Navegando por Palavras-chave "Ordered mesoporous silica"
Agora exibindo 1 - 6 de 6
Resultados por página
Opções de Ordenação
- ItemSomente MetadadadosEncapsulation study of citalopram and risperidone into nanostructured silica SBA-15 for in vitro release evaluation(Springer, 2017) Tanaka, Magali Naomi [UNIFESP]; Soares Santos, Solange Teixeira [UNIFESP]; Gouveia, Marize; dos Santos Filho, Mery; Cosentino, Ivana Conte; Barbosa Neto, Jair Borges; Tufik, Sergio [UNIFESP]; Matos, Jivaldo do Rosario; Mercuri, Lucildes Pita [UNIFESP]Ordered mesoporous silica, SBA-15, presents non-toxic nature
- ItemAcesso 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/2572450432314415A 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.
- ItemAcesso aberto (Open Access)Nanocompósitos TiO2:SBA-15 e suas potenciais aplicações em fotocatálise e fotoproteção(Universidade Federal de São Paulo, 2015-08-10) Jardim, Alice Antunes Muscas Leandro Ferreira [UNIFESP]; Martins, Tereza da Silva [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)Nanomaterials have been prominent in the research and development area. In particular, titanium dioxide (TiO2) has been extensively studied due to its interesting properties such as stability under severe conditions, low cost, absorbance in the ultraviolet region and high photocatalytic activity, being especially interesting as photocatalyst and photoprotector. The use of SBA-15 type ordered mesoporous silica to prepare TiO2:SBA-15 nanocomposites is advantageous since the final material has large surface area and, consequently, better performance in photocatalysis. For use in cosmetics, SBA-15 is recommended because it has micrometric particle size, less likely to penetrate the skin. This work aimed to study the influence of the synthesis parameters on the structural, textural and morphological properties of TiO2:SBA-15 nanocomposites and to establish the best synthesis conditions for application in photocatalysis and photoprotection. The studied parameters were: titanium dioxide molar ratio (10, 20 and 30% relative to silica amount), calcination temperature (540, 700 and 800 °C), synthesis route (standard or hydrothermal treatment (HT)), and presence of ionic liquid, IL, (CMIBF4, CMITf2N and CMIBr), acetylacetone and isopropyl alcohol. The nanocomposites were characterized by wide and small angle X ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption-desorption isotherms (NAI) and scanning electron microscopy (SEM). XRD measurements showed that the 20% TiO2 molar ratio resulted in more intense rutile phase peaks, whilst the ratio of 10% favored anatase phase. 10% and 20% ratios produced samples that retained the structure of SBA-15. Regarding the calcination temperature, it was observed that higher temperatures led to more intense rutile peaks, however, the crystallite size increased. FTIR spectra showed that titanium dioxide interacts weakly with SBA-15. Regarding IL presence, the molar ratio of 0.032LI:1TiO2 yielded structured materials. CMIBr has little influence on TiO2 crystalline phase selection, while CMITf2N favors rutile phase formation (for the 0.32:1 ratio) and CMIBF4 favors anatase. In the absence of alcohol, CMIBF4 (0.032:1) led to a nanocomposite with 100% anatase phase, suitable for application in photocatalysis. It was verified that both acetylacetone and HT synthesis route favor rutile phase, and the combined effect of the two resulted in a nanocomposite that would be interesting for application as photoprotector, with 90% rutile phase and small crystallite size incorporated into micrometric size silica. It was possible to visualize tubes with particle size of about 1 micrometer as expected for SBA-15, as well as the nanometric particles of titanium dioxide dispersed throughout the silica using SEM images. The exception was the sample prepared with CMITf2N in absence of alcohol, which exhibited SBA-15 particle size of about 0.1 micrometer, demonstrating the great influence of this IL in the silica's morphology.
- ItemAcesso 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.
- ItemSomente MetadadadosPreparation, characterization and electrical conduction mechanism of polyaniline/ordered mesoporous silica composites(Elsevier B.V., 2013-04-15) Santos Pedroso, Cassio Cardoso [UNIFESP]; Junqueira, Vania; Lacerda Rubinger, Carla Patricia; Martins, Tereza Silva [UNIFESP]; Faez, Roselena [UNIFESP]; Universidade Federal de São Paulo (UNIFESP); Univ Fed Itajuba; Universidade Federal de São Carlos (UFSCar)In this work, we have shown the preparation of polyaniline (PANI) and mesoporous ordered silica (SBA-15) composites. PANI/SBA-15 composites with different weight ratios were prepared in order to evaluate the electrical conduction mechanism. the analysis of the differential activation energy was carried out for composites, allowing the classification of the variable range hopping as one dimensional for the composites. the hopping parameter as a function of the sample mass ratio indicates that the insertion of aniline into the mesopores improves its intrinsic conductivity. A fibrilar morphology of the conducting PANI is formed by a controlled amount of the added polymer into SBA-15. It was confirmed by SEM and TEM analysis that the composites prepared with different PANI contents have different morphologies, indicating that the amount of polyaniline is crucial to obtain distinct morphologies. SAXS, NAI, TEM and SEM show that SBA-15 maintains its structure even after the polymerization process and the polymer is dispersed on the inorganic matrix. the parameters determined by the investigation of variable range hopping conduction by the differential activation energy method show that the PANI produced in these composites have higher electrical conductivity than pure PANI, possibly due to the improvement of the interparticle, interchain and intrachain processes for the charge transport, which are intimately related to the polymer morphology, fact coherent with SEM and TEM data. (C) 2013 Elsevier B.V. All rights reserved.
- ItemAcesso aberto (Open Access)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.