Thesis (Ph. D.)--Montana State University--Bozeman, 2005. / Typescript. Chairperson, Graduate Committee: Yves U. Idzerda. Includes bibliographical references (leaves 81-84).

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / On t.p. "2" is subscript. Includes bibliographical references. Also available in electronic version.

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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.

Thesis (doctoral)--Helsinki University of Technology, 2001. / Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.Sc.(Metallurgy)--University of Pretoria, 2000. / Summaries in Afrikaans and English. Includes bibliographical references (leaves 108-112).

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