Activated transport is one of the most important properties of microporous membranes which results in molecular sieving separation with very high selectivities. The flux J (mol.m ~(-2).s~(-1)) through microporous membranes as a function of temperature can be derived from the isosteric heat of adsorption Q st and the mobility energy E_m (kJ.mol~(-1)). In this work, high quality molecular sieving membranes have been successfully synthesised using sol-gel process to prepare weakly branched silica films. Maximum permselectivities calculated are 846 (He/CH_4), 130 (CO_2/CH_4) and 58 (H_2/CO_2). The effect of mobility energy on silica films is demonstrated by preparation methods such as single-step and two-step catalysed hydrolysis of tetraethoxysilane (TEOS) which leads to the production of weakly branched silica films.
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