Size-tunable hollow mesoporous carbon spheres for high-efficiency microwave absorption

Hollow mesoporous carbon spheres (HMCS), which feature a hollow core and a shell with uniformly sized mesopores, are highly promising microwave absorbers due to their unique structure, tunable electrical properties, and excellent stability. In this work, HMCS with varying sphere sizes were designed and fabricated by adjusting the amount of formaldehyde in an efficient core-shell assembly process, followed by carbonization and etching. The results indicated that optimal sphere size and Brunauer–Emmett–Teller (BET) surface area significantly enhanced the energy–dissipation capacity and impedance match to free space. The optimal sample, HMCS-3, delivered a minimum reflection loss (RL_min) of −51.70 dB and achieved an effective absorption bandwidth of 7.24 GHz at a thickness of 2.6 mm. The superior performance originates from the synergy between intrinsic attenuation mechanisms and the structural advantages of HMCS, particularly their unique porous nanoscale architecture. This work provides useful insights into designing high–attenuation microwave absorbers.