vii, 165 [14] leaves : ill. ; 26 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physical and Inorganic Chemistry, 1973

The current work investigates the photocatalytic reduction of selenium (Se) ions, selenate Se(VI) and selenite Se(IV), from two perspectives: Se ion removal from water and wastewater and the formation of nano-Se compounds. Se ion pollution has become an environmental issue in recent years, and hence there is an urgent need for an efficient removal technique. In addition, there is increasing interest in the formation of nano-size semiconductors for niche applications. Since Se is a semiconductor, its formation onto the semiconductor TiO2 could lead to the discovery of new composite materials. The current study has successfully elucidated the mechanism of Se ions reduction by photocatalysis. Factors such as the simultaneous adsorption of the Se ions (the electron scavenger in this case) and a suitable organic compound (the hole scavenger), and the chemical properties of the hole scavenger were crucial for effective and efficient Se ions photoreduction. Optimum conditions in relation to pH, concentrations and types of hole scavenger were reported and discussed. It was also found that stoichiometric adsorption ratio of formate and selenate resulted to optimum photoreduction rate. A modified Langmuir-Hinshelwood kinetic model that considered the simultaneous adsorption of both solutes was derived. The current investigation has also seen the successful formation Se deposits of different morphologies onto the TiO2 particles. Discrete Se particles of various sizes in the nano-size range as well as a Se film were deposited onto the TiO2 particles under different initial experimental conditions. The Se-TiO2 composite semiconductor was explored for the removal of cadmium Cd2+ ions, which resulted in the formation of CdSe-TiO2 systems. The photoreduction of Se ions using silver-modified TiO2 showed the enhanced reduction of Se ions to Se2- in the form of H2Se gas. It is suggested that the H2Se gas generated from the current photoreduction process could be used as a safer and cheaper technique in the formation of Se-compounds such copper selenide, cadmium selenide and zinc selenide. All these compounds were widely used in optical and semiconducting devices.

The current work investigates the photocatalytic reduction of selenium (Se) ions, selenate Se(VI) and selenite Se(IV), from two perspectives: Se ion removal from water and wastewater and the formation of nano-Se compounds. Se ion pollution has become an environmental issue in recent years, and hence there is an urgent need for an efficient removal technique. In addition, there is increasing interest in the formation of nano-size semiconductors for niche applications. Since Se is a semiconductor, its formation onto the semiconductor TiO2 could lead to the discovery of new composite materials. The current study has successfully elucidated the mechanism of Se ions reduction by photocatalysis. Factors such as the simultaneous adsorption of the Se ions (the electron scavenger in this case) and a suitable organic compound (the hole scavenger), and the chemical properties of the hole scavenger were crucial for effective and efficient Se ions photoreduction. Optimum conditions in relation to pH, concentrations and types of hole scavenger were reported and discussed. It was also found that stoichiometric adsorption ratio of formate and selenate resulted to optimum photoreduction rate. A modified Langmuir-Hinshelwood kinetic model that considered the simultaneous adsorption of both solutes was derived. The current investigation has also seen the successful formation Se deposits of different morphologies onto the TiO2 particles. Discrete Se particles of various sizes in the nano-size range as well as a Se film were deposited onto the TiO2 particles under different initial experimental conditions. The Se-TiO2 composite semiconductor was explored for the removal of cadmium Cd2+ ions, which resulted in the formation of CdSe-TiO2 systems. The photoreduction of Se ions using silver-modified TiO2 showed the enhanced reduction of Se ions to Se2- in the form of H2Se gas. It is suggested that the H2Se gas generated from the current photoreduction process could be used as a safer and cheaper technique in the formation of Se-compounds such copper selenide, cadmium selenide and zinc selenide. All these compounds were widely used in optical and semiconducting devices.

Thesis (Ph.D.) -- University of Adelaide, Dept. of Physical and Inorganic Chemistry, 1973.

Thesis (M.Sc.) -- Memorial University of Newfoundland. 1973. / Typescript. Bibliography : leaves 132-136. Also available online.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1928. / Typescript. Includes bibliographical references.

Thesis (Ph. D.)--Columbia University, 1922. / Vita. Bibliography: p. [29]-30.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Seven species of marine phytoplankters assigned to different taxonomic divisions were tested for toxic responses to two different molecular species of selenium known to be prevalent in seawater, selenite and selenate. Selenate proved to be more toxic than selenite, although severe toxicity was only observed at high concentrations (10⁻² and 10⁻³ M) of both selenate and selenite. At these concentrations, growth was completely or severely inhibited in most species tested. In some of the species that remained viable, both the percentage of motile cells and their swimming speed were drastically reduced. Scanning electron microscopy revealed that, under these circumstances, Dunaliella tertiolecta cells possessed much shorter flagella compared to the controls, while those that became non-motile lacked flagella altogether. Despite these striking alterations in both growth and morphology, cells of Amphidinium carterae, Dunaliella tertiolecta and Pavlova lutheri showed, after prolonged exposures, signs of adaptation to high selenium concentrations. Lower concentrations of selenium were generally non-toxic and frequently even stimulatory to growth. These observations suggest that for meaningful inferences on selenium toxicity both the concentration range and the length of the studies must be considered and the potential for adaptation to high selenium concentrations taken into consideration. The main ultrastructural and physiological changes in cells of Dunaliella tertiolecta, Pavlova lutheri and Amphidinium carterae treated with selenite or selenate involved the cell coat, mitochondria, chloroplasts as well as the respiratory and photosynthetic rates. Other changes were observed in the nucleus, lipids, vacuoles, nitrogen and carbon contents, but these showed greater variability among the microalgae studied. The major alterations suggested that energy transducing systems were severely affected by selenium toxicity. These led to significant decreases or even elimination of storage products which were indicative of severe shortage in energy and produced major reductions in growth. These occurred later upon exposure to the toxicant and coincided with the loss of cell coat material, suggesting that the shedding of cell surface material might play a major role in the detoxification and adaptation of the microalgae to toxic concentrations of selenium. / Science, Faculty of / Botany, Department of / Graduate

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