School of Chemistry - Theses
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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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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)