Utilização e recuperação de sílica gel impregnada com nitrato de prata

Argentation chromatography is used to increase the selectivity of the chromatographic process, chiefly in the resolution of complex mixtures of nonpolar substances. Although efficient, this technique generates residues containing heavy metal which makes its discarding through common procedures impracticable. In the present work a simple method for recycling of silica, and also silver, from argentation chromatography is described. This procedure uses initially a treatment of H2O2/HNO3, with subsequent treatment with H2O2/H2SO4 , allowing an efficient recycling of both components. This methodology is simple, costless, removes impurities efficiently, and does not modify retention parameters nor specific surface in a significant way.

Emprego de sílica gel organicamente modificada e impressa ionicamente para pré-concentração seletiva on-line de íons cobre

The present work purposes the preparation of a silica gel sorbent organically modified with 2-aminoethyl-3-aminobutylmethyldimethoxysilane (AAMDMS) and imprinted with Cu2+ ions by means surface imprinting technique and its use for selective on-line sorbent preconcentration of Cu2+ ions with further UV-VIS spectrophotometric determination by flow injection analysis. The Cu2+-imprinted silica gel, when compared with non imprinted silica gel and silica gel, showed from the binary mixture of Cu2+/Ni2+ relative selectivity coefficient (k') of 6.84 and 5.43 and 6.64 and 19.83 for the mixture Cu2+/Pb2+, thus demonstrating higher selectivity of Cu2+-imprinted silica gel towards Cu2+ ions. Under optimized condition, the on-line preconcentration method provided detection limit of 3.4 μg L-1 and linear range ranging from 30.0 up to 300.0 μg L-1 (r = 0.995). The accuracy of method was successfully assessed by analyzing different kind of spiked water samples with recovery values ranging from 92.2 up to 103.0%.

Estabilidade da sílica biogênica extraída de capim Jaraguá (Hyparrhenia rufa) em solução de NaOH

Biogenic silica is used to describe compounds of hydrated silica (SiO2.nH2O), with specific shapes and sizes, deposited in plants. The chemical composition of biogenic silica and its stability in Jaraguá grass was studied in increasing concentration of NaOH. The analytical results demonstrated high concentration of Si, Al, Fe, Mg, P and low of Cu, Cd and Zn in the phytoliths composition. The silica bodies stability in NaOH solution with increasing concentration was different among the shapes and sizes. Silicified stomata and silicified plant tissues were dissolved along with the dumbbells because they are the less stable forms of biogenic silica.

Impregnação do ácido 12-fosfotúngstico em sílica - parte I: determinação de parâmetros de impregnação, caracterização e avaliação da atividade catalítica

Catalyst based on Kegging-type heteropolyacids (H3PW12O40 - HPA), supported on SiO2 (H3PW), were prepared by the impregnation method under different thermal treatment conditions. The materials were characterized by different instrumental techniques and used as catalysts in the methyl esterification reactions of stearic acid. Using the catalyst with 15% of HPA, conversions higher than 60% were obtained after 2 h of reaction at 65 ºC. Recovery studies using hot-filtration with ethanol at 75 ºC showed satisfactory activity for two additional reaction cycles.

Síntese do material mesoporoso MCM-41 usando esponja de água-doce como fonte de sílica

Fresh water sponge was used as a silica source for the synthesis of MCM-41 via the hydrothermal process. The silica was extracted from the sponge by washing with nitric acid and piranha solution. Synthesis of MCM-41 was performed at 100 °C for 5 days and the procedure was optimized, with modifications made to the leaching temperature of the silica and the synthesis of mesoporous material, which was characterized by XRD, FT-IR, SEM and adsorption of N2. The optimal result was achieved at a temperature of 135 °C for 3 days, showing ordered mesoporous material with a surface area of 1080 m² g-1.

Impregnação do ácido 12-tungstofosfórico em sílica - parte II: efeito de diferentes solventes na impregnação e atividade catalítica na esterificação metílica de ácido esteárico

Materials obtained by the immobilization of 12-tungstophosphoric acid (PTA) on silica using the method of impregnation with excess solution in distinct solvents (aqueous HCl, methanol:H2O, and acetonitrile) were evaluated for use as catalysts in the methyl esterification of stearic acid. Optimum conditions were established for the impregnation of 0.5 g (w/w) of PTA on amorphous silica, under stirring at 150 rpm for 24 h, using 20 mL of 0.1 mol L-1 HCl as the solvent. After calcination at 200 ºC, high conversions were obtained under mild reaction conditions, resulting in high turnover numbers. The catalyst was evaluated in ten catalytic cycles of use, where the activity was reduced only slightly, attesting its stability and the possibility to apply it to industrial production of methylesters.

Catálise básica usando sílica mesoporosa estabilizada por acrilatos encapsulados

The synthesis of new type of silicas, with structures akin to that of MCM-41, containing polyacrylate-encapsulated micelles in their mesopores is reported. Initially, the monomers were inserted in the aqueous micelles of cetyltrimethylammonium cations. MCM-41 was then prepared in this microemulsion. Finally, the polymerization of the acrylates was initiated by UVC radiation. The presence of monomers and polymers in the interior of micelles in aqueous media were characterized by IR spectroscopy and small-angle Xray scattering. The presence of this polymer increased the stability of these new materials in catalytic transesterification.

