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Nanotechnology applications have emerged enormously in recent times. Of particular interest is that area that overlaps the areas of nanotechnology, biology and medicine: nanomedicine. One advantage of nanomedicines is it that it can be used as an enabling technology by pharmaceutical researchers and industry to overcome issues associated with the low bioavailability of hydrophobic drugs. In the first part of the current study, nanosuspensions of two of hydrophobic steroid drugs: hydrocortisone and prednisolone were produced. Nanosuspensions were prepared using a bottom-up approach: the anti-solvent precipitation method using microfluidic reactors. Surface modification was carried out on these nanosuspensions using cationic surfactants to obtain nanoparticles with different levels of surface positive charge as indicated by ¿-potential values. Dynamic light scattering (DLS) and transmission electron microscope (TEM) techniques were used to characterize the prepared nanoparticles. Powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) were also used to characterize hydrocortisone nanoparticles. In the second part, cellular uptake of both coated and uncoated nanoparticles by HaCaT keratinocytes cell line was examined and indicated by quantifying the anti- inflammatory effect of nanoparticles on the LPS-induced inflammation. Also, TEM was employed to evaluate the cellular uptake of hydrocortisone nanoparticles. Results showed higher ant-inflammatory effect of coated nanoparticles over uncoated nanoparticles. Furthermore, the anti-inflammatory effect of coated nanoparticles was correlated to the degree of positive surface charge. / Libyan government

This study is on thermodynamics of crystalline nanoparticles of materials. It provides measurements of the equilibrium melting point of nanocrystals of zinc in a size distribution of 30 - 120 nm, as observed by using Philips CM 12 TEM and JEOL 2010F TEM/STEM, and of the heat capacity, and melting enthalpy by using Perkin-Elmer Pyris-Diamond and TA Q100 Calorimeters. The observed melting point of zinc nanoparticles is lower than that of the bulk zinc, but their heat capacity increases and enthalpy of melting decreases. During heating, the nanoparticles oxidizes and forms zinc oxide surface layer reducing the amount and size of zinc nanocrystals. Calculations based upon the Debye theory for heat capacity show that the surface atoms on the zinc nanoparticles have ~ 55 % larger vibrational amplitude and therefore increase the entropy of the surface layer over that of the interior of the particles. During cooling, the crystallization of zinc oxide encaged zinc nanodroplets occurs in two stages, which are heterogeneous and homogeneous nucleations. As the amount of zinc nanocrystals decreases and the liquid-zinc oxide interface increases, homogeneous nucleation becomes less dominant and the two-stage crystallization merges. Nano-pharmaceuticals were produced by incorporating them in a nanoporous amorphous polymer matrix by using a technique based on diffusion method. The presence of embedded nano-pharmaceuticals is shown by their lower melting point relative to the bulk pharmaceuticals and by peak-broadening of x-ray diffraction, which shows that their size lies in 70 - 100 nm range. Although no phase inversion between allotropic forms of the pharmaceutical was observed, a sample calculation for polymorphs of tin shows that such phase inversion should occur at a smaller particle size at a lower temperature. In general, these findings show the effects of the increase in the surface energy relative to bulk energy of nanoparticles, and the consequent differences between the properties of their surface atoms relative to the interior atoms. / Thesis / Master of Applied Science (MASc)

