Introducing hydrophilic ultra-thin ZIF-L into mixed matrix membranes for CO2/CH4 separation

Mixed matrix membranes (MMMs) were developed by mixing hydrophilically modified two-dimensional (2D) imidazole framework (named as hZIF-L) flakes into a Pebax MH 1657 (Pebax) matrix, and designed to separate carbon dioxide/methane (CO2/CH4) mixtures. The hZIF-L flakes were important for increasing the effectiveness of the MMMs. First, the tannic acid (TA) etched hZIF-L flakes have a large number of microporous (1.8 nm) and two-dimensional anisotropic transport channels, which offered convenient gas transport channels and improved the permeability of CO2. Second, the TA molecules provide the surface of the ZIF-L flakes with more hydrophilic functional groups such as carbonyl groups (CO) and hydroxyl groups (–OH), which could effectively prevent non-selective interfacial voids and filler agglomeration in the Pebax matrix, and also presented strong binding ability to water and CO2 molecules. The satisfactory interface compatibility and affinity with the CO2 molecule promoted its permeability, solubility, and selectivity. As a result, the MMMs exhibited the highest performance of gas separation with the hZIF-L flake weight content of 5%, at which the CO2 permeability and CO2/CH4 selectivity were 502.44 barrer and 33.82 at 0.2 MPa and 25 °C, respectively.