Nanolayered Cobalt@Carbon Hybrids Derived from Metal–Organic Frameworks for Microwave Absorption

Abstract

High-performance broadband microwave absorbers are greatly required to cope with the increasingly serious microwave radiation pollution. Integration of dielectric and magnetic components is a promising strategy to achieve desirable microwave absorption performance. Herein, we demonstrated a facile and efficient approach to fabricate two-dimensional cobalt@carbon (Co@C) hybrids by solvothermal synthesis of cobalt–metal–organic framework (Co-MOF) nanosheets and subsequent thermal pyrolysis for efficient microwave absorption application. The resultant nanolayered Co@C hybrids inherit the two-dimensional architecture of the Co-MOF nanosheets. During the thermal pyrolysis of Co-MOF, its organic component is carbonized to amorphous carbon while its cobalt ions are carbothermally reduced to cobalt nanoparticles, thus in situ integrating the magnetic metal nanocrystal with the dielectric carbon. Consequently, a wide effective absorption bandwidth of 5.44 GHz at a small thickness of 1.76 mm and a minimum reflection loss value of −49.76 dB are achieved for the wax composite with 30 wt % of Co@C hybrid pyrolyzed at 800 °C. The outstanding microwave absorption performances are attributed to the synergistic effects of the Co@C hybrid nanosheets and their large shape anisotropy, which facilitates the strong dielectric loss and good impedance matching, thus promising the nanolayered Co@C hybrid as a lightweight and high-performance microwave absorber.

Hierarchical porous carbon derived from green cyclodextrin metal‐organic framework and its application in microwave absorption

“…In this article, we found that, unlike other MOF derived carbon materials with single‐stage or double‐stage porous structure, 22,24–26 our CD‐MOF derived carbon has a hierarchical(three‐stage) porous structure, containing micro‐, meso‐, and macro‐pores simultaneously. In order to guide the preparation of CD‐MOF derived HPC, the relationship between the morphological properties and prepared conditions is studied in this article.…”

Construction and Microwave Absorption Properties of Core@Double-Shell Structured Fe3O4@Polyaniline@MnO2 Nanospheres

“…In general, when evaluating the absorbing properties of a material, it is necessary to consider the following three main factors: the minimal RL, the absorber thickness and e®ective absorption bandwidth (the RL intensity is below -10 dB, which means the absorption e±ciency is over 90%). [39][40][41] However, the minimum RL value of FP is only À7.86 dB at a frequency of 9.78 GHz with the thickness of 3.5 mm. It can be inferred that the construction of the double-shell structure can e®ectively improve the microwave absorbing properties.…”

Hierarchical Cobalt Selenides as Highly Efficient Microwave Absorbers with Tunable Frequency Response

“…Thus, only eddy current loss, natural resonance and exchange resonance need to be taken into consideration. If the factor C0 = μ″(μ′) −2 f −1 (f is the frequency) keeps constant, the eddy current loss will be the sole reason for magnetic loss 51,52 . As shown in Figure S5, C0 for all the samples displays frequent dependence, suggesting the contribution comes from natural resonance and exchange resonance besides eddy current loss.…”

“…As a result, the steep peak in the μ″ curve between 2-6 GHz may benefit from the natural resonance. The following peaks in higher frequencies are attributed to the exchange resonance 52,53 .…”