Yes / Bimetallic nanoparticles are of immense scientific and technological interest given the synergistic properties observed when two different metallic species are mixed at the nanoscale. This is particularly prevalent in catalysis, where bimetallic nanoparticles often exhibit improved catalytic activity and durability over their monometallic counterparts. Yet despite intense research efforts, little is understood regarding how to optimize bimetallic surface composition and structure synthetically using rational design principles. Recently, it has been demonstrated that peptide-enabled routes for nanoparticle synthesis result in materials with sequence-dependent catalytic properties, providing an opportunity for rational design through sequence manipulation. In this study, bimetallic PdAu nanoparticles are synthesized with a small set of peptides containing known Pd and Au binding motifs. The resulting nanoparticles were extensively characterized using high-resolution scanning transmission electron microscopy, X-ray absorption spectroscopy, and high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Structural information obtained from synchrotron radiation methods was then used to generate model nanoparticle configurations using reverse Monte Carlo simulations, which illustrate sequence dependence in both surface structure and surface composition. Replica exchange with solute tempering molecular dynamics simulations were also used to predict the modes of peptide binding on monometallic surfaces, indicating that different sequences bind to the metal interfaces via different mechanisms. As a testbed reaction, electrocatalytic methanol oxidation experiments were performed, wherein differences in catalytic activity are clearly observed in materials with identical bimetallic composition. Taken together, this study indicates that peptides could be used to arrive at bimetallic surfaces with enhanced catalytic properties, which could be leveraged for rational bimetallic nanoparticle design using peptide-enabled approaches. / Air Force Office for Scientific Research (T.R.W., Grant No. FA9550-12-620 1-0226). S.P.E. and E.B.C. gratefully acknowledge financial support from the Army Research Office through a MURI award, W911NF-10-1-0520

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This century has seen a phenomenal growth in energy demands and environmental pollution, which has given rise to a worldwide awareness for the need to address these issues immediately. / This thesis focuses on the fabrication of high performance electrocatalysts applied in fuel cells and developing appropriate advanced oxidation processes for environmental remediation. It has been shown that ultrasonic irradiation is a promising method of synthesizing nanometre sized metal colloids with specific properties. Sonophotocatalysis has proved to be an effective process for the degradation of organic pollutants / The synthesis of platinum monometallic and platinum-ruthenium bimetallic nanoparticles was successfully achieved by using sonochemical irradiation. A chemical method and a hybrid method were used to reveal and understand the process of Ru(III) reduction by sonochemistry. TEM images of the Pt and PtRu monometallic/bimetallic particles indicate typical diameters of less than 10 nm. An effort was made to investigate the influence of two different methods, namely simultaneous and sequential sonochemical reduction, on the structure and formation of PtRu bimetallic nanoparticles. It has been shown that the sequential reduction method produces a relatively higher yield of core-shell nanoparticles than the simultaneous reduction method. It has been concluded that Pt nanoparticles, which are formed first, play an important role in catalysing the formation of Ru nanoparticles. / A number of methods including chemical, sonochemical and radiolytic synthesis were used to fabricate platinum and platinum-ruthenium monometallic/bimetallic nanoparticles. Furthermore, the evaluation of the electrocatalytic performance of these particles was performed by using cyclic voltammetry. Simultaneous and sequential methods for the synthesis of PtRu were adopted to investigate their influence on the electrocatalytic performance of these bimetallic nanoparticles. thas been shown that simultaneous reduction is an effective means of fabricating high performance electrocatalytic PtRu catalysts. A number of experiments with different ratios of platinum to ruthenium ions in precursor solution were carried out to study the effect of the ruthenium composition in platinum-ruthenium electrodes. It has been found that the methanol oxidation ability of platinum-ruthenium bimetallic nanoparticles can change with the alternation of ratio of Pt(II) to Ru(III) in the precursor solution. Simultaneous radiolytic reduction has the potential to fabricate higher performance electrocatalytic bimetallic nanoparticles. / Although both photo-oxidation and sono-oxidation techniques are fascinating solutions to the environmental problems at hand, the critical limit of these individual processes is their low efficiency of environmental remediation. In my project, sonolysis and photocatalysis (sonophotocatalysis) have been simultaneously employed to degrade selective organic pollutants in aqueous environments, such as methyl orange, p-chlorobenzoic acid, p-aminobenzoic acid and p-hydroxybenzoic acid. Experiments have been carried out in order to improve the efficiency of sonophotocatalytic reactions to ensure that a substantial amount of the electrical energy is utilized in degrading the organic pollutants. / Methyl orange, an azo dye, was selected as the degradation target for