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.