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.     

Microwave absorption performance of hierarchical structured composites of greigite and reduced graphene oxide

The greigite (Fe₃S₄)/reduced graphene oxide (RGO) hierarchical structural composites (F–R) with the Fe₃S₄ nanoparticles attached to the RGO layers were successfully prepared via a simple one-pot solvothermal method. The microwave absorption properties were evaluated by calculating the reflection loss (RL) values. The results show that the RGO content and the filler loading of composites in paraffin mixture are very critical to the microwave absorption properties because they can improve the electromagnetic parameters. Sample F–R-3 presents the best microwave absorption capacity, in which an optimum RL value of ??62.3 dB and an effective absorption bandwidth (EAB, RL value?<???10 dB) of 3.04 GHz (14.96–18 GHz) can be obtained when the matching thickness is only 1.29 mm. Meanwhile, the widest EAB reaches 4.08 GHz (13.92–18 GHz) at the matching thickness of only 1.37 mm. Impressively, when the matching thickness is in the range of 1.2–5.5 mm, all RL peaks are below ??20 dB, and the EAB can be 14.98 GHz (3.02–18 GHz), covering the whole C, X and Ku bands. The distinguished absorption property is mainly ascribed to the combined effect of strong loss ability and good impedance matching. Apparently, the F–R composite with strong absorption ability, thin thickness and wide EAB is suitable for the efficient microwave absorber.

Graphical abstract

     

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.     

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.     

D-xylose-derived carbon microspheres modified by CuFe2O4 nanoparticles with excellent microwave absorption properties

In this work, we studied the preparation and microwave absorption properties of D-xylose-derived carbon materials modified by CuFe₂O₄ nanoparticles and discussed the influence of the addition amount of carbon materials. It was prepared with a simple hydrothermal method, and various methods are used to characterize its microscopic morphology, chemical structure and microwave absorption properties.Results show that the modification of copper ferrite nanoparticles is effective in mitigating polarization and magnetic losses, enhancing the microwave absorption properties of the samples and absorption curves of the composite materials change from a single peak to double peaks. Comparing all samples it can be concluded that the effective absorption bandwidth of CuFe₂O₄ composite materials containing carbon microspheres (CuFe₂O₄/CMs-0.3) is 6.24 GHz. The minimum reflection loss (RL) is???50.4 dB at 14.64 GHz. The thickness of the above corresponds to 2.5 mm. This work not only provides a reference method for the preparation of microwave absorbing materials but also contributes to the understanding of absorption mechanisms.

     

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.     

Cu-Co Hybrid Crystals Assembled on Hollow Microsphere: Temperature-Dependent Top-Down Synthesis and Aggregation-Induced Conversion from Microwave Shielding to Absorption

The construction of hollow metallic microspheres with rationally designed building blocks of the metal shell is a promising way to achieve low density and functionality control, but the microengineering of the metallic structures on a micrometer spherical surface is a great challenge. In the present work, a novel and simple calcination-induced aggregation strategy is developed to realize the distribution status and microstructure control of Co-Cu bimetal building blocks assembled on a hollow glass microsphere support, and thus a series of low-density (0.58 g cm⁻³) dual shell composite hollow microspheres are constructed with gradient in electromagnetic property depending on the calcination temperature (CT). The optimized microwave shielding performance can be achieved at a CT of 500 °C, while further increasing CT to 700 °C leads to an interesting conversion from microwave shielding to absorption with an optimized effective absorption bandwidth of 4.64 GHz at a low matching thickness of 1.33 mm. The mechanism underlying the CT-dependent metallic shell structure variation and further the decisive effect of the shell structure on the microwave response behavior are proposed based on a series of contrast experiments.     

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.     

Tunable microwave absorption properties of B-doped SiC nanopowders prepared by arc-discharge method

In this study, we adopted a simple strategy of the arc discharge to prepare the B-doped SiC microwave nano-absorbers. Herein, the amorphous boron was selected as a doping B element source to tune the electromagnetic parameters of the SiC nanopowders. The experimental results indicate that the doping B in the SiC can conveniently tailor the microwave absorption capability of the SiC nanopowders. The appropriate doping B in the SiC can contribute to excellent synergistic effects among its defect dipoles, leakage, and magnetism. Among the doped SiC with B doping content of 0, 5, 10, and 15 at.%, the SiC with doping B content of 10 at.% acquired the optimized impedance matching and enhanced microwave absorption properties. And the optimal reflection loss (RL) value ? 51.2 dB at 6.76 GHz with a matching thickness of 2.9 mm is acquired. The RL of the B-doped SiC nanopowders with B doping content of 10 at.% exceeding ? 10 dB is about 3–5 times those of the other three samples in the ranges of 1–18 GHz at a matching thickness of 1.2–6.0 mm. Therefore, this work provided a feasible way to tune the microwave absorption properties of the B-doped SiC, which is of great significance to improve SiC-based high-temperature dielectric ceramics of microwave absorption performances by the defect-engineering strategy.

