Fully aromatic fluorinated polyamide nanofiltration membranes formed at gas/liquid interfaces with ultrafast nonpolar organic solvent permeance

Fully aromatic fluorinated polyamide nanofiltration membranes are manifesting the great potential in organic solvent nanofiltration (OSN) especially for their excellent structural stability when exposed to solvents and enhanced nonpolar organic solvent permeance compared with the conventional polyamide membranes. However, the fluorinated amino monomers are difficult to be dissolved in water that impedes the large-scale manufacture of fluorinated polyamide selective layers via the typical interfacial polymerization at the water-alkane interfaces. Herein, we report a straightforward and effective strategy for fabricating aromatic fluorinated polyamide nanofiltration membranes at gas/liquid interfaces while hydrophobic 2,2-bis(4-aminophenyl)hexafluoropropane gases and trimesoyl chloride solutions are selected as the gas and liquid phases, respectively. The obtained membranes show outstanding hydrophobicity with water contact angles of 92°, which is beneficial for the nonpolar organic solvent permeance. The molecular dynamics simulations could also prove that the fluorine-containing groups exhibit much lower absolute interaction energies with the nonpolar solvents compared with those of polar ones. Therefore, our membranes demonstrate an extremely high n-hexane permeance of 21.52 L m −2  h −1 ·bar −1 while maintaining a low MWCO of approximately 452 Da. Moreover, the high fluorine contents endow the membranes with good stability resulting in almost unchanged rejection and permeance during long-term operation.