The latitudinal motion of the Tibetan Himalayathe northernmost continental unit of the Indian plateis a key component in testing paleogeographic reconstructions of the Indian plate before the India-Asia collision. Paleomagnetic studies of sedimentary rocks (mostly carbonate rocks) from the Tibetan Himalaya are complicated by potentially pervasive yet cryptic remagnetization. Although traditional paleomagnetic field tests reveal some of this remagnetization, secondary remanence acquired prior to folding or tilting easily escapes detection. Here we describe comprehensive rock magnetic and petrographic investigations of Jurassic to Paleocene carbonate and volcaniclastic rocks from Tibetan Himalayan strata (Tingri and Gamba areas). These units have been the focus of several key paleomagnetic studies for Greater Indian paleogeography. Our results reveal that while the dominant magnetic carrier in both carbonate and volcaniclastic rocks is magnetite, their magnetic and petrographic characteristics are distinctly different. Carbonate rocks have wasp-waisted hysteresis loops, suppressed Verwey transitions, extremely fine grain sizes (superparamagnetic), and strong frequency-dependent magnetic susceptibility. Volcaniclastic rocks exhibit pot-bellied hysteresis loops and distinct Verwey transitions. Electron microscopy reveals that magnetite grains in carbonate rocks are pseudomorphs of early diagenetic pyrite, whereas detrital magnetite is abundant and pyrite is rarely oxidized in the volcaniclastic rocks. We suggest that the volcaniclastic rocks retain a primary remanence, but oxidation of early diagenetic iron sulfide to fine-grained magnetite has likely caused widespread chemical remagnetization of the carbonate units. We recommend that thorough rock magnetic and petrographic investigations are prerequisites for paleomagnetic studies throughout southern Tibet and everywhere in general.

Master of Science / Department of Grain Science & Industry / Xiuzhi Susan Sun / Bio-based protein adhesives derived from renewable resources, especially soy protein are becoming more significant due to the concerns about environment and health related issues and the limit of petroleum recourses. However, the relatively poor water resistance of soy-based protein adhesives limits its wide applications. The goal of this study was to improve the water resistance performance of soy-based protein adhesives by chemical modification. The specific objectives are 1) to modify soy protein with calcium carbonate (CaCO[subscript]3) and sodium bisulfite (NaHSO[subscript]3) as the denaturing agents; 2) to investigate the effects of calcium carbonate (CaCO[subscript]3) concentrations, curing time and curing temperatures on adhesion performance of the modified soy-based protein adhesives. In this study, the co-effects of NaHSO[subscript]3 and CaCO[subscript]3 on adhesion properties of soy protein adhesives were investigated. NaHSO[subscript]3 was added to soy flour slurry at constant concentration 6g/L, while concentration of CaCO[subscript]3 was chosen in the range of 0 to 23g/L. Soy protein adhesives modified with 4g/L and 16g/L CaCO[subscript]3 were selected to characterize the adhesion performance on 3 ply yellow pine plywood using the Response Surface Method (RSM). The effects of curing temperature and curing time on the adhesion properties were also studied. The major findings are 1) 4g/L CaCO[subscript]3, 6g/L NaHSO[subscript]3 modified soy protein adhesives (MSPA) had better adhesion performance (both dry and wet) than 16g/L CaCO[subscript]3, 6g/L NaHSO[subscript]3 MSPA; 2) Higher temperature (170°C) resulted in higher wet shear adhesion strengths; 3) Longer hot press time had positive impact on wet adhesion shear strength; and 4) 4g/L CaCO[subscript]3, 6g/L NaHSO[subscript]3 MSPA showed better adhesion shear strength after 2 weeks storage than 16g/L CaCO[subscript]3, 6g/L NaHSO[subscript]3 MSPA. In general, 4g/L CaCO[subscript]3, 6g/L NaHSO[subscript]3 MSPA, under longer hot press time and higher temperature would lead to a better adhesion performance.

