Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Swarm intelligence research was inspired by biological systems in nature. Working ants and bees has captivated researchers for centuries, with the ant playing a major role in shaping the future of robotic swarm applications. The ants foraging activity can be adapted for different applications of robotic swarm intelligence. Numerous researchers have conducted theoretical analysis and experiments on the ants foraging activities and communication styles. Combining this information with modern reconfigurable computing opens the door to more complex behaviour with improved system dynamics. Reconfigurable computing has numerous applications in swarm intelligence such as true hardware parallel processing, dynamic power save algorithms and dynamic peripheral changes to the CPU core. In this research a brief study is made of swarm intelligence and its applications. The ants' foraging activities were studied in greater detail with the emphasis on a layered control system designed implementation in a robotic agent. The robotic agent’s hardware was designed using a partial self reconfigurable FPGA as the main building element. The hardware was designed with the emphasis on system flexibility for swarm application drawing attention to power reduction and battery life. All of this was packaged into a differential drive chassis designed specifically for this project. / AFRIKAANSE OPSOMMING: Die motivering vir swerm robotika kom van die natuur. Vir eeue fassineer swerm insekte soos bye en miere navorsers. Dit is verstommend hoe ’n groep klein en nietige insekte sulke groot take kan verrig. Die mier speel ‘n belangrike rol en is die sentrale tema van menige publikasies. Die mier se kos-soek aktiwiteit kan aangepas word vir swerm robotika toepassings. Hierdie aktiwiteit vervat verskeie sleutel konsepte wat belangrik is vir robotika toepassings. Deur bv. die mier se aktiwiteite te kombineer met dinamies herkonfigureerbare hardeware, kan meer komplekse gedrag bestudeer word. Die stelsel dinamika verbeter ook, aangesien dit nou moontlik is om sekere take in parallel uit te voer. Deur ’n interne prosesseerder in die herkonfigureerbare hardeware in te sluit, is dit nou vir die stelsel moontlik om homself te verander tydens taak verrigting. Komplekse krag bestuur gedrag is ook moontlik deurdat die prosesseerder die spoed en rand apparaat kan verander soos benodig. ‘n Verdere voordeel is dat die stelsel aanpasbaar is en dus vir verskeie navorsingsprojekte gebruik kan word. In hierdie navorsing word ’n literatuur studie van swerm robotika gemaak en word daar ook na toepassings gekyk. Met die klem op praktiese implementering, word die mier se kos-soek aktiwiteit in detail ondersoek deur gebruik te maak van ’n laag beheerstelsel. In hierdie laag beheerstelsel verteenwoordig elke laag ’n hoër vlak gedrag. Stelsel aanpasbaarheid en lae kragverbruik speel ’n deurslaggewende rol in die ontwerp, en om hierdie rede vorm ’n FPGA die hart van die sisteem.

L’industrie microélectronique en perpétuelle évolution impose de nouvelles spécifications pour les futures générations de microbatteries au lithium. Pour ces dispositifs, il est désormais impératif d’améliorer la capacité volumique des matériaux actifs d’électrode positive ainsi que d’abaisser leur tension de fonction-nement aux alentours de 1,5 V. Ce travail propose d’étudier le comportement de sulfures de métaux de transition de formule MSx (M = Fe, Co, Ni, Ti ; x = 1, 2), réagissant vis-à-vis du lithium selon un mécanisme de conversion, à un potentiel adapté à l’application. Déposés sous forme de couches minces par pulvérisa-tion cathodique radiofréquence à cathode à effet magnétron, ces sulfures ont été caractérisés en termes de composition, morphologie et structure. Dans la plupart des cas, des films cristallisés avec une incorpo-ration minime d’oxygène ont été obtenus sans chauffage intentionnel des substrats. L’utilisation d’une configuration en couches minces et d’un électrolyte solide, propres aux microbatteries, permet une bonne réversibilité des réactions ainsi qu’une prévention des réactions parasites généralement observées pour ces sulfures en électrolyte liquide. Une caractérisation fine des propriétés électrochimiques de ces matériaux en microbatterie tout-solide au lithium a donc pu être réalisée, permettant de corréler la réver-sibilité des cycles d’insertion / extraction du lithium avec la nature du cation de métal de transition mais aussi avec la concentration en soufre dans l’électrode. / The overgoing evolution of the microelectronics industry implies new specifications when it comes to next generations of lithium microbatteries. It is now of utmost importance for these devices to increase the volumetric capacity of the positive electrode material and bring the working potential down to approxi-mately 1.5 V. Hence, this work is aimed at studying the behavior of transition metal sulfides, of formula MSx (M = Fe, Co, Ni ; x = 1, 2), which react towards lithium through conversion reaction mechanism at an adapted potential. Thin films of these materials, prepared via non-reactive radiofrequency magnetron sputtering were structurally, morphologically and compositionally characterized prior to their integration in microbatteries. In most cases, crystallized films were obtained without any intentional heating of the substrates. Also, very low oxygen incorporation within the deposited materials was observed. Thanks to the combined use of thin film and all-solid-state configuration in the microbatteries, good reversibility of the reactions is allowed and parasitic reactions generally observed for transition metal sulfides electrodes in conventionally used liquid electrolytes cells can be avoided. Thus, deep electrochemical characteriza-tions were successfully conducted on the microbatteries. For these materials, it was shown that the re-versibility of the lithium insertion / extraction cycles during operation is directly linked to the nature of the transition metal cation and to the overall sulfur concentration in the electrode material.

