Constructing ordered macropores in hollow Co/C polyhedral nanocages shell toward superior microwave absorbing performance

Co-Doped Porous Carbon/Carbon Nanotube Heterostructures Derived from ZIF-L@ZIF-67 for Efficient Microwave Absorption

Carbon-based magnetic metal composites derived from metal-organic frameworks (MOFs) are promising materials for the preparation of broadband microwave absorbers. In this work, the leaf-like co-doped porous carbon/carbon nanotube heterostructure was obtained using ZIF-L@ZIF-67 as precursor. The number of carbon nanotubes can be controlled by varying the amount of ZIF-67, thus regulating the dielectric constant of the sample. An optimum reflection loss of -42.2 dB is attained when ZIF-67 is added at 2 mmol. An effective absorption bandwidth (EAB) of 4.8 GHz is achieved with a thickness of 2.2 mm and a filler weight of 12%. The excellent microwave absorption (MA) ability is generated from the mesopore structure, uniform heterogeneous interfaces, and high conduction loss. The work offers useful guidelines to devise and prepare such nanostructured materials for MA materials.

Research progress and future perspectives on electromagnetic wave absorption of fibrous materials

Electromagnetic waves have caused great harm to military safety, high-frequency electronic components, and precision instruments, and so forth, which urgently requires the development of lightweight, high-efficiency, broadband electromagnetic waves (EMW) absorbing materials for protection. As the basic fibrous materials, carbon fibers (CFs) and SiC fibers (SiCf) have been widely applied in EMW absorption due to their intrinsic characteristics of low density, high mechanical properties, high conductivity, and dielectric loss mechanism. Nevertheless, it has remained a great challenge to develop lightweight EMW-absorbing fibrous materials with strong absorption capability and broad frequency range. In this review, the fundamental electromagnetic attenuation mechanisms are firstly introduced. Furthermore, the preparation, structure, morphology, and absorbing performance of CFs and SiCf-based EMW absorbing composites are summarized. In addition, prospective research opportunities are highlighted toward the development of fibrous absorbing materials with the excellent absorption performance.

Synthesis of a one-dimensional carbon nanotube-decorated three-dimensional crucifix carbon architecture embedded with Co7Fe3/Co5.47N nanoparticles for high-performance microwave absorption

Low-dimensional cell-decorated three-dimensional (3D) hierarchical structures are considered excellent candidates for achieving remarkable microwave absorption. In the present work, a one-dimensional (1D) carbon nanotube (CNT)-decorated 3D crucifix carbon framework embedded with Co₇Fe₃/Co_5.47N nanoparticles (NPs) was fabricated by the in-situ pyrolysis of a trimetallic metal-organic framework (MOF) precursor (ZIF-ZnFeCo). Co₇Fe₃/Co_5.47N NPs were uniformly dispersed on the carbon matrix. The 1D CNT nanostructure was well regulated on the 3D crucifix surface by changing the pyrolysis temperature. The synergistic effect of 1D CNT and the 3D crucifix carbon framework increased the conductive loss, and Co₇Fe₃/Co_5.47N NPs induced interfacial polarization and magnetic loss; thus, the composite manifested superior microwave absorption performance. The optimum absorption intensity was -54.0 dB, and the effective absorption frequency bandwidth reached 5.4 GHz at a thickness of 1.65 mm. The findings of this work could provide significant guidance for the fabrication of MOF-derived hybrids for high-performance microwave absorption applications.

Construction of porous carbon-based magnetic composites derived from iron zinc bimetallic metal-organic framework as broadband and high-efficiency electromagnetic wave absorbers

The fabrication of broadband and high-efficiency electromagnetic (EM) wave absorbers remains a huge challenge. Metal-organic framework (MOF) with large porosity and high specific surface area has been considered as a promising precursor for the preparation of novel EM wave absorbers. In this work, porous carbon-based magnetic composites derived from iron zinc bimetallic MOF were prepared by the two-step method of solvothermal reaction and high-temperature pyrolysis. Results of micromorphology analysis demonstrated that the morphology of carbon frameworks evolved from octahedron, polyhedron, sphere to porous sphere-like shape with the increase of pyrolysis temperature. Furthermore, the EM parameters and absorbing properties of obtained composites were regulated through simply changing the pyrolysis temperature. It was noteworthy that the as-prepared Fe₃O₄/C composite pyrolyzed at 700 °C exhibited the best EM absorption performance. The minimum reflection loss was as large as -60 dB and broad absorption bandwidth reached up to 4 GHz (8-12 GHz, covering the whole X band) at a matching thickness of 2.5 mm and a filler loading ratio of 40 wt%. Furthermore, the maximum absorption bandwidth could be enlarged to 5.4 GHz via reducing the matching thickness to 1.85 mm. Additionally, the probable EM attenuation mechanisms of attained composites were proposed. The results of this study would provide a reference for the preparation of porous carbon-based composites as broadband and high-efficiency EM wave absorbers.

Fabrication of nitrogen-doped reduced graphene oxide/hollow copper ferrite composite aerogels as lightweight, thin and high-efficiency electromagnetic wave absorbers in the X band

The development of lightweight, thin and high-efficiency electromagnetic (EM) wave absorbers remains a huge challenge in the field of EM absorption. Graphene aerogels with three-dimensional (3D) network structure and low bulk density have been considered as potential EM absorbing materials. In this work, nitrogen-doped reduced graphene oxide/hollow copper ferrite (NRGO/hollow CuFe₂O₄) composite aerogels were fabricated by the three-step method of solvothermal reaction, hydrothermal self-assembly and calcination treatment. The as-prepared composite aerogels had a unique 3D hierarchical porous network structure. Furthermore, results demonstrated that the EM absorption performance of attained composite aerogels could be improved by adjusting the calcination temperature. Notably, the obtained composite aerogel calcined at 400.0 ℃ exhibited the best EM absorption performance. When the loading ratio was as low as 15.0 wt%, the minimum reflection loss reached up to -54.5 dB with a matching thickness of 2.0 mm, and the maximum effective absorption bandwidth of 5.0 GHz could be achieved under an extremely thin thickness of 1.6 mm. Additionally, the probable EM attenuation mechanisms of attained composite aerogels were proposed. The results of this work could be helpful for developing graphene-based 3D composites as lightweight, thin and high-efficiency EM wave absorbers.