Custom-tailoring zwitterion-based nanofiltration membranes for organic molecule desalination with sub-200 Da molecular weight

Organic molecule desalination with nanofiltration has important practical application significance. Zwitterion-based nanofiltration membranes (ZNFMs) with selective channels for monovalent salts have been prepared to improve the separation performance. However, most ZNFMs tend to be restricted by their loose structures, which results in unsatisfactory rejection for small molecules with sub-200 Da molecular weight. In this study, a synchronous modification strategy during the heat treatment of interfacial polymerization was proposed, in which various multi-amine solutions were employed as the novel medium of heat treatment to regulate the structures of ZNFMs. The pore size distribution of membranes could be narrowed to a certain degree through cross-linking by corresponding multi-amines. The optimized ZNFMs exhibited excellent retention to small molecules. For example, the retention of glucose was dramatically increased to 96.5%. Meanwhile, the ZNFMs also had low rejection for monovalent salts, such as KCl (26.7 %). Consequently, the separation factor between glucose and KCl reached 21.2, which demonstrated a great potential for organic molecule desalination with sub-200 Da molecular weight.