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A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment for the requirements for a degree in Masters of Science. November 2017, Johannesburg. / Metal complexes have a wide range of applications in fields such as medicinal, industrial, environmental and so on. Determining the formations constants for metal complexes is thus essential to gather information on complexes. Conventional methods used to study complexation include spectroscopic methods and the use of voltammetric techniques such as direct current polarography using a mercury drop electrode. In this work alternative voltammetric methods to study complex formation are investigated. Bismuth complexes have important medicinal applications but not much is known about them because of the difficulties in studying them due to extensive bismuth hydrolysis and precipitation of hydrolysis products from very low pHs. The aim of this work was to investigate whether using low concentrations of bismuth (10-6 M) would prevent precipitation in nitrate solutions as predicted in literature. Differential pulse anodic stripping voltammetry (DPASV) was the technique of choice because of its low detection limit, even though it has not been widely used in complex formation studies before. The study revealed that electrochemical response for Bi3+ was not fully reversible using this technique. Additionally, even at the low concentration precipitation was observed in the acidic region (investigated via pH titration) and was suspected to be the formation of BiONO3 species. The second alternative method investigated was the use of mercury film electrodes to replace the use of the toxic mercury drop electrodes which are being phased out worldwide. This work looked at using in situ and ex situ plated films, where the in situ measurements proved more reproducible. A number of challenges were encountered, such as film degradation, peak splitting and ligand adsorption to the film electrode. Nonetheless, formation constants of lead-glycine complexes were determined under different experimental conditions and these were found to be reasonably compared to the literature values. / LG2018

In this project the link between species in solution and the solid state was considered. This is relevant due to the many applications in life where there is this interchange between solid and solution state, for example drug design, environmental metal speciation and the manufacture of materials that are in contact with solution (such as outdoor surface coatings, containers and so on). Complexation of two metal ions, namely cadmium(II) and bismuth(III), was studied. With bismuth showing so much promise in medicinal applications it was pertinent to investigate this interchange since the intake of medication is generally in the solid form which then converts to solution species as it dissolves in the body where it becomes active. For cadmium it is mainly the environmental concerns which we are faced with that call for the examination of speciation of complexes in solution, as well as their disposition upon precipitation or crystallization. A correlation was found between solution species and the complex that was isolated in the crystalline form with regards to pH for a number of metal-ligand species. We show how the results from solution experiments (achieved using direct current polarography) and those of crystalline complexes can complement each other when using species distribution diagrams as the intermediary. The distribution of species can be varied by changing the concentration and ligand-to-metal ratio at which the species distribution diagram is plotted. It is this characteristic which allows the solution and crystalline complexes – which are achieved using differing experimental conditions – to be correlated. The speciation diagram for a metal-ligand system, calculated using formation constants derived from solutions studies, was used in most instances to target specific species for their growth in the solid state. In some cases the solid state structure was used to confirm a suspected solution species, and in others the result was used to identify minor solution species which cannot be detected by the techniques used in determining formation constants. Further, we show that doing solution experiments at a range of temperatures can also aid in elucidating these minor species. The growth of crystalline species at low pH was important for this work because the pH titrations used for solution experiments were conducted from below pH 2 where the diffusion junction potential is large and changing. An in-situ witness ion was incorporated into the experiment to monitor the shifts due to the diffusion junction potential so that they could be compensated for. Additionally, for bismuth-ligand systems, hydrolysis and complexation with nitrates occurs in this same pH region. The formation constants and the species identified below pH 2 therefore do carry some uncertainty, so obtaining crystalline complexes of these species provides further confidence in their prediction in solution.

Thesis advisor: Michael Graf / Bismuth is an interesting element to study because the low effective mass of its charge carriers makes the material sensitive to quantum confinement effects. When bismuth is reduced to the nanoscale two interesting phenomena may occur: it may transition from a semimetal to a semiconductor, or charge carriers in special surface states may begin to dominate the behavior of the material. Arrays of bismuth nanowires of various diameters were studied to investigate these possibilities. The magnetoresistance of the arrays was measured and the period of Shubnikov-de Haas oscillations suggested an increase in the effective mass and density of the material’s charge carriers for small nanowire diameters. These increases suggested that electrons were present in surface states and strongly influenced the material’s behavior when its dimensions were sufficiently reduced. The magnetization of the nanowire arrays was also measured and the lack of de Haas-van Alphen oscillations for certain diameter nanowires suggested that electrons were not present in surface states and that instead the material was transitioning from a semimetal to a semiconductor. Heat capacity measurements were planned to reconcile the two experiments. My detailed calculations demonstrated that heat capacity measurements were feasible to determine the presence, or absence, of surface charge carriers. Because the electronic contribution to the material’s heat capacity is small a calorimeter platform was constructed with ultra-low heat capacity components. / Thesis (BS) — Boston College, 2009. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: College Honors Program. / Discipline: Physics.

