京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21590号 / 理博第4497号 / 新制||理||1646(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 寺西 利治, 教授 島川 祐一, 教授 吉村 一良 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The relationships that exist between soil and plant are very complicated and have aroused man's curiosity for centuries. Many studies have been done in order to understand and clarify this relation. Among these is the hypothesis that plant roots exhibit cation exchange capacity (CEC) and that this is in some way responsible for differential cation uptake . The CEC of the roots was defined by Helmy (l958a) as the total cations which can be exchanged or replaced from the root surface under a given set of conditions and is usually expressed as milli-equivalents per 100 grams (me/100 g) of dry roots. The CEC hypothesis of cation uptake proposes that the uptake of cations from soil by plants is in some extent controlled by the CEC of the plant roots and the valence of the cations. The CEC may therefore account for the differences between species in taking up different amounts of nutrients from the same soil.

A yellowing which develops in some plants growing on naturally calcareous soils is called lime-induced chlorosis. The problem is complex, as indicated by Brown and Holmes (1956) and Porter and Thorne (1955). Species and varieties of plants differ in their iron requirements, susceptibility to lime- induced chlorosis, and inter acting soil f actors which affect iron supply (Thorne et al 1950). Chlorosis of plants does not appear, therefore, to stem from a common causative factor. At least a part of this difference has been found to be associated with the plant roots. Thus, through the use of resistant root stock Wann (1941) was able to produce non-chlorotic grapes. These grapes grown under similar conditions without the resistant root stock would have been high1y chlorotic. Certain citrus root stocks have also been used on calcareous soils because they give citrus trees resistance to chlorosis.

Electrodialysis is a membrane separation process that uses an electrical potential to drive the separation. The performance of these systems is largely based on the performance of their ion exchange membranes (IEMs). This research focused on enhancing the performance of IEMs for electrodialysis through surface modification techniques involving chitosan bonded to the surface of commercially available cation exchange membranes (CEMs). The surface functionalization techniques resulted in membranes with improved electrodialysis performance. This research also explored the processing framework to produce functionalized sulfonated PEEK (sPEEK) nanofibers for future consideration as cation exchange membranes. Chitin was deacetylated to form the functionalized biopolymer chitosan, then applied to the surface of CEMs, rendering them more hydrophilic. These membranes were evaluated across several electrodialysis performance metrics. Results demonstrate that adjusting the degree of deacetylation of chitosan to enhance membrane hydrophilicity positively impacted electrodialysis performance. Furthermore, this research evaluated the effectiveness of similarly functionalized membranes to extract Lithium from brine solutions. The chitosan-coated membranes showed improved electrodialysis performance, including enhanced flux, limiting current density, system resistance, selectivity, and fouling resistance. Lastly, the sPEEK nanofibers were produced for the fabrication of ion exchange membranes by manipulating operational parameters to assess their impact. This research presents the successful functionalization of PEEK via sulfonation and electrospinning of the resulting sPEEK. These nanofibers were then pressed to form a solid sPEEK membrane. It was observed that changes in electrical potential and rotational speed influenced fiber diameter and spinnability. A correlation was established between membrane surface hydrophilicity and electrodialysis performance metrics in desalination and lithium extraction applications. This research advanced the understanding of structure-property relationships for CEMs. The research herein proposes techniques for industries such as desalination and lithium extraction that can meet growing demands for clean water and sustainable methods for producing high-value raw material streams.

