Jianna Ma

Strong Electromagnetic Wave Response Derived from the Construction of Dielectric/Magnetic Media Heterostructure and Multiple Interfaces

A novel yolk-shell structure of cobalt nanoparticle embedded nanoporous carbon@carbonyl iron (Co/NPC@Void@CI) was synthesized via metal organic chemical vapor deposition (MOCVD) and subsequent calcination treatment. The in situ generation of void layer, which originated from the shrink of a Co-based zeolitic imidazolate framework (ZIF-67) during carbonization, embodies distinct advantage compared to the conventional template method. Thanks to the introduction of custom-designed dielectric/magnetic media heterostructure and multiple interfaces, the composites filled with 40 wt % of Co/NPC@Void@CI samples in paraffin exhibit a maximum reflection loss of -49.2 dB at 2.2 mm; importantly, a broad absorption bandwidth (RL < -10 dB) of 6.72 GHz can be obtained, which covers more than one-third of the whole frequency region from 10.56 to 17.28 GHz. This study not only develops the application of carbonyl iron as a high-efficiency light absorber but also initiates a fire-new avenue for artificially designed heterostructures with target functionalities.

Direct synthesis of MOF-derived nanoporous CuO/carbon composites for high impedance matching and advanced microwave absorption

Nanostructured carbon materials with hollow structures derived from metal organic frameworks (MOFs) have attracted considerable attention due to their low density for microwave absorption. However, their poor impedance matching worsens the absorption properties. The rational design and fabrication of complex hollow nanocarbon materials with excellent impedance matching still remains a challenge. Herein, we report a simple strategy to fabricate porous CuO/carbon composites by nitrate impregnation into a MOF template (thermal decomposition of zeolitic imidazolate frameworks, ZIF-67). When used as microwave absorbing materials, these hollow CuO/carbon composite polyhedra exhibited excellent impedance matching, light weight and strong absorption. An optimal reflection loss (RL) of −57.5 dB is achieved at 14.9 GHz with a matching thickness of 1.55 mm and RL values less than −10 dB can be gained in the range of 13–17.7 GHz. The best absorbing performance of the composites mainly originates from the high loss of the porous carbon obtained by the carbonization of ZIF-67, and the improvement of the impedance matching with the embedding of CuO. This work may provide a general way for fabricating porous metal oxides/carbon composites for lightweight microwave absorbing materials.

Incorporation of the polarization point on the graphene aerogel to achieve strong dielectric loss behavior

The preparation of nanocomposites of reduced graphene oxide with loaded TiO2 nanoparticles (TRGO) by a facile one-step hydrothermal treatment is reported. We have successfully increased the contact area of TiO2 and RGO to enhance polarization point, which is in favor of strengthening interfacial polarization. The interfaregioncial polarization has been regarded as an important role on the attenuation of high-frequency electromagnetic waves. Therefore, a good absorber is prepared by inserting the polarization point on the graphene aerogel, which shows excellent electromagnetic wave absorbing properties. In detail, the minimum reflection loss value at 2.1mm is up to -27.2dB for the TRGO-1.5 composite and the frequency bandwidth of 5.2GHz can be obtained. Thus, it demonstrates that the adjustment of interface polarization would play a key role in the microwave-absorbing ability.

Achieving the interfacial polarization on C/Fe3C heterojunction structures for highly efficient lightweight microwave absorption

Design of dielectric/magnetic heterostructure and multiple interfaces is a challenge for the microwave absorption. Thus, in this study, a novel C/Fe3C nanocomposites have been fabricated by annealing the precursors obtained by the facile chemical blowing of polyvinyl pyrrolidone (PVP) and Fe(NO3)3·9H2O. By changing the content of Fe(NO3)3·9H2O, the honeycomb-like structure with scads of pores and electromagnetic parameters could be successfully tailored. When the addition of Fe(NO3)3·9H2O is ranging from 1 to 2g, honeycomb-structured nanocomposites possess high performance microwave absorption when mixed with 90wt% paraffin. The minimal reflection loss is -37.4dB at 13.6GHz and effective bandwidth can reach to 5.6GHz when the thickness is 2.0mm, indicating its great potential in microwave absorbing field. Its outstanding microwave performance is tightly related to the porous structure and substantial interface such as carbon/air and carbon/Fe3C, which are in favor of the impedance matching and interfacial polarization. Thus, our study may provide a good reference for the facile synthesis of light-weight carbon-based nanocomposites with effective interfacial polarization.

Adjustable 3-D structure with enhanced interfaces and junctions towards microwave response using FeCo/C core-shell nanocomposites

In this work, the 3-D honeycomb-like FeCo/C nanocomposites were synthesized through the carbon thermal reduction under an inert atmosphere. The enhanced microwave absorption properties of the composites were mainly attributed to the unique three dimensional structure of the FeCo/C nanocomposites, abundant interfaces and junctions, and the appropriate impedance matching. The Cole-Cole semicircles proved the sufficient dielectric relaxation process. The sample calcinated at 600°C for 4h showed the best microwave absorption properties. A maximum reflection loss of -54.6dB was achieved at 10.8GHz with a thickness of 2.3mm and the frequency bandwidth was as large as 5.3GHz. The results showed that the as-prepared FeCo/C nanocomposite could be a potential candidate for microwave absorption.