L’étude cinétique a permis de déterminer le temps d’équilibre atteint lors de la fixation du benzopurpurine 4B sur chaque composé, ainsi que l’ordre de la réaction et la nature du mécanisme de diffusion. Cette adsorption est favorisée par un milieu légèrement basique, et l’augmentation de la température a un effet positif sur l’amélioration des performances maximales de la fixation. L’étude des isothermes d’adsorption de ce colorant, a été établie pour déterminer l’efficacité de cette nouvelle classe d’adsorbants. Ces dernières sont de type L, et les donnés de sorption ont été traitées selon plusieurs modèles, afin de mieux comprendre le mécanisme d'adsorption du colorant sur les différents matériaux. L’analyse des résultats de l’étude thermodynamiques a montré que l’adsorption du colorant sur les différents composés est un phénomène spontané, endothermique et favorable, régie par une adsorption physique pour les matériaux CoFe-CO3/Ec, CoFe-CO3/A et MgAl-CO32- et par une adsorption physico-chimique pour les matériaux CoFe-Ac/p, CoNiFe-Ac/p , et MgAl-500. Ces résultats ont été confirmés par les analyses DRX et IR des différents matériaux avant et après adsorption. En comparant les résultats obtenus pour l’adsorption du colorant sur les différents matériaux, le composé CoNiFe-Ac/p constitue le meilleur adsorbant avec une capacité d’adsorption d’environ 593mg/g. Par conséquent, et compte tenu de l’ensemble des résultats fournis par cette étude, l’hydrolyse forcée en milieu polyol, s’avère une méthode très efficace pour l’élaboration des hydroxydes doubles lamellaire à base de métaux de transition avec une morphologie contrôlée, de taille nanométrique présentant un faible taux d’agglomération, et par conséquent une bonne dispersion de particules et un meilleur pouvoir adsorbant. Ces caractéristiques peuvent être à l’origine de l’application de ces matériaux avec succès dans l’élimination des colorants contenant dans les effluents industriels. / New layered double hydroxides (LDHs) CoFe-Ac, CoNiFe-Ac, ZnNiFe-Ac and ZnCoFe-Acwith MII/MIII molar ratio of 3, and acetate ions in the interlayer region have been preparedusing forced hydrolysis of acetate metallic salts in a polyol medium. The structure,morphology and properties of as-prepared product were investigated by X-ray Diffraction(XRD), FT-IR Spectroscopy, elemental analysis, transmission Electron Microscopy (TEM),Scanning Electron Microscopy (SEM), thermal analysis (DTA, TGA) and V-visibleSpectroscopy: showed that these nanocomposites present the typical features of hydrotalcitelikestructure, exhibit a turbostratic character and the intercalation of acetate anions into theinterlayer domain has been successfully done, giving an interlayer spacing value of 12.70,12.47, 13.64 and 14.69 Å for CoFe-Ac, CoNiFe-Ac, ZnNiFe-Ac and ZnCoFe-Acrespectively.We can note that there is some difference between the interlayer spacing for all synthesizedphases. That can be explained by the arrangement of inserted species (anions + water) indifferent orientation in the interlayer domain.57Fe Mössbauer spectrometry allows concluding the presence of Fe3+ cations which occupyoctahedral sites and confirming the absence of Fe2+ in the as-prepared compounds.In order to check the capacity of our materials synthesized in polyol medium to exchange theacetate anions inserted in their interlamellar space, anionic exchange in aqueous medium waseffected for CoFe-Ac compound as à model of synthesized LDH. All the physicochemicalmethods of analysis (DRX, IR, ATD/ATG and elemental analysis) carried out on the materialCoFe- Ac /EC (exchanged). The comparison with a lamellar phase containing oFeCO3/Asynthesized in aqueous medium, show a layered double hydroxide compound with aturbostratic disorder, and a new interlamellar distance d003 = 7.67Å which correspondsperfectly with the presence of the carbonate anions and the water molecules in the interfeuilletfield.In the second part of this study, we are interested to examine the capacities of these kinds ofmaterials for the adsorption of an anion dye benzopurpurine-4B-. The adsorption of direct red2 by CoFe-Ac, CoNiFe-Ac LDHs has been examined in order to measure the capability ofthis new organic/inorganic nanomaterial to eliminate this highly toxic azoic class of anionicdyes from wastewater. The sorption capacities of LDHs for Benzopurpurine4B are also compared with those of other adsorbents : CoFe- Ac /Ec, CoFeCO3/A (synthesized in aqueous medium), Mg-Al-CO3/A and its calcined product at 500°C “Mg-Al-500”. The quantity of dye eliminated was found to depend on contact time, pH, initial concentration of dye and heating temperature. The thermodynamic parameters ΔG°, ΔH° and ΔS° werecalculated to predict the nature of adsorption. Results suggested that the Benzopurpurine 4B adsorption on different compounds was a spontaneous and endothermic process. Adsorption kinetic data were tested using pseudo-first order, pseudo-second order, Elovitch’sequation and intra-particle diffusion models. Kinetic studies for all cases showed that the adsorption followed a pseudo-second order reaction. Studies revealed that intra-particle diffusion played an important role in the mechanism of dye adsorption by MgAl-500. Theequilibrium data were analyzed using Langmuir, Freundlich, Tempkin, Elovitch, Dubinin-Radushkevich, Redlich-Peterson and Toth isotherm models. [...] Taking these results into account, we can conclude that prepared LDHs by forced hydrolysis in a polyol medium can be used successfully in the removal of anionic dyes from aqueous solutions.

