Made available in DSpace on 2016-03-07T19:21:07Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-10-26. Added 1 bitstream(s) on 2016-03-07T19:23:56Z : No. of bitstreams: 1 000859128.pdf: 2157317 bytes, checksum: d8332508e0e93354e186db95a60a2b3e (MD5) / Estudamos a nanoestruturação de uma nanofolha de óxido de grafeno reduzido envelopada com o polímero poliesetireno sulfonado de sódio (GPSS) através de simulação computacional. Demos um primeiro passo no estudo sobre a formação das nanfolhas de GPSS, poi futuramente pretendemos estudar filmes automontados de GPSS depositados sobre uma membrana de Nafion. A motivação é melhor compreensão do mecanismo de redução da passagem de metanol e aumento da condução de íons H+ observada experimentalmente em uma célula combustível de metanol direto realizado pela Dra. Celina Miyazaki (POSMAT/UNESP). Neste trabalho, realizamos a simulação de uma nanofolha de óxido de grafeno reduzido (rGO) que se aproximasse o máximo possível daquela obtida experimentalmente, contendo defeitos (vacâncias) e os grupos químicos hidroxila, epóxido, carboxila e carbonila, resultantes da síntese química. Adicionalmente, verificamos como o rGO fica envelopado pelo polímero PSS, mesmo na presença de água, ocorrendo isso principalmente devido à atração eletrostática entre os oxigêncios presentes no PSS com os hidrogênios pertencentes aos grupos hidroxila e carboxila da nanofolhas de rGO. Observou-se que esse envelopamento é favorecido pela presença de água. Essas observações corroboram com os resultados experimentais / We studied the nanostructuration of reduced graphene oxide nanoplatelets wapped by the polymer poly (sodium4 styrenesulfonate) (GPSS), using compational simulation. A first step was taken for the study about formation of GPSS nanoplatelets, using coputational simulation, as we intend to study in a near future a self-assembled film of GPSS deposited onto Nafion® membranes. The motivation is a better comprehension of the blocking barrier mechanism to the passage of methanol and increasing the H+ ions conductivity observed experimentally in a direct methanol fuel cell setup made by Dra Celina M. Miyazaki (POSMAT, UNESP). We have made here the simulation of a reduced graphene oxide (rGO) nanoplatelet closer to that obtained experimentally, having defects (vacancies) and hydroxyl, epoxy, carboxyl and carbonyl chemical groups, resultant from the chemical synthesis. In addition, it was verified how rGO is surrounded by the PSS polymer, even in the presence of water, putting the system as close as possible to the experimental condition. The enveloping of rGO by PSS happened mainly by elestrostatic attraction between oxygen atoms present in PSS with hydrogen atoms present at hydroxyl and carbonyl groups in rGO, and it was favored by the presence of water. These observations are corroborated by the experimental results

Orientador: Marcelo Ornaghi Orlandi / Banca: Anderson Andre Felix / Banca: Valmor Roberto Mastelaro / Banca: Luis Vicente de Andrade Scalvi / Banca: Rosario Elida Suman Bretas / Resumo: Neste trabalho, as propriedades sensoras de gás de nanoestruturas de óxido de estanho puras (SnO2) e híbridas (SnO2-Pt, SnO2-CuO e SnO2-CuO-Pt) foram estudadas na presença de diferentes gases. Os materiais foram sintetizados pelo método de electrospinning seguido por tratamento térmico e, posteriormente, foram caracterizados por termogravimetria (TG), difração de raios X (DRX), microscopia eletrônica de varredura com emissão por campo (MEV-FEG), microscopia eletrônica de transmissão (MET), espectroscopia por dispersão em energia de raios X (EDS), microscopia de força atômica (AFM) e área de superfície específica e porosidade (BET). O foco principal do trabalho foi analisar a resposta dos materiais sintetizados como sensores de gás para a detecção de gases tóxicos e inflamáveis em baixas concentrações e em uma temperatura de operação de 300 °C. Os resultados obtidos a partir das caracterizações estruturais e morfológicas mostraram que o método de electrospinning permite a obtenção de materiais unidimensionais (1D) policristalinos com elevada homogeneidade morfológica e pureza cristalina. Além disso, os elementos químicos presentes nas estruturas de cada material sintetizado foram mapeados e identificados, onde verificou-se que todos os elementos estão homogeneamente distribuídos ao longo da estrutura das fibras. As características superficiais dos materiais, tais como rugosidade e porosidade também foram estudadas e os resultados indicaram que, dependendo da composição química... (Resumo completo, clicar acesso eletrônico abaixo) / Doutor

