Neste trabalho foi desenvolvido um procedimento experimental para a fabricação de estruturas 3D de nanotubos de carbono crescidos sobre substrato de cobre e decorados com partículas de óxido de titânio. Foram relacionados os três tipos diferentes de NTCs nesta estrutura (simples, dopados com nitrogênio e tratados com plasma) com a deposição do TiO2 por ALD. Foram igualmente propostas três aplicações para esta estrutura. A síntese dos NTCs verticalmente orientados, dopados e não dopados, foi otimizada dentre alguns parâmetros de síntese como temperatura, agente oxidante e principalmente, o filme catalisador. A introdução de defeitos nos NTCP através do tratamento a plasma oxidativo foi avaliada frente a variáveis como pressão, potência e tempo de exposição. A relação entre os defeitos destes três tipos de NTCs e a deposição de TiO2 por ALD foi avaliada por microscopia eletrônica de transmissão, Raman, XPS e TGA. O procedimento experimental para confecção da estrutura 3D foi desenvolvido etapa por etapa via diversas técnicas experimentais, desde caracterização química, imagem, até testes empíricos. Na estrutura final, foram avaliadas as propriedades fotocatalíticas pela decomposição de corante orgânico em meio aquoso, propriedades capacitivas por voltametria cíclica e propriedades de emissão por campo através de curvas de campo elétrico por corrente de emissão e diagramas F-N. Foram obtidas florestas de NTCs de boa qualidade com até 0.5mm de altura, de diâmetros e número de paredes regulares. Nestes foi possível introduzir defeitos de maneira controlável, mantendo o arranjo da floresta. As florestas de NTCNx alcançam uma altura de até 0,3mm com concentração de nitrogênio de 2% tendo os nanotubos uma estrutura típica “bamboo-like”. Os resultados mostram a relação entre o tipo de defeito e a deposição de TiO2 por ALD, obtendo-se partículas cristalinas para os NTCP e NTCNx, sendo neste ultimo as partículas homogeneamente distribuídas e com tamanho uniforme, enquanto nos NTCOx forma-se uma densa camada de TiO2 composta por grandes grãos monocristalinos A partir de processo como tratamentos térmicos e transferência dos NTC de substrato foi possível obter uma estrutura 3D composta de uma camada carbono grafítico e NTC-VAs sobre um substrato de cobre, sem alterar o arranjo inicial das florestas. As amostras mostraram efeito de emissão de elétrons por campo elétrico, porém estas requerem uma análise mais quantitativa. Os ensaios de fotocatálise mostraram que a imobilização do TiO2 em um suporte denso inviabiliza a degradação do corante em meio aquoso. Os NTCNx apresentaram maior capacitância que as mostras de NTCP, e o TiO2 foi aparentemente ineficaz para a melhoria desta propriedade. / In this work, we propose an experimental procedure for fabrication of 3D carbon nanotubes structures anchored with titanium oxide particles, on a copper substrate. We correlate three different types of CNTs from this structure (pristine, doped with nitrogen and treated with plasma) with the deposition of TiO2 by ALD. It was yet suggested, three applications for this structure. The synthesis of vertically aligned CNTs, doped and undoped, was optimized among several synthesis parameters such as temperature, oxidizing agent and specially, the catalyst film. The introduction of defects in NTCP by oxidative plasma treatment was evaluated against variables such as pressure, power and exposure time. The association between the defects from these three types of CNTs and the deposition of TiO2 by ALD was assessed by transmission microscopy, Raman, XPS and TGA. The experimental procedure for assembling the 3D structure had been studied step by step by various techniques, from chemical and imaging, up to empirical testing. In the final structure, the photocatalytic properties were evaluated by the organic dye decomposition in an aqueous medium, capacitive properties by cyclic voltammetry and field emission properties through electric field versus emission current curves and F-N diagram. Was obtained high quality NTCs with a height up to 0.5mm with regular diameters and number of walls. On these, it was introduced, in a controllable way, a high amount of defects without jeopardizing the forest structure. The NTCNx forest reach a 0,3nm height with a 2% nitrogen concentration in its typical structure “bamboo-like”. The results show the relation between the type of defect and the deposition of TiO2 by ALD, forming crystalline particles over the NTCP and NTCNx, in this last evenly distributed with uniform size, while on the NTCOx is is formed a dense TiO2 layer shaped by large monocrystalline grains. By process such as heat treatments and CNT transferring was achieved a 3d structure composed by a graphitic carbon layer and VACNTs over a cupper substrate, without disturb the forest assembly. The samples showed electron field emission effect, but its assessment for quantitative analysis was limited to technical issues. The photocatalysis tests showed that immobilization of TiO2 on a dense support prevents the dye degradation in an aqueous medium. The NTCNx shown higher capacitance than NTCP, and the TiO2 was apparently ineffective for improvement of this property.

