Another strategy investigated to modify the silica membrane materials consists in incorporating a metal and/or metal oxide in the sol–gel process to produce metal-doped molecular sieve silica membrane materials. For that purpose metal oxides or metal doped silica sols were prepared through the hydrolysis and con- densation of TEOS in ethanol and hydrogen peroxide (H2O2) or ni- tric acid with metal salts, such as hydrated cobalt and nickel nitrate salts or niobium alkoxide. Fine control of the silica matrix and pore size tuning was possible using sol–gel processes [12,21- 24]. However, metal-doped silica membrane material as cobalt- doped one showed hydrophilic behavior as it can adsorb water, with a lower water adsorption capacity compared with the blank (non-doped) silica membrane material, as reported by Uhlmann et al. [25].