Thesis (Ph.D)--Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Jacob. Karl; Committee Member: Griffin. Anselm; Committee Member: Tannenbaum. Rina; Committee Member: Thio. Yonathan S; Committee Member: Yao. Donggang. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph.D.) - University of St Andrews, June 2009. / Restricted until 1st June 2011.

Dissertação (mestrado)—Universidade de Brasília, Instituto de Química, Programa de Pós-Graduação em Química, 2016. / Submitted by Fernanda Percia França (fernandafranca@bce.unb.br) on 2016-06-02T17:57:51Z No. of bitstreams: 1 2016_MayaraResendeAlves.pdf: 2627878 bytes, checksum: 05fe8a5d8fcb2f4083f88cc64a2835a0 (MD5) / Approved for entry into archive by Raquel Viana(raquelviana@bce.unb.br) on 2016-07-21T15:49:47Z (GMT) No. of bitstreams: 1 2016_MayaraResendeAlves.pdf: 2627878 bytes, checksum: 05fe8a5d8fcb2f4083f88cc64a2835a0 (MD5) / Made available in DSpace on 2016-07-21T15:49:47Z (GMT). No. of bitstreams: 1 2016_MayaraResendeAlves.pdf: 2627878 bytes, checksum: 05fe8a5d8fcb2f4083f88cc64a2835a0 (MD5) / Heteropoliácidos (HPA) têm sido utilizados na forma protônica ou suportada, sendo esta forma preferível por adquirir propriedades melhoradas em aplicações catalíticas. Esse trabalho relata a preparação, caracterização e aplicação de sais de prata substituídos, derivados do H3PW12O40 (HPW) nas seguintes estequiometrias: AgxH3-xPW12O40, (sendo x= 1,0; 1,5; 2,0; 2,5 e 3,0). A atividade dos sais foi avaliada na reação de desidratação de etanol, a uma temperatura de 300 °C, tendo como objetivo a formação de etileno. Para a série de sais de prata testada foi observada que a conversão de etanol para o catalisador Ag2HPW foi a mais elevada. Diante deste comportamento excepcional do catalisador Ag2HPW, realizou-se um estudo da reação em diferentes temperaturas (200, 250, 300, 350 e 400 °C) obtendo-se conversões de 27,6; 50,2; 63,5; 69,9 e 77,1%, respectivamente. Por conseguinte, este sal foi escolhido para ser suportado em sílica mesoporosa do tipo SBA-15, com posterior avaliação na reação de desidratação. A estrutura do tipo Keggin da fase ativa foi mantida após a impregnação no suporte, enquanto a área específica aumentou de 5 para 576 m2g-1, após a deposição sobre o substrato mesoporoso. A conversão do catalisador suportado 20% Ag2HPW/SBA-15 foi testada nas temperaturas de 300 e 400 °C, apresentando uma conversão de 86 e 100% e seletividade para etileno de 88 e 100%, respectivamente. Esses resultados demonstraram que a conversão de etanol aumentou consideravelmente em comparação com a fase ativa pura do derivado de prata do HPW (i.e., Ag3PW). / Heteropolyacids (HPA) have been used in the protonic or supported form, which is preferential in order to acquire enhanced properties for catalytic applications. This work reports the preparation, characterization and application of substituted silver salts derivatives of H3PW12O40 (HPW) using the following stoichiometries: AgxH3-xPW12O40, (where x = 1.0; 1.5; 2.0; 2.5 and 3.0). The conversion of the salts was evaluated in the ethanol dehydration reaction, at a temperature of 300 °C, aiming the formation of ethylene. In the series of the synthesized silver salts, the conversion of ethanol by Ag2HPW catalyst was the highest. In view of this exceptional behavior of Ag2HPW catalyst, it was carried out a study of the same reaction at different temperatures (200, 250, 300, 350 e 400 °C), which showed conversions of 27.6, 50.2, 63.5, 69.9 and 77.1%, respectively. Therefore, this salt was chosen to be supported (20%) on the mesoporous silica type SBA-15 and evaluated their conversion. The active phase with the Keggin structure was maintained after impregnation on the support, while the specific area increased from 5 to 576 m2g-1 by deposition on the mesoporous substrate. The conversion of supported catalyst 20% Ag2HPW/SBA-15 was evaluated at temperatures of 300 to 400 °C, showing conversions of 86 and 100%, whereas the selectivity to ethylene were 88 and 100%, respectively. These results clearly demonstrate that the conversion of ethanol greatly increased compared to the active phase of silver salt derivative of HPW (i.e., Ag3PW).

