Microwave-assisted synthesis of metal–organic frameworks UiO-66 and MOF-808 for enhanced CO2/CH4 separation in PIM-1 mixed matrix membranes

Abstract

This study presents a sustainable microwave-assisted synthesis, based on the use of acetone and a water/acetic acid mixture instead of typical harmful DMF, to fabricate Zr-metal–organic frameworks (MOFs) UiO-66 and MOF-808 as fillers in a PIM-1 matrix for gas separation application. The mixed matrix membranes (MMMs) were prepared with varying loadings (2.5–10 wt%) of MOFs. The physicochemical properties (1H NMR, FTIR, XRD, N2 adsorption, TGA and SEM) of the resulting PIM-1, MOFs and MMMs were analyzed. The CO2/CH4 separation performance and membrane aging characteristics of the MMMs were evaluated. The incorporation of MOF fillers significantly improved CO2 permeability and CO2/CH4 selectivity, attributed to their CO2-philicity and narrowpore size (UiO-66 ≈ 0.6 nm and MOF-808 ≈ 1.8 nm). The MMMs with higher filler loadings (7.5 and 10 wt%) exhibited the most favorable separation performance. Due to the better crystallinity and textural properties, MOF-808 produced the best separation results at 10 wt% filler loading (a CO2/CH4 separation selectivity of 16.2 at 9090 Barrer of CO2 permeability). Aging led to a decrease in CO2 permeability but a slight increase in CO2/CH4 selectivity for all MMMs. Overall, the study highlights the potential of PIM-1/UiO-66 and PIM-1/MOF-808 MMMs as efficient materials for (CO2/CH4) separation comparing with the pristine PIM-1.