Influência de parâmetros de processo na obtenção de sílica a partir de cinza da casca de arroz pela ação de Fusarium oxysporum

In this work, an experimental design was used to analyze the influence of process parameters on the production of extracellular enzymes such as β-glucosidase and peroxidase, and their possible effect on the obtention of soluble and nanostructured silica from rice husk ash by the action of the fungus Fusarium oxysporum. Specifically, pH, fermentation time and glucose concentration in the culture medium were varied. Statistical analysis indicated that the silica synthesis in the aqueous medium was strongly dependent on pH and time. Although the glucose concentration does not exert a direct influence on the biosynthesis of silica, it is an important parameter in the production of extracellular enzymes. To prevent enzyme inhibition and provide higher dissolution of silica, it is recommended to work at a pH close to neutral with a glucose concentration of 3 g L-1 for at least 144 h.

Imobilização de lipase por encapsulação em sílica aerogel

Lipase from Burkholderia cepacia was immobilized in a silica matrix and dried in high pressure carbon dioxide media (aerogel). The protic ionic liquid (PIL) was used in the immobilization process by encapsulation. The objective of this work was to evaluate the influence of the drying technique using supercritical carbon dioxide in biocatalysts obtained through the sol-gel technique by evaluating temperature and pressure and, after selecting the best drying conditions, to investigate the application of the technique for the biocatalyst using ionic liquid as an additive in the immobilization process. The results for immobilized biocatalysts showed that the best conditions of pressure and temperature were 100 bar and 25 ºC, respectively, giving a total activity recovery yield of 37.27% without PIL (EN) and 44.23% with PIL (ENLI). The operational stability of the biocatalysts showed a half-life of 11.4 h for ENLI and 6 h for EN. Therefore, solvent extraction using supercritical CO2, besides shortening drying time, offers little resistance to the immobilization of lipases, since their macropores provide ample room for their molecules. The use of the ionic liquid as an additive in the process studied for the immobilization of enzymes produced attractive yields for immobilization and therefore has potential for industrial applications in the hydrolysis of vegetable oils.

ESTUDO DA IMOBILIZAÇÃO DE LIPASE EM SÍLICA OBTIDA PELA TÉCNICA SOL-GEL

The objective of this work was the immobilization of the enzyme Candida antarctica lipase B (CAL B) using the sol-gel method of immobilization and three different initiators of the polymerization reaction: one acid (HCl), one basic (NH4OH) and the other nucleophilic (HBr). Tetraethylorthosilicate was used as the silica precursor. The influence of the additive PEG 1500 on immobilization was assessed. The efficiency of the process was evaluated considering the esterification activity of the xerogels. The immobilization process provided enhanced thermal stability, storage and operational aspects relative to the free enzyme. Storage temperature proved one of the main variables to be considered in the process, with the xerogels stored under refrigeration showing better results in terms of residual activity (nearly 200 days with ≥ 90% residual activity of basic and nucleophilic xerogels) when compared with storage at ambient temperature (nearly 40 days). The results demonstrated the possibility of reuse of derivatives and a greater number of cycles (nine), considering a residual activity of 50%.

OBTENÇÃO E CARACTERIZAÇÃO DE MATERIAL HÍBRIDO ENTRE SÍLICA E CICLODEXTRINAS

The obtention of silica and cyclodextrin hybrid materials was accomplished by refluxing them in xylol using citric acid as a binding agent. The materials were characterized by infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and elemental analysis. Evidence for the docking of cyclodextrins α and γ was substantiated based on the variation in band intensity for groups such as ≡Si-OH. Additional docking evidence includes the displacement of some of the bands that are related to cyclodextrin such as the deformation of the C-H axial bond. The α and γ-CDSi materials were characterized as amorphous compounds. The products obtained in the synthesis showed changes in the decomposition temperatures of their isolated constituents, in which the mass of α and γ-CD docked to the silica surface gave the estimated values of 41% and 47%, respectively. The elemental constituents were shown to be consistent and close to their relative theoretical values. ​Thermogravimetric analysis showed that a reduction in the percentage of the hybrids was proportional to the amount of lost mass. This new material is an improvement over synthesized organosilane materials because the operator and the environment benefit from a less toxic methodology. In addition, the material has several potential applications in complexation systems with cyclodextrin.

Estudo de alguns esfeitos na precipitação de partículas esféricas de sílica via microemulsão inversa

Partículas esféricas de sílica foram obtidas via microemulsão inversa em sistema AOT / Heptano / H2O, utilizando-se soluções de silicato de sódio como precursor. Variações de condições experimentais durante a precipitação levam à mudanças no tamanho e na forma das partículas. O objetivo deste trabalho é otimizar a obtenção de partículas de sílica com homogeneidade de forma e tamanho, variando-se a ordem de adição dos reagentes, a concentração da solução de silicato de sódio, a razão água/surfactante (W), a ordem de mistura dos reagentes e a purificação do produto obtido. As micrografias evidenciaram que para se obter partículas esféricas, com faixa estreita de tamanho, utiliza-se duas microemulsões inversas a partir das soluções de ácido nítrico e de silicato de sódio, sendo que a mistura destas deve ser feita adicionando-se a microemulsão contendo o silicato de sódio sobre a microemulsão contendo o ácido nítrico. A relação silicato de sódio:água mais adequada de para os objetivos do trabalho é de 1:10. A purificação mais eficiente é aquela feita em duas etapas, com etanol e com água quentes. A partir dos resultados obtidos, pode-se verificar também que quanto maior o W maior será o tamanho médio de partícula.