The effect of incorporation two clays; layered double hydroxides (LDH) and montmorillonite layered silicates (MLS) in linear low density polyethylene (PE) matrix was investigated. MLS and LDH were added of 5, 15, 30 and 60 weight percent in the PE and compounded using a Brabender. Ground pellets were subsequently compression molded. Dispersion of the clays was analyzed using optical microscopy, SEM and XRD. Both the layered clays were immiscible with the PE matrix and agglomerates formed with increased clay concentration. The thermal properties were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Both clays served as nucleation enhancers increasing recrystallization temperatures in the composites. Flame retarding properties were determined by using the flammability HVUL-94 system. LDH indicated better flame retarding properties than MLS for PE. The char structure was analyzed by environmental scanning electron microscopy. Mechanical properties were studied by tensile testing and Vickers microhardness testing apparatus.

Content: The wastewater of leather industry contains pollution loads which includes anionic contaminants such as chloride, sulfate and phosphate. Different treatment technologies for tannery wastewater have been investigated. Adsorption is a promising technique due to its greater selectivity, simple operation, faster regeneration kinetics and high uptake capacity even at trace levels. In the present study, Mg-Al and Zn-Al Layered Double Hydroxides were synthesized by the co-precipitation method at variable pH through a semi-batch system. The prepared material was characterized by XRD, BET surface area determination, TGDTA and FTIR. The chloride, sulfate and phosphate adsorption properties onto Mg-Al and Zn-Al Layered Double Hydroxides from aqueous solutions were evaluated. The adsorption experiments of chloride, sulfate and phosphate were investigated through batch studies at initial concentrations of 100 mg/L of these anions as NaCl, K2SO4 and KH2PO4, respectively. The experiments were carried out separately for each anionic specie by mixing 10 ml of solution with 1 g/L of adsorbent for 5 h. Mixing was performed on a thermostatic shaker at 200 rpm and at room temperature (25 °C). The effect of co-existing anions on the adsorption capacity were also analyzed. After ion adsorption, chloride, sulfate and phosphate concentrations were measured by ion chromatography. The results showed a removal ratio for Mg-Al Layered Double Hydroxide of 24% and 51% for sulfate and phosphate, respectively, while chloride was not removed from the solution. For the adsorbent Zn-Al Layered Double Hydroxide, the removal ratio of sulfate, phosphate and chloride reached 12.76 %, 69.07 % and 6.34%, respectively. Take-Away: Both adsorbents exhibited a satisfactory removal ratio of phosphate. Therefore, Mg–Al and Zn–Al LDHs can be used as effective adsorbents for phosphate removal from industrial wastewaters.

Layered double hydroxides (LDHs) are clay-like minerals commonly referred to as anionic clays" with a wide range of physical and chemical properties. LDHs often find application in pharmaceuticals, as polymer additives, as additives in cosmetics, as nanomaterial's and in catalysis. This is due to having variable layer charge density, reactive interlayer space, ion exchange capabilities, a wide range of chemical compositions and rheological properties (Forano et al., 2006). Various techniques exist for the synthesis of layered double hydroxides. These include co-precipitation, the urea method, induced hydrolysis, sol-gel and hydrothermal methods. Many of these produce environmentally unfriendly effluents or by-products, are energy intensive, make use of metallic salts or require inert synthesis environments (Rives, 2001). Limitations associated with these existing processes make LDH synthesis at an industrial level expensive or difficult to achieve. The need for 'green', affordable and repeatable synthesis methods are therefore often sought after. Recently the use of mechanochemistry as an alternative synthesis technique has gained wide-spread attention. Mechanochemistry involves the breaking and forming of chemical bonds due to an induced mechanical force. Various mechanochemical techniques for the synthesis of LDH materials exist or have been explored. These include methods such as single-step, two-step and mechano-hydrothermal grinding techniques. Grinding methods can be conducted dry, wet or collectively (Qu, Zhang, et al., 2015a). Mechanochemistry has further been used in conjunction with micro-wave energy and ultrasonic irradiation. The use of mechanochemistry as a synthesis method has proven to be promising with successful and unique LDHs produced. Intercalation of unique or complex anions within the interlayer has further been proven possible. The versatility and robust nature of this synthesis method makes it ideal for industrial application. Although many studies exist it was noted that limited research has been conducted on single-step wet grinding for LDH synthesis and warrants further investigation (Qu, Zhang, et al., 2015a) (Iwasaki,Yoshii, et al., 2012). This was due to factors such as incomplete conversion, difficulties associated with grinding and morphological imperfections. Single step wet milling could be benifi cial as a synthesis procedure as it eliminates hazards associated with dry powder, contains less process steps and is therefore possibly more cost effective and can be conducted batch, semi-batch or continuously due to fluid flow. Throughout the literature research conducted it was further noted that not many different milling devices have been explored. Ball mills, mixer mills and manual grinding were the most common methods used to supply mechanical energy to a system. The study therefore aims to expand on single-step wet