An increase in nanotechnology has seen an associated rise in nanoparticles released into the environment. Their potential toxicity and exposure to humans and the environment, the field of nanoecotoxicology, is not yet well understood. The interactions at the nanoparticle surface will play a fundamental role in the nanoparticle behaviour once released into the environment. This study aims to characterise the particle surface interaction, determining key parameters influential in the nanoparticle fate. Evanescent Wave Cavity Ring Down Spectroscopy techniques have been applied to study molecular interactions at the silica-water charged interface. The adsorption of the electronic spectrum of Crystal Violet has demonstrated the formation of a monolayer with different binding site orientation at the interface. The binding affinity for the chromophore was calculated as 29.15 ± 0.02 kJmol-1 at pH 9 and this was compared with other interface structures involving both inorganic and organic components. The study of the model interface was extended to the properties of CeO2 nanoparticles, where the surface charge density was determined to be 1.6 ± 0.3 e- nm-2.The nanoparticle surface charge controls the suspension stability which was measured for CeO2 nanoparticles giving a stability half-life of 330 ± 60 hours in pure water, and 3.6 ± 0.6 hours in ISOFish water. Studies were extended to the toxicity of ZnO nanoparticles. An assay was developed to quantify the photo-electron production for nanoparticles exposed to UV light both in deionised water and soil suspensions with a photo-radical production yield of 19 ± 2 % and an electron production of 709 e-s-1np-1 for a 100 mgL-1 suspension. The species-specific photo-radical assay was subsequently used to determine the rate of ZnO nanoparticle dissolution in water and soil suspensions. Comparable dissolution rates in complex cell growth media were also measured, detecting total zinc by Inductively Coupled Plasma Atomic Emission Spectroscopy, with comparable dissolution rates derived.

Master of Science / Department of Chemical Engineering / Larry E. Erickson / The damage that can be inflicted by ultraviolet radiation has gained widespread interest. Traditionally sunscreens are made of organic and inorganic components that block two of the three types of ultraviolet radiation, UVA and UVB. This report is a literature review of several articles that have investigated the effects of inorganic UV filters; specifically titanium dioxide and cerium dioxide. There are concerns about absorption of titanium dioxide into the skin and the adverse reactions that could occur, but it was found that there is little to no absorption. Similarly the photostability of titanium dioxide is a concern; this was found to be remedied in part by a surface treatment to the titanium dioxide. The combination of titanium dioxide and carnauba wax was also studied and found to enhance the properties of both the organic and inorganic filters. Ceria was studied as a possible replacement for titanium dioxide. It was found to have similar ultraviolet shielding properties while minimizing the photocatalytic activity and photocytotoxicity seen in titanium dioxide.

O uso de dióxidos de metais de transição em aplicações tecnológicas é bastante amplo, pois esses compostos possuem características importantes de semicondutores. Apesar de existir um grande número de estudos experimentais e teóricos, o entendimento das propriedades estruturais e eletrônicas desses compostos ainda não é satisfatória, principalmente quando se envolve o estudo de clusters. Clusters podem ser definidos como uma fase embrionária da matéria, pois são partículas contendo um número muito reduzido de átomos em comparação com partículas macroscópicas. Logo, suas propriedades estruturais e eletrônicas são totalmente distantes da fase cristalina do material, o que permite o desenvolvimento de novos materiais para aplicações tecnológicas. Portanto, existe um grande interesse em compreender as propriedades estruturais e eletrônicas dos clusters. Neste projeto de mestrado temos como objetivo estudar as propriedades estruturais e eletrônicas de clusters de TiO2 e CeO2 , usando