Preparation of magnetic nanoparticles coated with chitosan (CS-coated Fe3O4 NPs) in one step by the solvothermal method in the presence of different amounts of added chitosan is reported here. The magnetic property of the obtained magnetic composite nanoparticles was confirmed by X-ray diffraction (XRD) and magnetic measurements (VSM). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) allowed the identification of spherical nanoparticles with about 150 nm in average diameter. Characterization of the products by Fourier transform infrared spectroscopy (FTIR) demonstrated that CS-coated Fe3O4 NPs were obtained. Chitosan content in the obtained nanocomposites was estimated by thermogravimetric analysis (TGA). The adsorption properties of the CS-coated Fe3O4 NPs for bovine serum albumin (BSA) were investigated under different concentrations of BSA. Compared with naked Fe3O4 nanoparticles, the CS-coated Fe3O4 NPs showed a higher BSA adsorption capacity (96.5 mg/g) and a fast adsorption rate (45 min) in aqueous solutions. This work demonstrates that the prepared magnetic nanoparticles have promising applications in enzyme and protein immobilization.

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In the face of electromagnetic pollution issues caused by the advancement of communication technology, it is of great significance to develop materials with high electromagnetic interference (EMI) shielding capability as well as high absorption efficiency. The nickel‐coated silicon carbide whiskers (Ni@SiCw)/graphene nanosheets (GNP)/polyvinylidene fluoride (PVDF) EMI shielding composites with the asymmetric structure are constructed by simple solution mixing and multiple hot pressing. Specifically, the Ni@SiCw in the top layer is prepared by simple electroless plating, and the saturation magnetization intensity reaches 12.50 emu/g. The combination of dielectric and magnetic losses provides reliable electromagnetic wave absorption performance with a reflection coefficient less than 0.35. GNP is selectively enriched in the bottom layer with a maximum conductivity of 85.43 S/m. The composite shows an EMI shielding performance of 36.83 dB when the GNP content is just 4 wt%, which means 99.98% of microwaves can be shielded. Furthermore, due to the distinct structure, the composites display various shielding mechanisms when electromagnetic waves are incident from different faces. Without a doubt, this asymmetric structure offers a novel approach to the preparation of directional EMI shielding materials.

In this work, magnetic PA6 microspheres (PPA6@ NiM) with porous structures were prepared using the solvent coprecipitation method and electroless nickel plating technology, and the stacked magnetic microspheres were encapsulated with polydimethylsiloxane (PDMS) to obtain PPA6@NiM/PDMS composites. The existence of the porous structure increases the attenuation path of the electromagnetic wave, and the presence of the nickel layer improves the magnetic loss of the composite material to the electromagnetic wave and synergistically improves the absorption of the electromagnetic wave. Among them, the total shielding effectiveness (SET) of the PPA6@NiM4/PDMS composite is as high as 39.9 dB, and the reflection coefficient (R) is 0.83. To further increase the absorption effect of the composite material, an asymmetric gradient structure was constructed by utilizing the difference in electrical conductivity between the magnetic microspheres. The electromagnetic wave is incident from the surface with lower conductivity (impedance matching layer). It is reflected by the consistency with higher conductivity (strong reflective layer) than the bottom layer to increase the loss of electromagnetic waves inside the material. The composite SET constructed with M1 and M4 particles with the most significant difference in conductivity achieved 35.5 dB with an absorption coefficient (A) of 0.42. It shows that the porous combined asymmetric gradient structure we designed can effectively improve the shielding efficiency and absorption capacity of the composite material against electromagnetic microwaves and serve as a reference for creating high-absorbing and high-performance electromagnetic shielding materials.