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This work examined the effects of thermal and chemical treatments on zeolite reactivity and determined the zeolite properties governing the development of compressive strengths and pozzolanic reactivity. Zeolites are naturally occurring aluminosilicate minerals found abundantly around the world. Incorporation of zeolites in cement mixtures has been shown by past research to increase concrete’s compressive strength and durability. In addition, use of zeolites as SCMs can decrease the environmental impact and energy demands associated with cement production for reinforced concrete structures. Further, in contrast to man-made SCMs such as fly ash, zeolite minerals provide a reliable and readily available SCM source, not affected by the production limits and regulations of unrelated industries such as the coal power industry. In this work, six sources of naturally occurring clinoptilolite zeolite were examined. The zeolites were first characterized using x-ray fluorescence, quantitative xray diffraction, thermal analysis, particle size analysis, pore size distribution and surface area analysis, and scanning electron microscopy. Cation exchange capacity was also tested for one of the zeolites. Following comprehensive material characterization, the six pozzolanic reactivity of the natural zeolites was determined by measuring the quantity of calcium hydroxide in paste after 28 or 90 days, by measuring calcium hydroxide consumption of the zeolite in solution and by tracking the development of strengths of zeolite-cement mortars. Pretreatments that attempted to increase the reactivity of the zeolites, including calcination, acid treatment, milling and cation exchange, were then tested and evaluated using the same methods of material characterization and testing mentioned previously. Last, the results of the reactivity testing were reanalyzed to determine which properties of natural zeolites, including particle size, nitrogen-available surface area, and composition, govern the development of compressive strengths, pozzolanic reactivity and improved cement hydration parameters of pastes and mortars using natural zeolites as SCMs. Pretreatment testing showed that milling and acid treatment successfully increased the reactivity of zeolites used as SCMs. Additionally, particle size was shown to be the dominant property in determining the development of compressive strengths while particle size and surface area of the zeolites contributed to zeolite pozzolanic reactivity. / text

Nanometer-sized semiconductor crystals, termed ‘quantum dots’, are of fundamental interest because of their size-tunable properties. Three-dimensional quantum confinement of charge carriers by the small crystal size results in discrete atomic-like electronic states. This dissertation describes the synthesis and in-depth characterization of lead chalcogenide colloidal quantum dots for forthcoming applications as near-infrared single photon emitters. An efficient single photon source that operates at telecommunication wavelengths (between 1.3 and 1.6 µm) is a basic requirement for many photonic quantum technologies, such as quantum computing and quantum cryptography. Chapters 1 and 2 of this work provide an introduction to colloidal quantum dots and their use as single photon emitters. It includes a description of photonic crystal microcavities and their ability to enhance the spontaneous emission rate of quantum dots. The synthesis and basic characterization of PbSe and PbS quantum dots is then discussed in chapter 3. In particular, a new synthetic method for the preparation of highly photoluminescent PbS quantum dots is presented. PbSe/CdSe core/shell quantum dots prepared by a cation exchange reaction are also described and a significant improvement in photo-stability is shown. Chapter 3 concludes with a description of three different surface modification techniques. PbSe core and PbSe/CdSe core/shell materials are investigated further in chapter 4 by advanced characterization techniques that include high-angle annular dark field (HAADF) imaging, energy-filtered transmission electron microscopy (EF-TEM) imaging, energy-dependent X-ray photo-electron spectroscopy (XPS), small angle X-ray scattering (SAXS), and small angle neutron scattering (SANS). The information obtained from these techniques is combined to form a structural model of the PbSe core and PbSe/CdSe core/shell quantum dots with greater complexity than previously reported. In chapter 5, the temperature-dependent photoluminescence from PbSe and PbSe/CdSe core/shell quantum dots is discussed and a thermal model is presented that accounts for the large (non-trivial) temperature dependence of the Stokes shift and photoluminescence lineshape over the entire temperature range (4.5 to 295 K). Chapter 6 examines two scalable methods to integrate the colloidal quantum dots into silicon two-dimensional photonic crystal slab microcavities (a requirement for efficient single photon emission). Finally, conclusions and possible future work are discussed in chapter 7. / Graduate

In Arctic tundra soils pH serves as an important parameter related to several biotic parameters such as, plant and microbial community composition, biodiversity, nutrient dynamics and productivity. Both abiotic and biotic factors, for instance, base saturation (BS) and plant nutrient uptake may exert a control on soil pH, while it is still unclear to what extent different factors can explain soil pH across different tundra vegetation types. The aim of this study was to investigate to what extent different abiotic and biotic factors influence soil pH in the humus layer across different tundra vegetation types. To do so, eight different tundra vegetation types of which four were underlaid by permafrost (Arctic Alaska) and four with no permafrost (Arctic Sweden) were studied in detail with regard to different properties affecting soil pH. I found that BS was the main factor controlling soil pH across the different vegetation types regardless if the soil was underlain by permafrost or not. Factors, such as, ionic strength or soil water content could not explain any overall pH variation and did only significantly affect the heath soils. Further, the uptake of the most abundant base cations (Ca2+, Mg2+ and K+) from meadow and heath vegetation revealed a high difference between plant functional groups within the same vegetation types. The higher dominance of slow growing woody species in heath vegetation which had a lower uptake corresponded with a lower BC content (especially (Ca2+), pH and BS in the humus soil relative the meadow meanwhile the content of K+ was more than three times higher in heath. Overall, this study suggests that the degree of neutralization (base saturation) regulates pH either via the influence of bedrock and hydrogeochemistry and/or via plant traits that affects the uptake and turnover of base cations.

