Organic–inorganic hybrid silica membranes with controlled silica network size: Preparation and gas permeation characteristics

Bis(triethoxysilyl) ethane (BTESE), which consists of Si–C–C–Si bonds, was used as a silica precursor to prepare organic–inorganic hybrid silica membranes with loose amorphous networks. Single-gas permeation and binary-component gas separation characteristics for hybrid silica membranes were examined to discuss the effect of silica precursors on amorphous networks. The pore size distribution, as determined by single-gas permeation, suggested BTESE-derived silica membranes have loose amorphous structures compared to TEOS-derived silica membranes due to the differences in the minimum units of silica networks. For example, BTESE-derived silica membranes showed a high hydrogen permeance (0.2–1 × 10−5 mol m−2 s−1 Pa−1) with a high selectivity of H2 to SF6 (H2/SF6 permselectivity: 1000–25,500) and a low H2 to N2 permselectivity (∼20). The binary-component gas separation of He and SF6 for a BTESE-derived silica membrane revealed that the swelling effect (adsorption-induced expansion of the zeolite crystals) by SF6 molecules, which has been suggested for zeolite membranes, was not observed in amorphous silica networks. In the present study, BTESE-derived silica membranes had high hydrothermal stability due to the presence of Si–C–C–Si bonds in the amorphous silica network.