Interfacial Engineering of Thin-Film Composite Membranes with Polyoxometalates as Salt Additives for High-Efficiency Forward Osmosis

Forward osmosis (FO) is an emerging low-energy membrane separation process for wastewater treatment, yet its efficiency is constrained by the inherent permeability-selectivity trade-off and membrane fouling. Polyoxometalates (POMs), featured with discrete crystalline structures ranging from subnanometers to tens of nanometers, have been frequently used as nanomaterial building blocks. This study explored their novel application as salt additives to modify thin-film composite membranes. The process involved constructing a hydrophilic interface through a simple, mild coating strategy that stabilized subsequent interfacial polymerization, leading to significantly enhanced FO performance with robust antifouling properties. The optimized forward osmosis process achieved a 50% increase in the water flux with minimal reverse salt flux. Long-term fouling tests demonstrated exceptional antifouling properties, with only 30% flux decline, indicating strong fouling resistance. The underlying mechanism was investigated through a comprehensive suite of techniques, including SEM, AFM, XPS, FTIR, contact angle, zeta potential, and EIS with equivalent circuit analysis. The results revealed that unlike conventional salt additives that often leach out during processing, POMs were retained in the membrane structure via electrostatic interactions and optimized interfacial properties and membrane performances by imparting superior hydrophilicity and negative surface charge. This strategy provides a low-cost, readily scalable fabrication route that advances the FO performance and supports the sustainable development of membrane technologies.