synthesis of LDH materials by making use of a different milling device, namely a Netzsch LME 1 horizontal bead mill. The selected mill is designed for wet grinding application and can easily be up-scaled to a commercial batch, semi-batch or continuous process. Raw materials selected were a combination of oxides, hydroxides and basic carbonates. This would eliminate hazardous salt by-products and effluent, promoting 'green' synthesis of LDH materials. It was noted that the synthesis of LDH with the use of these materials have previously proven to be challenging (Qu, Zhang, et al., 2015a). The study was divided up into two sections namely a 'parameter study' and a 'versatility study'. The 'parameter study' involved exploring the in influence of milling and experimental parameters, such as rotational speed, retention time, solids loading, bead size and jacket water temperature, on the synthesis of Mg-Al LDH. The raw materials selected were MgO and Al(OH)3 combined at a divalent to trivalent cationic ratio of 2:1. The parameters were individually investigated, with the exception of jacket water temperature as it was varied with a change in retention time and a change in rotational speed. Unless stated otherwise or under investigation, parameters were investigated at a set speed of 2000 rpm, jacket water temperature of 30 °C, solids loading of 10 %, retention time of 1 h and with 2 mm yttrium stabilised zirconia beads. Therefore when investigating a specific c parameter, the others remained as stated above. Comparatively the 'versatility' study further explores the synthesis of Mg-Al, Ca-Al, Cu-Al and Zn-Al LDH by adapting optimal synthesis conditions, derived from existing mechanochemical techniques and methods, to the selected process. These were related to the divalent to trivalent cationic ratio and selected starting materials. Ageing of the samples obtained through the 'versatility study' were further explored to determine if the potential for a two-step commercial process exists. The study was investigated at a set speed of 2000 rpm, jacket water temperature of 30 °C, solids loading of 10 %, retention time of 1 h and with 2 mm yttrium stabilised zirconia beads. Half of the sample collected was subjected to ageing at 80 °C for 24 h under atmospheric conditions. / Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2020. / This research was funded by Techsparks (Pty) Ltd and the Technology and Human Resources for Industry Programme (THRIP) administered by the Department of Trade and Industry, South Africa, (grant number THRIP/133/31/03/2016) / Chemical Engineering / MEng (Chemical Engineering) / Unrestricted

Ein fundiertes Verständnis der Mechanismen der Gummi-Vulkanisation von Dien-Kautschuken ist noch immer eine der größten Herausforderungen in der Chemie und Technologie der Elastomere. Die Schwefelvulkanisation von Elastomerwerkstoffen ist ein seit langem verwendeter, aber dennoch sehr anspruchsvoller Prozess, mit dessen Hilfe moderne Reifen hergestellt werden. Bei dieser chemischen Reaktion spielt Zinkoxid, zusammen mit den anderen Hilfsstoffen der Schwefelvulkanisation eine entscheidende Rolle. Um die Produkteigenschaften von mit Schwefel vulkanisierten Elastomermaterialien zu verbessern, sollten die Mechanismen der chemischen Vernetzung - und insbesondere auch die Rolle von Zink enthaltenden Verbindungen bei der Vulkanisationsreaktion besser verstanden werden. Zum Beispiel könnte das Eigenschaftsprofil von Reifen durch die Ausbildung von geeigneten Netzwerken aus Schwefel oder anderen Netzknoten optimiert werden. Nitrilkautschke aus der Klasse der Spezialelastomere und die meisten nicht-Tire- Kautschuk in der ganzen Welt eingesetzt, wecken ein großes Interesse der Forschung wegen ihrer einzigartigen Vulkanisationschemie bei der Vernetzung mittels Zinkverbindungen und wegen der besonderen Eigenschaften der dadurch erzeugten Elastomerwerkstoffe. In dieser Arbeit wurde besonderes Augenmerk darauf gelegt, die Rolle von verschiedenen Zinkverbindungen in der Schwefelvulkanisation von carboxylierten Nitrilkautschuken zu verstehen. In der vorliegenden umfangreichen und eingehenden Untersuchung konnte die Ausbildung einer weiteren Polymerphase im Elastomer nachgewiesen werden. Durch dieses Ergebnis kann nun das dynamische mechanische Verhalten von solchen Polymerwerkstoffen besser verstanden werden. Teile dieser Arbeit beschäftigen sich mit der Erforschung der Rolle von Zinkchlorid bei der Vernetzung von Nitrilkautschuken. Hierzu wurde festgestellt, dass Zinkchlorid einen besonderen Einfluss auf die chemische Vernetzung des NBR aufweist, auch in Abwesenheit anderer Vernetzungs- oder Vulkanisationsadditive. Die so vernetzten Elastomere weisen ein stark hydrophiles Verhalten auf, im Gegensatz zu den allgemeinen Eigenschaften solcher Elastomerwerkstoffe. Eine detaillierte Analyse dieser neuartigen Netzwerkstruktur, gebildet durch eine Koordinationsbindung zwischen dem Zinkatom des Zinkchlorids und dem Nitrilkautschuk, wurde durchgeführt. Carboxylierter Nitrilkautschuk (XNBR) wurde ebenfalls eingesetzt, um funktionale Kautschukmischungen mit neuartigen flammhemmenden Eigenschaften zu entwickeln. Zu dieser Thematik wurden Zink enthaltende Doppelhydroxide (Layered Doube Hydroxides, LDH) als multifunktionale Füllstoffe in XNBR-Kautschuk eingesetzt. Neben dem Flammschutzverhalten zeigt LDH einzigartige Eigenschaften als verstärkenden Füllstoff und gleichzeitig als aktivierendes Additiv für die Schwefelvulkanisation. Eine weitere Zink enthaltenden Verbindung, Zinkstearat, wurde eingesetzt um mechanoadaptive elastomere Materialien durch gezieltes Einstellen des kristallinen bzw. amorphen Charakters dieser Verbindung zu entwickeln. Dies könnte einen wichtigen Beitrag zur Entwicklung zukünftiger Reifenmaterialien mit intrinsisch adaptiven Eigenschaften liefern.