sonophotocatalysis. An orthogonal array analysis method was employed to clarify the correlation between the efficiencies of sonolysis, photocatalysis and sonophotocatalysis and the various operation conditions studied. Emphasis was placed on investigating the influence of pH and the ultrasound parameters on these three advanced oxidation processes. It was of interest to find that the degradation of methyl orange originates from hydroxylation and demethylation processes preceding aromatic ring-opening. / Sonophotocatalysis was also applied in the degradation of three aromatic carboxylic acids, p-chlorobenzoic acid, p-hydroxybenzoic acid and p-aminobenzoic acid. Experiments were carried out in order to get a thorough understanding of the synergy effects produced by combining the two oxidation techniques. A number of advanced analytical techniques, such as HPLC and Q-TOF MS/LC, were employed to comprehensively monitor and analyse the sonophotocatalytic degradation process. It has been found that synergistic effects of the combined system have been identified with respect to the parent organic pollutant as well as its degradation products. Additionally, products were quantitatively analysed by a kinetic simulation method in order to understand the reaction mechanism. This method also allowed us to quantify the synergy effects. It was observed that the solution pH played a key role in determining the degradation rate and controlling the direction of the degradation reaction. Based on the analytical data gathered, the sonophotocatalytic degradation pathway of the aromatic carboxylic acids was established. The experimental results suggest that the sonophotocatalytic technique is likely to lead to a complete mineralization of organic pollutants in aqueous solutions.

Nanopartículas bimetálicas de AuPd têm mostrado excelente atividade catalítica em reações de oxidação. O entendimento dos efeitos da variação da composição e morfologia das nanopartículas bimetálicas em suas propriedades catalíticas é fundamental para a preparação de catalisadores cada vez mais ativos e seletivos. Neste trabalho foram estudadas nanopartículas bimetálicas de AuPd de composição variável suportadas sobre um suporte constituído por nanopartículas de magnetita revestidas por sílica. O efeito da calcinação e da redução com hidrogênio sobre a morfologia e composição das nanopartículas bimetálicas foi acompanhado pelas técnicas de TEM, XEDS, XAS, XRD e XPS. A correlação entre estrutura, composição e atividade catalítica dos catalisadores preparados foi estudada pelo acompanhamento de reações de oxidação de monóxido de carbono e de oxidação de álcool benzílico. As amostras não calcinadas apresentaram segregação metálica em todas as composições estudadas. Após a etapa de calcinação, maior segregação metálica foi encontrada, com a formação de óxido de paládio na superfície das nanopartículas, exceto na amostra mais rica em ouro. O tratamento das amostras oxidadas com hidrogênio foi capaz de reduzir os metais oxidados na superfície das nanopartículas, mas um enriquecimento em paládio na superfície e maior segregação entre ouro e paládio foram observados. Uma melhora na atividade catalítica na oxidação de monóxido de carbono foi observada juntamente com um aumento na composição de paládio, além disso, observou-se uma maior atividade catalítica em relação às nanopartículas não calcinadas para as amostras calcinadas e reduzidas. Para a oxidação de álcool benzílico um aumento na atividade catalítica de até cinco vezes foi observado após a calcinação dos catalisadores, com maior atividade para a amostra de composição Au1Pd2. A queda na atividade catalítica após a redução dos catalisadores mostrou que a presença de óxido de paládio na superfície das nanopartículas é fundamental para que seja observada uma maior atividade catalítica. / AuPd bimetallic nanoparticles have shown excellent catalytic performance in oxidation reactions. Understanding the effects of composition and morphology of the bimetallic nanoparticles in their catalytic properties is key for the preparation of more active and selective catalysts. In this work, we studied AuPd bimetallic nanoparticles supported over silica coated magnetite nanoparticles. The effects of calcination and reduction with hydrogen on the morphology and composition of the bimetallic nanoparticles was investigated by TEM, XEDS, XAS, XRD and XPS. The correlation between structure, composition and catalytic activity of the prepared catalysts was studied by the oxidation of carbon monoxide and benzyl alcohol. The non calcined samples showed metal segregation for all investigated compositions. After the calcination step, greater metal segregation occurred, and the formation of palladium oxide on the surface of the nanoparticles was observed, except for the most gold-rich sample. The treatment of the oxidized samples with hydrogen reduced the metal oxides on the surface of the nanoparticles, but a palladium surface enrichment and greater metal segregation between gold and palladium was observed. The catalytic activity observed for the oxidation of carbon monoxide increased with increasing palladium concentrations. An increase in catalytic activity was observed for the calcined and reduced samples when compared to their non-calcined counterparts. For benzyl alcohol oxidation, a five-fold increase in catalytic activity after calcination was observed, with a peak in catalytic activity for the Au1Pd2 sample. A drop in catalytic activity after the reduction of the oxidized catalysts with hydrogen showed that the presence of palladium oxide on the surface of the nanoparticles is fundamental for an increased catalytic activity.