Energy conversion devices using solid-state magnetocaloric materials have the potential to reduce energy consumption and mitigate environmental pollutants. To overcome the limited magnetic entropy change of magnetocaloric materials, magnetic refrigeration devices typically use the active magnetic regenerator (AMR) cycle. AMR devices have demonstrated promising performance, however costs must be reduced for broad market penetration. Although the magnet cost is of greatest importance for commercialization, literature has decoupled magnet design from AMR optimization. And while multilayered regenerators can improve performance without increasing cost, a number of questions remain unanswered as a result of the prohibitive parameter space. This dissertation explores methods of improving AMR performance and decreasing cost both at the subsystem level, namely the magnetocaloric regenerator, fluid flow system and magnetic field source, and the device level by coupling the regenerator and magnet design problems in a cost optimization framework. To improve AMR performance, multilayered regenerators with second-order magnetocaloric materials are experimentally and numerically investigated, yielding insight on how individual layers behave and interact over a wide range of regenerator compositions and operating parameters. An efficient AMR modeling approach is presented where individual layers are treated as cascaded AMR elements, and simulations are in excellent agreement with experiments. Insights from the computationally efficient model are used to inform device modifications, and a no-load temperature span of 40 K is measured in close proximity to the simulated optimum; one of the highest in literature. To simultaneously decrease AMR costs, a permanent magnet optimization framework is explored that is conducive to nonlinear objectives and constraints. This is used to investigate the optimal design of permanent magnet structures with reduced rare-earth permanent magnet materials. The regenerator and magnet design problems are then coupled in a permanent magnet topology optimization to minimize the combined capital and operating costs of an AMR. The optimal magnetic field waveform and the optimal means of producing this waveform are simultaneously obtained. The lifetime ownership costs of the optimized AMR device are shown to be in the realm of existing entry-level cooling devices. The presented cost optimization framework is of interest to both scientists and engineers, and demonstrates the importance of fast AMR models in identifying system designs, regenerator compositions and operating regimes that increase AMR performance and decrease cost. / Graduate

[pt] O foco do presente estudo é desenvolvimento de uma heteroestrutura de dois semicondutores com capacidade de reduzir a taxa de recombinação elétron/buraco mediante uma intensa separação de carga, e ao mesmo tempo sendo sensível ao espectro de luz visível. A separação de carga estaria sendo alcançada por meio da injeção de elétrons livres dentro da banda de condução (BC) do TiO2 na forma de anatásio, provenientes do orbital molecular mais alto ocupado (HOMO) da acetilacetona (Acac), ligada às partículas de anatásio, seguida da sua injeção dentro dos orbitais d desocupados do Fe3+ localizados dentro da banda de energia proibida das nanofolhas de ferrititanatos. Ao mesmo tempo a absorção da luz visível poderia ser assegurada através das nanofolhas de ferrititanatos, considerando-se a interação dos níveis energéticos do Fe3+ com a luz e as bandas de valência e condução, bem como pela formação de complexo de transferência de carga (CTC), entre as nanopartículas de anatásio e Acac. Os nanohíbridos mesoporosos (as heteroestruturas) são produzidos pelas diferentes rotas de junção de nanofolhas de ferrititanato, obtidas da areia mineral ilmenítica e posteriormente esfoliadas, com nanopartículas de TiO2 modificadas com acetilacetona, estes útlimos formando CTC. As técnicas de caraterização empregadas tais como adsorção-dessorção de N2, espectroscopia de emissão de fotoluminescência (PL) e espectroscopia de refletância difusa (DRS), entre outras, confirmaram a formação das heteroestruturas mesoporosas sensíveis à luz visível e com forte mecanismo de separação de cargas. A fotodegradação do gás poluente NO no espectro de luz-visível por meio de vários nanohíbridos mesoporosos (fotocatalisadores) mostrou-se bem sucedida, exibindo uma eficiência até 7 vezes superior em comparação à atividade do material fotocatalítico padrão TiO2 (P-25 da Degussa). / [en] This work focues on the development of a heterostructure composed by two semiconductors, capable to decrease the electron/hole recombination rate through