The bottom-up assembly of functional devices requires novel building blocks to facilitate the incorporation of functional and structural hierarchy. Anisotropic building blocks can substantially broaden the creation of self-assembled devices with unique properties because of their morphological and/or chemical asymmetry. In this regard, we have created microspheres with one hemispherical face exposing silica and the other exposing gold. These microspheres were formed by the shadow deposition of gold onto silica microspheres. The two chemical surfaces allowed use of different surface reactions—silane chemistry for the silica side and thiol chemistry for the gold side—for immobilizing different oligonucleotide sequences on each of the two faces. These dual-functionalized microspheres were used in the selective orthogonal assembly of fluorophore-tagged target oligonucleotides. The DNA-directed assembly was confirmed by confocal microscopy of the microspheres. In essence, employing DNA as the linker molecule, these “Janus” particles can be assembled into various novel 1-D, 2-D, and 3-D structures, which are difficult to realize using symmetric building blocks. / Singapore-MIT Alliance (SMA)

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One of the most important advances in modern theoretical surface science and catalysis research has been the advent of Ab-Initio Density Functional Theory (DFT). Based on the electronic structure formulation of Pierre Hohenberg, Walter Kohn and Lu Jeu Sham, DFT has revolutionized theoretical research in heterogeneous catalysis, electrocatalysis, batteries, as well as homogeneous catalysis using first-principles electronic structure simulations. Combined with statistical mechanics, kinetic theory, and experimental inputs, DFT provides a powerful technique for investigating surface structure, reaction mechanisms, understanding underlying reactivity trends, and using them for rational and predictive design of materials for various catalytic chemistries, including those that can propel us towards a clean energy future – for example water gas shift (WGS), methanol synthesis, oxidation reactions, CO2 electroreduction, among many others. Fueled by advances in supercomputing facilities, numerous early and current DFT studies have been primarily focused on idealized simulations aimed at obtaining qualitative insights into experimental observations. However, as the immense potential of DFT has been unfolding, the demand for closer representation of realistic catalytic situations have rapidly emerged, and with it, the recognition of the need to reduce the disparity between theoretical DFT structures and real catalytic environments. Bridging this ‘materials gap’ necessitates using more rigorous catalyst structures in DFT calculations that can capture realistic experimental geometries, while at the same time, are creatively simplified to be computationally tractable. This thesis is a compilation of several projects on metals and metal/oxide systems that have been undertaken using DFT, in collaboration with experimental colleagues, with the goal of addressing some of the challenges in heterogeneous catalysis, while decreasing the ‘materials gap’ between theory and experiments.<div><br></div><div>The first several chapters of this thesis focus on bifunctional, metal/oxide systems. These systems are quintessential in numerous heterogeneous catalysis applications and have been the subject of extensive study. More interestingly, they sometimes exhibit synergistic enhancement in rates that is greater than the sum of the individual rates on the metal (on an inert support) or on the oxide in isolation. Such bifunctionality often stems from the modified properties at the nanoscale interface between the metal and the oxide and is an active field of research. In particular, while a large body of literature exists that investigates the activity of metals, the role of the support in bifunctional systems is often uncertain and is the subject of investigation of the first few chapters of this thesis. We chose to study WGS on Au as support effects are particularly prominent on this system. The second chapter examines WGS on Au/ZnO, where realistic catalytic environment at the interface is reproduced by analyzing the thermodynamics of surface hydroxylation of the oxide under reaction conditions, and its effect on WGS kinetics is quantified through a microkinetic analysis. This study highlights the importance of considering spectator species which can drastically influence the energetics and kinetics of a reaction at a metal/oxide interface. In addition, fundamental aspects of the effect of surface hydroxyls on the electronic structure at the interface is also discussed.<br></div><div><br></div><div>The third chapter of the thesis builds on this theme and analyzes the effect of systematic perturbation of electronic structure at the interface through substitutional doping of the oxide. Chapters 3 and 4 focus on Au/MgO, a system which has been previously studied in extensive detail in our group and benchmarked through experiments. The effects of a series of dopants of varying electronic valences have been analyzed on a number of properties at the interface – vacancy formation energies, adsorption energies of intermediates, scaling properties, activation energy barriers and so on. Exciting new scaling relationships are identified at this interface, having properties different from that observed on extended surfaces, and are interpreted using an electrostatic model. In the subsequent chapter, we identified Bronsted-Evans-Polanyi relationships for the different steps in the WGS pathway for a series of dopants. Coupled with the scaling relations, these trends were then used in conjunction with a dual-site microkinetic model to perform a volcano analysis for interfacial rates. Our analysis thus builds, for the first time, a rational design paradigm for electronic structure perturbation of the support at a bifunctional interface. The next chapter further investigates support effects, both geometric and electronic, in greater detail for Au supported on a series of oxide supports and discusses accelerated identification of an activity descriptor through a close fusion between computations and experiments.