Dissertations / Theses on the topic 'Bimetallic nano'

Nanocatalysis, catalysis using particles on the nanoscale, is an emerging field that has tremendous potential. Nanoparticles have different properties than bulk material and can be used in different roles. Macro sized precious metals, for example, are inert, but nanoparticles of them are becoming more widely used as catalysts. Understanding the manner in which these particles work is vital to improving their efficacy. This thesis focuses on two aspects of nanocatalysis. Chapter 1 begins with a brief introduction into nanotechnology and some of the areas in which nanoparticles are different than bulk particles. It then proceeds into an overview of catalysis and nanocatalysis more specifically. Focus is brought to the definitions of the different types of catalysis and how those definitions differ when applied to nanoparticles. Chapter 2 is in finding an inert support structure to more easily assist in recycling the nanoparticles. Polystyrene microspheres were studied and found to prevent platinum nanoparticles from aggregating in solution and possibly aid in recycling of the nanoparticles. These nanoparticles were used in catalysis, aiding in the reduction of 4-nitrophenol in the presence of sodium borohydride. While the rate decreased by a factor of ~ 7 when using the polystyrene, the activation energy of the reaction was unaltered, thus confirming the inactivity of the polystyrene in the reaction. In Chapter 3, nanocatalysis was studied by examining bimetallic hollow nanoparticles with specific attention to the effect of altering the ratios of the two metals. Ten different bimetallic nanocages were tested in an electron transfer reaction between hexacyanoferrate and thiosulfate. Five PtAg nanocages and five PdAg with varying metal ratios were prepared and studied. It was found that while silver cubes immediately precipitate out of solution when combined with thiosulfate, a small amount of either platinum or palladium allows the particles to remain in solution and function as a substantially more effective catalyst. However, as additional Pt was added the activation energy increased. To obtain a better understanding of the catalysis using bimetallic cages, the evolution of these cages was studied as the 2nd metal was added. Initially the particle edge length increased and then slowly decreased back to the size of the template cubes. The increase in edge length suggests of addition of material to the nanoparticles. This indicated the 2nd metal is on the outside of the cage, which was confirmed using UV-Vis spectroscopy and EDS mapping. By understanding how these bimetallic particles evolve, we may be able to manipulate these synthetic methods to more precisely design nanoparticles for catalysis.

Thesis (Ph.D.)--University of Cincinnati, 2009.
Advisors: Dionysios Dionysiou (Committee Chair), Souhail Al-Abed (Committee Member), George Sorial (Committee Member), Margaret Kupferle (Committee Member). Title from electronic thesis title page (viewed April 22, 2009). Keywords: PCBs; Dechlorination; Pd/Mg; Bimetallic; Reduction pathway; intermediates; aggressive anions; sediment; nano-synthesis; nano-scaling; sulfide poisoning. Includes abstract. Includes bibliographical references.

With the gradual depletion of the non-renewable fossil fuel resources and the emerging environmental concerns, the need of exploring renewable synthesis routes of our daily basic stocks is rising. Due to the large contribution to the global primary energy (up to 40% in some countries), biomass has recently been advocated to be one of the most promising alternatives for fossil fuel. This thesis focuses on the catalytic transformations of biomass or biomass derived molecules into valuable small alcohols such as methanol, ethanol, and propanol, which can be used as both fuel and chemical synthesis intermediates. Novel catalysts with high activity and selectivity toward target products are desperately required in the development of renewable chemical synthesis routes. In the past 200 years, platinum metal catalysts have been widely used in the industry. But nowadays, Pd is attracting increasing attentions due to (i) its similar physicochemical properties to those of Pt, (ii) its higher natural abundance than Pt. Alloying has been demonstrated as an effective method in enhancing the catalytic properties of noble metals. In this thesis, a new and facile method for the preparation of supported bimetallic NPs with tunable compositions is developed. Through the establishment of a type II hetero-junction in support, controllable amounts of metallic atoms can be derived from the reduction of the metal oxide support, with the assistance of a supported noble metal. A series of extremely small Pd-based bimetallic NPs with a variety of modifier atoms at tunable compositions, namely PdFe, PdCo, PdNi and PdZn, have been synthesized by this method. These novel bimetallic NPs are applied to the catalytic conversion of biomass or biomass derived molecules containing repeating vicinal diol units. It is demonstrated that the catalytic performance of Pd in bimetallic phase is governed by the d-band structure. The high degree of d-band filling and high d-band center position favour the selective C-O cleavage in hydrogenolysis of vicinal diol units. On the other hand, the selective C-C cleavage can be achieved by lowering the d-band filling of the Pd-based bimetallic NPs. The specificity of C-C bond rupture over that of C-O increases in order of PdZn < PdNi < PdCo < PdFe, with progressive d-band filling reduction, eventually reaches 95% in a series of vicinal diols hydrogenolysis. As a result, small alcohols are produced with high selectivity as the degradation products of biomass molecules when PdFe bimetallic NPs are employed as catalyst. Conversely, by incorporating Co atoms at high concentration, PdCo exhibits a high selectivity in breaking C-O bond of ethylene glycol due to the raised d-band center position and gives ethanol as the main product. Pd@Zn bimetallic NPs with an imperfect core(Pd)-shell(Zn) structure were used in a methanol synthesis route from biomass transformation via CO₂ hydrogenation (CO₂/H₂ is produced from low temperature reforming of biomass resource). The Zn shell not only enhances the catalytic activity of Pd metal towards methanol synthesis, but also suppresses the reverse water gas shift (RWGS) reaction in which CO is produced as a by-product. Methanol can be produced as the main product over CO on the Zn rich Pd@Zn surface, even at low pressure. The methanol turnover frequency (TOF) on the exposed Pd site reaches 1.9 ×10^-1 s^-1 with a selectivity of 70% at 2 MPa. The enhancement is attributed to the increasing d-band filling of Pd@Zn bimetallic NPs by the progressive decoration of Zn on Pd surface, which selectively stabilizes the precursor of methanol (HCOO) over that of CO (COOH). Also, the PdZn catalyst with high ability in dissociating H2 reduces the activation barrier for methanol synthesis. The results presented in this thesis, for the first time, signify the possibility of fine-tuning of product specificity of biomass conversion simply by rationally modifying the electronic properties of the Pd-based catalysts. More importantly, these catalysts will help to diversify the energy generation and relieve our dependence on fossil fuels.

The dissertation is split into two parts. The first part will be focused on changes in material properties found at the nanoscale, as miscibility and electronic structure can change significantly with size. The formation of classically-immiscible bimetallic nanoparticles (BNPs) becomes favorable at the nanoscale and novel catalytic properties can emerge from the bimetallic alloying. The formation of alloyed and non-alloyed BNPs is achieved through pulse laser ablation (PLA) and a significant increase in catalytic activity is observed for both. Recently discovered, the increased activity in the non-alloyed BNPs, deemed multicomponent photocatalysis, is examined and the proposed mechanism discussed. The second part of the talk will focus on thermal barrier coatings (TBCs), which are advanced, multi-layered coatings used to protect materials in high temperature environments. MCrAlY (M=Ni, Co) bond coats deposited via atmospheric plasma spray (APS) are intrinsically rough and initially the roughness provides a high surface area platform for the mechanical interlocking of the yttria stabilized zirconia (YSZ) top coat, which provides the bulk of the thermal insulation. After high temperature exposure, a protective oxide scale forms at the top coat/bond coat interface however the convex asperities of the bond coat can grow non-α-Al2O3 type oxides that can be detrimental for coating lifetime. A surface modification technique that removes the asperities while leaving intact the concavities is used to examine the role that roughness distribution has on 1100°C APS coating lifetime. Lastly, recent work validating a modelling strategy for evaluating 900°C TBC lifetimes, which can typically surpass 25 kh, is presented. Differences in coating-substrate interdiffusion behavior over 5-20 kh of 900°C exposure are discussed and reproduced with Thermo- Calc/DICTRA for three superalloys (1483, 247, X4) deposited with high velocity oxy fuel (HVOF) NiCoCrAlY coatings.

