Electromagnetic Wave Absorption Materials Research Articles

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.

Heterogeneous interface engineering of high-density MOFs-derived Co nanoparticles anchored on N-doped RGO toward wide-frequency electromagnetic wave absorption

Facing increasing electromagnetic (EM) wave pollution and interference issues, developing synergy EM wave absorption materials with rich heterogeneous interfaces is s an effective way to solve the above problems. In this work, two-dimensional (2D) cobalt-based metal-organic frameworks (Co-MOFs) nanosheets arrays are firstly growth on the 2D graphene oxide (GO) sheets. After undergoing the pyrolytic treatment in the N2 atmosphere, high-density MOFs-derived 0D Co nanoparticles (NPs) uniformly anchored on the Nitrogen-doped reduced graphene oxide (N-RGO), constructing 0D/2D magnetic-dielectric Co@N-RGO composites. By tuning the size of magnetic Co NPs by controlling the content of Co-MOFs nanosheets, the EM parameters and impedance match of Co@N-RGO sheets can be regulated to tune the EM wave absorption ability. Benefited from the synergy loss and high-density heterogeneous interfaces, obtained Co@N-RGO sheets exhibit excellent EM wave absorption intensity and tuning absorption frequency. The effective absorption bandwidth of the Co@N-RGO sheets ups to 6.0 GHz at 1.9 mm thickness, covering the entire Ku band (12–18 GHz). It can be concluded that constructing magnetic-dielectric system and high-density heterogeneous interfaces provides a new guide to obtain wide-frequency EM wave absorption materials.

Enoki-like carbon nanotubes coated with in situ growing nickel particles for enhanced electromagnetic wave absorption

With the increasingly serious electromagnetic pollution, the urgent demands for electromagnetic wave absorption (EMWA) materials are gradually developing towards performance integration and multi-dimensional scales. Herein, the enoki-like carbon nanotubes (CNTs) coated with nickel particles (CNT@Ni) were synthesized by a catalytic thermal decomposition method. The resulting CNT@Ni composites exhibited excellent EMWA performances with a minimum reflection loss value of − 60.4 dB at a thickness of 2.97 mm. It benefited from the synergy of collaborative electrical and magnetic losses and hierarchical structure. The conductive pathways formed by the intertwined CNTs greatly improved the EMWA capacity of the material, enabling large amounts of electromagnetic waves to enter the material for conversion and dissipation. In addition, the inherent graphite defects and oxygen-containing groups formed on the material surface during the process of high-temperature treatment provided polarization centers for dipole polarizations. More importantly, the abundant heterogeneous interfaces enhanced the interface loss effects of the material. This simple preparation strategy of the CNT-based EMWA material will provide a design inspiration for the novel electromagnetic absorber.

1D-3D biological template loaded NiCo nanowires at high temperatures as a broadband, lightweight electromagnetic wave absorbing material

To meet the requirements of electromagnetic radiation control, especially broadband and high temperature resistance, electromagnetic wave absorbing materials (EWAMs) have been intensively studied. In this work, NiCo NWs were synthesized by a one-step hydrothermal method. The composite has a one-dimensional(1D) NiCo NWs core-shell structure on a three-dimensional(3D) diatomite(De) surface and subsequently calcined at different temperatures. The samples calcined at 400 °C showed excellent EWA performance with a minimum reflection loss(RLmin) of −82 dB at a matched thickness of 7.1 mm and a maximum effective absorption bandwidth(EAB) of 9.53 GHz at a thickness of 8 mm. By adjusting the thickness, full coverage of X-band and Ku-band can be achieved. The conduction loss of the 1D material and the impedance matching of the bionic substrate De are considered to jointly contribute to the microwave attenuation capability. This combination of using bionic materials and 1D transition metal oxides provide a viable strategy for addressing electromagnetic pollution.

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.

