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571.
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573.
Rapee Gosalawit Suwabun Chirachanchai Sergey Shishatskiy Suzana P. Nunes 《Journal of membrane science》2008
A nanocomposite membrane of sulfonated montmorillonite/sulfonated poly(ether ether ketone) (SMMT/SPEEK) is proposed for direct methanol fuel cells (DMFCs). The SMMT is clay modified with silane of which the structure consists of a sulfonic acid group for proton conductivity improvement. The micro- and nano-scaled morphologies of the membranes perform the increase in inorganic aggregation with SMMT loading content as confirmed by SEM and AFM. The membrane stability, i.e., the liquid uptake in water and in methanol aqueous solution, as well as the mechanical stability increases with the SMMT loading content whereas thermal stability does not improve significantly. The methanol permeability reduction is obtained when the SMMT loading content increases for various methanol concentrations (1.5–4.5 M). A comparative study of the SPEEK nanocomposite membranes with SMMT and with pristine MMT shows fourfold proton conductivity enhancement after sulfonation. The DMFC single cell tests inform us that all nanocomposite membranes give the significant performance revealed by the plot of current density–voltage and power density. 相似文献
574.
Joyce Nunes Bianchin Renata Mior Cleide Sandra Tavares Araújo Eduardo Carasek 《Talanta》2009,78(2):333-2300
In this study a method for the determination of cadmium in fuel alcohol using solid-phase extraction with a flow injection analysis system and detection by flame atomic absorption spectrometry was developed. The sorbent material used was a vermicompost commonly used as a garden fertilizer. The chemical and flow variables of the on-line preconcentration system were optimized by means of a full factorial design. The selected factors were: sorbent mass, sample pH, buffer concentration and sample flow rate. The optimum extraction conditions were obtained using sample pH in the range of 7.3-8.3 buffered with tris(hydroxymethyl)aminomethane at 50 mmol L−1, a sample flow rate of 4.5 mL min−1 and 160 mg of sorbent mass. With the optimized conditions, the preconcentration factor, limit of detection and sample throughput were estimated as 32 (for preconcentration of 10 mL sample), 1.7 μg L−1 and 20 samples per hour, respectively. The analytical curve was linear from 5 up to at least 50 μg L−1, with a correlation coefficient of 0.998 and a relative standard deviation of 2.4% (35 μg L−1, n = 7). The developed method was successfully applied to spiked fuel alcohol, and accuracy was assessed through recovery tests, with recovery ranging from 94% to 100%. 相似文献
575.
X-ray reflectivity and atomic force microscopy analyses were performed in the Si/WTi (7 nm)/NiFe (5 nm)/FeMn (13 nm)/WTi (7 nm) exchange-biased system prepared by magnetron sputtering. Layer-by-layer analyses were done in order to have interfacial roughness parameters quantitatively. X-ray reflectivity results indicate that the successive layer deposition gives rise to a cumulative roughness. In addition, the atomic force microscopic images analyses have revealed that the roughness enhancement caused by the successive layer deposition can be associated with an appearance of a longer wavelength roughness induced by the NiFe layer deposition. 相似文献
576.
577.
I.A.A. Terra A.S.S. de Camargo M.C. Terrile L.A.O. Nunes 《Journal of luminescence》2008,128(5-6):891-893
Energy transfer processes were studied in two sets of Yb3+ and Tm3+ co-doped sodium-metaphosphate glasses, prepared in air and nitrogen atmospheres. Using Förster, Dexter, and Miyakawa theoretical models, the energy transfer parameters were calculated. The main ion–ion energy transfer processes analyzed were energy migration among Yb3+ ions, cross-relaxations between Yb3+ and Tm3+ ions, and interactions with OH? radicals. The results indicated that Yb→Tm energy transfer favors 1.8 μm emissions, and there is no evidence of concentration quenching up to 2% Tm2O3 doping. As expected, samples prepared in nitrogen atmosphere present higher fluorescence quantum efficiency than those prepared in air, and this feature is specially noted in the near-infrared region, where the interaction with the OH? radicals is more pronounced. 相似文献
578.
Dominique Gomes Irmgard Buder Suzana P. Nunes 《Journal of Polymer Science.Polymer Physics》2006,44(16):2278-2298
New functionalized particles were prepared by attaching sulfonated aromatic bishydroxy compounds onto fumed silica surface. First, a bromophenyl group was introduced onto the silica surface by reaction of bromophenyltrimethoxysilane with fumed silica. Then, sulfonated bishydroxy aromatic compounds were chemically attached to the silica surface by nucleophilic substitution reactions. The structure of the modified silica was characterized by elemental analysis: 13C‐NMR, 29Si‐NMR, and FTIR. Afterward, novel inorganic–organic electrolyte composite membranes based on sulfonated poly(ether ether ketone) have been developed using the sulfonated aromatic bishydroxy compounds chemically attached onto the fumed silica surface. The composite membrane prepared using silica with sulfonated hydroxytelechelic, containing 1,3,4‐oxadiazole units, has higher proton conductivity values in all range of temperatures (40–140 °C) than the membrane containing only the plain electrolyte polymer, while the methanol permeability determined by pervaporation experiment was unchanged. A proton conductivity up to 59 mS cm?1 at 140 °C was obtained. The combination of these effects may lead to significant improvement in fuel cells (fed with hydrogen or methanol) at temperatures above 100 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2278–2298, 2006 相似文献
579.
Puripong Totsatitpaisan Suzana P. Nunes Kohji Tashiro Suwabun Chirachanchai 《Solid State Ionics》2009,180(9-10):738-745
The present work shows a strategy to apply hydrogen bond connected benzimidazole compounds for improvement of proton conductivity and thermal stability of sulfonated poly(ether ether ketone) (SPEEK). A series of benzimidazole derivatives, i.e., mono-, di- and trifunctional benzimidazole, are applied to study the role of their packing structures related to the specific properties for SPEEK in being a proton exchange membrane. The benzimidazole-based compounds significantly increase the thermal stability of the SPEEK and, at the same time, improve proton conductivity of SPEEK under anhydrous condition at temperatures higher than 80 °C. The investigation of the structural effect of the benzimidazole based model compounds implies that the trifunctional benzimidazole molecule is the most effective compound to improve the thermal stability and the proton conductivity of SPEEK as compared to mono- and difunctional ones. 相似文献
580.
T. Dekola D. Isakov E. de Matos Gomes V. H. Nunes Rodrigues M. M.R. Costa 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,68(4):519-522
Glycine glycinium perrhenate is a new hydrogen bonded crystalline material that exhibits several phase transitions at low
and high temperature. At room temperature the structure shows some special features. One dimensional polar chains, linked
by strong hydrogen bonds exist parallel to [100], [010] and [–110]. The structural, thermal and dielectric properties of this
new perrhenic salt are presented and a relationship is established. 相似文献