a robust charge separation, and at the same time, this nanohybrid is sensitive to visible light spectrum. The charge separation is achieved by the injection of free electrons within the conduction band (BC) of TiO2 in anatase form, which come from the highest-occupied-molecular-orbital (HOMO) of acetylacetone (Acac), linked to the anatase nanoparticles, followed by the injection into unoccupied Fe3+ d-orbital within band-gap energy of the ferrititanate nanosheets. Additionally, the absorption of visible light could be assured by ferrititanate nanosheets, considering the interaction of the energy levels of Fe3+ with visible light and the valence and conduction bands, as well as, the formation of the charge transfer complex (CTC), between the anatase nanoparticles and Acac. The mesoporous nanohybrids (called also as heterostructures) were produced by different routes of junction of two components: i) ferrititanate nanosheets, which were synthesized from ilmenite mineral sands, and then they were exfoliated into single layers and ii) TiO2 nanoparticles, modified with Acac, which formed the CTC. The characterization techniques, such as N2 adsorption-desorption, photoluminescence emission spectroscopy (PL) and diffuse reflectance spectroscopy (DRS), and so on, confirmed the formation of the mesoporous heterostructures sensitive to visible light and with a robust mechanism of charge separation. The photodegradation of NO pollutant gas within the visible light spectrum through several mesoporous nanohybrids (photocatalysts) demonstrated being well succeeded, exhibiting an efficiency more than seven times higher than the activity benchmark TiO2 (Degussa P-25) photocatalyst.

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No. of bitstreams: 1 santos_cf_me_sjrp.pdf: 2242337 bytes, checksum: fa2ed2aede3ab1105b17fe2fc10b76c3 (MD5) Previous issue date: 2018-05-23 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / RESUMO Pesquisa destinada a melhorar e gerar rotas de produção de biocombustíveis como fonte alternativa a combustíveis derivados do petróleo está se tornando mais frequente. Nesta área, desenvolver novas técnicas que facilitem, ou ajudem a otimizar processos como a transesterificação de óleos vegetais ganham espaço no meio científico. Óxidos provenientes de materiais semelhantes a hidrotalcitas pertencentes à família de argilas aniônicas foram estudados recentemente como um substituinte para catalisadores básicos na síntese de biodiesel. Para testar estes catalisadores, a síntese de materiais de hidrotalcita como (HDLs) com fórmula molecular MgxXAly (CO3)(OH)16.4H2O em diferentes proporções x / y foi realizada com substituição total de Na2CO3 por amido de milho e amido de milho acidificado pelo ozono. A síntese dos HDLs foi realizada pelo método de coprecipitação e os materiais secados pela técnica de pulverização e para gerar os óxidos estes precursores foram calcinados a 450 e 600 °C . A caracterização do HDLs foi realizada por difração de raios-X (XRD), espectroscopia vibracional (ATR-FTIR) e decomposição térmica (TGA) e dos óxidos por XRD, BET, adsorção de CO2 (basicidade) e n-butilamina (acidez) e microscopia eletrônica de varredura (MEV). As reações de transesterificação foram processadas por 12 horas a 120 ° C na proporção molar de óleo de soja /etanol (1/20) com 20% (m / m) de catalisador em relação à massa, e os produtos foram quantificados por GC-FID. Com a introdução de amido de milho ou amido de milho acidificado no sólido, características físico-químicas típicas de HDLs foram alteradas com base nos dados obtidos das caracterizações. Foi observado o aumento nas áreas superficiais dos óxidos (800m2 g-1) e nas propriedades de acidez e basicidade. Nos testes iniciais o precursor sem a presença de amido (3:1 Mg:Al) alcançou 36,1% de conversão. Embora o melhor resultado de conversão tenha sido alcançado a partir do sólido sem amido de milho, existe uma correlação interessante entre as atividades catalíticas e as propriedades físico-químicas dos sólidos com os materiais modificados e seus respectivos homólogos. Estudos suplementares buscando melhorar o rendimento destes óxidos foram realizados resultando com resultados próximos a 50% de rendimento de biodiesel. / Research to improve biofuel production routes as an alternative source of petroleumderived fuels has been matter of recent efforts. In this area, developing new techniques that facilitate or help optimize processes such as transesterification of vegetable oils have been gaining attention. Oxides from hydrotalcite-like materials belonging to the anionic clays family were recently studied as substitute for basic catalysts in the synthesis of biodiesel. In order to