Ce travail évalue le potentiel du zinc et plus particulièrement des terres rares à tracer les différents processus le long d’une catena issue d’une formation carbonatée constituée d’une succession de bancs marneux et calcaires, et ayant subi des processus de décarbonatation, des conditions redox en lien avec l’hydromorphie et de l’éluviation. L’approche choisie repose (i) sur la spéciation des terres rares, à l’aide de méthodes physiques et chimiques, dans les traits pédologiques formés par les différents processus et des matériaux aux dépens desquels ils se sont développés, (ii) sur la quantification par bilan de masse des flux de terres rares et éléments majeurs associés. Ce travail a nécessité deux mises aux points méthodologiques : une méthode de normalisation des terres rares, basée sur l’enfoncement des fronts de transformation afin de quantifier l’impact des processus successifs sur le fractionnement des terres rares ; une méthodologie de reconstruction des matériaux parentaux pour chacun des horizons, l’approche par bilan de masse nécessitant une connaissance des stocks initiaux. L’impact de deux processus sur les fractionnements de terres rares est ensuite plus particulièrement abordé : la décarbonatation des matériaux parentaux et les processus d’oxydo-réduction. On montre ainsi l’importance de comparer les quantités mises en solution aux flux calculés par les bilans de masse pour prédire le devenir des éléments libérés et l’intérêt des terres rares pour quantifier les cycles de dissolution/précipitation des oxydes de fer et de manganèse. / This project aims at considering the potential of zinc and rare earth element (REEs) at quantifying pedogenetic processes along a soil sequence developed from a limestone formation consisting in a succession of marl and limestone strata which underwent carbonate dissolution, redox cycles related to soil hydromorphy and eluviation. The chosen approach relies on (i) the speciation of rare earth elements - by a method combining sequential extractions and physical separations - in the pedological features resulting from the different processes and in the materials from which they developed; (ii) the quantification of the REE and major element fluxes by mass balance calculation. To do so, two methodologies were developed: a methodology of normalization of REEs based on the theory of transformation fronts to quantify the impact of the processes on REE fractionations; an innovative approach of the reconstruction of the former parent material for each soil horizon as mass balance calculation requires the quantification of initial stocks in elements. Two processes were then further studied: carbonate dissolution and redox processes. We thus point out the necessity to compare max fluxes as computed by mass balance to quantities released by carbonate dissolution in order to forecast the fate of elements released into the soil solution. We also evidenced the potential of REEs to quantify the dissolution/precipitation cycles of iron and manganese oxides.

Muitos organismos vivos, tal como seus constituintes, são formados por sistemas químicos complexos que envolvem a interação entre compostos orgânicos e inorgânicos ligados química e/ou fisicamente. Nestes sistemas as matrizes orgânicas são geralmente compostas por macromoléculas como polissacarídeos e proteínas. Essas moléculas têm o papel de direcionar a nucleação e o crescimento da porção inorgânica. O uso de superfícies metálicas adequadas recobertas por este tipo de filme híbrido tem potencial aplicação em implantes de substituição óssea, no qual são requeridas superfícies quimicamente inertes, mas que ao mesmo tempo estimulem processos de calcificação. Nesta tese estudou-se o crescimento de CaCO3 sobre superfícies metálicas de alumínio e aço inox recobertas por matrizes orgânicas compostas por diferentes poliânions e pelo policátion quitosana, na forma de filmes montados camada-a-camada (do inglês LbL), na presença ou não de fosfolipídeos (filmes Langmuir-Blodgett), formando um meio confinado para o crescimento do mineral. Diferentes técnicas foram utilizadas: microscopia eletrônica, microscopia de força atômica, espectroscopias de reflexão nas regiões do Uv-vis, e do infravermelho, Raman, espalhamento e difração de raios-X. Estudou-se a influência de diferentes grupos carregados dos fosfolipídeos e dos poliânions, tal como sua conformação, no crescimento de CaCO3. O tipo de interação entre o poliânion e a quitosana leva ao crescimento de matrizes poliméricas com diferenças em suas espessuras e capacidade de retenção de líquido, modificando as condições de supersaturação local e influenciando no tipo de estrutura de CaCO3. Puderam ser identificados dois polimorfos formados sobre os filmes orgânicos de poli(ácido acrílico) e quitosana, sugerindo que existem dois diferentes sítios onde a nucleação pode ser iniciada: a partir da solução de CaCl2 aprisionada na matriz polimérica e o outro a partir dos íons cálcio ligados como contra-íons aos grupos negativamente carregados do poliânion. Na presença do pré-recobrimento LB, a natureza da cabeça polar do fosfolipídeo direciona o tipo de ligação