Biomass-derived 3D-printed absorbers with enhanced microwave attenuation via multiphasic heterointerface engineering

To meet the stealth requirements of complex electromagnetic environments, efficient, lightweight, and engineering-compatible electromagnetic wave-absorbing materials (MAMs) are critically important. In this study, waste coffee grounds were used as the carbon source, and a multiscale interface-engineering strategy integrating surface functionalization, in situ heterostructure assembly, and macroscopic printing was proposed to fabricate a 3D-printable composite with outstanding microwave absorption performance. First, polydopamine (PDA)-coated coffee-ground-derived carbon was employed to induce N doping, which not only improved the impedance-matching characteristics of the material but also provided anchoring sites for Fe-MOF. Second, the in situ growth of Fe-MOF on the surface of the N-doped carbon constructed a C/PDA/Fe-MOF three-phase interface, enabling magnetic-dielectric coupling to optimize impedance matching and activating the synergistic polarization of multiscale defects. As a result, the material achieved an effective absorption bandwidth (EAB) of 6.31 GHz at a thickness of 1.96 mm, together with a minimum reflection loss (RL_min) of -73.54 dB. To further verify its application potential in complex electromagnetic environments, the powder was dispersed into a polypropylene (PP) matrix for FDM 3D printing, successfully achieving effective reduction of the macroscopic radar cross section (RCS).