test these catalysts, the synthesis of hydrotalcite materials (HDLs) with molecular formula MgxXAly(CO3)(OH)16.4H2O in different x/y ratios was carried out with total substitution of Na2CO3 by corn starch and corn starch acidified by ozone. The synthesis of the HDLs was performed by the coprecipitation method and the materials dried by the spray technique and the oxides generated by calcination at 450 and 600 °C. The characterization of HDLs was performed by XRD, vibration spectroscopy (ATR-FTIR) and thermal decomposition (TGA) and the oxides by XRD, BET, CO2 adsorption (basicity) and nbutylamine (acidity), and scanning electron microscopy (SEM). The transesterification reactions were carried out for 12 hours at 120 °C in 1/20 molar ratio of soybean / ethanol with 20% (w/w) of catalyst and the products were quantified by GC-FID. With the introduction of corn starch or acidified maize starch into the solid, typical physico-chemical characteristics of HDLs were successfully modified based on the characterization data. It was observed the increase in the surface areas of the oxides (800 m2 g -1 ) and in the acidity and basicity properties. In catalytic assays the precursor without the presence of starch (3:1 Mg:Al) reached 36.1% conversion. Although the best conversion result has been achieved from the solid without cornstarch, there is an interesting correlation between the catalytic activities and the physico-chemical properties of the solids with the modified materials and their respective counterparts. Further studies to improve the yield of these oxides were performed resulting in results close to 50% biodiesel yield. / 380762/2016-1.

Ce travail de thèse s'intéresse à la relation entre la composition des phases Hydroxydes Doubles Lamellaires (HDL) et leurs propriétés structurales. La première partie de ce manuscrit est consacrée à la formation et aux propriétés structurales de ces matériaux. L'effet de la nature des cations (MgII, NiII, CoII ; AlIII, FeIII) et de leur stoechiométrie dans le feuillet (MII/MIII E [2 ; 10]) constitue les axes principaux de ces travaux. L'étude du comportement hydrolytique d'un mélange de cations divalents et trivalents en fonction de leurs proportions en solution a permis de proposer un mécanisme topotactique de formation de ces phases HDL. Il a aussi été montré que la variabilité stoechiométrique du feuillet ne dépend que de la nature des cations. Ainsi, des modèles électrostatiques ont été proposés afin de rationaliser et prédire la gamme de composition de ces phases HDL en fonction de la nature des cations. La seconde partie est dédiée aux propriétés du milieu interfoliaire. Une étude couplant des analyses par spectroscopies vibrationnelles infrarouge et Raman et par diffraction des Rayons X a permis d'apporter une description précise de l'influence de la nature des cations, et de leurs stoechiométries sur l'organisation des anions dans le milieu interfoliaire (Cl-, CO32-, NO3-, ClO4-, acides aminés). Le rôle de l'eau dans ces phases a également été étudié. Dans le cas des hybrides organo-minéraux, il a été montré que la charge dicte l'orientation des acides aminés intercalées et par conséquent, leur réactivité envers la formation de la liaison peptidique. Également, les propriétés énantioselectives du domaine interfeuillet sont mises en avant pour la formation de peptides / This manuscript is devoted to the comprehension of the relationship between the composition of Layered Double Hydroxides (LDH) and their structural properties. The first part of this manuscript is focalized on the formation and the structural properties of these materials. The influence of the cationic nature (MgII, NiII, CoII ; AlIII, FeIII) and their stoichiometries within the layer (MII/MIII E [2 ; 10]) constitutes the main axis of these investigations. The study of the hydrolytic behavior of a solution containing a mixture of divalent and trivalent cations as a function of their relative proportion allowed to propose a topotactic mechanism of formation of LDH phases. Moreover, it has been showed that the composition range is solely dependent on the nature of the cations. Thus, electrostatic models were designed to rationalize and predict the composition range as a function of the cationic nature. The second part is concerned with the properties of the interlayer domain. A joint study, coupling vibrational spectroscopies (Infrared and Raman) and X-ray diffraction allowed a detailed description of the influence of the cations and their stoichiometries on the organization of the interlayer anions (Cl-, CO32-, NO3-, ClO4-, aminoacids). The role of the interlayer water has also been investigated. Concerning hybrid organo-minerals, it has been showed that the layer charge dictates the orientation of the interlayered aminoacids, and consequently, their reactivity toward the formation of the peptide bonds. The enantioselective properties of the interlayer domain are highlighted toward the formation of peptides

