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Resumo O presente estudo teve como objetivo avaliar a termodinâmica e o equilíbrio de adsorção, em solução aquosa, do íon Cu2+ em uma montmorilonita organofuncionalizada por 3-aminopropiltrietoxissilano. Esse adsorvente foi preparado pela intercalação inicial de brometo de cetiltrimetilamônio e depois a funcionalização com o 3-aminopropiltrietoxissilano. A organofuncionalização ocorreu na superfície externa da matriz inorgânica. A capacidade máxima de adsorção de Cu2+ pela amostra organofuncionalizada, prevista pela densidade de imobilização (1,46.10-3 mol.g-1) foi de cerca de 92 mg de Cu2+ por grama de argila. A variação da entalpia na adsorção (ΔH) obtida por via calorimétrica foi de -1,4±0,3 kJ.mol-1, valor muito pequeno para ser determinado por aplicação de método da segunda lei. Tomando por base o modelo de Langmuir, com modificações, obtiveram-se valores de constantes de afinidade de 47±10, 41±9 e 48±6 dm3.mol-1, para as temperaturas de 25, 35 e 45 °C, respectivamente, o que evidenciou grandezas iguais dentro das incertezas experimentais. Abstract The aim of present study was to evaluate thermodynamics and the equilibrium of adsorption, in aqueous solution, of the Cu2+ ion in a montmorillonite organofunctionalized by 3-aminopropyltriethoxysilane. This adsorbent was prepared by the initial intercalation of cetyltrimethylammonium bromide and then functionalization by 3-aminopropyltriethoxysilane. The organofunctionalization occurred on the outer surface of the inorganic matrix. The maximum adsorption capacity of Cu2+ by the organofunctionalized sample, predicted by the immobilization density (1.46x10-3 mol.g-1), was about 92 mg of Cu2+ per gram of clay. The adsorption enthalpy change (ΔH), obtained by calorimetric method was -1.4±0.3 kJ.mol-1, a very small value to be determined by the application of second law method. Based on the modified Langmuir model, values of 47±10, 41±9 and 48±6 dm3.mol-1 for the affinity constants were obtained for temperatures of 25, 35 and 45 °C, respectively, which showed equal magnitudes for these physical quantities within the experimental uncertainties.

This study investigates the potential use of a silica gel modified with the silanizing 3- aminopropyltriethoxysilane as an adsorbent for the removal and possible recovery of the dyes: amaranth, ponceau 4r, acid red 17 and hydroxynaphtol blue, from aqueous solutions synthetic and aqueous industrial effluents. These dyes are anionic chromophore molecular structure. Initially, methods were validated and developed molecular absorption spectrophotometric in the region of the visible, reliable and low cost, for quantification of the azo dyes in aqueous medium, from adsorptive assays. Earplugs and cation sequestrants were used as stabilizing solutions in the methods. They went validated for concentrations of analytes (dyes) in the range of 5 to 60 mg.L-1. A silica gel was modified with the silanizing agent following the procedure of literature. Mean infrared spectra were determined to confirm the modification of the silica gel. The effect of pH, time and the temperature for the adsorbent prepared with each of the four dyes. The adsorptive removal of the dyes (kinetics and equilibrium) were performed in aqueous and batch phase monocomponents. The adsorption kinetic curves obtained were adjusted to pseudopress and pseudase 2 orders. The isotherms of determined were also adjusted using the Langmuir Freundlich. The differences in adsorption behavior of the four dyes with silica gel functionalized were also evaluated, being verified the influence of the auxochromic groups, which differentiate these dyes, in the adsorptive process. In addition, desorption of the dyes was studied with solutions of NaOH, KOH, Na2CO3 in the concentration of 0.025 mol.L-1 and NaHCO 3 of 0.1 mol L-1. In order to verify the efficiency of the adsorbent in real cases, Two samples of industrial effluents were collected: one from the textile industry and another from the foods, which use azide dyes in their production processes. The methods developed and validated were efficient in the quantification of dyes. The acidic pH was the most favorable for the adsorption of the dyes evaluated on the aminofunctionalized silica. An higher adsorption capacity was obtained at 25 ° C. The best models obtained were the pseudomain order and Langmuir models for kinetics and equilibrium, respectively. The time to reach equilibrium was around 6 hours for all dyes. According the Langmuir model, the maximum adsorption capacity of the dyes in the evaluated adsorbent obeys the following order: AR17

