In situ growth of multifunctional porous organic polymer nanofilms with molecular sieving and catalytic abilities

•Loose-structured, hydrophilic POP nanofilms were fabricated under mild conditions.•The role of synthesis parameters in membrane structure and performance was studied.•POP membranes show high water flux, and superior dye/salt separation properties.•POP membranes could be utilized as an efficient catalyst to yield propylene carbonate. Porous organic polymers (POPs) have evinced a huge potential for membrane-based separations owing to their impressive surface areas, high mesopore ratio, superior chemical stabilities, and catalytic abilities. In this study, for the first time, an o-hydroxy porous organic polymer (POP) thin film was in situ generated atop a (polyacrylonitrile) HPAN membrane support via diazo-coupling reaction under mild conditions. Analysis by FT-IR, XPS and SEM confirmed the successful formation of a coherent, thin POP nanofilm. Zeta potentials and water contact angle measurements demonstrated that the resultant POP film was hydrophilic (water contact angle = 48°) and negatively charged because of the abundance of hydroxyl groups. The roles of synthesis parameters (e.g., the solution pH and the reaction time) in the membrane microstructure and separation performance were explored in detail. The best-performing composite membranes show a high pure water permeability (66.5 L m−2h−1 bar−1), superior dye retentions (RCR = 99.6%, RDR = 98.0%, RMB = 98.8%), and low divalent salt retention (