Bin Quan

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.

A permittivity regulating strategy to achieve high-performance electromagnetic wave absorbers with compatibility of impedance matching and energy conservation

Permittivity plays crucial but reverse roles in impedance matching and attenuation loss in terms of electromagnetic wave absorption. In addition to unilateral superior performance, an ideal absorber needs to take into consideration both impedance matching and energy conservation. In order to acquire absorbing materials with moderate impedance matching and attenuation ability simultaneously, we have fabricated MoS2/rGO composites via a facile and effective hydrothermal approach. The dielectric constant of the obtained composite can be regulated by varying the molar ratio of the precursors and an optimal balance between impedance matching and energy conservation is eventually obtained upon addition of 6 mL GO. The maximum reflection loss is −67.1 dB at 14.8 GHz and the effective electromagnetic wave absorption bandwidth for RL < −10 dB covers from 12.08 to 18.00 GHz (5.92 GHz) with a small thickness of 1.95 mm. Moreover, the relationship between the matching thickness and the highest reflection loss value has also been discussed in detail. The results not only suggest that the MoS2/rGO composites developed through a simple procedure here can act as an ideal absorber with strong absorption, a broad frequency bandwidth and small thickness, but also offer a good reference for the design of microwave absorbers, including the compatibility of impedance matching and attenuation loss ability as well as matching thickness.

Novel nanoporous carbon derived from metal–organic frameworks with tunable electromagnetic wave absorption capabilities

Nanoporous carbon materials derived from metal organic frameworks (MOFs) have attracted considerable attention due to their low density for microwave absorption. Nevertheless, their poor impedance matching has reduced the absorber performance. The design and fabrication of complex nanocarbon materials with outstanding impedance matching is still a challenge. Here, we prepared a core–shell structured ZIF-8@ZIF-67 crystal through a new seed-mediated growth method. After the thermal treatment of ZIF-8@ZIF-67 crystals, we obtained selectively nanoporous carbon materials consisting of ZnO/NPC as the cores and highly graphitic Co/NPC as the shells. The shell thicknesses of ZIF-67 can be tuned simply by varying the feeding molar ratios of Co2+/Zn2+. The composites exhibited excellent impedance matching and strong absorption. The composite ZnO/NPC@Co/NPC-0.5 samples filling with 50 wt% of paraffin show a maximum reflection loss (RL) of −28.8 dB at a thickness of 1.9 mm. In addition, a broad absorption bandwidth for RL <−10 dB which covers from 13.8–18 GHz can be obtained. Our study not only bridges diverse carbon-based materials with infinite metal–organic frameworks but also opens a new avenue for artificially designed nano-architectures with target functionalities.

Quasi-noble-metal graphene quantum dots deposited stannic oxide with oxygen vacancies: Synthesis and enhanced photocatalytic properties.

Quasi-noble-metal graphene quantum dots (GQDs) deposited stannic oxide (SnO2) with oxygen vacancies (VOs) were prepared by simply sintering SnO2 and citric acid (CA) together. The redox process between SnO2 and GQDs shows the formation of oxygen vacancy states below the conduction band of stannic oxide. The produced VOs obviously extend the optical absorption region of SnO2 to the visible-light region. Meanwhile, GQDs can effectively improve the charge-separation efficiency via a quasi function like noble metal and promote the visible-light response to some degree. In addition, the samples calcinated at 450°C reveals the best performance because of its relatively high concentrations of VOs. What is more, the possible degradation mechanism has been inferred as extended visible-light response as well as raised charge-separation efficiency has also been put forward. Our work may offer a simple strategy to combine the defect modulation and noble metal deposition simultaneously for efficient photocatalysis.

