Synthesis of hollow Fe₃O₄ microboxes guided by the hard and soft acid-base principle for enhanced electromagnetic wave absorption

A novel strategy based on the hard and soft acid-base (HSAB) principle to synthesize high-quality Fe3O4 microboxes was investigated. Initially, an Fe3O4 thin shell was generated on the surface of Cu2O cubic templates by meticulously regulating the hydrolysis kinetics of Fe3+. The Cu2O templates were then selectively dissolved using NH4Cl as an etchant, in conjunction with the reduction of Fe3+, yielding the hollow architectures of Fe3O4 microboxes. Capitalizing on the inherent merits of the hollow microstructures, the Fe3O4 microboxes exhibited superior electromagnetic wave (EMW) absorption efficiency. The Fe3O4 microboxes/paraffin composites demonstrated remarkable EMW absorption performance. A sample with 60 wt% loading and 1.16 mm thickness achieved the minimum reflection loss (RLmin) of - 35.9 dB at 16.2 GHz, with an effective absorption bandwidth (EAB) of 3.5 GHz.