Porous Fe₃O₄/Carbon Core/Shell Nanorods: Synthesis and Electromagnetic Properties

The porous Fe 3 O 4 /carbon core/shell nanorods were fabricated via a three-step process. α-Fe 2 O 3 nanorods were first obtained, and α-Fe 2 O 3 /carbon core/shell nanorods were subsequently fabricated using glucose as a carbon source by a hydrothermal method, in which the thickness of the carbon coating was about 3.5 nm. Fe 3 O 4 /carbon core/shell nanorods were synthesized after an annealing treatment of the product above under a mixture of Ar/H 2 flow. After the H 2 deoxidation process, the Fe 3 O 4 core exhibited a character of porosity; the thickness of the carbon shell was decreased to about 2.5 nm, and its degree of graphitization was enhanced. The interesting core/shell nanostructures are ferromagnetic at room temperature, and the Verwey temperature was about 120 K. Electromagnetic properties of the core/shell nanorod–wax composite were investigated in detail. The maximum reflection loss was about −27.9 dB at 14.96 GHz for the composite with a thickness of 2.0 mm, and the absorption bandwidth with the reflection loss below −18 dB was up to 10.5 GHz for the absorber with the thickness of 2–5 mm. The excellent electromagnetic wave absorption properties of the porous Fe 3 O 4 /carbon core/shell nanorods were attributed to effective complementarities between the dielectric loss and the magnetic loss.