Made available in DSpace on 2014-06-11T19:25:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-03-06Bitstream added on 2014-06-13T20:53:37Z : No. of bitstreams: 1 saliba_lf_me_ilha.pdf: 2689127 bytes, checksum: 77157443fa70337c82aeb80e43ec516e (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A sílica mesoporosa do tipo MSU-4 foi sintetizada a partir do agente direcionador de estrutura Tween 20, utilizado como molde, e do precursor inorgânico tetraetilortosilicato (TEOS). Estruturas mesoporosas tem sido aplicadas em estudos luminescentes por apresentarem alto índice de organização, grande área superficial e distribuição regular de tamanho de poros. Nesse trabalho a sílica mesoporosa foi funcionalizada com 3-aminopropiltrietoxisilano (APTES) para aplicação luminescente. A sílica mesoporosa funcionalizada foi caracterizada por difração de raios-X a baixo ângulo (SAXS), espectroscopia no infravermelho (FT-IR) e adsorção e dessorção de nitrogênio (BET). O material luminescente foi preparado pela formação do complexo [Eu(tta)3] em meio metanólico e impregnado nos canais da sílica mesoporosa. Para a impregnação, o íon Eu3+ foi primeiramente encapsulado na sílica e posteriormente foi adicionado o ligante 2- tenoiltrifluoroacetona (tta). Esse procedimento foi realizado para as sílicas lavada, calcinada e funcionalizada. Uma amostra de sílica funcionalizada foi preparada com a impregnação do complexo já pronto. Todas as amostras foram caracterizadas por espectroscopia luminescente. O estudo espectroscópico foi realizado à temperatura ambiente e os espectros de excitação mostraram a absorção de energia pelo ligante tta na faixa do ultravioleta. Os espectros de emissão mostraram as transições características do íon Eu3+, dos estados de maior energia 5D0 para os de menor energia 7F0-4. Foi observado que a transferência de energia do ligante para o íon Eu3+ foi eficiente. A transição hipersensitiva 5D0→7F2 mostrou o efeito das diferentes superfícies da matriz de sílica. PALAVRAS CHAVE: Sílica mesoporosa, luminescência, európio. / MSU-4 type mesoporous sílica has been synthesized with polyoxyethylenesorbitan monolaurate (Tween 20) as structure-directing agent (MTS) as a template and tetraethyl orthosilicate Si(OEt)4 (TEOS) as silica source. The mesoporous structures have a wide application in the luminescence study because of their organization, large surface area, and size of pores. In this work, MSU-4 mesoporous silica was functionalized with 3-amino-propyl-triethoxysilane (APTES) for luminescence applications. Mesoporous silica and amino-functionalized silica was characterized by small-angle X-ray scattering (SAXS), infrared spectroscopy (FT-IR) and nitrogen adsorption/desorption isotherms at 77 K (BET). A luminescent material was prepared by formation of the complex Eu(tta)3 in methanolic medium within the channels of MSU-4 type ordered mesoporous silica. Using simple wet impregnation methods, the europium ion was first encapsulated followed by ligand 2-thenoyltrifluoracetonate (tta) addition. This process it was done for washed, calcined and functionalized mesoporous silica. Analogous one sample of functionalized silica was impregnated with the complex already ready. All samples were characterized by photoluminescence spectroscopy. The spectroscopy studies in room temperature showed the energy absorption of the ligand range ultraviolet in excitation spectra. The emission spectra this materials displayed the typical Eu3+ intra-4f6 lines ascribed to transitions between the 5D0,1 excited states and the ground multiplet (7F0-4). Negligible emission from the organic part of the encapsulated species was observed, indicating that energy transfer from the ligands to the Eu3+ ion was quite efficient. The hypersensitive 5D0→7F2 line showed the mesoporous silica effect in luminescence europium chelate.

