Recently, there has been increasing demands for high dielectric materials to replace SiO2 for high-density dynamic random access memories with ultralarge scale integration. TiO2 and BaTiO3 are very promising insulators for applications to DRAMs, as they exhibit higher dielectric constant.The growths of TiO2 and BaTiO3 thin films on (100) silicon are studied by MOCVD using Ti(i-OC3H7)4, Ba(DPM)2(tetraene)2 and N2O as precursors. The growth was performed in a cold wall horizontal system in the temperature range of 350~700¢J. The growth rates of TiO2 and BaTiO3 films are affected by the Ti flow rate, growth temperature and reactor pressure. The structures of TiO2 and BaTiO3 films are polycrystalline by X-ray diffraction examinations. The dielectric constant of as-grown TiO2 can reach 85 and BaTiO3 can reach 300 derived by C-V curves with the contact area 3.14¡Ñ10-4 cm2. In addition, the influences of postannealing treatment under an O2 and N2 ambient with different annealing temperature and time on the structural and electrical properties of as-grown TiO2 films will be also studied. However, TiO2 and BaTiO3 films have columnar structures acted the paths of leakage current. We use thermal annealing to reduce the leakage current. In the future, to enhance the dielectric constant and reduce the leakage current of the films is the goal in our study.

In recent years, there has been increasing demands for high dielectric materials to replace SiO2 for high-density dynamic random access memories with ultra large scale integration (ULSI). As the dimensions of the charge storage node decrease in high-density dynamic random access memories (DRAMs), TiO2 and BaTiO3 are very promising candidates for applications with exhibiting higher dielectric constant, high refractive index and high chemical stability. The growth of TiO2 and BaTiO3 thin films on various substrates i.e. (100) silicon¡B(100) GaAs¡B(100) InP and (100) MgO are studied by MOCVD using Ti(i-OC3H7)4, Ba(DPM)2, N2O and O2 as precursors. The growth was performed in a cold wall horizontal system in the temperature range of 280~750¢J. The growth rates and structure of TiO2 and BaTiO3 films are affected by the substrate temperature and reactor pressure, etc. The phase transition properties of TiO2 were studied via X-ray diffraction measurements. X-ray diffraction examination shows that phase transition of TiO2 films are at the same temperature of 450 oC on different substrates. Phase-pure rutile is obtained down to 450¢J on InP (100) and GaAs (100), while phase-pure anatase is obtained up to 450¢Jon MgO (100). The optical and electrical properties are associated with the film structures. TiO2 single phase films with rutile (110) orientation were successfully grown on InP (100) at 500¢J. In-plane epitaxial relationship of anatase TiO2 (100) // MgO (100) is present between 300¢J and 375¢J. In addition, the influences of substrate temperature and oxidizer on the structural and electrical properties of BaTiO3 films will be also studied. However, TiO2 and BaTiO3 films have columnar structures acted the paths of leakage current resulting low dielectric constant. We use thermal annealing to improve the quality of TiO2 with respect to leakage current density and dielectric constant. Dielectric constants of annealed TiO2 films were as high as 110.08. Leakage current density reduced to 5 ¡Ñ 10-5 A/cm2. In the future, to improve the crystal structure of the films is the goal in our study.

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In this research we produce a multi-layer Dye-Sensitized Solar Cell (DSSC) and formulate electrolyte to reduce electric leakage. In general, DSSC compound from FTO/ dense layer/ porous layer with Dye / electrolyte / counter Pt electrode. In this study, we use commercial dye Ruthenium N719, and own Lab-synthesized Coumarin series as dye. Ordinary DSSC use singular size TiO2 and mono-layer as active layer, but we demonstrate a multi-layer and multi-scale TiO2 particle of DSSC for increasing IPCE (incident photon-to- electron conversion efficiency). Compare with standard mono-layer DSSC, multi-layer DSSC has successful gotten promotion about 15%. We use FTO (SnO2:F) as substrate, because after annealing it has low resistance, and it is better to anti-erosion from electrolyte compare with ITO. Ruthenium N719 absorb photon to generate exciton, that separate off into electron and hole. Electron deliver to the FTO substrate through TiO2. But electrons also can deliver to electrolyte result in electron leakage. In order to decrease electron leakage, one solution is to mixed electrolyte with some chemicals. For example, tert-butylpyridine (TBP), that can adhere to sphere of TiO2 reducing electron leakage and promote the IPCE. Because of liquid state of electrolyte is hard to seal DSSC. Our future work is making gel-state electrolyte and improving its efficiency.

