Andrzej B. Więckowski

Colored sulfur species in EPD-solvents

Alkali polysulfides dissolve in EPD-solvents (e.g. dimethylformamide, dimethylsulfoxide, and hexamethylphosphoramide) to give deep green, blue and carmine red solutions. Vis. and u.v. spectrophotometric as well as e.s.r. spectrometric investigations showed that normal polysulfides S x 2− with different chain length are the carriers of the yellow and red color, whereas the radical ion S 3 − is the blue species, which gives clear blue solutions or, if it is mixed with polysulfide anions with × 6, green or carmine red. U.v. and e.s.r. spectra point to the existence of two further radical ions S 2 − (yellow) and S 4 − (red) in EPD-solvents, The behaviour of polysulfides in these solvents can be understood by assuming that anions are only poorly solvated due to dipole shielding of the solvent molecules.

Oxidation of demineralized coal and coal free of pyrite examined by EPR spectroscopy

The influence of oxidation on complex paramagnetic centres system of demineralized coal and coal free of pyrite was compared. Polish orthocoking coal with a carbon content of 87.8 wt% was studied. This coal was oxidized with nitric acid (HNO3), peroxyacetic acid (PAA) and in O2/Na2CO3 system. Multi-component structure of X-band EPR spectra of the coal samples was numerically analysed. The lineshape and the parameters of the component lines: linewidths and g-factors, were determined. Concentrations of paramagnetic centres were measured. The three groups of paramagnetic centres belonging to different molecular units were found in the studied samples. They were responsible for broad Gauss (DBpp: 0.49 ‐ 0.84 mT), broad Lorentz 1 (DBpp: 0.18 ‐ 0.35 mT), and narrow Lorentz 3 (DBpp: 0.04‐ 0.08 mT) EPR lines. Properties of paramagnetic centres of the simple molecular units with broad Gauss and Lorentz 1 lines were changed during demineralization of coal and after pyrite removing from coal. g-Values of Gauss and Lorentz 1 lines increased, Lorentz 1 lines were broadened and concentrations of paramagnetic centres with Lorentz 1 lines increased. Oxidation of both demineralized coal and coal free of pyrite with nitric acid led to the highest decrease of the concentration of paramagnetic centres with Gauss lines, narrowing of these lines and increase of g-factor. The higher effects of oxidation on paramagnetic centres responsible for broad lines were observed for coal free of pyrite. Paramagnetic centres with narrow Lorentz 3 lines belonging to multi-ring aromatic units in demineralized coal and coal free of pyrite were not susceptible for oxidation. q 2002 Elsevier Science Ltd. All rights reserved.

VO2 + Ions in Vanadia — Alumina Catalysts Studied by EPR

Three different EPR signals originating from vanadyl complexes were observed after different pretreatment procedures of vanadia —alumina catalysis. The analysis of the spectral parameters shows, that the vanadyl complexes differ in the degree of delocalization of the unpaired electron as well as in the V = 0 bond distance. The different values of the EPR parameters of the studied vanadyl complexes indicate differences in their localization on the alumina surface. On the grounds of the geometric analysis of the alumina exposed planes it was found that vanadyl complexes in symmetry Civ can be located on the (100) plane, on the C and D layers of the (110) plane, and on a dislocation of the (111) plane. An der Oberflache von Vanadiumoxid —Aluminiumoxid-Katalysatoren wurden drei EPR-Signale beobachtet, welche von Vanadylkomplexen herstammen. Eine Analyse der Spektralparameter zeigte, das die Komplexe sich durch den Delokalisierungsgrad des ungepaarten Elektrons und die Lange der Vanadylbindung V = O unterscheiden. Die Unterschiedlichkeit der EPR-Parameter weist auf eine unterschiedliche Lokalisierung der Vanadylkomplexe auf der Oberflache hin. Aufgrund einer geometrischen Analyse der exponierten Kristallflachen des y-Aluminiumoxids wurde gefunden, das die Vanadylkomplexe mit der Symmetrie C4„ an folgenden Stellen lokalisiert werden konnen : auf der Flache (100), auf den C- und D-Schichten der Flache (110) und an einer Dislokation der Flache (111).