Incorporation of dielectric constituents to construct ternary heterojunction structures for high-efficiency electromagnetic response

To satisfy the diverse requirements of low reflection and high absorption of microwave attenuation, the construction of multiple heterojunction structure is imperative. On the one hand, the impedance mismatching could be ameliorated via the addition of new component; on the other hand, the multiple interface polarizations derived from the architecture of heterojunction make for the dissipation of microwave. In this work, the ternary TiO2/RGO/Fe2O3 composites exhibit tremendous superiority compared with single TiO2 or RGO no matter the absorption coefficient or effective bandwidth. The maximum absorption value of the TiO2/RGO/Fe2O3 composites is -44.05dB at 14.48GHz with a low thickness of 2.0mm. In addition, the effective bandwidth (RL<-10dB) reaches 5.6GHz from 11.96 to 17.56GHz. The superior electromagnetic wave absorbing performance of the TiO2/RGO/Fe2O3 composites derived from the appropriate impedance matching as well as the multiple polarization effect. The results adequately demonstrate the accessibility of the prepared TiO2/RGO/Fe2O3 composites as a preeminent absorber.

Cross-linking-derived Synthesis of Porous CoxNiy/C Nanocomposites for Excellent Electromagnetic Behaviors

The magnet/dielectric composites with tunable structure and composition have drawn much attention because of their particular merits in magnetoelectric properties compared with the sole dielectric or magnetic composites. In addition, porous materials at the nanoscale can satisfy the growing requirements in many industries. Therefore, constructing porous metal alloy/carbon nanocomposites is to be an admirable option. Unfortunately, traditional synthesis methods involve multistep routes and complicated insert-and-remove templates approaches. Here we report a facile process to synthesize CoxNiy/C composites via a spontaneous cross-linking reaction and subsequent calcination process, during which multiple processes, including reducing polyvalent metal ions, forming alloy, and encapsulating alloy nanoparticles into porous carbon matrix, are achieved almost simultaneously. By adjusting the feed ratio of Co2+ to Ni2+ ions, controllable composition of CoxNiy/C composites can be gained. It should be noted that the CoxNiy/C composites are demonstrated to be excellent microwave absorbers from every aspect of assessment criteria including reflection loss, effective bandwidth, thickness, and weight of absorber. Our study opens up a promising technique for the synthesis of alloy/carbon composites with porous nanostructures with target functionalities.

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.

Achieving better impedance matching by a sulfurization method through converting Ni into NiS/Ni3S4 composites

Herein, we synthesized metallic Ni through a simple chemical reduction process. Unfortunately, the Ni showed poor microwave absorption performance because of the inferior impedance matching properties. To overcome this, a sulfurization method was employed to obtain a novel microwave absorber-NiS/Ni3S4 composite. The nickel sulfide composites displayed much better microwave absorption abilities than the metallic Ni. The reflection loss (RL) values that exceeded −10 dB were observed in the frequency range 13.8–18.0 GHz (a broad microwave absorption bandwidth of 4.2 GHz) with a thickness of only 1.8 mm. Besides, the minimum RL value was as high as −43.0 dB at 9.1 GHz with the thickness of 2.4 mm. On the basis of high dielectric loss, good impedance matching properties, as well as stronger interfacial polarization effect, it can be concluded that NiS/Ni3S4 composites possess strong-absorption properties and have great potential for application as light microwave absorbers.

Strong electric wave response derived from the hybrid of lotus roots-like composites with tunable permittivity

Lotus roots-like NiO/NiCo2O4 hybrids derived from Metal-organic frameworks (MOFs) are fabricated for the first time by using flake NiCo-MOF precursors as reactant templates. It was found that a thin sample consisting of 60 wt % NiO/NiCo2O4 hybrids in the wax matrix exhibited an effective microwave absorption bandwidth of 4.2 GHz at the thickness of 1.6 mm. The highest reflection loss of −47 dB was observed at 13.4 GHz for a sample with a thickness of 1.7 mm. Results obtained in this study indicate that hybrids of NiO and NiCo2O4 are promising microwave absorbing materials with adjustable permittivity, which can exhibit broad effective absorption bandwidth at low filler loading and thin thickness.