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

L'objectif principal de cette recherche est le développement de méthodes analytiques utilisant une technique de séparation couplée à la spectrométrie de masse pour l'analyse de complexes de fer de faible poids moléculaire et une technique de single-particle ICP MS pour la détection de nanoparticules bimétalliques.Dans la première partie, une méthode utilisant la chromatographie liquide avec spectrométrie de masse à double détecteur, spectrométrie de masse (MS) à haute résolution par électrospray (HRAM) et spectrométrie de masse à couplage inductif (ICPMS), a été développée pour les complexes du fer (Fe) de faible poids moléculaire, appelés 'sideophore', dans un échantillon d'un sol. La complexité des échantillons étudiés, les faibles concentrations et la labilité des analytes ont posé un défi dans le développement de méthodes pour leur identification et leur quantification. Pour éliminer la matrice, une extraction en phase solide (SPE) a été développée dans des conditions acides pour purifier la majeure partie des complexes 56Fe-sidérophore et concentrée par évaporation. Les complexes 56Fe-sidérophore ont été identifiés par chromatographie d'exclusion stérique rapide (FastSEC) - Orbitrap MSn sur la base de la masse moléculaire exacte (+ 1 ppm) et de la fragmentation MS2 ou MS3. Leur capacité à échanger facilement le 56Fe naturel contre le 58Fe ajouté a été démontrée par SEC avec détection par l'ICP MS et l'ESI MS. La méthode a été appliquée à l'analyse de tourbe prélevée dans la partie orientale des montagnes pyrénéennes françaises. Dix-neuf sidérophores appartenant à quatre classes différentes ont été identifiés et quantifiés sans avoir besoin d'un standard authentique. Les résultats ont été validés à l'aide de la détection ICP MS du fer en comparant la somme des complexes de fer déterminés par échange isotopique - ESI MS dans chaque pic observé par FastSEC-ICP MS.Dans la deuxième partie du manuscrit, une méthode utilisant la spectrométrie de masse à plasma à couplage inductif -ICP-MS en mode particule unique (SP-ICP-MS) et en mode conventionnel couplée au fractionnement d'écoulement de champ (FlFFF) a été développée. Les conditions de synthèse de nanoparticules bimétalliques (BNP) Ag-Au ont été optimisées pour appliquer celles-ci à la détection colorimétrique basée sur le concept d'agrégation. Les BNP Ag-Au, synthétisés par la réduction par le citrate des ions Ag et Au, ont été utilisées comme capteurs pour la détection du Co2+. Pour mieux comprendre la détection colorimétrique du Co2+ à l'aide de BNP Ag-Au, divers mélanges de solutions ont été étudiés, notamment : (i) uniquement des BNP Ag-Au ; (ii) BNP Ag-Au avec thiosulfate; (iii) BNP Ag-Au avec thiosulfate et éthylènediamine; et (iv) Ag-Au BNPs avec thiosulfate, Co2+ et éthylènediamine. SP-ICP-MS a été utilisé pour déterminer la taille du noyau, la distribution de taille et la concentration en nombre de particules, ainsi que l'hétérogénéité des particules synthétisées en utilisant diverses concentrations de citrate et un rapport de métal. FlFFF-ICP-MS a également été utilisé pour observer la taille hydrodynamique et le rapport d'intensité du signal de Ag et Au dans les BNP et donc pour étayer les informations obtenues à partir de SP-ICP-MS. La combinaison des techniques proposées dans des conditions appropriées a permis de surveiller la réaction de détection colorimétrique. Les informations supplémentaires du fractogramme fournies par FlFFF-ICP-MS ont également été utiles pour comprendre l'agrégation des BNP due au complexe [Co(II)(en)3]2+ autour de la surface des BNP. En outre, par rapport à la détection colorimétrique classique, la limite de détection (LOD) pour la détection des ions Co2+ a été réduite de 20 fois, du niveau ppb au niveau ppt
The research focuses on an analytical method development using chromatography coupled to mass spectrometry for the analysis of low molecular weight iron complexes. In the second part, the study explores the utilization of bimetallic nanoparticles for Co2+ detection.In the first part, a method using liquid chromatography with two detector mass spectrometry, i.e., electrospray high-resolution accurate mass (HRAM) mass spectrometry (MS) and inductively coupled mass spectrometry (ICP-MS), was developed for the analysis of low molecular weight iron (Fe) complexes, called ‘siderophores'. The complexity of the samples, their low concentrations, and the lability of the iron complexe were challenges in the development of methods for their identification and quantification. For the sample clean-up, solid phase extraction (SPE) using acidic conditions was developed to purify the samples, followed by evaporation to dryness. The individual 56Fe-siderophore complexes were identified by fast size-exclusion chromatography (FastSEC) - Orbitrap MSn based on the exact molecular mass (+ 1 ppm) and MS2. Their capability of exchanging the natural 56Fe with the spiked 58Fe was demonstrated by SEC with ICP-MS and ESI-MS detection. The method was applied to the analysis of peat collected in the Eastern part of the French Pyrenean mountains. Nineteen siderophores belonging to four different classes were presumptively identified and quantified. The results were compared with ICP-MS detection of iron and matching of the sum of the moles of iron complexes determined by the isotopic- ESI-MS within each peak as eluted from the fastSEC column.In the second part, a method using inductively coupled plasma mass spectrometry in the single particle mode and the conventional mode coupled to a flow field flow fractionation was developed to select suitable conditions for the synthesis of Ag-Au bimetallic nanoparticles and to monitor the colorimetric changes due to aggregations. Ag-Au BNPs, synthesized by using citrate reduction of Ag and Au ions, were used as sensors for the detection of Co2+. To better understand the colorimetric sensing of Co2+ using the Ag-Au BNPs, various mixtures were studied, viz. (i) only Ag-Au BNPs; (ii) Ag-Au BNPs with thiosulfate; (iii) Ag-Au BNPs with thiosulfate and ethylenediamine; and (iv) Ag-Au BNPs with thiosulfate, Co2+ and ethylenediamine. SP-ICP-MS was used to determine the core size, size distribution, and number concentration, as well as the heterogeneity of the particles synthesized by using various citrate concentrations and metal ratios. Fl-FFF-ICP-MS was also used to observe the hydrodynamic size and the Ag: Au signal intensity ratio of the BNPs to support information obtained from the SP-ICP-MS. The combination of the proposed techniques has been applied to monitor the reaction during colorimetric sensing. Additional information from fractograms provided by Fl-FFF-ICP-MS was also useful for the understanding of the aggregation of BNPs arising from the [Co(II)(en)3]2+ complex surrounding the surface of the BNPs. Furthermore, when compared to colorimetric sensing, the limit of detection for Co2+ ion, using the BNPs and SP-ICP-MS, were 20-fold lower, decreasing from ppb to ppt levels