e crescimento da matriz polimérica, que levam ao crescimento de partículas de CaCO3 com morfologia e tamanho variados, explicados em termos da presença de ambientes com diferenças de concentrações locais de Ca2+. Além disso, verificou-se que a rugosidade superficial dos suportes metálicos pode favorecer a formação do polimorfo de CaCO3 cineticamente mais estável, mostrando que o processo de cristalização sobre estes suportes é um processo governado por difusão. A hidrofilicidade dos suportes é aumentada pela presença da matriz orgânica e pela presença de CaCO3 sobre as matrizes. O crescimento de CaCO3 em meios confinados tridimensionais, formados por membranas de policarbonato modificadas com filme finos de polieletrólitos, também foi estudado. Este tipo de molde leva à formação de estruturas cilíndricas que seguem a morfologia dos poros da membrana. A presença de poli(ácido acrílico) leva a formação de estruturas cilíndricas ocas, enquanto que cilindros completamente preenchidos foram formados nos poros contendo quitosana na última camada. Estes resultados foram explicados com base em diferenças na etapa de nucleação: na presença de PAA a nucleação de CaCO3 deve iniciar-se a partir dos íons Ca2+ ligados ao poliânion que, por sua vez, está ligado diretamente às paredes do molde; já na presença que quitosana, com maior capacidade de retenção de liquido e sem interação específica com Ca2+ a nucleação e seqüente cristalização devem ocorrer por todo o poro da membrana. As estruturas formadas são em sua maioria monocristais de calcita hexagonal orientadas na direção cristalográfica <2 -2 1>. / Some living organisms as well as their constituents are formed by complex chemical systems which involves the interaction among organic and inorganic compounds bounded physically or chemically. In these systems the organic matrices are usually composed by macromolecules like polysaccharides and proteins. These molecules have an important hole in tailoring the nucleation and the sequent growth of the inorganic portion. Metallic surfaces coated with these hybrid films have potential application as implants for bone substitution for which the surfaces must be chemically inert but at the same time they should stimulate calcification processes. In this present thesis we studied the growth of CaCO3 over aluminium and stainless steal surfaces coated with layer-by-layer films composed by different polyanions and chitosan as polycation, in the presence or not of phospholipids (Langmuir-Blodgett films). These organic matrices formed a confined medium within which CaCO3 particles were growth. Different techniques were applied in order to understand these systems: electronic microscopy, atomic force microscopy, UV-Vis and infrared reflection spectroscopy, Raman, and X-ray scattering and diffraction. We studied the influence of the different charged groups of the phospholipids and the polyanion as well as their conformation on CaCO3 growth. The type of interaction between the polycation and the polyanions tailors the growth of the organic matrices, forming films with different thickness and different water retention abilities which change the local supersaturation conditions changing the structure of the CaCO3 formed. Two types of CaCO3 polymorphs were growth over poly(acrylic acid) (PAA) and chitosan films suggesting that there are two sites where the nucleation can be started: the CaCl2 solution retained in the gel-like organic films and the Ca2+ ions bounded to the negative groups of the polyanion. In the presence of the LB pre-coating, the nature of the phospholipid polar head tailors the binding and the growth of the polymeric matrices leading to the formation of CaCO3 particles with difference in their sizes and morphologies. This result was explained in basis of the differences in the Ca2+ local concentrations in each situation. Moreover, it was observed that the surface roughness of the supports can favour the formation of vaterite, the kinetically most stable CaCO3 polymorph, showing that the crystallization may be guided by diffusion processes. The hidrophilicity of the supports was improved by the presence of both organic and hybrid films. The growth of CaCO3 in tridimentional confined mediums was done using LbL modified polycarbonate membranes as template. This template leads to the formation of cylindrical CaCO3 particles following the morphology of the membrane pores. CaCO3 tube-like structures were formed in presence of PAA, while rod-like structures were formed in presence of chitosan in the top LbL layer. These results were explained on basis of the difference in the nucleation stages: in the presence of PAA the nucleation starts on the Ca2+ ions bounded to the polyanion that is linked to the walls of the template; in the presence of chitosan that presents higher water retention ability and has no specific interaction with Ca2+ ions, the nucleation and sequent crystallization should occur through the entire pore of the membrane. The electron diffraction patterns showed that the CaCO3 structures are single crystals of the calcite polymorph oriented in < 2 -2 1> crystallographic direction.

