A sacrificial ZIF-L seed layer for sub-100 nm thin propylene-selective ZIF-8 membranes

Extensive research has been conducted to synthesize polycrystalline zeolitic imidazolate framework-8 (ZIF-8) membranes with exceptional capability for diffusion-based propylene/propane separation. For practical applications of the membranes, membrane productivity must be enhanced to counterbalance the relatively high membrane production cost in comparison with those of polymeric membranes, which are currently dominating the membrane market. In this study, we demonstrate a facile membrane synthesis technique that enables the rapid formation of ultrathin ZIF-8 membranes with sub-100 nm thickness, thereby significantly improving the membrane productivity via enhanced propylene permeance. The key to producing ultrathin ZIF-8 membranes is the introduction of a sacrificial ZIF-L seed layer prior to evaporation-induced ZIF-8 crystallization (known as rapid thermal deposition, RTD). The fabricated membranes exhibit 12 times higher average propylene permeance (∼390 GPU) with twice the propylene/propane separation factor (∼50) as those of ZIF-8 membranes produced in the absence of a ZIF-L seed layer.