para isso cálculos de primeiros princípios com base na teoria do funcional da densidade (DFT). Um dos principais problemas no estudo de clusters é a determinação da estrutura atômica, devido as dificuldades experimentais envolvidas em se trabalhar com estruturas tão pequenas. Dessa forma, um dos nossos maiores desafios foi a determinação das estruturas atômicas dos clusters desses dois tipos de dióxidos de metais de transição, uma vez que, o nosso grupo (QTnano) já conta com grande experiência, principalmente no desenvolvimento e implementação de algoritimos de otimização global. Devido as dificuldades envolvidas no estudo de partículas tão pequenas, ficamos restritos ao estudo de clusters com composição (MO2)n , com n = 1-15, ou seja, os nossos maiores clusters tem um total de 45 átomos, formando estruturas com diâmetro de inferior a 3 nm. Além da obtenção das estruturas, foi realizado o estudo das propriedades eletrônicas, energéticas e vibracionais para cada uma das composições geradas, o que propiciou a melhor compreensão sobre os efeitos eletrônicos nas estrutura atômica dos clusters. / The use of transition metal dioxides in technological applications is wide spread, because these compounds have important characteristics of semiconductors. Although there a large number of theoretical and experimental studies, the acknowledgement about the structural and electronic properties these compounds are not yet satisfactory, especially when studying clusters. Clusters can be defined as an embryonic phase of matter, because they are particles that contain a very small number of atoms in comparison with macroscopic particles. So, the structural and electronic properties are very distinct of the material crystalline phase, when allow the development of new materials in technological applications. Therefore a large interest exist in understanding the structural and electronic properties of clusters. In this master\'s degree project we have as objective to study the electronic and structural properties of TiO2 and CeO2 clusters, using first principle calculations based on the density functional theory (DFT). One of the main problems in the study of clusters is to determine the atomic structure, due the experimental difficult of work with so small particles. Thus, a great challenge was to determine the atomic structures of these two different transition metal dioxides, considering that our group (QTnano), has a large knowledge in the development and implementation of global optimization algorithms. Due the difficulty involved in studying small particles, we were restricted to the clusters of composition (MO2)n, with n = 1-15. In other words, our largest clusters have 45 atoms and a diameter smaller than 3 nm. Along with securing the structures, we realize the study of electronic, energetic and vibrational properties to each generated composition, providing an understanding of electronic effects in the atomic structure of clusters.

Orientador: Alexandre Zirpoli Simões / Resumo: Devido à problemática das intoxicações com monóxido de carbono ser responsável pelo maior tipo de envenenamento do século 21, objetivou-se a produção de materiais nanoestruturados a base de céria, pura e dopada com lantânio (La 3+ ), através do método hidrotermal assistido por micro-ondas com posterior deposição na forma de filmes, para caracterização como dispositivos sensores na detecção de atmosfera de CO, por meio da técnica de sonda de duas pontas. O método de síntese empregado foi eficaz na produção de nanopartículas, com dimensões inferiores a 10 nm, apresentando elevada cristalinidade, caracterizada por um ordenamento periódico a curta e longas distâncias, além da ausência de fases secundárias, comprovadas pelas caracterizações realizadas por difratometria de raios-X (DRX), bem como pelas técnicas de espectroscopias Raman, Infravermelho, Ultravioleta- Visível ou ainda por Ressonância Paramagnética de Elétrons. Os filmes depositados apresentaram uma resposta frente ao gás CO extremamente rápida e seletiva, com tempos de resposta em 54, 12, 5.5 e 2 s para as amostras pura e dopadas com lantânio em 4, 8 e 12%, respectivamente. Além da resposta elétrica, os filmes apresentaram ainda uma resposta óptica, com destaque para a amostra com 8%, a qual muda de cor em menos de 1s, a 380 °C sob pressão de 5 mmHg de CO, tornando-se promissores sensores de gás com resposta dupla (óptica e elétrica). / Doutor