A green synthesis method for the synthesis of hydrotalcite has been previously developed but this process has not yet been optimised. The main focus of this dissertation was on aluminium-based LDHs. The purpose of this investigation were; to determine optimum synthesis conditions for the formation of hydrotalcite using the dissolution-precipitation method and to determine the possibility of partial substituting the divalent metal species in hydrotalcite and hydrocalumite with other metal species. During the optimisation process for the formation of hydrotalcite using the dissolution precipitation method, the formation of hydromagnesite was proved to be dominant reaction at lower reaction temperatures. With the increase in reaction time and temperature the decomposition of hydromagnesite occurred to form magnesite. At low temperatures the formation of Mg-Al-CO3 LDH is limited due to the low solubility of gibbsite. Mg-Al-CO3 LDH formation of 80 % was achieved at 140 oC after 2 hours reaction time, but crystallinity was low. To achieve an Mg-Al-CO3 LDH conversion higher than 96 % a reaction temperature of 160 oC for a minimum of 4 hours is required, but is achieved within 1 hour at 180 oC. A 99.37 % conversion was achieved at 180 oC for 5 hours with a high crystallinity and homogeneity. The surface area for Mg-Al-CO3 LDH at 180 oC after 5 hours reaction time proved to be 9.19 m2/g. The average particle size obtained for a high crystalline LDH was in the range of approx. 3 μm and 6.8 μm at temperatures of 160 oC and above for a minimum of 3 hours reaction time. The following are recommended for future work:  Determine the effect of mixing speed on the shape of the platelets.  Determine the difference between freshly precipitated metal oxides/hydroxides as reagents compared to aged metal oxides/hydroxides. The presence of Mg(OH)2 and Ca(OH)2 in solution (respectively) did increase the pH enough for the dissolution of gibbsite and most of the Mx+ metal species. A reaction time and temperature of 5 hours at 180 oC in a carbonate environment proved to be close to the ideal conditions for the formation of Mg/Mo-Al-CO3 LDH and Mg/Zn-Al-CO3 LDH. The results for the formation of Mg/Ti-Al-CO3 LDH were inconclusive. Isolation of the possible Mg/Ti-Al-CO3 LDH is recommended to determine the degree of substitution. The conditions for the dissolution of the metal species for the following experiments were proven to be successful:  Ca/Mn(lV)-Al  Ca/Mo-Al  Ca/Ni-Al  Ca/Ti-Al The following recommendations are made for the improvement on the formation of an Mx+-impregnated LDH/precursor:  Determine the effect of different reaction time and temperature.  Determine the effect of adding the carbonate source at temperatures above 100 oC under pressure.  Determine the effect of synthesising at different pH conditions. Cobalt and tin showed no/negligible amount of possible solubility. / Dissertation (MSc)--University of Pretoria, 2014. / Chemical Engineering / MSc / Unrestricted

O presente trabalho trata da preparação e caracterização de três tipos de materiais, todos envolvendo hidróxidos duplos lamelares (HDLs) contendo íons cobalto e alumínio na composição das lamelas. Primeiramente, avaliou-se a influência de parâmetros de síntese na obtenção de HDLs intercalados com os ânions inorgânicos carbonato, cloreto e nitrato. Segundo dados de espectroscopia eletrônica UV-VIS, ressonância paramagnética eletrônica (EPR) e espectroscopia de fotoelétrons excitados por raios X (XPS), ocorre a oxidação parcial do Co2+ em Co3+ na lamela de HDL e, no caso do material contendo íon carbonato, observa-se a presença de radical carbonato, demonstrando a reatividade redox das matrizes com íons cobalto. A segunda parte do trabalho consistiu na intercalação do ânion derivado do ácido 2- aminotereftálico (ATA) em HDL. A presença do cátion cobalto nas lamelas e do grupo amino na espécie orgânica promoveu alterações significativas nas propriedades eletrônicas e térmicas do material (abreviado Co2Al-ATA). Assim como na primeira parte desta tese, as transformações ocorridas com o íon ATA devem incluir a formação inicial de um radical orgânico (de modo similar à polimerização da anilina), para o qual o agente oxidante é o íon Co3+ lamelar. Os dados de espectroscopia vibracional (no infravermelho e Raman) e de XPS mostram a presença de segmentos reduzidos (benzenóide) e oxidados (quinóides) na espécie intercalada. A solubilização do HDL em meio ácido permitiu isolar um material orgânico de cor preta que possui segmentos semiquinóides (radical orgânico) em sua estrutura, além dos reduzidos. A última etapa da presente tese consistiu em pirolisar o material Co2Al-ATA mencionado acima. Verificou-se que a alteração no procedimento de pirólise, como a temperatura, o desenho do forno, a forma do cadinho (cilíndrico ou barca), o tempo de resfriamento do sistema ou a atmosfera dinâmica ou estática, por exemplo, afetam as propriedades do produto final de decomposição. Nos