Preparation of positively charged composite nanofiltration membranes by quaternization crosslinking for precise molecular and ionic separations

Preparation route of positively charged PVI/PSF composite NF membranes. [Display omitted] Developing nanofiltration (NF) membranes with highly efficient and precise separation ability is of great significance for the molecular and ionic separations. In this work, positively charged composite NF membranes were engineered via soaking of polysulfone (PSF) ultrafiltration membranes in poly(N-vinyl imidazole) (PVI) solutions followed by a quaternization crosslinking step. The PVI was firmly attached to the PSF membrane by this method and acted as an active separation layer of the composite NF membrane. The obtained composite NF membrane featured a high rejection (83%) to vitamin B12 (molecular radius: 0.74 nm) but a low rejection (24.6%) to vitamin B2 (molecular radius: 0.47 nm), exhibiting a great potential in precisely molecular separation. Furthermore, the ionic separation ability of the composite NF membrane was confirmed with a rejection order of Na2SO4