

Advanced electromagnetic wave absorption nanomaterials can play an important role in addressing the issue of increasing electromagnetic pollution in wireless communication field. Herein, a series of coralloid bimetallic Fe0.54Mo0.73/Mo2C@C (FMC)...

The development of a magnetic iron/nitrogen-doped graphitized carbon composite with boosted microwave attenuation ability as the wideband microwave absorber

Magnetic carbon-based composites have been attractive candidates for electromagnetic (EM) absorption due to their dual magnetic and dielectric loss ability. In this study, a novel magnetic carbon consisting of N-doped graphitized carbon and magnetic Fe nanoparticles was produced. First, the graphitized carbon doped with N has been demonstrated to be an efficient way to strengthen the conductivity loss ability. Based on the N-doped graphitized carbon (NGC), the magnetic Fe nanoparticles were further decorated on the NGC, which was not only favored the dielectric loss ability but also introduced the magnetic loss ability. The electromagnetic absorbing properties of the NGC-Fe nanoparticles were evaluated in the frequency range of 2-18 GHz, and as expected, the sample exhibited the excellent wideband EM absorbing ability, with an effective absorption region of 5.2 GHz under a thickness of 1.2 mm. Ulilization of element doping method consisted to modify magnetic carbon material can be a candidate for producing wideband EM absorbers but showing thin thickness.

Synthesis of 3D flower-like ZnO/ZnCo2O4 composites with the heterogeneous interface for excellent electromagnetic wave absorption properties

Reasonable structure and composition are essential for electromagnetic wave absorption (EMW). Herein, ZnO hollow spheres were prepared with carbon spheres as templates and then synthesized ZnO/ZnCo₂O₄ composites by the solvothermal method and annealing treatment. The flower-like ZnCo₂O₄ material was produced by self-assembly of ZnCo₂O₄ nanosheets. The absorbing material with the complex structure has multiple scattering and reflection, conduction loss, resonance, and eddy current loss characteristics. Furthermore, the addition of ZnO hollow spheres has a significant impact on electromagnetic parameters and absorption properties. As a result, the addition of ZnO hollow spheres can greatly enhance the complex permittivity of the ZnO/ZnCo₂O₄ composites and obtain excellent EMW absorbing properties. It is worth noting that ZnO/ZnCo₂O₄ composites show the best EMW absorption properties when the ZnO hollow spheres were added up to 5 mg. The minimum reflection loss is -55.42 dB and a matching thickness of 1.99 mm while the maximum effective absorption bandwidth can also reach 7.44 GHz with a matching thickness of 2.4 mm. Our research can prove that the structure and composition have a significant influence on the properties of the absorbing material, which provides ideas for the development of absorbing materials with high-performance.

Design of Ti3C2Tx/TiO2/PANI multi-layer composites for excellent electromagnetic wave absorption performance

Ti₃C₂T_x MXene is an excellent electromagnetic wave (EMW) absorber with excellent electrical conductivity and abundant surface functional groups. In this research, Ti₃C₂T_x/TiO₂/PANI multi-layer composites were successfully synthesized by HCl and LiF etching, one-step hydrothermal method and in-situ polymerization. Ti₃C₂T_x can provide more electron transfer paths due to its unique multilayer structure and high specific surface area. The growth of TiO₂ particles on the surface of Ti₃C₂T_x through hydrothermal reaction enhances the interface polarization, and then polyaniline (PANI) is doped on the surface of Ti₃C₂T_x where TiO₂ particles are grown by in-situ polymerization. Due to the excellent dielectric properties and synergistic effects of the material itself, Ti₃C₂T_x/TiO₂/PANI composites have excellent EMW absorption property. In this study, the Ti₃C₂T_x/TiO₂/PANI composites showed the strong reflection loss (RL) of at 13.92 GHz, which was -65.61 dB, and the thickness was only 2.18 mm. Moreover, the composites also exhibit a wide absorption band, with an effective absorption bandwidth (RL < -10 dB) of 5.92 GHz (11.84 GHz to 17.76 GHz) at 2.10 mm. The results show that the Ti₃C₂T_x/TiO₂/PANI composites are expected to become EMW absorber with thin thickness and high absorption strength.