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Hierarchical core–shell architectures with multi-walled carbon nanotubes as core and MnO2 sheets shaped in an array mode as shell (MWCNTs@MnO2) were successfully synthesized via a simple wet chemical method. X-ray diffraction patterns and X-ray photoelectron spectroscopy analysis revealed that the composites were successfully prepared. Morphological characterizations were made by scanning electron microscopy and transmission electron microscopy. Vector network analyzer was employed to investigate the electromagnetic parameters of the composites. A possible attenuation mechanism was discussed, and the high-performance microwave absorption properties were attributed to the porous microstructure, polarization effect, dielectric loss and the synergistic action between MWCNTs and δ -MnO2. A minimum reflection loss (RL) of − 50.6 dB was achieved at a thickness of 1.4 mm, and an effective absorption bandwidth (RL < − 1 0 dB) covered 4.2 GHz (from 13.8 GHz to 18 GHz) at a thickness of 1.3 mm. Therefore, these results suggested that the MWCNTs@ δ -MnO2 composites can be an excellent candidate for microwave absorption materials. The cross-linked δ-MnO2 nanoflakes attached on the sidewalls of MWCNTs and the unique open porous 3D conductive structure of the nanocomposites contributed to the multiple reflections and scattering of microwaves in long propagation periods. Moreover, MWCNTs with high electrical conductivity can generate loss current and energy dissipation by electron migration and hop across the interfaces. [ABSTRACT FROM AUTHOR]

Co-doped SnO2@multi-walled carbon nanotubes (MWCNTs) were fabricated by a one-pot hydrothermal process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), high-resolution electron microscopy, and X-ray photoelectron spectroscopy (XPS) were employed to characterize the morphology and structure of the composites. XRD, FT-IR, and XPS analyses demonstrated that Co was doped into SnO2 lattice, no other impure phases were detected. Co-doped SnO2, with a uniform size of 4-6nm, is coated on MWCNTs but separated from the nanotubes with some aggregation. The microwave absorption properties of Co-doped SnO2@MWCNTs were investigated at room temperature within 2-18GHz. Results indicated that Co-doping concentration plays an important role in the microwave absorption capability of Co-doped SnO2@MWCNTs. The maximum reflection loss (RL) is 22.8dB at 14.1GHz. The absorption bandwidth with RL less than 10dB is 4.2GHz (12.2-16.4) with coating thickness of only 1.5mm; hence, Co-doping can enhance the microwave absorption performance of SnO2@MWCNTs. The excellent microwave absorption performance may be attributed to interfacial polarization, conductivity loss, and changes in electromagnetic parameters and lattice constant caused by Co-doping. Consequently, Co-doped SnO2@MWCNTs can be considered as efficient microwave absorbers in high-frequency range. Co-doped SnO2@MWCNTs were prepared by a hydrothermal method. Co was doped into the SnO2 lattice. With an appropriate doping concentration, the maximum RL of Co-doped SnO2@MWCNTs reached −22.8 dB at 14.1 GHz, and the bandwidth (RL ≤ −10 dB) was 4.2 GHz (12.2-16.4), with a coating thickness of 1.5 mm. [ABSTRACT FROM AUTHOR]

In this study, Zn-doped Fe3O4 nanoparticles were successfully synthesized by a facile solvothermal method in the presence of sodium dodecyl sulfate (SDS). The morphology, magnetic properties and electromagnetic wave absorbing properties of these materials were characterized. Results showed that Zn played a significant role in the formation of Zn-doped Fe3O4. With the protection of SDS, highly dispersed Fe3O4 nanoparticles were obtained. The nanoparticle size decreased after Zn doping, and the dispersity deteriorated with increasing Zn doping concentration. Zn-doped Fe3O4 exhibited excellent electromagnetic wave absorbing property, which resulted in magnetic loss and dielectric loss at an appropriate doping concentration. The minimum reflection loss (RL) was approximately dB at 16.9GHz. As the coating layer thickness increased to 4.0mm, the bandwidth was approximately 5.0GHz corresponding to RL below dB, which nearly covered the entire S band (2-4GHz) and C band (4-8GHz). The peak frequency of RL and the number of peaks matched the quarter-wave thickness criteria. It was believed that the Zn-doped Fe3O4 could be a potential electromagnetic wave absorbing material in S and C bands. Zn-doped Fe3O4 nanoparticles were synthesized by a facile solvothermal method. Zn2+ plays a key role in the formation of Zn-doped Fe3O4. The as-synthesized Zn-doped Fe3O4 exhibited excellent electromagnetic wave absorbing property, as the coating layer thickness at 4.0mm, the bandwidth was approximately 5.0GHz corresponding to RL below −10dB, which covered nearly the entire S band (2-4GHz) and C band (4-8GHz). [ABSTRACT FROM AUTHOR]

In this work, reduced graphene oxide/CeO2 nanocomposites (RGO/CeO2) with two different RGO contents were synthesized using a facile one-step hydrothermal method, and the microwave absorption properties of RGO/CeO2 were investigated for the first time. Morphology and structure analysis shows that the CeO2 nanoparticles are uniformly dispersed on the RGO sheets with average size of 15nm. The as-prepared RGO/CeO2 exhibits excellent microwave absorbability. An optimal reflection loss (RL) of 32dB is found at 17GHz with a coating layer thickness of 1.5mm. The product with a coating layer thickness of only 2.0mm shows a bandwidth of 4.3GHz, corresponding to RL at 10dB (90% of electromagnetic wave absorption). Compared with pristine RGO or pure CeO2 nanoparticles, the reported nanocomposites achieved both wider and stronger wave absorption in the frequency range of 2-18GHz. The enhanced microwave absorption properties are attributed to the conductive loss and dielectric loss mainly caused by the higher oxygen vacancy concentration of CeO2 in RGO/CeO2, which is demonstrated by X-ray photoelectron spectroscopy. Moreover, multiple interfacial polarizations occurring in the multi-interfaces between CeO2 and RGO sheets may be beneficial to microwave absorption. RGO/CeO2 could be used as an attractive candidate for the new type of microwave absorptive materials. CeO2 well-dispersed nanocrystals, anchored on the reduced graphene oxide hybrid composites, were synthesized by a facile hydrothermal method. Microwave absorption properties measurement shows that the introduction of reduced graphene oxide significantly enhances the microwave absorption intensity of CeO2 nanocomposites, and the bandwidth of reflection loss is also broadened. The concentration of oxygen vacancy defects plays a key role in the enhanced microwave absorption properties. [ABSTRACT FROM AUTHOR]