Navegando por Palavras-chave "Nanotubos de TiO2"

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    Degradação de resíduo de levedura empregado em biossorção por processos eletro-oxidativos avançados
    (Universidade Federal de São Paulo, 2017-10-06) Bargas, Maria Francisca Ribeiro de Aguiar [UNIFESP]; Rodrigues, Christiane de Arruda [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    The use of agroindustrial waste as adsorbents has been evaluated as an alternative treatment of textile effluents, mainly for color removal. However, solutions are required for the proper fate of the adsorbent after sorption of the organic compound. In this way, the Advanced Oxidative Processes (POA) appear as an alternative of clean destination of the solid residues containing organic compound. The objective of this work was to evaluate the efficiency in the treatment of the degradation of dry yeast biomass, biosorbent from the residue of the sugar and alcohol industry, after the sorption of methylene blue reactive dye by means of photo-Fenton and heterogeneous photocatalysis (photocatalysis and photoelectrocatalysis) using a TiO2 nanotubular oxide layer as catalyst. The study was carried out with three yeast biomasses, washed yeast biomass (WYB), in nature Yeast Biomass (YB) and yeast biomass after the sorption of the methylene blue reactive dye (SYB). Initially the BL was washed with distilled water to remove the soluble residue in order to quantify the reduction of mass and mineralization only of the solid fraction. The optimization studies of the best conditions of degradation and mineralization of the organic matter were obtained with the WYB. The optimization studies of the best conditions of degradation and mineralization of the organic matter were obtained with the WYB. In the photo-Fenton process, the optimized condition was 2,500 mg L-1 of H2O2 and 40 mg L-1 of Fe2+ and 100 mg of biomass mass, with sequential addition of H2O2 during the degradation process, at 15 min intervals, during 2 hours of treatment, with a percentage of mineralization around 45% and destruction of the degraded biomass (lysed). While in heterogeneous photocatalysis, although there is no evidence of cell lysis, the photocatalytic treatment showed to be more efficient in reducing the organic load of the WYB and YB compared to the treatment by photoelectrocatalysis, with a mass reduction percentage of around 46,5% after 4 hours of treatment. In both studies, an irradiation source with a mercury vapor lamp of 80 W was used. Then, the combination of the optimized processes, photo-Fenton followed by photocatalysis, was employed in the treatment of YB and SYB. After the degradation, YB presented a reduction of mass and mineralization around 85% and SYB around 60% of mass reduction and 50% of mineralization. The combination of the photo-Fenton process followed by the heterogeneous photocatalysis showed to be a clean destination of solid residues formed by yeast biomass with adsorbed dye.
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    Desenvolvimento de um fotocatalisador de nanotubos de TiO2 decorados com Ru para degradação fotoeletroquímica de agrotóxico
    (Universidade Federal de São Paulo, 2015-11-26) Castelhano, Douglas Iafrate [UNIFESP]; Rodrigues, Christiane de Arruda [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    Brazil is a world leader in the production and exportation of several agricultural products. This remarkable performance of the national agricultural production is directly related to the growth of the pesticide market in Brazil, making it one of the six largest consumers of pesticides in the world. Parallel to this dramatic scenario of agrochemical industries in the national economy as well as increasing the production of this in Brazil, there are many cases of environmental contamination resulting from the irresponsibility of pesticide manufacturers and due to the leaching process after use of same, due to the porosity of the soil, reaching groundwater, rivers and water bodies. Among the pesticides used in Brazilian crops, there is carbendazim, a fungicide with medium toxicity, classified as a possible carcinogen in humans. Given the growing demand of using pesticides and the need to develop capable technologies to eliminate these contaminants in human drinking water, this manuscript studied the degradation of carbendazim pesticide by photocatalytic and photoelectrocatalytic process using as semiconductor TiO2 nanostructured with and without modification with Ru by electrodeposition process. TiO2 nanostructures were obtained by anodizing process in aqueous solution containing 0.3% (v/v) HF under a potential difference of 20 V for 2 h with a ramp potential of 2 V min-1. Nanotubes were obtained with length and internal diameter of approximately 330 nm and 90 nm, respectively. Then, the nanostructures were heat treated at 450 °C to obtain the anatase phase. Voltammetric studies were conducted to elucidate the Ru reduction route on the TiO2 surface and select the potential range for electrodeposition. Although the Ru has been electrodeposited in a potential range of -0.025 to -0.188 V vs. Ag / AgCl, the deposition at 0.3 mC cm-2 at -0.100 V resulted in a value of photocurrent ten times greater compared to that obtained for the unmodified TiO2 nanotubes. By analysis of diffuse reflectance spectroscopy and adjustments using the Kubelka-Munk function it was possible to observe a substantial reduction in energy band gap from 3.11 eV for TiO2 without modification to 1.87 eV for nanotubes modified with Ru. This drastic reduction in band gap energy makes it an attractive photocatalyst electrode for environmental applications using of sunlight. The performance of these electrodes were tested in degradation of carbendazim and a greater reduction in the fungicidal concentration was observed employing the TiO2 electrode modified with Ru by photoelectrochemical process under UV light radiation of 80W, with a density of energy of 0,808 W cm-2 and potential difference of 1V, with reduction of total organic carbon around 56%.
