Design of nanofiltration (NF) hollow fiber membranes made from functionalized bore fluids containing polyethyleneimine (PEI) for heavy metal removal

Effective methods are still lacking for large-scale production of thin-film composite (TFC) hollow fiber membranes made from interfacial polymerization. It is the bottleneck limiting the scale-up of TFC nanofiltration (NF) hollow fiber membranes for wastewater treatments. This study fills the niche in NF hollow fiber production by simplifying the interfacial polymerization process while maintaining the membrane's salt rejection. By blending sulfonated polysulfone (SPSf) in the polyethersulfone (PES) dope solution and using polyethyleneimine (PEI) in the bore fluid for hollow fiber production, amine groups are actively introduced onto membranes. The amine groups can be further modified with various molecules, for instance, poly(acrylic acid) (PAA), glutaraldehyde (GA) and 1,3,5-benzebetricarbonyl chloride (TMC), resulting in precisely designed membranes suitable for heavy metal removal. The best membrane formed in this study has a small mean effective pore size (μp) of 0.57 nm, a molecular weight cut-off (MWCO) of 157 Da and a good pure water permeability (PWP) of 5.14 LMH/bar. It also has over 90% rejections of heavy metal ions, such as Ni2+, Zn2+ and Cu2+. The membrane displays good performance stability in a continuous 96-h operation and in acid washes. The study may provide useful insights in designing TFC NF hollow fiber membranes that are suitable for large-scale production.