Depuis quelques dizaines d'années, l'élaboration de matériaux nanostructurés tend de plus en plus à se développer. En effet, ces matériaux présentent souvent des propriétés intéressantes et en particulier des propriétés mécaniques surprenantes vis-à-vis de leurs homologues sous forme massive. Les métaux nano-maclés ou nano-lamellaires par exemple, sont connus pour avoir une bonne résistance mécanique, une bonne stabilité thermique et une excellente résistance aux radiations. Au fur et à mesure que l'espacement entre les interfaces diminue, leur densité augmente de manière significative et les propriétés macroscopiques du matériau sont de plus en plus dépendantes des interactions défaut-interface. Dans ce contexte, nous avons étudié, via des simulations atomistiques, la formation de macles de déformation et les mécanismes d'interaction d'une macle nouvellement formée avec une interface préexistante (un joint de macle ou une interface entre 2 métaux), pour une configuration modèle de film mince auto-supporté. Des premiers résultats montrent l'influence de marches de surface sur le maclage, pour un cas modèle sans interface. Puis nous avons identifié un mécanisme inédit aboutissant à la formation d'une dislocation de Lomer suite à l’interaction d'une macle en formation avec un joint de macle préexistant. En faisant varier la densité de défauts de surface, nous montrons l'influence particulière d'un joint de macle sur la taille et le nombre de macles formées. Enfin, pour les systèmes bimétalliques Cu/Ag, nos résultats mettent en évidence le rôle des dislocations d'épitaxie (à l'interface) dans la nucléation et l'extension des macles ainsi qu'une influence directe du type d'interface considéré sur la propagation de ces macles
For several decades, the elaboration of nano-structured materials tends to develop more and more. Indeed, these materials often show interesting properties, and in particular surprising mechanical properties when compared to their bulk counterparts. For example, nano-twinned or nano-layered metals are known to have ultra-high mechanical strength, good thermal stability, and very good radiation resistance. As the interface spacing decreases to the nanometer-scale, the density of interfaces increases significantly and subsequently the macroscopic properties become largely governed by the interface-defect interactions. In that context, we have studied deformation twin formation and mechanisms of interaction between a new formed twin and a preexisting interface (a twin boundary or a bimetallic interface), using atomistic simulations and a thin film model configuration. First results show the influence of surface steps on mechanical twinning, for a model system without interface. Then we identify a new mechanism leading to the formation of a Lomer dislocation, following the interaction of a newly formed twin and a preexisting twin boundary. By varying the density of surface defects, we show the particular influence of a preexisting twin boundary on twin size and number. Finally, for the Cu/Ag bimetallic system, our results highlight the role of epitaxial dislocations (at the interface) in twin nucleation and extension as well as a direct influence of the interface type in twin propagation

Les réserves de combustibles fossiles diminuent et leur utilisation illimitée depuis la révolution industrielle a généré de profonds changements du climat, notamment des cycles de la température atmosphérique. Stocker l'énergie solaire sous forme d'hydrogène produit par dissociation de l'eau est un moyen idéal pour combattre le réchauffement climatique. Les matériaux de la famille des «metal organic framework» (MOF) commencent à être utilisés comme photo-électrocatalyseurs, notamment pour la photo-dissociation de l'eau. Leur porosité extrêmement élevée et leur grande polyvalence, tant chimique que structurelle, les désignent comme des candidats potentiels pour faciliter l'absorption du rayonnement solaire et catalyser la dissociation de l'eau dans les cellules photoélectrochimiques. En contrôlant la composition chimique et le dopage du linker utilisé dans le MOF, il est possible d'ajuster l'énergie de la bande interdite, de favoriser la fonctionnalisation sur des substrats très variés ou encore d'ajuster leur résistance à la corrosion dans divers environnements chimiques. Ce sont donc des matériaux d'un grand intérêt pour la catalyse, l'électrocatalyse ou la photo-électro-catalyse. D'autre part, le TiO₂ nano-structuré, par exemple sous forme de tapis d’épaisseur micrométrique de nanotubes ou de nanofils, parfois appelé TNA, est un matériau bien adapté à la construction de photoanodes pour le dégagement d'oxygène en milieu aqueux. Il a déjà été largement étudié et décrit dans la littérature. Au cours de notre thèse, nous avons fabriqué des matériaux composites constitués de MOF de métaux de transition (Ni, Co, Fe) déposés sur TNA (TDNR et TNTA). Pour cela, nous avons utilisé une méthode électrochimique d'électrodéposition. Cela nous a permis de déposer des nanoparticules métalliques sur du TNA à potentiel fixe - 1,0 V puis de les transformer par réaction chimique avec des ligands organiques (BTC, BDC, et 2MZ) par voie thermo-thermique. Les matériaux obtenus présentent une activité électrocatalytique significative et une excellente durabilité photoélectrochimique. Ces matériaux composites ont été utilisés avec succès comme phase active dans des photo-électrodes pour la réaction de dégagement d'oxygène moléculaire (OER)
The fossil fuel reserves are dwindling and their unrestricted use has generated profound changes in Earth's surface temperature and climate. Storing solar energy in the form of hydrogen produced by dissociation of water is an ideal way to mitigate global warming. Materials from the “metal organic framework” (MOF) family are starting to be used as photo-electrocatalysts, especially for photo-dissociation of water. Their extremely high porosity and their great versatility, both chemical and structural, designate them as potential candidates to facilitate the absorption of solar radiation and catalyze the dissociation of water in photoelectrochemical cells. By controlling the chemical composition and doping of the linker used in the MOF, it is possible to adjust the band gap energy, to favor the functionalization on very varied substrates or even to adjust their resistance to corrosion in various chemical environments. They are therefore materials of great interest for catalysis, electrocatalysis or photo-electro-catalysis. On the other hand, nano-structured TiO₂, for example in the form of nanotube or nanowire mats, sometimes called TiO₂ nanoarray (TNA), is a material very suitable for the construction of photoanodes for the evolution of oxygen in aqueous medium. It has already been extensively studied and described in the literature. During our thesis, we manufactured composite materials made up of MOFs of transition metals (Ni, Co, Fe) deposited on TNA (network of nanotubes or nanowires). For this we used an electrochemical method of electrodeposition (cyclic voltammetry). This allowed us to deposit metallic nanoparticles on TNA with fixed potential - 1.0 V and then transform them by chemical reaction with organic ligands (1,3,5-benzenetricarboxylic acid, BTC, 1,4-benzenedicarboxylic acid, BDC and imidazole, 2MZ) by thermal-thermal route. The materials obtained exhibit significant electrocatalytic activity and excellent photoelectrochemical durability. These composite materials have been successfully used as an active phase in photo-electrodes for the oxygen release reaction (OER)