     

Enhanced microwave absorption performance of nitrogen-doped porous carbon dodecahedrons composite embedded with ceric dioxide

CeO₂/Co/C dodecahedrons composites with excellent microwave absorption performance were synthesized by using a hydrothermal method. ZIF-67/CeO₂ was first prepared by introducing CeO₂ into the precursor of ZIF-67 and then CeO₂/Co/C composite was obtained after heat treatment. Impedance matching of the samples could be well adjusted by controlling the content of CeO₂. Unique dodecahedral structure for more interfacial reflection and cerium dioxide oxygen vacancies enhance microwave absorption performance. Specifically, the CeO₂/Co/C exhibited a minimum reflection loss of ?68.83 dB is observed at 5.92 GHz, while the thickness was 3.69 mm. The introduction of CeO₂ effectively enhanced the impedance matching of the materials and improved the microwave absorption performance. Therefore, this CeO₂/Co/C composite is a promising microwave absorber material with high performance.     

Investigation on the broadband electromagnetic wave absorption properties and mechanism of Co<Subscript>3</Subscript>O<Subscript>4</Subscript>-nanosheets/reduced-graphene-oxide composite

A cobaltosic-oxide-nanosheets/reduced-graphene-oxide composite (CoNSs@RGO) was successfully prepared as a light-weight broadband electromagnetic wave absorber.The effects of the sample thickness and amount of composite added to paraffin samples on the absorption properties were thoroughly investigated.Due to the nanosheet-like structure of Co3O4,the surface-to-volume ratio of the wave absorption material was very high,resulting in a large enhancement in the absorption properties.The maximum refection loss of the CoNSs@RGO composite was-45.15 dB for a thickness of 3.6 mm,and the best absorption bandwidth with a reflection loss below-10 dB was 7.14 GHz with a thickness of 2.9 mm.In addition,the peaks of microwave absorption shifted towards the low frequency region with increasing thickness of the absorbing coatings.The mechanism of electromagnetic wave absorption was attributed to impedance matching of CoNSs@RGO as well as the dielectric relaxation and polarization of RGO.Compared to previously reported absorbing materials,CoNSs@RGO showed better performance as a lightweight and highly efficient absorbing material for application in the high frequency band.     

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.

     

Microwave absorption performance of magnetic Fe–Ni–P nanoparticles electrolessly plated on hollow glass microspheres

Magnetic Fe–Ni–P nanoparticles have been successfully fabricated on hollow glass microspheres via electroless plating for the application of lightweight microwave absorbers. The resultant materials were characterized by field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX), X-ray diffraction analysis (XRD), vibrating sample magnetometer (VSM) and vector network analyzer. The results show that compact and uniform Fe–Ni–P nanoparticles with the average diameter of about 150 nm have been successfully plated on the hollow glass microspheres. The plated microspheres exhibit excellent soft magnetic characteristics with high saturation magnetization and low coercivity, and the soft magnetic characteristic behaves better with the increasing of iron content in the coatings. Microwave absorption performance shows the maximum reflection loss of the composite powder reaches −49.2 dB at the frequency of 7.7 GHz with the thickness of 5 mm, and the bandwidth with the reflection loss less than −20 dB exceeds 2.2 GHz.     

Double-layer microwave absorber based on nanocrystalline Zn0.5Ni0.5Fe2O4/α-Fe microfibers

The microwave absorption properties of the nanocrystalline NiZn ferrite (Zn_0.5Ni_0.5Fe₂O₄) and iron (α-Fe) microfibers with single-layer and double-layer structures were investigated in the frequency range of 2–18 GHz. The double-layer absorbers have much better microwave absorption properties than the single-layer absorbers, and the microwave absorption properties of the double-layer structure are influenced by the coupling interactions between the absorbing layer and matching layer. With the absorbing layer thickness 0.7 mm of α-Fe microfibers–wax composite and the matching layer thickness 1.5 mm of Zn_0.5Ni_0.5Fe₂O₄ microfibers–wax composite, the minimum reflection loss (RL) reaches about −71 dB at 16.2 GHz and the absorption band width is about 9.2 GHz ranging from 8.8 to 18 GHz with the RL value exceeding −10 dB. While, when the absorbing layer is the Zn_0.5Ni_0.5Fe₂O₄ microfibers–wax composite with thickness 1.8 mm and the matching layer is the α-Fe microfibers–wax composite with thickness 0.2 mm, the RL value achieves the minimum about −73 dB at 13.8 GHz and the absorption band width is about 10.2 GHz ranging from 7.8 to 18 GHz with the RL value exceeding −10 dB, which covers the whole X-band (8.2–12.4 GHz) and K_u-band (12.4–18 GHz).     

