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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.

本论文主要研究了各种可见光光催化剂的合成。包括了Cu₂S，CuO/ZnO复合物以及钒酸根掺杂的磷酸银材料。论文讨论了这些光催化剂的性质与光催化活性，机理同应用也在本文中进行了探讨。 / 首先，发现并合成了硫化亚铜十四面体纳米粒子。研究中发现三正辛基膦对硫化亚铜多面体的形成是必需的。得到的硫化亚铜多面体具有暴露的罕见的面。通过对其光电活性的研究发现，相对于常见的硫化亚铜六边形片状纳米粒子，这种多面体具有5倍以上的活性。 / 其次，异质结构的CuO/ZnO复合材料通过光化学沉积合成。在这两种半导体的接触面形成了p-n结，促进了电子在两者间的传递。在荧光谱图中发现，因电子空穴淬灭引发的荧光峰消失了。这代表由于异质节的形成电荷分离的效率大大提高，从而光催化的效率也得到了很好的提高。 / 最后，含氧根离子作为一种新型的掺杂材料被用于提高磷酸银的性质。磷酸银光解水的能力经过掺杂后得到了显著提高。同时，其在可见光下的稳定性也获得了很大的提高。含氧根离子掺杂物对于磷酸银材料的性质改变及机理在文中都进行了探讨。 / This thesis focuses primarily on the development of visible-light-driven photocatalysts. These include Cu₂S, CuO/ZnO composites and vanadate doped Ag₃PO₄. The property and activity of the materials were studied. The application and mechanism of the enhancement were also explored. / Firstly, 14-facet polyhedra Chalcocite Cu₂S Nanocrystals were synthesized utilizing solvothermal method. It was found that the presence of trio-n-octylphosphine was essential for the exposure of unconventional faces. Studies of the photoelectrochemical performance have indicated that the polyhedra bounded by facets exhibit much higher activities than Cu₂S hexagonal plates with only facets. / Secondly, a heterostructure of CuO/ZnO was fabricated via photochemical deposition. The formation of p-n junction improved the visible light absorption property of ZnO. Photoluminescence spectra showed diminished peaks caused by recombination of excited electrons and holes in the semiconductor which demonstrated that the heterostructure facilitated the charge separation and thus enhanced the photocatalytic activity. / Thirdly, an oxoanion doping method was employed to improve the properties of Ag₃PO₄. The water oxidation ability was found to be higher than the pure Ag₃PO₄. The doping method was proven to be effective in both improving activity and durability. The mechanism of the doping method was also discussed. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Li, Yecheng. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 71-77). / Abstracts also in Chinese. / Abstract (Chinese) --- p.i / Abstract --- p.ii / Acknowledgement --- p.iii / List of Figures --- p.v / Table of Contents --- p.viii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1. --- Basic Principles of Photocatalysis --- p.1 / Chapter 1.2. --- Strategies to Develop Visible-light-driven Photocatalysts --- p.4 / Chapter 1.2.1. --- Native visible-light-driven photocatalysts --- p.4 / Chapter 1.2.2. --- Ion substitution (doping) --- p.6 / Chapter 1.2.3. --- Solid solution photocatalysts --- p.10 / Chapter 1.2.4. --- Dye sensitization to harvest visible light --- p.13 / Chapter 1.3. --- Strategies to Enhance Photocatalytic Activity --- p.15 / Chapter 1.3.1. --- Interface engineering --- p.15 / Chapter 1.3.2. --- Band gap engineering (Tuning distribution of dopants) --- p.17 / Chapter 1.3.3. --- Crystal structure and morphology engineering --- p.19 / Chapter 1.3.4. --- Cocatalyst loading --- p.23 / Chapter 1.4. --- Summary --- p.25 / Chapter 1.5. --- Objective of the Thesis --- p.25 / Chapter Chapter 2 --- Facet Effect of Copper(I) Sulfide Nanocrystals on Photoelectrochemical Properties --- p.28 / Chapter 2.1. --- Introduction --- p.28 / Chapter 2.2. --- Experimental --- p.30 / Chapter 2.2.1. --- Synthesis --- p.30 / Chapter 2.2.2. --- Characterization --- p.30 / Chapter 2.2.3. --- Photoelectrochemical performance analysis --- p.31 / Chapter 2.3. --- Results and Discussion --- p.32 / Chapter 2.4. --- Conclusions --- p.40 / Chapter Chapter 3 --- CuO-ZnO Composites for Enhanced Photoelectrochemical Performance --- p.41 / Chapter 3.1. --- Introduction --- p.41 / Chapter 3.2. --- Experimental --- p.42 / Chapter 3.2.1. --- Synthesis --- p.42 / Chapter 3.2.2. --- Characterization --- p.43 / Chapter 3.2.3. --- Photoelectrochemical performance analysis --- p.44 / Chapter 3.3. --- Results and Discussion --- p.45 / Chapter 3.4. --- Conclusions --- p.56 / Chapter Chapter 4 --- Vanadate Doped Ag₃PO₄ and Its Enhanced Photoactivity and Durability --- p.57 / Chapter 4.1. --- Introduction --- p.57 / Chapter 4.2. --- Experimental --- p.59 / Chapter 4.2.1. --- Synthesis --- p.59 / Chapter 4.2.2. --- Characterization --- p.59 / Chapter 4.2.3. --- Oxygen evolution tests --- p.60 / Chapter 4.3. --- Results and Discussion --- p.61 / Chapter 4.4. --- Conclusions --- p.68 / Chapter Chapter 5 --- Summary --- p.69 / Reference --- p.71

Thesis (M.S.)--University of Delaware, 2006. / Principal faculty advisor: John S. Boyer, College of Marine and Earth Studies. Includes bibliographical references.

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