No description available.

A series of new planar complexes with the dianion of 2,3-quinoxalinedithiol ligand has been prepared. The complexes have been characterized from the study of their analyses, magnetic moment, conductance, polarograms, electron spin resonance spectra, and electronic spectra, and compared with the available data on the corresponding maleonitriledithiolene and toluene-3,4-dithiolene complexes.

Transition metal phosphide materials have found themselves at the forefront of research revolving around energy applications. Due to the vast range of properties possessed by marginally different phase compositions, binary and ternary metal phosphides are utilized as catalysts, semi-conductors and magnetocaloric materials along with many others. These attractive properties, which are highly phase dependent, call for a versatile and cost effective synthesis route for various phosphide materials without sacrificing properties important at the nanoscale such as particle size and morphology. The primary focus outlined in the work of this dissertation pertains to a versatile wet chemical synthesis capable of producing multiple phases of binary and ternary phosphides containing one or more of the transition metals cobalt, iron and nickel. These metals were of particular interest due to the proven catalytic activity of iron, cobalt or nickel binary phases and the lack of research conducted on the corresponding ternary phases. The challenge presented by wet chemical synthesis methods is the ability to separate different crystal phases of metal phosphide in a short amount of time, with less toxic and lower cost chemicals, and a simple synthetic process with the ability to produce products on a larger scale. Oleylamine was used as a solvent, capping agent and reducing agent along with trioctylphosphine or triphenylphosphine as a phosphorus source. Many binary phosphide phases were synthesized with the same method and purity of phase was controlled primarily with temperature or phosphorus to metal ratio (P:M). At lower temperatures (290-320°C) or lower P:M (4:1) Ni3P,Ni2P, Fe2P, and Co2P were synthesized while higher temperatures (330-360°C) or higher P:M (22:1) produced Ni5P4, Ni12P5, FeP and CoP. Ternary phosphides FeCoP and CoNiP were also successfully synthesized at temperatures of 300-330°C with small excesses of phosphorus (2-5 molar excess). Preliminary catalytic studies for the evolution of hydrogen gas were conducted to test the efficacy of phosphide materials produced via the simplistic oleylamine method. Ni2P was found to have the highest activity toward hydrogen evolution with an overpotential of 320 mV which is comparable and in some cases better than other unsupported phosphide catalysts of the same phase. The ability to control phase composition using a simple, cost effective wet chemical synthesis is promising for the future production of active metal phosphide materials.

L’objectif principal de la thèse concerne la mise au point d'une méthode de piégeage et d'analyse quantitative de métaux cancérogènes ou susceptibles de l'être dans les urines, en permettant de s'affranchir du transport de l'échantillon sous forme liquide. Parmi les éléments traces métalliques (ETM), nous nous sommes intéressés plus particulièrement aux espèces du cobalt et du nickel. L'approche présentée repose sur l'extraction solide/liquide des ions métalliques par complexation sur des matériaux mésoporeux hybrides organo-minéraux à grande surface spécifique. Les matériaux adsorbant sélectionnés sont des silices fonctionnalisées par des groupements dithiocarbamate. Après avoir préparé ces supports par greffage au moyen de nouveaux précurseurs siloxydithiocarbamate, les matériaux fonctionnels ont été caractérisés par diverses techniques physico-chimiques et leur comportement en solution a été étudié. Il en ressort que les interactions entre ces fonctions dithiocarbamate et la surface de la silice peuvent conduire à une perte des greffons en milieu aqueux surtout pour des séjours prolongés en solution. Néanmoins, ces solides ont pu être exploités avec succès pour l’immobilisation quantitative des espèces CoII et NiII à partir de solutions diluées (de 1 à 500 µg.L-1), et ce dans la gamme de pH susceptible d’être rencontrée en milieu urinaire. Cette étude a nécessité la mise au point d’une méthode analytique de routine pour la détermination simultanée et quantitative de ces éléments en solution. Il s’agit de la chromatographie haute performance pour laquelle les meilleurs résultats ont été obtenus au moyen la technique dite de commutation de colonne. Les opérations d’adsorption se sont révélées être rapides, ce qui a permis d’opérer efficacement lors de la mise en œuvre de cartouches au travers desquelles les échantillons ont été percolés. Des efforts ont également été consentis de manière à définir les conditions optimales de désorption en vue de l’analyse quantitative des analytes précédemment accumulés. / The main object of the thesis concerns the development of a trapping method for quantitative analysis of carcinogenic - or likely to be - metal ions in urine, allowing to avoid sample transport in a liquid form. Among the metal ions a trace levels, we have been particularly interested in cobalt and nickel species. The approach presented here is based on solid/liquid extraction of metal ions by complexation on mesoporous organic-inorganic hybrid materials with large specific surface areas. The selected adsorbents are silica gels functionalised with dithiocarbamate groups. After their preparation by post-synthesis grafting using new siloxydithiocarbamate precursors, the functionalized silica gels have been characterized by various physico-chemical techniques and their behaviour in solution has been investigated. It shows that interactions between dithiocarbamate moieties and the silica surface can lead to a loss of grafted groups in the external solution, especially for extended periods in aqueous medium. However, these hybrids have been successfully used for quantitative sequestration of CoII and NiII from dilute solutions (1 to 500 µg L-1), within the pH range likely to be encountered in urinary environment. This study has also involved the development of an analytical method for the simultaneous and quantitative determination of these elements in solution. This was based on high performance liquid chromatography for which the best results were obtained using the switching column technique. Adsorption operations have proven to be very fast, which has allowed operating effectively in the implementation of cartridges through which the samples have been percolated. Efforts have also been made to define the optimal conditions for desorption, which was then applied to the quantitative analysis of analytes previously accumulated in the cartridge.

