A magnetita, também chamada de ferrita de ferro, é um minério conhecido como imã natural e encontrada em depósitos de ferro. Além desse comportamento intrínseco, a magnetita possui a capacidade de remover os íons metálicos do meio aquoso por fenômenos de adsorção. O seu caráter fortemente magnético a distingue de outros tipos de adsorventes, visto que, é facilmente removida da solução por separação magnética. Neste trabalho estudou-se a adsorção de urânio(VI), na forma de íons UO22+, de solução nítrica pela magnetita sintética. Esta foi preparada por precipitação simultânea adicionando-se uma solução de NaOH à solução contendo os íons Fe2+ e Fe3+. A magnetita sintética, na forma de um pó preto, exibiu uma resposta magnética de atração intensa na presença de um campo magnético, sem contudo tornar-se magnética, um comportamento típico de material superparamagnético constatado por medidas de magnetização. Estudou-se a influência dos parâmetros de adsorção de íons UO22+ tais como o pH, a dose do adsorvente, tempo de contato e a isoterma de equilíbrio. A máxima adsorção de urânio foi encontrada no intervalo de pH entre 4 e 5. Verificou-se que quanto maior a dose de magnetita menor a capacidade de adsorção e maior a remoção de U. Da relação entre adsorção e tempo de contato verificou-se que a remoção aumentou rapidamente com o tempo e atingiu-se a condição de equilíbrio em 30 min. Os resultados da isoterma de equilíbrio apresentaram maior concordância com o modelo de Langmuir, o qual permitiu a determinação da capacidade teórica de saturação da magnetita para o urânio. A interação entre os íons UO22+ e a magnetita foi caracterizada como uma adsorção química e espontânea. / Magnetite, also known as iron ferrite, is a mineral iron and a natural magnet found in iron deposits. In addition to its magnetic intrinsic behavior, the magnetite has the capacity to remove the metallic ions from aqueous medium by adsorption phenomena. The strong magnetic character of magnetite distinguishes it from other adsorbent types, which it allows to be readily removed from solution by magnetic separation. In this work, uranium (VI) adsorption, as UO22+ ions, from nitric solution by synthetic magnetite was investigated. It was prepared by simultaneous precipitation process, adding a NaOH solution into a solution containing Fe2+ and Fe3+ ions. The synthetic magnetite, a black powder, has exhibited a strong magnetic response in presence of a magnetic field, without nevertheless becomes magnetic. This typical superparamagnetic behavior was confirmed by magnetization measurements. Adsorption parameters of UO22+ ions such as pH. the adsorbent dose, contact time and equilibrium isotherm were evaluated. Maximum uranium adsorption was observed in the pH 4.0-5.0 range. It was noticed that increase in magnetite dose increased the percent removal of uranium, but decreased the adsorption capacity of the magnetite. It was observed from the relation between adsorption and contact time that the removal has increased very fast with time, and achieved the equilibrium within 30 minutes. The results of equilibrium isotherm agreed well with the Langmuir model, and so the theorical saturation capacity of the magnetite was determined for uranyl ions. The interaction between UO22+ ions and the magnetite was defined as a spontaneous chemical adsorption.

