Preparation of MnO2@CNFs composites and their tunable microwave absorption properties

The MnO2@CNFs hierarchical structures have been successfully synthesized through a facile hydrothermal reduction method. By controlling the addition amount of KMnO4, the electromagnetic parameters and microwave absorption performance can be tuned effectively. When the mass ratio of CNFs and KMnO4 was 4:1, the obtained composites exhibited strong reflection loss of −42.77 dB at 4.32 GHz with an absorbent thickness of 4.5 mm. Meanwhile, the effective absorption region was 2.8 GHz (13.07–15.87 GHz) at a thin thickness of 1.5 mm. The superior electromagnetic attenuation performance of MnO2@CNFs is ascribed to the unique hierarchical structure. Further, the MnO2 nanoflakes vertically growing on CNFs modulate the complex dielectric parameters of MnO2@CNFs, leading to well-matched characteristic impedance. In addition, the interlaced conductive network is also beneficial for dissipating the incident EM waves through multiple scattering in the large surface area of MnO2. Prospectively, the synthetic strategy proposed in our work can be extended to the fabrication of other carbon-based microwave absorbing composites.