Synthesis of binary, ternary, and alloyed metal sulfides by a solvent-less route
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Date
2020
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University of Zululand
Abstract
The work outlined in this thesis entails recent advances in reaction protocols to afford high quality semiconductor materials. As a step towards sustainable and green synthesis, this thesis presents the use of a simple, scalable and environmentally benign solventless approach in the preparation of (Ag+, Cd2+, Cu2+, Ni2+, Zn2+and Fe3+) doped CoS and (Cu2+, Sb3+ and Fe3+) doped AgBiS2 by solid state pyrolysis of ethylxanthate precursors. In addition to the synthetic protocol, the work demonstrates the utility of xanthates as a single source precursor in the fabrication of semiconductor materials due to their low decomposition temperature and high possibility of forming pure crystalline products.
The synthesis part of this study was divided into two sections, the first section was to prepare complexes using ethyl xanthate as a ligand from potassium ethyl xanthate. This was prepared by dissolving a calculated mass of xanthate into a measured amount of distilled water at room temperature followed by reacting with an aqueous solution of the metal nitrate. The second section involves the melt (solvent less) method. This is as follows, a stoichiometric amount of xanthate complexes of the corresponding metal was mixed and crushed to obtain a homogenous mixture. The mixture was then placed in a ceramic boat which was then placed in a glass reactor tube inside the furnace with a temperature of 250 °C under inert conditions for an hour. This methodology was employed for both binary systems and ternary system for this study.
The first chapter reports fundamental aspects of semiconductors. The scope of this literature review chapter is narrowed to the band gap dependent properties of semiconductor materials. Doping of semiconductors has also been discussed as one of the methods used to enhance the conductivity of semiconductors. The chapter also focuses on synthetic routes which provide access to the modulation of the properties of the semiconductors to suit a specific applications. More importantly the chapter provides highlights on the melt method as an alternative approach to circumvent the limitations reported in the use of conventional methods. Examples of both binary and ternary metal chalcogenide semiconductors are also discussed briefly. General applications of metal sulfides are discussed in detail in this thesis.
The work demonstrated in chapter two focused on the synthesis of both ethyl xanthate complexes and (Ag+, Cd2+, Cu2+, Ni2+, Zn2+and Fe3+) doped CoS semiconductors. Thermogravimetric analyses of metal ethyl xanthate complexes show clean thermal
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decomposition at fairly moderate temperatures, the average decomposition began around 120 °C to and ends between 150 °C and 200 °C. The synthesis of (Ag+, Cd2+, Cu2+, Ni2+, Zn2+ and Fe3+) doped CoS were performed by thermal decomposition of a mixture containing 5% of each metal ethyl xanthate at 250°C. The physicochemical properties of the as-prepared semiconductor materials were elucidated by powder X-ray diffraction (p-XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDs) and ultraviolet visible spectrophotometer (UV-vis) techniques.
Chapter three presents facile cationic (Cu2+, Sb3+ and Fe3+) doping in AgBiS2 by the solventless route using xanthate complexes. Thermogravimetric analysis of the as-prepared complexes demonstrated that they all thermalize cleanly at fairly moderate temperatures. Likewise, the physicochemical properties of AgBiS2, Ag1-xCuxBiS2, AgSbxBi1-xS2 and AgFexBi1-xS2 systems were ascertained by p-XRD, TEM, SEM and EDX techniques.
The last (fourth chapter), concludes on the progress outlined in the above-mentioned studies towards the environmentally benign techniques for fabrication of semiconductor materials as well as their applicability in solar energy to solve the problem of non-renewable energy crises.
Description
A dissertation submitted in fulfilment of the requirement for the Degree of Master of Science in the Department of Chemistry, Faculty of Science, Agriculture and Engineering, at the University of Zululand, 2020.
Keywords
Binary, Ternary, Solvent-less route