Titanium dioxide or titania is applied in paints, in the paper industry, fibbers, cosmetics, sunscreen products, toothpaste, foodstuffs, optical coatings, beam splitters and anti-reflection coatings. It is also used as support catalyst and its use as humidity and high-temperature oxygen sensor is under consideration. These applications are related to its high refractive index, oil absorption, tinting strength and inert chemical properties. Commonly, titania is recovered either by leaching ilmenite with sulphuric acid and subsequently hydrolysing the resulting sulfate solution by boiling. In another process, titanium feedstock is converted into titanium tetrachloride and further oxidised to titanium dioxide. These methods are reportedly time-consuming and environmentally unfriendly. They are also unable to use all existing types of titanium minerals. In this study, a novel process for the extraction of titanium valuables from its minerals is presented. The process entails the roasting of titanium ore with alkaline metal salt. The roasted product is hydrolysed with water and acid, and subsequently reacted with sulphuric acid. Alternatively, the hydrolysed product can be used as feedstock in the chloride process. Roasting at 900°C and using a 2:1 (NaOH:ilmenite) mole ratio proved to be the most efficient in releasing titanium units from its ore. Ternary phases dominate under these conditions. Na0.75Fe0.75Ti0.25O2 was the dominant titanium-bearing phase. NaFeTiO4a ndNa2Fe2Ti3O10 were also present. Whenever the Ti:Fe atom ratio was different from one, the surplus titanium was accommodated in single titanates, mainly Na2TiO3, while iron was accommodated in NaFeO2. In many cases Na8Ti5O14 was also present as a result of Na2TiO3 polymerisation. This is consistent with a fusion period of one hour or more. Shorter fusion periods tended to produce binary phases. Similar results were obtained when lower fusion temperatures were employed, i.e. below 550°C. When anatase reactant was used to resemble an anatase ore, Na2Ti6O3,Na2TiO3, Na8Ti5O14 and Na16Ti10O28 were identified in the products. Optimum recoveries were obtained using a 1:1 NaOH:TiO2 mole ratio, and fusing at 800°C for 2 h. Close to 100% of the titanium was recovered. A one-step leaching process was found to be effective compared with multi-step leaching. The leaching step was found to be dependent on time, solid:liquid ratio and temperature. The optimum conditions for solid:liquid ratio, time and temperature were found to be 0.20, and 15 min at 75°C, respectively. Acidic hydrolysis was controlled by the relative amount of iron and titanium in solution. It was found that less than 1% was dissolved between 3 and 7 in pH units. Higher pH values are recommended, since less acid will be used. Any excess of sulphuric acid in the sulfation step proved to be unnecessary. No significant changes were observed in the amount of dissolved iron and titanium. Therefore the stoichiometric amount can be used in the sulfation process. / Thesis (PhD)--University of Pretoria, 2012. / Chemistry / unrestricted

1,4-dioxane is an emerging contaminant and fully miscible organic compound which has been found extensively in wastewater effluent. Conventional water treatment technologies like carbon adsorption, and air stripping are inefficient in removing this extremely mobile and persistent contaminant from water. In this study, different types of metallic nanoparticles, e.g., nanoscale zero-valent iron (nZVI), γFe2O3, and Fe(III)-doped TiO2 were used to investigate the removal of 1,4-dioxane under visible light. These nanoparticles were characterized with scanning electron microscope (SEM), transmission electron microscope (TEM) and dynamic light scattering (DLS). The experiments were first carried out using deionized water (DIW) at pH 7 and pH 3. nZVI was found more efficient than other nanoparticles under visible light irradiation at pH 3. No 1,4-dioxane removal was obtained for all cases at pH 7 under visible light, or at pH 3 in dark. Moreover, light intensity also plays a significant role in 1,4-dioxane removal. Removal of 22.3%, 40.0% and >99.9% of 1.4-dioxane was reached under 2.4 mW/cm2, 2.6 mw/cm2 and 3.25 mW/cm2 light intensities, respectively, after 6 h of irradiation. The most efficient nanoparticle nZVI was applied to wastewater effluent from Carbondale Southeast Wastewater Treatment Plant. From the results, it was found that 1,4-dioxane degradation took longer time in wastewater effluent than in DIW, because of the presence of other constituents in the wastewater sample. nZVI is also capable of removing 1,4-dioxane in presence of trichloroethylene (TCE) and tetrachloroethylene (PCE) at pH 3 under visible light. In comparison, TiO2 nanoparticle is capable of degrading 1,4-dioxane under visible light or under sunlight at pH 7. Moreover, TiO2 removed 1,4-dioxane in presence of both TCE and PCE at pH 7 under visible light or sunlight. This study found a cost-effective and efficient solution for removing 1,4-dioxane from wastewater effluent that can be reused, by using metallic nanoparticles under visible light.

