Philosophiae Doctor - PhD / In South Africa, almost 90 % of the country’s electricity is generated from coal combustion. This reliance on coal for energy production is projected to continue in the near and medium term due to the increasing demand for industrial and domestic energy. During coal combustion, a large quantity of fly ash is produced as the main waste product and in South Africa approximately 36 - 37 million tons of fly ash is produced on a yearly basis. The management of huge quantities of fly ash has been and still is a continuing challenge that requires urgent intervention. In this regard, there exists an urgent need to maximize fly ash beneficiation, thus forming the motivation for this research. The overall objectives of this thesis was to synthesize high pure phase zeolites A and X from South African fly ash, study their formation mechanism, and explore the potential of mine waters during the synthesis process as well as developing new and efficient zeolite synthetic protocols by the use of ultrasound. In order to address these objectives, the research was designed in a sequential manner so that the preceding results could act as a platform for the attainment of the next objective. In this case, the identification and optimization of synthesis conditions for producing zeolite A and X acted as a basis for understanding the influence of use of mine waters as a substitute for pure water. This further laid the foundation for the in-situ ultrasonic monitoring of the formation process of zeolite A and X from fly ash. The final stages of the study involved use of ultrasonic energy as an ageing tool to improve the conditions obtained during the hydrothermal synthesis of zeolite A as well as investigate the potential to synthesize zeolites directly by use of ultrasound without the need for the fusion, aging or conventional hydrothermal treatment step. The result of the optimized synthesis conditions for producing zeolite A starting either from clear extract of fused fly ash or unseparated, fused South African class F fly ash slurry were molar regimes of 1 Al2O3 : 30.84 Na2O : 4 SiO2 : 414.42 H2O or 1 Al2O3 : 5.39 Na2O : 2.75 SiO2 : 111.82 H2O respectively and at a hydrothermal synthesis temperature of 100 °C for 2 hours. The optimized procedure was simple, efficient and resulted in a considerable improvement of the quality and phase purity of the zeolite A product when the clear extract of fused fly ash was used instead of starting from unseparated, fused fly ash slurry. On the other hand, the optimized synthesis conditions for preparing the typical octahedral shaped zeolite X from South African fly ash was found to be a molar regime of 1 Al2O3 : 4.90 Na2O : 3.63 SiO2 : 115.92 H2O at a hydrothermal synthesis temperature of 80 ºC for hours.

Este trabalho objetivou estudar a síntese de zeólita NaA sob condições hidrotérmicas e aplicála na adsorção de metais pesados. Para a síntese de zeólita NaA, caulim do município de Ipixuna, Pará, foi calcinado a 700 °C por 3 horas para obtenção de metacaulim e usado como fonte de sílica e alumina. Para efeito de comparação, cloreto de alumínio e metassilicato de sódio também foram utilizados na síntese de zeólitas como precursores de Si e Al. A influência da alcalinidade na síntese dos produtos zeolíticos foi avaliada utilizando-se diferentes concentrações de NaOH. Todas as sínteses foram realizadas a 110 °C em autoclaves. Visando à compreensão da influência do tempo na quantidade e tipo de fase formada, foram realizadas sínteses com diferentes tempos de cristalização. Os produtos de reação foram caracterizados por difração de raios X, espectroscopia na região do infravermelho, análise termogravimétrica, análise térmica diferencial, microscopia eletrônica de varredura e adsorção de nitrogênio para cálculo de área específica pelo método BET. A amostra que apresentou maior proporção de zeólita NaA foi utilizada como adsorvente em soluções de Cu2+, Ni2+ e Cd2+ com concentrações iniciais de 25 a 400 mg/L. A concentração de equilíbrio desses metais, após remoção pela zeólita NaA, foi determinada por espectrofotometria de absorção atômica. Os resultados mostraram que o aumento da alcalinidade e do tempo de cristalização favoreceu a obtenção de sodalita, uma fase zeolítica concorrente à Zeólita A, nos produtos de síntese. A zeólita NaA provou ser um excelente adsorvente para remoção dos metais analisados, apresentando uma capacidade de adsorção máxima de aproximadamente 79, 65 e 32 mg/g para Cd2+, Cu2+ e Ni2+, respectivamente. O modelo de isoterma de adsorção que melhor descreveu a remoção de metais pela zeólita NaA foi o de Langmuir. / The aim of this work was to study the synthesis of zeolite NaA under hydrothermal conditions and use it as adsorbent of heavy metals. To synthesize zeolite NaA, kaolin from the city of Ipixuna, Pará, was calcined at 700 °C for 3 hours and used as source of silica and alumina. For comparison purposes, aluminum chloride and sodium metasilicate were also used in the synthesis of zeolites as precursors of Si and Al. The influence of alkalinity on the synthesis of the zeolitic products was evaluated using different NaOH concentrations. All the syntheses were performed at 110 °C by autoclaving. To understand the influence of time on the type and relative amount of the obtained phases, syntheses with different crystallization times were carried out. The reaction products were characterized by means of X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, thermal differential analysis, scanning electron microscopy and nitrogen adsorption for calculating surface area by the BET method. One of the samples, which exhibited the highest content of zeolite NaA, was used as adsorbent of Cu2+, Ni2+ and Cd2+ solutions with initial concentrations ranging from 25 to 400 mg/L. The equilibrium concentration of these heavy metals, after removal by zeolite NaA, was determined by atomic absorption spectrophotometry. The results showed that increasing alkalinity of the reaction medium led to the formation of sodalite, a concurrent zeolitic phase, in the products. Zeolite NaA turned out to be an excellent adsorbent for removing heavy metals, with an adsorption capacity of 79, 65 and 32 mg/g for Cu2+, Cd2+ and Ni2+, respectively. The Langmuir isotherm model was the most appropriate to describe the removal of metals by zeolite A.

