Metal-organic framework-based Fe/C@Co.sub.3O.sub.4 core-shell nanocomposites with outstanding microwave absorption properties in low frequencies

Microwave absorption materials are of great importance in various application nowadays. In this article, a new type of metal-organic framework (MOF)-based Fe/C@Co.sub.3O.sub.4 core-shell nanocomposites is introduced for microwave absorption coating applications, via a simple and low-cost fabrication process. The nanocomposites have been successfully synthesized via a controlled high-temperature treatment of a PB@Co(OH).sub.2 precursor, which was prepared earlier by a solvent-thermal method. The nanocomposites have excellent microwave absorption properties, and the maximum reflection loss (RL) value and effective bandwidth (RL < - 10 dB) can be tuned by the fabrication parameters. The results show that the different nanostructures and electromagnetic properties of the Fe/C@Co.sub.3O.sub.4 nanocomposites can be obtained by the heat treatments with different temperatures. With an excellent attenuation performance and distinguished impedance matching properties, the nanocomposite processed by a heat treatment at 700 °C (ICCO-700) has the best microwave absorption results. The maximum RL value reaches - 58.5 dB at 4.57 GHz, which is a remarkable valley in the low frequency range, when the absorber thickness is 2.5 mm. The effective bandwidth can be as wide as 11.0 GHz, when the sample thickness is 5.0 mm, which covers three quarters of the S band, one half of the C band, one half of the X band and the whole Ku band.