Navegando por Palavras-chave "Sílica mesoporosa ordenada"

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    Acesso aberto (Open Access)
    Estudo de filtros solares orgânicos e inorgânicos em sílicas mesoporosas ordenadas
    (Universidade Federal de São Paulo, 2019-05-13) Silva, Leonardo Braile [UNIFESP]; Martins, Tereza da Silva [UNIFESP]; Silva, Vânia Rodrigues Leite e [UNIFESP]; http://lattes.cnpq.br/0737387413540260; http://lattes.cnpq.br/9794349687385297; http://lattes.cnpq.br/2572450432314415
    A SBA-15, devido as suas propriedades ímpares, tais como alta área superficial, tamanho e volume de poro, alta estabilidade térmica e mecânica, pode incrementar as propriedades fotoprotetoras do metoxicinamato de octila, OMC (filtro solar orgânico) e dióxido de titânio nanométrico, TiO2 (filtro solar inorgânico), que devido à instabilidade química e térmica (OMC) e aglomeração de partículas (TiO2) têm eficácia de fotoproteção reduzida. Neste trabalho, compósitos SBA-15/TiO2, SBA-15/OMC e SBA-15/TiO2/OMC foram preparados e caracterizados no intuito de analisar a estabilidade térmica e aglomeração das espécies em estudo (TiO2 e OMC) e, também avaliar se a incorporação na SBA-15 oferece um incremento nas propriedades fotoprotetoras dos compósitos. Os materiais foram preparados empregando as metodologias de síntese direta e pós-síntese. A caracterização foi realizada empregando diversas técnicas, tais como: espectroscopia de absorção na região do ultravioleta e visível, espectrometria vibracional na região do infravermelho com transformada de Fourier, análise termogravimétrica, difratometria de raios X a alto e baixo ângulo, fisissorção de nitrogênio e microscopia eletrônica de varredura. Testes de fotoproteção solar, in vitro, também foram realizados. Os compósitos SBAOMC (proporções SBA:OMC de 1:1 e 2:1 em massa) preparados pelo método pós-síntese, empregando impregnação via úmida em etanol, tiveram propriedades estruturais e morfológicas similares a da SBA-15, indicando que o processo de incorporação do OMC na SBA-15 não causou nenhum dano a matriz. Resultados de fisissorção de N2 indicam que o OMC se encontra nos mesoporos da SBA-15 e a incorporação gera um incremento na estabilidade térmica do OMC bem como no fator de proteção solar. O compósito SBA-15/TiO2 preparado por síntese direta (porcentual molar de titânio de 20%) apresenta estrutura de mesoporos similar a SBA-15, mas pequena diferença na morfologia. Apresenta a fase predominante rutila do TiO2 e quando incorporado o OMC para produzir o compósito híbrido (SBA-15/TiO2/OMC) suas propriedades estruturais e morfológicas se mantêm com um incremento do fator de proteção solar do compósito híbrido quando comparado com o OMC e TiO2 puros.
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    Acesso aberto (Open Access)
    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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    Síntese e propriedades de nanocompósitos luminescentes de terras raras e SBA-15
    (Universidade Federal de São Paulo, 2017-08-17) Takamori, Dante Yugo [UNIFESP]; Martins, Tereza da Silva [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    Currently the elements known as rare earths are the object of much research due to their unique properties, amongst them, the possibility of producing luminescent materials. However, the direct excitation of rare earths is inefficient due to its low molar absortivity, making it necessary to employ other species, called matrixes, which have the purpose of absorbing electromagnetic radiation and transfering energy to luminescent ions, forming nanocrystals. A virtually unexplored method for controlling the properties of this kind of material is the use of ionic liquids (IL), which modify the reaction medium and influence the particle size, morphology and crystalline phase, consequently altering the luminescent properties. Nanocomposites that combine those luminescent materials and mesoporous silica are of great interest as they provide better stability and resistence besides having the ability of adsorbing other species. This work aimed to prepare and characterize nanocomposites made from SBA-type ordered mesoporous silica and nanocrystals (sodium yttrium fluoride (NaYF4) and yttrium oxide (Y2O3)) doped with erbium and europium rare earths, using for the latter the IL 1-butyl-3-methylimidazolium bromide (BMIBr), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4), 1-dodecyl-3-methylimidazolium bromide (DMIBr) and 1-dodecyl-3-methylimidazolium tetrafluoroborate (DMIBF4) in the reactium medium. The influence of the IL’s cations and anions on the properties of the material was studied, as well as the regular fluorescence phenomena (downshifting) in materials with europium and the upconversion phenomena in erbium doped samples preared with different matrixes, incorporated or not into SBA-15 (nanocrystal/nanocomposite mass proportion 0.2). It was possible to obtain luminescent materials for both matrixes, both with erbium and europium, even when incorporated into silica. Distinct morphologies were obtained for Y2O3 prepared with different IL, also resulting in different quantum yield for each morphology, although displaying the same cubic crystalline phase. For the composite prepared with BMIBr, the quantum yield was comparable to the unincorporated material. Obtaining a nanocomposite as luminescent as the pure crystal is interesting for its applicability, for its properties, stability and the possibility of its functionalization with drugs, allowing to track or photoactivate them in vivo using infrared excitation luminescence, as for the erbium doped material.