Unraveling the transport mechanism of trace organic compounds through loose nanofiltration membranes

Loose nanofiltration (LNF) membranes have demonstrated exceptional efficacy in removing trace organic pollutants (TrOCs) due to their distinctive structure and efficient solute transport characteristics. Despite significant advancements, the mechanism underlying solute transport within LNF membranes remain to be further elucidated. In this study, the Donnan-Steric Pore Model with Dielectric Exclusion (DSPM-DE) was employed to predict the selectivity and permeability of customized LNF membranes, with these theoretical predictions substantiated through filtration experiments utilizing particles of diverse sizes and charges. The observations reveal that when the pore size considerably exceeds the ionic sizes, the selective transport of organic pollutants and charged ions is predominantly governed by size exclusion rather than electrostatic repulsion. Moreover, in the selective transport of neutral and charged organic pollutants, charged pollutants are preferentially intercepted via electrostatic repulsion, whereas neutral pollutants are primarily influenced by convection and diffusion processes, resulting in partial interception. In addition, the ionization degree of organic substances directly affects the contribution of electrical migration to the retention rate. These observations will provide critical insights into the key solute mass transport processes for the efficient removal of TrOCs using LNF membranes.