The current option for the management of Intermediate-Level Waste (ILW) and High-Level Waste (HLW) in the UK is to store it in stainless steel containers and then placed in a deep underground Geological Disposal Facility (GDF). This may subsequently be backfilled with a cementitious material generating very high pH conditions. The eventual corrosion of the stainless steel canisters containing the waste used for disposal will lead to reducing conditions thereby promoting a low Eh environment. Electrochemical experiments are needed to determine which uranium species is/are present at a particular pH and to model the redox behaviour of aqueous uranium in a potential GDF. The main aim of this project is to use cyclic voltammetry to deduce peak potentials for the various uranium redox couples in aqueous solution across the pH range and in particular the hyperalkaline range, as the surroundings of a GDF will be in high pH conditions. Data in the literature have been obtained only under acidic conditions where they were subsequently extrapolated to obtain data for alkaline conditions in some reports. Is this valid however? Experiments are therefore needed to obtain fundamental data under alkaline conditions to fill in gaps in the literature. In addition to radionuclides, complexing organic ligands present in a cementitious repository could have an important effect on the immobilisation of radionuclides in concrete. This is due to the ability of the ligands to form complexes with cations, thereby enhancing their solubility and mobility in the cement pore water. Four different ligands were investigated in this project that are relevant to nuclear waste disposal which comprised of carbonate, ethylenediaminetetraacetic acid (EDTA), gluconic acid and α-isosaccharinic acid (α-ISA). The peak potentials of each uranium redox reaction in aqueous solution were measured and the potentials were compared in ligand and non-ligand systems. The voltammograms were compared to obtain their similarities and differences in terms of the shape of the cyclic voltammograms, peak potentials, reversibility, current responses and etc. Analysis of the similarities and differences was needed to be able to increase the understanding of the complexation effects of these ligands with uranium under different pH conditions in aqueous solution.

Para melhor entender a relação entre os oceanos e as variações climáticas são necessários registros destes eventos. O presente trabalho tem por objetivo principal estudar as variações climáticas e oceanográficas utilizando os registros de conteúdo de carbonato em dois sedimentos coletados na Bacia de Campos. A cronologia dos testemunhos foi primeiramente estabelecida através do conteúdo de carbonato. Sua validação foi feita através das análises de radiocarbono em duas amostras próximas do topo de cada testemunho. Outros métodos usados para corroborar a cronologia foram o biozoneamento com base nos foraminíferos planctônicos Globorotalia menardii e Pulleniatina obliquiloculata, executadas em ambos os testemunhos; análises de isótopos de oxigênio em foraminíferos planctônicos Globigerinoides ruber em amostras do KF-13; e dados de susceptibilidade magnética para o KF-14. Com exceção de radiocarbono, os outros métodos não fornecem idades absolutas Foi então necessário compará-los com estratos de idade conhecida. Para isso utilizaram-se dados do SPECMAP, tornando possível a inferência dos estágios isotópicos marinhos para estes testemunhos. Estabelecida a estratigrafia para os testemunhos com base no conteúdo de carbonato, identificamos as diferentes condições climáticas nas quais os sedimentos foram depositados. As curvas de conteúdo de carbonato para ambos os testemunhos, junto com os dados de isótopos de oxigênio para o KF-13 e a de susceptibilidade magnética para o KF-14 foram comparados com a curva de isótopos de oxigênio do SPECMAP, inferindo assim idades aproximadas para algumas das feições apresentadas. Também foram utilizadas as biozonas de foraminíferos planctônicos identificadas para estimar as idades aproximadas em pontos ao longo do testemunho, além dos dados de radiocarbono. Estabelecida essa cronologia foi possível fazer o cálculo das taxas de sedimentação. Os resultados aqui apresentados mostram a importância