Ion selective metal-phenolic network nanofiltration membranes: The role of counterions and predictive modeling

The development of high flux, selective and sustainable thin-film composite (TFC) membranes for nanofiltration (NF) is critical in addressing water purification challenges. In this work, a thin metal-phenolic network (MPN) selective layer was deposited on a porous support via a facile and scalable process, presenting a sustainable and efficient pathway for developing TFC membranes tailored for NF applications in water treatment and desalination. Here we explored the ion rejection and ion selectivity of MPN membranes for various complex feed solutions. Comprehensive characterization to determine the rejection performance of the MPN selective layer for single and mixed salt solutions, including NaCl, Na 2 SO 4 , MgCl 2 , and MgSO 4 are investigated. Furthermore, the application of the Donnan Steric Pore Model with Dielectric Exclusion (DSPM-DE) to predict the ion rejection and elucidate the transport and exclusion phenomena by a tannic acid (TA)-Fe 3+ separation layer is explored. The findings reveal that the TA-Fe 3+ selective layers exhibit excellent retention performance towards various salts, demonstrating the formation of a dense structure with higher retention with increasing Fe 3+ concentration of the casting solution. The TFC membranes exhibited up to 99 % Na 2 SO 4 , 92 % NaCl, 96 % MgSO 4 and 81 % MgCl 2 retentions during single salt filtration tests, indicating a strong potential for high performance nanofiltration or desalting applications. Detailed analysis of the mixed salt retention properties of the MPN membranes highlights a considerable and selectivities by the TA-Fe 3+ membranes. Computational elucidation using the DSPM-DE model indeed predicts the retention performance of ternary ion as well as quaternary ion mixtures, identifying dielectric and Donnan exclusions as key mechanisms for ion partitioning at the membrane-solution interface. • Study of salt retention and ion-ion separation behavior of TA-Fe 3+ TFC membranes. • Influence of counter ions on monovalent/divalent selectivity using MPN membranes. • and decrease in multi-ionic systems compared to ternary ion mixtures. • Elucidation of exclusion and mass transport mechanisms using DSPM-DE model. • Diffusion and convection control the anion and cation transport, respectively.