Significant promotion of porous architecture and magnetic FeO NPs inside honeycomb-like carbonaceous composites for enhanced microwave absorption.

Carbonaceous composites with tailored porous architectures and magnetic FeO components derived from walnut shells were fabricated by a solvothermal method and used as effective microwave absorbers. The porous composites were obtained by two carbonization processes at different temperatures and an etching process using potassium hydroxide. The introduction of a developed porous architecture inside the resulting materials distinctly improved the microwave absorption performance. Moreover, investigations revealed that the FeO nanoparticles were chemically bonded and uniformly decorated on the porous framework without aggregation. Owing to the combined advantages of the lightweight conductive biochar-like porous framework with a favorable dielectric loss and FeO nanoparticles with magnetic loss features, these newly fabricated porous carbonaceous composites exhibited excellent microwave absorption performance. A reflection loss (RL) of -51.6 dB was achieved at a frequency of 13.6 GHz. Besides, the effective absorption (below -10 dB) bandwidth reached 5.8 GHz (from 11.9 to 17.7 GHz) at an absorber thickness of only 2 mm. These results indicated that this type of porous FeO-biochar composite derived from biomass substances and prepared an easy-to-handle process can be considered as attractive candidates for the design and manufacture of high-efficiency microwave-absorbing materials.