que o conteúdo de carbonato nos sedimentos tem para estudos de variações climáticas. / Records of climatic variations are necessary for better understanding of the relationship between the oceans and these events. The main objective of this work is to study climate and ocean variations using carbonate records in two sediment cores collected from the Campos Basin. The chronology of the sediment cores was established through carbonate content. Validation was achieved through radiocarbon analysis in two samples from the top of each core. Other methods used to corroborate chronology were the establishment of biozones based on the planktonic foraminifera Globorotalia menardii and Pulleniatina obliquiloculata, used in both sediment cores; oxygen isotope analysis on the planktonic foraminifera Globigerinoides ruber in samples from KF-13; and magnetic susceptibility data for KF-14. With the exception of radiocarbon, other methods do not provide absolute ages, making it necessary therefore to compare with other stratum of known ages. Data from SPECMAP were used enabling inference of marine isotopic stages for this sediment cores. Once the stratigraphy was established based on the carbonate content, it was possible to identify the climate conditions in which the sediments were deposited. Carbonate content curves for both cores along with the oxygen isotope data for the KF-13 and KF-14 magnetic susceptibility data were compared with the oxygen isotope curve from SPECMAP, inferring approximate ages for some of the features presented. Identified foraminiferal biostratigraphic zones were used to estimate the approximate ages in certain points along the core, along with radiocarbon dating. Once this chronology was established, it was possible to calculate sedimentation rates along the sediment cores. The results here presented demonstrate the importance of carbonate content variations in sediment cores as a means to understanding climate variations.

Fractures can profoundly affect the capacity of carbonate reservoirs to store and permeate fluids, depending on the properties and abundance of fractures. Fractures exist abundantly in carbonate outcrops; however, their abundance in subsurface carbonates is obscure because of the data shortages and uncertainties about the factors that drive fracturing in sedimentary basins. The objective of this research is twofold. The first is to study abundance of fractures in gently deformed carbonates, which were generally overlooked. The second is to address measuring fracture abundance using electrical borehole imaging, which is the mostly used method to describe reservoir fractures. Fractures were studied from areas in the gently folded and shallowly (less than 2 km depth) buried interiors of the Arabian Platform. The study areas include outcrops and reservoirs of the Late Jurassic Arab carbonates in the sprawling homocline of Central Arabia and a low-relief dome in Eastern Arabia. The Cenozoic Rus carbonates in the dome outcrops were also studied. Fracture abundance was measured from the outcrops using scanlines and from the reservoirs using core and borehole images of extended-reach drilling. Many systematic properties were drawn on mineralization, orientation, and abundance of fractures. The fractures were found to be opening mode, mostly barren, and exist with subvertical dips, and some regional trends. The fractures display significantly differing ranges of abundance that were controlled by the subtle structural bending of the dome and homocline, carbonate lithofacies, and paucity of fracture mineralization. The borehole imaging was found to significantly lower fracture abundance. The detection of fractures was subject to several factors including size of fracture widths, nature of fracture roughness, and present-day stress field. The results have implications for modeling of fracture systems and tectonic regimes. For example, finding that fracture abundance varies drastically in such gently deformed regions indicates that carbonates are very sensitive to fracturing processes. Moreover, the borehole imaging limitations influence the models of fracture abundance and orientations, which are often used to deduce paleo tectonic regimes and present-day geodynamics in carbonate reservoirs.

