Porous magnetic carbon spheres with adjustable magnetic-composition and synergistic effect for lightweight microwave absorption

The chemical composition of reduced magnetic particles strongly correlates with the reduction potential of their metal species. However, this phenomenon rarely has been investigated in magnetic-dielectric absorbers. In this manuscript, a formaldehyde-assisted metal-ligand crosslinking strategy is employed to incorporate different metal species (Fe3+, Co2+, Co2+-Ni2+) into the colloidal frameworks by the chelating coordination. Because of their different reduction potentials, porous magnetic carbon spheres (PMCSs) with adjustable magnetic-composition and micro-mesoporous characteristics are constructed via the subsequent annealing process. Compared with self-assembly polyphenol derived porous carbon spheres (PCSs), these PMCSs, including Fe3O4-PMCSs, Co-PMCSs and CoNi-PMCSs, exhibit promoted impedance matching and superior microwave absorption attenuation owing to the additional magnetic resonance and synergistic effect. As results, the optimal reflection loss and corresponding bandwidth are −48.6 dB and 7.8 GHz, −45 dB and 8.6 GHz, −53.2 dB and 5.1 GHz for Fe3O4-PMCSs, Co-PMCSs and CoNi-PMCSs with only 15 wt% filler loading, both are higher than PCSs (−39.3 dB and 4.8 GHz). This study inspires us a novel inspiration in constructing of adjustable magnetic-composition and the fabricated PMCSs can be used as lightweight microwave absorbers in the application of electromagnetic protection.