Pillar[n]arenes are a class of macrocycles with outstanding properties given by its electron rich and symmetric cavity, and facile functionalization that allows to tune its solubility and host-guest properties. In this work, the versatility of pillar[n]arenes for the design of porous materials is studied. Pillar[n]arenes are stable to guest removal, giving solvent-free phases and thus resulting in permanent porous structures. From simple ethyl pillar[5,6]arenes, nonporous adaptive crystals are obtained and studied for the recognition and separation of butanol isomers. The cavity size of the pillar[n]arene hosts and the linear or branched characteristic of the butanol isomers influences the assembly of the pillararene to selectively adsorb an isomer. Then, an A1/A2 benzaldehyde-functionalized pillar[5]arene is used as a building block for the synthesis of an imine porous organic cage, which would result in material with intrinsic and extrinsic porosity. Finally, a lipoic acid modified pillar[5]arene is implemented as ligand for nanoclusters, improving their stability. Taking advantage of the cavity of the pillar[5]arene, a host-guest complex is formed, enhancing the optical properties of nanoclusters.

The surface and interface of the metal nanoclusters and semiconducting nanomaterials play a key role in determining the electronic structure and overall photophysical properties. A single strand DNA stabilizes the metal nanoclusters, but it also influences the structural change, solvation free energy, and photophysical properties. On the other hand, surface and interface states in Pb and Cd chalcogenide nanomaterials affect the phonon mediated hot carrier relaxation. We applied DFT and DFT based non-adiabatic dynamics methods to study the surface and interface?s effects on the photoexcited processes. In the first part, we have studied the Ag nanoclusters' photophysical properties that are affected by the structural isomers, redox potential, nucleobase passivation, and cluster size. Ag nanoclusters are shown alternative reduction potential, which makes nanoclusters of singlet spin multiplicity thermodynamically favorable. Besides, the optically bright transition in the range of 2.5-3.5 eV is shown metal to ligand charge transfer. It is modulated by the s+p+d orbital mixing in the hole and electron states. We also simulate the charge transfer from the photoexcited PbS QD to organic dye (PDI) attached to the QD surface. Depending on the linker group and the dipole moment of neighboring passivating ligands, the PDI-QD conformations are varies. In response to structural change, the total dipole moment is modulated, changing its electronic structure and hence the photoexcited electron transfer rate from the PbS QD to PDI. We also investigate the inorganic-inorganic interactions in the PbCl2 bridged PbSe NPL and PbSe|CdSe Janus heterostructure. The energy dissipation rate of hot electrons is slower in NPL than the hot hole, while hot e-h relaxed to the band-edge by ?1.0ps in the QD. The slower relaxation rate is rationalized by a large average intraband energy difference and smaller coupling term. Besides, the hot carriers in the NPL are spatially separated by ?1.00 ps, which is a favorable condition for the carrier multiplication process. In Janus QD, (100) interfacial layer creates a structural mismatch in the CdSe part. Besides, the energy offset between the valance localized on PbSe and CdSe part is minimum in the PbSe Janus QD of an interface of (111) facet.

