Composite nanofiltration membranes with PEI/SBE-β-CD interlayer: Preparation and desalination performance

To tackle the challenge of achieving high rejection for both divalent cations and anions simultaneously in polyamide membranes for desalination, a novel composite nanofiltration membrane (PES-PEI/SBE-β-CD-PA) was developed in this study. The membrane was fabricated by incorporating a layer-by-layer (LBL) self-assembled interlayer of polyethyleneimine (PEI) and sulfobutyl ether-β-cyclodextrin (SBE-β-CD), followed by interfacial polymerization (IP) to form the PA selective layer. The SBE-β-CD, leveraging its sulfonate groups and cavity structure, facilitated the enrichment and modulated diffusion of piperazine (PIP), enabling a significantly thinned (126 nm, down from the original 297 nm), defect-free PA layer with strong negative charge (−28.93 mV). The optimized membrane, relying on the synergistic mechanism of Donnan exclusion (electrostatic interaction) and steric hindrance, achieved a high pure water permeance of 15.42 L·m −2 ·h −1 ·bar −1 and excellent salt rejection performance of 98.41 %, 97.98 %, 91.81 %, 90.10 % and 54.28 % for Na 2 SO 4 , MgSO 4 , MgCl 2 , CaCl 2 and NaCl respectively, which is competitive compared to the state-of-the-art membranes. Moreover, the composite membrane maintained stable desalination performance over 72 h of continuous operation. This work demonstrates a promising strategy for fabricating high-performance desalination membranes through the construction of a hydrophilic LBL interlayer, offering potential applications in seawater and brackish water desalination.