Rozprawy doktorskie na temat „Mesoporous structures”

The field of mesoporous silica has been studied for about 20 years but it is still an area attracting a lot of attention. The use of novel templating molecules and several issues related to the synthesis and fine structural details are still poorly understood. These aspects are of special relevance to the theme of this thesis, which includes novel work on three fronts; the synthesis, characterization and applications of mesoporous materials. The work described in this thesis aims to contribute to the mesoporous field by developing novel methods of mesoporous silica synthesis without relying on surfactant micelles as the templating agent but focusing instead on the stacking arrangement of aromatic molecules such as folic acid. The novel route presented here leads to 2D hexagonal structures with p6mm symmetry possessing high mesoporosity and large surface areas. The versatility of this route at various synthesis temperatures and using hydrothermal treatments has also been investigated. A novel strategy is also proposed for the synthesis of mesocaged materials with Pm3n symmetry structures. The mechanism relies on the penetration of the neutral propylamino moiety of a co-structure directing agent into the hydrophobic core of the surfactant micelles. Beside these novel pathways, the effect of hydrothermal treatment (HT) at 100 oC on the 3D cubic Ia3d structure (AMS-6) over a long period of time was also examined, and the results show a phase transformation from a 3D cubic Ia3d to a 2D hexagonal p6mm structure and a return to the 3D cubic Ia3d structure at a later stage in the synthesis. This unexpected result is discussed. In this work, the detailed structural characterization of mesoporous materials using electron microscopy techniques is an important task. In particular, to extend previous knowledge, the fine structural details of mesocaged materials possessing Pm3n symmetry prepared with various amphiphilic surfactants under acidic and alkaline conditions has been investigated using electron crystallography and sorption studies. The results show subtle fine structural differences with materials prepared under alkaline conditions exhibiting the largest mesocage sizes. The cage and window sizes are primarily determined by the charge density of the surfactant and the thickness of the hydration layer surrounding the surfactant micelles. The relationship between the mesoporous structure and its function has been investigated by evaluating the rate of release of amphiphilic molecules, used as model molecules, from the internal pore structures of mesoporous materials with different pore geometries. In a similar study, the rate of proton diffusion from a liquid surrounding the mesoporous nanoparticles into the pore system of AMS-n was also assessed. The results show that the diffusion coefficients for the proton absorption process are higher than those for the release of the surfactant template molecules, with more complex 3D mesocaged particles showing the highest diffusion coefficients in both cases. Finally, the quantity of CO2 adsorption was measured by modifying the internal surfaces of mesocaged material with n-propylamino groups. Results show that the cage-connecting window sizes limit the surface coverage of n-propylamino groups by pore blocking and affect the volume of CO2 adsorption. In addition, at the molecular level, CO2 adsorption shows physisorption or chemisorption depending on the localized distribution of n-propylamino groups, as studied by in-situ infrared spectroscopy.

Les matériaux mésoporeux sont devenus des nanomatériaux d’une grande importance, et le contrôle des structures des matériaux mésoporeux est essentiel pour une variété d'applications pratiques. Les matériaux «cœur/coquille» structurés sont un type de matériaux hybrides qui non seulement possèdent les propriétés des composants individuels, mais présentent également de effets synergiques entre le «cœur» et la «coquille». La conception de matériaux mésoporeux et «cœur/coquille» structurés pour les appliquer avec succès dans la pratique devrait être une force de progrès importante pour le développement continu. Cette thèse se concentre principalement sur deux aspects: (1) une conception de matériaux mésoporeux «cœur/coquille» structurés en vue de résoudre les problèmes de synthèse, qui entravent leurs nouvelles applications et (2) l'application de matériaux mésoporeux dans la capture du CO2 cyclique pour améliorer la durabilité des sorbants de CO2 en prenant avantage du concept de «cœur/coquille». Visant le cyclage de l’hydroxyde de calcium, une technologie attrayante pour la capture du CO2 à grande échelle, nous avons établi un nouveau mésoporeux «cœur/coquille» structuré à base de CaO qui présentait une grande stabilité et d'excellentes performances de résistance à l’attrition, attribuées aux avantages des matériaux mésoporeux et à la configuration de «cœur/coquille». Notre procédé de fabrication peut être facilement réalisé à grande échelle et répond aux exigences de la circulation entre des réacteurs en lit fluidisé. Les nanoparticules métalliques ont normalement tendance à se coaguler ensemble dans des réactions catalytiques, et sont difficiles à séparer. Par conséquent, nous avons démontré une synthèse de microsphères Fe3O4@C-Pd@mSiO2 à composants multiples et polyvalentes avec une structure «cœur/coquille» bien définie et des nanoparticules catalytiques de Pd confinées, et ayant des canaux mésoporeux ordonnés et facilement accessibles. Récemment, des méthodes diverses ont été proposées pour fabriquer un revêtement de matériaux mésoporeux sur un cœur par un processus de «soft-templating». Cependant, les diamètres des mésopores générés sont généralement très faibles (< 3 nm), ce qui peut limiter leurs nouvelles applications. Ici, nous avons réalisé la synthèse de microsphères «cœur/coquille» structurées superparamagnétiques possédant une coquille externe de silice mésoporeuse ordonnée à larges pores (4,5 nm), en adoptant un copolymère tribloc comme agent tensioactif directeur de structure.
Mesoporous materials, especially ordered ones have become ones of great importance nanomaterials, which possess regular, uniform and interpenetrating mesopores in nanoscale. Morphology and texture controls towards mesoporous materials are critical for a variety of practical applications, the ultimate goal of which are the realization of their functional design. Core/shell composite materials are a type of functional hybrid materials which not only possess the properties of the individual components, but also exhibit some new or synergistic effects between the core and the shell. The design of mesoporous materials with unique core/shell configuration and multifunctions to make them successfully applied in practice, should be an important driving force for the continuous development of current material science. This thesis mainly focuses on two aspects: (1) careful design of core/shell structured mesoporous materials in order to solve the problem and difficulty in synthesis, which hinders their further applications and (2) application of mesoporous materials in cyclic CO2 capture to enhance the durability of CO2 sorbents by taking advantage of the core/shell concept. Aiming at the calcium looping cycle, an attractive technology for large-scale CO2 capture, we have prepared novel mesoporous core/shell structured CaO-based sorbents which exhibit highly stable cyclability and excellent attrition-resistance performances, attributed to advantages of both mesoporous materials and unique core/shell configuration. Our fabrication method could easily be realized in large-scale and meet the requirements of circulating fluidized bed reactors. Owing to their high surface energies, metallic nanoparticles normally tend to aggregate together during catalytic reactions, and their separation from a complex heterogeneous system is another obstacle. In this regards, we have demonstrated a facile and versatile synthesis of multicomponent and multifunctional microspheres Fe3O4@C-Pd@mSiO2 with well-defined core/shell structures, confined catalytic Pd nanoparticles and accessible ordered mesopore channels. Recently, various methods have been proposed for coating mesoporous shells on cores by soft-templating process. However, the generated mesopores are usually very small (< 3 nm), which may limit their further applications. In this work, we have accomplished the synthesis of superparamagnetic core/shell structured microspheres possessing an outer shell of ordered mesoporous silica with large pores (4.5 nm) by adopting triblock-copolymer Pluronic P123 as soft-template.