<br></div><div><br></div><div>In addition to interfacial effects of the support, this thesis also briefly examines a more apparent role of the oxide, wherein it influences the geometry of the supported metal. Two different Au-based systems are investigated using surface science approaches in Chapter 6 - the segregation properties of a bimetallic Au/Ir alloy on anatase and wetting behavior of Au-FexOy heterodimers – both of which are representative of the structural evolution of a supported catalyst under reaction conditions. Through our analysis, we show that the oxide directly influences these behaviors of the supported metal.<br></div><div><br></div><div>The next few chapters explore catalysis using metallic systems, focusing on transition metals, an important class of materials in heterogeneous catalysis and constitutes the major body of DFT literature for trend based catalytic analyses. A crucial factor that contributed to the success of such high-throughput screening studies was identification of linear scaling relationships on transition metals, whereby the adsorption energy of complex molecular fragments was linearly related to that of simple atomic adsorbates. However, while these relationships are valid for low adsorbate coverages, at higher, catalytically relevant coverages, deviations from linearity are common, thus presenting a materials gap in volcano analyses. The incorporation of coverage effects, therefore, in scaling relations has been a pressing challenge. This thesis describes a simple means of systematically capturing changes in reaction energies due to coverage effects through a pairwise interaction model, where the changes in adsorption energies are shown to be a direct function of the number of neighbors and interaction parameters determined through DFT. In addition, we also draw a mathematical correspondence between scaling relations at high coverage and that at low coverage and discuss its implications on the existence of linear scaling relations.<br></div><div><br></div><div>In Chapter 8, we discuss collaborative work on Pt based catalysts, an active catalyst for many chemical and electrochemical systems. We explore trends in WGS on bimetallic Pt-M systems and identify an activity descriptor by correlating experimental rates with the binding strength of OH* on model surfaces of bimetallic alloys. In addition, we also investigate the interaction between Na promoter and Pt under reaction conditions, using an inverse oxide model, to obtain insights into the nature of promotion of alkali metals on WGS on Pt catalysts.<br></div>

As tintas intumescentes vêm se tornando uma ótima alternativa para a proteção do aço contra o fogo. No entanto, o aço estrutural é aplicado em diversos setores da indústria, incluindo plataformas offshore de petróleo e gás e refinarias petroquímicas. Estas estruturas de alto desempenho ficam expostas a ambientes agressivos, o que torna necessário o desenvolvimento de tintas capazes de proteger o aço. Neste trabalho, foram preparadas tintas intumescentes epóxi formuladas com pó de gengibre e com casca de café como fonte de carbono e com trifenil fosfato (TPP) e fosfato de zinco (FZn) como fonte de fósforo. O objetivo principal deste trabalho foi desenvolver um sistema intumescente contendo compostos vegetais eficiente na proteção contra o fogo e capaz de proteger o substrato metálico contra a corrosão em ambiente salino. A avaliação foi realizada através de ensaio de resistência ao fogo (antes e após imersão em NaCl 3,5%), análise termogravimétrica (TGA), espectroscopia no infravermelho (FTIR), viscosidade Brookfield, aderência, ensaio estático de imersão, microscopia óptica (MO), microscopia eletrônica de varredura (MEV), difração de raios-X (DRX), pirólise acoplada à cromatografia gasosa e à espectrometria de massas (Py-GC/MS), espectroscopia de impedância eletroquímica (EIE), metalografia e microdureza Vickers. Os compostos vegetais apresentaram potencial de aplicação como fonte de carbono em sistemas intumescentes, enquanto que o FZn foi eficiente substituindo o TPP como fonte de fósforo. O sistema contendo gengibre e TPP apresentou os melhores resultados gerais, mantendo o fenômeno de intumescência após imersão em solução salina e apresentando a melhor proteção contra a corrosão dentre as amostras de tinta intumescente. Por fim, o revestimento contendo TPP apresentou propriedades anticorrosivas superiores ao FZn na aplicação em sistemas intumescentes. / The intumescent coating have become a great alternative for the protection of steel against fire. However, structural steel is applied in several industry sectors, including offshore oil and gas platforms and petrochemical refineries. These high performance structures are exposed to aggressive environments, which makes it necessary to develop coatings capable of protecting steel. In this work, epoxy intumescent coatings formulated with ginger powder and coffee husk as carbon source and with triphenyl phosphate (TPP) and zinc phosphate (ZnP) as phosphorus source were prepared. The main objective of this work was to develop an intumescent system containing vegetable compounds efficient in fire protection and able to protect the metal substrate against corrosion in saline environment. The evaluation was performed by fire resistance test (before and after immersion in NaCl 3.5%), thermogravimetric analysis (TGA), infrared spectroscopy (FTIR), Brookfield viscosity, adhesion tests, static immersion test, optical microscopy (OM), Scanning electron microscopy (SEM), X-ray diffraction (XRD), pyrolysis coupled to gas chromatography and mass spectrometry (Py-GC / MS), electrochemical impedance spectroscopy (EIS), metallography and Vickers microhardness. Vegetable compounds presented potential as a carbon source in intumescent systems, while ZnP was efficient replacing TPP as a source of phosphorus. The system containing ginger and TPP presented the best overall results, maintaining the intumescence phenomenon after immersion in saline solution and presenting the best protection against corrosion among the intumescent coating samples. Finally, the coating containing TPP presented anticorrosive properties superior to FZn in the application in intumescent systems.

