Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); The aggregation kinetics of solutions of vinyltriethoxysilane-derived organic/silica hybrid species were studied by small-angle X-ray scattering (SAXS) in a strongly basic medium. The SAXS intensity was analysed by a modified Sharp-Bloomfield (SB) global function and its evolution was found to be compatible with the growth, coiling and branching of the polymeric macromolecules in solution. A form factor valid for randomly and nonrandomly branched polycondensates and for polydisperse coils of linear chains was used in the modified SB model, instead of the Debye function valid for monodisperse coils of linear chains. The aggregation kinetics are accelerated with increasing base concentration in the studied range, but all the kinetics curves can be matched to a unique curve using an appropriate time scaling factor. The aggregation kinetics suggest that physical forces (hydrothermal forces) associated with phase coarsening could be active in the aggregation process, together with diffusion mechanisms.
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Poly(vinyl alcohol)/silica hybrid xerogels were prepared from sonohydrolysis of tetraethoxysilane (TEOS) and additions of water-solution of poly(vinyl alcohol) (PVA). The samples were Studied by small-angle X-ray scattering (SAXS), nitrogen adsorption, and differential scanning calorimetry (DSC). on drying it room temperature the resulting xerogels exhibit a fairly bimodal Porous structure Composed by small mesopores and micropores. The pore size distribution of the mesopores was found to follow approximately a power-law with the pore size. The micropore structure was associated to an evolution at a high resolution level of the mass fractal structure of the original wet gels. The role of the PVA addition oil the pore structure of the xerogels is to diminish the specific surface area, and the pore volume without to change substantially the pore mean size. (C) 2009 Elsevier B.V. All rights reserved.
Simas Vaz, Fernando Antonio; Moutinho, Arthur Damasio; Rodrigues Furtado de Mendonca, Jose Paulo; de Araujo, Ricardo Tavares; Lima Ribeiro, Sidney Jose; Polachini, Ferminio Cesar; Messaddeq, Younes; Leal de Oliveira, Marcone Augusto
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); The preparation of photo-polymerized sol-gel monolithic stationary phases (MSP) within 100 mu m internal diameter polyacrylate-coated fused-silica capillaries for use in capillary electrochromatography (CEC) was optimized. Eight mixtures containing different amounts of methacryloxypropyltrimethoxysilane (MPTMS) as the polymeric precursor, hydrochloric acid solution as the catalyst, toluene as the porogen and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure 819) as the photo-initiator were irradiated at 370 nm inside the capillaries in order to complete the MSP polymerization, according to a fractional factorial experimental design 2(IV)(4-1). All the preparation procedure, from capillary pretreatment until the MSP is ready to use in CEC, were made in less than four hours in mild conditions. A high pressurization injection device (HPID) useful for micro-volume syringes was built in order to achieve practical, controlled and precise injections of sols, solvents and electrolytes in the capillaries. The eight MSP were equally washed, conditioned and submitted to CEC procedures via short-end injection...
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Some aspects of the chemistry involved in the preparation and characterization of functionalized silicon oxide by sol-gel method are considered in this work. The synthesis was performed with different silicon alcoxide precursors and the influence of the acid and basic catalyst was investigated. Characterization was performed by infrared absorption spectroscopy, elemental analysis and 29Si NMR. Infrared data show Si-C and -CH2- vibrational modes at 1250 to 1280 and 2920 to 2940 cm-1, respectively. The elemental analysis confirmed the presence of organic groups in the inorganic silica network. 29Si NMR results show different hydrolisys depending on the acid or base catalysis.
Monolithic silica xerogels doped with different concentrations of Er3+, Yb3+ and Al3+ were prepared by sol-gel route. Densification was achieved by thermal treatment in air at 950degreesC for 120 h with a heating rate of 0.1degreesC/min. We studied the luminescence properties of the I-4(13/2)-->I-4(15/2) emission band of Er3+ as a function of the Al/Er/Yb concentration and we paid particular attention to the alumina effects. Raman spectroscopy and Vis-NIR absorption were used to monitor the degree of densification of the glasses and the residual OH content.