Epitaxial anatase TiO2 thin films were grown by pulsed laser deposition and ion beam sputter deposition, on STO and LAO substrates. Their phases and the crystallographic orientations were confirmed using X-ray diffraction measurements; the impurities concentration of the samples were examined using particle induced X-ray emission. The impurity concentration is too low to be the origin of the measured ferromagnetic signal after irradiation with low energetic ions. The as-grown samples show a small ferromagnetic signal without magnetic anisotropy and with Curie temperatures of TC ≈ 450 K. The origin of this magnetic signal may be related to a lattice mismatch between substrate and film and the resulting induced defects, defects generated during the growth process or annealing, or impurities. Irradiation with low energy Ar+ ions was shown to be a simple way to induce magnetism in anatase thin films. After the first irradiation, the magnetic moment at saturation increases by one order of magnitude with a high Curie temperature of TC ≈ 792 K. Further, a considerable out-of-plane magnetic anisotropy in the magnetization has been found. When increasing the irradiation fluence, the magnetic moment increases further until saturation is reached, whereas TC was reduced and the anisotropy vanished. XAS and XMCD experiments of the O K and Ti L3,2 absorption edges showed that the magnetic moment arises at the Ti 3d shell and not at the oxygen. The obtained magnetic moment per Ti di-Frenkel pair (FP) of m ≈ 2 µB agrees with literature reports. XAS and XMCD calculations of Ti di-FPs within an anatase lattice are in agreement with the results and the assumption that di-Frenkel pairs are responsible for the observed magnetism and anisotropy. Magnetic force microscopy proved the existence of oppositely aligned magnetic domains with out-of-plane magnetization directions. This explains the low remanence of these samples. The production method is efficient and non-destructive, and can be easily combined with other techniques, such as electron beam lithography. This allows the production of arbitrary magnetic patterns with perpendicular magnetic anisotropy at the anatase surface. There are some questions that could not be answered in depth, e.g. the connection between irradiation fluence and ion energy, and the saturation magnetic moment as well as the strength of the perpendicular magnetic anisotropy. More systematic experiments are necessary, preferably using a more sophisticated setup. The electric transport properties of single TiO2 nanotubes were measured. The temperature dependence of the resistance of the polycrystalline anatase nanotubes show a Mott variable range hopping behaviour. The results obtained with two contacts indicate the existence of a potential barrier between the Cr/Au contacts and samples surfaces. Impedance spectroscopy at room temperature indicates that the electronic transport of these polycrystalline tubes is dominated by the grain cores. Similar experiments were conducted on ZnO nanowires. The measurements were done on the as-prepared and after low-energy ion irradiation. The temperature dependence of the resistance of the wire before irradiation, can be described by two processes in parallel; the fluctuation induced tunneling conductance and an usual thermally activated process. Electron backscatter diffraction confirms the existence of different crystalline regions. After irradiation an additional thermally activated process appears that can be explained by taking into account the impurity band splitting. The previously mentioned experimental findings and methods where then applied to several different TiO2 nanotubes. Amorphous nanotubes were anodically grown on titanium foil and partially annealed to obtain anatase samples. Non-linear current–voltage characteristics were explained using the fluctuation induced tunneling conduction model. A clear enhancement of the conductance was induced in an insulating anatase nanotube through low-energy Ar/H ion irradiation. Confocal Raman spectroscopy shows that the annealed samples were in anatase phase and a blueshift due to phonon confinement was observed. Magnetic force microscopy is well known and established method to investigate magnetic samples of nanometer size. Focused electron beam induced deposition of cobalt was used to functionalize atomic force microscopy Akiyama tips for application in magnetic force microscopy. The grown tips have a content of ≈ 90 % Co after exposure to ambient air. In order to investigate the magnetic properties of the tips, current loops were prepared. Magnetic Akiyama tips open new possibilities for wide-range temperature magnetic force microscopy measurements. To continue the work on magnetic nanotubes, further experiments with single nanotubes would be interesting. These samples could be characterized with the help of MFM measurements or NV magnetometry. Also, experiments on nanotube bundles can be of interest, since the fabrication, irradiation and measurements of such more robust samples is easier to implement.:Declaration of Authorship iii List of Publications v Abstract vii Acknowledgements ix 1 Introduction 1 1.1 Defect-Induced Magnetism in Oxides . . . . . . . . . . . . . . . . . . . 1 1.1.1 Open Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Exchange Interactions and Magnetic Anisotropy . . . . . . . . . . . . . 3 1.3 Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.4 Magnetic Force Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.5 Sample Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 Introduction to Magnetism 7 2.1 Orbital Magnetic Moment . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2 Spin Magnetic Moment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.3 Localized Electron Model . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.4 Spin-Orbit Coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.5 Multiplets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.6 Classes of Magnetic Materials . . . . . . . . . . . . . . . . . . . . . . . . 11 2.6.1 Diamagnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.6.2 Paramagnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.6.3 Antiferromagnetism . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.6.4 Ferromagnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.6.5 Ferrimagnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.7 Exchange Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.7.1 Coulomb Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.7.2 Direct Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.7.3 Superexchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2.7.4 Ferromagnetic Superexchange . . . . . . . . . . . . . . . . . . . 22 2.7.5 Double Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.7.6 Orbital Ordering . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.8 Magnetism in Transition Metal Oxides . . . . . . . . . . . . . . . . . . . 27 2.8.1 Oxygen Coordination . . . . . . . . . . . . . . . . . . . . . . . . 28 2.8.2 Crystal Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.8.3 Weak-Field Solution for Single Electron . . . . . . . . . . . . . . 29 2.8.4 Interionic Exchange Interaction . . . . . . . . . . . . . . . . . . . 34 2.9 Magnetic Anisotropy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 2.9.1 Cubic Symmetry . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 2.9.2 Tetragonal Symmetry . . . . . . . . . . . . . . . . . . . . . . . . 39 xii 2.10 Defect-Induced Magnetism in TiO2 . . . . . . . . . . . . . . . . . . . . . 40 3 Defect Induced Magnetism in TiO2 Anatase Thin Films 43 3.1 Strong out-of-plane magnetic anisotropy in ion irradiated anatase TiO2 thin films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.2 Titanium 3d ferromagnetism with perpendicular anisotropy in defec- tive anatase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 4 Defect Induced Magnetism and Electrical Properties of TiO2 and ZnO Nan- otubes 69 4.1 Electrical properties of ZnO single nanowires . . . . . . . . . . . . . . . 71 4.2 Electrical transport properties of polycrystalline and amorphous TiO2 single nanotubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 4.3 Functionalized Akiyama tips for magnetic force microscopy measure- ments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 5 Summary and Outlook 93 Bibliography 99