O uso de dióxidos de metais de transição em aplicações tecnológicas é bastante amplo, pois esses compostos possuem características importantes de semicondutores. Apesar de existir um grande número de estudos experimentais e teóricos, o entendimento das propriedades estruturais e eletrônicas desses compostos ainda não é satisfatória, principalmente quando se envolve o estudo de clusters. Clusters podem ser definidos como uma fase embrionária da matéria, pois são partículas contendo um número muito reduzido de átomos em comparação com partículas macroscópicas. Logo, suas propriedades estruturais e eletrônicas são totalmente distantes da fase cristalina do material, o que permite o desenvolvimento de novos materiais para aplicações tecnológicas. Portanto, existe um grande interesse em compreender as propriedades estruturais e eletrônicas dos clusters. Neste projeto de mestrado temos como objetivo estudar as propriedades estruturais e eletrônicas de clusters de TiO2 e CeO2 , usando para isso cálculos de primeiros princípios com base na teoria do funcional da densidade (DFT). Um dos principais problemas no estudo de clusters é a determinação da estrutura atômica, devido as dificuldades experimentais envolvidas em se trabalhar com estruturas tão pequenas. Dessa forma, um dos nossos maiores desafios foi a determinação das estruturas atômicas dos clusters desses dois tipos de dióxidos de metais de transição, uma vez que, o nosso grupo (QTnano) já conta com grande experiência, principalmente no desenvolvimento e implementação de algoritimos de otimização global. Devido as dificuldades envolvidas no estudo de partículas tão pequenas, ficamos restritos ao estudo de clusters com composição (MO2)n , com n = 1-15, ou seja, os nossos maiores clusters tem um total de 45 átomos, formando estruturas com diâmetro de inferior a 3 nm. Além da obtenção das estruturas, foi realizado o estudo das propriedades eletrônicas, energéticas e vibracionais para cada uma das composições geradas, o que propiciou a melhor compreensão sobre os efeitos eletrônicos nas estrutura atômica dos clusters. / The use of transition metal dioxides in technological applications is wide spread, because these compounds have important characteristics of semiconductors. Although there a large number of theoretical and experimental studies, the acknowledgement about the structural and electronic properties these compounds are not yet satisfactory, especially when studying clusters. Clusters can be defined as an embryonic phase of matter, because they are particles that contain a very small number of atoms in comparison with macroscopic particles. So, the structural and electronic properties are very distinct of the material crystalline phase, when allow the development of new materials in technological applications. Therefore a large interest exist in understanding the structural and electronic properties of clusters. In this master\'s degree project we have as objective to study the electronic and structural properties of TiO2 and CeO2 clusters, using first principle calculations based on the density functional theory (DFT). One of the main problems in the study of clusters is to determine the atomic structure, due the experimental difficult of work with so small particles. Thus, a great challenge was to determine the atomic structures of these two different transition metal dioxides, considering that our group (QTnano), has a large knowledge in the development and implementation of global optimization algorithms. Due the difficulty involved in studying small particles, we were restricted to the clusters of composition (MO2)n, with n = 1-15. In other words, our largest clusters have 45 atoms and a diameter smaller than 3 nm. Along with securing the structures, we realize the study of electronic, energetic and vibrational properties to each generated composition, providing an understanding of electronic effects in the atomic structure of clusters.

