ZIF-8 hollow nanotubes based mixed matrix membranes with high-speed gas transmission channel to promote CO2/N2 separation

Abstract

Carbon nanotubes (CNTs) with 1D gas transport channel has great prospect in MMMs based CO2 separation. However, the insufficient compatibility with polymer and inner diameter of CNTs limit further improvement of their CO2 separation performances. In this work, the unique ZIF-8 hollow nanotubes (HNTs) were proposed to construct high-speed gas transmission channel in MMMs by a three-step method (electrospinning-calcination-hydrothermal), aiming at concurrently improving the gas permeability and selectivity. The hollow inner cavity provides long-range and low-resistance gas transmission channels to ensure high gas permeability. At the same time, the ZIF-8 crystals composing the tube wall can not only screen for gas molecules pair, but also strengthen the affinity between the filler and polymer matrix by its organic ligands, thus the gas selectivity can be raised. Compared with ZIF-8 nanoparticles and ZnO HNTs, ZIF-8 HNTs based MMMs present competitive CO2 separation. When the loading of ZIF-8 HNTs is 5 wt%, the gas separation performance shows the best, in which the CO2 permeability is 147 Barrer and the CO2/N2 selectivity is 68, approaching to the 2008 Robeson upper limit and surpassing most reported CNTs/Pebax based membranes. Therefore, the proposed ZIF-8 HNTs are promising for MMMs based CO2 separation.