Preparation of SnO2 supported membranes with ultrafine pores

The colloidal route of the sol-gel process was used to prepare supported SnO2 membranes. The influence of the sol and monoelectrolyte concentrations on the formation of the gel layer by sol-casting on the top of macroporous alpha-Al2O3 support was described. The stability of the colloidal suspension as a function of the concentrations was analyzed from creep-recovery measurements. The calcined supported membranes were characterized by nitrogen adsorption-desorption isotherms and scanning electron microscopy. The set of results show that homogeneous membrane layers containing the smallest quantity of cracks are formed in a critical interval of sol (1.01 less than or equal to[SnO2]less than or equal to 1.4 M) and electrolyte (2.O less than or equal to[Cl-]less than or equal to 4.0 mM) concentrations. The samples prepared from concentrated suspensions present a lot of interconnected cracks which favors the peeling of the coated layer. The membranes have pores of average diameter of about 1 nm.

Composites PVDF-TrFE/BT used as bioactive membranes for enhancing bone regeneration

In this paper a piezoelectric composite membranes were developed for charge generator to promoter bone regeneration on defects sites. Is known that the osteogenesis process is induced by interactions between biological mechanisms and electrical phenomena. The membranes were prepared by mixing Barium Titanate (BT) powders and PVDF-TrFE (PVDF:TrFE = 60:40 mol%) on dimethylformamide medium. This precursor solution was dried and crystallized at 100degreesC for 12 hours. Composites membranes were obtained by following methods: solvent casting (SC), spincoating (SP), solvent extraction by water addition (WS) and hot pressing (HP).The microstructural analysis performed by SEM showed connectivity type 3-0 and 3-1 with high homogeneity for samples of ceramic volume fraction major than 0.50. Powder agglomerates within the polymer matrix was evidenced were observed for composites with the BT volume fraction major than 40%. The composite of ceramic fraction of 0.55 presented the best values of remanent polarization (similar to33 muC/cm(2)), but the flexibility of these composites with the larger ceramic fraction was significantly affected.For in vivo evaluation PVDF-TrFE/BT 90/10 membranes with 3cm larger were longitudinally implanted under tibiae of male rabbit. After 21 days the animals were sacrificed. By histological analyses were observed neo formed bone with a high mitotic activity. In the interface bone-membrane was evidenced a pronounced callus formation. These results encourage further applications of these membranes in bone-repair process.

Lignin from sugar cane bagasse: Extraction, fabrication of nanostructured films, and application

Four lignin samples were extracted from sugar cane bagasse using four different alcohols (methanol, ethanol, n-propanol, and 1-butanol) via the organosolv-CO2 supercritical pulping process. Langmuir films were characterized by surface pressure vs mean molecular area (Pi-A) isotherms to exploit information at the molecular level carrying out stability tests, cycles of compression/expansion (hysteresis), subphase temperature variations, and metallic ions dissolved into the water subphase at different concentrations. Briefly, it was observed that these lignins are relatively stable on the water surface when compared to those obtained via different extraction processes. Besides, the Pi-A isotherms are shifted to smaller molecular areas at higher subphase temperatures and to larger molecular areas when the metallic ions are dissolved into the subphase. The results are related to the formation of stable aggregates (domains) onto the water subphase by these lignins, as shown in the Pi-A isotherms. It was found as well that the most stable lignin monolayer onto the water subphase is that extracted with 1-butanol. Homogeneous Langmuir-Blodgett (LB) films of this lignin could be produced as confirmed by UV-vis absorption spectroscopy and the cumulative transfer parameter. In addition, FTIR analysis showed that this lignin LB film is structured in a way that the phenyl groups are organized preferentially parallel to the substrate surface. Further, these LB films were deposited onto gold interdigitated electrodes and ITO and applied in studies involving the detection of Cd+2 ions in aqueous solutions at low concentration levels throughimpedance spectroscopy and electrochemical measurements. FTIR spectroscopy was carried out before and after soaking the thin films into Cd+2 aqueous solutions, revealing a possible physical interaction between the lignin phenyl groups and the heavy metal ions. The importance of using nanostructured systems is demonstrated as well by comparing both LB and cast films.

Formation of SnO2 supported porous membranes

In this work, the effect of the substrate microstructure on the formation of SnO2 membranes and of the sintering conditions on their porosity have been analysed. Samples have been prepared by colloidal suspensions cast on alumina or kaolin substrates. Supported membranes have been characterized by Hg porosimetry, MEV, XRD and N-2 adsorption-desorption isotherms. The results show that the narrower pore size distribution of alumina substrate allowed to prepare membranes more homogeneous and free of cracks than that supported on kaolin. The crystallite and pore sizes of the membranes could be controlled by adjusting the temperature of sintering, allowing materials with adequate microstructure with application for ultrafiltration process.

