Enhancing hardwater treatment using ultra-loose nanofiltration membranes modified with novel MOF nanoparticles

Nanomaterial incorporation has emerged as a powerful strategy to tune membrane permeability, selectivity and durability. In this study, ultra-loose polyamide nanofiltration membranes were fabricated by interfacial polymerisation of m -phenylenediamine and trimesoyl chloride on a commercial polyacrylonitrile substrate. Different configurations of UiO-66-NH₂ and ZIF-8-NH₂ nanoparticles were incorporated. Before membrane fabrication, nanoparticles characterization techniques confirmed nanoparticle synthesis and polyamide formation, and evaluated how nanoparticle type, configuration, and concentration influenced morphology, hydrophilicity, pore size, and separation. The aim was to understand how these structural modifications affect water permeability and hardness removal from surface waters. Active layer morphology and roughness differed clearly between configurations: membranes with nanoparticles in the interlayer had more irregular, textured surfaces, while those with nanoparticles in the active layer were smoother with visible particle deposition. ZIF-8-NH₂–modified membranes were more hydrophilic (contact angle 52°) than those with UiO-66-NH₂ (71°). All membranes had similar zeta-potential behaviour with isoelectric point (IEP) near pH 4.7, except M5—which combined ZIF-8-NH₂ in the active layer and UiO-66-NH₂ in the interlayer—showing lower IEP (pH 3.7), more negative surface charge, and the best overall performance. In addition, M5 increased permeability from 0.16 to 3.20 L/m 2 ·h·bar and substantially improved ion rejection—Mg 2+ by 107%, Ca 2+ by 137%, and SO₄ 2− by 101% compared with the control membrane. In addition, the average pore size was reduced by 26% and hydrophilicity was enhanced, lowering the contact angle from 86° to 40°. Overall, these improvements highlight the promise of modified NF membranes for efficient hardness removal in drinking water treatment.