abstract: DNA nanotechnology is one of the most flourishing interdisciplinary research fields. Through the features of programmability and predictability, DNA nanostructures can be designed to self-assemble into a variety of periodic or aperiodic patterns of different shapes and length scales, and more importantly, they can be used as scaffolds for organizing other nanoparticles, proteins and chemical groups. By leveraging these molecules, DNA nanostructures can be used to direct the organization of complex bio-inspired materials that may serve as smart drug delivery systems and in vitro or in vivo bio-molecular computing and diagnostic devices. In this dissertation I describe a systematic study of the thermodynamic properties of complex DNA nanostructures, including 2D and 3D DNA origami, in order to understand their assembly, stability and functionality and inform future design endeavors. It is conceivable that a more thorough understanding of DNA self-assembly can be used to guide the structural design process and optimize the conditions for assembly, manipulation, and functionalization, thus benefiting both upstream design and downstream applications. As a biocompatible nanoscale motif, the successful integration, stabilization and separation of DNA nanostructures from cells/cell lysate suggests its potential to serve as a diagnostic platform at the cellular level. Here, DNA origami was used to capture and identify multiple T cell receptor mRNA species from single cells within a mixed cell population. This demonstrates the potential of DNA nanostructure as an ideal nano scale tool for biological applications. / Dissertation/Thesis / Ph.D. Chemistry 2014

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.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Neste trabalho, nanopartÃculas magnÃticas de ferro (Fe3O4) (NPM) foram avalia- das como suporte para a imobilizaÃÃo de lipase de Candida antarctica do tipo B (CALB). O biocatalisador (CALB-NPM) foi analisado na catÃlise dos Ãsteres: oleato de etila (biodiesel), butirato de metila e etila. NanopartÃculas magnÃticas sÃo particularmente interessantes para imobilizaÃÃo enzimÃtica devido as suas propriedades magnÃticas favorecerem a fÃcil separaÃÃo da mistura reacional atravÃs do uso de magnetismo. A enzima CALB à uma enzima capaz de atuar em diversas reaÃÃes, como, hidrÃlises e transesterificaÃÃes. Contudo, um dos problemas do uso de enzimas como catalisadores homogÃneos à a sua recuperaÃÃo. Assim, à necessÃrio o uso de suportes que retenham a enzima, mantendo suas caracterÃsticas catalÃticas. As na- nopartÃculas foram produzidas pelo mÃtodo de co-precipitaÃÃo. Determinou-se o tamanho das nanopartÃculas (11 nm) atravÃs da tÃcnica de difraÃÃo de raios-X (DRX) com posterior refi- namento das fases obtidas pelo mÃtodo Rietveld. Espectros de infravermelho foram obtidos para anÃlise de presenÃa de hidroxilas usando pastilhas de KBr das ferritas magnÃticas. O espectro foi medido na regiÃo entre 400 e 4000 cm−1. ModificaÃÃes foram realizadas na su- perfÃcie das mesmas com γ-aminopropiltrietoxissilano (APTS) e glutaraldeÃdo. No processo de imobilizaÃÃo, a influÃncia da velocidade de agitaÃÃo (20-250 rpm), carga enzimÃtica (45-200 UpNPB.g−1), tempo de contato enzima-suporte (0,5-5 h), concentraÃÃo de glutaraldeÃdo (2,5 e 25 % (m/v)), aditivo dodecil sulfato de sÃdio (SDS 0,23 %) e reutilizaÃÃo do biocatalisador fo- ram avaliadas. A imobilizaÃÃo foi realizada na presenÃa de 100 mM de tampÃo bicarbonato de sÃdio, pH 10, a 25 ÂC. ApÃs a