Récemment, les nanostructures de polymères conjuguées π (CPN) ont émergé comme une nouvelle classe de catalyseurs pour diverses applications photocatalytiques comme le fractionnement de (ou photosplitting) de l’eau, la réduction du CO2, le traitement de l’eau (dégradation des polluants organiques et réduction de métaux lourds). Parmi la famille des polymères conjugués, le polypyrrole (PPy) a été le plus étudié en raison de sa stabilité environnementale, de sa synthèse facile, de son excellente stabilité. Dans cette thèse, les nanostructures PPy ont été synthétisées par différentes méthodes : polymérisation chimique dans des matrices souples (mésophases hexagonales ou lamellaires) et polymérisation par radiolyse. Ces nanostructures PPy présentent une activité photocatalytique prometteuse pour la dégradation de polluants organiques (phénol et méthylorgange) sous lumière visible et leurs activités sont supérieures à celle du PPy-bulk (PPy massif). De plus, nous avons modifié TiO2 avec du PPy nanostructuré pour la photodégradation de polluants organiques.Le nanocomposite montre une augmentation importante des performances photocatalytiques sous UV et lumière visible par rapport au TiO2 et PPy seuls pour le traitement de l’eau et de l’air. La production d'hydrogène vert par fractionnement photocatalytique de l'eau offre un moyen prometteur pour résoudre les problèmes d'environnement et d'énergie. Dans cette thèse, nous avons montré que les nanostructures depolypyrrole modifiées avec des nanoparticules mono et bimétalliques (Pt, Ni, Pt-Ni) sont très actives pour la génération d'hydrogène et qu'un effet de synergie est obtenu en alliant Pt avec Ni. Enfin, différentes nanostructures ternaires à base du composite PPy-TiO2 modifié de manière contrôlée avec des nanoparticules de platine ont été développées ((Pt-PPy) -TiO2, (Pt-TiO2)-PPy et Pt-(PPy-TiO2)). L'activité photocatalytique de Pt-(PPy-TiO2) pour la génération d'hydrogène sous UV et lumière visible est très élevée
Recently, π-conjugated polymer nanostructures (CPNs) emerge as a new class of catalysts for various photocatalytic applications such as water splitting, CO2 reduction, water treatment (degradation of organic pollutants and heavy metals reduction). Among the family of CPs, polypyrrole PPy has been the most extensively investigated owing to its environmental stability, facile synthesis, excellent stability. In this thesis, PPy nanostructures were synthesized by different methods: chemical polymerization by soft templates (hexagonal or lamellar mesophases) and polymerization by radiolysis. These PPy nanostructures exhibit promising photocatalytic activity for organic pollutants (phenol and methyl organge) degradation under visible light and their activities are higher than that of PPy- bulk.Besides, we modified TiO2 with nanostructured PPy for photodegradation of organic pollutants (methy orange and phenol as model water pollutants and toluene as air pollutant). The nanocomposite shows an important increase of the photocatalytic performance under UV and visible light compared to bare TiO2 and PPy. This work offers a facile and cheap way to fabricate the heterojunction in organic-inorganic hybrid materials interface and the composite nanomaterials represents a promising photocatalyst for water treatment and indoor application. In another hand, green hydrogen production by photocatalytic water splitting offers a promising way to solve environment and energy issues. In this thesis, we have shown that modified conjugated polymer polypyrrole nanostructures with mono- and bimetallic (Pt, Ni, Pt-Ni) nanoparticles are very active for hydrogen generation, and that a synergistic effect is obtained by alloying Pt with Ni. Lastly, different ternary nanostructures based on PPy-TiO2 composites with controlled active sites modification with Pt nanoparticles were developed ((Pt-PPy)-TiO2, (Pt-TiO2)-PPy and Pt-(PPy-TiO2)). The photocatalytic activity of Pt-(PPy-TiO2) for hydrogen generation under UV and visible light is very high and drastically surpasses those of (Pt-PPy)-TiO2 and (Pt-TiO2)-PPy

碩士
國立屏東科技大學
環境工程與科學系所
99
Chlorinated organic compounds are widely used in chemical, agricultural, and pharmaceutical industries. However, if the storage, use, and disposal of those compounds are not properly handled, they may leak into soil, and further pollute the aquifer. Chlorinated solvents due to their high acute toxicity and bioaccumulation cause environmental pollution and are harmful to human body. In this study, some modification techniques of nano zero valent iron (NZVI) were utilized to enhance the degradation of perchloroethylene (PCE). The experimental design included four stages. The first one was to select NZVI as the reactive materials for degradation of PCE. The second one was to coat palldium (Pd) onto NZVI as surface active agents to synthesize the nano-Pd/Fe bimetallic particles (nano-Pd/Fe). The third one was to employ the dispersed technology to raise the dispersion of NZVI using carboxymethyl cellulose (CMC) as dispersant. And the last one was to add CMC in solution to enhance the dispersion of nano-Pd/Fe. The average size, measured by particle size analyzer, of lab-synthesized NZVI, dispersed NZVI, nano-Pd/Fe (weight ratios of Pd to Fe of 1:100, 1:250, 1:500) and dispersed nano-Pd/Fe were between 101.5 to 111.1 nm. NZVI had the lowest specific surface area of 38.04 m2 g-1 and nano-Pd/Fe 1:100 had the largest one of 56.05 m2 g-1. The specific surface area of nano-Pd/Fe increased with higher Pd contents. In the PCE blank tests, PCE concentration did not obviously varied under various test conditions. Addition of CMC and buffer solution had little effects on PCE concentration and therefore would not interfere with the subsequent batch tests. For the tests of PCE degradation with NZVI and various proportions of nano-Pd/Fe, NZVI did not fully degrade PCE while various proportions of nano-Pd/Fe (1:100, 1:250, 1:500) did completely degrade PCE. It showed that the reduction capacity of nano-Pd/Fe on PCE degradation was obviously higher than that of NZVI. The pseudo first order reaction rate constant (kobs) of NZVI and nano-Pd/Fe (1:100, 1:250, 1:500) were 0.14, 2.55, 1.51, 1.59 hr-1, respectively. The more the amount of Pd contents on Pd/Fe particles, the higher their degradation capacity on PCE. For the tests of dispersed NZVI and nano-Pd/Fe on PCE degradation, both of 2.5 g and 5 g dispersed NZVI and 5 g dispersed nano-Pd/Fe was able to entirely degrade PCE. The kobs of various amounts of dispersed NZVI (5 g, 2.5 g, 1 g) and dispersed nano-Pd/Fe (5 g) were 2.88, 1.68, 0.62, and 10.45 hr-1, respectively. It showed that nano particles with dispersant could enhance their degradation capacity on PCE. For the tests of various pH buffer on PCE degradation, PCE was completely degraded with 5 g of Pd/Fe at reaction time of 3 min of the first sampling at pH buffer of 4, 7, and 8. At pH buffer equal to 9, PCE degradation with NZVI and nano-Pd/Fe was minimal. PCE As the amount of nano-Pd/Fe reduced to 1 g, PCE was also fully degraded at reaction time of 80 min at pH buffer of 8 with kobs equal to 3.08 hr-1 which was higher than that (2.55 hr-1) of 5 g nano-Pd/Fe without pH buffer. The kobs value of 0.31 hr-1 for 5 g NZVI at pH buffer of 8 was also higher than that (0.14 hr-1) without pH buffer. The concentration of Cl- released from PCE degradation was close to the theoretical release amount of Cl-. The higher the PCE degradation, the greater the Cl- concentration releases. In this study, dechlorinated by-products were not detected. The contents on the surface of nano particles measured by SEM-EDS showed no obvious differences under various test conditions. The surface morphology of nano particles observed by SEM also showed chain-like distribution and no significant variations between pre-reacted and post-reacted with PCE. With FTIR identification, some differences at wave number of 620 and 1110 cm-1 were observed on the surface of nano particles pre- and post-reacted with PCE. To solve the aggregation phenomenon of NZVI with dispersant will greatly enhance its reduction capacity on pollutants. NZVI modification with Pd plating and CMC dispersant to form dispersed nano-Pd/Fe is feasible and can significantly enhance the degradation of PCE that can provide an alternative for in-situ remediation of chlorinated solvents. Keywords: perchloroethylene (PCE), nano zero valent iron (NZVI), palladium/iron bimetal, carboxymethyl cellulose

