Modification of the surface characteristics of anodic alumina membranes using sol–gel precursor chemistry

The objective of the work reported here was to characterize the surface properties of anodic alumina membranes using streaming potential measurements and to modify those properties using sol–gel reactions to deposit titania or silica on the membrane surface. The zeta potential of the pore surface was determined from streaming potential measurements that were performed in KCl solutions of different pH. The isoelectric point of unmodified anodic alumina membranes was found to be at pH ∼8. Membranes whose surface properties had been modified showed zeta potentials in neutral or basic electrolyte that were lower than those observed for unmodified membranes. The isoelectric point for both SiO2 and TiO2 modified membranes was found to be at pH ∼6.5–7. However, the surface modifications appeared to be unstable in acidic solution, with zeta potentials of modified membranes returning to values observed for the unmodified membranes after exposure to electrolyte solutions at pH less than ∼6.