Ce travail de thèse s’articule autour de la synthèse et de la caractérisation d’hydroxydes doubles lamellaires (HDLs) par une approche combinant spectroscopie vibrationnelle, RMN du solide et diffraction des rayons X. Les objectifs portent sur la description de la distribution cationique dans les feuillets ainsi que sur l’étude des propriétés structurales et dynamiques des espèces interfoliaires. Les investigations sont principalement menées pour des HDLs de type MgII/AlIII (ratio compris entre 2 et 4) avec une complexification progressive des espèces intercalées : de l’anion carbonate pour lequel les matériaux possèdent une affinité préférentielle, à d’autres anions inorganiques comme les halogénures, le perchlorate et le nitrate, pour finir sur des hybrides organo-minéraux formés par intercalation d’anions organiques/biomolécules (acides aminés et cyclodextrines). Les recherches effectuées ont permis de mettre en évidence un ordre cationique local au sein des feuillets, conservé après échange anionique. Par ailleurs, il a été possible de rationaliser les comportements propres à chaque espèce anionique dans l’espace interfoliaire, qui dépendent fortement de la densité de charge des feuillets, ainsi que du taux d’hydratation des composés. En particulier, la coexistence des anions carbonate et hydrogénocarbonate dans l’espace interfoliaire et leur dynamique d’échange avec le dioxyde de carbone atmosphérique sont révélées. D’autre part, une nouvelle sonde de dynamique interfoliaire par RMN 27Al est proposée. Enfin, l’étude pas à pas des HDLs intercalant tout d’abord l’oxalate puis des acides aminés a permis le transfert des connaissances obtenues pour les HDLs inorganiques aux hybrides organo-minéraux. Le manuscrit se termine sur une application des hybrides contenant des cyclodextrines pour le traitement d’eaux polluées par des composés organiques polycycliques / This thesis work is based on the synthesis and the characterization of layered double hydroxides (LDHs) by an approach combining vibrational spectroscopy, solid-state NMR and X-ray diffraction. The objectives include a description of the cations distribution in the layers, as well as a study of the structural and dynamic properties of the interlayer species. Investigations are mainly carried out for MgII/AlIII LDHs (ratio between 2 and 4) with an increased complexity of the intercalated species: from carbonate for which the materials have a preferential affinity, to other inorganic anions such as halides, perchlorate and nitrate, to finish with organo-mineral hybrids obtained by intercalation of organic anions/biomolecules (amino acids and cyclodextrins).The research carried out highlighted a local cationic order in the layers, preserved after anionic exchange. Furthermore, it has been possible to rationalize the behaviour of each anion in the interlayer space, which strongly depends on the layers charge density, as well as on the hydration state of the compounds. In particular, the coexistence between carbonate and hydrogenocarbonate anions in the interlayer space and their dynamic exchange with atmospheric carbon dioxide are revealed. On the other hand, a new interlayer dynamics probe by 27Al NMR is proposed. Finally, the step-by-step study of LDHs, first intercalating oxalate and then amino acids, allowed the transfer of the knowledge obtained for inorganic LDHs to organo-mineral hybrids. The manuscript ends with an application of cyclodextrins-containing hybrids for the treatment of water polluted with polycyclic organic compounds

The economic development of the world in the last centuries has brought manypositive things, but also some new problems. The linear approach long used isbased on a long-term, unsustainable approach to economic activity and newmodels are required. The purpose of this report is to investigate newsustainability requirements that drive innovation with regard to business modelsand product development.A case study was carried out at the company Ecostrate, which is launching anew product with clear sustainability ambitions. A Triple Layered BusinessModel Canvas (TLBMC) is made for their product and from this case the roleof Circular Economics (CE) and sustainability in the formation of new businessmodels is evaluated. The case study was based on interviews made withcompany employees and other people in a focus group and on secondary dataprovided primarily from Ecostrate, but also