Durant cette thèse, des couches minces de fer, de fer-cuivre et de cuivre-zinc déposées par pulvérisation magnétron ont été oxydées par des post-décharges plasma pour synthétiser des nanostructures d’oxydes métalliques. L’oxydation par post-décharge permet un abaissement de la température par rapport à l’oxydation thermique dans la mesure où l’oxygène moléculaire est excité ou dissocié, ce qui fournit des espèces plus réactives comme l’oxygène singulet ou l’oxygène atomique. Cette oxydation à température modérée favorise une croissance anisotrope des cristaux. L’oxydation de couches minces de Fe-Cu a conduit à la croissance de nanolamelles de Fe2O3 et de nanoparois, nanotours et nanofils de CuO. La distribution surfacique de ces nanostructures dépend de la température d’oxydation, de la concentration des espèces réactives et de la composition initiale de la couche mince. L’oxydation de couches minces de Cu-Zn a conduit à la croissance de nanofils ultra-minces de ZnO dans lesquels un confinement quantique peut se produire. Les nanostructures obtenues ont été caractérisées par différentes techniques (microscopies électroniques, diffraction des rayons X et spectrométrie de masse des ions secondaires). Les mécanismes de croissance de ces nanostructures sont basés sur le rôle des contraintes, de la température, de la concentration des espèces réactives ainsi que sur l’influence de la taille des grains sous-jacents. Les nanostructures d’oxydes métalliques obtenues serviront comme photocatalyseurs pour produire de l’hydrogène par photolyse de l’eau. Par ailleurs, les nanofils ultra-minces de ZnO serviront de photocatalyseurs pour la purification de l’eau / In this manuscript, metallic oxide nanostructures were synthesized by the oxidation of iron, iron-copper and copper-zinc thin films by means of a plasma afterglow. Thin films were deposited by magnetron sputtering. The use of plasma afterglows allows a lowering of the temperature compared with the thermal oxidation conditions, given that molecular oxygen is excited or dissociated, which provides more reactive species such as singlet oxygen or atomic oxygen. This oxidation at moderate temperature promotes anisotropic crystal growth. The oxidation of iron–copper thin films leads to the synthesis of Fe2O3 nanoblades and CuO nanowalls, nanotowers and nanowires. The surface distribution of these nanostructures depends on the oxidation temperature, the concentration of the reactive species and the initial composition of the thin layers. The oxidation of copper-zinc thin films leads to the synthesis of ultra-thin ZnO nanowires in which quantum confinement could occur. As-grown nanostructures were characterized by various techniques (electron microscopy, X-ray diffraction and secondary ion mass spectrometry). The growth mechanisms described for these nanostructures relies on the role of stress, temperature, reactive species concentration and on the effect of underlying grain size. As-synthesized nanostructures will serve as photocatalysts to produce hydrogen by water splitting. In addition, ultra-thin ZnO nanowires will also serve as photocatalysts for water purification

Neste trabalho foi desenvolvido um procedimento experimental para a fabricação de estruturas 3D de nanotubos de carbono crescidos sobre substrato de cobre e decorados com partículas de óxido de titânio. Foram relacionados os três tipos diferentes de NTCs nesta estrutura (simples, dopados com nitrogênio e tratados com plasma) com a deposição do TiO2 por ALD. Foram igualmente propostas três aplicações para esta estrutura. A síntese dos NTCs verticalmente orientados, dopados e não dopados, foi otimizada dentre alguns parâmetros de síntese como temperatura, agente oxidante e principalmente, o filme catalisador. A introdução de defeitos nos NTCP através do tratamento a plasma oxidativo foi avaliada frente a variáveis como pressão, potência e tempo de exposição. A relação entre os defeitos destes três tipos de NTCs e a deposição de TiO2 por ALD foi avaliada por microscopia eletrônica de transmissão, Raman, XPS e TGA. O procedimento experimental para confecção da estrutura 3D foi desenvolvido etapa por etapa via diversas técnicas experimentais, desde caracterização química, imagem, até testes empíricos. Na estrutura final, foram avaliadas as propriedades fotocatalíticas pela decomposição de corante orgânico em meio aquoso, propriedades capacitivas por voltametria cíclica e propriedades de emissão por campo através de curvas de campo elétrico por corrente de emissão e diagramas F-N. Foram obtidas florestas de NTCs de boa qualidade com até 0.5mm de altura, de diâmetros e número de paredes regulares. Nestes foi possível introduzir defeitos de maneira controlável, mantendo o arranjo da floresta. As florestas de NTCNx alcançam uma altura de até 0,3mm com concentração de nitrogênio de 2% tendo os nanotubos uma estrutura típica “bamboo-like”. Os resultados mostram a relação entre o tipo de defeito e a deposição de TiO2 por ALD, obtendo-se partículas cristalinas para os NTCP e NTCNx, sendo neste ultimo as partículas homogeneamente distribuídas e com tamanho uniforme, enquanto nos NTCOx forma-se uma densa camada de TiO2 composta por grandes grãos monocristalinos A partir de processo como tratamentos térmicos e transferência dos NTC de substrato foi possível obter uma estrutura 3D composta de uma camada carbono grafítico e NTC-VAs sobre um substrato de cobre, sem alterar o arranjo inicial das florestas. As amostras mostraram efeito de emissão de elétrons por campo elétrico, porém estas requerem uma análise mais quantitativa. Os ensaios de fotocatálise mostraram que a imobilização do TiO2 em