In the context of the future hydrogen economy, effective production of hydrogen (H2) from readily available and sustainable resources is of crucial importance. Hydrogen generation via water splitting by solar energy or electricity has attracted great attention in recent years. In comparison with photocatalytic water-splitting directly using solar light, which is ideal but the relevant technologies are not yet mature, electrolysis of water with catalyst is more practical at the current stage. The Pt-group noble metals are the most effective electrocatalysts for hydrogen evolution reaction (HER) from water, but their high costs limit their applications. Due to the earth-abundance and low price, MoS2 is expected to be a good alternative of the Pt-group metals for HER. Plenty of researches have been conducted for improving the HER activities of MoS2 by optimizing its synthesis method. However, it remains challenging to prepare MoS2 catalysts with high and controllable activity, and more investigations are still needed to better understand the structure-performance correlation in this system. In this thesis, we report a new strategy for fabricating MoS2 eletrocatalysts which gives rise to much improved HER performance and allows us to tune the electrocatalytic activity by varying the preparation conditions. Specifically, we sulfurized molybdenum oxide on the surface of a Ti foil electrode via a facile chemical vapor deposition (CVD) method, and directly used the electrode for HER testing. Depending on the CVD temperature, the MoO2-MoS2 nanocomposites show different HER activities. Under the optimal synthesis condition (400ºC), the resulting catalyst exhibited excellent HER activity: an onset potential (overpotential) of 0.095 V versus RHE and the Tafel slope of 40 mv/dec. Such a performance exceeds those of most reported MoS2 based HER electrocatalysts. We demonstrated that the CVD temperature has significant influence on the catalysts in crystallinity degree, particle size and dispersion, morphology, and density of the edge sites etc., and these factors in turn determine the HER activity.

Zeolitic imidazolate frameworks (ZIFs) is a new class of metal-organic frameworks (MOFs) with zeolite-like properties such as permanent porosity, uniform pore size, and exceptional thermal and chemical stability. Until recently, ZIF materials have been mostly synthesized by solvothermal method. In this thesis, further analysis to tune the size and morphology of ZIF-8 is done upon our group’s recent success in preparing ZIF-8 crystals in pure aqueous solutions. Compositional parameters (molar ratio of 2-methylimidazole/Zn2+, type of zinc salt reagents, reagent concentrations, addition of surfactants) as well as process parameters (temperature and time) were systematically investigated. Upon characterizations of as-synthesized samples by X-ray powder diffraction, thermal gravimetric analysis, N2 adsorption, and field-emission scanning electron microscope, the results show that the particle size and morphology of ZIF-8 crystals are extremely sensitive to the compotional parameters of reagent concentration and addition of surfactants. The particle size and morphology of hydrothermally synthesized ZIF-8 crystals can be finely tuned; with the size ranging from 90 nm to 4 μm and the shape from truncated cubic to rhombic dodecahedron.

