Hydrothermal Synthesis of Co(II) Complex, a Precursor for the Synthesis of Octahedral Co3O4 Nanoparticles :An Active Catalyst for the Removal of Cr(VI)

This work presents the hydrothermal synthesis of [Co(2,2-bipyridine)(2)(NCS)(2)] (1) (150 degrees C, 48 h). The structure of 1 was characterized step by step by elemental analysis CHN, atomic absorption spectroscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential thermal analysis and single crystal X-ray diffraction. Complex 1 crystallizes in orthorhombic structure with space group Pbca of expected composition. The full geometry optimization and energy values of the highest occupied molecular orbital and the lowest unoccupied molecular orbital were performed using GAUSSIAN 09. Magnetic characterization of complex 1 revealed a paramagnetic behavior at room temperature. Complex 1 was used as a significant precursor to prepare nanoparticles of Co3O4 by thermal decomposition process. The obtained Co3O4 was characterized by various techniques such as FT-IR spectroscopy, powder X-ray diffraction, nitrogen adsorption-desorption isotherms, scanning electron microscope and vibrating sample magnetometer. Co3O4 nanoparticles revealed a ferromagnetic behavior at room temperature. The SEM images of Co3O4 nanoparticles showed an octahedral morphology with a particle size of about 25 nm. Complex 1, commercial, and synthetic Co3O4 nanoparticles were used for the removal of Cr(VI) ions from the aqueous solution. The results showed that Co3O4 nanoparticles which obtained through thermal decomposition of inorganic complex could be employed as an efficient adsorbent for the removal of Cr(VI). Batch adsorption studies were conducted to find the optimal adsorption conditions such as contact time and pH. The results indicate that the adsorption kinetics data followed a pseudo-second-order model.