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    The effect of acid mixtures on biomass cellulose poly (Furfuryl) alcohol nanocomposites
    (University of Zululand, 2022-12) Khumalo, Nduduzo Lungisani
    Recently, extraction of cellulose nanocrystals (CNCs) via acid hydrolysis using sulphuric acid has been intensively studied. Moreover, the use of sulphuric acid requires shorter hydrolysis time, while producing stable suspensions with high yield and crystallinity. However, it results in CNCs with lower thermal stability and higher aggregation due to the presence of sulphate ions. Hence, the overall aim of this study is to extract CNCs using mixture of acids and compare its morphology and thermal properties with sulphuric acid hydrolysed CNCs. In addition, the extracted CNCs were encapsulated in a poly (furfural) alcohol (PFA) matrix via in situ polymerization process in the presence of P-toluene sulfonic acid as a catalyst to produce cellulose PFA nanocomposites. Furthermore, the study investigates the effect of mixed acid concentration on the morphology, crystallinity and thermal properties. Varying concentrations of 45%, 55% and 65% H2SO4/HClO4 hydrolysed CNCs were studied. In conclusion, the study investigated and compared the thermal and morphology of green extracted CNCs and acetylated CNCs. The properties of raw biomass, extracted cellulose, extracted CNCs, and nanocomposites were analysed by Fourier transformed infrared (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetric analyser (TGA). H2SO4/HNO4 and H2SO4/HCl hydrolysed CNC/PFA nanocomposites showed the highest crystallinity while H2SO4/H3PO4 and H2SO4/HClO4 hydrolysed CNC/PFA nanocomposites showed highest thermal stability. The surface breakage and cracked PFA nanocomposite surface observed in SEM was dependent on the strength of acids used to hydrolysed CNCs. H2SO4/HClO4 hydrolysed CNC/PFA displayed good dispersion of CNCs in the PFA matrix with no observed surface breakage. With regards to the effect of mixed acid concentration, 55% H2SO4/HClO4 hydrolysed CNCs showed the highest crystallinity and thermal stability while 65% H2SO4/HClO4 hydrolysed CNCs showed the least thermal stability. SEM results showed fiber breakage for 65% H2SO4/HClO4 hydrolysed CNCs which proved to be acid concentration dependent. In conclusion, the acetylated CNCs showed higher crystallinity compared to the green extracted CNCs with evidence of allomorph transformation from cellulose I to cellulose II on the acetylated CNCs. In addition, the acetylated CNCs showed lower thermal stability compared to the green extracted CNCs. SEM also showed a structural transformation upon acetylation of CNCs from a rod like fiber to a crystal-like structure.
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    Physical, mechanical and durability properties of sugarcane ash enhanced compressed earth blocks stabilized with fly ash and lime powder
    (University of Zululand, 2019) Mohomane, Samson Masulubanye
    The construction sector is one of the principal component of anthropogenic activities and a major contributor of greenhouse gases (GHGs) emissions. Large quantities of solid wastes are being produced every year by industrial and agricultural industries which lead to environmental and health concerns such as flooding, air pollution and other public health scarce. These wastes have potential pozzolanic reactivity and may be used to develop cementitious materials that are sustainable, while maintaining requirements as affirmed in various standards. The sector is also an important economic sector that has a large environmental impact in terms of large quantities of construction and demolition wastes (C&DW) which are generated. These is mainly due to severe shortage of natural aggregates (NA) for the production of new concrete materials, and a boom in construction activities currently taking place worldwide. The utilization of recycled masonry and concrete (RCA) from C&DW will conserve the natural resources and reduce the environment impact of concrete manufacturing. Sugarcane bagasse ash (SCBA) is an industrial waste material obtained from sugar milling industry that can be used as pozzolanic material for the development of greenbricks. In this research, the application of various waste materials and the effects of fly ash and lime on the mechanical and durability properties of compressed earth bricks (CEBs) are investigated. Secondly, the applications of fly ash, recycled cement and masonry as industrial waste materials in construction industry are reviewed. Lastly, The SCBA greenbricks were developed using lime as a chemical stabilizer and tested for physical, mechanical and durability properties. In addition, several agricultural by-product such as sugar cane bagasse (SCB) and soft wood (SW) were treated as wastes until recent times when researchers considered incorporating them in polymeric matrices to mainly avoid environmental pollution and cost of a new synthesis. The properties of untreated sugarcane bagasse (SCB) and soft wood (SW), their respective celluloses, and corresponding composites and blends with thermoplastics (polypropylene and polyethylene) were analysed by DMA, SEM, XRD, FTIR, DSC and TGA. Three degradation models, Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (OFW), and Kissinger (KGR) methods were employed to determine apparent activation energy values of untreated SCB and SW, and their respective celluloses. The apparent activation energy values obtained from OFW and KAS models vary with the degree of conversion, and showed similar trends. The activation energies TGA analysis shows that the untreated SCB and SW degrade earlier than their respective celluloses and the prolonged treatment affects the onset of main degradation. PP/SCB were least thermally stable compared to PP/SW composites. The addition of extracted cellulose decreased the thermal stability of PP/SCB composites at higher filler content due to poor interfacial bonding as compared to PP/SW composites. Likewise, the cellulose containing blend composites were thermally stable compared to untreated fibre, and are less stable compared to neat PP/PE blend. DMA of both PP/SCB and PP/SW composites indicated improvement in the storage modulus compared with neat PP. Similar results were obtained for all blend composites, with the cellulose containing blend composites displaying higher values than untreated fibre. SEM results confirmed a rough morphology and the presence of many voids resulting from fibre pull-out in composites, especially for the ones with higher fibre content. However, a stronger interaction between PP/PE/SW as compared to PP/PE/SCB took place in the blend composites. DSC analysis reveals that the introduction of SCB or SW did not significantly change the melting and crystallization behaviour of both the PE and PP.