Enhancing electromagnetic absorption performance of Molybdate@Carbon by metal ion substitution

Transition metal molybdate (RMoO4) has been extensively studied in optics, electricity and catalysis due to its low cost and multivalent Mo atoms, while its poor electrical conductivity limits its application in electromagnetic wave absorption (EMA). Compounding molybdate with conductive materials is an effective way to improve its electrical conductivity. In this work, a homogeneous coating on the molybdate surface was achieved by utilizing a pyrrole oxidation polymerization mechanism, and then stabilized composites of Molybdate@Carbon (RMoO4@C) were obtained by high-temperature pyrolysis. The EMA properties of the nanocomposites were tuned by substituting the species of transition metal elements (RMoO4@C, R=Fe, Co, Cu). Among them, Fe2(MoO4)3@C has a minimum reflection loss of −60.62 dB at an ultra-low thickness of 1.7 mm, and the effective absorption bandwidth (EAB) can reach 4.75 GHz at 3.00 mm. This work expands the range of applications for molybdate and provides a new material basis for building high-performance EMA materials.

VSe2/CNTs nanocomposites toward superior electromagnetic wave absorption performance

Electromagnetic radiation pollution has become a serious threat, which will harm human health and interfere with electronic devices. However, it is still a challenge to develop high-efficiency electromagnetic wave absorbers with wide frequency band and strong absorption, especially for realizing the features of multi-bands absorption. Herein, VSe2/CNTs nanocomposites were successfully synthesized with crosslinked CNTs distributed on VSe2 nanoclusters composed of nanosheets. Importantly, the electromagnetic properties and absorption performance of the VSe2/CNTs nanocomposites can be effectively tailored by changing the hybrid ratio of CNTs and VSe2 nanosheets (VSe2-NSs). The increase of CNTs content promotes the formation of a conductive network and leads to the increase of permittivity. The VSe2/CNTs nanocomposite with CNTs of 40 mg exhibits the best electromagnetic wave absorption performance, the minimum reflection loss (RL) reaches −57.53 dB at 5.52 GHz and is about 6 times more than VSe2-NSs. Meanwhile, the VSe2/CNTs nanocomposite with CNTs of 30 mg shows dual-bands absorption performance with a minimum RL value of −50.06 dB at 3.84 GHz and the total effective absorption bandwidth of 3.32 GHz. This result proves that VSe2/CNTs nanocomposites can be promising candidates as high-efficiency electromagnetic wave absorption material and provides a feasible idea for designing a high-performance electromagnetic wave absorber.

In‐Situ Fabrication of Sustainable‐N‐Doped‐Carbon‐Nanotube‐Encapsulated CoNi Heterogenous Nanocomposites for High‐Efficiency Electromagnetic Wave Absorption

Developing carbon encapsulated magnetic composites with rational design of microstructure for achieving high-performance electromagnetic wave (EMW) absorption in a facile, sustainable, and energy-efficiency approach is highly demanded yet remains challenging. Here, a type of N-doped carbon nanotube (CNT) encapsulated CoNi alloy nanocomposites with diverse heterostructures are synthesized via the facile, sustainable autocatalytic pyrolysis of porous CoNi-layered double hydroxide/melamine. Specifically, the formation mechanism of the encapsulated structure and the effects of heterogenous microstructure and composition on the EMW absorption performance are ascertained. With the presence of melamine, CoNi alloy emerges its autocatalysis effect to generate N-doped CNTs, leading to unique heterostructure and high oxidation stability. The abundant heterogeneous interfaces induce strong interfacial polarization to EMWs and optimize impedance matching characteristic. Combined with the inherent high conductive and magnetic loss capabilities, the nanocomposites accomplish a high-efficiency EMW absorption performance even at a low filling ratio. The minimum reflection loss of -84.0dB at the thickness of 3.2mm and a maximum effective bandwidth of 4.3GHz are obtained, comparable to the best EMW absorbers. Integrated with the facile, controllable, and sustainable preparation approach of the heterogenous nanocomposites, the work shows a great promise of the nanocarbon encapsulation protocol for achieving lightweight, high-performance EMW absorption materials.