A oxidação seletiva de alcoóis é importante para a síntese de intermediários e produtos químicos utilizados na fabricação de inúmeros materiais. O interesse em novos métodos catalíticos para a oxidação de moléculas orgânicas tem aumentado juntamente com a busca por processos ecossustentáveis. Neste trabalho foram estudadas diferentes estratégias de deposição de nanopartículas bimetálicas de ouro e paládio sobre um suporte magnético, constituído por nanopartículas de magnetita revestidas por sílica. Dois métodos de síntese de nanopartículas bimetálicas de ouro e paládio foram estudados: (I) a síntese de nanopartículas bimetálicas formadas por ligas de ouro e paládio, seguida pela deposição dessas nanopartículas pré-formadas sobre o suporte catalítico e (II) a síntese de nanopartículas bimetálicas do tipo core-shell, por meio da redução sucessiva de ouro e paládio sobre o suporte catalítico. A morfologia dos catalisadores foi determinada por diferentes técnicas de microscopia eletrônica. O desempenho catalítico das nanopartículas bimetálicas foi estudado na reação modelo de oxidação de álcool benzílico com oxigênio. Os catalisadores mostraram-se ativos e seletivos para benzaldeído sem a necessidade do uso de solvente ou base e, após separação magnética, foram usados em sucessivas reações com desempenho satisfatório / The selective oxidation of alcohols is important for the synthesis of intermediates and chemical products used for the production of many materials. The interest in new catalytic methods for the oxidation of organic molecules has increased along with the search for eco-sustainable processes. In this thesis we studied different deposition strategies of gold and palladium bimetallic nanoparticles on a magnetic support, comprised by silica coated magnetite nanoparticles. Two synthetic methods for the preparation of supported gold and palladium bimetallic nanoparticles were investigated: (I) the synthesis of gold and palladium bimetallic nanoparticles, followed by deposition of the preformed nanoparticles on the catalytic support and (II) the synthesis of core-shell bimetallic nanoparticles, through the sequential reduction of gold and palladium on the catalytic support. The catalysts\' morphology was investigated by electronic microscopy techniques. The catalytic behavior of the bimetallic nanoparticles was investigated in the model reaction of the oxidation of benzyl alcohol with oxygen. The catalysts were active and selective for benzaldehyde without the use of solvent and base and, after magnetic separation, were able to be reused in successive runs and showed a good performance.

The aim of this thesis is to investigate the methodology of three dimensional chemical imaging of nanoparticles through the use of scanning transmission electron microscope (STEM) – energy dispersive X-ray (EDX) spectroscopy. In this thesis, an absorption correction factor is derived for spherical nanoparticles that can correct X-ray absorption effects. Quantification of EDX spectra of nanoparticles usually neglects X-ray absorption within the nanoparticle but may lead to erroneous results, thus an absorption correction is important for accurate compositional quantification. The absorption correction presented is verified through comparison with experimental data of Au X-ray peaks in spherical Au nanoparticles and is found to agree excellently. This absorption correction allows accurate compositional quantification of large ( > 100 nm) particles with STEM-EDX.Three dimensional chemical mapping is achievable through the use of EDX spectroscopy with electron tomography. Here, the methodology of STEM-EDX tomography is fully explored, with a focus on how to avoid artefacts introduced through detector shadowing and low counts per pixel. A varied-time acquisition scheme is proposed to correct for detector shadowing that is shown to provide a more constant intensity over a series of projections, allowing a higher fidelity reconstruction. The STEM-EDX tomography methodology presented is applied to the study of AgAu nanoparticles synthesized by the galvanic replacement reaction. The elemental distribution as a function of the composition of the as-synthesized nanoparticles is characterised and a reversal in the element segregated to the surface of the nanoparticles is found. The composition at which the reversal takes place is shown to correlate with a peak in the catalytic yield of a three component coupling reaction. It is hypothesized that a continuous Au surface results in the optimum catalytic conditions for the reaction studied, which guides the use of galvanically prepared AgAu nanoparticles as catalysts.

