Modification of nanofiltration membranes using beta-cyclodextrin derivatives with different functional groups for enhanced removal of organic micropollutants

Abstract

Simultaneous enhancement in the removal of organic micropollutants (OMPs) and water permeance is highly desirable for nanofiltration (NF)-based drinking water treatment. This study employed two cyclodextrin derivatives with different functional groups, i.e., (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD) and sulfobutylether-β-cyclodextrin (SBECD), as aqueous additives for polyamide (PA) membrane fabrication. Characterization results revealed that HP-β-CD tended to enrich piperazine (PIP) monomers through hydrogen bonding, resulting in a thin but dense PA layer. Conversely, SBECD moderated PIP diffusion through electrostatic forces and steric hindrance, participated more in the interfacial polymerization reaction and yielded an active layer with a coexistence of polyester and polyamide. Both the CD derivative modified membranes exhibited improved surface hydrophilicity, enhanced roughness, and reduced active layer thickness, leading to over 60 % water permeance improvement without the obvious variation of pore size. This enabled the optimal membranes, especially the HP-β-CD incorporated one, highly advantageous in overcoming the trade-off effect between water permeance and OMP rejection. Meanwhile, the strongly negatively charged SBECD modified membrane showed reduced rejections for divalent cations, making it more resistant to scaling. This study offers an efficient approach to tailoring membrane water/solute selectivity and solute/solute selectivity, which has great potential in NF membrane development for drinking water treatment.