Facile synthesis of size-tunable, multilevel nanoporous Fe3O4 microspheres for application in electromagnetic wave absorption

Multilevel nanoporous Fe3O4 microspheres were solvothermally synthesized using a functionalized ionic liquid [BMIM][FeCl4] as the iron source. Size of these microspheres could be easily tuned over the range of 26-411 nm by varying the volume ratio of alkali solution added. SEM, TEM and BET isotherm characterizations confirmed that Fe3O4 microspheres were formed by the assembly of nanoparticles with several nanometers in diameter and had a multilevel pore structure, including quasi-micropores, mesopores and macropores in/on each microsphere. The electromagnetic parameters of the Fe3O4 microspheres indicated that those nanopores contributed to the increase of dielectric loss and made an effective impedance match between dielectric loss and magnetic loss, thus enhancing the electromagnetic wave absorption of Fe3O4 microspheres. The minimum reflection loss of 80 wt% Fe3O4/epoxy resin composites showed excellent dual adsorptions at both low frequencies and high frequencies (−40.0 dB at 1.4 GHz with a sample thickness of 5.7 mm and −25.3 dB at 16.5 GHz with a sample thickness of 3 mm), which were related to the magnetic loss and dielectric loss offered by the porous Fe3O4 microspheres.