As tintas intumescentes vêm se tornando uma ótima alternativa para a proteção do aço contra o fogo. No entanto, o aço estrutural é aplicado em diversos setores da indústria, incluindo plataformas offshore de petróleo e gás e refinarias petroquímicas. Estas estruturas de alto desempenho ficam expostas a ambientes agressivos, o que torna necessário o desenvolvimento de tintas capazes de proteger o aço. Neste trabalho, foram preparadas tintas intumescentes epóxi formuladas com pó de gengibre e com casca de café como fonte de carbono e com trifenil fosfato (TPP) e fosfato de zinco (FZn) como fonte de fósforo. O objetivo principal deste trabalho foi desenvolver um sistema intumescente contendo compostos vegetais eficiente na proteção contra o fogo e capaz de proteger o substrato metálico contra a corrosão em ambiente salino. A avaliação foi realizada através de ensaio de resistência ao fogo (antes e após imersão em NaCl 3,5%), análise termogravimétrica (TGA), espectroscopia no infravermelho (FTIR), viscosidade Brookfield, aderência, ensaio estático de imersão, microscopia óptica (MO), microscopia eletrônica de varredura (MEV), difração de raios-X (DRX), pirólise acoplada à cromatografia gasosa e à espectrometria de massas (Py-GC/MS), espectroscopia de impedância eletroquímica (EIE), metalografia e microdureza Vickers. Os compostos vegetais apresentaram potencial de aplicação como fonte de carbono em sistemas intumescentes, enquanto que o FZn foi eficiente substituindo o TPP como fonte de fósforo. O sistema contendo gengibre e TPP apresentou os melhores resultados gerais, mantendo o fenômeno de intumescência após imersão em solução salina e apresentando a melhor proteção contra a corrosão dentre as amostras de tinta intumescente. Por fim, o revestimento contendo TPP apresentou propriedades anticorrosivas superiores ao FZn na aplicação em sistemas intumescentes. / The intumescent coating have become a great alternative for the protection of steel against fire. However, structural steel is applied in several industry sectors, including offshore oil and gas platforms and petrochemical refineries. These high performance structures are exposed to aggressive environments, which makes it necessary to develop coatings capable of protecting steel. In this work, epoxy intumescent coatings formulated with ginger powder and coffee husk as carbon source and with triphenyl phosphate (TPP) and zinc phosphate (ZnP) as phosphorus source were prepared. The main objective of this work was to develop an intumescent system containing vegetable compounds efficient in fire protection and able to protect the metal substrate against corrosion in saline environment. The evaluation was performed by fire resistance test (before and after immersion in NaCl 3.5%), thermogravimetric analysis (TGA), infrared spectroscopy (FTIR), Brookfield viscosity, adhesion tests, static immersion test, optical microscopy (OM), Scanning electron microscopy (SEM), X-ray diffraction (XRD), pyrolysis coupled to gas chromatography and mass spectrometry (Py-GC / MS), electrochemical impedance spectroscopy (EIS), metallography and Vickers microhardness. Vegetable compounds presented potential as a carbon source in intumescent systems, while ZnP was efficient replacing TPP as a source of phosphorus. The system containing ginger and TPP presented the best overall results, maintaining the intumescence phenomenon after immersion in saline solution and presenting the best protection against corrosion among the intumescent coating samples. Finally, the coating containing TPP presented anticorrosive properties superior to FZn in the application in intumescent systems.