In this work, the optical properties of two kinds of one-dimensional (1D) nanomaterials, mesoporous silicon nanowires (mpSiNWs) and plasmonic nanospirals (NSs), were studied. These emerging nanomaterials are of great interest because of their fundamental structure-derived properties and potential practical applications. Four aspects of these materials were analyzed in this work. First, although the fabrication mechanism of mpSiNWs has been studied previously via metal-assisted chemical etching, the porosification-induced disturbance to the etching direction, which plays a vital role in controlling the surface crystallinity of mpSiNWs, has not been characterized. In Chapter 2, I discuss the porosification etching mechanism of n-Si(111), which proceeds along the intrinsic back bond etching direction of [111] at room temperature. The porosification substantially weakens the back bonds under the sinking particles, resulting in the deviation of etching from [111]. The preferred direction of etching changes to that with a small angle α, because the direction-switching barrier increases with α and intrinsic back-bond etching is thermodynamically preferential. Second, mpSiNWs typically generate red photoluminescence (PL), but the PL mechanism is still under debate. A laser was used to oxidize the surfaces of mpSiNWs and tune the PL from red to greenish-blue (GB), as described in Chapter 3. The laser oxidation was tuned as a function of laser power, and a complex model of the laser-induced surface modification was proposed to account for the laser-power and post-annealing effect. The laser-induced modification of the PL of mpSiNWs may be useful for data encryption. Third, the fabrication of plasmonic NSs and the study of their optical activities are in their infancy. In Chapter 4, I describe the use of glancing-angle deposition (GLAD) to fabricate silver NSs (AgNSs) with controllable helicity and demonstrate that AgNSs have intrinsic optical responses that originate from their structural helicity. The optical activity of an AgNSs dispersion was characterized by circular dichroism (CD), and systematic engineering of the helicity revealed that their UV and visible optical activities have two different origins. Fourth, physical limits prohibit the sensitive differentiation of enantiomers. In Chapter 5, I describe the grafting of chiral molecules onto AgNSs, which dramatically enhanced the differentiation of L- and D-glutathione (GSH). AgNSs have very strong optical activities that are weakened by GSH adsorption. The severity of the chiroptical weakening effect varies with the absolute configuration of GSH, resulting in enantiomeric differentiation with an anisotropic g-factor of approximately 0.5. This chiral nanoplasmon-induced anisotropy g-factor is superior by 2 to 4 orders of magnitude to those obtained with other methods and about one-fourth of the theoretical value. This proposed method can be adapted to differentiate chiral drugs, which is highly desirable in the pharmaceutical industry for the production of single-enantiomer drugs.

M.Sc. (Chemistry) / Please refer to full text to view abstract

Matrix assisted laser desorption/ionisation mass spectrometry (MALDI-MS) for small molecule analysis has been plagued with inherent problems associated with matrix interference. The matrix plays an important role in MALDI-MS where it has the ability to absorb UV energy from the laser employed and transfer it to the analyte, acts as a proton donor and protecting the analytes from being obliterated. For decades, research has been performed to eradicate matrix interference by matrix avoidance, finding alternative matrices, suppression through sample preparation methods and via chemical modification.In this investigation a number of the above mentioned approaches have been undertaken. First, a mesoporous silica powder, SBA-16, functionalised with a phenyl group to absorb UV from the MALDI-MS laser gave unfruitful results due to inhomogeneous dispersion of the SBA-16 powder. Therefore the same material was prepared but as a thin film and a homogeneously coated surface was generated with the phenyl group incorporated into the silica and this was compared with a conventional matrix, 2,5-dihydroxybenzoic acid (DHB). This was by far the most sensitive method which was accurate, with little background noise and importantly for small molecule analysis clear of matrix interference. Other surface systems were also tested such as graphene on copper and silver on copper, but the functionalised SBA-16 thin film remained the best. Graphite and 2B pencil were also investigated for MALDI-MS but were compared with conventional matrices (DHB and α-cyano-4-hydroxycinnamic acid (CHCA)) in a functional genomics study. The ability of all methods to find subtle phenotypic differences in various yeast strains was assessed with the help of multivariate data analysis (MVDA). Although DHB came out best, 2B pencil produce notably good separations that correlated nicely with the different genotypes. Therefore in addition to conventional matrices, 2B pencil should be considered for functional genomic studies when MALDI-MS is used as it is such a rapid and inexpensive method. Finally, chemical modifications were performed on amino acids where picolinic acid was used to attach a chromophore to the compounds, therefore, allowing UV absorption from the laser. Upon attaching the picolinate UV absorbing group, the amino acid compounds were detected LC-MS at an increased intensity of 10 to 100-fold. Moreover, enhanced separation in LC-MS was also observed.This project has successfully investigated alternative approaches to matrix-free MALDI-MS analysis. Functionalised SBA-16 thin films were by far the best method and this novel surface for MALDI-MS has the potential to transform small molecule analysis.

