Magnetic hollow mesoporous carbon composites with impedance matching for highly effective microwave absorption

Lightweight hollow mesoporous carbon spheres (HMCSs) with large air/carbon interface in the mesoporous shell and interior void have been successfully synthesized via a ‘polymerization–pyrolysis–etching’ route. The complex permittivity of the HMCSs can be easily adjusted by carbonization temperature in the frequency range of 2–18 GHz, which is in favor of designing absorbers in different frequency range. The minimum reflection loss value of − 26.4 dB at 6.7 GHz with a thickness of 5.0 mm and the maximum effective absorption bandwidth (less than − 10 dB) of 5.5 GHz can be gained for the HC-700/paraffin composite with only 10 wt% HMCSs and a thickness of 2.5 mm. To enhance the magnetic loss and improve the impedance matching of the HMCSs, electroless plating methods are employed to deposit Ni and Fe nanoparticles on the HMCSs. Benefiting from the dielectric loss, magnetic loss and impedance characteristic, the new lightweight Fe/HMCSs composite with 40 wt% HC–Fe shows superior microwave absorption properties. The stronger reflection loss can be obtained at all designed thicknesses, and the peak value of reflection loss is less than − 20 dB at each thickness of greater than 1.2 mm. The minimum reflection loss reaches − 49.7 dB at 13.0 GHz, and the effective absorption bandwidth is 4.0 GHz with a thickness of 1.6 mm. This research is providing a new insight in the preparation and design of lightweight microwave absorption materials.