Thesis (Ph. D.)--University of Sydney, 2008. / Title from title screen (viewed Jan 07, 2009). Includes two published articles co-authored with others. Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Australina Key Centre for Microscopy and Microanalysis, Electron Microscope Unit, Faculty of Science. Includes bibliographical references. Also available in print form.

Orientador: Marystela Ferreira / Banca: Idalina Vieira Aoki / Banca: Steven Frederick Durrant / O Programa de Pós Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi / Resumo: O presente trabalho visa propor o uso de filmes nanoestruturados de PAni/MWCNT-COOH em sensores eletroquímicos aplicados à detecção de compostos fenólicos. A sinergia das propriedades condutoras dos nanotubos de carbono, CNT, com as propriedades mecânicas, como a moldabilidade, e comportamento eletroquímico bem conhecido do polímero condutor polianilina, PAni, foram os fatores determinantes para a proposta. Os filmes nanoestruturados foram construídos através da técnica Layer by Layer (LbL) variando-se o número de bicamadas do filme (1, 3, 5, 7 e 10 bicamadas) para avaliar a influência de sua arquitetura no funcionamento do sensor. Para avaliar as propriedades do compósito foram utilizados dois filmes, PAni/PVS (polivinilsulfato de sódio) e PEI/MWCNT-COOH (polietilenoimina / nanotubos de parede múltipla funcionalizados), com ambos os materiais isolados para comparação dos resultados obtidos. A análise por Voltametria Anódica de Redissolução por Onda Quadrada (SWASV) demonstrou que os filmes de PAni/MWCNT-COOH com 1, 3 e 5 bicamadas, assim como o filme de PAni/PVS não detectaram o analito 2-clorofenol. Por outro lado, o filme de PAni/MWCNT-COOH com 7 e 10 bicamadas e o filme de PEI/MWCNT-COOH detectaram a presença do analito, porém o limite de quantificação inferior do filme de 7 bicamadas foi superior a 1 ppm (7,78 μmol L-1) sendo ineficaz para aplicação ambiental. O filme que apresentou os melhores resultados para detecção dos analitos foi o filme PAni/MWCNT-COOH com 10 bica... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work proposes the use of PAni/MWCNT-COOH nanostructured films as electrochemical sensors applied to the detection of phenolic compounds. The synergy of carbon nanotubes, CNT, conductive properties with the mechanical properties, such as moldability, and well known electrochemical behavior of conducting polymer polyaniline, Pani, were the determining factors for this proposal. The nanostructured films were built using layer by layer (LbL) technique, changing the number of film bilayers (1, 3, 5, 7 and 10 bilayers) to evaluate the architectures influence on sensor performance. To compare the properties of the composite, two films were used, PAni/PVS (sodium poly(vinyl) sulfate) and PEI/MWCNT-COOH (polyethyleneimine / multi wall carbon nanotubes functionalized), with each isolated material for comparing the obtained results. Square-wave anodic stripping voltammetry (SWASV) analysis showed that the PAni/MWCNT-COOH films with 1, 3 and 5 bilayers, as well as the PAni/PVS film, did not detect the analyte 2-chlorophenol. On the other hand, the PAni/MWCNT-COOH film with 7 and 10 bilayers, and the PEI / MWCNT-COOH film detected the analyte, but the 7 bilayer film quantification limit was higher than 1 ppm (7.78 μmol L-1) being ineffective for environmental applications. The best results for analyte detection were presented by the PAni/MWCNT-COOH film. The values obtained for the 2-chlorophenol analyte were in the range from 4.7 to 15.9 μmol L-1, the detection limit was 1.35 μmol L... (Complete abstract click electronic access below) / Mestre