Ce travail qui a été effectué au sein du groupe radiochimie de l'IPN Orsay, participe à l'enrichissement des connaissances destinées à la compréhension du comportement des radionucléides à travers l'environnement. Le comportement et l'évolution des radionucléides sont des phénomènes souvent complexes à caractériser expérimentalement qui dépendent des interactions aux interfaces eau / surface minérale, lesquelles peuvent être modélisées grâce à des méthodes théoriques. Lors de cette étude, nous avons choisi d'utiliser des méthodes de dynamique moléculaire (DM), lesquelles permettent de considérer explicitement les effets du solvant, de la température et d'étudier la dynamique de l'ion uranyle. Dans un premier temps, des méthodes de dynamique moléculaire Car-Parrinello basées sur la théorie de la fonctionnelle de la densité (DFT) ont permis de caractériser finement les structures d'équilibres de l'ion uranyle en solution et à l'interface eau/ face (001) de gibbsite. Dans le cas d'un pH faible, les complexes d'adsorption présents à l’interface eau/ face (001) de gibbsite ont été identifiés et comparées aux données expérimentales disponibles. Leurs énergies relatives et les énergies d'activations impliquées dans le processus de sorption ont également été déterminées. Dans un deuxième temps, des méthodes de dynamique moléculaire classique ont été employées afin de modéliser des systèmes de plus grande taille, donc plus réalistes, sur des échelles de temps plus longues. La comparaison des résultats DM Car-Parrinello / DM classique a montré qu’une dynamique classique utilisée avec les potentiels non polarisables de Guilbaud, CLAYFF et SPC/E, permet de modéliser le comportement de l’ion uranyle à l’interface eau/ face (001) de gibbsite. Les longs temps de simulation permettent de mettre en avant le caractère diffusif de l’ion uranyle à l’interface eau/ face (001) de la gibbsite. Enfin, L’effet d’une élévation de la température a été étudié. La rétention de l’ion uranyle diminue avec la température. / This work was performed in the radiochemistry group of the IPN Orsay, it participates in the advancement of knowledge for understanding the behavior of radionuclides through the environment. The behavior and the evolution of the radionuclides, which are often complex phenomena to characterize experimentally, depend on interactions at the interfaces water / mineral surface and can be modeled using theoretical methods. In this study, we chose to use dynamics molecular methods (DM), which can explicitly consider the effects of solvent, temperature and allow to study the dynamics of the uranyl ion. At first, methods of Car-Parrinello dynamics molecular, based on the density functional theory (DFT), were used to characterize the structures of the uranyl ion in solution and at the interface water / (001) face of gibbsite. For low pH condition, the adsorption complexes present at the interface water / (001) face of gibbsite were identified and compared with available experimental data. Their relative energies and activation energies involved in the sorption process were also determined. Secondly, the classical molecular dynamics methods were used to model larger systems, thus more realistic, on longer time scales. Comparing the results DM Car-Parrinello / classical DM showed a classical dynamics, which use the non-polarizable Guilbaud, CLAYFF and SPC/E potentials, can model the behavior of the uranyl ion at the interface water / face (001) of gibbsite. The long simulation times, allow to show particularly the diffusive character of the uranyl ion to the interface water / face (001) of gibbsite. Finally, the effect of temperature rise was studied. Retention of the uranyl ion decreases with temperature.

The photo-oxygenation of 2-methylpropane and cyclohexane using visible light in aqueous acidic uranyl ion solutions at ambient temperature and pressure has been undertaken. For 2-methylpropane in the absence of oxygen, the main product (≈90%) is 2-methyl-2-propanol with a quantum yield of 0.021 ± 0.001. In the presence of molecular oxygen, both 2-methyl-2-propanol and 2-propanone (acetone) are found. Based on this, and results of gamma radiolysis of aqueous 2-methylpropane to give 'tert'-butyl radical by electronically excited uranyl ion is proposed. In the absence of oxygen, the quantum yield of 2-methyl-2-propanol shows a sigmoidal dependence on the concentration of perchloric acid. A two-species kinetic model involving an acid-base dissociation of the uranyl ion in the excited state accounts for the observed features. The addition of sodium perchlorate to the 2-methylpropane system has an inhibitory effect on the quantum yield. Excited-state ion pairing between the uranyl ion and perchlorate anion is proposed. Consequently, the two-species acid-base model is expanded upon to yield a three-species acid-base-perchlorate model that seems to account for the results from 0.01-0.4 M perchloric acid concentration. Potassium peroxydisulfate is proven effective to increase the quantum yield of 2-methyl-2-propanol from 0.021 ± 0.001 to greater than unity (1.5 ± 0.1) indicating the existence and importance of thermal chain reactions involving sulfate radical anion. The quantum yield of 2-methyl-2-propanol is found to be dependent on the concentrations of 2-methylpropane, perchloric acid and potassium peroxydisulfate, and inversely dependent on the light intensity. The net consumption of uranyl ion is zero in the presence of potassium peroxydisulfate meaning that the uranyl ion is regenerated, making this a catalytic cycle in terms of uranyl ion. The oxygenation of cyclohexane using photo-excited aqueous uranyl ion gives cyclohexanol and cyclohexanone as the two main isolated products (54%). The overall mechanism is expected to be similar to that for the 2-methylpropane system. Refluxing of this substrate with a reducing agent (CaH2 or LiAlH4) is required prior to photolysis to achieve consistent quantum yields of both products due to thermal autoxidation reactions. The presence of molecular oxygen is found to be important in determining the ratio of alcohol to ketone in the product distribution. Potassium peroxydisulfate significantly enhances the quantum yield of cyclohexanone, leaving the quantum yield of cyclohexanol relatively unchanged (as compared to without added potassium peroxydisulfate), while uranyl ion is not consumed. Possible reactions involving cyclohexyl and cyclohexyl peroxyl radicals are given to account for the experimental results.

