Preparation and characterization of mesoporous γ-Al₂O₃ membranes

Starting from alumina with particle size of 0.3-0.4 μm, disk α-Al₂O₃ supports were prepared via colloidal filtration with a mean pore size of ca. 70 nm as determined by Hg intrusion method. The polished supports with mirror-like surface were used for mesoporous membrane preparation. A stable Boehmite sol with a mean particle size of about 20 nm was successfully synthesized with aluminium sec-butoxide (ALSB) as a precursor through particle colloidal sol-gel route. Defect-free γ-Al₂O₃ mesoporous membranes with pore size of ca. 3 nm superimposed on the disk α-Al₂O₃ supports were then prepared by dip-coating with the Boehmite sol and subsequently calcined in a temperature range of 400-800°C. The molecular weight cut-off (MWCO) for PEG and the flux for pure water of these membranes are 2800-5300 and 11.5-25.9 L·m^-2·h^-1 [7.6·10⁵ Pa, (14±1)°C], respectively, which confirms the integrity of the mesoporous membranes. The results presented in this paper provide a feasible method for the preparation of defect-free mesoporous membranes with a pore size of about 3 nm directly by coating onto macroporous Al₂O₃ support with a pore size of about 70 nm.