Navegando por Palavras-chave "TiO2"

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    Estudo das interações entre ouro coloidal e óxidos de ítrio e titânio
    (Universidade Federal de São Paulo, 2016-03-15) Rosas, Victor Hildebrand [UNIFESP]; Giongo, Carolina Vautier Teixeira [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    Many practical applications of gold nanoparticles (AuNP), such as detection, monitoring and pollution remediation of waters and soils, in addition to diagnosis and treatment of diseases, are based on the nature and magnitude of interactions between AuNP and different molecules, molecular aggregates or other colloidal particles, that occur in adsorption and mutual aggregation processes. Homoaggregation phenomena (aggregation between identical particles) and mutual aggregation (aggregation between different colloidal particles) have been studied for decades and, considering the fact that great advances have been achieved in understanding these phenomena, the presence of this new knowledge has been growing ever since in the fields of industrial processes and nanosciences. In this dissertation, homoaggregation of aqueous dispersions of AuNP has been studied as a function of media pH and ionic strength. In addition, studies of mutual aggregation between AuNP and Y2O3, on the one hand, and AuNP and TiO2, on the other hand, were undertaken. Localized surface plasmonic resonance (LSPR) spectroscopy was utilized in order to obtain kinetic and thermodynamic information concerning the aggregation experiments. Characterization of the aqueous dispersions of AuNP and inorganic oxides was achieved by LSPR spectroscopy in the visible region, dynamic and electrophoretic light scattering (DLS and ELS, respectively), and by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Aggregation experiments were performed with (i) approximately spherical AuNP having a mean diameter of 23 + 4 nm and a zeta potential around -35 mV in the pH range from 3 to 9; (ii) irregular Y2O3 particles presenting an apparent mean diameter of 600 + 180 nm and an isoelectric point (IEP) at pH = 8.2 + 0.1 and (III) spherical TiO2 particles having a mean diameter of 170 + 20 nm with an IEP at pH = 8.2 + 0.1. AuNP homoaggregation kinetic studies yielded information concerning the initial rate of the process as a function of pH and NaCl concentrations, enabling the obtainment of the stability factors of the AuNP dispersions and the NaCl critical concentration for the process of AuNP aggregation. Mutual aggregation kinetic studies between AuNP and Y2O3, and AuNP and TiO2, at pH 3.5, yielded apparent rate constants that showed very clearly the differences between the processes. Specific adsorption of Y+3 ions, originated from Y2O3 solubilization at pH 3.5, is probably the main factor that explains the differences observed for the experiments of mutual aggregation between AuNP with Y2O3 and with TiO2. Mutual aggregation isotherms between AuNP and Y2O3 at pH 3.5, obtained at different temperatures, indicate that the process is spontaneous, endothermic and that it proceeds with an increase of entropy. The isotherms profiles, which do not present typical plateaus of maximum coverage of Y2O3 particles by AuNP, suggests that either the nanoparticles deposit in the form of aggregates on the Y2O3 particles or that deposition of AuNP on the surface of Y2O3 favors additional aggregation of the nanoparticles onto the oxide?s surface. Our experimental results were rationalized in terms of generalizations of Mie?s theory of light extinction by metallic particles and the DLVO theory of colloidal stability. Great part of our observations can be justified by these theories.
