The thesis discusses how to utilize Sol-gel method to prepare nano-sized TiO2 films of photoelectrodes and the their use in Dye-Sensitized Solar Cells. The main goal is the study on the production of TiO2 photoelectrodes. When making nano-sized TiO2 films of photoelectrodes, we have to first produce TiO2 sol via the Sol-gel method optical thin films are then made by spin coating. After its spin coating, we study the crystalline phase and morphology of nano-sized TiO2 films of photoelectrodes in terms of two ways: Supercritical drying and oven drying. Among the Dye-Sensitized Solar Cells that are made with different drying methods, owing to higher porosity and surface area, the nano-sized TiO2 films of photoelectrodes made by supercritical drying adsorb more dye molecules and are thus more efficient.

O objetivo deste trabalho consistiu-se no desenvolvimento de um método para a produção de aerogéis de amido para a impregnação de óleo de café verde. Para atingir este objetivo foram estabelecidas três etapas: (1) desenvolvimento de um método de secagem supercrítica usando misturas de dióxido carbono supercrítico (CO2-sc) e etanol (EtOH); (2) fabricação de aerogéis na presença de CO2 e (3) impregnação supercrítica de extrato de óleo de café verde nos aerogéis de amido produzidos. Os aerogéis produzidos na primeira e segunda etapa foram caracterizados por adsorção-dessorção de nitrogênio a baixa temperatura (BET e BJH), microscopia eletrônica de varredura (MEV), e por difração de Raio-X para conhecer seu padrão cristalino e cristalinidade. A metodologia de secagem desenvolvida durante o presente trabalho permitiu obter resultados bastante positivos dado que os materiais (monólitos) exibiram áreas superficiais de 95 m2/g que estão de acordo com os melhores materiais descritos na literatura. Por outro lado, esta metodologia (200 bar e 40°C utilizando 2 ml/min de CO2 com 11% de etanol) permitiu uma redução significativa do tempo e secagem (de 24 h para 6 h). No que diz respeito à fabricação dos aerogéis na presença de CO2 foram testadas diferentes condições para melhorar as caraterísticas dos materiais anteriormente descritos. Neste caso, a estratégia passou pelo desenvolvimento de partículas de aerogel em vez de monólitos, avaliando o impacto da quantidade de amido no sol e da temperatura de gelatinização nas caraterísticas físico-químicas dos materiais. Os resultados demonstraram que os melhores materiais exibiram áreas superficiais de 185 m2/g, sendo obtidos com 10% de amido a 40° C. Por outro lado, verificou-se igualmente que o aumento da temperatura era responsável pela diminuição do domínio cristalino. No entanto, na presença de CO2 este efeito de diminuição não foi tão extenso como na sua ausência. O último ponto do presente trabalho consistiu na impregnação dos matérias obtidos de modo a avaliar a sua aplicabilidade como matriz de impregnação para moléculas de interesse alimentar. Neste estudo foram utilizados os monólitos obtidos na primeira etapa como matriz de impregnação de óleo de café verde em condições supercríticas (300 bar e 40°C). Os resultados obtidos demostraram uma eficiência de impregnação de 39 mg de óleo /100 mg de monólito em 12h. O presente trabalho demonstrou ser possível desenvolver uma nova metodologia de secagem de aerogéis sem etapa de troca de solvente e com uma redução apreciável do tempo de secagem. Por outro lado, foi possível obter partículas de aerogéis com caraterísticas bastante interessante para a impregnação de moléculas de interesse alimentar. Por fim este trabalho apresenta ótimas perspectivas para o desenvolvimento de um processo integrado para a fabricação de aerogéis e impregnação dos mesmos em CO2 supercrítico, demostrando boas perspectivas para o desenvolvimento de materiais biocompatíveis para aplicações nas indústrias alimentar, dermatológica ou mesmo farmacêutica. / The objective of this work was the development of a method for the production of starch aerogels for the impregnation of green