Le dioxyde d'uranium (UO2) est le combustible nucléaire le plus largement utilisé dans les réacteurs nucléaires à travers le monde. En conditions d’exploitation, UO2 est soumis au flux de neutrons et subit des réactions en chaîne de fission nucléaire, ce qui crée un grand nombre de produits de fission et des défauts ponctuels. L'étude du comportement des produits de fission et des défauts ponctuels est importante pour comprendre les propriétés du combustible sous irradiation. Nous effectuons des calculs de structure électronique basés sur la théorie de la fonctionnelle de la densité (DFT) pour modéliser les dégâts d’irradiation à l'échelle atomique. La méthode DFT+U est utilisé pour décrire les fortes corrélations des électron 4f du cérium et des électrons 5f de l’uranium dans les matériaux étudiés (UO2, CeO2 et (U, Ce)O2). (U, Ce)O2 est étudié car il est considéré comme un matériau modèle peu radioactif d'oxydes d’actinides mixtes comme (U, Pu)O2 qui est le combustible d'oxydes mixtes (MOX) utilisé dans les réacteurs à eau légère et les réacteurs à neutrons rapides. Le dioxyde de cérium (CeO2) est étudié pour des données de référence de (U, Ce)O2. Nous effectuons une étude DFT+U des défauts ponctuels et des produits de fission gazeux (Xe et Kr) dans CeO2 et comparons nos résultats à ceux déjà existants pour l’UO2. Nous étudions les propriétés en volume, ainsi que le comportement des défauts pour (U, Ce)O2, et comparons nos résultats à ceux de (U, Pu)O2. En outre, pour l'étude des défauts dans UO2, des améliorations méthodologiques sont explorées considérant l'effet de couplage spin-orbite et l’effet de taille finie de la supercellule de modélisation. / Uranium dioxide (UO2) is the most widely used nuclear fuel in existing nuclear reactors around the world. While in service for energy supply, UO2 is submitted to the neutron flux and undergoes nuclear fission chain reactions, which create large number of fission products and point defects. The study of the behavior of the fission products and point defects is important to understand the fuel properties under irradiation. We conduct electronic structure calculations based on the density functional theory (DFT) to model this radiation damage at the atomic scale. The DFT+U method is used to describe the strong correlation of the 4f electrons of cerium and 5f electrons of uranium in the materials studied (UO2, CeO2 and (U, Ce)O2). (U, Ce)O2 is studied because it is considered as a low radioactive model material of mixed actinide oxides such as the MOX fuel (U, Pu)O2 used in light water reactors and fast neutron reactors. Cerium dioxide (CeO2) is studied to provide reference data of (U, Ce)O2. We perform a DFT+U study of point defects and gaseous fission products (Xe and Kr) in CeO2 and compare our results to the existing ones of UO2We study the bulk properties as well as the behavior of defects for (U, Ce)O2, and compare our results to the ones of (U, Pu)O2. Furthermore, for the study of defects in UO2, methodological improvements are explored considering the spin-orbit coupling effect and the finite-size effect of the simulation supercell.

Ceroxid (CeO2) wurde in den letzten Jahren als Katalysator für die Hydrierung von Alkinen zu Alkenen entdeckt und hat als solcher großes wissenschaftliches Interesse geweckt. Um weitere Einblicke in die Funktion von CeO2 in der Reaktion zu gewinnen, beschäftigt sich diese Arbeit mit der Adsorption von H2, CO2 und Propin, sowie mit der Interaktion von Hydroxylgruppen und Propin auf CeO2(111)-Oberflächen. Ein besonderer Fokus liegt dabei auf der Rolle von Sauerstoffleerstellen. / In recent years, ceria (CeO2) has attracted much scientific interest due to its activity as a catalyst in the selective hydrogenation of alkynes to alkenes. To gain further insights into the role of CeO2 in propyne hydrogenation, this thesis explores the fundamental processes of H2, CO2, and propyne adsorption, as well as the interaction of hydroxyls and propyne on well-defined CeO2(111) surfaces. A special emphasis thereby lies on the role of oxygen (O) vacancies in these processes.

