Elżbieta Wenda

XPS studies of nitrogen-containing conjugated polymers–palladium systems

Polyaniline (PANI) and polypyrrole doped with chloride ions (PPyCl) have been treated with PdCl 2 solutions in HCl of various concentrations. Basing on the results of XPS studies it is shown that the differences in the redox and basic properties of both polymers lead to different mechanisms of their interactions with palladium ions present in the PdCl 2 solutions studied. Thus, in the PdCl 2 solutions of low acidity in which [PdCl 2 (H 2 O) 2 ] predominates, both polymers are oxidized with simultaneous reduction of a part of Pd 2+ to Pd 0 . In the PdCl 2 solutions of high acidity in which [PdCl 4 ] 2 is the major complex, reduction of Pd 2 does not occur. Owing to stronger basic properties of PANI than those of PPyCl, palladium is incorporated into the former polymer as anionic chlorocomplexes via protonation reaction. In the case of PPyCl the situation is more complex. Detailed analysis of the possible surface reactions taking place in the PPyCl Pd systems studied is given in the paper.

Interactions between polyanilines and palladium ions: similarities and differences

Polyaniline (PANI), poly(o-toluidine) (POT) and poly(o-chloroaniline) (POC) were treated with PdCl 2 , palladium (II) acetate and palladium (II) acetylacetonate in organic solvents. It was found that polymer-palladium interactions involved predominantly a redox -type reaction which resulted in the partial oxidation of the polymer chain with simultaneous reduction of some Pd 2+ to Pd°. In the systems studied PANI exhibited the strongest redox properties towards Pd 2+ ions, POT weaker and POC the weakest ones.

Local structure of a Pd-doped polymer investigated using a linear combination of XANES spectra

Abstract Methods of principal components analysis and linear combinations of XANES (X-ray absorption near edge structure) spectra were applied to determine the composition of Pd species in Pd-doped poly-o-methoxyaniline (POM). A set of reference spectra reproducing the absorption spectrum of Pd/POM polymer was easy to find because of the square-planar structure common for the d8 metal ion Pd(II). Absorption spectra of reference samples such as PdO, Pd(C5H7O2)2, Pd(CH3COO)2, [Pd(NH3)4]Cl2, [Pd(NH3)4](NO3)2, (C3H5PdCl)2, PdCl2(CH3CN)2, PdCl2, (NH4)2[PdCl4], K2PdCl4 and Pd metallic foil were taken into account. Although the XANES fits for the best two sets of reference compounds, (1) Pd(CH3COO)2, (NH4)2[PdCl4], Pd foil and (2) [Pd(NH3)4]Cl2, (NH4)2[PdCl4], Pd foil, were in very good agreement with the experimental XANES spectrum of Pd/POM, only the first model was established as being correct. This was achieved by examining the Fourier transforms of reconstructed EXAFS spectra in comparison to the Fourier transform for the Pd/POM polymer. A quantitative XANES analysis of the composition of Pd/POM led to a final result of 46.0% Pd metal and 54% Pd2+ ions surrounded by four neighbours, including Cl and O ions in an average ratio of 2.6:1.4. The coordination numbers for the Pd–O, Pd–Cl and Pd–Pd near-neighbour shells in the Pd/POM polymer were simply evaluated from the XANES fit analysis.

Interactions of chromium ions with starch granules in an aqueous environment.

In this study, interactions of dichromate ions with potato starch granules in highly acidic aqueous solutions and at different temperatures were investigated. It was found that the process underwent a reduction of Cr(2)O(7)(2-) to Cr(3+) accompanied by the formation of intermediate Cr(5+) ions detected by electron paramagnetic resonance (EPR) spectroscopy. The reactions took place after the attachment of dichromate anions to the granules and resulted in a lowering of the Cr(2)O(7)(2-) initial content in the solution. The newly formed Cr(3+) ions were both accumulated by the granules or remained in the solution. It was observed for the first time that the quantity of such ions taken by the granules from the solution was noticeably higher than that delivered by trivalent chromium salt solution. It was revealed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX) that the chromium ions were not only adsorbed on the granule surface but also introduced into the granule interior and evenly distributed there. An activation energy of the reduction reaction equal to 65 kJ·mol(-1) and the optimal parameters of the process were established. The proposed mechanism could be useful for the bioremediation of industrial effluents polluted by hexavalent chromium compounds.

Determination of the inelastic mean free paths of electrons by elastic peak electron spectroscopy in organic samples

Abstract The inelastic mean free path (IMFP) values for selected polymers were determined using elastic peak electron spectroscopy (EPES). Large scatter between measured and calculated IMFPs for polymers has been observed. In the present work the IMFPs in CH3- and OCH3-substituted polyanilines undoped and doped with Pd of various concentrations using the EPES method with a standard are investigated. This method requires knowledge of surface composition and density. Composition was determined by X-ray photoelectron spectroscopy (XPS) and bulk density by helium pycnometry. Bulk Pd concentration was evaluated by atomic absorption (AA). The EPES measurements using the Ag standard covering the energy range 200–5000 eV were made with the ESA-31 spectrometer. The influence of Pd dopant in polymers on measured IMFPs has been investigated. The scatter between measured and the G1 of Gries predicted IMFPs and its reason are discussed.

Thermal properties and free radicals generation in starch isolated from pumpkin fruits

The selected thermal and rheological properties of pumpkin starches were compared with values evaluated for corn and potato starch. The pumpkin starches had lower pasting temperatures (by near 3°C and 24°C than potato or corn starch respectively), the peak viscosity (nearly 2300mPas lower than potato starch) and higher final viscosities (by 80-120mPas than those for potato starch and by 1700mPas in relation to corn starch). The thermal profile of pumpkin starches examined by the DSC method were quite similar to those of potato starch but lower than those of corn. The retrogradation degree of pumpkin starch was lower by 5-26% than that for corn or potato starches. The thermal treatment of starches led to the formation of radicals. Pumpkin starches were less susceptible to the formation of radicals than potato starch and had less about 0.3-1.3×1015radicals/g than potato starch.