coffee oil. To achieve this goal, three steps were established: (1) development of a supercritical drying method using mixtures of supercritical carbon dioxide (CO2-sc) and ethanol (EtOH); (2) fabrication of aerogels in the presence of CO2 and (3) supercritical impregnation of green coffee oil extract in the starch aerogels produced. The aerogels produced in the first and second stages were characterized by adsorptiondesorption of nitrogen at low temperature (BET and BJH), scanning electron microscopy (SEM), and by X-ray diffraction to know its crystalline pattern and crystallinity. The drying methodology developed during the present work allowed to obtain very positive results since the materials (monoliths) exhibited superficial areas of 95 m2/g that are in agreement with the best materials described in the literature. This methodology (200 bar and 40°C using 2 ml/min of CO2 with 11% of ethanol) allowed a significant reduction of the time and drying (from 24 h to 6 h). Regarding the manufacture of aerogels in the presence of CO2, different conditions were tested to improve the characteristics of the previously described materials. In this case, the strategy involved the development of aerogel particles instead of monoliths, evaluating the impact of the amount of starch in sol and the gelatinization temperature on the physical-chemical characteristics of the materials. The results showed that the best materials exhibited surface areas of 185 m2/g and were obtained with 10% starch at 40°C. On the other hand, it was also verified that the increase in temperature was responsible for the decrease of the crystalline domain. However, in the presence of CO2 this decrease effect was not as extensive as in its absence. The last point of the present work was the impregnation of the obtained materials in order to evaluate its applicability as impregnation matrix for molecules of alimentary interest. In this study, the monoliths obtained in the first stage were used as impregnation matrix of green coffee oil under supercritical conditions (300 bar and 40°C). The results showed an impregnation efficiency of 39 mg of oil/100 mg of monolith in 12 hours. The present work demonstrated that it is possible to develop a new drying methodology for aerogels without a solvent exchange step and with an appreciable reduction of the drying time. Likewise, it was possible to obtain particles of aerogels with very interesting characteristics for the impregnation of molecules of alimentary interest. Finally, this work leaves great prospects for the development of an integrated process for the manufacture of aerogels and their impregnation in supercritical CO2, demonstrating good prospects for the development of biocompatible materials for applications in the food, dermatological or even pharmaceutical industries.

Cette thèse présente un travail sur l’obtention d’aérogels d’HDL par séchage en conditions CO2 supercritique et l’élaboration de nouveaux bionanocomposites formés par la coprécipitation d’hydroxydes doubles lamellaire (HDL) dans l'espace confiné des billes d'alginate. Grâce à la combinaison d’une synthèse par coprécipitation Flash et d’un séchage en conditions supercritiques au CO2, des aérogels d’HDL possédant des surfaces spécifiques élevées sont élaborés. Parallèlement, l’alginate est utilisé comme une matrice de confinement pour la précipitation inorganique d’HDL. D’une part, les billes d'alginate sont synthétisées par complexation des ions Ca2+ et la coprécipitation des phases HDL s’effectue en réalisant des imprégnations successives de réactifs. D’autre part, des billes d'alginate sont formées directement en présence des cations divalents (Mg2+, Ni2++, Co2+, ...) et des cations des métaux trivalents (Al3+), précurseurs des composés inorganiques. La coprécipitation des HDL se produit dans ce cas lors d'une étape d'imprégnation dans une solution d'hydroxyde de sodium. Tous les composés HDL, aérogels ou encore bionanocomposites sont caractérisés