Five organic CO₂-philic functional groups were incorporated in silica matrixes for preparation of functionalized silica membranes to explore the CO₂ separation performance. Chemical groups including acetate, trifluoromethyl, methacrylate, urea and vinyl groups were anchored in the silica network using the co-condensation method.

The information from ²⁹Si solid-state NMR and FTIR analyses indicates the successful formation of a covalent bond between functional groups and the silica network. The thickness of the functionalized silica layers was measured by SEM and the thermal stability of the organic groups was determined by thermogravimetric analysis (TGA).

The gas permeance and mixed gas selectivity of CO₂/N₂ was measured in the temperature range of 253–373 K with a feed pressure of 9 bar. A maximum selectivity of as high as 10 was observed for a trifluoromethyl functionalized silica membrane with a CO₂ permeance of 5.5 × 10⁻⁷ mol s⁻¹ m⁻² Pa⁻¹. Permporometry measurements indicated that the contribution of flow through micropores to the total flow for all the functionalized silica membranes varied between 62 and 82%. All membranes were CO₂ selective.