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    Estudo de nanopartículas de dióxido de titânio (TiO2) e óxido de zinco (ZnO) para aplicação como eletrodos de células solares
    (Universidade Federal de São Paulo, 2022-12-15) Silva, Victoria Regina Herbst do Amaral [UNIFESP]; Mazzo, Tatiana Martelli [UNIFESP]; Trindade, Leticia Guerreiro da; http://lattes.cnpq.br/1719450522307763; http://lattes.cnpq.br/8843091201331133; http://lattes.cnpq.br/9204045606305316; Universidade Federal de São Paulo (UNIFESP)
    A demanda por energia sustentável, renovável e de baixo custo que pudessem vir a se tornar alternativa à demanda dos combustíveis fósseis fez nascer um mercado voltado a energias renováveis como a eólica, a oceânica e em destaque, a solar. Nesta pesquisa, foi realizado um estudo da viabilidade do uso de semicondutores como o ZnO e o TiO2, em suas formas puras bem como em compósitos com ambos os materiais, na fabricação de fotoeletrodos de célula solar. Estes materiais são conhecidos por apresentarem potencial fotovoltaico para aplicações em células solares de 3° geração. Além disso, são materiais de baixo custo e de grande abundância. Os materiais foram sintetizados utilizando os métodos de coprecipitação e sol-gel. O compósito ZnO/TiO2 foi preparado pelo método de mistura de óxidos, utilizando diferentes concentrações em massa de cada um dos materiais. Todos os materiais foram caracterizados utilizando diferentes técnicas para determinar as características estruturais e morfológicas, assim como a propriedade fotoeletroquímica. Pela técnica de difração de raios X observamos que foi obtido ZnO com estrutura do tipo wurtizita e TiO2 com estrutura do tipo anatase e ambos livres de fase secundária demonstrando que os métodos de síntese foram eficientes. As imagens obtidas por microscopia eletrônica de varredura mostram partículas de ZnO com formato de flores formadas por nanopétalas e de TiO2, formato esférico e aglomerado. A propriedade fotoeletroquímica dos eletrodos foi avaliada por voltametria linear e observamos que todos os materiais, puros e compósitos, apresentam densidade de corrente em 1,7 eV sendo que o compósito TiO2 /ZnO 25% foi o de melhor desempenho justificada pela técnica de impedância eletroquímica que mostrou que esse material apresenta uma ótima separação de carga.
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    Hysteresis-free deposition of TiOxNy thin films: Effect of the reactive gas mixture and oxidation of the TiN layers on process control
    (Elsevier B.V., 2014-03-01) Duarte, D. A.; Massi, M. [UNIFESP]; Sagas, J. C.; Silva Sobrinho, A. S. da; Irala, D. R.; Fontana, L. C.; Technol Inst Aeronaut; Universidade Federal de São Paulo (UNIFESP); Santa Catarina State Univ; Catholic Santa Catarina
    This paper investigates the effect of the reactive gas mixture (N-2 + O-2 + Ar) and oxidation of the nitride layers on the system stability during the reactive sputter deposition of TiOxNy thin films. the present research is an extension of previous investigations conducted by Severin et al. (Appl. Phys. Lett., 88 (2006) 161504) and Duarte et al. (Appl. Surf. Sci., 269 (2013) 55-59) in which the Berg's model was used. to study reactive deposition of oxynitrides. the results show that the addition of N-2 to the process avoids the formation of a hysteresis loop and facilitates the deposition of films with fractions of TiO2 at any value. These achievements are not possible without this procedure. in contrast, despite eliminating plasma instabilities, the addition of N-2 decreases the mass deposition rate due to the modifications in the sputtering yield. Other results show that the oxidation of TiN also plays a key role in the mass deposition rate and in the hysteresis loop. (C) 2013 Elsevier B.V. All rights reserved.
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    Preparação, propriedades e performance fotocatalítica de novos compósitos mesoporosos: TiO2-Ce:SiO2
    (Universidade Federal de São Paulo, 2017-07-04) Iwasaki, Mariana Tiemi [UNIFESP]; Martins, Tereza da Silva [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    TiO2:SBA-15 (TiSBA) e TiO2-CeO2:SBA-15 (TiCeSBA) composites were synthesized by direct synthesis (DS) and post-synthesis (PS) methods using Pluronic® P123 (EO20PO70EO20) as a structure-directing agent, in acidic solution, tetraethyl orthosilicate (TEOS), titanium (IV) isopropoxide and cerium (III) nitrate hexahydrate as the source of SiO2, TiO2 and CeO2, respectively. The composites obtained were characterized by several physical-chemical techniques and the results showed that all of them have a two-dimensional hexagonal mesoporous structure, characteristic of SBA-15. It was also verified that the composites prepared by DS presented higher surface area, pore volume, pore size and crystallinity, when compared to those obtained by PS. However, they had a mixed phase of anatase and rutile, whereas, those obtained by PS, there were a single-phase anatase formation. The composites obtained were used as photocatalysts in the degradation of phenol (100 mg L-1 of carbon) and methyl orange (10-50 mg L-1 of carbon) as model of organic pollutants present in aqueous systems. In these tests, medium pressure mercury lamp (125 W) was used as source of UV radiation, air (4 L min-1 flow), 400 mL reactor, commercial TiO2 (50 and 400 mg L-1 ), pH ≈ 4,5 and 3, composites TiSBA.SD, TiSBA.PS and TiCeSBA.PS (400 and 1600 mg L-1). The degradation of the pollutants, along the reaction time, was evaluated using the total organic carbon analyzer (TOC) and absorption spectroscopy in the UV-Vis region. The composites of TiSBA.SD and TiSBA.PS did not show significant photocatalytic activity in comparison to TiP25 in the phenol mineralization. However, under the studied conditions, TiSBA.SD, TiSBA.PS and TiCeSBA.PS composites showed to be efficient for degradation of the orange methyl dye, mainly at pH 3, showing that this parameter is an important factor.