Heteropolyacids (HPAs), such as phosphotungstic acid (PTA) and phosphomolybdic acid (PMA), with the Keggin structure are well known as solid superacids with estimated pKa of -13. High acidity of HPAs enabled their use as highly active homogeneous catalysts. However, homogeneous catalysis has many drawbacks, e.g. difficult and expensive separation of the used catalyst from the reaction mixture and its recycling. Application of pure HPAs in heterogeneous catalysis is limited by their low surface area and solubility in polar solvents. For increasing their surface area, HPAs should be immobilized on solid support. The objective of this work is the development of an active and stable HPA-containing catalyst for synthesis of long chain alkylbenzenes, which are essential precursors in the manufacture of surfactants. To prevent leachability of HPA from the support, it was covalently bonded into the silica matrix via Si‑O‑W bridges. The catalysts were obtained by co-condensation of tetraethoxysilane (TEOS) with PTA using sol-gel method in the presence of various surfactants as pore-forming agents. The synthesis was conducted by simultaneous addition of 20% HCl and ethanol solution of a mixture of TEOS and PTA to a solution of a surfactant. The reaction mixture was refluxed for 24 h. The obtained product was filtered, washed, air-dried, and calcined for total removal of a surfactant from pores. Use of Pluronic P123 as a non-ionic pore-forming agent produced the most acidic material. The synthesized mesoporous materials were tested as heterogeneous catalysts in liquid-phase alkylation of mesitylene by long-chain alkenes. They demonstrated higher activity than well-known zeolite HY. The analysis of catalyst recovered after the alkylation indicated no PTA leaching from silica matrix. Obtained superacidic mesoporous materials can potentially replace hazardous liquid Lewis acids currently used for long-chain alkylbenzene synthesis in petrochemical industry.

The main objective of this work was to evidence versatile applications of ordered siliceous mesoporous materials, especially in adsorption and catalysis. For these reasons four mesoporous molecular sieves (SBA-15, SBA-16, MCM-41, and MCM-48) with different structures and textural properties have been chosen. To show the possible application of mesoporous molecular sieves as a CO2 adsorbent, magnesium oxide, and potassium carbonate were incorporated into SBA-15, SBA-16, and MCM-48 silicas. In order to avoid destruction of silica supports, a novel procedure based on the precipitation of magnesium acetate on the silica surface was developed. Subsequent in situ chemical conversion of magnesium acetate provided magnesium oxalate, while magnesium oxide was formed by calcination. To introduce potassium carbonate, silica modified with MgO was impregnated with potassium oxalate followed by its conversion to carbonate. All prepared mesoporous adsorbents preserved characteristic features of mesoporous molecular sieve (large surface areas, narrow pore size distributions). The comparison of carbon dioxide isotherms obtained on prepared samples revealed that their adsorption properties are influenced by the type of mesoporous structure. The SBA-15 silica containing magnesium oxide and promoted by potassium...

Several self-supported and metal oxide supported cobalt Fisher-Tropsch (FT) catalysts were prepared applying incipient wetness impregnation method. The catalysts were characterized by TPR, adsorption-desorption, XRD, TEM and SEM. The gas products were characterized by GC. The effect of support was investigated. The selfsupported 3D ordered macro-porous (3DOM) Fe-Co and self-supported 2D ordered mesoporous catalyst showed low or no activity under typical F-T reaction conditions. The 3DOM Al2O3 supported cobalt catalyst showed much higher CO conversion and C4+ selectivity than conventional Co/Gamma-Al2O3 catalyst. However, the 3DOM Co/Al2O3 prepared by incorporated method showed no activity. The supported Co/SBA-15 performed better CO conversion than the conventional Co/SiO2. The effects of temperature and time on 3DOM Co/Al2O3 and Co/SBA-15 system were coherent with traditional catalysts. The well-defined structure of 3DOM Al2O3 and SBA-15 may favor to the selectivity of C4+ hydrocarbons product.