Synthesis of chitosan-NaA membranes with non-uniform seeds on defective supports

Abstract

It is of great significance to use cheaper macro-porous supports for NaA membranes. Herein, a chitosan modified strategy was designed to weaken the accurate matching between defective supports and seeds. Two types of defective α-alumina tubes were used as macro-porous supports. In order to further reduce the fabricating cost, non-uniform NaA seeds (0.3–3.2 μm) were prepared without the expensive structure-directing agent. By one simple dip coating process, the chitosan layer was coated on the surface of defective supports before applying seeds. Moreover, the binding strength of adsorbed crystals was qualitatively investigated by the ultrasonic treatment (35 kHz, 5 min). NaA membranes were subsequently prepared by the secondary crystallization process. The results indicated that the addition of a thin chitosan buffer layer really overcame the limitation of obvious defects (>10 μm). Meanwhile, as for the obvious cracks of 1.5% chitosan modified NaA membranes, the unbalanced hydrophilic swelling was offered as a feasible explanation. The optimized separation factor was 4000 with the flux of 1.32 kg m−2 h−1 (70 °C, 0.03 Pa). Overall, this efficient method can be treated as one potential strategy to prepare low-cost NaA membranes.