The main focus of the thesis is to have better understanding of the atomic and electronic structures, vibrational dynamics and thermodynamics of metallic surfaces and bi-metallic nanoparticles (NPs) via a multi-scale simulational approach. The research presented here involves the study of the physical and chemical properties of metallic surfaces and NPs that are useful to determine their functionality in building novel materials. The study follows the 'bottom-up' approach for which the knowledge gathered at the scale of atoms and NPs serves as a base to build, at the macroscopic scale, materials with desired physical and chemical properties. We use a variety of theoretical and computational tools with different degrees of accuracy to study problems in different time and length scales. Interactions between the atoms are derived using both Density Functional Theory (DFT) and Embedded Atom Method (EAM), depending on the scale of the problem at hand. For some cases, both methods are used for the purpose of comparison. For revealing the local contributions to the vibrational dynamics and thermodynamics for the systems possessing site-specific environments, a local approach in real-space is used, namely Real Space Green's Function method (RSGF). For simulating diffusion of atoms/clusters and growth on metal surfaces, Molecular Statics (MS) and Molecular Dynamics (MD) methods are employed.

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[pt] No presente trabalho, foram abordadas duas formas alternativas de materiais para a redução do cromo hexavalente. Para um dos materiais foram sintetizadas nanopartículas de ferro metálico, níquel metálico e sílica como suporte, e o outro material visando menor custo e maior acessibilidade foi uma lã de aço comercial. Ambos têm como objetivo a diminuição ou remediação de cromo hexavalente através de soluções de dicromato de potássio em concentrações que visam simular contaminações geradas por diversas operações industriais. A função destes materiais é de atuar como um forte agente redutor, doando elétrons para reduzir o cromo hexavalente em cromo trivalente. As nanopartículas de ferro zero valente, níquel zero valente suportadas em sílica foram sintetizadas empregando sulfatos em uma técnica de redução com borohidreto de potássio em solução aquosa. As nanopartículas foram caracterizadas com o auxílio da técnica de difração de raio-X para determinar as fases presentes, e de microscopia eletrônica de varredura com espectroscopia por dispersão de energia, definindo a composição química elementar e a morfologia das superfícies, e ICP para quantificar a composição dos elementos ferro e níquel. Finalmente, foram realizados os testes de redução do cromo hexavalente em cromo trivalente através do Espectrofotômetro UV-VIS, sendo quantificada a concentração de cromo hexavalente presente na solução através da técnica colorimétrica com o reagente altamente seletivo, o 1,5-difenilcarbazida (DFC). As nanopartículas e a lã de aço demonstraram eficiência na redução do cromo hexavalente em concentrações de 8,32 ppm (K2Cr2O7 80 Mmol/L), 6,241 (K2Cr2O7 60 Mmol/L) e 4,161 ppm (K2Cr2O7 40 Mmol/L) com tempos inferiores a 5 minutos. Contudo, as nanopartículas de Fe0-Ni0 suportadas em SiO2 reduziram o cromo hexavalente com uma quantidade em massa de Fe0 aproximadamente 110 vezes menor em relação a lã de aço, considerando que este é constituído unicamente por ferro metálico. Credita-se esta efetividade à maior área superficial por unidade de massa das partículas nanoestruturadas. / [en] In the present work, two alternative forms were approached using different materials. For one of the materials, nanoparticles of metallic iron, metallic nickel and silica as support were synthesized, and the other material aiming at lower cost and greater accessibility will be steel wool. Both have the objective of reducing or remediation of hexavalent chromium through solutions of potassium dichromate in concentrations that aim to simulate contaminations generated by various industrial operations. The function of these materials is to act as a strong reducing agent by donating electrons to reduce the hexavalent chromium to trivalent chromium. The nanoparticles of zero-valent Iron, zero-valent nickel supported on silica was synthesized using sulfates in a reduction technique with potassium borohydride in aqueous solution. The nanoparticles were characterized with the help of the XRD technique, from the diffraction pattern generated and quantifying the present phases, and SEM / EDS, defining elemental chemical composition and surface morphology and ICP to quantify the elemental composition. Finally, the tests of reduction of the hexavalent chromium in trivalent chromium through the UV-VIS spectrophotometer were carried out, and the concentration of hexavalent Chromium present in the solution was quantified through the Colorimetric technique with the highly selective reagent, 1,5-diphenylcarbazide (DFC). Nanoparticles and steel wool showed efficiency in the reduction of hexavalent chromium at concentrations of 8,32 ppm (K2Cr2O7 80 Mmol/L), 6,241 (K2Cr2O7 60 Mmol/L) e 4,161 ppm (K2Cr2O7 40 Mmol/L) with times less than 5 minutes. However, as Fe0-Ni0 nanoparticles supported in SiO2, they reduced the hexavalent content of a quantity of steel mass in relation to steel wool, considering that it consists only of metallic iron. The effectiveness in the most superficial part by the mass unit of the nanostructured particles is credited.

