Hierarchical construction of composite hollow structures of Co@CoO and their magnetic behavior

We report the facile wet-method to synthesize the cobalt hollow microspheres without surfactants, and then a series of Co@CoO composite hollow structures including Co@CoO concentric double-shell hollow spheres (CDSHS), Co@CoO hollow sphere in hollow sphere (HSIHS), and CoO hollow spheres are fabricated by simply oxidation-etching method in the same reaction system by adjusting reaction condition. The X-ray diffraction, electron diffraction, and X-ray photoelectron spectroscopy patterns evidence that the oxidized surface is composed of CoO, not Co3O4. The magnetism research shows Co@CoO CDSHS appears to have a ferromagnetic behavior below 6.7 K, which might attribute to the uncompensated spins on the surface of CoO shell.