Preparation and Characterization of Hydrophobic Microporous Silica Membranes Modified by Phenyl Groups

Silica membranes modified with phenyl groups were synthesized through the acid-catalyzed co-hydrolysis and condensation reaction of tetraethyl orthosilicate (TEOS) and phenyltriethoxysilane (PTES) The pore structure and hydrophobic properties of the modified silica membranes were characterized by means of SEM, nitrogen adsorption, water contact angle measurement, TG and FTIR. The single gas permeation and permselectivity of the hydrophobic silica membranes were also investigated at room temperature: The results show that the hydrophobic properties of the modified silica membranes are gradually enhanced with increasing amount of PTES in the mixture. When the molar ratio of PTES/TEOS increases to 0.6 and the molar ratio of H2O/TEOS to 9.6, the modified silica membranes exhibit an excellent hydrophobic property with a water contact angle of 115 degrees +/- 0.5 degrees and a desirable microporous structure with 4 pore volume of 0.17 cm(3)/g and a sharp pore size distribution centered at 0.4-0.5 nm. The modified silica membranes conform to a combination of a surface diffusion mechanism associated with micropores and a Knudsen diffusion mechanism related to the larger pores or microcracks, with a H-2 permeance of 1.49 x 10(-6) mol/(m(2).Pa.s) and a permselectivity of 4.64 for H-2/CO3 and 365.69 for H-2/SF6.