Fig. 4: Ion transport performance and molecular interactions of NML-Qx-NH2 Membranes.
From: Monovalent anion-selective membranes fabricated via in situ interfacial polymerization
a Current-voltage (I−V) curves of NML-Qx and NML-Qx-NH₂ membranes, illustrating the impact of surface functionalization on conductivity. b Schematic representation of the ED setup using NML-Qx-NH2 membranes for selective separation of ions. The ED setup consists of two CEMs on either side of a central NML-Qx-NH2 membrane with a membrane area of 7.07 cm2. Ion transport is driven by an applied current density of 5 mA cm−2. The electrolyte used is 0.3 mol L−1 Na2SO4, with feed solutions of 0.1 mol L−1 NaCl/Na2SO4, and 0.01 mol L−1 KNO3 (except for NO3− tests, where deionized water is used). and (c, d) Ion flux and selectivity (S) for Cl⁻ and SO42− using NML-Qx and NML-Qx-NH2 membranes. The modified membranes show higher Cl⁻ flux and significantly enhanced Cl⁻/SO42− selectivity, demonstrating the effect of surface modification on monovalent ion transport. e Hydration energy versus ionic radius for F⁻, Cl⁻, Br⁻, NO3⁻, and SO42−, revealing the correlation between hydration properties and transport behavior. f Free energy profiles as a function of distance from the polymer center, showing preferential interaction zones for Na⁺, Cl⁻, and SO42− ions. Ion and water behavior in a polymer environment from MD simulations. g Radial distribution functions (G(r)) for SO₄²⁻ with different atomic groups, highlighting differential ion-polymer interactions. h Radial distribution functions (G(r)) for Cl⁻ with different atomic groups in the polymer, indicating specific interactions. i Comparison of Cl⁻/SO₄²⁻ selectivity normalized to ion flux for NML-Qx-NH₂ membranes with other reported membranes, demonstrating the high selectivity and transport efficiency achieved in this work.
