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Fe3O4/SiO2 nanocomposites (NCs) were prepared by the interaction of alkyne-functionalized ferric oxide (Fe3O4-Alk) nanoparticles (NPs) and azide-functionalized silicon dioxide (SiO2-N3) NPs via the click reaction. The morphology and structure of the Fe3O4/SiO2 NCs were investigated using scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and infrared analyses, and the electromagnetic parameters were measured using a vector network analyzer. For the Fe3O4/SiO2 nanocomposites obtained via the click reaction, the minimum reflection loss reached − 37.15 dB at 16.68 GHz and a matching thickness of 5.0 mm, and the bandwidth below − 10 dB ranged from 3.2 to 6.7 GHz and 15.7 to 17.6 GHz. The Fe3O4/SiO2 composites synthesized via the click reaction exhibited better microwave absorption performance than the physically blended sample. This is mainly because Fe3O4 and SiO2 are covalently bonded through the click reaction in the composites, creating multiple heterogeneous interfaces, which enhance dielectric loss and impedance matching. [ABSTRACT FROM AUTHOR]

Enhancing polarization as an effective strategy has attracted wide attention to improve electromagnetic wave absorption performance. In this work, a simple self-template multiple oxidation–etching method is used to prepare the fishing-net-like yolk–shell MnO2@MWCNTs (MYS@MWCNTs) absorber. The structural effects of MYS@MWCNTs and multi-walled carbon nanotube (MWCNTs) dispersion on the microwave absorption properties are investigated in detail. Related SEM and TEM images showed that the MWCNTs disappeared uniformly in MYS@MWCNTs after adjusting the PVP dispersant, thereby weakening the adverse influence of skin effect on impedance matching. One-dimensional MWCNTs penetrated through MnO2 yolk–shell (MYS) microsphere and formed unique fishing-net-like conductive network PVP-optimized MYS@MWCNTs with enhanced impedance matching. MYS@MWCNTs-2 obtains excellent microwave absorption performance with a minimum reflection loss (RLmin) of -52.8 dB at 3.76 GHz because of interface polarization, dipole polarization, and enhanced conductive loss. Therefore, the as-prepared MYS@MWCNTs has potential applications in the field of electromagnetic wave absorption. [ABSTRACT FROM AUTHOR]

In this study, flower sphere alumina was synthesized autonomously by hydrothermal and annealing processes. The in situ polymerization of polypyrrole on the surface of alumina at low temperatures based on the principle of component synergy has enabled the construction of a core–shell structure for Al2O3@ppy materials, resulting in excellent electromagnetic wave absorption properties. The effect of the addition of alumina and the morphology of the materials on the microwave absorption properties of Al2O3@ppy composites was also discussed. Various methods are used for the characterization of the material. The Al2O3@ppy composites were effective in matching thicknesses of 2.5 mm with a minimum reflection loss (RL) of − 65.8 dB at a frequency of 11.52 GHz and a maximum effective absorption bandwidth (EAB) of 5.6 GHz at a matched thickness of 2.0 mm. The results show that Al2O3@ppy composites can provide a reference for EMW absorber material research. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Al@MnO2 composites were synthesized by flake aluminum powder and potassium permanganate via a facile one-step method. As a multi-band stealth material, the composites have both enhanced microwave absorbing property and low infrared emissivity. We can use XRD, XPS, SEM, and TEM to detect structure and performance, respectively. The microwave absorbing properties and infrared emissivity were investigated by vector network analyzer and dual-band infrared emissometer. It was found that the MnO2 nanoparticles were anchored on the aluminum sheets densely, and the concentration of MnO2 nanoparticles had a certain effect on absorption performance and infrared emissivity. As an absorber, with its polarization effect, resonance effect, and good impedance matching, the composite with the filler loading is 60 wt% can perform excellent microwave absorption performance (Chen et al. in Optik (Stuttg) 172:840–846, 2018). The minimum reflection loss reached − 42.93 dB at 12.72 GHz with a thickness of 1.0 mm, and the bandwidth that exceed − 10 dB ranged from 12.08 GHz to 13.36 GHz (Li et al. in J Colloid Interface Sci 507:131–138, 2017). As an infrared stealth material, the composite exhibits low infrared emissivity in the band range of 8–14 µm, which was attributed to the existence constituent of flake aluminum powder. The infrared emissivity reached 0.55 at the lowest, as well as enlarged with the increase of MnO2 concentration. Therefore, the Al@MnO2 composites could be a potential superior microwave and infrared compatible stealth material. [ABSTRACT FROM AUTHOR]

Hexagonal flake Co3O4 was prepared by calcining Co-MOF precursors in air. Co3O4@PANI was obtained via hydrothermal and oxidative polymerization processes, and the electromagnetic wave absorption properties of the composites were investigated. Scanning emission microscopy and transmission electron microscopy images show that hexagonal flake Co3O4 possesses a diameter in the range of 2-4 µm and a side length 550-950 nm. With the decrease in Co3O4 content, the absorption performance of Co3O4@PANI increases gradually. When the mass ratio of Co3O4 to PANI is 1:8, the minimum reflection loss value is − 37.39 dB at 7.28 GHz with a layer thickness of 4 mm. Co3O4@PANI also has effective absorption with the entire test thickness, and the maximum absorption bandwidth can reach 3.52 GHz. Therefore, the as prepared hexagonal flake Co3O4@PANI has potential for application in the field of electromagnetic wave absorption. [ABSTRACT FROM AUTHOR]