Size-controlled synthesis of CoCO3 and Co3O4 nanoparticles by free-surfactant hydrothermal method

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 °C), and (1:6–1:0.5) (Co2+:CO32−) molar ratios. Pure cobalt carbonate nanoparticles were obtained in high yield (94%) at 120 °C for 0.5 h, with (1:3) (Co2+:CO32−) 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 °C 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.

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► Cobalt carbonate nano-architectures were prepared via hydrothermal approach.
► Spinel cobalt oxide nanoparticles were prepared by thermal decomposition at 300 °C.
► The optical characteristics of the as-prepared cobalt oxide revealed the presence of two band gaps.