Philosophiae Doctor - PhD / The commercial need to improve the performance of low-cost organic solar cells has led to the idea for this research. The study discusses the synthesis of one dimensional TiO2 and ZnO nanowire arrays synthesised using a hydrothermal autoclave method and their application in bulk heterojunction inverted organic solar cells. Previous literature has shown that the precise manipulation, positioning and assembly of 1D nanostructures remain one of the greatest challenges in the field of nanotechnology, with much of the difficulty arising primarily from the lack of size and scale of the materials as well as the inability to visualise the nanostructures. In particular, one dimensional metal-oxides such as TiO2, ZnO and Fe2O3 have emerged as attractive alternatives to traditional semiconductor structures such as Si and GaAs as they are simple and inexpensive to manufacture, with research showing that application of ZnO nano-cones yield efficiencies of 8.4%, which is very attractive given the scope that exists in optimising the metal-oxide architecture. Much is still to be learned from the precise structural features of these materials and their influence on device performance. In this regard, this work largely focuses on this aspect of metal-oxide nanowires prior their application in organic solar cells.

京都大学 / 新制・課程博士 / 博士(エネルギー科学) / 甲第24302号 / エネ博第453号 / 新制||エネ||85(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 佐川 尚, 教授 萩原 理加, 教授 野平 俊之 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

The work presented in this thesis is divided into two research areas. In part I, the synthesis and guest intercalation of inorganic-organic metal halide ammonium layered perovskites is discussed. Comparisons are made between the solid matrix before and after the intercalations, and all solids are characterized using thermogravimetric analysis (TGA) and powder X-ray diffraction (XRD). In part II, “templateree” hydrothermal synthesis of tin oxide spheres in the presence of different ortho-substituted anilines is discussed. The aim is to determine whether there are differences in the structures, shapes and surface morphology of the tin oxide spheres that correspond to the identity/shape of the ortho-substituent on the anilines. Solids were characterized by XRD, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques.

Multifunctional nanomaterials can be engineered to aid in the diagnosis of diseases, enable efficient drug delivery, monitor treatment progress over time, and evaluate treatment outcomes. This strategy, known as theranostics, focuses on the combination of diagnostic and therapeutic techniques to provide new clinically safe and efficient personalized treatments. The evaluation of different nanomaterials’ properties and their customization for specific medical applications has therefore been a significant area of interest within the scientific community. Iron oxide nanoparticles, specifically those based on iron (II, III) oxide (magnetite, Fe3O4), have been prominently investigated for biomedical, theranostic applications due to their documented superparamagnetism, high biocompatibility, and other unique physicochemical properties. The aim of this thesis is to establish a viable set of methods for preparing magnetite (iron oxide) nanoparticles through hydrothermal synthesis and modifying their surfaces with organic functional groups in order to both modulate surface chemistry and facilitate the attachment of molecules such as peptides via covalent bond formations. Modifying their surfaces with biomolecules such as peptides can further increase their uptake into cells, which is a necessary step in the mechanisms of their desired biomedical applications. The methods of nanoparticle synthesis, surface functionalization, and characterization involving electron microscopy (e.g., SEM, TEM), zeta potential measurements, size analysis (i.e., DLS), and FT-IR spectroscopy will be presented. / Bioengineering

Zeolites are crystalline aluminosilicates with diverse structures and uniform porosities. They are widely used as catalysts, adsorbents and ion-exchangers in industry. Direct or post modifications optimize the performance of zeolites for different applications. In this thesis, IZM-2 and TON-type zeolites were synthesized, modified and studied. In addition, FAU-type zeolite and silicoaluminophosphate (SAPO) molecular sieves were applied as templates for the preparation of microporous carbons. In the first part of this thesis, the IZM-2 zeolite with an unknown structure was synthesized. We focused on the increasing the secondary porosity and the varied framework compositions upon post modifications. The structure determination of this IZM-2 zeolite was hindered by the small size of crystals. In the second part of this thesis, the synthesis composition was directly modified in order to increase the crystal sizes. IZM-2 crystals were enlarged by excluding the aluminium atoms from the framework. The micropores of the obtained pure-silica polymorphs were activated by ion-exchanging alkali-metal ions with protons. Typically, TON-type zeolites that are synthesized at hydrothermal conditions under stirring have needle-shaped crystals. In the third part of this thesis, snowflake-shaped aggregates were produced by using static hydrothermal conditions for the synthesis of TON-type zeolites. The effects of synthesis parameters on the growth and morphology of crystals were discussed in detail. In the last part of this thesis, microporous carbons with a structural regularity were prepared by chemical vapour deposition (CVD) of propylene using a silicoaluminophosphate (SAPO-37) template. Compared to the conventional zeolite templates, the SAPO template could be removed under mild conditions, without using hydrofluoric acid, and the generated carbons had a large specific surface area and a high fraction of ultrasmall micropores. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

