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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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.

Nanosized metal particles have become an important class of materials in the field of catalysis, optical, electronic, magnetic and biological devices due to the unique physical and chemical properties. This research deals with the synthesis of structured bimetallic nanoparticles for the dechlorination of toxic organics. Nanoparticle synthesis in aqueous phase for dechlorination studies has been reported. However, in the absence of polymers or surfactants particles can easily aggregate into large particles with wide size distribution. In this study, we report a novel in-situ synthesis method of bimetallic nanoparticles embedded in polyacrylic acid (PAA) functionalized microfiltration membranes by chemical reduction of metal ions bound to the carboxylic acid groups. Membrane-based nanoparticle synthesis offers many advantages: reduction of particle loss, prevention of particle agglomeration, application of convective flow, and recapture of dissolved metal ions. The objective of this research is to synthesize and characterize nanostructured bimetallic particles in membranes, understand and quantify the catalytic hydrodechlorination mechanism, and develop a membrane reactor model to predict and simulate reactions under various conditions. In this study, the PAA functionalization was achieved by filling the porous PVDF membranes with acrylic acid and subsequent in-situ free radical polymerization. Target metal cations (iron in this case) were then introduced into the membranes by ion exchange process. Subsequent reduction resulted in the formation of metal nanoparticles (around 30 nm). Bimetallic nanoparticles can be formed by post deposition of secondary appropriate metal such as Pd or Ni. The membranes and bimetallic nanoparticles were characterized by: SEM, TEM, TGA, and FTIR. A specimen-drift-free X-ray energy dispersive spectroscopy (EDS) mapping system was used to determine the two-dimensional element distribution inside the membrane matrix at the nano scale. This high resolution mapping allows for the correlation and understanding the nanoparticle structure, second metal composition in terms of nanoparticle reactivity. Chlorinated aliphatics such as trichloroethylene and conjugated aromatics such as polychlorinated biphenyls (PCBs) were chosen as the model compounds to investigate the catalytic properties of bimetallic nanoparticles and the reaction mechanism and kinetics. Effects of second metal coating, particle size and structure and temperature were studied on the performance of bimetallic system. In order to predict reaction at different conditions, a two-dimensional steady state model was developed to correlate and simulate mass transfer and reaction in the membrane pores under convective flow mode. The 2-D equations were solved by COMSOL (Femlab). The influence of changing parameters such as reactor geometry (i.e. membrane pore size) and Pd coating composition were evaluated by the model and compared well with the experimental data.

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.

Zero-valent metals such as bulk iron and zinc are known to dechlorinate toxicorganic compounds. Enhancement in reaction rates has been achieved through bimetallicnanosized particles such as nickel/iron (Ni/Fe) and palladium/iron (Pd/Fe). Batchdegradation of model compounds, trichlroethylene (TCE) and 2,2'-dichlorobiphenyls(DCB), were conducted using bimetallic Ni/Fe and Pd/Fe nanoparticles. Completedegradation of TCE and DCB is achieved at room temperature. Zero-valent iron, as themajor element, undergoes corrosion to provide hydrogen and electrons for the reductivecatalytic hydrodechlorination reaction. The second dopant metals of nickel and palladium(in nanoscale) act as catalyst for hydrogenation through metal hydride formation thatproduces completely dechlorinated final product. Different compositions of bimetallicNi/Fe and Pd/Fe nanoparticles were synthesized and their reactivity was characterized interms of reaction rate constants, hydrogen generation through iron corrosion, andproducts formation. The observed TCE degradation rate constant was two orders ofmagnitude higher than the bulk iron and nanoiron, indicating that the bimetallicnanoparticles are better materials compared to the monometallic iron systems. Longevitystudy through repeated cycle experiments showed minimum loss of activity. The surfacearea-normalized rate constant was found to have a strong correlation with the hydrogengeneration by iron corrosion reaction. A mathematical model was derived thatincorporates the reaction and Langmuirian-type sorption terms to estimate the intrinsicreaction rate constant and rate-limiting step in the degradation process. Bimetallicnanoparticles were also immobilized into the chitosan matrix for the synthesis of ananocomposite membrane reactor to achieve membrane-phase destruction of chlorinatedorganics under convective flow condition. Formation of uniformly distributed nanosizedparticles is confirmed by high resolution transmission electron microscopy. Themembrane-phase degradation results demonstrated similar trends with the previoussolution phase analysis with the observed enhanced reaction rates. The advantage of themembrane system is its ability to prevent the agglomeration of the nanoparticles in themembrane matrix, to minimize the loss of precious metals into the bulk solution phase,and to prevent the formation of precipitated Fe(III) hydroxide. These are due to thechelating effect of the amine and hydroxyl functional groups in the chitosan backbones.

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.