Template-free synthesis of Co3O4 nanorings and their catalytic application

Abstract

A facile, template-free and easily scalable approach has been developed for the preparation of Co₃O₄ nanorings, which can be divided into two stages: (1) formation of CoOOH nanorings and (2) high-temperature calcination of CoOOH nanorings in air. The key step for the synthesis of Co₃O₄ nanorings is the formation of CoOOH nanorings, prepared by the oxidation of β-Co(OH)₂ nanoplates with H₂O₂ under strong basic conditions. The plausible growth mechanism governing the formation of CoOOH nanorings was correlated with Ostwald ripening. It was found that the dosage of H₂O₂ played a vital role in the formation of CoOOH nanorings. To a large extent, other experimental variables including the H₂O₂ concentration, Co²⁺ concentration, the molar ratio of Co²⁺ to OH⁻ and the reaction temperature did not affect the preparation of the CoOOH nanorings. Furthermore, the as-prepared Co₃O₄ nanorings exhibited superior activity in comparison with Co₃O₄ nanoplates and commercial Co₃O₄ towards the catalytic decomposition of H₂O₂. The apparent rate constant of the as-prepared Co₃O₄ nanorings was 0.38 min⁻¹, which is 2.2 times the value of Co₃O₄ nanoplates.