This work describes the synthesis of a first-generation iron porphyrin catalyst entrapped in a silica matrix by the sol-gel route, leading to spherical particles. The catalyst was synthesized by the method of Stober, through hydrolysis and condensation of the alkoxysilane TEOS in a mixture of alcohol, water and ammonia, in the presence of the iron porphyrin Fe(TPP)Cl. The relation between particle morphology and catalytic activity of the different Fe(TPP)-SiO2, obtained using different H2O/silane molar ratios and ammonia concentrations in the xerogel syntheses, was studied.The obtained catalysts were characterized by UV-vis spectroscopy, NMR Si-29. thermogravimetric analysis and transmission electron microscopy. Their ability to catalyze (Z)-cyclooctene epoxidation and cyclohexane oxidation was tested using iodosylbenzene as oxygen donor; the oxidation products were analyzed by gas chromatography and the catalysts obtained in a form of particles spherical and monodispersed showed to be a promising catalytic system for selective oxidation. (c) 2005 Elsevier B.V. All rights reserved.
The carbonyl complexes [WCl(CO)(3)(bipy) (HgCl)] (1), [Fe(CO)(4)(HgCl)(2)] (2) and W(CO)(6)] (3) were immobilized on a silica gel surface organofunctionalized with piperazine groups. The products obtained were studied by IR spectroscopy and small angle X-ray scattering (SAXS) techniques. The IR data show that the immobilization of heterobimetallic compounds 1 and 2, on the functionalized surface, occurred through the mercury atom, while for 3 the displacement of one CO group by the nitrogen of a piperazine molecule was observed. The data obtained from SAXS indicate that particles have a uniform size and reveal suitable modifications on the functionalized surface after immobilization of metal carbonyl complexes. The average intermolecular distance (l(ij)) for piperazine ligands on support is 8.7 Angstrom, for the metal carbonyl complex 1 it is 18.8 Angstrom, for complex 2 it is 16.2 Angstrom and for complex 3 it is 15.3 Angstrom. Copyright (C) 1996 Elsevier B.V. Ltd
Spherical silica nanoparticles were prepared using a basic amino acid catalysis route and the kinetics of the particles growth was investigated by small angle X-ray scattering (SAXS). L-arginine was used in the polar aqueous phase as the basic catalyst whereas the tetraethylorthosilicate (TEOS) was dissolved in the cyclohexane oil phase as the silicate monomer source. The SAXS measurements were taken in the aqueous phase at different reaction times. A high degree of monodispersity was clearly evidenced for the spherical nanoparticles as a result of the pronounced high-order oscillations observed in the SAXS curves. The SAXS data show that the particles number density remains unchanged since both the particle size as well as the volume fraction gradually increase. This process was discussed based on a reaction-controlled addition of monomer species at the surface of the growing particles. Consequently, the monodispersed spherical nanoparticles radius can as such be finely tuned from 7 to 12 nm by varying the reaction time. (C) 2010 Elsevier B.V. All rights reserved.
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 09/11079-1; Processo FAPESP: 10/12524-6; In the present work, we investigated the immobilization and electrochemical behavior of Reactive Blue 4 dye on 3-aminopropyl-functionalized silica. The electrochemical behavior of the modified electrode and the electro-oxidation of dipyrone were studied by cyclic voltammetry. The modified electrode showed a well-defined redox coupling with a formal potential of 0.45 V (vs. saturated calomel reference electrode) assigned to anthraquinone/anthrahydroquinone redox process (pH = 2). The modified electrode also demonstrated electrocatalytic activity and an increased peak current towards the oxidation of dipyrone at a reduced overall potential. The electrocatalytic process was found to be highly dependent on the pH of the supporting electrolyte. The voltammetric responses for dipyrone were linear in the concentration range of 49.9 to 440 mu mol L-1 at a pH of 2.0 with a detection limit and sensitivity of 22.0 mu mol L-1 and 0.0278 mu A mmol L-1, respectively.
Pb2CrO5 nanoparticles were embedded in an amorphous SiO2 matrix by the sol-gel process. The pH and heat treatment effects were evaluated in terms of structural, microstructural and optical properties from Pb2CrO5/SiO2 compounds. X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), energy dispersive spectroscopy (EDS), and diffuse reflectance techniques were employed. Kubelka-Munk theory was used to calculate diffuse reflectance spectra that were compared to the experimental results. Finally, colorimetric coordinates of the Pb2CrO5/SiO2 compounds were shown and discussed. In general, an acid pH initially dissolves Pb2CrO5 nanoparticles and following heat treatment at 600 A degrees C crystallized into PbCrO4 composition with grain size around 6 nm in SiO2 matrix. No Pb2CrO5 solubilization was observed for basic pH. These nanoparticles were incorporated in silica matrix showing a variety of color ranging from yellow to orange.
