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 (R_L,min) and broadband effective absorption bandwidth (EAB) are achieved with only 10 wt.% filler loading. Specifically, the R_L,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.