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.

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A simple and practical approach for synthesizing ultrafine Ni fibers under normal pressure via the reduction of Ni 2+ ions by hydrazine hydrate in the absence of any templates or external magnetic field is reported. The mechanisms and a simplified model of formation for the Ni fibers are proposed, and the correlated magnetic properties and electromagnetic characteristics of the Ni products are studied systematically. The results of a series of comparative studies indicate that the feeding sequence of the reactants and the concentration of NaOH solution are critical to controlling the shape of the target products from fiber to sphere. The Ni fibers have an enhanced magnetic coercivity compared with that of the Ni spheres. The composites filled with Ni fibers have an electromagnetic wave absorbance within the frequency range 2.0-18.0 GHz stronger than that for the Ni sphere-filled composites. Specifically, by properly adjusting the matching thicknesses, a minimum reflection loss (RL) of -39.5 dB at 4.8 GHz and an absorbance band of less than -20 dB within 3-16 GHz are obtained for the Ni fiber-filled composites, showing that the Ni fibers may have promising application for electromagnetic wave absorbance.

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 = 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 NHNO and annealing (∼1.21 kΩ/□ at ∼72.4% transmittance).