other organizations and companies.From the case study, it can be seen how the business model of the product was,from start, designed in accordance with circular economic principles and with afocus on sustainability, where the starting point was a used material that wasthen altered to once again provide the consumer with a value offer. Accordingto profitability estimates, the product will competitive while significantenvironmental and social savings are possible. General conclusions can bedrawn that CE and sustainability are an important part of future business modeldesign, without which companies will not be competitive in the future andfuture markets with increasing raw material prices, stricter regulations and moreaware and sustainability-prioritizing customers.The primary limitation has been the calculations, which were not carried out asexhaustively as would have been needed in order to give the case study a morestable empirical foundation. In this study, they have been used as approximativevalues to draw generalizable conclusions so to understand the product, itsimpact and in order to get more precise implications for the rest of the market,there exists possible future research.

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No. of bitstreams: 2 santos_rmm_me_araiq_int.pdf: 4136391 bytes, checksum: 50ec17cef563517b2a5199c9c72d9a0f (MD5) santos_rmm_me_araiq_par.pdf: 1040758 bytes, checksum: a18d1d9fa74ec9c42cb002b3084f4a61 (MD5) Previous issue date: 2016-01-15 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A contaminação de recursos hídricos por diversos poluentes orgânicos, como os corantes têxteis, tem causado sérios problemas ambientais. Alguns processos de descontaminação utilizam materiais sólidos para adsorção/sorção, com características apropriadas para a implantação em escala industrial, apresentando alta eficiência e baixo custo. Os Processos Avançados de Oxidação (AOP), como a fotocatálise heterogênea, também têm sido empregados na descontaminação de águas, convertendo os poluentes orgânicos em substâncias mais facilmente degradáveis, inertes ou inofensivas. Materiais multifuncionais como os Hidróxidos Duplos Lamelares (HDL) e seus derivados se mostram promissores tanto em processos adsortivos como fotocatalíticos. No presente trabalho foi dado enfoque ao processo de adsorção de um azocorante têxtil, utilizando HDL do sistema ZnAl-CO3 e o óxido misto obtido no tratamento térmico a 450°C. Os materiais apresentaram características interessantes e alta capacidade de remoção do corante. As isotermas de adsorção apresentaram boa correlação com o modelo de Langmuir e o cálculo de seus parâmetros revelou que a capacidade máxima adsortiva do material calcinado foi cerca de 6 vezes superior ao material não calcinado, 1587,1 mg⋅g-1 e 261,8 mg⋅g-1, respectivamente. A maior capacidade de adsorção/sorção foi atribuída ao melhoramento das propriedades texturais e ao comportamento da “regeneração” da estrutura HDL pelo precursor calcinado. Os resultados revelaram que o controle cinético do processo é uma etapa de adsorção química, e os parâmetros termodinâmicos calculados mostraram que o processo de adsorção é espontâneo e endotérmico. Os experimentos de conversão fotocatalítica de corante mostraram que os derivados da calcinação dos HDL são materiais promissores para serem utilizados nos AOP. A formação do nanocompósito ZnAl2O4/ZnO no material calcinado a 850°C, mostrou os melhores resultados de conversão, pela estratégia de acoplamento de bandas para separação de cargas, que diminui os problemas relacionados com a recombinação dos portadores de carga, além da maior absorbância no UV. Dessa forma, os resultados obtidos mostram a multifuncionalidade desses materiais, e fornecem novas evidências sobre a reconstrução de HDL pelo “efeito memória”, tópico de intensa discussão na literatura. / The contamination of water resources by several organic pollutants, including textile dyes, which have caused serious environmental problems. Solid materials for adsorption with appropriate features to be employed in industrial scale, such as high efficiency and low cost have been used in some decontamination processes. The Advanced Oxidation Processes (AOP) including heterogeneous photocatalysis, have also been used in water treatment, converting the organic pollutants into easily degradable, inert or harmless substances. Multifunctional materials, such as the Layered Double Hydroxides (LDH) and their derivatives, show potential in both adsorptive and photocatalytic processes. In this work the textile azo dye adsorption process using a ZnAl-CO3 LDH and the mixed oxide obtained from thermal treatment at 450 °C were focused. The materials