Bimetallic MOF-derived CoZn-C/MWCNTs composite for lightweight and wideband microwave absorption

Microwave absorption materials have drawn significant attention due to their potential application in information safety and military stealth. In this work, we report a facile strategy to synthesize carbon nanofiber/MnOx core-shell composites (CNF@MnOx) in order to collaborate their advantage for high-performance microwave absorption application. Through a simple ozone pretreatment process, ultrathin MnOx nanoflakes can be uniformly coated onto CNFs by a hydrothermal method. The mixture of several MnOx forms coexists in CNF@MnOx composites because of the readily available crystalline phase transformation from different manganese oxides. The investigation of microwave absorption properties shows that the absorbing capabilities CNF@MnOx composites have significant improvement compared to the pure CNFs and most of single-phase manganese oxides. The minimum reflection loss for CNF@MnOx can arrive at −47.2 dB at 9.4 GHz with a thickness of 2.8 mm, and the widest effective absorption bandwidth was measured to be 5.0 GHz. Furthermore, polymorphic MnOx endows CNF@MnOx with selective-frequency microwave absorption. The dramatic enhancement of microwave absorption is ascribed to dielectric loss, magnetic loss, impedance matching and geometrical effect. Hence, the present CNF@MnOx may be a capable candidate for strong-absorption, broadband and lightweight microwave absorber.

Correlating metal-organic framework (MOF) synthesis processes and microwave absorption (MA) enhancement mechanisms is a pioneer project. Nevertheless, the correlation process still relies mainly on empirical doctrine, which hardly corresponds to the specific mechanism of the effect on the dielectric properties. Hereby, after the strategy of modulation of protonation engineering and solvothermal temperature in the synthesis route, the obtained sheet-like self-assembled nanoflowerswereconstructed.Porous structures with multiple heterointerfaces, abundant defects, and vacancies are obtained by controlled design of the synthesis procedure. The rearrangement of charges and enhanced polarization can be promoted. The designed electromagnetic properties and special nano-microstructures of functional materials have significant impact on their electromagnetic wave energy conversion effects. As a consequence, the MA performance of the samples has been enhanced toward broadband absorption (6.07GHz), low thickness (2.0mm), low filling (20%), and efficient loss (-25dB), as well as being suitable for practical environmental applications. This work establishes the connection between the MOF-derived materials synthesis process and the MA enhancement mechanism, which provides insight into various microscopic microwave loss mechanisms.

Facile synthesis of MOF-derived concave cube nanocomposite by self-templated toward lightweight and wideband microwave absorption

The electromagnetic and microwave absorption properties of 15 wt% cobalt/polystyrene (Co/PS) nanocomposite in the X-band of microwave frequency are studied for seeking its usage as light weight and wideband microwave absorber. The melt blending and automated injection molding methods are employed to prepare the cobalt/polystyrene nanocomposite sheet successfully. The reflection and transmission coefficients of the prepared sample are measured using the vector network analyzer (VNA) in the X-band. The complex permittivity (e r ) and complex permeability (μ r ) of the prepared Co/PS nanocomposite are extracted from the measured reflection and transmission coefficients. The maximum reflection loss (absorption) of 18.17 dB (98.48%) at 12.40 GHz with 1 GHz bandwidth is obtained for 5 mm thick sample comprising of 15 wt% Co/PS nanocomposite.

In this letter, a wideband microwave absorber with high angular stability is proposed based on the integrated design of frequency selective surface (FSS) and lattice structure. The proposed absorber is composed of a resistive FSS sheet embedded within two lattice structures. With the aid of the upper lattice structure, the wave impedance of the absorber is compensated at oblique incidence and the angular stable absorption is achieved. The performance of the absorber is investigated with an equivalent circuit model and full-wave simulations. The 80% and the 90% absorption bands are ranging from 1.4GHz to 6.2GHz and 1.5GHz to 6.1GHz, with a fractional bandwidth of 126.3% and 121%, respectively. Meanwhile, the absorption rate keeps above 80% within 65° for both TE and TM polarizations and remains above 90% within 50° incident angle. For further verification, a prototype has been fabricated and measured. Good agreements between the simulated and measured results can be observed. Considering the wideband absorption characteristics and high angular stability, the proposed absorber can be applied to construct EM wave shelters.

Thin-walled carbon nanotubes (CNTs) filled with different ferromagnetic alloy (FeCo, FeNi, and FeCoNi) nanowires were prepared by using trichlorobenzene as carbon precursor. They were dispersed into epoxy resin and then coated onto 180×180 mm2 aluminum substrates to form microwave-absorption coatings with 2.0 mm thickness. Reflection loss exceeding −5 dB was obtained between 5 and 18 GHz for coating containing 1.3 wt % FeCo-filled CNTs. A minimum reflection loss value of −28.2 dB was achieved at 15.2 GHz in FeCoNi-filled CNTs/epoxy coating. The areal densities of coatings are only 2.35 kg/m2, which is favorable for the applications requiring low density.

Carbon nanotubes filled with ferromagnetic metal nanowires (M-CNTs) were synthesized by using chlorine-contained benzene (e.g. trichlorobenzene) as precursor. The wall thicknesses of M-CNTs synthesized by trichlorobenzene are much thinner than those by precursor without Cl (e.g. benzene). As-synthesized thin-walled M-CNTs exhibit remarkably enhanced field electron emission performance with a low turn-on field of 0.3 V/μm and better field-emission stability. Microwave-absorption coatings were made by dispersing as-synthesized M-CNTs into epoxy resin matrix. It is found that the reflection losses in S-band (2–4 GHz), C-band (4–8 GHz) and X-band (8–12 GHz) are enhanced in the order of FeCoNi-CNTs < FeNi-CNTs< FeCo-CNTs. The areal density of as-prepared coatings is only 2.35 kg/m2 when the coating thickness is 2.0 mm. This demonstrates that M-CNTs are promising to be used as lightweight and wide-band microwave absorbers.