Doutoramento em Ciência e Engenharia de Materiais
Os materiais multiferróicos possuem simultaneamente pelo menos duas das três propriedades ferróicas: i) ferroelectricidade; ii) ferromagnetismo; e / ou iii) ferroelasticidade. Estes materiais têm despertado considerável interesse na indústria microeletrónica devido ao seu potencial para serem usados em dispositivos de armazenamento de informação com elevada capacidade e eficiência energética. A constante procura pela redução do tamanho e aumento da funcionalidade dos dispositivos, imposta pela Lei de Moore, exige materiais ferróicos, na forma de filmes finos e multifuncionalidade. Contudo, à medida que a espessura dos filmes diminui, as propriedades ferróicas ficam comprometidas em virtude de constrangimentos provocados pelo substrato ou outros efeitos. Neste contexto, esta tese estuda a possibilidade de utilizar a porosidade em filmes funcionais para criar sistemas compósitos multifuncionais. Assim, desenvolveram-se estratégias para a preparação de filmes de ferroeléctricos, ferromagnéticos e multiferroícos com porosidade uniforme e ordenada. O efeito dessa porosidade foi avaliado nas propriedades físicas locais e macroscópicas. Foram estudados óxidos multimetálicos com estrutura de perovisquite ou de espinela por serem promissores para aplicação em sensores; atuadores; condensadores; memórias; etc. Escolheu-se uma metodologia química em que os filmes são depositados por técnica de mergulho em soluções sol-gel contendo um copolímero em bloco que se organiza espontaneamente conjuntamente com os precursores durante o processo de evaporação. PbTiO3 foi a composição inicialmente escolhida para entender o efeito da nanoporosidade nas propriedades eléctricas locais por ser o material piezoeléctrico protótipo que possui o mais alto coeficiente piezoeléctrico conhecido. Assim, foram preparados filmes nanoporosos e densos de PbTiO3 com espessura de cerca de 100 nm e diâmetro de poro na ordem dos 50 nm. A presença da nanoporosidade contribui para a cristalização precoce da fase cristalina por aumento local da temperatura durante a decomposição do copolímero e / ou por funcionarem como núcleos de cristalização. Consequentemente, os fimes porosos exibem melhores coeficientes piezoeléctricos e baixo campo coercivo, sendo mais fácil inverter a direção da polarização por efeito do campo elétrico. Sendo a porosidade um meio para atingir propriedades melhoradas, esta pode funcionar como uma ferramenta para ajustar as propriedades ferroeléctricas à aplicação desejada. Todos os resultados de PFM foram previstos através de modelação teórica usando o modelo de elementos finitos. Foi também investigada a preparação de filmes porosos de titanado de bário enquanto protótipo de um ferroeléctrico sem chumbo. Neste contexto, foi avaliado o efeito de vários parâmetros, tais como: i) o aquecimento da solução de precursores; ii) adição de precursores inorgânicos / solventes orgânicos; e iii) envelhecimento da solução inicial, na estrutura final dos filmes.Verificou-se que o uso de uma solução fresca de precursores sem qualquer ciclo de aquecimento contribuía para uma melhor organização dos filmes porosos de BaTiO3. Verificou-se também que o tamanho dos blocos num copolímero à base de poliestireno e poli(óxido de etileno) era preponderante para a ordem e microestrutura cristalina dos filmes finais. Copolímeros em bloco com cadeias de bloco mais longas são preferíveis para obter uma estrutura ordenada e aparentemente desempenham um papel na cristalização precoce da fase ferroeléctrica tetragonal, contribuindo para uma melhoria da resposta piezoeléctrica. Em analogia com o PbTiO3, os resultados indicam que nos filmes nanoporosos de BaTiO3, a cristalização ocorre a temperaturas mais baixas do que nos filmes densos. Utilizou-se a deposição electroquímica para inserir nanopartículas metálicas de cobalto dentro dos poros dos filmes de BaTiO3. O carácter multiferróico dos filmes foi constatado através da avaliação nanoscópica das propriedades elétricas e pela medida das propriedades magnéticas macroscópicas à temperatura ambiente. Verificaram-se as dificuldades de conseguir um preenchimento uniforme dos poros e de otimizar a interface entre as duas fases ferróicas. Assim com vista a tentar ultrapassar estas dificuldades, prepararam-se filmes mais finos e em que a porosidade estivesse devidamente organizada, com poros perpendiculares à superfície. Conceberam-se filmes nanotexturados ordenados de óxidos multimetálicos com propriedades ferroelétricas, ferromagnéticas e multiferróicas com espessuras e texturas de dimensão inferior a 100 nm. As composições escolhidas foram PbTiO3, CoFe2O4 e BiFeO3. Os filmes finos porosos nanotexturados PbTiO3 apresentaram a fase cristalográfica tetragonal mesmo em espessuras de filme de 22 nm. Os filmes finos de CoFe2O4 apresentaram uma orientação preferencial no plano e elevadas magnetizações de saturação. Deduziu-se que os filmes teriam uma impureza ferromagnética compatível com uma liga metálica rica em platina. A presença desta impureza não só melhora o desempenho magnético dos filmes mas também fornece uma forte evidência para a potencial aplicabilidade dos filmes de CoFe2O4 como catalisadores para a oxidação de hidrocarbonetos através do mecanismo de Mars-Van-Krevelen. Foram também preparados filmes finos porosos nanotexturados de BiFeO3, com 66 nm de espessura e tamanho médio de diâmetro de 100 nm. Verificou-se o caráter multiferróico destes filmes e mais uma vez a melhoria clara das propriedades eléctricas locais induzida pela porosidade. A estrutura porosa também tem um efeito positivo nas propriedades magnéticas no plano, mostrando uma componente ferromagnética 50% maior que a medida em filmes densos. Verificou-se também que porosidade dos filmes de BiFeO3 pode ter interesse para aplicações fotocatalíticas, conjugando reduzido valor do hiato óptico direto (2.58 eV) com relativamente elevada área porosa (ca. 57 %). Para testar a aplicabilidade dos filmes nanotexturados na construção de um filme multiferróico compósito, uma matriz porosas ferroelétricos (BaTiO3) foi funcionalizada por preenchimento dos poros com nanopartículas ferromagnéticas de níquel. A estratégia de funcionalização dos poros foi a deposição por arrastamento com CO2 supercrítico, seguida de redução da espécie metálica a 250 ºC ativada por etanol. Pequenas nanopartículas de níquel com cerca de 21 nm foram depositadas dentro dos poros da matriz porosa, tendo-se verificado as propriedades estruturais e magnéticas do compósito. Esta tese, provou a adequação desta metodologia química de baixo custo na concepção de materiais multifuncionais, criando novas perspectivas para a indústria da microeletrónica na sua abordagem contínua de redução de tamanho e custo, enquanto aumenta a complexidade de funcionamento.
Multiferroic materials, exhibiting simultaneously at least two of the three ferroic properties: i) ferroelectricity; ii) ferromagnetism; and iii) ferroelasticity, have attracted considerable interest from the microelectronics industry. Due to their potential, these materials can be used in information storage applications with significantly high energetic efficiencies and elevated capacities. During the last decades and owing the increasing need for miniaturization of electronic devices, the ferroic materials, mainly in the format of thin films, have been extensively studied both theoretically and experimentally. However, as the film thickness decreases the ferroics properties progressively decreases due to the in-plane strain relaxation constrained by the substrate or others intrinsic and extrinsic effects. Within this context, here we exploit the role of nanoporosity on local and macroscopic properties of ferroelectrics, ferromagnetic and multiferroics thin films. Although, porosity is normally considered as a defect (or secondary phase) having usually a detrimental effect on the electrical macroscopic response; it can also be regarded as an asset, in terms of: i) density (light weight) and ii) capacity to host other functionality/ies. Oxides with perovskite and spinel structures are promising materials because they possess extraordinarily useful properties namely to be used as piezoelectrics sensors, as ferroelectric actuators, capacitors and memories, in high-strength dielectrics, for ferromagnetics or even multiferroics. Among the bottom-up approaches, the sol-gel method and evaporation-induced self-assembly methodology are the most suitable, low-cost and easy preparation method to prepare nanoporous and nanopatterned thin films of different compositions. PbTiO3 is the chosen composition to understand the role of the nanoporosity on the local electric properties. Thus, nanoporous and dense ferroelectric PbTiO3 thin films with 100 nm and ~ 50 nm pore size formed using a block polymer as a structure-directing agent are prepared. The presence of nanoporosity markedly affects the microstructure, crystallization and ferroelectric film properties. The crystallization of tetragonal phase is enhanced in nanoporous films. It seems that the decomposition of the block-copolymer in porous films triggers the crystallization of the perovskite phase at low temperatures via the local increase of temperature. Moreover, pores may work as initiators of the crystallization. Consequently, nanoporous films with improved tetragonality exhibit enhanced piezoelectric coefficients, switchable polarization and low local coercivity. In fact, the porosity induces instability in the dipole-dipole interactions and consequently the reverse polarization can be favoured for low bias values. By providing a means of achieving enhanced properties, nanoporosity may work as a tool to tune electric properties to the desired ferroelectric application. All the PFM results were supported by theoretical modelling using Finite Element Model. To have a more complete picture of the role of the nanoporosity on the crystallization and electric properties, the procedure is applied to prepare a nanoporous lead-free material, BaTiO3. However, this expantion was not trivial whereas the crystallization temperature of the tetragonal phase necessary for the ferroelectric properties is much higher than the decomposition temperature of the block-copolymer used as template. From this, several parameters such as: heating the solution, addition of inorganic precursors / organic solvent and aging time of solution are studied in order to understand the effect of these on the micellization process and consequently in the final porous BaTiO3 films. Based on the results of this study, for this specific multimetallic oxide system it is preferable to use a very fresh solution, without any heating cycles. In addition, block-copolymers based on polystyrene and poly(ethylene oxide) with different block sizes are used to investigate their influence on the order and crystalline microstructure of the final films. Blocks-copolymers with longer block chains are preferable to get an ordered structure and apparently play a role on the earliest crystallization of the tetragonal ferroelectric perovskite phase, contributing to an enhancement of the piezoelectric response. Similarly to PbTiO3, our results indicate that in nanoporous BaTiO3 films the crystallization occurs as well before in dense films. Moreover, besides providing a means of achieving enhanced properties, nanoporosity may work as a tool to tune electric properties to the desired ferroelectric application. BaTiO3 nanoporous films are tested as a kind of “golf course” full of holes to accommodate ferromagnetic particles. In this way, electrochemical deposition is used to insert the cobalt metal nanoparticles into the pores of BaTiO3 films. Films containing cobalt particles within the pores are obtained and piezoelectric and ferromagnetic properties are evaluated. For many applications would be a challenge to prepare ferroelectric thin films with lateral sizes well below 100 nm. Furthermore, the design of nanofeatures, uniformed in size and shape at a reasonable large-range order, i.e. “nanopatterning”, would extend their utility for electronic devices and integrated circuits, which require that each pixel feature can be individually addressable. Additionally, nanopatterned porous ferroelectric thin films may be interesting to develop vertical composite structures with perfect strain coupling at the interface. Thus, and using the chemical self-assembly method, different functional nanopatterned porous thin films: PbTiO3, BiFeO3 and CoFe2O4 are designed. Nanopatterned PbTiO3 thin films display the tetragonal ferroelectric crystallographic phase even when the films are as thin as 22 nm. CoFe2O4 thin films present a preferential in-plane orientation. High saturation magnetizations (close or even higher than in bulk CoFe2O4) are determined in all films, pointing to the presence of a ferromagnetic impurity compatible with a platinum-rich metal alloy. The presence of this impurity not only enhances the magnetic performance but also provides evidence for the catalytic activity of these CoFe2O4 films for hydrocarbon oxidation through a Mars-Van-Krevelen mechanism. For the BiFeO3 composition, crystalline nanopatterned BiFeO3 layers with 66 nm of thickness and average pore diameter of 100 nm at 600 ºC are obtained. The large vertical porosity markedly enhances the local electric and macroscopic magnetic properties when compared with the dense counterparts. The porous structure also has a positive effect on the parallel magnetic characteristics of the system, displaying a 50% larger ferromagnetic component and enhanced remanent magnetization when compared to the dense thin films counterpart. The porosity is also important for the photocatalytic applications conjugating the smallest direct band gap (2.58 eV) and extended porous area (ca. 57 %). The nanopatterned thin films allow the exploitation of a new concept to prepare multiferroic nanocomposite thin films. The multiferroic films based on in two chemical-based bottom-up steps, including: i) the formation of a porous ferroic matrix and ii) the accomodation of nanoparticles from another ferroic phase within the pores. Hexagonal-arranged pores with diameter of ca. 95 nm, running perpendicularly to the substrate are filled with nickel nanoparticles using the supercritical fluid deposition technique from reduction of hydrated nickel nitrate in a supercritical CO2-ethanol mixture at 250 ºC. Small nickel nanoparticles with ca. 20 nm are deposited inside the pores of the porous matrix. Structural and magnetic properties proved the coexistence of both phases. The chemical based methodology offers thus an excellent control of the physical and chemical properties of nanostructured materials such as: stoichiometry, thickness, size, array and porous distribution. Moreover the self-assembly of block-copolymers provides a versatile platform to prepare functional nanostructured materials, namely mesostructured oxide thin films, due to their capability to form large pores and thick walls, apart from being industrially available and hazard-free. Additionally, the chemical-assembly method can allow the direct nanopatterning of large substrate areas with a functional oxide at a cost-effective price, in the absence of expensive equipment or etching processes (which typically affect negatively the ferroic properties).Besides, the functional properties of the porous films by themselves, the porous films are extremely promising to achieve multiferroic composites.

