Wettability, pore structure and performance of perfluorodecyl-modified silica membranes

Perfluorodecyl-modified silica membranes were prepared by the sol-gel technique using tetraethyl orthosilicate (TEOS) and 1H,1H,2H,2H-Perflouorodecyltriethoxysilane (PFDTES) as precursors under acidic and clean room conditions. The wettability and pore structure of the modified silica membranes were characterized by means of water contact angle measurement, Fourier translation infrared spectroscopy (FT-IR), solid state 29Si magic angle spinning nuclear magnetic resonance (29Si MAS NMR) and nitrogen adsorption. The membrane performances including gas permeation/separation and long-term hydrothermal stability were also investigated in detail. The results show that perfluorodecyl groups have been successfully incorporated, resulting in a transformation from hydrophility to hydrophobicity for the modified silica membranes. With a low PFDTES/TEOS molar ratio of 0.2, the modified silica membranes exhibit a water contact angle of 112.6±0.5° and a pore size ranging from 0.45 to 0.9 nm. The hydrogen permeance increases with increasing temperatures, leading to a considerably high value of 9.71×10−7 mol m−2 s−1 Pa−1 at 300 °C. At such a temperature, the H2/CO2 permselectivity and binary gas separation factor are 7.19 and 12.11, respectively. Under a humid condition with a temperature of 250 °C and a water vapor molar ratio of 5%, the single H2 permeance and H2/CO2 permselectivity remain almost constant for at least 200 h, indicating that the modified membranes possess an outstanding hydrothermal stability.