Evaluation of anionic collagen membranes in the treatment of class II furcation lesions: an histometric analysis in dogs

This study aims to evaluate the effect of using anionic collagen membranes in guided tissue regeneration treatment of Class II furcation lesions in dogs. The defects were created in the buccal furcation of 16 mandibular premolars of four dogs. After 56 days without plaque control, the sites were scaled and divided into two groups according to the treatment applied: control sites, open flap debridement; and test sites, guided tissue regeneration treatment. The animals were killed after 3 months. Histological and histometrical analyses showed that the collagen membrane was better than open flap debridement in terms of newly formed cementum and epithelial migration prevention. It provided effective blockade of epithelial tissue and promoted regeneration of lost periodontal tissues, suggesting that the membrane warrants further study. (C) 1997 Elsevier B.V. Limited. All rights reserved.

Valor nutritivo do feno de Brachiaria decumbens Stapf cv. Basilisk submetido a tratamento com amônia anidra ou uréia

The effects of the ammoniation of Brachiaria decumbens hay was evaluated. The hay bales were distributed into a complete randomized block design, with four replications and they were submitted to the treatments: untreated or treated with anhydrous ammonia (NH3)(2,0 and 3,0% of the DM) or with urea (3,6 and 5,4% of the DM). All the hays bales remained under plastic cover for 45 days. After three days of aeration, samples were collected for the determination of the chemical composition, nitrogenous compounds fraction and the in vitro dry matter (IVDDM) and organic matter (IVDOM) digestibility. In the metabolic study, Saanen goats breed was used in a 5x5 Latin squares design, where the apparent digestibility, the voluntary intake and the nutritive value index were evaluated. The ammoniation increased the contents of the total N, N ammonia (N-NH3) and non-protein N, with high effect on the levels of 3,0% of NH3 and 5,4% of urea. There were no differences between the level of 3,0% of NH3 and 5,4% of urea for the total N, N-NH3 and NPN. However, the treatment with 3,0% of NH3 allowed a larger fixation of N in ADIN and NDIN forms. The ammoniation increased the IVDMD and IVDMO and reduced the contents of neutral detergent fiber (NDF), hemicellulose, acid detergent fiber (ADF) and lignin, but it did not alter the cellulose and gross energy contents. The ammoniation increased the DM, OM, CP, NDF, ADF, hemicellulose, cellulose and gross energy apparent digestibility and as well as the voluntary intake of DM, digestible DM, digestible OM, digestible protein, digestible energy and the nutritive value index. The ammoniation increased the hay nutritive value index, but there were no differences between the levels of NH3 and urea.

Uso de indicadores para estimar fluxos de matéria seca ileal em eqüinos fistulados

This experiment was carried out with six half-bred Bretao-Campolinacolts with ileum fistulated to evaluate the difference in the ileum dry matter flow estimated by chromic oxide, cellulose, NDF, lignin and fecal lignin through the collection of ileum samples digesta at 28 h intervals, totalizing six samples per animal, starting at 10:00 a.m. The animals were fed ad libitum with the following diets: R1: clephantgrass, R2: elephantgrass plus ground corn, and R3: elephantgrass plus ground corn plus soybean meal. The data was statistically described, based on the coefficient of variation. The values of dry matter prececal digestion coefficients were, respectively, for diets 1, 2 and 3, at six schedules, for cellulose (-16.4; 21.4 and 6.6%), NDF(-34.7; 28.8 and -12.8%), to lignin (-51.5; -5.1 and -25.7%), in two schedules for cellulose (-13.4; 25.6 and 21.5%), fecal lignin (-37.1, 16.6 and -6.4%) and chromic oxide (-219.3, 36.4 and 9.5%). The coefficients of variation were, respectively, for the diets i, 2 and 3, at six schedules, for cellulose (148.3; 107.5 and 522.7%), NDF (95.4; 80.9 and 314.3%), lignin (210.2; 752.3 and 209.6%), at two schedules for cellulose(148.5; 80.7 and 70.0%), fecal lignin, (262.4; 177.9 and 723.5%) and chromic oxide (141.1; 158.9 and 473.4%). In diet i, the ileum dry matter now were over estimated for all markers, showing that chosen collection lime to estimate the flows were not adequate. Based on the coefficient of variation of the diets 2 and 3, the cellulose at two schedules was the most marker indicator to determine the ileum dry matter flow.