Thesis (Ph.D.)--Kent State University, 2008.
Title from PDF t.p. (viewed Dec. 17, 2009). Advisor: Mietek Jaroniec. Keywords: mesoporous, FDU-1, SBA-16, organosilicas, pendant groups, bridging groups, adsorption, isocyanurate, template removal, cage-like structures. Includes bibliographical references (p. 219-238).

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Capes
A pesquisa no desenvolvimento de estruturas do tipo micro-mesoporosas tem por intuito a obtenção de materiais porosos com características superiores, uma vez que busca unir a ácidez elevada da zeólita MCM-22, com o sistema de mesoporos, da peneira molecular MCM-41, consequentemente melhorar a difusão de moléculas volumosas. Nesta pesquisa foram sintetizadas as seguintes estruturas porosas: Inicialmente foi obtido o percussor lamelar MCM22-(P) com razão molar SiO2\Al2O3 = 30 e ativada para obter sua forma zeólítica MCM-22 a 550 0C por 5 horas. Em seguida, foi realizada a síntese do material micro-mesoporoso do tipo MCM-22/MCM-41, tratando 2 g da zeólita MCM-22, com uma solução de 25 mL de brometo de cetiltrimetilamônio (CTABr) a 10 % em massa, onde o material permaneceu em estufa a 1100C por 7 dias. Com o intuito de obter um novo material com melhor organização estrutural, utilizou-se a MCM-22 nas seguintes proporções (5%, 10% e 15%), permanecendo em estufa a 300C por 24 horas, sendo ativado em corrente de ar por 5500C por 5 horas. Os resultados das caracterizações de difratometria de raios-X, evidenciaram a formação do precursor MCM-22 (P) e sua forma zeólítica MCM22, com os picos da topologia MWW. A curvas obtidas por meio da análise termogravimétrica (TG/DrTG), demostraram as perdas de massa da água e demais adsorvatos. As micrografias (MEV), apresentou formato toroidal com depreciamento na região central para a MCM-22. Por meio dos resultados de adsorção física de N2, verifica-se que as zeólitas MCM-22, com isotermas do tipo I e loop de histerese do tipo H4. A partir dos difratogramas de raios - X para os materiais micro-mesoporosos foi possível observar a formação das estruturas porosas, com a identificação dos picos de reflexão pertinentes a fase microporosa da MCM-22 e da peneira molecular MCM-41, coexistindo em uma única fase estrutural. As imagens obtidas por MEV, detectam a formação de aglomerados de partículas da fase mesoporosa sendo constituída em torno da fase microporosa. A análise textural mostraram uma diminuição do volume de microporos e um aumento do volume de mesoporos, com isotermas do tipo IV e histereses 2. Demonstrando assim que as caracterizações foram eficazes na elucidação das estruturas porosas. Foi possível obter os materiais micromesoporosos para ambas as metodologias adotadas, sendo o teor de 5% de zeólita MCM-22 a melhor condição de síntese para obtenção desse novo material.
The research on the development of micro-mesoporous structures has the purpose of obtaining porous materials with superior characteristics, once it seeks to join the high acidity of MCM-22 zeolite with the mesoporous system of MCM41 molecular sieve, consequently improving the diffusion of bulky molecules. In this research, the following porous structures were synthesized: Initially, the MCM-22-(P) lamellar precursor was obtained with molar ratio of SiO2\Al2O3 = 30 and was activated to obtain its MCM-22 zeolite form at 550 °C for 5 hours. Then, MCM-22/MCM-41 micro-mesoporous material was synthesized by treating 2 g of MCM-22 zeolite with a solution of 25 mL of 10% wt cetyltrimethylammonium bromide (CTABr), where the material remained in an incubator at 110 °C for 7 days. In order to obtain a new material with better structural organization, the MCM-22 was used in the following proportions (5%, 10% and 15%), remaining in an incubator at 30 °C for 24 hours, being activated in air stream at 550 °C for 5 hours. The results of the X-ray diffraction characterization demonstrated the MCM-22 (P) precursor formation and its MCM-22 zeolite form, with MWW topology peaks. The curves obtained by means of the thermogravimetric analysis (TG/DrTG), showed the losses of water mass and other adsorbates. The micrographs (SEM) presented toroidal format with depreciation in the central region for MCM-22. By means of the results of physical adsorption of N2, it was verified for MCM-22 zeolites: type I isotherms and hysteresis loops of type-IV. From the X-ray diffractograms for the micro-mesoporous materials, it was possible to observe the formation of the porous structures, with the identification of the reflection peaks pertinent to the microporous phase of MCM-22 and the MCM-41 molecular sieve, coexisting in a single structural phase. The SEM images detected the formation of particle agglomerates of the mesoporous phase being constituted around the microporous phase. The textural analysis showed a decrease in the volume of micropores and an increase in the volume of mesopores, with type IV isotherms and hysteresis loops of type-II. Thus demonstrating that the characterizations were effective in elucidating the porous structures. It was possible to obtain the micro-mesoporous materials for both methodologies, being the 5% content of MCM-22 zeolite the best synthesis condition to obtain this new material.

