CF3-functionalized polyamide layers enhancing solvent permeability of polyimide-based organic solvent nanofiltration membranes for pharmaceutical separation

An organic solvent nanofiltration (OSN) membrane was fabricated through interfacial polymerization (IP) to form a selective layer containing hydrophilic amide (–CONH–) and hydrophobic trifluoromethyl (–CF 3 ) groups on a polyimide (PI) substrate. Piperazine (PIP) and 5-trifluoromethyl-1,3-phenylenediamine (TFMPD) were employed as aqueous phase monomers, reacting with trimesoyl chloride (TMC) in the organic phase. The effects of TFMPD incorporation on the chemical structure, morphology, surface properties, separation performance, and stability of the membranes were systematically investigated. The results revealed that the competitive reaction between TFMPD and PIP led to a thinner selective layer with reduced cross-linking degree, thereby enhancing solvent permeance while maintaining consistent pharmaceutical rejection. Specifically, the introduction of –CF 3 groups improved non-polar solvent transport, achieving a 3.2-fold increase in n-hexane permeance. After 91 days of immersion in N , N -dimethylformamide (DMF), the membrane retained ~94 % rifampicin (RFP) rejection and maintained an ethanol/water permeance of ~4.5 L·m −2 ·h −1 ·bar −1 . This work demonstrates a rational design strategy for developing solvent-resistant OSN membranes with balanced permeability-selectivity-stability for pharmaceutical separation in organic solvents.