Engineering novel thin-film composite membranes with crater-like surface morphology using rigidly-contorted monomer for high flux nanofiltration

Abstract Developing thin-film composite (TFC) nanofiltration (NF) membranes with high water permeability and salt rejection is highly desirable in water desalination. In this study, a new TFC membrane with high NF performances was developed to achieve such a goal by constructing active separation layer with a special crater-like surface morphology using a rigidly-contorted spirocyclic monomer, 5,5,6′,6′-tetrahydroxy-3,3,3′,3′-tetramethyl spirobisindane (TTSBI), as the co-monomer with piperazine (PIP) in aqueous phase during interfacial polymerization (IP) process. This design endowed the separation layer with the characteristics of low thickness, high microporosity, and high permeation surface area. The pure water permeability was therefore increased to 9.9 L m−2 h −1 bar−1, approximately two times higher than that of the typical TFC NF membrane prepared with PIP and trimesoyl chloride, without compromise in the rejection (the rejection of Na2SO4 up to 98%). The introduction of TTSBI tuned the diffusion and reaction behaviors of monomers at the aqueous-organic interface and controlled the special microporous structure and surface morphology, which are advantageous to the improvement of water permeability. This study provides new insights for synthesizing highly permeable TFC NF membranes with remarkable rejection characteristics to address the crisis of the current potable water scarcity.