M. Tech. (Department of Chemistry, Faculty of Applied and Computer Science): Vaal University of Technology / Here, we report the synthesis and characterization of silver (Ag) and silver selenide (Ag2Se) nanoparticles using the metal-organic route method. This method involves the reduction of selenium powder and silver nitrate in the presence of trioctylphosphine as a solvent. Tri-n-octylphosphine oxide (TOPO) and hexadecylamine (HDA) were used in the study as capping molecules. The optical properties of the as-prepared nanoparticles were studied using UV-Visible and photoluminescence spectroscopy (PL). Transmission electron microscopy (TEM) and X-ray powder diffraction (XRD) were used to study the structural properties. The effect of capping molecules and temperature were investigated on the growth of the nanoparticles. The prepared nanoparticles seem to depend on the reaction temperature were the increase in temperature led to an increase in particle sizes. The growth of the as-prepared TOPO-capped Ag2Se nanoparticles was influenced by temperature, this was evident when the temperature was increased, the nanoparticles evolved from sphere to hexagonal shape. TOPO-capped nanoparticles showed the tendency of agglomeration with increase in temperature compared to HDA-capped nanoparticles. The X-ray diffraction results showed peaks which were identified as due to α-Ag2Se body centered cubic compound for both TOPO/HDA-capped Ag2Se nanoparticles. Some evidence of impurities were observed in the XRD analysis and indexed to metallic silver. HDA-capped Ag nanoparticles were found to be affected by temperature variation. The prepared nanoparticles were characterized with UV-Vis spectroscopy and transmission electron microscopy. XRD analysis was not performed due to small yield obtained. The absorption spectra of HDA-capped Ag nanoparticles at different temperatures show a surface Plasmon resonance (SPR) band in the regions 418 - 428 nm. Uniform spherical shapes were obtained for both 130 and 190 °C and fewer particles were obtained at 160 °C. The synthesis of TOPO–capped Ag nanoparticles was unsuccessful since none of the particles were isolated from the solution due to its lower capping ability or it may be that TOPO is binding too strongly to Ag. The polymer nanofibres were electrospun using electrospinning technique. Parameters such as concentration and voltage were investigated. These parameters significantly affect the formation of fibre morphology. PVP and PMMA polymers were used for this study. The electrospun composite fibres were characterized using UV-Visible spectroscopy, scanning electron microscopy (SEM), Thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and Fourier transformer infrared (FTIR) spectroscopy. The SEM results show that increasing the polymer concentration resulted in increased fibre diameters. Hence increasing the voltage decreases the fibre diameters. Ag2Se nanoparticles were incorporated into PVP and PMMA and electrospun using electrospinning to produce composite fibres. Their addition into PVP polymer fibres improved the fibre’s uniformity and further decreased their diameters. The SEM of composite fibres for PMMA is not shown. The absorption bands for PVP composites fibres show a blue shift from the pure Ag2Se nanoparticles, whereas the one for PMMA show a red shift from the pure Ag2Se nanoparticles. Both the composite fibres for PVP and PMMA show a blue shift from the bulk of Ag2Se. The XRD analysis of the composite fibres shows no significant effect upon addition of Ag2Se nanoparticles on the amorphous peak of the PVP polymer, whereas on the PMMA, it shows peaks which were due to the face centered cubic phase of Ag. The FTIR spectra of the composite fibres and pure polymers (PVP and PMMA) gave almost identical features. TGA curves show no significant effect on the thermal properties of the PVP polymer and its composites, however, on the PMMA composite fibres it show an increase in the thermal stability of the polymers upon addition of Ag2Se nanoparticles. The study was based on silver nanoparicles and its antibacterial activities. One of the synthetic challenges for silver nanoparticles is their solubility and yield. Selenide was introduced in the study to improve such shortcomings of silver nanoparticles and also for possible improved properties, chemical stability and increased activity against bacteria. The selenide group on the metal also provides stronger chemical interaction between the nanoparticles and the polymer. Therefore, the intension was to use these nanoparticles into polymer fibres for potential use in wound dressing.