Microwave saturation of EPR spectra of oxidised coal

Microwave saturation of multi-component EPR spectra of oxidized lignite Mequinenza (Spain) with a carbon content of 65.1 wt % and with a high sulphur content of 10.3 wt % was studied. The coal was oxidized with nitric acid (NHO3), peroxyacetic acid (PAA), and in O2/Na2CO3 system. Three different groups of paramagnetic centres exist in the coal samples analyzed. The EPR spectrum of the demineralised coal was a superposition of broad Gauss (ΔBpp = 0.75 mT), broad Lorentz 1 (ΔBpp = 0.42 mT) and narrow Lorentz 3 lines (ΔBpp = 0.08 mT). The three EPR components with linewidths: 0.58–0.77 mT (Gauss line), 0.30–0.39 mT (Lorentz 1 line) and 0.05–0.06 mT (Lorentz 3 line) were recorded for the oxidized coal. The g-values were obtained for the samples studied in the ranges 2.0043–2.0046 (Gauss lines), 2.0035–2.0038 (Lorentz 1 lines) and 2.0032–2.0034 (Lorentz 3 lines). The broad Gauss and Lorentz 1 lines saturate at low microwave powers. The narrow Lorentz 3 lines of demineralised coal were not saturated at microwave power from the range considered. After the coal oxidation with HNO3, PAA and in O2/Na2CO3 system, the microwave saturation of the narrow Lorentz 3 lines was also observed, which indicated a degradation of the multi-ring aromatic structures upon oxidation.

Temperature dependence of the EPR linewidth of ultramarine blue

The colour centres S3− in ultramarine blue have been studied by EPR. Measurements of the temperature dependence of the linewidth have shown that the linewidth can be approximated by the formula: ΔBpp = a + bT7, which according to the Kronigs theory is describing the two‐phonon Raman process of the transfer of energy to the vibrations of the lattice. Copyright

Groups of paramagnetic centres in coal samples with different carbon contents

Complex systems of paramagnetic centres existing in demineralised flame coal (71.4 wt% C), medium-rank coal (85.6 wt% C) and anthracite (94.9 wt% C) were analysed by electron paramagnetic resonance spectroscopy (EPR). Different groups of paramagnetic centres were searched in macerals (exinite, vitrinite, inertinite) of coals with carbon contents of 73.8 wt% C and 85.6 wt% C. Experimental EPR spectra were fitted by different superposition of theoretical lines. Total concentration of paramagnetic centres both in coal and macerals increases with carbon content in the sample. Total concentration of paramagnetic centres in macerals increases from exinite to inertinite. Four groups of paramagnetic centres were found in medium-rank coal, and only two groups exist in flame coal and anthracite. The EPR spectrum of medium-rank coal is a superposition of two broad and two narrow lines. Both broad and narrow, and two narrow lines were measured in EPR spectra of flame coal and anthracite, respectively. Two types of paramagnetic centres with broad lines and one group with narrow lines exist in exinite and vitrinite from medium-rank coal. Two narrow components were observed in EPR spectra of its inertinite. Two different broad electron paramagnetic resonance signals were detected for macerals from low-coalificated coal. Paramagnetic centres systems of medium-rank coal samples reveal the most complex character. Broad EPR lines were not observed for the higher coalificated samples, i.e., anthracite and inertinite from medium-rank coal. Narrow lines do not occur in EPR spectra of low-coalificated macerals. Strong dipolar interactions and fast spin-lattice relaxation processes are characteristic for paramagnetic centres with broad lines. Strong exchange interactions and short spin-lattice relaxation time were measured for paramagnetic centres with the narrowest EPR signals.

