School of Chemistry - Theses
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ItemThe adsorption of polydisperse nonionic surfactants at the solid/aqueous interface( 1987)A high resolution capillary gas chromatography technique has been adapted to the analysis of polydisperse non-ionic surfactants. This technique has enabled the complete characterization of the oligomer distributions of very small samples of surfactants (typically 0.1 µg to 0.5 µg). It has made possible the determination of changes in the oligomer distribution on adsorption of surfactant at the solid/aqueous interface. Isotherms have been measured for the adsorption of a series of polyoxyethylene nonylphenol surfactants from aqueous solution on to various solids. These isotherms indicate that the surfactant – surface interaction increases with an increase in the hydrophobicity of the adsorbent. They also show a dependence upon the average length of the ethylene oxide chain and the ratio of the surface area/solution volume. These latter factors affect both the total partition of surfactant between the surface and the solution, and also the selectivity of the solid surface. A detailed study of the adsorption of N8 (a commercial non-ionic surfactant) by a precipitated silica at various surface area/solution ratios, has been undertaken, where the equilibrium surfactant oligomer distributions in the adsorbed and solution phases have been determined. At surfactant concentrations above the critical micelle concentration, the phase separation approach has been used to estimate the surfactant oligomer distributions in free monomer solution and in micelles. This information has been combined with a surface phase model to interpret the results of the adsorption distribution studies.
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ItemThe structure of the oxide/aqueous electrolyte interface( 1975)The structure of the oxide/aqueous electrolyte interface has been studied. The surface porosity of several oxides to ions is evaluated and the contribution of such porosity to the double layer properties determined by surface charge measurements. The oxides studied are B.D.H. precipitated silica, before and after heat treatment, rutile, goethite, hematite and amorphous ferric oxide. The surface porosity was evaluated using nitrogen adsorption for physical porosity, tritium exchange for surface hydration and dissolution for surface crystallinity. It is found that the surfaces of metal oxides may be divided into two categories; those that are porous to ions and those that are non-porous. Of those studied only the precipitated silica and the amorphous ferric oxide are porous. The porosity is probably due to an easily permeated layer of hydrolysed oxidic material. It does lead to exceptionally high surface charges. However the non-porous oxides also exhibit high surface charges so that while surface porosity may, in some cases, contribute to oxide double layer properties, it cannot be a general explanation of the high differential capacities observed. A site-binding model for non-porous oxide/aqueous electrolyte interfaces is introduced, in which it is proposed that the adsorbed counter ions form interfacial ion pairs with discrete charged surface groups. This model is used to calculate theoretical surface charge densities and potentials at the Outer Helmholtz Plane. The calculated values are consistent with experimental data for oxides provided a high value of the inner zone capacity is accepted. An explanation is provided for the difference between silica and most other oxides in terms of the dissociation constants of the surface groups.
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ItemInterfacial effects on aqueous sonochemistry and sonoluminescence( 1999-06)The dissolution of quantum sized CdS and MnO2 particles in water was conducted using 20 kHz ultrasound. CdS particles were found to dissolve chemically via an oxidation process while MnO2 particles dissolved via a reductive process. It was found that the dissolution of the colloids could be controlled via the addition of surface active chemicals to solution and by varying the saturation gas type. In the presence of Na2S or propan-2-ol and argon gas, the dissolution of CdS was inhibited, whereas the addition of alcohols (methanol, ethanol, propan-2-ol, butan-1-ol and pentan-1-ol) to the MnO2 system led to an increase in the amount of dissolution for a given time of sonication. This increase in dissolution was found to be dependent on the ability of the surface active radical scavenger to accumulate around the bubble interface during the cavitation process. Eventually, at higher alcohol concentration there was a plateau or a limiting value reached for the efficiency of colloid dissolution which was common for each alcohol. (For complete abstract open document)