High power impulse magnetron sputtering has shown a lot of promise as a way of depositing photocatalytic thin films of titanium dioxide at low temperatures, however, the films deposited are often amorphous and display uncertain photocatalytic abilities. This thesis explores the deposition and characterization of photocatalytic thin films deposited with high power impulse magnetron sputtering.  Multiple films were deposited with reactive sputtering in both the oxide and metal mode of operations at different temperatures, duty cycles and substrate biases. The crystal structure, microstructure and photocatalytic activity of the samples were then characterized in order to correlate to each other as well as the growth conditions. Crystallinities were determined via a combined use of gracing incidence x-ray diffraction and Raman spectroscopy, microstructures were explored in cross-sectional images taken using scanning electron microscopy and the photocatalytic ability was measured by quantifying the rate constant during degradation of stearic acid while under UV-illumination.  It was found that the crystal structure of the sputtered films was influenced by the deposition mode used: oxide mode depositions yielded an anatase structure while metal mode depositions resulted in rutile or mixed structures. The only crystalline films were formed with substrate heating, the application of bias was found to correlate with the formation of more rutile and the most crystalline films were deposited with a higher duty cycle.  Photocatalytic films were successfully deposited at room temperature, even though they were amorphous. Interestingly, the anatase samples were not found to be the most reactive, instead it was found that the crystal structure only displayed a weak correlation to the reactivity of the films. The findings in this work suggest that the reactivity was also heavily influenced by the surface roughness of the samples as well as their microstructures.

