Electromagnetic Wave Absorption Properties Research Articles

Enhanced Electromagnetic Wave Absorption Properties of FeCo-C Alloy by Exploiting Metamaterial Structure

This study presents a tri-layer broadband metamaterial absorber that operates in the GHz range. The absorber was composed of a polyhedral iron-cobalt alloy/graphite nanosheet material arranged in a flat sheet with two punched-in rings for the top layer, a continuous FR-4 layer at the middle, and a continuous copper layer at the bottom. For the normal incidence of the electromagnetic wave, the proposed absorber demonstrated an exceptional broadband absorption in a frequency range of 7.9–14.6 GHz, revealing an absorption exceeding 90%. The absorption magnitude remains to be above 90% in a frequency range of 8–11.1 GHz for transverse-electric-polarized waves at incident angles up to 55°. For both the transverse-magnetic- and electric-polarized waves, the absorption exceeds 90% in a frequency range of 9.5–14.6 GHz. The physical mechanism behind the absorption properties is analyzed thoroughly through the electric and magnetic field distributions. The obtained results could contribute potentially to the development of microwave applications based on metamaterial absorbers, such as radar-stealth technology, electromagnetic shielding for health safety, and reduced electromagnetic interferences for high-performance communications and electronic devices.

Multifunctional performance of core–shell rGO@Fe3O4 on the mechanical, electrical/thermal, EMI, and microstructure properties of cement-based composites

This research study focuses on the development of a multifunctional cement nanocomposite using reduced graphene oxide (rGO) nanosheets. To address the challenges of rGO dispersion, a core–shell structure of rGO@Fe3O4 (rGO@F) was investigated in cement paste. The rGO@F nanohybrid was thoroughly characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The main objectives of this study were to improve the mechanical properties, electrical conductivity, thermal conductivity, and chemical properties of the cement composite through the incorporation of rGO@F. The performance of the cement paste containing rGO0.1@Fe3O4 (0.1 wt% rGO and 1 wt% Fe3O4) was evaluated, and it was found that its toughness and compressive strength were significantly enhanced compared to the reference sample. Furthermore, the addition of rGO@F led to a remarkable increase in the electrical and thermal conductivity of the modified cement composite, attributed to the formation of conductive pathways facilitated by the rGO nanosheets. Comprehensive analyses including XRD, TGA, differential scanning calorimetry (DSC), thermally assisted microscopy (TAM), FTIR, and X-ray photoelectron spectroscopy (XPS) confirmed that the rGO@F nanohybrid had a significant impact on the chemical properties and hydration process of the hardened cement paste. SEM images revealed a more compact microstructure of the cement paste in the presence of rGO@F, demonstrating its role in crack inhibition. Additionally, an increase in the formation of improved hydration crystals such as tobermorite and jennite was observed. The core–shell structure of rGO@F exhibited exceptional electromagnetic wave absorption properties due to its layered configuration, effectively trapping the electromagnetic waves. Overall, this research study highlights the successful fabrication of a multifunctional cement nanocomposite through the incorporation of rGO@F. The findings demonstrate significant improvements in mechanical strength, electrical conductivity, thermal conductivity, chemical properties, crack inhibition, and electromagnetic wave absorption. This research contributes to the advancement of cement-based materials with enhanced performance and opens up avenues for various applications in fields such as construction, infrastructure, and telecommunications.

Construction of magnetic nanoparticle channels in SiC/SiO2 composite foam toward efficient electromagnetic wave absorption

The combination of dielectric-magnetic loss synergy and rational microstructure construction is conducive to satisfy the thin thickness, strong absorption and wide frequency bandwidth of the absorbers. In this study, a novel strategy of constructing magnetic nickel nanoparticle channels inside SiC/SiO2 composite foams for the synthesis of Ni/SiC/SiO2 porous composites (NSPC). The magnetic nickel nanoparticle channels retain SiC/SiO2 composite foam internal pore structure, which can optimize the impedance matching and satisfy the dielectric-magnetic loss synergy effect. The results confirm that the presence of multiple heterogeneous interfaces in NSPC, the magnetic and conductive losses imparted by magnetic particles and the unique foam porous structure synergistically make it have extremely excellent electromagnetic wave (EMW) absorption properties. NSPC can obtain ultra-strong reflection loss of −64.86 dB (1.46 mm) and the effective absorption range covers 13.20 GHz (4.80–18 GHz) at a total thickness of 1.79 mm (1.21–3 mm), representing 82.5 % of the whole range of frequencies. Additionally, RCS simulation confirms that NSPC can dissipate more electromagnetic capability in a real environment. In short, this work provides a new reference for the development of materials with rational microstructure construction while achieving thin thickness, strong absorption and broadband absorption.