Redução de crômio hexavalente por substâncias húmicas aquáticas imobilizadas em aminopropil sílica

Estudou-se a redução de Cr(VI) à Cr(III) utilizando-se um novo suporte preparado pela ativação de aminopropil sílica com substâncias húmicas aquáticas (ATPS-SiO2-SHA). Coletaram-se amostras de água no Corrégo Itapitangui localizado no município de Cananéia-SP e extraíram-se as SHA utilizando-se procedimento recomendado pela Sociedade Internacional de Substâncias Húmicas. Após purificação por diálise, fez-se a imobilização das SHA na aminopropil sílica (APTS-SiO2) em pH 7,0, sob agitação mecânica por 48 horas à temperatura ambiente. Adicionaram-se 150 mg de APTS-SiO2-SHA à 150 mL de soluções 9,5 mimol L-1 de Cr(VI), fixou-se o pH em 2,5, 4,5 e 6,0 e mantiveram-se as misturas sob agitação mecânica à temperatura ambiente. Coletaram-se alíquotas em função do tempo (0-72 horas) e as concentrações de Cr(VI) foram determinadas por espectrofotometria baseada na reação com 1,5-difenilcarbazida. A porcentagem de redução de Cr(VI) por APTS-SiO2-SHA foi de 50, 4 e 0 % em pH 2,5, 4,5 e 6,0, respectivamente. Dobrando a massa do suporte APTS-SiO2-SHA verificou-se em pH 2,5, a redução de 70 % de Cr(VI). Esses resultados preliminares mostram forte influência do pH e da quantidade de APTS-SiO2-SHA no processo de redução do Cr(VI). Após outros estudos, a utilização do suporte APTS-SiO2-SHA pode ser uma alternativa viável a ser aplicada para o tratamento de resíduos e/ou estudos de especiação de crômio.

Avaliação do emprego dos adsorventes: carvão ativo, chromosorb W e membrana C18 na preparação de amostras de ar para a determinação de d-aletrina em ambientes fechados

Os piretróides sintéticos são inseticidas amplamente utilizados para o controle de agentes patogênicos, desde a produção agrícola até a proteção da saúde humana, porém, apesar de suas inúmeras vantagens podem causar intoxicações em indivíduos potencialmente expostos a suas diversas apresentações. Amostras de ar foram coletadas pela geração da atmosfera padrão, onde a d-aletrina foi adsorvida em cartuchos contendo Carvão Ativo, Chromosorb W e/ou Membrana C18. As determinações das concentrações da d-aletrina foram efetuadas empregando um sistema de cromatografia gasosa. Os adsorventes Carvão ativo, Chromosorb W e Membrana C18 apresentaram adsorções de 100,8., 104,1 e 100,5%, com um desvio padrão relativo de 4,1, 7,5 e 7,9%, respectivamente. Coletou-se amostras de ar para a determinação da concentração da d-aletrina em diferentes em ambientes fechados, em diferentes dias da semana, obtendo-se níveis de concentração de d-aletrina de 3,4., 8,5 e 12,7 mig.m³, respectivamente.

Desenvolvimento de um método analítico rápido e eficiente para a determinação de corticosteróides plasmáticos por injeção direta em coluna cromatográfica ISRP-C18 por CLAE

O presente trabalho teve como objetivo o desenvolvimento de um método analítico simples, rápido e eficiente para a determinação de corticosteróides (cortisona, corticosterona, acetato de hidrocortisona e acetato de dexametasona) em amostras sangüíneas de ratos empregando um sistema isocrático de cromatografia líquida de alta eficiência (CLAE) com detecção ultravioleta. O método envolveu a injeção direta da amostra sangüínea em uma coluna cromatográfica com superfície interna de fase reversa (ISRP-C18), empregando a fase móvel composta por tampão fosfato pH 4,0: acetonitrila (65:35 v/v). A detecção dos analitos foi obtida, através de um detector de ultravioleta de comprimento de onda variável (Varian Modelo 2550) ajustado em 240 nm e um integrador SP 4400 Chromaject (Varian Associates, Inc, Sunnyvale, CA, USA). A extração do analito resultou em valores de recuperação entre 90% e 108%, e coeficiente de variação entre 1,1% a 2,5%. Os limites de detecção e quantificação do método foram de 0,02 e 0,04 µg mL-1, respectivamente. Assim, o método analítico proposto possibilitou a injeção direta (on-line) da amostra sem tratamento prévio apresentando também várias vantagens, tais como: rapidez, exatidão, precisão e especificidade.