Topological MOFs deformation for the direct preparation of electromagnetic functionalized Ni/C aerogels with good hydrophobicity and thermal insulation

Magnetic carbon-based aerogels are nowadays a kind of emerging candidates for high-performance electromagnetic wave absorbing materials (EWAMs), because their unique structural advantages lay a good foundation for the propagation and attenuation of electromagnetic (EM) wave. However, traditional post-treatment methods for magnetic carbon-based aerogels often face difficulties in maintaining aerogel structure, regulating the content of magnetic components, and dispersing magnetic particles. Herein, we first induce a topological deformation of bulky Ni-MOF particles to generate Ni-MOF aerogel assembled by crosslinked fibers, and then convert this intermediate aerogel to final Ni/C composite aerogels (NCCAs) through controllable high-temperature pyrolysis. This novel strategy achieves high loading and uniform dispersion of magnetic metal nanoparticles throughout carbon skeleton. Pyrolysis temperature plays a very important role to determine the overall attenuation capability and impedance matching of NCCAs, because it has a remarkable impact on the dielectric loss of carbon skeleton but negligible effect on magnetic loss. When the temperature is 700 °C, the optimum product (NCCA-2) will show the best EM absorption performance among this series of composites, including strong reflection loss and broad effective absorption bandwidth. Surprisingly, the integrated advantages of aerogel structure and MOFs transformation not only render NCCA-2 as a highly competitive candidate for high-performance EWAMs as compared with various Ni/C composites, but also bestow it on excellent hydrophobic and thermal insulation properties.

Transformation from Electromagnetic Inflection to Absorption of Silicone Rubber and Accordion-Shaped Ti3C2MXene Composites by Highly Electric Conductive Multi-Walled Carbon Nanotubes.

Electromagnetic (EM) pollution becomes more penetrating in daily life and work due to more convenience provided by multi-electrical devices, as does secondary pollution caused by electromagnetic reflection. EM wave absorption material with less reflection is a good solution to absorb unavoidable EM radiation or reduce it from the source. Filled with two-dimensional Ti3SiC2MXenes, silicone rubber (SR)composite demonstrated a good electromagnetic shielding effectiveness of 20 dB in the X band by melt-mixing processes for good conductivity of more than 10-3 S/cm and displayed dielectric properties and a low magnetic permeability; however, the reflection loss was only -4 dB. By the combination of one-dimensional highly electric conductive multi-walled carbon nanotubes (HEMWCNTs) and MXenes, the composites achieved the transformation from electromagnetic inflection to an excellent absorbing performance to reach a minimum reflection loss of -30.19 dB due to electric conductivity of above 10-4 S/cm, a higher dielectric constant, and more loss in both dielectric and magnetic properties. Ni-added multi-walled carbon nanotubes were not able to achieve the transformation. The as-prepared SR/HEMWCNT/MXene composites have potential application prospects in protective layers, which can be used for electromagnetic wave absorption, electromagnetic interference suppression of devices, and stealth of the equipment.

Multifunctional SiC aerogel reinforced with nanofibers and nanowires for high-efficiency electromagnetic wave absorption

Ceramic aerogels with recoverable compressibility, super-insulation capacity, and remarkable thermal and chemical stability are fascinating for use in the field of high-level electromagnetic wave (EMW) absorption. However, integrating multiple functions into a monolithic ceramic aerogel using presently available fabrication techniques remains a challenge. Therefore, we employed a novel strategy to successfully synthesize a multifunctional and monolithic SiC ceramic aerogel using a simple freeze casting technique with a subsequent carbonation and calcination process. The as-synthesized SiC aerogel-2 exhibits ultralow density, fire resistance, high-temperature chemical and thermal stability, and excellent insulating properties. Notably, the one-dimensional SiC nanofibers and nanowires inside the SiC aerogel-2 act as a reinforcement to ensure the presence of a stable porous structure. The sample exhibits excellent mechanical performance and also achieves ideal impedance matching to present high-efficiency EMW-absorbing properties, including a minimum reflection loss (RLmin) of − 61.56 dB and a maximum effective absorption bandwidth (EABmax) of 9.82 GHz. Thus, the successful fabrication of multifunctional SiC aerogels will pave the way for the development and widespread application of high-level EMW absorption materials in aviation and aerospace fields.