Ce manuscrit présente une étude expérimentale autour de la synthèse des nanotubes de carbone et de leurs possibles intégrations dans des dispositifs. Les remarquables propriétés électroniques et optiques des nanotubes en font un matériau de choix pour entre autres, la nanoélectronique. Néanmoins, l’intégration des nanotubes dans des dispositifs performants est encore aujourd’hui un défi. Cela repose principalement sur la difficulté d’obtenir de grandes quantités de nanotubes mono-paroi avec des propriétés uniformes, propriétés qui sont définies par la structure du nanotube (i.e. leur angle chiral et leur diamètre). Ainsi, réaliser des synthèses de nanotube de carbone avec un contrôle de leur structure représente un point clé pour le progrès dans ce domaine.Nous avons donc mis en place une nouvelle méthode de synthèse de nanotubes de carbone basée sur la chimie de coordination et le dépôt chimique en phase vapeur activé par filament chaud. Cette synthèse permet la conception de nombreux nouveaux catalyseurs bimétalliques pour la croissance des nanotubes de carbone. Comme le procédé mis en place est très générique, des études paramétriques peuvent être réalisées de manière à mieux comprendre l’influence des différents paramètres de la croissance sur la structure des nanotubes obtenue. Nous discuterons ici du rôle de la température et de la composition chimique du catalyseur. Les nanotubes obtenus sont principalement caractérisés par spectroscopie Raman et par microscopies électroniques.Afin de valider les observations obtenues par spectroscopie Raman, les nanotubes synthétisés ont aussi été intégrés dans des dispositifs de type transistor à effet de champ. Une analyse des performances des transistors en fonction des différents nanotubes utilisés dans le canal est présentée.Enfin, les nanotubes intégrés dans ces transistors ont été fonctionnalisés avec un chromophore de ruthénium. Nous avons montré que cette fonctionnalisation nous permet de moduler, grâce à une impulsion lumineuse, la conductivité du dispositif sur trois ordres de grandeur. / This manuscript presents an experimental study around the single wall carbon nanotubes (SWCNT) synthesis and their possible integration in nanodevices. The unique electronic and optical properties of carbon nanotubes make them a choice material for various applications, particularly in nano-electronics.Nevertheless, their integration in effective devices is still a challenge. This is mainly due to the difficulty to obtain large quantity of SWCNT with uniform properties, defined by their structure (i.e. chiral angle and diameter). Therefore, structure controlled growth of SWCNTs is a key point for progress in this field.Here, we established a new synthesis approach based on coordination chemistry and hot-filament chemical vapor deposition. This approach allows the design of various bimetallic catalyst nanoparticles for the SWCNT growth. As the synthesis process is generic, parametric study can be performed in order to better understand the influence of the various parameters on the structure of the as-grown SWCNTs. In particular, we will discuss the role of the growth temperature and the chemical composition of the catalyst on the final SWCNTs structure. The obtained SWCNTs are mainly characterized by Raman spectroscopy and electronic microscopy.In order to validate the observations performed by Raman measurement, the synthesized SWCNTs have been also integrated in field effect transistors (FET) devices. An analysis of the performance of the FET-device as a function of the SWCNTs used in its channel will be presented.Finally, SWCNTs integrated in these transistors have been functionalized with an inorganic chromophore of ruthenium.We demonstrate that the functionalization of the SWCNTs leads to a three order of magnitude reversible switch of the device conductivity triggered by visible light.