Il est bien connu que les propriétés optiques des nanoparticules de métaux nobles, en particulier d'or et d'argent, s'écartent fortement de celles de métaux macroscopiques. Pour les tailles comprises entre dix et quelques centaines de nanomètres, elles sont dominées par les plasmons de surface (SP) décrites par des modèles purement classiques. En revanche, les agrégats de quelques dizaines d’atomes se comportent comme des systèmes quantiques, ce qui induit des comportements optiques nouveaux. La structure des nanoparticules et l'environnement diélectrique peuvent affecter les propriétés optiques. Dans cette thèse, j'ai utilisé un microscope électronique à transmission à balayage (STEM) équipé d'un spectromètre à perte d'énergie des électrons (EELS) pour mesurer, en parallèle, les propriétés optiques et structurales de nanoparticules individuelles. Je présente comment des expériences complémentaires (STEM-EELS et absorption optique) sur de petites nanoparticules d'argent triées en taille et encapsulées dans une matrice de silice donnent au premier abord des résultats incohérents: tandis que, d’une part, l'absorption optique ne montre aucun effet de taille entre quelques atomes et environ 10 nm, un décalage en énergie est observé dans les mesures STEM-EELS. Notre interprétation quantitative, fondée sur un modèle mixte classique/quantique qui prend en compte tous les effets quantiques pertinents, a résolu les apparentes contradictions non seulement dans nos données expérimentales, mais également dans celles de la littérature. Notre modèle décrit comment l'environnement local est le paramètre crucial contrôlant la manifestation ou l'absence d'effets de taille quantique. En second lieu, je me suis intéressé à la région purement classique à travers des structureslithographiées de quelques centaines de nanomètres. Bien que les cavités plasmoniques triangulaires aient été largement étudiées dans la littérature, une classification en termes de modes de respiration et de bords plasmoniques manquait. Dans cette étude, les résultats expérimentaux de STEM-EELS, des modèles analytiques et des simulations classiques nous ont permis de décrire la nature des différents modes. / It is well known that the optical properties of nanoparticles of noble metals, in particular gold and silver, deviate strongly from those of macroscopic metals. For sizes between ten and a few hundred nanometers, they are dominated by surface plasmons (SPs) described by purely classical models. On the other hand, clusters of a few tens of atoms behave like quantum systems inducing new optical behaviors. The structure of the nanoparticles and the dielectric environment can affect the optical properties. In this thesis I used a scanning transmission electron microscope (STEM) fitted with an electron energy loss spectrometer (EELS) to measure, in parallel, the optical and structural properties of individual nanoparticles. I present how complementary experiments (STEM-EELS and optical absorption) on sizeselected small silver nanoparticles embedded in silica yield at first inconsistent results: while optical absorption shows no size-effect in the range between only a few atoms and ~10 nm, a clear spectral shift is observed in STEM-EELS technique. Our quantitative interpretation, based on a mixed classical/quantum model which takes into account all the relevant quantum effects, resolves the apparent contradictions, not only within our experimental data, but also in the literature. Our comprehensive model describes how the local environment is the crucial parameter controlling the manifestation or absence of quantum size effects. Secondly, I was interested in the purely classical region through lithographed structures of a few hundred nanometers. Although triangular plasmonic cavities have been widely studied in the literature, a classification in terms of plasmonic modes of breathing and edge was missing. In this study, experimental STEM-EELS results, analytical models and classical simulations enabled us to describe the nature of the different modes.

Gold nanoclusters possess both theoretical and practical importance in the development of ultrasensitive biosensors based on surface-enhanced Raman spectroscopy (SERS). Manipulation of gold nanoclusters in a predictable and reproducible manner for the application of refined biochemical analysis still remains challenging. In this study, high-purity gold nanoclusters are isolated via a simple method based on density gradient centrifugation. Three distinct bands including monomers, small aggregates (2-4 nanospheres), and large aggregates (>5 nanospheres) can be separated via density gradient centrifugation. The isolated gold nanoclusters greatly enhance the Raman intensity of the trapped dye molecules such that single nanocluster detection is feasible. To develop a gold nanoparticle-based biosensor for influenza virus, effort was also made to modify recognition moieties such as aptamers to gold nanoparticles via distinct approaches. The increase of hydraulic diameter and the shift of optical absorbance spectrum indicate the success of surface modification to gold nanoparticles. / Master of Science