um suporte denso inviabiliza a degradação do corante em meio aquoso. Os NTCNx apresentaram maior capacitância que as mostras de NTCP, e o TiO2 foi aparentemente ineficaz para a melhoria desta propriedade. / In this work, we propose an experimental procedure for fabrication of 3D carbon nanotubes structures anchored with titanium oxide particles, on a copper substrate. We correlate three different types of CNTs from this structure (pristine, doped with nitrogen and treated with plasma) with the deposition of TiO2 by ALD. It was yet suggested, three applications for this structure. The synthesis of vertically aligned CNTs, doped and undoped, was optimized among several synthesis parameters such as temperature, oxidizing agent and specially, the catalyst film. The introduction of defects in NTCP by oxidative plasma treatment was evaluated against variables such as pressure, power and exposure time. The association between the defects from these three types of CNTs and the deposition of TiO2 by ALD was assessed by transmission microscopy, Raman, XPS and TGA. The experimental procedure for assembling the 3D structure had been studied step by step by various techniques, from chemical and imaging, up to empirical testing. In the final structure, the photocatalytic properties were evaluated by the organic dye decomposition in an aqueous medium, capacitive properties by cyclic voltammetry and field emission properties through electric field versus emission current curves and F-N diagram. Was obtained high quality NTCs with a height up to 0.5mm with regular diameters and number of walls. On these, it was introduced, in a controllable way, a high amount of defects without jeopardizing the forest structure. The NTCNx forest reach a 0,3nm height with a 2% nitrogen concentration in its typical structure “bamboo-like”. The results show the relation between the type of defect and the deposition of TiO2 by ALD, forming crystalline particles over the NTCP and NTCNx, in this last evenly distributed with uniform size, while on the NTCOx is is formed a dense TiO2 layer shaped by large monocrystalline grains. By process such as heat treatments and CNT transferring was achieved a 3d structure composed by a graphitic carbon layer and VACNTs over a cupper substrate, without disturb the forest assembly. The samples showed electron field emission effect, but its assessment for quantitative analysis was limited to technical issues. The photocatalysis tests showed that immobilization of TiO2 on a dense support prevents the dye degradation in an aqueous medium. The NTCNx shown higher capacitance than NTCP, and the TiO2 was apparently ineffective for improvement of this property.

Une opportunité attrayante consisterait à utiliser l'énergie solaire, abondante et (quasi)inépuisable, pour valoriser le CO2 en carburants. Ceci permettrait de répondre à une double préoccupation : le dérèglement climatique imputable à l’augmentation de la concentration de gaz à effet de serre dans l’atmosphère d’une part, et d’autre part la raréfaction annoncée des ressources en énergie. Les végétaux sont capables de réduire le dioxyde de carbone en composés hydrogénocarbonés et d’oxyder simultanément l’eau en dioxygène par photosynthèse. Cette étude se propose d’élaborer des matériaux capables d’absorber la lumière et d’imiter le processus naturel, notamment son schéma énergétique en Z. La création de systèmes inorganiques comportant des hétérojonctions SCp (cathode) - Métal - SCn (anode) a été envisagée pour répondre à la problématique. Deux stratégies de synthèse ont alors été mises au point afin d’élaborer différents photocatalyseurs composite SCp@M/SCn notamment Cu2O@Pt/TiO2. L’évaluation des performances photocatalytiques a permis de révéler les bénéfices apportés par la présence d’hétérojunctions en termes de séparation des charges photogénérées et de sélectivité quant à la production de composés hydrogénocarbonés par photocatalyse. Ces travaux apportent une pierre importante à l’édifice d’un procédé de « photosynthèse artificielle » / An enticing opportunity would consist in using abundant and inexhaustible solar energy to valorise CO2 into fuels. That might answer in an elegant way to environmental and energetic concerns: the global warming due to atmospheric CO2 concentration increase and the dreaded shortage of energy resources. Green plants are able to reduce carbon dioxide into hydrocarbonated compounds and to oxidise simultaneously water into dioxygen by using photosynthesis. This study will focus on the design of materials able to absorb light and to imitate this natural process and more particularly its typical energetic Z-scheme. The chosen strategy is the creation of inorganic systems with SC-p (cathode) - Metal - SC-n (anode) heterojunctions. Two synthesis strategies were elaborated to obtain composite photocatalysts SCp@M/SCn, and more particularly Cu2O@Pt/TiO2. The evaluation of photocatalytic performances reveals heterojunctions benefits in term of charge separation and selectivity for photocatalytic hydrocarbonated compounds production. This study seems to do its bit towards “artificial photosynthesis” process

