Room-temperature synthesis of ionic covalent organic frameworks for efficient removal of diclofenac sodium from aqueous solution

The excessive use of diclofenac sodium (DCF) has led to environmental and food safety problems. Effective removal of DCF in aqueous environment is of great significance. Ionic covalent organic frameworks (iCOFs) are effective adsorbents for the removal of pollutants due to their unique structure and properties, but conventional synthesis of iCOFs is limited by high temperature and long reaction time. Herein, we report a room-temperature strategy to synthesize iCOFs in 24 h for the first time. The room-temperature synthesized ionic COF (RT-iCOF) shows better crystallinity, lager uptake capacity and faster kinetics than those synthesized at high temperature with long reaction time. The adsorption kinetics, isotherms and thermodynamics, the effects of ionic strength, pH, humic acid, and reusability of RT-iCOF for DCF were studied in detail. The prepared RT-iCOF gave the maximum adsorption capacity of 857.5 mg g-1, featuring the highest uptake capacity for DCF so far. The adsorption of DCF on the RT-iCOF are driven by ion exchange, pi-pi interactions, electrostatic and hydrogen bonds interaction. The adsorption efficiency of RT-iCOF for DCF was still above 90% after 5 regeneration cycles. This work also promotes the facile synthesis and application of iCOFs for the removal of pollutants.