Morphology-controlled self-assembly synthesis and excellent microwave absorption performance of MnO2 microspheres of fibrous flocculation

Pure dielectric absorbers with a tunable wide-band response and strong attenuation capability for electromagnetic wave (EMW) absorption are challenging to synthesize. Herein, a series of hierarchical MnO2 microspheres composed of MnO2 nanofibers are synthesized via a simple one-step hydrothermal method. By varying the hydrothermal synthesis conditions, the surface architectures of the MnO2 microspheres could be adjusted, thereby tuning their EMW absorption performance. In addition, nickel doping causes defects in the MnO2 nanofibers, which further boosts microwave absorption performance. Compared to 2D MnO2 nanorods, the hierarchical microspheres formed by the self-assembly of MnO2 nanofibers offer tunable microwave absorption in the X and Ku bands. The Ni-doped microspheres with the optimized morphology show a maximum reflection loss of 40 dB is observed at 8.31 GHz, and an effective absorption bandwidth of 6.1 GHz at 2 mm thickness.