Facile manufacturing of core-shell MnO@C microspheres toward enhanced electromagnetic wave attenuation

Exploring highly efficient electromagnetic wave (EMW) absorbing materials with strong absorption and low density is a viable strategy to address the growing issue of electromagnetic pollution. A type of carbon-coated MnO (MnO@C) microspheres with enhanced EMW absorption properties was synthesized via the precipitation method, followed by a facile sol-gel process. The results demonstrate that the carbon source content is critical in determining the thickness of the carbon shell, which in turn has a great impact on impedance matching and attenuation constant. Due to the moderately complex permittivity of MnO@C microspheres, the minimum reflection loss (RLmin) reaches -43.69 dB at 15.03 GHz with an ultra-thin matching thickness of only 1.53 mm. Additionally, the corresponding effective absorption bandwidth (EAB) is 4.81 GHz. The enhanced performance can mainly be attributed to appropriate impedance matching and multiple attenuation mechanisms, including interfacial polarization, defect-induced polarization, and conduction loss. Therefore, the MnO@C microspheres are considered to be suitable for high-efficiency microwave absorbers.