ZIFs-modified GO plates for enhanced CO2 separation performance of ethyl cellulose based mixed matrix membranesf

Abstract

Graphene oxide (GO) has been employed as filler in mixed matrix membranes (MMMs) to enhance gas selectivity as its high-aspect ratio structure makes the path of gas diffusion longer and tortuous, improving diffusivity selectivity of gases with different molecular sizes. However, the stacking and folding structure of GO nano-sheets leads to gas barrier effects which reduce gas permeability. In this paper, a strategy of modifying continuous ZIF-8 layer with ultra-microporosity and high gas permeability on the surface of GO nano-sheets was proposed to increase the size and connectivity of gas transfer passage. ZIF-8@GO nano-sheets were successfully prepared by two-step ultrasonic synthesis method of growing ZIF-8 on GO surface at room temperature and the flexibility of nano-sheets could be easily tuned by different reaction times. CO2 permeability of ethyl cellulose (EC)/ZIF-8@GO MMMs achieves continuous enhancement with the increased loading of ZIF-8@GO compared with pure GO based MMMs which shows rare effective improvement in CO2 permeability. EC/ZIF-8@GO membrane containing 20 wt% fillers exhibits CO2 permeability of 203.3 Barrer together with CO2/N2 selectivity of 33.4, increased by 139% and 65% from that of pristine EC membrane respectively, and this performance is also higher than that of MMMs containing independent GO or ZIF-8. Having distinct improvement of CO2 separation performance, the modification strategy using ultra-porosity MOFs to enhance gas transfer of 2D nano-sheets is promising for fabrication of high performance CO2 separation membranes.