Preparation of γ-alumina thin layer with bimodal pore size distribution for diminution of transport resistance in bi-layered membrane

Porous γ-alumina with bimodal pore size distribution (average pore size of primary mesopores is 4–5 nm and diameter of secondary mesopores is ca. 50 nm) was introduced into bi-layered membranes as an intermediate layer for diminution of transport resistance. The secondary mesopores were tailored in γ-alumina using nanosized polystyrene beads (ca. 50 nm) as templating units. Surfactant templated silica was stacked on top of the γ-alumina with different pore structures to form bi-layered membranes. Besides characterizing using X-ray diffraction, transmission electron microscope, scanning electron microscope and X-ray microanalysis, bi-layered membranes with different types of intermediate layers were also studied using a dead-end stirred cell. The water permeabilities of the bi-layered membranes with secondary mesopores in intermediate layers are much higher than the permeability of the conventional bi-layered membrane. The molecular weight cut-off of the improved membrane was estimated at 400 Da, same as the molecular weight cut-off of the conventional membrane.