Rapid fabrication of composite membranes based on conjugated microporous polymers: Microstructural design for performance optimization

Composite membranes based on conjugated microporous polymer (CMPs) with permanent porosity and high tolerance to harsh environments have been considered as one of the most promising separation methods to treat wastewater. Nevertheless, using simple and low-cost methods to accomplish the rapid fabrication of CMPs-based membranes with excellent performance is challenging. Herein, unidirectional diffusion synthesis in diffusion cells of different inner diameters achieved the rapid fabrication and adjustable size of three CMPs-based composite membranes (i.e., TpMa-H, TpMa-CH3 and TpMa-Cl). Among them, TpMa-CH3 or TpMa-Cl was obtained by replacing -H of Carbon 4 in the amine moieties of TpMa-H with -CH3 or -Cl groups. This microstructural design enhanced the rejection rates of TpMa-CH3 and TpMa-Cl to model waste molecules compared with TpMa-H. In addition, the composite membranes had strong hydrolytic resistance, thermal stability and acid-base resistance. Interestingly, TpMa-CH3 showed better rejection to positively charged methyl violet (Mw.358) than that to negatively charged sodium cresol (Mw.404), probably due to the electrostatic adsorption of bigger positive portion of methyl violet on the membrane surface and resultant bridging effect. Such electrostatic adsorption and the adjustable microstructures significantly varied the repellence of CMPs-based membranes to different charged molecules. This work provides a beneficial idea to optimize the separation performance of the CMPs-based membrane.