imobilizaÃÃo, a enzima imobilizada exibiu melhor estabilidade tÃrmica e operacional do que na forma solÃvel. As condiÃÃes Ãtimas de imobilizaÃÃo foram: velocidade de agitaÃÃo de 45 rpm, carga enzimÃtica (80 UpNPB.g−1), tempo de imobilizaÃÃo de 1 h, soluÃÃo de glutaraldeÃdo (25 % (m/v)), possibilitando um rendimento de imobilizaÃÃo de 41,8 % e atividade enzimÃtica do derivado de 29,1 UpNPB/g. AlÃm disso, o biocatalisador manteve aproximadamente, 53% de atividade catalÃtica inicial apÃs cinco ciclos consecutivos de reaÃÃo hidrolÃtica. ApÃs a imobilizaÃÃo, a estabilidade tÃrmica dos derivados foi realizada a partir da reaÃÃo de hidrÃlise com 0,01 g de CALB-NPM. atividade catalÃtica da enzima livre e imobilizada foi analisada a 60 ÂC. A produÃÃo de esteres foi realizada com o biocatalisador na melhor condiÃÃo catalÃtica. AlÃm das nanopartÃculas foram analisadas a bioconversÃo de esteres por resinas acrÃlicas comerciais (CALB imobilizada). A conversÃo de oleato de etila foi de aproximadamente 90% para os biocatalisadores testados. Os ciclos de reaÃÃo consecutivos (14) mostram a manutenÃÃo da produÃÃo de biodiesel. A mÃxima conversÃo de buitrato de etila (96,8%) e metila (93,9%) foram obtidos apÃs 8 h de reaÃÃo a 25 ÂC com CALB imobilizada em nanopartÃculas magnÃticas. Os ciclos de reaÃÃo consecutivos (12) mostram a manutenÃÃo da produÃÃo dos Ãsteres (aproximadamente 76% para as nanopartÃculas e 79% para a resina acrÃlica). / In this work, magnetic nanoparticles of iron (Fe3O4) (NPM) were evaluated as a support for the immobilization of lipase Candida antarctica B (CALB). The biocatalyst (CALB- NPM) was analyzed in the catalysis of esters: ethyl oleate (biodiesel), methyl and ethyl buty- rate. Magnetic nanoparticles are particularly interesting for enzyme immobilization due to their magnetic properties favoring the easy separation from the reaction mixture by use of magne- tism. The CALB enzyme is an enzyme capable of acting in various reactions, such as hydrolysis and transesterifications. However, one problem of using enzymes as homogeneous catalysts is their recovery. Thus, it is necessary to use brackets that retain the enzyme while maintaining its catalytic characteristics. Nanoparticles were produced by co-precipitation method. We de- termined the size of the nanoparticles (11 nm) using the technique of X-ray diffraction (XRD) with subsequent refining of the phases obtained by the Rietveld method. Infrared spectra were obtained for analysis of the presence of hydroxyls using KBr pellets of magnetic ferrites. The spectrum was measured in the region between 400 and 4000 cm −1. Modifications were car- ried out on the nanoparticlesâ surfaces with γ-aminopropyltriethoxysilane (APTS) and glutaral- dehyde. The influence of stirring speed (20-250 rpm), enzyme load (45-200 UpNPB/gsupport), immobilization time (0.5-5 h), glutaraldehyde solution (2.5 and 25%), additive (SDS 0.23%) and reuse of the biocatalyst (six hydrolytic cycles reactions) were evaluated. The immobiliza- tion was performed in the presence of 100mMsodium bicarbonate buffer, pH 10, at 25 ÂC. After immobilization, CALB exhibited improved thermal and operational stabilities. The best result (Immobilization yield: 53% and immobilized enzyme activity: 29.1 UpNPB/gsupport) was obtained at 45 rpm, using 200 UpNPB/gsupport and 1h of immobilization. Furthermore, immo- bilized Calb maintained approximately 41.8 % of initial activity after five cycles of hydrolysis. The ethyl oleate production was analyzed with the best condition and compared to commercial acrylic resins (CALB immobilized). The ethyl oleate conversion was approximately 90 % for the two biocatalyst at 48 h. The consecutive reaction cycles (14) show the maintenance in the production of biodiesel. Maximum conversion of methyl butyrate (93.9 %) and ethyl butyrate (96.8 %) were achieved after 8 h of reaction at 25 ÂC for CALB immobilized onto magnetic nanoparticles. The consecutive reaction cycles (12) show the maintenance in the production of esters (approximately 76 % for nanoparticles and 79 % for acrylic resin).