compósitos obtidos, as fases inorgânicas provenientes da decomposição do HDL foram uma mistura de óxidos mistos de cobalto e alumínio (Co(CoxAl1-x)2O4), óxido de cobalto (CoO) e cobalto metálico. A fase de carbono apresentou perfil espectral de carbono grafítico nanocristalino e foi obtida em valores de temperatura de pirólise superiores a 800°C. Os compósitos contendo nanopartículas de cobalto metálico são ferromagnéticos. A reatividade redox dos HDLs de cobalto e as propriedades de seus produtos de decomposição apresentam potencial para aplicação em dispositivos eletroquímicos. / The present work reports the preparation and characterization of three types of materials, all involving layered double hydroxides (LDHs) containing cobalt and aluminum ions in the layer composition. First, the influence of synthetic parameters on the production of LDHs intercalated with the inorganic anions carbonate, chloride and nitrate was evaluated. According to UV-VIS electronic spectroscopy, electron paramagnetic resonance (EPR) and x-ray photoelectron spectroscopic (XPS) data, the partial oxidation of Co2+ to Co3+ occurs in the LDH layer and, in the case of the material containing carbonate ion, the presence of carbonate radical species demonstrates the redox reactivity of the matrices with cobalt ions. The second part of the work comprised the intercalation of the anion derived from 2- aminoterephthalic acid (ATA) in to LDH. The presence of the cobalt cation in the layer and the amino group in the organic species promoted significant changes in the electronic and thermal properties of the material (abbreviated Co2Al-ATA). As in the first part of this thesis, transformations occurring with the ATA ion should include the initial formation of an organic radical (similar to aniline polymerization), for which the oxidizing agent is the Co3+ ion in the layer. The vibrational (infrared and Raman) spectroscopy and XPS data show the presence of reduced (benzenoid) and oxidized (quinoids) segments in the intercalated species. The solubilization of HDL in acid medium allowed the isolation of a black organic material that has semiquinoid (organic radical) segments in its structure besides the reduced one. The last stage of the present thesis consisted of pyrolysis of the Co2Al-ATA material mentioned above. It was observed that the change in pyrolysis procedure, such as temperature, furnace design, crucible shape (bark or cylinder), system cooling time or dynamic or static atmosphere, for example, affects the properties of the final product of decomposition. In the obtained composites, the inorganic phases from the HDL decomposition were a mixture of mixed oxides of cobalt and aluminum (Co(CoxAl1-x)2O4), cobalt oxide (CoO) and metallic cobalt. The carbon phase showed nanocrystalline graphite carbon spectral profile and was obtained at pyrolysis temperature values above 800 °C. The composites containing metallic cobalt nanoparticles are ferromagnetic. The redox reactivity of HDLs containing cobalt and the properties of their decomposition products present potential for application in electrochemical devices

Esta tese se insere no contexto da química prebiótica, que estuda a evolução química que ocorreu antes do surgimento da vida na Terra. Tal área pertence ao ramo de pesquisa da Astrobiologia, que estuda o surgimento, a evolução, distribuição e futuro da vida na Terra ou em outro lugar do Universo. Dentre as várias hipóteses abordadas na química prebiótica, a hipótese mineral é foco de estudo deste trabalho, ou seja, se os minerais podem ter agido como preconcentradores ou protetores de moléculas biologicamente relevantes para a química prebiótica e como catalisadores de reações. A classe mineral de hidróxidos duplo lamelares (HDL) é estudada inicialmente considerando se sua síntese seria possível em um ambiente prebiótico. Desta forma, o HDL foi sintetizado por dois métodos de síntese (coprecipitação e reconstrução) e em quatro composições distintas de água do mar sintética, que mimetizam diferentes fases geológicas da Terra, os resultados mostraram a formação deste mineral em todas as composições de água do mar analisadas. Posteriormente, o estudo da interação de biomoléculas com HDL foi feito visando caracterizar se estas poderiam estar inseridas no espaço interlamelar deste mineral. O íon tiocianato, precursor de biomoléculas, e as bases nitrogenadas adenina, timina, e uracila mostraram-se presentes nas amostras de HDL sintetizadas pelos dois métodos, coprecipitação e reconstrução. As amostras foram caracterizadas por difratometria de raios X, análise termogravimétrica, análise elementar e por espectroscopia vibracional, Raman e no infravermelho. Embora os resultados iniciais indiquem que as biomoléculas possam estar interagindo com o mineral por adsorção e não necessariamente estejam intercaladas, estudos com lavagem das amostras com carbonato de sódio mostraram a troca iônica das biomoléculas pelo ânion inorgânico e sugerem que estas