<p>The solid oxide fuel cell (SOFC) technology has been under research since thelate 1950s, and most of the research has been on designs utilizing yttria stabilized zirconia (YSZ) as the electrolyte of choice. However, the SOFC technology has the major drawback of requiring high operation temperatures (up to 1000 degrees Celcius), so research of alternative materials have come into interest that would possibly require a lower working temperature without any significant loss of conductivity.One such material of interest for the electrolyte is compounds of ceriumdioxide (ceria). Ceria is well known for its ability to release oxygen by formingoxygen vacancies under oxygen-poor conditions, which increases its oxygen ionconductivity, and works at a lower temperature than the YSZ compounds whenproperly doped. Conversely, ceria is also able to absorb oxygen under oxygen-rich conditions, and those two abilities make it a very good material to use in catalytic converters for reduction of carbon monoxide and nitrogen oxide emission. The ability for the oxygen ions to easily relocate inbetween the different lattice sites is likely the key property of oxygen ion transportation in ceria. Also, in oxygen-rich conditions, the absorbed oxygen atom is assumed to join the structure at either the roomy octrahedral sites, or the vacant tetrahedral sites. Following that, the oxygen atom may relocate to other vacant locations, given it can overcome a possible potential barrier.</p><p>This thesis studies how those interstitial oxygen vacancies (defects) affect theenergy profile of ceria-based supercells by first principles calculations. The system is modeled within the density functional theory (DFT) with aid of (extended) local density approximation (LDA+U) using the software VASP. Furthermore, it is studied how those vacancies affect neighbouring oxygen atoms, and wether or not it is energetically benificial for the neighbouring atoms to readjust their positions closer or further away from the vacancy. The purpose of this thesis is to analyze wether or not it is theoretically possible that interstitial oxygen vacancies may cause neighbouring oxygen atoms to naturally relocate to the octahedral site in ceria, and how this affects the overall energy profile of the material.</p>

The solid oxide fuel cell (SOFC) technology has been under research since thelate 1950s, and most of the research has been on designs utilizing yttria stabilized zirconia (YSZ) as the electrolyte of choice. However, the SOFC technology has the major drawback of requiring high operation temperatures (up to 1000 degrees Celcius), so research of alternative materials have come into interest that would possibly require a lower working temperature without any significant loss of conductivity.One such material of interest for the electrolyte is compounds of ceriumdioxide (ceria). Ceria is well known for its ability to release oxygen by formingoxygen vacancies under oxygen-poor conditions, which increases its oxygen ionconductivity, and works at a lower temperature than the YSZ compounds whenproperly doped. Conversely, ceria is also able to absorb oxygen under oxygen-rich conditions, and those two abilities make it a very good material to use in catalytic converters for reduction of carbon monoxide and nitrogen oxide emission. The ability for the oxygen ions to easily relocate inbetween the different lattice sites is likely the key property of oxygen ion transportation in ceria. Also, in oxygen-rich conditions, the absorbed oxygen atom is assumed to join the structure at either the roomy octrahedral sites, or the vacant tetrahedral sites. Following that, the oxygen atom may relocate to other vacant locations, given it can overcome a possible potential barrier. This thesis studies how those interstitial oxygen vacancies (defects) affect theenergy profile of ceria-based supercells by first principles calculations. The system is modeled within the density functional theory (DFT) with aid of (extended) local density approximation (LDA+U) using the software VASP. Furthermore, it is studied how those vacancies affect neighbouring oxygen atoms, and wether or not it is energetically benificial for the neighbouring atoms to readjust their positions closer or further away from the vacancy. The purpose of this thesis is to analyze wether or not it is theoretically possible that interstitial oxygen vacancies may cause neighbouring oxygen atoms to naturally relocate to the octahedral site in ceria, and how this affects the overall energy profile of the material.