TiO2 films as electron collecting interlayers are important in determining the efficiency of organic photovoltaics (OPVs). Various methods of film deposition have been explored, and they revealed the tradeoff between pinhole free coverage (large shunt resistance) and small film thickness (small series resistance). It is hypothesized that atomic layer deposition (ALD) with its self-limiting nature and sub-nanometer level control would be able to circumvent this problem and provide TiO2 films of pinhole free coverage and small thickness. TiO2 films made by chemical vapor deposition (CVD) and ALD were investigated and compared. Conductive atomic force microscopy (CAFM) was used to characterize film morphology and conductivity. X-ray photoelectron spectroscopy (XPS) was utilized to analyze film composition and chemical state. Cyclic voltammetry (CV) was able to reveal the hole blocking capability of films. Finally, organic photovoltaic devices were made with different TiO2 films to reveal the relationship between device property and film characteristic. It is found that both CVD and ALD created TiO2 films with Ti4+ species containing oxygen from hydroxyl groups. They both showed conformal coverage of the electrode via CAFM and CV measurements, and clearly ALD method achieved this with a thinner film and smaller series resistance. This work provided the evidence of effective and surprising capabilities of electron harvesting and hole blocking of ultrathin ALD TiO2 films for OPVs.

In this study, the photocatalytic mineralization of the industrial dump-site leachate was evaluated using an internally-irradiated 18-Litre pilot-scale aerated annular bubble column photoreactor. The study includes evaluating the effect of catalyst loading, leachate initial concentration, initial solution pH, light intensity and oxygen partial pressure. The reaction runs were performed over a 48-hours period at room temperature and atmospheric pressure. Titanium catalyst loading was optimized to be 3 gL-1 where the reaction rate constant 20x10-6 mol L-1 min-1.Beyond this dosage, the effect of light scattering by the catalyst particles were noticed on dropping the degradation rate. Moreover, at high catalyst loading, particles aggregates reduce the interfacial area between the reaction solution and the photocatalyst resulting in significant reduction in the number of active sites on the catalyst surface. It is also noticed that when the initial leachate concentration is high, the number of the active sites are decreased because of their competitive adsorption on the TiO2 particles; while on the other hand, during the light intensity illumination period, the OH radicals formed on the catalyst surface are remaining constant as evidenced by constant hydroxyl production rate. Thus, the reactive O2 attacking the contaminants molecules decrease and simultaneously the overall photodegradation efficiency also decrease dramatically. The plot of the apparent reaction rate constant versus the initial leachate concentration exhibits almost a quadratic behaviour which has an optimum value at concentration of 50 mM. Finally, it was found that the degradation rate constant increased with O2 partial pressure until a maximum was obtained around 50% O2/N2 of gas feed composition. The drop in the rate beyond 50% can be explained by the fact that the dissolved oxygen molecular oxygen is strongly electrophilic and thus increasing the dissolved oxygen content probably reduced electron-hole recombination rate and hence the system was able to maintain favourable charge balance necessary for the photocatalytic-redox process. Moreover, in the presence of excess O2, the photocatalyst surface may become highly hydroxylated to the point of inhibiting the adsorption of organic species causing decrease in the degradation rate. Effect of upflow co-current and counter current continuous operation mode were performed in the 18-litre bubble column photoreactor for the photooxidation degradation tratment of the dump-site landfill leachate. The best situation is liquid flow rate at 800 mL min-1 and total gas flow rate at 5 Lmin-1 for the counter current operation, while for the up-flow co-current operation, the best situation is liquid flow rate at 600 mL min-1 and total gas flow rate at 5 Lmin-1

Orientador: João Manuel Marques Cordeiro / Resumo: Com a constante busca o avanço tecnológico para satisfazer as necessidades da nossa sociedade, verifica-se uma preocupação da sociedade com menor degradação do meio ambiente. Em função disso, busca-se um melhor aproveitamento dos recursos naturais, o que, por sua vez, requer tecnologia apropriada. Na indústria optoeletrônica, a utilização de materiais com propriedades ópticas e condutoras cresce continuamente, porém esta tecnologia está fortemente baseada em óxido de índio (In2O3), que é um material bastante caro, já que é naturalmente escasso. Apresente pesquisa pretende contribuir com o conhecimento, em nível microscópio, das propriedades que governam a condutividade de óxidos de chumbo e óxidos de titânio dopados visando sua utilização como óxido transparente condutor, já que titânio e chumbo são mais baratos que o índio. Estudou-se propriedades eletrônicas de filmes finos de dióxido de titânio (TiO2) e dióxido de chumbo (PbO2) em sua principal fase cristalográfica, a fase rutila, em função da superfície exposta, Empregou-se cálculos ab initio dentro da teoria do funcional de densidade (DFT) implementada no programa CRYSTAL14. Procurou-se entender os fatores responsáveis pela condutividade desses materiais e formular propostas que contribuam para a transformação desses materiais em óxidos condutores transparentes. / Mestre

