Preparation of organic–inorganic hybrid silica membranes using organoalkoxysilanes: The effect of pendant groups

Organic–inorganic hybrid silica membranes were prepared via a sol–gel process using organoalkoxysilanes with pendant groups. Two kinds of organoalkoxysilanes, methyltriethoxysilane (MTES) and phenyltriethoxysilane (PhTES), were used to investigate the effect of the pendant groups on the gas permeation properties and micropore structures of hybrid silica membranes. The hybrid silica membranes showed relatively low H2 permeance, and the H2 permeance decreased with the pendant group size. Moreover, based on pore sizes determined by normalized Knudsen-based permeance (NKP), the hybrid silica membranes showed large pore sizes that increased with the size of the pendant groups. Compared with silica membranes prepared from tetraethoxysilane (TEOS) and 1,2-bis(triethoxysilyl)ethane (BTESE), which have no pendant groups, the large pore sizes of silica membranes derived from MTES and PhTES were not associated with high H2 permeance. This could be ascribed to the different membrane structures of MTES- and PhTES-derived silica membranes, due to the presence of pendant groups in the silica matrix.