Construction of Self-Assembled Nanofiltration Membranes Based on TA/PEI Interlayer and Performance Study

To overcome the chemical inertness of polyethersulfone (PES) flat-sheet membrane surfaces and expand their application in printing and dyeing wastewater filtration, a PES flat-sheet membrane was prepared as a support membrane using PES as the membrane-forming polymer and zinc oxide (ZnO) as the modifier. A tannic acid/polyethyleneimine (TA/PEI) interlayer was constructed on the support membrane via co-deposition. Polyethyleneimine/sodium alginate (PEI/SA) polyelectrolyte multilayers were then self-assembled layer-by-layer on the interlayer. A self-assembled composite nanofiltration membrane was also prepared. SEM, AFM, FTIR, XPS, a water contact angle goniometer, and a cross-flow filtration apparatus were used to study the effects of the TA/PEI mass ratio and deposition time on the micromorphology, chemical composition, hydrophilicity, separation performance, and stability of the nanofiltration membrane. The results show that, at a TA/PEI mass ratio of 1:1 and a deposition time of 2 h, the interlayer completely covered the substrate and provided stable chemical anchoring sites for subsequent layer-by-layer (LbL) self-assembly. The resulting T1P1-2-L4 nanofiltration membrane has a water contact angle of 47.6 degrees, an average roughness of 14.5 nm, and a separation layer thickness of about 78.6 nm. Filtration tests show that the membrane rejects more than 97.4% of Rhodamine B, crystal violet, Congo red, and acid fuchsin. Its permeate flux ranges from 40.5 to 48.2 L·m−2·h−1. After 24 h of continuous operation, the rejection of the Congo red solution remains above 99.3%. The flux decline is only 8.56%. From 6 to 24 h, the flux remains stable at about 38.5 L·m−2·h−1. The membrane shows good short-term operational stability. This work provides a theoretical basis for preparing high-performance and stable nanofiltration membranes.