Polyindole-Derived Nitrogen-Doped Carbon Nanosphere/Al2O3 Composites with High-Performance Microwave Absorption

In this study, polyindole-derived nitrogen-doped carbon nanosphere/Al2O3 (PINNC/Al2O3) composites are fabricated by hydrothermal, in situ aggregation and high-temperature pyrolysis using potassium aluminum sulfate dodecahydrate, urea, and indole as raw materials. The results show that the introduction of alumina modulates the impedance matching and results in the formation of a great deal of interfaces with polyindole-derived nitrogen-doped carbon nanospheres, which promotes the reinforcement of interfacial polarization. Moreover, the unique semicircular spherical structure of alumina and the pleated structure of carbon nanospheres facilitate multiple microwave attenuation. The abundance of in situ nitrogen atom doping in the carbon material and the defects that formed after pyrolysis can supply a great deal of polarization sites for dipole polarization, thus enhancing dipole polarization loss. As the matching thickness reached 2.5 mm, the minimum reflection loss (RL) of the PINNC/Al2O3 composites is −46.08 dB at 16.72 GHz (fill ratio of 0.5). And as the matching thickness is merely 3.0 mm, the effective absorption bandwidth (EAB) is 7.04 GHz. This study can serve as a good guide for the devising of polyindole-derived nitrogen-doped carbon-based electromagnetic microwave absorbents.