A stochastic dynamic micromagnetics code using the LLG equation has been developed and applied to study the seed induced magnetic reversal of a cobalt element array. The spin orientation of the seed element is chosen to be antiparallel to the spin orientation of the first element in the array producing a domain wall that is stabilized by the strong crystalline anisotropy and exchange interactions of cobalt. By exposing the element array to an applied magnetic field for a specific time, the domain wall moved along the easy axis and was pinned at a specific position. In this manner, the portions of the element array to be switched could be controlled arbitrarily and information can be stored in the array in terms of the total magnetization of the array. The effects of the magnitude of applied field, the cutting area and the cellsize of the element array were also studied.

No description available.

No description available.

Fischer-Tropsch (FT) synthesis is a reaction which entails the conversion of synthesis gas, also known as syngas (a mixture of H2 and CO gases), to liquid hydrocarbon fuels, oxygenated hydrocarbons, chemicals and water. This syngas mixture is obtained from natural gas, coal, petroleum, biomass or even from organic wastes. In this study cobalt catalysts supported on novel carbon spheretitania (CS-TiO2) composite materials were synthesized and tested for their performance in the FT process. Initially carbon spheres (d = 80-120 nm) were prepared in a vertical swirled floating chemical vapour deposition reactor without the use of a catalyst. The rate of production was controlled and the highest production rate of about 195 mg/min was obtained at an acetylene (C2H2) flow rate of 545 mL/min at 1000 °C. The produced carbon spheres (CSs) had a narrow size distribution with a uniform diameter size. Purification and functionalisation of the CSs improved the total surface area, due to the removal of PAHs which blocked the CS pores. The introduction of functional groups to the CSs was achieved and these changed the wetting properties of the CSs. Functionalising the CSs for longer than 17 h in HNO3 destroyed the morphology of the CSs. After successful preparation of functionalised CSs, the interactions between CSs and TiO2 were studied by in the TiO2 composite using two different sol-gel methods, namely the conventional sol-gel and the surfactant wrapping sol-gel method. The surfactant wrapping sol-gel method entailed the modification of the CSs by dispersing them in a surfactant, in this case hexadecyltrimethylammonium bromide or CTAB [(CH3(CH2)15N(CH3)3Br]. This introduced alkyl “tails” which eased the dispersability of the CSs before coating them with Ti[O(CH2)3CH3]4 (a source of TiO2) to produce a homogeneously coated CS-TiO2 composite material (defined as ASW3). It should be mentioned that many, many experiments were performed to develop an efficient and reliable method to make homogeneously coated CS-TiO2 composites since it was found to be very difficult to achieve an interaction between carbonaceous materials and TiO2 especially by sol-gel procedures. The traditional sol-gel method was used to prepare CS-TiO2 composites with different ratios viz. 1CS-1SG, 1CS-2.5SG, 1CS-5SG, 1CS-10SG, 1CS-25SG and 1CS-50SG. These composites showed weak interactions between CSs and TiO2 even at high TiO2 loading ratio. Interestingly the surface area of these composites showed high values of 80 and 85 m2/g for 1CS-5SG and 1CS-10SG, respectively. At lower TiO2 ratios the measured surface area was similar to that of CSs, i.e 10 m2/g for 1CS-1TiO2. At high TiO2 ratios the measured surface area was similar to that of TiO2, i.e 49 m2/g for 1CS-50TiO2. The TEM images of CS-TiO2 (ASW3) composites prepared by surfactant wrapping methods showed a successful TiO2 coating of CSs. The TiO2 grain size was 8.0 nm with both anatase and rutile phases. High surface areas (up to 98 m2/g) of composite materials were achieved by employing this procedure. The