Evolution of smart nanofiltration membranes: from traditional modification to intelligent precise filtration

As a novel class of functional separation media, smart nanofiltration (NF) membranes are capable of dynamically regulating separation performance upon external environmental stimuli, enabling intelligent and precise filtration with high efficiency. Unlike traditional static NF membranes with fixed, unadjustable separation capacity, such smart membranes offer unique advantages in tunability. Faced with global water scarcity and the growing pressure of industrial wastewater remediation, research communities across the globe have significantly expanded research and development investment in smart NF membranes in recent years. This review systematically summarizes mainstream modification strategies of smart NF membranes, typical stimuli-responsive categories, as well as their practical engineering applications. Five dominant modification techniques, including surface grafting, interfacial polymerization, blending modification, surface coating, and layer-by-layer self-assembly are elaborated, with their respective advantages and drawbacks in practical industrial scenarios comprehensively summarized. In terms of responsive behaviors, five mainstream stimuli-responsive modes are illustrated, along with representative membrane materials corresponding to each responsive type. The state-of-the-art applications and inherent bottlenecks of stimuli-responsive NF membranes are thoroughly discussed. In addition, the emerging multi-stimuli response and its existing application scenarios are also introduced. Finally, this work identifies critical bottlenecks restricting the further industrial translation of smart NF membranes and proposes targeted optimization strategies. We anticipate that smart NF membranes will provide viable solutions to diverse water pollution challenges and deliver prominent advances in resource recovery, precise ion separation, and sustainable industrial circulation in future practical processes.