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ItemOptical properties of silica-coated metal particles( 1999)The significance of silica coating technology for stabilising metal semiconductor nanoparticles was demonstrated. The physicochemical properties of silica coated colloidal silver (Ag@Si02) and the optical properties of films containing uncoated and silica coated colloidal gold (Au@Si02) were investigated. The factors governing the deposition of silica onto silane-primed silver particles were examined and the deposition conditions (pH and reagent concentrations) optimised. Thin silica shells deposited from aqueous/ethanolic sodium silicate solutions were porous and non-rigid. The shells remained insensitive to boiling in an aqueous-ethanolic solution but were substantially dissolved when boiled in pure water. The silver cores participated in a variety of chemical reactions with charged and neutral molecules to form new structures such as hollow silica nonobubbles, semiconductor cores and silica coated alloys of silver and gold. The rate of the reactions of the core with solution phase substrates decreased with increasing silica shell thickness. The silver cores of Ag@Si02 still remained catalytically active and colloidally stable during the reduction of water. Homogeneous films containing uncoated and silica coated gold particles were prepared using a self-assembly technique. The optical properties of the films were investigated as a function of film thickness and the separation between core particles. For interparticle separations below a silica shell thickness of ≈ 6.3 nm, the absorption band red-shifted and narrowed with increasing film thickness. Moreover, with increasing interparticle separation, the band blue-shifted, and both the transmittance and reflectance spectra increasingly began to resemble those of the same isolated particles in solution, in agreement with the Maxwell-Garnett model. In contrast, above a shell thickness of ≈ 6.3 nm, the absorption peak position remained insensitive to film thickness and interparticle separation, suggesting that the gold cores were no longer electromagnetically coupled. For silica shell thicknesses above 12.2 nm, the dependence of the reflectance spectra o interparticle separation and film thickness still needs to be quantified. Possible scientific and industrial applications associated with the Ag@Si02 particles and Au@Si02 particle films are suggested.
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ItemHeavy metal ion activation of zinc sulphide( 1978)This thesis deals with the activation of zinc sulphide by the heavy metal ions Cu ll, Cd 11 and Pb II over a wide range of pH, metal ion concentration, zinc sulphide concentration and incident light conditions. At acid to neutral pH values the uptake of a heavy metal ion has been observed to take place in two stages: a fast, initial step followed by a second, slower step. Kinetic data have shown that heavy metal ion uptake generally follows a logarithmic dependence on time. At alkaline pH values heavy metal ion uptake is complicated by hydrolysis effects. A sensitive mass spectrometric technique has been developed and is capable of quantitatively detecting down to 1% of a nominal monolayer of elemental sulphur on a mineral of surface area 0.7 m2 g-1. Elemental sulphur was detected on sphalerite surfaces activated by Cu11 and Pb II up to pH 6.6, both in the dark and under UV irradiation. Elemental sulphur was only detected on Cd II activated and unactivated zinc sulphide surfaces under UV irradiation. A mechanism for the activation of zinc sulphide is advanced at acid, neutral and alkaline pH values. At acid to neutral pH values, metal ion uptake occurs by an exchange reaction This is coupled with a surface redox process, which is linked with the semiconductor properties of zinc sulphide. As a result of this surface redox process, elemental sulphur may form on the zinc sulphide surface, depending on the type of metal ion involved and on the incident light conditions. It is proposed that the rate determining step in the exchange reaction is the transfer of an adsorbed metal ion from a surface, adsorbed site to a lattice site. This leads to a logarithmic dependence of metal ion uptake on time, as observed experimentally. At alkaline pH values, the mechanism at acid to neutral pH values is complicated by metal ion hydrolysis, adsorption and precipitation effects. An overall mechanism is proposed which accounts for the observed behaviour.
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ItemTheoretical and spectroscopic studies of anticonvulsant drugs( 1969)Once upon a time, people who suffered from grand mal were fed mustard, and weasels' blood, and some had their skulls perforated. Grand mal, the falling sickness, had been known since the time of Hippocrates, but even the empirical Greeks resorted to mystical explanations for the thunderclap onset of a grand mal fit, and the churchmen and surgeons of the Middle Ages were of the opinion that a glass of human urine, preferably provided by the first witness to the seizure, would hasten the departure of the offending demon. Although logically reasonable, this and other treatments! failed to alleviate grand mal or any of the related cerebral conditions which are now known collectively as epilepsy, and it was not until 1857 that the first useful anticonvulsant drug, potassium bromide, was introduced. (From introduction)
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ItemRadionuclide determination and behaviour in marine and freshwater systems( 1997)A range of radio analytical techniques have been developed and optimised for the determination of naturally occurring and artificial radionuclides present in the Australian environment. The behaviour of these radionuclides has been investigated to provide a basis for dose assessments from the human consumption of potable waters, estimates of fish ages and estimates of sedimentation rates in marine sediments.