high surface areas achieved suggest that the interaction between CSs and TiO2 was homogeneous and the increase was due to the “bridge” formed between CSs and TiO2. A series of cobalt catalysts (10% by weight) supported on these materials was carried out by the deposition precipitation method using Co(NO3)2·6H2O as the metal precursor. After appropriate drying and calcination the catalysts were characterized using traditional characterisation techniques and tested in the FT reaction using a fixed bed reactor. The the 10%Co/CS catalyst produced a CO conversion of 15.2% while the catalyst had a low total BET surface area (6 m2/g) compared to non-carbonaceous catalysts with higher BET surface areas. This observation suggests that the surface area did not necessarily play a role in the CO conversion, but that other properties (reducibility and dispersion) of CSs influenced the catalyst activity. After coating CSs with TiO2 and loading cobalt to produce 10%Co/ASW3 both the BET surface area of the catalyst and the CO conversion increased to 83 m2/g and 20.1%, respectively. CO-TPD of 10%Co/ASW3 showed a large amount of strongly adsorbed CO. This increased CO was due to the interaction between CSs and TiO2 which developed CO adsorptive sites.

The effect of the addition of ethanol (2% and 6%) during the Fischer-Tröpsch (FT) synthesis has been investigated using a 10%Co/TiO2 catalyst in a stirred basket reactor (T = 220°C, P = 8 bar, H2/CO = 2). The transformation of ethanol vapour (2% and 6% in nitrogen) over the Co/TiO2 catalyst was also studied in the absence of the synthesis gas under FT reaction conditions. Ethanol was observed to be incorporated in the growing chain and was found to (i) increase the selectivity to light products, (ii) increase the olefin to paraffin ratio and (iii) significantly decrease the catalyst activity. These effects were almost completely reversed when the ethanol in the feed was removed. Thermodynamic predictions, TPR and XRD analysis have shown that cobalt metal particles were oxidised to CoO by ethanol but that re-reduction to Co metal was possible when ethanol was removed from the feed stream allowing the catalyst to recover most of its initial performance, in particular when high flow rates were used. The effect of the cobalt carboxylate chain length (C2, C5 and C9) used in the preparation of alumina supported cobalt catalysts has been studied by TPR, XRD and hydrogen chemisorption techniques. The activity and selectivity of the prepared catalysts have been evaluated for the Fischer-Tröpsch (FT) reaction in a stirred basket reactor. It is shown that for catalysts with Co content of 10 wt.% the activity increases as the carboxylate chain length increases while the selectivity towards methane and light hydrocarbons decreases with the carboxylate chain length. The catalyst prepared using cobalt acetate was found to present the highest metal-support interaction and the poorest performance for the Fischer-Tröpsch reaction. When the metal content was increased to 15 wt.% Co and 20 wt.% Co respectively, the metal-support interaction for the catalyst prepared from cobalt acetate significantly decreased making it a better catalyst for the FT reaction compared to the catalysts prepared from C5 and C9 cobalt carboxylates. The effect of the addition of Au to a Co FT catalyst supported on titania, alumina and silica respectively, has been investigated by varying the amount of Au (0.2 to 5 wt.%) added to the catalyst. The catalysts were characterized by atomic absorption spectroscopy, XRD, XPS and TPR analysis. The catalyst evaluation for the Fischer- Tröpsch reaction activity and selectivity was achieved in a fixed bed micro-reactor (H2:CO = 2; 20 bar; 220°C). Addition of Au to supported Co catalysts improved the catalyst reduction and the cobalt dispersion on the catalyst surface. The catalyst activity for the FT reaction and the methane and light product selectivity increased with Au loading in the catalyst.

