Designed water channels and sieving effect for heavy metal removal by a novel silica-poly(ionic liquid) nanoparticles TFN membrane

Thin film nanocomposite membranes have become a feasible technology for heavy metal wastewater treatment. However, how to enhance the dispersibility and compatibility of nanomaterials in the selective layer is an important issue to improve the membrane performance of heavy metal removal. In this study, silica-poly(ionic liquid) nanoparticles were incorporated in the selective layer of TFN membranes. 1-Allyl-3-methyl imidazolium hexafluorophosphate ([AMIm]PF 6 ) was selected to modify silica (SiO 2 ) particles. The formed poly([AMIm]+) brushes provided charge properties to enhance dispersibility and organic part to improve compatibility in the polyamide layer of NF membranes. The resultant TFN membranes incorporated with SiO 2 -[AMIm]PF 6 particles exhibited an increment of 34% water permeation and 41.6% MgCl 2 rejection. Moreover, with an average rejection improvement of around 15% for heavy metal ions at pH = 5–6, the SiO 2 -[AMIm]PF 6 /PA membrane showed its superiority beyond the PA membrane. The electropositivity and microporous structure of the SiO 2 -[AMIm]PF 6 particles enhanced their dispersibility and compatibility in the polyamide layer. Meanwhile, the proper pore size and structure of the SiO 2 -[AMIm]PF 6 particles contributed to the channels for water transport and the sieving effect for most heavy metal ions. This work may facilitate the applications of TFN membranes in heavy metal wastewater treatment to alleviate the “trade-off” phenomenon. • Ionic liquid was polymerized on the SiO 2 to enhance its dispersity and electropositivity. • SiO 2 -[AMIm]PF 6 offered channels to lift water flux and divalent cation selectivity. • SiO 2 -[AMIm]PF 6 /PA membrane could reject over 97% of Cu 2+ , Ni 2+ , Cd 2+ , Zn 2+ . • Low pH, SO 4 2− as anion, or low ionic strength was beneficial for heavy metal removal.