Tesis por compendio / Las especies de metal con diferentes tamaños (átomos individuales, nanocristales y nanopartículas) muestran un comportamiento catalítico diferente para diversas reacciones catalíticas heterogéneas. Se ha demostrado en la bibliografía que muchos factores que incluyen el tamaño de partícula, la forma, la composición química, la interacción metal-soporte, la interacción metal-reactivo / disolvente, pueden tener influencias significativas sobre las propiedades catalíticas de los catalizadores metálicos. Los desarrollos recientes de metodologías de síntesis bien controladas y herramientas de caracterización avanzada permiten correlacionar las relaciones a nivel molecular. En esta tesis, he llevado a cabo estudios sobre catalizadores metálicos desde átomos individuales hasta nanoclusters y nanopartículas. Al desarrollar nuevas metodologías de síntesis, el tamaño de las especies metálicas puede modularse y usarse como catalizadores modelo para estudiar el efecto del tamaño sobre el comportamiento catalítico de los catalizadores metálicos para la oxidación del CO, la hidrogenación selectiva, la oxidación selectiva y la fotocatálisis. Se ha encontrado que, los átomos metálicos dispersados por separado y los grupos subnanométricos de metal pueden aglomerarse en nanoclusters o nanopartículas más grandes en condiciones de reacción. Para mejorar la estabilidad de los catalizadores subnanométricos de metal, he desarrollado una nueva estrategia para la generación de átomos individuales y clusters en zeolitas. Esas especies subnanométricas de metales son estables en tratamientos de oxidación-reducción a 550 oC. Siguiendo esta nueva metodología de síntesis, este nuevo tipo de materiales puede servir como catalizador modelo para estudiar la evolución de especies subnanométricas de metales en condiciones de reacción. La transformación estructural de las especies subnanométricas de Pt ha sido estudiada mediante microscopía electrónica de transmisión in situ. Se ha demostrado que el tamaño de las especies de Pt está fuertemente relacionado con las condiciones de reacción, que proporcionan importantes conocimientos para comprender el comportamiento de los catalizadores de metales subnanométricos en condiciones de reacción. En la otra línea de investigación para catalizadores de metales no nobles, he desarrollado varias estrategias generales para obtener catalizadores de metales no nobles, ya sea soportados sobre óxidos metálicos o protegidos por capas delgadas de carbono. Estos materiales muestran un rendimiento excelente para varias reacciones importantes, como la hidrogenación quimioselectiva de nitroarenos, incluso cuando se comparan con los catalizadores de metales nobles convencionales. En algunos casos, los catalizadores de metales no nobles pueden incluso alcanzar selectividades para productos inviables que no ha sido posible conseguir en catalizadores de metales nobles convencionales, que es causado por la diferente ruta de reacción en catalizadores de metales no nobles. Sin embargo, la espectroscopía fotoelectrónica de rayos X a presión ambiente ha revelado que la irradiación de la luz puede modular la selectividad a los alcoholes y los hidrocarburos C2 +, lo que abre una nueva posibilidad para ajustar el comportamiento catalítico de los catalizadores metálicos. Con base en los trabajos anteriores de diferentes aspectos relacionados con catalizadores metálicos heterogéneos, las perspectivas sobre las direcciones futuras hacia una mejor comprensión del comportamiento catalítico de diferentes entidades metálicas (átomos individuales, nanoagrupamientos y nanopartículas) de una manera unificadora también se han dado en esta tesis. / Les espècies metàl·liques de diferents dimensions (àtoms individuals, nanoclusters i nanopartícules) mostren diferents comportaments catalítics per a diverses reaccions catalítiques heterogènies. S'ha demostrat a la literatura que, molts factors que inclouen la mida de la partícula, la forma, la composició química, la interacció amb el suport metàl·lic, la reacció metàl·lica i la interacció amb dissolvents poden tenir influències significatives sobre les propietats catalítiques dels catalitzadors metàl·lics. Els desenvolupaments recents de metodologies de síntesi ben controlades i eines de caracterització avançada permeten relacionar les relacions a nivell molecular. En aquesta tesi, he realitzat estudis sobre catalitzadors metàl·lics d'àtoms únics a nanoclústers i nanopartícules. Mitjançant el desenvolupament de noves metodologies de síntesi, la mida de les espècies metàl·liques es pot modular i utilitzar com a catalitzadors model per estudiar l'efecte de mida sobre el comportament catalític dels catalitzadors metàl·lics per a l'oxidació de CO, hidrogenació selectiva, oxidació selectiva i fotocatàlisi. S'ha trobat que, els àtoms metàl·lics dispersos individualment i els clústers metàl·lics subnanomètrics poden aglomerar-se en nanoclústeres o nanopartícules més grans en condicions de reacció. Per millorar l'estabilitat dels catalitzadors subnanomètrics de metall, he desenvolupat una nova estratègia per a la generació d'àtoms i racimos en zeolites. Aquestes espècies metàl·liques subnanométricas són estables en tractaments de reducció d'oxidació a 550 oC. Després d'aquesta nova metodologia de síntesi, aquest nou tipus de materials poden servir com a model de catalitzador per