This work describes the synthesis and characterization of 5-amino-1,3,4-thiadiazole-2-thiol modified silica gel (SiATT), and the results of a study of the adsorption and preconcentration (in batch, and in flow using a column technique) of Cd(II), Co(II), Cu(II), Fe(III), Ni(II), Pb(II) and Zn(II) in ethanol medium. The adsorption capacities for each metal ion were (in mmol g -1): Cd(II) = 0.11, Co(II) = 0.10, Cu(II) = 0.20, Fe(III) = 0.20, Ni(II) = 0.16, Pb(II) = 0.08 and Zn(II) = 0.12. The results obtained in the flow experiments, showed a recovery of ca. 100% of the metal ions adsorbed in a column packed with 2 g of SiATT, using 5 mL of 2.0 mol L -1 HCl solution as eluent. The sorption-desorption of the metal ions made possible the development of a preconcentration method and quantification by Flame AAS of metal ions at trace level in fuel ethanol.
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Ordered hexagonal mesoporous silica was prepared using Pluronic P123 template and removal of the polymer by washing in ethanol. The thermal stability and the pore elimination was studied under heat treatment by a fixed time at 500, 600, 750, 825, 900, and 1050 degrees C. The most part of the porosity is built up by cylindrical pores belonging to the ordered hexagonal 2D pore structure. The lattice parameter and the pore volume of the hexagonal 20 structure diminish regularly with the temperature up to 900 degrees C. All porosity is eliminated at 1050 degrees C. The porosity elimination occurs in a mechanism described by a geometric model of contracting area, in which the diameter of the cylindrical pore diminishes while its length is kept constant. An activation energy of (92 +/- 2) kJ/mol was estimated for the process. The ordered porosity of an ethanol-washed and vacuum dried sample was found to be even larger with a narrower pore size distribution in comparison to a sample directly calcined at 500 degrees C without previous washing in ethanol. (C) 2014 Elsevier Inc. All rights reserved.
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Processo FAPESP: 11/23047-7; Processo FAPESP: 12/17689-9; This work describes the preparation, characterization and application of a hybrid material composed of disordered mesoporous silica (SiO2) modified with multiwalled carbon nanotubes (MWCNTs), obtained by the sol-gel process using HF as the catalyst. This hybrid material was characterized by N-2 adsorption-desorption isotherms, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission microscopy (HR-TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). This new hybrid material was used for the construction of a thin film on a glassy carbon electrode. The modified electrode using this material was designated SiO2/MWCNT/GCE. The electrocatalytic properties of the electrode toward dopamine, uric acid and paracetamol oxidation were studied by differential pulse voltammetry. Well-defined and separated oxidation peaks were observed in phosphate buffer solution at pH 7.0, in contrast with the ill-defined peaks observed with unmodified glassy carbon electrodes. The electrode had high sensitivity for the determination of dopamine...
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Processo FAPESP: 2012/07067-0; Processo FAPESP: 2012-05013-0; Surface-modified silica nanoparticles have a plenty of applications, such as coatings, dyes or biomarkers, catalysts and encapsulated products. When modified with 3-(trimethoxysilyl)propyl methacrylate (SiO2-MPS) or covered with a polymeric shell obtained from a reaction between divinylbenzene and styrene (SiO2-Pol), these SiO2 nanoparticles induced distinct arrangements in polymer nanocomposites (PNC) prepared with commercial carboxylated nitrile rubber (XNBR). The hydrophilicity character of the modified SiO2 nanoparticles was also altered, improving their interaction with the XNBR macromolecules. Consequently, choosing the PNC properties for different conditions and applications became possible due to the adjustment of the nanoparticle surface characteristics. Although the final characteristics of the nanocomposites films varied according to the nanoparticle used, the PNC prepared with SiO2-Pol presented better homogeneity than those with SiO2-MPS.