Aquesta Tesi doctoral comprèn la síntesi mitjançant nanoemmotllament (de l’anglès, nanocasting) i autoassemblatge per evaporació induïda (de l’anglès, evaporation–induced self–assembly) i la caracterització exhaustiva de pols i capes de SnO2 mesoporós dopat amb Ni i Cu. L’origen de les propietats magnètiques d’aquests materials es discuteix en detall. En primer lloc, es van sintetitzar per nanoemmotllament a partir de motlles de sílice KIT–6, pols mesoporosa ordenada de SnO2 dopada amb diferents quantitats de Ni. Es va verificar la replicació correcta del motlle de sílice mitjançant microscòpia electrònica de rastreig. No es van detectar fases extres atribuïbles a Ni o NiO en els corresponents difractogrames excepte per a la mostra amb el dopatge més alt (9 at.% Ni), per a la qual es va observar la presència de NiO com a fase secundària. Es va estudiar l’estat d’oxidació i la distribució espaial de Ni en la pols mitjançant espectroscòpia fotoelectrònica de raigs X i espectroscòpia de pèrdua d’energia d’electrons, respectivament. Les mostres dopades amb Ni presenten resposta ferromagnètica tant a temperatura ambient com a baixa temperatura, com a conseqüència de la presència d’espins no compensats a la superfície de nanopartícules de NiO i vacants d’oxigen. En segon lloc, es van sintetitzar capes primes continues i mesoporoses de SnO2 dopades amb Ni a partir de diferents relacions molars [Ni(II)]/[Sn(IV)] mitjançant un procés d’autoassemblatge sol–gel, utilitzant el copolímer tribloc P–123 com a agent director d’estructura. Una caracterització estructural profunda va evidenciar l’obtenció d’una estructura nanoporosa 3–D, de gruix comprès entre els 100 i 150 nm, i mida de porus de 10 nm. Els experiments de difracció de raigs X d’incidència rasant van posar de manifest que el Ni ocupava posicions substitucionals en la xarxa tipus rutil del SnO2, tot i que les anàlisis per dispersió d’energies de raigs X també van revelar la presència de petits clústers de NiO en les capes produïdes a partir de les relacions molars [Ni(II)]/[Sn(IV)] més elevades. Convé remarcar que les propietats magnètiques de les capes mesoporoses varien significativament en funció del percentatge de dopant. Les capes de SnO2 no dopades presenten un comportament diamagnètic, mentre que les dopades amb Ni mostren un clar senyal paramagnètic amb una petita contribució ferromagnètica. En tercer lloc, també es van estudiar les propietats magnètiques de pols mesoporosa ordenada de SnO2 dopada amb Cu, obtinguda mitjançant nanoemmotllament a partir de sílice KIT–6. Per bé que una eventual contaminació amb impureses de Fe or la presència de vacants d’oxigen podrien explicar el comportament ferromagnètic observat a temperatura ambient, el ferromagnetisme a baixa temperatura es va atribuir únicament a la naturalesa nanoestructurada de les nanopartícules antiferromagnètiques de CuO formades (espins no compensats i shape–mediated spin canting). La menor temperatura de bloqueig, situada entre 30 i 50 K, i l’existència de petits desplaçaments verticals en els cicles d’histèresi van confirmar efectes de mida en les nanopartícules de CuO
This Thesis dissertation covers the synthesis by means of nanocasting and evaporation–induced self–assembly (EISA) methods as well as the advanced characterization of Ni, Cu–doped mesoporous SnO2 powders and films. The origin of the magnetic properties in these materials is also discussed in detail. Firstly, ordered mesoporous SnO2 powders doped with different Ni amounts were synthesized by nanocasting from mesoporous KIT–6 silica. Successful replication of the silica template was verified by scanning electron microscopy. No extra phases attributed to Ni or NiO were detected in the corresponding X–ray diffractograms except for the sample with the highest doping amount (e.g., 9 at.% Ni), for which NiO as secondary phase was observed. The oxidation state and spatial distribution of Ni in the powders was investigated by X–ray photoelectron spectroscopy and electron energy loss spectroscopy, respectively. Ni–containing powders exhibit ferromagnetic response at low and room temperatures, due to uncompensated spins at the surface of NiO nanoparticles and the occurrence of oxygen vacancies. Secondly, continuous mesoporous Ni–doped SnO2 thin films were synthesized from variable [Ni(II)]/[Sn(IV)] molar ratios through a sol–gel based self–assembly process, using P–123 triblock copolymer as a structure directing agent. A deep structural characterization revealed a truly 3–D nanoporous structure with thickness in the range of 100–150 nm, and average pore size about 10 nm. Grazing incidence X–ray diffraction experiments indicated that Ni had successfully substituted Sn in the rutile–type lattice, although energy–dispersive X–ray analyses also revealed the occurrence of small NiO clusters in the films produced from high [Ni(II)]/[Sn(IV)] molar ratios. Interestingly, the magnetic properties of these mesoporous films significantly vary as a function of the doping percentage. The undoped SnO2 films exhibit a diamagnetic behaviour, whereas a clear paramagnetic signal with small ferromagnetic contribution dominates the magnetic response of the Ni–doped mesoporous films. Thirdly, the magnetic properties of ordered mesoporous Cu–doped SnO2 powders, prepared by hard–templating from KIT–6 silica, were also studied. While Fe contamination or the presence of oxygen vacancies might be a plausible explanation of the room temperature ferromagnetism, the low–temperature ferromagnetism was mainly and uniquely assigned to the nanoscale nature of the formed antiferromagnetic CuO nanoparticles (uncompensated spins and shape–mediated spin canting). The reduced blocking temperature, which resided between 30 and 5 K, and small vertical shifts in the hysteresis loops confirmed size effects in the CuO nanoparticles.

