Mechanochemical synthesis of Ni(OH)2 and the decomposition to NiO nanoparticles: Thermodynamic and optical spectra

Nickel hydroxide (Ni(OH)2) was prepared through a mechanochemical route using simple manual milling. NiO nanoparticles were obtained through subsequent calcinations. X-ray diffraction (XRD), differential thermal analysis and thermal gravimetric (DTA/TG), transmission electronic microscopy (TEM), Fourier transforming infrared spectroscopy (FTIR) and ultraviolet to visible spectroscopy (UV-vis) were adopted to characterize the structural, morphological, and optical properties of the obtained NiO products. Intensive study to the DTA curves of the Ni(OH)2 precursor was conducted to understand the thermal behavior and derive the activation energy, for which the Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods were introduced and were applied respectively. The average activation energy required to de-composite the Ni(OH)2 precursor in ambient condition was 117.8 kJ/mol, which determined that the decomposition is controlled by the chemical reaction. NiO with cubic shape was obtained. Size of the products increased from 8.3 nm at 350 °C to 43.4 nm at 600 °C. Carbonates were found to co-exist with the product, which were generated in the preparing procedures. Band gap energy of the NiO was in the range of 3.30 ± 0.11 eV, which have no obvious relationship with the preparing conditions.