RESUMO
Hydrophobic-hydrophilic composite membranes containing silicalite-1 and Al-beta zeolites are prepared on the outer surface of the porous alpha-alumina tube for the first time. The hydrophilic layer with aluminum serves as an active catalytic domain, whereas the hydrophobic layer containing silicalite-1 with medium pore-size is expected to assist in separating the reaction products based on their hydrophobicity as well as shape-selectivity. The continuous defect-free composite membranes are fabricated by two-step synthesis approach by initial deposition of Al-beta crystals on the outer surface of porous alumina tube followed by coating of silicalite-1 crystals over the Al-beta layer in the second step under hydrothermal conditions. The composite membranes exhibited a high thermal stability of up to 550 degrees C. The powder X-ray diffraction patterns of samples collected at the bottom of crystallization vessel as well as coated membranes indicated typical BEA and MFI structures consisting of ca. 0.5-0.7 nm size micropores, and free from impurity phase. The field emission scanning electron microscopic (FE SEM) analysis of the silicalite-1 sample exhibited uniform rectangular crystals of size about 20 microm; whereas Al-beta showed spherical morphology with crystal size of approximately 0.6-0.7 microm. The surface and cross-sectional analyses of composite membranes both before and after calcinations exhibited defect-free microstructures for the composite membranes. The calcined membranes exhibited single gas permeation and the observed values for composite membranes are an order of magnitude lower than that of the individual membranes.
RESUMO
Helices composed of stacked layers are present in the novel silicate obtained from a silica sol and NaOH by hydrothermal synthesis in the presence of tetramethylammonium (TMA) hydroxide and 1,4-dioxane. The helical morphology is evident in scanning electron micrographs (see picture). The TMA and sodium ions of the silicate are readily replaced by protons, and on heating to 200°C a reversible phase transition occurs in which water molecules are lost from between the layers.
RESUMO
Zeolites are able to adsorb proteins on their surface and might be suitable as a new type of chromatographic carrier material for proteins and for their conjugates (Matsui et al., Chem. Eur. J. 7 (2001) 1555-1560). Interestingly, maximum adsorption was observed at the isoelectric point (pI) of each protein. The current study was performed to investigate the desorption of proteins from the zeolites at pI. Proteins adsorbed to zeolites could be desorbed at pI by polyethylene glycol (PEG), but not by conventional eluents. The eluted proteins still retained their activities. The zeolite Na-BEA was an especially good composite for desorption by PEG. Using this method for the adsorption and desorption of proteins at pI, we succeeded in separating various proteins. The application of zeolites to biochemistry and biotechnology is also discussed.