A Cross-Linking Modification toward a High-Performance Polyimide Nanofiltration Membrane for Efficient Desalination

The performance of a cross-linked polyimide (PI) nanofiltration membrane was assessed by interfacial polymerization (IP) combined with the chemical imidization method. With the IP process with m-phenylenediamine and pyromellitic chloride monomers, trimesoyl chloride (TMC) for cross-linking, and the subsequent chemical imidization process, a PI thin film composite (TFC) nanofiltration (NF) membrane was prepared. The results showed that the PI TFC membrane had a high flux of ∼9.13 L m–2 h–1 bar–1 at 4 bar. The effects of the amount of cross-linking agent and reaction time on the NF membranes' nanofiltration performance were systematically investigated. We selected a CaSO4 salt solution to evaluate the performance of the nanofiltration membrane because the PI TFC nanofiltration membrane's molecular weight cutoff was in the range of 600–800 Da. The PI membrane rejection to CaSO4 aqueous solution under the optimal preparation conditions reached 93%. When the FCF/water, FCF/DMF, and FCF/ethanol solutions were filtered, the TMC cross-linked PI TFC membrane exhibited a <8% solvent permeation decline but FCF rejection remained at 98%. The PI TFC membrane maintained permeability and salt rejection during the 120 h filtration.