estudiar l'evolució de les espècies metàl·liques subnanométricas en condicions de reacció. La transformació estructural de l'espècie Pn subnanométrica ha estat estudiada per microscòpia electrònica de transmissió in situ. S'ha demostrat que la mida de les espècies de Pt està fortament relacionada amb les condicions de reacció, que proporcionen idees importants per comprendre el comportament dels catalitzadors de subnanometria en condicions de reacció. En l'altra línia de recerca dels catalitzadors de metalls no nobles, he desenvolupat diverses estratègies generals per obtenir catalizadors de metalls no nobles recolzats en òxids metàl·lics o protegits per capes de carboni primes. Aquests materials presenten un excel·lent rendiment per a diverses reaccions importants, com la hidrogenació quimioelectiva de nitroarenes, fins i tot quan es comparen amb els catalitzadors convencionals de metall noble. En alguns casos, els catalitzadors de metalls no nobles poden fins i tot aconseguir selectivitats a productes no factibles que no s'han pogut assolir en catalitzadors de metall noble convencionals, que es deuen a la via de reacció diferent en catalitzadors de metalls no nobles. No obstant això, s'ha observat una espectroscòpia de fotoelèctria de raigs X amb pressió d'atmosfera que la irradiació lleugera pot modular la selectivitat als alcohols i hidrocarburs C2 +, la qual cosa obre una nova possibilitat per sintonitzar el comportament catalític dels catalitzadors metàl·lics. A partir d'aquests treballs de diferents aspectes relacionats amb els catalitzadors metàl·lics heterogenis, també s'ha donat en aquesta tesi perspectives sobre les futures orientacions cap a una millor comprensió del comportament catalític de diferents entitats metàl·liques (àtoms individuals, nanoclústers i nanopartícules). / Metal species with different size (single atoms, nanoclusters and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that, many factors including the particle size, shape, chemical composition, metal-support interaction, metal-reactant/solvent interaction, can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow to correlate the relationships at molecular level. In this thesis, I have carried out studies on metal catalysts from single atoms to nanoclusters and nanoparticles. By developing new synthesis methodologies, the size of metal species can be modulated and used as model catalysts to study the size effect on the catalytic behavior of metal catalysts for CO oxidation, selective hydrogenation, selective oxidation and photocatalysis. It has been found that, singly dispersed metal atoms and subnanometric metal clusters may agglomerate into larger nanoclusters or nanoparticles under reaction conditions. To improve the stability of subnanometric metal catalysts, I have developed a new strategy for the generation of single atoms and clusters in zeolites. Those subnanometric metal species are stable in oxidation-reduction treatments at 550 oC. Following this new synthesis methodology, this new type of materials can serve as model catalyst to study the evolution of subnanometric metal species under reaction conditions. The structural transformation of subnanometric Pt species has been studied by in situ transmission electron microscopy. It has been shown that the size of Pt species is strongly related with the reaction conditions, which provide important insights for understanding the behavior of subnanometric metal catalysts under reaction conditions. In the other research line for non-noble metal catalysts, I have developed several general strategies to obtain non-noble metal catalysts either supported on metal oxides or protected by thin carbon layers. These materials show excellent performance for several important reactions, such as chemoselective hydrogenation of nitroarenes, even when compared with conventional noble metal catalysts. In some cases, non-noble metal catalysts can even achieve selectivities to unfeasible products which has not been possible to achieve on conventional noble metal catalysts, which is caused by the different reaction pathway on non-noble metal catalysts. Nevertheless, it has been revealed by ambient-pressure X-ray photoelectron spectroscopy that light irradiation can modulate the selectivity to alcohols and C2+ hydrocarbons, which opens a new possibility for tuning the catalytic behavior of metal catalysts. Based on the above works from different aspects related with heterogeneous metal catalysts, perspectives on the future directions towards better understanding on the catalytic behavior of different metal entities (single atoms, nanoclusters and nanoparticles) in a unifying manner have also been given in this thesis. / Liu, L. (2018). Heterogeneous Metal Catalysts: From Single Atoms to Nanoclusters and Nanoparticles [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/113169 / Compendio

Yes / The fabrication of osmium nanoclusters from single atoms has been studied in real-time on B-doped and B-free graphitic surfaces. The dynamics of nucleation on both surfaces are identified, captured, and reported. The nucleation is ca. 2× faster on B-doped surface compared to the B-free surface (38 pm min−1versus 18 pm min−1), suggesting osmium–boron interactions within the nanomaterials.

