HIGHLIGHTS• Hierarchically porous Fe-Co/N-doped carbon/rGO (Fe-Co/NC/rGO) composites were successfully prepared. Macropores, mesopores, and micropores coexisted in the composites.• Hierarchically porous Fe-Co/NC/rGO showed effective bandwidth of 9.29 GHz.ABSTRACT Developing lightweight and broadband microwave absorbers for dealing with serious electromagnetic radiation pollution is a great challenge. Here, a novel Fe-Co/N-doped carbon/reduced graphene oxide (Fe-Co/NC/rGO) composite with hierarchically porous structure was designed and synthetized by in situ growth of Fe-doped Cobased metal organic frameworks (Co-MOF) on the sheets of porous cocoon-like rGO followed by calcination. The Fe-Co/NC composites are homogeneously distributed on the sheets of porous rGO. The Fe-Co/NC/rGO composite with multiple components (Fe/Co/NC/rGO) causes magnetic loss, dielectric loss, resistance loss, interfacial polarization, and good impedance matching. The hierarchically porous structure of the Fe-Co/NC/rGO enhances the multiple reflections and scattering of microwaves. Compared with the Co/NC and Fe-Co/NC, the hierarchically porous Fe-Co/NC/rGO composite exhibits much better microwave absorption performances due to the rational composition and porous structural design. Its minimum reflection loss (RL min ) reaches − 43.26 dB at 11.28 GHz with a thickness of 2.5 mm, and the effective absorption frequency (RL ≤ − 10 dB) is up to 9.12 with the same thickness of 2.5 mm. Moreover, the widest effective bandwidth of 9.29 GHz occurs at a thickness of 2.63 mm. This work provides a lightweight and broadband microwave absorbing material while offering a new idea to design excellent microwave absorbers with multicomponent and hierarchically porous structures.
γ-Fe2O3 nanotube/porous reduced graphene
oxide (rGO) composites were prepared using a controllable method.
Uniform γ-Fe2O3 nanotubes with a diameter
of about 85 nm and a length of about 230 nm are well distributed between
porous rGO sheets. Compared with the γ-Fe2O3 nanorod/porous rGO and γ-Fe2O3 nanotube/nonporous
rGO, the γ-Fe2O3 nanotube/porous rGO composites
with both unique hollow and porous structure show an advantage for
the attenuation of microwaves. The appropriate dielectric loss and
magnetic loss result in a good impedance matching. The minimum reflection
loss of γ-Fe2O3 nanotube/porous rGO composite
reaches −34.20 dB with a thickness of 2.0 mm, and the absorption
bandwidth is 4.59 GHz. These results reveal that the synthesis of
hollow and porous composites is a promising way for getting lightweight
microwave materials with high performance.
A novel
porous cocoon-like reduced graphene oxide (rGO) with high
porosity and low density was fabricated by a simple and green reduction
reaction using ascorbic acid as the reductant in combination with
a freeze-drying process without annealing. The bulk density of porous
cocoon-like rGO is only 28.49 mg/cm3, and the porosity
reaches 94.57%. The reaction times have an important influence on
the formation of porous cocoon-like rGO and the reduction degree of
rGO. The porous cocoon-like rGO exhibits an excellent microwave-absorbing
property with a low mass filling ratio of 7.0 wt %; its minimum reflection
loss (RL) is −29.05 dB at 15.96 GHz with a sample thickness
of 2.0 mm and the effective absorption bandwidth (RL < −10
dB) is 5.27 GHz. The microwave-absorbing property of porous cocoon-like
rGO is much better than that of GO and other porous rGO. The in-depth
analyses of the reduction degree, porosity, and microwave-absorbing
performance illustrate that the microwave-absorbing performance of
rGO is significantly related to the reduction degree and porosity.
In addition, the synthetic route for porous cocoon-like rGO is simple,
has low energy consumption, and is environmentally friendly. Our work
demonstrates that the porous cocoon-like rGO is a promising lightweight
microwave absorber with high performance.
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