Controlled Synthesis of Mof-Derived Nano–Microstructure Toward Lightweight and Wideband Microwave Absorption

Microwave Absorption In article number 2302633, Zhengjun Yao, Jintang Zhou, Ping Chen, and co-workers utilize protonation engineering and solvent thermodynamic modulation strategies to controllably design sheet-like self-assembled nanoflowers. The controlled design of the synthetic routes results in structures with multiple heterogeneous interfaces, abundant defects and vacancies. A correlation model between the synthesis process of metal–organic framework (MOF)-derived materials and the microwave loss mechanism is developed to achieve enhanced microwave absorption properties.

HighlightsA flexible and lightweight microwave absorber was prepared by a vacuum filtration method.The remarkable microwave absorbency makes the absorber paper attractive in wireless wearable electronics field.

Double-shell hollow conductive poly(acrylonitrile) microspheres@polyaniline@Ag (PANS@PANI@Ag) was synthesized by a facile two-step method. Polyaniline-coated poly(acrylonitrile) microspheres (PANS@PANI) prepared by in situ polymerization exhibited a porous, corrugated and compact conductive network, making for the formation and attachment of Ag nanoparticles. Incorporating these hollow conductive spheres and reduced graphene oxide (RGO) into epoxy resin, a lightweight microwave absorber was brought out. The chemical composition, micro-structure surface morphology and electromagnetic properties were thoroughly characterized and analyzed. The calculated results showed that the optimal reflection loss (RL) was − 44.9 dB at 9.16 GHz with a constitution of 1 wt% dielectric RGO and 1 wt% conductive PANS@PANI@Ag, and the corresponding effective bandwidth was about 2 GHz. However, the microwave absorption capacity gradually reduced with the raise of PANS@PANI@Ag content, derived from the high conductivity leading to more microwave reflection. As the PANS@PANI@Ag content increased to 5 wt%, the minimum RL was − 14.7 dB and still remained an effective absorption performance with a lower density of 0.47–0.53 g/cm3. Therefore, the as-obtained composites paved a new route for lightweight and strong absorption microwave absorbers in commercial and military application.

Ordered mesoporous carbon (OMC) is considered to be a prospective carbon-based material for microwave absorption because of its abundant well-ordered mesoporous structures, high specific surface area, numerous active sites, and facile preparation process. However, its development has been seriously hindered by its poor impedance-matching characteristic. Herein, silica-modified OMC composites with a designable impedance-matching transition layer are successfully fabricated via a self-assembly method and succeeding calcination treatment. In addition, the silica in OMC@SiO2 composites can maintain the mesoporous structure, which facilitates the scattering and reflection of microwaves in the tunnel structure. The as-prepared sample OMC-5@SiO2 exhibits a minimum reflection loss (RL) value of -40.7 dB at 10.8 GHz with 2 mm and an effective absorption bandwidth (RL ≤ -10 dB) of 4.8 GHz with a thinner absorber thickness of 1.5 mm. We believe that the as-prepared OMC@SiO2 composites can be prospective candidates as high-efficiency and lightweight microwave absorbers.

The tune of shell numbers of multi-shell hollow mesoporous carbon microspheres for enhanced microwave absorption

To construct effective electromagnetic parameters of reduced graphene oxide (RGO)-based composites for lightweight and high efficiency microwave absorption, Ni/RGO composites were prepared via a facile in-situ hydrothermal process. Due to the strong high-frequency polarization effect related to the large surface contact area of the obtained Ni/RGO hybrids, the composites presented strong electromagnetic wave attenuation ability even when the filler content is only 1.6 wt. %. This work might deepen the understanding of the effective dielectric loss mechanism and impedance matching and provide an effective strategy for the practical application of RGO as a lightweight and high-performance microwave absorption material.

Carbon-based materials are considered to be promising candidates for lightweight microwave absorption materials (MAMs). However, single carbon-based materials cannot meet the requirements of wide effective absorption bandwidth (EAB) and strong microwave absorption due to the missing magnetic loss. Combining with lightweight magnetic materials via rational design of microstructures attends to be an effective way to achieve high-performance microwave absorption. In this study, core-shell carbon nano-onions@fluorinated boron nitrides (CNOs@F-BNNOs) nanocomposites with N-C and F-B bridging were obtained by a simple in situ pyrolytic polymerization as well as a hydrothermal fluorination strategy and exhibited excellent microwave absorption properties. Furthermore, the results indicate that the addition of F-BNNOs not only improves polarization loss and optimizes impedance matching but also enhances the magnetic loss effect, thereby improving the electromagnetic wave absorption performance (EWAP). Among these compositions, CNOs@F-BNNOs achieve an excellent minimum reflection loss (RLmin) value of -43.23 dB at 17.23 GHz, with an EAB of 10.54 GHz at a thickness of 2.80 mm. Additionally, CNOs@F-BNNOs have excellent thermal conductivity. Therefore, this work presents a novel approach to constructing lightweight, efficient, and promising core-shell microwave absorption materials (MAMs).