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    Estabilidade Eletroquímica do sistema TiO2-CuO/Cu2O na degradação fotoeletrocatalítica do RB4
    (Universidade Federal de São Paulo, 2021-02-24) Nascimento, Josué Santos [UNIFESP]; Rodrigues, Christiane de Arruda [UNIFESP]; Almeida, Juliana de; http://lattes.cnpq.br/4592824194700065; http://lattes.cnpq.br/9871865009697049; http://lattes.cnpq.br/5333850352435575
    Nos tempos atuais, há uma grande demanda por produções industriais capazes de abastecer as necessidades da sociedade. Consequentemente, há uma crescente preocupação em busca de práticas sustentáveis e economicamente viáveis, pois o aumento na produção de bens de consumo acarreta em uma maior produção de resíduos e impactos ambientais. Na indústria têxtil, a produção de resíduos é um problema recorrente, pois a baixa aderência do corante têxtil ao tecido gera grandes volumes de efluentes que não recebem um tratamento adequado. Geralmente, a carga de corante extra não utilizada é lançada indevidamente em rios, sendo o corante uma substância cancerígena e mutagênica que pode afetar negativamente a fauna e a flora dos ecossistemas aquáticos. Dessa forma, os Processos Oxidativos Avançados (POA) surgiram como uma alternativa para amenizar o problema. Este processo consiste em usar um semicondutor energizado pela luz solar e/ou UV, gerando lacunas h+ na banda de valência que geram radicais hidroxilas a fim de degradar o corante têxtil. O semicondutor mais usado nesses processos é TiO2, material com baixa toxicidade e alta estabilidade fotoeletroquímica. Porém, ele possui alta taxa de recombinação das cargas fotogeradas e necessita de alta energia em função de seu amplo band gap (energia de banda proibida). Para que esse semicondutor possa ter sua eficiência melhorada, é necessário modificá-lo com óxidos de cobre ou outros compostos metálicos ou não. Deste modo, seu band gap será reduzido e as cargas fotogeradas permanecem mais tempo disponíveis para reação, com a criação de níveis intermediários em seu gap. Mudanças na estrutura do semicondutor podem ser feita via processo de eletrodeposição. Neste trabalho, será avaliada a eficiência do eletrodo TiO2 decorado com óxido de cobre em degradar o corante têxtil Reativo Azul 4 via POA, e a estabilidade do eletrodo devido à lixiviação do cobre durante o processo de degradação. O corante RB4 foi escolhido nesse estudo por pertencer a classe dos corantes antraquinonas, que é uma das classes mais importantes da indústria têxtil. Ao final do trabalho, o eletrodo otimizado se mostrou eficiente em degradar a carga orgânica do corante chegando à uma redução de 95%. Além disso, o semicondutor apresentou uma baixa lixiviação do cobre, o que comprova sua durabilidade para ser usado em processos de degradação. Porém, a alteração da morfologia da nanoestrutura do óxido foi constada, acompanhada da formação do par-redox Cu+2/Cu0, como observado pela análise de reflectância difusa.
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    Fotoeletrorredução de CO2 empregando óxidos nanoestruturados
    (Universidade Federal de São Paulo, 2016-02-15) Almeida, Juliana de [UNIFESP]; Rodrigues, Christiane de Arruda [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    The performance of the heterogeneous photocatalysis in wastewater treatment for the removal of organic pollutants, as well as for gaseous emissions, is associated to semiconductor photo-activity. TiO2 is a semiconductor commonly employed for photocatalytic processes, due to its corrosion resistance, chemical stability, low toxicity, and photoactivity. It has an energy band gap of 3.2 eV, which is equivalent to an absorption wavelength (?) shorter than 388 nm, which corresponds to UV radiation and becomes a major obstacle for its use under sunlight. In this study, TiO2 nanotubes (NT/TiO2) were modified with Cu nanoparticles, creating a p-n heterostructure in order to increase the photocatalytic activity, by the change of the absorption spectrum to longer wavelengths, the decrease of the rate of recombination of photogenerated charges, and the optimization of its application for photoreduction processes. The NT/TiO2 were synthesized on Ti substrate by anodic process and modified by electrodeposition. Voltammetric studies employing 0.01 mmol L-1 CuSO4 in different electrolytes, 0.1 mol L-1 of Na2SO4 or 0.01 mol L-1 C3H6O3 were performed to investigate the influence of the electrolyte and the potential range to be applied in electrodeposition process. In both electrolytes, the morphology, amount and distribution of Cu nanoparticles on NT/TiO2 showed strong influence of applied potential. High values of cathodic current was obtained in photocurrent experiments using NT/TiO2 modified with Cu at 0,70 and -0,85 V vs. Ag/AgCl, using Na2SO4 e C3H6O3, respectively, These samples were submitted to heat treatment to convert metallic Cu in Cu2O (NT/TiO2-Cu2O) and CuO (NT/CuO-TiO2). The NT/TiO2-Cu2O and NT/CuO-TiO2, synthesized in different electrolytes, were applied in CO2 photoelectroreduction in 0.1 mol L-1 NaHCO3, pH 8.0. Only the NT/TiO2-CuO electrode synthesized in C3H6O3 solution was able to produce acetone, ethanol and methanol. The result shows that the morphology and size of the cupric oxide nanoparticles are fundamental in the electrode efficiency, making it more attractive to contribute as a source for the production of fuels. The efficiency was certificated by its band gap energy which value was 46 % lower than that of undecorated NT/TiO2.