Coaxial double-layer-coated multiwalled carbon nanotubes toward microwave absorption

A novel coaxial double-layer-coated multiwalled carbon nanotube (MWCNTs) was synthesized to obtain excellent electromagnetic-wave-absorbing materials. Hydrochloric-acid-doped polyaniline (PANI) served as the first shell via in situ redox polymerization using FeCl3 as the oxidizing agent. The introduction of PANI effectively solved the problem in which ferroferric oxide (Fe3O4)-coated carbon nanotubes had poor integrity and easily fell off in the previous experiment. After the reaction, the oxidizing agent directly provided Fe3+ and Fe2+ ions for the second Fe3O4 shell, which was deposited on the surface of hydrochloric-acid-doped PANI interlayer via coprecipitation. The hybrid fully combined MWCNTs with prominent dielectric properties and Fe3O4 with outstanding magnetic properties and showed excellent electromagnetic wave absorption performance with high reflection loss (−15.65 dB at 15.45 GHz) and broad effective bandwidth (←−10 dB) of 3.5 GHz (14-17.5 GHz) at lowest thickness (1.5 mm).