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As restrições difusionais aos reagentes, causadas pelos microporos, limitam o uso das zeólitas no processamento de moléculas pesadas. Isto demanda o desenvolvimento de materiais que combinem as propriedades de zeólitas com as de materiais mesoporosos. Um número significativo de procedimentos experimentais, pré ou pós síntese, vem sendo sugerido para a obtenção de zeólitas hierarquicamente estruturadas. As metodologias de síntese mais bem sucedidas envolvem o uso de agentes geradores de mesoporosidade (agentes orgânicos e nanopartículas) ou nanomoldes (moldagem em nanoespaços), que geram sólidos com mesoporosidade intracristalina com uma estreita distribuição de tamanho de poros; isto resulta em sólidos contendo mesoporos, além dos microporos intrínsecos das zeólitas. Entretanto, ainda não existem estudos sistemáticos, que permitam estabelecer o efeito das variáveis de preparação sobre as características dos sólidos finais. A fim de superar essa dificuldade, neste trabalho foi estudado o efeito do tempo e da temperatura de cristalização do gel de síntese sobre as características de materiais baseados em mordenita com estrutura hierárquica de poros. Na preparação das amostras, adicionou-se um organossilano gerador de mesoporosidade (TPOAC, cloreto de [3- (trimetoxissilil)propil]octadecildimetilamônio), ao gel de síntese da mordenita, que foi cristalizado por diferentes períodos e em distintas temperaturas. Os sólidos obtidos foram submetidos à troca iônica com cloreto de amônio e posterior calcinação, de modo a obter a forma ácida do material. As amostras foram caracterizadas por termogravimetria, espectroscopia no infravermelho com transformada de Fourier, difração de raios X, análise textural por adsorção de nitrogênio, ressonância magnética nuclear de 29Si e de 27Al, microscopia eletrônica de varredura e medidas de acidez por dessorção de amônia à temperatura programada. Observou-se que a formação da mordenita contendo mesoporos é influenciada pelo tempo e temperatura de cristalização do gel da zeólita. O emprego de tempos relativamente curtos ou baixas temperaturas favorece a formação de um sólido amorfo, enquanto longos tempos ou elevadas temperaturas favorecem a formação de mesoporos intracristalinos na mordenita. Por outro lado, tempos e temperaturas intermediárias favoreceram a formação da mordenita com uma estrutura hierárquica de poros e mesoporos desordenados. O aumento da cristalinidade da mordenita acarreta uma diminuição na área e no volume de mesoporos, mas promove um acréscimo na área e no volume de microporos. A área externa também tende a diminuir devido ao aumento do tamanho do cristal da mordenita em função da cristalinidade. Os sólidos obtidos foram susceptíveis à desaluminação durante a etapa de calcinação. A extensão da desaluminação diminuiu com o aumento do tempo ou da temperatura de cristalização, devido à inserção dos átomos de alumínio na rede da zeólita em formação. Porém, em tempos de cristalização longos e temperaturas altas, pode ocorrer a redispersão dos átomos de alumínio. Todos os sólidos apresentaram elevada acidez que aumentou com a cristalinidade. Entretanto, nas amostras preparadas em tempos curtos e temperaturas baixas, a maioria dos sítios apresentou força ácida moderada, enquanto aquelas obtidas em tempos longos e temperaturas altas apresentaram maior quantidade de sítios ácidos fortes.
The diffusion restrictions of the reactants caused by the micropores limit the use of zeolites for processing heavy molecules. This demands for the development of materials that can combine the properties of zeolites and of mesoporous materials. A significant number of experimental procedures, pre or post synthesis, has been suggested for obtaining hierarchically structured zeolites. The most successful synthesis involve the use of mesoporosity generating agents (nanoparticles and organic agents) or nanotemplates (templating in nanospaces), which generate solids with intracristaline mesoporosity with a narrow pore size distribution. This results in solids containing mesoporous besides the intrinsic zeolite micropores. However, there is not any systematic study which allows to state the effect of crystallization time and temperature of the synthesis gel on the properties of the final solid. In order to overcome this difficulty, the effect of time and temperature of the synthesis gel on the properties of mordenite-based materials with hierarchical pore structure was studied in this work. In the samples preparation a mesoporosity generating organosilane (TPOAC, [3-(trimethoxysilyl) propyl] octadecyldimethylammonium chloride) was added to the synthesis gel of mordenite, which was crystallized for different times and temperatures. The solids were then submitted to ion exchange with ammonium chloride and further calcination to obtain the acidic form of the zeolite. The samples were characterized by thermogravimetry, Fourier transformed infrared spectroscopy, X-ray diffraction, textural analysis by nitrogen adsorption, 29Si and 27Al NMR, scanning electron microscopy and acidity measurements by ammonia desorption. It was observed that the formation of mordenite containing mesoporous is affected by the time and temperature of crystallization of the zeolite gel. The use of relatively short times and low temperatures favors the formation of an amorphous solid, while long times or high temperatures favor the formation of intracristaline mesoporosity in the mordenite. On the other hand, intermediate times and temperatures favor the formation of mordenite with hierarchical pore structure and disordered mesopores. The increase in mordenite crystallinity leads to a decrease in mesopore area and volume but promotes an increase in micropore area and volume. The external area also tends to decrease due to the increased crystal size as a function of mordenite crystallinity. The solids obtained were susceptible to dealumination during the calcination step. The degree of dealumination decreased with the increasing crystallization time or temperature due to the insertion of aluminum atoms in the zeolite lattice. However, at long crystallization times and high crystallization temperatures the redispersion of aluminum atoms can occur. All solids showed high acidity which increased as a function of crystallinity. However, the samples prepared at short times and low temperatures showed the majority of moderate acid sites of medium strength, whereas those obtained at long times and high temperatures have more strong acid sites. Thus, intermediate times and temperatures favor the formation of solids having zeolitic characteristics and high mesoporosity.

Ce travail s'est intéressé à la conception et à l'élaboration de nouveaux agents structurants de silice constitués d'assemblages induits et réversibles de copolymères originaux : les copolymères séquencés doublement hydrophiles (DHBC). Un des systèmes étudiés est constitué d'un DHBC neutre-anionique PAPEO-b-PAA ou poly(acrylate methoxy poly(oxyde d'éthylène))-b-poly(acide acrylique). La séquence PAA est un polyacide faible dont le degré d'ionisation dépend du pH. En solution aqueuse et pour un pH bien choisi, l'association de ce copolymère à une polybase faible, de charge opposée à celle du PAA, (typiquement un oligochitosane) conduit à la formation de micelles complexes de polyions (PIC) sphériques de type cur/couronne. Ces micelles peuvent dans un premier temps conduire à la formation de matériaux mésostructurés hybrides hautement organisés. Dans un second temps, en jouant notamment sur les conditions de pH et de force ionique, il est possible de « contrôler » le taux d'extraction des espèces organiques pour obtenir des matériaux poreux fonctionnels capables de piéger des espèces de charge opposée à la fonctionnalité. Si des matériaux hybrides organisés sont obtenus, c'est parce que les équilibres des interactions mises en jeu entre les espèces organiques et inorganiques y sont favorables. Si une interaction polyamine/silice s'exerce aux dépens de l'interaction polyamine/DHBC, elle peut limiter le processus de mésostructuration par les micelles. Lorsqu'un DHBC neutre-cationique PEO-b-PDMAEMA ou poly(oxyde d'éthylène)-b-poly(méthacrylate de 2-(diméthylamine)éthyle) est utilisé en présence d'un polymère anionique tel que le PVS ou poly(acide sulfonique de vinyle), il joue un double rôle dans la synthèse des matériaux siliciques : une partie gère la croissance des particules de silice en interagissant avec les silicates et l'autre partie qui est complexée par des PVS joue le rôle d'agent structurant en apportant une mésostructuration au matériau. Enfin, une approche très prometteuse a permis d'encapsuler des principes actifs hydrosolubles chargés dans un matériau en les utilisant comme agent complexant du DHBC
This study focused on the design and development of new structuring agents of silica constituted of induced and reversible assemblies of original copolymers, the double hydrophilic block copolymers (DHBC). The first system studied consists of a neutral-anionic DHBC PAPEO-b-PAA ou poly(acrylate methoxy poly (ethylene oxide))-b-poly (acrylic acid). The PAA block is a weak polyacid with a degree of ionization depending on the pH. In aqueous solution and in a right pH range, the association of this copolymer with a weak polybase, an oppositely charged polyamine, such as an oligochitosan, leads to the formation of polyion complex micelles (PIC) with a core/corona structure. These micelles can direct the structure of highly organized inorganic materials with different types of mesostructures. In a second step, by adjusting the conditions of pH, ionic strength, it is possible to "control" the extraction of organic species to get functional porous materials able to trap species of charge opposite to the functionality. Organized materials are obtained because of a favourable balance of the interactions between organic and inorganic species. If a polyamine/silica interaction occurs at the expense of the interaction polyamine/DHBC, the mesostructuring process by the micelles is limited. A neutral-cationic DHBC PEO-b-PDMAEMA poly(ethylene oxide)-b-poly(2-(dimethylamine)ethyl) associated with an anionic PVS poly(vinyl sulfonic acid) polymer can play a dual role in the synthesis of silica materials: firstly managing the growth of silica particles by interacting with the silicates and secondly acting as a structuring agent in association with PVS, confering a mesostructuration to the material. Finally, a very promising approach allowed to encapsulate water-soluble and charged drugs in a material by using as silica complexing agent a complex between the drug and a DHBC