Clusters e nanoclusters têm recebido grande atenção devido à suas propriedades físicas e químicas, as quais divergem bastante dos materiais na fase bulk. Essas propriedades podem variar de acordo com a composição e tamanho do cluster. Uma compreensão da evolução das propriedades em relação a estes parâmetros é de grande importância para potencializar diversas aplicações, entretanto, esse entendimento permanece insatisfatório. Este trabalho foi dividido em duas etapas, em que a primeira busca investigar parâmetros energéticos, por meio do cálculo da energia de excesso, e estruturais, analisando parâmetro de ordem química, função de distribuição radial central, comprimento médio de ligação e número de coordenação efetiva, dos sistemas ZrnCum-n, ZrnAlm-n, CunAlm-n e ZrnCunAlm-2n para n = 55 e 561 átomos com o incremento n tomado de 1 em 1 para o sistema de 55 átomos e de 20 em 20 para os sistemas de 561 átomos. A segunda etapa consiste de investigar como variam as propriedades energéticas e estruturais do sistema ZrCu em função da evolução do tamanho do sistema. Para alcançar os objetivos propostos, neste trabalho foi usado o algoritmo de otimização global de clusters e nanopartículas basin-hopping Monte Carlo revisado. O potencial de interação atômica utilizado é o método do átomo imerso, que é bastante utilizado na descrição de sistemas metálicos. Os resultados obtidos sugerem que: (i) os sistemas puros apresentaram energia de coesão mais alta que seu análogo material na fase bulk, sugerindo que estes tendem a aglomerar-se formando estruturas bulk. Para os sistemas binários e ternários, foi identificado que todas as composições são energeticamente estáveis devido aos valores negativos obtidos pelo excesso de energia e, para o sistema ZrCu verificou-se a presença de efeitos de tamanho. (ii) Com relação à estrutura, as composições puras estudadas apresentaram simetria icosaédrica. Para o estudo da evolução do tamanho do sistema, Zr e Cu apresentaram estrutura com simetria icosaédrica até a composição de 561 átomos, além deste tamanho a simetria icosaédrica é quebrada. Para os sistemas binários e ternários foi obtido que os átomos tendem a distribuir-se dentro do nanocluster além de apresentarem quebra da simetria icosaédrica apresentando ausência de camadas atômicas ordenadas acompanhada de redução da coordenação efetiva. Os sistemas ZrCu e ZrAl demonstraram seguir a lei de Vegard, enquanto que os sistemas CuAl e ZrCuAl apresentaram desvio da lei de Vegard providos por efeitos eletrônicos, além de apresentarem a presença de efeitos de tamanho. / Clusters and nanocluster have attracted great attention due to their physical and chemical properties, very different from their analogous bulk. These properties can vary with composition and size cluster. An understanding of the properties evolution with respect these parameters is essential to improve several applications. However, this understanding is not complete. This study was piecemeal in two stage, being the first the investigation of energetic properties, by excess energy analisys, and structural properties, by chemical order parameter, radial distribution function, effective coordination number and average bond length, from ZrnCum-n, ZrnAlm-n, CunAlm-n and ZrnCunAlm-2n systems, where n = 55, 561 atoms and the increment n vary in one unit for 55-atoms system and twenty unit for 561-atoms system. The second stage is the investigation of how vary the energetic and structural properties from the size evolution ZrCu system. To do this study, was employed the global optimization algorith for cluster and nanoparticle Revised basin-hopping Monte Carlo, were this method use the classical calculation to determine the total energy of the system. The interatomic potential used was the embedded atom method, that was very usefull to describe metallic systems. Our results suggest: (i) the unary systems present cohesive energy higher than their analogous bulk, that indicate the trend of clusters to form bulk. To the binary and ternary systems, we had that all systems are favorable to form nanoalloys by negative value of excess energy. From ZrCu system, the stability decrease when increase the size of system. With respect the structure, the unary compounds present icosahedral symmetry. From the size-evolution study, the unary compounds present icosahedral symmetry until 561-atoms composition, after this size the icosahedral symmetry is broken. To binary and ternary systems, the atoms trend form mixture into the nanocluster, the icosahedral symmetry is broken with respect the unary compounds and presenting absence of ordered layers followed by effective coordination reduction. The ZrCu and ZrAl systems follow the Vegard law, while the CuAl and ZrCuAl systems present deviation from Vegard law, because electronic effects.

