Call number: LD2668 .T4 1950 O2 / Master of Science

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science Johannesburg September 2012 / Electron spin resonance (ESR) was used to characterize a suite of carbon nanospheres (CNS) samples with varying nitrogen concentrations at room temperature. The CNS were produced using two different reactors (vertical and horizontal) under different preparatory conditions. Resonance spectra of samples produced from the vertical reactor showed resonance lines- a narrow paramagnetic component, and broader component. They were attributed to nitrogen paramagnetic impurities and carrier spins, respectively. Samples produced in the horizontal reactor revealed stronger line spectra that were narrower and Dysonian in shape. The nitrogen content of the samples produced by the horizontal reactor was determined through ESR analysis which involves integration of the resonance peak, and normalizing to the mass of the sample. The relative g-shift was also measured by using a DPPH reference sample. Room temperature power saturation experiments were performed on samples produced from the horizontal reactor with the aim of estimating the spin relaxation times. Two samples from the horizontal reactor were further investigated at low temperatures (4 K- 320 K) at a constant microwave power. The resonance parameters investigated were linewidth, asymmetry ratio and amplitude, and possible spin-lattice relaxation mechanisms were investigated. The variation of the amplitude with temperature was investigated using two models: (1) a model based on lattice vibrations, and (2) a model based on nanographites assembly (considered interaction between carrier and localized spins). At low temperatures both models have amplitude that changes inversely with temperature in accordance with Curie law. At high temperatures (T > 200 K) a model based on nanographites assembly provide an alternative; it describes the rise in the signal amplitude in terms of thermally activated paramagnetic electrons from non-magnetic ground state to excited state at energy . Analysis of linewidth and asymmetry ratio data confirmed that the spin-lattice relaxation governed by thermal activated electrons is a dominant relaxation mechanism at high temperatures.

The NRT2 (high affinity nitrate transporter 2) family is a part of the iHATS (inducible high affinity system) that studies have shown is responsible for the influx of nitrate into the plant cell after provision of nitrate. The ZmNRT2.1 from Zea mays was constitutively expressed in Nicotiana tabacum. To assess how over-expression of this foreign NRT2.1 affects nitrate influx by plants, nitrate content in leaf and root tissue, gene expression, and vegetal growth were analyzed in media with deficient or high nitrate concentrations (0.1, 1, or 10 mM). Compared to wild type plants: the transgenic lines had a significantly larger fresh weight in all nitrate conditions; primary root length was significantly longer in the 0.1 and 1 mM nitrate conditions; both the fresh weight and the primary root length were significantly higher when 50 mM NaCl was applied as a stress factor to medias containing 0.1 and 10 mM nitrate. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection

by Kwok Chun-kiu. / Thesis (M.Ph.)--Chinese University of Hong Kong, 1987. / Bibliography: leaves 69-74.

Wheat (Triticum aestivum L. cv Minaret) was grown long-term under CO₂ partial pressures of 36 and 70 or 100 Pa with various N applications (4 to 23 g m-2 N), to test hypotheses of N re-allocation: 1) a decrease in N from leaves to other organs, 2) a relative decrease in N from Rubisco to other photosynthetic components. Elevated CO₂ did not affect phenology, main stem leaf appearance, the pattern of N allocation throughout the plant, or the fraction of crop N in grain at harvest, but 1) stimulated biomass and yield by 5 to 20% over the N range used, and 2) caused a faster loss of N and components from flag leaves during grain-fill. Responses of photosynthesis to varying pCi were fitted, and rates of maximal carboxylation and non-photorespiratory respiration estimated. The former, was proportional to Rubisco content, and light-saturated photosynthetic rate at 70 Pa CO₂ was proportional to A TP-synthase. Potential photosynthetic rates at 70 Pa CO₂ were calculated, compared with observed, and used to estimate excess investment in Rubisco. The excess was greater in high N treatments than low, declining as leaves senesced. The fraction of Rubisco estimated to be in excess, was strongly dependent on leaf N content, increasing from - 5% in leaves with 1 g N m-2 to -40% in leaves with 2 g N m-2. Growth at elevated CO₂ usually decreased the excess somewhat, but only as a consequence of a general decrease in leaf N, given that relationships of components to leaf N content were independent of CO₂ and N treatment, demonstrating that no direct CO₂ effect on N allocation within leaves had occurred. It is concluded that there is scope for improving the N-use efficiency of C₃ crop plants in elevated CO₂ conditions, by genetic manipulation to decrease the amount of Rubisco.

