Facile synthesis of hydrophobic microporous silica membranes and their resistance to humid atmosphere

The ethylene-modified silica membranes were prepared by the acid-catalyzed co-hydrolysis and condensation reaction of tetraethylorthosilicate (TEOS) and ethylenetriethoxysilane (TEVS) in ethanol and the final materials were characterized by scanning electron microscope (SEM), water contact angle measurement, solid-state ²⁹Si magic angle spinning nuclear magnetic resonance (²⁹Si MAS NMR), and N₂ adsorption. The modification leads to a transform from superhydrophilicity for the unmodified silica membranes to hydrophobicity for the modified materials. The ethylene-modified silica membranes are much less water sensitive than the unmodified materials because the hydrophobic ethylene groups replace a portion of the hydrophilic hydroxyl groups on the pore surface. The modified materials process a microporous structure with a narrow pore size distribution centered at 1.1 nm. Such a microporous structure can be stabilized after exposured to humid atmosphere for 450 h, in intense contrast to the collapse of the micropores in the unmodified silica membranes.