3 research outputs found

    Efficient and Lightweight Electromagnetic Wave Absorber Derived from Metal Organic Framework-Encapsulated Cobalt Nanoparticles

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    Porous-carbon-based nanocomposites are gaining tremendous interest because of good compatibility, lightweight, and strong electromagnetic wave absorption. However, it is still a great challenge to design and synthesize porous-carbon-based composites with strong absorption capability and broad frequency bandwidth. Herein, a facile and effective method was developed to synthesize Co magnetic nanoparticles/metal organic framework (MOF) (Co NPs/ZIF-67) nanocomposites. Co NPs/porous C composites were subsequently obtained by annealing Co NPs/ZIF-67 nanocomposites at different temperatures under an inert atmosphere. The carbonized nanocomposites showed highly efficient electromagnetic wave absorption capability. Specifically, the optimal composite (i.e., Co/C-700) possessed a maximum reflection loss (RL) value of −30.31 dB at 11.03 GHz with an effective absorption bandwidth (RL ≤ −10 dB) of 4.93 GHz. The electromagnetic parameters and the absorption performance of the composites are readily tunable by adjusting the carbonization temperature and the concentration of Co NPs in the composites. Because of the combination of good impedance matching, dual-loss mechanism, and the synergistic effect between Co NPs and porous carbon composites, these Co NPs/MOF-derived composites are attractive candidates for electromagnetic wave absorbers

    Ferromagnetism and Microwave Electromagnetism of Iron-Doped Titanium Nitride Nanocrystals

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    Titanium nitride (TiN) nanocrystals doped with different dosages of iron were prepared by calcinating nanotubular titanic acid precursor in flowing ammonia. The structure of as-prepared Fe-doped TiN nanocrystals was characterized, and their ferromagnetism and microwave electromagnetism were investigated. It has been found that as-prepared Fe-doped TiN nanocrystals exhibit distinct room temperature ferromagnetic properties and improved microwave electromagnetic loss behavior when compared with the undoped counterpart. Considering the crystal structure and chemical feature of as-synthesized products, we suppose that structural defects are responsible for the observed ferromagnetism and microwave electromagnetism of as-synthesized Fe-doped TiN, and it may be feasible to tune the magnetic and electromagnetic properties by manipulating the generation of the structural defects. Hopefully, the present research is to shed light on Fe-doped TiN nanocrystal as a promising microwave absorption material and to help acquiring insights into the origin of ferromagnetism and microwave electromagnetism in a broad range of nanostructures, thereby broadening the scope of dilute magnetic and electromagnetic wave absorbing materials

    Preparation of Graphene Sheets by Electrochemical Exfoliation of Graphite in Confined Space and Their Application in Transparent Conductive Films

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    A novel electrochemical exfoliation mode was established to prepare graphene sheets efficiently with potential applications in transparent conductive films. The graphite electrode was coated with paraffin to keep the electrochemical exfoliation in confined space in the presence of concentrated sodium hydroxide as the electrolyte, yielding ∼100% low-defect (the D band to G band intensity ratio, <i>I</i><sub>D</sub>/<i>I</i><sub>G</sub> = 0.26) graphene sheets. Furthermore, ozone was first detected with ozone test strips, and the effect of ozone on the exfoliation of graphite foil and the microstructure of the as-prepared graphene sheets was investigated. Findings indicate that upon applying a low voltage (3 V) on the graphite foil partially coated with paraffin wax that the coating can prevent the insufficiently intercalated graphite sheets from prematurely peeling off from the graphite electrode thereby affording few-layer (<5 layers) holey graphene sheets in a yield of as much as 60%. Besides, the ozone generated during the electrochemical exfoliation process plays a crucial role in the exfoliation of graphite, and the amount of defect in the as-prepared graphene sheets is dependent on electrolytic potential and electrode distance. Moreover, the graphene-based transparent conductive films prepared by simple modified vacuum filtration exhibit an excellent transparency and a low sheet resistance after being treated with NH<sub>4</sub>NO<sub>3</sub> and annealing (∼1.21 kΩ/□ at ∼72.4% transmittance)
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