Novel tight ultrafiltration membrane with uniform pore size and ultra-high permeability designed by ionic liquid induced in-pore interfacial polymerization

The separation of dyes and salts in printing and dyeing wastewater is crucial for the recovery of valuable resource. Loose nanofiltration (LNF) membranes, which can achieve the separation of dye/salt, usually have relatively lower water permeability due to the presence of dense and thick polyamide (PA) layer on top of the polysulfone (PSf) ultrafiltration membrane. Compared to LNF membranes, tight ultrafiltration (TUF) membranes with uniform pore size and distribution will be helpful for the improvement of permeability and achieve the goal for dye/salt separation. Here, novel TUF membrane is designed by regulation of interfacial polymerization (IP) process via the introduction of ionic liquid 1-Hexyl-3-methylimidazolium chloride (HMIC) as co-solvent in aqueous phase. The π-π interaction between HMIC and monomers effectively slow down the diffusion rate, leading to the in-pore IP reaction resulting in narrowed pore size and distribution compared to the original PSf membrane, instead of the formation dense and thick PA layers on top of the PSf membrane. As a result, the resultant TUF membrane with PA located in the pore of PSf membrane possesses smaller pore size ∼10 nm and higher water permeability. The prepared TUF-40 membrane exhibits excellent separation performance with water flux up to 371.25 L m -2 h -1 , together with Congo Red (CR) rejection of 99.00% and highest dye/salt selectivity of 15.79. In addition, the TUF-40 membrane exhibits outstanding antifouling performance, with a flux recovery rate (FRR) of 82.99%, which will be benefit for the application in treating the dyeing wastewater.