A ciência básica na área de cimentos e concretos tem incorporado pesquisas relacionadas ao entendimento dos efeitos da adição de nanossílica e, mais recentemente, de nanossílica funcionalizada nas propriedades de pastas de cimento, argamassas e concretos. Neste contexto, o objetivo deste trabalho foi preparar nanossílicas funcionalizadas com grupos amina a partir de uma nanossílica comercial (NS), fornecida como uma suspensão coloidal aquosa, empregando-se o reagente 3-aminopropiltrietoxissilano (APTS) e avaliar as características das amostras obtidas. As reações de funcionalização foram realizadas em um sistema reacional bifásico constituído de diclorometano e água, empregando-se diferentes razões molares APTS/NS. Os materiais foram obtidos como suspensões aquosas, cujas características foram avaliadas em pH 4, 7 e 10. A funcionalização da NS foi evidenciada pela presença das bandas relativas ao grupo aminopropil nos espectros de infravermelho, onde também foram observadas bandas dos grupos silanol (-SiOH) e alcóxido (Si-OCH2CH3), indicando que as reações de hidrólise e condensação não foram completas. Os sinais nos espectros de RMN de 29Si característicos de ligações Si-C confirmaram a funcionalização. As curvas termogravimétricas indicaram que houve aumento no teor de grupos aminopropil incorporados à NS com o aumento da razão APTS/NS empregada. As imagens de microscopia eletrônica de transmissão mostraram um aumento do tamanho médio das partículas após a funcionalização. As nanopartículas funcionalizadas em suspensão aquosa apresentaram potencial zeta positivo em pH 4 (+23 a +27 mV) e em pH 7 (+14 a +29 mV), indicando a presença de grupos amina protonados. Já em pH 10, o potencial zeta foi fracamente negativo (-0,10 a -7,6 mV) para amostras preparadas com menor razão APTS/NS (7,1 e 14,2 x 10-2), e positivos (+11 e +15 mV) para aquelas preparadas com razão molar maior (28,5 e 42,7 x 10-2), sugerindo um maior teor de grupos amina superficiais nestas últimas. Os raios hidrodinâmicos médios das partículas funcionalizadas foram maiores (22 a 281 nm) do que o da NS (12 nm) para todos os valores de pH, com valores maiores para partículas suspensas em pH 10. O teor de agregados de maior tamanho (~100 a 2000 nm) foi maior para as amostras preparadas com menor razão APTS/NS. Essas características variadas são interessantes para estudos comparativos dos efeitos de adição dessas suspensões em pastas de cimento, sobre a microestrutura e propriedades dos materiais resultantes. The basic science on cements and concretes has incorporated research related to the understanding of the effects of the addition of nanosilica, and more recently functionalized nanosilicas, on the properties of cement pastes, mortars and concretes. In this context, the aim of this work was to prepare amino-functionalized nanosilicas from a commercial nanosilica (NS), provided as an aqueous colloidal suspension, by employing 3-aminopropiltrietoxissilano (APTS) as reactant, and to evaluate the characteristics of the samples. The functionalization reactions were performed in a biphasic system composed of dichloromethane and water, and employing different APTS/NS molar ratios. The materials were obtained as aqueous suspensions and their characteristics were evaluated at pH 4, 7 e 10. The functionalization of NS was evidenced by the presence of infrared bands associated to the aminopropyl group. Bands associated to silanol (-SiOH) and alcoxide (Si-OCH2CH3) groups were observed indicating that the hydrolysis and condensation reactions were not complete. The 29Si NMR signals of Si-C bonds confirmed the functionalization. The thermogravimetric curves indicated an increase of the amount of aminopropyl groups incorporated on NS as the APTS/NS ratio increased. Transmission electron microscopy images showed an increase in the mean particle sizes after functionalization. The aqueous suspended nanoparticles showed a positive zeta potential at pH 4 (+23 to +27 mV) and at pH 7 (+14 to +29 mV), indicating the presence of protonated amine groups. The zeta potential at pH 10 was weakly negative (-0.10 to -7,6 mV) for the samples prepared from the lower APTS/NS molar ratios (7.1 and 14.2 x 10-2), and still positive (+11 and +15 mV) for those prepared from the higher molar ratios (28.5 and 42.7 x 10-2), suggesting the existence of a higher amount of superficial amino groups within the latter. The mean hydrodynamic radius of the functionalized particles were greater (22 a 281 nm) than that of the NS (12 nm) at all pH values, with superior values for suspended particles at pH 10, particularly for samples prepared from the lower APTS/NS ratios. The amount of aggregates of bigger size (~100 to 2000 nm) was greater for samples prepared from the lower APTS/NS ratios. These variable characteristics are interesting for comparative studies involving the effects of the addition of these suspensions in cement pastes over the microstructure and properties of the resulting materials.

