Sulfonated polyaniline interlayer with controllable doping conditions for high-performance nanofiltration

Thin-film composite (TFC) membranes have been widely used in water purification, seawater desalination and waste treatment, etc. The interface between a support layer and a selective skin layer not only plays a crucial role in the separation performance of membrane but also regulate the formation of the selective layer. Herein, we report an interlayer enhanced TFC membrane with an interlayer composed of self-doping sulfonated polyaniline (SPANI) nanofibers which possess both excellent hydrophilicity and unique chemical properties. The surface properties prior to the interfacial polymerization (IP) process can be readily tuned by adding different kinds of alkaline solutions to the SPANI interlayer, forming skin layers with various morphology in the subsequent IP process. By simply adding NaHCO3 to the SPANI interlayer, a thin and defect-free polyamide (PA) selective layer with dual morphology of crumple and nanobubble structures can be formed. The optimal i-TFC-NaHCO3-3 membrane shows excellent permeate flux of 35.35 ± 1.35 L m−2 h−1 bar−1 with good capacities of retention for both Na2SO4 (98.95 ± 0.29%) and MgSO4 (95.37 ± 0.43%). This work provides a facile route to enhance the membrane performance by simply adjusting the chemical properties of membrane interlayers.