[pt] O dióxido de titânio é amplamente utilizado pela indústria e pesquisa como fotocatalisador, cuja principal desvantagem ainda é sua aplicação sob luz visível. Propriedades como quantidade de fases, tamanho do cristalito, área de superfície específica, volume de poros e valor da banda proibida (Eg) são explorados por métodos de síntes e para aprimorar a performance do TiO2. No entanto, elas são ajustadas empiracamente. O presente trabalho foi realizado a fim de descrever uma relação analítica entre essas propriedades para a fotocatálise, usando Redes Neurais Artificiais (RNAs) como ferramente estatística. Afim de ter o banco de dados mais representativo, foram usados 53 artigos. O Eg foi considerado a medida a qual avalia a performance fotocatalítica, sendo o parâmetro de saída da rede. Dois blocos A e B, distintos pelas variáveis de entrada, foram arranjados em grupos para investigar a influência das variáveis em pares, com 257 e 220 fotocatalisadores para cada, respectivamente. Exploraram-se diferentes algoritmos de treinamento (baseados em Retropropagação), tipos de redes (Feedforward, Cascade forward e Elman), funções de transferência, número de neurônios e redemulticamadas. Avaliaram-se os modelos pela Soma dos Erros Quadráticos (SSE),pelo coeficiente de correlação de regressão (R2) tanto para o treinamento e quanto para o teste, pelo comportamento de predição do banco de dados e pelo diagrama de regressão dos valores preditos pelos observados. Os resultados do bloco A sugerem que as variáveis não aparentam ter uma relação. Os modelos de múltiplas camadas no bloco B revelaram um aumento no desempenho. O resultado de maior coeficiente teve topologia de 4-4-6-1, correspondendo a camada de entrada, primeira camada oculta, segunda camada oculta e camda de saída, respectivamente. Obteve-se R2 de 84 por cento para o treinamento e 50 por cento para o teste, com SSE de 2.24.Esse resultado sugere que a rede não é capaz de prever o Eg, mas ela pode ser aprimorada. Os parâmetros estruturais devem ser revisados, de acordo com padrões de caracterizações e dados estatísticos. Consequentemente, o modelo pode ser bem ajustado, otimizado e usado na melhoria da fotocatálise. / [en] Titanium dioxide has been widely applied by industry and scientific research as a photocatalyst,whose main drawback still has been the application under visible light.Properties such as phases amount,crystallite size, specific surface area, pore volume, and band gap value (Eg)have been explored by synthesis methods to improve TiO2 s performance. However, they are empirically adjusted.The present work was carried out to describe an analytical relation between those properties for photocatalysis, using Artificial Neural Networks (ANNs) as a statistical tool. Aiming the most representative set, 53 literature papers were used for the database. Eg was considered the measurement which evaluates the photocatalytic performance, namely the network s out put variable. Two blocks A and B, which are distinguished by input variables, were arranged into groups to investigate the variables pair influences, using 257 and 220 photocatalysts vectors for each,respectively. Modelling attempts examined different training algorithms(based on Back- propagation), types of networks (Feedforward, Cascade forward and Elman), transfer functions, number of hidden neurons, and multilayer network.The developedmodelswereevaluatedbythesumofsquarederror(SSE),the correlation coefficient(R2) of regression for both training and test data, the prediction behaviour of the dataset,and the regression diagram of predicted and observed values. The block A results suggest the variables do not have an apparent relationship. Multilayers models on block B revealed an increase of network identification performance. The result with the highest coefficient showed 4-4-6-1 topology; corresponding, respectively, to input, first hidden, second hidden and output layers.It had R2 of 84 percent for training and to 50 percent fortest, with SSE of 2.24.This result suggests this network is not able topredict the Eg, but it can be improved. The structural properties should be reviewed, according to standards of characterization and statistical data. Hence, the model could be well fitted, optimized, and used for photocatalysis improvement.

Treatment of wastewater using magnetic technology is a rising field. In this thesis, the latest research on the subject is reviewed and several adsorbents with different coatings, which impart them unique properties, are discussed. Separation of particles from aqueous solution using magnetic technology is more convenient compared to conventional techniques, such as filtration and centrifugation. The adsorbents described in this thesis are effective for adsorption of several types of contaminants, such as heavy metals and different types of dyes.    Magnetic microspheres were synthesised using porous polystyrene microspheres as template. The microspheres were first sulfonated using chlorosulfonic acid followed by stirring in the presence of ferrous chloride which then was oxidised and magnetic nanoparticles were formed on the surface.    The sulfonated microspheres had a surface area of 420 m2/g and the magnetic 175 m2/g, indicative of Fe3O4 nanoparticles were successfully formed in the pores. The weight fraction of the Fe3O4 nanoparticles in the magnetic microspheres was 33 %.    Adsorption and desorption studies of the cationic dye, methylene blue, using mesoporous magnetic microspheres were performed. The results show that the mesoporous magnetic microspheres have good ability to adsorb methylene blue at low concentrations. In a cycle study the adsorption efficiency were nearly 100 % throughout the study. Using a 6/4 EtOH/H2O with saturated KCl solution the desorption efficiency in the cycle study were about 95 %.      The microspheres were used as carriers for TiO2 in order to overcome the problem with the separation of TiO2 from solution. The TGA results show that the microspheres contained about 12 % of TiO2. The TiO2 coated microspheres were used for the photocatalytic degradation of phenol. However, the TiO2 microspheres did not work. This was a result from that the phenol had too little contact with the TiO2. A possible way of solving this problem could be to decrease the size of the microspheres, thus increase the surface area.    