Ce travail de thèse a consisté en l’étude de catalyseurs ultradispersés, composés de clusters nanométriques ou d’atomes isolés (single-atom catalysts, SACs) de métal, une nouvelle classe de catalyseurs faisant actuellement l’objet d’un engouement mondial. Les systèmes Pt/?-Al2O3 et Pt/TiO2 ont été préparés, caractérisés et testés en oxydation de CO et photogénération d’hydrogène, respectivement. Plusieurs méthodes d’imprégnation et de traitement thermique ont été comparées, notamment grâce à l’analyse de la dispersion du platine par microscopie électronique en transmission à balayage (STEM). Pour la préparation de SACs, notre choix s’est finalement porté sur l’imprégnation à humidité naissante d’une faible charge de précurseur Pt(NH3)4(NO3)2, suivie d’une calcination à l’air. L’étude des performances catalytiques et de l’évolution structurale des catalyseurs au cours des réactions a permis de montrer que les atomes isolés (cations) de platine étaient moins actifs que les clusters (réduits) pour les deux systèmes catalytiques étudiés. Dans le cas de Pt/?-Al2O3, des suivis par spectroscopie d’absorption X (XAS) operando en rayonnement synchrotron, spectroscopie infrarouge par réflexion diffuse (DRIFTS) operando et microscopie environnementale (E-STEM) ont montré la formation et la déstabilisation des SACs, cette dernière étant toutefois moindre en conditions oxydantes. En effet, l’oxygène stabilise le platine isolé via la formation de plusieurs liaisons Pt-O-Al comme montré par modélisation DFT, alors que la présence d’un composé réducteur (CO, H2) conduit à la formation de clusters, mobiles sur leur support. Ce travail met en évidence les limites possibles concernant la stabilisation et la mise en œuvre des SACs dans des réactions catalytiques impliquant des conditions réductrices / This PhD work is focused on the study of ultradispersed catalysts, composed of nanometer-sized clusters or isolated atoms (single-atom catalysts, SACs) of metal, a new class of catalysts which are currently the object of worldwide interest. The Pt/?-Al2O3 and Pt/TiO2 systems were prepared, characterized and evaluated for CO oxidation and hydrogen photogeneration, respectively.Several methods of impregnation and thermal treatment were compared, in particular through platinum dispersion analysis using scanning electron microscopy (STEM). For the preparation of SACs, our choice finally turned to the incipient wetness impregnation of Pt(NH3)4(NO3)2 precursor at low loading, followed by calcination in air.For the two catalytic systems of interest, the study of the performances and the structural evolution of the catalysts during the reactions shows that isolated Pt atoms (cations) are less active than their (reduced) cluster counterparts.In the case of Pt/?-Al2O3, operando X-ray absorption spectroscopy (XAS) using synchrotron radiation, operando diffuse reflectance infrared spectroscopy (DRIFTS), and environmental microscopy (E-STEM) allowed us to monitor the SAC formation and destabilization, the latter being however limited in oxidizing conditions. Indeed, the presence of oxygen stabilizes single Pt atoms via the formation of several Pt-O-Al bonds as shown by DFT modeling, whereas the presence of a reducing compound (CO, H2) leads to the formation of Pt clusters, mobile on their support.This work highlights the possible limitations in the stabilization and implementation of SACs for catalytic reactions involving reducing conditions

Les méta-matériaux sont une nouvelle classe de matériaux composites artificiels quiprésentent des propriétés inédites. Ils sont typiquement sous divisés en unité appelées méta-atomes.Un design approprié de ces méta-atomes, architecturés à l’échelle nanométrique, permet d’induire despropriétés aussi extraordinaires qu’un indice de réfraction négatif. Dans ce contexte, nous avonsdéveloppé des particules à patchs, capable de développer des interactions selon des directionsprédéterminées. Des clusters multipodiques fait de ces particules (diélectrique) entourées d’un nombrecontrôlé de satellites plasmoniques (or) ont été développés. Nous nous sommes focalisés sur desclusters isotropes, dérivant de géométries tétraédriques, octaédriques et icosaédriques (trois des cinqsolides de Platon). Pour cela, nous avons utilisé des clusters