Effect of divalent cations on permeate volume flux through porous titania membranes

Titania (TiO2) membranes with molecular weight cut-offs controlled at 250, 400, and 2000 were successfully prepared by the sol-gel process. These porous membranes rejected electrolytes based on Donnan exclusion, and the permeate volume flux, based on the electroviscous effect, was pH-dependent, similar to polymeric porous membranes. Moreover, divalent counterions (Ca2+, Mg2+) which were strongly adsorbed by ion-exchange at alkali pH, drastically reduced volume flux, compared with monovalent cations (Na+, K+); this tendency was pronounced for porous membranes with smaller pore sizes. The evidence for hydrodynamic resistance by the adsorbed divalent cations was shown based on permeation and zeta potential measurements of mixtures.

Titania nanofiltration membranes were successfully prepared. The findings here suggest that adsorbed divalent counterions reduced the effective pore sizes and hydrodynamically resisted the permeation of fluid through nanoporous membranes.