Effect of seeding methods on growth of NaA zeolite membranes

NaA zeolite membranes were prepared by secondary growth on the outer surface of tubular mullite supports. Support surface was found to have obvious effect on the quality of as-made NaA zeolite membranes. Three seeding methods were compared for the quality of as-made NaA zeolite membranes, which included dip-coating, rubbing, and the combination of rubbing and dip-coating. The dip-coating treatment could provide well-distributed seeds on flat area of support surface, but poor coverage on dents and pinholes. Rubbing treatment with seed paste, however, could preferentially provide seeds into the defects but non-uniform coverage on the flat area. The combined seeding approach was better than the former two seeding methods, which produced high performance membranes with high reproducibility.