Leung Cheuk-wan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.i / Abstract (Chinese) --- p.ii / Acknowledgement --- p.iii / Table of Contents --- p.v / Lists of Tables --- p.ix / Lists of Figures --- p.x / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- TiO2 Photocatalysis --- p.1 / Chapter 1.1.1 --- Mechanisms of TiO2 Photocatalysis --- p.1 / Chapter 1.2 --- Visible Light Photocatalyst --- p.4 / Chapter 1.2.1 --- Preparation of Visible Light Ti02 Photocatalysts --- p.5 / Chapter 1.2.1.1 --- Dye Sensitization --- p.5 / Chapter 1.2.1.2 --- Metal Doping --- p.6 / Chapter 1.2.1.3 --- Coupling of Semiconductors --- p.6 / Chapter 1.2.1.4 --- Nonmetal Doping --- p.7 / Chapter 1.3 --- Enhanced TiO2 Photocatalytic Activity under UV Light --- p.8 / Chapter 1.3.1 --- Preparation of TiO2 Photocatalyst with Enhanced Activity in UV Light --- p.8 / Chapter 1.3.1.1 --- Loading of Metal --- p.8 / Chapter 1.3.1.2 --- Impurity Co-doping --- p.9 / Chapter 1.3.1.3 --- Morphological Control --- p.10 / Chapter 1.3.1.4 --- Increasing Surface Area --- p.10 / Chapter 1.4 --- Summary --- p.11 / Chapter 1.6 --- Aim of This Research and its Significance --- p.12 / Chapter 1.7 --- References --- p.13 / Chapter Chapter 2 --- Preparation of N-doped TiO2 with Enhanced Surface Area: A Detailed Characterization and Mechanism --- p.19 / Chapter 2.1 --- Introduction --- p.19 / Chapter 2.2 --- Experimental --- p.21 / Chapter 2.2.1 --- Materials and Catalyst Preparation --- p.21 / Chapter 2.2.2 --- Characterization --- p.21 / Chapter 2.2.3 --- Photocatalytic Activity --- p.23 / Chapter 2.3 --- Results and Discussion --- p.24 / Chapter 2.3.1 --- XRD Analysis --- p.24 / Chapter 2.3.2 --- UV-Vis Absorption Spectroscopy and Bandgap Energies --- p.27 / Chapter 2.3.3 --- N2 Sorption Analysis --- p.29 / Chapter 2.3.4 --- SEM Analysis --- p.33 / Chapter 2.3.5 --- TEM Analysis --- p.35 / Chapter 2.3.6 --- FT-IR Spectroscopy --- p.36 / Chapter 2.3.7 --- Raman Spectroscopy --- p.39 / Chapter 2.3.8 --- XPS Studies --- p.44 / Chapter 2.3.9 --- PL Measurements --- p.49 / Chapter 2.3.10 --- Photocatalytic Activity Measurements --- p.50 / Chapter 2.3.11 --- Advantages of Using Urea as a N-doping Source --- p.54 / Chapter 2.3.12 --- Mechanisms for N-doping --- p.56 / Chapter 2.4 --- Conclusions --- p.58 / Chapter 2.5 --- References --- p.59 / Chapter Chapter 3 --- Preparation of Nanoporous Interstitial B-doped TiCO2 with Enhanced Photocatalytic Activity --- p.63 / Chapter 3.1 --- Introduction --- p.63 / Chapter 3.2 --- Experimental --- p.65 / Chapter 3.2.1 --- Materials and Catalyst Preparation --- p.65 / Chapter 3.2.2 --- Characterization --- p.66 / Chapter 3.2.3 --- Photocatalytic Activity --- p.67 / Chapter 3.3 --- Results and Discussion --- p.68 / Chapter 3.3.1 --- XRD Analysis --- p.68 / Chapter 3.3.2 --- UV-Vis Absorption Spectroscopy and Bandgap Energies --- p.71 / Chapter 3.3.3 --- N2 Sorption Analysis --- p.73 / Chapter 3.3.4 --- SEM and TEM --- p.76 / Chapter 3.3.5 --- FT-IR Spectroscopy --- p.80 / Chapter 3.3.6 --- Raman Spectroscopy --- p.82 / Chapter 3.3.7 --- PL Measurements --- p.84 / Chapter 3.3.8 --- XPS Studies --- p.85 / Chapter 3.3.9 --- Photocatalytic Activity Measurements --- p.89 / Chapter 3.3.10 --- State and Form of Boron in TiO2 Lattice and its Effects --- p.91 / Chapter 3.4 --- Conclusions --- p.93 / Chapter 3.5 --- References --- p.94 / Chapter Chapter 4 --- Conclusions --- p.97

