Synthesis and characterization of mesoporous silica membranes via dip-coating and hydrothermal deposition techniques

Two types of mesoporous silica membranes have been prepared and characterized. A membrane fabricated via sol dip-coating was deposited on the polished surface of an alumina support disk. For the purpose of comparison, a membrane fabricated via hydrothermal processing with a three-dimensional pore network was deposited on the surface and within the pores of a macroporous alpha-alumina support disk. Both membranes were gas tight prior to calcinations, indicating the deposition of initially defect free silica layers. Gas permeation experiments show the gas permeation for N-2, Ar, O-2 and He to be strongly governed by Knudsen diffusion. Results of multigas separation experiments for N-2 over Ar show near ideal Knudsen separation factors for both membranes. Single gas pressure drop experiments show linear fluxes with respect to the inverse square of the molecular weight and square of temperature of each gas at pressure drops of 1.01325 x 10(5) Pa (1 atm). Additional single gas pressure drop experiments indicated no contribution by viscous flow to the net gas transport. X-ray diffraction (XRD) results show that each membrane possesses a periodic mesoporous structure. N-2 physisorption experiments show that each membrane layer has a surface area of over 850 m(2) g(-1) and nearly monodisperse pore size distribution in the mesoporous regime. (C) 2003 Elsevier Science B.V. All rights reserved.