The reduction and stabilization of atmospheric CO2 concentration is currently one of the most challenging problems being investigated. Carbon mineralization has recently received much attention as one of the most promising options for CO2 sequestration. The engineered weathering of silicate minerals as a means of permanent carbon storage has unique advantages such as the abundance of naturally occurring calcium and magnesium-bearing minerals and the formation of environmentally-benign and geologically stable solids via a thermodynamically favored carbonation reaction. However, several challenges need to be overcome to successfully deploy carbon mineralization on a large-scale. The current limitation of the carbon mineralization scheme for permanent storage of anthropogenic CO2 is the slow reaction kinetics, since the natural weathering of silicate minerals occurs on geological time-scales. Another problem of mineral carbonation is that the cost of the carbon mineralization process for sequestration is dominated by up front energy costs during the mineral processing and carbonation. In this study, chemically enhanced mineral dissolution via various chelating agents was investigated to accelerate the overall reaction rate of ex-situ and in-situ mineral carbonation. To reduce the overall cost of the carbon mineralization process, the utilization of solid products as value-added materials, e.g. precipitated magnesium carbonates (PMC) and precipitated calcium carbonates (PCC), was studied. Wollastonite (CaSiO3) and antigorite, which is a kind of serpentine (Mg3(OH)4(Si3O5)) group minerals, were selected for this work. They are representative of calcium silicate minerals and magnesium silicate minerals, respectively. This work starts with development of an experimental framework for the systematic investigation of mineral dissolution and carbonation behaviors with mineral pre-processing considerations (e.g., the removal of fines (< 5 μm) to standardize the reaction surface of the minerals), experimental set-up (e.g., syringe pump reactor for the investigation of mineral dissolution and high temperature, high pressure batch reactor for the study of direct aqueous mineral carbonation) and post reaction analyses (e.g., the evaluation of various carbon analysis techniques for the accurate estimation of the extent of carbon mineralization). Accelerated wollastonite weathering is experimentally studied first. For large scale carbon mineralization, generally Mg-bearing silicate minerals such as serpentine or olivine (Mg2SiO4) are the most suitable minerals due to not only their significant abundance in nature but also their high capacity. New York State, however, has one of the largest deposits of wollastonite in the United States and is considered to be a suitable place to adapt CO2 mineralization using Ca-bearing minerals as a CO2 storage option. Moreover, the technologies developed for enhancing carbonation of Ca-bearing minerals can also be applied to the industrial wastes with similar chemistry, such as steel slag and cement kiln dust. The effect of various types of chelating agents on the dissolution rate of wollastonite minerals is explored to accelerate its weathering rate. It is found that chelating agents such as acetic acid and gluconic acid can significantly improve the dissolution kinetics of wollastonite even at a much diluted concentration of 0.006 M by complexing with calcium in the mineral matrix. Calcium extracted from wollastonite is then reacted with a carbonate solution to form PCC, and the study shows that by controlling the reaction temperature, the morphological structure of the synthesized PCC can be tuned for various applications (i.e., paper fillers, plastic fillers and construction materials). Microbial and chemical enhancement of ex-situ and in-situ antigorite carbonation is investigated as well as synthesis of PMC to mimic commercially available CaCO3-based filler materials. The effect of various chelating agents, including volatile fatty acids produced via anaerobic digestion of food waste, on antigorite dissolution is investigated in a syringe pump reactor. It is found that oxalate performs best among over fifteen kinds of chelating agents on accelerating dissolution rate of antigorite minerals. Among the volatile fatty acids, valerate works best on antigorite dissolution followed by acetate. The concentration of valerate, however, is very low in the produced mixture of volatile fatty acids via anaerobic digestion. On the other hand, acetate is the dominant component in the mixture, so it is considered as the most valuable product of anaerobic digestion of food waste. Magnesium extracted from antigorite is then reacted with carbonates to form precipitated magnesium carbonates. The effects of various chelating agents, reaction time, reaction temperature and pH on the mean particle size, particle size distribution, composition, and particle morphological structures of precipitated magnesium carbonates are systematically studied. Finally, the effect of volatile fatty acids on direct aqueous mineral carbonation is studied in a high temperature, high pressure batch reactor with antigorite and olivine minerals to predict the effect of volatile fatty acids on in-situ mineral carbonation. Volatile fatty acids can enhance the overall reaction rate via direct aqueous mineral carbonation route slightly. Volatile fatty acids may be not good enough for accelerating ex-situ direct aqueous mineral carbonation. However, they may be suited to in-situ mineral carbonation, which takes years.

