Preparation and performance of a charge-mosaic nanofiltration membrane with novel salt concentration sensitivity for the separation of salts and dyes

Abstract In this research, l -lysine was adopted as a new aqueous monomer to react with 1,3,5-benzenetricarbonyl trichloride (TMC) for the preparation of polyamide thin-film composite (PA TFC) membrane (denoted as l -lysine TFC membrane in our research) via interfacial polymerization method. A novel salt concentration sensitive charge-mosaic nanofiltration membrane for the separation of salts and dyes was prepared. The chemical properties, morphologies, surface properties, permeability and selectivity of the l -lysine TFC membranes were carefully investigated. Surprisingly, the l -lysine TFC membranes showed very high separating efficiency to salts/dyes mixtures (above 99.2% for Naphthol green B retention and 2.75% for NaCl rejection), and an unusual salt concentration sensitivity, i.e. the water flux of the l -lysine TFC membrane significantly increased along with the increase of salt concentration of the feed solution, maximized to 13.05 times larger compared with its pure water flux in this research (36.15 L/m2 h bar compared with 2.77 L/m2 h bar). The salt concentration sensitivity was verified during over 30 cycles of repeated test. This novel membrane might have potential application in many areas, such as the separation of salts and dyes in textile industry or pre-treatment for the desalination or purification. Moreover, a series of experiments including molecular weight cut-off, ionic exchange capacity measurement and permeability test were carefully designed and performed to explore the mechanism of the interesting salt concentration sensitivity of the membrane. A possible mechanism was proposed.