Kapok fibers-derived carbon microtubes as efficient electromagnetic wave absorption materials

The superior electromagnetic wave absorption materials have the characteristics of thin matching thickness, low density, wide absorption bandwidth and strong absorption intensity, which can effectively deal with electromagnetic pollution. With the further research, biomass-derived carbon has received great focus due to abundant biological reserves and unique natural structure. Herein, we put forward an excellent electromagnetic wave absorption material, carbon microtubes (CMTs) with a one-dimensional hollow tubular structure, which derived from kapok fibers (KFs) via a facile annealing method. The result shows that the effective absorption bandwidth (EAB) of CMTs is 6.78 GHz under 900 °C annealing conditions. Especially, the filling ratio is just 3 wt% and the matching thickness is 2.06 mm. The superior electromagnetic wave absorption properties of CMTs can be related to its microstructural characteristics. This one-dimensional tubular structure has a large specific surface area increasing the interaction area between the material and electromagnetic waves, while the hollow tube cavity can make the incident electromagnetic waves for multi-ply scattering and reflection strengthening the dissipation capability of the material. This work offers a convenient way to produce effective electromagnetic wave absorption materials with low cost and eco-friendly environment.

Core@shell CoNi2S4/Co9S8@SiO2@MoS2 flower-like multicomponent nanocomposites: An effective strategy to aggrandize interfacial polarization for microwave absorption

Interfacial polarization had a great impact on the attenuation of electromagnetic wave. To aggrandize interfacial polarization, a strategy of constructing the abundant interfaces was proposed and investigated. Herein, CoNi nanospheres, CoNi@SiO2 nanospheres and core@shell CoNi2S4/Co9S8@SiO2@MoS2 flower-like multicomponent nanocomposites (MCNCs) were elaborately designed and successfully fabricated through a simple continuous hydrothermal process, classical Stöber method and hydrothermal treatment. The obtained results demonstrated that the elaborately constructed abundant interfaces greatly boosted the polarization loss ability, which resulted in the enhanced interfacial polarization. Therefore, the as-prepared CoNi2S4/Co9S8@SiO2@MoS2 flower-like MCNCs presented the superior electromagnetic wave absorption properties (EMWAPs) compared to the CoNi and CoNi@SiO2 precursors. Furthermore, the EMWAPs of CoNi2S4/Co9S8@SiO2@MoS2 flower-like MCNCs could also be further improved by optimizing the hydrothermal temperature and filler loading. The obtained CoNi2S4/Co9S8@SiO2@MoS2 flower-like MCNCs presented the excellent comprehensive EMWAPs including strong absorption capability, broad absorption bandwidth and thin matching thickness, which could be attributed to the unique structure, excellent interfacial polarization and synergistic effect. Therefore, this finding not only demonstrated that introducing the abundant interfaces was an effective strategy to strengthen interfacial polarization for the promotion of EMWAPs, but also provided an alternative approach to exploit the novel high-efficiency microwave absorbers.

Carbon cloth based flexible electromagnetic wave absorbing materials loaded with Co3O4 array and tunable electromagnetic wave absorption performance

The demand for flexible electromagnetic wave (EMW) absorbing materials has increased, highlighting the importance of designing efficient and adaptable EMW absorbing materials. In this study, flexible Co3O4/carbon cloth (Co3O4/CC) composites with high EMW absorption properties were prepared via a static growth method and annealing process. The composites exhibited remarkable properties, with the minimum reflection loss (RLmin) and maximum effective absorption bandwidth (EAB, RL ≤ –10 dB) of –54.43 dB and 4.54 GHz, respectively. The flexible carbon cloth (CC) substrates exhibited outstanding dielectric loss due to their conductive networks. Moreover, the uniformly and tightly organized Co3O4 arrays on the flexible CC substrate played a crucial role in fine-tuning the impedance matching and facilitating abundant multiple scattering and interface polarization. This study proposes a promising approach to preparing flexible Co3O4/CC composites with a significant reference value for the field of flexible EMW.