Thesis submitted in fulfilment of the requirements for the Degree Master of Technology: Chemical Engineering in the Faculty Of Engineering at the Cape Peninsula University of Technology / It is known when synthesising nanomaterial on laboratory scale, a variation in a single synthesis parameter may alter the product. Numerous synthesis techniques have been employed in the synthesis of titanium dioxide with varying phase, size and shape. It was found that changes in the phase directly affect their properties and application, such as treating of textile wastewater by photodegradation. However, when synthesising nanoparticles, changes to any reaction parameters and/or kinetics can have a desirable or undesirable effect on titanium dioxide nanoparticles. There is therefore a need to understand how HCl acid concentration (homogeneous catalyst) and shortened gel formation duration affect synthesis of TiO2 nanoparticles and photocatalytic properties. A sol-gel followed by hydrothermal treatment was employed to synthesise 2.8 grams of titanium dioxide nanorods for the duration of 96 hours, initially. A systematic study was conducted to exploit reaction kinetics by varying HCl acid concentration (3, 4, 5 molar), water feed for TiO2 gel formation (72, 24, 12 hours), and hydrothermal treatment time for the transformation of gel to crystalline TiO2 (1–20 hours). The photocatalytic activity of synthesised TiO2 nanoparticle was evaluated, when irradiated with a UV-C bulb to degrade an industrial textile dye, methylene blue. Systematic studies were successful in identifying the effects HCl acid concentration, gel formation time and lengthened hydrothermal treatment time have on TiO2 nanoparticles’ phase, size and shape. Increased HCl concentrations for shortened gel formation times resulted in mixed phases of TiO2, decreases in particle size and particle shape deformed from nanorods. Increased photocatalytic activity was found for a decrease in the rutile and increase in the brookite phase percentage, but this plateaued after 42% brookite phase. Furthermore, lengthened hydrothermal treatment assisted in phase transformation of particles synthesised at shortened gel formation times for high HCl acid concentrations. Pure rutile TiO2 was synthesised at a sixth of the initial synthesis time. Furthermore, the effects of changes in nanoparticles on the photocatalytic activity was discussed. Moreover, exploiting reaction kinetics resulted in the synthesis of a more efficient photocatalytically active TiO2 nanoparticle sample at shortened synthesis time.