Lysozyme was adsorbed and separated using the porous microspheres. The lysozyme adsorption worked best at pH 9.6, which is the pI for lysozyme. The lysozyme could be extracted from the microspheres by using a pH 13 buffer. Also, by using MeOH/H2O and EtOH/H2O solutions with saturated KCl the lysozyme could be desorbed. An adsorption and desorption mechanism was also presented. / Vattenrening med magnetisk teknologi är en ny och alltmer uppmärksammad teknik. Magnetisk separation är ett enkelt och snabbt sätt att separera något från en lösning. Magnetisk separation är mer lätthanterligt jämfört med traditionell separationsteknik såsom centrifugering och filtrering.  Med porösa polystyren mikrosfärer som mall, syntetiserades magnetiska mikrosfärer. Först så sulfonerades mikrosfärerna med klorosulfonisk syra, följt av att de rördes om i en järnkloridlösning. Magnetiska nanopartiklar bildades i porerna och på ytan av mikrosfärerna.    Sulfonerade mikrosfärerna hade en specifik ytarea på 420 m2/g och de magnetiska 175　m2/g, detta indikerar att Fe3O4-nanopartiklar bildades på ytan och i porerna. Massfraktionen av Fe3O4 var 33 %.    Adsorption- och desorptionsstudier på de magnetiska mikrosfärerna utfördes. Färgämnet metylblått användes i studien. Resultaten visade att magnetiska mikrosfärerna hade en bra adsorptionsförmåga vid låga koncentrationer av metylblått. Cykelstudier visade att adsorptionsverkningsgraden var nära 100 % under flera adsorptionscykler. Desorptionsförsök med olika lösningsmedel visade att en mättad KCl 6/4 EtOH/H2O lösning gav en desorptions-verkningsgrad på ca 95 %.   Mikrosfärerna användes som mall och kärna för att syntetisera en TiO2-fotokatalysator, detta för att överkomma problemet som finns med separation av rent TiO2 pulver från lösning. TGA resultaten visade att mikrosfärerna innehöll ca 12 % TiO2. De syntetiserade TiO2-mikrosfärerna användes till att bryta ner fenol fotokatalytiskt. Dock fungerade inte detta experiment. En anledning var att fenolen hade för lite kontakt med TiO2. En lösning på detta problem är att använda mikrosfärer med högre specifik ytarea.    Proteinet lysozym användes som modellprotein för försök att separera proteiner från lösning genom att använda porösa mikrosfärer. Resultatet visade att lysozym kunde adsorberas vid pH 9.6. Med en pH 13 buffer kunde lysozymet sedan extraheras från mikrosfärerna. En mekanism för adsorptionen och desorptionen på mikrosfärerna presenterades.

No description available.

Doctor of Philosophy / Department of Chemical Engineering / Larry E. Erickson / Over the past decade, nanomaterials have been the subject of enormous interest. Their defining characteristic is a very small size in the range of 1-100 nm. Due to their nanometer size, nanomaterials are known to have unique mechanical, thermal, biological, optical and chemical properties, together with the potential for wide-ranging industrial applications. Here, we synthesized nanocrystalline metal oxides through the sol-gel process and used these materials as desulfurization adsorbents and photocatalysts. Deep desulfurization of fuels has received more and more attention worldwide, not only because of health and environmental consideration but also due to the need for producing ultra-low-sulfur fuels, which can only be achieved under severe operating conditions at high cost using hydrodesulfurization (HDS). Consequently, development of new and affordable deep desulfurization processes to satisfy the decreasing limit of sulfur content in fuels is a big challenge. Sol-gel derived Cu/Al[subscript]2O[subscript]3 and Zn/Al[subscript]2O[subscript]3 adsorbents have been demonstrated to be effective in the removal of thiophene from a model solution. Results showed that Cu[superscript]+ was the active site and thermal treatment under vacuum was critical for Zn/Al[subscript]2O[subscript]3 since a defective, less crystalline spinel led to stronger interaction between zinc ions and thiophene molecules in the adsorption process. The kinetic study suggested that most of the adsorption occurred in the first 30 min, and adsorption equilibrium was attained after 1.5 h. Both adsorbents showed good regenerative property. TiO2 is considered the most promising photocatalyst due to its high efficiency, chemical stability, non-toxicity, and low cost for degradation and complete mineralization of organic pollutants. However, the use of TiO[subscript]2 is impaired because it requires ultraviolet (UV) activation ([Lambda]<387 nm). The shift of optical response of TiO[subscript]2 from the UV to the visible light region would have a profound positive effect on the efficient use of solar energy in photocatalytic reactions. We shifted the optical response of TiO[subscript]2 and improved the photocatalytic efficiency through size modification and transition metal ion and nonmetal atom doping. Experimental results showed that C and V co-doped TiO[subscript]2 catalysts had much higher activity than commercial P25 TiO[subscript]2 towards the degradation of acetaldehyde under visible light irradiation. For the first time, we reported that activities were comparable in the dark and under visible light irradiation for co-doped TiO[subscript]2 with 2.0 wt% V. C and N co-doped TiO[subscript]2 exhibited higher activity for the degradation of methylene blue than pure TiO[subscript]2 under visible light and UV irradiation. Possible mechanisms were discussed based on the experimental results.

