Cobalt oxide (Co3O4) nanorings prepared from hexagonal β-Co(OH)2 nanosheets

Hexagonal cobalt hydroxide (β-Co(OH)2) nanosheets over a size range from 100 nm to 1 μm were synthesized using a very simple hydrothermal route with cobalt naphthenate as the cobalt source. Additionally, hexagonal cobalt oxide (Co3O4) nanorings over a size range from 100 nm to 1 μm consisting of cubic nanocrystals were obtained via a hydrothermal method using as-prepared β-Co(OH)2 nanosheets as the precursors. A probable mechanism of formation of the hexagonal Co3O4 nanorings is proposed on the basis of time-dependent experimental results.

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► Hexagonal cobalt oxide (Co3O4) nanorings can be obtained via a simple hydrothermal method using acetic acid and precursors (as-prepared hexagonal β-Co(OH)2 nanosheets).
► The hexagonal Co3O4 nanorings can be controlled by adjusting the size of the precursor.
► Etching and oxidation are responsible for the formation of the Co3O4 nanorings.