Influence of crystal growth on organic liquid phase separation efficiency in polycrystalline PCN-250 membranes

Molecular separations involving organic liquid phases, such as organic solvent nanofiltration (OSN) and pervaporation (PV), demand robust membrane materials with excellent stability in aggressive organic solvents of a wide pH range. Porous crystalline framework materials, such as metal-organic frameworks (MOFs), have emerged as promising membrane materials for such separations due to their uniform and tunable pore sizes and high stability in organic solvents. However, the impact of membrane thickness on separation efficiency has rarely been reported. PCN-250 is a type of MOF exhibiting suitable pore size, excellent stability, and facile membrane-forming ability. Herein, we fabricated polycrystalline PCN-250 membranes of different membrane thicknesses and studied their impact on OSN and PV performance. The two membranes, PCN-250-s and PCN-250-t, were fabricated through secondary and tertiary growth, respectively. With robustness in organic solvents containing acid, PCN-250-s membrane exhibited good OSN performance, with rejections of 97.2–99.2 % to methyl blue (799 Da) in ethanol. Meanwhile, PCN-250-t membrane demonstrated 1600 h continuous PV working ability in dehydrating acidic water/ethanol (10/90 wt%) mixtures containing 5 wt% acetic acid, exhibiting a total flux of 4.42 kg m −2  h −1 and a water/ethanol (5/95 wt%) separation factor of 591. Our study unveils the influence of membrane thickness on organic liquid separation, suggesting that broadened applications of polycrystalline MOF membranes can be achieved simply by adjusting the crystal growth methods and relevant membrane fabrication procedures.