encontravam-se realmente no espaço interlamelar do mineral. Foram feitas então simulações de ambientes extremos nos sistemas HDL + biomoléculas para avaliar se a presença do mineral aumenta a estabilidade das biomoléculas frente a aquecimento, radiação UVC e radiação ionizante já que tais condições extremas estariam presentes na Terra primitiva / This thesis subject is related to prebiotic chemistry, which studies the chemical evolution that happened before the origin of life on Earth. This subject belongs to the Astrobiology research area, which studies the origin, evolution, distribution and future of life on Earth and elsewhere in the Universe. Among the many hypothesis that prebiotic chemistry encompass, the mineral hypothesis is the aim of this thesis, that is, if minerals could have had a role in preconcentrating and protecting molecules relevant to prebiotic chemistry, and also if they could have acted as catalists. The layered double hydroxide (LDH) minerals are studied and the first question is if they could have been synthetized in a prebiotic environment. Four different seawater compositions are analyzed, considering many geological periods of Earth, and two synthesis methods were studied: coprecipitation and reconstruction. The results showed that the LDHs are formed in all seawater types studied. Following these studies, we discuss whether biomolecules could be in the interlayer space of this mineral. Thiocyanate, a biomolecule precursor, and the nucleic acids adenine, thymine and uracil were present in the LDH samples synthetized either by coprecipitation and reconstruction, and they were characterized by X-Ray diffraction, thermogravimetric analysis, elemental analysis and by vibrational spectroscopy: IR and Raman. Although the preliminary results showed that the biomolecules are not necessarily intercalated, but may simply be adsorbed on the minerals, after washing with a sodium carbonate solution, the biomolecules were replaced by the inorganic anion, suggesting that the former was in fact intercalated in the mineral. Extreme conditions simulations were then performed on the LDH plus biomolecules systems to evaluate whether the mineral may act as a protector and stabilize the biomolecules when these were heated or irradiated with UV-C and ionizing radiation, since such scenarios would be common on early Earth

Os hidróxidos duplos lamelares (HDLs) são matrizes inorgânicas bidimensionalmente estruturadas que apresentam propriedades diversas e interessantes para a formação de materiais híbridos. Em especial na área medicinal e farmacológica, o emprego de HDLs com lamelas contendo os íons Mg/Al e Zn/Al tem mostrado resultados promissores como antiácidos e como carregadores de fármacos. Por outro lado, anti-inflamatórios não esteroidais como o sulindaco são moléculas orgânicas ionizáveis que podem ser intercalados em HDLs levando à formação de materiais híbridos com potencial para uso na área farmacêutica. Este trabalho consistiu na síntese e na caracterização de materiais híbridos baseados em matrizes de HDLs de ZnRAl e MgRAl (R é a razão molar MII/Al) e o ânion derivado do fármaco sulindaco (abreviados M2IIAl-Sul). Foram avaliadas as condições experimentais mais apropriadas para a obtenção de materiais com alta cristalinidade e alto conteúdo do fármaco. Os materiais híbridos preparados por um método simples de coprecipitação (one pot) à temperatura ambiente e a 55°C apresentaram capacidade de carregamento de 50 a 55% (em massa) de sulindaco. Os difratogramas de raios X dos híbridos M2IIAl-Sul indicaram a formação de materiais mais cristalinos a 55°C, com várias reflexões basais indicando alto grau de organização das lamelas e distância interplanar de cerca de 2,74 nm. O arranjo bidimensional interdigitado dos ânions sulindaco entre as lamelas foi proposto através do mapa de densidade eletrônica unidimensional (1D Plot). A análise morfológica por microscopias eletrônicas de varredura e transmissão revelou a formação de estruturas nanométricas planas, flexíveis e desordenadas no caso do Mg2Al-Sul; as partículas de Zn2Al-Sul também apresentam nanoscrolls, com cerca de 100 nm de diâmetro, uma morfologia que não havia sido reportada até então para HDLs. Os espectros vibracionais no infravermelho dos materiais híbridos mostraram bandas típicas do sulindaco atribuídas ao vS=O em 1011 e 1039 cm-1, ao vC-F em 1163 cm-1 e bandas referentes aos estiramentos antissimétrico e simétrico do grupo COO- em aproximadamente 1564 e 1394 cm-1, que confirmam a presença do sulindaco na forma aniônica no sistema híbrido. Deslocamentos de picos observados nos espectros de ressonância magnética nuclear de carbono-13 no estado sólido sugerem que o confinamento entre as lamelas promove alterações na densidade de carga da espécie orgânica. As técnicas espectroscópicas confirmam a manutenção da integridade química do fármaco após o processo de intercalação. As atribuições dos espectros vibracionais e de ressonância magnética nuclear