Recently, researchers on nanoparticles and nanostructures has received a great deal of attention not only in the area of synthesis and characterization but also in their potential application in various high-technological applications. Nanomaterials are widely used not only for environmental and biological applications but also for electronic and sensing applications. Among various classes of nanomaterials, the metal oxide nanostructures possess particular important because of their significant physical and chemical properties which allowed them to be used for the fabrication of highly efficient nanodevices. The metal oxide nanomaterials are widely used for catalysis, sensing, and electronic devices, and so on. Due to the high-efficient applications, researchers have developed several synthesis strategies to prepare metal oxide nanostructures with tailored geometry and utilize them for a variety of applications. However, it is still desirable to prepare metal oxide nanomaterials with environment-friendly precursors and processes with varied size and morphology for their effective utilization in specific applications. This thesis focuses on the synthesis, characterizations and specific applications of two undoped and doped metal oxide nanostructures, i.e. zinc oxide (ZnO) and iron oxide (α-Fe2O3). The thesis highlights the development of novel synthesis techniques/procedures which are rapid, consume less energy and time, and are less cumbersome, more economical, especially because of the low temperature process. The other aspect of the thesis is to use the as-synthesized nanomaterials for several important applications such as sensors, photovoltaic, and photocatalysis. The thesis is divided into several chapters. Chapter 1 starts with a brief introduction of the metal oxide nanostructures and their various synthetic methods. In addition to this, a short review on the targeted applications, i.e. sensing, photovoltaic and photocatalytic, of this thesis was also discussed in this chapter. Finally, the chapter describes the objective and importance of the thesis. Chapter 2 deals with the details of the synthesis and characterization techniques used in this thesis. Two specific techniques, i.e. hydrothermal and thermal evaporation, have been used for the synthesis of various undoped and doped nanomaterials explored in this thesis. The synthesized nanomaterials were examined by variety of techniques in terms of the morphological, structural, optical, compositional and electrical properties. Moreover the prepared nanomaterials together were used for various applications such as sensing, photovoltaic and photocatalytic applications. In a word, this chapter provides all the detailed procedures for the synthesis, characterizations and applications of targeted nanomaterials in this thesis. Chapter 3 describes the main results and discussion of the thesis. This chapter is divided into several sections and each section describes the synthesis, detailed characterizations and particular application of a single metal oxide nanomaterial. Section 1 describes the growth, characterization and ammonia chemical sensing applications of well-crystalline ZnO nanopencils grown via facile and simple hydrothermal process using commonly used laboratory chemicals. Importantly, the fabricated ammonia chemical sensor exhibited ultra-high sensitivity. Section 2 demonstrates the use of ZnO balls made of intermingled nanocrystalline nanosheets for photovoltaic device application. Successful growth, characterizations and phenyl hydrazine chemical sensing applications based on Ag-doped ZnO nanoflowers was demonstrated in section 3 of this chapter. Section 4 describes the Ce-doped ZnO nanorods for the detection of hazardous chemical; hydroquinone. Section 5 exemplifies the facile growth and detailed structural and optical characterizations of In-Doped ZnO hollow spheres composed of nanosheets networks and nanocones. Finally, section 6 illustrates the utilization of α-Fe2O3 hexagonal nanoparticles for environmental remediation and smart sensor applications. Moreover the synthesized α-Fe2O3 hexagonal nanoparticles were characterized in detail in terms of their morphological, structural, compositional and optical properties. Chapter 4 briefly highlights