Made available in DSpace on 2014-06-11T19:25:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-01-26Bitstream added on 2014-06-13T19:12:22Z : No. of bitstreams: 1 sa_ac_me_ilha.pdf: 1061286 bytes, checksum: b370fdf160f4689709efe584af803c2a (MD5) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) O objetivo deste trabalho esta resumido através de três etapas. 1 - A primeira etapa consistiu em funcionalizar e caracterizar a sílica gel com grupos 3- aminopropiltrietoxisilano. Nesta etapa o material obtido (Si) foi caracterizado por técnicas de Ressonância Magnética Nuclear no estado sólido (24Si e 13C) e espectroscopia vibracional (FTIR). 2- Numa segunda etapa promoveu-se a adsorção de íons de cobre (II) e de cobalto (II) na superfície da sílica (Si). Os materiais obtidos (SiCu e SiCo) foram caracterizados por espectroscopia vibracional e voltametria cíclica. 3- Na terceira etapa reagiu-se os materiais preparados (SiCu e SiCo) com nitroprussiato de sódio para formar os complexos binucleares (SiCuNP e SiCoNP). Estes materiais também foram caracterizados por espectroscopia vibracional e voltametria cíclica. Estes materiais foram utilizados na construção do eletrodo de pasta de grafite e testados na oxidação eletrocatalítica de substâncias biologicamente importantes tais como a hidrazina e N-acetilcisteína sendo empregado para isto a técnica de voltametria cíclica. Observou-se que o eletrodo de SiCuNP apresentam dois pares redox nos potenciais (Em)1 = 0,34 V e (Em)2 = 0,76 V vs Ag/AgCl, O primeiro foi atribuído ao processo de oxidação do par Cu(I)/Cu(II) e o segundo ao processo de oxidação Fe(II)(CN)5NO / Fe(III)(CN)5NO do complexo binuclear. O sistema SiCoNP foram observados dois pares redox distintos com os seguintes potenciais médios (Em); (Em)1 = 0,29 V e (Em)2 = 0,56 V vs Ag/AgCl, o primeiro foi atribuído ao processo redox do par Co(II)/Co(III) e o segundo ao processo redox Fe(II)(CN)5NO / Fe(III)(CN)5NO do complexo binuclear formado. O sistema SiCuNP foi sensível a concentração de hidrazina apresentando um limite de detecção e sensibilidade amperométrica de 3,07×10-4 mol L-1 e 5,84×10-6 A / mol L-1... The objective of this work is summarized in three stages. 1 - The first stage functionalizes and characterizes the silica gel with 3-aminopropyltriethoxysilane groups. At this stage the material obtained (Si) was characterized by solid state Nuclear Magnetic Resonance techniques (24Si and 13C) and vibrational spectroscopy (FTIR). 2 - The second stage promotes the adsorption of copper (II) and cobalt (II) ions on the surface of the silica (Si). The materials obtained (SiCu and SiCo) were characterized by vibrational spectroscopy and cyclic voltammetry. 3 - The third stage prepares the reaction of the materials (SiCu and SiCo) with sodium nitroprusside to form the binuclear complex (SiCuNP and SiCoNP). These materials were characterized by vibrational spectroscopy and cyclic voltammetry. These materials were used to construct the electrode carbon paste and were tested for electrocatalytic oxidation of biologically important substances such as hydrazine and N-acetylcysteine using the cyclic voltammetry technique. It was observed that the electrode SiCuNP has two redox pairs in the potential (Em)1 = 0.34 V and (Em)2 = 0.76 V vs. Ag/AgCl, the first was attributed to the oxidation process of the pair Cu(I)/Cu(II) and the second to the oxidation process Fe(II)(CN)5NO / Fe(III)(CN)5NO of the binuclear complex. For the SiCoNP system, two distinct redox couples were observed with the following mean potentials (Em); (Em)1 = 0.29 V and (Em)2 = 0.56 V vs Ag/AgCl, the first one was assigned to the redox process of the Co(II)/Co(III) pair and the second one to the redox process Fe(II)(CN)5NO / Fe(III)(CN)5NO of the binuclear complex formed. The SiCuNP system was sensitive to the hydrazine concentration, exhibiting a detection limit and amperometric sensitivity of 3.07×10-4 mol L-1 and 5.84×10-6 A / mol L-1 respectively and was also... (Summary complete electronic access click below)