Ces travaux de thèse portent sur le développement d’un dispositif de synthèse de nanoparticules (NPs) par une voie physique basée sur la pulvérisation laser d’une cible suivie d’une trempe du panache plasma ainsi formé. L’association de cette source à une enceinte d’ablation laser conventionnelle a permis de synthétiser des NPs d’argent et de vanadium empilées sur des substrats ou noyées dans des matrices synthétisées par ablation laser. Des analyses par microscopie électronique en transmission (MET) et microscope à force atomique (AFM) ont révélé des NPs cristallisées en vol, de forme sphérique et de tailles relativement monodisperses (~ 3 nm de diamètre) fonction de leur temps de séjour dans la cavité de nucléation. La réalisation de nanocomposites Al2O3 amorphe dopée par des NPs d’argent métallique de différentes tailles a montré l’influence de la taille de ces entités nanométriques sur la position et la largeur de la résonance plasmon de surface (RPS) du matériau nanostructuré. Les NPs gardent leur forme originelle après impact sur le substrat ce qui conduit à des empilements de nanoparticules fortement poreux (de l’ordre de 50%). Des NPs de dioxyde de vanadium ont pu être synthétisées par recuit d’empilements de NPs de vanadium. Du fait de leur individualité, les NPs de VO2 présentent une température de transition plus faible (~50°C) et une largeur d’hystérésis plus importante (~10-30°C) qu’un film mince (température de transition d’environ 68°C et largeur d’hystérésis d’environ 3°C). En associant un film mince synthétisé par PLD à un empilement de NPs il est alors possible de combiner leurs propriétés et d’obtenir un matériau nanocomposite présentant une transition par palier. / The work presented in this thesis is focused on the development of an experimental setup for the synthesis of nanoparticles (NPs) by a physical route, based on the laser vaporization of a target and followed by the rapid quenching of the plasma plume. Combining such a NP source with conventional laser ablation makes possible to synthesize silver and vanadium NPs in stacks on substrates or embedded in different matrices synthesized by laser ablation. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) analysis revealed crystallized spherical NPs relatively monodisperse in size (~ 3 nm in diameter) depending on the residence time in the nucleation cavity. The synthesis of amorphous Al2O3 nanocomposites doped with metallic silver NPs of different sizes showed the influence of the size on the position and the width of the surface plasmon resonance (SPR) of the nanostructured material. The NPs keep their original shape during impact on the substrate, leading to highly porous NPs stacks (approximately 50%). Vanadium dioxide nanoparticles (VO2 NPs) have been synthesized by annealing vanadium NPs stacks. Due to their individual behaviour, VO2NPs exhibit lower transition temperature (~ 50°C) and larger hysteresis width (~ 10-30°C) than thin films (transition temperature around 68°C and hysteresis width around 3°C). By coupling a PLD thin film and a NPs stack, it is possible to combine their properties and obtain a nanostructured material having a step transition.

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The Fe- and Ru-promoted vanadium phosphorus oxide (VPO) catalysts were synthesized via the organic route in iso-butanol to form the VPO precursor, VOHPO4·0.5H2O. The resulting precursor was then activated in a stream of nitrogen to form an amorphous (VO)2P2O7, which crystallized after conditioning in the reactor in the presence of n-butane. The promoted catalysts were synthesized at 0.1%, 0.3% and 1% loading, pelletized and sieved to give a 300-600 μm pellet size. The catalysts were tested in a fixed-bed continuous flow micro-reactor and the products were analyzed by GC’s equipped with a flame ionization detector (FID) to monitor maleic anhydride and n-butane and a thermal conductivity detector (TCD) to monitor the carbon oxides. A range of characterization techniques were employed to determine the influence of the promoting elements on a VPO catalyst and to associate the composition of the catalysts obtained from such techniques with their performance. The characterization techniques used include X-ray diffraction (XRD), BET-surface area, ICP-OES, EDS, 31PNMR, TPR, redox titrations, ATR and SEM to determine the phase composition of the catalysts, the surface area of the promoted catalysts relative to the un-promoted VPO, elemental mole ratios, the reducibility of the catalysts, average vanadium oxidation state, determination of the anions present in the surface of the catalysts and the variations in the morphology of the catalysts, respectively. Optimization of the system involved variation of the GHSV, the reactor temperature and the promoter loading. (Activation of a 0.75% n-butane in air mixture was performed at an optimum temperature of 400oC while varying the gas hourly space velocity to establish a range of feed conversions and subsequently determine the activity of each catalyst with respect to n-butane conversion). The promoted catalysts modified the morphology of the catalysts as evidenced by the scanning electron microscopy and the X-ray diffraction patterns. Furthermore an improved conversion was obtained with these catalysts. However, only the 0.1% iron-promoted catalyst improved maleic anhydride yield leading to ca. 10% maleic anhydride yield increment. Yields of 46% and 55% were obtained at GHSVs of 2573 and 1450 per hour respectively and a temperature of 400oC. Electronic and structural modifications were encountered leading to an improved catalytic performance. The performance of this catalyst is associated with a vanadyl pyrophosphate phase (XRD), and a limited and controlled amount of V5+ species as illustrated in the TPR, and solid state 31P NMR data. Moreover, this modification can be considered both structural and electronic in nature as observed in the SEM images and FTIR spectra of this catalyst. Furthermore, this improved performance is possible at higher conversions 80 to 90% conversion. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2009.

