Rational design of multi-shell hollow carbon submicrospheres for high-performance microwave absorbers

Multi-shell hollow carbon submicrospheres (CSs) were designed for the improvement in microwave absorption performance. Solid/hollow CSs with a single shell or multiple shells were successfully synthesized by a combination of hydrothermal method, calcination, and etching process. Microstructures, dielectric and microwave absorption properties in the frequency range of 2–18 GHz of these CSs were compared and studied systematically to investigate the effect of the multi-shell hollow structure of CSs on the microwave absorption properties. Results revealed that the hollow and solid CSs had the same crystallinity, degree of graphitization, and carbon bonds. Thus, the improved complex permittivity and tangent loss of hollow CSs were mainly related to their unique structure. The multi-shell CSs possessed more reflections of microwaves and stronger conductive loss than the single-shell one. The enhanced polarization occurring on the interfaces among the different shells of the multi-shell hollow CSs improved the dielectric loss ability. The reflection loss (RL) of the triple-shell hollow CSs/paraffin composites therefore reached −48.5 dB with a wide effective absorption bandwidth (RL < −10 dB) of 4.2 GHz, which indicated that the multi-shell hollow CSs are promising high-performance microwave absorbers.