Uniform cobalt carbonate nanopowders were synthesized through free-surfactant hydrothermal
treatment of a mixture of cobalt acetate and ammonium carbonate in an autoclave. The size, phase
and purity of CoCO3 particles were controlled by adjusting reaction time (05–24 h), temperature
(80–160 1C), and (1:6–1:0.5) (Co2þ:CO3 2) molar ratios. Pure cobalt carbonate nanoparticles were
obtained in high yield (94%) at 120 1C for 0.5 h, with (1:3) (Co2þ:CO3 2) molar ratio and crystallite size
in ranges 80–90 nm. Moreover, cobalt oxide nanoparticles with an average crystallite size of 25 nm
have been obtained by thermal decomposition of cobalt carbonate microspheres at 300 1C for 2 h.
Chemical structure of the products was confirmed by powder X-ray diffraction (XRD) and Fourier
transform infrared (FT-IR). Morphology of the products was investigated by transmission electron
microscope (TEM) and scanning electron microscope (SEM). Optical properties of Co3O4 nanoparticles
revealed the presence of two band gaps (2.0 and 1.46 eV) whose values confirm the purity and
semiconducting properties of the oxide.