Enhancing PPCP and salt separation in polyamide nanofiltration membranes with polydopamine and ZnO functionalized nanofiber support

Abstract

Achieving the removal of pharmaceuticals and personal care products (PPCPs) while selectively rejecting divalent cations like Ca²⁺ and Mg²⁺ without compromising water productivity and recovery remains a challenge for existing commercial nanofiltration (NF) membranes used in drinking water treatment. These challenges stem from the limited pore size and insufficient negatively charged surface density of conventional NF membrane. This study employed a polydopamine-coated nanofibrous membrane, uniformly embedded with in-situ grown ZnO nanoparticles, as a porous support layer. In the interfacial polymerization process, the fabricated substrate regulated the diffusion of aqueous monomers, thereby optimizing the polyamide layer on composite NF membrane with thinner thickness, stronger surface density, crumple structure and appropriate pore size. This resulting membrane demonstrated excellent PPCP rejection while maintaining high permeability to essential minerals. Under optimal conditions, the designed membrane achieved an impressive water flux at about 21 L m⁻² h⁻¹ bar⁻¹ and showed significant selectivity for PPCP and divalent cation, with diclofenac sodium rejection exceeding 90 % and Ca²⁺ rejection of below 20 %. The incorporation of ZnO nanoparticles enlarged the active filtration surface and created additional water pathways, resulting in a water permeation rate that was double that of a pristine NF membrane, without compromising PPCP/divalent cation selectivity. This work provides valuable insights and important correlations for developing NF membranes aimed at enhancing water production while preserving selectivity for PPCP/divalent cation.