The effect of dielectric exclusion on the rejection performance of inhomogeneously charged polyamide nanofiltration membranes

Nanofiltration has been applied as a promising way in water treatment because of its special separation mechanisms. As the main class of nanofiltration membranes available on the market, most thin-film polyamide nanofiltration membranes obtained by interfacial polymerization possess active layer containing amine and carboxylic acid groups that are distributed in a highly non-uniform fashion, leading to an inhomogeneous fixed charge distribution. This feature has been reported only under consideration of steric hindrance and electric repulsion while the intensity of dielectric exclusion is worth being taken into account. The primary objective of this work was to investigate the influence of dielectric exclusion on the relationship between fixed charge distribution and electrolyte rejection performance. CaCl₂ rejection rate has been computed as a function of different dielectric constants inside the pore for various inhomogeneous charge distributions with an identical average volume charge density. Electric field behavior and ion concentration distribution inside the nanopore reflect that the variation of dielectric effect affects the repulsive force to co-ions so that the electrolyte rejection performance has been changed. The simulations performed in this work supplement the theoretical research of nanofiltration separation mechanism to support the accuracy of rejection performance prediction and the results drawn in this work are beneficial for the comprehension of fixed charge distribution and dielectric effect.