presented interesting features and high removal capacity for the dye. The adsorption isotherms showed good correlation with the Langmuir isotherm model and the calculated parameters revealed that the maximum adsorption capacity of the calcined material was about 6 times higher than the non-calcined material, 1587.1 mg⋅g-1 and 261.8 mg⋅g-1, respectively. The higher adsorption capacity was assigned to the improvement of the textural properties and to the LDH-structure recovery from the calcined precursor. The results showed kinetic control of the process is a chemical adsorption step, and the calculated thermodynamic parameters showed the adsorption process is spontaneous and endothermic. The dye photocatalytic conversion experiments presented that the derivatives of the LDH calcination are promising materials to be used in the AOP. The formation of a ZnAl2O/ZnO nanocomposite from calcination at 850 °C showed the best conversion results from the coupling semiconductors for charge separation strategy that diminish some problems associated with charge carrier recombination and its higher UV absorbance. Thus, the results show the multi-functionality of these materials, giving some light to the discussion about LDH recovery by "memory effect" that remains a topic of intense debate in the literature. / FAPESP: 2013/25043-4

En dépit de l’importance considérable des matériaux alumino- et borosilicates pour la catalyse, l’origine moléculaire de leur activité demeure mal comprise. Ceci tient à la difficulté de caractériser le désordre structural local généré au sein du réseau silicaté par l’incorporation d’hétéroatomes. Le caractère local de la résonance magnétique nucléaire (RMN) à l’état solide en fait une technique adaptée pour résoudre cette question majeure. Les silicates en feuillés auto-assemblés en présence de surfactants sont d’excellents systèmes modèles pour l’étude de la structure locale autour d’hétéroatomes de B ou d’Al car la synthèse, la structure moléculaire et la signature RMN 29Si simple de leurs formes siliceuses sont parfaitement maîtrisées. L’incorporation dans leurs réseaux silicatés de différentes quantités d’Al ou de B et leurs conséquences ont été étudiées par des méthodologies avancées de RMN permettant de sonder les interactions à travers l’espace ou les liaisons chimiques entre noyaux de 29Si, 27Al, 11B et/ou 1H, une approche qui peut être étendue à la substitution atomique dans une argile aluminosilicate et un nouveau borosilicate de calcium. Ces résultats ont été combinés à la modélisation moléculaire pour construire et valider des modèles structuraux capables de décrire les distorsions et les réarrangements parfois profonds du réseau résultant de la substitution. Cela a révélé des différences frappantes entre les conséquences de l’incorporation d’Al ou de B dans deux matériaux de morphologie semblables mais de structures moléculaires différentes, et offre une occasion unique de comprendre les propriétés régissant l’incorporation d’hétéroatomes dans les silicates. / While alumino- and borosilicate materials have paramount importance in catalysis, the molecular origin of their activity is not completely understood. This is mainly because the incorporation of heteroatoms into the silicate framework deteriorates the molecular order by generating local disorder that is particularly difficult to establish. Because of its local vision of ordered and disordered environments, solid-state nuclear magnetic resonance (NMR) can play a key role to solve this long-standing issue. Surfactant-directed layered silicate materials with short-range molecular order are particularly interesting model systems to study the local structures around Al or B heteroatoms because the synthesis, molecular structures, and simple 29Si NMR signatures of their pure-silicate forms are well understood. Various amounts of Al and B atoms were incorporated into their frameworks, and their consequences on the local structure were investigated by state-of-the-art multidimensional NMR measurements probing spatial proximities or bonding interactions between 29Si, 11B, 27Al, and 1H nuclei, an approach that could be extended to atomic substitution in an aluminosilicate clay and a new calcium borosilicate. These results were combined with molecular modeling to build and evaluate structural models that capture the local framework distortions and sometimes profound rearrangements resulting from the atomic substitutions. This reveals remarkable differences between the consequences of the incorporation Al or B in two distinct frameworks of otherwise strongly-related materials, and offers a unique opportunity to understand the properties that drive heteroatom incorporation.