碩士
義守大學
生物技術與化學工程研究所碩士班
94
This research is aimed at studying the preparations of anodic nano-catalysts for direct methanol fuel cells by a method of modified polyol reduction, utilizing ethylene glycol (EG), diethylene glycol (DiEG) and triethylene glycol (TriEG) as reducing agent and solvent. Metals such as Sn, W, Mo and Ru, as well as carbon black and multi-walled carbon nano-tubes were employed for the fabrication of supported Pt-based bimetallic catalysts to explore effects on the anodic behaviors of methanol electro-oxidation and CO tolerance. Electrochemical investigations involving cyclic voltammetry, chronoamperometry and chronopotentiometry coupled with analytical tools of x-ray diffraction (XRD), transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) were undertaken to establish a novel technology to prepare nano-catalysts most appropriate for DMFC anodes. It was found that catalysts fabricated by TriEG as reducing agent and multi-walled carbon nanotube as support exhibited far better anodic behaviors than those prepared by DiEG and EG and carbon black, respectively. This is attributable to the smaller particle size and better dispersion obtained with TriEG and multi-walled carbon nanotube. Pt-Sn/MWCNT catalysts exhibited the most superior anodic behaviors among the carbon black- or MWCNT-supported alloys of Pt-Sn, Pt-W, Pt-Mo and Pt-Ru. The particle size of the alloys prepared ranged from 3 to 6 nm, proving that the preparation method developed is highly effective to fabricate nano-catalysts. In view of the fact that particle size and size distribution depend on the rate of particle nucleation, microwave irradiation of the precursor solutions was sought in order to enhance reducing reaction. As a result, the microwave-irradiated samples exhibited better anodic properties in terms of methanol electro-oxidation and drastically shorten processing time than those heated in conventional oven. Fabricated in this manner, the TriEG-prepared catalysts also exhibited better anodic behaviors. Thus, microwave irradiation may prove to be a promising method to fabricate anodic nano-catalysts for DMFC.

碩士
國立中央大學
環境工程研究所
100
Zerovalent iron and bimetallic iron have been studied mostly for the degradation of chlorinated compounds in aqueous phase. In this study, laboratory synthesized particles of nano zerovalent iron and commercial bimetallic iron were applied to investigate the reduction kinetics and degradation mechanisms of pentachlorophenol (PCP) spiked sandy soil. Degradation of PCP by nZVI and BioCAT follows the first-order kinetics. The 98% PCP removal efficiency from soil slurries in contact with nano zerovalent iron (nZVI) was mostly attributable to adsorption to nZVI surfaces and only 4% was due to dechlorination. By comparison, approximately 70% dechlorination rate were achieved along with 90% PCP removal efficiency with BioCAT dosage of 600 mg after 21 days of treatment. Possible explainations for the differences in the reaction rates between iron and bimetallic iron may involve competitive sorption of chlorinated phenols and reactive hydrogen on iron and catalytic surfaces as well as the effects of sorption on corrosion. PCP dechlorination was confirmed by the appearance of the intermediate products as well as chloride release. Additionally, the increase of pH values and rapid decrease of ORP values during the reaction also proved reductive dechlorination of PCP. The lower chlorinated phenols and the endproduct including three TeCP isomers; four TrCP isomers; four DCP isomers; two MCP isomers and phenol by BioCAT were found. The intermediates by nZVI contained one TeCP isomer, one TCP isomer. The stepwise dechlorination pathways of PCP by nZVI and BioCAT were proposed in this study. After reductive dechlorination reactions, these intermediates are less toxic than PCP. Furthermore, these lower chlorinated phenols can be biodegraded or photodegraded more easily than PCP in the environment. These findings indicate that using BioCAT with mild temperature and no pH adjustment could have implications for field treatment of PCP-contaminated soil.

碩士
國立屏東科技大學
環境工程與科學系所
100
The aim of this study is to investigate the degradation efficiency of target pollutant, perchloroethylene (PCE), by nano-palladium/iron (Pd/Fe) bimetallic metal particles enhanced by electrolysis. The experiments were divided into four stages. The first stage was to characterize the properties of quartz sand and nano-Pd/Fe particles. The second stage was to conduct the batch tests under various pH values (pH 8-9) on the effects of PCE degradation with nano-Pd/Fe. The third stage was to observe the transport behaviors of solutes through the porous media in a bench-scale sand box. And the fourth stage was to identify the variations of nano-Pd/Fe before and after the reaction with PCE by SEM-EDS and FTIR analysis. The average size and specific surface area of lab-synthesized nano-Pd/Fe particles were 111.1 nm and 56.05 m2 g-1, respectively. The absorption peaks of nano-Pd/Fe analyzed by the X-ray diffraction detector (XRD) only identified Fe. That may be due to the trace amount of Pd on bimetallic metals. For the tests of various pH values (pH 8-9) on PCE degradation with nano-Pd/Fe, the efficiency decreased with higher pH values. The concentration of Cl- released from PCE degradation was close to the theoretical values. The PCE degradation levels were positive correlated with the release amounts of Cl-. In this study, the by-products of PCE degradation such as trichlorethylene (TCE), cis-1,2-dichloroethylene (cis-1,2-DCE), trans-1,2-dichloroethylene (trans-1,2-DCE), 1,1-dichloroethylene (1,1-DCE), and vinyl chloride (VC) were not detected. Via the tracer tests, the average residence time was about 1.7 times higher than the theoretical value. For the test of permeable reactive barrier (PRB) packed with nano-Pd/Fe on PCE degradation, the duration of reactivity of nano-Pd/Fe could be maintained about 28 hr which was around 2 to 4 times higher than that of nano zero valent iron. During the tests, ORP values were steadily maintained below -300 mV in the PRB showing a reduction state was kept in the system. Dechlorination of PCE with nano-Pd/Fe particles were identified by the significant increase of Cl- concentration. The test of nano-Pd/Fe PRB enhanced by electrolysis on PCE degradation, H+ released near the anode was able to acid-washed the surface of Pd/Fe particles to increase their reactivity. The results showed that PCE was not completely degraded by the nano-Pd/Fe particles. The reactivity of Pd/Fe was observed to maintain about 16 to 20 hr. Therefore, more researches on the aspects of current, potential, and electrolyte to the performance of electrolysis enhanced PRB packed with nano-Pd/Fe technology are needs to facilitate its application to in-situ remediation of groundwater contaminated by chlorinated solvents. From the images observed by SEM-EDS, the surface morphology of nano-Pd/Fe particles displayed chain-like structure and irregular flakes pre-reacted and post-reacted with PCE, respectively. The spectrum of fresh nano-Pd/Fe particles analyzed by FTIR showed that a strong and broad absorption signal ranged from 3200 to 3500 cm-1 was identified to be O-H and at 1539, 1385, 967 cm-1 to be the nitro compounds (NO2), alkane (CH3), and alkene (C = CH), respectively. Finally, a signal ranged from 600 to 800 cm-1 was C-Cl. Keywords: perchloroethylene, nano-palladium/iron, tracer, permeable reactive barrier, electrolysis

