Uniform core–shell PPy@carbon microsphere composites with a tunable shell thickness: the synthesis and their excellent microwave absorption performances in the X-band

Abstract

Highly uniform core–shell polypyrrole@carbon microspheres (PPy@CM) have been successfully constructed by oxidation polymerization of pyrrole as the shell on the core of carbon microspheres. The thickness of the PPy shell can be easily controlled by modulating the weight ratio of pyrrole monomer and carbon microspheres. Hydrophilic carbon microspheres with abundant hydroxyl groups have a very strong affinity to the conjugated chains of PPy, which is responsible for the spontaneous formation of the uniform core–shell structure. Coating the PPy shell on the carbon core could increase the complex permittivity and dielectric loss due to an additional interfacial polarization. With a proper thickness of the PPy shells, the improved dielectric loss would be induced. The microwave absorbing properties of the PPy@CM powders were investigated by dispersing them in paraffin wax with 40 wt% powders in the frequency range of 2–18 GHz. The PPy@CM-0.6 (0.6 g CM) sample exhibits the maximum reflection loss of −38.1 dB at 11.6 GHz and a bandwidth of less than −10 dB covering 11.17 to 12.26 GHz with the thickness of 3 mm. In addition, the absorption peak sites and bandwidth of the PPy@CM composites can be easily modulated not only by the thickness of the absorbers but also of the PPy shell of the PPy@CM composite. Thus, the PPy@CM composites can be considered as a new type of promising lightweight microwave absorbers to satisfy the applications of microwave absorption in the 8–18 GHz range.