Tunable and broad-band electromagnetic wave absorption using W-type Hexaferrites in 1–40 GHz range

W-type Sr-hexaferrites, Sr0.75Ca0.25Zn2-xCoxFe16O27 (0.0 ≤ x ≤ 2.0), were synthesized, and their magnetic and electromagnetic (EM) wave absorption properties were investigated. As x increased from 0.0 to 2.0, the saturation magnetization value increased and reached a maximum at x = 1.25, followed by a decrease, while the magnetic anisotropic field (Hani) decreased and showed a minimum at x = 1.0, then increased again. The variation in Hani could be controlled by adjusting the value of x, which also changed the ferromagnetic resonance (FMR) frequency and enabled control over the frequency band of EM wave absorption. It is demonstrated that the EM wave absorption is primarily controlled by imaginary part of permeability (μ") induced by FMR. Composite of the W-type hexaferrite-epoxy (10 wt%) with x = 0.75–2.0 showed a broad-band EM wave absorption in the 1–18 GHz range, while the composites with x = 0–0.4 showed it in the 26.5–40 GHz. The x = 1.25 sample satisfied RL < − 10 dB in the 7–17 GHz range with a thickness of 2.1 mm, while x = 0.3 sample satisfied RL < − 10 dB in the 27–39 GHz with a thickness of 0.8 mm. Sr0.75Ca0.25Zn2-xCoxW is a very promising material for tunable wideband EM wave absorbers in 1–40 GHz range.

Heterogeneous and hierarchical ni/C/SiO2 composite with tunable electromagnetic wave absorption

Structure design, conductivity regulation and electromagnetic matching are important to optimize the electromagnetic wave (EMW) absorbing properties. Therefore, exploring a strategy which kill these three birds with one stone is extraordinary. In this work, the heterogeneous and hierarchical Ni/C/SiO2 composite with tunable EMW absorption properties was synthesized through a simple calcination process. The introduction of SiO2 and Ni prompted a relatively large hole generated in the center of carbon fiber and formed hierarchical porous structure with the circumambient small holes which extended the propagation path of EMW, realized multiple reflection and scattering and endowed sufficient interfacial polarization. Meanwhile, the SiO2 and Ni nanoparticles played an important role in conductivity regulation and electromagnetic matching. Owing to the ingenious hierarchical porous structure and synergistic effect of multiple loss mechanisms, the Ni/C/SiO2-0.5 exhibited the optimal absorption properties with the maximum reflection loss (RL) of −47.65 dB at 3.1 mm with the filler content of 10 wt%. This research would provide a novel strategy for the exploitation route of the EMW absorbing materials.

Synthesis of dendritic cobalt with flower-like structure by a facile wet chemistry method as an excellent electromagnetic wave absorber

In this study, a three-dimensional (3D) floral dendritic cobalt (FDC) consisting of layered flakes was effectively synthesized using a facile wet chemistry method. The impact of the molar amount of NaOH on the microscopic morphology, magnetic characteristics, and electromagnetic wave (EMW) absorption properties of the FDC magnetic materials was comprehensively investigated. The results revealed that the prepared FDC features primary, secondary, and multi-level branches, with the majority of secondary branches being parallel to one another. The dendrites grew closely towards the flower's center at one end, while the tips extend in various directions, forming a dendritic flower cluster. The optimal reflection loss (RL) of S3 at 9.3 GHz was −56.34 dB with a thickness of 1.89 mm, and the maximum effective absorption bandwidth (EAB, RL < -10 dB) reached 6.0 GHz (12.0–18.0 GHz) at a thickness of 1.30 mm. Consequently, the FDC magnetic materials produced in this study presented a method for fabricating high-performance electromagnetic wave absorption (EMWA) materials.

Polymer-derived NixSiy/Graphene/SiCN composite ceramics with enhanced electromagnetic wave absorption performance

Benefiting from its light weight, unique microstructure and high thermal stability, SiCN ceramics have attracted extensive attention in the field of electromagnetic wave (EMW) absorption. However, due to its poor impedance matching performance and single loss mechanism, the EMW absorption performance of SiCN ceramics requires further improvement. Herein, we introduced Ni and graphene into polysilazane to fabricate NixSiy/Graphene/SiCN composite ceramics by polymer derived ceramics (PDCs) route. The introduction of Ni not only facilitated the formation of various phases, including Si3N4, Ni2Si, Ni31Si12, graphite carbon and Si2N2O, but also catalyzed the in-situ generation of one-dimensional carbon nanotubes (1D CNTs). When the addition content of Ni was 6 wt% and the addition content of graphene was 2 wt%, the NixSiy/Graphene/SiCN composite ceramics exhibited the optimal EMW absorption performance. The minimum reflection loss (RLmin) of NixSiy/Graphene/SiCN composite ceramics reached -52.13 dB at 7.6 GHz with the thickness of 2.7 mm, and widest effective absorption bandwidth (EAB) reached 3.56 GHz (14.44-18 GHz) at 1.26 mm. The dielectric loss was enhanced by carbon materials (turbostratic carbon, 1D CNTs and 2D graphene) and various phases, while the magnetic loss was improved by Ni and nickel silicide. The synergism of multiple loss mechanisms and good impedance matching lead to excellent EMW absorption properties of NixSiy/Graphene/SiCN ceramics.

