SDS Induces the Cross-Linking of PEI Molecules by Electrostatic Attraction to Prepare PVDF Ultrafiltration Membrane

In this study, PVDF/SMA membranes were fabricated via non-solvent induced phase separation(NIPS), followed by grafting of polyethyleneimine (PEI) onto the membrane surface through reaction with the anhydride groups of SMA, yielding PVDF/SMA-PEI membranes. Owing to the considerable free volume of PEI chains, stacking tends to occur during cross-linking with SMA, resulting in a loose selective layer and poor retention of small- to medium-sized dye molecules. To address this, the small-molecule additive sodium dodecyl sulfate (SDS) was introduced into the PEI solution. The electrostatic interaction between the sulfate ions of SDS and PEI promotes a more uniform distribution of PEI on the membrane surface, reducing inter-chain aggregation and forming a denser selective layer. The resulting PEI-SDS membrane maintained a high pure-water flux of 220 L/m 2 ·h while achieving methyl blue, indigo carmine, and acid fuchsin rejection rates of 98.86%, 99.57%, and 86.77%, respectively. In conclusion, this work provides a simple method for preparing highly efficient positively charged membranes for dye removal.