Hollow size optimization of α-MoC modified nitrogen-doped carbon spheres for efficient microwave absorption

Recently, electromagnetic pollution has become a serious concern. Existing microwave absorbers cannot achieve the goals of being lightweight, broadband, and strongly absorbing simultaneously. The design of hollow structures has attracted a great deal of attention because they can optimize impedance matching and enhance microwave attenuation while reducing mass. However, the effect of the hollow size on microwave absorption is not yet clear. In this study, we synthesized nitrogen-doped hollow carbon microspheres embedded with alpha-MoC nanoparticles (alpha-MoC/C, MNC) using template pyrolysis. The hollow size of MNC nanospheres was successfully controlled by adjusting the size of carboxylated PS nanospheres. The hollow structure improves microwave absorption in MNC nanospheres by facilitating the construction of the 3D conductive network. This prevents carbon aggregation, improves impedance matching, increases conductive loss, and promotes multiple reflections and scattering. Additionally, the alpha-MoC nanoparticles embedded in the carbon shells generate abundant nanointerfaces, which promote interfacial polarization and further attenuate the electromagnetic waves. The MNC3 sample with the carbon sphere size of around 300 nm achieved the best reflection loss of -58.9 dB (3.16 mm thickness) and an effective absorption bandwidth of 4.80 GHz (2.07 mm thickness). This work demonstrates that the microwave absorption capacity of nanoscale carbonaceous spheres is effectively enhanced by adjusting the hollow size, providing the basis for designing and optimizing wave-absorbing materials by hollow structure.