Quaternary Nanocomposites Consisting of Graphene, Fe₃O₄@Fe Core@Shell, and ZnO Nanoparticles: Synthesis and Excellent Electromagnetic Absorption Properties

Abstract

This paper presents for the first time a successful synthesis of quaternary nanocomposites consisting of graphene, Fe(3)O(4)@Fe core/shell nanopariticles, and ZnO nanoparticles. Transmission electron microscopy measurements show that the diameter of the Fe(3)O(4)@Fe core/shell nanoparitcles is about 18 nm, the Fe(3)O(4) shell's thickness is about 5 nm, and the diameter of ZnO nanoparticles is in range of 2-10 nm. The measured electromagnetic parameters show that the absorption bandwidth with reflection loss less than -20 dB is up to 7.3 GHz, and in the band range more than 99% of electromagnetic wave energy is attenuated. Moreover, the addition amount of the nanocomposites in the matrix is only 20 wt %. Therefore, the excellent electromagnetic absorption properties with lightweight and wide absorption frequency band are realized by the nanocomposites.

Broadening Electromagnetic Absorption Bandwidth: Design from Microscopic Dielectric‐Magnetic Coupled Absorbers to Macroscopic Patterns

“…On the other hand, the presence of rectangular corners at the multiplelayer steps is able to serve as the location for creating corner scattering (Figures 11d and 10h). [37][38][39][40] Consequently, these two mechanisms compete for generating unique absorption performance; and 4) The microwave absorption performance in Figure 5 along with the scheme in Figure 11 suggests that the magnetic materials enable to deliver multiple absorption bands in the investigation, and such observation is mainly associated with the coexistence of (2n þ 1)/4 wavelength resonance via tuning the electromagnetic parameters. As schemed in Figure 11, the multiple-layer array structure are apparently promising in offering broadband absorption because of the intrinsic larger absorption regions in the 2D projections ( Figures 5, 11a, and 10e).…”

Cobalt Oxide and Cobalt‐Graphitic Carbon Core–Shell Based Catalysts with Remarkably High Oxygen Reduction Reaction Activity

“…[[qv: 5h]] Moreover, the intimate contact between Co core and carbon shell hinders the possible agglomeration of metal NPs at high temperature and also facilitate the electron transport from nitrogen‐doped carbon sheets to Co cores, leading to a synergistic effect toward oxygen reduction reaction. [[qv: 5m]],[[qv: 8c]],21 The LSV of Co@GC‐NC‐12 m HCl‐192 h again resembles that of Co@GC‐NC (Figure 4b). Aiming to test the possible oxidation of Co core to cobalt oxide, our last resort was the oxidation of CoO x /Co@GC‐NC in air at 250 °C for 192 h, resulting in the sample we designate as CoO x /Co@GC‐NC‐250 °C‐192 h. Despite the partial oxidation possibility, Co still predominantly appears in the powder XRD pattern of CoO x /Co@GC‐NC‐250 °C‐192 h (Figure S13, Supporting Information).…”

Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles

“…Thus, there is an increasing need for microwave absorbing materials which can attenuate unwanted electromagnetic signals. Most microwave absorbing materials are composed of magnetic loss powders such as ferrites or Co and dielectric loss materials such as carbon materials, metal oxides or polymers [22,[423][424][425][426][427][428]. In simple terms, the perfect absorber should have a strong absorption in a wide frequency bandwidth (i.e., a large working frequency range), it should work at zero applied magnetic field and it should be thin and light weight [341].Thus, in recent years there has been an increase in the search for novel types of microwave absorbers and, in particular, in systems involving bi-magnetic hard-soft core/shell nanoparticles [80][81][82].…”