Counter diffusion self-assembly synthesis of nanostructured silica membranes

This paper reports experimental efforts to synthesize ordered mesoporous silica membranes within macroporous ceramic supports by a new method of acid catalyzed counter diffusion self-assembly with cetyltrimethylammonium bromide as the surfactant. Synthesis experiments were conducted to examine the effects of pore size (0.16–22μm) and surface chemistry (hydrophilicity and hydrophobicity) of the support on the formation of mesporous silica membranes. Hydrophilic supports of various pore sizes resist the transfer of silica precursor through the support and lead to formation of low quality silica membranes. The surface of macroporous alumina supports was modified by grafting octadecyltrichlorosilane or hexyltrichlorosilane. Good quality silica membrane can be formed as 260μm plugs within the macroporous alumina supports with hydrophobic internal pore facilitating transfer of silica precursor. Gas permeation data for the silica membranes exhibits Knudsen type permeation mechanism, with 0.45×10−7mol/sm2Pa nitrogen permeance, confirming the mesoporous nature of the silica membranes grown within the macroporous alumina supports.