Recent advances on outstanding microwave absorption and electromagnetic interference shielding nanocomposites of ZnO semiconductor

The electromagnetic interference shielding and microwave attenuation capabilities of ZnO semiconductor nanocomposites have recently been improved using a variety of approaches by correctly modifying their permittivity. To improve microwave attenuation, ZnO semiconductor nanostructures have been combined with graphene, multi-wall carbon nanotubes, metal nanoparticles and their alloys, two-dimensional MXene, spinel ferrite magnetic nanoparticles, polymer systems, and textiles. This paper covers the opportunities and constraints that these cutting-edge nanocomposites in the field of electromagnetic wave absorption encounter as well as the research progress of ZnO semiconductor-based nanocomposite. The structure-function relationship of electromagnetic wave absorption nanocomposites, design strategies, synthesis techniques, and various types of advanced nanocomposites based on ZnO semiconductor are also covered. In order to design and prepare high efficiency ZnO semiconductor based electromagnetic wave absorbing materials for use in applications of next-generation electronics and aerospace, this article can offer some useful ideas.

C/MnO@void@C with Triple Balances for Superior Microwave Absorption Performance

It is very promising and challenging to construct a yolk-shell structure with highly efficient microwave absorption (MA) performance through a simple fabrication process. Here, a novel C/MnO@void@C (MCC) yolk-shell structure has been successfully synthesized by one-step calcination without additional processing. The as-obtained MCC composites with tunable crystallinity degrees and hollowness can be obtained by treatment at various temperatures. The MCC composites treated at 700 °C (MCC-700) show an impressive MA performance, and the optimal reflection loss of -53.2 dB and an effective absorption bandwidth of 5.4 GHz can be obtained. This excellent performance results from multiple balance mechanisms. First, the regulated permittivity of MCC-700 due to proper crystallinity and hollowness is beneficial for the balance between dielectric loss (tan δ_ε) and impedance match (Z_im). Second, the optimal balance between the increasing polarization range and decreasing polarization intensity can be achieved, which is favorable for the improvement of the MA performance. Third, the multicore yolk-shell structure of MCC-700 is conducive to multiple scattering and continuous energy dissipation. Thus, our new findings provide a rational way for the utilization of yolk-shell structural manganese-based materials.

Controllable Fabrication of Fe₃O₄/ZnO Core⁻Shell Nanocomposites and Their Electromagnetic Wave Absorption Performance in the 2⁻18 GHz Frequency Range

In this study, Fe₃O₄/ZnO core⁻shell nanocomposites were synthesized through a chemical method of coating the magnetic core (Fe₃O₄) with ZnO by co-precipitation of Fe₃O₄ with zinc acetate in a basic medium of ammonium hydroxide. The phase structure, morphology and electromagnetic parameters of the Fe₃O₄/ZnO core⁻shell nanocomposites were investigated. The results indicated that the concentration of the solvent was responsible for controlling the morphology of the composites, which further influenced their impedance matching and microwave absorption properties. Moreover, Fe₃O₄/ZnO nanocomposites exhibited an enhanced absorption capacity in comparison with the naked Fe₃O₄ nanospheres. Specifically, the minimum reflection loss value reached −50.79 dB at 4.38 GHz when the thickness was 4.5 mm. It is expected that the Fe₃O₄/ZnO core⁻shell structured nanocomposites could be a promising candidate as high-performance microwave absorbers.

Co7Fe3 and Co7Fe3@SiO2 Nanospheres with Tunable Diameters for High-Performance Electromagnetic Wave Absorption

Ferromagnetic metal/alloy nanoparticles have attracted extensive interest for electromagnetic wave-absorbing applications. However, ferromagnetic nanoparticles are prone to oxidization and producing eddy currents, leading to the deterioration of electromagnetic properties. In this work, a simple and scalable liquid-phase reduction method was employed to synthesize uniform Co₇Fe₃ nanospheres with diameters ranging from 350 to 650 nm for high-performance microwave absorption application. Co₇Fe₃@SiO₂ core-shell nanospheres with SiO₂ shell thicknesses of 30 nm were then fabricated via a modified Stöber method. When tested as microwave absorbers, bare Co₇Fe₃ nanospheres with a diameter of 350 nm have a maximum reflection loss (RL) of 78.4 dB and an effective absorption with RL > 10 dB from 10 to 16.7 GHz at a small thickness of 1.59 mm. Co₇Fe₃@SiO₂ nanospheres showed a significantly enhanced microwave absorption capability for an effective absorption bandwidth and a shift toward a lower frequency, which is ascribed to the protection of the SiO₂ shell from direct contact among Co₇Fe₃ nanospheres, as well as improved crystallinity and decreased defects upon annealing. This work illustrates a simple and effective method to fabricate Co₇Fe₃ and Co₇Fe₃@SiO₂ nanospheres as promising microwave absorbers, and the design concept can also be extended to other ferromagnetic alloy particles.

Enhanced Microwave Absorption Properties by Tuning Cation Deficiency of Perovskite Oxides of Two-Dimensional LaFeO3/C Composite in X-Band

Development of microwave absorption materials with tunable thickness and bandwidth is particularly urgent for practical applications but remains a great challenge. Here, two-dimensional nanocomposites consisting of perovskite oxides (LaFeO₃) and amorphous carbon were successfully obtained through a one pot with heating treatment using sodium chloride as a hard template. The tunable absorption properties were realized by introducing A-site cation deficiency in LaFeO₃ perovskite. Among the A-site cation-deficient perovskites, La_0.62FeO₃/C (L_0.62FOC) has the best microwave absorption properties in which the maximum absorption is -26.6 dB at 9.8 GHz with a thickness of 2.94 mm and the bandwidth range almost covers all X-band. The main reason affecting the microwave absorption performance was derived from the A-site cation deficiency which induced more dipoles polarization loss. This work proposes a promising method to tune the microwave absorption performance via introducing deficiency in a crystal lattice.

Facile synthesis of NiS2@MoS2 core–shell nanospheres for effective enhancement in microwave absorption

Core–shell structural NiS₂@MoS₂ nanospheres have been successfully fabricated and they possess enhanced microwave absorption properties as compared to single NiS₂ nanospheres or MoS₂ nanoplates due to this core–shell structure.