Highly regulated Fe₃O₄–polyelectrolyte-modified polyaniline (Fe₃O₄–PE@PANI) hollow sphere nanocomposites were successfully synthesized using an electrostatic self-assembly approach. The morphology and structure of the Fe₃O₄–PE@PANI nanocomposites were characterized using field-emission scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray powder diffraction, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The results showed that the as-prepared nanocomposites had well-defined sizes and shapes, and the average size is about 500 nm. The assembly process was investigated. Magnetization measurements showed that the saturation magnetization of the nanocomposites was 38.6 emu g⁻¹. It was also found that the Fe₃O₄–PE@PANI nanocomposites exhibited excellent reflection loss abilities and wide response bandwidths compared with those of PANI hollow spheres in the range 0.5–15 GHz. The Fe₃O₄–PE@PANI nanocomposites are, therefore, promising for microwave absorption applications.

Multiple-phase nanocomposites filled with carbon nanotubes (CNTs) have been developed for their significant potential in microwave attenuation. The introduction of other phases onto the CNTs to achieve CNT-based heterostructures has been proposed to obtain absorbing materials with enhanced microwave absorption properties and broadband frequency due to their different loss mechanisms. The existence of polyaniline (PANI) as a coating with controllable electrical conductivity can lead to well-matched impedance. In this work, a one-dimensional CNT@BaTiO3@PANI heterostructure composite was fabricated. The fabrication processes involved coating of an acid-modified CNT with BaTiO3 (CNT@BaTiO3) through a sol–gel technique followed by combustion and the formation of CNT@BaTiO3@PANI nanohybrids by in situ polymerization of an aniline monomer in the presence of CNT@BaTiO3, using ammonium persulfate as an oxidant and HCl as a dopant. The as-synthesized CNT@BaTiO3@PANI composites with heterostructures were confirmed by various morphological and structural characterization techniques, as well as conductivity and microwave absorption properties. The measured electromagnetic parameters showed that the CNT@BaTiO3@PANI composites exhibited excellent microwave absorption properties. The minimum reflection loss of the CNT@BaTiO3@PANI composites with 20 wt % loadings in paraffin wax reached −28.9 dB (approximately 99.87% absorption) at 10.7 GHz with a thickness of 3 mm, and a frequency bandwidth less than −20 dB was achieved from 10 to 15 GHz. This work demonstrated that the CNT@BaTiO3@PANI heterostructure composite can be potentially useful in electromagnetic stealth materials, sensors, and electronic devices.