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    Synthesis of binary, ternary, and alloyed metal sulfides by a solvent-less route
    (University of Zululand, 2020) Zibane, Philangezwi Welcome
    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 ix 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.
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    Solventless Synthesis of Nanostructured Spinel Ferrite Solid Solutions for Supercapacitance and Electromechenical Water Splitting Application
    (University of Zululand, 2021) Malima, Nyemaga Masanje
    Metal oxide nanocrystals that adopt the spinel crystal structure, such as spinel ferrites exhibit a variety of interesting electronic, magnetic, and optical properties, which render them suitable for numerous technologically relevant applications. Interestingly, tuning the composition of spinel nanoferrites via the design of solid solutions is recognized as an effective way to improve their electrochemical properties towards supercapacitance and water splitting. In this regard, achieving synthetic control over the composition is critical to tuning the properties of spinel ferrite nanocrystals. Efforts to find sustainable approaches to nanoparticle synthesis have focused on green chemistry principles, including reducing waste, improving yield and atom economy, and minimizing auxiliaries and reaction steps. The solventless approach, in which the synthesis of nanomaterials proceed by thermal decomposition of precursors has attracted considerable research interest and proven to be simple, economical, time-effective, scalable, and eco-friendly. The work described in this thesis demonstrates the suitability of the solventless thermolysis route for the fabrication of a series of nanostructured spinel ferrite solid solutions using metal acetylacetonate precursors. Investigation on the efficacy of the synthesized ferrite solid solutions for supercapacitance and water splitting applications is also described. The thesis is organized into seven chapters as described hereunder. The first chapter presents the introduction and literature review which are the foundations upon which the entire research work is based. This chapter gives insight into electrochemical energy systems with a special focus on the theory behind electrocatalytic water splitting and the mechanism of hydrogen production in both acidic and alkaline electrolytes. Similarly, the description, classification and working principles of supercapacitors are described. It also shades light into the concept and potential applications of spinel ferrites and their corresponding solid solutions. The first chapter is culminated by highlighting the research justification and establishes the working scope and objectives of the study. The work described in chapter two entails the scalable synthesis of nanostructured Ni1-xCoxFe2O4 solid solutions via a solventless thermolysis method. The physicochemical analysis of the as-prepared solid solutions is established by a suite of characterization techniques, while the procedures of materials fabrication and electrochemical analysis are also presented. The p-XRD analysis confirmed the formation of a series of monophasic cubic spinel ferrites with space group Fd3m. Investigation of the synthesized materials for vi supercapacitance revealed that the nanospinel Ni0.4Co0.6Fe2O4 electrode demonstrated a longer charge-discharge time, signifying superior charge storage capacity. For efficient HER electrocatalysis, the Ni0.6Co0.4Fe2O4 electrode showed high performance manifested by low overpotential of 168 mV and Tafel slope of 120 mV/dec. Similarly, Ni0.8Co0.2Fe2O4 exhibited a lower overpotential of 320 mV with a low Tafel slope of 79 mV/dec, indicating enhanced OER activity. Chapter three describes scalable nanofabrication of composition-tuneable spinel Co1xZnxFe2O4 solid solutions via a solvent-free thermolysis approach. The discussion of the experimental results regarding the materials’ structural, compositional, morphological and optical properties is provided. Experimental results revealed that incorporation of diamagnetic Zn2+ in the crystal lattice of CoFe2O4 significantly enhanced both the physicochemical and electrochemical properties of the resultant material. Higher discharge time displayed by Co0.4Zn0.6Fe2O4 is indicative of higher specific capacitance of the material compared to the pristine CoFe2O4. For OER, the Co0.8Zn0.2Fe2O4 solid solution exhibited higher performance reflected by low overpotential of 317 mV along with a small Tafel slope of 56 mV/dec. As for HER in alkaline electrolyte, Co0.6Zn0.4Fe2O4 displayed decent performance with a low overpotential of 169 mV and Tafel slope of 136 mV/dec compared to other electrode compositions. Chapter four demonstrates that by regulating the molar composition of Mg and Ni in the preparation of Ni1-xMgxFe2O4 solid solutions, the physicochemical and the electrochemical performance of the material were tuned. The Ni1-xMgxFe2O4 (x = 0.6) nanoparticles exhibited the best electrocatalytic activity for HER with an overpotential of only 121 mV which is much smaller compared to its analogues, at current density of 10 mA/cm2 and the electrode exhibits good stability during long-term electrolysis. Meanwhile, Ni0.2Mg0.8Fe2O4 showed the best OER activity, requiring an overpotential of 284 mV to deliver the same current density within the window of potential examined. In chapter five, a series of Ni1-xZnxFe2O4 (0 ≤ x ≤ 1) solid solutions with varying amounts of zinc and nickel have been efficaciously fabricated via a solventless pyrolysis method. The p-XRD and EDX analyses confirmed the formation of homogeneous phase-pure Ni1-xZnxFe2O4 (0 ≤ x ≤ 1) nanoparticles. In comparison, the incorporation of zinc in the crystal lattices of nickel ferrite endowed a larger benefit on HER and OER than on supercapacitance. Specifically, the Ni1-xZnxFe2O4 (x = 0.8) nanocatalyst displays excellent HER performance with superior activity which is manifested by a small overpotential of 87 vii mV, whereas Ni1-xZnxFe2O4 (x = 1) catalyst exhibited superior OER performance with a small overpotential of 330 mV. The main aim of the sixth chapter was to employ the same solventless pyrolysis approach to afford uniform Co1-xMgxFe2O4 (0 ≤ x ≤ 1) nanoparticles using metal acetylacetonate precursors. Structural analysis showed that all samples exhibited a cubic spinel ferrite structure with space group Fd3m. All samples showed the same morphology irrespective of the amount of Mg being incorporated in the CoFe2O4 system. Considering the band gap value of pristine cobalt ferrite, a blue shift was observed for all compositions except for x = 0.2 and 1, which were red shifted. The results and findings of this chapter are of profound significance for the design of novel electronic and optoelectronic devices. Chapter 7 culminates the entire research project by presenting a brief summary of the work and possible areas to be considered for future work. Overall, it was observed in this study that compared to the parent spinel ferrites, their corresponding solid solutions demonstrated improved physicochemical and electrochemical activity, except for Ni1-xZnxFe2O4 where the parent ZnFe2O4 exhibited higher OER activity than the solid solutions.
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    Synthesis and evaluation of Pd(II) and Ni(II) complexes as catalyst for ethylene polymerization
    (University of Zululand, 2017) Dube, Zanele Felicia; Segapelo, T.V.
    This study entailed the synthesis and evaluation of asymmetric palladium(II) and nickel(II) pyrazolyl hydrazide complexes, C1-C6, as catalyst for ethylene transformation reactions. The complexes were prepared from their respective pyrazolyl hydrazide ligands L5a, L5b and L5c, which were also prepared in this study. The synthesis of all ligands was achieved in five (5) steps from 3-bromomethyl benzoate, L2. Compound L2 was prepared from bromination of methyl 3-methyl benzoate L1, using NBS. Benzene methylene pyrazolyl acids (L3a-L3c) were prepared from the reaction of L2 with different pyrazolyl moieties, namely 3,5-dimethyl pyrazole (Me)2Pz = L3a, 3,5-diphenyl pyrazole (Ph)2Pz = L3b and 3,5-ditertiarybutyl pyrazole (tBu)2Pz = L3c, under basic reaction conditions and were obtained in good yields of between 75-80%. Interestingly, the basic conditions used to anchor the pyrazole moieties readily hydrolyses the ester groups back to their corresponding acids. This meant the esterification reaction to be repeated to turn the acids back to esters for hydrozonolysis to be possible. Thus, preparation of the pyrazolyl hydrazide ligands L5a, L5b and L5c was successfully carried out from the corresponding pyrazolyl esters L4a, L4b and L4c, and the ligands were obtained in moderate yields of between 53-63%. All compounds including the final ligands were characterised using common analytical techniques. The pyrazolyl hydrazide ligands L5a-L5c were successfully complexed with PdCl2(NCMe)2 and NiCl2.DME giving square planar complexes C1-C3 and tetrahedral metal complexes C4-C5, respectively, with a general formula MLCl2. The complexes were obtained in moderate yields of 49-63% and were also characterised using appropriate analytical techniques. The pyrazolyl hydrazide complexes (C1-C6) were successfully evaluated in the ethylene transformation reactions where the catalyst structure, type of solvent used and reaction conditions were found to play a vital role in activity and product distribution. For example, when toluene was used as solvent a mixture of hexene and alkylated toluene products were obtained with hexene and butyltoluenes being the major products. On the other hand running the reactions using chlorobenzene displayed better activities to produce C10-C20 oligomers. The pyrazolyl hydrazide nickel(II) complexes, C4-C6, generally showed better activities when compared to the palladium(II) analogues.
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