Magnetic γ-Fe₂O₃, Fe₃O₄, and Fe nanoparticles confined within ordered mesoporous carbons as efficient microwave absorbers

Abstract

A series of magnetic γ-Fe2O3, Fe3O4, and Fe nanoparticles have been successfully introduced into the mesochannels of ordered mesoporous carbons by the combination of the impregnation of iron salt precursors and then in situ hydrolysis, pyrolysis and reduction processes. The magnetic nanoparticles are uniformly dispersed and confined within the mesopores of mesoporous carbons. Although the as-prepared magnetic mesoporous carbon composites have high contents of magnetic components, they still possess very high specific surface areas and pore volumes. The magnetic hysteresis loops measurements indicate that the magnetic constituents are poorly-crystalline nanoparticles and their saturation magnetization is evidently smaller than bulky magnetic materials. The confinement of magnetic nanoparticles within the mesopores of mesoporous carbons results in the decrease of the complex permittivity and the increase of the complex permeability of the magnetic nanocomposites. The maximum reflection loss (RL) values of -32 dB at 11.3 GHz and a broad absorption band (over 2 GHz) with RL values <-10 dB are obtained for 10-Fe3O4-CMK-3 and 10-γ-Fe2O3-CMK-3 composites in a frequency range of 8.2-12.4 GHz (X-band), showing their great potentials in microwave absorption. This research opens a new method and idea for developing novel magnetic mesoporous carbon composites as high-performance microwave absorbing materials.

Fe‐, Co‐, and Ni‐Loaded Porous Activated Carbon Balls as Lightweight Microwave Absorbents

“…This primarily leads to different trends for the complex permittivity changes with frequencyf or the FeCB, CoCB, and NiCB composites. As imilaro b- www.chemphyschem.org servation has also been reported for other absorbing materials, for example, dendrite-likeF e 3 O 4 , g-Fe 2 O 3 ,a nd Fe magnetic absorbents, [41] and g-Fe 2 O 3 /Fe 3 O 4 /Fe-CMK-3 composites, [54] where the phase composition had al arge influence on the relative complexp ermittivity. The real part (m')a nd imaginary part (m'')o ft he relative permeability are plotteda safunction of frequency in Figure 7b 1b 3 .T hese samples show as imilar dispersive behavior and the difference betweent he permeability values is insignificant.…”

Electromagnetic Shielding Materials in GHz Range

“…The increase of the former is due to the existence of multiple dielectric relaxations in the magnetic nanocomposites. Thus the impedance matching performance of these composites is improved, which increase the absorption ability . For this reason, magnetic nanoparticles have been incorporated to composites in order to improve the shielding efficiencies.…”

Solvothermal synthesis and good microwave absorbing properties for magnetic porous-Fe3O4/graphene nanocomposites

“…3(c), the excellent wave absorbing properties including the optimal minimum RL value of -43.7 dB at 6.8 GHz with a sample thickness of 5 mm can be obtained in Fe 3 O 4 /GO composites with 7 wt% GO additions, which is superior to those of the most of magnetite-based composites reported in the previous literatures. 24,25 From 3D RL images shown in Fig. 3(d) that for this composite sample, the large minimum RL values and broad absorption bandwidth can be achieved at low frequency range with increasing sample thickness, which can present their practical application scopes so as to guide their actual application as high-performance microwave absorbing materials.…”