Sol-gel preparation and characterization of Co₃O₄ nanocrystals

A new citrate acid-hydrazine sol-gel route for preparation of Co₃O₄ nanoparticles has been developed. Co₃O₄ nanoparticles with different particle-sizes and morphology were prepared at different heat-treatment temperatures and the pure cubic nanocrystals of Co₃O₄ were obtained at 600℃. The synthesis process was monitored by infrared spectroscopy (IR), thermal gravimetric and differential thermal analysis (TG-DTA). The structure and morphology of Co₃O₄ nanocrystals were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and X-ray-photoelectron spectroscopy (XPS). The infrared absorption bands blue-shifted with particle size decreasing, which could be attributed to increasing surface effect. XPS results showed that predominant species at surface layers of Co₃O₄ nanocrystals are octahedral Co (Ⅲ).