A pH-responsive covalent organic framework membrane based on flexible building blocks for superhigh-flux dye/salt separation

The purification of dyeing wastewater has become an urgent demand in recent years. In this context, the covalent organic framework (COF) membranes are envisioned as promising materials for dye separations in wastewater due to their advantages of low energy consumption, high efficiency, low maintenance cost and high economic benefit. In this work, a pH-responsive hydrazone bonded flexible building blocks (FBBs) based COFs membrane was successfully prepared via an interfacial polymerization process. Systemical characterization analysis demonstrated that the as-synthesized membrane exhibited good crystallinity with flexible, continuous, as well as self-standing properties. Interestingly, it showed an extremely high-water flux of 1162.5 LMH/bar and maintained good rejection rates. In addition, the membrane exhibits a sensitive pH responsive behaver showing reversible discoloration at different pH, and the rejection rate of methylene blue (MB) could be elevated to 99.9 % when increased the pH value to 12, revealing the “functional group interaction and adsorption” separation mechanism. This work is the pioneering exploitation in FBBs based COFs self-standing membrane for dye/salt separation, which may provide useful information for development of new functional membranes.