Construction of a platform to develop 3D ionic porous organic polymers via a post-modification strategy for efficient adsorption of charged organic pollutants

The development of ionic porous organic polymer (POPs) for the efficient removal of charged organic pollutants is of paramount significance. Herein, in this work, a 2D conjugated POP based on tetraphenyl ethylene moiety was firstly synthesized, and then it was further cross-linked to prepare a building block via the Friedel-Crafts alkylation reaction and “knitting” method. Two functional groups with opposite charges including the cationic quaternary ammonium group and anionic sulfonate group have been subsequently introduced to synthesize 3D ionic POPs named TCN-7 and TCN-8 under mild conditions to improve the hydrophilicity and enhance the adsorption affinity (primarily electrostatic interaction). Although the surface areas have decreased after post-modification, they still exhibited improved adsorption performance toward diverse charged organic dyes and herbicides. Especially for an anionic dye congo red (CR) and a cationic dye methylene blue (MB), TCN-7 and TCN-8 showed a removal efficiency > 99.5 % within a contact time of merely 1 min, respectively. Moreover, TCN-7 displayed an adsorption capacity of 2246 and 386 mg/g for CR and an anionic herbicide 2,4-dichlorophenoxyacetic acid, and TCN-8 reaches 1984 and 327 mg/g for MB and a cationic herbicide paraquat, which has surpassed the as-prepared 2D POPs and most of the recently reported adsorbents. More importantly, they exhibited excellent stability after five cycles and superfast removal ability in the column adsorption experiments, demonstrating potential application in real wastewater treatment scenarios. Our work may provide a platform to develop 3D ionic POPs via a post-modification strategy in one step under mild conditions, which is promising in the efficient removal of charged organic pollutants.