This thesis summarizes the methods of preparation and optical properties of hybrid assemblies of Au NPs and cadmium selenide (CdSe) QDs. First chap-ter deals with the literature survey and theoretical aspects of plasmonics and discussions on optical excitations of metal (plasmons) and semiconducting QDs (excitons). Variation of energy levels of CdSe QDs and its optical properties i e. absorption and emission properties under strong confinement regime have been discussed with respect to effective mass approximation (EMA) model. This is followed by the discussion on optical properties of Au NPs and rods, describing absorption properties, based on Mie theory. Size and shape depen-dent variation of absorption properties. Theoretical discussions of collective effects in QDs assemblies and plasmonic interactions with the QDs assemblies i.e. plasmonic Dicke effect and metal nanoantenna interaction with CdSe QDs arrays is provided. In the second chapter a discussion on experimental techniques used for the study is provided. It starts with a discussion on the synthesis methods for CdSe QDs and Au NPs/rods with different capping ligands. Different techniques of preparation of CdSe QDs assemblies and their hybrid with metallic nanoparti-cles has been discussed. Further discussion on optical microscopy techniques, confocal, near field scanning microscopy (NSOM), Brewster angle microscopy and electron microscopy techniques i. e transmission electron microscopy and scanning electron microscopy and thermogravimetry analysis of the samples is provided. In the third chapter the details of the different self-assembly methods of preparation of hybrid assemblies of CdSe QDs and Au NPs /rods are given. The different strategies are used for different type of hybrids. In first method of Langmuir-Blodgett (LB) , effect of different capping agents, core size, and number ratios of Au NPs/rods to CdSe QDs, effect of anisotropy of Au NPs on the LB films of CdSe QDs assemblies is discussed. In another method of dip coating several control parameters like dip time, concentration of the solution and dip speed of transferring an aligned GNRs is given. Finally a combination of LB and dip coating methods is described for transferring aligned GNRs over a compact layer of CdSe QDs. At the end, a section is devoted to hit and trials of self-assemblies of hybrid of GNRs and CdSe QDs using LB method, the failures of which resulted in devising a method which uses a combination of LB and dip coating. In fourth chapter effects of plasmons on the collective emission of CdSe QDs assemblies are investigated. A plasmonic tuning of photoluminescence from semiconducting QD assemblies using Au NP in different ratio and different packing density has been discussed. We have described how the emission from a closed pack assemblies, prepared with different packing densities depends on the packing density and extent of spectral overlap between QD photolumi-nescence and the metal nanoparticle absorbance. We have provided possible evidence for plasmon mediated coherent emission enhancement from some of these assemblies from the case of strong spectral overlap between CdSe QDs and Au nanoparticle. In fifth chapter, we have demonstrated non local far field enhancement of PL in QDs assemblies induced by isolated and partially aligned GNRs nano-antenna located on such assemblies. It is shown that the emission is also anisotropic with the maxima being near such GNRs assembly which decays to finite, nonzero and significantly large values even away from the vicinity of any such assemblies. For this novel effect it is shown to have a clear spec-tral dependence. It is shown to be maximum when the longitudinal surface plasmon resonance absorption maxima is resonant with the CdSe QD photolu-minescence maxima and the excitation wavelength and is always non-existent for the off resonant case. We have also shown that finite difference time do-main simulations could model some of the observed near field effects but the far field effects could not be modelled in such simulations.

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.

The aim of the present thesis is to understand the phase transformation behavior of embedded alloy nanoparticles embedded in immiscible matrices. Embedded alloy inclusions have been dispersed in immiscible matrix via rapid solidification method. The present work deals with synthesis of embedded particles, evolution of microstructure, morphology and crystallographic orientation relation relationships among different phases, phase transformation and phase stability behavior of embedded alloy inclusions in different matrices. In the present investigation the systems chosen are Bi-Sn and Bi-Pb in Zn matrix and Cd-Sn in Al matrix. Chapter 1 gives the brief introduction of present work Chapter 2 gives a brief review of nanoscale materials, various synthesis techniques, microstructure evolution, solidification and melting theories. Chapter 3 discusses the processing and experimental techniques used for characterization of the different samples in the present work. Melt-spinning technique used to synthesize the rapidly solidified ribbons. The structural characterization is carried out using X-ray diffraction and transmission electron microscopy. Chapter 4 illustrates the size dependent solubility and phase transformation behavior of Sn-Cd alloy nanoparticles embedded in aluminum matrix. X-ray diffraction