A plasmônica é a área que faz a junção entre fotônica e nanoestruturas. As implicações tecnológicas resultantes do acoplamento entre campos eletromagnéticos e oscilações eletrônicas em um material condutor fazem desta área uma das mais excitantes da óptica atualmente. Neste contexto, o objetivo deste trabalho é o projeto, fabricação e caracterização de nanoestruturas metálicas visando aplicações em óptica difrativa, incluindo filtros e lentes. Inicialmente, uma extensa revisão bibliográfica permitiu definir quais tipos de estruturas seriam abordadas, levando em conta tanto a capacidade computacional para fazer a modelagem numérica quanto a infraestrutura necessária na fabricação dos elementos. A primeira estrutura analisada foi um filtro óptico baseado em ressonância de modo guiado e ressonância plasmônica. Foram projetados e fabricados três filtros operando no azul, verde e vermelho. Resultados experimentais mostraram eficiência acima de 80% e largura de banda em torno de 20 nm, consideravelmente menor que os ~60 nm obtidos previamente na literatura considerando estrutura semelhante. Foi possível verificar as cores puras associadas à ressonância de modo guiado. Além disso, foi demonstrado como gerar as três cores primárias - azul, verde e vermelho - usando apenas o filtro vermelho. A segunda estrutura proposta consiste em uma lente tipo zonas de Fresnel integrada com um filme metálico. Resultados numéricos identificaram uma estrutura ressonante do tipo Fabry-Perot que possibilita uma redução dos lóbulos laterais gerada pela lente por um fator 3.0 na polarização TM e 4.8 na polarização TE. A estrutura foi fabricada usando litografia por nanoimpressão. Por fim, a terceira estrutura analisada foi um holograma binário baseado em metassuperfície, cuja célula básica é composta de um ressoador tipo nanorod. Foi proposta uma geometria na qual a diferença de fase entre os elementos é igual a π independente do comprimento de onda. Assim, o holograma pode operar em uma faixa espectral definida pela largura de banda transmitida. É descrito o inicio da fabricação do elemento usando litografia por feixe de elétrons. / Plasmonics is a field of study that merge photonics and nanostructures. The advanced technological implications makes it one of the most exciting field in Optics in current days. Therefore the objective of this study is the design and fabrication of metallic nanostructures aiming at applications in diffractive optics. Firstly, an extensive literature review allowed to define what types of structures would be addressed, taking into account both software simulations and the require infrastructure for the elements\' fabrication. The first analyzed structure was an optical color filter based on guided mode resonance and surface plasmon resonance. Three filters, operating in blue, green and red, were designed and fabricated using interferometric lithography. Experimental results show above 80% efficiency and ~20 nm bandwidth, which is significantly smaller than ~60 nm previously obtained in the literature with similar structures. It was possible to show the pure colors associated with the modal resonance. Furthermore, it was shown how to obtain the primary red, blue, and green colors using only the red filter. The second structure proposed consists of Fresnel zones plates integrated with a metallic film. Numerical results show a resonant structure which enables side lobe reduction by a factor 3.0 in the TM polarization and 4.8 in the TE polarization. This structure was fabricated using nanoimprint lithography. The third analyzed structure was a binary hologram based on metasurface whose basic cell is composed of a nanorod metallic resonator. The phase difference between two elements is equal to π, regardless of the wavelength; thus, the hologram operates in a spectral band defined by transmitted bandwidth. The first steps of its fabrication process using electron beam lithography are presented and described.

