Synthesis and structural studies of NiS and PdS nanoparticles/nanocomposites from dithiocarbamates single source precursors

Abstract

The main aim of this research is to synthesize Ni(II) and Pd(II) dithiocarbamate complexes and use them as single source precursors for the synthesis of NiS and PdS nanoparticles and metal sulphides potato starch nanocomposites. Four dithiocarbamate ligands were synthesized and characterized using elemental analysis and spectroscopic techniques. The ligands were used to prepared homoleptic Ni(II) and Pd(II) complexes of the dithiocarbamate ligands. The metal complexes were characterized with elemental analysis, UV-Vis, FTIR and 1H-NMR spectroscopic techniques. Conductivity measurements indicate that all the complexes are non-electrolytes in solution and results from the electronic spectra studies confirmed the proposed 4-coordinate square planar geometry around the metal ions. The nickel complexes showed d-d transitions around 477 nm while in the palladium complexes, no d-d transitions were observed but the compounds showed strong metal to ligand charge transfer transitions. From the FTIR spectra studies, it can be confirmed that the complexes were successfully synthesised because all peaks of interest were observed at expected regions from the literature. The νC-N was observed around 1469-1495 cm-1, νC=S around 1101-1188 cm-1 and νC-S around 738-1060 cm-1 for both Ni(II) and Pd(II) complexes. νNi-S was observed around 375-543 cm-1 and νPd-S around 529-545 cm-1. The FTIR also confirmed that the dithiocarbamate ligands act as bidentate chelating ligands through the sulfur atoms. The complexes were used as single source precursors and thermolysed in hexadecylamine (HDA) at 220 °C to prepare four HDA-capped nickel sulfide nanoparticles and four palladium sulfide absorption spectra, photoluminescence, powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The optical studies results showed that NiS have large band gaps that are greater than that of the bulk, therefore they are found to be blue shifted relative to the bulk, which shows that they have small particle size and thus confirming their quantum confinement effect. PL spectra reveal that the emission peaks are red shifted compared to the absorption band edges of the nanoparticles. The XRD patterns confirmed the formation of cubic and rhombohedral phase for NiS nanoparticles and cubic phase for PdS nanoparticles. SEM images of both NiS and PdS show uniform surface morphology at low and high magnification with different shapes. EDS analyses confirmed the presence of Ni, S, and Pd in each of the spectrum indicating that the nanoparticles were successfully synthesized. TEM images showed that the synthesised nanoparticles have uniform and narrow size distribution with no agglomeration. The sizes of the NiS nanoparticles were found to be in the range of 12-38 nm for NiS1, 8-11 nm for NiS2, 9-16 nm for NiS3 and 4-9 nm for NiS4. The TEM images for the as-prepared PdS nanoparticles showed that the average crystallite sizes are 6.94-9.62 nm for PdS1, 8-11 nm for PdS2, 9-16 nm for PdS3 and 4-9 nm for PdS4 respectively. The nanoparticles were used to prepare potato starch nanocomposites and SEM images indicate that the surface morphology of starch polymer nanocomposites compose of potato starch and few particles in between the pores of the matrix, this is due to the small ratio of nanoparticles used.