study shows the presence of fcc Al, bct Sn, hcp Cd solid solution and hcp Cd phases. Based on Zen’s law, the amount of Sn present Cd solid solution is estimated. Using overlapped sterograms, the orientational relationships among various phases are found. Microscopy studies reveal that majority of the alloy nano inclusions exhibit a cuboctahedral shape with 111 and 100 facets and they are bicrystalline. STEM-EDS analysis shows that both phases exhibit size dependent solubility behavior and for particles size smaller than 18 nm, single phase solid solution could only be observed. Calorimetric studies reveal a depression in eutectic melting point of bimetallic particles. In situ heating studies show that melting initiates at triple line junction corner and melt first grows into the interior of the Sn rich phase of the particle and then later the melt grows into the interior of the Cd phase of the particle. During cooling first Cd phase solidifies later Sn phase solidifies and on further cooling at low temperatures entire particle transforming into complete solid solution phase particle. Size dependent melting studies show that during heating smaller particles melted first, later bigger particles melted. During cooling first bigger particle solidified later smaller particles solidified. High resolution imaging indicates presence of steps across particle-matrix interface that may get annihilated during heating. During cooling, molten particles in the size range of 16-30 nm solidify as solid solution which for molten particles greater than 30 nm solidify as biphasic particle. Insitu heating studies indicates that for solid particles less than 15 nm get dissolved in the Al matrix at temperatures at around 135°C. Differential scanning calorimetry (DSC) studies show in the first heating cycle most of the particles melt with an onset of melting of at 166.8°C which is close to the bulk eutectic temperature of Sn-Cd alooy. The heating cycle reveals that the melting event is not sharp which can be understood from in-situ microscopy heating studies. In the second and the third cycles, the onset of melting observed at still lower temperatures 164.3°C and 158.5°C .The decrease in onset melting point in subsequent heating cycles is attributed to solid solution formation of all small particles whose size range below 30 nm during cooling. cooling cycles exhibit an undercooling of 90°C with respect to Cd liquidus temperature. Thermal cycling experiments using DSC were carried out by arresting the run at certain pre-determined temperatures during cooling and reheating the sample to observe the change in the melting peak position and area under the peak. The areas of these endothermic peaks give us an estimate of the fraction of the particles solidified upto the temperature when the cycling is reversed. Based on experimental observations, a thermodynamic model is developed, to understand the solubility behavior and to describe the eutectic melting transition of a binary Sn-Cd alloy particle embedded in Al matrix. Chapter 5 discusses the phase stability and phase transformation behavior of nanoscaled Bi-Sn alloys in Zn matrix. Bi-Sn alloys with eutectic composition embedded in Zn matrix using melt spinning technique. X-ray diffraction study shows the presence of rhombohedral Bi, pure BCT Sn and hcp Zn phases. In X-ray diffractogram, there are also other new peaks observed, whose peak positions (interplanar spacings) do not coincide either with rhombohedral Bi or bct Sn or hcp Zn. Assuming these new phase peaks belong to bct Sn rich solid solution(based on earlier work on Bi-Sn rapidly solidified metastable alloys) whole pattern fitting done on x-ray diffractogram using Lebail method. The new phase peaks indicated as bct M1(metastable phase1), bct M2(metastable phase2) phases. The amount of Bi present in M1, M2 solid solution is estimated using Zens law. Two sets of inclusions were found, one contains equilibrium bismuth and tin phases and the other set contains equilibrium bismuth and a metastable phase. In-situ TEM experiments suggest that as temperature increases bismuth diffuses into tin and becomes complete solid solution. Melting intiates along the matrix–particle interface leading to a core shell microstructure. During cooling the entire inclusion solidify as solid solution and decomposes at lower temperatures. High temperature XRD studies show that as temperature increases M1, M2 phases peaks merge with Sn phase peaks and Bi phase peak intensities slowly disappear and on further increasing temperature Sn solid solution phase peaks also disappear. During cooling diffraction studies show that first Sn solid solution phase peaks appear and later Bi phase peaks appear. But, the peaks belong to metstable phases not appeared while cooling. Chapter 6 presents morphology and phase transformation of nanoscaled bismuth-lead alloys with eutectic (Pb44.5-Bi55.5) and peritectic (Pb70-Bi30) compositions embedded in zinc matrix. using melt spinning technique. In alloy1[ Zn-2at%(Pb44.5-Bi55.5)] inclusions were found to be phase separated into two parts one is rhombohedral Bi and the other is hcp Pb7Bi3 phase. X-ray diffraction study shows the presence of rhombohedral Bi, hcp Pb7Bi3 and hcp Zn phases in Zn-2at%(Pb44.5-Bi55.5) melt spun sample. The morphology and orientation relationships among various phases have been found. In-situ microscpy heating studies show that melt initially spreads