Amphoteric composite membranes for nanofiltration prepared from sulfated chitosan crosslinked with hexamethylene diisocyanate

• Thin-film amphoteric composite (TFC) NF membranes.
• Cross-linking sulfated chitosan (SCS) with hexamethylene diisocyanate (HDI).
• Rejection performance dependent on pH value of feed solution.
• Rejection order to inorganic salts solutions.

A novel kind of amphoteric composite nanofiltration (NF) membranes were prepared via the method of coating and crosslinking, using an amphoteric derivative of chitosan, i.e. sulfated chitosan (SCS), as the active layer material, poly (acrylonitrile) (PAN) ultrafiltration (UF) membrane and hexamethylene diisocyanate (HDI) as the support membrane and crosslinker, respectively. The chemical structure of the resultant membrane was characterized with attenuated total reflection infrared spectroscopy (ATR-IR), revealing the reaction of hydroxyl groups and amino groups with HDI. The rejection properties of the developed composite membranes could be adjusted by changing the composition of the casting solution of the active layer and the preparing technique. The rejection performance to salt was dependent on the pH value of the feed solutions, and reached the minimum as the pH value of feed solution was equal to the isoeletric point (pI) of SCS. The rejection to different inorganic salts decreased in the order of K2SO4, Na2SO4, MgSO4, KCl, NaCl, and MgCl2.