silice/polystyrène, obtenus parpolymérisation ensemencée en émulsion, qui ont servi de préformes. Ils ont ainsi permis d’obtenir desparticules dont les patchs sont en fait des fossettes au fond desquelles subsiste un résidu de chaînespolystyrène greffées. En modifiant chimiquement ces chaînes, nous avons permis soit l’accrochage aufond de ces fossettes de colloïdes d’or puis leur croissance, soit l’accostage de satellites de silice surlesquels nous avons ensuite fait croître une coquille d’or. La seconde voie à offert un meilleur contrôlede la morphologie des clusters et notamment de la distance entre les satellites d’or (quelquesnanomètres) qui est primordiale pour assurer un couplage plasmonique optimal. Les propriétés desclusters obtenus ont été modélisées et mesurées. / Metamaterials are a novel class of artificial composite materials, typically made of subunit called meta-atoms and exhibiting unusual properties. Such meta-atoms, have to be architecturedat the nanometric level, to induce as extraordinary properties as a negative refractive index. In thiscontext, we developed patchy particles, capable to create interactions along predetermined directions.Multipodic clusters made of those (dielectric) particles surrounded by a controlled number ofplasmonic satellites (gold) were developed. We focused on isotropic clusters deriving fromtetrahedral, octahedral and icosahedral geometry (three of the fifth Platonic solids). For that purpose,we used silica/polystyrene clusters, obtained from seeded emulsion polymerization, as template. Byderiving those clusters, patchy particles bearing dimples containing grafted residual polystyrene chainswere obtained. By chemically deriving those chains, we explored two synthetic pathways, thedecoration of the dimples with gold colloids subsequently grown or the anchoring of silica satellitesonto which gold shells were subsequently grown. The second one was prove to offer a better controlover the cluster morphology as well as the inter-satellites gap (few nanometer) which is pivotal toensure an optimal plasmonic coupling. Then, the optical properties of the as obtained clusters weresimulated and measured.

Nanoscience dominates almost all areas of science and technology in the 21st century. Nanoparticles are of fundamental interest since they possess unique size dependent properties (optical, electrical, mechanical, chemical, magnetic etc.), which are quite different from the bulk and the atomic state. The research work presented in the thesis is on the preparation, characterization and studies on Ir, Os and graphene oxide-based systems. Interconnected Ir and Os nanochains are prepared under environmentally friendly conditions in aqueous media and subsequently used as substrates for surface enhanced Raman scaterring studies and also as electrocatalysts for oxygen reduction and formaldehyde oxidation. Ir and IrOx nanostructures are prepared using borohydride at different temperatures. The nature of interaction of heme proteins with IrOx is studied using spectroscopic techniques. Electrochemical studies on reduced graphene oxide include sensing of biomolecules with high sensitivity and oxygen reduction reaction (ORR) in aqueous alkaline medium. rGO is also used as support for anchoring Ir nanoparticles and the catalyst is used for the oxidation of benzyl amines to corresponding imines. The thesis is divided in to seven chapters and details are given below. Chapter 1 gives an introduction about the synthetic strategies and properties of metal nanostructures. This is followed by literature survey on Ir, Os and graphene oxide-based systems relevant to the present study. Aim and scope of the present investigation is given at the end. Chapter 2 discusses the experimental procedures and characterization techniques used in the present study. Chapter 3 involves the preparation, characterization and studies on interconnected Ir nanochains. Assemblies of small sized nanoparticles forming network-like structures have attracted enormous interest and different metal nanoassemblies have been reported using different procedures. Ir3+ reduction is kinetically not a very favourable process and hence there are not many attempts to synthesize Ir-based nanostructures. Assemblies of interconnected Ir nanoparticles