Chlorine resistant polyamide desalination membrane prepared via organic-organic interfacial polymerization

Abstract

Desalination of seawater, brackish water and urban sewage is an important way to solve the global water shortage. Polyamide (PA) membranes, including reverse osmosis (RO) membrane and nanofiltration (NF) membrane, are the primary technology for seawater desalination and clean water production. However, traditional thin-film composite PA (TFC-PA) membranes prepared from interfacial polymerization (IP) of amine monomers (either piperazine or m-phenylenediamine) in water and acyl chloride monomers in organic solvent are incapable of tolerating strong acid and chlorine environment. Here, we develop a new IP process, which takes place at the immiscible interface between dimethylacetamide (DMAc) and hexane (referred to as organic/organic IP), to prepare both chlorine-resistant and acid-resistant TFC-PA membranes. Compared to conventional water/oil IP process, the organic/organic IP process can adapt more kinds of amine monomers rather than just PIP, such as tetra (4-aminophenyl) methane (TMAP), tris (4-aminophenyl) amine (TAPA), and 4,4′,4''-(1,3,5-triazine-2,4,6-triyl) triphenylamine (TTA), which we studied in this work, thereby extending the PA molecular structure and enabling the membranes with greatly improved chemical stability. Among them, the TAPM-based TFC-PA membrane exhibits a NaCl rejection of 95.9% and no obvious NaCl rejection deterioration after soaking in a high concentration of NaClO (1000 ppm, pH 7) for more than 30 h, indicating excellent chlorine resistance. The TTA-based TFC-PA membrane shows a Na2SO4 rejection of 97% and remains unchanged after being exposed to a wide pH scan of 2–12. The Organic/organic IP provides a new and easy-to-operate platform for designing chlorine and acid resistant TFC-PA membranes, which will greatly improve their environmental stability as the most advanced desalination membrane at present.