Synthesis and optical properties of cubic Co3O4 nanoparticles via thermal treatment of a trinuclear cobalt complex

Cubic cobalt oxide nanoparticles with the formula of Co3O4 were synthesized via thermal treatment in air, using [CoII{(µ-L)(µ-OAc)CoIII(NCS)}2]; [H2L=salen=1,6-bis(2-hydroxyphenyl)-2,5-diazahexa-1,5-diene]; as precursor. Effect of calcination temperature and citric acid, as emulsifier, was investigated on the phase formation and particle size distribution of the products. Calcination of the precursor at 600 °C in the presence of citric acid results in the formation of Co3O4 nanoparticles with the average crystallite size of ∼13 nm. The presence of citric acid provides conditions for the formation of more pure Co3O4 crystalline phase with smaller particles. The as-prepared nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), particle size analyzer (PSA), transmission electron microscopy (TEM), UV–vis and Photoluminescence (PL) spectroscopies. The optical property studies indicate that the absorption peaks of Co3O4 nanoparticles, prepared in the presence of citric acid, shift towards short wavelengths. This blueshift is related to the quantum size effect.