The Outside-In Approach To Construct Fe3O4 Nanocrystals/Mesoporous Carbon Hollow Spheres Core–Shell Hybrids toward Microwave Absorption

It is widely accepted that building a core–shell structure is an effective way to modify impedance matching behavior and induce interfacial polarization relaxtion. In this work, we adopted a novel impregnation process and subsequent calcination treatment to construct Fe3O4 nanocrystals/mesoporous carbon hollow spheres (MCHS) core–shell hybrids. From the perspective of microwave absorption, MCHS possess favorable dielectric loss ability and lightweight features. Fe3O4 could produce magnetic loss and regulate impedance matching characteristics. Besides, hollow voids and mesopores facilitate microwave absorption, while multiple interfacial polarization induced between Fe3O4 nanocrystals and MCHS contributes to microwave attenuation. Combining these advantages, a maximum reflection loss value of −60.2 dB at 15.5 GHz and a broad effective bandwidth of 5.7 GHz can be achieved for the as-prepared sample at a thickness of 2.3 mm. Furthermore, the excellent microwave absorption properties with a ultrawide bandwidth of 8.0 GHz (10.0–18.0 GHz) at 2.6 mm of thickness was achieved. Therefore, the as-prepared hybrids can act as a lightweight and broadband microwave absorber; moreover, the corresponding method could be a sustainable and low-cost route for designing multicore–shell hybrids.