The current study investigated application of natural adsorbents in brine treatment. Brines are hypersaline waters generated in power stations and mining industries rich in Mg2+, K+, Ca2+, Na+, SO4 2- , Cl- and traces of heavy metals, thus there is a need for these brines to be treated to recover potable water and remove problematic elements. Natural adsorbents have been successfully used in waste water treatment because of their high surface area and high adsorptive properties when they are conditioned with acid or base. The investigation of pH showed that natural adsorbents did not perform well at low pH of 4 and 6. The adsorbents were able to work efficiently at the natural pH of 8.52 of the brine solution. These results show that natural adsorbents hold great potential to remove cationic major components and selected heavy metal species from industrial brine wastewater. Heterogeneity of natural adsorbents samples, even when they have the same origin, could be a problem when wastewater treatment systems utilizing natural clinoptilolite and bentonite are planned to be developed. Therefore, it is very important to characterize the reserves fully in order to make them attractive in developing treatment technologies.

Membrane chromatography was investigated as an alternative method to packed-bed chromatography for protein recovery. The purification of lysozyme from egg white with Natrix adseptTM weak cation-exchange membranes was investigated under two different binding configurations: (1) a non-flow, static set-up with variable pH and sodium chloride (NaCl) concentrations during the binding and elution steps, and (2) a dynamic, cross-flow set-up with recycle at pH 7.5 and no NaCl addition during binding. The weak cation-exchange membrane consisted of a carboxylic acid-based, environmentally-responsive hydrogel layer bonded to a polymer matrix. Lysozyme was chosen to illustrate protein-membrane binding interactions due to its well-characterized nature and positive surface charge over a large pH range. For the static binding set-up, two sources of lysozyme were studied: pure lysozyme and egg whites treated with 60 % (v/v) ethanol (ESEW). Elution of bound protein was performed with 1 M NaCl under two pH strategies: binding and elution at a constant pH, and binding at pH 4.5 and variable elution pH. The highest maximum total protein binding capacity for pure lysozyme and ESEW was observed at pH 4.5 with no NaCl addition; however, poor total protein and lysozyme activity recovery were achieved during separation. As well, other egg white proteins, such as ovomucoid, were observed to bind to the membrane surface at pH 4.5, despite possessing similar charge polarity to the anionic membrane surface, indicating a non-electrostatic binding mechanism during operation below the membrane’s pKa (4.7). Based on the conditions tested, the highest total protein and lysozyme activity recovery was demonstrated for the separation of lysozyme from ESEW at pH 7.5 binding and elution and no NaCl addition. In the dynamic binding study, very high pure lysozyme dynamic binding capacity was achieved at 10 % breakthrough (167.3 mg/ml membrane for a 0.35 mg/ml lysozyme solution). The lysozyme dynamic binding capacity was 2.2 times greater than the static binding capacity under similar conditions, significantly higher than published results for other cation-exchange membranes. The separation of lysozyme from four lysozyme sources was tested: pure lysozyme, ESEW, and aqueous egg whites with (ASEW) and without (AEW) 100 mM NaCl. The highest lysozyme activity recovery during separation and lysozyme purity was achieved from the ESEW feed. Lysozyme separation from aqueous egg whites was not as effective, likely due to a high concentration of negatively-charged protein impurities fouling the surface of the membrane. Competitive binding to the membrane limited lysozyme binding and reduced the purity of the recovery elution stream. The application of feed-side pressure during the separation of ESEW produced a high purity, high recovery lysozyme elution stream with a significant reduction in processing time; however, protein aggregates were observed to form on the membrane surface, limiting the applicability of high-pressure operation and reducing protein functionality in the elution stream. The weak cation-exchange membrane system was shown to successfully separate out a target protein from a low concentration protein mixture through electrostatic interactions, and may be further applied to other protein systems.