Pore-size-controlled silica membranes with disiloxane alkoxides for gas separation

Pore-size-controlled silica membranes were prepared using hexaethoxy disiloxane (HEDS) by a “spacer” technique, which is a novel strategy to control the pore size of silica membranes using bridged alkoxides. HEDS-derived silica gel powders prepared with acid and base catalysts were microporous and mesoporous, respectively. HEDS-derived silica membranes prepared from HCl-catalyzed sol showed high H2 permeance (0.73–2.0 × 10−6 mol m−2 s−1 Pa−1) with low H2/N2 (∼20) and high H2/SF6 perm-selectivity (∼2000). Pore size by single gas permeation and normalized Knudsen-based permeance (NKP) showed that silica membranes with bridged alkoxides had a loose amorphous silica structure. Judging from NKP fitting curves for tetraethylorthosilicate (TEOS), HEDS, tetraethoxydimethyl disiloxane (TEDMDS), and bis(triethoxysilyl) ethane (BTESE)-derived silica membranes, the order was TEOS < HEDS < BTESE ≈ TEDMDS. These results suggested that the pore size of silica membranes can be tuned with various structured alkoxides of di-silicon.