foram efetuadas com o auxílio do método da Teoria do Funcional de Densidade (DFT) para a espécie orgânica. A avaliação do comportamento térmico por termogravimetria acoplada à calorimetria exploratória diferencial e à espectrometria de massas (TG-DTA-MS) evidencia sensível aumento na estabilidade térmica do fármaco intercalado em matriz de Zn2Al. Esse fato foi interpretado através da análise dos espectros vibracionais de amostras aquecidas a 250°C. Propõe-se que a desidroxilação das lamelas do HDL de zinco promove a coordenação do grupo carboxilato do ânion sulindaco ao metal divalente, aumentando sua estabilidade térmica. Os ensaios de dissolução in vitro evidenciam um mecanismo difusional de liberação modificada (prolongada) do fármaco a partir do material híbrido, que ocorre em cerca do dobro do tempo observado para o sulindaco não intercalado. Resultados preliminares de estudo in vivo de pastilhas dos materiais híbridos implantadas em região intramuscular de ratos atestam a biocompatibilidade e a antigenicidade dos materiais HDL-Cl e dos híbridos HDL-Sul. / Layered double hydroxides (LDHs) are two-dimensionally structured inorganic matrices that show diverse and interesting properties for hybrid materials development. Particularly in the medical and pharmaceutical area, the use of LDHs with layers containing Zn/Al and Mg/Al ions has shown promising results. On the other hand, nonsteroidal drugs such as sulindac are ionizable organic molecules that can be intercalated into LDH leading to the formation of hybrid materials with potential usage in the pharmaceutical area. This work involved the synthesis and characterization of hybrid materials based on matrices of LDHs ZnRAl and MgRAl (R is the MII/Al molar ratio) and the anion derived from the sulindac drug (abbreviated M2IIAl-Sul). The most suitable experimental conditions for obtaining materials with high crystallinity and also high drug contents were evaluated. Hybrid materials prepared by a simple coprecipitation method (one pot) at room temperature and 55 °C showed loading capacity of about 50 - 55% (by mass) of sulindac. X-ray diffraction revealed the formation of higher crystalline materials at 55 °C; various basal reflections indicate a high degree of layers stacking and an interlayer distance of about 2.74 nm to M2IIAl-Sul hybrids. A two-dimensional array of interdigitated sulindac anions between the layers was proposed by one-dimensional electron density map (1D Plot). The morphological analysis by electronic scanning and transmission microscopies revealed the formation of flat, flexible and disordered nanoscale structures in the case of Mg2Al-Sul; nanoscrolled particles of about 100 nm in diameter are also present in Zn2Al-Sul sample, a morphology which had not been reported so far for LDHs. The vibrational spectra of hybrid materials in the infrared showed the characteristic sulindac bands assigned to vS=O at 1011 and 1039 cm-1, the vCF at 1163 cm-1 and bands related to the antisymmetric and symmetric stretching of the -COO- group at approximately 1564 and 1394 cm-1 which confirmed the presence of the anion sulindac in the hybrid system. Shift peaks observed in carbon-13 nuclear magnetic resonance spectra in solid state suggest that the confinement between the layers promotes variations in the organic species charge density. Spectroscopic techniques confirm the maintenance of the chemical integrity of the drug after the intercalation process. The spectral assignments of the organic species were supported by Density Functional Theory (DFT). The evaluation of the thermal behavior by thermogravimetry coupled with differential scanning calorimetry and mass spectrometry (TG-DSC-MS) shows substantial increase in the thermal stability of the drug intercalated into Zn2Al matrix. This effect was interpreted by analysis of vibrational spectra of samples calcined at 250 °C. It is proposed that dehydroxylation of the Zn2Al layers promotes the coordination of the sulindac carboxylate group to the divalent metal. In vitro dissolution tests of hybrid material show a diffusional mechanism of modified drug release (sustained), which occurs in about twice the time observed for sulindac not intercalated. Preliminary results from in vivo study of hybrid materials\' pellets implanted in the intramuscular region of rats attest to biocompatibility and antigenicity of LDH-Cl and LDH-Sul hybrid materials

