Simple and facile synthesis of pure nanocrystalline spinel cobaltite by thermal decomposition of solid solution precursors

Abstract

Water assisted cobalt quinolinate complex with general formula [Co(Hqui)2(H2O)2], is used as the solid solution precursors for the synthesis of the spinel cobaltite at low temperature by convenient method (i.e., thermal decomposition). The cobalt precursor was characterized by spectroscopic, thermal and powder X-ray diffraction studies. The crystal and molecular structure of cobalt quinolinate complex is crystallized in monoclinic crystal system with P21/n space group. Generally, the quinolinate anion acts as a tridentate ligand to create polymeric structure, but in this complex, the anion attains bidentate (O, N) mode to generate monomeric structure and it is rare. The parent quinolinic acid (H2qui; λem. = 383 nm) and its complex displays a strong fluorescence emission at 405 nm when excitation at 330 nm. The compound exhibits endo-followed by exothermic decomposition to produce cobalt oxides around 450 °C by simultaneous TG–DTA method. The cobaltite (Co3O4) derived from the cobalt quinolinate solid solution precursor are obtained by heating the complex at 450, 550 and 650 °C in a silica crucible for 3 h in muffle furnace. The high homogeneity of spinel cobaltite nanoparticles were characterized by infrared, UV–Visible, powder X-ray diffraction, scanning electron microscope coupled with EDX analysis and transmission electron microscope studies. The characterization shows that the spinel cobaltite oxide is highly homogenous and nano crystalline nature (~ 70 nm).