Ultrathin surface-amination-modified membrane with ion-charge shielding effect for ultraselective nanofiltration

While membrane-based separation represents the preeminent technology for addressing the global challenge of water scarcity through desalination and potable wastewater reuse, existing nanofiltration membranes with monocharged surface properties remain deficient at achieving high-precision selectivity for harmful constituents with varying chargeability. In response to these issues, a membrane fabrication strategy was devised in this study to achieve ultraselective separation; essentially, a neutral-charged polyamide-based membrane was prepared by grafting of polyallylamine (PAA) onto the terminus of carboxylic nanochannels. The PAA monomers, which had controllable amine sites, were aligned at the membrane interface to neutralize the surface charge and minimize the pore size. The newly developed ultrathin (~23-nm thickness) surface-aminated membrane, with intensified ion-charge shielding and promoted size-exclusion effects, achieved remarkably precise separation property for a wide range of solutes, including near-perfect rejection of mixed-charge multivalent ions, near-complete removal of various trace emerging contaminants (ECs), and high boron retention (>74.7 %). The PAA-modified membrane demonstrated an exceptionally comprehensive desalination performance that exceeded the existing upper bound of ion permselectivity versus water permeability (14.2 L·m⁻²·h⁻¹·bar⁻¹), thereby surpassing state-of-the-art nanofiltration membranes.