Multi-wall carbon nanotube/Fe3O4 hybrids were prepared by a chemical synthesis-hydrothermal treatment method and their electromagnetic wave absorbing properties were investigated in the frequency range of 8.2–12.4 GHz (X band). As-prepared hybrids were characterized by transmission electron microscopy, X-ray diffraction and vibrating sample magnetometer. Results indicated that the surface of multi-wall carbon nanotubes was attached to magnetic Fe3O4 nanoparticles. The Fe3O4 content increased and the magnetism of the hybrids was enhanced by increasing the concentrations of Fe2+ and Fe3+ in solution. The minimum reflection loss (−18.22 dB, 12.05 GHz) was the lowest and the absorbing bandwidth was the widest when the concentrations of Fe2+ and Fe3+ were 0.02 and 0.04 mol/L, respectively.

Composites that effectively absorb microwave in the frequency range of 2–18 GHz have been strongly demanded during the past decades. To enhance the absorption of microwave, composites are generally capable of wide absorption bandwidth and low reflection loss. Here, we used La(NO3)3-doped multi-walled carbon nanotubes (MWCNTs) as absorber and polyvinyl chloride (PVC) as matrix to fabricate MWCNT-La(NO3)3/PVC composites, where La(NO3)3-doped MWCNTs broadened the absorption bandwidth and decreased the reflection loss of the composites. Due to the insertion of diamagnetic La3+, the absorbing properties of as-prepared composites were enhanced, while the mechanical properties of such composite were slightly changed. The amount of doped La(NO3)3 was experimentally optimized to be 6 wt.%.Highlights► Carbon nanotubes doped La(NO3)3 was used for the absorber. ► The frequency range of the reflectivity became larger below − 10 dB in 2–18 GHz. ► The minimum shifted to higher frequency region by doping La(NO3)3. ► The mechanical property slightly changed compare with no La(NO3)3-doped.