Controllable preparation of PPTA/PEMs/PPy composite nanofiltration membranes for multi-environmental desalination performance

Using a porous ultrafiltration membrane made of poly(terephthalamide) (PPTA) as the base membrane, and using poly (allylamine hydrochloride) (PAH) and poly (styrene sulfonate) (PSS) respectively as the polycation and polyanion, a PPTA/PEMs multilayer membrane was prepared via the layer-by-layer (LBL) assembly method. Subsequently, polypyrrole (PPy) as a conductive separation layer was in situ polymerized on the surface of the PPTA/PEMs multilayer membrane using pyrrole (Py) and ferric chloride (FeCl 3 ) as the reactant and activating initiator, respectively, through chemical vapor deposition (CVD). By directing the control of the number of PEMs charged layers and their charge properties, a PPTA/PEMs/PPy composite nanofiltration membrane with stable and controllable interlayer structure was prepared. Further, the surface microstructure, chemical composition, hydrophilicity, and surface charge of the PPTA base membrane and the PPTA/PEMs/PPy composite nanofiltration membrane were characterized using SEM, AFM, FTIR, water contact angle, and zeta potential measurements. The results showed that when the number of polyelectrolyte layers was three (PAH/PSS) 3 , the PPTA/PEMs/PPy composite nanofiltration membrane exhibited high desalination performance and good permeability under a transmembrane pressure of 0.8 MPa. Subsequently, its structural performance stability was investigated under high-temperature (20°C and 80°C), acidic (pH=2), and alkaline (pH=13) conditions. After 10 hours of testing, the permeability of the PPTA/PEMs/PPy composite nanofiltration membrane for a 5 g/L Na 2 SO 4 solution decreased slightly, but the rejection rate remained almost stable. Compared to the PPTA/PPy composite nanofiltration membrane from previous studies, the PPTA/PEMs/PPy composite nanofiltration membrane obtained in this study showed improved permeability and rejection rate in high-concentration saline wastewater, with good thermal stability and chemical corrosion resistance. This provides guidance for the application of nanofiltration membranes in the treatment of saline wastewater under harsh conditions.