One-step synthesis of different morphologies of magnetic Co modified by ethylenediamine

Stable cobalt (Co) nanosized particles (NPs) have been synthesized with core–shell structures, in which the core is hcp, the shell is amorphous. The morphology of these samples can be modified by addition of ethylenediamine (en), a strong chelating molecule for transition metal ions. Uniform-sized and monodisperse Co NPs were produced with the diameters as 2–5 nm when the ratios of Co2+ to en are 1:2 and 1:4. Uniform-sized and monodisperse hollow sphere-like magnetic Co NPs were fabricated when the ratio of Co2+ to en is 1:3, which the diameter was determined to be 285–305 nm, the thickness of the shell was 57–67 nm. Kirkendall effect was employed to explain the forming processes of the hollow structure. Different magnetic properties of the samples were obtained by changing the ratio of Co2+ to en. The samples exhibited excellent water treatment performance for removing Congo Red. The maximum adsorption capacity was calculated to be 49.9 mg/g.