Designing hydrothermally stable nanoporous silica membranes

Despite the use of sol-gel derived ultramicroporous silica membranes in substitution of traditional gas-separation processes is expected to lead to vast energy savings, their intrinsic poor steam-stability hampers their application at an industrial level. Indeed, it is well established that steam exposure may cause densification and defect formation in ultramicroporous silica membranes, at the detriment of both permeability and selectivity. Hydrothermal stability of silica membranes can be improved by transition metal oxide doping. However, the impact that dopant type and concentration have on the pore structure, the stability and the permeability of amorphous silica-based membranes is not clear yet, and the development of these membranes is mainly attained by an empirical approach. Here we present a quantitative study, providing information on how to design chemical compositions and synthetic paths for the fabrication of silica-based membranes with a well accessible and highly stabile microporous structure.