Previous studies on dwarf bean plants have found a very limited growth response to CO₂ enrichment (Jolliffe and Ehret, 1985; Ehret and Jolliffe, 1985b). There was no increase in leaf area, and leaf injury was observed after about three weeks of CO₂ enrichment (Ehret and Jolliffe, 1985a). Although dry weight was increased, the increase may be limited due to restricted carbon utilization (e.g. no increases in leaf area). In this study, non-photosynthetic limitations, such as the partitioning of dry matter among plant parts, the partitioning of carbon among photosynthetic end products, and the interactive effects of nutrient and carbon supply on growth, that may contribute to the observed growth responses were investigated. Bean plants responded to CO₂ enrichment by increasing their total dry weights. This weight increase was caused by higher growth rate, at least at early growth stages, and higher unit leaf rate. The dry weight increase was mainly in the leaves, and was not evenly distributed among all plant parts. Leaf expansion and branching were not enhanced by CO₂ enrichment. The differential effects of CO₂ enrichment on growth of different parts caused significant increases in specific leaf weight and shoot root ratio, and a decrease in leaf area ratio. These results indicated that the bean plants used in this study have a limited ability to utilize the extra carbon that was fixed under CO₂ enrichment. There were small increases in glucose, fructose, and sucrose concentrations early in the CO₂ treatments. These increases became much larger after three weeks of CO₂ enrichment. The timing of the higher increases in leaf soluble sugars coincided with the timing of increases in stem and roots dry weight. There was also a large increase in starch concentration shortly after plants were transfered to CO₂ enriched condition. The higher starch concentration accounted for the majority of the weight increase in CO₂ enriched leaves, and this starch level was maintained for several days after plants were switched back to ambient CO₂ levels. A ¹⁴C study on the partitioning of carbon between leaf pools showed that carbon transfer out of the storage pool under CO₂ enrichment was limited. CO₂ enrichment had no effects on leaf protein and amino acid concentrations. No difference, or slight increases, were found in inorganic nutrient concentrations per unit leaf area. Plants grown under CO₂ enrichment, however, show a higher loss of nutrients (especially N and K) from older shoot parts (primary leaves and older trifoliates) to younger parts. High NO₃ ̄ supply increased plant dry weight and leaf area under both CO₂ enriched and ambient conditions. The dry weight increases of the stem and roots caused by CO₂ enrichment, however, were much higher and earlier for high NO₃ ̄treated plants. Furthermore, lower leaf starch concentration was also observed for those CO₂ enriched high NO₃ ̄ treated plants. High NO₃ ̄ supply also increased the leaf nutrient concentrations (N, K, Mg, Ca). Increased uptake of nutrients for high NO₃ ̄ treated plants may be partly contributed by the enhanced root growth. In addition to the growth responses, foliar abnormalities developed gradually in beans under CO₂ enrichment. Chlorosis, assessed by a loss in total chlorophyll concentration, was observed in the primary leaves after about three weeks of CO₂ enrichment. The disorder eventually appeared in the oldest trifoliate leaves after more prolonged CO₂ enrichment. The onset of leaf injury was correlated with the timing of the increases in leaf soluble sugars and the redistribution of nutrient elements from the older shoot parts to the younger parts. High NO₃ ̄ supply delayed the development of leaf injury induced by high CO₂. Results in the present studies indicate that growth responses of dwarf bean plants to CO₂ enrichment were affected by the limited carbon partitioning, and the restriction of starch degradation was indicated to be the probable cause. A higher carbon input under CO₂ enrichment may create a higher demand for inorganic elements. Effects of nutrient supply (NO₃ ̄) on growth responses and leaf injury of CO₂ enriched plants suggested that an imbalance between carbon and nutrient input could be partly related to the limited growth responses of dwarf bean plants to CO₂ enrichment. / Land and Food Systems, Faculty of / Graduate

