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The influence of gold on the properties of silica mesoporous materials

100%
Gac W., Pasieczna-Patkowska S., Kępiński L.
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2010
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vol. 65
100-120
EN
The properties of gold modified silica mesoporous materials were investigated on the successive preparation stages. Samples were obtained by the direct introduction of HAuCl4 aqueous solution to the synthesis mixture of silica. It was stated that partial substitution of -Cl with -OH ligands occurred in the diluted solutions of HAuCl4. The replacement of -Cl with -Br groups in gold complexes took place in the synthesis mixture containing hexadecyltrimethylammonium bromide surfactant molecules. It was found that gold species influenced the removal of organic templates from the channels of silica materials. Pore arrangement was not strongly distorted by the presence of small amounts of gold. Heat treatment led to the pronounced changes of the nature of gold species.
2
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The Influence of Reduction Process on the Iron-Molybdenum Nanoparticles in Modified MCM-41 Silica

100%
Surowiec Z., Wiertel M., Gac W., Budzyński M.
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vol. 125
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issue 3
846-849
EN
Iron-molybdenum silica mesoporous materials were obtained by the application of direct hydrothermal method. The influence of high temperature samples reduction in the H_2 flow on their structural and magnetic properties was studied. Four samples with different metal contents relative to silica were investigated. The study was carried out by means of X-ray diffraction, ^{57}Fe Mössbauer spectroscopy and the temperature programmed reduction method. With an increasing metals content, primary pores of MCM-41 transformed into the bottle-like pores, and then into the slit-like ones. Reduction and heat treatment caused the α-Fe, Fe_2Mo, and Fe-Mo alloy formation. Iron and molybdenum atoms after being released into the silica matrix, where they were embedded, create clusters or crystallites. It was observed that the high temperature reduction caused partial transformation of highly dispersed Fe-Mo oxides species initially embedded in silica walls into crystallites big enough to give magnetic sextet component in the Mössbauer spectra.
3
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The Synthesis and Properties of High Surface Area Fe_{2}O_{3} Materials

100%
Surowiec Z., Gac W., Wiertel M.
Acta Physica Polonica A
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2011
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vol. 119
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issue 1
18-20
EN
Two types of the silica materials were used for the preparation of iron oxides. The MCM-48 type silica support and wide-pore silica gel were impregnated with iron nitrates. The samples were investigated by the nitrogen adsorption/desorption method, X-ray diffraction, scanning electron microscopy, and ^{57}Fe Mössbauer spectroscopy. Redox properties were studied by the temperature programmed reduction method. Strongly dispersed hematite was evidenced on the supports. An application of the MCM-48 silica mesoporous materials led to the development of the oxide phases within the ordered porous structure. The detailed temperature programmed reduction studies evidenced slight differences of the redox properties of the species located within the silica templates and after their removal. Magnetic properties of iron oxides were related to the porous structure of the silica supports. The Mössbauer study of high surface area materials Fe/SiO_{2} and Fe/MCM-48 type silicate templates revealed existence of ferro- and superparamagnetic phases. The relative contribution of the superparamagnetic doublet component in Mössbauer spectra is 15% and 80% for Fe/SiO_{2}/c and Fe/MCM-48/c samples, respectively.
4
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Positron Annihilation in MnFe_2O_4/MCM-41 Nanocomposite

100%
Wiertel M., Surowiec Z., Gac W., Budzyński M.
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vol. 125
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issue 3
793-797
EN
In the paper results of studies of MnFe_2O_4/MCM-41 nanocomposites have been presented. The influence of manganese ferrite loading on changes of porous properties of mesoporous MCM-41 structure was studied by means of N_2 sorption/desorption method and positron annihilation lifetime spectroscopy. Disappearance of the longest-lived ortho-positronium component (τ_5) of pure MCM-41 mesoporous material in the positron annihilation lifetime spectra of MnFe_2O_4/MCM-41 measured in vacuum is a result of either o-Ps quenching or the Ps inhibition mechanism. Filling of pores in the studied nanocomposites by air at ambient pressure causes partial reappearance of the (τ_5) component except for the sample with maximum ferrite content. Both the (τ_5) component lifetime and intensity are suppressed together with increasing MnFe_2O_4 content by chemical quenching and inhibition of Ps formation occur. Observed anti-quenching effect of air is a result of two processes: neutralization of some surface active centres acting as inhibitors and considerably weaker paramagnetic quenching by O_2 molecules.
5
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Positron Annihilation Studies of Mesoporous Iron-Molybdenum Modified MCM-41 Silica

100%
Surowiec Z., Wiertel M., Gac W., Budzyński M.
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vol. 125
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issue 3
789-792
EN
Iron-molybdenum modified MCM-41 mesoporous materials were obtained by the application of direct hydrothermal method. An incorporation of iron and molybdenum ions in the synthesis stage led to structural changes of the MCM-41 support. With an increasing metals content, cylindrical pores of silica are destroyed. X-ray diffraction investigations indicated that both iron and molybdenum ions were first embedded in the silica walls and then formed highly dispersed species in the pores. The porous structure of the studied samples was examined by means of N_2 adsorption/desorption and PALS methods. The longest-lived o-Ps lifetime component remains constant but its intensity monotonically decreases, except for the sample with the highest metals content. These results indicate that an effect of o-Ps formation inhibition occurs.
6
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Investigation of surface properties of lunar regolith - Part IV

46%
Robens E., Dąbrowski A., Mendyk E., Goworek J., Skrzypiec K., Drewniak M., Dumańska-Słowik M., Gac W., Dobrowolski R., Pasieczna-Patkowska S., Huber M., Iwan M., Kurzydłowski K., Płociński T., Ryczkowski J., Rzączyńska Z., Sobczak J.
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2008
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vol. 63
144-168
EN
We investigated three lunar regolith powder samples from the Apollo missions. Apollo 11 and Apollo 12 samples come from lunar maria and Apollo 16 sample from a highland region. In the present paper we summarise in brief results of measurements using photoelectron spectroscopy (XPS), micro-Raman spectroscopy (RM), x-ray diffraction (XRD), x-ray fluorescence spectroscopy (XRF), temperature programmed reduction and oxidation (TPRO), thermogravimetry (TG), differential thermal analysis (DTA) and nitrogen adsorption. Parts of samples are visualised by means of scanning electron microscopy (SEM/EDX) and atomic force microscopy (AFM).
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