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 small-sized 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.