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Synthesis, morphological, optical and photocatalytic studies of lead sulfide and tin sulfide nanoparticles.

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Five dithiocarbamate ligands were synthesized from morpholine, thiomorpholine, N-(2-hydroxyethyl)aniline, 4-methylpiperidine, and 4-benzylpiperidine. Five lead(II) dithiocarbamate and five tin(II) dithiocarbamate complexes were synthesized from the dithiocarbamate ligands. The ligands and their respective lead(II) and tin(II) complexes were analyzed by NMR, FTIR, UV-Vis, elemental analysis and mass spectrometry. Two of the lead(II) complexes were characterized by single-crystal X-ray crystallography. The infrared spectra studies confirmed bidentate coordination of the dithiocarbamato anions to the metal(II) ions to form four coordinate complexes. Single crystal X-ray structures of bis(4-methylpiperidine-1-carbodithioato)-lead(II) and bis(4-benzylpiperidine-1-carbodithioato)-lead(II) confirmed four coordinate distorted tetrahedral geometries. The synthesized lead(II) and tin(II) complexes were used as single-source precursors to prepare fourteen metal sulfide nanoparticles. The optical and morphological properties of nanoparticles were studied using UV-Visible spectroscopy, photoluminescence (PL), powder X-ray diffraction (p-XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Nine lead sulfide nanoparticles were prepared using Pb(II) complexes as single-source precursors. Three lead(II) were thermolyzed at 180°C to investigate the effect of the precursor on the structural and optical properties of the PbS nanoparticles. To study the effect of capping agents on the structural and optical properties of the nanoparticles, the other two lead(II) complexes were each thermolyzed using three different capping agents, hexadecylamine (HDA), octadecylamine(ODA), and trioctylphosphine oxide (TOPO). The p-XRD diffraction patterns for all PbS nanoparticles were indexed to the face-centered cubic phase of PbS. The shape and particles sizes of the PbS nanoparticles were determined using HRTEM which showed some agglomeration and varying shapes from quasi-spherical to cubic shapes. Five Sn(II) dithiocarbamate complexes were thermolyzed at 180℃ to study the effect of precursor on the morphological and optical properties of the SnS nanoparticles. The p-XRD patterns revealed that the SnS nanoparticles have orthorhombic phase of SnS. SEM images showed varying surface morphology with different precursor and the EDX confirmed the presence of sulfur and metals in the particles. The optical studies revealed that the PbS and SnS nanoparticles are quantum confined as the calculated energy band gaps showed blue shift relative to bulk. The interaction of the capping agents with the nanoparticles was confirmed with FTIR. The as-prepared PbS and SnS nanoparticles were used as photocatalysts for the decomposition of methylene blue, rhodamine B, phenol and brilliant green. The photodegradation efficiencies of 47-75% for methylene blue, 30 - 45% for rhodamine B, 11-32 % for phenol and 90- 93% for brilliant green were observed. In the assessment of the influence of pH and recyclability studies of the as-prepared nanoparticles, the dyes were found to degrade better in the alkaline medium than in an acidic medium. The PbS nanoparticles were found to be recyclable up to four cycles and SnS were reusable for five cycles of photocatalytic reaction with good stability.


Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.