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published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Titanium dioxide (TiO2) photocatalysis, which can oxidise or reduce organic and inorganic pollutants, is a developing technology for water and wastewater treatment. The current work investigates the photocatalytic reduction of cadmium and selenium species as the presence of these elements in water are of environmental concern. Although TiO2 has been widely used for the photocatalytic process, its light absorption is limited to the UV region of the solar spectrum. Hence, the current project also explores the possibility to deposit cadmium selenide (CdSe) onto TiO2 to extend the photoresponse to the visible region. This study demonstrated that cadmium (Cd(II)) could be reduced to its metallic form by photocatalysis. The choice of hole scavengers and reaction pH are of importance in determining whether the photocatalytic reduction reaction will occur. It is also essential that both Cd(II) and organic additives are adsorbed on the surface of TiO2. A mechanism for cadmium photoreduction in the presence of formate as the hole scavenger was proposed. The current investigation elucidated the mechanism for the photoreduction of selenite (Se(IV)). Selenite was found to be photoreduced to its elemental form (Se(0)) as films, by direct photoreduction of Se(IV), and as discrete particles, by the reaction between Se(IV) and selenide (Se(2-)) ions. The Se(2-) ions are believed to have been generated from the 6 electron photoreduction of Se(IV) and/or the further photoreduction of the Se(0) deposits. Photocatalytic reduction reactions of Se(IV) and selenate (Se(VI)) using different commercial TiO2 materials was also studied. The current work also successfully deposited CdSe by photocatalysis using Se-TiO2 obtained from the photoreduction of Se(IV) and Se(VI). The mechanism for CdSe deposition was clarified and attributed to the reaction of Cd(II) present in the system and the Se(2-) released from the reduction of Se(0) upon further illumination. The Se??TiO2 photocatalysts obtained from the photoreduction of different selenium precursors (Se(IV) and Se(VI)) resulted in the dominance of different morphologies of the CdSe particles. This suggests a new approach to manipulate the properties of CdSe during its formation, and hence control over electrical and optical properties of this semiconductor.

Time-of-Flight (TOF) and Interrupted-Field Time-of-Flight (IFTOF) measurements were performed repeatedly on several different samples of amorphous Selenium (a-Se) alloys as they aged from deposition or after annealing above the glass transition temperature (Tg) in order to examine the relaxation of the electrical properties. The mobility was found to relax slightly, but the relaxation did not fit well to a stretched exponential. The increase in the mobility for electrons was significantly more than the increase in mobility for holes in all sample compositions measured. For electrons, the mobility increased by 20-40%, whereas for holes, the mobility only increased by less than 10%. The relaxation of the lifetime, on the other hand, fit well to a stretched exponential. Furthermore, the overall increase in lifetime as it relaxed was much greater than the increase in the mobility. The average increase in lifetime was 85% for holes and 45% for electrons. The stretched exponential fits consisted of two important factors: the structural relaxation time ôsr and the stretching factor â. For a given a-Se alloy, ôsr was approximately the same for relaxation from both immediately after sample deposition, and annealing above Tg, indicating that the relaxation is readily repeatable and has the same physical origin. The relaxation was found to be dependent on the a-Se alloy composition. While the general shape of the relaxation was consistently a stretched exponential, ôsr increased with increasing arsenic (As) concentration in the alloy, while â remained constant between 0.6-0.7. Additionally, ôsr was found to be the same for both electron and hole relaxations for a given composition. Thus, the relaxation in both the electron and hole lifetime seems to be controlled by the same structural relaxation process, that is, the electron and hole traps are structural in origin.