Architecture Design of a Bamboo Cellulose/Nb2CTx MXene/ZIF-67-Derived Lightweight Co/Nb2CTx/Carbon Aerogel for Highly Efficient Electromagnetic Wave Absorption, Thermal Insulation, and Flame Retardant

Designing biomass-derived carbon-based lightweight electromagnetic wave (EMW) absorbers with multiple functions is promising research. However, the design of carbon-based EMW absorbers with multifunctionality for practical application remains a substantial challenge. Herein, a porous architecture engineering strategy was used to prepare a high-performance EMW absorption composite material with thermal insulation and flame-retardant properties The multifunctional Co/Nb2CTx/carbon aerogel with porous architecture composed of a bamboo-derived carbon aerogel, two-dimensional (2D) Nb2CTx, and ZIF-67-derived Co nanoparticles was prepared. Bamboo cellulose and few-layered Nb2CTx MXene constructed the three-dimensional (3D) aerogel architecture, ZIF-67 was then uniformly anchored on the aerogel skeleton through chemical deposition, and the Co/Nb2CTx/carbon aerogel was finally prepared by pyrolysis. The 3D interconnected network heterostructure not only contributes to conduction loss but also prolongs multiple reflection and scattering paths of EMW, which can improve the dielectric loss. Nb2CTx and Co nanoparticles play an important part in modulating the impedance matching and promoting the EMW attenuation ability due to the plenty of dipole/interfacial polarization loss and supplementary magnetic loss. The obtained Co/Nb2CTx/carbon aerogel possesses low density (54.03 mg cm–3) and achieves excellent reflection loss and broad effective absorption bandwidth (−60.25 dB and 4 GHz, respectively) at an ultrathin thickness of 1.67 mm with an ultralow filling content of 10 wt %. The radar cross section (RCS) reduction value can reach 31.24 dB m–2, indicating that the absorber can effectively reduce the probability of the target being detected by the radar detector. The strategy of porous architecture engineering provides guidance for the design of biomass-based electromagnetic wave absorption materials with thermal insulation property and flame-retardant capacity.

Interstitial boron-doped FeCoNiCr high entropy alloys with excellent electromagnetic-wave absorption and resistance to harsh environments

High entropy alloys (HEAs) are new promising electromagnetic-wave absorbing (EMA) materials due to their advantages in terms of corrosion resistance and high electrical conductivity. In the present work, FeCoNiCrBx (x = 0, 0.01, 0.05, 0.1, and 0.5) HEAs were prepared by a 3D high-energy ball-milling method. There was a phase change from face-centered cubic to body-centered cubic in the FeCoNiCrBx HEAs as the B content increased, which led to anomalous changes in mechanical properties, static magnetic properties and corrosion resistance. By tuning B contents, FeCoNiCrB0.05 HEAs delivered excellent electromagnetic-wave absorption performances. The minimum reflection loss (RLmin) values reached −62.5 dB at 11.74 GHz as thin as 2.11 mm, and the widest bandwidth was 5.78 GHz (11.90–17.68 GHz). In addition, B-doped FeCoNiCr HEAs had excellent mechanical properties, corrosion resistance and high temperature oxidation resistance. This work has important significance for the exploration of practical EMA materials that are resistant to harsh environments.