Student Number : 0107507J - PhD thesis - School of Chemistry - Faculty of Science / Periodic mesoporous organosilica (PMO) materials (consisting of ethane groups in the framework) and bifunctional periodic mesoporous organosilica materials (consisting of ethane groups in the framework and either glycidoxypropyl groups or aminopropyl groups in the channels) were synthesized by the sol-gel method under basic conditions. Ethanesilica materials were synthesized by condensation of 1,2-bistrimethoxysilylethane (BTME) and by co-condensation of BTME with tetraethylorthosilicate (TEOS). Bifunctional periodic mesoporous organosilica materials were synthesized by the co-condensation of BTME with either 3- glycidoxypropyltriethoxysilane (GPTS) or 3-aminopropyltriethoxysilane (APTS). Cetyltrimethylammonium bromide was used as the structure-directing template. Cobalt ion incorporated ethanesilica and modified ethanesilica materials were synthesized in situ by adding cobalt nitrate to the reaction mixture. Cobalt was also supported on ethanesilica materials and APTS-modified materials by using the incipient wetness impregnation method. Raman spectroscopy and diffuse reflectance infrared spectroscopy (DRIFTS) results confirmed the formation of organosilica materials and showed that the surfactant was removed by solvent extraction. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) showed that the ethane portion of the materials (originating from the bridging ethane group in BTME) only decomposed at temperatures > 400 oC. These techniques also showed that the surfactant is removed by solvent extraction. Cobalt ion incorporation was confirmed by Raman spectroscopy and UV-vis diffuse reflectance spectroscopy. Powder powder X-ray diffraction (XRD) and nitrogen adsorption data indicated that the mesophase and textural properties of the materials are dependent on the reaction conditions (i.e. ageing duration, ageing temperature, amount of silica precursor(s), amount of water and amount of base (NH4OH)). The periodicity of the materials was indicated by the presence of low angle diffraction peaks in powder X-ray diffraction patterns. Cubic and hexagonal mesophases were identified using powder X-ray diffraction. When solvent extraction is prolonged, the BET surface area and the pore volume increase, while the average pore diameter decreases. Materials with more dominant XRD structural features and larger d values, higher surface areas, lower pore volumes and average pore diameters are obtained when low ageing temperatures are used. For samples prepared from a mixture of BTME and TEOS at a given temperature, the surface area was found to increase with increasing amount of TEOS added. This trend was observed for materials with and without cobalt. Type IV isotherms, typical of mesoporous materials, were obtained for ethanesilica and modified ethanesilica materials prepared without cobalt. For cobalt incorporated periodic mesoporous ethanesilica materials, the XRD lattice parameter (d100) increased whereas surface area and pore volume decreased with increasing cobalt loading. Nitrogen gas adsorption on samples with varying ratios of BTME:GPTS or BTME:APTS revealed that increasing the amount of GPTS or APTS affects pore size, surface area and pore volume as well as shapes of the isotherms and hysteresis loops. The hysteresis loops of the Type IV isotherms obtained for GPTS-modified ethane silica materials (without cobalt) change from Type H3 to Type H4. There is a tendency for pore sizes to change from mesopore to micropore when the amount of GPTS is increased. Isotherms of cobalt incorporated GPTS-modified ethane silica materials changed from Type IV to Type I. The surface area, pore volume and pore diameter decreased with increasing loading of GPTS or APTS as well as after cobalt incorporation.