Porous Three-Dimensional Flower-like Co/CoO and Its Excellent Electromagnetic Absorption Properties

Abstract

The porous three-dimensional (3-D) flower structures assembled by numerous ultrathin flakes were favor for strengthen electromagnetic absorption capability. However, it still remains a big challenge to fabricate such kind of materials. In this study, an easy and flexible two-step method consisting of hydrothermal and subsequent annealing process have been developed to synthesize the porous 3-D flower-like Co/CoO. Interestingly, we found that the suitable heat treatment temperature played a vital role on the flower-like structure, composition, and electromagnetic absorption properties. In detail, only in the composite treated with 400 °C can we gain the porous 3-D flower structure. If the annealing temperature were heated to 300 °C, the Co element was unable to generate. Moreover, when the annealing temperature increased from 400 to 500 °C, these flower-like structures were unable to be kept because the enlarged porous diameter would wreck the flower frame. Moreover, these 3-D porous flower-like structures presented outstanding electromagnetic absorption properties. For example, such special structure enabled an optimal reflection loss value of -50 dB with the frequency bandwidth ranged from 13.8 to 18 GHz. The excellent microwave absorption performance may attribute to the high impedance matching behavior and novel dielectric loss ability. Additionally, it can be supposed that this micrometer-size flower structure was more beneficial to scatter the incident electromagnetic wave. Meanwhile, the rough surface of the ultrathin flake is apt to increase the electromagnetic scattering among the leaves of the flower due to their large spacing and porous features.

A green and facile method toward synthesis of waste paper-derived 3D functional porous graphene via in situ activation of cobalt(ii)

“…1D and Fig. S2D respectively further confirmed the existence of Co 3 O 4 and Co. 22 X-ray photoelectron spectroscopy (XPS) showed the main component of the composite (Fig. 4A, and Table S2) and high resolution XPS spectra further confirmed the chemical compositions of active sites.…”

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

“…Furthermore, alternative methods including using frequency selective radar absorbing materials, graded-dielectric multilayer, and employment of concise design of the microscopic structures of the fillers are promising methods for achieving high-performance microwave absorption materials and composites. [41][42][43][44][45][46][47] Moreover, the mechanical properties and the significant factors that impact the performance should be concerned. [48][49][50][51][52][53] Figure 12 displays the effective absorption bandwidth of the materials and structures.…”

Dependency of tunable microwave absorption performance on morphology-controlled hierarchical shells for core-shell Fe3O4@MnO2 composite microspheres

“…However, both of the ionic polarization and electronic polarization usually occur in the ultraviolet or infrared frequency range, thus the two polarizations are negligible [42]. Based on the free electron theory, ߝ ᇱᇱ ≈ 1 ߨߝ ߩ݂ ⁄ , where ߩ is the resistivity, the high ߝ ᇱᇱ value means the low resistivity, which illuminates the good electronic transmission performance and excellent conductivity [14,43]. It can be inferred that the conductive loss exists and the high conductivity may stem from the generation of microcurrent in the special microstructure with the altering electromagnetic field [36,[44][45].…”

“…Sun [13]. Hierarchical three-dimensional flower-like Co/CoO composites have enabled an optimal reflection loss value of -50.0 dB (7.2 GHz) and a broad effective bandwidth ranging from 13.8 to 18 GHz [14]. Moreover, among the three hierarchical Co 20 Ni 80 microspheres with different morphologies, the urchin-like ones displayed the minimum reflection loss value of -33.5 dB (3.0 GHz) while the flower-like ones possessed the absorption bandwidth of 5.5 GHz [15].…”