O interesse por aplicações que utilizam efeitos de plásmons poláritons de superfície (SPP) vem crescendo, pois as ondas SPPs apresentam enorme potencial no desenvolvimento de filtros e biossensores ópticos. A sensibilidade da ressonância de plásmons em nanoestruturas permite o estudo em tempo real de variações mínimas em índice de refração, solutos e antígenos. Neste trabalho foram aplicadas técnicas de nanofabricação (litografia por feixe de elétrons e íons) para o desenvolvimento de estruturas plasmônicas e sua posterior caracterização. As estruturas foram utilizadas para verificar propriedades de absorção e fluorescência em moléculas opticamente ativas - Porfirina e Rodamina 6G. As estruturas - conjuntos de fendas e matrizes de buracos circulares com diversos períodos - foram fabricadas em um filme fino de ouro (Au) sobre substrato de vidro (Borofloat 33 - Schott), usando um feixe de íons de Gálio (FEI Quanta Quanta 3D 200i). A transmissão óptica foi estudada na região de 400nm a 900nm (VIS-NIR). Os resultados experimentais foram comparados com simulações computacionais. O estudo da absorção molecular da porfirina foi conduzido observando-se a variação na intensidade da transmissão. Ao alterar a concentração da porfirina sobre as estruturas, foi possível caracterizar a curva de absortividade ε(λ) da porfirina para concentrações entre 100 μg/ml e 500 μg/ml em quantidades mínimas de analito (20 μl). A técnica de microscopia confocal foi empregada no estudo da fluorescência da Rodamina 6G diluída num filme fino de PMMA sobre as estruturas. Ao avaliar a fluorescência da Rodamina 6G na reflexão das estruturas, observou-se o efeito de quenching devido a emissão de plásmons. Os resultados obtidos poderão ser utilizados de apoio a trabalhos futuros, desenvolvidos em plasmônica aplicada a biossensores. / The interest in applications that use the effects of surface plasmon polaritons (SPP) has been increasing. SPPs waves have an enormous potential for the construction of optical filters and biosensors. The sensitivity of plasmon resonance in nano-structures allows studying in real-time minimal variations in the refractive index, solutes and antigens. In this work, we have studied nanofabrication techniques (electron and ion beam lithography) and the characterization of plasmonic structures. Plasmonic effects were used as biosensors of absorption and fluorescence in optically active molecules - Porphyrin and Rhodamine 6G. The structures - sets of slits and arrays of circular holes with different periods - were manufactured in gold (Au) thin film on a glass substrate (Borofloat 33 - Schott) using a galium ion beam equipment (FIB FEI Quanta Quanta 3D 200i). Optical transmission was studied in the region of 400 nm to 900 nm (VIS-NIR). The characterization of structures was realized used the Ocean Optics USB-2000 spectrometer. The experimental results were compared to computer simulations. The study of molecular absorption of porphyrin was conducted by observing the variation in intensity of transmission. By changing the porphyrin concentration in the structures, it was possible to characterize the porphyrin absorptivity curve ε(λ) in concentrations between 100 μg/ml and 500 μg/ml in minimum amounts of analyte (20 μl). Confocal microscopy was used to study the fluorescence of Rhodamine 6G on plasmonic structures. The plasmon quenching effect was observed in the evaluation of the fluorescence of Rhodamine 6G in the reflection of the structures. The results will support future works linking plasmonics and biosensors.

La nano-optique est un vaste domaine permettant d'étudier et d'exalter l'interaction lumière-matière à l'échelle nanométrique. Ce domaine couvre notamment la plasmonique, mais depuis quelques années, un effort est porté sur les nanostructures diélectriques à fort indice de réfraction (typiquement des semiconducteurs comme le silicium). Des effets similaires aux nanoparticules plasmoniques peuvent être obtenus, tels un comportement d'antenne et l'exaltation de phénomènes non linéaires (génération d'harmoniques), avec l'avantage de faibles pertes. Dans cette thèse, une analyse des propriétés optiques linéaires et non linéaires de nanostructures individuelles. Une première partie est dédiée aux nanofils de silicium qui supportent de fortes résonances optiques dont le nombre et la gamme spectrale, du proche UV au proche IR, sont fonction de leur diamètre. Dans ces conditions, l'exaltation du champ proche optique et un rapport surface sur volume élevé favorisent l'apparition de processus non linéaires. Ainsi la génération de seconde harmonique (SHG) par rapport au silicium massif est augmentée de deux ordres de grandeur. En outre, différentes contributions à l'origine de la SHG peuvent être adressées individuellement en fonction de la