Electromagnetic Wave Absorption Properties of Silver-Decorated Nickel-Coated Copper with Frequency Selective Surface

In this study, Ag-decorated Ni@Cu powders were prepared by electroless plating method with Ni@Cu powders as the raw material. The various characteristics of the composite powders, such as their phase composition and structure, were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The effects of different Ag content on the size distribution of the particles were also studied by a laser particle size analyzer. The network vector analyzer additionally measured the electromagnetic properties of Ag-decorated Ni@Cu powders/paraffin samples. The electromagnetic wave absorption properties of the samples with different thicknesses were studied. The results of XRD and SEM show that with the increase of Ag content, the Ag plating effect of Ni@Cu powders increases first and then decreases. The results of laser particle size analyzer show that with the increase of Ag content, the particle size and distribution of Ag-decorated Ni@Cu powders become larger and wider. Through the analysis of the microwave absorption performance of Ag-decorated Ni@Cu powders/paraffin sample, it can be concluded that in the frequency range of 8.2–12.4[Formula: see text]GHz, when the thickness is 2.6[Formula: see text]mm, the Ag-decorated Ni@Cu powders with a silver mass ratio of 25[Formula: see text]wt.% have good electromagnetic wave absorption performance. The reflection loss is less than −10 dB in the whole frequency range, and the peak value reaches −55.36 dB at 9.92[Formula: see text]GHz. In addition, the frequency selective surface coupled by circular element and square ring element improves the microwave absorption performance of the sample containing 15[Formula: see text]wt.% Ag content with 2[Formula: see text]mm thickness. The reflection loss is lower than −10 dB with the peak reflection loss of −36.73 dB at 10.98[Formula: see text]GHz in the whole frequency range. The simulation results show that the loading frequency selective surface can reduce the silver content and make it have better microwave absorption performance and low cost.

Synthesis of hollow CuFe2O4 microspheres decorated nitrogen-doped graphene hybrid composites for broadband and efficient electromagnetic absorption

The development of graphene-based electromagnetic wave (EMW) absorbers with broad bandwidth, strong absorption and low filling ratio remains a big challenge. In this work, hollow copper ferrite microspheres decorated nitrogen-doped reduced graphene oxide (NRGO/hollow CuFe2O4) hybrid composites were prepared by a two-step route of solvothermal reaction and hydrothermal synthesis. Results of microscopic morphology analysis showed that the NRGO/hollow CuFe2O4 hybrid composites had a special entanglement structure between hollow CuFe2O4 microspheres and wrinkled NRGO. Moreover, the EMW absorption properties of as-prepared hybrid composites could be regulated by changing the additive amounts of hollow CuFe2O4. It was worth noting that when the additive amount of hollow CuFe2O4 was 15.0 mg, the attained hybrid composites showed the optimal EMW absorption performance. The minimum reflection loss reached up to −34.18 dB at a thin matching thickness of 1.98 mm and a low filling ratio of 20.0 wt%, and the corresponding effective absorption bandwidth was as large as 5.92 GHz, covering almost the whole Ku band. Furthermore, when the matching thickness was increased to 3.02 mm, the EMW absorption capacity was significantly enhanced, and the optimal reflection loss value of −58.45 dB was achieved. In addition, the possible EMW absorption mechanisms were proposed. Therefore, the structural design and composition regulation strategy presented in this work would provide a great reference value for the preparation of broadband and efficient graphene-based EMW absorbing materials.