In the mid-1980's until the late 1990's, Lesser Scaup (<i>Aythya affinis</i>)populations in the boreal forest declined and have remained at historical low levels since that time. This has resulted in a population well below conservation goals. Potential causes for this population decline include a reduction in productivity, which could be related to changes in boreal forest habitat, nutritional condition during reproduction, or due to contaminants acquired during migration or wintering. Though several studies have assessed contaminant levels in Lesser Scaup on wintering, staging and migration routes, relatively little data exist from northern boreal forest areas, one of the core breeding habitats of the Lesser Scaup population and where population declines appear to be most severe. To this end,male Lesser Scaup were trapped from sites in the northern boreal forest in 2004 and 2005 to assess trace element contaminant levels. Previous research has shown that trace elements including cadmium and selenium can influence hormonal status in waterfowl. Specifically, a positive relationship between cadmium and corticosterone and a negative correlation between liver selenium and corticosterone have been observed. The purpose of this study was to test the hypothesis that trace element contaminants can influence hormonal status and related physiological functions in male Lesser Scaup, and that interactions between contaminants, physiological variables such as body condition and social status can modify expression of toxic effects. Blood samples were collected from trapped males to assess stress related changes in blood chemistry (corticosterone, testosterone, glucose and thyroxine) and males were then collected for contaminant analysis and assessment of reproductive physiology. The geometric mean levels of kidney cadmium, liver selenium and liver mercury were 9ppm, 4.33 ppm, 1.31 ppm dry weight respectively. Several variables and interactions including pair status, cadmium, selenium, mercury, body condition and body size influenced corticosterone levels. In male Scaup with high cadmium levels, corticosterone was negatively related to liver selenium in birds with good body condition (R2=0.701,n=9, P=0.005) but not in birds with poor body condition (R2=0.033, n=10,P=0.61). Likewise, in birds with high cadmium, a negative association was found between liver mercury and corticosterone in structurally smaller males (R2=0.491,n=10, P=0.024), whereas no such relationship was found in larger males(R2=0.307, n=9, P=0.12). In birds with low cadmium and low mercury, selenium and corticosterone were negatively correlated (R2=0.568, n=10, P=0.012) while no association was found in males with high mercury (R2=0.325, n=10, P=0.085). Unpaired birds had higher corticosterone than in ducks with low cadmium(F1,17=6.70, P=0.023), while there was no difference between groups in ducks with high cadmium. Glucose levels were not influenced by contaminants or other variables in this study (R2=0.551, F21,17=0.99, P=0.51). Thyroxine levels were positively correlated to mercury levels in paired birds (R2=0.485, n=19, P<0.001)but were not related in unpaired birds (R2=0.063, n=20, P=0.28). Thyroxine levels also showed a relationship with date of capture (F1,37=6.77, n=39, P=0.014). Pair status was influenced by body condition and body size (P2 =9.997, df=2, P=0.007)with larger birds being in better condition and larger, while hormone levels and testicular morphology did not appear to influence pair status. Mass of testes (F9,27=0.45, P=0.90) and testosterone concentrations (F10,28=0.31, P=0.10) were not influenced by contaminant levels, body condition or body size. Seminiferous tubule diameter was positively related to testes mass (R2=0.397, n=39, P<0.0001) and negatively related to liver selenium levels (R2=0.123, n=39, P=0.009). To clarify the influence of selenium on corticosterone, captive male Lesser Scaup were fed diets dosed with selenomethionine. Dose groups accumulated different levels of selenium (control group=0.19 ng/ml, 7.5 ppm group=0.74 ng/ml and 15 ppm=1.01 ng/ml) (F2,12=155.12; P<0.001) but this appeared to have no effect on corticosterone levels (Wilks Lambda=0.659, F4,10=1.29, P=0.34) or behavioral patterns (Wilks Lambda=0.659, F4,10=1.294, P=0.34) in captive birds. Results from the field portion of this study support the hypothesis that trace element levels can influence hormonal status in wild Lesser Scaup and that interactions of contaminants and physiological variables can modify expression of toxic effects. Studies such as this one display the complex nature of biological systems and emphasize the importance of considering interactions between different contaminants and other variables to clearly assess their influences on physiology.

In the mid-1980's until the late 1990's, Lesser Scaup (<i>Aythya affinis</i>)populations in the boreal forest declined and have remained at historical low levels since that time. This has resulted in a population well below conservation goals. Potential causes for this population decline include a reduction in productivity, which could be related to changes in boreal forest habitat, nutritional condition during reproduction, or due to contaminants acquired during migration or wintering. Though several studies have assessed contaminant levels in Lesser Scaup on wintering, staging and migration routes, relatively little data exist from northern boreal forest areas, one of the core breeding habitats of the Lesser Scaup population and where population declines appear to be most severe. To this end,male Lesser Scaup were trapped from sites in the northern boreal forest in 2004 and 2005 to assess trace element contaminant levels. Previous research has shown that trace elements including cadmium and selenium can influence hormonal status in waterfowl. Specifically, a positive relationship between cadmium and corticosterone and a negative correlation between liver selenium and corticosterone have been observed. The purpose of this study was to test the hypothesis that trace element contaminants can influence hormonal status and related physiological functions in male Lesser Scaup, and that interactions between contaminants, physiological variables such as body condition and social status can modify expression of toxic effects. Blood samples were collected from trapped males to assess stress related changes in blood chemistry (corticosterone, testosterone, glucose and thyroxine) and males were then collected for contaminant analysis and assessment of reproductive physiology. The geometric mean levels of kidney cadmium, liver selenium and liver mercury were 9ppm, 4.33 ppm, 1.31 ppm dry weight respectively. Several variables and interactions including pair status, cadmium, selenium, mercury, body condition and body size influenced corticosterone levels. In male Scaup with high cadmium levels, corticosterone was negatively related to liver selenium in birds with good body condition (R2=0.701,n=9, P=0.005) but not in birds with poor body condition (R2=0.033, n=10,P=0.61). Likewise, in birds with high cadmium, a negative association was found between liver mercury and corticosterone in structurally smaller males (R2=0.491,n=10, P=0.024), whereas no such relationship was found in larger males(R2=0.307, n=9, P=0.12). In birds with low cadmium and low mercury, selenium and corticosterone were negatively correlated (R2=0.568, n=10, P=0.012) while no association was found in males with high mercury (R2=0.325, n=10, P=0.085). Unpaired birds had higher corticosterone than in ducks with low cadmium(F1,17=6.70, P=0.023), while there was no difference between groups in ducks with high cadmium. Glucose levels were not influenced by contaminants or other variables in this study (R2=0.551, F21,17=0.99, P=0.51). Thyroxine levels were positively correlated to mercury levels in paired birds (R2=0.485, n=19, P<0.001)but were not related in unpaired birds (R2=0.063, n=20, P=0.28). Thyroxine levels also showed a relationship with date of capture (F1,37=6.77, n=39, P=0.014). Pair status was influenced by body condition and body size (P2 =9.997, df=2, P=0.007)with larger birds being in better condition and larger, while hormone levels and testicular morphology did not appear to influence pair status. Mass of testes (F9,27=0.45, P=0.90) and testosterone concentrations (F10,28=0.31, P=0.10) were not influenced by contaminant levels, body condition or body size. Seminiferous tubule diameter was positively related to testes mass (R2=0.397, n=39, P<0.0001) and negatively related to liver selenium levels (R2=0.123, n=39, P=0.009). To clarify the influence of selenium on corticosterone, captive male Lesser Scaup were fed diets dosed with selenomethionine. Dose groups accumulated different levels of selenium (control group=0.19 ng/ml, 7.5 ppm group=0.74 ng/ml and 15 ppm=1.01 ng/ml) (F2,12=155.12; P<0.001) but this appeared to have no effect on corticosterone levels (Wilks Lambda=0.659, F4,10=1.29, P=0.34) or behavioral patterns (Wilks Lambda=0.659, F4,10=1.294, P=0.34) in captive birds. Results from the field portion of this study support the hypothesis that trace element levels can influence hormonal status in wild Lesser Scaup and that interactions of contaminants and physiological variables can modify expression of toxic effects. Studies such as this one display the complex nature of biological systems and emphasize the importance of considering interactions between different contaminants and other variables to clearly assess their influences on physiology.