en détail par DRX, spectroscopie IR, MEB/MET, adsorption/désorption d’azote et ATG/DTG, pour obtenir un meilleur aperçu de la structure des particules, de leur taille et de leur morphologie. Des études menées sur l’adsorption de la trypsine pour les aérogels ou encore sur les performances d’électrodes modifiées HDL-alginate ont permis de montrer qu’il était possible d'améliorer les performances des HDL en augmenter leur porosité et en élaborant des bionanocomposites. / In this work, we investigated both the use of CO2 supercritical drying conditions and the use of biopolymer to modify the growth and aggregation of inorganic Layered Double Hydroxide (LDH) particles. Indeed, one possibility to enhance their performances is to increase the LDH porosity and to design them as nanostructured open structure. Thanks to the combinaison of fast coprecipitation and CO2 supercritical drying, highly porous LDH aerogels were obtained with enhanced textural properties. In parallel, the coprecipitation of Layered Double Hydroxides (LDH) in the confined space of alginate beads is reported. In our approach, Alginate acts as a template to support and confined the inorganic precipitation. In one hand, beads made of Alginate are synthesized by complexation of Ca2+ ions and LDH phases are coprecipitated using successive impregnations of reactants. In another hand, Alginate beads are formed directly in presence of the divalent (Mg2+, Ni2+, Co2+,…) and trivalent metal cations (Al3+), precursors of the inorganic compounds. LDH coprecipitation then occurs during a further impregnation step in a sodium hydroxide solution. All the LDH aerogels and LDH nanocomposites beads are deeply characterized using XRD, SEM/TEM, FTIR spectroscopic, adsorption/desorption of nitrogen and TGA/DTG to get better insight on particle structure, size and morphology Aerogels display enhanced adsorption behavior toward trypsine immobilization whereas a net improvement of the electrochemical response is noticed for the NiAl based bionanocomposites prepared by confined coprecipitation into Alginate.

Tato práce se zabývá systematickou studií syntézy a zpracováním pokročilých tepelně stabilních aerogelů pro potenciální vysokoteplotní aplikace. V první části dizertační práce jsou podrobně popsány syntetické implikace pro přípravu aerogelů a jejich aplikace spolu s popisem depozičních metod povlaků vytvořených pomocí sol-gel procesu. Experimentální postup je rozdělen do tří částí. První z nich představuje syntetické protokoly k přípravě ZrO2, YSZ, Ln2Zr2O7 (Ln = La3+, Nd3+, Gd3+, and Dy3+) aerogelů, Ln2Zr2O7 prášků a xerogelů. Dále je popsána depoziční metoda, která byla použita pro přípravu povlaků z aerogelů na kovových substrátech. Poté jsou následně specifikovány techniky, jež byly použity pro charakterizaci. Bylo zjištěno, že množství vody a kyseliny dusičné hraje rozhodující roli v přípravě gelů vhodných pro transformaci na aerogely. Po kalcinaci při 500 °C mají ZrO2 a YSZ aerogely velký povrch, a to až do 114 m2 g-1, avšak při 1000 °C dochází k úplnému zhuštění a ztrácí se tak veškerá jejich porézní struktura. Naopak ve srovnání s ZrO2 and YSZ jsou aerogely Ln2Zr2O7 tepelně stabilnější, protože si zachovávají svou porozitu při vyšší kalcinační teplotě (1000 °C), při které dosahují hodnot > 160 m2 g-1. Experimentálně bylo dále zjištěno, že ve studovaném teplotním rozsahu ZrO2 aerogel tvoří tetragonální komplex monoklinický fázový přechod řízený velikostí krystalitů, zatímco YSZ je tvořena jedinou tetragonální fází. Fázové složení zirkoničitanů vzácných zemin je vysoce závislé na způsobu syntézy; všechny Ln2Zr2O7 materiály jsou pyrochlorické nebo fluoritové krystalické fáze. Přímým odléváním aerogelu na kovový substrát dochází k úplnému rozpraskání povlaku z důvodu smršťování, zatímco máčením kovového substrátu v suspenzi je možné vyrobit homogenní, silné a hrubé povlaky z aerogelu. Tyto povlaky neobsahují fázové změny a zůstávají vysoce porézní i po různých tepelných úpravách.