polarisation du laser d'excitation et de la taille des nanofils. Les résultats expérimentaux sont confrontés à des simulations numériques (méthode dyadique de Green, GDM), qui permettent d'identifier les différentes contributions. Dans une seconde partie, la méthode dyadique de Green est couplée à des algorithme évolutionnistes (EO) pour la conception et l'optimisation de propriétés optiques choisies de nanostructures semiconductrices ou métalliques, par exemple diffusion résonnante de différentes longueurs d'ondes pour différentes polarisations.Des échantillons de nanostructures de silicium, réalisés à partir des résultats de l'EO, vérifient avec succès les prédictions de l'algorithme d'optimisation, démontrant l'énorme potentiel de l'EO pour de nombreuses applications en nanophotonique requérant une optimisation simultanée de différents paramètres. / Nano-photonic structures offer a highly interesting platform to enhance light-matter interaction on a nanometer scale. Recently, high-index dielectric structures have gained increasing attention as possible low-loss alternatives to plasmonic nano-antennas made from noble metals. Furthermore, since non-linear effects offer many unique functionalities like the coherent up-conversion of photons, including the generation of harmonics, many efforts are being made to exploit such phenomena in nano-photonics. In this thesis, an analysis is presented on nonlinear optical effects in individual dielectric structures, specifically in silicon nanowires (SiNWs). Nanowires develop strong optical resonances in the visible and infrared spectral range. In this context, strong enhancement of the optical near-field together with a large surface to volume ratio support the appearance of nonlinear effects. We show that, compared to bulk Si, a two orders of magnitude increase in second harmonic generation (SHG) is feasible and furthermore unravel different polarization and size-dependent contributions at the origin of the SHG. Numerical simulations are carried out to reaffirm these experimental findings for which a numerical technique is presented to describe nonlinear effects on the basis of the Green Dyadic Method (GDM). In the last part of the thesis, the GDM is used together with evolutionary optimization (EO) algorithms to tailor and optimize optical properties of photonic nano-structures. We eventually fabricate samples, based on EO design, and successfully verify the predictions of the optimization algorithm. It turns out that EO is an extremely versatile tool and has a tremendous potential for many kinds of further applications in nano-optics.

Philosophiae Doctor - PhD / Polypyrrole composites of polyaromatic hydrocarbon sulphonic acids (β–naphthalene sulphonic acid (NSA) and 1, 2-napthaquinone-4-sulphonic acid (NQS)), as well as those of transition metal oxides (tungsten (VI) oxide (WO3) and zirconium (IV) oxide (ZrO2)), were prepared and characterised for use as electrocatalytic sensors. The polymerization of pyrrole in β–naphthalene sulphonic acid (NSA) gave rise to nanotubules, nanomicelles or nanosheets polypyrrole (PPy) morphologies depending on the amount of NSA in the polymer and the polymerisation temperature. Scanning electron microscopy (SEM) measurements showed that the diameters of the nanostructured polypyrrole-β-naphthalene sulphonic acid (PPyNSA) composites were 150-3000 nm for the tubules, 100-150 nm for the micelles and 20 nm for the sheets. A red shift in the UV-Vis absorption spectra of PPy was observed for PPyNSA which is indicative of the involvement of bulky β-naphthalene sulphonate ion in the polymerization process. The UV-Vis also showed the existence of polaron and bipolaron in the polymer which may be responsible for the improved solubility of PPyNSA compared to PPy. All the characteristic IR bands of polypyrrole were observed in the FTIR spectra of PPyNSA, with slight variation in the absolute values. However, the absence of N–H stretching at 3400 cm-1 and 1450 cm-1 usually associated with neutral polypyrrole confirms that the polymer is not in the aromatic state but in the excited polaron and bipolaron defect state. Electrochemical analysis of PPyNSA reveals two redox couples: a/a′ - partly oxidized polypyrrole-naphthalene sulphonate radical cation/neutral polypyrrole naphthalene sulphonate; b/b′ - fully oxidized naphthalene sulphonate radical cation/partly reduced polypyrrole-naphthalene sulphonate radical anion. The corresponding formal potentials measured at 5 mV/s, Eº'(5 mV/s), are 181 mV and 291 mV, respectively. Analysis of the amperometric response of GCE/PPyNSA film to phenol gave sensitivities of 3.1 mA/mole dm-3 with a linear correlation coefficient of 0.982 for phenol concentrations of 19.8 μM to 139.5 μM. The apparent Michaelis-Menten constant (Km′) was estimated