Nanostructured metal films were electrodeposited through the hexagonal lyotropic liquid crystalline phase (HI). The mesoporous structure consists of porous channels (a few nm in diameter) arranged in an hexagonal array. These mesoporous metal films exhibit high surface areas supplied by the concave surface within the pores. The properties of these mesoporous materials have been investigated to gain an insight on the mesoporous structure. Cyclic voltammetry in acid of HI mesoporous Pt is similar to polycrystalline Pt made up of low index Pt facets. However CO stripping voltammetry shows differences between the HI mesoporous Pt and polished Pt electrodes. The CO stripping voltammogram for the HI mesoporous Pt electrode exhibits a CO oxidation pre-wave and CO oxidation at lower overpotentials. These differences result from the presence of trough sites corresponding to the intersection of two pore walls within the mesoporous structure. The adsorption of foreign atoms Bi and Ge on HI mesoporousPt was investigated to identify the different crystalline Pt facets. The features of the voltammetric profiles recorded in acid revealed the absence of large (111) domains and the presence of (100) terraces sites. CO stripping voltammetry for HI mesoporous Pt modified with Bi suggests the presence of a CO-Bi mixed ad layer. However, the absence of the aforementioned pre-wave was attributed to the adsorption of Bi on the trough sites thus causing inefficiency in oxygen transfer for CO oxidation. In contrast, the significant pre-wave observed for HI mesoporous Pt-Ge leads to an enhancement for CO oxidation. HI mesoporous metal films grown on microelectrodes show good stability of the measurement of hydrogen peroxide. HI mesoporous Rh with a variety of film thicknesses was extensively studied over a wide range of hydrogen peroxide concentrations. A kinetic model is proposed to describe the diffusion of hydrogen peroxide and the surface reaction in the pore. The accessibility of the ionic liquid BMIM-PF6 in the pores was investigated to assess the performance of mesoporous electrodes in supercapacitors. HI mesoporous Pt of diverse pore size and polished Pt electrodes were characterised in 1 M sulphuric acid and then tested in BMIM-PF6. The double layer capacitances were higher for the HI mesoporous Pt films thanks to their internal surface area leading to the confirmation that the ionic liquid penetrates into the pores. The analysis of electrochemical impedance spectroscopy shows that the results fit a transmission line model and provides useful parameters for the characterisation of the nanostructured Pt film in BMIM-PF6. 11.

Thesis (Ph.D.)--Kent State University, 2008.
Title from PDF t.p. (viewed May 28, 2009). Advisor: Mietek Jaroniec. Keywords: mesoporous carbons, inverse replication, hard templating, OMC, CMK-3, CMK-5, mesoporous silicas, OMS, SBA-15, MCM-48, KIT-6, colloids, colloidal crystal, nanomaterials, gas adsorption. Includes bibliographical references (p. 184-194).

Due to high consumption rates of petroleum derived fuels and environmental regulations, significant search has been initiated for the development of environmental friendly and efficient fuels, which were derived from more abundant feedstocks. Dimethyl ether (DME), as having a good combustion quality and high cetane number, is an efficient alternative for diesel fuel. With improved combustion quality, the emissions from DME used engines are greatly decreased. DME synthesis can be carried out via two different methods
methanol dehydration on acidic catalysis and syn-gas conversion on bifunctional catalysis. In this study, the aim is to synthesize acidic catalysts using direct hydrothermal synthesis method for DME synthesis as using methanol as feed stock via dehydration and to characterize these materials. The support of the synthesized materials comprises of MCM-41 structure and silicotungstic acid (STA) and metals (Zr / Ni / Cu) were incorporated into the MCM-41 structure during synthesis. Two different techniques were used to extract the surfactant (CTMABr) from catalyst matrix. First one is the conventional calcination technique (at 350°
C) and the second is supercritical fluid extraction (at various operating conditions) with methanol modified CO2. The effect of metal loading on extraction performance is analyzed through characterizations of Ni and Cu incorporated materials. In addition, The effect of operation parameters on catalyst properties are also investigated with performing extraction at different pressures for different durations. By changing the type of metal incorporated into the catalyst, the extraction performance is also monitored. The characterization results indicated that, SFE process is also a promising method for surfactant removal. The activities of zirconium added catalysts are tested in methanol dehydration reaction towards DME. It is concluded that the conversion of methanol and selectivity of DME in presence of extracted samples are lower (maximum yield -0.54- obtained at 450°
C with sceSZ1) compared to the calcined materials (maximum yield -0.80- obtained at 300°
C with cSZ6). This result can also be foreseen by DRIFTS analysis of pyridine adsorbed samples. The acid sites of extracted materials are not as strong as in the calcined catalysts.

Throughout this body of work, three classes of sorbent materials were created and optimized, each designed to selectively capture organics or desired metals from natural water sources. These target species included toxic heavy metals, uranium, rare earths, and simple organics, such as benzene. Each class of sorbent materials is functionalized nanostructured silicas, created by the development of several functionalization methods: utilizing thiol-ene click chemistry, aromatic interactions, and the formation of inclusion complexes. Thiol-ene click surface modification gave rise to sorbent materials with impressive affinities for both soft metals, such as gold, and harder metals, such as uranium and rare earth elements. Applications of these materials for aqueous mining of uranium and rare earth elements from various natural water sources are presented. Two classes of materials based on supramolecular functionalization methods were prepared. In the first class, aromatic interactions allowed for surface functionalization with thiol containing aryl ligands. These materials proved to have an excellent affinity for heavy metals from natural waters, and hold promise for regenerable nanostructured silica sorbents. The second class of materials utilizes the ability of β-cyclodextins to form inclusion complexes with small molecule organics, such as benzene. The formation of inclusion complexes drove both surface functionalization and the capture of small molecule organics from aqueous solutions. This work serves to inspire the development of novel functionalized nanostructured sorbents for trace collection of toxic organics from aqueous streams. These supramolecular methods for surface medication can be expanded to nanomaterials at large. This dissertation includes both previously published/unpublished and co-authored material.
10000-01-01

Mesoporous silica crystals have a large variety of structures mainly due to the versatility of their structure template. The configuration and the chemical state of the templating micellar surfactants, together with the kinetic process of silica will determine the final outcome of the synthesis. Increasing the understanding of the complex formation processes involved will enable a possibilityto fine tune the material for specific uses, today focused into the fields of photoniccrystals, drug delivery, catalysis and separation technology. In this thesis emphasis is put on (1) increasing the understanding the formation mechanism yielding the different species of mesoporous silica crystals through an in depth study of quasicrystallinity (2) Characterization and description of the structural complexity through various characterization techniquesand also by studying the kinetic structural transformation phenomenon related to the minimal G- and D-surfaces. (3) The structural studies of the versatile surfactant liquid crystals for establishing a thermodynamically stable basis to evaluate the kinetic mesoporous silica growth processes. Furthermorethe thesis both enlightens the possibilities of and contributes to the developmentof electron microscopy characterization techniques. In these studies, electron microscopy is largely employed in the characterization to give a thorough picture of the mesoporous structures. This is combined with the sample preparation techniques cross-section polishing and ionslicing. Low voltage scanning electron microscopy is utilized for studying the surfaces and cross-sections of various materials at the limit of the resolution. Here, a deep understanding of the electron beam-material interaction is used for a better interpretation of the detected signals. Transmission electron microscopyis combined with electron crystallographic reconstruction to yield a three dimensional structural model. For determination of the quasicrystallinity level for a structure of dodecagonal tiling, revealed in the scope of this study,a phason strain analysis was made.

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 7: Manuscript.

Increasingly global warming and air pollution caused by the consumption of fossil fuel have imposed the priority of using green energy. As a result, the use of rechargeable lithium-ion batteries (LIBs) has increased rapidly Olivine-structured LiFePO4 is considered as one of the most promising positive electrode materials owing to its significant advantages of nontoxicity, low cost of raw materials, good structural stability at high temperature, excellent safety performance, and relatively high theoretical specific capacity (170 mAhg-1) with a flat discharge-charge potential (3.45V vs. Li+/Li). Therefore, LiFePO4 battery becomes a reliable material for energy storage system used in hybrid electric vehicles (HEVs), full electric vehicles (EVs), plug-in hybrid electric vehicles (PHEVs), and portable devices. However, the poor rate performance of LiFePO4, resulting from its intrinsic low Li+ diffusivity (10-17 to 10-14 cm2s-1) and low electronic conductivity (10-9 to 10-8 S cm-1), has become a technical bottleneck to confine its widely practical applications. Following previous studies, a systematic study on controllable preparation of LiFePO4 positive electrode material with nanoscale size, or hierarchical micro/nano mesoporous structure has been carried out using various synthesis methods, including impinging stream reaction (ISR), ultrasonic-intensified impinging stream reaction (UISR), two-step co-precipitation method, and two-step hydrothermal method (UIHT). The physical and chemical properties of as-synthesized products are measured by XRD, FTIR, SEM, TEM, BET, Mastersizer, CV, and charge-discharge test. Based on these observations, the relationship among particle morphology, electrochemical performance, and impacts of fluid dynamics is evaluated in this work.

