Interfacial Engineering of Sulfonated Polyethersulfone/ZIF-8 Forward Osmosis Membranes: Applying Sulfonation and Interlayers for Enhanced Desalination Performance

This study explores the strategic synthesis of sulfonated polyethersulfone (SPES) with tunable sulfonation degrees to engineer selective interfacial layers (SLs) for thin-film composite (TFC) forward osmosis (FO) membranes. To overcome the persistent trade-off between water permeability and salt rejection in conventional TFC membranes, this work introduces an interlayer engineering strategy utilizing zeolitic imidazolate framework-8 nanoparticles (ZIF-8 NPs). Unlike traditional approaches that focus solely on membrane surface modification, the integration of ZIF-8 as a nanostructured interlayer addresses interfacial defects and enhances solute screening by leveraging its molecular sieving capabilities and hydrophilicity through the Janus membrane effect. SPES-based membranes exhibited a notable enhancement for water flux from 15.23 to 32.12 L/m² h compared to neat polyethersulfone (PES) SLs. Simultaneously, the salt rejection effectively reached 93.9% for SPES/ZIF-8/PA(#2). XRD and FTIR analyses confirmed the crystallinity and chemical integrity of ZIF-8 NPs, while FESEM revealed their uniform dispersion across the SL surface. Notably, the sulfonation process not only enhanced surface porosity but also created a chemically reactive interface for ZIF-8 anchoring, a dual-functionality rarely achieved in prior studies. The findings offer a scalable framework for designing high-performance TFC membranes with hierarchically engineered interfaces, paving the way for next-generation desalination and resource recovery systems.