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

Abstract

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 (<15.0%), thus promising for separation of dye/salt mixtures. In addition, the thus-obtained POP film was utilized as the catalyst to yield propylene carbonate in aqueous solution with a high conversion rate of 80% at room temperature. The significance of this study is expected to provide a useful guideline of in situ fabrication of multifunctional POP membranes for separation of dye/salt mixtures and catalysis.