Hollow core–shell Co@SiO2@PPy composites with efficient electromagnetic wave absorption

In this study, hollow Co@SiO 2 @PPy composites with excellent electromagnetic wave (EMW) absorption performance were successfully synthesized. The monodisperse hollow Co microspheres were prepared using a solvent-thermal method. The microspheres were then coated with an SiO 2 layer by a modified Stöber method. Finally, the SiO 2 layer was surface-coated by polypyrrole (PPy) through in-situ polymerization to obtain Co@SiO 2 @PPy composite materials with hollow core–shell structures. The prepared CSP2 composite achieved a minimum reflection loss (RL min ) of −65.83 dB at 1.86 mm, demonstrating an effective absorption bandwidth (EAB) of 4.84 GHz. The CSP3 composite achieved a widest EAB (EAB max ) of 5.4 GHz at a thickness of 1.83 mm, while simultaneously maintaining the RL level at −50.70 dB. Additionally, it demonstrated an RL min value of −61.66 dB with a thickness as thin as 1.66 mm. The observed shift of FTIR absorption peaks by 20 cm −1 in the PPy ring provides compelling evidence for the involvement of multilayered structures in polarization loss. The SiO 2 layer not only enhances the interface polarization but also prevents corrosion of the Co core by acidic solutions. The exceptional EMW absorption characteristics can be attributed to the effective impedance matching and the combined effect of magnetic and dielectric losses.