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Thiosemicarbazone, xanthate and dithiocarbamate single source precursors for cadmium, lead and indium sulfide nanoparticles

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dc.contributor.advisor Revaprasadu, N.
dc.contributor.author Masikane, Siphamandla Cecil
dc.date.accessioned 2019-08-28T10:36:49Z
dc.date.available 2019-08-28T10:36:49Z
dc.date.issued 2018
dc.identifier.uri http://hdl.handle.net/10530/1801
dc.description Thesis Submitted for the Degree of Doctor of Philosophy (PhD) In the Department of Chemistry, Faculty of Science and Agriculture at the University of Zululand, 2019. en_US
dc.description.abstract The work outlined in this thesis entails recent advances in reaction protocols to afford high quality nanoparticles. It also incorporates practices of green chemistry to ascertain that the quality of nanoparticles does not take precedence over environmental impacts, pre and post-synthetic processes. Furthermore, the work has provided a step towards opening new horizons in the research field of nanoparticles and related nanomaterials, particularly on introducing other reaction parameters which have not been either explored or exploited prior to this work. All the aspects mentioned above have, and not limited to, been objectives of the individual studies presented in this work. Thus, they have been easily dealt with following a chapter approach, as outlined below. In the first chapter, the emphasis is on the fundamental aspects of nanomaterials and nanoscience. The scope of this literature review chapter is narrowed to synthetic protocols which provide access to the manipulation of the properties of the nanomaterials to suit a specific application. The synthetic protocols focus on the use of metal-organic compounds as molecular sources; a similar approach which has been applied in the studies reported in this thesis. Examples on common applications that exploit the properties of the nanomaterials are also outlined briefly. In the second chapter, eight CdX2 (X = Clˉ, Iˉ) thiosemicarbazone complexes were prepared and subsequently evaluated as single source molecular precursors towards the fabrication of oleylamine-capped CdS nanoparticles through a solvent thermolysis route. Various reaction parameters were explored with respect to the properties of the nanoparticles obtained. A combination of reaction temperature and the nature of ligands on the Cd(II) centre showed a significant influence on the particle size, morphology and optical absorption properties of the nanoparticles. Different analytical tools were used to establish the properties of the nanoparticles, among them are powder X-ray diffraction, the transmission electron microscopy and UV-Vis spectroscopy. The chapter recognized the crucial importance of facilitating ligand addition reaction as opposed to the common practice of substitution reaction in the preparation of single source molecular precursors. This retains the halide ligands present in the parent metal halide salt used. These halide ligands were found to have v a relatively major influence on the particle size, morphology and absorption optical properties compared to the thiosemicarbazone ligands. The third chapter reports the work which is a sequel to the second chapter, albeit investigating the broader halide series (i.e. Clˉ, Iˉ and Brˉ) and a non-halogenated counterpart on the material mostly reported to prefer a cubic-like morphology, PbS. Thus, the study focused mainly on the morphology control. For this purpose, one thiosemicarbazone ligand was chosen due to the consistency in trends observed in the previous chapter, while the halide ligands were varied. Four Pb(II) cinnamaldehyde thiosemicarbazone complexes were prepared and used for this study. Morphology control was significantly minor; however, particle shape could easily improve (to perfect cube) or deteriorate (to irregular cube) based on the combination of halide ligands and reaction temperature. Regardless of shape transformation, the particle sizes showed an increase with reaction temperature. The main aim of the fourth chapter was to devise eco-friendly synthetic protocols to afford non-toxic semiconducting nanoparticles, an alternative to those reported in the previous two chapters. Although the class of thiosemicarbazone compounds used in the previous chapters are famously known for their excellent biological applications, complexation to toxic metal centres and oleylamine-mediation fabrication protocols to obtain CdS and PbS nanoparticles compromised the eco-friendly practice. Thus, in this chapter, non-toxic β-In2S3 and CuInS2 nanoparticles were prepared in two eco-friendly alternatives to oleylamine, which are castor oil and olive oil. Different classes of ligands (xanthates and dithiocarbamates) were investigated on their influence in the properties of the nanoparticles, in addition to the choice of capping agent and reaction temperature. Two In(III) and two Cu(II) complexes were used in this work. Very few reports on the use of these castor oil and olive oil capping agents are available, and none of them focus on the fabrication of non-toxic nanoparticles, marking this work a first of its kind. The fifth chapter reports an additional eco-friendly approach to prepare indium sulfide, a continuation of the work reported in the fourth chapter. In this work, however, the use of capping agents is disregarded. Thus, low decomposition temperatures observed for the In(III) xanthate complexes used were found suitable for the proposed vi solventless fabrication route. The route entails the formation of indium sulfide through the thermal decomposition of complexes by solventless thermolysis and melt reaction mechanisms. This practical, inexpensive and a scalable greener route was able to afford various crystallographic phases which were identified through their good quality powder X-ray diffraction patterns. Phase transformation was largely influenced by both decomposition reaction temperature and the nature of the alkyl backbone of the xanthate ligands. Five In(III) xanthate complexes were used in this work, inclusive of one complex used in the fourth chapter. The study provided easy access to investigate the material obtained through mild conditions compared to the earlier traditional practice which used the multielement (indium metal + elemental sulfur) approach at excessive heat (>1000°C) resulting to explosions. The final, sixth chapter, concludes on the progress outlined in the above-mentioned studies towards the eco-friendly reaction protocols for nanoparticles synthesis. The preparation of CdS and PbS nanoparticles using common reaction parameters was necessary to demonstrate the efficacy of alternative eco-friendly protocols to produce non-toxic β-In2S3 and CuInS2 nanoparticles exhibiting similar properties to the former materials. Advantages of using metal-organic as molecular precursors are outlined, based on the experimental results obtained from the studies. en_US
dc.language.iso en en_US
dc.publisher University of Zululand en_US
dc.subject Thiosemicarbazone en_US
dc.subject Xanthate en_US
dc.subject nanoparticles en_US
dc.title Thiosemicarbazone, xanthate and dithiocarbamate single source precursors for cadmium, lead and indium sulfide nanoparticles en_US
dc.type Thesis en_US

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