Orientador: David Mario Comedi / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-04T02:13:38Z (GMT). No. of bitstreams: 1 IniguezCalero_AnaCarola_D.pdf: 1593724 bytes, checksum: 56fea847e5f2ce6d5f980c55771d8073 (MD5) Previous issue date: 2004 / Resumo: Neste trabalho foram estudadas as propriedades morfológicas, estruturais e elétricas de filmes finos de TiOx depositados pelo método de rf-sputtering em função da temperatura de aquecimento do substrato (Ts) e do fluxo de oxigênio (FO2). Também foi explorada a possibilidade de aplicação dos filmes na detecção de fenol em água através da medida da fotocorrente em uma célula fotoeletroquímica com eletrodo de TiOx.O valor de x foi obtido por espectrometria de retroespalhamento Rutherford (RBS), a razão anatase/rutilo (A/R) e o tamanho de grão (D) por difração de raios-X (XRD), e a morfologia e a rugosidade por microscopia de força atômica (AFM). Os estados de oxidação foram determinados por espectroscopia de fotoelétrons (XPS). A eficiência de conversão fóton ¿ elétron ( f ) foi determinada a partir de medidas da fotocorrente na célula fotoeletroquímica. A maioria dos filmes obtidos é subestequiométrica (1.80<x<2.04), onde x aumenta com FO2 e Ts. Não se encontrou evidencias de outros óxidos de Ti além do TiO2. A deposição apresenta três regimes principais:(I) Para valores baixos de Ts(= RT), o crescimento é limitado pela mobilidade dos precursores, os filmes atingem a maior rugosidade, o menor D (» 7 nm) e oa menor f (» 0.1). (II) Para 160oC<T<250oC a mobilidade dos precursores aumenta, a rugosidade diminui, enquanto que D e A/R aumentam com Ts. Dados da literatura, em conjunto com a observação da dependência linear da rugosidade média com a espessura dos filmes, indicam que variações locais da taxa de deposição devido às irregularidades da superfície (mecanismo conhecido como "efeito sombra") domina a morfologia neste regime e no regime I.(III) Para 250oC<T<350oC, a rugosidade e a razão A/R dos filmes independe de Ts. Isto é atribuído ao progressivo aumento da mobilidade dos precursores e do D, o qual leva à estabilização da fase rutilo e à dominação do facetamento na determinação da morfologia.Os valores de f medidos para os filmes nos regimes I e II estão em torno de 0,6, comparáveis aos reportados na literatura, e alcançam o valor de » 1 no regime III. O aumento da FO2 (em TS=160o C), por outro lado, resultou na diminuição de D e na queda da intensidade dos picos de XRD. Isto é atribuído à diminuição da mobilidade dos precursores no crescimento devido à diminuição da sua energia cinética média, que por sua vez decorre da oxidação do alvo de Ti durante a deposição e à ejeção de moléculas de TiO e TiO2 do mesmo. A corrente eletrolítica no sistema TiOx (iluminado)/água(fenol)/Pt é linearmente sensível à concentração de fenol na água ( CF), sendo que a sensibilidade e a corrente de troca extrapolada para CF=0 [I0(0)] dependem dos parâmetros da deposição dos filmes.I0(0) diminui em correlação com o aumento de D, indicando que o transporte nos filmes pode ser via fronteiras de grão ou que a transferência de carga na interface TiOx /solução acontece preferencialmente em sítios que se encontram nas regiões entre grãos / Abstract: The morphological, structural and electrical properties of rf-sputter deposited TiOx films were studied as a function o the substrate temperature (TS) and the oxygen flow rate (FO2). The possibility of applying the TiOx films as electrodes for phenol detection in water through photocurrent measurements in a photoelectrochemical cell was also explored.The x values were obtained by Rutherford backscattering spectrometry (RBS), the anatase-to-rutile ratio (A/R) and crystallite size (D) by X-ray diffraction (XRD) and the morphology and roughness by atomic force microscopy (AFM). The oxidation states in the samples were determined by X-ray photoelectron spectroscopy (XPS). The photon-to-electron conversion efficiency ( f ) was deduced from photocurrent measurements in the photoelectrochemical cell. Most of the films were found to be substoichiometric (1.80<x<2.04), while x increases with FO2 and TS. No evidences for the presence of oxides other than the TiO2 were found.The deposition proceeds at three main growth regimes: (I) For low TS (=RT), film growth is limited by low precursor mobilities, the films reaching the highest roughness and the lowest D (» 7 nm) and f (» 0.1). (II) For 160oC<x<250oC the precursors mobility increases, the roughness diminishes, while D and A/R increase with TS. Literature data together with the observed linear dependence of the average roughness with the film thickness indicate that local variations of the deposition rate due to surface irregularities (the so-called "shadowing effect" mechanism) dominates the morphology in this and also in regime I. (III) For 160oC <x<350oC the roughness and the A/R ratio is independent of TS. This is attributed to a gradual increase of the precursors mobility and of D, which stabilizes the rutile phase and leads to increased faceting, an effect that turns to dominate the morphology in this regime. The measured f values for the films grown within regimes I and II are around 0.6, in agreement with data from the literature, while for the samples prepared within regime III the f reaches values close to » 1. Increasing the FO2 (for TS=160oC), on the other hand, leads to the reduction of D and to the weakening of the X-ray diffraction peaks. This is attributed to a reduction of the precursors mobility in the growth due to a lowering of their mean kinetic energy. This effect, in turn, results from the oxidation of the Ti sputtering target that occurs during the deposition and the ejection of TiO and TiO2molecules from it. The current measured in the TiOx(illuminated)/water(phenol)/Pt system is found to be linearly sensible to the phenol concentration (CF) in water. The corresponding sensitivity and the exchange current extrapolated to CF=0 [I0(0)] depend on the deposition parameters used during film growth. In particular, I0(0) diminishes in correlation with the growth of D, indicating that the electrical transport in the films may be through the grain boundaries or that charge transfer at the TiOx/solution interface happens preferentially at sites located in the inter-grain regions / Doutorado / Física / Doutor em Ciências

thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2016. / Selective CO methanation (SMET), as an alternative process for cleaning trace CO in reformate gas feed for fuel cell applications, has gained increasing attention recently. This is mostly due to the fact that the technique can circumvent the major setbacks experienced in the preferential oxidation (PROX) reaction of CO to CO2. The PROX technique is a more established process and has been extensively researched over the years. In this project, we have focused on studying Ru supported on carbon and titania based materials for the selective CO methanation reaction. A rutile morphology in the form of a novel dandelion like structure was synthesized using TiCl4. The rutile dandelion like structure was composed on rutile nanorods which were radially arranged and they had fairly high surface area (61 m2g-1). Titania rutile was also synthesized by calcining anatase at 900 ℃ for 10 h. It was observed that the rutile grains had grown larger after the transformation from anatase to rutile and this was accompanied by a collapsed surface area (from 52 to 9 m2/g). The two rutile morphologies were employed as Ru catalyst supports and applied in both CO and selective CO methanation reactions. The dandelion like supported catalyst demonstrated higher catalytic performance compared to the thermally prepared rutile supports. This was attributed to the smaller Ru particles sizes which were found to be sinter resistant. Small RuO2 nanoparticle sizes supported on carbon nanotubes (CNTs) were obtained by the use of a microwave polyol synthesis. Tuning the microwave temperature generated the different RuO2 sizes without changing the percentage loading or conventionally heat treating the catalyst. The CNTs were synthesized by a chemical vapour deposition (CVD) method using a Fe-Co/CaCO3 catalyst. The microwave polyol synthesized catalysts were compared to a wet impregnated catalyst. It was noted that the impregnated catalyst preparation method showed little control over the RuO2 particle size distribution. The catalysts were tested in both selective CO and CO methanation. The catalyst with smaller particle sizes, prepared using a short microwave induction time, performed better when compared to the other catalysts. It was also observed that all the catalysts promoted the undesired reverse water gas shift reaction for all the catalyst at temperatures above 260 ℃. Abstract The surface of the CNTs were altered by introducing pyridinic nitrogen in an in situ doping process to give nitrogen doped CNTs (N-CNTs). The doping was confirmed by TEM as the CNTs were seen to show bamboo compartments in the tubular CNT structure. A composite of CNT-TiO2 was prepared by a facile hydrothermal process and used to modify the CNTs. The TiO2 (anatase) coated CNTs were synthesized using titanium butoxide as anatase source. A solution containing CNTs and the TiO2 source was reacted in an autoclave. Images from TEM and SEM revealed partially coated anatase N-CNTs and CNTs. Both the doping and the coating of the CNTs resulted in an improved surface area. The coated samples showed significantly improved thermal stability which was attributed to the shielding effect of the TiO2. Raman analysis revealed that the N-CNTs had a high defect content compared to the CNTs. When these materials were employed as Ru catalyst supports for methanation reactions, the nitrogen doped CNTs demonstrated superior catalytic activity compared to the CNT supported catalyst. They both promoted the reverse water gas shift reactions. The NCNT-TiO2 and CNT-TiO2 catalysts showed higher activity and significantly retarded the reverse water gas shift reaction. Mesoporous solid carbon spheres (CSs-H) synthesized via the hydrothermal route using sugar as carbon