Preparation of Silica/γ‐Alumina Membrane with Bimodal Porous Layer for Improved Permeation in Ions Separation

Creating secondary pores in the intermediate layer of hierarchical ceramic membranes successfully increases the permeability of bi‐layered membranes by reducing the density of the separating layer. With the optimum secondary pore volume, the permeability of the silica/γ‐alumina membrane with low secondary volume is enhanced with a satisfactory retention of organic ions and inorganic ions. However, the silica layer is not well formed when excessive secondary pores were generated in the intermediate layer. This is likely because the bimodal porous structure of γ‐alumina with high secondary pore volume is inadequate to prevent the penetration of silica sol into the α‐alumina support during dip coating. Thus, the bi‐layered membrane with high secondary pore volume shows insufficient retention of Reactive Orange 16 dye and NaCl at low pH.