the overall conclusion and an outlook for further investigations suggested by the work undertaken here for this thesis. / Τα τελευταία χρόνια τα νανοσωματίδια και οι νανοδομές έχουν προσελκύσει μεγάλο ερευνητικό ενδιαφέρον λόγω των σημαντικών δυνατοτήτων που προσφέρουν για εφαρμογές υψηλής τεχνολογίας. Τα νανοϋλικά χρησιμοποιούντα ευρέως τόσο για περιβαλλοντικές και βιολογικές εφαρμογές όσο και για εφαρμογές στην ηλεκτρονική και τους αισθητήρες. Μεταξύ των διάφορων κατηγοριών νανοϋλικών, οι νανοδομές μεταλλικών οξειδίων παρουσιάζουν ιδιαίτερο ενδιαφέρον λόγω των φυσικών και χημικών ιδιοτήτων τους, που τους επιτρέπουν να χρησιμοποιούνται για την κατασκευή νανοσυσκευών υψηλής απόδοσης, με χαρακτηριστικά πεδία εφαρμογών την κατάλυση, την ηλεκτρονική και τους αισθητήρες. Για τους σκοπούς αυτούς, έχει αναπτυχθεί πληθώρα μεθόδων για την σύνθεση και προετοιμασία νανοδομών μεταλλικών οξειδίων με επιθυμητές γεωμετρίες, ώστε να είναι κατάλληλα για διαφορετικές εφαρμογές. Παρόλα αυτά, εξακολουθεί να υπάρχει έντονο ενδιαφέρον για την παραγωγή τέτοιων υλικών σε διάφορα μεγέθη και μορφολογίες, με περιβαλλοντικά φιλικές μεθόδους, με απώτερο σκοπό την χρησιμοποίησή τους σε συγκεκριμένες εφαρμογές. Η παρούσα διατριβή εστιάζει στην σύνθεση, τον χαρακτηρισμό και τις εφαρμογές των νανοδομών δύο συγκεκριμένων μεταλλικών οξειδίων (ZnO και α-Fe2O3) με ή χωρίς προσμείξεις. Η διατριβή δίνει έμφαση σε νέες τεχνικές σύνθεσης, οι οποίες είναι γρήγορες, καταναλώνουν λιγότερη ενέργεια και είναι πιο οικονομικές κυρίως λόγω χαμηλότερης θερμοκρασίας επεξεργασίας. Οι δομές των νανοϋλικών που προκύπτουν, χρησιμοποιούνται σε διάφορες σημαντικές εφαρμογές, όπως είναι οι αισθητήρες, τα φωτοβολταϊκά και η φωτοκατάλυση. Η διατριβή χωρίζεται σε 4 κεφάλαια. Στο κεφάλαιο 1 δίνεται μία σύντομη εισαγωγή στις νανοδομές των μεταλλικών οξειδίων και τις διάφορες μεθόδους σύνθεσης. Παρουσιάζονται συνοπτικά τα είδη των εφαρμογών τα οποία θα αποτελέσουν αντικείμενο μελέτης και τέλος περιγράφονται οι αντικειμενικοί στόχοι και η σημασία της διατριβής. Το κεφάλαιο 2 πραγματεύεται λεπτομερώς τις τεχνικές σύνθεσης και χαρακτηρισμού που υιοθετούνται στο μεγαλύτερο μέρος της μελέτης. Συγκεκριμένα, για την σύνθεση των νανοϋλικών (με ή χωρίς προσμίξεις) χρησιμοποιούνται οι τεχνικές της υδροθερμικής και της θερμικής εξάχνωσης. Τα παραγόμενα νανοϋλικά μελετήθηκαν ως προς την σύνθεσή τους, καθώς επίσης και τις μορφολογικές, δομικές, οπτικές και ηλεκτρικές ιδιότητες. Στην συνέχεια, χρησιμοποιούνται για τα διάφορα είδη εφαρμογών που αναφέρθηκαν παραπάνω. Με άλλα λόγια, στο κεφάλαιο αυτό περιέχονται όλες οι λεπτομέρειες των διαδικασιών παραγωγής και των εφαρμογών. Το κεφάλαιο 3 περιλαμβάνει την παρουσίαση και συζήτηση των αποτελεσμάτων. Αποτελείται από διάφορες παραγράφους η κάθε μία εκ των οποίων περιγράφει την σύνθεση, τον χαρακτηρισμό και τις εφαρμογές ενός εκ των υλικών. Στην Παράγραφο 1 περιγράφονται η ανάπτυξη, ο χαρακτηρισμός των κρυσταλλικών ZnO νανομολυβδιών μέσω μίας απλής και εύκολης υδροθερμικής διαδικασίας, χρησιμοποιώντας συνηθισμένα εργαστηριακά υλικά, καθώς επίσης και η εφαρμογή τους ως χημικοί αισθητήρες αμμωνίας. Αξίζει να σημειωθεί ότι οι αισθητήρες που κατασκευάστηκαν επέδειξαν υπέρ-υψηλή ευαισθησία. Η παράγραφος 2 επιδεικνύει την χρήση ZnO σφαιρών που είναι κατασκευασμένες απο αναμιγμένα νανοκρυσταλλικά νανοφύλλα για φωτοβολταϊκές εφαρμογές. Η επιτυχής ανάπτυξη και χαρακτηρισμός ZnO νανολουλουδιών εμπλουτισμένα με Άργυρο καθώς επίσης και η χρήση τους σε εφαρμογές αισθητήρων φαινυλο-υδραζίνης παρουσιάζονται στην παράγραφο 3. Στην παράγραφο 4 περιγράφεται η χρήση ZnO νανοράβδων εμπλουτισμένων με Δημήτριο για την ανίχνευση της επικίνδυνης χημικής ουσίας υδροκινόνης. Στην Παράγραφο 5 παρουσιάζεται η ανάπτυξη και ο λεπτομερής δομικός και οπτικός χαρακτηρισμός κοίλων σφαιρών ZnO εμπλουτισμένων με Ίνδιο που αποτελούνται απο δίκτυα νανοφύλλων και νανοκώνους. Τέλος στην παράγραφο 6 περιγράφεται η χρήση εξαγωνικών νανοσωματιδίων α-Fe2O3 για περιβαλλοντική αποκατάσταση και εφαρμογές ευφυών αισθητήρων. Οι δομές αυτές χαρακτηρίστηκαν λεπτομερώς ως προς τη σύνθεση τις μορφολογικές, τις δομικές και τις οπτικές ιδιότητες. Στο κεφάλαιο 4 παρουσιάζονται τα συμπεράσματα της παρούσας διατριβής καθώς επίσης και προστάσεις για την περεταίρω διερεύνηση των υπό μελέτη συστημάτων.