have been synthesized in the present studies using borohydride as reducing agent and ascorbic acid as capping agent, at high temperatures. Polyfunctional capping molecules such as ascorbic acid and vitamin P play important role for the formation of network- like Ir nanostructures. Optical properties of the networks are probed using UV-Vis spectroscopy and evolution of coupled plasmon of Ir nanochains at 418 nm (figure 1) is observed. The nanochains are used as substrates for SERS studies while the catalytic activity is followed for the reduction of nitroaromatics. Electrocatalytic activity of Ir nanochains is exemplified using oxygen reduction and formaldehyde oxidation. Ir nanochains show better electrocatalytic activities than nanoparticles as shown in figure 2. Figure 1. Time dependent UV-Vis absorption spectra of Ir nanoparticles recorded at various time intervals of (a) 5; (b) 15; (c) 30 and (d) 60 minutes of reduction of Ir3+ using borohydride and the corresponding TEM images. Figure 2. Polarization curves for oxygen reduction on (i) Ir nanochains and (ii) Ir nanoparticles in (A) 0.5 M H2SO4 and (B) 0.1 M KOH at a scan rate of 0.005 V/s. Rotation speed used is 1000 rpm. Chapter 4 discusses the preparation of Ir and IrOx using borohydride. The reaction temperature determines the product. Various physicochemical, microscopic and spectroscopic techniques have been used to understand the evolution of nanostructures. Borohydride reduces Ir3+ at high temperatures to form high surface area foams, while at 25oC, it results in an alkaline environment that helps in the hydrolysis of the Ir precursor to form IrOx nanoparticles. Porous IrOx is formed when Ir foams are annealed at high temperatures. Water oxidation has been demonstrated using IrOx nanoparticles and foams. Biocompatibility of IrOx is used to study the nature of interaction of heme proteins and the formation of bioconjugates using spectroscopic techniques. IrOx forms bioconjugates with substantial changes observed in secondary and tertiary structures of proteins. Chapter 5 explores the synthesis of interconnected ultrafine Os nanoclusters and the nanostructured materials are used as SERS substrates. Os nanochains are prepared under environmentally friendly conditions using polyfunctional molecules like ascorbic acid and vitamin P as both reducing agent and capping agent in aqueous media. Small sized (1-1.5 nm) Os nanoparticles spontaneously self-assemble to form clusters of few tens of nm that in turn self-organize to form branched nanochains of several microns in size. The as-formed nanochains show surface plasmon absorption in the visible region 540 nm which make them active substrates for surface enhanced Raman scattering (SERS) studies. High SERS activity is observed for fluorescent analyte, rhodamine 6G and non-fluorescent analyte, mercaptopyridine, with different laser excitation sources. Efficient energy transfer from fluorescent R6G dye to Os nanochains is observed based on steady state and time resolved fluorescence measurements.Figure 3. (I) Time dependent UV-Vis absorption spectra of Os nanochains recorded at different time intervals of (a) 5; (b) 7; (c) 15; (d) 30 and (e) 60 minutes. Inset shows the TEM images of Os nanochains after 60 minutes of reduction. (II) SERS spectra of 4-MPy adsorbed on Os nanochains from (a) 1 mM; (b) 10 µM and (c) 1 µM solutions using 514 nm laser excitation. Chapter 6 discusses the studies based on reduced graphene oxide. Reduced graphene oxide (rGO) is explored as electrodes for simultaneous determination of dopamine (DA), ascorbic acid (AA) and uric acid (UA) at low concentrations useful in medical diagnostics (figure 4A). It is also used as metal-free electrocatalyst for ORR (figure 4B). The use of rGO as a support for anchoring Ir nanoparticles is probed and subsequently the Ir/rGO is used as catalyst for direct aerobic oxidation of benzyl amine derivatives to corresponding imines. Chapter 7 describes the summary of the work and scope for further studies. Appendix 1 discusses the preparation of different Ir nanostructures using simple galvanic displacement reaction on copper foil while appendix 2 describes the preparation of different sized Ir nanoparticles and their electrocatalytic activity towards oxygen reduction reaction