along the matrix–particle interface leading to a core-shell microstructure. And in the core of the core-sell particles, first Bi phase melts later Pb7Bi3 phase will melt and during cooling the whole particle solidify as biphase particle with large undercooling. In-situ heating studies carried out to study the size dependent melting and solidification behavior of biphase particles. During heating smaller particles melt melt first later bigger particle will melt. In contrast, while cooling smaller particles solidifies first, later bigger particles will solidify. Detailed high temperature x-ray diffraction studies indicate there increases first Bi phase peaks disappear later Pb7Bi3 phase peaks disappear and during cooling first Pb7Bi3 phase peaks appear and later Bi phase peaks appear. In alloy2[ Zn-2at%(Pb70-Bi30)] inclusions were found to be single phase particles. X-ray diffraction study shows the presence of hcp Pb7Bi3 and hcp Zn phases in Zn-2at%(Pb70-Bi30) melt spun sample. The crystallographic orientation relationship between hcp Pb7Bi3 and hcp Zn phases. In-situ microscpy heating studies show that melting initiates across the matrix–particle interface grows gradually into the interior of the particle. Three phase equilibrium at peritectic reaction temperature is not observed during insitu heating TEM studies. Size dependent melting point depression of single phase particles is not observed from in-situ heating studies. Detailed high temperature x-ray diffraction studies show that while heating the Pb7Bi3 phase peak intensities start decreasing after 170°C and become zero at 234°C. And during cooling Pb7Bi3 phase peaks starts appearing at 200°C and on further cooling the Pb7Bi3 phase peak intensities increase upto 150°C, below this temperature peak intensities remain constant.

The extensive growth of nanotechnology has necessitated the development of economical and robust methods for large scale production of nanomaterials. It requires detailed quantitative understanding of lab-scale processes to enable effective scale-up and development of new contacting strategies for their controlled synthesis. In this thesis, attempts are made in both the directions using experimental and modelling approaches for synthesis of different nanoparticles. The two-phase Brust--Schiffrin protocol for the synthesis of gold nanoparticles was investigated first. The mechanism of transfer of reactants from aqueous to organic phase using phase transfer catalyst (PTC) was investigated using the measurement of interfacial tension, viscosity, SLS, SAXS, 1H NMR, DOSY-NMR, and Karl-Fischer titration. The study shows that the reactants are transferred to organic phase through the formation of hydrated complexes between reactants and PTC rather than through the solubilization of reactants in water core of inverse micelles of PTC, proposed recently in the literature. The particle synthesis reactions thus occur in the bulk organic phase. The extensive body of seemingly disparate experimental findings on Brust--Schiffrin protocol were put together next. The emerging picture ruled out both thermodynamic considerations and kinetics based arguments as exemplified by the classical LaMer's mechanism with sequential nucleation growth capping for size control in Brust--Schiffrin protocol. A new model for particle synthesis was developed. The model brought out continued nucleation--growth--capping based size control, an hitherto unknown mechanistic route for the synthesis of monodisperse particles, as the main mechanism. The model not only captured the reported features of the synthesis but also helped to improve the uniformity of the synthesized particles, validated experimentally. The two-step mechanism of Finke--Watzky---first order nucleation from precursor and autocatalytic growth of particles---proposed as an alternative to LaMer model to explain an induction period followed by a sigmoidal decrease in precursor concentration for the synthesis of iridium nanoparticles was investigated next. The mechanism is tested using an equivalent population balance model for its ability to explain the experimentally observed near constant breadth of the evolving size distribution as well. The predictions show that while it captures precursor conversion well, it fails to explain particle synthesis on account of its inability to suppress nucleation. A minimal four-step mechanism with additional steps for nucleation from reduced iridium atoms and their scavenging using particle surface is proposed. The new mechanism when combined with the first or second order nucleation, or classical nucleation with no scavenging of reduced atoms also fails to suppress nucleation. A burst like onset of nuclei formation with homogeneous nucleation and the scavenging of reduced atoms by particles are simultaneously required to explain all the reported features of the synthesis of iridium nanoparticles. A new reactor is proposed for continuous production of CaCO3 nanoparticles in gas-liquid reaction route. The key feature of the new reactor is the control of flow pattern to ensure efficient mixing of reactants. A liquidliquid reaction route for production of CaCO3 nanoparticles is also optimized to produce nanoparticles at high loading. Optimum supersaturation combined with efficient breakup of initial gel-like structure by mechanical agitation and charge control played a crucial role in producing nano sized CaCO3 particles.

