Surfactant-free large scale synthesis of Co3O4 quantum dots at room temperature

Co 3 O 4 quantum dots (QDs) with diameter of 3–5   nm were successfully prepared by a facile surfactant-free large-scale synthesis strategy at room temperature in ethanol. The formation of Co 3 O 4 QDs follows the sequence of Co 2+   +   2OH −   →   Co(OH) 2   →   CoOOH   →   Co 3 O 4 . It is demonstrated that the dissolved oxygen and the bubbling of compressed air are the two keys for the synthesis of Co 3 O 4 QDs. The produced Co(OH) 2 was oxidized to CoOOH by the oxygen dissolving in ethanol. In order to synthesize pure phase Co 3 O 4 QDs, compressed air has to be bubbled into the solution vigorously to promote the decomposition of CoOOH by removing the oxygen evolved from the decomposition reaction. Due to small particle size and inherent properties of Co 3 O 4 , the QDs have excellent electrochemical performance and high long-term electrochemical stability.