L'étude des mécanismes de sorption de l'ion uranyle sur le substrat SrTiO$_3$ en fonction de la température a fait l'objet de cette étude. Tout d'abord, une caractérisation physico¬chimique a été réalisée à l'aide de plusieurs techniques structurales (DRX, FTIR) et morphologique (MEB). La spectroscopie XPS a permis d'identifier deux sites de surface (Ti¬OH et Sr-OH). En utilisant les titrages potentiométriques de SrTiO$_3$ à différentes températures, les caractéristiques acido-basiques ont été déterminées. Ensuite, la simulation des titrages potentiométriques, entre 25 et 90°C, a été réalisée à l'aide du code FITEQL, les constantes d'équilibre ainsi obtenues montrent une nette variation avec la température: la protonation du site $\equiv Sr – OH$ suit un processus endothermique tandis que la déprotonation du site $\equiv Ti – OH$ implique un processus exothermique. A partir de ces constantes d'équilibre, les grandeurs thermodynamiques, enthalpie et entropie de protonation/déprotonation ont été calculées en utilisant la relation de van't Hoff. Les études de sorption de l'ion uranyle sur le substrat SrTiO$_3$ ont été réalisées dans un intervalle de pH de 0.5 à 5. Les sauts de sorption ainsi obtenus montrent une nette augmentation du pourcentage de sorption avec l'augmentation de la température, traduisant un phénomène globalement endothermique. Deux sites de sorption différents ont été identifiés à la surface du solide par SLRTIF. Ils sont associés aux temps de vie de fluorescence de l'uranyle sorbé de 12 $\pm$ 2 et 60 $\pm$ 5 $\mu$s. Les sauts de sorption ont été modélisés à l'aide du code FITEQL en utilisant le modèle à capacitance constante. Cette simulation des sauts de sorption a été réalisée en tenant compte des résultats de l'étude structurale (deux sites de surface $\equiv Sr - OH$ et $\equiv Ti – OH$ et formation de complexe surfacique de sphère interne bidendate, mononucléaire) et des données obtenues dans la modélisation des titrages potentiométriques. Les équilibres de sorption modélisés ont confirmé la formation de deux complexes de surface de caractère bidendate : [($\equiv SrOH)($\equivTiOH)UO_2]^{2+}$ et [($\equiv TiOH)($\equivTiO)UO_2]^{2+}$. Suite à l'obtention des constantes thermodynamiques obtenues par cette simulation, la relation van't Hoff a été appliquée pour déterminer les variations d'enthalpie et d'entropie associés au processus de sorption. Finalement, une étude sur les transferts d'énergie a été présentée entre deux ions sorbés sur le solide SrTiO$_3$. Ainsi, le transfert d'énergie non-radiatif des ions Tb$^{3+}$ vers les ions EU$^{3+}$ a été étudié. L'application du modèle de Inokuti-Hirayama et Dexter a conduit à l'évaluation du rayon de la sphère d'interaction (2,7-3,4 Å) entre les deux ions (Tb$^{3+}$ et EU$^{3+}$)

This thesis aims to investigate different infrared absorbing molecules and how their properties are affected by their incorporation into polymer nanoparticles. Metal-free phthalocyanine-H2Pc, uranyl super phthalocyanine-USPc, and europium bisphthalocyanine were studied-EuPc2; the latter two capable of IR absorption. Due to the discovery of USPc’s moisture sensitivity, only H2Pc and EuPc2 were derivatized to facilitate encapsulation in polystyrene nanoparticles through a miniemulsion polymerization. These novel phthalocyanines attained loadings of up to 41wt% and exhibit substantial broadening of absorption peaks. Furthermore, the EuPc2 loaded particles also reveal an unprecedented gain in extinction coefficient of the NIR and radical absorption peaks. The leaching behavior of the dye was also studied, as this had not been undertaken in the literature, and revealed the need for a method of polymerizing/chemically binding phthalocyanines into nanoparticles; with preliminary steps taken to realize this goal.

This thesis aims to investigate different infrared absorbing molecules and how their properties are affected by their incorporation into polymer nanoparticles. Metal-free phthalocyanine-H2Pc, uranyl super phthalocyanine-USPc, and europium bisphthalocyanine were studied-EuPc2; the latter two capable of IR absorption. Due to the discovery of USPc’s moisture sensitivity, only H2Pc and EuPc2 were derivatized to facilitate encapsulation in polystyrene nanoparticles through a miniemulsion polymerization. These novel phthalocyanines attained loadings of up to 41wt% and exhibit substantial broadening of absorption peaks. Furthermore, the EuPc2 loaded particles also reveal an unprecedented gain in extinction coefficient of the NIR and radical absorption peaks. The leaching behavior of the dye was also studied, as this had not been undertaken in the literature, and revealed the need for a method of polymerizing/chemically binding phthalocyanines into nanoparticles; with preliminary steps taken to realize this goal.

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