by Chan Wing Fat. / Bibliography: leaves 134-136 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1986

by Yu-Kit Lam =鉍系超導體在各製備階段之機械及超導特性 / 林宇傑. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Yu-Kit Lam = Bi xi chao dao ti zai ge zhi bei jie duan zhi ji xie ji chao dao te xing / Lin Yujie. / Table of Contents --- p.i / Acknowledgments --- p.iv / Abstract --- p.v / Chapter Chapter 1 --- Related Work on Bulk Bi-based High Tc Superconductor --- p.1 / Chapter 1.1 --- Historical Background of Superconductivity --- p.1 / Chapter 1.2 --- Basic Properties of Superconductivity --- p.4 / Chapter 1.3 --- Basic Properties of Bi-based Superconductor --- p.7 / Chapter 1.4 --- Fabrication Methods of Bi-based Superconductor --- p.12 / Chapter 1.4.1 --- Precursor Preparation --- p.12 / Chapter 1.4.1.1 --- Solid State Reaction Method --- p.12 / Chapter 1.4.1.2 --- Sol-gel Method --- p.15 / Chapter 1.4.1.3 --- Co-decomposition Method --- p.17 / Chapter 1.4.1.4 --- Freeze-drying and Spray-drying Methods --- p.17 / Chapter 1.4.1.5 --- Comparison for precursor preparation methods --- p.18 / Chapter 1.4.2 --- Pelletization and Sintering --- p.20 / Chapter 1.5 --- Potential applications of Bi-based superconductors --- p.22 / Chapter 1.5.1 --- Criteria for practical applications --- p.22 / Chapter 1.5.2 --- Superconducting tapes --- p.23 / Chapter 1.5.3 --- Current leads --- p.26 / Chapter 1.6 --- Objectives of the Project --- p.27 / Chapter 1.7 --- References --- p.28 / Chapter Chapter 2 --- Fabrication of Bulk Bi(Pb)-2223 Superconductor --- p.33 / Chapter 2.1 --- Introduction --- p.33 / Chapter 2.2 --- Precursor Preparation --- p.33 / Chapter 2.3 --- Grinding Process --- p.34 / Chapter 2.4 --- Pelletization Process --- p.35 / Chapter 2.5 --- The Sintering --- p.37 / Chapter 2.6 --- Characterizations --- p.38 / Chapter 2.7 --- References --- p.40 / Chapter Chapter 3 --- Principles and Instruments of Characterizations --- p.41 / Chapter 3.1 --- Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy --- p.41 / Chapter 3.1.1 --- Basic Principle --- p.41 / Chapter 3.1.2 --- Sample Preparation --- p.42 / Chapter 3.2 --- Crystal Structure Determination Using X-ray Diffraction Spectroscopy --- p.44 / Chapter 3.3 --- Vibrating Sample Magnetometer --- p.48 / Chapter 3.3.1 --- Basic Principle --- p.48 / Chapter 3.3.2 --- Sample Preparation --- p.49 / Chapter 3.4 --- Standard Four-Probe Method for Electrical Measurement --- p.51 / Chapter 3.5 --- Density Measurement of Sintered Samples --- p.52 / Chapter 3.6 --- Hardness Tests --- p.54 / Chapter 3.7 --- Determination of Flexural Strength of Sintered Samples --- p.56 / Chapter 3.8 --- References --- p.57 / Chapter Chapter 4 --- Results and Discussions / Chapter 4.1 --- Results from X-Ray Diffraction Spectroscopy --- p.58 / Chapter 4.1.1 --- Green Pellet --- p.58 / Chapter 4.1.2 --- 50-Hour Sintered Pellet --- p.58 / Chapter 4.1.3 --- "100-Hour, 150-Hour, and 200-Hour Sintered Pellets" --- p.59 / Chapter 4.1.4 --- Volume Fraction of the High Tc Phase --- p.59 / Chapter 4.2 --- Microstructure Observed by Scanning Electron Microscopy --- p.63 / Chapter 4.2.1 --- Green Pellet --- p.63 / Chapter 4.2.2 --- 50-Hour Sintered Pellet --- p.64 / Chapter 4.2.3 --- "100-Hour, 150-Hour, and 200-Hour Sintered Pellets" --- p.64 / Chapter 4.3 --- Chemical Composition Using Energy Dispersive X-ray Spectroscopy --- p.68 / Chapter 4.4 --- Results from Vibrating Sample Magnetometer --- p.71 / Chapter 4.5 --- Densification of Sintered Samples --- p.75 / Chapter 4.6 --- Hardness at Various Stages of Processing --- p.77 / Chapter 4.7 --- Flexural Strength at Various Stages of Processing --- p.79 / Chapter 4.8 --- I-V Characterization Using Standard Four-Probe Method --- p.82 / Chapter 4.9 --- Weibull Modulii of Sintered Samples --- p.85 / Chapter 4.10 --- Future Oultlook --- p.86 / Chapter 4.11 --- References --- p.87 / Chapter Chapter 5 --- Summary --- p.89 / Appendix A Polishing of Pelletizing Mold / Chapter A.1 --- Introduction --- p.92 / Chapter A.2 --- Grinding Process --- p.92 / Chapter A.3 --- Final Polishing Process --- p.93