碩士
國立臺灣科技大學
化學工程系
97
This investigation mainly consists of two topics: (a) development of novel, bimetallic nanocatalyst PtIr/C and employing nanocatalyst in hydrogen peroxide oxidation reaction (HOPR). (b) Fabrication of the mini-biosensor with the homogeneous catalyst/enzyme composite structure by electrophoresis deposition (EPD) method. The crystalline and particle size of nanocatalyst were investigated by XRD and TEM, respectively. The catalytic activity was obtained by the amperometric determination of HOPR. The studies of synchrotron based- X ray absorption spectroscopy (XAS) and density functional theory (DFT) calculation demonstrated that the addition of Ir atom modify the d band electronic configuration of Pt atom and enhance the nanocatalyst functionality, consequently promote the HOPR activity. Furthermore, the HOPR mechanism on the catalyst surface has been proposed and the “deprotonation“step was considered to be rate determining step via this investigation. Moreover, EPD method has been employed to simultaneously deposit the nanocatalyst and enzyme onto the electrode surface. The depth profile analysis of ESCA provided the evidences that EPD method enables to create the homogeneous nanocatalyst/enzyme composite domain. The long term stability and the low value of Michaelis-Menten constant ( Kmapp =5.68 mM ) revealed that the composite matrix provide a stable and three dimensions structure. After the parameter optimization, the fabricated mini-biosensor showed a linear detection of glucose ranges from 2 mM to 20 mM with a detection limit of 0.1 mM and the maximal sensitivity of 2.89 μA/mM．cm2 (R2=0.995, R.S.D. =3.26%, N=3). Overall, EPD method has been used for fabricating the homogeneous nanocatalyst/enzyme composite mini-biosensor with favorable reproducibility, stability and accuracy.

碩士
國立臺灣科技大學
化學工程系
94
In this work, a reduction method based on microwave reaction was used to synthesize Pt-Ag bimetallic catalysts in ethylene glycol solution. A step by step procedure was adopted to prepare Ptcore @ Agshell/C and Agcore @ Ptshell/C nano-sized bimetallic catalysts. By employing the X-ray Absorption Spectroscopy(XAS) and the extracted atomic structure parameters the structure of the bimetallic catalysts was analyzed. The relationship between the structure of the synthesize catalysts and activity toward CO oxidation. From the XRD analysis, the grain size of synthesized catalysts were about 1~3 nm wich is consistent with TEM observation. From XRD analysis, the Ag @ Pt/C catalysts with larger grain size exhibit a separated fcc structure, it was found that some of Agcore @ Ptshell/C catalysts were aggregated. In this work Temperature Programmed Surface Reaction (TPSR) was employed to evaluate the activity for CO oxidation and the electrochemical activity for CO stripping. The results show that the Pt-Ag/C-R1-1 catalyst shows the bast performance for CO oxidation. The Pt-Ag bimetallic catalysts were synthesized by changing the sequential procedure and the solution composition. The relationship between their structure and CO oxidation in both gas and liquid phase was established. The best structure of the synthesized catalyst for CO oxidation was found in this studty.

碩士
國立屏東科技大學
環境工程與科學系所
103
In this study, electrolysis-enhanced dispersed permeable reactive barrier (PRB) packed with nano-scale palladium/iron (Pd/Fe) bimetallic particles coupling with persulfate were used to degrade trichlorethylene (TCE) in water The experiments were performed within a sand box. The experimental procedures were divided into five parts as follows: (1) characterization of nano-sacle Fe, nano-scale Pd/Fe, and dispersed nano-scale Pd/Fe, (2) test water quality analysis and adsorption test of TCE on quartz sand, (3) transport tests in porous media, (4) TCE degradation experiments with electrolysis- enhanced PRB packed with nano-sacle dispersed Pd/Fe, (5) TCE degradation experiments with electrolysis-enhanced PRB packed with nano-sacle dispersed Pd/Fe coupling with persulfate.   The average specific surface area of dispersed nano-sized Pd/Fe (1:1000) particles was 167 m2/g. X-ray diffraction (XRD) analysis showed that the nano-sacle Pd/Fe particles had peaks at 2θ = 44.980 and 650 identified for Fe and 2θ = 27.450 and 31.880 for Pd, respectively. The ethane formed by TCE reduced by Fe was identified on dispered nano-scale Pd/Fe particles with a Fourier Transform Infrared Spectrometry (FTIR). TCE reduction using dispersed nano-sized Pd/Fe particles showed an increase in pH values and a decline in oxidation-reduction (redox) potential. The formation amount of chloride ions is proportional to the reduction amount of TCE in the reduction process. The persulfate oxidation test showed that the ferrous ions produced by the TCE reduction process with dispersed nano-scale Pd/Fe particles could activate persulfate to form sulfate radical (SO4-･) to further oxidize TCE. For the tests of electrolysis-enhanced PRB, the potential gradient set at 2 V/cm was better for TCE degradation than 1 V/cm. As the potential gradient was set at 2 V/cm, some phenomena were observed such as precipitates within the PRB and TCE evaporation by enormous amount of bubbles owing to the heat production. Therefore, the potential gradient 1 V/cm is the optimal parameter for following electrolysis tests. The results showed that TCE degradation by the treatment train of electrolysis-enhanced dispersed permeable reactive barrier (PRB) packed with nano-scale palladium/iron (Pd/Fe) bimetallic particles coupling with persulfate is feasible for remediation of groundwater contaminated by chlorinated solvents. Keywords: dispersion, persulfate, trichlorethylene, electrolysis,

