A. Kosiński

XANES investigations of Pd-doped polyaniline

Polyaniline doped with palladium (PANI-Pd) demonstrated a particular catalytic activity and selectivity in reaction of the hydrogenation of the triple C-C bond. Pd K-edge X-ray absorption near edge structure (XANES) studies were performed for PANI-Pd and several palladium compounds like PdCl 2 , (NH 4 ) 2 PdCl 4 , Pd(NH 3 ) 4 Cl 2 , (NH 4 ) 2 PdCl 6 , K 2 PdCl 4 , [(C 3 H 5 )PdCl] 2 , PdCl 2 (CH 3 CN) 2 and PdO. The measurements were carried out in transmission mode at the station Xl in HASYLAB. Chemical shifts of Pd K edge for PANI-Pd and other palladium compounds were evaluated. The experimental XANES spectra were compared with the theoretical XANES spectrum calculated for PdCl 2 by applying the FEFF8 program. It was found that the Pd K edge XANES spectrum for PANI-Pd was similar to that for ammonium tetrachloropalladate (NH 4 ) 2 PdCl 4 . Our results indicated that in the PANI-Pd catalyst the tetrachloropalladate ion [PdCl 4 ] -2 is coordinated to the amine part of the polymer chain and is responsible for specific catalytic properties.

Recoil effect in carbon structures and polymers

Abstract The recoil effect on quasi-elastic scattering of electrons has been described by Boersch. The Rutherford type scattering on the nucleus produces a shift of the elastic peak maximum of Δ E em , proportional to 1/ M (atomic mass) and electron energy. Laser et al. studied the recoil effect for exact calibration of the energy scale for XPS. The other effect is broadening of the elastic peak. Reflection electron energy loss spectra were studied by an electron spectrometer ESA 31 of high energy resolution. Various modifications of C (electrode and reactor graphite, glassy C, powder) and conducting polymers (polyacetylene, polyaniline, polythiophene) have been studied with varying composition of C, O, H, S, Pd etc. In the case of the samples containing different elements the complex nature of the elastic peaks (consisting of the sum of components having different intensities and shifts) was clearly observed. Possible explanations for the recoil effects detected are reviewed.

Determination of the inelastic mean free path of electrons in polythiophenes using elastic peak electron spectroscopy method

Abstract The inelastic mean free path (IMFP) is an important parameter for quantitative surface characterisation by Auger electron spectroscopy, X-ray photoelectron spectroscopy or electron energy loss spectroscopy. An extensive database of the IMFPs for selected elements, inorganic and organic compounds has been recently published by Powell and Jablonski. As it follows from this compilation, the published material on IMFPs for conductive polymers is very limited. Selected polymers, such as polyacetylenes and polyanilines, have been investigated only recently. The present study is a continuation of the research on IMFPs determination in conductive polymers using the elastic peak electron spectroscopy (EPES) method. In the present study three polythiophene samples have been studied using high energy resolution spectrometer and two standards: Ni and Ag. The resulting experimental IMFPs are compared to the respective IMFP values determined using the predictive formulae proposed by Tanuma and Powell (TPP-2M) and by Gries (G1), showing a good agreement. The scatter between the experimental and predicted IMFPs in polythiophenes is evaluated. The statistical and systematic errors, their sources and the possible contributions to the systematic error due to influence of the accuracy of the input parameters, such as the surface composition and density, on the IMFPs derived from the experiments and Monte Carlo calculations, are extensively discussed.

Determination of the electron inelastic mean free path in polyacetylene by elastic peak electron spectroscopy using different spectrometers

Abstract The inelastic mean free path (IMFP) values for organic materials are very limited. Numerous data have been published mainly for elemental solids, binary alloys and semiconductors. Generally, the IMFP values for different energies can be determined from the theoretical models involving the optical data, from predictive formulas, and from the experimental method called the elastic peak electron spectroscopy (EPES). In the present work the IMFPs in N–(CH)x polyacetylene (unstretched), synthesised according to Naarmann and Theophilou, and this polyacetylene doped with Pd were determined. The IMFPs energy dependence for the above samples has been obtained from the EPES in the primary electron energy range of 200–5000 eV. The experimental data have been recorded using three different spectrometers and compared with the theoretical data available.

Determination of the inelastic mean free path of electrons in polyaniline samples by elastic peak electron spectroscopy

Application of x-ray photoelectron spectroscopy, Auger electron spectroscopy and electron energy loss spectroscopy for quantitative characterisation of surfaces requires knowledge of the electron inelastic mean free path and its energy dependence. Inelastic mean free path values have been determined for a wide variety of solids using theoretical and experimental methods. However, the number of published inelastic mean free path values for polymers is limited. In principle, these values for polymers can be estimated using predictive formulae such as TPP-2M and the G1 formula of Gries. An alternative method for inelastic mean free path determination in polymers is elastic peak electron spectroscopy. In the present work, the surface chemical composition of polyaniline samples (undoped and doped with palladium) was analysed quantitatively using x-ray photoelectron spectroscopy. The inelastic mean free path values were determined by elastic peak electron spectroscopy using a high-energy-resolution hemispherical analyser in the energy range 500– 5000 eV. The resulting inelastic mean free path values evaluated using Ni and Ag standards are smaller than the values resulting from the G1 predictive formula of Gries and the TPP-2M predictive formula of Tanuma et al. The discrepancies in the inelastic mean free path values are discussed extensively. Copyright

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.

Evaluation of the inelastic mean free path (IMFP) of electrons in polyaniline and polyacetylene samples obtained from elastic peak electron spectroscopy (EPES)

The inelastic mean free path (IMFP) of electrons was determined experimentally for selected polyaniline and polyacetylene samples with Ag and Ni references using elastic peak electron spectroscopy (EPES). The surface composition was determined by XPS and density by helium pycnometry. The high resolution hemispherical ESA-31 and ADES-400 spectrometers were used for measurements in the energy range E = 0.5–3.0 keV and E =0.4 − 1.6 keV, respectively. The integrated elastic peak intensity ratios for sample and reference were calculated using the Monte Carlo (MC) algorithm based on the electron elastic scattering cross-sections database NIST SRD64 version 3.1 and applying TPP-2M IMFPs for polymers. Surface excitation parameters (SEP) and material parameters (ach) for polymers were determined, using the model of Chen, from comparison of measured and MC calculated elastic peak intensity ratios. These corrections proved to be efficient in decreasing the percentage deviations between the obtained IMFPs and the TPP-2M formula IMFPs. The elastic peak of hydrogen was observed in the EPES spectra of polymers. The experimental contribution of the hydrogen to the total elastic peak was 0.58%, while this value obtained from the MC simulations was 1.98%.

Catalytic reactivity and surface chemistry of polyaniline(EB)–Pd–H2O systems

Catalytic reactivity and surface chemical effects induced by the presence of water in the molecular system polyaniline(EB)–Pd–H2O were investigated. The polyaniline(EB) doped with palladium reveals its high activity and selectivity in the semihydrogenation: hexyne → hexenes (→ hexane). However, to demonstrate these effects, the specimen has to be submitted to a special treatment to lose most of its water. The XPS analysis allowed identification of the catalytically active sites of the studied system. They were ascribed to the [PdCl4]2− complex anions present at the surface of the dry specimens.