Orientador: Marcelo Ornaghi Orlandi / Banca: Sonia Maria Zanetti / Banca: Luis Vicente de Andrade Scalvi / Resumo: O trabalho objetiva a realização do crescimento de materiais nanoestruturados de óxido de zinco (ZnO) pelo método de redução carbotérmica e um estudo de suas propriedades como sensor, utilizando ZnO e distintas fontes de carbono (grafite e negro de fumo) como materiais de partida. Para efeito de comparação, o método hidrotermal assistido por micro-ondas (HAM) também foi utilizado como processo de síntese das nanoestruturas. Os materiais obtidos das sínteses foram caracterizados por difração de raios X (DRX), microscopia eletrônica de varredura com canhão de emissão por campo (MEV-FEG), além de microscopia eletrônica de transmissão (MET). Por meio destas técnicas de caracterização, mostrou-se a eficiência da obtenção de nanoestruturas de óxido de zinco, sendo que a morfologia do material resultante é fortemenete dependente do método utilizado. Testes para sensor de gás e luz foram realizados em amostras selecionadas utilizando como critério sua morfologia nanométrica e uniformidade de crescimento. Para medidas com gás, utilizou-se o oxigênio e também o hidrogênio. A medida foi realizada em uma câmara hermeticamente fechada com controle da temperatura e do fluxo dos gases, onde foi inserido um eletrodo interdigital de alumina com trilhas de contato de ouro para qual foi utilizado para depositar as estruturas de ZnO. Para alimentação do sistema, foi utilizada uma fonte de tensão estabilizada, que é operada remotamente e tem sensibilidade na medida da corrente em picoampére, possibilitando assim maior precisão nas medidas. Para as medidas de sensor de luz, foi utilizado o mesmo eletrodo interdigital supracitado, mas o material foi exposto a uma lâmpada de xenônio com intensidade equivalente à metade da intensidade da luz solar. Com relação às medidas das propriedades como sensor de gás e luz, foram analisados parâmetros como: resposta de sensor, sinal, sensibilidade e tempo de resposta / Abstract: The work aims to conduct a study on the growth of nanostructured materials of zinc oxide (ZnO) by carbothermal reduction process and its sensor properties for both gas and light stimulus. For comparison, the microwave-assisted hydrothermal method (MAH) was also used as synthesis process of nanostructures. The synthesizes materials were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FEG-SEM) and transmission electron microscopy (TEM). Through these characterization techniques it was showed that synthesis methods are efficient, and the morphology of the resulting materials depends on the method used. Sensor tests were performed for some samples, using a selection criteria the size and morphology of the material. For sensor characterization it was used hydrogen and oxigen gases. A sealed chamber with controlled temperature and gas flow was used to perform the measurements, whichwas connected to a stabilized voltage source. This source is operated remontly and has a sensibility in the current measurement of picoampére, allowing greater accuracy in the measurement. For the deposition ZnO nanostructures, was used an Alumina interdigital electrode with tracks of gold contact. To measure the light sensor, the same electrode above mentioned was exposed to the beam with an intensity of half of sun radiation (xenon lamp). Regarding the sensor properties (gas ans radiation) it was analyzed the response of the sensor, signal, sensibility and response time, which are essential parameters for the efficiency a sensor material. Through analysis of sensor measurements, it was found that the samples synthesized by HAM had batter sensor performance than the obtained by carbothermal reduction process / Mestre

