COF/MXene composite membranes compact assembled by electrostatic interactions: A strategy for H2/CO2 separation

H2 and CO2 separation in processes such as reforming hydrocarbons or gasifying fossil fuels using membranes has gained attention as an energy-efficient separation method. Covalent organic frameworks (COFs) are a promising class of organic porous crystalline materials, but their pore sizes (typically >0.5 nm) exceed the kinetic diameters of H2 (0.289 nm) and CO2 (0.33 nm). Herein, we aimed to improve the H2/CO2 selectivity of COF (TpPa-1) membranes by fabricating a two-dimensional composite membrane. This strategy involved the compact assembly of mesoporous COF (TpPa-1) nanosheets facilitated by non-porous MXene (Ti3C2Tx), driven by electrostatic interactions. The objective was to reduce the pore sizes of gas transport channels, enabling molecular sieving for H2/CO2 separation. Additionally, strong adsorptive interactions between CO2 and the COF/MXene composite membranes were leveraged to impede the transport of CO2 molecules. The results demonstrated that the 2D COF/MXene composite membranes with a Ti3C2Tx doping amount of 65 wt% achieved the highest H2/CO2 selectivity of 64.0 at 298 K, which was 5.67 times that of the pristine COF (TpPa-1) membrane. The H2 permeance reached 2.35×10−7 mol m−2 s−1 Pa−1, surpassing the latest Robeson upper bound. This innovative strategy not only presents a high-performance candidate for H2/CO2 separation but also provides inspiration for pore regulation of COF compactly assembled with non-porous MXene through electrostatic interactions.