In situ synthesis of hierarchical rose-like porous Fe@C with enhanced electromagnetic wave absorption

To satisfy the requirements of high-performance electromagnetic wave absorbers, composites of carbon and ferromagnetic metal with designed morphologies and abundant interfaces are highly desirable to balance impedance matching and attenuation. However, the synthesis of composites to meet these requirements and analysis of the electromagnetic wave energy loss mechanism remain great challenges. In this study, hierarchical rose-like assemblies of carbon-wrapped iron (Fe@C) nanoparticles with a porous structure were successfully synthesized via an in situ route using an iron alkoxide precursor with a rose-like morphology. Under the studied pyrolysis atmosphere and temperature, rose-like Fe@C and pure iron can be well modulated. The carbon shell is graphitic and highly ordered due to the catalytic effects of the iron nanoparticles, which affect the electromagnetic properties of the composites. The electromagnetic wave absorption properties of the Fe@C composite and iron are estimated in the frequency range of 2.0-18.0 GHz, and as expected, the hierarchical rose-like porous Fe@C demonstrates outstanding reflection loss characteristics with a minimum value of -71.47 dB with a thin matched thickness of 1.48 mm. Moreover, an ultra-wide response bandwidth (reflection loss of less than -10 dB) of 2.88-18.0 GHz is achieved. Analysis of the electromagnetic properties revealed that the hierarchical rose-like Fe@C presents very different electromagnetic functions in comparison to pure iron and Fe@C particles without the rose-like structure derived from the iron alkoxide precursor with the same structure. The carbon shells and special morphology with a certain microstructure can effectively regulate the complex permittivity and permeability to modify the impedance matching characteristic as well as enhance the attenuation ability via electromagnetic wave multiple reflection and scattering in the hierarchical rose-like Fe@C particles. Analysis of the attenuation constant and matched characteristic impedance validates that the enhanced electromagnetic wave absorption of the rose-like Fe@C with a porous structure is due to the significant enhancement of matched impedance and collective multiple loss mechanism.