Synthesis and microwave absorbing properties of N-doped carbon microsphere composites with concavo-convex surface

Concavo-convex surface can increase the external surface area and provide multi-directional reflective surface, which has significant advantages in improving the microwave absorbing performance of materials. In this paper, a series of N-doped carbon microsphere composites with concavo-convex surface (NCMCCS) and their preparation method have been reported. The precursors organic-inorganic hybrid microspheres with concavo-convex surface (OHMCS) are synthesized by solvothermal method. NCMCCS with different ZnS and ZnO loadings are prepared by calcining OHMCS at different temperatures. Their microwave absorbing properties have been evaluated. NCMCCS obtained at different temperatures exhibit excellent microwave absorbing performance under optimal filler content. The samples calcined at lower temperature have significant advantages in low frequency. The maximum reflection loss (RL_max) of the sample obtained at 750 °C is −60.4 dB@7.2 GHz@3.7 mm, and the effective absorption bandwidth (EAB) is 2.6 GHz. The higher temperature calcined sample shows the characteristic of ultra-low filler content, the RL_max of the sample prepared at 900 °C reaches −46.8 dB@10.4 GHz@2.7 mm under a filler content of only 6%. Meanwhile, the microwave attenuation mechanism has been systematically analyzed and explained. This work provides a new way for constructing high efficiency microwave absorbers with complex surface.