Synthesis of Nanorod-Shaped Cobalt Hydroxycarbonate and Oxide with the Mediation of Ethylene Glycol

Cobalt hydroxycarbonate nanorods are prepared by precipitation of cobalt acetate with sodium carbonate in ethylene glycol. Structural and chemical analyses of the intermediate phases during the precipitation and aging process revealed that amorphous cobalt hydroxide acetate is formed at the initial stage where ethylene glycol acts as a simple solvent and a coordinating agent. With the slow addition of sodium carbonate, carbonate anions are gradually intercalated into the interlayers by replacing the acetate and hydroxyl anions. This anion-exchange process induces a dissolution-recrystallization process in which ethylene glycol serves as a rate-controlling agent, producing rod-like cobalt hydroxide carbonate. During the aging process, ethylene glycol gradually incorporates into the structure to replace the carbonate and acetate anions; the interlayer structure is collapsed, and the nanorod-shape turns into thin crimped sheets. Co3O4 nanorods with a diameter of about 10 nm and a length of 200-300 nm are then obtained by calcination of the nanorod-shaped cobalt hydroxycarbonate precursor. This spontaneous shape transformation from the precursor to the oxide is attributed to the unique thermal stability of the cobalt hydroxycarbonate nanorods with the presence of ethylene glycol and acetate anions in the interlayers. The Co3O4 nanorods show a much superior catalytic activity for CO oxidation to the conventional spherical Co3O4 nanoparticles, clearly demonstrating the morphology-dependent nanocatalysis.