Smart shape memory composite foam enabled rapid and conformal manipulation of electromagnetic wave absorption performance

With the development of communication and electronic technologies, smart electromagnetic wave (EMW) absorption materials with tunable performance are highly desirable for applications under complicated electromagnetic circumstances. However, the performance of the ordinary EMW absorption materials is dominated by their electromagnetic parameters which are constant unless their compositions are changed. This study presents a porous EMW absorption material with adjustable effective absorption bandwidth (EAB) and reflection loss (RL) to satisfy the requirements of tunability for complex electromagnetic applications. First, a composite foam is fabricated by assembling the reduced graphene oxide (rGO) to the melamine sponge (MS) framework. Next, the thermoplastic polyurethane (TPU) is introduced to endow the MS/rGO composites with the desired shape memory property after crosslinking. In specific, the obtained MS/rGO composites show high flexibility, elasticity, and low density of 10.7 mg cm−3, and present the minimum RL of −63.29 dB with EAB of 7.18 GHz. Additionally, the tunable EMW absorption performance of MS/rGO-TPU composites is achieved through their shape memory effect. Notably, the EAB can be adjusted to a wide range from 5.5 to 18 GHz under the compressive deformations of those composites as modulated by cooling/heating, and correspondingly the minimum RL changes from −15.4 dB down to −39.2 dB. In a word, the smart, lightweight MS/rGO and MS/rGO-TPU composite foams with adjustable EMW absorption performance are strong candidates for practical applications in complex electromagnetic fields.

Constructing multiple heterogeneous interfaces in porous bimetallic FeNi3/C and CoNi/C flowers towards brilliant electromagnetic wave absorption performance

Construction of materials with multiple interfaces has always been a significant research direction to the high-performance electromagnetic wave (EMW) absorption materials. Here, the composites, consisted of three-dimensional (3D) flower-like NiFe layered double hydroxide (LDH) and regular dodecahedron CoNi-MOF, are synthesized at the first time, and their electromagnetic absorption capacity can be efficaciously improved by altering the proportion of NiFe-LDH (NFL) and CoNi-MOF. Benefiting from the suitable ratio of constituents, at a matching thickness of 2.29 mm, the minimum reflection loss (RLmin) of Z@NFL-2 is −61.87 dB, and the effective absorption bandwidth (EAB, RLmin < −10 dB) is reach up to 6.1 GHz. Especially, Z@NFL-4 can obtain a large EAB of 7.23 GHz (10.77–18 GHz) at a thickness of only 2.06 mm. Amazingly, under the far domain circumstance, the lowest radar cross-section acreage can accomplish −44.72 dB m2. The remarkable EMW absorption performance is mainly attributed to the collaborative effect of abundant electrical-magnetic loss mechanism, and remarkable impedance matching characteristics. Therefore, this work furnishes a fresh idea for exploring the application of LDH-based materials in electromagnetic wave absorption filed.

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.

Carbon nanotube arrays@cobalt hybrids derived from metal-organic framework ZIF-67 for enhanced electromagnetic wave absorption

Highly efficient electromagnetic wave (EMW) absorption materials with excellent thermal management are urgently required to solve the problem of electromagnetic pollution. Herein, bead-curtain-like carbon nanotube arrays@cobalt (CNT As@Co) hybrids are designed to enhance the EMW absorption performance by using CNT As templates. After the in-situ growth of ZIF-67, CNT As@Co hybrids are successively fabricated by thermal pyrolysis of CNT As@ZIF-67 at high annealing temperature. Owing to the unique three-dimensional (3D) bead-curtain-like microstructures, the CNT As@Co hybrid pyrolyzed at 500 °C (CNT As@Co-500) with an ultra-low filler loading of 2 wt% exhibits optimal EMW absorption properties. The minimum reflection loss (RLmin) is −36.86 dB at a thickness of 5.5 mm, and the effective absorption bandwidth (RL < −10 dB) reaches as broad as 5.78 GHz with a thickness of 2.5 mm. In addition, CNT As@Co hybrids possess superior thermal conductivity (9.25 W m−1 K−1) among most similar CNT-based composites, which is conducive to the rapid dissipation of thermal energy converted from electromagnetic energy. This work provides a new paradigm for designing high-performance 3D EMW absorbers with multifunctionality in electronic devices.