Le séchage d’organogels, gels composés d’un organogélateur de type acide aminé dissous dans un solvant, conduit à la formation d’aérogels, solides très légers et très poreux. Ces aérogels constituent entre autres de très bons isolants thermiques. La préparation des aérogels nécessitent plusieurs étapes. Ce procédé supercritique est composé de trois étapes : préparation de CO2 supercritique, séchage d’organogel dans l’autoclave en le balayant par un courant de CO2 et séparation de CO2-solvant au sein d’une cascade de trois séparateurs cyclones. Dans cette étude, les deux dernières étapes ont été abordées afin d’optimiser les paramètres du procédé. Les solvants utilisés sont la tétraline et le toluène. La cinétique de séchage au sein de l’autoclave a été étudiée, trois approches différentes ont été explorées : le transport de tétraline dans le CO2 supercritique au sein du gel est gouverné uniquement par le phénomène de diffusion dans les deux premières, il est régi par les phénomènes de diffusion et de convection dans la troisième approche. Les équations de transfert de matière ont été résolues à l’aide de deux logiciels numériques Matlab et ANSYS-Fluent. La troisième approche semble donner les résultats les plus cohérents avec les résultats expérimentaux. La compréhension des raisons du dysfonctionnement des séparateurs cycloniques en aval de l’autoclave pour le cas du toluène a nécessité deux études : une étude hydrodynamique MFN a permis de simuler le transport des fluides au sein du premier séparateur cyclone, à l’aide du logiciel ANSYS-Fluent. Cette étude a montré que le toluène liquide n’était pas entraîné dans la sortie gaz du cyclone, indiquant ainsi que l’hydrodynamique favorise la séparation. Afin d’expliquer ce dysfonctionnement, une étude thermodynamique portant sur les deux solvants, toluène et tétraline a été réalisée. La séparation cyclonique a été considérée comme un simple étage théorique et simulée avec le logiciel PRO/II. Cette étude a bien expliqué les résultats expérimentaux pour les deux solvants et a permis d’optimiser les paramètres du procédé / Drying of organogels, gels composed of an organogelator such as amin acids dissolved in a solvent, leads to the formation of aerogels, very light solids with high porosity. These aerogels are expected to be very good heat insulating materials. Preparation of aerogels includes several steps. This process consists of three steps: preparation of supercritical CO2, drying of the gel in an autoclave with a CO2 flow and CO2-solvent separation carried out in a cascade of three separators. In this study both the last steps were discussed in order to optimize the process parameters. The used solvents are tetralin and toluene. The drying kinetic in the autoclave was studied, three different approaches have been exploited. Tetralin transport in supercritical CO2 within the gel is governed only by the diffusion phenomenon in the first two approaches, although, it is governed by diffusion and convection phenomena in the third approach. The mass transfer equations were solved by two numerical software Matlab and ANSYS-Fluent. It seemed that the third approach gave the most consistent results with experimental results. The understanding of the malfunction reasons of cyclonic separators downstream from the autoclave for the case of toluene required two studies: A CFD hydrodynamic study was used to simulate the fluids transport within the first cyclone separator, using the ANSYS-Fluent software. This study showed that the liquid toluene was not carried over into the gas outlet of the cyclone, indicating that hydrodynamic promotes the separation. For this reason, a thermodynamic study of both solvents, toluene and tetralin was performed. Cyclonic separation was regarded as a simple theoretical stage and simulated with PRO / II software. This study has explained very well the experimental results for both solvents and allowed to optimize the process parameters