Single-source-precursor derived SiOC ceramics with in-situ formed CNTs and core–shell structured CoSi@C nanoparticles towards excellent electromagnetic wave absorption properties

In this work, novel CNTs/CoSi/SiOC nanocomposite ceramics with<em> in-situ </em>formed multi-walled carbon nanotubes (CNTs) and core-shell structured CoSi@C nanoparticles were successfully prepared <em>via</em> a single-source-precursor derived ceramic approach. The polymeric precursor characterization as well as phase evolution, microstructure and electromagnetic wave (EMW) absorption properties of the ceramics was investigated in detail. The results show that the <em>in-situ</em> formed CNTs and magnetic CoSi@C nanoparticles provide a synergistic effect on both dielectric loss and magnetic loss, leading to outstanding EMW absorption properties of the ceramics annealed at only 1100 °C, as follows: 1) For the Co feeding 6.25 wt.%, the minimum reflection loss (RLmin) is -53.1 dB and the effective absorption bandwidth (EAB) is 4.96 GHz (7.12-12.08 GHz) with a ceramic-paraffin hybrid sample thickness of 3.10 mm, achieving the full X-band coverage; 2) For the Co feeding 9.09 wt.%, the RLmin value of -66.4 dB and the EAB value of 3.04 GHz (8.4-11.44 GHz) were achieved with a thickness of only 2.27 mm. Therefore, the present CNTs/CoSi/SiOC nanocomposite ceramics have potential applications for thin, lightweight and efficient EMW absorption in harsh environments.

Construction of Self-Assembly Based Tunable Absorber: Lightweight, Hydrophobic and Self-Cleaning Properties

HighlightsNiCo/C aerogel was prepared by pyrolysis carbonization self-assembly of NiCo- metal–organic frameworks (MOFs).The assembly mechanism of MOF aerogel was studied by adjusting the ratio of metal ion /BTC.Aerogel combines hydrophobic, lightweight, self-cleaning, and electromagnetic wave absorption properties.

Facile synthesis and excellent electromagnetic wave absorption properties of Air@RGO/CoNi hollow microspheres

The rational synergy of chemical composition and spatial nanostructures plays an important role in high-performance electromagnetic wave (EMW) absorption materials. Here, reduced graphene oxide (RGO) hollow microspheres loaded with CoNi alloy nanoparticles (Air@RGO/CoNi) were constructed by a facile water-in-oil emulsification route followed by high-temperature thermal treatment. The crystal structure, composition, microstructure, and magnetic properties of Air@RGO/CoNi were characterized by XRD, XPS, TEM, and VSM, respectively. The results demonstrated that the as-obtained Air@RGO/CoNi composites showed a uniform spherical morphology with a remarkably hollow structure. Impressively, nano-CoNi particles were compactly and uniformly distributed on the surface of RGO. Benefiting from the unique structure and compositional merits, the optimized Air@RGO/CoNi hollow microspheres exhibit superior (EMW) absorption performance. The minimum reflection loss (RLmin) value reached up to −56.16 dB at 13.67 GHz with a thin thickness of 2.55 mm and the widest effective absorption bandwidth (RL values are below −10 dB) covered 8.65 GHz (9.15–17.8 GHz) with a thinner thickness of 2.4 mm. Furthermore, possible EMW attenuation mechanisms had been proposed. Given these outstanding findings, we believe the as-fabricated Air@RGO/CoNi hollow microspheres can be promising candidates as highly microwave absorption materials with thin thickness, wide absorption bandwidth, and high absorption capacity.

Exchange-coupled Core/shell Structure CoFe2O4@NiFe2O4/CNFs Composites with Enhanced Microwave Absorption Performance

One strategy to solve the electromagnetic pollution is proposed to fabricate electromagnetic wave absorption materials. The CoFe2O4@NiFe2O4/CNFs composites with magnetic exchange-coupled core/shell structure were synthesized by a facial solvothermal method. The CoFe2O4@NiFe2O4 particles with core/shell structure was anchored on surface of carbon nanofibers. Compared with CoFe2O4 /CNFs whose the minimum reflection loss is −39.17 dB at 15.45 GHz and the effective absorbing band is 3.32 GHz at 1.5 mm, the composite exhibits excellent microwave absorption performance that the minimum reflection loss at 12.32 GHz reaches −51.46 dB when the mass ratio of CoFe2O4 to NiFe2O4 is 3:1 and the thickness is 1.80 mm and the effective absorbing bandwidth reaches 3.85 GHz at 1.5 mm. The results indicate that the exchange coupling effect could enhance the electromagnetic wave absorption. Also, the content of NiFe2O4 could influence the properties if its content is too heavy, the exchange coupling effect will decrease and the impedance will be mismatched. Therefore, CoFe2O4@NiFe2O4/CNFs particles can be used as thin layer materials with strong absorption of low frequency microwave. The study provides a novel way to improve electromagnetic wave absorption properties based on exchange-coupled core/shell structure and the composition control.