Le travail de thèse porte sur les méthodes de synthèse de nanostructures de dioxyde de titane et de leurs études physicochimiques afin de préciser les corrélations entre la morphologie, le dopage métallique, les caractéristiques structurales avec l'efficacité photocatalytique. Le grand intérêt pour les nanomatériaux TiO2 réside dans la mise au point de nouvelles sources d'énergie ou la conservation de l’environnement par des processus photocatalytiques. Cependant, la limitation principale de TiO2 est du au large gap électronique (eV ~3,2) du polymorphe Anatase. Ainsi, un des objectifs importants pour l'amélioration de l’efficacité des nanomatériaux TiO2 est d'augmenter leur photoactivité en décalantla création de paires d'électron-trou de l’UV à la gamme du visible. D'ailleurs, on a montré que l'utilisation de nanostructures 1D de TiO2 (nanotubes) a amélioré la collection de charges, en favorisant leur transport dans les structures 1D, qui par conséquent réduit au minimum la recombinaison et prolonge les durées de vie des électrons.La première partie de ce travail est dédiée à la synthèse des nanopoudres TiO2 dopées par des ions métalliques (Ag, Cu, Eu) préparés par sol-gel. Même avec différents éléments de dopage qui apparemment peuvent adopter le même état de valence (2+) (Cu2+, Ag2+, Eu2+), différents comportements ont été démontrés pour l'incorporation efficace de ces ions dans la structure de TiO2. L'anomalie entre les rayons ioniques des différents éléments utilisés module le rapport du dopage substitutionnel. Ceci est en effet réalisé pour Cu2+ mais dans moins d'ampleur pour Ag2+ tandis que les ions d'europium forment une ségrégation de phase Eu2Ti2O7. La dégradation de colorants de bleu de méthylène (MB) a étéaméliorée légèrement avec les échantillons dopés Ag. La raison a été attribuée aux clusters métalliques Ag qui ont été en effet mis en évidence à travers leur bande d’absorption plasmonique. La deuxième partie porte sur des couches minces de TiO2 dopés (Cu, Ag, et Eu) qui ont été élaborés par sol-gel et spin-coating et dipcoating. Les paramètres optimaux ont été obtenus pour réaliser les films cristallins mais présentant une organisation mésoporeuse qui dépend également du processus de dopage. Des études de Photocatalyse ont été également réalisées et l'efficacité des films ont été comparées en fonction des éléments dopants. La troisième partie de la thèse est liée à la modification morphologique des nanoparticules pour former des nanotubes à l'aide de la méthode hydrothermale sous pression contrôlée. Un plan d'expérience basé sur la méthode Taguchi a été utilisé pour la détermination des paramètres optimaux.Les nanotubes TiO2 augmentent la surface spécifique en comparaison avec les nanoparticules. La dégradation de bleu deméthylène par les nanotubes a montré une efficacité photocatalytique plus élevée qu’avec les nanopoudres TiO2 pures etdopés Ag. / The thesis work is focused on the synthesis methods of titanium dioxide nanostructures and their physico-chemical studies in order to point out the correlations between the morphology, metal doping, structural features with the photocatalytic efficiency. The great interest on TiO2 nanomaterials deals with new sources of energy or in the environment preservation through the photocatalytic properties. However, the main limitations is due to the wide band gap (~3.2 eV) of the anatase polymorph. Thus, a major objective for improvement of the performance of TiO2 nanomaterials is to increase theirphotoactivity by shifting the onset of the electron-hole pairs creation from UV to the visible range. Moreover, it was found that using onedimensional (1-D) TiO2 (nanotubes) improved the charge collection by 1D nanostructures which consequently minimizes the recombination and prolongate the electron lifetimes. The first part of this work is focused on the synthesis of TiO2 nanopowders doped with metallic ions (Ag, Cu, Eu) prepared by Solgel. Even with different doping elements which apparently can adopt the same valence state (2+) such as (Cu2+, Ag2+,Eu2+), different behaviors were demonstrated for the effective incorporation of these ions in the host structure of TiO2. The discrepancy between ionic radii of the different used elements modulates the ratio of the substitutional doping. This is indeed achieved for Cu2+ but in less extent for Ag2+ while Europium ions form segregated phase as Eu2Ti2O7. The experiments on the degradation of methylene blue (MB)dyes have shown slight improvement with Ag-doped samples. The reason was tentatively attributed to the Ag clusters which were indeed demonstrated through their plasmon optical band. The second part of the work concerns thin films of TiO2 doped (Cu, Ag, and Eu) which were elaborated by spin coating and dip coating. The optimal parameters were obtained to achieve crystalline films but presenting mesoporous organisation which also depends on the doping process. Photocatalysis investigations were also realized and the efficiency of the films compared as function of the doping elements.The third part of the thesis is related to the morphological modification from nanoparticles to nanotubes by using the hydrothermal method with controlled pressure. An experimental design based on Taguchi Method was employed for the determination of the optimal parameters. TiO2 nanotubes increase the surface area in comparison with TiO2nanoparticles. TiO2 nanotubes were tested for the methylene blue degradation and show a higher photocatalytic efficiency than TiO2 nanopowders and TIO2 doped with Ag.