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A fluorine‐SiO2 membrane was prepared using triethoxyfluorosilane (TEFS) as a Si precursor, and its hydrothermal stability was evaluated. The TEFS membrane calcined at 750°C had fewer Si‐OH and Si‐F groups in its network structure and showed H2 permeance that was greater than 10−6 mol m−2 s−1 Pa−1 with H2/N2 and N2/SF6 permeance ratios of 10 and 210, respectively. This membrane performance was relatively stable under the temperature (< 500°C) used for steam treatment, regardless of the steam partial pressure (30, 90 kPa). On the other hand, when the steam treatment temperature was increased beyond 500°C, gas permeance decreased significantly and the membrane became highly selective for He and H2 over smaller molecules (He/N2: > 600, H2/N2: > 100). The relationship between the activation energy of H2 and the permeance ratios (He/H2, He/H2O, H2/H2O) of a TEFS‐derived membrane under steam treatment higher than 600°C resulted in a network pore size that approximated in conventional microporous SiO2 membranes.

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A series of pendant–type alkoxysilane structures with various carbon numbers (C1–C8) were used to fabricate sol–gel derived organosilica membranes to evaluate the effects of the C/Si ratio and fluorine doping. Initially, this investigation was focused on the effect that carbon-linking (pendant–type) units exert on a microporous structure and how this affects the gas-permeation properties of pendant–type organosilica membranes. Gas permeation results were compared with those of bridged–type organosilica membranes (C1–C8). Network pore size evaluation was conducted based on the selectivity of H2/N2 and the activation energy (Ep) of H2 permeation. Consequently, Ep (H2) was increased as the C/Si ratio increased from C1 to C8, which could have been due to the aggregation of pendant side chains that occupied the available micropore channel space and resulted in the reduced pore size. By comparison, these permeation results indicate that pendant–type organosilica membranes showed a somewhat loose network structure in comparison with bridged–type organosilica membranes by following the lower values of activation energies (Ep). Subsequently, we also evaluated the effect that fluorine doping (NH4F) exerts on pendant−type [methytriethoxysilane (MTES), propyltrimethoxysilane (PTMS)] and bridged-type [1,2–bis(triethoxysilyl)methane (BTESM) bis(triethoxysilyl)propane (BTESP)] organosilica structures with similar carbon numbers (C1 and C3). The gas-permeation properties of F–doped pendant network structures revealed values for pore size, H2/N2 selectivity, and Ep (H2) that were comparable to those of pristine organosilica membranes. This could be ascribed to the pendant side chains, which might have hindered the effectiveness of fluorine in pendant–type organosilica structures. The F–doped bridged–type organosilica (BTESM and BTESP) membranes, on the other hand, exhibited a looser network formation as the fluorine concentration increased.

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