Investigations on size dependent phase stability and transformations in isolated nanoparticles have gained momentum in recent times. Size dependent phase stability generates size specific particle microstructure which consequently yields size specific functionality. One important prerequisite for conducting studies on nanoparticles is their synthesis. A substantial amount of research effort has therefore been focused on devising methodologies for synthesizing nanoparticles with controlled shapes and sizes. The present thesis deals with both these two aspects: (a) synthesis of nanoparticles and (b) phase transformations in nanoparticles. The system chosen in this study is AuCu intermetallic nanoparticles. The choice of AuCu nanoparticle was due to the fact that the literature contains abundance of structural and thermodynamic data on Au–Cu system which makes it a model system for investigating size dependence of phase transformations. With respect to synthesis, the present thesis provides methodologies for synthesizing alloyed Au–Cu nanoparticles of different sizes, Au–Cu nano-chain network structures and uniform Au–Cu2S hybrid nanoparticles. For every type, results are obtained from a detailed investigation of their formation mechanisms which are also presented in the thesis. With respect to phase transformation, the thesis presents results on the size dependence of fcc to L10 transformation onset in Au–Cu nanoparticles under isothermal annealing conditions. The present thesis is divided into eight chapters. A summary of results and key conclusions of work presented in each chapter are as follows. The ‘introduction’ chapter (chapter I) describes the organization of the thesis. Chapter II (literature study) presents a review of the research work reported in the literature on the various methodologies used for synthesizing Au–Cu based nanoparticles of different shapes and sizes and on ordering transformation in AuCu nanoparticles. The chapter also presents a brief discussion on the reaction variables that control the process of nucleation and growth of the nanoparticles in solution. Chapter III titled ‘experimental details and instrumentation’ describes the synthesis procedures that were used for producing various nanoparticles in the present work. The chapter also briefly describes the various characterization techniques that were used to investigate the nanoparticles. The fourth chapter titled ‘synthesis and mechanistic study of different sizes of AuCu nanoparticles’ provides two different methodologies for synthesis, referred as ‘two-stage process’ and ‘two-step process’ that have been used for producing alloyed AuCu nanoparticles of different sizes (5, 7, 10, 14, 17, 25 nm). The ‘two-stage’ process involved sequential reduction of Au and Cu precursors in a one pot synthesis process. Whereas, the ‘two-step’ process involved a two-pot synthesis in which separately synthesized Au nanoparticles were coated with Cu to generate alloyed AuCu nanoparticles. In the two-stage synthesis process it was observed that by changing the total surfactant-to-metal precursor molar ratio, sizes of the alloyed AuCu nanoparticles can be varied. ‘Total surfactants’ here include equal molar amounts of oleic acid and oleylamine surfactants. Interestingly, it was observed that there exists a limitation with respect to the minimum nanoparticle size that can be achieved by using the two-stage process. The minimum AuCu nanoparticle size achieved using the two-stage synthesis process was 14 nm. Mechanism of formation of AuCu nanoparticles in the two-stage synthesis process was investigated to find out the reason for this size limitation and also to determine how the synthesis process can be engineered to synthesize alloyed AuCu nanoparticles with smaller (<14nm) sizes. Studies to evaluate mechanism of synthesis were conducted by investigating phase and size of nanoparticles present in the reaction mixture extracted at various stages of the synthesis process. Their studies revealed that (a) the nanoparticle formation mechanism in the two-stage synthesis process involves initial formation of Au nanoparticles followed by a heterogeneous nucleation and diffusion of Cu atoms into these Au rich seeds to form Au–Cu intermetallic nanoparticles and (b) by increasing the relative molar amount of the oleylamine surfactant, size of the initial Au seed nanoparticles can be further reduced from the minimum size that can be achieved in the case when equal molar amounts of oleylamine and oleic acid surfactants are used. The information obtained from the mechanistic study was then utilized to design the two-step synthesis process. In the two-step process, Au nanoparticles were synthesized in a reaction mixture containing only the oleylamine surfactant. Use of only oleylamine resulted in production of pure Au nanoparticles with sizes that were well below 10 nm. These Au nanoparticles were washed and dispersed in a solution containing Cu precursor. Introduction of a reducing agent into this reaction mixture led to the heterogeneous nucleation of Cu onto the Au seed particles and their subsequent diffusion into them to form alloyed AuCu nanoparticles with sizes of ~5, 7 and 10 nm. The study present in this chapter essentially signified that the surfactants used in the reaction mixture not only prevent nanoparticles from agglomerating in the final dispersion but also control their nucleation and growth and therefore can be used as a tool to tune nanoparticle sizes. The fifth chapter titled ‘size dependent onset of FCC-to-L10 transformations in AuCu alloy nanoparticles’ illustrates the effect of AuCu nanoparticle size on the onset of ordering under isothermal annealing conditions. Nanoparticles in this study were annealed in-situ in a transmission electron microscope. Samples were prepared by drop drying a highly dilute dispersion of as-synthesized nanoparticles onto an electron transparent TEM grid. Nanoparticles sitting on the TEM grid were well separated from each other to minimize particle sintering during the annealing operation. It was however observed that during the isothermal annealing, particle coarsening due to atomic diffusion was appreciable for 5 nm particles but negligible for 7 and 10 nm particles. Therefore for this study only 7 nm and 10 nm sized particles were considered. Onset of ordering was determined from the time when first sign of the diffraction spot, corresponding to the ordered phase, appears in the selected area electron diffraction pattern from a region containing large number of AuCu nanoparticles. Through a series of isothermal experiments it was observed that the time for onset of ordering increased with decrease in size of the nanoparticles. It is speculated that the delay in onset of ordering may be due to the fact that with a decrease in nanoparticle size the probability of a nanoparticle containing a fluctuation that shall generate a thermodynamically stable nuclei of the ordered phase decreases. A sharp interface between the ordered and the disordered phase inside the particle was also observed which suggested that the ordering transformation in as-synthesized fcc AuCu nanoparticles is a first order transformation. The sixth chapter titled ‘synthesis and characterization of Au1-xCux–Cu2S hybrid nanostructures: morphology control by reaction engineering’ provides a modified polyol method based synthesis strategy for producing uniform Au–Cu2S hybrid nanoparticles. Detailed compositional and structural characterization revealed that the hybrid nanoparticles are composed of cube shaped Au-rich, Au–Cu solid solution phase and hemispherical shaped Cu2S phase. Interestingly, the hemispherical Cu2S phase was attached to only one facet of the cube shaped phase. A study on the formation mechanism of hybrid nanoparticles was also conducted by characterizing specimens extracted from the reaction mixture at different stages of the synthesis process. The study revealed that the mechanism of formation of hybrid nanoparticles involved initial formation of isolated cube shaped pure Au nanoparticles and Cu–thiolate complex with a sheet morphology. With increase in time at 180°C, the Cu–thiolate complex decomposed and one part of the Cu atoms that were produced from the decomposition were utilized in forming the spherical Cu2S and other part diffused into the Au nanoparticles to form Au–Cu solid solution phase. The chapter also presents a study on the effect of dodecanethiol (DDT) on achieving the hemisphere-on-cube hybrid morphology. In this study it is illustrated that an optimum concentration of dodecanethiol is required both for achieving size and morphological uniformity of the participating phases and for their attachment to form a hybrid nanoparticle. The seventh chapter titled ‘synthesis of Au–Cu nano-chains network and effect of temperature on morphological evolution’ provides methodology for synthesizing fcc Au– Cu nano-chain network structures using polyvinylprrolidone (PVP) surfactant. It was observed that with increase in the molar amount of PVP in the reaction mixture, morphology of the as-synthesized product gradually changed from isolated nanoparticles to branched nano-chain like. The nano-chains contained twins which indicated an absence of continuous growth and possibility of growth by oriented attachment of initially formed Au–Cu nanoparticles. Both in-situ and ex-situ annealing of the nano-chains led to their decomposition into isolated nanoparticles of varying sizes. Annealing also caused fcc-to¬L10 phase transformation. Investigation of the wave length of perturbation leading to breaking of a nano-chain into particles indicated that the surface energy anisotropy affects the splitting of nano-chain network structure into nano-sized particles. The thesis ends with a last chapter where we have presented possible future extension of current work.