O objetivo desta Tese é preparar e caracterizar nanopartículas de TiO2 e SiO2@ TiO2 e obter filmes finos baseados nesses materiais nanoestruturados usando a metodologia de preparação de filmes conhecida como layer-by-layer (LbL). Primeiramente, TiO2 amorfo sintetizado a partir de sulfato de titanila (TiOSO4) foi cristalizado por método de tratamento hidrotérmico brando (HTT). O efeito da temperatura e tempo de tratamento hidrotérmico na cristalinidade, tamanho de partícula e fotoatividade de TiO2 foi estudado. A análise de MET, DRX e área de superfície confirmou que o HTT a temperatura tão baixa quanto 105°C pode ser utilizada para obter as nanopartículas de anatase com boa cristalinidade (~95%), pequeno tamanho de cristalito (<10 nm), alta área de superfície (>200 m2.g-1) e excelente seletividade da fase. Em uma segunda etapa do projeto, o nanocatalisador de TiO2 foi depositado, via rota sol-gel, na superfície de NPs de sílica Stöber (diâmetro 200 nm), formando um sistema core@shell (SiO2@ TiO2). O objetivo desse processo foi de se obter melhor estabilidade térmica (1000°C), boa dispersão e menor aglomeração do nanocatalisador (TiO2). As análises de microscopia eletrônica (MEV e MET) confirmaram a formação de uma camada porosa (espessura 10-30 nm) de TiO2 formadas por cristalitos com cerca de 5 nm. Um estudo das propriedades ópticas das amostras SiO2@ TiO2 mostrou que o deslocamento no onset de absorção é função do espalhamento Rayleigh. Finalmente, desenvolveu-se um novo e versátil procedimento LbL para a preparação de filmes multicamadas, porosos e uniformes de TiO2 empregando fosfato de celulose (CP) como polieletrólito eficiente e não convencional. A formação dos filmes (CP/ TiO2 e CP/ TiO2/HPW) foi monitorada por espectroscopia UV/Vis e a interação entre os componentes dos filmes (CP, TiO2 e HPW) foi estudada pelas técnicas MET, XPS e FTIR. Estes filmes LbL apresentaram boa fotoatividade para degradação de ácido esteárico, cristal violeta e azul de metileno sobre irradiação UV. Os filmes CP/HPW formados em celulose bacteriana apresentaram boa resposta fotocrômica, que é aumentada pela presença do TiO2 devido a uma transferência eletrônica interfacial do TiO2 para o HPW. A interface entre nanopartículas de titânia e nanopartículas de ácido fosfotungstico foi pela primeira vez caracterizada por Microscopia Eletrônica de Transmissão como sendo não-cristalina. Este método simples e ambientalmente amigável pode ser utilizado para formar recobrimentos em uma grande variedade de superfícies com filmes fotoativos de TiO2 e TiO2/HPW. / The aim of the present investigation was to prepare and characterize TiO2 and core@shell (SiO2@TiO2) nanoparticles (CSNs) and form layer-by-layer (LbL) films with these nanoparticles (NPs) on various substrates. Firstly, amorphous TiO2 were prepared from oxotitanium (IV) sulfate (TiOSO4) and crystallized by low-temperature hydrothermal treatment (HTT). The effect of hydrothermal temperature and treatment time on crystallinity, particle size and photoactivity of TiO2 was studied. The TEM, XRD and BET surface area analysis confirmed that HTT at temperature as low as 105°C can be used to obtain phase-pure anatase nanoparticles with good crystallinity (~95%), small crystallite size (<10 nm), high surface area (>200 m2.g-1) and excellent phase selectivity. Secondly, TiO2 nanocatalyst was directly deposited, via sol-gel route, on the surface of Stöber silica NPs of around 200 nm in a core@shell (SiO2@ TiO2) configuration to obtain better thermal stability, good dispersion and less agglomeration of the nanocatalyst. SEM and TEM observation confirmed the formation of a porous anatase shell of crystalline TiO2 consisting of around 5-8 nm small crystallites, in accordance with XRD results. The shell thickness was varied between 10-30 nm by varying the quantity of precursor titanium (IV) isopropoxide (TiP). Compared to the uncoated silica, the BET surface area also increased by 147-365% depending on the amount of TiP added during synthesis step. The effect of shell morphology and TiO2 loading on surface area and photoactivity has been studied and compared among different CSNs. Finally, a new and versatile LbL procedure for the preparation of porous and highly dispersed multilayer films of TiO2 and phosphotungstic acid (HPW) on different substrates was developed using Cellulose Phosphate (CP) as an efficient and non-conventional binder. The films formation was monitored by UV/Vis spectroscopy and the interaction between the films components (CP, TiO2 and HPW) was studied by HRTEM, XPS and FTIR techniques. These CP/ TiO2 and CP/ TiO2/HPW LbL films showed good photoactivity against stearic acid (SA), crystal violet (CV) and methylene blue (MB) under UV irradiation. The CP/HPW films formed on bacterial cellulose showed good photochromic response, which is enhanced in presence of TiO2 due to an interfacial electron transfer from TiO2 to HPW. This simple and environmentally safe method can be used to form coatings on a variety of surfaces with photoactive TiO2 and TiO2/HPW films.

Hindered-bed separators have been used in several different mineral processing fields for many years. Recent improvements in designs have led to the development of the CrossFlow separator. This new design employs a tangential feed system that has shown promise in several applications. This paper investigates the use of this relatively new technology to upgrade heavy mineral concentrates using Florida type ores. The intended use of this separatory device in this particular application is the removal of gangue quartz from other valuable heavy minerals such as ilmenite, leucoxene, rutile, zircon, and staurolite. The results of two different pilot-scale in-plant testing investigations are discussed. In general, quartz rejections in excess of 80% were achieved while maintaining TiO2 and heavy mineral recoveries above 98% and 99%, respectively. In addition to field test work, two separate unit models have been developed. The first model is an empirical investigation into understanding unit operation and functionality. The second model is a statistical prediction of unit operation based on specific field test work. These models can be used to effectively scale-up a CrossFlow unit for full-scale installation at any Florida heavy mineral sands operation. Emphasis is placed on unit capacity and other operational parameters such as elutriation flowrate and bed level. / Master of Science