Fabrication of MOFs/PDMS mixed matrix membranes and defect-free composite membranes for efficient air separation

Membrane is a potential candidate to solve the challenge of air separation to meet the huge industrial demand of N 2 or O 2 . In this contribution, four types of prominent metal organic frameworks (MOFs) with different pore sizes and series, including ZIF-8 (3.4 Å), ZIF-71 (4.2 Å), UiO-66 (6 Å) and MIL-53(Al) (16.3 Å) were synthesized, and used as a nanoporous filler combined with polydimethylsiloxane (PDMS) substrate to prepare MOFs/PDMS mixed matrix membranes (MMMs) for air separation, which were compared to derive the optimal MOFs with high O 2 /N 2 selectivity ( α O2/N2 ) and O 2 permeability ( P O2 ). Gas permeation test was done to analyze the influences of MOFs content, feed gas pressure and gas composition on the O 2 /N 2 separation performance. 10 wt% ZIF-71/PDMS MMMs exhibits the optimal separation performance ( α O2/N2 = 3.14, P O2 = 630 Barrer), while pressure has small effect on O 2 /N 2 separation performance. P O2 is higher under pure gas test conditions, while α O2/N2 is better under mixed gas conditions, which is caused by the competitive adsorption-diffusion of O 2 and N 2 molecules. Further, ZIF-71/PDMS/PVDF composite membrane that could produce 30 vol% oxygen-enriched permeate stream was prepared, and the P O2 (1047 Barrer) is improved by 66% compared with MMMs.