Chemical graphitized r-GOs, as the thinnest and lightest material in the carbon family, exhibit high-efficiency electromagnetic interference (EMI) shielding at elevated temperature, attributed to the cooperation of dipole polarization and hopping conductivity. The r-GO composites show different temperature-dependent imaginary permittivities and EMI shielding performances with changing mass ratio.

In this work, reduced graphene oxide (r-GO) and graphite nanosheet (GN) were obtained via the chemical approach. Furthermore, r-GO composites and GN composites were prepared with a paraffin wax host. r-GO composites show high dielectric properties and electromagnetic interference shielding efficiency (EMI SE). Compared with the GN composites, the loss tangent and EMI SE of the r-GO composites with the same mass ratio are enhanced ∼5 to 10 times and ∼3 to 10 times, respectively. The enhanced attenuation capacity arises from higher specific surface area, clustered defects and residual bonds of the r-GOs, which increase the polarization loss, scattering and conductivity of the composite. Moreover, the higher conductivity of r-GO composites leads to higher EMI SE compared with that of GN composites. These results suggest that r-GOs are highly promising fillers for microwave attenuation in the carbon family and that r-GO composites are high-performance EMI shielding materials with application anticipated to many fields.

Light weight and high efficiency are two key factors for microwave absorption materials. In particular, it is extremely important that absorption materials meet the harsh requirements of thermal environments. In this work, multi-wall carbon nanotubes decorated with ZnO nanocrystals (ZnO@MWCNTs) were synthesized by a mild solution-process synthesis. The high-temperature dielectric and microwave absorption properties of SiO 2 -based composites loaded with ZnO@MWCNTs (ZnO@MWCNTs/SiO 2 ) are investigated in 8.2-12.4GHz and in the 373-673 K temperature range. The imaginary permittivity 3 00 of the composite with 5 wt% loading presents a weak downward trend, while those of the composites with 10 and 15 wt% loading show an upward trend with increasing temperature, which reveals different temperature dependences of 3 00 . The 3 00 for 15 wt% loading is about 10 times that for 5 wt% loading. The maximum loss tangent tan d values of the composites with 10 and 15 wt% loading exceed 0.8, while that of the composites with 5 wt% loading is less than 0.3. High tan d is mainly attributed to the conductivity of ZnO@MWCNTs, which is dominated by the hopping of electrons in the ZnO@MWCNT network, which increases with elevated temperature. The addition of ZnO properly adjusts the complex permittivity to endow the ZnO@MWCNT/SiO 2 composites with highly efficient and thermally stable microwave absorption coupled with a broad attenuation bandwidth, which almost covers the full X-band for RL # À10 dB. A series of outstanding properties of ZnO@MWCNTs imply that it is a promising functional material in the world of microwave absorption.

Ideal electromagnetic attenuation material should not only shield the electromagnetic interference but also need strong absorption. Lightweight microwave absorber with thermal stability and high efficiency is a highly sought-after goal of researchers. Tuning microwave absorption to meet the harsh requirements of thermal environments has been a great challenge. Here, grape-like Fe3O4-multiwalled carbon nanotubes (MWCNTs) are synthesized, which have unique multiscale-assembled morphology, relatively uniform size, good crystallinity, high magnetization, and favorable superparamagnetism. The Fe3O4-MWCNTs is proven to be a smart microwave-absorber prototype with tunable high intensities in double belts in the temperature range of 323-473 K and X band. Maximum absorption in two absorbing belts can be simultaneously tuned from ∼-10 to ∼-15 dB and from ∼-16 to ∼-25 dB by varying temperature, respectively. The belt for reflection loss ≤-20 dB can almost cover the X band at 323 K. The tunable microwave absorption is attributed to effective impedance matching, benefiting from abundant interfacial polarizations and increased magnetic loss resulting from the grape-like Fe3O4 nanocrystals. Temperature adjusts the impedance matching by changing both the dielectric and magnetic loss. The special assembly of MWCNTs and magnetic loss nanocrystals provides an effective pathway to realize excellent absorbers at elevated temperature.

We fabricated NiO nanorings on SiC, a novel hierarchical architecture, by a facile two-step method. The dielectric properties depend on temperature and frequency in the range from 373 to 773 K and X band. The imaginary part and loss tangent increase more than four times and three times with increasing temperature, respectively. The architecture demonstrates multirelaxation and possesses high-efficient absorption. The reflection loss exceeds -40 dB and the bandwidth covers 85% of X band (approximately -20 dB). The synergistic effect between multirelaxation and conductance is beneficial to the microwave absorption. Our findings provide a novel and feasible strategy to tune microwave absorption.