Vita. / Digitized by Kansas Correctional Industries

Digitized by Kansas Correctional Industries

Typescript (Photocopy). / Digitized by Kansas Correctional Industries

Dissolved organic matter (DOM) is found in all freshwaters globally, by dissolving in rainwaterduring its path through soil and on to oceans via. rivers and streams. To provide potable water fit for human consumption, selected streams and rivers are used by either direct abstraction, or by diversion into reservoirs prior to treatment. For ca.100 years, chlorine and its compounds have been used by water treatment companies to disinfect water. However, research has shown that reactions between chlorine and DOM can produce compounds (disinfection by-products, or DBPs) which may be hazardous to human health. This thesis explores the relationship between catchment character, organic matter concentration, and the potential formation of DBPs. In particular, trihalomethanes (THMs) were measured as these are currently the only regulated DBPs in the UK. To achieve this, water samples were collected quarterly over one year from two contrasting catchments, to study seasonal variations in DOM concentration and character. A third catchment was also sampled, with similar catchment characters to the first two catchments, to determine whether geographical location and land use types affected the data. Each catchment was studied to see if catchment characteristics (e.g. class of vegetation, soil type or bedrock) could be mapped using a Geographical Information Systems (GIS) approach), to observe any effects on DOM and/or the DBPs found in treated water, with the aim of producing a risk assessment map to aid the choice of future abstraction locations for drinking water. Hence, samples were chlorinated and chloraminatedin the laboratory before being analysed for DBP formation and residual chlorine concentrations were measured. Catchment specific GIS derived data were statistically analysed with water chemistry data, and detected relationships were explored statistically. Major findings include medium to strong positive correlations between the standardised THM4 (STHM4 - the concentration of THM4 formed from 1 mg L-1 dissolved organic carbon (DOC)) concentration and geology, where an increase of the area of inland rock in a catchment increases STHM4 concentration. Medium strength positive correlations were found between STHM4 and vegetation classes, where, as the area of acid grassland, and heather increase, so does the concentration of STHM4. Negative relationships were discovered showing the obverse, where, as loamy and clayey floodplain soils with naturally high groundwater increased in area, STHM4 concentration dropped (at the Hampshire Avon ii and Conwy catchments combined). The occurrence of coniferous woodland in a catchment was found to correlate with the CHCl3 formation potential of waters (Pearsons, f=0.530, p= < 0.05, n=20), supporting findings in published literature. Laboratory based chlorination and chloramination of sample waters, followed by gas chromatography provided DBP data, specifically THM4. These data show that more chloroform was formed after chlorination than chloramination, and that chloramination formed 3 times more CHBr3 (another THM4 compound) than chlorination, under laboratory formation potential conditions. Results showed that the chlorination of water prior to DOM removal could result in a THM4 concentrations 5 times greater than the current UK regulatory limit, per mg L-1 dissolved organic carbon (DOC), whereas chloramination forms ca.5 times less than the current UK regulation per 1 mg L-1 DOC. However, chlorination of water prior to DOM removal is never done in practice, so this data provides information on the composition of the organic matter and whether DOM from a specific catchment contains specific components that are responsible for an increase in a specific DBP. Data also show that increasing organic nitrogen or organic carbon does not necessarily increase nitrogenous or carbonaceousDBPs (N-DBPs or C-DBPs). However, importantly, data shows that an increase in the area of land use classed as 'urban', results in an increase in DON (likely due to human influences) in the water draining from them, posing potential issues for eutrophication in downstream water bodies and the formation of N-DBPs at water treatment works. Whilst N-DBP detection was explored from several different angles, the development of a definitive method was not possible due to very low N-DBP concentrations, time and financial constraints. However, various methods were adapted to aid in the detection of them, showing promising initial results, providing the background for future projects into the discovery of a suite of N-DBPs such as haloacetonitriles and halonitromethanes. Finally, the data in this thesis have been inputted into maps for each major catchment to present data with a high visual impact, but also to illustrate land use types that have been found to correlate with increases in DBPs and specific nutrients in the water draining from them. However, the high variation in DOM concentration and character from site to site make extrapolation of these risk assessment data, to other catchments, unsafe. Nevertheless, collection of data from a catchment (similar to the work presented here) where a new water abstraction location is desired can prove advantageous in providing information to utility companies of what difficulties they may encounter when treating the water. Though this can be done by grab sampling at each site of interest, this can prove costly and timely and involves both field and laboratory based work aspects, wheras the method presented here requires less cost and time, once the method is initialised, to derive data of similar value. Despite the fact that disinfection performance would always trump DBP minimalisation, this is likely to be a vital tool in ensuring the provision of safe and healthy water fit for the consumption of an ever increasing human population.