Surface enriched sulfonated polyarylene ether benzonitrile (SPEB) that enhances heavy metal removal from polyacrylonitrile (PAN) thin-film composite nanofiltration membranes

This study aims to develop a new strategy to fabricate nanofiltration (NF) membranes with high removal efficiency for heavy metal ions in wide acidic pH range. Unlike conventional polyacrylonitrile (PAN) based thin film composite (TFC) membranes that requires multiple coating steps, the new NF membrane was fabricated through direct interfacial polymerization with positively charged polyethyleneimine (PEI) on PAN substrates blended with sulfonated polyarylene ether benzonitrile (SPEB). The unique surface migration effect of SPEB led to a smoother, more hydrophilic surface and sponge-like structure of the substrate. Such a modified structure was found to be crucial to achieve smaller pore size as well as better adhesion of the selective layer and the substrate of the modified TFC membrane. The resultant NF membrane has a reasonably high pure water permeability of 7.62 ± 0.81 LMH·bar⁻¹, and a molecular weight cut-off of 300 Da. It achieved a reasonably high rejection towards heavy metal cations such as Pb²⁺, Cd²⁺, Ni²⁺ over 93.0% in a wide acidic pH range. This work may provide insightful guidelines for upgrading current NF membranes for heavy metal removals in harsh acidic environments.