In Situ Real‐Time Quantitative Characterization of Nanofiltration Membrane Pore Orientation for Enhanced Ion Separation

Abstract Nanofiltration membranes hold great promise for ion separation but often suffer from a trade‐off between selectivity and flux, limiting their use in precise separation processes. A key challenge is achieving precise control over pore orientation, as existing methods fail to provide real‐time, quantitative insights for optimizing membrane structure and performance. To address this, an innovative in situ, real‐time quantitative technique is developed that links pore alignment directly to separation efficiency. Using β‐cyclodextrin as a model pore‐forming compound, fluorescent labeling enables continuous monitoring of pore orientation and distribution during membrane fabrication. This method enables the capture of the complete distribution of pore orientation across the entire membrane surface, allowing for precise adjustments in membrane design. This approach provides the real‐time quantification of pore alignment, facilitating the design of NF membranes with enhanced ion selectivity and permeability. The optimized membranes demonstrate exceptional Mg 2+ /Li + separation efficiency, with a separation factor of 15.55 and permeance of 35.85 L m −2 h −1 bar −1 , representing a significant step forward in high‐performance nanofiltration membranes with broad applications in resource recovery, environmental remediation, and water treatment.