Les matériaux pour la photocatalyse en lumière visible ont attiré un grand intérêt car ils peuvent exploiter tout le spectre d'irradiation solaire notamment afin de détruire des polluants organiques pour l'environnement comme dans la purification de l’eau. Dans ce contexte, le bismuth de vanadates (BiVO4) est digne d'intérêt en raison de sa largeur de bande interdite électronique (~ 2,3 eV) et sa potentielle activité photocatalytique. Des études systématiques ont été menées pour les caractéristiques physico- chimiques de poudres BiVO4 synthétisées par voie hydrothermale et par broyage mécanique à haute énergie. La pertinence de la méthode de mécano-synthèse a été démontrée grâce notamment à son faible coût de fonctionnement, de mise en œuvre facile ainsi que le nombre limité de paramètres et la possibilité d’obtenir des particules à taille réduite (20-100 nm) avec une phase cristalline monoclinique. En couches minces, les matériaux BiVO4 ont été synthétisés par pulvérisation ultrasonique (USP) et par pulvérisation cathodique radiofréquence (rf). Les paramètres pour des dépôts optimaux ont été identifiés permettant d’obtenir des films minces sans fissures, suffisamment denses avec des surfaces texturées à morphologies contrôlées. Les études structurales, vibrationnelles, et les propriétés électroniques et optiques ainsi que leur interprétation grâce à des modèles ont été menées pour une parfaite connaissance des caractéristiques des matériaux BiVO4. Pour les applications visées, BiVO4 sous forme de poudres et de films minces ont été utilisés comme photocatalyseurs pour la dégradation de rhodamine 6G (Rh6) et le bleu de méthylène (MB) sous irradiation en lumière visible. La structure scheelite monoclinique de nanoparticules sphérique de BiVO4 obtenues par mécano-synthèse, ont montré une efficacité améliorée (+50%) de l’activité photocatalytique par rapport à des particules de forme aciculaire obtenues par voie hydrothermale. Dans le cas de films minces, le taux de dégradation du BM est de l’ordre est de 66% pour les films synthétisés par USP alors qu’un taux de 99% a été atteint avec des films obtenus par pulvérisation cathodique rf. Ces travaux valident les propriétés photocatalytiques remarquables de BiVO4 par rapport aux matériaux existants avec des applications prometteuses, notamment dans la résolution de problèmes environnementaux. / Visible light photocatalysts have attracted a great interest since it may exploit the wide solar irradiation spectrum to destroy organic dyes as required for environmental need such as water purification. In this context, bismuth vanadate (BiVO4) is worth of interest due to its narrow band gap (~ 2.3 eV) and the ability to exhibit efficient photocatalytic activity. Systematic studies have been carried out on the physico-chemistry of BiVO4 synthesized as powders by hydrothermal and mechano-chemical techniques. The relevance of ball milling method was demonstrated through its low processing cost and easy scaling up as well as limited variable parameters to obtain reduced particle sizes down to (20-100 nm). As thin films, BiVO4 were grown by ultrasonic spray pyrolysis (USP) and rf-sputtering techniques. Optimum deposition parameters were identified, leading to the formation of crack free, dense media with textured surfaces composed by controlled morphologies. Analysis of the structural, vibrational, electronic and optical experiments, interpretation and development of models were carried out for deep insight on the properties of BiVO4 materials. For concrete applications, BiVO4 as powders and thin films were used as photocatalysts for the degradation of rhodamine 6G (Rh6) and methylene blue (MB) under visible light irradiation. Monoclinic scheelite structure of spherical-like BiVO4 nanoparticles obtained by mechano-chemical process, have shown 50% more efficient photocatalytic activity compared to acicular-like BiVO4 grains obtained by hydrothermal method. The average degradation rate of MB using USP grown films was found to be 66% during 120 minutes. A significant rate increase in the photocatalytic activity up to 99% was achieved by using rf-sputtered films. Thus, BiVO4 was demonstrated as efficient photocatalysts compared to existing materials with promising applications notably in solving environmental problems.