Paramagnetic centres in exinite, vitrinite and inertinite

Exinite, vitrinite and inertinite from durain, vitrain and clarain of Polish medium-rank coal with 85.6% C were investigated by X-band (9.3 GHz) electron paramagnetic resonance spectroscopy. Multicomponent structure of the EPR spectra of these macérais was analysed. The number of component lines, their lineshapes and parameters: linewidths andg factors, were determined. Total concentrations and concentrations of paramagnetic centres responsible for the component lines were measured. The broad Gaussian, broad Lorentzian and narrow Lorentzian lines were observed in the experimental spectra of exinite and vitrinite. The EPR spectra of inertinite are superposition of two narrow Lorentzian lines with different linewidths. The evolution of paramagnetic centres during heating of the macerais at 300–650°C was studied. Paramagnetic centres with broad Lorentzian lines are the most active ones in the thermal decomposition. The EPR results indicate reactions between individual macerais during thermal decomposition of coal. Thermally excited multiplet states were found in exinite and vitrinite.

Influence of heating time and pressure treatment of potato starch on the generation of radicals: EPR studies

The influence of heating time and pressurizing time under pressure of 1 GPa on radicals generation in potato starch polymer was investigated by EPR. Potato starch was heated at two temperatures: 413 ± 2 K (140 °C) and 473 ± 2 K (200 °C) for 15, 30, 60, 120, 180, 240, 270 and 300 min and subdued to pressurizing under pressure of 1 ± 0.002 GPa for 6, 60, 300 and 1440 min. In starch heated at 413 K (140 °C) a decrease in the relative intensity of the EPR signal as a function of the pressurizing time can be observed, whereas in starch heated at 473 K (200 °C) such a decrease is not observed. The EPR spectra analysis indicates that they are powder spectra due to the paramagnetic centers leading to Lorentzian line shapes with weak spectroscopic splitting factor g anisotropies and linewidth anisotropies. We have shown that pressurization of starch causes a decrease in the number of radicals in a temperature range in which the polymer is not yet disintegrated. The results of the EPR investigations indicate the existence of a carbon radical center situated at the carbon C1 of the glucose ring. In the EPR spectra of the samples heated with no oxygen access, the hyperfine structure is poorly visible. In the registered EPR spectra of the samples heated with oxygen access, the hyperfine structure is not observed.

Influence of microwave power on EPR spectra of coal macerals

The paper contains a numerical analysis of the electron paramagnetic resonance (EPR) spectra of coal macerals (exinite, vitrinite, inertinite) obtained from Polish medium-rank coal (85.6 wt% C). We determine the lineshapes and the parameters of the component lines, i.e., the intensities and linewidths. As a result, we find that the EPR spectra of the studied macerals are superpositions of broad Gaussian, broad Lorentzian 1 and narrow Lorentzian 3 lines for vitrinite and exinite and two narrow Lorentzian 2 and Lorentzian 3 lines for inertinite. The influence of microwave power on the component lines of the EPR spectrum is studied. A comparison of the results obtained at 223 and 293 K shows that the EPR lines at both temperatures saturate at the same microwave power. It also indicates similar changes of the linewidths with changes of microwave power at both temperatures, a slight increase with increasing microwave power.

Electron-acceptor and electron-donor properties of sulfate-containing aluminas

ESR spectra of perylene and tetracyanoethylene adsorbed on alumina were measured. The spectra of perylenium ions on sulfate-containing aluminas, in contrast to those on pure alumina samples, show a well-resolved hyperfine structure in the absence of oxygen, which persists even after 75 hrs.The electron-donor properties of sulfate-containing aluminas are not different from those of pure alumina.AbstractВыли сняты ЭПР спектры перилена и тетрацианозтилена, адсорбированных на окиси алюминия. Ъыло найдено, что спектры перилениевых ионов на окисях алюминия, содержащих сульфаты, в противололожиость образцам на чистой окиси алюмкния, обладают СТС в отсутствии кислорода и эта СТС хорошо разрешена даже после 75 часов стояния.Электронодонорные свойства окисей алюминия, содержащих сульфаты, не отличаются от свойств чистой окиси алюминия.