As tintas intumescentes vêm se tornando uma ótima alternativa para a proteção do aço contra o fogo. No entanto, o aço estrutural é aplicado em diversos setores da indústria, incluindo plataformas offshore de petróleo e gás e refinarias petroquímicas. Estas estruturas de alto desempenho ficam expostas a ambientes agressivos, o que torna necessário o desenvolvimento de tintas capazes de proteger o aço. Neste trabalho, foram preparadas tintas intumescentes epóxi formuladas com pó de gengibre e com casca de café como fonte de carbono e com trifenil fosfato (TPP) e fosfato de zinco (FZn) como fonte de fósforo. O objetivo principal deste trabalho foi desenvolver um sistema intumescente contendo compostos vegetais eficiente na proteção contra o fogo e capaz de proteger o substrato metálico contra a corrosão em ambiente salino. A avaliação foi realizada através de ensaio de resistência ao fogo (antes e após imersão em NaCl 3,5%), análise termogravimétrica (TGA), espectroscopia no infravermelho (FTIR), viscosidade Brookfield, aderência, ensaio estático de imersão, microscopia óptica (MO), microscopia eletrônica de varredura (MEV), difração de raios-X (DRX), pirólise acoplada à cromatografia gasosa e à espectrometria de massas (Py-GC/MS), espectroscopia de impedância eletroquímica (EIE), metalografia e microdureza Vickers. Os compostos vegetais apresentaram potencial de aplicação como fonte de carbono em sistemas intumescentes, enquanto que o FZn foi eficiente substituindo o TPP como fonte de fósforo. O sistema contendo gengibre e TPP apresentou os melhores resultados gerais, mantendo o fenômeno de intumescência após imersão em solução salina e apresentando a melhor proteção contra a corrosão dentre as amostras de tinta intumescente. Por fim, o revestimento contendo TPP apresentou propriedades anticorrosivas superiores ao FZn na aplicação em sistemas intumescentes. / The intumescent coating have become a great alternative for the protection of steel against fire. However, structural steel is applied in several industry sectors, including offshore oil and gas platforms and petrochemical refineries. These high performance structures are exposed to aggressive environments, which makes it necessary to develop coatings capable of protecting steel. In this work, epoxy intumescent coatings formulated with ginger powder and coffee husk as carbon source and with triphenyl phosphate (TPP) and zinc phosphate (ZnP) as phosphorus source were prepared. The main objective of this work was to develop an intumescent system containing vegetable compounds efficient in fire protection and able to protect the metal substrate against corrosion in saline environment. The evaluation was performed by fire resistance test (before and after immersion in NaCl 3.5%), thermogravimetric analysis (TGA), infrared spectroscopy (FTIR), Brookfield viscosity, adhesion tests, static immersion test, optical microscopy (OM), Scanning electron microscopy (SEM), X-ray diffraction (XRD), pyrolysis coupled to gas chromatography and mass spectrometry (Py-GC / MS), electrochemical impedance spectroscopy (EIS), metallography and Vickers microhardness. Vegetable compounds presented potential as a carbon source in intumescent systems, while ZnP was efficient replacing TPP as a source of phosphorus. The system containing ginger and TPP presented the best overall results, maintaining the intumescence phenomenon after immersion in saline solution and presenting the best protection against corrosion among the intumescent coating samples. Finally, the coating containing TPP presented anticorrosive properties superior to FZn in the application in intumescent systems.

