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Molecular-level understanding of ion–membrane interactions in polyamide nanofiltration systems.

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Title: Molecular-level understanding of ion–membrane interactions in polyamide nanofiltration systems.
Authors: Neyband, Razieh Sadat1 (AUTHOR) Rneyband@gmail.com
Source: Journal of Polymer Research. Jun2026, Vol. 33 Issue 6, p1-20. 20p.
Subjects: Polyamide membranes, Electrostatic interaction, Quantum chemistry, Ion-permeable membranes, Hydrogen bonding, Density functional theory, Adsorption (Chemistry)
Abstract: Polyamide thin-film composite (PA-TFC) membranes, particularly those based on poly (piperazine amide), are widely employed in nanofiltration due to their high separation efficiency and intrinsic negative charge. However, the molecular-scale origins of ion selectivity in these charged polymeric membranes remain insufficiently understood. In this work, Density Functional Theory (DFT) calculations were performed to investigate the interactions between a representative polyamide membrane fragment and common inorganic ions (Mg2⁺, Ca2⁺, Na⁺, and K⁺), considering both chloride and sulfate counterions. All calculations were carried out at the M06-2X/6–311 + G** level of theory to evaluate adsorption energies and elucidate the role of ionic charge density in ion–membrane interactions. The results demonstrate a strong correlation between cation–membrane interaction energies and cationic charge potential, highlighting electrostatic interactions as the dominant driving force for cation adsorption. In contrast, anion interactions (Cl⁻ and SO₄2⁻) are primarily governed by hydrogen bonding with functional groups within the polyamide matrix. Moreover, in systems containing both cations and anions, a cooperative interaction energy parameter (Ecoop) was introduced to quantify ion-pair effects. Negative Ecoop​ values indicate a synergistic enhancement of ion–membrane interactions arising from coupled cation–anion binding. Overall, this quantum chemical study provides molecular-level insights into ion–polymer interactions and establishes a theoretical framework linking membrane chemistry to ion selectivity, offering guidance for the rational design of advanced nanofiltration membranes. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:Polyamide thin-film composite (PA-TFC) membranes, particularly those based on poly (piperazine amide), are widely employed in nanofiltration due to their high separation efficiency and intrinsic negative charge. However, the molecular-scale origins of ion selectivity in these charged polymeric membranes remain insufficiently understood. In this work, Density Functional Theory (DFT) calculations were performed to investigate the interactions between a representative polyamide membrane fragment and common inorganic ions (Mg2⁺, Ca2⁺, Na⁺, and K⁺), considering both chloride and sulfate counterions. All calculations were carried out at the M06-2X/6–311 + G** level of theory to evaluate adsorption energies and elucidate the role of ionic charge density in ion–membrane interactions. The results demonstrate a strong correlation between cation–membrane interaction energies and cationic charge potential, highlighting electrostatic interactions as the dominant driving force for cation adsorption. In contrast, anion interactions (Cl⁻ and SO₄2⁻) are primarily governed by hydrogen bonding with functional groups within the polyamide matrix. Moreover, in systems containing both cations and anions, a cooperative interaction energy parameter (Ecoop) was introduced to quantify ion-pair effects. Negative Ecoop​ values indicate a synergistic enhancement of ion–membrane interactions arising from coupled cation–anion binding. Overall, this quantum chemical study provides molecular-level insights into ion–polymer interactions and establishes a theoretical framework linking membrane chemistry to ion selectivity, offering guidance for the rational design of advanced nanofiltration membranes. [ABSTRACT FROM AUTHOR]
ISSN:10229760
DOI:10.1007/s10965-026-04964-w