Robert Pietrzak

X-ray photoelectron spectroscopy study of oxidized coals with different sulphur content

The aim of the study reported was to determine the effect of oxidation on the surface composition of coal as studied by X-ray photoelectron spectroscopy (XPS) method. Five coals characterized by a different degree of coalification and different amounts of sulphur were subject to oxidation with peroxyacetic acid (PAA). The process of oxidation was carried out for coal samples demineralised by the Radmacher method. Carbon, oxygen, sulphur and nitrogen peaks were registered and analysed. The effect of oxidation depended on coal rank. In case of S 2p, three or four peaks were found for the oxidized samples, corresponding to tiophene, sulphoxides (Ph 2 -SO type), sulphonic acids and in some cases, more oxidized forms of sulphur, possibly inorganic sulphates. The surface sulphur content increased upon oxidation. A possible reason could be the mobility of the S-containing species.

Active carbons prepared by chemical activation of plum stones and their application in removal of NO2

A technology of obtaining active carbon from plum stones by chemical activation with KOH is described. The effect of carbonisation temperature as well as activation procedure on the textural parameters, acid-base character of the surface and sorption properties of active carbons has been checked. The sorption properties of the activated carbons obtained were characterised by determination of nitrogen dioxide adsorption in dry and wet conditions. The final products were microporous activated carbons of well-developed surface area varying from 2174 to 3228 m(2)/g and pore volume from 1.09 to 1.61 cm(3)/g, showing different acid-base character of the surface. The results obtained in our study have proved that a suitable choice of the carbonisation and activation procedure for plum stones can produce activated carbons with high capacity of nitrogen dioxide, reaching to 67 and 42 mg NO(2)/g in dry and wet conditions, respectively. The results of our study have also shown that the adsorption ability of carbonaceous sorbents depends both on the method of preparation as well as on the textural parameters and acid-base properties of their surface.

Carbonaceous adsorbents prepared by physical activation of pine sawdust and their application for removal of NO2 in dry and wet conditions.

Carbonaceous adsorbents from sawdust pellets from coniferous trees (pines) were obtained by CO(2) activation and used as nitrogen dioxide adsorbents. Activation was performed at 800 degrees C for four different periods of time (30, 60, 90 and 120 min). The effect of NO(2) adsorption in dry and wet conditions on the sorption ability of the activated samples obtained was tested. The results have shown that NO(2) sorption properties of the activates increase with increasing time of activation and reach maximum for the samples activated for 90 min. On the basis of measurements in dry and wet conditions, the presence of water was found to increase the NO(2) breakthrough capacity. The sorption capacity of the adsorbents obtained towards NO(2) was proved to be determined by the surface chemistry and the reactions taking place on the surface rather than by the specific surface area development.

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.

AP-TPR study of sulphur in coals subjected to mild oxidation. Part 1. Demineralised coals

Abstract Five samples of coal characterised by different degree of coalification and different content of sulphur have been subjected to oxidation in the dry phase and in aqueous media in order to determine the effect of oxidation on the sulphur groups. The transformations were studied by the classical chemical methods and by atmospheric pressure–temperature programmed reduction. It has been shown that the greatest changes in sulphur groups occurs in the case of the oxidation with HNO3 and peroxyacetic acid, while the air oxidation and the oxidation in the O2/Na2CO3 system is much less effective. The oxidation leads to formation of sulphoxides, sulphones and sulphonic acids. The non-thiophene groups have been found much more susceptible to oxidation than the thiophene ones.

Sawdust pellets from coniferous species as adsorbents for NO2 removal.

Carbonaceous adsorbents based on sawdust pellets from coniferous tree species were obtained by carbonisation at different temperatures and different periods of time. The effect of NO(2) adsorption in dry and wet condition on the sorption ability of the chars obtained was tested. The results have shown that NO(2) sorption properties of chars depend on the conditions of pyrolysis and the conditions of adsorption. The best NO(2) sorption capacity of 18.3 and 43.1mg/g in dry and wet conditions, respectively, was noted for the char sample pyrolysed at 800 degrees C for 60 min. The FTIR spectra of the exhausted samples reveal a great increase in the intensity of the band at approximately 1380 cm(-1) assigned to the vibrations of -NO(2), -ONO(2) or NO(3)(-), while in the DTG curves a new peak appears in the range 200-400 degrees C assigned to the release of nitrogen compounds of low stability in high temperatures.

Ordered mesoporous silica modified with lanthanum for ibuprofen loading and release behaviour

The ordered mesoporous silicas SBA-15 and KIT-6, modified with lanthanum, have been for the first time applied in investigation of ibuprofen adsorption and release. The materials of hexagonal and regular structure were obtained by the hydrothermal method using a triblock copolymer Pluronic P123 as a template. The mesoporous silicas were impregnated with an aqueous solution of lanthanum(III) chloride in the amount necessary to obtain 1, 3 and 5wt.% La loading. The physicochemical properties of the modified silicas were characterised by X-ray diffraction, transmission electron microscopy, UV-Vis spectrophotometry and low-temperature nitrogen sorption. The results showed that lanthanum strongly determined structural as well as textural properties of the silicas. The samples of modified silica were checked for the ability to adsorb and release of ibuprofen. The storage capacity of the modified silicas obtained increased with increasing their average pore diameter and percentage content of lanthanum. The amount of ibuprofen adsorbed onto KIT-6 silica modified with La was higher than that adsorbed onto SBA-15 materials. The high coverage of lanthanum on the surface of KIT-6 and SBA-15 solids was found to increase the amount of ibuprofen and the rate of its release.

β-Cyclodextrin complexation as an effective drug delivery system for meropenem.

Following the preparation of an inclusion complex of β-cyclodextrin and meropenem, methods based on FT-IR, Raman and DSC were used for its characterization. An analysis of changes in the stability of meropenem after complexation showed that the complex may serve as a valuable delivery system significantly contributing to enhanced meropenem stability in aqueous solutions and in the solid phase. Due to a sustained transfer of meropenem from the cavity of the cyclodextrin it was possible to maintain a constant desired meropenem concentration over a period of 20 h, as confirmed by a release study. An evaluation of microbial activity not only demonstrated that the bactericidal action of meropenem was not stopped as a result of complexation but even pointed to greater growth inhibition in certain clinically important strains. The fact that investigations of meropenem stability and microbial activity proposed the carbonyl groups as those domains of a meropenem molecule that are instrumental in the formation of a complex with β-cyclodextrin supports the findings of theoretical studies based on molecular modeling.

Porous carbon material containing CaO for acidic gas capture: Preparation and properties

A one-step process for the preparation of CaO-containing porous carbons is described. Mixtures of poly(ethylene terephthalate) with natural limestone were pyrolyzed and thus hybrid sorbents could be easily obtained. The polymeric material and the mineral served as a carbon precursor and CaO delivering agent, respectively. We discuss effects of the preparation conditions and the relative amounts of the raw materials used for the preparations on the porosity of the hybrid products. The micropore areas and volumes of the obtained products tended to decrease with increasing CaO contents. Increase in the preparation temperature entailed a decrease in the micropore volume, whereas the mesopore volume increased. The pore creation mechanism is proposed on the basis of thermogravimetric and temperature-programmed desorption measurements. The prepared CaO-containing porous carbons efficiently captured SO2 and CO2 from air. Washing out of CaO from the hybrid materials was confirmed as a suitable method to obtain highly porous carbon materials.

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.