Planar membranes interaction

The system of two parallel planar, arbitrarily charged surfaces immersed in a solution containing only one ionic species, the counterions, is completely analyzed under a mean field Poisson-Boltzmann approach. Results for the pressure, reduced potential, and counterionic concentration are graphically displayed for two dissociating membranes and for a dissociating and an adsorbing membrane. The results indicate that the system of two planar parallel dissociating membranes acts as a buffer for pressure values and for counterionic concentration values in regions interior to and far from the membranes. The results are related to properties of planar or quasiplanar structures in biological cells.

Preparation of ceramic membranes from surface modified tin oxide nanoparticles

The preparation of crack-free SnO2 supported membranes requires the development of new strategies of synthesis capable to allow controlled changes of surface chemistry and to improve the processability of supported layers. In this way, the controlled modification of the SnO2 nanoparticle surface by adding capping molecules like Tiron(R) ((OH)(2)C6H2(SO3Na)(2)) during the sol-gel process was studied, aiming to obtain high performance membranes. Colloidal suspensions were prepared by hydrolyzing SnCl4.5H(2)O aqueous solution with NH4OH in presence of Tiron(R). The effect of the amount of Tiro(R) (from I to 20 wt.%) on the structural features of nanoparticles, powder redispersability and particle-solution interface properties was investigated by X-ray powder diffraction (XRPD), extended X-ray absorption fine structure (EXAFS), quasi-elastic light scattering and electrophoretic mobility measurements. XRPD and EXAFS results showed that the addition of Tiron(R) up to 20 wt.% to colloidal suspensions does not affect the crystallite size of SnO2 primary particles, determined around 2-3 nm. This value is comparable to the hydrodynamic size measured after redispersion of powder prepared with amount of Tiro(R) higher than 7.5 wt.%, indicating the absence of condensation reactions between primary particles after the initial precipitation step. As a consequence the powder with amount of Tiron(R) > 7.5 wt.%, can be fully redispersed in aqueous solution at pH greater than or equal to I I until a nanoparticle concentration of 6 vol.%. The electrophoresis measurements showed a decrease of the isoelectric point by increasing the amount of grafted Tiron(R) at the SnO2 nanoparticle surface, resulting in negatively charged particle-solution interface in all the studied pH range (2-11). These features govern the gelation process favoring the preparation of crack-free SnO2 supported membranes. The control exercised by Tiron(R) modifying agent in the aggregation process allows the fine-tuning of the porosity, from 0.124 to 0.065 cm(3) g(-1), and mean pore size, from 6.4 to 1.9 nm, as the amount of grafted molecules increases from 0 to 10 wt.%. In consequence, the membrane cut-off determined by filtration of polyethylene glycol standard solutions can be screened from 1500 to 3500 g mol(-1). (C) 2002 Elsevier B.V. B.V. All rights reserved.

Lability of heavy metal species in aquatic humic substances characterized by ion exchange with cellulose phosphate

Labile metal species in aquatic humic substances (HSs) were characterized by ion exchange on cellulose phosphate (CellPhos) by applying an optimized batch procedure. The HSs investigated were pre-extracted from humic-rich waters by ultrafiltration and a resin XAD 8 procedure. The HS-metal species studied were formed by complexation with Cd(II), Ni(II), Cu(II), Mn(II) and Pb(II) as a function of time and the ratio ions to HSs. The kinetics and reaction order of this exchange process were studied. At the beginning (<3 min), the labile metal fractions are separated relatively quickly. After 3 min, the separation of the metal ions proceeds with uniform half-lives of about 12-14 min, revealing rather slow first-order kinetics. The metal exchange between HSs and CellPhos exhibited the following order of metal lability with the studied HSs: Cu > Pb > Mn > Ni > Cd. The required metal determinations were carried out by atomic absorption spectrometry.

Thermal decomposition of microcrystalline cellulose and its pure and containing adsorbed cadmium cations derivatives.

We have studied the thermal decomposition of the microcrystalline cellulose and some of its derivative such as pure carboxymethylcellulose (CMCH), phosphate cellulose (FOSCEL) and oxycellulose (OXICEL) and also these same derivatives containing adsorbed cadmium cations. We have used the TG,DTG tecniques in order to determine the quantity of retained cadmium II cations on the surface of these adsorbents.

Utilization of Spirillum volutans for monitoring the toxicity of effluents of a cellulose and paper industry

The motility of Spirillum volutans was used for monitoring the toxicity of effluents of a cellulose and paper industry. Results indicated that there was no correlation between organic content and the toxic effects of the residues in the effluents. The effluents from the chlorination step and from the sludge ponds presented the highest toxicity. on the other hand, the final effluent from the biological treatment basin had no toxic agent. This bioassay showed to be a simple and reliable technique that can be used for adequately monitoring the toxicity of effluents.