Synthesis structural and optical studies of copper sulphide and silfide nanoparticles from Cu(II) and Ag(I) dithiocarbamate single source precursors.

Abstract

Eight dithiocarbamate ligands were synthesized from butylamine, diallylamine, N-ethyl aniline, N-methyl benzyl amine, piperidine, morpholine, dibenzyl amine and phenyl piperizine. Eight copper(II) dithiocarbamate complexes and Eight silver(I) dithiocarbamate complexes were synthesized. Spectroscopy techniques were used to characterise the obtained compounds. The structure of the synthesized dithiocarbamate ligands was confirmed using NMR spectroscopy. Proton NMR showed all the expected peaks and showed the ligands to be pure with no extra peaks for contaminations. 13C NMR showed the peak corresponding to the carbon in the carbon disulphide resonation at around 200 to 220 ppm in all the ligands confirming their formation.

FTIR was carried out for all the compounds, ligands and their corresponding metal complexes. In the ligands the C – S, C = S and C – N vibrations were observed corresponding to the dithio- moiety. In the copper complexes the C – S and C = S frequency merged and gave one vibration which confirmed the coordination of the metal to the ligands. UV-Visible was also used to confirm the geometry of the complexes. The ligands gave the bands corresponding to π – π* and n – π* due to N–C=S and S–C=S groups. The copper complexes showed the intra-ligand transitions and two extra bands in the visible region corresponding to the d-d transition of the square planar geometry of copper(II) complexes. Crystal structures of four complexes were isolated, two copper(II)complexes which confirmed the square planar geometry given by the UV-Vis data and two Silver(I) complexes. However, it turned out that silver complexes obtained are the metal clusters. The sixteen metal dithiocarbamate complexes were used as single source precursors to synthesize thirty-two metal sulphide nanoparticles. Four single source precursors, from each metal ion were thermolyzed at 220°C to study the effect of the precursor on the nanoparticle structural and optical properties. The other four precursors for each metal ion were further thermolyzed at three different temperatures, 220°C, 180°C and 120°C, to study the influence of the temperature on the structural and optical properties of the nanoparticles. The obtained nanoparticles were further studied using p-XRD. The X-ray data showed the copper sulphide nanoparticles to have Cu1.8S digenite phase. Silver sulphide nanoparticles have α-Ag2S phase that is usually obtained at lower temperature. The shape and crystallite sizes of the nanoparticles were determined using TEM/HRTEM.

TEM images showed the silver nanoparticles synthesized at 220°C all adapted the same spherical shape that are monodispersed. Their size ranged from 8 nm to 78 nm. When the thermolysis was done at 180°C the sizes ranged from 5 to 71 nm and 2-23 nm when thermolyzed at 120°C. For the copper sulphide nanoparticles synthesized at 220°C the size ranged from 5 to 125 nm. 180°C and 120°C gave size ranges of 10 to 55 nm and 4 to 40 nm respectively. The copper sulphide nanoparticles showed some effect of agglomeration and a mixture of shapes from spherical to hexagonal shapes. Their surface morphology was examined with SEM and they changed with different temperature and precursors. EDX was used to confirm the metals and sulphur present in the particles. The interaction of the capping agents and nanoparticles was studied by FTIR. Their optical properties were studied using photoluminescence and UV-Visible spectroscopy. The nanoparticles were found to be quantum confined as the estimated band gap energies showed blue shift when compared to that of the bulk.