Thermolytic synthesis of cobalt and cobalt sulfide nanoparticles using Cobalt(II) N$\wedge $O Schiff base complexes as single molecular precursors

Authors: SANDILE H KHOZA, SIPHAMANDLA C MASIKANE, SIXBERTH MLOWE, ITEGBEYOGENE P EZEKIEL, THOMAS MOYO, NEERISH REVAPRASADU

Abstract: Two novel N$\wedge $O-type Schiff base ligands and the corresponding Co(II) complexes are reported. Thermogravimetric analysis indicated that the complexes are potential molecular precursors for the fabrication of cobalt and cobalt-containing nanomaterials. The significant difference in the thermal decomposition profiles is recognized as an influence of structural differences on the complexes. Thus, the complexes were thermally decomposed using the melt and hot injection methods to examine the properties of the obtained cobalt and cobalt sulfide nanoparticles, respectively. The reaction parameters employed during the fabrication processes, in addition to structural differences, influenced the morphological and crystallographic phases and magnetic properties of the synthesized nanoparticles. We have investigated the morphological properties and the crystallographic phase compositions of the nanoparticles by various electron microscopy and diffraction techniques, as well as energy-dispersive X-ray spectroscopy. The melt reactions produced phase-pure cobalt nanoparticles, which exhibit ferromagnetic behavior. The hot injection method utilized 1-dodecanethiol (DDT) as both sulfur source and capping agent. We indexed the DDT-capped cobalt sulfide nanoparticles to cubic Co$_{9}$S$_{8}$ and Co$_{3}$S$_{4}$ phases using powder X-ray diffraction, high-resolution transmission electron microscopy imaging, and selected area electron diffraction. The crystallite sizes for Co$_{9}$S$_{8}$ and Co$_{3}$S$_{4}$ nanoparticles, based on the Scherrer equation, were 12.4 nm and 14.1 nm, respectively. We find significant differences in the magnetic properties, attributed to nonmagnetic inclusions and vacancies due to the presence of S atoms.

Keywords: Cobalt, cobalt sulfide, melt, 1-dodecanethiol, Schiff base

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