as 160 μM. Novel polypyrrole thin film microelectrodes prepared from an aqueous solution of the sodium salt of 1, 2- apthaquinone-4-sulphonic acid and pyrrole in hydrochloric acid as the supporting electrolyte was characterized electrochemically for the first time and found to exhibit good electronic and spectroscopic properties. The modified PPyNQS consisted of nano micelles with diameters of 50–100 nm. It also exhibited more pronounced voltammetric redox responses, improved solubility and stronger UV-Vis absorptions at wavelengths for polarons (380 nm), bipolarons (750 nm) and overlapped bi-polarons (820 nm) compared to conventional PPy. Voltammetric investigations showed that the polymer exhibited quasi-reversible kinetics in a potential window of - 400 mV to +700 mV, with a formal potential of 322 mV vs. Ag/AgCl. The diffusion coefficient was calculated to be 1.02 x 10-6 cm2/s for a thin film with a surface concentration of 1.83 x 10-7 mol/cm2 and a standard rate constant of 2.20 x 10-3 cm/s at 5 mV/s. Substractively normalised in situ Fourier transform infrared spectroscopy (SNIFTIR) confirmed the incorporation of the surfactant into the polypyrrole film, and for the first time structural changes within the polymer were observed and used to explain the electrochemistry of the polymer. Electrochemical impedance spectroscopy (EIS) results validated the quasi-reversible kinetics observed in the voltammetric experiment. The changes in electrical properties of the polymer during electrochemical p-doping and n-doping were quantified by equivalent electrical circuit fitting. Impedimetric nanosensor systems for the determination of two anthropogenic organic pollutants, namely benzidine and naphthalene, were constructed with smart Pt/PPyNQS nanomaterials. Analysis of sensor systems containing tungsten oxide or zirconium oxide-modified polypyrrole showed that nanohybrids of the polypyrrole were generated by the in-situ polymerisation of pyrrole in acidic solutions. Results from morphological and spectroscopic investigation confirmed the pattern of metal distribution within the nanohybrid polymers matrix. However, this class of polymers were devoid of charge carriers characteristics required for electrocatalytic sensor applications. The thesis provided justification for the preparation of nanostructured conducting polypyrrole for use as anodes for the determination of phenol, benzidine and naphthalene. / South Africa

Silicon is an essential element in today’s modern world. Nanostructured Si is a more recently studied variant, which has currently garnered much attention. When its spatial dimensions are confined below a certain limit, its optical properties change dramatically. It transforms from an indirect bandgap material that does not absorb or emit light efficiently into one which can emit visible light at room temperatures. Although much work has been conducted in understanding the properties of nanostructured Si, in particular porous Si surfaces, a clear understanding of the origin of photoluminescence has not yet been produced. Typical synthesis approaches used to produce nanostructured Si, in particular porous Si and nanocrystalline Si have involved complex preparations used at high temperatures, pressures, or currents. The purpose of this thesis is to develop an easier synthesis approach to produce nanostructured Si as well as arrive at a clearer understanding of the origin of photoluminescence in these systems. We used a simple chemical etching technique followed by sonication to produce nanostructured Si suspensions. The etching process involved producing pores on the surface of a Si substrate in a solution containing hydrofluoric acid and an oxidant. Nanocrystalline Si as well as nanoscale amorphous porous Si suspensions were successfully synthesized using this process. We probed into the phase, composition, and origin of photoluminescence in these materials, through the use of several characterization techniques. TEM and SEM were used to determine morphology and phase. FT-IR and XPS were employed to study chemical compositions, and steady state and time resolved optical spectroscopy techniques were applied to resolve their photoluminescent properties. Our work has revealed that the type of oxidant utilized during etching had a significant impact on the final product. When using nitric acid as the oxidant, we formed nanocrystalline Si suspensions composed of particles with a crystal structure different than the common polymorph of Si. These particles emitted UV to blue wavelengths. Iron(III) chloride was also employed as an oxidant, and it created amorphous Si nanostructures from a bulk crystalline Si source. These suspensions showed ultra-bright visible photoluminescence, which could be tuned through engineering the surface.