Małgorzata Zimowska

Alterations of the surface and morphology of tetraalkyl-ammonium modified montmorillonites upon acid treatment

The effect of short alkyl chain cations on the modification of the structure, surface and textural properties of organo-montmorillonites upon their acid treatment was investigated. Samples prepared from Ca-SAz montmorillonite and tetramethylammonium (Me(4)N(+)-), tetraethylammonium (Et(4)N(+)-), tetrapropylammonium (Pr(4)N(+)-) and tetrabutylammonium (Bu(4)N(+)-) salts were treated in 6 M HCl at 80 °C for 2-8 h and analyzed by different methods. Acid treatment of organo-montmorillonites caused gradual release of Al and Mg from the octahedral sheets and destruction of their layered structure. The extent of the changes depended significantly on the size of organo-cation. While large plate-like particles of Ca-SAz and Me(4)N-SAz were disintegrated during acid treatment and smaller fine grains were created, the morphology of Bu(4)N-SAz was modified only slightly. Pore size analysis showed generation of pore network upon organo-montmorillonites dissolution. After longer acid attack, pore volume increased and pore size distribution curves were shifted to pores with diameter above 25 Å. The surface area of acid-treated samples increased due to destruction of the montmorillonite layers and formation of the SiO(2)-rich reaction product. The highest value 475 m(2)/g was observed for Me(4)N-SAz treated 4 h. Surface area of Et(4)N-SAz, Pr(4)-SAz and Bu(4)N-SAz was 441, 419 and 293 m(2)/g, respectively, after 8 h treatment. Similar decomposition level was observed for Ca-SAz and Me(4)N-SAz, and less destruction was found for Et(4)N-SAz, Pr(4)-SAz and very low for Bu(4)N-SAz. Though Bu(4)N(+) is short alkyl chain cation, its size is large enough to cover the inner and outer surfaces of montmorillonite and thus to protect the clay layers from acid attack.

Layered Sodium Disilicates as Precursors of Mesoporous Silicas. Part I: Optimisation of the Synthesis Procedure of δ-Na2Si2O5 and α-Na2Si2O5

Layered Sodium Disilicates as Precursors of Mesoporous Silicas. Part I: Optimisation of the Synthesis Procedure of δ-Na2Si2O5 and α-Na2Si2O5 Optimization of the synthetic procedures described in literature aimed at preparing pure δ-Na2Si2O5 has been carried out. The results show that a substantial shortening of the calcination time of amorphous silicate precursor is required, in order to minimize the appearance of the thermodynamically stable α-Na2Si2O5. The use of commercial water glass solution rather than freshly synthesized silica/NaOH slurry is the preferred source of the starting amorphous silicate. Optimized preparative routes for synthesis of single-phase δ-Na2Si2O5 and α-Na2Si2O5 have been described. Warstwowe krzemiany sodu jako prekursory mezoporowatych krzemionek. I: Optymalizacja syntezy δ-Na2Si2O5 i α-Na2Si2O5 Zweryfikowano opisaną w literaturze procedurę syntezy czystego δ-Na2Si2O5. Stwierdzono, że skrócenie czasu kalcynacji amorficznego prekursora krzemianowego z 5-6 godz. do 1 godziny zapewnia otrzymanie niemal czystego δ-Na2Si2O5, przy minimalnej ilości termodynamicznie stabilnej fazy α-Na2Si2O5. Preferowanym źródłem wyjściowego amorficznego krzemianu sodu jest szkło wodne w miejsce syntetyzo-wanego roztworu SiO2/NaOH. Użycie szkła wodnego i krótki czas kalcynacji w 700°C prowadzą do otrzymania monofazowego δ-Na2Si2O5. Czysty α-Na2Si2O5 można otrzymać kalcynując amorficzny krzemian sodu w temperaturze 825°C.

PDDA-Montmorillonite Composites Loaded with Ru Nanoparticles: Synthesis, Characterization, and Catalytic Properties in Hydrogenation of 2-Butanone

The effect of synthesis parameters on the physicochemical properties of clay/ polydiallyldimethylammonium (PDDA)/Ru composites and their applicability in hydrogenation of 2-butanone under very mild conditions (room temperature, atmospheric pressure, and aqueous solution) was studied. Three synthetic procedures were employed, differing in the order of addition of components and the stage at which metallic Ru species were generated. The materials were characterized with XRD (X-ray diffraction), XRF (X-ray fluorescence), EDS (energy-dispersive spectroscopy), AFM (atomic force microscopy), TEM/HRTEM (transmission electron microscopy/high resolution transmission electron microscopy), and TG/DSC (thermal gravimetry/differential scanning microscopy techniques. The study revealed that the method of composite preparation affects its structural and thermal properties, and controls the distribution and size of Ru particles. All catalysts are active in hydrogenation of 2-butanone. For best catalytic performance (100% conversion within 30 min) both the size of Ru particles and the load of polymer had to be optimized. Superior catalytic properties were obtained over the composite with intermediate crystal size and intermediate PDDA load, prepared by generation of metallic Ru species in the polymer solution prior to intercalation. This method offers an easy way of controlling the crystal size by modification of Ru/PDDA ratio.

Layered Sodium Disilicates as Precursors of Mesoporous Silicas. Part II: Hydration of δ-Na2Si2O5 and α-Na2Si2O5

Layered Sodium Disilicates as Precursors of Mesoporous Silicas. Part II: Hydration of δ-Na2Si2O5 and α-Na2Si2O5 Reaction of δ-Na2Si2O5 and α-Na2Si2O5 with water at ambient conditions has been studied. The first substrate produced kanemite, the other a crystalline solid, assumed to be the layered hydrated α phase of yet unknown structure. Important differences have been observed in the kinetics of δ-Na2Si2O5 and α-Na2Si2O5 reactions with water, the phase transformation of the latter being distinctly slower. The observed different rates of hydration were associated with the different structural properties of the disilicates investigated. Hydrated δ-Na2Si2O5 and α-Na2Si2O5 possess, respectively, the platy and the needle-like morphology. Hydrated α-Na2Si2O5 contains less interlayer water, which is considered the reason for basal spacing being lower than that of kanemite. The interlayer water trapped between the layers of hydrated α-Na2Si2O5 is more strongly bound than that in kanemite. Warstwowe krzemiany sodu jako prekursory mezoporowatych krzemionek. II: Hydratacja δ-Na2Si2O5 i α-Na2Si2O5 Reakcje δ-Na2Si2O5 i α-Na2Si2O5 z wodą prowadzą do powstania uwodnionych krzemianów sodu, odpowiednio - kanemitu (z fazy δ-Na2Si2O5) i z fazy α - jej uwodnionej formy o nieznanej strukturze. Kinetyki hydratacji tych krzemianów są zdecydowanie różne; faza δ ulega szybkiej transformacji, faza α - wolnej. Różne szybkości hydratacji można wiązać z różnicami strukturalnymi obu krzemianów sodu. Uwodniony δ-Na2Si2O5 wykształcony jest w formie płytek, podczas gdy uwodniony α-Na2Si2O5 ma morfologię typu igieł. Różna jest również ilość wody międzypakietowej w obu hydratach; uwodniony δ-Na2Si2O5 posiada jej więcej ale słabiej związanej, natomiast uwodniony α-Na2Si2O5 mniej, lecz związanej silniej.