Mesoporous γ-alumina is the most extensively used catalysts support in a wide range of catalytic processes. The usefulness of γ-alumina relies on its favorable combination of physical, textural, thermal, and chemical properties. Pore structure properties are among the most important properties, since high surface area and large pore volume enable higher loading of active catalytic phases, while design of pore size and pore size distribution is critical to optimize pore diffusional transport and product selectivity. In addition, accurate determination of surface area (SA), pore volume (PV) and pore size distribution (PSD) of porous supports, catalysts, and nanomaterials is vital to successful design and optimization of these materials and to the development of robust models of pore diffusional resistance and catalyst deactivation.In this dissertation, we report a simple, one-pot, solvent-deficient process to synthesize mesoporous γ-alumina without using external templates or surfactants. XRD, TEM, TGA and N2 adsorption techniques are used to characterize the morphologies and structures of the prepared alumina nanomaterials. By varying the aluminum salts or the water to aluminum molar ratio in the hydrolysis of aluminum alkoxides, γ-alumina with different morphologies and pore structures are synthesized. The obtained alumina nanomaterials have surface areas ranging from 210 m2/g to 340 m2/g, pore volumes ranging from 0.4 cm3/g to 1.7 cm3/g, and average pore widths from 4 to 18 nm. By varying the alcohols used in the rinsing and gelation of boehmite/bayerite precursors derived from a controlled hydrolysis of aluminum alkoxides, the average pore width of the γ-aluminas can be tuned from 7 to 37 nm. We also report improved calculations of PSD based on the Kelvin equation and a proposed Slit Pore Geometry model for slit-shaped mesopores of relatively large pore size (>10 nm). Two structural factors, α and β, are introduced to correct for non-ideal pore geometries. The volume density function for a log normal distribution is used to calculate the geometric mean pore diameter and standard deviation of the PSD. The Comparative Adsorption (αs) Method is also employed to independently assess mesopore surface area and volume.

Mesoporous alumina (Al2O3) in the gamma (γ) phase is widely used as a support in catalytic applications because of its high surface area, large pore volume, acid-base characteristics, and thermal stability. To improve the thermal stability of gamma alumina, dopants such as lanthanum, magnesium, zirconia, and silica are often introduced. Current laboratory-based methods for synthesizing gamma alumina generally involve 10-15 steps and/or use toxic, expensive surfactants and solvents. Industrial methods, while simpler, lack control of pore properties and surface chemistry. In contrast, we have developed an innovative solvent deficient, one-step method that is able to synthesize a wide range of pure and silica-doped aluminas with high surface areas, pore volumes from 0.3 to 1.8 cm3/g, and pore diameters from 5 to 40 nm. More significantly, our silica-doped aluminas are stable up to temperatures as high as 1300<°>C, which is 200<°>C higher than other pure and doped gamma alumina materials.The usefulness of gamma-alumina as a catalyst support is dependent on its favorable combination of textural, thermal, structural, and chemical properties, yet the relationship between structure and these other properties is still not clearly understood due to the poorly crystallized nature of the material. In particular, the mechanism by which the gamma structure is stabilized thermally by so many dopants is still not well understood. Based on our previous PDF experiments on pure and La-doped alumina, we have developed a hypothesis regarding the mechanism by which dopants increase thermal stability. To validate or refute this hypothesis, we collected PDF data on a wider range of laboratory and industrial alumina samples. Herein, we have utilized PDF analysis to study the local to intermediate-range structure of a series of our pure and silica-doped aluminas calcined at 50<°>C intervals between 50 and 1300<°>C as well as pure and silica-doped aluminas from commercial sources and other synthetic methods. This thorough study of alumina local structure will allow us to separate general trends in the local structure from idiosyncrasies based on synthetic method/conditions, and it will help us identify the structural features responsible for improved thermal stability. Having access to these PDF experiments, we have validated our current hypothesis on the nature of stabilization afforded by dopants and, more generally, developed a better understanding of the role structure plays in the properties of aluminas.

This thesis identifies a facile and versatile technique for creating multi-scale porous titania with tunable meso-scale morphology. Three templating approaches were simultaneously utilized in achieving this; namely, soft-templating by template-free self-assembly of an aligned macroporous structure, freeze-casting for the preservation of particle dispersion found in suspension, and hard-templating by the use of cellulose nanocrystals (CNCs) as sacrificial material. A systematic study was conducted wherein three synthesis parameters (water content, alcohol solvent content, and drying method) were varied in the hydrolysis of titanium tetra-isopropoxide (TTIP) by the sol-gel method to determine their contribution to the formation of multi-scale porous titania exhibiting aligned macrochannels and mesoporosity. The optimal synthesis settings for producing multi-scale porous titania were identified as H2O/TTIP molar ratio of 30, without any isopropanol (acting as solvent), and freeze-drying after freezing at -40�C. Subsequently, CNCs were added in various quantities (0-50vol%) to the hydrolysis of TTIP using these optimized settings to achieve more direct and precise control of the final titania meso-structure. Morphological studies revealed that the final titania bodies maintained the formation of macrochannels 1-3 μm in diameter as a result of hydrolysis in excess water in the absence of an organic solvent and exhibited successful templating mutually affected by CNC addition and freeze-casting. Freeze-drying preserved particle dispersion in the colloid suspension, hindering agglomeration otherwise found after oven-drying and enhanced the CNCs� role of disrupting titania aggregation and increasing interconnectivity. Thus, meso-structured multi-scale porous titania was prepared by a combined templating strategy using template-free self-assembly, freeze-casting, and CNC hard-templating.
MS

Ordered Mesoporous Carbons (OMCs) with well-controlled pore structure and narrow pore size distribution demonstrated great potential as highly functional adsorbents. The pore size and surface chemistry of OMCs were considered two of the most important factors that affect the adsorption capacity of organic compounds. The objective of this study is to optimize the structure of OMCs for resorcinol adsorption by changing the pore size and oxygen content using computational approach. New rhombic OMC models with varied pore size and oxygen content were constructed using Materials Visualizer module. The specific surface area, total pore volume, small angle X-ray diffraction patterns, and resorcinol adsorption capacity results were calculated by Forcite and sorption module in Materials Studio package. The simulation results were validated by the experimental data. Experimentally, the OMCs were synthesized using sucrose as carbon precursor by hard-template method. The tunable pore size (4nm to 15nm) and oxygen content of the OMCs are obtained by adjusting the amount of boric acid as a pore-expanding reagent. The experimental results, such as BET surface area, X-ray power diffraction patterns, and adsorption capacity of resorcinol, were compared with the simulation results. The optimal pore size of OMC for resorcinol removal was found to be 6 nm. The simulation results confirmed that oxygen containing functional group was an important factor for adsorption on OMCs. The improvement of adsorption capacity was not so significant comparing with the influence of specific surface area, since the adsorption process was a more of a physical process rather than a process with chemical interaction.

Micro Hall probe magnetometry has been used to investigate the magnetisation of various electrodeposited microcrystals. Superconducting tin crystals of almost perfect square cuboid shapes exhibit a strong size dependence of the supercooling of the superconducting state and, for the smallest accessible crystals, the crossover to the mesoscopic regime can be readily explored close to their critical temperatures. Experimental results are in good agreement with Ginzburg-Landau simulations using the exact experimental parameters. Electroplating of the tin cores with another material provides unique core-shell structures of either two superconductors (S-S’: tin-lead) or of a superconducting core, covered with a ferromagnetic shell (S-F: tin/lead-nickel). The critical parameters of the tin core in Sn-Pb core-shell crystals are considerably enhanced and superconductivity in the tin core is detected up to 1:16 TSn c . Little-Parks oscillations in the shell can be analysed to reveal the extent of the superconducting sheath and hence can be utilised to measure the range of the proximity effect close to the critical temperature of the shell. In S-F core-shell structures, field cancellation effects govern the overall behaviour. Under certain conditions it was possible to switch the overall magnetic response from para(ferro-)magnetic to diamagnetic and back at finite applied fields. Micromagnetic simulations qualitatively reproduce the experimentally observed effects. Applications for the core-shell structures include magnetic guidance or memory devices.

