Solubility-Controlled Synthesis of High-Quality Co3O4 Nanocrystals

A liquid-phase redox process has been designed to prepare monodispersed Co3O4 nanocrystals with particle sizes of 2 nm (spherical), 2.5 nm (cubelike), and 4.7 nm (cubelike). The nanocrystals were characterized by transmission electron microscopy (TEM), high-resolution TEM, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric techniques. The nucleation and growth, which were tracked by UV−visible spectroscopy, can be separated by adjusting the solubility of sodium nitrate, and the smallest possible Co3O4 nanocubes, 2.5 nm on a side, were obtained. A solubility-controlled mechanism for the redox reaction is discussed which is critical in avoiding secondary nucleation and interparticle ripening growth of Co3O4 nanocrystals.