Lignosulfonate-Coated ZIF‑8 as an Effective Nanofiller to Prepare High-Performance Thin-Film Nanocomposite Forward Osmosis Membrane for Heavy Metal Ions Removal

Metal–organic frameworks (MOFs) are most investigated for preparing effective forward osmosis (FO) membranes, mainly due to their uniform and highly adjustable pore sizes, high specific surface area, and good compatibility with polymers. In this study, we report an in situ method for the synthesis and coating of Zn-based MOF with sodium lignosulfonate (SL) to obtain a hydrophilic nanoparticle (ZIF-8@SL). The obtained nanoparticles were homogeneously dispersed into an aqueous media containing m-phenylenediamine (MPD) monomers and incorporated into the polyamide thin layer via interfacial polymerization. The SL coating assisted the ZIF-8 dispersion in the MPD solution, resulting in good compatibility between the nanofiller and the polyamide layer. Moreover, the effect of the ZIF-8@SL content on the membrane characteristics was thoroughly evaluated by various analysis methods. Also, the effect of the ZIF-8@SL content on the total FO performances of membranes was assessed. In comparison to the unmodified membrane, the TFN-ZSL800 membrane (thin-film nanocomposite membrane modified with 800 ppm ZIF-8@SL) under an optimal ZIF-8@SL concentration presented improved water flux, water permeability, and membrane selectivity. In addition, the high rejection of Cr3+ ions (98.8%) and Co2+ ions (98.3%) for the TFN-ZSL800 membrane confirms their superior heavy metal ions removal efficiency in the FO process.