Além do interesse intrínseco pelos seus aspectos mecanísticos, as reações de hidrólise de compostos carbonílicos apresentam também a interessante particularidade da reação pelo próprio solvente, a água. Dentre estas reações, conhecidas como \"reações de água\" (Robertson, 1967; Johnson, 1967), estudou-se neste trabalho a hidrólise de carbonatos, através do cálculo das energias de transferência da fase gasosa para o solvente, de reagentes (R), estado de transição (ET) e produtos (P). O estudo da solvatação de modelos moleculares para R e ET indica uma correlação entre reatividade e estrutura molecular. Os resultados usando o enfoque de \"super-molécula\" mostram maior concordância com os dados experimentais do que o cálculo de solvatação da molécula simples e indicam que a solvatação dos modelos de ET é mais eficiente que para R e, portanto, há um aumento da reatividade. O estudo mais detalhado das estruturas de R, ET e P, em misturas água/acetonitrila para carbonatos de difenila e bis(2,4-dinitrofenila), sugere a existência de duas ligações de hidrogênio: entre o oxigênio da água do \"cluster\" e um dos hidrogênios dos anéis aromáticos (CF e CDNF), e entre o hidrogênio da água e o oxigênio do grupo nitro do outro anel aromático (CDNF). A consequente diminuição da liberdade conformacional em relação à fase gasosa, provocada por estas ligações de hidrogênio (CF e CDNF), expõe um dos hemisférios da carbonila ao ataque da água, provocando então uma aceleração entrópica do processo. Os efeitos eletrônicos, devidos às ligações de hidrogênio, estão de acordo com a maior acidez esperada dos hidrogênios dos anéis do CDNF em relação ao CF. Também mostram uma compensação no CDNF, pouco contribuindo para alterar a densidade eletrônica no seu carbono carbonílico, enquanto que indica uma soma de efeitos no CF, contribuindo então para um aumento desta densidade eletrônica no CF, de acordo com sua conhecida baixa reatividade. O trabalho permite ainda concluir sobre o relativo sucesso do uso de método semi-empírico PM3 e modelo relativamente simples de solvatação (Cramer & Truhlar, 1991), para o cálculo de energia de transferência em misturas de água/acetonitrila, na faixa de fração molar da água (0,40 a 1,00) onde o método apresenta resultados concordantes com os valores experimentais. / In addition to their intrinsic mechanistic interest, hydrolysis reactions of carbonyl compounds in aqueous media exhibit the interesting peculiarity of direct reaction with the solvent itself, i.e., water. In the present work, we have investigated a representative example of one of these \"water reactions\" (Robertson, 1967; Johnson, 1967), the hydrolysis of carbonates, via quantum chemical ca1culation of the free energies of transfer of the reagents (R), the transition state (TS) and the products (P) from the gas phase to water. A model study of the solvation of R and TS points to a correlation between reactivity and molecular structure. Results using the \"super-molecule\" approach show greater agreement with experiment than solvation ca1culations on the isolated molecule and imply that the solvation of the TS is more effective than that of R in increasing reactivity. A more detailed study of the structures of R, TS and P for diphenyl- (DPC) and bis(2,4-dinitrophenyl)carbonates (DNPC) in acetonitrile/water mixtures suggests the existence of two possible types of hydrogen bonds, i.e., between oxygen of the water c1uster and an aromatic ring hydrogen (DPC and DNPC) or, in the case of DNPC, between the protons of water and the oxygens of the nitro group of the second aromatic ring. The decrease in conformational degrees of freedom reI ative to the gas phase provoked by these hydrogen bonds exposes one of the hemispheres of the carbonyl group to attack by water, resulting in an entropic acceleration of the reaction. The electronic effects on the hydrogen bonds are in line with the greater acidity of the aromatic ring hydrogens of DNPC relative to those of DNP. In DNPC, there is a compensation effect, with very little alteration of the electron density on the carbonyl carbon, while in DPC a sum of effects increases the electron density on the carbonyl carbon, in line with the known lower reactivity of the latter. This work points to the relative success of the semi-empirical PM3 method combined with relatively simple solvation models (Cramer & Truhlar, 1991) for ca1culating free energies of transfer involving acetonitrile/water mixtures in the water mole fraction range from 0.40-1.00.