Compostos lamelares do tipo da hidrotalcita ou hidróxidos duplos lamelares (HDL), são materiais que possuem notáveis propriedades estruturais, químicas, eletrônicas, iônicas, ópticas e magnéticas. Em função dessas propriedades, os HDL apresentam uma diversidade de aplicações tais como adsorventes e catalisadores. Este trabalho tem por objetivo utilizar polímeros e macromoléculas na preparação e caracterização de HDL, visando melhorar as propriedades texturais dos HDL de MgAl-CO3 preparados em meio contendo polímeros orgânicos ou a intercalação direta de dendrímeros tipo PAMAM de gerações -0,5 e +0,5 em HDL do sistema Zn/Al. Os HDL de MgAl-CO3 foram preparados pela adaptação do método de coprecipitação a pH decrescente, com a presença de polímeros solubilizados no meio, como molde. Os materiais foram caracterizados por difração de Raios X, análise termogravimétrica, espectroscopia no infravermelho e medidas de área superficial por BET. Baseando-se nos resultados obtidos, pode-se concluir que propriedades texturais dos HDL preparados são modificadas, quando na presença de alguns polímeros. Na maioria dos casos, os valores calculados de área superficial específica foram mais elevados, em comparação com aquele obtido para o HDL preparado em meio reacional sem polímero. Isto pode ser explicado pela diminuição do tamanho de partículas e aumento no diâmetro médio de poros dos materiais preparados, provocada pela presença de polímeros no meio reacional. Os HDL intercalados com dendrímeros PAMAM G-0,5 e PAMAM G+0,5 foram preparados por duas rotas diferentes: coprecipitação a pH constante e troca iônica em fase dupla. Os materiais obtidos foram caracterizados por meio de difração de Raios X, análise de termogravimétrica associada à espectrometria de massas e espectroscopia no infravermelho. Utilizando os dois procedimentos de preparação, a intercalação de PAMAM G-0,5 deu origem a HDL com os mesmos espaçamentos basais, concordando com a intercalação dos ânions do dendrímero em um arranjo perpendicular à lamela do HDL, enquanto que para a intercalação do PAMAM G+0,5, espaçamentos basais muito menores do que o tamanho da molécula foram obtidos. A diferença entre a distância interlamelar observada e a esperada pode ser explicada por um arranjo peculiar das moléculas desse dendrímero em uma forma elipsoidal, devido às interações intramoleculares. Espectros no infravermelho confirmam a presença dos dendrímeros nos materiais Zn2Al-PAMAM G-0,5 e Zn2Al-PAMAM G+0,5. Finalmente, a presença destes dendrímeros foi confirmada por análise térmica associada com espectrometria de massas. Os estudos de Raios X com variação de temperatura in situ e as análises termogravimétricas revelaram que o material obtido pela intercalação do PAMAM G+0,5 é termicamente menos estável do que aquele intercalado com PAMAM G-0,5, concordando com a diferença de estabilidade entre os dendrímeros livres. / Hydrotalcite-like lamellar compounds or layered double hydroxides (LDH) are materials that present notable structural, chemical, electronic, ionic, optical and magnetic properties. Depending on these properties, the LDH present a great variety of applications such as adsorbents and catalysts. The aim of this work is to prepare and to characterize MgAl-CO3-LDH prepared in aqueous media containing organic polymer to improve textural properties, and to prepare HDL by intercalation of dendrimer (PAMAM) of generations -0.5 and +0.5 in ZnAl-HDL. MgAl-CO3-HDL samples were prepared by an adaptation of the coprecipitation method at decreasing pH, with the presence of polymers in the aqueous media as template. The materials were characterized by powder X-ray diffraction, termogravimetric analysis, infrared spectroscopy and BET isotherms. Based on the obtained results, it can be concluded that the textural properties of the prepared LDH were modified. The calculated values of specific surface area were higher in most of the cases compared with those obtained by the LDH prepared without polymer due to a decrease of the particle size and an increase in the average pore diameter of the prepared materials due to the presence of polymers. HDL with intercalated (PAMAM) dendrimers G-0.5 and G+0.5 were prepared by two different methods: coprecipitation at constant pH, and ionic exchange in double phase. The obtained materials were characterized by powder X-ray diffraction, thermal gravimetric analysis associated with mass spectrometry, and infrared spectroscopy. X-ray powder diffraction patterns exhibit the characteristic profiles of the lamellar materials with basal spacing depending on the nature of the dendrimer. For both preparation methods, the intercalation of PAMAM G-0.5 gives rise to LDH with basal spacing in agreement with the dendrimer molecules perpendicular to the layer of the host structure, while for PAMAM G+0.5 a basal spacing smaller than the molecule size was obtained. The difference between the obtained and the expected value is explained by an accommodation of the dendrimer molecule in an ellipsoidal shape, due to the intra-molecular interactions. Infrared spectra confirm the presence of dendrimers in the Zn2Al-PAMAM G-0.5 and Zn2Al-PAMAM G+0.5 materials. Finally, thermal analyses associated with mass spectrometry confirm the presence of these dendrimers. Powder X-ray diffraction with in situ temperature variation reveals that the material obtained by the PAMAM G+0.5 intercalation is thermally less stable than that prepared by PAMAM G-0.5 intercalation, in agreement with the difference in the thermal stability of the free dendrimers.