Metal-phenolic coordination crystals derived magnetic hollow carbon spheres for ultrahigh electromagnetic wave absorption

Owing to the tunable compositions and versatile functionality, the development of eco-friendly metal-phenolic coordination crystals derivatives is highly anticipated for electromagnetic wave absorption. In this study, three kinds of magnetic hollow carbon spheres (HCSs) with macro-meso-microporous characteristics, including Fe/HCS, Co/HCS, and CoNi/HCS, are successfully fabricated via the co-operative hard template and self-assembling process, in which magnetic particles are encapsulated in carbon shell matrix after the pyrolysis of metal-polyphenol coordination crystals and further subsequent template removal. On the one hand, hierarchical macro-meso-micropores effectively balance the impedance gap between absorbers and air and introduce structural defects or distortion, leading to matched impedance and enhanced dipolar/defect polarization. On the other hand, wrapped magnetic particles provide uncountable hetero-interfaces and induce ferromagnetic resonance, resulting in strengthened interfacial polarization and additional magnetic loss. In particular, enhanced minimum reflection loss (RL,min) and broadband effective absorption bandwidth (EAB) are achieved with only 10 wt.% filler loading. Specifically, the RL,min and EAB values are -57.5 dB and 7.2 GHz for Fe/HCS, -50.0 dB and 5.8 GHz for Co/HCS, and -52.1 dB and 6.7 GHz for CoNi/HCS, respectively. Moreover, this work provides us a modular-assembly strategy to regulate the hollow cavity of absorbers and simultaneously manipulates the chemical components of absorbers to regulate electromagnetic wave absorption performance.