Characterization and electrical properties of polypyrrole/multiwalled carbon nanotube composites synthesized by in situ chemical oxidative polymerization

This study describes the preparation of polypyrrole (PPy)/multiwalled carbon nanotube (MWNT) composites by in situ chemical oxidative polymerization. Various ratios of MWNTs, which served as hard templates, were first dispersed in aqueous solutions with the surfactant cetyltrimethylammonium bromide to form micelle/MWNT templates and overcome the difficulty of MWNTs dispersing into insoluble solutions of pyrrole monomer, and PPy was then synthesized via in situ chemical oxidative polymerization on the surface of the templates. Raman spectroscopy, Fourier transform infrared (FTIR), field‐emission scanning electron microscopy (FESEM), and high‐resolution transmission electron microscopy (HRTEM) were used to characterize the structure and morphology of the fabricated composites. Structural analysis using FESEM and HRTEM showed that the PPy/MWNT composites were core (MWNT)–shell (PPy) tubular structures. Raman and FTIR spectra of the composites were almost identical to those of PPy, supporting the idea that MWNTs served as the core in the formation of a coaxial nanostructure for the composites. The conductivities of these PPy/MWNT composites were about 150% higher than those of PPy without MWNTs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1413–1418, 2006     

Activity evaluation of carbon paste electrodes loaded with pt nanoparticles prepared in different radiolytic conditions

Three Pt-based catalysts prepared in different radiolytic conditions and supported on graphite powder were packed into a carbon paste electrode configuration. They were compared to each other, to the commercial (Pt) deposited on activated carbon powder (Johnson Matthey) and to pure Vulcan XC-72 for their respective abilities toward the hydrogen evolution reaction (HER). The Tafel parameters were determined for all these electrodes. From the I–V curves and their quantitative treatment, the following order of activity emerged unambiguously and reads: (PtCO)₂ (fcc structure) > (PtCO)₁ (Chini cluster) > (Pt)_neat > (Pt)_JM (Johnson Matthey) ≫ (Vulcan XC-72). As expected, all the Pt-loaded electrodes were more efficient than Vulcan XC-72. The classification appears to be linked with the mean nanoparticle size, and for comparable sizes, with the surface morphology of the materials. The results and the stability of the electrodes suggest that the small particle sizes and the good dispersity on the carbon support were maintained during the HER.     

Electroanalytical and chromatographic determination of pentachlorophenol and related molecules in a contaminated soil: a real case example

Electroanalytical and chromatographic methodologies have been applied for the determination of pentachlorophenol (PCP) and some of its derivatives in real soil samples contaminated by industrial discharge. The analytes were extracted with hexane from soil samples collected at different points of the site and mixed to produce a representative sample. Square wave voltammetry (SWV) experiments were carried out on either a boron-doped diamond (BDD) electrode or a gold ultramicroelectrode (Au-UME) in an analyte composed by the Britton-Robinson (B-R) buffer at pH 5.5 with the direct addition of proper amounts of the extract. The voltammetric responses revealed an irreversible anodic peak at approximately 0.80 V vs. Ag/AgCl with a peak current showing a linear dependence on PCP concentration. This linear relationship yielded a detection limit (DL) of 2×10⁻⁸ mol l⁻¹ (or 5.5 μg l⁻¹) for the BDD electrode and 6.9×10⁻⁸ mol l⁻¹ (18.4 μg l⁻¹) for the Au-UME, while the independently measured HPLC detection limit was 1.1×10⁻⁸ mol l⁻¹ (3.0 μg l⁻¹). The application of electroanalytical and chromatographic methodologies in the analysis of soil extracts revealed, besides the PCP responses, signals for some related molecules such as o-tetrachlorobenzoquinone (o-chloranil), hexachlorobenzene and tetrachlorophenol. Recovering experiments for PCP showed a concentration of 27.5 mg kg⁻¹ for the electroanalytical determinations and 26.8 mg kg⁻¹ for the HPLC analysis, values exceedingly high if considering that the maximum residue limit established for natural waters by the Brazilian Environmental Agency is 10 μg l⁻¹.     

细胞色素C的电化学行为研究

本文评述了细胞色素Ｃ电化学研究的发展概况，重点介绍了细胞色素Ｃ在促进剂作用下的电化学行为，促进剂种类，影响促进作用的因素及促进机理。     

有机硅耐磨透明涂层的固化分析

ＦＴＩＲ、ＴＧ、ＴＢＡ等对有机硅耐磨涂料（有机硅溶胶）的热固化过程研究表明有机硅胶体中缔合羟基间的脱水缩合速率很高；羟基脱水程度与固化温度有关，温度越高，达平衡时羟基的浓度越低，在１０５～１３０℃间羟基的浓度变化最大，加入适当的固化剂，对羟基的脱水交联有促进作用，在较高的固化温度下，反应体系中出现了环氧环异构化产生的酮羰基的吸收峰     

导电性聚西佛碱的研究：Ⅰ含硫聚西佛碱的合成,性能及表征

采用对氯苯甲醛和联苯二胺为原料,合成了4,4′-二氯代苄叉联苯胺,发现该化合物具有热致液晶性。利用所合成的二氯代化合物与硫化钠在醋酸锂催化下缩取得得到了含硫聚西佛碱探讨了高分子量含硫聚西佛碱的合成方法。测出该含硫聚西佛碱具有3.4×10~(-11)S/cm本征导电率。使用红外光谱、元素分析等方法表征了所合成的聚合物。     

Voltammetric sizing of a sphere.

The size of a glass sphere positioned in the center of a microdisk electrode is determined by using a simple electrochemical procedure and is confirmed, additionally, by a microscopical measurement of the sphere at the time of the electrochemical measurement. The cyclic voltammetric response of the naked electrode and of the electrode with the sphere positioned in its center is recorded over a wide range of scan rates (0.002-1.5 V s(-1)). The size of the sphere is then determined by comparison of the experimental voltammogram with simulations for each individual scan rate.     

Thermally reversible light scattering films based on the melting/crystallization of organic crystals dispersed in an epoxy matrix

Films that can be reversibly switched from opaque to transparent states by varying temperature (TRLS films), have potential applications in thermal sensors, optical devices, recording media, etc. A dispersion of organic crystals in a thermoset may be used for these purposes provided that at temperatures higher than the melting point there is a matching of refractive indices of both phases. A model system consisting on a dispersion of diphenyl (DP) crystals in an epoxy matrix based on diglycidyl ether of bisphenol A and m-xylylenediamine, was analyzed as a possible TRLS film encapsulated between transparent covers to avoid sublimation of DP. To obtain a uniform dispersion of DP-rich domains in the epoxy matrix by polymerization-induced phase separation, it was necessary to add 5 wt% of polystyrene (PS) to the initial formulation. Phase separation induced by polymerization at 80 °C led to a dispersion of PS/DP domains in the epoxy matrix due to the low compatibility of PS with the epoxy and its high compatibility with DP. Crystallization and melting processes were confined to the interior of dispersed domains leading to an excellent reproducibility of the optical properties of TRLS films in the course of successive heating-cooling cycles.