It was recently shown that V-doped acid-prepared mesoporous silica (APMS) nanoparticles are active catalysts for the oxidation of the mustard gas analogue 2-chloroethyl ethyl sulfide (CEES) under ambient conditions in the presence of aldehydes, using O2 from air as the oxidation source. However, the vanadium ion leached from the surface when water was present, leading to decreased catalytic activity. Therefore, in this work, the environment around the vanadium is changed, using diethylenetriamine pentaacetic acid (dtpa) as a ligand and anchoring it to the surface of a mesoporous silica nanoparticle, to investigate its effect on vanadium’s ability to perform oxidation reactions. VO(dtpa)-APMS was synthesized by covalently linking the multi-dentate chelator dtpa onto the surface through peptide coupling of one of the acetate groups to aminopropyltriethoxysilane (APTES), condensing the dtpa-APTES molecule onto the mesoporous silica surface, and then exchanging a vanadyl salt into the resulting solid. Physical characterization of the material confirmed that the substrate retained its porosity after modification, and that the vanadium did not leach from the solid, in contrast to samples that did not contain dtpa. Solid-state EPR spectroscopy, combined with ongoing computational modeling, indicated that the vanadium was in a distorted five-coordinate environment. Various vanadium catalysts have been shown to oxidize alkanes, alkenes, alcohols and aromatic compounds. To further understand the catalyst’s ability to perform oxidation reactions, mechanisms of sulfides and alkenes were studied. Two model substrates were chosen for the investigation: CEES and cis-cyclooctene. The catalytic system effectively oxidizes CEES at room temperature in less than 15 minutes and cis-cyclooctene at 47 °C within 3 hours, using a peroxyacid generated in situ as the oxidant source. Kinetic experiments demonstrated that the mechanism of the sulfide reaction changed at higher temperatures, while the alkene reaction did not. In each reaction, a partial negative charge on the peroxyacid during the oxidation process was indicated. The confirmation of radical formation in the mechanism was experimentally shown by the appearance of an induction period when diphenylamine, a radical trap, was introduced into the reaction. VO(dtpa)-APMS performs two catalytic oxidations: the oxidation of propionaldehyde to make the peroxyacid and the oxidation of alkenes or sulfides. In the first reaction, O2 binds to the vanadium complex to form a superoxo eta-1-bound O2 radical. This species leads to the formation of peroxyacid through a radical process. The peroxyacid produced in this manner can then react with a sulfide or an alkene in a process also catalyzed by the VO(dtpa) complex. The peroxyacid coordinates with the vanadium center. Upon coordination, the sulfide or alkene directly reacts with the oxygen of the peroxyacid while the peroxyacid is being deprotonated. A 6-coordinate catalyst intermediate is formed prior to the release of the oxidation product and propionic acid to regenerate the VO(dtpa) complex.

Les matériaux utilisés dans le nucléaire (combustible, matrice de conditionnement, matériaux de structure…) sont soumis à des contraintes importantes liées à la création de défauts qui modifient leurs propriétés. Plusieurs études ont montré que les interfaces peuvent agir comme un puits pour les défauts causés par l'irradiation, ce qui suggère que les nanomatériaux pourraient avoir une plus grande résistance à l'irradiation que les matériaux présentant une structure « micrométrique ». Par ailleurs, les silices mésoporeuses ont gagné en popularité ces dernières années et sont envisagées pour le traitement des effluents radioactifs (séparation, conditionnement…). Bien que de nombreuses études aient été réalisées sur le comportement de silices non poreuses sous irradiation, très peu de travaux s’intéressent à celui de la silice mésoporeuse en particulier lorsqu’elle est irradiée en régime d‘électronique.Le but de cette thèse est de comprendre et d'expliquer les modifications induites par irradiation dans les silices mésoporeuses en régime électronique. Ce travail a permis de quantifier l’évolution de propriétés physico-chimiques (polymérisation du réseau, création de défauts…) et structurales (volume poreux, diamètre et distribution des pores…) de la silice mésoporeuse irradiée par des faisceaux d'ions de haute énergie dans une gamme de pouvoirs d'arrêt variant entre 1 keV/nm et 12 keV/nm, ainsi que par des électrons (10 - 300 keV et 0.6 - 2.4 MeV). Des méthodes de caractérisation post-irradiation (réflectivité des rayons X, adsorption de gaz, SAXS et FTIR, etc.) ont été utilisées, ainsi que le suivi in situ de la structure des pores à l'aide de microscopie électronique. Les résultats expérimentaux ont indiqué que la structure des pores était sensible à l'irradiation conduisant dans certaines conditions à son effondrement, tandis que le réseau de silice lui-même évolue peu par rapport à la silice non poreuse. Parallèlement, un modèle TS3D (modèle de pointe thermique 3D) a été utilisé avec succès pour décrire et expliquer le comportement de contraction des pores observé en réponse à l'irradiation ionique. De plus, le mécanisme de contraction des pores sous irradiation par des électrons a été délimité en fonction du domaine des énergies incidentes des électrons et de la dose. Cette recherche a montré que par rapport à une silice non poreuse, la présence de pores nanométriques réduit l’accumulation des dommages causés par les irradiations. Conjointement à cet effet bénéfique, le pore se contracte jusqu’à disparaitre sous l’impact de l’irradiation. Par conséquent, d’un point de vue applicatif cette caractéristique pourrait être mise à profit pour imaginer de nouvelles voies de traitement des effluents radioactifs, par une stratégie de type « séparation/conditionnement » ou pour l'autoguérison des couches de gel poreux formées à la surface des colis de déchets vitrifiés dont l’exutoire envisagé est le stockage géologique profond
Materials used in nuclear energy (fuel, packaging matrix, structural materials...) are subject to significant stresses due to the creation of defects that modify their properties. Several studies have shown that interfaces can act as a sink for defects caused by irradiation, which suggests that nanomaterials could have a higher resistance to irradiation than materials with a "micrometric" structure. Simultaneously, mesoporous silica materials have grown in popularity in recent years and are becoming more involved in the domain related to radiation conditioning, such as the prospective use of conditioning for nuclear waste. While research has begun to focus on the behavior of non-porous silica materials when exposed to radiation, no extensive investigations have been conducted on the behavior of mesoporous silica when exposed to radiation, particularly at electronic irradiation regime.This thesis aims to comprehend and explain the radiation-induced changes in mesoporous silicas under electronic regimes. This work quantified the evolution of physical (pore volume, pore diameter and distribution...) and structural (polymerization of the network, creation of defects...) properties of mesoporous silica irradiated with high-energy ion beams with stopping powers ranging from 1 keV/nm to 12 keV/nm, and with electron beams (10 - 300 keV and 0.6 - 2.4 MeV). Post-irradiation characterization methods (X-ray reflectivity, gas adsorption, SAXS, FTIR, etc.) have been used, as well as in-situ pore structure monitoring using electron microscopes. The experimental findings indicated that pore structures were susceptible to a certain degree of irradiation-induced shrinking. In contrast, evidence shows that the silica network itself does not alter much in porous silica compared to non-porous silica. Meanwhile, a 3DTS (3D thermal spike) model has been successfully applied to describe and explain the observed pore contraction behavior in response to ionic irradiation. Additionally, the mechanism of pore contraction under electron irradiation has been delineated according to the domain of incident electron energies. When compared to non-porous silica, this research has demonstrated that the existence of nanoscale pores reduces the accumulation of damage induced by irradiation. In conjunction with this effect, the pore contracts until it completely disappears under the impact of irradiation. This characteristic could, from an applicative point of view, be of interest to practitioners in the context of new methods of treating radioactive effluents, such as through the use of a "separation/conditioning" strategy, or in the context of the self-healing of porous gel layers formed on the surface of vitrified waste packages whose final destination is deep geological disposal