A sílicica-gel superficical 560 m. g foi funcionalizada covalentemente com 2-, 3- ou 4-aminopiridina, originando-se os produtos SIL-2, SIL-3 e SIL-4, respectivamente. As análises elementares de nitrogênio acusaram a seguinte ordem decrescente no grau de funcionalização: SIL-4> SIL-3 > SIL-2, que é invertida em relação às áreas superficiais específicas. OS materiais suportados foram equilibrados com soluções de cloretos de Co(II), Ni(II), Cu(II) ou Zn(II) em etanol e acetona. As quimissorções que então se passaram seguiram o modelo de Langmuir, sendo que, para um mesmo íon a capacidade de fixação obedeceu à mesma ordem de funcionalização dos materiais. O grau de quimissorção dos cloretos metálicos em acetona, Cu > Co > Zn, é a mesma ordem de estabilidade de complexos com íons metálicos em meio homogêneo. As titulações calorimétricas possibilitaram a determinação de DH de interação íon metálico-ligante ancorado. Os materiais funcionalizados foram testados cineticamente quanto à capacidade de decomporem a água oxigenada em meio etanólico. SIL-4 complexado com CoCI2 mostrou-se mais efetivo nesta decomposição. Assim sendo, este material foi selecionado para ser testado como catalisador na reação de epoxidação do ciclohexeno. Os resultados catalíticos indicaram uma conversão de cerca de 68% do hidroperóxido originalmente presente.; Silica gel of 560 m. g superficial area was functionalized covalently with 2-...
One of the most popular preventive measures to minimize the occurrence of chemical expansive reactions, namely the alkali-silica reaction (ASR) and delayed ettringite formation (DEF) in hardened concrete is the use of supplementary cementing materials (SCMs). Several studies have been performed along the last few years related with the use of fly ashes in the suppression of expansion due to ASR. However, relatively little attention are been focused in its effectiveness to control the DEF in concrete, and the use of metakaolin to control the ASR and DEF.
The research work presented in this paper deals with the influence of fly ashes (FA) and metakaolin (MK) in the inhibition of ASR and DEF in concrete. The mechanisms of FA and MK in the suppression of ASR are discussed. Results obtained indicated that the reduction of the calcium hydroxide content is the most beneficial effect of FA and MK in ASR inhibition mechanism. Furthermore, the results obtained indicate that the use of FA and MK, for partial replacement of cement in concrete, is effective in the inhibition of expansion by DEF.
This contribution compares experimental nitrogen adsorption isotherms with molecular simulation results on effective non-porous silica models. A Molecular Dynamic (MD) annealing temperature scheme was adopted for the formulation of three samples of the solid surface. By means of Grand Canonical Monte Carlo (GCMC) simulations, nitrogen adsorption isotherms were obtained for each sample, with charged and uncharged nitrogen molecules, and compared with relevant experimental data. Following comparison of the experimental and simulated nitrogen results, a tuning process over the energetic parameter of the oxygen atoms was performed for the final proposed model. Specifically, the results are presented in terms of adsorption isotherms with an emphasis on the annealing effect over relevant model parameters, such as the surface concentration and the distribution of non-bridging oxygen atoms.
The methoxylation of a-pinene was studied over sulfonic acid-functionalized mesoporous silica (MCM-41, PMO) at 60ºC. The support functionalization was achieved by the introduction of 3-(mercaptopropyl)trimethoxysilane onto the surface of these materials either by grafting or by co-condensation. The thiol groups were oxidized to SO3H by treatment with H2O2. All the catalysts were active in the studied reaction being the PMO-SO3H-g the best one. Good values of selectivity to a-terpinyl methyl ether were obtained with these catalysts. Catalytic stability of the PMO-SO3H-g was evaluated by performing consecutive batch runs with the same catalyst sample. After the third batch it was observed a stabilisation of the activity.
With the objective to evaluate PCR-mediated detection of Mycobacterium tuberculosis DNA as a diagnostic procedure for diagnosis of tuberculosis in individuals attending ambulatory services in Primary Health Units of the City Tuberculosis Program in Rio de Janeiro, Brazil, their sputum samples were collected and treated with a DNA extraction procedure using silica-guanidiniumthiocyanate. This procedure has been described to be highly efficient for extraction of different kind of nucleic acids from bacteria and clinical samples. Upon comparing PCR results with the number of acid-fast bacilli, no direct relation was observed between the number of bacilli present in the sample and PCR positivity. Part of the processed samples was therefore spiked with pure DNA of M. tuberculosis and inhibition of the PCR reaction was verified in 22 out of 36 (61%) of the samples, demonstrating that the extraction procedure as originally described should not be used for PCR analysis of sputum samples.
Some modifications made at silanization step and the introduction of r-nitrobenzil bromide as an alternative reagent to the 8-hydroxiquinolein immobilization in silica gel were important points that brought up the reduction of synthesis time, efficency improvement of the immobilization process and better hydrolysis stabilization to the final materials. The caracterization was made by infrared spectroscopy, elementary analysis, complexing capacity and acid-base properties.