High-performance multifunctional porous iron Acetylacetonate/N, O-doped carbon nanospheres for electromagnetic wave absorption at 2–18 GHz and methyl orange absorption

Nowadays, multifunction is regarded as an advanced development direction of new-generation electromagnetic wave absorption (EMWA) materials to fulfill the ever-growing demands in complex environment and situation. Environmental pollution and electromagnetic pollution are all difficult problems for human beings all the time. Now, there is no multifunctional materials for collaborative treatment of environmental and electromagnetic pollution. Herein, We synthesized nanospheres with divinyl benzene (DVB) and N-[3-(dimethylamino)propyl]methacrylamide (DMAPMA), using a simple one-pot method. After calcination at 800 ℃ in N2, porous N, O-doped porous carbon materials were prepared. By regulating the mole ratio of DVB and DMAPMA, the ratio was 5:1 reached excellent EMWA property. Remarkably, the introduction of iron acetylacetonate into the reaction of DVB and DMAPMA was effective in enhancing the absorption bandwidth to 8.00 GHz at a 3.74 mm thickness, which depended on the synergistic effects from dielectric and magnetic losses. Simultaneously, the Fe-doped carbon materials had a methyl orange adsorption capacity. The adsorption isotherm conformed to the Freundlich model. After methyl orange absorption, the EMWA property did not greatly change. Thus, this research paves the way for the creation of multifunctional materials to solve environmental pollution and electromagnetic pollution together.

Construction of core-shell ZnO@ZnO/FeNi microrods with improved impedance matching and electromagnetic wave absorption performance

Functional core-shell heterostructure, which can integrate the characteristics of multiple components to achieve synergistic effects, have been widely explored in electromagnetic wave (EMW) absorption materials. In this work, core-shell ZnO@ZnO/FeNi microrods (MRs) derived from ZnO@ZnFeNi hydroxide (ZnFeNi OH) are prepared by a simple hydrothermal reaction and subsequent pyrolysis process. The introduction of FeNi alloy helps to optimize the impedance matching of ZnO, thus improving the EMW absorption performance. The different impedance matching properties of core-shell ZnO@ZnO/FeNi MRs are realized by adjusting the ZnO/FeNi shell thickness by changing the hydrothermal reaction time. When the hydrothermal time is 10 h, the core-shell ZnO@ZnO/FeNi MRs supplies the optimal EMW absorption performance with the minimum reflection loss of −53.7 dB and the widest absorption bandwidth of 5.3 GHz at a filler content of 33%. The synergistic effect of ZnO–FeNi interfacial polarization and the strong dielectric-magnetic loss are responsible for its superior EMW absorption performance. This work provides a valuable strategy for constructing core-shell dielectric@ magnetic composites to obtained high efficiency absorber.

Heating induced self-assemble pomegranate-like Fe3C@Graphite magnetic microspheres on amorphous carbon for high-performance microwave absorption

Difficulty of multicomponent regulation and nanostructure design make it challenging to fabricate high-performance electromagnetic wave (EMW) absorption materials. Herein, pomegranate-like Fe3C@graphitic carbon embedded in amorphous carbon matrix (Fe3C@GC/AC) is successfully prepared through a viable heating induced self-assembly strategy. By adjusting carbonization temperature, controllable electromagnetic parameters and impedance matching characteristics of Fe3C@GC/AC nanocomposites could be acquired. Besides, dielectric loss and magnetic loss are offered by GC and Fe3C, while the amorphous carbon not only disperse Fe3C@GC nanoparticles well, but also strengthens interface polarization. The detailed analysis show that Fe3C@GC/AC nanocomposites exhibit excellent EMW absorption performance under the combined function of unique pomegranate-like nanostructure and various loss mechanisms of multi-components. Moreover, the strongest reflection loss value of optimal sample (RCF-700) is up to −96.3 dB (loss of EMW above 99.99999%) with a matching thickness of 2.08 mm, and the effective absorption bandwidth (EAB, RL < −10 dB) covers 6.38 GHz (11.62–18.0 GHz, covering Ku-band). In addition, the EAB can reach 14.08 GHz with the simulated thickness varies from 1.0 to 5.0 mm, covering 88% of the measured frequency range. The deep exploration of the bio-inspired structure of multi-component system provides a creative and effective way for high-performance EMW absorbers.