Facile synthesis of small crystal ZSM-5 zeolite by acid-catalyzed hydrolysis of tetraethylorthosilicate

Small crystal zeolites ZSM-5 with sizes of 150-300 nm were synthesized using the colloidal silicate precursors as the silica source created by the acid-catalyzed hydrolysis of tetraethylorthosilicate with tetrapropylammonium bromide as the structure-directing agent within a short crystallization time of 20-35 h. The precursors and final products were detected by XRD, SEM, ICP and DLS.

Preparation of Composite Microporous Silica Membranes Using TEOS and 1,2-Bis(triethoxysilyl)ethane as Precursors for Gas Separation

This paper reports on a new microporous composite silica membrane prepared via acid-catalyzed polymeric route of sol-gel method with tetraethylorthosilicate(TEOS)and a bridged silsesquioxane[1,2-bis(triethoxysilyl)ethane, BTESE]as precursors.A stable nano-sized composite silica sol with a mean volume size of^5 nm was synthesized. A 150 nm-thick defect-free composite silica membrane was deposited on disk support consisting of macroporous α-Al2O3 and mesoporousγ-Al2O3 intermediate layer by using dip-coating approach,followed by calcination under pure nitrogen atmosphere.The composite silica membranes exhibit molecular sieve properties for small gases like H2,CO2,O2,N2,CH4 and SF6 with hydrogen permeances in the range of(1-4)×10 -7mol·m -2·s -1·Pa -1(measured at 200°C,3.0×105 Pa).With respect to the membrane calcined at 500°C,it is found that the permselectivities of H 2 (0.289 nm)with respect to N2(0.365 nm),CH4(0.384 nm)and SF6(0.55 nm)are 22.9,42 and>1000,respectively, which are all much higher than the corresponding Knudsen values(H2/N2=3.7,H2/CH4=2.8,and H2/SF6=8.5).

Sol-Gel Materials with Pesticide Delivery Properties

Pesticides are widely used in agriculture, although they may create hazards both to humans and to the environment. In order to reduce the harmful effects of their administration, there has been made a great effort to find solutions. The porous sol-gel silica materials which are able to entrap different organic molecules represent new studied controlled release carriers. The aim of the present work was to prepare and characterize sol-gel composites based on trichlorfon as organophosphorous pesticide embedded in silica matrices generated from three different SiO2 sources: tetraethylorthosilicate (TEOS), colloidal silica (CS), and sodium silicate (SS). Similar samples to those containing only trichlorfon have also been synthesised, in which α-, β-, and γ-cyclodextrin have been included in order to study the possibility of improving the release of the pesticide from the silica matrices. The porous sol-gel silica materials generated from TEOS and CS are able to entrap the trichlorfon and ensure an efficient delivery of the pesticide. In the absence of cyclodextrins, better results are obtained in the case of TEOS precursor, compared to colloidal silica. The addition of cyclodextrins in order to improve the release of the pesticide from the silica matrices was successful only in the case of CS as SiO2 precursor. The best release of the pesticide was obtained with β-CD.

FABRICATION AND CHARACTERATION OF NANOPOROUS SILICA FILM

Colloidal silica sol is formed by a novel hydrolyzing procedure of tetraethyl orthosilicate(TEOS) catalyzing with NH 3 ·H 2 O in aqueous mediums. Glycerol, combining with the hydrolyzed intermediates of TEOS, controls growing of the silica particles; poly(vinyl vinyl alcohol makes the colloidal silica sol with polymeric structure and spinning, thermal strain makes the gel silica film changed into a nanoporous structure with diameter ranging 50-150 nm. Morphologies of the nanoporous silica film have been characterized; the porosities (%) is 32-64; the average dielectric constant at 1MHz region is 2.0 and 2.1; the thermal conductivity is less than 0.8. Chemical mechanism of the sol gel process is discussed.