Hydrothermal synthesis is one of the most widely used methods for preparing nanoparticles of titanium dioxide. The process carried out at elevated temperatures and pressure, which facilitates the transformation of amorphous to crystalline titanium dioxide. Change of reaction conditions of the process (reactants concentration, temperature, time, pH, etc.) leads to change in morphology, microstructure and crystallinity of titanium dioxide nanoparticles. In this work the method of titanium dioxide preparation is briefly described. The titanium dioxide was prepared from a precursor titanium oxochloride and potassium hydroxide as the precipitating agent. Thus prepared titanium dioxide was immobilized on a glass substrate by material printing. This is a modern, highly precise and contactless method for preparing thin films. The photocatalytic activity of printed thin films of titanium dioxide was investigated by degradation of 2,6-dichlorindophenol at different irradiance. It was found that the sample prepared by hydrothermal treatment at 160 °C shows very similar photocatalytic activity to Degussa P25.

No description available.

Magister Scientiae - MSc (Chemistry) / Drinking water with high concentrations of inorganic and organic contaminants can cause adverse health defects. Specifically methyl orange dye is an organic water contaminant that has been known (along with others like methyl blue etc.) to have an increase in our water systems over the past few years due to increasing demand in industrial processes. It is therefore of utmost importance to remediate organic contaminants and ultimately enable prevention. The contaminants can be removed by photocatalysis. Anatase TiO2 is known for its photocatalytic degradation of environmental pollutants and photoelectro-chemical conversion of solar energy. However its application is limited since it is a wide band gap semiconductor, (Eg = 3.2 eV). The following study deals with the enhancement of the photocatalytic properties of TiO2 for remediation of organic water contaminants.

No description available.

Luminescence techniques are sensitive, selective, and widely used in analysis. Luminescence intensity is attenuated by quenchers. This research has focused on the use of surfactants such as CTAB, SDS, and TX-100 singly or together with TiO2 nanoparticles to evaluate their individual and combined effects on some fluorescent aromatic compounds such as pyrene, fluoranthene, anthracene, phenanthrene, and carbazole. Rutile phase TiO2 was synthesized using the low temperature sol-gel method. Carbazole and phenanthrene were severely quenched by all surfactants singly or in combination with TiO2. Anthracene and fluoranthene showed some enhancement in their luminescence intensity. The most dramatic effect was observed on the fluorescence intensity of pyrene. Pyrene showed enhanced fluorescence after degassing the solution alone or with the addition of the surfactants alone or in combination with TiO2 after degassing. These results showed that surfactants and TiO2 nanoparticles either singly or in combination should be useful for analysis employing luminescence techniques.

Within statistical methods, design of experiments (DOE) is well suited to make good inference from a minimal amount of data. Two types of designs within DOE are screening designs and optimization designs. Traditionally, these approaches have been necessarily separated by a gap between the objectives of each design and the methods available. Despite being so separated, in practice these designs are frequently connected by sequential experimentation. In fact, from the genesis of a project, the experimentor often knows that both designs will be necessary to accomplish his objectives. Due to advances in the understanding of experimental designs with complex aliasing and their analysis, a current topic within statistics is how to desegregate these methods into a more unified and economical approach. This project is one treatment of that issue.