Ultrathin UiO-66-NH2 polycrystalline membrane for CO2/CH4 separation

MOF membranes exhibit impressive performance in gas separation due to their large surface area, controllable pore size and unique affinity. Here, the ultrathin UiO-66-NH2 polycrystalline membranes with thickness of ∼320 nm are successfully prepared within 1 h using a combination of ultrasound-assisted and microwave synthesis strategies. During the reaction, high-density small MOF nuclei are produced by sodium formate ultrasound-assisted, which act as sufficient nucleation sites for heterogeneous nucleation during membrane growth, aiming for development of a continuous MOF membrane on the porous substrate. The obtained UiO-66-NH2 membrane shows an ideal CO2/CH4 selectivity of 40 due to the enhanced the interaction between CO2 molecules and the membrane. Moreover, the narrowed pore structure further hinders the diffusion of larger-sized molecules owing to -NH2 occupying the pore channels, resulting in elevated CO2/CH4 selectivity. Compared to many other MOF membranes, the UiO-66-NH2 polycrystalline membranes exhibit a well balance of gas permeance and CO2/CH4 selectivity, which presents a new route for CO2 capture.