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    Production of TiO2 Coated Multiwall Carbon Nanotubes by the Sol-Gel Technique
    (Univ Fed Sao Carlos, Dept Engenharia Materials, 2017) Ardila Rodriguez, Laura Angelica [UNIFESP]; Pianassola, Matheus [UNIFESP]; Travessa, Dilermando Nagle [UNIFESP]
    In recent years, efforts in developing high strength-low density materials are increasing significantly. One of the promising materials to attend this demand is the carbon nanotube (CNT), to be used mainly as a reinforcing phase in lightweight metal matrix composites (MMC). In the present work, the sol-gel technique has been employed to obtain TiO2 coating on the surface of commercial multiwall carbon nanotubes (MWCNT). The aim of such coating is to improve the thermal stability of MWCNT in oxidize environment, which is necessary in most of MMC processing routes. Calcination in inert atmosphere was performed in order to crystallize a stable coating phase. The hybrid CNT/TiO2 nanocomposite was characterized by X-Ray Diffractometry (XRD), Raman spectroscopy, Thermogravimetry (TGA) and Field Emission Gun - Scanning Electron Microscopy (FEG-SEM). The coating structure was observed to change from anatase to rutile, as the calcination temperature increases from 500 to 1000 degrees C. Results from thermogravimetric analysis showed that the samples calcined at 1000 degrees C were more resistant to oxidation at high temperatures.
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    Síntese e Caracterização deTiO2 Puro e TiO2 Modificado com Zr-MOF: Potencial para Aplicação em Células Solares
    (Universidade Federal de São Paulo, 2022-12-15) Oliveira, Karine Vilares de [UNIFESP]; Mazzo, Tatiana Martelli [UNIFESP]; Trindade, Leticia Guerreiro da; lattes.cnpq.br/1719450522307763; http://lattes.cnpq.br/8843091201331133; http://lattes.cnpq.br/7831466203961554; Universidade Federal de São Paulo (UNIFESP)
    Impactos causados pela revolução industrial e a crescente preocupação com as questões ambientais fomentam a procura por matrizes energéticas sustentáveis. Diante deste desafio a energia fotovoltaica apresenta grande potencial para o fornecimento de energia limpa. A fim de obter maior eficiência ao menor custo possível a procura por materiais que atendam esses critérios vêm sendo pesquisados e testados. O dióxido de titânio (TiO2) apresenta grande potencial semicondutor, no entanto possui limitada capacidade de absorção de luz. As MOFs (metal-organic frameworks) possuem características promissoras para a melhora da atividade fotovoltaica do TiO2. O presente trabalho teve como objetivo analisar o potencial fotovoltaico do TiO2 puro e modificado com Zr-MOF através da síntese e caracterização destes materiais. O método utilizado para a síntese do TiO2 foi o sol-gel por apresentar vantagens como a obtenção de um material mais homogêneo e puro e com poucos defeitos cristalinos. Para a síntese do Zr-MOF utilizou-se o método solvotérmico que também oferece benefícios como a obtenção de partículas com maior uniformidade em sua composição e não requerer tratamentos térmicos a altas temperaturas posteriormente à síntese. Os materiais foram caracterizados pelas técnicas de difração de raios X (DRX), microscopia eletrônica de varredura com emissão de campo (MEV-FEG) e a propriedade fotoeletroquímica foi avaliada por voltametria linear (VL) e espectroscopia de impedância eletroquímica (EIE). A técnica de DRX mostrou que os métodos de síntese utilizados foram eficientes para obtenção dos materiais livres de fase secundárias, pela microscopia nota-se que foram obtidas nanopartículas sendo o TiO2 no formato esférico e aglomerado e o Zr-MOF no formato octaédrico, pela VL e pela EIE observou-se que o material TiO2 quando modificado com a inserção de 50% de Zr-MOF ocasiona melhoria significativa em sua propriedade fotoeletroquímica.