Broadband microwave-absorbing GO–CNT nanocomposites enabled by synergistic FeCoNi ternary catalysis

The realization of strong attenuation and broadband microwave absorption in carbon-based materials through controllable structural design remains highly challenging. In this work, a three-dimensional graphene oxide-carbon nanotube (GO-CNT) network is constructed by <i>in situ</i> growth of carbon nanotubes on graphene oxide substrates <i>via</i> chemical vapor deposition, using melamine as the carbon source and a ternary Fe-Co-Ni synergistic catalyst. Subsequent oxidation yielded a composite material featuring spinel oxide shell structures. The N-doped graphitized framework and uniformly dispersed alloy nanoparticles cooperatively form continuous conductive pathways and abundant heterogeneous interfaces, facilitating efficient dissipation of electromagnetic energy. After oxidation, the introduction of spinel-type oxide shells and additional surface defects finely regulates the balance between dielectric and magnetic responses. As a result, GO-CNTs exhibit a minimum reflection loss (RL_min) of -49.4 dB and an effective absorption bandwidth (EAB) of 4.33 GHz at a thickness of 2.2 mm, whereas the oxidized GO-CNT-O sample achieves an EAB of 5.33 GHz at a reduced thickness of 1.8 mm while maintaining an RL_min better than -35 dB. This complementary behavior demonstrates that oxidation-mediated regulation of <i>ε</i>-<i>μ</i> coupling with a single three-dimensional carbon network enables switching between deep-attenuation and broadband-absorption modes under thin-layer conditions. This study provides a practical and scalable route to tunable microwave-absorbing materials and lays a foundation for the integrated application of multidimensional carbon networks in advanced electromagnetic protection systems.