Based on two template-free secondary growth methods

the formation mechanism of single-layer and multi-layer zeolite membranes was investigated. The composition of the synthesis solution did not affect the membrane structure

whereas the position-setting of the seeded support in the synthesis solution and the ageing process of the synthesis solution were two critical factors in the formation of the membrane. The synthesis solution with lower viscosity could easily penetrate into the gap between seeds boundaries

resulting in the formation of multi-layer membranes.