Neste trabalho foram empregados os métodos hidro e solvotérmico para sintetizar três diferentes catalisadores à base de bismuto (Bi2WO6, BiOI e BiVO4), visando aplicação em fotocatálise heterogênea sob radiação visível. Foram investigadas as influências do tempo de síntese, da calcinação, da adição de polivinilpirolidona (PVP) e do tipo de solvente usado durante a síntese sobre a morfologia, cristalinidade, área superficial específica e band gap das amostras. Os catalisadores foram caracterizados por microscopia eletrônica de varredura (MEV), espectroscopia de refletância difusa (ERD), difração de Raios-X (DRX) e adsorção de N2. Para avaliar a atividade fotocatalítica das amostras sintetizadas foram realizados experimentos em um reator batelada agitado, com o catalisador em suspensão e uma lâmpada de LED como fonte de radiação visível. As moléculas testes escolhidas foram o corante rodamina B, para determinação das amostras com maior atividade e, posteriormente, o fármaco prednisolona, sendo então estudados a influência da concentração de catalisador e do pH inicial do meio reacional. Foram realizados, também, ensaios de toxicidade com o organismo Lactuca sativa – sementes de alface, para avaliar a toxicidade da prednisolona pura, da mistura água e catalisador de BiOI e das alíquotas provenientes da reação de degradação da prednisolona após diferentes tempos. As amostras de Bi2WO6 apresentaram boa cristalinidade e semelhanças morfológicas apesar dos diferentes tratamentos. As amostras de BiOI, por sua vez, apresentaram diferenças significativas de morfologia, de microesferas para microplacas, quando foi feita a mudança de solvente e a amostra de BiVO4 apresentou um formato de paralelepípedo. Nos testes fotocatalíticos com a rodamina B, o catalisador que se mostrou mais ativo foi o BiOI cuja síntese continha PVP e etilenoglicol (kap = 0,0207 min-1) e o BiVO4 foi o que apresentou a menor atividade (kap = 0,0013 min-1). Na degradação da prednisolona, a maior taxa de degradação foi obtida com 1 g L-1 de catalisador e no pH natural do fármaco, 6,8. Os ensaios de toxicidade revelaram que nem a prednisolona nem a mistura água e catalisador são tóxicas para as sementes de alface, as alíquotas provenientes da reação, porém, tiveram um aumento de sua toxicidade com o aumento do tempo de reação. / In this work, solvo and hydrothermal methods were applied to synthesize three types of bismuth catalysts (Bi2WO6, BiOI and BiVO4) aiming to the apply it in heterogeneous photocatalysis under visible light. Were investigated the influences of reaction time, calcination, addition of poly (vinyl pyrrolidone) (PVP) and the solvent type during synthesis on their morphology, crystallinity, surface area and band gap. The catalysts were characterized by scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), X-ray powder diffraction (XRD) and nitrogen adsorption/desorption. To evaluate photocatalytic activity of the synthesized samples, experiments were carried out in a stirred batch reactor, with the catalyst in suspension and a LED lamp as a source of visible light. The test molecules chosen were the rhodamine B dye for determination of the samples with higher activity and subsequently the drug prednisolone, and then was studied the effect of catalyst concentration and initial pH of the reaction medium. Toxicity tests were also perfomed with organism Lactuca sativa – lettuce seeds, to the toxicity of pure prednisolone, water and BiOI catalyst mixture and aliquots from prednisolone degradation after different reaction times. As a result, the Bi2WO6 samples presented good crystallinity and morphological similarities despite having undergone different treatments. The BiOI catalysts presented a significant difference in morphology, microspheres to microplates, when changed the solvent, while the BiVO4 sample presented a parallelepiped shape. In the photocatalytic tests with rhodamine B, the catalyst with the highest activity was BiOI, containing PVP and ethylene glycol (kap = 0.0207 min-1) in its synthesis, and the BiVO4 was the catalyst with the lowest activity (kap = 0.0013 min-1). In the prednisolone degradation, the highest degradation rate was obtained with 1 g L-1 of catalyst and natural pH of the drug, 6.8. The toxicity tests showed that neither prednisolone nor water and catalyst mixture are toxic to lettuce seeds, aliquots from reaction, however, had an increase in their toxicity with increasing reaction time.