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Os materiais ferroelétricos têm sido utilizados em muitas áreas da tecnologia e da ciência, pois possuem um grande número de aplicações, como: sensores; transdutores; capacitores; dispositivos ópticos; dentre outras. A busca por novos materiais cerâmicos ferroelétricos tem sido grande. Um dos materiais cerâmicos ferroelétricos mais estudados é o titanato de bário (BT). São vários os métodos de produção e caracterização do titanato de bário. Neste trabalho, pós cerâmicos de titanato de bário foram obtidos por reação do estado sólido a partir de misturas reacionais calcinadas em diferentes temperaturas entre 400C e 900C. Foram três as misturas reacionais: não dopadas; dopadas com 1%; e dopadas com 5% de dióxido de cério (CeO2). A identificação da formação do BT, nos pós cerâmicos produzidos, foi feita a partir de três técnicas de caracterização: difração de raios X (DRX); espectroscopia fotoacústica (PAS); e técnicas de análise térmica. Com a técnica DRX, difratogramas mostraram que a plena formação do titanato de bário ocorreu a partir da temperatura de calcinação de 700C. Para a amostra não dopada com cério e calcinada a 800C, houve deslocamento de todos os picos de difração. Nas amostras dopadas com dióxido de cério houve deslocamento de todos os picos de difração, em relação as amostras não dopadas. Observou-se também que nas amostras dopadas com 5% de CeO2, e calcinadas a 700C e 800C, resíduos de dióxido de cério foram observados nos difratogramas. Com a técnica PAS, espectros de absorção foram obtidos. Foi possível observar uma grande diferença de absorção da amostra calcinada a 600 e 630C, indicando a formação do titanato de bário a partir da temperatura de 630&#61616;C, nas amostras sem a dopagem dióxido de cério. Houve um alargamento nas bandas de absorção a partir da temperatura de 600C, quando o dióxido de cério entrou na matriz. Foi também possível determinar as energias de band-gap das amostras utilizando o método de Tauc. Com as técnicas de análise térmica, em especial através da técnica termogravimétrica (TG/DTG), foi comprovado que até 400C não havia formação de titanato de bário. Visto que nesta temperatura de calcinação houve a maior perda de massa durante a rampa de aquecimento. O início da formação do titanato de bário foi observado a partir da temperatura de calcinação de 500C, assim como nas técnicas DRX e PAS. Portanto, com os resultados apresentados, foi demonstrada a identificação da formação do titanato de bário nas misturas reacionais calcinadas, com auxílio das potencialidades das três técnicas utilizadas. / Ferroelectric materials have been used in many areas of technology and science, because they have a large number of applications, such as sensors; transducers; capacitors; optical devices; among others. The search for new ferroelectric ceramics has been great. One of the most studied ferroelectric ceramic material is barium titanate (BT). There are several methods for production and characterization of barium titanate. In this work, ceramic powders of barium titanate were obtained by solid state reaction from reaction mixtures calcined at different temperatures between 400C and 900C. Three reaction mixtures were used: undoped; doped with 1%; and 5% doped with cerium dioxide (CeO2). The identification of the formation of BT, for the ceramic powders produced, was taken from three characterization techniques: X-ray diffraction (XRD); photoacoustic spectroscopy (PAS); and thermal analysis techniques. With the technique XRD diffraction patterns showed that complete formation of the barium titanate occurred after the calcination temperature of 700C. For the sample not doped with cerium and calcined at 800C, there was displacement of all diffraction peaks. In samples doped with cerium dioxide was no displacement of all diffraction peaks, comparing to undoped samples. It was also observed that the samples doped with 5% CeO2 and calcined at 700C and 800C, cerium dioxide residues were observed in the diffraction pattern. The absorption spectra were obtained with the technique PAS. It was possible to observe a large difference in absorption spectra in the samples calcined at 600C and 630C, indicating the formation of barium titanate at temperature of 630C in the samples without doping of cerium dioxide. There was an enlargement in the absorption band above temperature of 600C when the cerium dioxide was introduced into the matrix. It was also possible to determine the band-gap energy of the samples using the method of TAUC. With thermal analysis techniques, in particular by thermogravimetric technique (TG/DTG), has been proven that up to 400C there was no formation of barium titanate. Once, in this calcination temperature there was the largest mass loss during the heating ramp. The onset of formation of barium titanate was observed from the calcination temperature of 500C, as it has been found by the XRD and PAS techniques. Therefore, with the results presented, the identification of the formation of barium titanate calcined in reaction mixtures with the aid of the potentialities of the three techniques was demonstrated.