Le développement d'un colorant naturel sensibilisateur pour les applications de cellules solaires a attiré beaucoup d'attention en raison de ses avantages inhérents, tels que son faible coût, la préparation simple, les ressources facilement disponibles et le respect de l'environnement. Toutefois, les principaux problèmes liés à la cellule solaire sensibilisée par colorant (CSSC) sont une faible photostabilité et une faible efficacité. Dans cette thèse, la bixine extrait de graines de rocou (Bixa orellana L.) a été utilisée comme sensibilisateur. Pour améliorer sa stabilité et la performance des CSSC, l’utilisation de la kaolinite activée a également été étudiée. Une CSSC à haute efficacité nécessite une photo-électrode avec une grande surface spécifique pour adsorber efficacement le colorant. Ainsi le couple TiO2/kaolinite a été préparé dans ce but. Il est considéré que la kaolinite peut confiner la lumière incidente à l'intérieur de l'électrode et peut aussi améliorer la conduction d'électrons. Dans ce système, la kaolinite a également un rôle important pour accroître la photostabilité de la bixine. Un autre facteur affectant les performances des CSSC est le rôle important de l’électrolyte. Dans ces travaux, les carbonates organiques cycliques qui ont une constante diélectrique élevée et aussi un point d’ébullition élevé (plus de 300oC) ont été évalués comme solvants de l’électrolyte. Ces travaux ont été réalisés en quatre étapes: (1) extraction, purification et caractérisation de la bixine, (2) préparation, activation et caractérisation de la kaolinite, (3) étude d’adsorption de la bixine sur la surface de la kaolinite et du TiO2, et (4) fabrication des cellules solaires sensibilisées par la bixine (CSSB). Les résultats montrent que l’extraction accélérée par solvant en utilisant un mélange de 60% de cyclohexane et 40% d’acétone peut être une méthode d’extraction efficace pour la bixine. Après purification par la chromatographie flash, la bixine est isolée avec un dégré de pureté de 99,86%. Elle est composée de 88,11% de cis-bixine et 11,75% de dicis- bixine. L’activation par l’ammoniaque de la kaolinite calcinée (la métakaolinite) est une bonne méthode pour produire la kaolinite avec une très grande surface spécifique et un rapport Si/Al élevé. L’étude d’absorption de la bixine a montré que le carbonate de diméthyle est un solvant approprié pour la bixine. Il permet à la bixine un coefficient d’absorption élevé et de bonnes caractéristiques d’adsorption sur la surface de la photo-électrode. L’adsorption de monocouche de la bixine sur la surface de TiO2 ou la surface de la kaolinite est plus favorable pour obtenir un rendement énergétique plus élevée. La présence de la métakaolinite activée dans la photo-électrode TiO2 a contribué à améliorer les performances et la stabilité de la CSSB par rapport à la CSSB fabriquée avec la photoélectrode de TiO2 pur. Ces performances sont reproductibles. L’électrolyte exerce un effet synergétique avec la métakaolinite activée en faveur de l’amélioration des paramètres électriques de la CSSB. Sous une intensité lumineuse de 200 W/m2, la CSSB comprenant une photo-électrode de TiO2 modifié par 5% de métakaolinite activée et un système électrolyte de KiI/I2 dans l’acétate de carbonate de glycérol produit un rendement énergétique de (0,050+0,006)%, ce qui est plus élevé que celui de la CSSB comprenant une photo-électrode de TiO2 pur (0,027+0,012)%. L’utilisation d’un couple redox de LiI/I2 dans l’acétate de carbonate de glycérol produit le rendement maximum (0,086+0,014)%. La fonction de stockage et de chargement d’énergie des CSSB fonctionnent bien jusqu’au troisième jour de l’analyse. A ce jour, la CSSB fabriquée en utilisant la photoélectrode de TiO2 modifiée par la métakaolinite activée est 16 fois plus stable que celle de la CSSB fabriquée en utilisant la photo-électrode de TiO2 pur.