Investigations on size dependent phase stability and transformations in isolated nanoparticles have gained momentum in recent times. Size dependent phase stability generates size specific particle microstructure which consequently yields size specific functionality. One important prerequisite for conducting studies on nanoparticles is their synthesis. A substantial amount of research effort has therefore been focused on devising methodologies for synthesizing nanoparticles with controlled shapes and sizes. The present thesis deals with both these two aspects: (a) synthesis of nanoparticles and (b) phase transformations in nanoparticles. The system chosen in this study is AuCu intermetallic nanoparticles. The choice of AuCu nanoparticle was due to the fact that the literature contains abundance of structural and thermodynamic data on Au–Cu system which makes it a model system for investigating size dependence of phase transformations. With respect to synthesis, the present thesis provides methodologies for synthesizing alloyed Au–Cu nanoparticles of different sizes, Au–Cu nano-chain network structures and uniform Au–Cu2S hybrid nanoparticles. For every type, results are obtained from a detailed investigation of their formation mechanisms which are also presented in the thesis. With respect to phase transformation, the thesis presents results on the size dependence of fcc to L10 transformation onset in Au–Cu nanoparticles under isothermal annealing conditions. The present thesis is divided into eight chapters. A summary of results and key conclusions of work presented in each chapter are as follows. The ‘introduction’ chapter (chapter I) describes the organization of the thesis. Chapter II (literature study) presents a review of the research work reported in the literature on the various methodologies used for synthesizing Au–Cu based nanoparticles of different shapes and sizes and on ordering transformation in AuCu nanoparticles. The chapter also presents a brief discussion on the reaction variables that control the process of nucleation and growth of the nanoparticles in solution. Chapter III titled ‘experimental details and instrumentation’ describes the synthesis procedures that were used for producing various nanoparticles in the present work. The chapter also briefly describes the various characterization techniques that were used to investigate the nanoparticles. The fourth chapter titled ‘synthesis and mechanistic study of different sizes of AuCu nanoparticles’ provides two different methodologies for synthesis, referred as ‘two-stage process’ and ‘two-step process’ that have been used for producing alloyed AuCu nanoparticles of different sizes (5, 7, 10, 14, 17, 25 nm). The ‘two-stage’ process involved sequential reduction of Au and Cu precursors in a one pot synthesis process. Whereas, the ‘two-step’ process involved a two-pot synthesis in which separately synthesized Au nanoparticles were coated with Cu to generate alloyed AuCu nanoparticles. In the two-stage synthesis process it was observed that by changing the total surfactant-to-metal precursor molar ratio, sizes of the alloyed AuCu nanoparticles can be varied. ‘Total surfactants’ here include equal molar amounts of oleic acid and oleylamine surfactants. Interestingly, it was observed that there exists a limitation with respect to the minimum nanoparticle size that can be achieved by using the two-stage process. The minimum AuCu nanoparticle size achieved using the two-stage synthesis process was 14 nm. Mechanism of formation of AuCu nanoparticles in the two-stage synthesis process was investigated to find out the reason for this size limitation and also to determine how the synthesis process can be engineered to synthesize alloyed AuCu nanoparticles with smaller (<14nm) sizes. Studies to evaluate mechanism of synthesis were conducted by investigating phase and size of nanoparticles present in the reaction mixture extracted at various stages of the synthesis process. Their studies revealed that (a) the nanoparticle formation mechanism in the two-stage synthesis process involves initial formation of Au nanoparticles followed by a heterogeneous nucleation and diffusion of Cu atoms into these Au rich seeds to form Au–Cu intermetallic nanoparticles and (b) by increasing the relative molar amount of the oleylamine surfactant, size of the initial Au seed nanoparticles can be further reduced from the minimum size that can be achieved in the case when equal molar amounts of oleylamine and oleic acid surfactants are used. The information obtained from the mechanistic study was then utilized to design the two-step synthesis process. In the two-step process, Au nanoparticles were synthesized in a reaction mixture containing only the oleylamine surfactant. Use of only oleylamine resulted in production of pure Au nanoparticles with sizes that were well below 10 nm. These Au nanoparticles were washed and dispersed in a solution containing Cu precursor. Introduction of a reducing agent into this reaction mixture led to the heterogeneous nucleation of Cu onto the Au seed particles and their subsequent diffusion into them to form alloyed AuCu nanoparticles with sizes of ~5, 7 and 10 nm. The study present in this chapter essentially signified that the surfactants used in the reaction mixture not only prevent nanoparticles from agglomerating in the final dispersion but also control their nucleation and growth and therefore can be used as a tool to tune nanoparticle sizes. The fifth chapter titled ‘size dependent onset of FCC-to-L10 transformations in AuCu alloy nanoparticles’ illustrates the effect of AuCu nanoparticle size on the onset of ordering under isothermal annealing conditions. Nanoparticles in this study were annealed in-situ in a transmission electron microscope. Samples were prepared by drop drying a highly dilute dispersion of as-synthesized nanoparticles onto an electron transparent TEM grid. Nanoparticles sitting on the TEM grid were well separated from each other to minimize particle sintering during the annealing operation. It was however observed that during the isothermal annealing, particle coarsening due to atomic diffusion was appreciable for 5 nm particles but negligible for 7 and 10 nm particles. Therefore for this study only 7 nm and 10 nm sized particles were considered. Onset of ordering was determined from the time when first sign of the diffraction spot, corresponding to the ordered phase, appears in the selected area electron diffraction pattern from a region containing large number of AuCu nanoparticles. Through a series of isothermal experiments it was observed that the time for onset of ordering increased with decrease in size of the nanoparticles. It is speculated that the delay in onset of ordering may be due to the fact that with a decrease in nanoparticle size the probability of a nanoparticle containing a fluctuation that shall generate a thermodynamically stable nuclei of the ordered phase decreases. A sharp interface between the ordered and the disordered phase inside the particle was also observed which suggested that the ordering transformation in as-synthesized fcc AuCu nanoparticles is a first order transformation. The sixth chapter titled ‘synthesis and characterization of Au1-xCux–Cu2S hybrid nanostructures: morphology control by reaction engineering’ provides a modified polyol method based synthesis strategy for producing uniform Au–Cu2S hybrid nanoparticles. Detailed compositional and structural characterization revealed that the hybrid nanoparticles are composed of cube shaped Au-rich, Au–Cu solid solution phase and hemispherical shaped Cu2S phase. Interestingly, the hemispherical Cu2S phase was attached to only one facet of the cube shaped phase. A study on the formation mechanism of hybrid nanoparticles was also conducted by characterizing specimens extracted from the reaction mixture at different stages of the synthesis process. The study revealed that the mechanism of formation of hybrid nanoparticles involved initial formation of isolated cube shaped pure Au nanoparticles and Cu–thiolate complex with a sheet morphology. With increase in time at 180°C, the Cu–thiolate complex decomposed and one part of the Cu atoms that were produced from the decomposition were utilized in forming the spherical Cu2S and other part diffused into the Au nanoparticles to form Au–Cu solid solution phase. The chapter also presents a study on the effect of dodecanethiol (DDT) on achieving the hemisphere-on-cube hybrid morphology. In this study it is illustrated that an optimum concentration of dodecanethiol is required both for achieving size and morphological uniformity of the participating phases and for their attachment to form a hybrid nanoparticle. The seventh chapter titled ‘synthesis of Au–Cu nano-chains network and effect of temperature on morphological evolution’ provides methodology for synthesizing fcc Au– Cu nano-chain network structures using polyvinylprrolidone (PVP) surfactant. It was observed that with increase in the molar amount of PVP in the reaction mixture, morphology of the as-synthesized product gradually changed from isolated nanoparticles to branched nano-chain like. The nano-chains contained twins which indicated an absence of continuous growth and possibility of growth by oriented attachment of initially formed Au–Cu nanoparticles. Both in-situ and ex-situ annealing of the nano-chains led to their decomposition into isolated nanoparticles of varying sizes. Annealing also caused fcc-to¬L10 phase transformation. Investigation of the wave length of perturbation leading to breaking of a nano-chain into particles indicated that the surface energy anisotropy affects the splitting of nano-chain network structure into nano-sized particles. The thesis ends with a last chapter where we have presented possible future extension of current work.