Oriented ionic covalent organic framework membranes for efficient organic solvent nanofiltration

Developing effective organic solvent nanofiltration (OSN) membranes to separate molecular solutes from organic solvents is highly desired yet requires a suitable material platform and an in-depth investigation of membrane selectivity. Herein, an oriented ionic covalent organic framework membrane (oi-COM) was fabricated, which features well-ordered channels that are vertically aligned towards the membrane surface and lined with abundant sulfonate groups. Filtration experiments of multifarious organic solvents and solutes with different charges and molecular sizes were conducted. The oi-COM exhibited above 99% rejection for negatively charged dye (Evans blue), much higher than that for positively charged dye with similar molecular size, while maintaining high solvent permeance for ethanol of 63 L m−2 h−1 bar−1. These results demonstrated the significance of electrostatic repulsion effect in membrane selectivity, providing insights for the design of high-performance OSN membranes. Oriented ionic COF nanosheet membranes are fabricated, which demonstrate high organic solvent nanofiltration performance and charge-controlled molecular separation. [Display omitted] •Oriented ionic COF nanosheet membranes were fabricated and applied to organic solvent nanofiltration.•The membranes displayed well-defined, vertically aligned and high-density charged channels.•The membranes exhibited excellent solvent permeance for ethanol of 63 L m−2 h−1 bar−1.•The membranes exhibited