M.Sc., Faculty of Science, University of the Witwatersrand, 2011 / In this work, the primary investigation has been on the development of the laser pyrolysis setup and its optimization for the synthesis of nano-size VO2-x films. More specifically the focus was on making VO2-x depositions using various laser pyrolysis parameters and establish in this way (1) an optimum laser wavelength threshold for the photon induced dissociation of the molecular precursors while the thermal contribution was kept minimal by using low power density (laser energy of 30 W) and (2) the lower threshold for pure thermal contributions by working with wavelengths far from resonance in order to minimize pure photon induced contributions. The interest in synthesizing nano-size VO2-x materials stems from the low metal-insulator transition temperature at near room temperature with opto-electronic and thermo-electronic properties that can be used in specialised applications. A large number of samples were synthesized under various conditions and annealed under argon atmosphere for 17 hours. XRD analysis identified the VO2 (B) and/or β-V2O5 vanadium oxide phases characteristic for certain samples grown under optimum conditions. Raman spectroscopy also confirmed these vanadium oxide phases with bands observed at 175, 228, 261, 303, 422 and 532 cm-1. SEM analysis revealed a plethora of different nanostructures of various size and shapes. The particles have a range of sizes between 55 nm to 185 nm in diameter. The particles showed morphologies which included nano-rods, nanospheres and nano-slabs. An interesting phenomenon was observed on the samples synthesized with high power density, which was observed and reported by Donev iii et al. EDS analysis on the particles was also used to probe the elemental composition of the sample. Optical studies were performed on the samples which showed transitions in the visible and infrared region in accordance with the ones observed in the international literature using different nano-synthesis methods.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Tatyana Polenova, Dept. of Chemistry & Biochemistry. Includes bibliographical references.

Recently, controlling the shape of nanoparticles during their fabrication has become a new and interesting research area. In fact, the nanoparticle has been proven that its physical properties are strikingly related to the shape of itself. After finding the carbon nanotubes in 1911, more and more nanostructure materials have been synthesized. The radical nano-scale vanadium oxide VO2.24(C12H14N2)0.061 is synthesized by hydrothermal method. VO2.24(C12H14N2)0.061 has various physical properties, and we would focus on it¡¦s magnetic properties in the thesis, including magnetic susceptibility and magnetization. The magnetic susceptibility measurements show that the antiferromagnetic transition occurs at T = 20K ~ 25K, and it has been found the specific transition at T = 265K ~ 275K in some samples. Based on the magnetization data, these materials are ferromagnetic, and the hysteresis loops exhibit unusual steps. Whenever these materials process thermal treatments or not, the steps still exist. In addition, we will analyze the impact of the production date, thermal treatment, and preserved environment to discover more colorful properties of these materials.

Reproductin de : Thèse de doctorat : Chimie moléculaire : Metz : 1983. / Titre provenant de l'écran-titre. Notes bibliographiques. Index.

Thesis (M.S.)--University of North Carolina at Wilmington, 2003. / Includes bibliographical references (leaves : [35]-[43]).