Size-controlled growth of Co3O4 nanocubes

Recently we investigated a nitrate-salt-mediated formation route of Co3O4 spinel nanocubes with a uniform size of ca. 47 nm in aqueous solution at 95 degreesC (J. Phys. Chem. B 2003, 107 (4), 926-930). In the present work, we examined various synthetic parameters of this new method. By varying reaction temperature and time, the size control of Co3O4 nanocubes has been achieved, which produces the spinel nanocubes with a controllable edge length in the regime of 10-100 nm. A linear relationship between the cube size and reaction time has been revealed. Furthermore, a process has been developed to separate (or to purify) the growing Co3O4 nanocubes from remaining solid products at different synthetic stages. With a large amount of nitrate salt added, we have been able to observe some irregular crystalline intermediates, although the majority of the Co3O4 nanocrystals have highly symmetrical cubelike morphology. On the basis of the observed crystallite morphologies, we have elucidated in this work a mechanism - "surface wrapping" - to describe the size-controlled growth of Co3O4 nanocubes.