There are many challenges in materializing the applications utilizing inorganic nanoparticles. The primary drawback is the degradation of properties due to aggregation and sintering either due to elevated temperatures or prevailing chemical/electrochemical conditions. In this thesis, various wet chemical synthesis methods are developed to obtain metal nanostructures with enhanced thermal stability. The thesis is organized as below: Chapter 1 presents the problems and challenges in materializing the application of nanomaterials associated with the thermal stability of nanomaterials. A review of the existing techniques to improve the thermal stability and the scope of the thesis are presented. Chapter 2 gives a summary of the various materials synthesized, the method adopted for the synthesis and the characterization techniques used in the material characterization. Chapter 3 presents a general template-less strategy for the synthesis of nanoporous alloy aggregates by controlled aggregation of nanoparticles in the solution phase with excellent control over morphology and composition as illustrated using PdPt and PtRu systems as examples. The Pt-based nanoporous clusters exhibit excellent activity for methanol oxidation with good long term stability and CO tolerance. Chapter 4 presents a detailed study on the thermal stability of spherical mesoporous aggregates consisting of nanoparticles. The thermal stability study leads to a general conclusion that nanoporous structures transform to hollow structures on heating to elevated temperatures before undergoing complete densification. Chapter 5 presents a simple and facile method for the synthesis of single crystalline intermetallic PtBi hollow nanoparticles. A mechanism is proposed for the formation of intermetallic PtBi hollow structures. The intermetallic PtBi hollow structures synthesised show excellent electrocatalytic activity for formic acid oxidation reaction. Chapter 6 presents a robust strategy for obtaining a high dispersion of ultrafine Pt and PtRu nanoparticles on graphene. The method involves the nucleation of a metal precursor phase on graphite oxide surfaces and subsequent reduction with a strong reducing agent. The electrocatalytic activity of the composites is investigated for methanol oxidation reaction. Chapter 7 presents a microwave-assisted synthesis method for selective heterogeneous nucleation of metal nanoparticles on oxide supports leading to the synthesis of high activity catalysts. The catalytic activity of the hybrids synthesized by this method for investigated for H2 combustion. Chapter 8 presents thermal stability studies carried out on nanostructures by in-situ heating in transmission electron microscope. The microstructural changes during the sintering process are observed in real time and the observations lead to the understanding of the mechanism of particle growth and sintering. At the end, the results of the investigations were summarized with conclusions drawn.

Many studies addressing the toxicity of silver nanomaterials have found that smaller sized silver nanoparticles are usually more toxic to organisms and in cell culture than particles of larger sizes yet it is not entirely clear why. We investigated the size dependent toxicity of silver nanoparticles by measuring the response of embryonic zebrafish (Danio rerio) following exposure to a library of thirteen distinct silver nanoparticle size distributions with mean diameters between 8.9 nm and 112.6 nm. Data analysis using dose���response modeling revealed that silver nanoparticles (AgNP) induced embryo toxicity that is dependent on the total surface area and not on the mass or particle number in solution. Included in this study is a comparison between embryo toxicity induced by silver nitrate (AgNO���) and AgNPs for cardiovascular endpoints, as well as an investigation into the influence of the chorion on AgNP toxicity. This study demonstrates the importance of using alternative dose metrics in nanotoxicology, and highlights the value of using the embryonic zebrafish to explore nanomaterial structure activity relationships. / Graduation date: 2013