source was functionalized by acid treatment. The data were compared to an un-functionalized CSs-H used as a Ru catalyst support. Raman data suggested a high defect content for the functionalized spheres and the carbons had a slightly higher surface area when compared to the un-functionalized spheres. Two catalysts were prepared from the functionalized solid carbon spheres; a microwave irradiation prepared catalyst and a wet impregnation prepared catalyst. The microwave prepared catalyst, with slightly smaller Ru particles, performed slightly better in both CO and selective CO methanation reactions than the impregnated catalyst. In the CO2 only methanation reaction almost similar activity was obtained for both catalysts which implied the preparation method did not have much effect on the reaction. The un-functionalized supported catalyst performed poorly in both the reactions due to the poorly dispersed Ru nanoparticles which had sintered. Despite the poor performance, the catalyst did not promote the undesired RWGS reaction. This was attributed to the absence of oxygenated functional groups such as OH. / LG2017

The hydrothermal method of synthesis was successfully utilized to produce the rutile dandelion support onto which different noble metals were deposited using the deposition precipitation method to prepare the Au-TiO2, Pt-TiO2, Pd-TiO2 and Rh-TiO2 catalysts. The catalysts were prepared at different metals loadings. The deposition precipitation method was also employed to deposit the same metals (Au, Pt, Pd and Rh) onto the rutile (110) and (111) crystal surfaces to model the catalysts. Transmission electron microscopy, scanning electron microscopy and powder X-ray diffraction were used as the main characterization techniques to study the preferred deposition sites of the metals as well as the composition of the catalysts. TEM analysis showed the metals to deposit onto the sides and tips of the rutile nanorods making up the dandelion support structure. SEM analysis showed the metals to deposit onto the (110) and (111) crystal surfaces with the exception of Pd which deposited onto the (111) and (001) surfaces only. TEM analysis showed that the metals agglomerated following Temperature-Programmed Reduction (TPR) under H2 gas. TPR analysis showed strong-metal-support interaction for the Pt, Pd and Rh catalysts.

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This thesis work focused on polymer modification of silicon surface to improve its resistance to protein adsorption. Surface modification was achieved through surface-initiated atom transfer radical polymerization (SI-ATRP) grafting of poly(N,N-dimethyl amino) ethyl methacrylate (PDMAEMA). Since PDMAEMA is CO2-responsive, CO2 cleaning of the modified surface was also investigated. SI-ATRP was chosen to graft PDMAEMA brushes on silicon surface for high graft densities and its good control of polymer molecular weight and polydispersity. Surface characterization of PDMAEMA-modified silicon surfaces included hydrophilicity, layer thickness and surface chemical elemental composition. Protein adsorption experiments were carried out to evaluate the protein resistance of the modified surfaces. Albumin adsorption from single protein solution, as well as from human plasma, decreased significantly after PDMAEMA grafting, and the adsorbed amount decreased with increasing polymer chain length. The maximum decrease in adsorption of 90% relative to the unmodified silicon, was reached at a graft layer thickness of 40 nm (measured in the dry state). Protein resistance in plasma showed PDMAEMA -modified silicon provided significant resistance to most of the tested proteins. Compared to the PEO-modified surface, the PDMAEMA surface showed much greater resistance to albumin adsorption, but, surprisingly, it adsorbed relatively large amounts of vitronectin and prothrombin. Vitronectin may have been degraded in contact with PDMAEMA-modified surface. Also, it was the only surface out of the four, which adsorbed significant amounts of prothrombin. These unexpected observations indicate further investigation will be required to fully assess the protein-resistant properties of these PDMAEMA surfaces. CO2-induced protein desorption was also studied. Cleaning experiments were performed by bubbling CO2 into vials containing the protein-adsorbed PDMAEMA-modified surface after 2 h protein solution exposure. Radiolabelling of albumin showed that the CO2 cleaning effectiveness was related with the PDMAEMA thickness. It was found that a surface with graft thickness 20 nm (dry) responded more strongly to CO2 than one with 15 nm thickness. Western blotting results confirmed that CO2 contributed to protein desorption from the PDMAEMA surface. / Thesis / Master of Applied Science (MASc)

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