M.Sc. / This dissertation describes the synthesis and characterization of CdSe/ZnO and Ag/ZnO core/shell nanoparticles using water as a solvent. The effects of the concentration of the shell precursor, pH, and stabilizing agents on the properties of the nanoparticles were investigated. In general, the type of capping agents had an influence on the crystallite size of the core nanocrystals. The particle size distributions which were calculated from TEM images show that thioglycolic acid as a capping agent produced larger particle sizes compared to thioglycerol. For example, thioglycolic acid produced on average 5.0 nm CdSe nanoparticles while 4.0 nm average CdSe particle size was obtained when using thioglycerol as stabilizer. This observation was confirmed by UV/Vis absorption results which showed that thioglycerol capped CdSe NCs exhibited excitonic peaks positioned at lower wavelength than thioglycolic capped CdSe NCs. XRD results showed that the capping agents used in the current work had no influence upon crystal structure of the CdSe nanocrystals as the cubic structure was obtained with both stabilizers. The effect of shell precursor concentration at pH 12 showed heterogeneous formation of ZnO nanoparticles at high shell precursor concentrations. Various ZnO morphologies including nanoflowers and nanotriangles were observed on TEM images when 50 mL and 25 mL of zinc nitrate solution were used as shell precursors. UV/Vis absorption results also confirmed the presence of ZnO absorption peaks for samples prepared with 50 mL and 25 mL of zinc nitrate solution as shell precursors. PL results showed an increase in peak intensity as a function of precursor volumes. XRD results showed diffraction patterns due to the wurtzite structure of ZnO. CdSe diffraction patterns in these samples were not detected by the XRD instrument. At low volume of the shell precursor, which was 5 mL of 0.05 M zinc nitrate, TEM results showed that spherical CdSe/ZnO core/shell nanoparticles were obtained at pH 12 with 5 mL of 0.05 M zinc nitrate solution and 0.1 M sodium hydroxide used as shell precursor solutions, and thioglycerol as a stabilizer. XRD analysis of the v sample exhibited ZnO diffraction patterns and the CdSe patterns were not detected owing to their low peak intensities compared to those of the ZnO. Similar results were obtained when thioglycolic acid was used a stabilizing agent. However, TEM images showed the hexagonal shape of the CdSe/ZnO core/shell nanoparticles. The pH level was found to influence the photoluminescence properties of the CdSe/ZnO core/shell nanoparticles. The enhanced PL intensity was obtained with CdSe/ZnO core/shell nanoparticles with pH 9 in comparison with CdSe/ZnO core/shell nanoparticles prepared at pH 12. TEM images showed the presence of a thin ZnO shell on the surface of CdSe cores for CdSe/ZnO prepared at pH 9 which could be attributed to the PL enhancement. Although EDS results confirmed the presence of elements such as Cd, Se, Zn and O for both the CdSe core and ZnO shell, the XRD results confirmed the presence of only CdSe diffraction patterns, which suggested the ZnO shell had low peak intensity or was amorphous. A similar effect of these capping agents was observed for Ag nanoparticles as thioglycerol produced average particle size of 16.0 nm whereas 31.0 nm as the average particle size was obtained with thioglycolic acid as stabilizing agent. The crystal phase of Ag NPs was independent of the type of stabilizer. The Ag NPs precipitated in face centred cubic phase. Core/shell Ag/ZnO nanoparticles were produced with 5 ml of zinc nitrate as shell precursor. Higher volumes (50 ml and 25 ml) of zinc nitrate shell precursor induced heterogeneous precipitation of ZnO nanoparticles. XRD patterns confirmed peaks due to ZnO and Ag for Ag/ZnO core/shell nanoparticles.

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

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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

The characterization, properties and applications of the novel nanostructured microgel (nanoparticle network and microgel crystal) composed of poly-N-isopropylacrylanmide-co-allylamine (PNIPAM-co-allylamine) and PNIPAM-co-acrylic acid(AA) have been investigated. For the novel nanostructured hydrogels with the two levels of structure: the primary network inside each individual particle and the secondary network of the crosslinked nanoparticles, the new shear modulus, drug release law from hydrogel with heterogeneous structure have been studied. The successful method for calculating the volume fraction related the phase transition of colloid have been obtained. The kinetics of crystallization in an aqueous dispersion of PNIPAM particles has been explored using UV-visible transmission spectroscopy. This dissertation also includes the initial research on the melting behavior of colloidal crystals composed of PNIPAM microgels. Many new findings in this study area have never been reported before. The theoretical model for the columnar crystal growth from the top to bottom of PNIPAM microgel has been built, which explains the growth mechanism of the novel columnar hydrogel colloidal crystals. Since the unique structure of the novel nanostructured hydrogels, their properties are different with the conventional hydrogels and the hard-sphere-like system. The studies and results in this dissertation have the important significant for theoretical study and valuable application of these novel nanostructured hydrogels.

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In this thesis, I firstly report high field measurements of graphene/NbN junctions, in which NbN makes edge contact to graphene. Transport measurements at zero field demonstrate clear features associated with both retro and specular Andreev reflection. By applying perpendicular magnetic field, field dependence of junction transparency at Quantum Hall (QH) / superconductor (SC) interface is calculated and explained by a picture of superposition of electron and hole edge excitation. Zeeman splitting is induced in graphene by applying in plane magnetic field. We observe changes in the Andreev reflection spectrum that are consisting with spin splitting of the graphene band structure. This edge contact technique provides the opportunity to create hybrid SC/graphene or SC/QH system to illustrate new physics such as non-Abelian zero modes of Majorana physics. Secondly, other potential material candidates for SC/graphene junctions are discussed, high field transport measurement of FeSeTe/graphene junction is discussed, Superconductor/quantum spin Hall (QSH) interface and superconductor-graphene-superconductor weak link are also discussed, respectively. At last, via contact, a new contact method for two-dimensional materials, especially air-sensitive materials is discussed, the via contact method provides a new and reliable fabrication technique for two dimensional materials.