Rational construction and microwave absorption properties of porous FeOx/Fe/C composites

To satisfy the growing demand for military and civil applications, it is necessary to develop high-efficiency microwave-absorbing materials. Herein, a pyrolysis process was developed to construct FeOx/Fe/C composites using filter papers saturated with ferric nitrate solution as the precursor. The three-dimensional textures of filter paper are well maintained during the pyrolysis process. Ferric nitrate is decomposed to Fe2O3 and subsequently reduced to Fe2O3 and Fe nanoparticles embedded in the carbon matrix via carbothermal reduction. Various gases produced during the pyrolysis process create foam and generate additional nanoscale pores in the carbon matrix. The chemical composition and structure of composites can be tailored by controlling the pyrolysis conditions. The microwave absorption properties of FeOx/Fe/C composites are closely related to the chemical composition and structure. The optimized product shows excellent microwave absorption properties: The strongest reflection loss (RL) is -37 dB at -12 GHz; the effective absorption bandwidth (RL < -10 dB) is 6.5 GHz with a thickness of 2.0 mm. The superior absorption properties of the optimized product can be ascribed to the synergies of multiple chemical components, hierarchically porous structures and abundant interfaces. This study also suggests a large-scale synthesis strategy for high-yield carbon-coated magnetic nanoparticles for high-performance microwave absorption materials. (C) 2020 Elsevier B.V. All rights reserved.