Facile synthesis of hollow porous cobalt spheres and their enhanced electromagnetic properties

We report a template-free approach to prepare hollow porous cobalt spheres by combining a facile solvent-thermal route with a chemical reduction process. The synthesized cobalt microspheres with diameter of approximately 2–4 μm have a shell thickness of about 150 nm. The hollow Co microsphere is built from particle-like ligaments with diameter of ca. 80–150 nm and there are a lot of pores with size of several tens of nm on the shell. The hollow porous cobalt spheres exhibited saturation magnetization (Ms) of 163.0 emu g−1 and large coercivity (Hcj) of 307.9 Oe. The epoxy resin composites with 30 wt% and 60 wt% hollow porous cobalt sample showed efficient EM wave absorption characteristics (RL < −20 dB) in the ranges of 11.3–18.0 GHz and 4.0–12.0 GHz over absorber thicknesses of 1.4–2.0 mm and 1.4–4.0 mm, respectively. Our study demonstrates the potential application of hollow porous ferromagnetic materials as a more efficient electromagnetic wave absorber.