Enhanced electromagnetic wave absorption properties of ultrathin SnO nanosheets/carbon nanotube hybrids

The construction of thin electromagnetic wave (EMW) absorbing materials with strong absorption, low filler load and broadband is significant for attenuating EMWs. In this work, 2-dimensional-1-dimensional (2D–1D) SnO/carbon nanotube (CNT) nanohybrids were prepared successfully by a facial hydrothermal method. The excellent EMW absorption performance of SnO/CNT hybrids can be achieved by adjusting CNT content. SnO/CNT exhibits excellent EMW absorption properties, including a minimum reflection loss (RLmin) of − 68.83 dB (1.44 mm) and a maximum effective absorption bandwidth (EAB) of 4.53 GHz (12.71–17.24 GHz, 1.49 mm). In addition, to analyze the mechanism of EMW absorption, the electronic properties of heterogeneous interfaces (SnO and CNT) were calculated by density functional theory (DFT). Both experiments and theory results prove that the synthesized SnO/CNT nanohybrids have excellent electromagnetic wave loss ability, which is attributed to rich dipole polarization, interface polarization, and good conduction loss. Therefore, SnO/CNT nanohybrids have been proven to be an ultralight, efficient and promising EMW absorber.

Effect of Graphite Defect Type and Heterogeneous Atomic Doping Structure on the Electromagnetic Wave Absorption Properties of Sulfur-Doped Carbon Fibers

The heterogeneous atom-doped structure breaks the atomic-level symmetry of the local microstructure, and it and the defect design are considered to be an efficient way to fabricate microwave absorbers with a wide effective bandwidth and strong absorption capability. Herein, we have successfully designed and synthesized sulfur-doped carbon fibers by combining a strategy of introducing heterogeneous atoms with defect engineering. The analysis of Raman spectroscopy and transmission electron microscopy data reveals the correspondence between the type of graphite defects in sulfur-doped carbon fibers and their microwave absorption properties. The heterostructure formed by graphite and amorphous carbon can be considered a boundary-type defect, which is beneficial for microwave absorption. The introduction of vacancy defects and sulfur atom doping in graphite crystals breaks the symmetry of the graphite structure and leads to changes in dipole polarization. The ratio of the two sulfur-doped structures, C═S and C–S–C, is controlled to achieve the microwave absorption properties of the material in the high-frequency region. The three-dimensional structure formed by the cross-linking of one-dimensional fibers is more conducive to the formation of macroscopic eddy current losses. The strong absorption of microwaves at extremely thin thicknesses has been achieved with S-doped carbon fibers due to the synergy of multiple loss mechanisms. When the absorber thickness is only 0.98 mm, the optimized S-doped carbon fiber can reach a minimum reflection loss (RL) of −69.232 dB, and when the thickness is 1.04 mm, the widest effective bandwidth reaches 3.9 GHz (14.1–18 GHz), demonstrating a strong electromagnetic wave absorption capability.

Designing flower-like MOFs-derived N-doped carbon nanotubes encapsulated magnetic NiCo composites with multi-heterointerfaces for efficient electromagnetic wave absorption

In order to acquire exceptional electromagnetic wave absorption properties, the microstructure design and component modification of composites are essential. Metal-organic frameworks (MOFs), due to the unique metal–organic crystalline coordination, tunable morphology, high surface area, and well-defined pores, have been regarded as promising electromagnetic wave absorption materials precursors. However, the inadequate contact abilities between adjacent MOFs nanoparticles endow it with undesirable electromagnetic wave dissipation capacity at a low filler loading, which is a great challenge to break size effect of nanoparticles to achieve efficient absorption. Herein, NiCo-MOFs derived N-doped carbon nanotubes encapsulated with NiCo nanoparticles anchored on flowers-like composites (denoted as NCNT/NiCo/C) were successfully prepared through facile hydrothermal method followed by thermal chemical vapor deposition with melamine-assisted catalyst. By controlling the Ni/Co ratio in precursor, the tunable morphology and microstructure of MOFs are achieved. Most importantly, the derived N-doped carbon nanotubes tightly connect the adjacent nanosheets to construct the special 3D interconnected conductive network, which effectively accelerates the charge transfer and improves the conduction loss. And notably, the NCNT/NiCo/C composite delivers excellent electromagnetic wave absorption performance with minimum reflection loss of −66.1 dB and wide effective absorption bandwidth up to 4.64 GHz when the Ni/Co ratio is 1:1. This work provides a novel method for the preparation of morphology controllable MOFs-derived composites and realizes high-performance electromagnetic wave absorption properties.

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 (RLmin) 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.