Doctor of Philosophy / Department of Chemical Engineering / Keith L. Hohn / Vanadium phosphorous oxide (VPO) is traditionally manufactured from solid vanadium oxides by synthesizing VOHPO[4subscript][dot in middle of line]0.5H[2subscript]O (the precursor) followed by in-situ activation to produce (VO)[2subscript]P[2subscript]O[subscript]7 (the active phase). These catalysts considerably improve their performance when prepared as nanostructured materials and this study discusses an alternative synthesis method based on sol-gel techniques capable of producing nanostructured VPO. Vanadium(V) triisopropoxide oxide was reacted with ortho-phosphoric acid in tetrahydrofuran (THF). This procedure yielded a gel of VOPO[4subscript] with interlayer entrapped molecules. The gels were dried at high pressure in an autoclave with controlled excess and composition of THF-2-propanol mixtures. The surface area of the obtained materials was between 50 and 120 m[2superscript]/g. Alcohol produced by the alkoxide hydrolysis and incorporated along with the excess solvent reduced the vanadium during the drying step. Therefore, after the autoclave drying, the solid VOPO[4subscript] was converted to the precursor; and, non-agglomerated platelets were observed. Use of additional 2-propanol increased the amount of precursor in the powder but reduced its surface area and increased its crystallite size. In general, sol-gel prepared catalysts were significantly more selective than the traditionally prepared materials, and it is suggested that the small crystallite size obtained in the precursor influenced the crystallite size of the active phase increasing their selectivity towards maleic anhydride. The evaluation of these materials as catalysts for the partial oxidation of n-butane at 673 K under mixtures of 1.5% n-butane in air yielded selectivity of 40% at 50% conversion compared to 25% selectivity at similar level of conversion produced by the traditionally prepared catalysts. Variations in the catalytic performance are attributed to observed polymorphism in the activated materials, which is evidenced by remarkable differences in the intrinsic activity. All precursors and catalysts were characterized by IR, XRD, SEM and BET, and the products of the catalytic tests were analyzed by GC.

Cette thèse s’inscrit dans une volonté de développer un procédé de synthèse de phyllominéraux de type talc en continu et en utilisant la technologie supercritique (plus spécifiquement utilisant l’eau comme solvant) afin d’avoir des temps de synthèses compatibles avec le milieu industriel (très courts) : une dizaine de secondes seulement. Cette voie innovante offre la possibilité d'obtenir un talc synthétique présentant des propriétés uniques telles qu’une haute pureté minéralogique et chimique, une grande surface spécifique(plusieurs centaines de m²/g) et un caractère hydrophile (gel de talc synthétique stable) qui a ainsi conduit à la formulation du premier minéral de talc liquide (son homologue naturel étant hydrophobe). De plus, il a été mis en place un procédé de séchage de ce minéral liquide par CO2 supercritique permettant l’obtention d’un solide de très haute surface spécifique et facilement réhydratable. Ce procédé a permis également la fonctionnalisation du talc synthétique élargissant ainsi les domaines d’applications de ce nouveau minéral liquide. La voie supercritique semble être la voie privilégiée pour un développement à l’échelle industrielle de la fabrication de particules minérales synthétiques (phyllosilicatées, silicatées et autres) en milieu aqueux. Une étude sur l’impact environnemental de ce nouveau procédé a été réalisée afin d’identifier les pistes d’optimisation possibles pour que cette voie soit la plus durable possible. / This thesis project was carried out to develop a continuous process for supercritical fluid synthesis of phyllominerals (especially using water as solvent) to fit synthesis time with industrial requirements: about ten seconds only. This innovative route provides synthetic talc with properties such as high mineralogical and chemical purity, large surface area (several hundred m²/g) and hydrophilic nature resulting in the formulation of the first liquid talc mineral (its natural counterpart being hydrophobic). Moreover, supercritical CO2 drying process implementation allows the obtention of very high specific surface area solid material easily rehydratable to prepare stable synthetic talc gel. This process allows synthetic talc functionalization, thus widening the fields of application for this new liquid mineral. Supercritical route appears as the optimal route to develop industrial scale mineral synthesis preparation (phyllosilicates, silicates and others). Environmental impact study of this new process further identifies possible optimization trails to make this route as sustainable as possible.