Preparation and characterization of small-size amorphous MOF mixed matrix membrane

In recent years, amorphous metal-organic frameworks (AMOFs) with original structural units but no long-range ordering have attracted much attention. However, AMOFs with abundant open metal sites (OMSs) have seldom been applied for gas separation membranes mainly attributed to poor membrane-forming property caused by large particle sizes. In this work, we proposed the method of polymer induction for the first time to obtain smallsized AMOFs particles with stronger alkaline stability, higher hydrophilicity and better CO2/N2 adsorption selectivity than crystal, which were applied to mixed matrix membranes (MMMs) as filler, exhibiting good separation performance. First, polyethyleneimine (PEI) was used as an inducer to obtain small-sized UiO-66-NH2 particles (SU-1) and improve the membrane-forming property. Additionally, we adopted a thermal-treatment method to treat the particles and obtained an amorphous SU-1 (ASU-1). Furthermore, MMMs were prepared by uniformly mixing ASU-1 filler with strong basic polymer polyvinylamine (PVAm), and the prepared MMMs showed the optimal CO2 separation performance at an ASU-1 loading of 28.5 wt%, with a CO2/N2 selectivity of 71.33 at 1.5 bar and a CO2 permeance of 721 GPU, which was much higher than the MMM using pristine PVAm and SU-1. This study provides a promising strategy for preparing high-performance MMMs through decreasing particle size and increasing the separation performance of MOF fillers.