The method involved the secondary or seeded growth of ZIFs crystal into the support that contained attached seeding crystals (Figure ). A seed crystal of ZIFs materials can be attached to the membrane supports via physical or chemical treatments. The method is different from the insitu synthesis method. There is no crystal nucleation, growth, and intergrowth in secondary growth synthesis. The choice of ex-situ procedure is critical for the membrane's performance. Generally speaking, ZIF8-based membranes synthesized using rubbing seeding produce higher gas permeability than the electrospinning seeding procedure.