Time-of-Flight (TOF) and Interrupted-Field Time-of-Flight (IFTOF) measurements were performed repeatedly on several different samples of amorphous Selenium (a-Se) alloys as they aged from deposition or after annealing above the glass transition temperature (Tg) in order to examine the relaxation of the electrical properties. The mobility was found to relax slightly, but the relaxation did not fit well to a stretched exponential. The increase in the mobility for electrons was significantly more than the increase in mobility for holes in all sample compositions measured. For electrons, the mobility increased by 20-40%, whereas for holes, the mobility only increased by less than 10%. The relaxation of the lifetime, on the other hand, fit well to a stretched exponential. Furthermore, the overall increase in lifetime as it relaxed was much greater than the increase in the mobility. The average increase in lifetime was 85% for holes and 45% for electrons. The stretched exponential fits consisted of two important factors: the structural relaxation time ôsr and the stretching factor â. For a given a-Se alloy, ôsr was approximately the same for relaxation from both immediately after sample deposition, and annealing above Tg, indicating that the relaxation is readily repeatable and has the same physical origin. The relaxation was found to be dependent on the a-Se alloy composition. While the general shape of the relaxation was consistently a stretched exponential, ôsr increased with increasing arsenic (As) concentration in the alloy, while â remained constant between 0.6-0.7. Additionally, ôsr was found to be the same for both electron and hole relaxations for a given composition. Thus, the relaxation in both the electron and hole lifetime seems to be controlled by the same structural relaxation process, that is, the electron and hole traps are structural in origin.

Abstract Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a powerful tool for the analysis of biomolecules such as peptides and proteins and soft ionization technique using the organic matrix. Because of the high concentration of the organic matrix produces high background signals in the low mass range, nanopatticles have been intensively applied in the surface-assisted Laser desorption/ionization-mass spectrometry (SALDI-MS) to reduce the background interferences in the MALDI.-MS. This thesis includes two projects. The first project applied the copper oxide nanorods, which absorbs 337 nm UV laser energy and has the large area, as the matrix for SALDI-TOF MS to detect four large antibiotics, peptides and proteins. The optimized conditions of the four antibiotic drugs were: 1000 £gM of copper oxide nanorods and incubation for 30 minutes to get the best signals. The LODs of the Lasalocid, Monensin, Salinomycin and Narasin are 200 nM, 25 nM, 50 nM and 50 nM, respectively. In addition, in this project, the CuO nanorods also can be mixed with glycerol to enhance the detection sensitivity for peptides and proteins. The second project presents the zinc selenium quantum dots (ZnSe QDs) modified with 3-mercaptopropionic acid (3-MPA) as the matrix and affinity probes in the SALDI-TOF MS. It strengthens the interaction between the gramicidin and zinc selenium quantum dots by electric interaction in the pH 6 phosphate buffer solution according to the pI value of the gramicidin and the pKa of. 3-mercaptopropionic acid. The best sensitivity of the gramicidin can be obtained under the optimized conditions: 50 £gM of zinc selenium quantum dots, 30 minutes incubation time and pH 6 of phosphate buffer solution. The LOD of the gramicidin is 0.08 £gM. This approach also can be successfully applied in the SALDI-TOF MS to enhance the sensitivity of peptides and proteins.

Thesis (M.Sc.(Anatomy))--University of Pretoria, 2009. / Includes bibliographical references.