La médecine s’intéresse de plus en plus à des systèmes nanométriques visant la détection précoce de cellules malignes, le traitement de ces dernières ou la compréhension de mécanismes biologiques. Des nanoparticules fluorescentes et des nanocristaux harmoniques aux propriétés non-linéaires intéressantes ont été étudiés comme agents de contraste pour l’imagerie biomédicale.Dans ce travail, nous avons recherché un matériau non-centrosymétrique dont la matrice permet un dopage d’ions lanthanides afin de développer des sondes multifonctionnelles, c’est-à-dire à la fois luminescentes et harmoniques. Nous nous sommes orientés vers l’iodate de lanthane de phase alpha, α-La(IO3)3, non-centrosymétrique. Dans un premier temps, nous avons développé des synthèses hydrothermales assistées par micro-ondes pour permettre de cristalliser la phase alpha et produire des particules de taille nanométrique (< 100 nm). La présence de nombreux pseudo-polymorphes nécessite le contrôle précis des paramètres de synthèse, en particulier de la température de synthèse, pour obtenir exclusivement des nanoparticules de α-La(IO3)3. L’étude de différents intermédiaires réactionnels (La(IO3)3(OH2), La(IO3)2.66(OH)0.33) nous a permis de mettre en évidence une transformation de phase entre ces composés et la phase α-La(IO3)3. Dans un deuxième temps, nous avons utilisé deux dispositifs optiques permettant de mesurer l’efficacité de génération de second harmonique : l’un permettant l’étude de nanocristaux de α-La(IO3)3 individuels et l’autre utilisant un ensemble de nanocristaux en suspension dans un solvant. Ce dernier, basé sur la diffusion Hyper-Rayleigh, nous a permis de quantifier la réponse non-linéaire de nanocristaux α-La(IO3)3 de diamètre 20-50 nm et de déterminer un coefficient non-linéaire < d > de 8 pm.V-1, comparable aux valeurs obtenues pour d’autres nanocristaux harmoniques tels que BaTiO3 ou LiNbO3. Enfin, nous avons montré la possibilité d’incorporer des ions lanthanides tels que Er3+ et Yb3+ dans ces nanocristaux d’iodate de lanthane, conduisant à des nanocristaux de α-La1-x-yYbyErx(IO3)3. Ces nanocristaux sont toujours actifs en génération de second harmonique et émettent simultanément un signal de photoluminescence. Ainsi, pour une excitation dans le proche infra-rouge (800 nm ou 980 nm par exemple), nous avons observé simultanément un signal de second harmonique et de photoluminescence par up-conversion. Nous avons démontré l’intérêt d’un co-dopage Yb3+/Er3+ pour une optimisation du signal d’up-conversion sous une excitation à 980 nm. Ainsi, par un dopage d’ions lanthanides tels que Er3+ et Yb3+, les nanocristaux de α-La(IO3)3 présentent une émission simultanée de génération de second harmonique et de photoluminescence. La combinaison de ces deux propriétés permet d’envisager d’utiliser ces nanocristaux bifonctionnels pour une imagerie par luminescence, technique classique, tout en la couplant avec une imagerie multiphoton, plus coûteuse mais présentant des avantages non-négligeables (rapidité de scans, meilleure sélectivité spatiale, sensibilité à la polarisation). / Medicine is increasingly interested in nanometric systems for the early detection of malignant cells, their treatment or understanding of biological mechanisms. Fluorescent nanoparticles and harmonic nanocrystals with interesting non-linear properties have been studied as contrast agents for biomedical imaging.In this work, we explored a non-centrosymmetric material whose matrix allows a doping of lanthanide ions in order to develop multifunctional probes, i. e. both luminescent and harmonic. We focused on non-centrosymmetric iodate phase: alpha lanthanum iodate, α-La(IO3)3. First, we developed microwave-assisted hydrothermal syntheses to crystallize the alpha phase and produce nano-sized particles (< 100 nm). The presence of many pseudo-polymorphs requires precise control of the synthesis parameters, in particular the synthesis temperature, to obtain exclusively nanoparticles of α-La(IO3)3. The study of different reaction intermediates (La(IO3)3(OH2), La(IO3)2.66(OH)0.33) allowed us to identify a phase transformation between these compounds and the phase α-La(IO3)3. Secondly, we used two optical devices to evaluate the second harmonic generation efficiency of the synthesized α-La(IO3)3 nanocrystals: one set-up allowed us to study individual α-La(IO3)3 nanocrystals and the other used an ensemble of α-La(IO3)3 nanocrystals in suspension in a solvent. The latter, based on Hyper-Rayleigh scattering, quantified the non-linear response of nanocrystals α-La(IO3)3 with a diameter of 20-50 nm and allowed us to determine a non-linear coefficient < d > of 8 pm.V-1, a value comparable to the ones obtained for other harmonic nanocrystals such as BaTiO3 or LiNbO3. Finally, we showed the possibility of incorporating lanthanide ions such as Er3+ and Yb3+ into these lanthanum iodate nanocrystals, leading to α-La1-x-yYbyErx(IO3)3 nanocrystals. These nanocrystals are still active in second harmonic generation and simultaneously emit a photoluminescence signal. Thus, for excitation in the near infrared (800 nm or 980 nm for instance), we simultaneously observed a signal of second harmonic and a photoluminescence signal based on up-conversion processes. We demonstrated the interest of an Yb3+/Er3+ co-doping for an optimization of the up-conversion signal under excitation at 980 nm. Thus, Er3+ and Yb3+-doped nanocrystals of α-La(IO3)3 exhibit simultaneous emission of second harmonic generation and photoluminescence. The combination of these two properties makes it possible to consider using these bifunctional nanocrystals for conventional luminescence imaging, while coupling it with multiphoton imaging, which is more expensive but has significant advantages (scan speed, better spatial selectivity, polarization sensitivity).