Broad Ku-Band Microwave Absorption of the Prussian Blue Analogue-Derived FeCo@NC/ g -C3N4 Hollow Nanocubes

Abstract Hollow nanostructured microwave absorbers based on FeCo-PBA/PDA and coated with g-C3N4 were fabricated via a facile pyrolysis approach, yielding the FeCo@N-doped C/g-C3N4 hollow nanocubes. The phases, morphologies, and microwave absorption properties in 2–18 GHz of the nanocubes were systematically characterized to clarify the effect of the inner/outer dual interfaces on the electromagnetic properties at microwave frequencies. The results indicate that the g-C3N4 coating lowers the outer interfacial impedance of the N-doped carbon frameworks and facilitates microwave penetration. In contrast, the inner interface consists of the carbon matrix embedded with FeCo/C core/shell nanoparticles, with a high impedance enabling multiple scattering. Besides, the introduction of g-C3N4 decreases the carbon content in the composites, thereby depressing the overall dielectric attenuation. The sample with FeCo-PBA/PDA:melamine mass ratio of 1:0.5 demonstrates the optimal microwave absorbing performance at 16.04 GHz with a minimum RL of –55.98 dB and an ultra-thin thickness of 1.775 mm, as well as a maximum effective absorbing bandwidth (RL < –10dB) of 5.76 GHz at 1.9 mm. Furthermore, the competing effects of the inner/outer impedance and the polarization modulation, as well as the nanoarchitecture design, on the tunable microwave absorption performance were discussed.