Enhanced electromagnetic wave absorption properties of polyaniline-coated Fe3O4/reduced graphene oxide nanocomposites

Fe₃O₄-reduced graphene oxide-polyaniline (Fe₃O₄–RGO–PANI) ternary electromagnetic wave absorbing materials were prepared by in situ polymerization of aniline monomer on the surface of Fe₃O₄–RGO nanocomposites. The morphology, structure and other physical properties of the nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, vibration sample magnetism, etc. The electromagnetic wave absorbing properties of composite materials were measured by using a vector network analyzer. The PANI–Fe₃O₄–RGO nanocomposites demonstrated that the maximum reflection loss was ?36.5 dB at 7.4 GHz with a thickness of 4.5 mm and the absorption bandwidth with the reflection loss below ?10 dB was up to 12.0 GHz with a thickness in the range of 2.5–5.0 mm, suggesting that the microwave absorption properties and the absorption bandwidth were greatly enhanced by coating with polyaniline (PANI). The strong absorption characteristics of PANI–Fe₃O₄–RGO ternary composites indicated their potential application as the electromagnetic wave absorbing material.     

Fabrication of polypyrrole/nano-exfoliated graphite composites by in situ intercalation polymerization and their microwave absorption properties

Polypyrrole/nano-exfoliated graphite composites were synthesized using an in situ intercalation polymerization of pyrrole into the layers of expanded graphites. The morphologies and nanostructures of obtained composites were characterized by field emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction analysis. Results showed that the in situ intercalation polymerization of pyrrole cation into the layers of expanded graphites could separate graphite into nano-exfoliated graphite sheets. The interactions between polypyrrole and the graphite sheet were also confirmed by Fourier transformed infrared spectroscopy. The fabricated nanocomposites polypyrrole/nano-exfoliated graphite-1.5 showed obvious improvement in microwave absorption compared with those of the polypyrrole or the expanded graphite itself. With a thickness of 2.7 mm, the optimal absorption peak reached −48 dB at 13.4 GHz and the bandwidth corresponding to the reflection loss at −10 dB was 3.4 GHz (from 13.2 to 16.6 GHz). The minimum RL reached −34 dB with a thickness of 2.5 mm for Polypyrrole/nano-exfoliated graphite-1.5. Moreover, it could be observed that the absorption bandwidth with RL below −10 dB was obtained in the frequency range of 5–18 GHz for polypyrrole/nano-exfoliated graphite-1.5 with a thickness of 2–5 mm. This would open a path toward the fabrication of microwave absorption materials of light-weight.     

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

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

3D architecture reduced graphene oxide-MoS2 composite: Preparation and excellent electromagnetic wave absorption performance

High-performance electromagnetic absorbers with wide absorption band, strong absorption and lightweight are necessary for industry and military application. To obtain the desired materials, two-dimensional (2D) atomic layers structure nanosheets, such as graphene and graphene-like, were adopted due to its unique structure and properties. Here, 3D architecture reduced graphene oxide-molybdenum disulfide (RGO-MoS₂) composite was prepared by one-pot hydrothermal reaction. MoS₂ generated on graphene oxide intercalation through hydrothermal process and rGO is obtained in the meanwhile. 3D architecture RGO-MoS₂ composite can effectively prevent two-dimensional nanosheets re-stacked and can be applied in electromagnetic wave absorption field. In this paper, composites consist of RGO and various MoS₂ were prepared and their electromagnetic performances were investigated for the first time. Maximum absorption bandwidth (R_L < −10 dB) is 5.92 GHz with thickness of 2.5 mm. We may reasonably conclude that RGO-MoS₂ composite can serve as excellent light-weight electromagnetic wave absorbers and can be widely used in practice.     

Fabrication and electromagnetic characteristics of microwave absorbers containing carbon nanofibers and NiFe particles

The objective of this study is to develop microwave absorbers by using both dielectric and magnetic lossy materials. Carbon nanofibers (CNFs) were used as dielectric lossy materials and NiFe particles were used as magnetic lossy materials. Twelve kinds of composite specimens were fabricated and classified into dielectric, magnetic, and mixed types. Their complex permittivities and permeabilities in the range of 2–18 GHz were measured. Parametric studies to aid in the design of single-layered radar absorbing materials (RAMs) were performed. The mixed RAMs generally showed improved absorbing characteristics with thinner matching thicknesses. The present mixed RAM showed the 10 dB absorbing bandwidth of 4.0 GHz in the X-band (2.00 mm thickness) and 6.0 GHz in the Ku-band (1.49 mm thickness). The measured absorbing properties of selected specimens were in very good agreements with simulations.     

Enhanced microwave absorption properties of flake-shaped FePCB metallic glass/graphene composites

A novel kind of composite absorber, i.e. FePCB/graphene composite, with excellent microwave absorption properties was successfully fabricated by a simple and scalable ball milling method. After being milled, the FePCB particles displayed flaky morphology with large aspect ratio. The complex permittivity and permeability of the flaky FePCB distinctly increased compared with those before milling. Furthermore, with the introduction of graphene, the flaky FePCB/graphene composite exhibited excellent microwave absorption performance with strong absorption and wide absorption band. In particular, for FePCB/graphene composite with an absorber thickness of 2 mm, the reflection loss (RL) reached a minimum of −45.3 dB at 12.6 GHz and the effective absorption bandwidth (RL < −10 dB) covered 5.4 GHz. The enhanced microwave absorption performance of the FePCB/graphene composite was attributed to the high magnetic loss and improved impedance matching which were closely related to the flake-shaped FePCB particles and the introduction of graphene sheets.